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Title: The Organism as a Whole, from a Physicochemical Viewpoint

Author: Jacques Loeb

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The
Organism as a Whole
From a Physicochemical Viewpoint

By

Jacques Loeb, M.D., Ph.D., Sc.D.
Member of the Rockefeller Institute for Medical Research

With 51 Illustrations

G. P. Putnam’s Sons
New York and London

Copyright, 1916
by

JACQUES LOEB

To

THE MEMORY OF

DENIS DIDEROT
Of the Encyclopédie and the Système de la nature

“He was one of those simple,
disinterested, and intellectually sterling
workers to whom their own personality
is as nothing in the presence of the vast
subjects that engage the thoughts of
their lives.”
John
Morley.
(Article Diderot, Encyclopædia
Britannica.)

PREFACE
It is generally admitted that the individual physio­logical processes, such as
diges­tion, metabolism, the produc­tion of heat or of electricity, are of a
purely physico­chemical character; and it is also conceded that the func­tions
of individual organs, such as the eye or the ear, are to be analysed from the
viewpoint of the physicist. When, however, the biologist is confronted with
the fact that in the organism the parts are so adapted to each other as to give
rise to a harmonious whole; and that the organisms are endowed with
structures and instincts calculated to prolong their life and perpetuate their
race, doubts as to the adequacy of a purely physico­chemical viewpoint in
biology may arise. The difficulties besetting the biologist in this problem
have been rather increased than diminished by the discovery of Mendelian
heredity, according to which each character is transmitted independently of
any other character. Since the number of Mendelian characters in each
organism is large, the possibility must be faced that the organism is merely
a mosaic of independent hereditary characters. If this be the case the ques­‐
tion arises: What moulds these independent characters into a harmonious
whole?
The vitalist settles this ques­tion by assuming the existence of a pre-
established design for each organism and of a guiding “force” or “principle”
which directs the working out of this design. Such assump­tions remove the
problem of accounting for the harmonious character of the organism from
the field of physics or chemistry. The theory of natural selec­tion invokes
neither design nor purpose, but it is incomplete since it disregards the
physico­chemical constitu­tion of living matter about which little was known
until recently.
In this book an attempt is made to show that the unity of the organism is
due to the fact that the egg (or rather its cytoplasm) is the future embryo
upon which the Mendelian factors in the chromo­somes can impress only

individual characteristics, probably by giving rise to special hormones and
enzymes. We can cause an egg to develop into an organism without a
spermato­zoön, but apparently we cannot make a spermato­zoön develop into
an organism without the cytoplasm of an egg, although sperm and egg
nucleus transmit equally the Mendelian characters. The concep­tion that the
cytoplasm of the egg is already the embryo in the rough may be of
importance also for the problem of evolu­tion since it suggests the
possibility that the genus- and species-heredity are determined by the
cytoplasm of the egg, while the Mendelian hereditary characters cannot
contribute at all or only to a limited extent to the forma­tion of new species.
Such an idea is supported by the work on immunity, which shows that
genus- and probably species-specificity are due to specific proteins, while
the Mendelian characters may be determined by hormones which need
neither be proteins nor specific or by enzymes which also need not be
specific for the species or genus. Such a concep­tion would remove the
difficulties which the work on Mendelian heredity has seemingly created
not only for the problem of evolu­tion but also for the problem of the
harmonious character of the organism as a whole.
Since the book is intended as a companion volume to the writer’s former
treatise on The Comparative Physiology of the Brain a discussion of the
func­tions of the central nervous system is omitted.
Completeness in regard to quota­tion of literature was out of the ques­tion,
but the writer notices with regret, that he has failed to refer in the text to so
important a contribu­tion to the subject as Sir E. A. Schäfer’s masterly
presidential address on “Life” or the addresses of Correns and Goldschmidt
on the determina­tion of sex. Credit should also have been given to Professor
Raymond Pearl for the discrimina­tion between species and individual
inheritance.
The writer wishes to acknowledge his indebtedness to his friends Professor
E. G. Conklin of Princeton, Professor Richard Goldschmidt of the Kaiser
Wilhelm Institut of Berlin, Dr. P. A. Levene of the Rockefeller Institute,
Professor T. H. Morgan of Columbia University, and Professor Hardolph

Wasteneys of the University of California who kindly read one or more
chapters of the book and offered valuable sugges­tions; and he wishes
especially to thank his wife for suggesting many correc­tions in the
manuscript and the proof.
The book is dedicated to that group of freethinkers, including d’Alembert,
Diderot, Holbach, and Voltaire, who first dared to follow the consequences
of a mechanistic science—incomplete as it then was—to the rules of human
conduct and who thereby laid the founda­tion of that spirit of tolerance,
justice, and gentleness which was the hope of our civiliza­tion until it was
buried under the wave of homicidal emo­tion which has swept through the
world. Diderot was singled out, since to him the words of Lord Morley are
devoted, which, however, are more or less characteristic of the whole group.
J. L.
The Rockefeller Institute
for Medical Research,
August, 1916

CONTENTS
PAGE

CHAPTER I
Introductory Remarks 1

CHAPTER II
The Specific Difference between Living and
Dead Matter and the Quest­ ion of the
Origin of Life 14

CHAPTER III
The Chemical Basis of Genus and Species: 40
I.—The Incompatibility of Species not
Closely Related 44
II.—The Chemical Basis of Genus and
Species and of Species Specificity 53

CHAPTER IV
Specificity in Fertilization 71

CHAPTER V
Artificial Parthenogenesis 95

CHAPTER VI
Determinism in the Formation of an Organism
from an Egg 128

CHAPTER VII
Regenera­tion 153

CHAPTER VIII

Determina­tion of Sex, Secondary Sexual
Characters, and Sexual Instincts:
I.—The Cytological Basis of Sex
Determination 198
II.—The Physiological Basis of Sex
Determination 214

CHAPTER IX
Mendelian Heredity and its Mechanism 229

CHAPTER X
Animal Instincts and Tropisms 253

CHAPTER XI
The Influence of Environment 286

CHAPTER XII
Adapta­tion to Environment 318

CHAPTER XIII
Evolu­tion 346

CHAPTER XIV
Death and Dissolution of the Organism 349

Index 371

The Organism as a Whole

CHAPTER I
INTRODUCTORY REMARKS

1. The physical researches of the last ten years have put the atomistic theory
of matter and electricity on a definite and in all probability permanent basis.
We know the exact number of molecules in a given mass of any substance
whose molecular weight is known to us, and we know the exact charge of a
single electron. This permits us to state as the ultimate aim of the physical
sciences the visualiza­tion of all phenomena in terms of groupings and
displacements of ultimate particles, and since there is no discontinuity
between the matter constituting the living and non-living world the goal of
biology can be expressed in the same way.
This idea has more or less consciously prevailed for some time in the
explana­tion of the single processes occurring in the animal body or in the
explana­tion of the func­tions of the individual organs. Nobody, not even a
scientific vitalist, would think of treating the process of diges­tion,
metabolism, produc­tion of heat, and electricity or even secre­tion or
muscular contrac­tion in any other than a purely chemical or physico­‐
chemical way; nor would anybody think of explaining the func­tions of the
eye or the ear from any other standpoint than that of physics.
When the actions of the organism as a whole are concerned, we find a
totally different situa­tion. The same physiologists who in the explana­tion of
the individual processes would follow the strictly physico­chemical
viewpoint and method would consider the reac­tions of the organism as a
whole as the expression of non-physical agencies. Thus Claude Bernard, 1
who in the investiga­tion of the individual life processes was a strict
mechanist, declares that the making of a harmonious organism from the egg
cannot be explained on a mechanistic basis but only on the assump­tion of a
“directive force.” Bernard assumes, as Bichat and others had done before

him, that there are two opposite processes going on in the living organism:
(1) the phenomena of vital crea­tion or organizing synthesis; (2) the
phenomena of death or organic destruc­tion. It is only the destructive
processes which give rise to the physical manifesta­tions by which we judge
life, such as respira­tion and circula­tion or the activity of glands, and so on.
The work of crea­tion takes place unseen by us in the egg when the embryo
or organism is formed. This vital crea­tion occurs always according to a
definite plan, and in the opinion of Bernard it is impossible to account for
this plan on a purely physico­chemical basis.
There is so to speak a pre-established design of each being and of
each organ of such a kind that each phenomenon by itself depends
upon the general forces of nature, but when taken in connec­tion
with the others it seems directed by some invisible guide on the road
it follows and led to the place it occupies. . . .
We admit that the life phenomena are attached to physico­chemical
manifesta­tions, but it is true that the essential is not explained
thereby; for no fortuitous coming together of physico­chemical
phenomena constructs each organism after a plan and a fixed design
(which are foreseen in advance) and arouses the admirable
subordina­tion and harmonious agreement of the acts of life. . . .
We can only know the material conditions and not the intimate
nature of life phenomena. We have therefore only to deal with
matter and not with the first causes or the vital force derived
therefrom. These causes are inaccessible to us, and if we believe
anything else we commit an error and become the dupes of
metaphors and take figurative language as real. . . . Determinism can
never be but physico­chemical determinism. The vital force and life
belong to the metaphysical world.
In other words, Bernard thinks it his task to account for individual life
phenomena on a purely physico­chemical basis—but the harmonious
character of the organism as a whole is in his opinion not produced by the

same forces and he considers it impossible and hopeless to investigate the
“design.” This attitude of Bernard would be incomprehensible were it not
for the fact that, when he made these statements, the phenomena of
specificity, the physi­ology of development and regenera­tion, the Mendelian
laws of heredity, the animal tropisms and their bearing on the theory of
adapta­tion were unknown.
This explanation of Bernard’s attitude is apparently contradicted by the fact
that Driesch 2 and v. Uexküll, 3 both brilliant biologists, occupy today a
standpoint not very different from that of Claude Bernard. Driesch assumes
that there is an Aristotelian “entelechy” acting as directing guide in each
organism; and v. Uexküll suggests a kind of Platonic “idea” as a peculiar
characteristic of life which accounts for the purposeful character of the
organism.
v. Uexküll supposes as did Claude Bernard and as does Driesch that in an
organism or an egg the ultimate processes are purely physico­chemical. In an
egg these processes are guided into definite parts of the future embryo by
the Mendelian factors of heredity—the so-called genes. These genes he
compares to the foremen for the different types of work to be done in a
building. But there must be something that makes of the work of the single
genes a harmonious whole, and for this purpose he assumes the existence of
“supergenes.” 4 v. Uexküll’s ideas concerning the nature of a Mendelian
factor and of the “supergenes” are expressed in metaphorical terms and the
assump­tion of the “supergenes” begs the ques­tion. The writer is under the
impression that this author was led to his views by the belief that the egg is
entirely undifferentiated. But the unfertilized egg is not homogeneous, on
the contrary, it has a simple but definite physico­chemical structure which
suffices to determine the first steps in the differentia­tion of the organism. Of
course, if we suppose as do v. Uexküll and Driesch that the egg has no
structure, the development of structure becomes a difficult problem—but
this is not the real situa­tion.

2. Claude Bernard does not mention the possibility of explaining the
harmony or apparent design in the organism on the basis of the theory of
evolu­tion, he simply considers the problem as outside of biology. It was
probably clear to him as it must be to everyone with an adequate training in
physics that natural selec­tion does not explain the origin of varia­tion.
Driesch and v. Uexküll consider the Darwinian theory a failure. We may
admit that the theory of a forma­tion of new species by the cumulative effect
of aimless fluctuating varia­tions is not tenable because fluctuating varia­tion
is not hereditary; but this would only demand a slight change in the theory;
namely a replacement of the influence of fluctuating varia­tion by that of
equally aimless muta­tions. With this slight modifica­tion which is proposed
by de Vries, 5 Darwin’s theory still serves the purpose of explaining how
without any pre-established plan only purposeful and harmonious
organisms should have survived. It must be said, however, that any theory
of life phenomena must be based on our knowledge of the physico­chemical
constitu­tion of living matter, and neither Darwin nor Lamarck was
concerned with this. Moreover, we cannot consider any theory of evolu­tion
as proved unless it permits us to trans­form at desire one species into
another, and this has not yet been accomplished.
It may be of some interest to point out that we do not need to make any
definite assump­tion concerning the mechanism of evolu­tion and that we
may yet be able to account for the fact that the surviving organisms are to
all appearances harmonious. The writer pointed out that of all the
100,000,000 conceivable crosses of teleost fish (many of which are
possible) not many more than 10,000, i. e., about one-hundredth of one per
cent., are able to live and propagate. Those that live and develop are free
from the grosser type of disharmonies, the rest are doomed on account of a
gross lack of harmony of the parts. These latter we never see and this gives
us the erroneous concep­tion that harmony or “design” is a general character
99
of living matter. If anybody wishes to call the non-viability of 99 100 per
cent. of possible teleosts a process of weeding out by “natural selec­tion” we
shall raise no objec­tion, but only wish to point out that our way of

explaining the lack of design in living nature would be valid even if there
were no theory of evolu­tion or if there had never been any evolu­tion.
3. v. Uexküll is perfectly right in connecting the problem of design in an
organism with Mendelian heredity. The work on Mendelian heredity has
shown that an extremely large number of independently transmissible
Mendelian factors help to shape the individual. It is not yet proven that the
organism is nothing but a mosaic of Mendelian factors, but no writer can be
blamed for considering such a possibility. If we assume that the organism is
nothing but a mosaic of Mendelian characters it is difficult indeed to
understand how they can force each other into a harmonious whole 6; even if
we make ample allowance for the law of chance and the corresponding
wastefulness in the world of the living. But it is doubtful whether this idea
of the rôle of Mendelian factors is correct. The facts of experi­mental
embryology strongly indicate the possibility that the cytoplasm of the egg is
the future embryo (in the rough) and that the Mendelian factors only
impress the individual (and variety) characters upon this rough block. This
idea is supported by the fact that the first development—in the sea urchin to
the gastrula stage inclusive—is independent of the nucleus, which is the
bearer of the Mendelian factors. Not before the skeleton or mesenchyme is
formed in the sea urchin egg is the influence of the nucleus noticeable. This
has been shown in the experi­ments of Boveri in which an enucleated
fragment of an egg was fertilized with a spermato­zoön of a foreign species.
If this is generally true, it is conceivable that the generic and possibly also
the species characters of organisms are determined by the cytoplasm of the
egg and not by the Mendelian factors.
In any case, we can state today that the cytoplasm contains the rough
preforma­tion of the future embryo. This would show then that the idea of
the organism being a mosaic of Mendelian characters which have to be put
into place by “supergenes” is unnecessary. If the egg is already the embryo
in the rough we can imagine the Mendelian factors as giving rise to specific
substances which go into the circula­tion and start or accelerate different
chemical reac­tions in different parts of the embryo, and thereby call forth

the finer details characteristic of the variety and the individual. The idea
that the egg is the future embryo is supported by the fact that we can call
forth a normal organism from an unfertilized egg by artificial means; while
it is apparently impossible to cause the spermato­zoön to develop into an
organism outside the egg.
4. The influence of the whole on the parts is nowhere shown more strikingly
than in the field of regenera­tion. It is known that pieces cut from the plant
or animal may give rise to new growth which in many cases will restore
somewhat the original organism. Instead of asking what is the cause of this
so-called regenera­tion we may ask, why the same pieces do not regenerate
as long as they are parts of the whole. In this form the mysterious influence
of the whole over its parts is put into the foreground. We shall see that
growth takes place in certain cells when certain substances in the circula­tion
can collect there. The mysterious influence of the whole on these parts
consists often merely of the fact that the circulating specific or non-specific
substances—we cannot yet decide which—will in the whole be attracted by
certain spots and that this will prevent them from acting on other parts of
the organism. If such parts are isolated the substances can no longer flow
away from these parts and the parts will begin to grow. It thus becomes
utterly unnecessary to endow such organisms with a “directing force” which
has to elaborate the isolated parts into a whole.
5. The same difficulty which we have discussed in regard to morphogenesis
exists also in connec­tion with those instincts which preserve the life of the
organism and of the race. The reader need only be reminded of all the
complicated instincts of mating by which sperm and eggs are brought
together; or those by which the young are prevented from starva­tion to
realize the apparently desperate problems in store for a mechanist, to whom
the assump­tion of design is meaningless. And yet we are better off in regard
to our knowledge of the instincts than we are in regard to morphogenesis, as
in the former we can show that the apparent instincts in some cases obey
simple physico­chemical laws with almost mathematical accuracy. Since the
validity of the law of gravita­tion has been proved for the solar system the

idea of design in the motion of the planets has lost its usefulness, and this
fact must serve us as a guide wherever we attempt to put science beyond the
possibility of mysticism. As soon as we can show that a life phenomenon
obeys a simple physical law there is no longer any need for assuming the
action of non-physical agencies. We shall see that this has been
accomplished for one group of animal instincts; namely those which
determine the rela­tion of animals to light, since these are being gradually
reduced to the law of Bunsen and Roscoe. This law states that the chemical
effect of light equals the product of intensity into dura­tion of illumina­tion.
Some authors object to the tendency toward reducing everything in biology
to mathematical laws or figures; but where would the theory of heredity be
without figures? Figures have been responsible for showing that the laws of
chance and not of design rule in heredity. Biology will be scientific only to
the extent that it succeeds in reducing life phenomena to quantitative laws.
Those familiar with the theories of evolution know the extensive rôle
ascribed to the adapta­tions of organisms. The writer in 1889 called atten­tion
to the fact that reac­tions to light—e. g., positive helio­tropism—are found in
organisms that never by any chance make use of them; and later that a great
many organisms show definite instinctive reac­tions towards a galvanic
current—galvano­tropism—although no organism has ever had or ever will
have a chance to be exposed to such a current except in laboratory experi­‐
ments. This throws a different light upon the seemingly purposeful
character of animal reac­tions. Heliotropism depends primarily upon the
presence of photo­sensitive substances in the eye or the epidermis of the
organism, and these substances are inherited regardless of whether they are
useful or not. It is only a metaphor to call reac­tions resulting from the
presence of photo­sensitive substances “adapta­tion.” In this book other
examples are given which show that authors have too often spoken of
adapta­tion to environ­ment where the environ­ment was not responsible for
the phenomena. The blindness of cave animals and the resistance of certain
marine animals to higher concentra­tions of sea water are such cases. Cuénot
speaks of “preadapta­tion” to express this rela­tion. The fact is that the

“adapta­tions” often existed before the animal was exposed to surroundings
where they were of use. This relieves us also of the necessity of postulating
the existence of the inheritance of acquired characters, although it is quite
possible that the future may furnish proof that such a mode of inheritance
exists.
6. We have mentioned that according to Claude Bernard two groups of
phenomena occur in the living organism: (1) the phenomena of vital crea­‐
tion or organizing synthesis (especially in the egg and during development);
(2) the phenomena of death or organic destruc­tion. These two processes are
briefly discussed in the first and last chapters.
These introductory remarks may perhaps make it easier for the reader to
retain the thread of the main ideas in the details of experi­ments and tables
given in this book.

CHAPTER II
THE SPECIFIC DIFFERENCE BETWEEN LIVING AND
DEAD MATTER AND THE QUESTION OF THE ORIGIN
OF LIFE

1. Each organism is characterized by a definite form and we shall see in the
next chapter that this form is determined by definite chemical substances.
The same is true for crystals, where substance and form are definitely
connected and there are further analogies between organisms and crystals.
Crystals can grow in a proper solu­tion, and can regenerate their form in
such a solu­tion when broken or injured; it is even possible to prevent or
retard the forma­tion of crystals in a supersaturated solu­tion by preventing
“germs” in the air from getting into the solu­tion, an observa­tion which was
later utilized by Schroeder and Pasteur in their experi­ments on spontaneous
genera­tion. However, the analogies between a living organism and a crystal
are merely superficial and it is by pointing out the fundamental differences
between the behaviour of crystals and that of living organisms that we can
best understand the specific difference between non-living and living
matter. It is true that a crystal can grow, but it will do so only in a
supersaturated solu­tion of its own substance. Just the reverse is true for
living organisms. In order to make bacteria or the cells of our body grow,
solu­tions of the split products of the substances composing them and not the
substances themselves must be available to the cells; second, these solu­tions
must not be supersaturated, on the contrary, they must be dilute; and third,
growth leads in living organisms to cell division as soon as the mass of the
cell reaches a certain limit. This process of cell division cannot be claimed
even metaphorically to exist in a crystal. A correct apprecia­tion of these
facts will give us an insight into the specific difference between non-living
and living matter. The forma­tion of living matter consists in the synthesis of
the proteins, nucleins, fats, and carbohydrates of the cells, from the split

products. To give an historical example, Pasteur showed that yeast cells and
other fungi could be raised on the following sterilized solu­tion: water,
100 gm., crystallized sugar, 10 gm., ammonium tartrate, 0.2 gm. to 0.5 gm.,
and fused ash from yeast, 0.1 gm. 7 He undertook this experi­ment to
disprove the idea that protein or organic matter in a state of decomposi­tion
was needed for the origin of new organisms as the defenders of the idea of
spontaneous genera­tion had maintained.
2. That such a solu­tion can serve for the synthesis of all the compounds of
living yeast cells is due to the fact that it contains the sugars. From the
sugars organic acids can be formed and these with ammonia (which was
offered in the form of ammonium tartrate) may give rise to the forma­tion of
amino acids, the “building stones” of the proteins. It is thus obvious that the
synthesis of living matter centres around the sugar molecule. The
phosphates are required for the forma­tion of the nucleins, and the work of
Harden and Young suggests that they play also a rôle in the alcoholic
fermenta­tion of sugar.
Chlorophyll, under the influence of the red rays of light, manufactures the
sugars from the CO2 of the air. This makes it appear as though life on our
planet should have been preceded by the existence of chlorophyll, a fact
difficult to understand since it seems more natural to conceive of
chlorophyll as a part or a product of living organisms rather than the
reverse. Where then should the sugar come from, which is a constituent of
the majority of culture media and which seems a prerequisite for the
synthesis of proteins in living organisms?
The investiga­tions of Winogradsky on nitrifying, 8 sulphur and perhaps also
on iron bacteria have to all appearances pointed a way out of this difficulty.
It seemed probable that there were specific micro-organisms which
oxidized the ammonia formed in sewage or in the putrefac­tion of living
matter, but the attempts to prove this assump­tion by raising such a nitrifying
micro-organism on one of the usual culture media, all of which contained
organic compounds, failed. Led by the results of his observa­tions on

sulphur bacteria it occurred to Winogradsky that the presence of organic
compounds stood in the way of raising these bacteria, and this idea proved
correct. The bacteria oxidizing ammonia to nitrites were grown on the
following medium; 1 gm. ammonium sulphate, 1 gm. potassium phosphate,
1 gm. magnesium carbonate, to 1 litre of water. From this medium, which is
free from sugar and contains only constituents which could exist on the
planet before the appearance of life, the nitrifying bacteria were able to
form sugars, fatty acids, proteins, and the other specific constituents of
living matter. Winogradsky proved, by quantitative determina­tion, that with
the nitrifica­tion an increase in the amount of carbon compounds takes place.
“Since this bound carbon in the cultures can have no other source than the
CO2 and since the process itself can have no other cause than the activity of
the nitrifying organism, no other alternative was left but to ascribe to it the
power of assimilating CO2.” 9 “Since the oxida­tion of NH3 is the only
source of chemical energy which the nitrifying organism can use it was
clear a priori that the yield in assimila­tion must correspond to the quantity
of oxidized nitrogen. It turned out that an approximately constant ratio
exists between the values of assimilated carbon and those of oxidized
nitrogen.” This is illustrated by the results of various experi­ments as shown
in Table I.
TABLE I

No. 5 No. 6 No. 7 No. 8
mg. mg. mg. mg.
Oxidized N 722.0 506.1 928.3 815.4
Assimilated C 19.7 15.2 26.4 22.4
Ratio N : C 36.6 33.3 35.2 36.4

It is obvious that 1 part of assimilated carbon corresponds to about 35.4
parts oxidized nitrogen or 96 parts of nitrous acid.
These results of Winogradsky were confirmed in very careful experi­ments
by E. Godlewski, Sr. 10

The nitrites are further oxidized by another kind of micro-organisms into
nitrates and they also can be raised without organic material.
Winogradsky had already previously discovered that the hydrogen sulphide
which is formed as a reduc­tion product from CaSO4 or in putrefac­tion by
the activity of certain bacteria can be oxidized by certain groups of bacteria,
the sulphur bacteria. Such bacteria, e. g., Beggiatoa, are also commonly
found at the outlet of sulphur springs. They utilize the hydrogen sulphide
which they oxidize to sulphur and afterwards to sulphates, according to the
scheme:
(1) 2H2S + O2 = 2H2O + S2
(2) S2 + 3O2 + 2H2O = 2H2SO4
The sulphuric acid is at once neutralized by carbonates.
Winogradsky assumes that the oxida­tion of H2S by the sulphur bacteria is
the source of energy which plays the same rôle as the oxida­tion of NH3
plays in the nitrifying bacteria, or the oxida­tion of carbon compounds—
sugar and others—in the case of the other lower and higher organisms.
Winogradsky has made it very probable that sulphur bacteria do not need
any organic compounds and that their nutri­tion may be accomplished with a
purely mineral culture medium, like that of the nitrite bacteria. On the basis
of this assump­tion they should also be able to form sugars from the CO2 of
the air.
Nathanson 11 discovered in the sea water the existence of bacteria which
oxidize thiosulphate to sulphuric acid. They will develop if some Na2S2O3,
is added to sea water. These bacteria can only develop if CO2 from the air is
admitted or when carbonates are present. For these organisms the CO2
cannot be replaced by glucose, urea, or other organic substances. Such
bacteria must therefore possess the power of producing sugar and starch
from CO2 without the aid of chlorophyll. Similar observa­tions were made
by Beijerinck on a species of fresh-water bacteria. 12

Finally the case of iron bacteria may briefly be mentioned though
Winogradsky’s views are not accepted by Molisch.
We may, therefore, consider it an established fact that there are a number of
organisms which could have lived on this planet at a time when only
mineral constituents, such as phosphates, K, Mg, SO4, CO2, and O2 besides
NH3, or SH2, existed. This would lead us to consider it possible that the first
organisms on this planet may have belonged to that world of micro-
organisms which was discovered by Winogradsky.
If we can conceive of this group of organisms as producing sugar, which in
fact they do, they could have served as a basis for the development of other
forms which require organic material for their development.
In 1883 the small island of Krakatau was destroyed by the most violent
volcanic erup­tion on record. A visit to the islands two months after the erup­‐
tion showed that “the three islands were covered with pumice and layers of
ash reaching on an average a thickness of thirty metres and frequently sixty
metres.” 13 Of course all life on the islands was extinct. When Treub in 1886
first visited the island, he found that blue-green algæ were the first colonists
on the pumice and on the exposed blocks of rock in the ravines on the
mountain slopes. Investiga­tions made during subsequent expedi­tions
demonstrated the associa­tion of diatoms and bacteria. All of these were
probably carried by the wind. The algæ referred to were according to Euler
of the nostoc type. Nostoc does not require sugar, since it can produce that
compound from the CO2 of the air by the activity of its chlorophyll. This
organism possesses also the power of assimilating the free nitrogen of the
air. From these observa­tions and because the Nostocaceæ generally appear
as the first settlers on sand the conclusion has been drawn that they or the
group of Schizophyceæ to which they belong formed the first settlers of our
planet. 14 This conclusion is not quite safe since in the settlement of
Krakatau as well as in the first colonizing of sand areas the nature of the
first settler is determined chiefly by the carrying power of wind (or waves
and birds).

We may now return from this digression to the real object of our discussion,
namely that the nutritive solu­tions of organisms must be very dilute and
consist of the split products of the complicated compounds of which the
organisms consist. The examples given sufficiently illustrate this statement.
The nutritive medium of our body cells is the blood, and while we take up
as food the complicated compounds of plants or animals, these substances
undergo a diges­tion, i. e., a splitting up into small constituents before they
can diffuse from the intestine into the blood. Thus the proteins are digested
down to the amino acids and these diffuse into the blood as demonstrated
by Folin and by Van Slyke. From here the cells take them up. The different
proteins differ in regard to the different types of amino acids which they
contain. While the bacteria and fungi and apparently the higher plants can
build up all their different amino acids from ammonia, this power is no
longer found in the mammals which can form only certain amino acids in
their body and must receive the others through their food. As a consequence
it is usually necessary to feed young animals on more than one protein in
order to make them grow, since one protein, as a rule, does not contain all
the amino acids needed for the manufacture of all the proteins required for
the forma­tion of the material of a growing animal. 15
3. The essential difference between living and non-living matter consists
then in this: the living cell synthetizes its own complicated specific material
from indifferent or non-specific simple compounds of the surrounding
medium, while the crystal simply adds the molecules found in its
supersaturated solu­tion. This synthetic power of trans­forming small
“building stones” into the complicated compounds specific for each
organism is the “secret of life” or rather one of the secrets of life.
What clew have we in regard to the nature of this synthetic power? We
know that the comparatively great velocity of chemical reac­tions in a living
organism is due to the presence of enzymes (ferments) or to catalytic
agencies in general. Some of these catalytic agencies are specific in the
sense that a given catalyzer can accelerate the reac­tion of only one step in a

complicated chemical reac­tion. While these enzymes are formed by the
action of the body they can be separated from the body without losing their
catalytic efficiency. It was a long time before scientists succeeded in
isolating the enzyme of the yeast cell which causes the alcoholic fermenta­‐
tion of sugar; and this gave rise to the premature statement that it was not
possible to isolate this enzyme since it was bound up with the life of the
yeast cell. Such a statement was even made by a man like Pasteur, who was
usually a model of restraint in his utterances, and yet the work of Buchner
proved him to be wrong.
The general mechanism of the action of the hydrolyzing enzymes is known.
The old idea of de la Rive, that a molecule of enzyme combines transitorily
with a molecule of substrate; the further idea, which may possibly go back
to Engler, that the molecule of substrate is disrupted in the “strain” of the
new combina­tion and that the broken fragments fall off or are easily
knocked off by collision from the ferment molecule which is now ready to
repeat the process, seems to be correct. On the assump­tion that the velocity
of enzyme reac­tion is propor­tional to the mass of the enzyme and that de la
Rive’s idea was correct, Van Slyke and Cullen were able to calculate the
coefficients of the velocity of enzyme reac­tions for the fermenta­tion of urea
and other substances, and the agreement between calculated and observed
values was remarkable. 16

While the hydrolytic action of enzymes is thus clear the synthesis in the cell
is still a riddle. An interesting sugges­tion was made by van’t Hoff, who in
1898 expressed the idea that the hydrolytic enzymes should also act in the
opposite direc­tion, namely synthetically. Thus it should not only be possible
to digest proteins with pepsin but also to synthetize them from the products
of diges­tion with the aid of the same enzyme. This expecta­tion was based
on the idea that the enzyme did not alter the equilibrium between the
hydrolyzed and non-hydrolyzed part of the substrate but only accelerated
the rate with which the equilibrium was reached. Van’t Hoff’s idea omitted,
however, the possibility that in the transitory combina­tion between enzyme
molecule and substrate a change in the molecular configura­tion of the

substrate or in the distribu­tion of intramolecular strain may take place. The
first apparently complete confirma­tion of van’t Hoff’s sugges­tion appeared
in the form of the synthesis of maltose from grape sugar by the enzyme
maltase, which decomposes maltose into grape sugar. By adding the
enzyme maltase from yeast to a forty per cent. solu­tion of glucose Croft
Hill 17 obtained a good yield of maltose. It turned out, however, that what he
took for maltose was not this compound but an isomer, namely isomaltose,
which has a different molecular configura­tion and cannot be hydrolyzed by
the enzyme maltase.
Lactose is hydrolyzed from kephyr by an enzyme lactase into galactose and
glucose; by adding this enzyme to galactose and glucose a synthesis was
obtained not of lactose but of isolactose; the latter, however, is not
decomposed by the enzyme lactase.
E. F. Armstrong has worked out a theory which tries to account for this
striking phenomenon by assuming “that the enzyme has a specific influence
in promoting the forma­tion of the biose which it cannot hydrolyze.” 18 The
theory is very ingenious and seems supported by fact. This then would lead
to the result that certain hydrolytic enzymes may have a synthetic action but
not in the manner suggested by van’t Hoff.
The principle enunciated by Armstrong, that in the synthetic action of
hydrolytic enzymes not the original compound but an isomer is formed
which can not be hydrolyzed by the enzyme, may possibly be of great
importance in the understanding of life phenomena. It shows us how the
cell can grow in the presence of hydrolytic enzymes and why in hunger the
disintegra­tion of the cell material is so slow. It was at first thought that the
forma­tion of isomers contradicted the idea of the reversible action of
enzymes, but this is not the case; on the contrary, it supports it but makes an
addi­tion which may solve the riddle of what Claude Bernard called the
creative action of living matter. We shall come back to this problem in the
last chapter.

Kastle and Loevenhart demonstrated the synthesis of a trace of
ethylbutyrate by lipase if the latter enzyme was added to the products of the
hydrolysis of ethylbutyrate, ethyl alcohol, and butyric acid by the same
enzyme. 19 Taylor 20 obtained the synthesis of a slight amount of triolein

by the addi­tion of the dried fat-free residue of the castor bean to a
mixture of oleinic acid and glycerine. . . . No synthesis occurred
with acetic, butyric, palmitic, and stearic acids with glycerine,
mannite, and dulcite, and the experi­ments with the last two alcohols
and oleinic acid likewise yielded no synthesis.
This suggests possibly a specific action of the enzyme. If this slight
reversible action had any biological significance (which might be possible,
since in the organism secondary favourable condi­tions might be at work
which are lacking in vitro) there should be a parallelism between masses of
lipase in different kinds of tissues and fat synthesis. Loevenhart indicated
that this might be a fact, but a more extensive investiga­tion by H. C.
Bradley has made this very dubious. 21

Very little is known concerning the reversible action of the hydrolytic
protein enzymes. A. E. Taylor digested protamine sulphate with trypsin and
found that after adding trypsin to the products of diges­tion a precipitate was
formed after long standing; and we may also refer to experi­ments of
Robertson with pepsin on the products of caseinogen to which we shall
return in the next chapter. It therefore looks at present as if van’t Hoff’s idea
of reversible enzyme action might hold in the modifica­tion offered by
Armstrong. It remains doubtful, however, whether this reversibility can
explain all the synthetic processes in the cell. No objec­tion can be offered at
present if any one makes the assump­tion that each cell has specific
synthetic enzymes or some other synthetic mechanisms which are still
unknown.
The mechanisms for the synthesis of proteins must have one other
peculiarity: they must be specific in their action. We shall see in the next
chapter that each species seems to possess one or more proteins not found

in any other but closely related species. Each organism develops from a tiny
microscopic germ and grows by synthetizing the non-specific building
stones (amino acids) into the specific proteins of the species. This must be
the work of the yet unknown synthetic enzymes or mechanisms. The
elucida­tion of their character would seem one of the main problems of
biology. Needless to say crystallography is not confronted with problems of
such a nature.
The fact that the living cell grows after taking up food has given rise to
curious misunderstandings. Traube has shown that drops of a liquid
surrounded with a semipermeable membrane may increase in volume when
put into a solu­tion of lower osmotic pressure. This has led and is possibly
still leading to the statement that the process of growth by a living cell has
been imitated artificially. Only one feature has been imitated, the increase in
volume; but the essential feature of the process in the living cell, i. e., the
forma­tion of the specific constituents of the living cell from non-specific
products, has of course not been imitated.
4. The constant synthesis then of specific material from simple compounds
of a non-specific character is the chief feature by which living matter differs
from non-living matter. With this character is correlated another one;
namely, when the mass of a cell reaches a certain limit the cell divides. This
is perhaps most obvious in bacteria which on the proper nutritive medium
take up food, grow, and divide into two bacteria, each of which takes up
food, divides, and grows ad infinitum, as long as the food lasts, provided the
harmful products of metabolism are removed. If it be true that specific
synthetic ferments exist in each cell it follows that the cell must synthetize
these also, 22 as otherwise the synthesis of specific proteins would have to
come to a standstill.
This problem of synthesis leads to the assump­tion of immortality of the
living cell, since there is no a priori reason why this synthesis should ever
come to a standstill of its own accord as long as enough food is available
and the proper outside physical condi­tions are guaranteed. It is well known

that Weismann has claimed immortality for all unicellular organisms and
for the sex cells of metazoa, while he claimed the necessity of death for the
body cells of the latter. Leo Loeb was led by his investiga­tions on the
transplanta­tion of cancer to assume immortality not only for the cancer cell
but also for the body cell of the organism. He had found in transplanting a
malignant tumor from one individual to another that the tumor grew; that it
was not the cells of the host but the transplanted tumor cells of the graft
which grew and multiplied, and that this process could be repeated
apparently indefinitely so that it was obvious that the transplanted tumor
cells outlived the original animal. Such experi­ments have since been carried
on so long that we may now say that an individual cancer cell taken from an
animal and transplanted from time to time on a new host lives apparently
indefinitely. Leo Loeb had found that these tumor cells are simply modified
somatic cells. He therefore suggested that the somatic cells might be
considered immortal with the same right as we speak of the immortality of
the germ cells of such animals. 23

This view receives its support first from the fact that certain trees like the
Sequoia live several thousand years and may therefore be considered
immortal and second, from the method of tissue culture. The method of
cultivating tissue cells in a test tube, in the same way as is done for bacteria,
was first proposed and carried out by Leo Loeb, in 1897, 24 but his test-tube
method did not permit the observa­tion of the transplanted cell under the
microscope. This was made possible by a modifica­tion of the method by
Harrison, who established the fact that the axis cylinder grows out from the
ganglionic cell. Harrison and Burrows then perfected the method for the
cultiva­tion of the cells of warm-blooded, animals, and with the aid of these
methods Carrel succeeded in keeping connective-tissue cells of the heart of
an early chick embryo alive more than four years, and these cells are still
growing and dividing. 25 Only very tiny masses of cells can be kept alive in
this way since all the cells in the centre of a piece die on account of lack of
oxygen; and every two days a few cells from the margin of the piece have
to be transferred to a new culture medium.

This effect of lack of oxygen explains also why the immortality of the
somatic cells is not obvious. Death in a human being consists in the
stopping of heart beat and respira­tion, which also terminates the action of
the brain or at least of consciousness. Immediately after the cessa­tion of
heart beat and respira­tion the cells of muscle and of the skin and probably
many or most other organs are still alive and might continue to live if
transferred to another body with circula­tion and respira­tion. As a
consequence of the lack of oxygen supply in the dead body they will,
however, die comparatively rapidly. It may be stated that hearts taken out of
the body after a number of hours can still beat again when put into the
proper solu­tions and upon receiving an adequate oxygen supply.
The idea that the body cells are naturally immortal and die only if exposed
to extreme injuries such as prolonged lack of oxygen or too high a
temperature helps to make one problem more intelligible. The medical
student, who for the first time realizes that life depends upon that one organ,
the heart, doing its duty incessantly for the seventy years or so allotted to
man, is amazed at the precariousness of our existence. It seems indeed
uncanny that so delicate a mechanism should func­tion so regularly for so
many years. The mysticism connected with this and other phenomena of
adapta­tion would disappear if we could be certain that all cells are really
immortal and that the fact which demands an explana­tion is not the
continued activity but the cessa­tion of activity in death. Thus we see that the
idea of the immortality of the body cell if it can be generalized may be
destined to become one of the main supports for a complete physico­‐
chemical analysis of life phenomena since it makes the durability of
organisms intelligible.
5. This generalized idea of the immortality of some or possibly most or all
somatic cells has a bearing upon the problem of the origin of life on our
planet. The experi­ments of Spallanzani, Schwann, Schroeder, Pasteur,
Tyndall, and all those who have worked with pure cultures of micro-
organisms, have proved that no spontaneous genera­tion of living from non-
living matter can be demonstrated; and the statements to the contrary were

due to experi­mental errors inasmuch as the new organisms formed were the
offspring of others which had entered into the culture medium by mistake.
In the last chapter of that most fascinating book Worlds in the Making, 26
Arrhenius discusses the possibility of life being eternal and of living germs
of very small dimensions—e. g., the spores of micro-organisms—being
carried through space from one planet to another or even from one solar
system to another. If it be true that there is no spontaneous genera­tion; if it
be true that all cells are potentially immortal, we may indeed seriously raise
the ques­tion: May not life after all be eternal? Such ideas were advocated
by Richter in a rather phantastic way and more definitely by Helmholtz as
well as Kelvin. The latter authors assumed that in the collision of planets or
worlds on which there is life, fragments containing living organisms will be
torn off and these fragments will move as seed-bearing stones through
space. “If at the present instant no life existed upon this earth, one such
stone falling upon it might . . . lead to its becoming covered with vegeta­‐
tion.” Arrhenius points out the difficulties which oppose such a view, as,
e. g., the fact “that the meteorite in its fall towards the earth becomes
incandescent all over its surface and any seeds on it would therefore be
deprived of their germinating power.”
Arrhenius suggests another and much more ingenious idea based on the fact
that for particles below a certain size the mechanical pressure produced by
light waves—the radia­tion pressure—can overcome the attractive force of
gravita­tion.
Bodies which according to Schwarzschild would undergo the
strongest influence of solar radia­tion must have a diameter of
0.00016 mm. supposing them to be spherical. The first ques­tion is
therefore: Are there any living seeds of such extraordinary
minuteness? The reply of the botanist is that spores of many bacteria
have a size of 0.0003 or 0.0002 mm., and there are no doubt much
smaller germs which our microscopes fail to disclose.
This assumption is undoubtedly correct.

We will, in the first instance, make a rough calcula­tion of what
would happen if such an organism were detached from the earth and
pushed out into space by the radia­tion pressure of our sun. The
organism would first of all have to cross the orbit of Mars; then the
orbits of the smaller and of the outer planets. . . . The organisms
would cross the orbit of Mars after twenty days, the Jupiter orbit
after eighty days, and the orbit of Neptune after fourteen months.
Our nearest solar system would be reached in nine thousand years.
For the assump­tion of eternity of life only the transference of germs from
one solar system to another would have to be considered and the ques­tion
arises whether or not germs can keep their vitality so many thousands of
years. Arrhenius thinks that this is possible on account of the low
temperature (which must be below -220° C.) at which no chemical reac­tion
and hence no decomposi­tion and deteriora­tion are possible in the spores;
and on account of the absence of water vapour.
The ques­tion then arises: Have we any facts to warrant the assump­tion that
spores may remain alive for thousands of years under such condi­tions and
retain their power of germina­tion? We know that seeds have a very limited
vitality, and the statement that grain found in the Egyptian tombs was still
able to germinate has long been recognized as a myth. Miss White 27 found
that in wheat grains, there appeared a well-marked drop in their germinating
power after about the fourth year, reaching zero in eleven to seventeen
years. In a drier climate they last longer than in a moist climate. It is of
importance that the hydrolyzing enzymes in the seeds, such as diastase,
erepsin, remained unimpaired even after the germinating power of the seeds
had disappeared. The seeds were able to resist for two days the temperature
of liquid air, though the subsequent germina­tion was delayed by this
treatment. Macfadyen 28 exposed non-sporing bacteria, viz., B. typhosus, B.
coli communis, Staphylococcus pyogenes aureus, and a Saccharomyces to
liquid air.

The experi­ments showed that a prolonged exposure of six months to
a temperature of about -190° has no appreciable effect on the
vitality of micro-organisms. To judge by the results there appeared
no reason to doubt that the experi­ment might have been successfully
prolonged for a still longer period.
Paul Becquerel 29 found that seeds which possess a very thick integument
may live longer than the grain in Miss White’s experi­ments. The thickness
of the integument prevents the exchange of gases between air and seed.
Thus seeds of leguminoses (Cassia bicapsularis, Cytisus biflorus, Leucæna
leucocephala, and Trifolium arvense) had retained their power of germina­‐
tion for eighty-seven years. Becquerel has shown that the dryness of the
membrane is very essential for such a dura­tion of life, since when dry it is
impermeable for gases and the slow chemical reac­tions inside the grain
become impossible.
In the cosmic space there is no water vapour, no atmosphere, and a low
temperature, and there is hence no reason why spores should lose
appreciably more of their germinating power in ten thousand years than in
six months. We must therefore admit the possibility that spores may move
for an almost infinite length of time through cosmic space and yet be ready
for germina­tion when they fall upon a planet in which all the condi­tions for
germina­tion and development exist, e. g., water, proper temperature, and the
right nutritive substances dissolved in the water (inclusive of free oxygen).
While thus everything is favourable to Arrhenius’s hypothesis, Becquerel
raises the objec­tion that the spores going through space would yet be
destroyed by ultraviolet light. This danger would probably exist only as
long as the germ is not too far from a sun. The difficulty is a real one since
the ultraviolet rays have a destructive effect even in the absence of oxygen.
It is possible, however, that there are spores which can resist this effect of
ultraviolet light. Arrhenius’s theory can not of course be disproved and we
must agree with him that it is consistent not only with the theories of

cosmogony but also with the seeming potential immortality of certain or of
all cells.
The alternative to Arrhenius’s theory is that living matter did originate and
still originates from non-living matter. If this idea is correct it should one
day be possible to discover synthetic enzymes which are capable of forming
molecules of their own kind from a simple nutritive solu­tion. With such
synthetic enzymes as a starting point the task might be undertaken of
creating cells capable of growth and cell division, at least in the apparently
simple form in which these phenomena occur in bacteria; viz., that after the
mass has reached a certain (still microscopic) size it divides into two cells
and so on. If Arrhenius is right that living matter has had no more beginning
than matter in general, this hope of making living matter artificially appears
at present as futile as the hope of making molecules out of electrons.
The problem of making living matter artificially has been compared to that
of constructing a perpetuum mobile; this comparison is, however, not
correct. The idea of a perpetuum mobile contradicts the first law of
thermodynamics, while the making of living matter may be impossible
though contradicting no natural law.
Pasteur’s proof that spontaneous genera­tion does not occur in the solu­tions
used by him does not prove that a synthesis of living from dead matter is
impossible under any condi­tions. It is at least not inconceivable that in an
earlier period of the earth’s history radio-activity, electrical discharges, and
possibly also the action of volcanoes might have furnished the combina­tion
of circumstances under which living matter might have been formed. The
staggering difficulties in imagining such a possibility are not merely on the
chemical side—e. g., the produc­tion of proteins from CO2, and N—but also
on the physical side if the necessity of a definite cell structure is considered.
We shall see in the sixth chapter that without a structure in the egg to begin
with, no forma­tion of a complicated organism is imaginable; and while a
bacterium may have a simple structure, such a structure as it possesses is as
necessary for its existence as are its enzymes.

Attempts have repeatedly been made to imitate the structures in the cell and
of living organisms by colloidal precipitates. It is needless to point out that
such precipitates are of importance only for the study of the origin of
structures in the living, but that they are not otherwise an imita­tion of the
living since they are lacking the characteristic synthetic chemical processes.

CHAPTER III
THE CHEMICAL BASIS OF GENUS AND SPECIES

1. It is a truism that from an egg of a species an organism of this species
only and of no other will arise. It is also a truism that the so-called
protoplasm of an egg does not differ much from that of eggs of other
species when looked at through a microscope. The ques­tion arises: What
determines the species of the future organism? Is it a structure or a specific
chemical or groups of chemicals? In a later chapter we shall show that the
egg has a simple though definite structure, but in this chapter we shall see
that the egg must contain specific substances and that these substances
which determine the “species” and specificity in general are in all
probability proteins. Since solu­tions of different proteins look alike under a
microscope we need not wonder that it is impossible to discriminate
microscopically between the protoplasm of different eggs.
The idea of definiteness and constancy of species, a matter of daily observa­‐
tion in the case of man and higher animals in general, was not so readily
accepted in the case of the micro-organisms, which on account of their
minuteness and simplicity of structure are not so easy to differentiate. There
existed for a long time serious doubt whether or not the simplest organisms,
the bacteria, possessed a definite “specificity” like the higher organisms, or
whether they were not endowed, as Warming put it, with an “unlimited
plasticity,” which forbade classifying them according to their form into
definite species as Cohn had done. An interesting episode in this discussion,
which was settled about twenty-five years ago arose concerning the sulphur
bacteria, which often develop in large masses on parts of decaying plants or
animals along the shore. Sir E. Ray Lankester found collec­tions of red
bacteria covering putrefying animal matter in a vessel and forming a
continuous membrane along its wall. These red bacteria were of very

different shape, size, and grouping, but they seemed to be connected by
transi­tion forms. They had a common character, however, namely, their
peach-coloured appearance. This common character, together with their
associa­tion in the same habitat, led Lankester to the then justifiable belief
that they all belonged to one species which was protean in character and
that the different forms were only to be considered as phases of growth of
this one species. The presence of the same red pigment “Bacterio-purpurin”
seemed justly to indicate the existence of common chemical processes.
Cohn, on the contrary, considered the different forms among these red
bacteria (they are today called sulphur bacteria since they oxidize the
hydrogen sulphide produced by bacteria of putrefac­tion to sulphur and
sulphates) as definite and distinct species, in spite of their common colour
and their associa­tion. Later observa­tions showed that Cohn was right.
Winogradsky 30 succeeded in proving by pure culture experi­ments that each
of these different forms of sulphur bacteria was specific and did not give
rise to any of the other forms of the same colour found in the same condi­‐
tions.
The method of pure line breeding inaugurated by Johannsen 31 has shown
that the degree of definiteness goes so far that apparently identical forms
with only slight differences in size may breed true to this size; but for
reasons which will become clear later on we may doubt whether they are to
be considered as definite species.
The fact of specificity is supported by the fact of constancy of forms. de
Vries has pointed out that regardless of the possible origin of new species
by muta­tion the old species may persevere. Walcott has found fossils of
annelids, snails, crustaceans, and algæ in a precambrian forma­tion in British
Columbia whose age (estimated on the rate of forma­tion of radium from
uranium) may be about two hundred million years and estimated on the
basis of sedimenta­tion sixty million years. And yet these invertebrates are
so closely related to the forms existing today that the systematists have no
difficulty in finding the genus among the modern forms into which each of
these organisms belongs. W. M. Wheeler, in his investiga­tions of the ants

enclosed in amber, was able to identify some of them with forms living
today, though the ants observed in the amber must have been two million
years old. The constancy of species, i. e., the permanence of specificity may
therefore be considered as established as far back as two or possibly two
hundred millions of years. The definiteness and constancy of each species
must be determined by something equally definite and constant in the egg,
since in the latter the species is already fixed irrevocably.
We shall show first that species if sufficiently separated are generally
incompatible with each other and that any attempt at fusing or mixing them
by grafting or cross-fertilizing is futile. In the second part of the chapter we
shall take up the facts which seem destined to give a direct answer to the
ques­tion as to the cause of specificity. It is needless to say that this latter
ques­tion is of paramount importance for the problem of evolu­tion, as well
as for that of the constitu­tion of living matter.

I. The Incompatibility of Species not closely Related

2. It is practically impossible to transplant organs or tissues from one
species of higher animals to another, unless the two species are very closely
related; and even then the transplanta­tion is uncertain and the graft may
either fall off again or be destroyed. This specificity of tissues goes so far
that surgeons prefer, when a transplanta­tion of skin in the human is
intended, to use skin of the patient or of close blood rela­tions. The reason
why the tissues of a foreign species in warm-blooded animals cannot grow
well on a given host has been explained by the remarkable experi­ments of
James B. Murphy of the Rockefeller Institute. 32 Murphy discovered that it is
possible to transplant successfully any kind of foreign tissue upon the early
embryo of the chick. Even human tissue transplanted upon the chick
embryo will grow rapidly. This shows that at this early stage the chick
embryo does not yet react against foreign tissue. This lack of reac­tion lasts
until about the twenty-first day in the life of the embryo; then the growth of
the graft not only ceases but the graft itself falls off or is destroyed. Murphy

noticed that this critical period coincides with the development of the spleen
and of lymphatic tissue in the chick and that a certain type of migrating
cells, the so-called lymphocytes, which develop in the lymphatic tissue,
gather at the edge of the graft in great numbers, and he suggested that these
lymphocytes (by a secre­tion of some substance?) rid the host of the graft.
He applied two tests both of which confirmed this idea. First he showed that
when small fragments of the spleen of an adult chicken are transplanted into
the embryo the latter loses its tolerance for foreign grafts. The second proof
is still more interesting. It was known that by treatment with Roentgen rays
the lymphocytes in an animal could be destroyed. It was to be expected that
an animal so treated would have lost its specific resistance to foreign
tissues. Murphy found that this was actually the case. On fully grown rats in
which the lymphocytes had been destroyed by X-rays (as ascertained by
blood counts) tissues of foreign species grew perfectly well. These experi­‐
ments have assumed a great practical importance since they can also be
applied to the immuniza­tion of an animal against transplanted cancer of its
own species. Murphy found that by increasing the number of lymphocytes
in an animal (which can be accomplished by a mild treatment with X-rays)
the immunity against foreign grafts as well as against cancer from the same
species can be increased. It is quite possible that the apparent immunity to a
transplanta­tion of cancer produced by Jensen, Leo Loeb, and Ehrlich and
Apolant through the previous transplanta­tion of tissue in such an animal
was due to the fact that this previous tissue transplanta­tion led to an
increase in the number of lymphocytes in the animal. The medical side,
however, lies outside of our discussion, and we must satisfy ourselves with
only a passing notice. The facts show that each warm-blooded animal seems
to possess a specificity whereby its lymphocytes destroy transplanted tissue
taken from a foreign species.
A lesser though still marked degree of incompatibility exists also in lower
animals for grafts from a different species. 33 The graft may apparently take
hold, but only for a few days, if the species are not closely related. Joest
apparently succeeded in making a permanent union between the anterior

and posterior ends of two species of earthworms, Lumbricus rubellus and
Allolobophora terrestris. Born and later Harrison healed pieces of tadpoles
of different species together. An individual made up of two species Rana
virescens and Rana palustris lived a considerable time and went through
metamorphosis. Each half regained the characteristic features of the species
to which it belonged. It seems, however, that if species of tadpoles of two
more distant species are grafted upon each other no lasting graft can be
obtained, e. g., Rana esculenta and Bombinator igneus. These experi­ments
were made at a time when the nature and bearing of the problem of
specificity was not yet fully recognized. The rôle of lymphocytes in these
cases has never been investigated. The grafted piece always retained the
characteristics of the species from which it was taken.
Plants possess no leucocytes and we therefore see that they tolerate a graft
of foreign tissues better than is the case in animals. As a matter of fact
hetero­c grafting is a common practice in horticulture, although even here it
is known that indiscriminate hetero­plastic grafting is not feasible and that
therefore the specificity is not without influence. The host is supposed to
furnish only nutritive sap to the graft and in this respect does not behave
very differently from an artificial nutritive solu­tion for the raising of a plant.
The law of specificity, however, remains true also for the grafted tissues:
neither in animals nor in plants does the graft lose its specificity, and it
never assumes the specific characters of the host, or vice versa. The
apparent excep­tions which Winkler believed he had found in the case of
grafts of nightshade on tomatoes turned out to be a further proof of the law
of specificity. Winkler, after the graft had taken, cut through the place of
grafting, after which opera­tion a callus forma­tion occurred on the wound. In
most cases either a pure nightshade or a pure tomato grew out from this
callus. In some cases he obtained shoots from the place where graft and
host had united, which on one side were tomato, on the other side
nightshade. What really happened was that the shoots had a growing point
whose cells on the one side consisted of cells of nightshade, on the other

side of tomato. 34 We know of no case in which the cell of a graft has lost its
specificity and undergone a trans­forma­tion into the cell of the host.
3. Another manifesta­tion of the incompatibility of distant species is found in
the domain of fertiliza­tion. The eggs of the majority of animals cannot
develop unless a spermato­zoön enters. The entrance of a spermato­zoön into
an egg seems also to fall under the law of specificity, inasmuch as in
general only the sperm of the same or a closely related species is able to
enter the egg. The writer 35 has found, however, that it is possible to
overcome the limita­tion of specificity in certain cases by physico­chemical
means, and by the knowledge of these means we may perhaps one day be
able to more closely define the mechanism of specificity in this case. He
found that the eggs of a certain Californian sea urchin, which cannot be
fertilized by the sperm of starfish in normal sea water, will lose their
specificity towards this type of foreign sperm if the sea water is rendered a
little more alkaline, or if a little more Ca is added to the sea water, or if both
these varia­tions are effected. Godlewski has confirmed the efficiency of this
method for the fertiliza­tion of sea-urchin eggs with the sperm of crinoids.
If such hetero­geneous
hybridiza­tions are carried
out, two striking results are
obtained. The one is that the
resulting larva has only
maternal characteristics
(Figs. 1 and 2), as if the
Fig. 1. Five-days-old larvæ from a sea urchin (Strongy­‐
sperm had contributed no lo­cen­tro­tus purpuratus) ♀ and a starfish (Asterias) ♂ .
hereditary material to the (Front view.)
developing embryo. This
result could not have been
predicted, for if we fertilize
the egg of the same
Californian sea urchin,
Strongylo­centrotus

purpuratus, with the sperm
of a very closely related sea
urchin, S. franciscanus, the
hereditary effect of the
spermato­zoön is seen very
distinctly in the primitive
skeleton formed by the Fig. 2. Five-days-old larvæ of Strongylo­cen­tro­tus pur­‐
larva. 36 (Fig. 3.) In the case pur­atus produced by artificial parthenogenesis. (Side
view.) The larvæ in Figs. 1 and 2 are identical in
of the hetero­geneous appearance, proving that hetero­geneous hybridiza­tion
hybridiza­tion the spermato­‐ leads to a larva with purely maternal characters.

zoön acts practically only
as an activating agency
upon the egg and not as a
transmitter of paternal
qualities.
The second striking fact is
Fig. 3. Five-days-old larvæ of two closely related forms of sea that while the sea-urchin
urchins (S. purpuratus ♀ and S. franciscanus ♂). In this case
eggs fertilized with
the larva has also paternal characters as shown by the
skeleton. starfish sperm develop at
first perfectly normally
they begin to die in large numbers on the second and third day of their
development, and only a very small number live long enough to form a
skeleton; and these are usually sickly and form the skeleton considerably
later than the pure breed. It is not quite certain whether the sickliness of
these hetero­geneous hybrids begins or assumes a severe character with the
development of a certain type of wandering cells, the mesenchyme cells; it
would perhaps be worth while to investigate this possibility. The writer was
under the impression that this sickliness might have been brought about by
a poison gradually formed in the hetero­geneous larvæ.
He investigated the effects of hetero­geneous hybridiza­tion also in fishes,
which are a much more favourable object. The egg of the marine fish

Fundulus hetero­clitus can be fertilized with the sperm of almost any other
teleost fish, as Moenkhaus 37 first observed. This author did not succeed in
keeping the hybrids alive more than a day, but the writer has kept many
hetero­geneous hybrids alive for a month or longer, 38 and found the same
two striking facts which he had already observed in the hetero­geneous cross
between sea urchin and starfish: first, practically no transmission of paternal
characters, and second, a sickly condi­tion of the embryo which begins early
and which increases with further development. The hetero­geneous fish
hybrids between, e. g., Fundulus hetero­clitus ♀ and Menidia ♂ have
usually no circula­tion of blood, although the heart is formed and beats and
blood-vessels and blood cells are formed; the eyes are often incomplete or
abnormal though they may be normal at first; the growth of the embryo is
mostly retarded. In excep­tional cases circula­tion may be established and in
these a normal embryo may result, but such an embryo is chiefly maternal.
This incompatibility of two gametes from different species does not show
itself in the case of hetero­geneous hybridiza­tion only, but also though less
often in the case of crossing between two more closely related forms. The
cross between the two related forms S. purpuratus ♀ and S. franciscanus ♂
is very sturdy and shows no abnormal mortality as far as the writer’s
observa­tions go. If, however, the reciprocal crossing is carried out, namely
that of S. franciscanus ♀ and S. purpuratus ♂, the development is at first
normal, but beginning with the time of mesenchyme forma­tion the majority
of larvæ become sickly and die; and again the ques­tion may be raised
whether or not the beginning of sickliness coincides with the development
of mesenchyme cells. If we assume that the sickliness and death are due to
the forma­tion of a poison, we must assume that the poison is formed by the
protoplasm of the egg, since otherwise we could not understand why the
reciprocal cross should be healthy.
All of these data agree in this one point, that the fusion by grafting or
fertiliza­tion of two distant species is impossible, although the mechanism of
the incompatibility is not yet understood. It is quite possible that this
mechanism is not the same in all the cases mentioned here, and that it may

be different when two different species are mixed and when incompatibility
exists between varieties, as is the case in the graft on mammals.

II. The Chemical Basis of Genus and Species and of Species Specificity

4. Fifty or sixty years ago surgeons did not hesitate to transfuse the blood of
animals into human beings. The practice was a failure, and Landois 39
showed by experi­ment that if blood of a foreign species was introduced into
an animal the blood corpuscles of the transfused blood were rapidly
dissolved and the animal into which the transfusion was made was rendered
ill and often died. The result was different when the animals whose blood
was used for the purpose of transfusion belonged to the same species or a
species closely related to the animal into which the blood was transfused.
Thus when blood was exchanged between horse and donkey or between
wolf and dog or between hare and rabbit no hemoglobin appeared in the
urine and the animal into which the blood was transfused remained well. 40
This was the beginning of the investiga­tions in the field of serum specificity
which were destined to play such a prominent rôle in the development of
medicine. Friedenthal was able to show later that if to 10 c.c. of serum of a
mammal three drops of defibrinated blood of a foreign species are added
and the whole is exposed in a test tube to a temperature of 38°C. for fifteen
minutes the blood cells contained in the added blood are all cytolyzed; that
this, however, does not occur so rapidly when the blood of a related species
is used. He could thus show that human blood serum dissolves the
erythrocytes of the eel, the frog, pigeon, hen, horse, cat, and even that of the
lower monkeys but not that of the anthropoid apes. The blood of the
chimpanzee and of the human are no longer incompatible, and this
discovery was justly considered by Friedenthal as a confirma­tion of the idea
of the evolu­tionists that the anthropoid apes and the human are blood
rela­tions. 41
This line of investiga­tion had in the meanwhile entered upon a new stage
when Kraus, Tchistowitch, and Bordet discovered and developed the

precipitin reac­tion, which consists in the fact that if a foreign serum (or a
foreign protein) is introduced into an animal the blood serum of the latter
acquired after some time the power of causing a precipitate when mixed
with the antigen, i. e., with the foreign substance originally introduced into
the animal for the purpose of causing the produc­tion of antibodies in the
latter; while, of course, no such precipita­tion occurs if the serum of a non-
treated rabbit is mixed with the serum of the blood of the foreign species.
In 1897 Kraus discovered that if the filtrates from cultures of bacteria (e. g.,
typhoid bacillus) are mixed with the serum of an animal immunized with
the same serum (e. g., typhoid serum) it causes a precipitate; and that this
precipitin reac­tion is specific. This fact was confirmed and has been
extended by the work of many authors.
Tchistowitch in 1899 observed that the serum of rabbits which had received
injec­tions of horse or eel serum caused a precipitate when mixed with the
serum of these latter animals.
Bordet found in 1899 that if milk is injected into a rabbit the serum of such
a rabbit acquires the power of precipitating casein, and Fish found that this
reac­tion is specific inasmuch as the lactoserum from cow’s milk can
precipitate only the casein of cow’s milk but not that of human or goat milk.
Wassermann and Schütze reached the same result independently of each
other.
Myers and later Uhlenhuth showed that if white of egg from a hen’s egg is
injected into a rabbit, precipitins for white of egg are found in the serum of
the latter, and Uhlenhuth 42 found, by trying the white of egg of different
species of birds, that the precipitin reac­tion called forth by the blood of the
immunized animal is specific, inasmuch as the proteins from a hen’s egg
will call forth the forma­tion of precipitins in the blood of the rabbit which
will precipitate only the white of egg of the hen or of closely related birds.
To Nuttall 43 belongs the credit of having worked out a quantitative method
for measuring the amount of precipitate formed, and in this way he made it

possible to draw more valid conclusions concerning the degree of
specificity of the precipitin reac­tion. He found by this method that when the
immune serum is mixed with the serum or the protein solu­tion used for the
immuniza­tion a maximum precipitate is formed, but if it is mixed with the
serum of related forms a quantitatively smaller precipitate is produced. In
this way the degree of blood rela­tionship could be ascertained. He thus was
able to show that when the blood of one species, e. g., the human, was
injected into the blood of a rabbit, after some time the serum of the rabbit
was able to cause a precipitate not only with the serum of man, or
chimpanzee, but also of some lower monkeys; with this difference,
however, that the precipitate was much heavier when the immune serum
was added to the serum of man. The method thus shows the existence of not
an absolute but of a strong quantitative specificity of blood serum. This
statement may be illustrated by the following table from Nuttall. The
antiserum used for the precipitin reac­tion was obtained by treating a rabbit
with human blood serum. The forty-five bloods tested had been preserved
for various lengths of time in the refrigerator with the addi­tion of a small
amount of chloroform.
TABLE II
Quantitative Tests with Anti-Primate Sera
Tests with Antihuman Serum

Precipitum
Blood of Percentage
Amount
Primates
Man .031 100
130 (loose
Chimpanzee .04
precipitum)
Gorilla .021 64
Ourang .013 42
Cynocephalus
.013 42
mormon

Cynocephalus sphinx .009 29
Ateles geoffroyi .009 29
Insectivora
Centetes ecaudatus .0 0
Carnivora
10 (loose
Canis aureus .003
precipitum)
Canis familiaris .001 3
10 (concentrated
Lutra vulgaris .003
serum)
Ursus tibetanus .0025 8
Genetta tigrina .001 3
Felis domesticus .001 3
Felis caracal .0008 3
Felis tigris .0005 2
Ungulata
Ox .003 10
Sheep .003 10
Cobus unctuosus .002 7
Cervus porcinus .002 7
Rangifer tarandus .002 7
Capra megaceros .0005 2
Equus caballus .0005 2
Sus scrofa .0 0
Rodentia
7 (concentrated
Dasyprocta cristata .002
serum clots)
Guinea-pig .0 0
Rabbit .0 0
Marsupialia

Petrogale xanthopus
Petrogale penicillata
Onychogale frenata
Onychogale
.0 0
unguifera
Onychogale
unguifera
Macropus bennetti
Thylacinus
cynocephalus

Among the Primate bloods that of the Chimpanzee gave too high a
figure, owing to the precipitum being flocculent and not settling
well, for some reason which could not be determined. The figure
given by the Ourang is somewhat too low, and the difference
between Cynocephalus sphinx and Ateles is not as marked as might
have been expected in view of the qualitative tests and the series
following. The possibilities of error must be taken into account in
judging of these figures; repeated tests should be made to obtain
something like a constant. Other bloods than those of Primates give
small reac­tions or no reac­tions at all. The high figures (10%)
obtained with two Carnivore bloods can be explained by the fact
that one gave a loose precipitum, and the other was a somewhat
concentrated serum. 44
We have mentioned that even the proteins of the egg are specific according
to Uhlenhuth. Graham Smith, one of Nuttall’s collaborators, applied the
latter’s quantitative method to this problem and confirmed the results of
Nuttall. A few examples may serve as an illustra­tion.
TABLE III
Tests with Anti-Duck’s-Egg Serum

Amount of
Material tested Percentage
precipitum

egg-
Duck’s .0384 100
albumin
Pheasant’s " .0328 85
Fowl’s " .0234 61
Silver
" .0140 36
Pheasant’s
Blackbird’s " .0065 15
Crane’s " .0051 14
Moorhen’s " .0046 12
Thrush’s " .0046 12
Emu’s " .0018 5
Hedge-
" trace ?
Sparrow’s
Chaffinch’s " · 0
Tortoise
trace ?
serum
Turtle
" ?
serum
Alligator
· 0
serum

Frog, Amphiuma, and Dogfish sera, as well as Tortoise and Dogfish
egg-albumins, were also tested, with negative results.
TABLE IV
Tests with Anti-Fowl’s-Egg Serum

Amount of
Material tested Percentage
precipitum
egg-
Fowl’s albumin .0159 100
(old)
"
Fowl’s .0140 88
(fresh)

Silver
" .0075 47
Pheasant’s
Pheasant’s " .0075 47
Crane’s " .0046 29
Blackbird’s " .0046 29
Duck’s " .0037 23
Moorhen’s " .0028 18

Thrush, Emu, Greenfinch, and Hedge-sparrow egg-albumins were
tested and gave traces of precipita, as also did Tortoise and Turtle
sera. The egg-albumins of the Tortoise, Frog, Skate, and two species
of Dogfish did not react. Alligator, Frog, Amphiuma, and Dogfish
sera also yielded no results. 45

By improving the quantitative method in various ways, Welsh and
Chapman 46 were able to explain why the precipitin reac­tion with egg-white
was not strictly specific but gave also, though quanti­tatively weaker, results
with the egg-white of related birds. They found that by a new method
devised by them “it is possible to indicate in an avian egg-white antiserum
the presence of a general avian antisubstance (precipitin) together with the
specific antisubstance.”
The Bordet reaction was not only useful in indicating the specificity and
blood rela­tionship for animals but also among plants. Thus Magnus and
Friedenthal 47 were able to demonstrate with Bordet’s method the rela­‐
tionship between yeast (Saccharomyces cerevisiæ) and truffle (Tuber
brumale).
5. We must not forget, while under the spell of the problem of immunity,
that we are interested at the moment in the ques­tion of the nature of the
specificity of living organisms. It is only logical to conclude that the fossil
forms of invertebrate animals and of algæ and bacteria, which Walcott
found in the Cambrian and which may be two hundred million years old,
must have had the same specificity at that time as they or their close
relatives have today; and this raises the ques­tion: What is the nature of the

substances which are responsible for and transmit this specificity? It is
obvious that a definite answer to this ques­tion brings us also to the very
problem of evolu­tion as well as that of the constitu­tion of living matter.
There can be no doubt that on the basis of our present knowledge proteins
are in most or practically all cases the bearers of this specificity. This has
been found out not only with the aid of the precipitin reac­tion but also with
the anaphylaxis reac­tion, by which, as the reader may know, is meant that
when a small dose of a foreign substance is introduced into an animal a
hypersensitiveness develops after a number of days or weeks, so that a new
injec­tion of the same substance produces serious and in some cases fatal
effects. This hypersensitiveness, which was first analysed by Richet, 48 is
specific for the substance which has been injected. Now all these specific
reac­tions, the precipitin reac­tion as well as the anaphylactic reac­tion, can be
called forth by proteins. Thus Richet, in his earliest experi­ments, showed
that only the protein-containing part of the extract of actinians, by which he
called forth anaphylaxis, was able to produce this phenomenon, and later he
showed that it was generally impossible to produce anything resembling
anaphylaxis by non-protein substances, e. g., cocain or apomorphin. 49 Wells
isolated from egg-white four different proteins (three coagulable proteins
and one non-coagulable) which can be distinguished from each other by the
anaphylaxis reac­tion, although all come from the same biological object. 50
Michaelis as well as Wells found that the split products of the protein
molecule are no longer able to call forth the anaphylaxis reac­tion. Since
peptic diges­tion has the effect of annihilating the power of proteins to call
forth anaphylaxis, we are forced to the conclusion that the first cleavage
products of proteins have already lost the power of calling forth immunity
reac­tions.
A pretty experiment by Gay and Robertson 51 should be mentioned in this
connec­tion. Robertson had shown
that a substance closely resembling paranucleins both in its
properties and its C, H, and N content can be formed from the

filtered products of the complete peptic hydrolysis of an
approximately four per cent. neutral solu­tion of potassium caseinate
by the action of pure pepsin at 36°C.
He considered this a case of a real synthesis of proteins from the products
of its hydrolytic cleavage. This interpreta­tion was not generally accepted
and received a different interpreta­tion by Bayliss and other workers. Gay
and Robertson were able to show that paranuclein when injected into an
animal will sensitize guinea-pigs for anaphylactic intoxica­tion for either
paranuclein or casein and apparently indiscriminately. The products of
complete peptic diges­tion of casein had no such effect, but the synthetic
product of this diges­tion obtained by Robertson’s method has the same
specific antigenic properties as paranuclein, thus making it appear that
Robertson had indeed succeeded in causing a synthesis of paranuclein with
the aid of pepsin from the products of diges­tion of casein by pepsin.
There are a few statements in the literature to the effect that the specificity
of organisms might be due to other substances than proteins. Thus Bang and
Forssmann claimed that the substances (antigens) responsible for the
produc­tion of hemolysis were of a lipoid nature, but their statements have
not been confirmed, and Fitzgerald and Leathes 52 reached the conclusion
that lipoids are non-antigenic. Ford claims to have obtained proof that a
glucoside contained in the poisonous mushroom Amanita phalloides can act
as an antigen. But aside from this one fact we know that proteins and only
proteins can act as antigens and are therefore the bearers of the specificity
of living organisms.
Bradley and Sansum 53 found that guinea-pigs sensitized to beef or dog
hemoglobin fail to react or react but slightly to hemoglobin of other origin.
The hemoglobins tried were dog, beef, cat, rabbit, rat, turtle, pig, horse,
calf, goat, sheep, pigeon, chicken, and man.
6. It would be of the greatest importance to show directly that the
homologous proteins of different species are different. This has been done
for hemoglobins of the blood by Reichert and Brown, 54 who have shown by

crystallographic measurements that the hemoglobins of any species are
definite substances for that species.
The crystals obtained from different species of a genus are
characteristic of that species, but differ from those of other species
of the genus in angles or axial ratio, in optical characters, and
especially in those characters comprised under the general term of
crystal habit, so that one species can usually be distinguished from
another by its hemoglobin crystals. But these differences are not
such as to preclude the crystals from all species of a genus being
placed in an isomorphous series (p. 327).
As far as the genus is concerned it was found that the hemoglobin crystals
of any genus are isomorphous.
In some cases this isomorphism may be extended to include several
genera, but this is not usually the case, unless as in the case of dogs
and foxes, for example, the genera are very closely related.
The most important ques­tion for us is the following: Are the differences
between the corresponding hemoglobin crystals of different species of the
same genus such as to warrant the statement that they indicate chemical
differences? If this were the case we might say that blood reac­tions as well
as hemoglobin crystals indicate that differences in the constitu­tion of
proteins determine the species specificity and, perhaps, also species
heredity. The following sentences by Reichert and Brown seem to indicate
that this may be true for the crystals of hemoglobin.
The hemoglobins of any species are definite substances for that
species. But upon comparing the corresponding substances
(hemoglobins) in different species of a genus it is generally found
that they differ the one from the other to a greater or less degree; the
differences being such that when complete crystallographic data are
available the different species can be distinguished by these
differences in their hemoglobins. As the hemoglobins crystallize in
isomorphous series the differences between the angles of the

crystals of the species of a genus are not, as a rule, great; but they
are as great as is usually found to be the case with minerals or
chemical salts that belong to an isomorphous group (p. 326).
As Professor Brown writes me, the difficulty in answering the ques­tion
definitely, whether or not the hemoglobins of different species are
chemically different, lies in the fact that there is as yet no criterion which
allows us to discriminate between a species and a Mendelian muta­tion
except the morpho­logical differences. It is not impossible that while species
differ by the constitu­tion of some or most of their proteins, Mendelian
heredity has a different chemical basis.
It is regrettable that work like that of Reichert and Brown cannot be
extended to other proteins, but it seems from anaphylaxis reac­tions that we
might expect results similar to those in the case of the hemoglobins. The
proteins of the lens are an excep­tion inasmuch as, according to Uhlenhuth,
the proteins of the lens of mammals, birds, and amphibians cannot be
discriminated from each other by the precipitin reac­tion. 55

7. The serum of certain humans may cause the destruc­tion or agglutina­tion
of blood corpuscles of certain other humans. This fact of the existence of
“isoagglutinins” seems to have been established for man, but Hektoen states
that he has not been able to find any isoagglutinins in the serum of rabbits,
guinea-pigs, dogs, horses, and cattle. Landsteiner found the remarkable fact
that the sera of certain individuals of humans could hemolyze the
corpuscles of certain other individuals, but not those of all individuals. A
systematic investiga­tion of this variability led him to the discovery of three
distinct groups of individuals, the sera of each group acting in a definite
way towards the corpuscles of the representatives of each other group. Later
observers, for example Jansky and Moss, established four groups. These
groups are, according to Moss, 56 as follows:
Group 1. Sera agglutinate no corpuscles.
Corpuscles agglutinated by sera of Groups 2, 3, 4.

Group 2. Sera agglutinate corpuscles of Groups 1, 3.
Corpuscles agglutinated by sera of Groups 3, 4.
Group 3. Sera agglutinate corpuscles of Groups 1, 2.
Corpuscles agglutinated by sera of Groups 2, 4.
Group 4. Sera agglutinate corpuscles of Groups 1, 2, 3.
Corpuscles agglutinated by no serum.
The relative frequency of the four groups follows from the following
figures. Of one hundred bloods tested by Moss in series of twenty there
were found:
10 belonging to Group 1.
40 belonging to Group 2.
7 belonging to Group 3.
43 belonging to Group 4.
Groups 2 and 4 are in the majority and in overwhelming numbers, which
indicates that, as a rule, the sera agglutinate the blood corpuscles of
individuals of the other groups, but not those of individuals belonging to the
same group. The phenomenon that a serum agglutinates no corpuscles
(Group 1), or that the corpuscles are agglutinated by no serum (Group 4),
are the excep­tions. It is obvious that, as far as our problem is concerned,
only Groups 2 and 3 are to be considered. There is no Mendelian character
which refers only to one half of the individuals except sex. Since nothing is
said about a rela­tion of Groups 2 and 3 to sex such a rela­tion probably does
not exist.
8. The facts thus far reported imply the sugges­tion that the heredity of the
genus is determined by proteins of a definite constitu­tion differing from the
proteins of other genera. This constitu­tion of the proteins would therefore
be responsible for the genus heredity. The different species of a genus have
all the same genus proteins, but the proteins of each species of the same
genus are apparently different again in chemical constitu­tion and hence may
give rise to the specific biological or immunity reac­tions.

We may consider it as established by the work of McClung, Sutton, E. B.
Wilson, Miss Stevens, Morgan, and many others, that the chromo­somes are
the carriers of the Mendelian characters. These chromo­somes occur in the
nucleus of the egg and in the head of the sperm. Now the latter consists, in
certain fish, of lipoids and a combina­tion of nucleinic acid and protamine or
histone, the latter a non-coagulable protein, more resembling a split product
of one of the larger coagulable proteins.
A. E. Taylor 57 found that if the spermatozoa of the salmon are injected into
a rabbit, the blood of the animal acquires the power of causing cytolysis of
salmon spermatozoa. When, however, the isolated protamines or nucleinic
acid or the lipoids prepared from the same sperm were injected into a rabbit
no results of this kind were observed. H. G. Wells more recently tested the
relative efficiency of the constituents of the testes of the cod (which in addi­‐
tion to the constituents of the sperm contained the proteins of the testicle).
From the testicle he prepared a histone (the protein body of the sperm
nucleus), a sodium nucleinate, and from the sperm-free aqueous extract of
the testicles a protein resembling albumin was separated by precipita­tion. 58

The albumin behaved like ordinary serum albumin or egg albumin,
producing typical and fatal anaphylactic reac­tions and being specific
when tried against mammalian sera. The nucleinate did not produce
any reac­tions when guinea-pigs were given small sensitizing and
larger intoxicating doses (0.1 gm.) in a three weeks’ interval; a result
to be expected, since no protein is present in the prepara­tion. The
histone was so toxic that its anaphylactic properties could not be
studied.
It is not impossible that protamines and histones might be found to act as
specific antigens if they were not so toxic. The positive results which Taylor
observed after injec­tion of the sperm might have been due to the proteins
contained in the tail of the spermatozoa, which in certain animals at least
does not enter the egg and hence can have no influence on heredity.

It is thus doubtful whether or not any of the constituents of the nucleus
contribute to the determina­tion of the species. This in its ultimate
consequences might lead to the idea that the Mendelian characters which
are equally transmitted by egg and spermato­zoön, determine the individual
or variety heredity, but not the genus or species heredity. It is, in our present
state of knowledge, impossible to cause a spermato­zoön to develop into an
embryo, 59 while we can induce the egg to develop into an embryo without a
spermato­zoön. This may mean that the protoplasm of the egg is the future
embryo, while the chromo­somes of both egg and sperm nuclei furnish only
the individual characters.

CHAPTER IV
SPECIFICITY IN FERTILIZATION

1. We have become acquainted with two characteristics of living matter: the
specificity due to the specific proteins characteristic for each genus and
possibly species and the synthesis of living matter from the split products of
their main constituents instead of from a supersaturated solu­tion of their
own substance, as is the case in crystals. We are about to discuss in this and
the next chapter a third characteristic, namely, the phenomenon of fertiliza­‐
tion. While this is not found in all organisms it is found in an overwhelming
majority and especially the higher organisms, and of all the mysteries of
animated nature that of fertiliza­tion and sex seems to be the most
captivating, to judge from the space it occupies in folklore, theology, and
“literature.” Bacteria, when furnished the proper nutritive medium, will
synthetize the specific material of their own body, will grow and divide, and
this process will be repeated indefinitely as long as the food lasts and the
temperature and other outside condi­tions are normal. It is purely due to
limita­tion of food that bacteria or certain species of them do not cover the
whole planet. But, as every layman knows, the majority of organisms grow
only to a certain size, then die, and the propaga­tion takes place through sex
cells or gametes: a female cell—the egg—containing a large bulk of
protoplasm (the future embryo) and reserve material; and the male cell
which in the case of the spermato­zoön contains only nuclear material and
no cytoplasmic material except that contained in the tail which in some and
possibly many species does not enter the egg. The male element—the
spermato­zoön—enters the female gamete—the egg—and this starts the
development. In the case of most animals the egg cannot develop unless the
spermato­zoön enters. The ques­tion arises: How does the spermato­zoön
activate the egg? And also how does it happen that the spermato­zoön enters
the egg? We will first consider the latter ques­tion. These problems can be

answered best from experi­ments on forms in which the egg and the sperm
are fertilized in sea water. Many marine animals, from fishes down to lower
forms, shed their eggs and sperm into the sea water where the fertiliza­tion
of the egg takes place, outside the body of the female.
The first phenomenon which strikes us in this connec­tion is again a
phenomenon of specificity. The spermato­zoön can, as a rule, only enter an
egg of the same or a closely related species, but not that of one more
distantly related. What is the character of this specificity? The writer was
under the impression that a clue might be obtained if artificial means could
be found by which the egg of one species might be fertilized with a distant
species for which this egg is naturally immune. Such an experi­ment would
mean that the lack of specificity had been compensated by the artificial
means. It is well known that the egg of the sea urchin cannot as a rule be
fertilized with the sperm of a starfish in normal sea water. The writer tried
whether this hybridiza­tion could not be accomplished provided the constitu­‐
tion of the sea water were changed. He succeeded in causing the fertiliza­‐
tion of a large percentage of the eggs of the Californian sea urchin,
Strongylo­centrotus purpuratus, with the sperm of various starfish (e. g.,
Asterias ochracea) and Holothurians by slightly raising the alkalinity of the
sea water, through the addi­tion of some base (NaOH or tetra­ethyl­‐
ammonium­hydroxide or various amines), the optimum being reached when
0.6 c.c. N/10 NaOH is added to 50 c.c. of sea water. It is a peculiar fact that
this solu­tion is efficient only if both egg and sperm are together in the
hyperalkaline sea water. If the eggs and sperm are treated separately with
the hyperalkaline sea water and are then brought together in normal sea
water no fertiliza­tion takes place as a rule, while with the same sperm and
eggs the fertiliza­tion is successful again if both are mixed in the
hyperalkaline solu­tion. From this the writer concluded that the fertilizing
power depends on a rapidly reversible action of the alkali on the surface of
the two gametes. It was found that an increase of the concentra­tion of
calcium in the sea water also favoured the entrance of the Asterias sperm

into the egg of purpuratus; and that if CCa was increased it was not
necessary to add as much NaOH.
The spermato­zoön enters the egg through the so-called fertiliza­tion cone,
i. e., a proto­plasmic process comparable to the pseudo­podium of an
amœboid cell. The analogy of the process of phago­cytosis—i. e., the taking
up of particles by an amœboid cell—and that of the engulfing of the
spermato­zoön by the egg presents itself. We do not know definitely the
nature of the forces which act in the case of phago­cytosis—although surface
tension forces and agglutina­tion have been suggested; both are surface
phenomena and are rapidly reversible.
We should then say that the specificity in the process of fertiliza­tion
consists in a peculiarity of the surface of the egg and spermato­zoön which
in the case of S. purpuratus ♀ and Asterias ♂ can be supplied by a slight
increase in the COH or CCa.
By this method fifty per cent. or more of the eggs of purpuratus could be
fertilized with the sperm of the starfish Asterias ochracea, capitata,
Ophiurians, and Holothurians, while with the sperm of another starfish,
Pycnopodia spuria, only five per cent., and with the sperm of Asterina only
one per cent. could be fertilized. 60 Godlewski succeeded by the same
method in fertilizing the eggs of a Naples starfish with the sperm of a
crinoid. 61 The writer did not succeed in bringing about the fertiliza­tion of
the egg of another sea urchin in California, Strongylo­centrotus
franciscanus, with the sperm of a starfish. Although these eggs formed a
membrane in contact with the sperm, the latter did not enter the egg; nor has
the writer as yet succeeded in causing the sperm of Asterias to enter the egg
of Arbacia.
Kupelwieser 62 observed that the spermato­zoön of molluscs may
occasionally enter into the egg of S. pur­pur­atus in normal sea water and
later, at Naples, he observed the same for the sperm of annelids. In these
cases no development took place. In teleost fishes the spermato­zoön can

enter the eggs of widely different species but with rare excep­tions all the
embryos will die in an early stage of development. 63
2. The fact that an increase in the alkalinity or in the concentra­tion of
calcium allowed foreign sperm to enter the egg of the sea urchin, suggested
the idea that a diminu­tion of alkalinity or calcium in the sea water might
block the entrance of the sperm of sea urchin into eggs of their own species.
This was found to be correct; when we put eggs and sperm of the same
species of sea urchin into solu­tions whose concentra­tion of Ca or of OH is
too small, the sperm, although it may be intensely active, cannot enter the
egg.
For the purpose of these experi­ments the ovaries and testes of the sea
urchins were not put into sea water, but instead into pure m/2 NaCl and
after several washings in this solu­tion were kept in it (they remain alive for
several days in pure m/2 NaCl). Several drops of such sperm and one drop
of eggs were in one series of experi­ments put into 2.5 c.c. of a neutral
mixture of m/2 NaCl and 3⁄8 m MgCl2 in the propor­tion in which these two
salts exist in the sea water. In such a neutral solu­tion eggs of Arbacia or
purpuratus are not fertilized no matter how long they remain in it, although
the spermatozoa swim around the eggs very actively. That no spermato­zoön
enters the eggs can be shown by the fact that the eggs do not divide
(although they can segment in such a solu­tion if previously fertilized in sea
water or some other efficient solu­tion). When, however, eggs and sperm are
put into 2.5 c.c. of the same solu­tion of NaCl+MgCl2, containing in addi­‐
tion one drop of a N/100 solu­tion of NaOH (or NH3 or benzylamine or
butylamine) or eight drops of m/100 NaHCO3, most, and often practically
all of the eggs at once form fertiliza­tion membranes and segment at the
proper time, indicating that fertiliza­tion has been accomplished. The same
result can be obtained if the eggs are transferred into a neutral mixture of
NaCl+MgCl2+CaCl2 (in the propor­tion in which these salts exist in the sea
water) or into a neutral mixture of NaCl+MgCl2+KCl+CaCl2. In such
neutral mixtures the eggs form fertiliza­tion membranes and begin to

segment. The eggs are not fertilized in a neutral solu­tion of NaCl or of
NaCl+KCl. 64
It is, therefore, obvious that if we diminish the alkalinity of the solu­tion
surrounding the egg and deprive this solu­tion of CaCl2 we establish the
same block to the entrance of the spermato­zoön of Arbacia into the egg of
the same species as exists in normal sea water for the entrance of the sperm
of the starfish into the egg of purpuratus.
The “block” created in this way, to the entrance of the sperm of Arbacia
into the egg of the same species is also rapidly reversible.
We reach the conclusion, therefore, that the specificity which allows the
sperm to enter an egg is a surface effect which can be increased or
diminished by an increase or diminu­tion in the concentra­tion of OH as well
as of Ca. The writer has shown that an increase in the concentra­tion of both
substances may cause an agglutina­tion of the spermatozoa of starfish to the
jelly which surrounds the egg of purpuratus. 65 It is thus not impossible that
the specificity which favours the entrance of a spermato­zoön into an egg of
its own species may consist in an agglutina­­tion between spermato­zoön and
egg protoplasm (or its fertiliza­tion cone); and that this agglutina­tion is
favoured if the COH or CCa or both are increased within certain limits.
Godlewski discovered a very interesting form of block to the entrance of
the spermato­zoön into the egg which takes place if two different types of
sperm are mixed. He had found that the sperm of the annelid Chætopterus
is able to enter the egg of the sea urchin and that in so doing it causes
membrane forma­tion. The egg, however, does not develop but dies rapidly,
as is the case when we induce artificial membrane forma­tion, as we shall
see in the next chapter.
Godlewski found that if the sperm of Chætopterus and the sperm of sea
urchins are mixed the mixture is not able to induce development or
membrane forma­tion, since now neither spermato­zoön can enter; blood has

the same inhibiting effect as the foreign sperm. The mixture does not
interfere with the development of the eggs if they are previously fertilized. 66
The phenomenon was further investigated by Herlant 67 who found that if
the sperm of a sea urchin is mixed with the sperm of certain annelids
(Chætopterus) or molluscs, and if after some time the eggs of the sea urchin
are added to the mixture of the two kinds of sperm no egg is fertilized. If,
however, the solu­tion is subsequently diluted with sea water or if the egg
that was in this mixture is washed in sea water, the same sperm mixture in
which the egg previously remained unfertilized will now fertilize the egg.
From these and similar observa­tions Herlant draws the conclusion that the
block existed at the surface of the egg, inasmuch as a reac­tion product of
the two types of sperm is formed after some time which alters the surface of
the egg and thereby prevents the sperm from entering. This view is
supported not only by all the experi­ments but also by the observa­tion of the
writer that foreign sperm or blood is able to cause a real agglutina­tion after
some time if mixed with the sperm of a sea urchin or a starfish. 68 We can
imagine that the precipitate forms a film around the egg and acts as a block
for the agglutina­tion between egg and spermato­zoön. The block can be
removed mechanically by washing.
3. The fact has been mentioned that the most motile sperm will not be able
to enter into the egg if certain other condi­tions (specificity or COH or CCa)
are not fulfilled. On the other hand, living but immobile sperm cannot enter
the egg under any condi­tions. If we add a trace of KCN to the sperm of
Arbacia so that the spermato­zoön becomes immobile no egg is fertilized
even if the eggs and the sperm are thoroughly shaken together; while the
same spermatozoa will fertilize these eggs as soon as the HCN has
evaporated and they again become motile. It was formerly thought that the
spermato­zoön had to bore itself into the egg, being propelled by the
movements of the flagellum. It is, however, more probable that only a
certain energy of vibra­tion is needed on the part of the spermato­zoön to
make the latter stick to the surface of the egg and agglutinate and that later

forces of a different character bring the spermato­zoön into the egg. The fact
that under normal condi­tions a very slight degree of motility on the part of
the spermato­zoön allows it to enter the egg of its own species seems to
favour such a view.
It is a common experience that spermatozoa become very active when they
reach the neighbourhood of an egg. v. Dungern assumed that only foreign
sperm became thus active, but F. R. Lillie 69 has pointed out that this may be
a specific effect. The writer tested this idea on the sperm and eggs of two
species of starfish and of sea urchins. It should be men­tioned that the eggs
of the starfish used in this experi­ment were completely immature and could
not be fertilized, while the eggs of the sea urchins were mature. The
testicles and ovaries had been kept in NaCl and all the sperm was immotile.
Eggs and sperm were mixed together in a pure m/2 NaCl solu­tion where the
sperm was only rendered motile by the proximity of eggs. The following
table gives the result. 70
TABLE V
Specificity of Activation of Sperm by Eggs

Asterias♂ Asterina♂ Franciscanus♂ Purpuratus♂
Asterias♀ Immediately No activa­‐ Moderately Slight effect
(immature) very tion. active. in
motile. immediate
contact with
egg.
Asterina♀ Not motile. Violent Violent activity. Slight effect
(immature) activity. only near
the egg.
Franciscanus♀ Slightly No Immediately Immediately
(mature) motile. motility. active. active.
Purpuratus♀ Slightly Slight Immediately Immediately
(mature) motile effect in active. active.
after some immediate
time.

contact
with eggs.
The spermatozoa of starfish show a marked specificity inasmuch as they are
strongly activated only by the eggs of their own species, although in this
experi­ment these were immature, and to a slight degree only by the eggs of
the sea urchin purpuratus. But it is also obvious that the specificity is far
from exclusive since the immature eggs of Asterina activate the sperm of
the sea urchin franciscanus as powerfully as is done by the mature eggs of
the sea urchin purpuratus and franciscanus. In studying these results the
reader must keep in mind first that all these experi­ments were made in a
NaCl solu­tion and second that it requires a stronger influence to activate the
spermatozoa of the starfish, which are not motile at first even in sea water,
than the sea urchin spermatozoa which are from the first very active in such
sea water, and which may therefore be considered as being at the threshold
of activity in pure NaCl solu­tion.
Wasteneys and the writer (in experi­ments not yet published) did not succeed
in demonstrating an activating effect of the eggs of various marine teleosts
upon sperm of the same species.
4. F. R. Lillie 71 has studied the very striking phenomenon of transitory
sperm agglutina­tion which takes place when the sperm of a sea urchin or of
certain annelids is put into the supernatant sea water of eggs of the same
species. If we put one or more drops of a very thick sperm suspension of the
Californian sea urchin S. purpuratus carefully into the centre of a dish
containing 3 c.c. of ordinary sea water and let the drop stand for one-half to
one minute and then by gentle agita­tion mix the sperm with the sea water
the mass of thick sperm which is at first rather viscous is distributed equally
in sea water in a few seconds and the result is a homogeneous sperm
suspension. When, however, the same experi­ment is made with the sea
water which has been standing for a short time over a large mass of eggs of
the same species, the thick drop of sperm seems to be less miscible and
instead of a homogeneous suspension we get, as a result, the forma­tion of a
large number of distinct clusters which are visible to the naked eye and

which may possess a diameter of 1 or 2 mm. The rest of the sea water is
almost free from sperm. These clusters of spermatozoa may last for from
two to ten minutes and then dissolve by the gradual detachment of the
spermatozoa from the periphery of the cluster.
This phenomenon seems to occur in sea urchins and annelids. The writer
has vainly looked for it in different forms of the Californian starfish or
molluscs and in fish at Woods Hole. Lillie failed to find it in the starfish at
Woods Hole.
The writer found that the sperm of the Californian sea urchin Strongylo­‐
centrotus purpuratus will form clusters with the egg sea water of
purpuratus but not with that of franciscanus; while the sperm of
franciscanus will agglutinate with the egg sea water of both species, but the
clusters last a little longer with the eggs of its own species.
He also found that the clusters are more durable in a neutral than in a
slightly alkaline solu­tion and that the agglutina­tion disappears the more
rapidly the more alkaline the solu­tion. The presence of bivalent ca­tions,
especially Ca, also favours the agglutina­tion.
It was also found that this agglutina­tion occurs only when the spermatozoa
are very motile; thus if a trace of KCN is added to a mass of thick sea-
urchin sperm so that the spermatozoa become immotile a drop of this sperm
will not agglutinate when put in egg sea water of the same species; while
later, after the HCN has evaporated, the same sperm will agglutinate when
put into such sea water.
The writer suggests the following explana­tion of the phenomenon. The egg
sea water contains a substance which forms a precipitate with a substance
on the surface of the spermato­zoön whereby the latter becomes slightly
sticky. This precipitate is slowly soluble in sea water and the more rapidly
the more alkaline (within certain limits). Only when the spermatozoa run
against each other with a certain impact will they stick together, as Lillie
suggested. Lillie assumes that this agglutinating substance contained in egg
sea water is required to bring about fertiliza­tion and he therefore calls it

“fertilizin.” 72 But this assump­tion seems to go beyond the facts inasmuch as
the existence of such an agglutinating substance can only be proved in a
few species of animals (sea urchins and annelids); and as, moreover, sea-
urchin sperm can fertilize eggs which will not cause the sperm to
agglutinate, e. g., the egg of franciscanus can be fertilized by sperm of
purpuratus, although the egg sea water of franciscanus causes no agglutina­‐
tion of the sperm of purpuratus. When the jelly surrounding the egg of the
Californian sea urchin S. purpuratus is dissolved with acid and the eggs are
washed, the eggs will not cause any more sperm agglutina­tion; and yet one
hundred per cent. of such eggs can be fertilized by sperm. 73
5. It is well known that if an egg is once fertilized it becomes impermeable
for other spermatozoa. This cannot well be due to the fact that the egg
develops; for the writer found some time ago that eggs of Strongylo­‐
centrotus purpuratus which are induced to develop by means of artificial
parthenogenesis can be fertilized by sperm. The following observa­tion
leaves no doubts in this respect. When the unfertilized eggs of purpuratus
are put for two hours into hypertonic sea water (50 c.c. of sea water+8 c.c.
21⁄2 m NaCl) and then transferred into sea water it occasionally happens that
a certain percentage of the eggs will begin to divide into 2, 4, 8 or more
cells, without developing any further. When to such eggs after they have
remained in the resting stage for a number of hours or a day, sperm is
added, some or all of the blasto­meres form a fertiliza­tion membrane and
now begin to develop into larvæ; and if the spermato­zoön gets into a
blastomere of the 2- or 4-cell stage normal plutei will result. When the
sperm is added while the eggs are in active partheno­genetic cell division the
individual blasto­meres into which a spermato­zoön enters will also form a
fertiliza­tion membrane, but such blasto­meres perish very rapidly. It is not
yet possible to state why it should make such a difference for the possibility
of development whether the spermato­zoön enters into a blastomere when at
rest or when it is in active nuclear division, although the idea presents itself
that in the latter case an abnormal mix-up and separa­tion of chromo­somes
and other constituents may be responsible for the fatal result. Whatever may

be the explana­tion of this phenomenon it proves to us that it is not the
process of development in itself which acts as a block to the entrance of a
spermato­zoön into an egg which is already fertilized. 74

When the spermato­zoön enters the egg of the sea urchin it calls forth the
forma­tion of a membrane—the fertiliza­tion membrane. It might be
considered possible that this membrane forma­tion or the altera­tion
underlying or accompanying it is responsible for the fact that an egg once
fertilized becomes immune against a spermato­zoön. We shall see in the next
chapter that it is possible to call forth the membrane in an unfertilized sea-
urchin egg by treating it with butyric acid. This membrane is so tough in the
egg of Strongylo­centrotus that no spermato­zoön can get through it; in the
egg of Arbacia the membrane is occasionally replaced by a soft gelatinous
film. If no second treatment is given to such eggs they will disintegrate in a
comparatively short time, but when sperm is added some or most of the
eggs will develop in the way characteristic of fertilized eggs. 75 When the
membrane is too tough to allow the spermato­zoön to enter the egg it can be
shown that if the membrane is torn mechanically the egg can still be
fertilized by sperm.
Should it be possible that the spermato­zoön can no longer agglutinate with
the fertilized egg or that those phagocytotic reac­tions which we suppose to
play a rôle in the entrance of the spermato­zoön into the egg are no longer
possible after a spermato­zoön has entered? The mere fact of development is
apparently not the cause which bars a spermato­zoön from entering an egg
already fertilized by sperm.
Lillie assumes that the egg loses its “fertilizin” in the process of membrane
forma­tion since the sea water containing such eggs no longer gives the
agglutinin reac­tion with sperm, and he believes that the lack of “fertilizin”
in the fertilized egg or in the egg after membrane forma­tion is the cause of
the block in the fertilized egg. But we have seen that the artificial
membrane forma­tion does not create such a block although it puts an end to
the “fertilizin” reac­tion. In the egg of purpuratus the “fertilizin” reac­tion

ceases when the jelly surrounding the egg is dissolved by an acid and the
eggs are repeatedly washed; yet such eggs can easily be fertilized by sperm.
Lillie does not assume that the “fertilizin” causes an agglutina­tion between
egg and spermato­zoön—we should assent to such an assump­tion—but that
the “fertilizin” acts like an “amboceptor” between egg and spermato­zoön,
the latter being the complement, the former the antigen. The pathologist
would probably object to this interpreta­tion since no “amboceptor” is
needed for agglutina­tion. The writer has had some doubts concerning the
value of Ehrlich’s side-chain theory which, besides, can only be applied in a
metaphorical sense to the mechanism of the entrance of the spermato­zoön
into the egg. 76
6. The reason that an egg once fertilized with sperm cannot be fertilized
again may be found in a group of facts which we will now discuss, namely,
the self-sterility of many hermaph­ro­dites. The fact that hermaph­ro­dites are
often self-sterile, while their eggs can be fertilized with sperm from a
different individual of the same species has played a great rôle in the
theories of evolu­tion. We are here only concerned with the mechanism
which determines the block to the entrance of a spermato­zoön into an egg
of the same hermaph­ro­ditic individual.
Castle 77 observed and studied the phenomenon of self-sterility in an
Ascidian, Ciona intestinalis, which is hermaph­ro­ditic. Animals which were
kept isolated discharged both eggs and sperm into the surrounding sea
water. Often no egg was fertilized, but in some cases five, ten, or as many
as fifty per cent. of the eggs could be successfully fertilized with sperm
from the same individual; while if several individuals were put into the
same dish as a rule one hundred per cent. of the eggs which were
discharged segmented. Morgan 78 found that the eggs of various females
differ in their power of being fertilized by sperm of the same individual
while one hundred per cent. could usually be fertilized with sperm of a
different individual. He found in addi­tion that if the eggs of Ciona are put
for about ten minutes into a two per cent. ether solu­tion in sea water in a

number of cases the percentage of eggs fertilized by sperm of the same
individual shows a slight increase. Fuchs 79 has reported results similar to
those of Castle and Morgan.
A new point of attack has been introduced into the work of self-sterility in
plants by the considera­tion of heredity. Darwin found that in Reseda which
is monœcious (or hermaph­ro­ditic) certain individuals are either completely
self-sterile or completely self-fertile; and Compton showed that apparently
self-fertility is a Mendelian dominant to self-sterility. 80
According to Jost this self-sterility in hermaph­ro­ditic plants is due to the
fact that if pollen of the same plant is used the normal growth of the pollen
tube is inhibited, while this inhibi­tion does not exist for pollen from a
different individual. Correns calls these substances which prevent the
adequate growth of pollen, “inhibitory” substances, and finds that they can
apparently be transmitted to the offspring. He made experi­ments on
Cardamine pratensis which is self-sterile. 81 He fertilized two individuals of
Cardamine crosswise and raised sixty plants of the first genera­tion. He
compared the fertility of these F1 plants toward (a) their parents, and (b)
foreign plants. All the fertiliza­tions with the foreign plants were successful,
but the fertiliza­tions with the parents were only partly successful. According
to their reac­tion they could be divided into four groups:

(A) fertile with both parents. Type bg
(B) fertile with one (B), sterile with the other parent (G).
(a) fertile with B, sterile with G. Type bG
(b) fertile with G, sterile with B. Type Bg
(C) sterile with both parents. Type BG
It was found that approximately fifteen of the sixty children belonged to
each of the four groups. This should be expected if the inhibitory substance
to each parent is transmitted to the children independently. Half of the
children will thus inherit the inhibitory substance of one parent and the
other half will inherit the inhibitory substance of the other parent. This
agrees with the assump­tion that there are definite determiners for the
inhibitory substances in the children which will be transmitted to half of the
children. Rather complicated assump­tions are needed to explain all the facts
observed by Correns on this basis and since the subject is still under
investiga­tion we need not go further into the details.
To us the assump­tion and experi­mental support of the idea that self-sterility
is caused by the presence of a substance inhibitory to the entrance of a
spermato­zoön is important. Should it be possible that the block created by
the entrance of a spermato­zoön into the egg is also due to an inhibitory
substance carried by a spermato­zoön into the egg; and furthermore that the
effect of the inhibitory substance should be the preven­tion of further
agglutina­tion of the spermato­zoön with the egg or of the growth of the
pollen tube in plants? On such an assump­tion self-sterility would be due to
a lack of agglutina­tion between the egg of a hermaph­ro­dite and a spermato­‐
zoön of the same individual. The experi­ments on the agglutinins have
shown that while isoagglutinins (i. e., agglutinins for other individuals of
the same species) are common auto-agglutinins (i. e., agglutinins for cells
of the same individual) rarely if ever occur.
7. A positive chemotropism of the spermatozoa toward an egg of the same
species has been demonstrated in a few cases, but it seems that this
phenomenon is not determined by that type of substances which give rise to

species specificity. The famous experi­ment of Pfeffer on the spermatozoa of
ferns inaugurates this line of investiga­tion. He found that such spermatozoa
when moving in a straight line through the water will be deviated in their
course if they come near an archegonium; they will then turn toward it,
enter it, and enter the egg. Pfeffer showed that 0.01 per cent. malic acid if
put into a capillary tube will attract the spermatozoa of ferns.
When the liquid in the tube contains only 0.01 per cent. malic acid
the spermatozoa of ferns very soon move toward the opening of the
capillary tube and within from five to ten minutes many hundreds of
spermatozoa may accumulate in the tube. The malic acid acts as
well in the form of a free acid as in the form of salts. 82

These experi­ments were continued and amplified by Shibata. Bruchmann 83
found that the spermatozoa of Lycopodium are positively chemotactic to
citric acid and salts of this acid, although no citric acid could be shown in
the contents of the archegonia. They are also positively chemotactic to the
watery extract from archegonia.
Dewitz, Buller, and the writer have vainly tried to prove the existence of a
positive chemotropism of spermatozoa to eggs of the same species. Lillie
claims to have proved a positive chemotropism of the sperm of sea urchins
to “fertilizin,” but such a conclusion is only justified if a method similar to
that of Pfeffer’s with capillary tubes, gives positive results; such a method
was not used in Lillie’s experi­ments. It seems that the fertiliza­tion of the
egg by sperm is rendered possible by two facts; first that where fertiliza­tion
takes place outside the body egg and sperm are shed simultaneously by the
two sexes. This can be easily observed in the case of fish. But it is also the
case in invertebrates. Thus the writer has observed that the sea urchins
Strongylo­centrotus purpuratus at the shore of Pacific Grove all spawn
simultaneously. The examina­tion extended over several miles of shore. At
such spawning seasons the sea water becomes a suspension of sperm.
The second fact guaranteeing the fertiliza­tion of the eggs is the
overwhelming excess of spermatozoa over eggs. The enormous waste in

animated nature is in agreement with the idea of a lack of purpose; since in
this case the laws of chance must play a great rôle; and the origin of durable
organisms by laws of chance is only comprehensible on the basis of an
enormous wastefulness, for which evidence is not lacking.

CHAPTER V
ARTIFICIAL PARTHENOGENESIS

1. The majority of eggs cannot develop unless they are fertilized, that is to
say, unless a spermato­zoön enters into the egg. The ques­tion arises: How
does the spermato­zoön cause the egg to develop into a new organism? The
spermato­zoön is a living organism with a complicated structure and it is
impossible to explain the causa­tion of the development of the egg from the
structure of the spermato­zoön. No progress was possible in this field until
ways were found to replace the action of the living spermato­zoön by well-
known physico­chemical agencies. 84 Various observers such as Tichomiroff,
R. Hertwig, and T. H. Morgan had found that unfertilized eggs may begin to
segment under certain condi­tions, but such eggs always disintegrated in
their experi­ments without giving rise to larvæ. In 1899 the writer succeeded
in causing the unfertilized eggs of the sea urchin Arbacia to develop into
swimming larvæ, blastulæ, gastrulæ, and plutei, by treating them with
hypertonic sea water of a definite osmotic pressure for about two hours.
When such eggs were then put back into normal sea water many segmented
and a certain percentage developed into perfectly normal larvæ, blastulæ,
gastrulæ, and plutei. 85 Soon afterward this was accomplished by other
methods for the unfertilized eggs of a large number of marine animals, such
as starfish, molluscs, and annelids. None of these eggs can develop under
normal condi­tions unless a spermato­zoön enters. These experi­ments
furnished proof that the activating effect of the spermato­zoön upon the egg
can be replaced by a purely physico­chemical agency. 86

The first method used in the produc­tion of larvæ from the unfertilized eggs
did not lend itself to an analysis of the activating effect of the spermato­zoön
upon the egg, since nothing was known about the action of a hypertonic
solu­tion, except that it withdraws water from the egg; and there was no

indica­tion that the entrance of the spermato­zoön causes the egg to lose
water. No further progress was possible until another method of artificial
parthenogenesis was found. When a spermato­zoön enters the egg of a sea
urchin or starfish or certain annelids, the surface of the egg undergoes a
change which is called membrane forma­tion; and which consists in the
appearance of a fine membrane around the egg, separated from the latter by
a liquid (Figs. 4 and 5). O. and R. Hertwig and Herbst had observed that
such a membrane could be produced in an unfertilized egg if the latter was
put into chloroform or xylol, but such eggs perished at once. It was
generally assumed, moreover, that the process of membrane forma­tion was
of no significance in the phenomenon of fertiliza­tion, except perhaps that
the fertiliza­tion membrane guarded the fertilized egg against a further
invasion by sperm. However, since the fertilized egg is protected against
this possibility by other means the membrane is hardly needed for such a
purpose.

Fig. 4 Fig. 5
Fig. 4. Unfertilized egg surrounded by spermatozoa (whose fla­‐
gel­lum is omitted in the drawing).
Fig. 5. The same egg after a spermato­zoön has entered. The fer­‐
til­iza­­tion membrane is separated from the egg by a clear space.

In 1905 the writer found that membrane forma­tion, or rather the change of
the surface of the egg underlying the membrane forma­tion, is the essential
feature in the activa­tion of the egg by a spermato­zoön. He observed that
when unfertilized eggs of the Californian sea urchin Strongylo­centrotus
purpuratus are put for from one and a half to three minutes into a mixture
of 50 c.c. of sea water+2.6 c.c. N/10 acetic or propionic or butyric or

valerianic acid and are then put into normal sea water all or the majority of
the eggs form membranes; and that such eggs when the temperature is very
low will segment once or repeatedly and may even—if the temperature is as
low as 4°C. or less—develop into swimming blastulæ 87; but they will then
disintegrate. On the other hand, if they are kept at room temperature they
will develop only as far as the aster forma­tion and nuclear division and then
begin to disintegrate. It should be men­tioned that the time which elapses
between artificial membrane forma­tion and nuclear division is greater than
that between the entrance of a spermato­zoön and nuclear division.
It was obvious, therefore, that artificial membrane forma­tion induced by
butyric acid initiates the processes underlying development of the egg but
that for some reason the egg is sickly and perishes rapidly.
When, however, such eggs were given a short treatment with hypertonic sea
water or with lack of oxygen or with KCN they developed into normal
larvæ. This new or improved method of artificial parthenogenesis is as
follows: The eggs are put for from two to four minutes into 50 c.c. sea
water containing a certain amount of N/10 butyric acid (2.6 c.c. in the case
of S. purpuratus in California and 2.0 c.c. in the case of Arbacia in Woods
Hole). Ten or fifteen minutes later the eggs are put into hypertonic sea water
(50 c.c. sea water+8 c.c. 21⁄2 m NaCl or Ringer solu­tion or cane sugar) in
which they remain, at 15° C. from thirty-five to sixty minutes in the case of
purpuratus, and from 171⁄2 minutes to 221⁄2 minutes at 23° in the case of
Arbacia at Woods Hole. If the eggs are then transferred to normal sea water
they will develop. In making these experi­ments, which have been repeated
and confirmed by numerous investigators, it should be remembered that this
effect of the hypertonic solu­tion has a high temperature coefficient (about
two for 10° C.) and that a slight overexposure to the hypertonic sea water
injures the eggs so that development is abnormal. By this method it is
possible to imitate the activating effect of the living spermato­zoön upon the
egg in every detail and eggs treated in this way will develop in large
numbers into perfectly normal larvæ. We shall see later that they can also be
raised to the adult state.

2. The next task was to find out the nature of the action of the two agencies
upon the development of the egg. It soon became obvious that the
membrane forma­tion (or the altera­tion underlying membrane forma­tion)
was the more important of the two, since in the eggs of starfish and annelids
this was sufficient for the produc­tion of larvæ, and that the second treatment
had only the corrective effect, of overcoming the sickly condi­tion in which
mere membrane forma­tion had left the eggs. It was, therefore, of great
interest to ascertain what substances or agencies caused membrane forma­‐
tion in the egg, since it now became clear that the spermato­zoön could only
cause membrane forma­tion by carrying one such substance into the egg.
These investiga­tions led the writer to the result that all those substances and
agencies which are known to cause cytolysis or hemolysis (see Chapter III)
will also induce membrane forma­tion, and that the essential feature in the
causa­tion of development is a cytolysis of the superficial or cortical layer of
the egg. As soon as this layer is destroyed the development of the egg can
begin.
The substances and agencies which cause cytolysis and hence, if their
action is restricted to the surface of the egg, will induce development are,
besides the fatty acids: (1) saponin or solanin or bile salts; (2) the solvents
of lipoids, benzol, toluol, amylene, chloroform, aldehyde, ether, alcohols,
etc.; (3) bases; (4) hypertonic or hypotonic solu­tions; (5) rise in
temperature, and (6) certain salts, e. g., BaCl2 and SrCl2 in the case of the
egg of purpuratus, and according to R. Lillie, NaI or NaCNS in the egg of
Arbacia. Whenever we submit an unfertilized sea-urchin egg to any of these
agencies and restrict the cytolysis to the superficial or cortical layer of the
egg (i. e., if we transfer the egg to normal sea water before the cytolytic
agent has had time to diffuse into the main egg) the egg will form a
membrane and behave as if the membrane forma­tion had been called forth
by a fatty acid, with this difference only, that the various agencies are not all
equally harmless for the egg. 88
If the idea was correct that the change underlying membrane forma­tion was
essentially a cytolysis of the cortical layer of the egg, it was to be expected

(from the data contained in Chapter III) that the blood serum or the cell
extracts of foreign species would also cause membrane forma­tion and thus
induce the development of the unfertilized egg, while serum of animals of
the same species or genus would have no such effects. This was found to be
correct. In 1907 the writer showed that the blood serum of a Gephyrean
worm, Dendrostoma, was able to cause membrane forma­tion in the egg of
the sea urchin. When added in a dilu­tion of 1 c.c. of serum to 500 or
1000 c.c. of sea water to eggs of purpuratus a certain number formed
fertiliza­tion membranes. It was found later that the serum and tissue
extracts of a large number of animals, especially of mammals (rabbit, pig,
ox, etc.), had the same effect, though it was necessary to use higher
concentra­tions, one-half sea water and one-half isotonic blood serum. The
eggs of every female sea urchin, however, did not give the reac­tion and not
all the eggs even of sensitive females formed membranes. The writer found,
however, that it was possible to increase the susceptibility of the eggs
against foreign blood serum by putting them into a 3⁄8 m solu­tion of SrCl2
for from five to ten minutes (or possibly a little longer) before exposing
them to the foreign blood serum. BaCl2 acts similarly. The fact that SrCl2
alone can cause membrane forma­tion in unfertilized eggs if they are left
long enough in the solu­tion suggests that the sensitizing effect of the
substance consists in a modifica­tion of the cortical layer similar to that
underlying membrane forma­tion; and that the subliminal effect of a short
treatment with SrCl2 and the subliminal effect of the foreign serum when
combined suffice to bring about the membrane forma­tion.
Not only the watery extract of foreign cells but also that of foreign sperm,
induces membrane forma­tion in the sea-urchin egg. The watery extract of
sperm of starfish is especially active, but the degree of activity varies
considerably with the species of starfish from which the sperm is taken. The
eggs of different species of sea urchins also show a different degree of
susceptibility for the sperm of foreign species. Thus the eggs of Strongylo­‐
centrotus purpuratus require a higher concentra­tion of sperm extract than
the eggs of S. franciscanus. For the latter the amount of foreign cell

constituents which suffices to call forth membrane forma­tion is so small
that contact with almost any foreign living spermato­zoön produces this
effect; and as a rule no previous sensitizing action of SrCl2 is required.
When we bring the unfertilized eggs of S. franciscanus into contact with the
living sperm of starfish or shark or even of fowl, the eggs form a fertiliza­‐
tion membrane without previous sensitiza­tion. A specific substance from
the foreign spermato­zoön causes membrane forma­tion before the spermato­‐
zoön has time to enter the egg. The effect is the same as if artificial
membrane forma­tion had been called forth with butyric acid, i. e., they
begin to develop and then disintegrate unless they receive a second short
treatment.
When, however, we treat the eggs with the watery extracts from the cells of
their own or closely related species we find that these extracts are utterly
inactive, even if used in comparatively strong concentra­tions. This agrees
with the results given in Chapter III.
These phenomena lead to a very paradoxical result; namely that while in the
case of foreign sperm we can cause membrane forma­tion by both the living
and the dead spermato­zoön, only the living spermato­zoön of the same
species can induce membrane forma­tion. This might find its explana­tion on
the assump­tion that the active substance contained in the foreign sperm or
serum is water-soluble and a protein, while the activating or membrane-
forming substance in the spermato­zoön is insoluble in water but soluble in
the egg (or in lipoids). If this assump­tion is correct the two substances are
essentially different.
Robertson 89 has succeeded in extracting a substance from the sperm of the
sea urchin which causes membrane forma­tion of the sea-urchin egg after the
latter has been sensitized by a treatment with SrCl2. It seems to the writer
that if the substance extracted by Robertson were the real fertilizing agent
contained in the spermato­zoön it should fertilize the egg without a previous
sensitiza­tion of the egg with SrCl2 being required.

3. The action of acids in the mechanism of artificial parthenogenesis
provides some interesting physio­logical problems. When unfertilized sea-
urchin eggs are left in sea water containing any of the lower fatty acids up
to capronic, the eggs will form no membranes, while in such sea water, and
they will show no outer signs of cytolysis (swelling). When, however, the
eggs are left in sea water containing any of the fatty acids from heptylic
upward the eggs will form membranes while in the acid sea water and soon
afterward will cytolyze completely and swell enormously. In solu­tions of
the mineral acids no membranes are formed and none are formed as a rule
when the eggs are transferred back to sea water. When both a mineral and a
lower fatty acid, e. g., butyric, are added to sea water the mineral acid acts
as if it were not present, i. e., the eggs form membranes when transferred
back to sea water if the concentra­tion of the butyric acid is high enough. All
these data are comprehensible if we assume that only that part of the acid
causes membrane forma­tion which is lipoid soluble, while the water soluble
part is not involved in the process of membrane forma­tion; and that the
cytolysis or swelling of the whole egg can only take place in the higher
fatty acids (heptylic or above) which are little soluble in water and very
soluble in lipoids, while the lower fatty acids, whose water solubility is
comparatively high, can only bring about a cytolysis and swelling in the
cortical layer but not in the rest of the egg. This makes it appear as though
the part undergoing an altera­tion in membrane forma­tion was a lipoid; and
this would harmonize with the assump­tion that the specific membrane-
inducing substance in the spermato­zoön is not soluble in water, but soluble
in fat.
4. These and other observa­tions led the writer to the view that the essential
process which causes development might be an altera­tion of the surface of
the egg, in all probability an altera­tion of the superficial layer probably of
the nature of a superficial cytolysis. The ques­tion remains: What could be
the physico­chemical nature of this cytolysis? The writer had suggested in
former papers that in the cytolysis underlying membrane forma­tion lipoids
were dissolved, and he supposed that the substance to be dissolved might be

a calcium-lipoid compound which might form a continuous layer under the
surface of the egg. 90 v. Knaffl, working on the cytolysis of eggs in the
writer’s laboratory, gave the following idea of the process:
Protoplasm is rich in lipoids; probably it is mainly an emulsion of
these and proteins. Any physical or chemical stimulus which can
liquefy the lipoids causes cytolysis of the egg. The protein of the
egg can really only swell or be dissolved if the condi­tion of
aggrega­tion of the lipoid is altered by chemical or physical agencies.
The mechanism of cytolysis consists in the liquefac­tion of the
lipoids and thereupon the lipoid-free protein swells or is dissolved
by taking up water. . . . Hence this supports Loeb’s view that
membrane forma­tion is induced by the liquefac­tion of lipoids. 91

The writer suggested that the destruc­tion of an emulsion in the cortical layer
might possibly be the essential feature of the altera­tion leading to
membrane forma­tion and development. It had been long observed that
unfertilized starfish eggs may begin to develop apparently without any
outside “stimulus,” and A. P. Mathews found that slight mechanical agita­‐
tion of these eggs in sea water increased the number which developed. It
has been shown in numerous experi­ments by Delage, R. S. Lillie, and the
writer, that the substances causing development in the starfish egg are
identical or closely related to those which bring about this effect in the egg
of the sea urchin and in both cases the development is preceded by a
membrane forma­tion.
But how can membrane forma­tion be produced by mere agita­tion? It
seems to me that this can be understood if we suppose that it
depends upon the destruc­tion of an emulsion in the cortical layer of
the egg. It is conceivable that in the egg of certain forms the
stability of this emulsion is so small that mere shaking would be
enough to destroy it and thus induce membrane forma­tion and
development. 92

The durability of emulsions varies, and where an emulsion is very durable
shaking has no effect, while where it is at the critical point of separating
into two continuous phases a slight shaking will bring about the separa­tion,
and where the emulsion is still less durable we observe the phenomenon of
a “spontaneous” parthenogenesis. Eggs like those of most sea urchins
belong to the former, eggs like those of some starfish and annelids belong to
the second or third type.
It is impossible to state at present whether the fertiliza­tion membrane is
preformed in the fertilized egg and merely lifted off from the egg or
whether its forma­tion is due to the hardening of a colloidal substance
separated from the emulsion (or excreted) and hardened in touch with sea
water. But we can be sure of one thing, namely, that the liquid between egg
and membrane contains some colloidal substance which determines the
tension and spherical shape of the membrane. The membrane is obviously
permeable not only to water but also to dissolved crystalloids, while it is
impermeable to colloids. When we add some colloidal solu­tion (e. g., white
of egg, blood serum, or tannic acid) to the sea water containing fertilized
eggs of purpuratus, the membrane collapses and lies close around the egg;
while if the eggs are put back into sea water or a sugar solu­tion the
membrane soon assumes its spherical shape. This is intelligible on the
assump­tion that in the process of membrane forma­tion (or in the destruc­tion
of the emulsion in the cortical layer) a colloidal substance goes into solu­tion
which cannot diffuse into the sea water since the membrane is impermeable
to the colloidal particles. The membrane is, however, permeable to the
constituents of sea water or to sugar. Consequently sea water will diffuse
into the space between membrane and egg until the tension of the
membrane equals the osmotic pressure of the colloid dissolved in the space
between egg and the membrane. If we add enough colloid to the outside
solu­tion so that its osmotic pressure is higher than that of the colloidal solu­‐
tion inside the membrane the latter will collapse.
It should also be stated that the unfertilized eggs of many marine animals
are surrounded by a jelly (chorion) which is dissolved when the egg is

fertilized. 93 The writer has shown that the same chemical substances which
will induce membrane forma­tion and artificial parthenogenesis will as a
rule also cause a swelling and liquefac­tion of the chorion.
We have devoted so much space to the mechanism of membrane forma­tion
since it is likely to give a clearer insight into the physico­chemical nature of
physio­logical processes than the phenomena of muscular stimula­tion and
contrac­tion or nerve stimula­tion, upon which the majority of physiologists
base their conclusions concerning the mechanism of life phenomena.
Before we come to the discussion of the second factor in the activa­tion of
the egg it should be stated more definitely that for the eggs of some forms
the first factor, the process underlying membrane forma­tion, suffices for the
development of the egg into a larva and that no second factor is required in
these cases. This is true for the eggs of starfish and certain annelids. Thus in
1901 Loeb 94 and Neilson showed that a short treatment with HCl and HNO3
sufficed to cause some eggs of Asterias in Woods Hole to develop into
larvæ without a second treatment being needed, and Delage 95 showed the
same for CO2; and in 1905 the writer found that the eggs of the Californian
starfish Asterina can be induced to form a membrane by butyric acid
treatment and that ten per cent. of these eggs developed into normal larvæ.
Quite recently R. S. Lillie observed that the eggs of Asterias at Woods Hole
can be caused to form membranes and develop into larvæ by a treatment
with butyric acid and that the time of exposure required to get a maximal
number of larvæ varies approximately inversely with the concentra­tion of
the acid, within a range of 0.0005 to 0.006 N butyric acid. If the exposure is
too short membrane forma­tion will occur without normal development. 96

All this leads us to the conclusion that the main effect of the spermato­zoön
in inducing the development of the egg consists in an altera­tion of the
surface of the latter which is apparently of the nature of a cytolysis of the
cortical layer. Anything that causes this altera­tion without endangering the
rest of the egg may induce its development. The spermato­zoön, therefore,

causes the development of the egg by carrying a substance into the latter
which effects an altera­tion of its surface layer.
5. We will now discuss the action of the second, corrective factor, in the
inducement of development. When we cause membrane forma­tion in a sea-
urchin egg by the proper treatment with butyric acid it will commence to
develop and segment but will disintegrate rapidly if kept at room
temperature and the more rapidly the higher the temperature. If, however,
the eggs are treated afterward for a certain length of time (from thirty-five
to sixty minutes at 15° C. for purpuratus and 171⁄2 to 221⁄2 minutes for
Arbacia at 23° C.) in a solu­tion which is isosmotic with 50 c.c. sea
water+8 c.c. 21⁄2 m NaCl, 97 they will develop into larvæ, many of which
may be normal. Any hypertonic solu­tion of this osmotic pressure, sea water,
sugar, or a single salt, will suffice provided the solu­tion does not contain
substances that are too destructive for living matter. The hypertonic solu­tion
produces its corrective effect only if the egg contains free oxygen; and in a
slightly alkaline medium more rapidly than in a neutral medium. The time
of exposure in the hypertonic solu­tion diminishes in certain limits with the
concentra­tion of OH ions in the solu­tion.
It is strange that in the eggs of purpuratus the corrective effect can also be
brought about by exposing the eggs after the artificial membrane forma­tion
for about three hours to normal sea water free from oxygen; or to sea water
in which the oxida­tions have been retarded by the addi­tion of KCN. This
method is not so reliable as the treatment with hypertonic solu­tion.
What does the hypertonic solu­tion do to prevent the disintegra­tion of the
egg after the artificial membrane forma­tion? The writer suggested in 1905
that the artificial membrane forma­tion alone starts the development but
leaves the eggs usually in a sickly condi­tion and that the hypertonic solu­tion
or the lack of oxygen allows them to recuperate from such a condi­tion. The
second factor is, according to this view, merely a corrective or curative
factor. The following observa­tions will explain the reasons for such an
assump­tion.

The writer found that if we keep the unfertilized eggs after artificial
membrane forma­tion in sea water deprived of oxygen the disintegra­tion of
the egg following artificial membrane forma­tion is prevented for a day at
least. The same result can be obtained by adding ten drops of 1⁄10 per cent.
KCN to 50 c.c. of sea water, and certain narcotics, e. g., chloral hydrate, act
in the same way. Wasteneys and the writer found that chloral hydrate (and
other narcotics) in the concentra­tion required do not suppress or even lower
the oxida­tions in the egg to any considerable extent, 98 but they prevent the
processes of cell division. Hence it seems that the egg disintegrates so
rapidly after artificial membrane forma­tion because it is killed by those
processes leading to nuclear division or cell division which are induced by
the artificial membrane forma­tion. If we suppress these phenomena of
development (for not too long a time) we give the egg a chance to recover
and if now the impulse to develop is still active we notice a perfectly
normal development. If the egg is kept too long without oxygen it suffers
for other reasons and cannot develop; the writer has shown that if eggs
fertilized by sperm are kept for too long a time without oxygen they also
will no longer be able to develop normally. The short treatment with a
hypertonic solu­tion supplies the corrective factor required, so that the egg
can then undergo cell division at room temperature without disintegrating.
The correctness of this interpreta­tion, which is in reality mainly a statement
of observa­tions, is proved by the two following groups of facts. The older
observers had already noticed that the unfertilized eggs of the sea urchin
when lying in sea water will die after a day or more, and that occasionally
such eggs show nuclear division or even the beginning of cell division
shortly before disintegra­tion sets in. The writer has studied this
phenomenon in the unfertilized eggs of purpuratus and found that only the
eggs of certain females show this cell division before disintegra­tion and that
the cell division is preceded by an atypical form of membrane forma­tion;
the eggs surrounding themselves by a fine gelatinous film comparable to
that produced in the egg of Arbacia by a treatment with butyric acid. It is
difficult to state what induces the altera­tion of the surface in the eggs that

lie so long in sea water. It may be due to the CO2 formed by the eggs—
since we know that CO2 may induce membrane forma­tion—or it may be
due to the alkalinity of the sea water or to a substance originating from the
jelly surrounding the eggs. It was found that if such eggs are kept without
oxygen their disintegra­tion (and cell division) will be delayed considerably.
The presumable explana­tion for this is that the lack of oxygen prevents the
internal changes underlying cell division and thus prevents the disintegra­‐
tion of the egg. The direct proof that an egg in the process of cell division is
more endangered by abnormal solu­tions than an egg at rest has been
furnished by numerous observa­tions of the writer. He showed in 1906 that
the fertilized egg of purpuratus dies rather rapidly in a pure m/2 NaCl or
any other abnormal isotonic solu­tion, while the unfertilized egg can live for
days in such solu­tions. 99 In a series of papers, beginning in 1905, he showed
that the fertilized egg will live longer in hypertonic, hypotonic, and
otherwise abnormally constituted solu­tions when the cell divisions are
suppressed by lack of oxygen or by the addi­tion of KCN or of chloral
hydrate. 100 It is thus obvious that coincident with the changes underlying
nuclear division or cell division altera­tions occur in the sensitiveness of the
egg to salt solu­tions of abnormal concentra­tion or constitu­tion, e. g.,
NaCl+CaCl2 isotonic with sea water, hypertonic, or hypotonic solu­tions.
We must, therefore, conclude that artificial membrane forma­tion induces
development but that it leaves the egg in a sickly condi­tion in which the
very processes leading to cell division bring about its destruc­tion; that if it
is given time it can recover from this condi­tion and that the treatment with
the hypertonic solu­tion also brings about this recovery rapidly and reliably.
Herlant 101 suggested that the corrective effect of the hypertonic solu­tion
consisted in the proper development of the astrospheres required for cell
division. According to this author mere membrane forma­tion does not lead
to the forma­tion of sufficiently large astrospheres and hence cell division
may remain impossible. 102 The writer has no a priori objec­tion to this
sugges­tion which agrees with earlier observa­tions by Morgan except that it

is at present difficult to harmonize it with all the facts. Why should it be
possible to replace the treatment with the hypertonic solu­tion by a
suspension of the oxida­tions in the egg for three hours while we know that
lack of oxygen suppresses the forma­tion of astrospheres in the fertilized
eggs? What becomes of the astrospheres if the treatment with the
hypertonic solu­tion precedes the membrane forma­tion by a number of hours
or a day (which is possible as we shall see), and why do they not induce cell
division, if Herlant’s idea is correct? Nevertheless the sugges­tion of Herlant
deserves to be taken into serious considera­tion.
6. How can an altera­tion of the surface of the egg—e. g., a cytolytic or other
destruc­tion of the cortical layer—lead to a beginning of development? The
answer is possibly given in the rela­tion of oxida­tion to development. The
writer found in 1895 that if oxygen is withdrawn from the fertilized sea-
urchin egg it can not segment and this seems to be the case for eggs in
general. 103 In 1906 he found that the rapid disintegra­tion of the eggs of the
sea urchin which follows artificial membrane forma­tion could be prevented
when the eggs were deprived of oxygen or when the oxida­tions were
suppressed in the eggs by KCN. This suggested a connec­tion between the
disintegra­tion of the egg after artificial membrane forma­tion and the
increase in the rate of oxida­tions; and he found further that the forma­tion of
acid is greater in the fertilized than in the unfertilized egg. He, therefore,
expressed the view in 1906 that the essential feature (or possibly one of the
essential features) of the process of fertiliza­tion was the increase of the rate
of oxida­tions in the egg and that this increase was caused by the membrane
forma­tion alone. 104 These conclusions have been since amply confirmed by
the measurements of O. Warburg as well as those of Loeb and Wasteneys,
both showing that the entrance of the spermato­zoön into the egg raises the
rate of oxida­tions from 400 to 600 per cent., and that membrane forma­tion
alone brings about an increase of similar magnitude. Loeb and Wasteneys
found that the hypertonic solu­tion does not increase the rate of oxida­tions in
a fertilized egg. It does do so, however, in an unfertilized egg without
membrane forma­tion, but merely for the reason that in such an egg the

hypertonic solu­tion brings about the cytolytic change in the cortex of the
egg underlying membrane forma­tion. 105 According to Warburg it is probable
that the oxida­tions occur mainly if not exclusively at the surface of the egg
since NaOH, which does not diffuse into the egg, raises the rate of oxida­‐
tions more than NH4OH which does diffuse into the egg. And finally, the
same author showed that the oxida­tions in the sea-urchin egg are due to a
catalytic process in which iron acts as a catalyzer. 106 In view of all these
facts and their harmony with the methods of artificial parthenogenesis the
sugges­tion is justifiable that the altera­tion or cytolysis of the cortical layer
of the egg is in some way connected with the increased rate of oxida­tions.
The question remains then: How can membrane forma­tion or the altera­tion
of the cortical layer underlying membrane forma­tion cause an increase in
the rate of oxida­tions? One possibility is that the iron (or whatever the
nature of the catalyzer may be) exists in the cortex of the egg in a masked
condi­tion—or in a condi­tion in which it is not able to act—while the altera­‐
tion of the cortical layer makes the iron active. It might be that either the
iron or the oxidizable substrate is contained in the lipoid layer in the
unfertilized condi­tion of the egg and that the destruc­tion or cytolysis of the
cortical layer brings both the iron and the oxidizable substrate into the
watery phase in which they can interact.
Another possibility is that the act of fertiliza­tion increases the permeability
of the egg. This idea, which seems attractive, was first suggested and
discussed by the writer in 1906. 107 He had found that when fertilized and
unfertilized eggs were put into abnormal salt solu­tions, e. g., pure solu­tions
of NaCl, the fertilized eggs died more rapidly than the unfertilized eggs and
he pointed out that these experi­ments suggested the possibility that fertiliza­‐
tion increases the permeability of the egg for salts. The reason for his
hesita­tion to accept this interpreta­tion was, that the fertilized egg is also
more easily injured by lack of oxygen than the unfertilized egg and in this
case the greater sensitiveness of the fertilized egg was obviously due to its
greater rate of metabolism. Later experi­ments by the writer showed that the

fertilized egg can be made more resistant to abnormal salt solu­tions if its
development is suppressed by lack of oxygen or by KCN or by certain
narcotics. With our present knowledge it does not seem very probable that
lack of oxygen diminishes the permeability of the egg, but we know that it
inhibits the developmental processes. Warburg has made it appear very
probable that the fertilized egg is impermeable for NaOH and if this is the
case it should also be impermeable for NaCl. 108
The idea that fertiliza­tion and membrane forma­tion cause an increase in the
permeability of the egg was later accepted and elaborated by R. Lillie. This
author assumes that the unfertilized egg cannot develop because it contains
too much CO2 but that the CO2 can escape from the egg as soon as its
permeability is increased through the destruc­tion of the cortical layer of the
egg. 109 After the CO2 has escaped, the excessive permeability must be
restored to its normal value and this is the rôle of the hypertonic treatment.
It is, however, difficult to harmonize the assump­tion of an impermeability
of the unfertilized egg for CO2 with the fact that if the unfertilized sea-
urchin egg is cut into two, as is done in merogony, no development takes
place, while such pieces will develop when a spermato­zoön enters. The
cortical layer is removed along the cut surface and there is no reason why
the CO2 should not escape. Besides, the experi­ments of Godlewski and the
writer prove that the cortical layer of the unfertilized sea-urchin egg is
apparently very permeable for CO2 since the latter causes membrane forma­‐
tion if contained in the sea water in sufficiently high concentra­tion.
Lillie assumes that the hypertonic treatment restores the permeability raised
to excess by the butyric acid treatment, but this assump­tion is not in
harmony with the following facts. The writer has shown that it is immaterial
whether the eggs are treated first with the hypertonic solu­tion and then with
butyric acid or the reverse, if only the eggs remain longer in the hypertonic
solu­tion when the hypertonic treatment precedes the butyric acid treatment.
It was stated in the beginning of this chapter that the development of the
egg can be induced by hypertonic sea water, and we know the reason since
hypertonic sea water is a cytolytic agency. The writer found that when we

expose unfertilized eggs of purpuratus for from two to two and a half-hours
to hypertonic sea water they will often not develop and only a few eggs will
undergo the first cell divisions, then going into a condi­tion of rest. When
these eggs, both the segmented and unsegmented, were treated twenty-four
or thirty-six hours later with butyric acid, so that they formed a membrane,
they all developed into larvæ without further treatment. It is impossible to
apply Lillie’s theory to these facts, for the simple reason that the treatment
with hypertonic sea water was just long enough to induce development in
some eggs and hence according to Lillie’s ideas must have increased the
permeability of these eggs. Yet these same eggs were induced to develop
normally when subsequently treated with butyric acid, which according to
Lillie also acts by increasing the permeability. Nothing indicates that the
treatment of the eggs with a hypertonic solu­tion diminishes their
permeability; the reverse would be much more probable.
Lillie’s theory also fails to explain that mere treatment of the eggs with a
hypertonic solu­tion can bring about their development into larvæ. This,
however, is intelligible on the assump­tion that the hypertonic solu­tion in
this case has two different effects, first a cytolysis of the cortical layer of
the egg and second an entirely different effect, possibly upon the interior of
the egg, which represents the second or corrective effect.
McClendon 110 has shown that the electrical conductivity of the egg is
increased after fertiliza­tion, and J. Gray 111 has found that this increase in
conductivity is only transitory and disappears in fifteen minutes. This might
indicate that the egg becomes transitorily more permeable for salts after the
entrance of the spermato­zoön or after membrane forma­tion; although an
increase in conductivity might be caused by other changes than a mere
increase in permeability of the egg. The writer is of the opinion that it is
necessary to meet all these and other difficulties before we can state that the
altera­tion of the cortical layer, which is the essential feature of
development, acts chiefly or exclusively by an increase in the permeability
of the egg. 112

7. When the experi­ments on artificial parthenogenesis were first published
they aroused a good deal of antagonism not only among reac­tionaries in
general but also among a certain group of biologists. O. Hertwig had
defined fertiliza­tion as consisting in the fusion of two nuclei, the egg
nucleus and the sperm nucleus. No such fusion of two nuclei takes place in
artificial parthenogenesis since no spermato­zoön enters the egg, and it
became necessary, therefore, to abandon Hertwig’s defini­tion as wrong. The
objec­tion raised that the phenomena are limited to a few species soon
became untenable since it has been possible to produce artificial
parthenogenesis in the egg of plants (Fucus, according to Overton) as well
as of animals, from echinoderms up to the frog; and it may possibly one day
be accomplished also in warm-blooded animals. A second objec­tion was
that the eggs caused to develop by the methods of artificial parthenogenesis
could never reach the adult stage and that hence the phenomenon was
merely pathological. There was no basis for such a statement, except that it
is extremely difficult to raise marine invertebrates. Delage 113 was
courageous enough to make an attempt to raise partheno­genetic larvæ of the
sea urchin beyond the larval stage and he succeeded in one case in carrying
the animal to the mature stage. It proved to be a male.
Better opportunities were offered when a method was discovered which
induced the development of the unfertilized eggs of the frog. In 1907,
Guyer made the surprising observa­tion that if he injected lymph or blood
into the unfertilized eggs of frogs he succeeded in starting development and
he even obtained two free-swimming tadpoles. “Apparently the white rather
than the red corpuscles are the stimulating agents which bring about
development, because injec­tions of lymph which contains only white
corpuscles produce the same effects as injec­tions of blood.” Curiously
enough, Guyer thought that probably the cells which he introduced and not
the egg were developing. In 1910, Bataillon showed that a mere puncture of
the egg with a needle could induce development but he believes that for the
full development the introduc­tion of a fragment of a leucocyte is required.
Bataillon has called atten­tion to the analogy with the writer’s results on

lower forms, the puncturing of the egg corresponding to the cytolysis of the
surface layer of the egg and the introduc­tion of a leucocyte as the analogue
of the second or corrective factor. The method of producing artificial
parthenogenesis by puncturing the egg has thus far been successful only in
the egg of the frog. The writer has tried it in vain on the eggs of many other
forms. He has at present seven partheno­genetic frogs over a year old,
produced by merely puncturing the eggs with a fine needle (Fig. 6). These
frogs have reached over half the size of the adult frog. They can in no way
be distinguished from the frogs produced by fertiliza­tion with a spermato­‐
zoön. This makes the proof conclusive that the methods of artificial
parthenogenesis can result in the produc­tion of normal organisms which can
reach the adult stage.
Bancroft and the writer tried to determine the sex of a partheno­genetic
tadpole and of a frog just carried through metamorphosis. Since in early life
the sex glands of both sexes in the frog contain eggs it is not quite easy to
determine the sex, except that in the male the eggs gradually disappear and
from this and other criteria we came to the conclusion that both partheno­‐
genetic specimens, which were four months old, were males.
The writer has recently examined the gonads of a ten months old partheno­‐
genetic frog. Here no doubt concerning the sex was possible since the
gonads were well-developed testicles containing a large number of
spermatozoa of normal appearance, and no eggs. 114 (Figs. 7 and 8.) This
would indicate that the frog belongs to those animals in which the male is
hetero­zygous for sex.
8. The fact that the egg of so high a form as the frog can be made to develop
into a perfect and normal animal without a spermato­zoön—although
normally the egg of this form does not develop unless a spermato­zoön
enters—corroborates the idea expressed in previous chapters that the egg is
the future embryo and animal; and that the spermato­zoön, aside from its
activating effect, only transmits Mendelian characters to the egg. The ques­‐
tion arises: Is it possible to cause a spermato­zoön to develop into an

embryo? The idea has been expressed that the egg was only the nutritive
medium on which the spermato­zoön developed into an embryo, but this
idea has been rendered untenable by the experi­ments on artificial
parthenogenesis. Nevertheless the ques­tion whether or not the spermato­‐
zoön can develop into an embryo on a suitable culture medium remains, and
it can only be decided by direct experi­ments. It was shown by Boveri,
Morgan, Delage, Godlewski, and others, that if a spermato­zoön enters an
enucleated egg or piece of egg it can develop into an embryo, but since the
cytoplasm of the egg is the future embryo this experi­ment proves only that
the egg nucleus may be replaced by the sperm nucleus; and also that the
sperm nucleus carries into the egg, the substances which induce
development. Incidentally these experi­ments on merogony also prove that
the mere mechanical tearing of the cortical layer,—which must happen in
the separa­tion of the unfertilized egg into parts with and without a nucleus,
—by dissec­tion or by shaking, is not sufficient to start development in the
sea-urchin egg.
J. de Meyer put the spermatozoa of sea urchins into sea water containing an
extract of the eggs of the same species but found only that the spermatozoa
swell in such a solu­tion. Loeb and Bancroft made extensive experi­ments in
cultivating spermatozoa of fowl in vitro on suitable culture media. In yolk
and white of egg the head of the spermato­zoön underwent trans­forma­tion
into a nucleus, but no mitosis or aster forma­tion was observed. 115 These
experi­ments should be continued.

CHAPTER VI
DETERMINISM IN THE FORMATION OF AN ORGANISM
FROM AN EGG

1. The writer in a former book (Dynamics of Living Matter, 1906, p. 1),
defined living organisms as chemical machines consisting chiefly of
colloidal material and possessing the peculiarity of preserving and
reproducing themselves. Some authors like Driesch, and v. Uexküll seem to
find it impossible to account for the development of such machines from an
undifferentiated egg on a purely physico­chemical basis. A study of
Driesch’s very interesting and important book 116 shows that he assumes the
eggs of certain animals, e. g., the sea urchin, to consist of homogeneous
material; and he concludes that nature has solved, in the forma­tion of highly
differentiated organisms from such undifferentiated material, a problem
which does not seem capable of a solu­tion by physico­chemical agencies
alone. But the supposi­tion of a structureless egg is wrong, since Boveri has
demonstrated the existence of a very simple but definite structure in the
unfertilized egg of the sea urchin; and a similar simple structure has been
demonstrated by other authors, especially Conklin, in the eggs of other
forms.
In this chapter we shall attempt the task among others of showing how, on
the basis of the simple physico­chemical structure of the unfertilized egg, the
main organ of self-preserva­tion of the organism, the intestine, is formed
through the mere process of cell division and growth. Cell division is the
most general of the specific func­tions of living matter and it is the basis
underlying the differentia­tion of the comparatively simple structure of the
egg into a more complex organism. If cell division and growth were equal
in all parts of the egg no differentia­tion would be possible, but the different
regions of the unfertilized egg contain different constituents and these,

probably on account of their chemical difference, do not all begin to grow
or divide simultaneously and equally.
Boveri 117 found that in the
unfertilized egg of the sea urchin
Strongylo­centrotus lividus at Naples
a definite structure is indicated by
the fact that the yellowish-red
pigment is not equally distributed
over the whole surface of the egg
but is arranged in a wide ring from
the equator almost to one of the
poles. Thus three zones can be
recognized in the egg (Fig. 9), a
small clear cap A at one pole, a
Fig. 9
pigmented ring B, and the rest again
unpigmented C. Observa­tion has
shown that each one of these regions gives rise to a definite constituent of
the egg: A furnishes the mesenchyme from which the skeleton and the
connective tissue originate; B is the material for the forma­tion of the
intestine, and C gives rise to the ectoderm.
The pigment is only at the surface of the egg, and its collec­tion at B
indicates only that the material in B differs physicochemically from A and
C. The real determiners of the three different groups of organs are three
different groups of substances whose distribu­tion is approximately but
probably not wholly identical with the regions indicated by distribu­tion of
pigment. The intestine-forming material is probably not entirely lacking in
C but is contained here in a lower concentra­tion and probably the more so
the greater the distance from B; and the same may probably be said for the
substances determining mesenchyme and ectoderm forma­tion. Hence the
unfertilized egg contains already a rough preforma­tion of the embryo
inasmuch as the main axis of the embryo and the arrangement of its first
organs are determined.

Fig. 10 Fig. 11

After the egg is fertilized the cell divisions begin. The first division is as a
rule at right angles to the stratifica­tion of the egg, each of the two cells
contains one-half of the pigment ring (and of each of A and C) (Fig. 10),
and after the next division each contains one-fourth of the pigmented part.
Each of the four cells is a diminutive whole egg since each contains the
three layers in the normal arrangement (Fig. 11). The next divisions bring
about an unequal division of the material. Four cells will be formed of
ectoderm material C and only little intestine material B, the other four cells
containing B and A. These latter form at the next division four very small
colourless cells, the so-called micromeres, A (Fig. 12), from which the
mesenchyme, skeleton, and connective tissue are formed, four larger cells,
B, from which the intestine is formed, and eight cells, C, from which the
ectoderm will arise. The separa­tion of the three groups of substances is
probably not as complete as our purely diagrammatic drawing (Fig. 12)
indicates.
The cell division proceeds and the cells become smaller and smaller and all
gather at the surface of the egg, thus forming a hollow sphere. It is not
known what brings about this gathering of the cells at the surface, whether
it is protoplasmic creeping or streaming or whether the cells are held by a
jelly-like layer which covers the surface of the egg (hyaline membrane)
(Fig. 13). Then the cilia are formed at the external surface of these cells and

the egg begins to swim; we say it has
reached the first larval, the so-called
blastula stage. This happens according
to Driesch after the tenth series of cell
divisions, when the number of cells is
theoretically 1024, in reality not quite so
many (between 800 and 900). The next
step consists in the cells derived from
the material A (mesenchyme and
micromeres) gliding into the hollow
Fig. 12
sphere, where they form a ring, the
physico­chemical process responsible for
this gliding being yet unknown. At the opening of this ring an active
growing of the cells of the entoderm into the hollow sphere takes place and
the hollow cylinder formed by this growth is the intestine (Fig. 14). Why
the cells grow into the hollow sphere and not into the opposite direc­tion is
unknown. The next step is the forma­tion of a skeleton by the forma­tion of
crystals consisting of the CaCO3 by the mesenchyme cells surrounding the
intestine. For the establishment of the principle in which we are interested
the descrip­tion of morphogenesis need not be carried farther.

Fig. 13 Fig. 14

This principle which is under discussion here is the development of a
purposeful arrangement of organs out of the egg. If we assume that the egg
consists of homogeneous material we are indeed confronted with a riddle.
Since the facts contradict such an assump­tion but show, as Boveri has
pointed out, a prearrangement which allows us to indicate in the unfertilized
egg already the exact spot where the intestine will grow into the blastula
cavity, we are on solid physico­chemical ground, although many ques­tions
of detail cannot yet be answered. Such a preforma­tion as Boveri has
demonstrated is only conceivable if the material of the egg has not too high
a degree of fluidity; we may consider it as consisting essentially of a semi-
solid gel which is not homogeneous throughout the egg but divided into
three strata.
2. Lyon 118 tried to ascertain whether by centrifuging the sea-urchin egg it
was possible to modify its structure and thereby affect the later embryo. He
and subsequent experi­menters found that it only is possible to change the
posi­tion of the nucleus and the distribu­tion of the pigment in the egg. It
follows from this that the nucleus and the pigment are suspended in rather
fluid material, the former in the centre, the pigment at or near the surface.
The posi­tion of the nucleus determines the first plane of segmenta­tion, since
the nuclear division precedes the division of the cytoplasm of the egg and
the plane of nuclear division becomes also the plane of the division of the
whole egg—a point which need not be discussed here. It was found,
however, by Lyon and the subsequent investigators that the place where the
micromeres are formed and where the intestine of the embryo later
originates is little influenced by the centrifuging of the egg. The localiza­tion
of this spot must therefore be determined by a structure sufficiently solid
not to be shifted by the centrifugal force. The intestinal stratum in the egg
contains the forerunners of the tissues which secrete hydrolyzing enzymes,
e. g., trypsin into the digestive tract.
When the surrounding solu­tion is altered in constitu­tion or when the
temperature is too high, the intestine instead of growing into the hollow
sphere grows outside, we get an evagina­tion instead of an invagina­tion of

the intestine. Such larvæ may live for a few days but they cannot grow into
a living organism. The forces which make the intestine grow into the
hollow sphere are unknown; it may possibly be only the difference between
the tension on the external and internal surfaces of the hollow sphere; under
normal condi­tions, the resistance on the inner surface being smaller, the
intestine grows into the hollow sphere.
The intestine is one of the organs required for the self-preserva­tion of a
more complicated organism, in fact a higher organism without a digestive
tract is not capable of living for any length of time. In the gastrula—i. e.,
the blastula with an intestine—we have an organism which is durable, but
the processes leading up to the forma­tion of the intestine are so simple that
it is difficult to understand why the assump­tion of a “supergene” should be
required in this case.
3. Driesch 119 was the first to show that if
we isolate one of the first two cells of a
dividing egg each develops into a whole
embryo of half size. This is perfectly
intelligible, since each of the two cells
contains all the three layers in the normal
arrangement (Fig. 10). The cells divide
Fig. 15
and the cells having the tendency to creep
to the surface of the mass arrange
themselves in a hollow sphere, the blastula. Since micromeres and intestine
material are present and in their normal posi­tion an intestine will grow into
the blastula and a whole organism will result. All of this is as necessary as is
the forma­tion of one embryo from the whole egg material. Yet the two half-
embryos betray their origin from two cleavage cells of the same egg, in that
the two gastrulæ formed are often if not always symmetrical to each other
(Fig. 15), as the writer had a chance to observe in the egg of Strongylo­‐
centrotus purpuratus 120 in the following experi­ment. The eggs of the sea
urchin Strongylo­centrotus purpuratus are put soon after fertiliza­tion into
solu­tions which differ from sea water in two points; namely that they are

neutral or very faintly acid (through the CO2 absorbed from the air) instead
of being faintly alkaline, and second, that one of the following three
constituents of the sea water is lacking; namely: K, Na, or Ca. When the
eggs are allowed to segment in such a solu­tion the first two cleavage cells
are as a rule in a large percentage of cases—often as many as ninety per
cent.—separated from each other, and when the eggs are put into normal
sea water (about twenty minutes after the cell division) each cell develops
into a normal embryo. In a number of cases the embryos remained inside
the egg membrane and did not move until after the invagina­tion of the
intestine was far advanced; in such cases it was found quite often that the
invagina­tion began at the plane of cleavage at symmetrical points of the two
embryos, and the growth of the intestine was symmetrical in both embryos.
This symmetry is probably due to the following fact: the first cleavage
plane goes through that spot where the intestine grows into the blastula
cavity. If the micromere material does not change its posi­tion after the two
cleavage cells are separated and the new blastulæ do not become
completely spherical the symmetry which we observed is bound to occur.
The occurrence is a confirma­tion of Boveri’s observa­tion. It is natural that
Driesch also found that each cell in the four-cell stage should give rise to a
full embryo, since each of these cells is in reality a diminutive egg
containing the three strata in the right arrangement. When, however, the
cells of the eight- or sixteen-cell stage were isolated Driesch’s results were
different. In this case the isolated cells from the ectoderm material did no
longer all form a gastrula; when such a cell still formed a gastrula it was
probably due to the fact that it contained some entoderm material; while the
cells taken from the entoderm region all formed embryos and therefore
contained ectoderm material. 121 The isolated ectoderm cells of a blastula
could no longer form an intestine; they were lacking the entoderm material.
It looks as if a gradual migra­tion of all the entoderm material from the
ectoderm into the entoderm took place during the blastula forma­tion.
When the contents of the egg are displaced by pressure the result will be
determined by the loca­tion of the main mass of the intestine-forming

material; where the main mass of this body is located the invagina­tion of
the intestine will take place. In his earlier work Driesch assumed from
pressure experi­ments that the egg had a great power of “regula­tion.” In a
later paper 122 he expressed to a large extent his agreement with Boveri who
denied this power of “regula­tion” and showed that the existence of the
structure of the egg—i. e., a division into three strata, one forming the
ectoderm, the second the entoderm, and the third the mesoderm—was
sufficient to explain the various phenomena of apparent “regula­tion.”
Driesch’s idea of a regula­tion in this case has often been used to insist upon
the non-explicability of the phenomena of development from a purely
physico­chemical viewpoint. It is, therefore, only fair to point out that
Boveri 123 has furnished the facts for a simpler explana­tion, which seems to
have escaped the notice of antimechanists. 124

The objection may be raised that in accepting Boveri’s facts and interpreta­‐
tion we pushed the miracle only one step farther and that we now have to
explain the origin of the structure in the unfertilized egg. This Boveri has
done by showing that the egg grows from the wall of the ovary and that that
part of the egg which is connected with the wall of the ovary gives rise to
the ectoderm layer, while the opposite part gives rise to the mesenchyme
and the intestine. This shows a connec­tion between the orienta­tion of the
egg in the wall of the ovary and its stratifica­tion. While this does not solve
the problem of stratifica­tion in the egg it gives the clue to its solu­tion.
The ultimate origin of stratifica­tion probably goes back to the fact of the
presence of watery and water-immiscible substances, such as fats. The
experi­ments by Beutner and the writer have shown that the electromotive
forces which are observed in living tissues originate at the boundaries
between a watery and a water-immiscible phase, like oleic acid or
lecithin. 125 In his earlier writings 126 the writer had thought that the colloids
had special significance and this idea seems to prevail today; but the actual
observa­tions have shown that the phase boundary fat-water is of greater

importance. Needless to say the fats if not present in the cell from the
beginning can be formed in the metabolism.
4. All the “regulation” in the egg is of a purely physico­chemical character;
it consists essentially of a flow of material. If this idea is correct, the
apparent power of “regula­tion” of the blasto­meres should differ according
to the degree of fluidity and the possibility of different layers separating,
and this assump­tion is apparently supported by facts. The first plane of
segmenta­tion of the egg is usually the plane of symmetry of the later
organism and where the degree of fluidity is less than in the sea-urchin egg,
a separa­tion of the two first blasto­meres should easily result in the forma­‐
tion of two half-embryos instead of two whole embryos.
This is the case for the frog’s egg as Roux showed in a classical experi­ment.
Roux destroyed one of the two first cleavage cells of a frog’s egg with a hot
needle and found that as a rule the surviving cell developed into only a
half-embryo. 127 The frog’s egg consists of two substances, a lighter one
which is on top and a heavier one below. Although viscous, the two
substances are not too viscous to prevent a flow if the egg is turned upside
down. O. Schultze found that if a normal egg is turned upside down in the
two-cell stage and held in that posi­tion, two full embryos arise, one from
each of the two blasto­meres. Through the flow of the lighter liquid in the
egg upwards the two halves of the protoplasm on top become separated and
develop independently into two whole embryos instead of into two half-
embryos. In Roux’s experi­ment this flow of protoplasm was avoided.
Morgan showed that if Roux’s experi­ment is repeated with the modifica­tion
that the egg is put upside down after the destruc­tion of the one cell, the
intact cell will give rise not to a half but to a whole embryo. 128 These
experi­ments prove that each of the first two cleavage cells of the frog’s egg
represents one-half of the embryo and that a whole embryo can develop
from each half only when a redistribu­tion of material takes place, which in
the egg of the frog can be brought about by gravita­tion since the egg
consists of a lighter and a heavier mass.

When, therefore, in the egg of the sea urchin each of the first two blasto­‐
meres naturally gives rise to a whole embryo it is due to a greater degree of
fluidity of the protoplasm and not to a lack of preforma­tion of the embryo
in the cytoplasm. This idea is confirmed by the observa­tions on the egg of
Ctenophores whose cytoplasm seems to be more solid than that of most
other eggs. Chun found that the isolated blastomere of the first cell division
produced a half-larva, possessing only four instead of the eight locomotor
plates of the normal animal.
It seems that in the egg of molluscs, also, the simple symmetry rela­tions of
the body are already preformed. It is well known that there are shells of
snails which turn to the right while others turn in the opposite direc­tion. The
shells of Lymnæus turn to the right, those of Planorbis to the left. It was
observed by Crampton 129, Kofoid, and Conklin that the eggs of right-wound
snails do not segment in a symmetrical, but in a spiral, order, and that in
left-handed snails the direc­tion of the spiral segmenta­tion is the reverse of
that of the segmenta­tion in the right-handed snails. Conklin was able to
show that the asymmetrical spiral structure is already preformed in the egg
before cleavage. The asymmetry of the body in snails is therefore already
preformed in the egg. 130
E. B. Wilson 131 has found a marked differentia­tion in the eggs of some
annelids and molluscs. He isolated the first two blasto­meres of the egg of
Lanice, an Annelid. These two blasto­meres are somewhat different in size;
from the larger one of the first two blasto­meres, the segmented trunk of the
worm originates. Wilson found that
when either cell of the two-cell stage is destroyed, the remaining
cell segments as if it still formed a part of an entire embryo. 132 The
later development of the two cells differs in an essential respect, and
in accordance with what we should expect from a study of the
normal development. The posterior cell develops into a segmented
larva with a prototroch, an asymmetrical pre-trochal or head region,
and a nearly typical metameric seta-bearing trunk region, the active

movements of which show that the muscles are normally developed.
The pre-trochal or head region bears an apical organ, but is more or
less asymmetrical, and, in every case observed, but a single eye was
present, whereas the normal larva has two symmetrically placed
eyes. The development of the anterior cell contrasts sharply with
that of the posterior. This embryo likewise produces a prototroch
and a pre-trochal region, with an apical organ, but produces no post-
trochal region, develops no trunk or setæ, and does not become
metameric. Except for the presence of an apical organ, these anterior
embryos are similar in their general features to the corresponding
ones obtained in Dentalium. None of the individuals observed
developed a definite eye, though one of them bore a somewhat
vague pigment spot.
This result shows that from the beginning of development the
material for the trunk region is mainly localized in the posterior cell;
and, furthermore, that this material is essential for the development
of the metameric structure. The development of this animal is,
therefore, to this extent, at least, a mosaic work from the first
cleavage onward—a result that is exactly parallel to that which I
earlier reached in Dentalium, where I was able to show that the
posterior cell contains the material for the mesoblast, the foot, and
the shell; while the anterior cell lacks this material. I did not succeed
in determining whether, as in Dentalium, this early localiza­tion in
Lanice pre-exists in the unsegmented egg. The fact that the larva
from the posterior cell develops but a single eye, suggests the
possibility that each of the first two cells may be already specified
for the forma­tion of one eye; but this interpreta­tion remains doubtful
from the fact that the larva from the anterior cell did not, in the five
or six cases observed, produce any eye.
Conklin has established the existence of a definite structure in the
unfertilized eggs of Ascidians, Amphioxus, and many molluscs. In all cases

the results of the isola­tion of the first blasto­meres seem to agree with the
demonstrable structure of the unfertilized egg.
5. These examples may suffice to show that the egg has from the beginning
a simple structure, and we will now point out by which means further
differentia­tion may come about. Sachs suggested that all differentia­tion and
the forma­tion of every organ presupposes the previous existence of specific
substances responsible for the forma­tion. These substances which are now
called internal secre­tions or hormones develop gradually during embryonic
development. What exists first is a jelly-like block of protoplasmic material
with a varying degree of viscosity and with just enough differentia­tion to
indicate head and tail end, a right and left, and a dorsal and ventral side of
the future embryo.
Aside from such simple differences phenomena of protoplasmic streaming
contribute to the further differentia­tion. Such streaming begins, according to
Conklin, 133 in the egg just before fertiliza­tion when the surface layer of the
egg protoplasm
streams to the point of entrance of the sperm, and these movements
may lead to the segrega­tion of different kinds of plasma in different
parts of the egg and to the unequal distribu­tion of these substances
in different regions of the egg.
One of the most striking cases of this is found in the Ascidian Styela
in which there are four or five different kinds of substances in the
egg which differ in colour, so that their distribu­tion to different
regions of the egg and to different cleavage cells may be easily
followed and even photographed while in the living condi­tion. The
peripheral layer of protoplasm is yellow and when it gathers at the
lower pole of the egg where the sperm enters it forms a yellow cap.
This yellow substance then moves following the sperm nucleus, up
to the equator of the egg on the posterior side and there forms a
yellow crescent extending around the posterior side of the egg just
below the equator. On the anterior side of the egg a grey crescent is

formed in a somewhat similar manner and at the lower pole between
these two crescents is a slate-blue substance, while at the upper pole
is an area of colourless protoplasm. The yellow crescent goes into
cleavage cells which become muscle and mesoderm, the grey
crescent into cells which become nervous system and notochord, the
slate-blue substance into endoderm cells, and the colourless
substance into ectoderm cells.
Thus within a few minutes after the fertiliza­tion of the egg and
before or immediately after the first cleavage, the anterior and
posterior, dorsal and ventral, right and left poles are clearly
distinguishable, and the substances which will give rise to ectoderm,
endoderm, mesoderm, muscles, notochord, and nervous system are
plainly visible in their characteristic posi­tions. 134

We may finally allude briefly to the fact that when once a number of tissues
are differentiated each one may influence the other by calling forth tropistic
reac­tions. Thus the writer showed that in the yolk sac of the fish Fundulus
the pigment cells lie at first without any definite order but that they
gradually are compelled to creep entirely on the blood-vessels and form a
sheath around them with the result that the yolk sac assumes a tiger-like
marking. 135 Driesch 136 has pointed out that the mesenchyme cells are
directed in their migra­tion; and it seems that the direc­tion of the growth of
the axis cylinder is determined by the tissues into which it grows. The idea
of tropistic reac­tions in the forma­tion of organs has been discussed by
Herbst. 137

6. As a consequence of further changes definite anlagen or buds originate
later in the embryo which are destined to give rise to definite organs. Thus
in the tadpole early mesenchyme cells are formed which are the anlagen for
the four legs, which will grow out under the proper condi­tions. These
anlagen are specific inasmuch as from the anlage of a foreleg only a
foreleg, and from the anlage for a hindleg only a hindleg, will develop.
Braus 138 has proved this by transplanting the anlage of a foreleg to different

parts of the body. No matter into which part of the body they are
transplanted the mesenchyme cells for the foreleg will give rise to a foreleg
only; even if they are transplanted into the spot from which the hindlegs
grow out under natural condi­tions. There is therefore nothing to indicate
“regula­tion.”
The same is true for the forma­tion of the eye and probably in general. We
have to consider the forma­tion of the various organs of the body as being
due to the development of specific cells in definite loca­tions in the
organisms which will grow out into definite organs no matter into which
part of the organism they are transplanted. It is at present unknown what
determines the forma­tion of these specific anlagen. They may lie dormant
for a long time and then begin to grow at definite periods of development.
We shall see later that we know more about the condi­tions which cause
them to grow.
7. The fact that the egg, and probably every cell, has a definite structure
should determine the limits of the divisibility of living matter. In most cases
the complete destruc­tion of a cell means the cessa­tion of life phenomena. A
brain or kidney which has been ground to a pulp is no longer able to
perform its func­tions; yet we know that such pulps can still perform some
of the characteristic chemical processes of the organ; e. g., the alcoholic
fermenta­tion characteristic of yeast can be caused by the press juice from
yeast; or characteristic oxida­tions can be induced by the ground pulp of
organs. The ques­tion arises as to how far the divisibility of living matter can
be carried without interfering with the total of its func­tions. Are the smallest
particles of living matter which still exhibit all its func­tions of the order of
magnitude of molecules and atoms, or are they of a different order? The
first step toward obtaining an answer to this ques­tion was taken by Moritz
Nussbaum, 139 who found that if an infusorian be divided into two pieces,
one with and one without a nucleus, only the piece with a nucleus will
continue to live and perform all the func­tions of self-preserva­tion and
development which are characteristic of living organisms. This shows that
at least two different structural elements, nucleus and cytoplasm, are needed

for life. We can understand to a certain extent from this why an organ after
being reduced to a pulp, in which the differentia­tion into nucleus and
protoplasm is definitely and permanently lost, is unable to accomplish all its
func­tions. 140

The observa­tions of Nussbaum and those who repeated his experi­ments
showed that although two different structures are required, not the whole
mass of an infusorian is needed to maintain its life. The ques­tion then arose:
How small a fraction of the original cell is required to permit the full
maintenance of life? The writer tried to decide this ques­tion in the egg of
the sea urchin. He had found a simple method by which the eggs of the sea
urchin (Arbacia) can easily be divided into smaller fragments immediately
after fertiliza­tion. When the egg is brought from five to ten minutes after
fertiliza­tion (long before the first segmenta­tion occurs) into sea water which
has been diluted by the addi­tion of equal parts of distilled water, the egg
takes up water, swells, and causes the membrane to burst. Part of the
protoplasm then flows out, in one egg more, in another less. If these eggs
are afterward brought back into normal sea water those fragments which
contain a nucleus begin to divide and develop. 141 It was found that the
degree of development which such a fragment reaches is a func­tion of its
mass; the smaller the piece, the sooner as a rule its development ceases. The
smallest fragment which is capable of reaching the pluteus stage possesses
the mass of about one-eighth of the whole egg. Boveri has since stated that
it was about one twenty-seventh of the whole mass. Inasmuch as only the
linear dimensions are directly measurable, a slight difference in
measurement will cause a great discrepancy in the calcula­tion of the mass.
Driesch’s results disagree with the statement of Boveri and support the
observa­tion of the writer.
If we raise the ques­tion why such a limit exists in regard to the divisibility
of living matter, it seems probable that only those fragments of an egg are
capable of development into a pluteus which contain a sufficient amount of
material of each of the three layers. If this be correct, it would certainly not
suffice to mix the chemical constituents of the egg in order to produce a

normal embryo; this would require besides the proper chemical substances
a definite arrangement or structure of this material. The limits of divisibility
of a cell seem therefore to depend upon its physical structure and must for
this reason vary for different organisms and cells. The smallest piece of a
sea-urchin egg that can reach the pluteus stage is still visible with the naked
eye, and is therefore considerably larger than bacteria or many algæ, which
also may be capable of further division.
8. The most important fact which we gather from these data is that the
cytoplasm of the unfertilized egg may be considered as the embryo in the
rough and that the nucleus has apparently nothing to do with this
predetermina­tion. This must raise the ques­tion suggested already in the
third chapter whether it might not be possible that the cytoplasm of the eggs
is the carrier of the genus or even species heredity, while the Mendelian
heredity which is determined by the nucleus adds only the finer details to
the rough block. Such a possibility exists, and if it should turn out to be true
we should come to the conclusion that the unity of the organism is not due
to a putting together of a number of independent Mendelian characters
according to a “pre-established plan,” but to the fact that the organism in the
rough existed already in the cytoplasm of the egg before the egg was
fertilized. The influence of the hereditary Mendelian factors or genes
consisted only in impressing the numerous details upon the rough block and
in thus determining its variety and individuality; and this could be
accomplished by substances circulating in the liquids of the body as we
shall see in later chapters.

CHAPTER VII
REGENERATION

1. The action of the organism as a whole seems nowhere more pronounced
than in the phenomena of regenera­tion, for it is the organism as a whole
which represses the phenomena of regenera­tion in its parts, and it is the
isola­tion of the part from the influence of the whole which sets in action the
process of regenera­tion. The leaf of the Bermuda “life plant”—Bryophyllum
calycinum—behaves like any other leaf as long as it is part of a healthy
whole plant, while when isolated it gives rise to new plants. The power of
so doing was possessed by the leaf while a part of the whole, and it was the
“whole” which suppressed the formative forces in the leaf. When a piece is
cut from the branch of a willow it forms roots near the lower end and shoots
at the upper end, so that a tolerably presentable “whole” is restored. How
does the “whole” prevent the basal end of the shoot from forming roots as
long as it is part of the plant? A certain fresh-water flatworm has the mouth
and pharynx in the middle of the body. When a piece is excised between the
head and the pharynx a new head is formed at the oral end, a new tail at the
opposite end, and in the middle of the remaining old tissue a new mouth
and pharynx is formed. How does the “whole” suppress all this formative
power in the part before the latter is isolated? It almost seems as if the isola­‐
tion itself were the emancipa­tion of the part from the tyranny of the whole.
The explana­tion of this tyranny or of the correla­tion of the parts in the
whole is to be found, however, in a different influence. The earlier
botanists, Bonnet, Dutrochet, and especially Sachs, 142 pointed out that the
phenomena of correla­tion are determined by the flow of sap in the body of a
plant. These authors formulated the idea that the forma­tion of new organs in
the plant is determined by the existence of specific substances which are
carried by the ascending or descending sap. Specific shoot-producing

substances are carried to the apex, while specific root-producing substances
are carried to the base of a plant. When a piece is cut from a branch of
willow the root-forming substances must continue to flow to the basal end
of the piece, and since their further progress is blocked there they induce
the forma­tion of roots at the basal end. Goebel 143 and de Vries have
accepted this view and the writer made use of it in his first experi­ments on
regenera­tion and hetero­morphosis in animals. 144 At that time the idea of the
existence of such specific organ-forming substances was received with
some scepticism, but since then so many proofs for their existence have
been obtained that the idea is no longer ques­tioned. Such substances are
known now under the name of “internal secre­tions” or “hormones”; their
connec­tion with the theory of Sachs was forgotten with the introduc­tion of
the new nomenclature.
It may be well to enumerate some of the cases in which the influence of
specific substances circulating in the blood upon phenomena of growth has
been proven. One of the most striking observa­tions in this direc­tion is the
one made by Gudernatsch on the growth of the legs of tadpoles of frogs and
toads. 145 The young tadpoles have no legs, but the mesenchyme cells from
which the legs are to grow out later are present at an early stage. From four
months to a year or more may elapse before the legs begin to grow.
Gudernatsch found that legs can be induced to grow in tadpoles at any time,
even in very young specimens, by feeding them with the thyroid gland (no
matter from what animal). No other material seems to have such an effect.
The thyroid contains iodine, and Morse 146 states that if instead of the gland,
iodized amino acids are fed to the tadpole the same result can be produced.
We must, therefore, draw the conclusion that the normal outgrowth of legs
in a tadpole is due to the presence in the body of substances similar to the
thyroid in their action (it may possibly be thyroid substance) which are
either formed in the body or taken up in the food.
Thus we see that the mesenchyme cells giving rise to legs may lie dormant
for months or a year but will grow out when a certain type of substances,

e. g., thyroid, circulates in the blood. There may exist an analogy between
the activating effect of the thyroid substance and the activating effect of the
spermato­zoön or butyric acid (or other partheno­genetic agencies) upon the
egg, but we cannot state that the thyroid substance activates the
mesenchyme cells by altering their cortical layer.
The fact that the substance of the thyroid may induce general growth in the
human is too well known to require more than an allusion in this connec­‐
tion. When growth stops in children as a consequence of a degenera­tion of
the thyroid, feeding of the patient with thyroid again induces growth. It may
also suffice merely to call atten­tion to the connec­tion between acromegaly
and the hypophysis.
It was formerly believed that the nervous system acted as a regulator of the
phenomena of metamorphosis in animals, but it was possible to show by
simple experi­ments that the central nervous system does not play this rôle
and that the regulator must be the blood or substances contained therein. In
the metamorphosis of the Amblystoma larva the gills at the head and tail
undergo changes simultaneously, the gills being absorbed completely. The
writer showed that in larvæ in which the spinal cord was cut in two, no
matter at which level,—the sympathetic nerves were in all probability also
cut—the two organs continued to undergo metamorphosis
simultaneously. 147 Uhlenhuth found that if the eye of a salamander larva is
transplanted into another larva the transplanted eye undergoes its
metamorphosis into the typical eye of the adult form, simultaneously with
the normal eyes of the individual into which it was transplanted. 148 These
and other observa­tions of a similar character leave no doubt that substances
circulating in the blood and not the central nervous system are responsible
for the phenomena of growth and metamorphosis.
An interesting observa­tion on the rôle of internal secre­tion in growth was
made by Leo Loeb. 149 When the fertilized ovum comes in contact with the
wall of the uterus it calls forth a growth there, namely the forma­tion of the
maternal placenta (decidua). This author showed that the corpus luteum of

the ovary gives off a substance to the blood which alters the tissues in the
uterus in such a way that contact with any foreign body induces this
deciduoma forma­tion. The case is of interest since it indicates that the
substance given off by the corpus luteum does not induce growth directly,
but that it allows mechanical contact with a foreign body to do so while
without the interven­tion of the corpus luteum substance no such effect of
the mechanical stimulus would be observable. The action of the substance
of the corpus luteum is independent of the nervous system, since in a uterus
which has been cut out and retransplanted the same phenomenon can be
observed.
Bouin and Ancel 150 have shown that the corpus luteum, which in the case of
pregnancy continues to exist for a long time, is responsible for the changes
in the mammary gland in the first half of pregnancy, when an active cell
prolifera­tion takes place in the gland. This process can be interrupted by
destroying the corpus luteum artificially. During the second half of
gravidity no further cell prolifera­tion takes place, but the cells begin to
secrete milk while during the period of cell prolifera­tion such secre­tions do
not occur.
Claude Bernard and Vitzou had shown that the period of growth and
moulting of the higher crustacea is accompanied by a heaping up of
glycogen in the liver and subdermal connective tissue. Smith 151 found that
during the period between two moultings, when there is no growth, the
storage cells are seen to be filled with large and numerous fat globules
instead of with glycogen. He also found that in the Cladocera “the period of
active growth is accompanied by glycogen—as opposed to fat—
metabolism.” He observed, moreover, that if Cladocera are crowded at a
low temperature the fat metabolism (with inhibi­tion to growth) is favoured,
while at high temperatures and with no crowding of individuals the
glycogen metabolism is favoured. In the latter case a purely partheno­genetic
mode of propaga­tion is observed, while in the former sexual reproduc­tion
takes place. The effect of crowding of individuals is possibly due to

products of excre­tion, which then act on growth and reproduc­tion indirectly
by changing the “glycogen metabolism” to “fat metabolism.”
All these cases agree in this, that apparently specific substances induce or
favour growth, not in the whole body, but in special parts of the body. Sachs
suggested that there must be in each organism as many specific organ-
forming substances as there are organs in the body.
We will now show that the assump­tion of the existence of such “organ-
forming” substances (which may or may not be specific) and of their flow
in definite channels explains the inhibitory influence of the whole on the
parts as well as the unbridled regenera­tion of the isolated parts.
2. We have seen that the resting egg can be aroused to development and
growth by substances contained in a spermato­zoön or by certain other
substances mentioned in the preceding chapter. We will assume that plants
contain a large number of cells or buds which are comparable to the resting
egg cell, but which can be aroused to action by certain substances
circulating in the sap; and that the same is effected for animal cells by
substances in the blood. In plants the cells which can be aroused to new
growth have very often a rather definite loca­tion while in lower animals
they are more ubiquitous. For experi­mental purposes organisms where these
buds have a definite loca­tion are more favourable, since we are better able
to study the mechanism underlying the process of activa­tion and inhibi­tion
(correla­tion). When a leaf of the plant Bryophyllum calycinum is cut off and
put on moist sand or into water or even into air saturated with water vapour,
new plants will arise from notches of the leaf. This is the usual way of
propagating the plant and in no other part of the leaf except the notches will
new plants arise. These notches therefore contain cells comparable to seeds
or to unfertilized eggs or to the mesenchyme cells which give rise to legs in
the tadpole of the frog. The ques­tion arises: Why do notches in the leaf
never begin to grow while the leaf is attached to an intact plant, and why do
they grow when the leaf is isolated? To this we are inclined to give an
answer in the sense of Bonnet, Sachs, de Vries, and Goebel, namely that the
flow of (specific?) substances in the plant determines when and where

dormant buds or anlagen shall begin to grow. Such substances may
originate or may be present in the leaf; but as long as it is connected with a
normal plant they will be carried by the circula­tion to the growing points of
the stem and of the roots and they cannot reach the notches; while when we
detach the leaf, either a new distribu­tion or a new flow of liquids will be
established whereby the substances reach some of the notches; and in these
notches new roots and a new shoot will be formed. When we cut off a leaf
and put it into moist air, not all but only a few of the notches will, as a rule,
grow out (Fig. 16); but when we isolate each notch leaving as much of the
rest of the leaf as possible attached to it, each notch will give rise to a new
plant. 152 (Fig. 17.) We see, therefore, that it does not even require a whole
plant to cause inhibi­tion but that we may observe the tyranny of the whole
over the parts in a single leaf. The explana­tion is as follows: When we
isolate a leaf, some of the notches will commence to grow into new plants
and this growth will arrest the development of the other notches of the leaf
in the same way as their development was suppressed by the whole plant.

Fig. 16. Growth of roots and shoots in a Fig. 17. If all the notches of a leaf are isolated
few notches of an isolated leaf of from each other each notch will give rise to
Bryophyllum calycinum roots and a shoot, but the growth will be less
rapid than in Fig. 16. Figs. 16 and 17 were
two leaves taken from the same node of a
plant.

The explana­tion is the same; those notches which begin to grow first will
attract the flow of substances to themselves, thus preventing the other
notches from getting those substances. This idea is supported by the fact
that if all the notches are isolated from the leaf each notch will give rise to a
slowly growing plant, while if the leaf is not cut into pieces, and a few
notches only grow out, their growth is much more rapid.
In all these experi­ments the idea
that the “isola­tion” in itself is
responsible for the growth still
presents itself. It can be disposed
of by the following experi­ment
which never fails. Three leaves
of Bryophyllum calycinum are
suspended in an atmosphere
saturated with water vapour but
their tips are submersed in water
(Figs. 18, 19, 20). The first leaf,
Fig. 20, is entirely separated
from its stem, the second leaf,
Fig. 19, remains connected with
the adjacent piece of stem, and
the third leaf, Fig. 18, remains
also connected with this piece of
stem but the latter still possesses
Fig. 18 Fig. 19 Fig. 20
both leaves. The first leaf, Fig.
20, produces new roots and
shoots in the submerged part in a few days; the second leaf, Fig. 19,
produces no roots or shoots for a long time. This might find its explana­tion
by the assump­tion that the first leaf, being more isolated than the second,
regenerates more quickly. But this explana­tion becomes untenable owing to
the fact that the third leaf, Fig. 18, being less isolated than both (possessing
a second leaf in addi­tion to the stem), forms new roots and shoots also more

quickly than the second leaf. The phenomena become intelligible in the
following way. The fact that in the second leaf shoots and roots are formed
very late, if at all, finds its explana­tion not in the lessened isola­tion of this
leaf, but in the fact that the forma­tion of a new shoot or of a callus in the
piece of stem takes place more quickly than the forma­tion of roots and
shoots in the notches of a completely isolated leaf. The stem acts therefore
as a centre of suc­tion for the flow of substances from the leaf and this
prevents or retards the forma­tion of roots and shoots in the notches. In the
isolated leaf of Bryophyllum calycinum no callus forma­tion takes place and
hence no flow of the sap away from the leaf will occur. This will allow one
or more of the notch buds of this leaf to grow out and then a flow will be
established towards these growing buds.
In the third specimen, Fig. 18, the presence of two leaves suppresses or, as a
rule, retards the growth of a shoot on the stem and possibly also the flow
from one leaf may block to some extent the flow from the opposite leaf if
the piece of stem is very short. This puts the leaves in a condi­tion not as
good as that in leaf Fig. 20, but better than in leaf Fig. 19. 153
In the normal plant the buds in the notches of the leaf remain dormant since
the flow of the “stimulating” substances takes place towards the tips of the
stem and root, and because these substances are retained there in excess.
This is probably the real basis of the mysterious dominance of the “whole”
over its “parts” or of the anlagen of the tip of the stem over those farther
below. When a piece of the stem of Bryophyllum is cut off and its leaves are
removed, the two apical buds will grow out first. This “dominance” finds its
explana­tion probably in the anatomical structure and the mechanism of sap
flow which tend to bring the “stimulating” substances first to the anlagen in
the tip. In Laminaria Setchell has been able to show directly that regenera­‐
tion always starts from that tissue which conducts nutritive material.
When we cut out a piece of a stem of Bryophyllum, and remove all the
leaves, new shoots will be formed from the two apical buds of the stem, and
roots will arise from the most basal nodes; provided that the stem is

suspended in air saturated with water vapour. The growth in such a stem
deprived of all leaves is slow. If we remove all the leaves on such a piece of
stem except the two at the apical end, the stem will form only roots, but
these will develop much more rapidly than on a stem without leaves. If we
remove all the leaves except the two at the basal end, the stem will only
form shoots (at the apical end) but these will develop much more rapidly
than in a leafless stem. Hence the leaves accelerate the growth of roots
towards the basal end and inhibit it towards the apical end; and they favour
the growth of shoots towards the apical end and inhibit it in the nodes
located nearer the base.
We thus see that while the stem inhibits the growth of the leaves connected
with it, the latter accelerate the growth in the stem. Both facts can probably
be explained on the same basis; namely, on the assump­tion that it is the
flow of substances from the leaf to the stem which inhibits the growth of
the notches and accelerates the growth of the buds in the stem. On this
assump­tion it would also follow that the leaves send root-forming
substances towards the basal and shoot-forming substances towards the
apex of the stem. It also seems to follow from recent as yet unpublished
experi­ments by the writer that the root-forming substances are associated or
identical with the substances which cause geotropic curvature in the stem.
These observa­tions show that the phenomena of correla­tion or of the
influence of the whole over the parts is due to peculiarities of circula­tion or
the flow of sap; and that the isola­tion prevents the sap from flowing away to
other parts of the plant. There is no need for assuming the existence of a
mysterious force which directs the piece to grow into a whole.

Fig. 22

Fig. 21

3. Phenomena of inhibi­tion or correla­tion such as we have described in
Bryophyllum are not lacking in the regenera­tion of animals, as experi­ments
on Tubularia show. 154 Tubularia mesembryanthemum (Fig. 21) is a hydroid
consisting of a long stem terminating at one end in a stolon which attaches
itself to solid bodies such as rocks, at the other end in a polyp. The writer
found that if we cut a piece from a stolon and suspend it in an aquarium it
forms as a rule a polyp at either end (Fig. 22), but the velocity with which
the two polyps are formed is not the same, the polyp at the oral end of the
piece being formed much more rapidly—a day or one or two weeks sooner
—than the aboral polyp. The process of polyp regenera­tion at the aboral
pole could, however, be accelerated and its velocity made equal to that of
the regenera­tion of the oral polyp by suppressing the forma­tion of the latter.
This was accomplished by depriving the oral pole of the oxygen necessary
for regenera­tion, e. g., by merely putting the oral end of the piece of stem
into the sand. It was, therefore, obvious that the forma­tion of the oral polyp
retarded the forma­tion of the aboral polyp. This inhibi­tion might have been
due to the fact that a specific organ-forming material needed for the forma­‐
tion of a polyp existed in sufficient quantity in the stem for the forma­tion of
one polyp only at a time. This idea, however, was found to be incorrect
since when the stem was cut into two or more pieces each piece formed a
polyp at once at its oral pole and regenerated the aboral polyps also, but

again with the usual delay. It seemed more probable then that the cause of
the difference in the rapidity of polyp forma­tion at both ends lay in the fact
that certain material flowed first to the oral pole and induced polyp forma­‐
tion here but that this flow was reversed as soon as the polyp at the oral
pole was formed or as soon as the forma­tion of the oral polyp was inhibited
by lack of oxygen. The partial or full comple­tion of the forma­tion of the
oral polyp acted as an inhibi­tion to the further flow of material to this pole.
This idea was supported by an observa­tion made independently by
Godlewski and the writer that if a piece of stem be cut out of a Tubularia,
and if the piece be ligatured somewhere between the two ends, the oral and
the aboral polyps are formed simultaneously. This would be comprehensible
on the assump­tion that the retarding effect which the forma­tion of the oral
has on the aboral polyp was indeed of the nature of a flow of material
towards the oral pole.
Miss Bickford 155 found that the difference in time between the
forma­tion of the two polyps disappears also when the piece
cut from the stem becomes so small that it is of the order of
magnitude of a single polyp. In that case two incomplete
polyps are formed simultaneously at each end (Fig. 23). The
new head in the regenera­tion of Tubularia arises, as Miss
Bickford observed, from the tissue near the wound. At some
distance from the wound in the old tissue two rows of
tentacles arise, which are noticeable as rows of longitudinal
lines inside the stem before the head is formed. Driesch
noticed that the newly formed head is the smaller the smaller
Fig. 23
the whole piece. (This is true, however, only in rather small
pieces.) There is, therefore, in small pieces a rough propor­‐
tionality between size of head and size of regenerating piece. Driesch 156
uses this interesting fact to prove the existence of an entelechy, while we are
inclined to see in it an analogue to the observa­tion of Leo Loeb, that the
velocity of the process of healing in the case of a deficiency of the
epithelium decreases when the size of the uncovered area diminishes. While

we do not wish to offer any sugges­tion concerning the mechanism of these
quantitative phenomena—they may be related in some way with the
velocity of certain chemical reac­tions—we see no reason for assuming that
they cannot be explained on a purely physico­chemical basis.
The writer noticed that certain pigmented cells from the entoderm of the
organism always gather at that end where a new polyp is about to be
formed. These red or yellowish cells always collect first at the oral end of a
piece of stem. It may be that certain substances given off by the pigmented
cells at the cut end are responsible for the polyp forma­tion, but this is only a
surmise.
Another sugges­tion made by Child, 157 is that there exists an axial gradient in
the stem whereby the cells regenerate the more quickly the nearer they are
to the oral pole. If this were correct, and we cut a long piece from the stem
of a Tubularia and bisect the piece, the oral pole of the anterior half should
regenerate more quickly than the oral pole of the posterior half. According
to the writer’s observa­tions on a Tubularian (T. crocea) growing in the
estuaries near Oakland, California, both oral ends regenerate equally fast in
such cases.
4. The phenomena of regenera­tion in Cerianthus membranaceus, a sea
anemone, can be easily understood from the experi­ments on Tubularians, if
we imagine the body wall of Cerianthus to consist of a series of
longitudinal elements running parallel to the axis of symmetry of the animal
from the tentacles to the foot. The number of these elements may be
supposed to correspond to the number of tentacles in the outer row of the
normal animal. Each such element behaves like a Tubularian, with this
difference, however, that the elements in Cerianthus are more strongly
polarized than in Tubularia, and that each one is able to form a tentacle at
its oral pole only. This fact can be nicely illustrated in the following way: if
a square or oblong piece (a b c d, Fig. 24) be cut from the body wall of a
Cerianthus in such a way that one side, a c, of the oblong is parallel to the
longitudinal axis of the animal, tentacles will grow on one of the four sides

only; namely, on the side a b. 158 (Fig. 25.) The other three free edges are not
able to produce tentacles. If an incision be made in the body wall of a
Cerianthus, tentacles will grow on the lower edge of the incision (Fig. 26).

Fig. 24 Fig. 25 Fig. 26

The writer tried whether or not by tying a ligature around the middle of a
piece of an Actinian this polarity could be suppressed; but the experi­ments
did not succeed, inasmuch as the cells compressed by the ligature died, and
were liquefied through bacterial action so that the pieces in front and behind
the ligature fell apart. It is therefore impossible to decide whether or not a
current or a flow of substances in a certain direc­tion through these elements
is responsible for this polarity, though this may be possible. The writer
found, however, that one condi­tion is necessary for the growth and
regenera­tion of tentacles which also plays a rôle in the corresponding
phenomena in plants, namely turgidity. The tentacles of Cerianthus are
hollow cylinders closed at the tip, and by liquid being pressed into them
they can be stretched and appear turgid. If, however, an incision is made in
the body, the tentacles above the incision can no longer be stretched out. In
one experi­ment the oral disk of a Cerianthus was cut off; very soon new
tentacles began to grow at the top, and after having reached a certain size,
an incision was made in the animal. The tentacles above the incision

collapsed in consequence and ceased to grow, while growth of the others
continued. On the lower edge of the incision new tentacles began to grow.

Fig. 28

Fig. 27 Fig. 29

It seems also possible that Morgan’s well-known experi­ment on regenera­‐
tion in Planaria can be explained by a flow of substances. He 159 found that
if a piece a c d b be cut out of a fresh-water Planarian at right angles to the
longitudinal axis (Fig. 27), at the front end a new normal head, at the back
end a new tail, will be regenerated (Fig. 28); but that if a piece a c d b be
cut from a Planarian obliquely (Fig. 29) instead of at right angles to the
longitudinal axis a tiny head is formed at the foremost corner of the piece a
and a tiny tail at the hindmost corner b (Fig. 30). Why is it that in the
oblique piece the head is formed in the corner and not all along the cut
surface as is the case when the cut is made at right angles to the longitudinal
axis? The writer is inclined to believe that the right answer to this ques­tion
has been given by Bardeen. 160 This author has pointed out the apparent rôle
that the circulatory (or so-called digestive) canals in Planarians play in the
localiza­tion of the phenomena of regenera­tion, inasmuch as the new head
always forms symmetrically at the opening of the circulatory vessel or
branch which is situated as much as possible at the foremost end of the
regenerating piece of worm. He assumes that through muscular action the

liquids of the body are forced to stream toward this end, and that this fact
has some connec­tion with the forma­tion of a new head. There can be no
doubt that the facts here mentioned agree with Bardeen’s sugges­tion. The
oblique pieces in Morgan’s experi­ments which at first have the heads and
tails outside the line of symmetry of the middle piece, gradually assume a
normal posi­tion (Figs. 31, 32). The writer is inclined to believe that this is
due to mechanical condi­tions. The head a e c of such an oblique piece is
asymmetrical, the one side a e being less stretched than the other e c. The
higher tension of the piece e c will have the effect of bringing e nearer c,
since we know that acid forma­tion and hence energy produc­tion increases
in propor­tion to surface, i. e., it must be the greater the more it is stretched.
The reverse is true for the tail d f b, and the effect here will be that f will be
pulled nearer d. In this way purely mechanical condi­tions are responsible
for the fact that the soft tissues of the animal are gradually restored to their
true orienta­tion.

Fig. 30 Fig. 31 Fig. 32

As a final possible example of the influence of internal secre­tion or
substances contained in the blood may be mentioned the following curious
observa­tion of Przibram. 161 In a crustacean, Alpheus, the two chelæ
(pincers) are not equal in size and form, one being very much larger than
the other. Przibram found that when he cut off the larger pincer in such
crustaceans the remaining pincer assumes in the next moulting the size and
shape of the removed large pincer; while in place of the removed pincer one
of the small type is produced. Hence a reversal of the two pincers is thus

brought about. If later on the large pincer is again cut off the process is
repeated and the original dissymmetry is restored. Przibram was able to
show that the nervous system has no connec­tion with this phenomenon.
The elements which have entered into the discussion thus far are, first, the
flow of substances in preformed channels; second, the existence of general
or specific substances required for the growing or regenerating organ. A
third element is to be added; namely the “suc­tion” effect upon these
substances of a developing organ. Thus we see that if one or a few of the
notches in a leaf of Bryophyllum grow out the other notches of the leaf are
inhibited from growing. There is enough material present in the leaf for all
the notches to grow into shoots as is proved by the fact that all will grow
out if they are isolated from each other. This was explained on the assump­‐
tion that the notches of a whole which happen to develop first, create a flow
of these substances from the rest of the leaf to themselves and thus prevent
any getting to the other notches. We stated that this is supported by the fact
that the few notches growing out in an undivided leaf grow more rapidly
than the many shoots growing from each notch of a divided leaf. But why
should a growing shoot or a growing point in general produce such a
suction? I think this may be possible on the assump­tion that the consump­‐
tion of these substances by the growing organs causes a low osmotic
pressure of these substances in the growing region and this fall of osmotic
potential will act as a cause for the further flow. This brings about the
apparent “suc­tion” effect of the growing elements upon the flow of
substances.
5. We mentioned that when a piece is cut from a Planaria between pharynx
and head a new mouth is formed in the middle. It should also be mentioned
that according to Child the piece after regenera­tion is smaller than it was
before. 162 This indicates that material in the old cells has been digested or
has undergone hydrolysis in order to furnish the nutritive material for the
new head and tail, since the piece cannot take up any food from the outside
before a mouth is formed. These phenomena of autodiges­tion—the process
itself will be discussed in the last chapter—seem to occur in many (if not

all) phenomena of regenera­tion. It may be that the collecting of red cells at
the end in a Tubularian where regenera­tion is about to begin has to do with
the furnishing of material by self-diges­tion, since these cells are partly at
least destroyed in the process. It is of interest to look for more examples of
autodiges­tion accompanying phenomena of regenera­tion.

Fig. 33 Fig. 34

The writer has observed more closely the
trans­forma­tion of an organ into more
undifferentiated material in Campanularia
(Fig. 33), a hydroid. 163 This organism
shows a remarkable stereotropism. Its
stolons attach themselves to solid bodies, Fig. 35
and the stems appear on the side of the
stolon exactly opposite the point or area of contact with the solid body. The
stems grow, moreover, exactly at right angles to the solid surface element to
which the stolon is attached. If such a stem be cut and put into a watch glass
with sea water, it can be observed that those polyps which do not fall off go
through a series of changes which make it appear as if the differentiated
material of the polyp were trans­formed into undifferentiated material. The
tentacles are first put together like the hairs of a camel’s-hair brush (Fig.
34), and gradually the whole fuses to a more or less shapeless mass which

flows back into the periderm (Fig. 35). It follows from this that in this
process certain solid constituents of the polyp, e. g., the cell walls, must be
liquefied. This undifferentiated material formed from the polyp may
afterward flow out again, giving rise to a stolon or a polyp; to the former
where it comes in contact with a solid body, to the latter where it is
surrounded by sea water. These observa­tions suggest the idea of
reversibility of the process of differentia­tion of organs and tissues, in certain
forms at least. We have to imagine that some of the cells or interstitial tissue
is digested and that as a consequence the organ loses its characteristic
shape.
Giard and Caullery have found that a regressive metamorphosis occurs in
Synascidians, and that the animals hibernate in this condi­tion. The muscles
of the gills of these animals are decomposed into their individual cells. The
result is the forma­tion of a parenchyma which consists of single cells and of
cell aggregates resembling a morula. 164
Driesch, 165 experi­menting on the regenera­tion of an Ascidian, found that
when he cut off the gills and siphons of the animal the portion removed was
able to regenerate a whole animal. The gill-piece excised contained no
heart, no intestine, and no stolon, and all these organs were regenerated
from the gills. In a number of cases the regenera­tion took place by bud
forma­tion at the edge of the wound, but in other cases the gills were trans­‐
formed into an undifferentiated mass of tissue from which the missing parts
of the animals arose by budding and new gills were formed.
It is probable that the two cases are only quantitatively different. In both,
autodiges­tion of certain cell constituents and possibly of whole cells must
take place in order to obtain material for the forma­tion of the lost part of the
Ascidian. If an interstitial tissue is digested it becomes a ques­tion of how
much of this tissue undergoes hydrolysis. If there is little destroyed the old
shape of the gills remains, if too much is digested the old gills become a
shapeless mass in which a certain number of the old cells are maintained
and give rise to the new animal by cell division. The material for the new

organs must of course be furnished from old cells which have been
digested.
If regenera­tion takes place in pieces which take up no food the newly
formed organs must originate from material absorbed from cells of the
animal which are hydrolyzed and whose material serves as food for those
cells which grow. Very often this process of diges­tion takes place without
loss of the total form of the organ and is overlooked by the pure
morphologists. In Campanularia also the process of collapse described
above is only apparent in a fraction of the cases as in Driesch’s observa­tions
on Clavellina. 166 It is also possible that the red and yellow entoderm cells
which gather at the end where the new polyp forms furnish the material
which is utilized for the process of growth of the cells from which the
tentacles arise (with or without giving off specific “hormones” besides).
6. We have mentioned the ideas concerning a design, or “entelechy,” acting
as a guide to the developing egg and have shown that this revival of
Platonic and Aristotelian philosophy in biology was due to a misconcep­tion;
namely, that the egg consisted of homogeneous material which was to be
differentiated into an organism. For this supernatural task supernatural
agencies seemed required. But we have seen that the unfertilized egg is
already differentiated in a way which makes the further differentia­tion a
natural affair. This idea of a quasi superhuman intelligence presiding over
the forces of the living is met with in the field of regenera­tion, and here
again it is based upon a misconcep­tion. The lens of the eye is formed in the
embryo from the epithelium lying above the so-called optic cup (the
primitive retina). Where this retina touches the epithelium the latter begins
to grow into the cup, the ingrowing piece of epithelium is cut off and forms
the lens, which probably under the influence of substances secreted by the
optic cup becomes transparent. Certain animals like the salamander are able
to form a new lens when the old one has been removed by opera­tion, but
the new lens is formed in an entirely different way; namely, from the upper
edge of the iris. G. Wolf, who observed this regenera­tion used it to endow
the organism with a knowledge of its needs; the idea of a Platonic

preconceived plan or an Aristotelian purpose suggested itself. But it can be
shown that the organism does in this case what it is compelled to do by its
physical and chemical structure.
Uhlenhuth 167 has shown by way of tissue culture that the cells of the iris
cannot grow and divide as long as they are full of pigment granules as they
normally are. When the fine superficial membrane of the iris is torn the
pigment granules fall out and the cells can now grow and multiply. If the
lens is taken out of the eye of the salamander the fine membrane of the iris
is torn and the pigment cells at the edge (especially the upper edge) lose
their pigment granules which fall down on account of their specific gravity.
As soon as this happens the cells will proliferate. A spherical mass of cells
is formed which become transparent and which will cease to grow as soon
as they reach a certain size. The unanswered ques­tion is: Why does the
mass of cells become transparent so that it can serve as a lens? The answer
is that young cells when put into the optic cup always become transparent
no matter what their origin; it looks as if this were due to a chemical
influence exercised by the optic cup or by the liquid it contains. Lewis has
shown that when the optic cup is transplanted into any other place under the
epithelium of a larva of a frog the epithelium will always grow into the cup
where the latter comes in contact with the epithelium; and that the
ingrowing part will always become transparent. This leaves us then with
one puzzle still: Why is the growth of the lens limited? The limita­tion in the
growth of organs is one of the most important problems in growth and
organ forma­tion, though unfortunately our knowledge of this topic is
inadequate.
7. The botanist J. Sachs was the first to definitely state that in each species
the ultimate size of a cell is a constant, and that two individuals of the same
species but of different size differ in regard to the number, but not in regard
to the size of their cells. 168 Amelung, a pupil of Sachs, determined the
correctness of Sachs’s theory by actual counts. Sachs, in addi­tion,
recognized that wherever there were large masses of protoplasm, e. g., in
siphoneæ and other cœloblasts, many nuclei were scattered throughout the

protoplasm. He inferred from this that “each nucleus is only able to gather
around itself and control a limited mass of protoplasm.” 169 He points out
that in the case of the animal egg the reserve material—fat granules,
proteins, and carbohydrates—are partly trans­formed into the chromatin
substances of the nuclei, and that the cell division of the egg results in the
cells reaching a final size in which each nucleus has gathered around itself
that mass of protoplasm which it is able to control. Morgan 170 and
Driesch 171 tested and confirmed the idea of Sachs for the eggs of
Echinoderms. We stated in the previous chapter that Driesch produced
artificially larvæ of sea urchins of one-eighth, one-fourth, and one-half their
normal size by isolating a single cleavage cell in one of the first stages of
segmenta­tion of the fertilized sea-urchin egg. He counted in each of the
dwarf gastrulæ resulting from these partial eggs the number of mesenchyme
cells and found that the larvæ from a one-half blastomere possessed only
one-half, those from a one-fourth blastomere only one-fourth, and those
from a one-eighth blastomere only one-eighth of the number of cells which
a normal larva developing from a whole egg possessed. Moreover, he could
show that when two eggs were caused to fuse so as to produce a single larva
of double size, the gastrulæ of such larvæ had twice the number of
mesenchyme cells. Driesch drew the conclusion from his observa­tions that
each morphogenetic process in an egg reaches its natural end when the cells
formed in the process have reached their final size.
Since each daughter nucleus of a dividing blastomere has the same number
of chromo­somes as the original nucleus of the egg, it is clear that in a
normally fertilized egg each nucleus has twice the mass of chromo­somes
that is contained in the nucleus of a merogonic egg, i. e., an enucleated
fragment of protoplasm into which a spermato­zoön has entered and which
is able to develop. Such a fragment has only the sperm nucleus. This
phenomenon of merogony was discovered by Boveri and was elaborated by
Delage. 172 Boveri, in comparing the final size of the cells in normal and
merogonic eggs after the cell divisions had come to a standstill, found that
this size is always in propor­tion to the original mass of the chromatin

contained in the egg; the cells of the merogonic embryo, e. g., the
mesenchyme cells, are only half the size of the same cells in the normally
fertilized embryo. Driesch furnished a further proof of Boveri’s law, that the
final ratio of the mass of the chromatin substance in a nucleus to the mass
of protoplasm is a constant in a given species. Driesch compared the size of
the mesenchyme cells in a sea-urchin embryo produced by artificial
parthenogenesis with those of a normally fertilized egg and found them half
of the size of the latter. When the fertilized eggs and the partheno­genetic
eggs are equal in size from the start,—which is practically the case if eggs
of the same female are used,—the process of the forma­tion of mesenchyme
cells comes to a standstill when their number in the normally fertilized eggs
is half as large as the final number in the partheno­genetic egg. 173 Boveri’s
results as well as those of Driesch were obtained by counting the cells
formed by eggs of equal size and not by simply measuring the size of the
cells. It is most remarkable that certain apparent excep­tions to Boveri’s law
which Driesch has actually found had been predicted by Boveri.
These facts show that the growth of an organ comes to a standstill when a
certain size is reached or a certain number of cells are formed. We cannot
yet state why this should be, but we are able to add that the forma­tion of a
lens of normal size in the regenera­tion of the eye is in harmony with the
phenomena in the embryo. There seems therefore no reason for stating that
the regenera­tion of the lens cannot be explained on a purely physico­‐
chemical basis. The only justifica­tion for such a statement on the part of
Wolf is that he was not in possession of the more complete set of facts now
available through the work of Fischel and Uhlenhuth.
The healing of a wound is a process essentially similar to the regenera­tion
of the lens. Normally the cells which begin to proliferate after a wound is
made in the skin lie dormant, inasmuch as they neither grow nor divide.
When a wound is made certain layers of epidermal cells undergo rapid cell
division. Leo Loeb 174 has studied this case extensively. He found that if the
skin is removed anywhere, epidermis cells from the wound edge creep upon
the denuded spot and form a covering. This may be a tropism

(stereotropism) or it may be a mere surface tension phenomenon. Next a
rapid process of cell division begins in the cells adjacent to the wound these
cells having been heretofore dormant. He is inclined to attribute this
increase in the rate of cell division to the stretching of the epithelial cells,
and he is supported in this reasoning by the observa­tion that the larger the
wound the more rapid the process of healing. 175 During wound healing the
mitoses first increase markedly in the old epithelium. With the closure of
the wound a sudden fall in the mitoses takes place. The closure of the
wound causes an increase in the number of epithelial rows over the defect.
This increase is therefore reached at an earlier period in the larger wound
since the process of mitosis is more rapid here. Leo Loeb thinks that the
pressure of the epithelial cells upon each other leads to a rapid diminu­tion
in the mitotic prolifera­tion. 176
Should it be possible that this is more generally the case, e. g., also in the
lens after it has reached a certain size? The condi­tions limiting growth
require further investiga­tion.
It is hardly necessary to point out that in these cases we are seemingly
dealing with cases of the inhibi­tion of growth which cannot be explained by
the tyranny of the whole over the parts, and that there must be condi­tions at
work other than the mere flow of substances which can cause a cessa­tion of
growth. This can be illustrated by certain observa­tions on the egg.
8. The history of the egg shows a reversible condi­tion of rest and of activity.
The primordial egg cell multiplies actively until a large number of eggs are
formed in the ovary which may reach into the millions in the case of sea
urchins or certain annelids. These cell divisions then stop and the egg goes
into the resting stage in which it deposits the reserve material for the
development of the embryo. From this condi­tion it can only be called into
activity again by the spermato­zoön or the agencies of artificial
parthenogenesis.
It seemed of interest to find out whether or not the development of the egg
may be reversed once more after it has been activated. From all that has

been said in the chapter on artificial parthenogenesis, such a reversal should
take place in the cortical layer. The result of these experi­ments seems to be
that if a complete destruc­tion or change in the cortical layer has once taken
place—such as that caused by the entrance of a spermato­zoön into the egg
—no reversal is possible; although the development of the fertilized egg
may be suppressed for a long time by either low temperature or lack of
oxygen, or, in the case of seeds and spores, by lack of water. But as soon as
the condi­tions for the chemical reac­tions in the egg are normal again, the
development may go on unless the egg has suffered by the methods used to
prevent development or by the long dura­tion of the suppression. With an
incomplete destruc­tion of the cortical layer both development as well as
reversal of development are possible. Thus the writer has shown that in the
egg of Arbacia the effect of the cortical altera­tion of the egg induced by the
butyric acid treatment or by the treatment with bases can be reversed. When
unfertilized eggs of Arbacia are put for from two to five minutes into
50 c.c. sea water + 2.0 c.c. N/10 butyric acid they will all form a gelatinous,
somewhat atypical fertiliza­tion membrane; when put back into normal sea
water all will perish in a few hours unless they are submitted to the short
treatment with a hypertonic solu­tion mentioned in the previous chapter,
while if submitted to this treatment they will develop. If, however, these
eggs are transferred from the butyric acid sea water not into normal sea
water but into sea water containing some NaCN (10 drops of 1⁄10 per cent.
NaCN or KCN in 50 c.c. sea water), and if they remain here for some time
(e. g. overnight) they will not perish when subsequently transferred back to
normal sea water. Such eggs will develop when fertilized with sperm. The
activating effect of the membrane forma­tion has, therefore, been reversed
and the eggs have gone back into the resting stage. 177 Wasteneys has found
that the rate of oxida­tion which was raised considerably by the artificial
membrane forma­tion goes back to the value characteristic for the resting
eggs after the reversal of their developmental tendency. 178 Similar results
were obtained in eggs activated with NH4OH. It appears from this as
though the change in the cortical layer which leads to the development of

the egg and the increase in the rate of oxida­tions were reversible in the egg
of Arbacia. 179
The writer had previously noticed that eggs of Strongylo­centrotus
purpuratus, which had been treated for two hours with hypertonic sea
water, not infrequently began to divide into two, four, or eight cells (and
sometimes more) and then went back into the resting state (except that they
possessed the second factor required for development as stated in Chapter
V). It may be remarked incidentally that such eggs at the time of cell
division contained the centrosomes and astrospheres, and yet went back into
a resting state, thus showing that the centrosomes are only transitory organs
or organs which are only active under certain condi­tions. It is quite possible
that in these phenomena of reversal not the whole of the cortical layer has
undergone altera­tion.
The writer must leave it undecided whether the changes from the resting to
the active state in body cells can also be explained in analogy with these
experi­ments.
9. In the formation of the lens we have already noticed an instance where
the adjacent organ influences growth inasmuch as the optic cup controlled
the forma­tion of the lens. Such influences are quite commonly observed. A
piece of Tubularia when cut out from a stem and suspended in water will
regenerate at the aboral pole not a stolon but a polyp, so that we have an
animal terminating at both ends of its body in a head. The writer called such
cases in which an organ is replaced by an organ of a different kind hetero­‐
morphosis.

Fig. 36

Contact with a solid body favours the formation of stolons. Fig. 36 shows a
piece of a stem of Pennaria another hydroid, which was lying on the bottom
of an aquarium and which formed stolons at both ends a and b. In Margelis,
another hydroid, the writer observed that without any opera­tion the apical
ends of branches which were in contact with solid bodies continued to grow as
stolons, while those surrounded by sea water continued to grow as stems.
Herbst discovered a very interesting form of hetero­morphosis in certain
crustaceans; namely, that in the place of an eye which was cut off, an entirely
different organ could be formed, namely, an antenna. He showed that the
experi­menter has it in his power to determine whether the crustacean shall
regenerate an eye or an antenna in place of the eye. The latter will take place
when the optic ganglion is removed with the eye, the former when it is not
removed. These experi­ments were carried out successfully on Palæmon,
Palæmonetes, Sicyonia, Palinurus, and other crustaceans.
The influence of gravitation is very familiar in plants; in stems of
Bryophyllum placed hori­zon­tally the roots usually come out from the lower
end of the callus. Such phenomena are not often found in animals but they
exist here too as the following observa­tion shows.
If we cut a piece a b (Fig. 37), from the stem s s of Anten­nu­laria an­ten­nina
(Fig. 38), a hy­droid, and put it into the water in a hori­zon­tal pos­i­tion, new
stems c d (Fig. 37) may arise on its upper side. The small branches on the
under side of the old stem a b begin sud­den­ly to grow ver­ti­cal­ly down­ward. 180
In ap­pear­ance and func­tion these downward-growing elements are entirely

different from
the branches of
the normal
Antennularia;
they are roots.
In order to
understand
better the
trans­forma­tion
which thus Fig. 37
occurs in these
branches, it may be stated that under normal condi­tions
they have a limited growth (see Fig. 38), are directed
upward, and have polyps on their upper side. The parts
which grow down (Fig. 37) have no polyps, but attach
themselves like true roots to solid bodies. Thus the
changed posi­tion of the stem alone, without any opera­‐
tion, suffices to trans­form the lateral branches, whose
growth is limited, into roots with unlimited growth. The
lateral branches on the upper side of the stem do not
undergo such a trans­forma­tion into roots except in the
immediate surroundings of the place where a new stem
arises. It seems that the forma­tion of a new stem also
causes an excessive growth of roots, possibly because
the forma­tion of new branches causes the removal of
substances which naturally inhibit the forma­tion of
roots. If a piece from the stem be put vertically into the
water with top downward, the uppermost point may
continue to grow as a stem, while the lowest point may
give rise to roots. In this case, therefore, a change in the
Fig. 38 orienta­tion of organs has the effect of changing the
character of organs.

There are only two ways by which we can account for these influences of
gravita­tion. Either certain substances flow to the lowest level and collecting
there induce growth and possibly changes in the character of growth (as in
Anten­nularia) or if the cells have elements of different specific gravity the
relative posi­tion of these elements may possibly change and influence in this
way the condi­tions for growth. The influence of gravita­tion as well as of
contact upon life phenomena are at present little understood.
In all these cases of hetero­morphosis the original form is not restored. It is
needless to say that they are incompatible with the theory of natural selec­tion.
The reader will have noticed that in this chapter one term has not been
mentioned which is commonly met with in the literature, namely the “wound
stimulus.” As the writer had indicated in a former publica­tion, 181 the word
“stimulus” is generally used to disguise our ignorance of (and also our lack of
interest in) the causes which underlie the phenomena which we investigate.
Regenera­tion very often does not take place near the wound but at some
distance from it. But even when the regenera­tion takes place at the edge of the
wound the latter only serves to create condi­tions for regenera­tion, and these
condi­tions cannot be expressed by the word “stimulus.”
While our knowledge of the rôle of the whole in regenera­tion is incomplete in
a great many details it seems that the known facts warrant the statement that
the phenomena of regenera­tion belong as much to the domain of determinism
as those of any of the partial phenomena of physi­ology.

CHAPTER VIII
DETERMINATION OF SEX, SECONDARY SEXUAL
CHARACTERS, AND SEXUAL INSTINCTS

I. The Cytological Basis of Sex Determina­tion

1. It is a general fact that both sexes appear in approximately equal numbers,
provided a sufficiently large number of cases are examined. This fact has
furnished the clue for the discovery of the mechanism which determines the
relative number of the two sexes. The honour of having pointed the way to the
solu­tion of the problem belongs to McClung. 182 It has been known that certain
insects, e. g., Hemiptera and Orthoptera, possess two kinds of spermatozoa
but only one kind of eggs. The two kinds of spermatozoa differ in regard to a
single chromo­some, which is either lacking or different in one-half of the
spermatozoa.
The first one to recognize the existence of two kinds of spermatozoa was
Henking, who stated that in Pyrrhocoris (a Hemipteran) one-half of the
spermatozoa of each male possessed a nucleolus, while in the other half it was
lacking. Montgomery afterward showed that Henking’s nucleolus was an
accessory chromo­some. McClung was the first to recognize the importance of
this fact for the problem of sex determina­tion. He observed an accessory
chromo­some in one-half of the spermatozoa of two forms of Orthoptera,
Brachystola and Hippiscus, and reached the following conclusion:
A most significant fact, and one upon which almost all investigators
are united in opinion, is that the element is appor­tioned to but one-half
of the spermatozoa. Assuming it to be true that the chromatin is the
important part of the cell in the matter of heredity, then it follows that
we have two kinds of spermatozoa that differ from each other in a
vital matter. We expect, therefore, to find in the offspring two sorts of
individuals in approximately equal numbers, under normal condi­tions,

that exhibit marked differences in structure. A careful considera­tion
will suggest that nothing but sexual characters thus divides the
members of a species into two well-defined groups, and we are
logically forced to the conclusion that the peculiar chromo­some has
some bearing upon the arrangement.
N. M. Stevens and E. B. Wilson 183 have not only proved the correctness of this
idea for a number of animals but have laid the founda­tion of our present
knowledge of the subject. Wilson showed that in those cases where there are
two types of spermatozoa, one with and one without an accessory or as it is
now called an X chromo­some, all the cells of the female have one chromo­‐
some more than the cells of the male. From this he concludes correctly that in
such species a female is produced when the egg is fertilized by a spermato­‐
zoön containing an X chromo­some, while a male is produced when a
spermato­zoön without an X chromo­some enters the egg.
Such a form is Protenor, one of the Hemiptera. Wilson made sure that all the
eggs are alike in the number of chromo­somes, each egg containing an X
chromo­some in addi­tion to the six chromo­somes characteristic of the species
Protenor. There are two types of spermatozoa in equal numbers in this
species, each with six chromo­somes, but one with, the other without, an X
chromo­some. The two possible chromo­some combina­tions between egg and
spermatozoa are therefore as follows (see the diagrammatic Fig. 39):
Egg Spermatozoön Result
(1) 6 +
+6 = 12 + X = Male
X
(2) 6 + = 12 + 2X =
+6+X
X Female
The egg which receives a spermatozoön without an X chromo­some has after
fertiliza­tion 12+X chromo­somes and develops into a male; while the egg into
which a spermato­zoön with an X chromo­some enters gives rise to a female.
Since all the body cells arise from the fertilized egg by nuclear division and
the chromo­somes remain constant in number in all cells, the consequence is

that all the cells of a female Protenor have two X chromo­somes; while all the
cells of a male Protenor have only one X chromo­some.

Fig. 39

The chromosome situation in Protenor is a somewhat extreme case, inasmuch
as one X chromo­some is entirely lacking in the male. In other forms of
Hemiptera, e. g., Lygæus, there are also two types of spermatozoa appearing
in equal numbers differing in regard to the X chromo­some, but here it is only
a difference in size; one-half of the spermatozoa having a large X chromo­‐
some, the other half instead a smaller chromo­some. Calling this latter the Y
chromo­some, the sex determina­tion in this form is as follows: leaving aside
the chromo­somes which are equal in both egg and spermato­zoön we may say
that there is one type of egg containing one large X chromo­some; there are
two types of spermatozoa in equal numbers, one possessing a large X chromo­‐
some, the other possessing a small Y chromo­some. Wilson showed by a study
of the chromo­somes in males and females that when one of the spermatozoa
containing a large X chromo­some enters the egg, the egg will develop into a
female; while when one of the spermatozoa containing a small Y chromo­some

enters it will give rise to a male. Leaving aside the common chromo­somes of
both sexes, a fertilized egg containing XX gives rise to a female, while one
containing XY gives rise to a male. There is in this case as in that of Protenor
a preponderance of chromo­some material in the female, but this quantitative
difference is not essential for the determina­tion of sex, since in some species
the Y chromo­some may be as large as the X chromo­some.
The main fact is that the female cells have the chromatin composi­tion XX, the
male cells the composi­tion XY, where Y is apparently qualitatively different
and often, but not necessarily, smaller than X, or entirely lacking.
It may be mentioned in passing that indirect evidence exists indicating that in
man there are also two kinds of spermatozoa and one kind of egg, and that sex
depends on whether a male determining or a female determining spermato­‐
zoön enters the egg.
2. This mode of sex determination holds only for those animals in which there
is one type of egg and two types of spermatozoa. Experimental evidence
furnished first by Doncaster in 1908 on a moth, Abraxas, indicated that a
number of other forms exists in which matters are reversed, inasmuch as there
are two types of eggs and one type of spermatozoa. This condi­tion of affairs
exists not only in the moth Abraxas, but also in the fowl as shown by Pearl. In
these forms it is assumed that all the spermatozoa have one sex chromo­some
X, while there are two types of eggs, one possessing the sex chromo­some X,
the other possessing Y. When a spermato­zoön enters an egg with an X
chromo­some, the egg will give rise to a male, while if it enters a Y egg, a
female will arise. The evidence pointing toward this result is chiefly contained
in experi­ments on sex-limited or more correctly sex-linked heredity; i. e., a
form of heredity which follows the sex in a peculiar way. Thus colour-
blindness is a case of sex-linked inheritance, since this abnormality appears
overwhelmingly in the male offspring of a colour-blind person. Doncaster
crossed two varieties of Abraxas differing in one character which was sex-
linked, and the results of his crossings indicated that in this form there are two
types of eggs and one type of spermatozoa. 184

These observations on sex-linked heredity confirm the idea that the sex
chromo­somes determine the sex. The most extensive and conclusive experi­‐
ments along this line are those by Morgan on the fruit fly Drosophila. In this
form there are two kinds of spermatozoa and one kind of eggs; the egg has
one X chromo­some, while one-half of the spermatozoa has an X the other a Y
chromo­some; the entrance of the latter into an egg gives rise to a male, of the
former to a female.
While the eyes of the wild fruit fly Drosophila ampelophila are red, Morgan 185
noticed in one of his cultures a male that had white eyes. This white-eyed
male was mated to a red-eyed female. The offspring, the F1 genera­tion, were
all red eyed, males as well as females. These were inbred and now gave in the
F2 genera­tion the following three types of offspring:
(1) 50 per cent. females, all with red eyes.
25 per cent. with red eyes.
(2) 50 per cent. males
25 per cent. with white eyes.
The character white eye was therefore transmitted only to half the grandsons;
it was a sex-linked character. It is known from a study of the pedigrees of
colour-blind individuals that if the corresponding experiment had been carried
out with them, instead of with white-eyed flies, the same propor­tions of
normal and colour-blind would have been found: namely, normal colour
vision in the F1 genera­tion, in both males and females, and half of the males
of the F2 genera­tion colour-blind, the other half and all the females with
normal vision. Of course, in man, intermarriage between two different F1
strains would have been required in place of the inbreeding of the F1 genera­‐
tion, which took place in Morgan’s experi­ments. Morgan interprets his experi­‐
ments as follows. The normal red-eyed Drosophila has one kind of eggs, each
possessing one X chromo­some. This X chromo­some has also the factor for the
development of red-eye pigment. The white-eyed male has two kinds of
spermatozoa, one with an X chromo­some, the other with a Y chromo­some,
both lacking the factor for red-eye pigment. If we designate the X chromo­‐
some with the factor for red-eye pigment by X and the X and Y chromo­somes
lacking the factor for redness with X and Y the following combina­tions must
result if we cross a normal red-eyed female with a white-eyed male:

Eggs Sperm Result
XX red-eyed
X X
female
XY red-eyed
X Y
male
It is obvious that all the offspring of the first genera­tion (the F1 genera­tion)
must be red eyed, since all the eggs have one X chromo­some with the factor
for red. According to the results obtained from cytological studies which will
be explained in the next chapter, the females with the chromatin constitu­tion
XX will form two types of eggs in equal numbers: namely, eggs with an X
and eggs with an X, i. e., all eggs have one X chromo­some, but in fifty per
cent. of the eggs the X has the factor for red, in fifty per cent. this factor is
lacking (X). The males having the chromo­some constitu­tion XY form two
types of spermatozoa, one with an X possessing the factor for red pigment and
one, the Y chromo­somes, lacking this factor. If inbred the next F2 genera­tion
will give rise to the following four types of offspring: (1) XX, (2) XX, (3) XY,
(4) XY, all four types in equal numbers.
(1) and (2) give females, both red eyed, since both contain a red-factored X
chromo­some. (3) and (4) give males, (3) giving rise to red-eyed males, since it
contains a red-factored X chromo­some, (4) producing males with white eyes
since this X chromo­some is lacking the factor for red eyes. Since all four
combina­tions must appear in equal numbers (provided the experi­mental
material is ample enough, which was the case in these experi­ments), in the F1
genera­tion both males and females should have red eyes and in the F2 genera­‐
tion all the females should have red eyes and half of the males should have
red, half white eyes. These results were obtained.
The experiments were carried further. No white-eyed females had appeared
thus far. On the same assump­tions of the rela­tion of the X, X, and Y chromo­‐
somes to the heredity of sex as well as to eye colour it was possible to predict
under what condi­tions and in which propor­tions white-eyed females should
arise. Thus if a red-eyed female of the F1 genera­tion (a cross between white-
eyed male and normal female) be mated with a white-eyed male the result
should be an equal number of white-eyed males and white-eyed females if the

chromo­some theory of sex determina­tion were correct. The reasoning would
be as follows:
The red-eyed female, having the chromo­some constitu­tion XX should form
two kinds of eggs in equal numbers with the constitu­tion X and X; the white-
eyed male having the chromo­some constitu­tion XY should form two kinds of
spermatozoa X and Y. The following four types of individuals must then be
produced in equal numbers:
(1) XX, (2) XX, (3) XY, and (4) XY.
In this case (2) must give rise to white-eyed females and (4) to white-eyed
males, while (1) must give rise to red-eyed females and (3) to red-eyed males.
Hence white-eyed males and females and red-eyed males and females are to
be expected in this case in equal numbers, and this was actually observed.
The numerical agreement in this and the other experi­ments between the
expected and observed result cannot well be an accident. The fact that the
inheritance of sex-linked characters in man follows the same laws as in
Drosophila is a strong argument in favour of the assump­tion that in man, also,
sex is determined by two kinds of spermatozoa.
Morgan and his students discovered no less than thirty-six sex-linked
characters in Drosophila, and each behaved in a similar way to the red and
white eye colour in regard to sex-linked inheritance, so that the chromo­some
theory of sex determina­tion rests on a safe basis. That sex is merely
determined by the number of X chromo­somes, not by the Y chromo­some, is
proved by the facts that the Y chromo­some may be completely absent as in
Protenor and that Bridges 186 has found a type of female Drosophila with a
chromo­some formula XXY whose sex was not affected by the super­numerary
Y.
3. On the basis of all these experi­ments and theories it is comparatively easy
to explain a number of phenomena concerning sex ratios which before had
been very puzzling. In bees it had been shown many years ago by Dzierzon
that the males develop from unfertilized eggs while the females, queens and
workers, develop from fertilized eggs. This is intelligible on the assump­tion

that the unfertilized egg contains only one X chromo­some while the spermato­‐
zoön carries into the egg the second X chromo­some. But if the male bee
produces two types of spermatozoa we should expect that only one-half of the
fertilized eggs should be females, the other half males. But it happens that of
the two types of spermatozoa only one is formed since in one of the cell
divisions which lead to the forma­tion of spermatozoa one viable spermato­‐
zoön only is formed while the other one perishes. It is, therefore, quite
possible that it is the female-producing spermato­zoön which survives while
the male-producing spermato­zoön dies.
It is occasionally observed that an insect shows one sex on one side of its
body and the opposite sex on the other side. Boveri suggested that this
phenomenon of gynandro­morphism is due to the fact that the spermato­zoön
for some unknown reason does not fuse with the egg nucleus until after the
egg has undergone its first cell division. In this case it fuses with the nucleus
of one of the two cells into which the egg divides (or in some cases even one
of the later cells?). As a consequence the one-half of the embryo which arises
from the cell which was not fertilized would have only one X chromo­some
and in a case like the bee would develop partheno­genetically, while the other
half of the body, developing from the cell into which a spermato­zoön has
penetrated, would be fertilized. The latter half of the body would be female,
the former male. In his last paper before his untimely death, Boveri has given
proof for the correctness of this interpreta­tion as far as gynandro­morphism in
the bee is concerned. 187
It seems to be generally true that where sexual reproduc­tion leads only to the
forma­tion of females the case finds its explana­tion in the fact that the male-
producing spermatozoa perish and only the female-producing spermatozoa
survive. Such an observa­tion was made by Morgan on a certain species of
phylloxerans.
The slight preponderance in the number of one sex which is occasionally
found—an excess of six per cent. males over females in the human race—may
well find its explana­tion on the assump­tion of a slightly greater mortality of
the female-determining spermatozoa.

In certain forms partheno­genetic and sexual reproduc­tion may alternate in a
cycle, e. g., in plant lice, Daphnia, and rotifers. In plant lice it has been
observed for a long time that when the plant is normal and the weather warm
the aphides remain wingless, reproduce partheno­genetically, and only females
exist, and this may last for years and for more than fifty genera­tions; but that
when the plant is allowed to dry out both sexes appear.
Here we are dealing with a limited determina­tion of sex inasmuch as the
experi­menter has it in his power to prevent or allow the produc­tion of males.
The facts do not in all probability contradict the statements made concerning
the rôle of the X chromo­somes in the determina­tion of sex. We have seen that
where sex is determined by two types of spermatozoa one type of eggs is
produced which possesses only one X chromo­some. Such eggs might produce
males if not fertilized (as they do in bees), but they cannot produce females
because for that purpose they must have two X chromo­somes. It has been
shown for certain cases, and it may be true generally, that if eggs of this type
give rise to partheno­genetic females they may do so because they have for
some reason two X chromo­somes. Usually such an egg loses one of the X
chromo­somes in a process of nuclear division (the so-called reduc­tion
division) which usually precedes fertiliza­tion. If this reduc­tion division is
omitted the egg has two X chromo­somes and if such an egg develops
partheno­genetically it gives rise to a female. These cases do not, therefore,
contradict the connec­tion between X chromo­somes and sex determina­tion
established by cytological observa­tions and breeding experi­ments, on the
contrary, they confirm it. The ques­tion remains: How can external condi­tions
bring it about that the reduc­tion division is omitted? To this ques­tion no
definite answer can be given at present.
We may in passing mention the well-known observa­tion that twins which
originate from the same egg always have the same sex; while twins arising
from different eggs show the usual varia­tion as to sex. Twins coming from one
egg have the same chorion and can thereby be diagnosed as such. They can be
produced as we have stated in Chapter V by a separa­tion of the first two
cleavage cells of the egg, each one giving rise to a full embryo. It harmonizes
with all that has been said above that the sex of two such individuals must be

the same since they have the same number of X chromo­somes, the latter being
determined in the human race by the nature of the spermato­zoön which enters
the egg.
4. While thus far all the facts agree with the dominating influence of certain
chromo­somes upon sex determina­tion, one group of facts has not yet been
explained: namely, hermaph­ro­ditism. By hermaph­ro­ditism is meant the
existence of complete and separate sets of female and male gonads in the
same individual. This condi­tion exists regularly not only in definite groups of
animals, e. g., certain snails, leeches, tape-worms, but also, as everybody
knows, in flowering plants. While in some forms both kinds of sex cells, male
and female, are formed and mature simultaneously, as, e. g., in the Ascidian
Ciona (see Chapter IV), in others they are formed successively, very often the
spermatozoa appearing first (protandric hermaph­ro­ditism). In the long
tapeworm Tænia each ring has testes and ovaries, but the young rings are only
male while in the older rings the testes disappear and the ovaries are formed.
The same ring is in succession male and female. How can we reconcile the
facts of hermaph­ro­ditism with the chromo­some theory of sex determina­tion?
Rhabdo­nema nigro­venosum, a parasite living in the lungs of the frog, is
hermaph­ro­ditic, but its eggs produce not a hermaph­ro­ditic genera­tion but one
with the two separate sexes; this genera­tion is not parasitic and lives in the
soil. The genera­tion produced by these separate males and females gives rise
again to a hermaph­ro­dite which migrates into the lungs of the frogs.
According to Boveri and Schleip 188 the cells of the hermaph­ro­dite have twelve
chromo­somes. It produces two types of spermatozoa with six and five
chromo­somes respectively (one-half of the cells losing one chromo­some
which is left at the line of cleavage between the two cells); and one type with
six chromo­somes. In this way separate males and females are produced by the
hermaph­ro­dite, females with twelve and males with eleven chromo­somes.
The males produce again two kinds of spermatozoa, male and female
producing, but the male-producing spermatozoa become func­tionless. This
fusion of the other spermato­zoön containing six chromo­somes with an egg
having six chromo­somes leads again to the forma­tion of the herm­aph­rodite
with twelve chromo­somes. It is obvious that in this case the cause for the

herm­aph­roditism is not disclosed. If chromo­somes have anything to do with
hermaph­ro­ditism there must be an undiscovered element in the chromo­somes
which may explain why the female as well as the herm­aph­rodite have the
same chromo­some constitu­tion; or we are forced to look for another
determinant outside the X chromo­somes or the chromo­somes altogether. This
seems to be the only cytological work on the problem of hermaph­ro­ditism.
Experimental work has been begun by Correns 189 and by Shull on the
determina­tion of hermaph­ro­ditism in plants but lack of space forbids us to
give details.

II. The Physiological Basis of Sex Determina­tion

5. As stated at the beginning of this chapter, the chromo­some theory of sex
determina­tion explained only one feature of the problem, namely, the relative
numbers in which both sexes or only one sex, as the case may be, are
produced; and in this respect the evidence is so complete that we must accept
it. But with all this, the problem of sex determina­tion is not exhausted, since a
physio­logical solu­tion of the problem of sex determina­tion demands an
account of how the sex chromo­somes can induce the forma­tion not only of
ovaries and testes but also of the other sex characters. For the solu­tion of this
problem biology will have to depend largely on experi­ments in which it is
possible to influence the forma­tion of sex characters and of the sex glands
themselves.
The most striking observa­tions in this direc­tion were made by Baltzer on a
marine worm, Bonellia. In this animal the two sexes are very different, the
male being a tiny parasite, a few millimetres in length, which spends its life in
the uterus of the female, whose size is about five centimetres. A female carries
as a rule several and often a large number of the male parasites in its uterus,
which indicates that the males prevail numerically. The fertilized eggs of the
animals are laid in the sea water where the larvæ hatch. At the time of
hatching all larvæ are alike. The differentia­tion of the larvæ into the dwarf
males and the giant females can be determined at will. The larvæ have a
tendency to attach themselves to the proboscis of the female as soon as they

hatch. If given a chance to do so and if they stick to the proboscis for more
than three days they will develop into males, which soon afterwards creep into
the female where they continue their parasitic existence. If, however, no adult
female Bonellia is put into the aquarium in which the larvæ hatch, about
ninety per cent. of the larvæ will, after a period of rest, develop into females;
the rest develop into males. Those which develop into females will often show
a primary maleness which may manifest itself in the produc­tion of sperm or of
other secondary male sexual characters. This tendency is stronger the longer
the period of rest lasts. If the larvæ are allowed to settle on the proboscis of
the adult female but are removed too early hermaph­ro­dites are produced
having male and female characters mixed.
Baltzer has suggested on the basis of some observa­tions that the larvæ while
on the proboscis of the female absorb some substance secreted by the
proboscis, and this substance accelerates the further development into a male
and suppresses the female tendency. If this substance from the proboscis does
not reach the larvæ the tendency to become males is gradually suppressed in
the majority and only a few develop into pure males or protandric hermaph­ro­‐
dites, while the female characters are given a chance to develop. Baltzer
assumes, therefore,—as it seems to us correctly—that in all larvæ the
tendency for both sexual characters is present, that they are, in other words,
hermaph­ro­dites, but the chance for the suppression of one and the
development of the other group of characters can be influenced by certain
chemical substances which the larva may take up. 190

Giard has studied the effects of a curious form of castra­tion brought about by
parasites, which is followed by a change in the sexual character of the
castrated animal. The phenomenon is very striking in certain forms of crabs
when they are attacked by a parasitic crustacean, Sacculina. The two sexes
differ in the crab Carcinus mænas by the form of the abdomen, but when a
male is attacked by the parasite its abdomen assumes the female shape. Smith
observed in another crab that in such cases even the abdominal appendages of
the male may be trans­formed into those of a female. The trans­forma­tion is so
complete that the older observers had reached the conclusion that the parasite
attacked only the females, since they overlooked the fact that the castra­tion by

the parasite trans­formed the secondary sexual characters of the male into those
of a female.
Giard observed that in a diœcious plant, Lychnis dioica, a parasitic fungus
brings about the trans­forma­tion of the host into a hermaph­ro­dite.
G. Smith has discovered a fact which shows that chemical changes must
underlie these morpho­logical trans­forma­tions of primary or secondary sexual
characters. He noticed that in male crabs the presence of the parasite
Sacculina changes the contents of the fatty constituents in the blood, making
them equal to that of the female. Vaney and Meignon had previously shown
that during the chrysalid stage the female silkworms have always more
glycogen and less fat than the males. The castra­tion by parasites is paralleled
by what Caullery calls the castra­tion by senility. 191 In certain birds and also in
mammals at the time when the sexual glands cease to func­tion certain
secondary sexual characters of the other sex make their appearance. The most
common case is that certain secondary male characters appear in the old
female (excep­tionally also in the young female with abnormal ovaries)
(arrhenoidy). Thus old female pheasants assume the plumage of the male, and
in the human female after the menopause and especially among sterile women
a beard may begin to grow. The opposite phenomenon, the old male assuming
female characters, is not so common. Very interesting observa­tions on changes
in the plumage of castrated fowl have recently been made by Goodale. 192

It had long been observed by cattle breeders that in the case of twins of
different sex the female—the so-called free-martin—is usually sterile. F.
Lillie 193 has recently discovered the cause of this interesting phenomenon.
Such twins originate from two different eggs since the mother has two corpora
lutea, one in each ovary. In normal single pregnancies in cattle there is never
more than one corpus luteum present. The two eggs begin to develop
separately in each horn of the uterus.
The rapidly elongating ova meet and fuse in the small body of the
uterus at some time between the 10 mm. and the 20 mm. stage. The
blood-vessels from each side then anastomose in the connecting part
of the chorion; a particularly wide arterial anastomosis develops, so

that either fetus can be injected from the other. The arterial circula­tion
of each also overlaps the venous territory of the other, so that a
constant interchange of blood takes place. If both are males or both
are females no harm results from this; but if one is male and the other
female, the reproductive system of the female is largely suppressed,
and certain male organs even develop in the female. This is unques­‐
tionably to be interpreted as a case of hormone action.
The reproductive system of these sterile females is for the most part of
the female type, though greatly reduced. The gonad is the part most
affected; so much so that most authors have interpreted it as testis.
It should be added, however, that this result cannot at present be generalized,
since in the hermaph­ro­dites the specific hormones of both sexes must circulate
without suppressing each other’s efficiency.
All these facts indicate that certain substances secreted by the ovaries or testes
may inhibit the development of certain sexual characters of the opposite sex.
When these inhibi­tions are partly or entirely removed the secondary sexual
characters of the opposite sex may appear. This fact may also be interpreted as
an indica­tion of a latent hermaph­ro­ditism and if this be correct the real and
latent hermaph­ro­dites differ only by the degree of inhibi­tion for one sex, this
inhibi­tion being lacking or less complete in the real than in the latent
hermaph­ro­dite.
In the light of this conclusion the observa­tions on the regenera­tion of both
ovaries and testicles which Janda observed in a hermaph­ro­ditic worm,
Criodrilus lacuum, 194 is no longer so mysterious. This worm normally
possesses in the segments near the head a pair of ovaries and several pairs of
testes. Janda found that if the anterior parts containing the gonads of these
worms are cut off a complete regenera­tion takes place, including both types of
gonads, ovaries as well as testes. As a rule, more than one pair of ovaries
appear in the regenerated piece. This important experi­ment shows that in a
hermaph­ro­dite both types of sex organs can be produced from body cells or
from latent buds resembling body cells. This phenomenon would be
intelligible on the assump­tion that in the body of a hermaph­ro­dite substances

circulate which favour the development of both types of sex organs, while in a
diœcian animal probably only one type of sex organ would be developed; the
forma­tion of the other being inhibited.
Richard Goldschmidt has discovered in his breeding experi­ments on the
gipsy-moth (Lymantria dispar) a phenomenon which will probably throw
much light on the physi­ology of sex determina­tion. He found that certain
crosses between the Japanese and the European gipsy-moth do not give pure
sexes, males or females, but mixtures of the sexual characters of both sexes,
and this mixture is a very definite one for definite crosses. These differences
are such that it is possible to grade the hybrids according to their manifesta­‐
tions of maleness or femaleness, both in morpho­logical characters and
instincts. Goldschmidt calls this peculiar phenomenon intersexualism, and its
essential feature is that the various degrees of intersexualism can be produced
at will by the right combina­tion of races.
Female intersexualism begins with animals which show feathered
antennæ of medium size (feathered antennæ are a male character), but
which are otherwise entirely female in appearance except that they
produce a smaller number of eggs which are fertilized normally. In the
next stage patches of the brown male pigment appear on the white
female wings in steadily increasing quantity. The instincts are still
female, the males are attracted and copulate. But the characteristic egg
sponge laid by the animal contains nothing but anal hairs in spite of
the fact that the abdomen is filled with ripe eggs. In the next stage
whole sections of the wings show male coloura­tion, with cuneiform
female sectors between, the abdomen becomes smaller, contains fewer
ripe eggs, the instincts are only slightly female, the males are attracted
very little, and reproduc­tion is impossible. In the next stage the male
pigment covers practically the whole wing, the abdomen is almost
male, but still contains ovaries with a few ripe eggs, the instincts are
intermediate between male and female. Then follow very male-like
animals which still show in different organs their female origin and
have rudimentary ovaries. . . . The end of the series is formed by

males, which show in some minor characters, such as the shape of
wings, still some traces of their female origin.
The series of the male intersexes starts with males showing a few
white female spots on their wings. These become larger and larger, the
amount of brown pigment correspondingly decreasing. . . . Hand in
hand with this the abdomen increases in size, reaching in the most
extreme cases two-thirds of the female size (without containing eggs).
The same is true for the instincts which become more and more
female.
(And also for the copulatory organs which also become more and more
female.)
As stated above, the main fact that every desired degree of intersexualism can
be produced at will by properly combining the races for breeding, and the
intersexual potencies of the different races has been worked out by
Goldschmidt. 195

6. The rela­tion between chemical substances circulating in the body—either
derivatives of food taken up from without or of chemical compounds formed
naturally inside the body—and the produc­tion of sexual characters is best
shown in the polymorphism found among the social ants, bees, and wasps.
Here we have, as a rule, in addi­tion to the two sexes a third one, the workers,
which are in reality rudimentary and for that reason sterile females. They
differ more or less markedly from both the typical male and female in their
external form, and, as a rule cannot copulate owing to their deficient structure.
This third sex, the sterile neuters, can be trans­formed at desire into sexual
females in certain species, as P. Marchal has demonstrated. He worked with a
form of social wasps in which the workers are sterile and smaller than the real
females. In such a society of wasps all the males and workers die in the fall
and only the fertilized females survive, each one founding a new nest in the
following spring. From the first eggs laid, workers arise, small in stature and
sterile; these workers are nourished by their mother. Then these workers take
care of the feeding of all those larvæ which arise from the eggs which their
mother continues to lay. Throughout the spring only workers arise from the

eggs. The males appear in the summer, the real females towards the end of the
season when the sexes copulate.
Marchal isolated a number of the sterile workers, providing them with food
but giving them no larvæ to raise. He found that the workers which thus far
had been sterile became fertile, producing, however, only males. This latter
fact is easily understood from what has been said regarding the bees, namely,
that the female produces only one type of eggs, hence the unfertilized egg can
give rise only to males. The astonishing or important point is that the ovaries
of the workers begin to develop as soon as they no longer have a chance to
nourish the larvæ, provided the food which would have been given to the
larvæ is now at their disposal. In other words, the development of their ovaries
is the outcome of eating the food which under normal condi­tions they would
have given to the larvæ. The food must, therefore, contain a substance which
induces the development of eggs. The natural sterility of the neuters or
workers is, therefore, to use P. Marchal’s expression, a case of “food castra­‐
tion,” (“castra­tion nutriciale”). 196 The workers originate from fertilized eggs
and are therefore females, but for the full development of the ovaries and the
other sexual characters something else besides the XX chromo­somes is
needed and this is supplied in this case by the quantity or quality of the food.
May we not conclude that the same thing may happen generally, except that
these substances are formed by the body under the normal condi­tions of nutri­‐
tion through the influence of constituents of the second X chromo­some?
It is known that the future queens among the bees receive also a special type
of food which the workers do not receive. Again the idea of “food castra­tion”
of the latter is suggested.
In rotifers Whitney 197 has shown that the cycle in the produc­tion of males and
females can be regulated by the food. In some species a scanty supply of
green flagellates produced purely female offspring, while a copious diet of the
same green flagellates produced a predominance of male grandchildren,
sometimes as high as ninety-five per cent. This was confirmed by Shull and
Ladoff. 198

7. The effects of the removal of the ovaries or testes upon the development of
secondary sexual characters differ for different species. In insects the
secondary sexual characters are not altered by an operative removal of the
sexual glands as in the caterpillar, e. g., Ocneria dispar, according to
Oudemans. This result has been invariably confirmed by all subsequent
workers, especially by Meisenheimer. Crampton grafted the heads of pupæ of
butterflies upon the bodies of other specimens of the opposite sex, but the
sexual characters of the head remained unaltered.
In vertebrates, however, there exists a distinct influence of a secre­tion from
the sexual glands upon the development of certain of the secondary sexual
characters, which do not develop until sexual maturity. In a way the observa­‐
tions on arrhenoidy and thelyidy referred to above are indica­tions of this
influence.
Bouin and Ancel had already suggested that the sexual glands of mammals
have two independent constituents, the sexual cells and the interstitial tissue;
and that the latter tissue is responsible for the development of the secondary
sexual character. This has been proved definitely by Steinach, 199 who showed
that when young rats are castrated certain secondary sexual characters are not
fully developed. The seminal vesicles and the prostate remain rudimentary
and the penis develops incompletely. Such animals when adult recognize the
female and seem to follow it, but do not persist in their atten­tion and neither
erec­tion nor cohabita­tion occurs. When, however, the testes are retransplanted
into the muscles of the castrated young animal (so that they are no longer
connected with their nerves) seminal vesicles, prostate, and penis develop
normally, and these animals show normal sexual ardour and cohabitate with a
female although the female cannot become pregnant since the males cannot
ejaculate any sperm. When the retransplanted testes were examined it was
found that all the sperm cells had perished, only the interstitial tissue of the
testes remaining. It was, therefore, proved that the development of the seminal
vesicles, the prostate, the penis, and the normal sexual instincts and activities
depends upon the internal secre­tions from this interstitial tissue and not upon
the sex cells proper. This agrees with the conclusions at which Bouin and
Ancel had arrived by ligaturing the vasa deferentia of male animals.

Steinach in another series of experi­ments castrated young male rats and
transplanted into them the ovaries of young females. These ovaries did not
disintegrate, the eggs remaining, and corpora lutea were formed. In such
feminized individuals the seminal vesicles, prostate, and penis did not reach
their normal development, and it was thereby proved that the internal secre­‐
tions from the ovary do not promote the growth of the secondary sexual male
characters. On the contrary, Steinach was able to show that the growth of the
penis was directly inhibited by the ovary, since in the feminized males this
organ remained smaller than in the merely castrated animals. On the other
hand the infantile uterus and tube when transplanted into the young male with
the ovaries grow in a normal way, and Steinach thinks that pregnancy in such
feminized males is possible if sperm be injected into the uterus. In some
regards the feminized males showed the morpho­logical habitus of females.
Soon after the transplanta­tion of ovaries into a castrated male the nipples of its
mammary glands begin to grow to the large size which they have in the
female and by which the two sexes can easily be discriminated. In addi­tion the
stronger longitudinal growth of the body in the male does not occur in the
feminized specimens, the body growth becomes that of a female; and likewise
the fat and hair of the feminized male resemble that of a real female.
While the castrated males show an interest in the females, the feminized males
are absolutely indifferent to females and behave like them when put together
with normal males; and, what is more interesting, they are treated by normal
males like normal females. The sexual instincts have, therefore, also been
reversed in the feminized males by the substitu­tion of ovaries for testes.
The inhibi­tion of the growth of the penis by the ovary is of importance; it
supports the idea already expressed that in hermaph­ro­dites this inhibi­tion of
the growth of the secondary organs of the other sex is only feeble or does not
exist at all.
We may finally ask whether there is any connec­tion between the cytological
basis of sex determina­tion by special sex chromo­somes and the physio­logical
basis of sex determina­tion by specific substances or internal secre­tions. It is
possible that the sex chromo­somes determine or favour, in a way as yet
unknown, the forma­tion of the specific internal secre­tion discussed in the

second part of this chapter. In this way all the facts of sex determina­tion might
be harmonized, and it may become clear that when it is possible to modify
secre­tions by outside condi­tions or to feed the body with certain as yet
unknown specific substances the influence of the sex chromo­somes upon the
determina­tion of sex may be overcome.

CHAPTER IX
MENDELIAN HEREDITY AND ITS MECHANISM 200

I

1. The scientific era of the investiga­tion of heredity begins with Mendel’s
paper on plant hybridiza­tion which was not appreciated by his
contemporaries. Mendel invented a method for the quantitative study of
heredity which consisted essentially in crossing two forms of peas differing
only in one well-defined hereditary character; and in following statistically
and separately the results of this crossing and that of the inbreeding of the
second and third genera­tions of hybrids. This led him to the recogni­tion of one
essential feature of heredity; namely, that while the hybrids of the first genera­‐
tion are all alike, each hybrid produces two types of sex cells in equal
numbers, one for each of the pure breeds which has been used for the
crossing. This takes place not only when the forms used for the crossing differ
in regard to one character only but also if they differ for two or more
characters. The statement made is Mendel’s law of heredity, or, more
correctly, Mendel’s law of the segrega­tion of the hereditary characters of the
parents in the sex cells of the hybrids. 201 Mendel’s law allows us to tabulate
and calculate beforehand the relative number of different forms which appear
if the offspring of a mating of two varieties are bred among themselves.
In order to do this it must be remembered also that while in some cases the
hybrid is an intermediate between the two parent forms, in other cases it
cannot be discriminated from one of the two parent forms. In such cases the
character which appears in the hybrid was called by Mendel the dominant
character and the one which disappeared the recessive character. According to
Bateson, who was the first to systematize the phenomena of Mendelian
heredity, recessiveness means generally the absence of a character which is
present in the dominant type. When, e. g., the cross between a tall and a dwarf

form of pea gives in the first genera­tion only tall peas, on the basis of the
presence and absence theory the dominant form contains a factor for growth
which is lacking in the dwarf form. While this theory fits many cases it meets
with difficulties in others. Thus the presence of a factor for pigment should be
dominant over the absence of such a factor, which is usually the case,
inasmuch as the cross of a coloured rat or rabbit with an albino is black or
coloured. There is, however, also a case where whiteness is dominant over
colour, as we shall see later. This fact does not necessarily contradict the
presence and absence theory. 202

When two pure breeds of parents differ in one character, e. g., two varieties of
beans, one with a violet the other with a white flower, the cross between the
two species (the F1 genera­tion) has pale violet flowers, approximately
intermediate between the two parents. If these hybrids are bred among
themselves the offspring is called the F2 genera­tion. According to Mendel’s
law the hybrids of the first F1 genera­tion all have two kinds of eggs in equal
numbers, one kind representing the pure breed of the parents with violet, the
other of the pure breed with white flowers. The same is true for the pollen
cells. Hence the following possible combina­tions must appear in the offspring
when the pale violet hybrids are inbred:

The four possible combina­tions are: (1) violet—violet; (2) violet—white; (3)
violet—white; (4) white—white. The first will result in pure violet flowers,
the fourth in pure white, and the second and third in pale violet flowers. Since
all four combina­tions will appear in equal numbers when the number of
crossings is sufficiently large the numerical result will be:
violet : pale violet : white = 1 : 2 : 1
Fifty per cent. of the F2 genera­tion will be pale violet, 25 per cent. violet, and
25 per cent. white. The violets and whites each will breed true when bred
among themselves since they are pure, and produce only one type of eggs and

pollen. The pale violets are hybrids and will again produce the two types of
eggs and pollen, that is, if bred among themselves will again give violets, pale
violets, and whites in the ratio 1:2:1. This the experi­ment confirms.
As has been stated, it not infrequently happens that all the hybrids of the first
genera­tion are alike. In such cases the one character is “recessive,” i. e.,
overshadowed or covered by the other the “dominant” character, which alone
appears in the hybrids. Thus when Mendel crossed peas having round seeds
with peas having angular seeds all the hybrids had round seeds. The round
form is dominant, the angular recessive, i. e., all the hybrids have round seeds.
When these hybrids were bred among themselves the next genera­tion
produced round and angular seeds in the ratio of 3:1 (5474 round to 1850
angular). The explana­tion is as follows. Let R denote round, A angular
character; the pure breeds of parents have the gametic constitu­tion RR and AA
respectively. When crossed, all the offsprings have the constitu­tion RA and
since A is recessive this hybrid genera­tion resembles the pure RR parents. The
F1 genera­tion produces two kinds of eggs R and A and two kinds of pollen R
and A in equal numbers, and these if inbred give the following four combina­‐
tions in equal numbers:
RR, RA, AR, AA.
Since RA, AR, and RR all give round seeds the F2 genera­tion produces round
seeds to angular seeds in the ratio of 3:1. The two organisms with the gametic
constitu­tion RR and RA look alike, yet they are different in regard to heredity.
The gametically pure form RR is called homo­zygous, the impure form RA
hetero­zygous.
2. W. S. Sutton 203 was the first to show that the behaviour of the chromo­somes
furnishes an adequate basis on which to account for Mendel’s law of the
segrega­tion of the characters in the sex cells of the hybrids. If we disregard the
cases of parthenogenesis and the X chromo­somes, we may state that each
species is characterized by a definite number of chromo­somes, e. g. 204
man (probably) 24 corn 20
evening
mouse 20 7
primrose

snail (Helix
22 nightshade 36
hortensis)
potato beetle 18 tobacco 24
cotton 28 tomato 12
four o’clock 16 wheat 8
garden pea 7
In the fertiliza­tion of the egg the number of chromo­somes is doubled (if we
disregard for the moment the complica­tion caused by the X and Y chromo­‐
somes which was considered in the previous chapter). It was noticed by
Montgomery that each chromo­some had a definite size and individuality, and
he suggested that homologous chromo­somes existed in sperm and egg and
that in fertiliza­tion the homologous chromo­somes of egg and sperm always
joined and fused in the special stage designated as synapsis, which will
interest us later. On the basis of this sugges­tion Sutton developed the chromo­‐
some theory of the mechanism of Mendelian heredity or segrega­tion.
According to this theory, all the cells of an individual (inclusive of the egg
cells and sperm cells) have two sets of homologous chromo­somes, one from
the father, the other from the mother. Before the egg and sperm are ready for
the produc­tion of a new individual, each loses one set of homologous chromo­‐
somes in the so-called reduc­tion division, but the lost set is made up
indiscriminately of maternal as well as paternal chromo­somes, so that while
one egg retains the maternal chromo­some A the other will retain the paternal
one, and so on. If before the reduc­tion division all the eggs had the chromo­‐
some constitu­tion AA1, BB1, CC1, DD1 (where A B C D are the paternal and
A1 B1 C1 D1 the maternal chromo­somes), after the reduc­tion division each
daughter cell has a full set of four chromo­somes, but maternal and paternal
mixed. Thus the one cell may have AB1CD1, the other A1B1C1D1, etc. This,
according to Sutton, is the basis of the Mendelian heredity. Suppose the
determiner of a certain character (violet colour of flower in the bean) is
located in a chromo­some A of this species. The homologous chromo­some in
beans with white colour may be designated as a. According to the chromo­‐
some theory of Mendelian heredity a differs from A in one point, though this
difference is probably only of a chemical character and not visible.

If an egg with A is fertilized by a pollen with a (or vice versa), after fertiliza­‐
tion the chromo­some constitu­tion of the fertilized egg is Aa. All the other
homologous chromo­somes are identical and therefore need not be considered.
All the nuclei of the F1 genera­tion have the chromo­some constitu­tion Aa. All
will form eggs and pollen with nuclei of the same chromo­some constitu­tion
Aa, but all these sex cells will go through the matura­tion division before they
are fertilized; and this reduc­tion division leads to the existence of two kinds of
eggs in equal numbers, one containing only the A, the other only the a
chromo­some; and the same happens in the pollen. When therefore the hybrids
F1 are mated among themselves, the following four chromo­some combina­‐
tions will be produced:

Possible combina­tions in fertilized eggs AA, Aa, aa, in the ratio 1:2:1.
Now this is exactly the ratio of Mendelian heredity in the F2 genera­tion. The
plant with the chromo­some constitu­tion AA will form violet flowers, those
with the chromo­some constitu­tion Aa will form pale violet flowers, and those
with the chromo­some constitu­tion aa will form white flowers.
To quote Sutton’s words:
The result would be expressed by the formula AA: Aa: aa which is the
same as that given for any character in a Mendelian case. Thus the
phenomena of germ cell division and of heredity are seen to have the
same essential features viz., purity of units (chromo­somes, characters)
and the independent transmission of the same; while as a corollary it
follows in each case that each of the two antagonistic units (chromo­‐
somes, characters) is contained by exactly half the gametes produced.
It is obvious that Sutton by this idea did for heredity in general what McClung
had done for sex determina­tion or sex heredity, that is, he showed that the
numerical results obtained in Mendelian heredity can be accounted for on the
basis that factors for hereditary characters are carried by definite chromo­‐

somes. The cytological basis of sex determina­tion becomes only a special case
of the cytological basis of Mendelian heredity. In the examples quoted the
plants giving rise to violet and to white flowers are homo­zygous for the colour
of flower having the chromo­some constitu­tion AA and aa respectively; while
the plants with pale violet flowers are hetero­zygous, having the chromo­some
constitu­tion Aa in their nuclei. The former give rise to identical sex cells A
and A or a and a; while the hetero­zygous plants give rise to different sex cells
A and a.
From this point of view in Drosophila (and very probably also in man) the
female is homo­zygous for sex having in all its cells the critical chromo­some
constitu­tion XX and giving rise to one type of eggs only, each with one X
chromo­some; while the male in these forms is hetero­zygous for sex having in
all its cells the chromo­some constitu­tion XY and forming two different types
of spermatozoa in equal numbers X and Y. In Abraxas and in the fowl the
female is hetero­zygous for sex and the male homo­zygous.
3. If the chromo­somes are the vehicle for Mendelian heredity it should be
possible to show that the various hereditary characters which follow Mendel’s
law must be distributed over the various chromo­somes; and it should be
possible to find out which characters are contained in the same chromo­some.
It has already been stated that sex-linked heredity is intelligible on the
assump­tion that the X chromo­some carries the sex-linked characters. T. H.
Morgan and his pupils have shown with the greatest degree of probability that
corresponding linkages occur in the other chromo­somes and that there are in
Drosophila exactly as many groups of linkage as there are different chromo­‐
somes, namely four. 205

Mendel had found that when he crossed two species of peas differing in
regard to two pairs of characters, he obtained in the F2 genera­tion results
which he calculated on the assump­tion that the segrega­tion of the two pairs of
characters in the sex cells of the hybrids took place independently of each
other. To illustrate by an example: When crossing a yellow round pea with a
green wrinkled variety in which the characters round and yellow are
dominant, green and wrinkled recessive, all the hybrids of the F1 genera­tion

had the characters round and yellow. When these were inbred the F2 genera­‐
tion produced four types of seed in the ratio 9: 3: 3: 1, namely:
(1) yellow round (315 seeds)
(2) yellow wrinkled (101 seeds)
(3) green round (108 seeds)
(4) green wrinkled (32 seeds)
The explana­tion according to Mendel’s theory is as follows: Since the
segrega­tion of each pair of characters occurs independently, there must be 3
yellow to 1 green and also 3 round to 1 wrinkled in the F2 genera­tion. The
yellow will, therefore, be round and wrinkled in the ratio of 3:1, which will
give 9 yellow round to 3 yellow wrinkled. The green will also be round and
wrinkled in the ratio of 3:1, which will give 3 green round to 1 green
wrinkled, which is the ratio of 9: 3: 3: 1 found by Mendel.
On the basis of the chromo­some theory the following explana­tion could be
given of this numerical rela­tion. The peas with yellow round seeds have sex
cells with a factor for both yellow and for round in two different chromo­‐
somes; these two different chromo­somes we will designate with Y and R. The
peas with green and wrinkled seeds will have in their sex cells factors for
these characters in two homologous chromo­somes g and w, where g is the
homologue of Y and w of R. The cells of the hybrids of the F1 genera­tion will
have the chromo­some constitu­tion Yg Rw, where Y and g and R and w are
homologous chromo­somes which will lie alongside each other YR gw
. In the
forma­tion of sex cells a reduc­tion of these four chromo­somes to two takes
place whereby, according to the theory of Sutton, the following two types of
separa­tion can take place: YR and gw, or gR and Yw. (A separa­tion into Yg
and Rw is impossible since the division takes place only between homologous
chromo­somes.) Hence there will be four types of eggs, YR, gw, gR, and Yw
and the same four types of pollen cells. The F2 genera­tion will produce the
sixteen possible combina­tions in equal numbers: namely,
YRYR YRgw YRgR YRYw
gwYR gwgw gwgR gwYw

gRYR gRgw gRgR gRYw
YwYR Ywgw YwgR YwYw
Since w and g are recessives and therefore disappear when in combina­tion
with their respective dominants Y and R the result will be 9 YR (yellow
round), 3 Yw (yellow wrinkled), 3 Rg (round green), and 1 gw (green
wrinkled) as Mendel actually observed and as all investigators since have
confirmed.
Bateson made the discovery that these Mendelian ratios 9: 3: 3: 1 did not
always occur when forms differing in two characters were crossed. He found
typical and very constant devia­tions from this ratio in definite cases and these
cases he interpreted as being due to “gametic coupling.”
These phenomena demonstrate the existence of a complex interrela­‐
tion between the factorial units. This interrela­tion is such that certain
combina­tions between factors may be more frequent than others. The
circumstances in which this interrela­tion is developed and takes effect
we cannot as yet distinguish, still less can we offer with confidence
any positive concep­tion as to the mode in which it is exerted. 206

Morgan has given an ingenious explana­tion of these devia­tions on the basis of
the chromo­some theory of Mendelian heredity. He assumes that they occur in
those cases where the two or more characters are contained in the same
chromo­some. In that case the two factors lying in the same chromo­some
should generally be found together. Such was the case for instance in the
experi­ments with flies having red eyes and yellow body colour versus white
eyes and grey body colour, the character for white eyes and yellow body being
located in the X chromo­some (see preceding chapter), or in the experi­ments
on Abraxas. These phenomena are called linkage, and the numerical results of
linkage were given in the preceding chapter in connec­tion with the crossing of
sex-linked characters.
We have already mentioned that before the matura­tion division occurs the
homologous maternal and paternal chromo­somes fuse—the so-called synapsis
of the cytologists—and afterward separate again. It had been observed by
Janssens that in this stage of fusion and subsequent separa­tion a partial

twisting and a partial exchange between two chromo­somes may take place.
Morgan assumes that this exchange accounts for certain devia­tions in the ratio
of linkage. If in Fig. 40 the white and black signify two homologous chromo­‐
somes I and I1 containing the two pairs of homologous factors AB and ab
respectively, the synapsis state would be as in Fig. 41. If the separa­tion were
complete, either I or its homologue I1 might be lost in the matura­tion division
of the egg. If, however, the synapsis is slightly irregular, as in Fig. 42, where
the chromo­somes are slightly twisted, I and I1 will not separate completely but
an exchange will take place, part of I1 and I becoming exchanged. This would
result in the forma­tion of two mixed chromo­somes Ab and aB (Fig. 42). This
partial exchange of homologous chromo­somes, which Morgan calls “crossing
over,” occurs, as he found in Drosophila, in the egg only, not in the matura­tion
division of the sperm. He informs me that in the silkworm moth Tanaka found
that it occurs only in the male, while in Primula it takes place both in the
ovules and in the pollen as shown by Gregory.

Fig. 40 Fig. 41 Fig. 42

Morgan and his fellow-workers have put this theory to numerous tests by
breeding experi­ments and the results have fully supported it. According to the
chromo­some theory linkage should occur only when factors lie in the same
chromo­some. Hence it should be possible, on the basis of this linkage theory,
to foretell how many linkage groups there may occur in a species; namely, as
many as there are chromo­somes. In Drosophila there are four pairs of chromo­‐

somes, and Morgan and his fellow-workers found only four groups of linked
characters. 207 This agreement can be no mere accident.

Carrying the assump­tion still farther, these authors were able to show that
each individual character has in all probability a definite loca­tion in the
chromo­some, so that it seems as if each individual chromo­some consisted of a
series of smaller chromo­somes, each of which may be a factor in the
determina­tion of a hereditary character which is transmitted according to
Mendel’s law of segrega­tion. Biology has thus reached in the chromo­some
theory of Mendelian heredity an atomistic concep­tion, according to which
independent material determiners for hereditary characters exist in a linear
arrangement in the chromo­somes.

II

4. We are not concerned in this volume with the many applica­tions of the
theory of heredity to the breeding of plants, animals, and man; the reader will
find a discussion of these topics in the numerous writings of the special
workers on genetics. 208 We are, however, interested in the bearing this work
has on the concep­tion of the organism. Two ques­tions present themselves: Is
the organism nothing but a mosaic of hereditary characters determined
essentially by definite elements located in the chromo­somes; and if this be
true, what makes a harmonious whole organism out of this kaleidoscopic
assortment? We call it a kaleidoscopic assortment since a glance at the list of
hereditary characters found in one chromo­some, according to Morgan, shows
that there is apparently no physio­logical or chemical connec­tion between
them, and second: How can a factor contained in the chromo­some determine a
hereditary character of the organism? To the first ques­tion we venture to offer
the answer which has been already suggested in various chapters of this book,
that the cytoplasm of the egg is the future embryo in the rough; and that the
factors of heredity in the sperm only act by impressing the details upon the
rough block. This metaphor will receive a more definite meaning by the
answer to the second ques­tion. The characters which follow Mendelian
heredity are morpho­logical features as well as instincts. For the former we
have already had occasion to show in previous chapters to what extent they

depend upon the internal secre­tions or the existence of specific compounds in
the circula­tion, and the same is true for the instincts (Chapters VIII and X).
This then leads us to the sugges­tion that these determiners contained in the
chromo­somes give rise each to the forma­tion of one or more specific
substances which influence various parts of the body. We probably do not
notice all the effects in each case, but when a special organ is affected in a
conspicuous way, we connect the factor with this organ or the special feature
of the organ which is altered, and speak of a determiner or factor for that
organ, or for one of its characters. We also understand in this way why outside
condi­tions should be able to overcome the hereditary tendency in certain
cases, for instance why the influence of certain hereditary factors for
pigmenta­tion should depend upon temperature as E. Baur observed.
The view, according to which the determiners in the chromo­somes only tend
to give special characters to the embryo or to the adult while the cytoplasm of
the egg may be considered the real embryo, receives some support from the
fact that the first development of the egg is purely maternal, even if the egg
nucleus has been replaced by sperm of a different species. If an egg of a sea
urchin be cut into two pieces, one with and one without a nucleus, and the
enucleated piece be fertilized with the sperm of a different species of sea
urchin, the blastula and gastrula stages are purely maternal and only the
skeleton of the pluteus stage begins to betray the influence of the foreign
sperm inasmuch as this skeleton is purely paternal, according to Boveri. In all
experi­ments on hybridiza­tion it has been found that the rate of cell division of
the egg is a purely maternal character. Thus when fish eggs of a species, in
which the rate of first segmenta­tion of the egg is about eight hours, are
fertilized with sperm of a species for which the same process requires about
thirty minutes or less at the same temperature, the rate of segmenta­tion is
again about eight hours. There is then no chromo­some influence noticeable in
the early development.
When two forms of sea urchins, Strongylo­centrotus franciscanus and
purpuratus, 209 are crossed, certain features of the skeleton of the embryo, e. g.,
the so-called cross-bars, are a dominant, inasmuch as they are found in
purpuratus and both the crosses, while they are absent in franciscanus. The

development prior to the forma­tion of the skeleton is purely maternal. These
observa­tions again lend support to the idea that the Mendelian factors of
heredity must have the embryo to work on and that the organism is not to be
considered a mere mosaic of Mendelian factors. This is further supported by
the idea that the species specificity resides in the proteins of the unfertilized
egg (see Chapter III), and it is quite likely that this species specificity decides
which type of animal should arise from an egg.
The idea had been suggested that the factors which determine the future
character might be ferments or enzymes, or substances from which such
ferments develop. A. R. Moore 210 pointed out that the cross-bars in the
skeleton of the hybrid between S. purpuratus and franciscanus develop more
slowly than in the pure breed and that this should be expected if the
determiners were enzymes. Since the pure purpuratus has two determiners for
the development of the cross-bars (from both egg and sperm), the hybrids only
one (from either egg or sperm), the pure purpuratus should have twice the
enzyme mass of the hybrid. It is known that the velocity of a chemical reac­‐
tion increases in propor­tion with the mass (or in some cases in propor­tion with
the square root of the mass) of the enzyme; the cross-bars should therefore
develop faster in the pure than in the hybrid breeds, as was observed by
Moore. It was, however, not possible to obtain quantitative data.
On the other hand, it is obvious that this reasoning would not hold for all
cases. Thus when beans with violet flowers are crossed with white-flowered
beans the hybrids are pale blue, which indicates that the hybrids have less
pigment than the pure violet. Now we know that the mass of enzyme does not
influence the chemical equilibrium but only the velocity of the reac­tion. The
hybrids and pure violets differ, however, in the mass of violet pigment formed,
that is to say, in regard to the equilibrium. Hence the idea that the determiners
are enzymes or give rise to enzymes is probably not applicable to cases of this
type.
The experi­ments on the heredity of pigments are at present almost the only
ones which can be used for an analysis of the chemical nature of the character
and its possible determiner. The important work of G. Bertrand 211 and of

Chodat 212 on the produc­tion of black pigment in the cells of animals and
plants with the aid of enzymes has paved the way for such work. Bertrand has
shown that tyrosine (p-oxy­phenyl­amino­propionic acid) is trans­formed into a
black pigment by an enzyme tyrosinase which occurs in numerous organisms
and is obviously the cause of pigment and coloura­tion in a great number of
species. This discovery was utilized in the study of the heredity of pigments
by Miss Durham, Gortner, 213 and very recently by Onslow. 214 The latter
showed that from the skins of certain coloured rabbits and mice a peroxidase
can be extracted which behaves like a tyrosinase toward tyrosine in the
presence of hydrogen peroxide. This peroxidase was found in the skins of
black agouti, chocolate and blue rabbits, but not in yellow or orange rabbits.
The recessive whiteness in rabbits and mice according to this author is due to
the lack of the peroxydase. There exists a dominant whiteness in the English
rabbit which is due to a tyrosinase inhibitor which destroys the activity of the
tyrosinase “and the dominant white bellies of yellow and agouti rabbits are
due to the same cause.” “Varia­tions in coat colour are probably due to a
quantitative rather than to a qualitative difference in the pigment present.”
One point might still be mentioned since it may help to overcome a difficulty
in visualizing the connec­tion between the localiza­tion of a factor in the
chromo­some and the produc­tion of a comparatively large quantity of a
specific chemical compound, e. g., a chromogen or a tyrosinase. We must
remember that all the cells of an organism have identical chromo­somes, so
that a factor for an enzyme like tyrosinase is contained in every cell
throughout the whole body. It is likely, however, that the same factor (which
we may conceive to be a definite chemical compound) will find a different
chemical substrate to work on in the cells of different organs of the body,
since the different organs differ in their chemical composi­tion. Thus it is
conceivable that in the produc­tion of tyrosinase or of tyrosine not a single
chromomere of one single cell is engaged, but the sum total of all these
individual chromomeres of all the cells in one or several organs of the body.
The writer has added this remark especially in considera­tion of the fact that
some authors seem to feel that the chromo­some concep­tion of heredity is
incompatible with a physico­chemical view of this process.

Since we have mentioned this difficulty which some writers seem to find in
the chromo­some theory of Mendelian heredity, it may be added that a single
factor may suffice to determine a series of complicated reflexes. Thus the
helio­tropic reac­tions of animals are due to the presence of photo­sensitive
substances, and it suffices for the hereditary transmission of the complicated
purposeful reac­tions based on these tropisms that a factor for the forma­tion of
the photo­sensitive substance should exist. 215
5. Another point should be emphasized, namely that for Mendelian heredity it
is immaterial whether the character is introduced by the spermato­zoön or by
the egg. This fact which Mendel himself already recognized is in full harmony
with the conclusion that the chromo­somes and not the cytoplasm are the
bearers of Mendelian heredity, since only in respect to the chromo­some
constitu­tion are egg and sperm alike, while they differ enormously in regard to
the mass of protoplasm they carry. We can, therefore, be tolerably sure that
wherever we deal with a hereditary factor which is determined by the egg
alone the cytoplasm of the latter is partly or exclusively responsible for the
result.
We have already mentioned the fact that the rate of segmenta­tion of the egg is
such a character. Yet this character is as definite as any Mendelian character,
and it would be as easy to discriminate two species of eggs by the time
required from insemina­tion to the beginning of cell division as it would be by
any Mendelian character of their parents.
The applica­tion of our modern knowledge of heredity to human affairs has
been discussed in a very original way by Bateson in his address before the
British Associa­tion in Sydney to which the reader may be referred. 216

CHAPTER X
ANIMAL INSTINCTS AND TROPISMS 217

1. The idea that the organism as a whole cannot be explained from a physico­‐
chemical viewpoint rests most strongly on the existence of animal instincts
and will. Many of the instinctive actions are “purposeful,” i. e., assisting to
preserve the individual and the race. This again suggests “design” and a
designing “force,” which we do not find in the realm of physics. We must
remember, however, that there was a time when the same “purposefulness”
was believed to exist in the cosmos where everything seemed to turn literally
and metaphorically around the earth, the abode of man. In the latter case, the
anthropo- or geocentric view came to an end when it was shown that the
motions of the planets were regulated by Newton’s law and that there was no
room left for the activities of a guiding power. Likewise, in the realm of
instincts when it can be shown that these instincts may be reduced to
elementary physico­chemical laws the assump­tion of design becomes
superfluous.
If we look at the animal instincts purely as observers we might well get the
impression that they cannot be explained in mechanistic terms. We need only
consider what mysticism apparently surrounds all those instincts by which the
two sexes are brought together and by which the entrance of the spermato­zoön
into the egg is secured; or the remarkable instincts which result in providing
food and shelter for the young genera­tion.
We have already had occasion to record some cases of instincts which suggest
the possibility of physico­chemical explana­tion; for example the curious
experi­ment of Steinach on the reversal of the sexual instincts of the male
whose testes had been exchanged for ovaries. There is little doubt that in this
case the sexual activities of each sex are determined by specific substances
formed in the interstitial tissue of the ovary and testes. The chemical isola­tion

of the active substances and an investiga­tion of their action upon the various
parts of the body would seem to promise further progress along this line.
Marchal’s observa­tions on the laying of eggs by the naturally sterile worker
wasps are a similar case. The fact that such workers lay eggs when the queen
is removed or when they are taken away from the larvæ may be considered as
a manifesta­tion of one of those wonderful instincts which form the delight of
readers of Maeterlinck’s romances from insect life. Imagine the social
foresight of the sterile workers who when the occasion demands it “raise”
eggs to preserve the stock from extinc­tion! And yet what really happens is that
these workers, when there are no larvæ, can consume the food which would
otherwise have been devoured by the larvæ; and some substance contained in
this food induces the development of eggs in the otherwise dormant ovaries.
What appeared at first sight as a mysterious social instinct is revealed as an
effect comparable to that of thyroid substance upon the growth of the legs of
tadpoles in Gudernatsch’s experi­ment (Chapter VII).
2. If we wish to show in an unmistakable way the mechanistic character of
instincts we must be able to reduce them to laws which are also valid in
physics. That instinct, or rather that group of instincts, for which this has been
accomplished are the reac­tions of organisms to light. The reader is familiar
with the tendency of many insects to fly into the flame. It can be shown that
many species of animals, from the lowest forms up to the fishes, are at certain
stages—very often the larval stage—of their existence, slaves of the light.
When such animals, e. g., the larvæ of the barnacle or certain winged plant
lice or the caterpillars of certain butterflies, are put into a trough or test-tube
illuminated from one side only, they will rush to the side from which the light
comes and will continue to do this whenever the orienta­tion of the trough or
test-tube to the light is changed; while they will be held at the window side of
the vessel if the light or the posi­tion of the vessel remains unchanged. This
instinct to get to the source of light is so strong that, e. g., the caterpillars of
Porthesia chrysorrhœa die of starva­tion on the window side of the vessel,
with plenty of food close behind. This powerful “instinct” is, as we intend to
show, in the last analysis, the expression of the Bunsen-Roscoe law of photo­‐
chemical reac­tions. A large number of chemical reac­tions are induced or

accelerated by light, and the Bunsen-Roscoe law shows that the chemical
effect is in these cases, within certain limits, equal to the product of the
intensity into the dura­tion of illumina­tion.
The “attraction” or “repulsion” of animals by the light had been explained by
the biologists in an anthropo­morphic way by ascribing to the animals a
“fondness” for light or for darkness. Thus Graber, who had made the most
extensive experi­ments, gave as a result the statement that animals which are
fond of light are also fond of blue while they hate the red, and those which are
fond of the “dark” are fond of red and hate the blue. 218 In 1888 the writer
published a paper in which he pointed out that the so-called fondness of
animals for light and blue and for dark and red was simply a case of an
automatic orienta­tion of animals by the light comparable to the turning of the
tips of a plant towards the window of the room in which the plant is raised. 219
The phenomenon of a plant bending or growing to the source of light is called
positive helio­tropism (while we speak of negative helio­tropism in all cases in
which the plant turns away from the light, as is observed in many roots). The
writer pointed out that animals which go to the light are positively helio­tropic
(or photo­tropic) and do so because they are compelled automatically by the
light to move in this direc­tion, while he called those animals which move
away from the light negatively helio­tropic; they are automatically compelled
by the light to move away from it. What the light does is to direct the motions
of the animals and to explain this the following theory was proposed. Animals
possess photo­sensitive elements on the surface of their bodies, in the eyes, or
occasionally also in epithelial cells of their skin. These photo­sensitive
elements are arranged symmetrically in the body and through nerves are
connected with symmetrical groups of muscles. The light causes chemical
changes in the eyes (or the photo­sensitive elements of the skin). The mass of
photo­chemical reac­tion products formed in the retina (or its homologues)
influences the central nervous system and through this the tension or energy
produc­tion of the muscles. If the rate of photo­chemical reac­tion is equal in
both eyes this effect on the symmetrical muscles is equal, and the muscles of
both sides of the body work with equal energy; as a consequence the animal
will not be deviated from the direc­tion in which it was moving. This happens

when the axis or plane of symmetry of the animal goes through the source of
light, provided only one source of light be present. If, however, the light falls
sidewise upon the animal, the rate of photo­chemical reac­tion will be unequal
in both eyes and the rate at which the symmetrical muscles of both sides of the
body work will no longer be equal; as a consequence the direc­tion in which
the animal moves will change. This change will take place in one of two ways,
according as the animal is either positively or negatively helio­tropic; in the
positively helio­tropic animal the resulting motion will be toward, in the
negatively helio­tropic from, the light. Where we have no central nervous
system, as in plants or lower animals, the tension of the contractile or turgid
organs is influenced in a different way, which we need not discuss here.
The reader will perceive that according to the writer’s theory two agencies are
to be considered in these reac­tions: first, the symmetrical arrangement of the
photo­sensitive and the contractile organs, and second, the relative masses of
the photo­chemical reac­tion products produced in both retinæ or photo­sensitive
organs at the same time. If a positively helio­tropic animal is struck by light
from one side, the effect on tension or energy produc­tion of muscles
connected with this eye will be such that an automatic turning of the head and
the whole animal towards the source of light takes place; as soon as both eyes
are illuminated equally the photo­chemical reac­tion velocity will be the same
in both eyes, the symmetrical muscles of the body will work equally, and the
animal will continue to move in this direc­tion. In the case of the negatively
helio­tropic animal the picture is the same except that if only one eye is
illuminated the muscles connected with this eye will work less energetically.
The theory can be nicely tested for negatively helio­tropic animals in the larvæ
of the blowfly when they are fully grown, and for positively helio­tropic
animals on the larvæ of Balanus, and many other organisms.
One of the difficulties in identifying the motions of animals to or from the
light with the positive and negative helio­tropism of plants consisted in the fact
that plants are mostly sessile (and respond to a one-sided illumina­tion with
helio­tropic curvatures to or from the light), while most animals are free
moving and respond to the one-sided illumina­tion by being turned and
compelled to move to or from the light. This difficulty was overcome by the

observa­tion that sessile animals
like the hydroid Eudendrium
(Fig. 43) or the tube worm
Spirographis (Fig. 44) react to a
one-sided illumina­tion also with
helio­tropic curvatures like sessile
plants. 220 On the other hand, it
had been found before by
Strassburger that free-swimming Fig. 43
plant organisms like the
swarmspores of algæ move to or
from the source of light as do
free-swimming animals.
3. The writer suggested in 1897 221
that the light acts chemically in
the helio­tropic reac­tions and in
1912 that the helio­tropic reac­‐
Fig. 44
tions probably follow the law of
Bunsen and Roscoe, 222 and it was possible to confirm this idea by direct
experi­ments. 223 This law states that the photo­chemical effect of light equals i t
where i is the intensity of the light and t the dura­tion of illumina­tion. The
experi­ments were carried out on young regenerating polyps of Eudendrium by
measuring the time required to cause fifty per cent. of the polyps to bend to
the source of light. The intensity of light was varied by altering the distance of
the source of light from the polyps. Table VI gives the result.
TABLE VI

Time Required to Cause Fifty Per
Cent. of the Polyps to Bend towards
Distance between the Source of Light
Polyps and
Source of Light Calculated from
Observed Bunsen-Roscoe
Law

Metres Minutes Minutes
0.25 10
0.50 between 35 and 40 40
1.00 150 160
between 360 and
1.50 360
420

We must therefore conclude that the helio­tropic curvature of the polyps is
determined by a photo­chemical action of the light. The light brings about or
accelerates a chemical reac­tion which follows the Bunsen-Roscoe law. As
soon as the product of this reac­tion on one side of the polyp exceeds that on
the other by a certain quantity, the bending occurs. When the product i t is the
same for symmetrical spots of the organism no bending can result. This is
what our theory suggested.
It is very difficult to prove directly the applicability of the Bunsen-Roscoe law
for free-moving animals, but it can be shown that intermittent light is as
effective as constant light of the same intensity, provided that the total dura­‐
tion of the illumina­tion by the intermittent light is equal to that of the constant
light, and the dura­tion of the intermission is sufficiently small (Talbot’s law).
Talbot’s law is in reality only a modifica­tion of the Bunsen-Roscoe law.
Ewald has proved in a very elegant way the applicability of Talbot’s law to the
orienta­tion of the eyestalk of Daphnia. 224 This makes it probable that the law
of Bunsen-Roscoe underlies generally the helio­tropic reac­tion of animals.
It is of importance for the theory of the identity of the helio­tropism of animals
and plants that in the latter organisms the law of Bunsen and Roscoe is also
applicable. This had been shown previously by Fröschel 225 and by Blaauw. 226
In the following table are given the results of Blaauw’s experi­ments on the
applicability of the Bunsen-Roscoe law for the helio­tropic curvature of the
seedlings of oats (Avena sativa). The time required to cause helio­tropic
curvatures for intensities of light varying from 0.00017 to 26520 metre-
candles was measured. The product i t, namely metre-candles-seconds, varies
very little (between 16 and 26).
TABLE VII

III III
I II I II
Metre- Metre-
Duration of Metre- Duration of Metre-
Candles- Candles-
Illumination Candles Illumination Candles
Seconds Seconds
43 hours 0.00017 26.3 25 seconds 1.0998 27.5
13 " 0.000439 20.6 8 " 3.02813 24.2
10 " 0.000609 21.9 4 " 5.456 21.8
6 " 0.000855 18.6 2 " 8.453 16.9
3 " 0.001769 19.1 1 " 18.94 18.9
100 minutes 0.002706 16.2 2⁄5 " 45.05 18.0
60 " 0.004773 17.2 2⁄25 " 308.7 24.7
30 " 0.01018 18.3 1⁄25 " 511 .4 20.5
20 " 0.01640 19.7 1⁄55 " 1255 22.8
15 " 0.0249 22.4 1⁄100 " 1902 19.0
8 " 0.0498 23.9 1⁄400 " 7905 19.8
4 " 0.0898 21.6 1⁄800 " 13094 16.4
40 seconds 0.6156 24.8 1⁄1000 " 26520 26.5

It is, therefore, obvious that the blind instinct which forces animals to go to
the light, e. g., in the case of the moth, is identical with the instinct which
makes a plant bend to the light and is a special case of the same law of Bunsen
and Roscoe which also explains the photo­chemical effects in inanimate
nature; or in other words, the will or tendency of an animal to move towards
the light can be expressed in terms of the Bunsen-Roscoe law of photo­‐
chemical reac­tions.
The writer had shown in his early publications on light effects that aside from
the helio­tropic reac­tion of animals, which as we now know depends upon the
product of the intensity and dura­tion of illumina­tion, there is a second reac­tion
which depends upon the sudden changes in the intensity of illumina­tion.
di
These latter therefore obey a law of the form: Effect = f ( dt ). 227 Jennings has
maintained that the helio­tropic reac­tions of unicellular organisms are all of
this kind, but investiga­tions by Torrey and by Bancroft 228 on Euglena have
shown that Jennings’s statements were based on incomplete observa­tions.

4. In these experiments only one source of light was applied. “When two
sources of light of equal intensity and distance act simultaneously upon a
helio­tropic animal, the latter puts its median plane at right angles to the line
connecting the two sources of light.” 229 This fact has been amply verified by
Bohn, by Parker and his pupils, and especially by Bradley Patten, who used it
to compare the relative efficiency of two different lights.
The behaviour of the animals under the influence of two lights is a confirma­‐
tion of our theory of helio­tropism inasmuch as the animal moves in such a
direc­tion that the symmetrical elements of the surface of the body are struck
by light of the same intensity at the same angle, so that as a consequence
equal masses of photo­sensitive substances are produced in symmetrical
elements of their eyes or skin in equal times. The effect on the symmetrical
muscles will be identical. As soon as one of the lights is a little stronger the
animal will deviate towards this light, in case it is positively helio­tropic and
towards the weaker light if it is negatively helio­tropic. This devia­tion again is
not the product of chance but follows a definite law as Patten 230 has recently
shown. He used the negatively helio­tropic larvæ of the blowfly. These larvæ
were made to record their trail while moving under the influence of the two
lights. The results of the measurements of 2500 trails showing the progressive
increase in angular devia­tion of the larvæ (from the perpendicular upon the
line connecting the two lights), with increasing differences between the lights,
are given in the following table. Since the devia­tion or angular deflec­tion of
the larvæ is towards the weaker of the two lights it is marked negative.
TABLE VIII

Average Angular
Percentage
Deflection of the Two
Difference in the
Paths of the Larvæ
Intensity of the
towards the Weaker
Two Lights
Light
Per Cent. Degrees
0 -0.09
8 1⁄3 -2.77

16 2⁄3 -5.75
25 -8.86
33 1⁄3 -11.92
50 -20.28
66 2⁄3 -30.90
83 1⁄3 -46.81
100 -77.56

Let us assume that the negatively helio­tropic animal is at an equal distance
from the two unequal lights and placed so that at the beginning of the experi­‐
ment its median plane is at right angles to the line connecting the two lights,
but with its head turned away from them. In that case the velocity of reac­tion
in the symmetrical photo­sensitive elements of the eyeless larvæ is greater on
the side of the stronger light. Since the animal is negatively helio­tropic this
will result in a greater relaxa­tion or a diminu­tion of the energy produc­tion of
the muscles turning the head of the animal towards the side of the stronger
light. Hence the animal will automatically deviate from the straight line
towards the side of the weaker light. By the altera­tion of the posi­tion of its
body the photo­sensitive elements exposed to the stronger of the two lights will
be put at a less efficient angle and hence the rate of photo­chemical reac­tion on
this side will be diminished. The devia­tion from the perpendicular in which
the animal will ultimately move will be such that as a consequence, the rate of
photo­chemical reac­tion in symmetrical elements is again equal. The ultimate
direc­tion of motion will, according to our theory always be such that the mass
of chemical products formed under the influence of light in symmetrical
photo­sensitive elements during the same time is equal.
Patten also investigated the ques­tion whether the same difference of
percentage between two lights would give the same devia­tion, regardless of
the absolute intensities of the lights used. The absolute intensity was varied by
using in turn from one to five glowers. The relative intensity between the two
lights varied in succession by 0, 81⁄3, 162⁄3, 25, 331⁄3, and 50 per cent. Yet the
angular deflec­tions were within the limits of error identical for each relative
difference of intensity of the two lights no matter whether, 1, 2, 3, 4, or 5
glowers were used. The following table shows the result.

TABLE IX
A Table Based on the Measurements of 2700 Trails Showing
the Angular Deflections at Five Different Absolute
Intensities

Number Difference of Intensity between the Two Lights
of 0 81⁄3 162⁄3 25 331⁄3 50
Glowers per cent. per cent. per cent. per cent. per cent. per cent.
Deflec­tion in Degrees
1 -0.55 -2.32 -5.27 -9.04 -11.86 -19.46
2 -0.10 -3.05 -6.12 -8.55 -11.92 -22.28
3 +0.45 -2.60 -5.65 -8.73 -13.15 -20.52
4 -0.025 -2.98 -6.60 -9.66 -11.76 -19.88
5 -0.225 -2.92 -5.125 -8.30 -10.92 -19.28
Average -0.09 -2.77 -5.75 -8.86 -11.92 -20.28

Such constancy of quantitative results is only possible where we are dealing
with purely physico­chemical phenomena or where life phenomena are
unequivocally determined by purely physico­chemical condi­tions.
5. It seems difficult for some biologists, even with the validity of the Bunsen-
Roscoe law proven, to imagine that the movements of the animals under the
influence of light are not voluntary (or not dictated by the mysterious “trial
and error” method of Jennings). 231 But one wonders how it is possible on such
an assump­tion to account for the fact that the angle of deflec­tion of the larva
of the fly when under the influence of two lights of different intensities should
be always the same for a given difference in intensity; or why the time for
curvature in Eudendrium should vary inversely with the intensity of illumina­‐
tion. It is, however, possible to complete the case for the purely physico­‐
chemical analysis of these instincts. John Hays Hammond, Jr., has succeeded
in constructing helio­tropic machines which in the dark follow a lantern very
much in the manner of a positively helio­tropic animal. The eyes of this helio­‐
tropic machine consist of two lenses in whose focus is situated the “retina”
consisting of selenium wire. The two eyes are separated from each other by a

projecting piece of wood which represents the nose and allows one eye to
receive light while the other is shaded. The galvanic resistance of selenium is
altered by light; and when one selenium wire is shaded while the other is
illuminated, the electric energy (supplied by batteries inside the machine)
which makes the wheels turn (these take the place of the legs of the normal
animal) no longer flows symmetrically to the steering wheel, and the machine
turns towards the light. In this way the machine follows a lantern in a dark
room in a way similar to that of a positively helio­tropic animal. Here we have
a model of the helio­tropic animal whose purely mechanistic character is
beyond suspicion, and we may be sure that it is not “fondness” for light or for
brightness nor will-power nor a method of “trial and error” which makes the
machine follow the light.
6. It may also be of interest to
know that in helio­tropism the
motions of the legs are
automatically controlled by the
chemical changes taking place in
symmetrical elements of the retina.
In order to prove this point we will
turn to the phenomenon of galvano­‐
tropism. The galvanic current
forces certain animals to move in
the direc­tion of one of the two
electrodes just as the light forces
the helio­tropic animals to move
towards (or from) the source of
light. The change in the concentra­‐
tion of the ions at the boundary of
the various organs, especially the
nerves, determines the galvano­‐ Fig. 45
tropic reac­tions. When the shrimp
Palæmonetes is put into a trough with dilute salt solu­tion through which a
current of a certain intensity flows, the animal is compelled to move towards

the anode. 232 It can walk forwards, backwards, or sidewise. Here we can
observe directly that the effect of the current consists in altering the tension of
the muscles of the legs in such a way as to make it easy for the animal to
move toward the anode and difficult to move toward the cathode. Thus if the
current be sent sidewise through the animal, say from left to right (Fig. 45),
the legs of the left side assume the flexor posi­tion, those of the right the
extensor posi­tion. With this posi­tion of its legs the animal can easily move to
the left, i. e., the anode, and only with difficulty to the right, i. e., the cathode.
This change in the posi­tion of the legs occurs when the animal is not moving
at all, thus showing that the galvano­tropic movements take place not because
the animal intends to go to the anode, but that the animal goes to the anode
because its legs are practically prevented by the galvanic current from
working in any other way. This is exactly what happens in the helio­tropic
motions of animals. 233
To understand what happens when the
current goes lengthwise through the
body it should be stated that
Palæmonetes uses the third, fourth,
and fifth pairs of legs for its locomo­‐
tion. The third pair pulls in the
forward movement, and the fifth pair
pushes. The fourth pair generally acts
like the fifth, and requires no further
atten­tion. If a current be sent through
the animal longitudinally, from tail to
head, and the strength be increased
gradually, a change soon takes place
in the posi­tion of the legs (Fig. 46). In
the third pair the tension of the flexors
predominates, in the fifth the tension
of the extensors. The animal can thus
move easily with the pulling of the
third and the pushing of the fifth pairs

of legs, that is to say, the current Fig. 46

changes the tension of the muscles in
such a way that the forward motion is rendered easy, the backward motion is
difficult. Hence it can easily move toward the anode, but only with difficulty
toward the cathode. If a current be sent through the animal in the opposite
direc­tion, namely, from head to tail, the third pair of legs is extended, the fifth
pair bent; that is, the third pair can push, and the fifth pair pull. The animal
will thus move backward easily and forward with difficulty, and it is thus
driven to the anode again.
The explanation which Loeb and Maxwell proposed for this influence of the
current on the legs assumes that there are three groups of ganglion cells in the
central nervous system of these animals which are oriented according to the
three main axes of the body; (1) right-left and left-right, (2) backward, and (3)
forward. It depends upon whether the ganglion cells or the nerve elements are
in anelectro­tonus, which muscles are bent and which relaxed. It would lead us
too far to recapitulate the theory in this place, and the reader who is interested
in it is referred to Loeb and Maxwell’s paper. 234 The importance of the
observa­tions lies in the fact that they show that any element of will or choice
on the part of the animal in these motions is eliminated, that the animal moves
where its legs carry it, and not that the legs carry the animal where the latter
“wishes” to go.
7. This may be the place to dispel an error which has sometimes crept into the
discussion of the tropistic reac­tions of animals. It has been stated occasionally
that it is the energy gradient and not the automatic orienta­tion of the animal by
the light which makes the positively helio­tropic animal move towards the
source of light and the negatively helio­tropic away from it. Thus the positively
helio­tropic animal would be compelled to move towards the source of light as
a consequence of the fact that the intensity of the light increases the more the
nearer the animal approaches the source of light. If the source of light be the
reflected sky-light the difference of intensity at both ends of a microscopic
organism is so slight that it is beneath the limit capable of influencing the
motions.

A simple experiment published by the
writer in 1889 suffices to dispel the idea
that the energy gradient determines the
direc­tion of the motion of an animal in
tropistic reac­tions. Let direct sunlight (S,
Fig. 47) fall through the upper half of a
window (w w) upon a table, and diffused
daylight (D) through the lower half of the
window on the same table. A test-tube a c
is placed on the table in such a way that its
long axis is at right angles to the plane of
the window; and one half a b is in the
direct sunlight, the other half in the shade.
Fig. 47
If at the beginning of the experi­ment the
positively helio­tropic animals are in the
direct sunlight at a, they promptly move toward the window, gathering at the
window end c of the tube, although by so doing they go from the sunshine
into the shade. 235 This experi­ment is in harmony with our idea that the effect
of light consists in turning the head of the animal and subsequently its whole
body toward the source of light. By going from the strong light into the shade
the reac­tion velocity in both eyes is diminished equally and hence there is no
reason for the animal to change its orienta­tion, though its progressive motion
may be stopped for an instant by the change. But at the boundary between
sunlight and daylight a sudden change from strong to weak light occurs. If the
energy gradient determined the direc­tion of the positively helio­tropic animal,
the motion should stop at the boundary from strong to weak light, which may
happen for an instant but which will not interfere with the progressive motion
of the animal.
8. Graber had found that when animals are put into a trough covered half with
blue and half with red glass, those that are “fond” of light go under the blue,
those that are “fond” of darkness go under the red glass. The writer pointed
out that this result should be expected on the basis of his theory of helio­‐
tropism, if the assump­tion be correct that the red light is considerably less

efficient than light which goes through blue glass (such glass also allows
green rays to go through). The botanists had already shown that red glass is
impermeable for the rays which cause helio­tropic reac­tions of plants, and the
writer was able to show the same for the helio­tropic reac­tions of animals. Red
glass acts, therefore, almost like an opaque body for these animals.
A closer examination of the most efficient rays for the helio­tropic reac­tions of
different organisms has revealed the fact that for some organisms a region in
the blue λ = 460–490 µµ, for others a region in the yellowish-green, near
about λ = 520–530 µµ is the most efficient. 236 For many plants and for some
animals, like Eudendrium and the larvæ of the worm Arenicola, a region in the
blue is most efficient; for certain, if not most, animals a region in the yellow-
green is most efficient. Among unicellular green algæ, Chlamydomonas, has
its maximal efficiency in the yellowish-green and Euglena in the blue.
According to observa­tions by Mast, some green unicellular organisms like
Pandorina, Eudorina, and Spondylomorum seem to behave more like
Chlamydomonas, while certain others behave more like Euglena. 237
Wasteneys and the writer suggested that there are two groups of helio­tropic
substances, one with a maximum of photo­sensitiveness in the blue, the other
in the yellowish-green; and that the latter group may or may not be related or
identical with the visual purple which is most rapidly bleached by light of a
wave length near λ = 520–530 µµ.
The ophthalmologist Hess 238 has utilized the helio­tropic reac­tions of animals
in an attempt to prove that all animals from the lowest invertebrates up to the
fishes inclusive suffer from total colour-blindness. This statement was based
on the observa­tion that for most positively helio­tropic animals the region in
the yellowish-green near λ = 520 µµ seems the most efficient. Since this
region of the spectrum appears also as the brightest to a totally colour-blind
man, he concluded that all these animals are totally colour-blind. There is no
reason why helio­tropic reac­tions should be used as an indicator for colour
sensa­tions; if totally colour-blind human beings were possessed of an
irresistible impulse to run into a flame Hess’s assump­tion might be
considered, but no such phenomenon exists in colour-blind man. Moreover, v.

Frisch 239 has shown by experi­ments on the influence of the background on the
coloura­tion of fish as well as by experi­ments on bees and on Daphnia that the
reac­tions of these animals to light of different wave-lengths indicate different
effects besides those of mere intensity. Thus v. Frisch could train bees to go to
a blue piece of cardboard distributed among many cardboards of different
shades of grey. Bees thus trained would alight on any blue object even if it
contained no food. It would be impossible to do this with totally colour-blind
organisms.
9. Heliotropic reactions play a great rôle in the preserva­tion of individuals as
well as of species. In order to understand this rôle it must be stated that the
photo­sensitive substances appear often only under certain condi­tions and that
their effect is inhibited under other condi­tions. Thus among ants the winged
males and females alone show positive helio­tropism, 240 while the wingless
workers are free from this reac­tion. This positive helio­tropism becomes
violent at the time of the nuptial flight and this phenomenon itself seems to be
a helio­tropic phenomenon since it takes place in the direc­tion of the light.
When the queen founds her nest she loses her wings and becomes negatively
helio­tropic again. Kellogg 241 has shown that the nuptial flight of the bees is
also a purely helio­tropic phenomenon. When a part of the hive remote from
the entrance is illuminated the bees rush to the light and can thus be prevented
from swarming. These phenomena suggest that the presence of some
substance secreted by the sex glands may cause the intensifica­tion of the
helio­tropism which leads to the nuptial flight.
In certain species of Daphnia, fresh-water copepods, and of Volvox, a trace of
CO2 suffices to make negatively helio­tropic or indifferent specimens violently
positively helio­tropic. 242 Certain forms of marine copepods and the larvæ of
Polygordius can be made positively helio­tropic by lowering the temperature 243
and the larvæ of the barnacle can be made negatively helio­tropic by strong
light. 244 It is quite possible that a change in the sense of helio­tropism by
temperature and light is to some extent at least responsible for the periodic
depth migra­tions of helio­tropic animals. Many if not all positively helio­tropic
animals can be made negatively helio­tropic by exposure to ultraviolet light. 245

A most interesting example of the rôle of helio­tropism in the preserva­tion of a
species is shown in the caterpillars of Porthesia chrysorrhœa. The butterfly
lays its eggs upon a shrub. The larvæ hatch late in the fall and hibernate in a
nest on the shrub, as a rule not far from the ground. As soon as the
temperature reaches a certain height, they leave the nest; under natural condi­‐
tions, this happens in the spring when the first leaves have begun to form on
the shrub. (The larvæ can, however, be induced to leave the nest at any time in
the winter provided the temperature is raised sufficiently.) After leaving the
nest, they crawl directly upward on the shrub where they find the leaves on
which they feed. Should the caterpillars move down the shrub, they would
starve, but this they never do, always crawling upward to where they find their
food. What gives the caterpillar this never-failing certainty which saves its
life, and for which a human being might envy the little larva? Is it a dim
recollec­tion of experiences of former genera­tions? It can be shown that it is
the light reflected from the sky which guides the animal upward. When we put
these animals into a horizontal test-tube in a room, they all crawl toward the
window, or toward a lamp; the animal is positively helio­tropic. It is this
positive helio­tropism which makes them move upward where they find their
food, when the mild air of the spring calls them forth from their nest. At the
top of the branch, they come in contact with a leaf, and chemical or tactile
influences set the mandibles of the young caterpillar into activity. If we put
these larvæ into closed test-tubes which lie with their longitudinal axes at
right angles to the window, they will all migrate to the window end, where
they stay and starve, even if their favourite leaves are close behind them. They
are slaves of the light.
The few young leaves on top of a twig are quickly eaten by the caterpillar. The
light, which saved its life by making it creep upward where it finds food,
would cause it to starve could it not free itself from the bondage of positive
helio­tropism. The animal, after having eaten, is no longer a slave of the light,
but can and does creep downward. It can be shown that a caterpillar, after
having been fed, loses its positive helio­tropism almost completely and
permanently. If we submit unfed and fed caterpillars of the same nest
contained in two different test-tubes to the same artificial or natural source of

light, the unfed will creep to the light and stay there until they die, while those
that have eaten will pay little or no atten­tion to the light. Their sensitiveness to
light has disappeared; after having eaten they become independent of light and
can creep in any direc­tion. The restlessness which accompanies the condi­tion
of hunger makes the animal creep downward—which is the only direc­tion
open to it—where it finds new young leaves on which it can feed. The
wonderful hereditary instinct, upon which the life of the animal depends, is its
positive helio­tropism in the unfed condi­tion and its loss of this helio­tropism
after having eaten. The latter phenomenon is in harmony with the experi­ments
which show that the helio­tropism of certain species of Daphnia disappears
when the water becomes neutral.
And finally it may be pointed out that the majority of green plants could not
exist if their stems were not positively, their roots negatively, helio­tropic. It is
the positive helio­tropism which makes the top grow toward the light, which
enables the leaves to get the light necessary for assimila­tion, and the roots to
grow into the soil where they find the water and nutritive salts.
10. While we do not wish to deal here with the different tropisms it should be
stated that aside from helio­tropism, chemotropism as well as stereotropism
play the most essential rôle in the so-called instinctive ac­tions of animals. It is
a problem of orienta­tion by the diffusion of molecules from a centre when a
male butterfly is deviated from its flight and alights on the wooden box in
which is enclosed a female of the same species. We have already alluded to
certain phenomena of chemotropism in Chapter IV. Certain organisms have a
tendency to bring their bodies as much as possible on all sides in contact with
solid bodies; thus the butterfly Amphipyra, which is a fast runner, will come to
rest under a glass plate when the plate is put high enough above the ground so
that it touches the back of the butterfly. The animals which live under stones
or underground or in caves are as a rule both negatively helio­tropic and
positively stereotropic. Their tropisms predestine or force them into the life
they lead.
The sensitive area which forms the basis of tropisms is as a rule developed not
in the whole organism but only in certain segments of the body. Thus the eyes
are located in the head. But when the action of one segment becomes

overpowering the whole organism follows the segment. It has been customary
among physiologists to speak of reflexes in such cases. Thus, e. g., the arms of
the male frog develop a powerful positive stereotropism on their ventral
surface during the spawning season. It would avoid confusion to realize that
there is nothing gained in applying to this tropism the meaningless term
“reflex”; it is better to call them tropisms since the organism as a whole is
involved. If necessary we might speak of segmental tropisms. The act of
seeking the female as well as that of cohabita­tion are in many cases combina­‐
tions of chemotropism and stereotropism. The development of these tropisms
depends upon the presence of certain specific substances in the body, a fact
emphasized already in the case of helio­tropism. In case of the development of
the segmental stereotropism of the male frog at the time of spawning it has
been shown that it depends on an internal secre­tion from the testes.
It has been suggested by some authors that the tropistic reac­tions are
determined by some feeling or emotion on the part of the organism. We have
no means of judging the emotions of lower animals (except by “intui­tion”).
The writer suggested in 1899 in his book on brain physi­ology that emotions
may be determined by specific substances which also determine the tropistic
reac­tion (as well as phenomena of organ forma­tion, although this latter
phenomenon has nothing to do with the subject of instincts); and the excellent
work of Cannon 246 has shown the rôle of adrenalin in the expression of fear. It
is, therefore, both unwarranted and unnecessary to state that hypothetical
emotions determine the tropistic reac­tions.

CHAPTER XI
THE INFLUENCE OF ENVIRONMENT

1. The term environ­ment in rela­tion to an organism may easily assume a
mystic rôle if we assume that it can modify the organisms so that they become
adapted to its peculiarities. Such ideas are difficult to comprehend from a
physico­chemical viewpoint, according to which environ­ment cannot affect the
living organism and non-living matter in essentially different ways. Of course
we know that proteins will as a rule coagulate at temperatures far below the
boiling point of water and that no life is conceivable for any length of time at
temperatures above 100° C., but heat coagula­tion of proteins occurs as well in
the test-tube as in the living organism. If we substitute for the indefinite term
environ­ment the individual physical and chemical forces which constitute
environ­ment it is possible to show that the influence of each of these forces
upon the organism finds its expression in simple physico­chemical laws and
that there is no need to introduce any other considera­tions.
We select for our discussion first the most influential of external condi­tions,
namely temperature. The reader knows that there is a lower as well as an
upper temperature limit for life. Setchell has ascertained that in hot springs
whose temperature is 43° C., or above, no animals or green alga are found. 247
In hot springs whose temperature is above 43° he found only the
Cyanophyceæ, whose structure is more closely related to that of the bacteria
than to that of the algæ, inasmuch as they have neither definitely differentiated
nuclei nor chromophores. The highest temperature at which Cyanophyceæ
occurred was 63° C. Not all the Cyanophyceæ were able to stand temperatures
above 43° C., but only a few species. The other Cyanophyceæ were found at a
temperature below 40° C., and were no more able to stand higher
temperatures than the real algæ or animals. The Cyanophyceæ of the hot
springs were as a rule killed by a temperature of 73°. From this we must
conclude that they contain proteins whose coagula­tion temperature lies above

that of animals and green plants, and may be as high as 73°. Among the fungi
many forms can resist a temperature above 43° or 45°; the spores can
generally stand a higher temperature than the vegetative organs. Duclaux
found that certain bacilli (Tyrothrix) found in cheese are killed in one minute
at a temperature of from 80° to 90°; while for the spores of the same bacillus a
temperature of from 105° to 120° was required. 248
Duclaux has called atten­tion to a fact which is of importance for the investiga­‐
tion of the upper temperature limit for the life of organisms. According to this
author it is erroneous to speak of a definite temperature as a fatal one; instead
we must speak of a deadly temperature zone. This is due to the fact that the
length of time which an organism is exposed to a higher temperature is of
importance. Duclaux quotes as an example a series of experi­ments by
Christen on the spores of soil and hay bacilli. The spores were exposed to a
stream of steam and the time determined which was required at the various
temperatures to kill the spores.
It took at 100° over sixteen hours
" " " 105–110° two to four hours
" " " 115° thirty to sixty minutes
" " " 125–130° five minutes or more
" " " 135° one to five minutes
" " " 140° one minute
In warm-blooded animals 45° is generally considered a temperature at which
death occurs in a few minutes; but a temperature of 44°, 43°, or 42° is also to
be considered fatal with this difference only, that it takes a longer time to
bring about death. This fact is to be considered in the treatment of fever.
It is generally held that death in these cases is due to an irreversible heat
coagula­tion of proteins. According to Duclaux, it can be directly observed in
micro-organisms that in the fatal temperature zone the normally
homogeneous, or finely granulated, protoplasm is filled with thick, irregularly
arranged bodies, and this is the optical expression of coagula­tion. The fact that
the upper temperature limit differs so widely in different forms is explained by
Duclaux through differences in the coagula­tion temperature of the various

proteins. It is, e. g. known that the coagula­tion temperature varies with the
amount of water of the colloid. According to Cramer, the mycelium of
Penicillium contains 87.6 water to 12.4 dry matter, while the spores have 38.9
water and 61.1 dry substance. This may explain why the mycelium is killed at
a lower temperature than the spores. According to Chevreul, with an increase
in the amount of water, the coagula­tion temperature of albuminoids decreases.
The reac­tion of the protoplasm influences the temperature of coagula­tion,
inasmuch as it is lower when the reac­tion is acid, higher when the reac­tion is
alkaline. The experi­ments of Pauli show also a marked influence of salts upon
the temperature of coagula­tion of colloids.
The process of heat coagula­tion of colloids is also a func­tion of time. If the
exposure to high temperature is not sufficiently long, only part of the colloid
coagulates; in this case an organism may again recover.
Inside of these upper and lower temperature limits we find that life
phenomena are influenced by temperature in such a way that their rate is
about doubled for an increase of the temperature of 10° C., and that this
temperature coefficient for 10°, Q10, very often steadily diminishes from the
lower to the higher temperature; so that near the lower temperature limit it
becomes often considerably greater than 2 and near the higher temperature
limit it becomes very often less than 2. 249 This influence of temperature is so
general that we are bound to associate it with an equally general feature of life
phenomena; and such a feature would be most likely the chemical reac­tions. It
is known through the work of Berthelot, van’t Hoff, and Arrhenius that the
temperature coefficient for the velocity of chemical reac­tions is also generally
of about the same order of magnitude; namely ≧2 for a difference of 10°. In
chemical reac­tions there is also a tendency for Q10 to become larger for lower
temperature, and coefficients of Q10 about 5 or 6 have repeatedly been found
for purely chemical reac­tions between 0° and 10°, e. g., for the inversion of
cane sugar by the hydrogen ion. The temperature coefficient for the reac­tion
velocity of ferments shows the same diminu­tion of Q10 with rising
temperature which is also noticed in most life phenomena. Thus Van Slyke
and Cullen 250 found that the reac­tion rate of the enzyme urease “is nearly
doubled by every 10° rise in temperature between 10° and 50°. Within this

range the temperature coefficient is nearly constant and averages 1.91. From
O° to 10° it is 2.80, from 50° to 60° it is only 1.09. The optimum is at about
55°.” The rapid fall of the temperature coefficient for enzyme action at the
upper temperature limit has been ascribed by Tammann to a progressive
destruc­tion of the active mass of enzyme by the higher temperature (by
hydrolysis). This will, however, not account for the high value of the
coefficient near the lower limit. But is it not imaginable that at low
temperature an aggrega­tion of the enzyme particles exists which is also
equivalent to a diminu­tion of the active mass of the enzyme and that this
aggrega­tion is gradually dispersed by the rising temperature? This would
account for the fact that at a temperature near 0°C life phenomena stop
because the enzymes are all in a state of aggrega­tion or gela­tion; that then
more and more are dissolved and the rate of chemical reac­tion increases since
the mass of enzyme particles increases until all the enzyme molecules are
dissolved or rendered active. Under this assump­tion three processes are
superposed in the varia­tion of the value of Q10 with temperature: (1) the
supposed increase in the number of available ferment molecules with
increasing temperature near the lower temperature limit; (2) the temperature
coefficient of the reac­tion velocity which is nearly = 2 for 10°C.; (3) the
diminu­tion of the number of available ferment molecules by hydrolysis or
some other action of the increasing temperature. This latter is noticeable near
the upper temperature limit. The reason that 1 and 3 interfere more strongly in
life phenomena than in the chemical reac­tions of crystalloid substances may
possibly be accounted for by the fact that the enzymes and most of the
constituents of living matter are colloidal, i. e., consist of particles of a
considerably greater order of magnitude than the molecules of crystalloids. 251
We will now show the rôle of the temperature coefficient upon phenomena of
development. F. R. Lillie and Knowlton 252 first determined the influence of
temperature upon the development of the egg of the frog and showed that it
was of the same nature as that of a chemical reac­tion. These experi­ments were
repeated a year later by O. Hertwig. 253

The time required for the eggs to reach definite stages was measured for
different temperatures and it was found that the temperature coefficient Q10
between 2.5° and 6° was equal to 10 or more; between 6° and 15° it was
between 2.6 and 4.5; between 10° and 20° it was 2.9 to 3.3, and between 20°
and 24° it was between 1.4 and 2.0. To anybody who has worked on this
problem it is obvious that no exact figures can be obtained in this way, since
the point when a certain stage of development is reached is not so sharply
defined as to exclude a certain latitude of arbitrariness. The writer found that
very exact figures can be obtained on the influence of temperature upon
development of the sea-urchin egg by measuring the time from insemina­tion
to the first cell division. Such experi­ments were carried out in a cold-water
form Strongylo­centrotus purpuratus and a form living in warmer water,
Arbacia. 254 The figures on Arbacia have been verified by different observers
in different years.
TABLE X
Influence of Temperature upon the Time (in Minutes)
Required From Insemination to the First Cell Division

Arbacia
Loeb and Loeb and Strongylo­centrotus
Temperature
Wasteneys Chamberlain purpuratus
1911 1915
°C. Minutes Minutes Minutes
3 532
4 469
5 352
6 275
7 498 291
8 410 411 210
9 308 297.5 159
10 217 208 143
11 175 175
12 147 148 131

13 129
14 116 121
15 100 100 100
16 85.5
17 70.5
18 68 68 87
19 65 78
20 56 56 75
21 53.3 78
22 47 46 75
23 45.5 Upper temperature
24 42 limit
25 40 39.5
26 33.5
27.5 34
30 33
31 37

These figures permitted the determina­tion of the temperature coefficients Q10
with a sufficient degree of accuracy (see next table). It seemed of importance
to attempt to decide what the chemical reac­tion underlying these reac­tion
velocities is (if it is a chemical reac­tion). Loeb and Wasteneys 255 investigated
the temperature coefficient for the rate of oxida­tions in the newly fertilized
egg of Arbacia and found that the temperature coefficient Q10 for that process
does not vary in the same way as the temperature coefficient for cell division.
TABLE XI
Temperature Coefficients Q10 for the Rate of Segmentation
and Oxidations in the Eggs of Strongylocentrotus and
Arbacia

Q10 for Rate of Segmentation in Q10 for Rate of
Temperature Oxidations in
Strongylocentrotus Arbacia Arbacia
°C.

3–13 3.91 2.18
4–14 3.88
5–15 3.52 2.16
7–17 3.27 7.3 2.00
8–18 6.0
9–19 2.04 4.7
10–20 1.90 3.8 2.17
11– 21 3.3
12–22 1.74 3.1
13–23 2.8 2.45
15–25 2.5 2.24
16–26 2.6
17.5–27.5 2.2 2.00
20–30 1.7 1.96

It is obvious that the temperature coefficient of the rate of oxida­tions is
remarkably constant, about 2 for 10°, for various temperatures and does not
show the varia­tion from 7 or more to 2.2 for Q10 for the rate of segmenta­tion.
Kanitz 256 has shown that in a graph in which the logarithms of the segmenta­‐
tion velocities are drawn as ordinates and the temperatures as abscissæ the
logarithms form two straight lines which are joined at an angle. According to
the law of van’t Hoff and Arrhenius concerning the influence of temperature
upon velocities of chemical reac­tions the logarithms should lie in a straight
line. We are dealing therefore in these cases with two exponential curves, one
representing in Arbacia the interval 7–13° and the second from 13–26°; in
Strongylo­centrotus between 3–9° and 9–20°.
It was found in these experi­ments that if measurements of the Q10 of later
stages of development are attempted the varia­tions due to unavoidable
difficulties become too great to permit an equal degree of reliability in the
determina­tions.
The vast importance of this influence of temperature upon the rate of
development is seen in the fact that in addi­tion to the food supply the rate of
the maturing of plants and animals depends on this factor.

2. This influence of temperature upon development has been used to find the
condi­tions determining fluctuating varia­tion. The reader knows that by this
expression are understood the differences between individuals of a pure strain
or breed. These varia­tions are not inherited, a fact contrary to the idea of
Darwin, who assumed that by the selec­tion of extreme cases of fluctuating
varia­tion new varieties could develop. What is the basis of this fluctuating
varia­tion? The writer concluded that if fluctuating varia­tions were due to a
slight varia­tion in the quantity of a specific substance—in some cases an
enzyme—required for the forma­tion of a hereditary character, the temperature
coefficient might be used to test the idea. We have just seen that the time
required from insemina­tion until the cell division of the first egg occurs is
very sharply defined for each temperature. If a large number e. g. one hundred
or more eggs are under observa­tion simultaneously in a microscopic field it
can be seen that they do not all segment at the same time but in succession;
this is the expression of fluctuating varia­tion. Miss Chamberlain and the
writer have measured the time which elapses between the moment the first
egg of such a group segments and the moment the last egg begins its
segmenta­tion, and found that this latitude of varia­tion is also very definite for
each temperature, and that its temperature coefficient is for each interval of
10° practically identical with the temperature coefficient of the segmenta­tion
for the same interval. 257 The slight devia­tions are practically all in the same
sense and accounted for by a slight deficiency in the nature of the experi­‐
ments. The two following tables give the latitude of varia­tions for different
temperatures for the first segmenta­tion in Arbacia and the temperature
coefficient for this latitude and the rate of segmenta­tion. These two latter
coefficients are practically identical.
TABLE XII

Latitude of Latitude of
Temperature Temperature
Variation Variation
°C. Minutes °C. Minutes
9 52.5 18 12.0
10 39.5 19 12.5

11 26.0 20 9.6
12 22.5 21 8.0
13 19.2 22 7.8
14 17.5 23 8.0
15 13.0 24 8.0
25 5.0

TABLE XIII

temperature coefficient of
Temperature
Interval Latitude of
Segmentation
Variation
°C.
9–19 4.2 4.7
10–20 3.9 3.8
11–21 3.2 3.3
12–22 2.8 3.1
13–23 2.4 2.8
14–24 2.3 2.8
15–25 2.6 2.5

If we assume that the temperature coefficient for the segmenta­tion of the egg
is that of a chemical reac­tion (other than oxida­tion) underlying the process of
segmenta­tion, the fluctuating varia­tion in the time of the segmenta­tions of the
various eggs fertilized at the same time is due to the fact that the mass of the
enzyme controlling that reac­tion varies within definite limits in different eggs.
The first egg segmenting at a given temperature has the maximal, the last egg
segmenting has the minimal mass of enzyme. It should be added that the time
of the first segmenta­tion is determined by the cytoplasm and is not a
Mendelian character, as was stated in a previous chapter.
3. The point of importance to us is that the influence of temperature upon the
organism is so constant that if disturbing factors are removed it would be
possible to use the time from insemina­tion to the first segmenta­tion of an egg
of Arbacia as a thermometer on the basis of the table on page 295.

Facts of this character should dispose of the idea that the organism as a whole
does not react with that degree of machine-like precision which we find in the
realm of physics and chemistry. Such an idea could only arise from the fact
that biologists have not been in the habit of looking for quantitative laws,
chiefly, perhaps, because the difficulties due to disturbing secondary factors
were too great. The worker in physics knows that in order to discover the laws
of a phenomenon all the disturbing factors which might influence the result
must first be removed. When the biologist works with an organism as a whole
he is rarely able to accomplish this since the various disturbing influences,
being inseparable from the life of the organism, can often not be entirely
removed. In this case the biologist must look for an organism in which by
chance this elimina­tion of secondary condi­tions is possible. The following
example may serve as an illustra­tion of this rather important point in
biological work. Although all normal human beings have about the same
temperature, yet if the heart-beats of a large number of healthy human beings
are measured the rate is found to vary enormously. Thus v. Körösy found
among soldiers under the most favourable and most constant condi­tions of
observa­tions—the soldiers were examined early in the morning before rising
—varia­tions in the rate of heart-beat between 42 and 108. In view of this fact,
those opposed to the idea that the organism as a whole obeys purely physico­‐
chemical laws might find it preposterous to imagine that the rate of heart-beat
could be used as a thermometer. Yet if we observe the influence of
temperature on the rate of the heart-beat of a large number of embryos of the
fish Fundulus, while the embryos are still in the egg, we find that at the same
temperature each heart beats at the same rate, the devia­tions being only slight
and such as the fluctuating varia­tions would demand. 258 This constancy is so
great that the rate of heart-beat of these embryos could in fact be used as a
rough thermometer. The influence of temperature upon the rate of heart-beat is
completely reversible so that when we measure the rate for increasing as well
as for decreasing temperatures we get approximately the same values as the
following table shows.
TABLE XIV

Time Required for Nineteen Heart-beats
Temperature
in the Embryo of Fundulus
°C. Seconds
30 6.25
25 8.5
20 11. 5
15 19.0
10 32.5
5 61.0
10 33.5
15 18.8
20 12.0
25 10.0
30 6.0

Why does each embryo have the same rate of heart-beat at the same
temperature in contradistinc­tion to the enormous variability of the same rate in
man? The answer is, on account of the elimina­tion of all secondary disturbing
factors. In the embryo of Fundulus the heart-beat is a func­tion almost if not
exclusively of two variables, the mass of enzymes for the chemical reac­tions
underlying the heart-beat and the temperature. By inheritance the mass of
enzymes is approximately the same and in this way all the embryos beat at the
same rate (within the limits of the fluctuating varia­tion) at the same
temperature. This identity exists, however, only as long as the embryo is
relatively quiet in the egg. As soon as the embryo begins to move this equality
disappears since the motion influences the heart-beat and the motility of
different embryos differs.
In man the number of disturbing factors is so great that no equality of the rate
for the same temperature can be expected. Differences in emotions or the
internal secre­tions following the emotions, differences in previous diseases
and their after-effects, differences in metabolism, differences in the use of
narcotics or drugs, and differences in activity are only some of the number of
variables which enter.

4. As stated above the temperature influences practically all life phenomena in
a similar characteristic way, e. g., the produc­tion of CO2 in seeds 259 and the
assimila­tion of CO2 by green plants. 260 The writer would not be surprised if
even the aberra­tions in the colour of butterflies under the influence of
temperature turned out to be connected with the temperature coefficient. The
experi­ments of Dorfmeister, Weismann, Merrifield, Standfuss, and Fischer, on
seasonal dimorphism and the aberra­tion of colour in butterflies have so often
been discussed in biological literature that a short reference to them will
suffice. By seasonal dimorphism is meant the fact that species may appear at
different seasons of the year in a somewhat different form or colour. Vanessa
prorsa is the summer form, Vanessa levana the winter form of the same
species. By keeping the pupæ of Vanessa prorsa several weeks at a
temperature of from 0° to 1° Weismann succeeded in obtaining from the
summer chrysalids specimens which resembled the winter variety, Vanessa
levana.
If we wish to get a clear understanding of the causes of varia­tion in the colour
and pattern of butterflies, we must direct our atten­tion to the experi­ments of
Fischer, who worked with more extreme temperatures than his predecessors,
and found that almost identical aberra­tions of colour could be produced by
both extremely high and extremely low temperatures. This can be seen clearly
from the following tabulated results of his observa­tions. At the head of each
column the reader finds the temperature to which Fischer submitted the pupæ,
and in the vertical column below are found the varieties that were produced.
In the vertical column A are given the normal forms:
TABLE XV

0° to 0° to A +35° to +36° to +42° to
-20°C. +10°C. (Normal +37°C. +41°C. +46°C.
Forms)
ichnusoides polaris urticæ ichnusa polaris ichnusoides
(nigrita) (nigrita)
antigone fischeri io —— fischeri antigone
(iokaste) (iokaste)

testudo dixeyi polychloros erythromelas dixeyi testudo
hygiæa artemis antiopa epione artemis hygiæa
elymi wiskotti cardui —— wiskotti elymi
klymene merrifieldi atalanta —— merrifieldi klymene
weismanni porima prorsa —— porima weismanni

The reader will notice that the aberra­tions produced at a very low temperature
(from 0° to -20°C.) are absolutely identical with the aberra­tions produced by
exposing the pupæ to extremely high temperatures (42° to 46°C.). Moreover,
the aberra­tions produced by a moderately low temperature (from 0° to 10°C.)
are identical with the aberra­tions produced by a moderately high temperature
(36° to 41°C.).
From these observa­tions Fischer concludes that it is erroneous to speak of a
specific effect of high and of low temperatures, but that there must be a
common cause for the aberra­tion found at the high as well as at the low
temperature limits. This cause he seems to find in the inhibiting effects of
extreme temperatures upon development.
If we try to analyse such results as Fischer’s from a physico­chemical point of
view, we must realize that what we call life consists of a series of chemical
reac­tions, which are connected in a catenary way; inasmuch as one reac­tion or
group of reac­tions (a) (e. g., hydrolyses) causes or furnishes the material for a
second reac­tion or group of reac­tions (b) (e. g., oxida­tions). We know that the
temperature coefficient for physio­logical processes varies slightly at various
parts of the scale; as a rule it is higher near 0° and lower near 30°. But we
know also that the temperature coefficients do not vary equally for the various
physio­logical processes. It is, therefore, to be expected that the temperature
coefficients for the group of reac­tions of the type (a) will not be identical
through the whole scale with the temperature coefficients for the reac­tions of
the type (b). If therefore a certain substance is formed at the normal
temperature of the animal in such quantities as are needed for the catenary
reac­tion (b), it is not to be expected that this same perfect balance will be
maintained for extremely high or extremely low temperatures; it is more
probable that one group of reac­tions will exceed the other and thus produce

aberrant chemical effects, which may underlie the colour aberra­tions observed
by Fischer and other experi­menters.
It is important to notice that Fischer was also able to produce aberra­tions
through the applica­tion of narcotics. Wolfgang Ostwald has produced
experimentally, through varia­tion of temperature, dimorphism of form in
Daphnia.
5. Next or equal in importance with the temperature is the nature of the
medium in which the cells are living.
It has often been pointed out that the marine animals and the cells of the body
of metazoic animals are surrounded by a medium of similar constitu­tion, the
sea water and the blood or lymph, both media being salt solu­tions differing in
concentra­tion but containing the three salts NaCl, KCl, and CaCl2 in about the
same relative concentra­tion, namely 100 molecules NaCl : 2.2 molecules of
KCl : 1.5 molecules of CaCl2. This has suggested to some authors the poetical
dream that our home was once the ocean, but we cannot test the idea since
unfortunately we cannot experi­ment with the past. Plants, unicellular fresh-
water algæ, and bacteria do not demand such a medium for their existence.
Herbst had shown that when sea-urchin larvæ were raised in a medium in
which only one of the constituents of the sea water was lacking (not only
NaCl, KCl, or CaCl2, but also Na2SO4, NaHCO3, or Na2HPO4), the eggs
could not develop into plutei; from which he concluded that every constituent
of the sea water was necessary. This would indicate a case of extreme adapta­‐
tion to all the minutiæ of the external medium.
Experiments on a much more favourable animal for this purpose, namely, the
eggs of the marine fish Fundulus, gave altogether different results. The eggs
of this marine fish develop naturally in sea water but they develop just as well
in fresh or in distilled water, and the young fish when they are made to hatch
in distilled water will continue to live in this medium. This proves that these
eggs require none of the salts of the sea water for their development. When
these eggs are put immediately after fertiliza­tion into a pure solu­tion of NaCl
of that concentra­tion in which this salt exists in the sea water practically all
the eggs die without forming an embryo; but if a small quantity of CaCl2 is

added every egg is able to form one, and these embryos will develop into fish
and the latter will hatch. This led the writer to the conclusion that these fish
(and perhaps marine animals in general) need the Ca of the sea water only to
counteract the injurious effects which a pure NaCl solu­tion has if it is present
in too high a concentra­tion. 261 When we raise the eggs in a pure NaCl solu­tion
of a concentra­tion ≦m/8 practically every egg will develop; and even in a m/4
or 3⁄8 m many or some eggs will form embryos without adding Ca; it may be
that a trace of Ca present in the membrane of the egg may suffice to counter-
balance the injurious action of a weak salt solu­tion.
The concentra­tion of the NaCl in the sea water at Woods Hole (where these
experi­ments were made) is about m/2, and as soon as this concentra­tion of
NaCl is reached the eggs are all killed as a rule before they can form an
embryo, unless a small but definite amount of Ca is added. It was found that
the eggs can be raised in much higher concentra­tions of NaCl, but in that case
more Ca must be added. The following table gives the minimal amount of
CaCl2 which must be added in order to allow fifty per cent. of the eggs to
form embryos. (The eggs were put into the solu­tion an hour or two after
fertiliza­tion.)
TABLE XVI

Cc. m/16
CaCl2
Concentration Required
of NaCl for 50 c.c.
NaCl
Solution
m.
3⁄ 8 0.1
4⁄ 8 0.3
5⁄ 8 0.5
6⁄ 8 0.6
7⁄ 8 0.9
8⁄ 8 1.2–1.4

9⁄ 8 1.8–2.0
10⁄ 8 2.0–2.5
11⁄ 8 2.0?
12⁄ 8 3.0–3.5
13⁄ 8 6.0

This indicates that the quantity of CaCl2 required to counteract the injurious
effects of a pure solu­tion of NaCl increases approximately in propor­tion to the
square of the concentra­tion of the NaCl solu­tion. 262 The reader will notice that
the eggs can survive and develop in a solu­tion of three times the concentra­tion
of sea water, provided enough Ca is added.
It was found also that not only Ca but a large number of other bivalent metals
were able to counteract the injurious action of an excessive NaCl solu­tion;
namely Mg, Sr, Ba, Mn, Co, Zn, Pb, and Fe; 263 only Hg and Cu could not be
used since they are themselves too toxic. The antagonistic efficiency of the
bivalent cations other than Ca was, however, smaller than that of Ca. The
following table gives the highest concentra­tion of NaCl solu­tion in which the
newly fertilized eggs of Fundulus can still form an embryo. 264

50 c.c. 10⁄8 m NaCl+4 c.c. m/1 MgCl2
50 c.c. 14⁄8 m NaCl+1 c.c. m/1 CaCl2
50 c.c. 11⁄8 m NaCl+1 c.c. m/1 SrCl2
50 c.c. 7⁄8 m NaCl+1 c.c. m/1 BaCl2
On the other hand it was seen that in all the chlorides with a univalent cation,
LiCl, KCl, RbCl, CsCl, NH4Cl, the eggs could form embryos up to a certain
concentra­tion of the salt; but that this concentra­tion could be raised by the
addi­tion of Ca.
TABLE XVII
Concentrations at which the Eggs no longer Are Able to
Form Embryos

In the Same Salts
In the Pure Salts with the Addition of 1 c.c. m CaCl2
to 50 c.c. Solution
LiCl about 6/ 32 m >5/ 8 m
NaCl m/ 2 >14/ 8 m
KCl >11/ 16 m >8/ 8 m
<6/ 8 m
RbCl >8/ 8 m >9/ 8 m
<7/ 8 m
CsCl >3/ 8 m >8/ 8 m
<4/ 8 m
In short it turned out that the injurious action of the pure solu­tion of any
chloride (or any other anion) with a univalent metal could be counteracted to a
considerable extent by the addi­tion of small quantities of a salt with a bivalent
metal. It was also found in the early experi­ments of the writer that the bivalent
or polyvalent anions had no such antagonistic effect upon the injurious action
of the salts with a univalent cation.
We therefore see that what at first sight appeared in the experi­ments of Herbst
a necessity, namely, the presence of each constituent of the sea water, turns out
as a special case of a more general law; the salts with univalent ions are
injurious if their concentra­tion exceeds a certain limit and this injurious action
is diminished by a trace of a salt with a bivalent cation.
Why was it not possible to prove this fact for the eggs of the sea urchin?
Before we answer this ques­tion, we wish to enter upon the discussion of the
nature of the injurious action of a pure NaCl solu­tion of a certain concentra­‐
tion and of the annihila­tion of this action by the addi­tion of a small quantity of
Ca. The writer suggested in 1905 that the injurious action of a pure NaCl solu­‐
tion consisted in rendering the membrane of the egg permeable for NaCl,
whereby the germ inside the membrane is killed; while the addi­tion of a small
amount of Ca (or any other bivalent metal) prevents the diffusion of Na into
the egg, 265 possibly, as T. B. Robertson 266 suggested, by forming a precipitate
with some constituent of the membrane, whereby the latter becomes more

impermeable. The correctness of this idea can be demonstrated in the
following way. When eggs of Fundulus, which are three or four days old and
contain an embryo, are put into a test-tube containing 3 m NaCl they will float
on this solu­tion for about three or four hours; after that they will sink to the
bottom. Before this happens the egg will shrink and when it ceases to float the
embryo is usually dead. This is intelligible on the assump­tion that the NaCl
solu­tion entered the egg, increased its specific gravity so that it could not float
any longer and killed the embryo. When we add, however, 1 c.c. 10⁄8 m CaCl2
to 50 c.c. 3 m NaCl the eggs will float, the heart will continue to beat
normally and the embryo will continue to develop for three days or more,
because the calcium prevents the NaCl from entering into the egg. 267 For if we
put a newly hatched embryo into 50 c.c. NaCl+1 c.c. 10⁄8 m CaCl2 it will die
almost instantly; hence the membrane must have acted for three or more days
as a shield which prevented the NaCl from diffusing into the egg in the
presence of CaCl2.
The same experiments cannot be demonstrated in the sea-urchin egg, first,
because it can live neither in distilled water nor in very dilute nor very
concentrated solu­tions; and second, because it is not separated as is the germ
of the Fundulus egg from the surrounding solu­tion by a membrane which is
under proper condi­tions practically impermeable for water and salts.
Nevertheless it can be shown that the results at which we arrived in our
experi­ments on Fundulus are of a general applica­tion. Osterhout 268 has shown
that plants which grow in the soil or in fresh water are readily killed by a pure
NaCl solu­tion of a certain concentra­tion, while they can resist the same
concentra­tion of NaCl if some CaCl2 is added. Wo. Ostwald 269 has shown the
same for a species of Daphnia. We, therefore, come to the conclusion that the
injurious action following an altera­tion in the constitu­tion of the sea water is
in some of the cases due to an increase in the permeability of the membranes
of the cell, whereby substances can diffuse into the cell which when the
proper balance prevails cannot diffuse. For this balance the ratio of the
concentra­tion of the salts with univalent cation Na and K over those with
CNa+K salts
bivalent cation Ca and Mg is of the greatest importance.
CCa+Mg salts

6. The importance of this quotient appears in the so-called “behaviour” of
marine animals. We have mentioned the newly hatched larvæ of the barnacle
in connec­tion with helio­tropism. These larvæ swim in a trough of normal sea
water at the surface, being either strongly positively or negatively helio­tropic.
They collect as a rule in two dense clusters, one at the window and one at the
room side of the dish. If such animals are put into a solu­tion of NaCl+KCl (in
the propor­tion in which these salts exist in the sea water), they will fall to the
bottom unable to rise to the surface. They will, however, rise to the surface
and swim energetically to or from the window if a certain quantity of any of
the chlorides of a bivalent metal, Mg, Ca, or Sr, is added, but these
movements will last only a few minutes when only one of these three salts is
added; and then the animals will fall to the bottom again. If, however, two
salts, e. g., MgCl2 and CaCl2, are added the animals will stay permanently at
the surface and react to light as they would have done in normal sea water.
These animals also can resist comparatively large changes in the concentra­tion
of the sea water, and it seemed of interest to find out whether the quotient
CNaCl+KCl
, which just allowed all the animals to swim at the surface, had a
CMgCl2+CaCl2
constant value. The MgCl2+CaCl2 solu­tion was 3⁄8 m and contained the two
metals in the propor­tion in which they exist in the sea water; namely, 11.8
molecules MgCl2 to 1.5 molecules CaCl2. The next table gives the result. 270
Since these experi­ments lasted a day or more each, usually two different
concentra­tions of NaCl+KCl of the ratio 1 : 2 or 1 : 4 were compared in one
experi­ment.
TABLE XVIII

Number Concentration C.c. Value of
of of 3/8 m CaCl2+MgCl2 CNa+K
Experiment NaCl+KCl Required CMg+Ca

m/16 0. 3 27.8
1 m/8 0.4–0.5 37.0
m/8 0. 5 33.3
2 m/4 0.9–1.0 35.1

3/16 m 0. 7 35.7
3 3/8 m 1. 3 38.5
m/8 0. 5 36.0
4 m/2 1.8–1.9 39.2
m/4 0.8–0.9 39.2
5 m/2 1.6–1.7 40.3
5/16 m 0. 9 46.3
6
5/8 m 1. 7 49.0
3/16 m 0. 6 41.7
7
6/8 m 2. 4 41.7
CNa+K
These experiments indicate that the ratio of remains very nearly
CCa+Mg
constant with varying concentra­tions of CNa+K.
In former experiments on jellyfish the writer had shown that there exists an
antagonism between Mg and Ca 271, and this observa­tion was subsequently
confirmed by Meltzer and Auer 272 for mammals. It was observed that in a
solu­tion of NaCl+KCl+MgCl2 the larvæ of the barnacle were also not able to
remain at the surface for more than a few minutes, while an addi­tion of some
CaCl2 made them swim permanently at the surface. Various quantities of
MgCl2 were added to a mixture of m/4 or m/2 NaCl+KCl, to find out how
much CaCl2, was required to allow them to swim permanently at the surface.
TABLE XIX

C.c. of m/16 CaCl2 Necessary
to Induce the Majority of
the Larvæ to Swim in
m/2 (Na+K) m/4 (Na+K)
50 c.c. NaCl+KCl+0.75 c.c. 3⁄8 m MgCl2 0.2
50 c.c. NaCl+KCl+ 1.5 c.c. 3⁄8 m MgCl2 0.4 0.3
50 c.c. NaCl+KCl+ 2.5 c.c. 3⁄8 m MgCl2 0.4 0.4
50 c.c. NaCl+KCl+ 5.0 c.c. 3⁄8 m MgCl2 0.7–0.8 0.7–0.8

50 c.c. NaCl+KCl+10.0 c.c. 3⁄8 m MgCl2 1.6 1.6
50 c.c. NaCl+KCl+15.0 c.c. 3⁄8 m MgCl2 1.8
50 c.c. NaCl+KCl+20.0 c.c. 3⁄8 m MgCl2 1.8

In order to interpret these figures correctly we must remember that we are
dealing with two different antagonisms, one between the salts with univalent
and bivalent metals and the other between Mg and Ca. The former antagonism
is satisfied by the addi­tion of Mg, inasmuch as enough Mg was present for
this purpose in all solu­tions. What was lacking was the balance between Mg
and Ca. The experi­ments in Table XIX therefore answer the ques­tion of the
ratio between Mg and Ca. If we consider only the concentra­tions of Mg
between 2.5 and 10.0 c.c. 3⁄8 m MgCl2—which are those closest to the normal
concentra­tion of Mg in the sea water—we notice that CCa must vary in
propor­tion to CMg. If we now combine the results of this and the previous
paragraph we may express them in the form of the theory of physio­logically
balanced salt solu­tions, by which we mean that in the ocean (and in the blood
or lymph) the salts exist in such ratio that they mutually antagonize the
injurious action which one or several of them would have if they were alone in
solu­tion. 273 This law of physio­logically balanced solu­tions seems to be the
general expression of the effect of changes in the constitu­tion of the salt solu­‐
tions for marine or all aquatic organisms.
This chapter would not be complete without an intima­tion of the rôle of
buffers in the sea water and the blood, by which the reac­tion of these media is
prevented from changing in a way injurious to the organism. These buffers are
the carbonates and phosphates. Instead of saying that the organisms are
adapted to the medium, L. Henderson has pointed out the fitness of the
environ­ment for the development of organisms and one of these elements of
fitness are the buffers against altera­tions of the hydrogen ion concentra­tion. 274
The ratio in which the salts of the different metals exist in the sea water is
another. It is obvious that the quantitative laws prevailing in the effect of
environ­ment upon organisms leave no more room for the interference of a
“directing force” of the vitalist than do the laws of the motion of the solar
system.

CHAPTER XII
ADAPTATION TO ENVIRONMENT

1. It is assumed by certain biologists that the environ­ment influences the
organism in such a way as to increase its adapta­tion. Were this correct it
would not contradict a purely physico­chemical concep­tion of life; it would
only call for an explana­tion of the mechanism by which the adapta­tion is
brought about. There are striking cases on record which warn us against the
universal correctness of the view that the environ­ment causes an adaptive
modifica­tion of the organism. Thus the writer pointed out in 1889 that
positive helio­tropism occurs in organisms which have no opportunity to
make use of it, 275 e. g., Cuma rathkii, a crustacean living in the mud, and the
caterpillars of the willow borer living under the bark of the trees. We
understand today why this should be so, since helio­tropism depends upon
the presence of photo­sensitive substances, and it can readily be seen that the
ques­tion of use or disuse has nothing to do with the produc­tion of certain
harmless chemical compounds in the body. A much more striking example
is offered in the case of galvano­tropism. Many organisms show the
phenomenon of galvano­tropism, yet, as the writer pointed out years ago,
galvano­tropism is purely a laboratory product and no animal has ever had a
chance or will ever have a chance to be exposed to a constant current except
in the laboratory of a scientist. This fact is as much of a puzzle to the selec­‐
tionist and to the Lamarckian (who would be at a loss to explain how
outside condi­tions could have developed this tropism) as to the vitalist who
would have to admit that the genes and supergenes indulge occasionally in
queer freaks and lapses. The only consistent attitude is that of the physicist
who assumes that the reac­tions and structures of animals are consequences
of the chemical and physical forces, which no more serve a purpose than
those forces responsible for the solar systems. From this viewpoint it is

comprehensible why utterly useless tropisms or structures should occur in
organisms.
2. A famous case for the apparent adapta­tion of animals to environ­ment has
been the blind cave animals. It is known that in caves blind salamanders,
blind fishes, and blind insects are common, while such forms are
comparatively rare in the open. This fact has suggested the idea that the
darkness of the cave was the cause of the degenera­tion of the eyes. A closer
investiga­tion leads, however, to a different explana­tion. Eigenmann has
shown that of the species of salamanders living habitually in North
American caves, two have apparently quite normal eyes. They are Spelerpes
maculicauda and Spelerpes stejnegeri. Two others living in caves have
quite degenerate eyes, Typhlotriton spelæus and Typhlomolge rathbuni. If
disuse is the direct cause of blindness we must inquire why Spelerpes is not
blind.
Another difficulty arises from the fact that a blind fish Typhlogobius is
found in the open (on the coast of southern California) in shallow water,
where it lives under rocks in holes occupied by shrimps. The ques­tion must
again be raised: How can it happen that in spite of exposure to light
Typhlogobius is blind?
The most important fact is perhaps the one found by Eigenmann in the
fishes of the family of Amblyopsidæ. Six species of this group live
permanently in caves, are not found in the open, and have abnormal eyes,
while one lives permanently in the open, is never found in caves, and one
comes from subterranean springs. The one form which is found only in the
open, Chologaster cornutus, has a simplified retina as well as a
comparatively small eye, in other words, its eye is not normal. This
indicates the possibility that the other representatives which are found only
in caves also might have abnormal eyes even if they had never lived in
caves.
Through these facts the old idea becomes ques­tionable, namely, that the
cave animals had originally been animals with normal eyes which owing to

disuse had undergone a gradual hereditary degenera­tion.
Recent experi­ments made on the embryos of the fish Fundulus have yielded
the result that it is possible to produce blindness in fish by various means
other than lack of light. 276 Thus the writer found that by crossing the egg of
Fundulus with the sperm of a widely different species, namely, Menidia,
blind embryos were produced very frequently; that is to say such embryos
had the degenerate eyes characteristic of blind cave fishes. Very often no
other external trace of an eye, except a gathering of pigment, could be
found, while a close histological examina­tion would possibly have resulted
in the demonstra­tion of rudiments of a lens and other tissues of the eye.
Another method of producing blind fish embryos consists in exposing the
egg immediately, or soon after fertiliza­tion, to a temperature between 0° and
2° C. for a number of hours. Many embryos are killed by this treatment, but
those which survive behave very much like the hybrids between Fundulus
and Menidia, i. e., a number of them have quite degenerated eyes. If the
eggs have once formed an embryo they can be kept at the temperature of 0°
for a month or more without giving rise to blind animals. Occasionally such
rudimentary eyes were also observed when eggs were kept in a solu­tion
containing a trace of KCN. Stockard has succeeded in producing cyclopean
eyes in Fundulus by adding an excess of magnesium salt to the sea water in
which the eggs developed or by adding alcohol, and McClendon has
confirmed and added to these results.
The writer tried repeatedly, but in vain, to produce Fundulus with deficient
eyes by keeping the embryos in the dark. Sperm and egg were not allowed
to be exposed to the light yet the embryos without excep­tion had normal
eyes.
F. Payne raised sixty-nine successive genera­tions of a fly Drosophila in the
dark, but the eyes and the reac­tion of the insects to light remained perfectly
normal.
Uhlenhuth has recently demonstrated in a very striking way that the
development of the eyes does not depend upon the influence of light or

upon the eyes func­tioning. He transplanted the eyes of young salamanders
into different parts of their bodies where they were no longer connected
with the optic nerves. The eyes after transplanta­tion underwent a degenera­‐
tion which was followed by a complete regenera­tion. He showed that this
regenera­tion took place in complete darkness and that the transplanted eyes
remained normal in salamanders kept in the dark for fifteen months. Hence
the eyes which were no longer in connec­tion with the central nervous
system, which had received no light, and could not have func­tioned,
regenerated and remained normal. The degenera­tion which took place in the
eyes immediately after being transplanted was apparently due to the
interrup­tion of the circula­tion in the eye, and the regenera­tion commenced
in all probability with the re-establishment of the circula­tion in the
transplanted organ.
In our own experi­ments it can be shown that the circula­tion in the embryo
was deficient in all cases where the eyes degenerated. The hybrids between
Fundulus and Menidia have often a beating heart but rarely a circula­tion
(although they form blood); and the same phenomenon occurred in the
embryos which were exposed to a low temperature at an early period of
their lives. Hence all the facts agree that condi­tions which lead to an
abnormal circula­tion (and consequently also to an abnormal or inadequate
nutri­tion of the embryonic eye) may prevent development and lead to the
forma­tion of blind fishes. Eigenmann states that no blood-vessels enter the
eye of the blind cave salamander Typhlotriton. The presence or absence of
light does not usually interfere with the circula­tion or nutri­tion of the
embryonic eye, and hence does not as a rule lead to the forma­tion of
degenerated eyes.
This would lead us to the assump­tion that the blind fish owe their
deficiency not to lack of light but to a condi­tion which interferes with the
circula­tion in the embryonic eye. Such a condi­tion might be brought about
by an anomaly in the germ plasm or in one chromo­some, the nature and
cause of which we are not able to determine at present; but which, since it
occurs in the germ plasm or the chromo­somes, must be hereditary. This

would explain why it is, that animals with perfect eyes may occur in caves
and why perfectly blind animals may occur in the open. It leaves, however,
one point unexplained; namely, the greater frequency of blind species in
caves or in the dark and the relative scarcity of such forms in the open.
Eigenmann has shown that all those forms which live in caves were adapted
to life in the dark before they entered the cave. 277 These animals are all
negatively helio­tropic and positively stereotropic, and with these tropisms
they would be forced to enter a cave whenever they are put at the entrance.
Even those among the Amblyopsidæ which live in the open have the
tropisms of the cave dweller. This eliminates the idea that the cave adapted
the animals for the life in the dark.
Only those animals can thrive in caves which for their feeding and mating
do not depend upon visual mechanisms; and conversely, animals which are
not provided with visual mechanisms can hold their own in the open, where
they meet the competi­tion of animals which can see, only under excep­tional
condi­tions. This seems to account for the fact that in caves blind species are
comparatively more prevalent than in the open.
In other words, the adapta­tion of blind animals to the cave is only apparent;
they were adapted to cave life before they entered the cave. Many animals
are obviously burdened with a germinal abnormality giving rise to
imperfec­tion and smallness of the eye—the hereditary factor involved may
have to do with the development of the blood-vessels and lymphatics of the
eye. Such mutants can survive more easily in the cave, where they do not
have to meet the competi­tion of seeing forms, than in the open. In man also
an hereditary form of blindness is known, the so-called hereditary
glaucoma. It has nothing to do with light, but the disease seems to be due to
an hereditary anomaly of the circula­tion in the eye.
Kammerer 278 has recently reported that by keeping the blind European cave
salamander Proteus anguinus under certain condi­tions of illumina­tion he
succeeded in producing two specimens with larger eyes. According to him
the eyes of Proteus may develop to a certain point and then retrogress

again. He states that by keeping young salamanders alternately for a week
or two in sunlight and in a dark room where they were exposed to red
incandescent light, two males formed somewhat larger eyes. The first year
no altera­tion was visible. In the second year a slight increase in the size of
the eyes was noticeable under the skin. In the third year the eye protruded
slightly and this increased somewhat in the fourth year.
There is thus far only one case on record in animal biology in which the
light influences the forma­tion of organs. The writer found that the regenera­‐
tion of the polyps of the hydroid Eudendrium does not take place if the
animals are kept in the dark, while the polyps will regenerate if exposed to
the light; 279 and the time of exposure may be rather short according to
Goldfarb. 280 It is possible that Proteus resembles in this respect
Eudendrium; it should be stated, however, that of many different forms tried
by the writer over a number of years, Eudendrium was the only one which
gave evidence of such an influence of light. Of course it is not impossible
that the light might influence reflexly the development of blood-vessels in
the eyes of certain animals, e. g., Proteus, and thus allow the eyes of
Proteus to grow a little larger.
We therefore come to the conclusion that it is not the cave that made
animals blind but that animals with a hereditary tendency towards a
degenera­tion of the eyes can survive in a cave while they can only excep­‐
tionally survive in the open. The cause of the degenera­tion is a disturbance
in the circula­tion and nutri­tion of the eye, which is as a rule independent of
the presence or absence of light.
We may by way of a digression stop for a moment to consider the most
astonishing and uncanny case of adapta­tion; namely, the forma­tion of the
transparent refractive media, especially the lens in front of the retina. It is
due to these media that the rays which are sent out by a luminous point can
be united to an image point on the retina. One part of this process is
understood; namely, the forma­tion of a lens. Wherever the optic cup of the
embryo is transplanted under the epithelium the latter will be trans­formed

into a transparent lens. When the upper edge of the iris is injured in the
salamander so that the cells can multiply, the mass of newly formed cells
also becomes transparent and a lens is formed. This indicates the existence
of a substance in the optic cup which makes the epithelial cells transparent;
and which also limits the size of the lens which is formed. The lens is not
always a perfect optical instrument, on the contrary, it is as a rule somewhat
defective. Of course, a great many details concerning the process of lens
regenera­tion have still to be worked out.
3. It is well known that most marine animals die if put into fresh water and
vice versa; and in salt lakes or ponds with a concentra­tion of salt so high
that most marine animals would succumb if suddenly transferred to such a
solu­tion we have a limited fauna and flora. The common idea is that marine
animals become adapted to fresh water or vice versa; or to the condi­tions in
salt lakes; especially if the changes take place gradually. Yet it can be
shown that the existence of these different faunas can be explained without
the assump­tion of an adaptive effect of the environ­ment. The writer has
worked with a marine fish Fundulus whose eggs develop naturally in sea
water which, however, will develop just as well in distilled water; and the
young fish hatching in distilled water live and grow in this medium. Most
of the adult fish die after several days, when put suddenly into distilled
water, but they can live in fresh water which contains only a trace of salt.
They can also live in very concentrated sea water, e. g., twice the normal
concentra­tion. Suppose that a bay of the ocean containing such fish should
suddenly become landlocked and the concentra­tion of the sea water be thus
raised to twice its natural amount; the majority of forms would die and only
Fundulus and possibly a few other species with the same degree of
resistance would survive. An investigator examining the salinity of the
water and not knowing the natural resistance of Fundulus to changes in
concentra­tion would be inclined to assume that he had before him an
instance of a gradual adapta­tion of the fish to a higher concentra­tion of the
sea water; whereas the fish was already immune to this high concentra­tion
before coming in contact with it.

This fish seemed a favourable object from which to find out how far an
adapta­tion to the environ­ment really existed; and the result was surprising.
By changing the concentra­tion of the sea water gradually it is possible to
raise the natural resistance of the fish only a trifle, not much over ten per
cent. The concentra­tion of the natural sea water is a little over that of a m/2
solu­tion of NaCl+KCl+CaCl2 in the propor­tion in which these three salts
exist in the sea water. When adult Fundulus are put into a 10⁄8 m solu­tion of
NaCl+KCl+CaCl2 in the propor­tion in which these salts occur in sea water
they die in less than a day, but when put from sea water directly into a 8⁄8 m
or 9⁄8 m solu­tion they can live indefinitely. It was found 281 that if the
concentra­tion of the sea water was raised gradually (by m/8 a day) the fish
on the fifth day could resist a 10⁄8 m solu­tion of NaCl+KCl+CaCl2 for a
month (or possibly indefinitely; the experi­ment was discontinued after that
period). When a 10⁄8 m solu­tion was allowed to become more concentrated
slowly by evapora­tion (at room temperature) all the fish died rapidly when
the concentra­tion was 12⁄8 m or even below. In higher concentra­tions they
can live only a day or two. These experi­ments show that while the fish is
naturally immune to a 9⁄8 m NaCl+KCl+CaCl2 solu­tion, by the method of
slowly raising the concentra­tion it may be made to tolerate a 10⁄8 m or 11⁄8 m
solu­tion, but not more. These fish when once adapted to a 10⁄8 m solu­tion
can be put suddenly into a very weak solu­tion, e. g., a m/80 NaCl, without
suffering and when brought back into a 10⁄8 m solu­tion of NaCl+KCl+CaCl2
they will continue to live. If they remain for several days in the weak solu­‐
tion their power of resistance to 10⁄8 m NaCl+KCl+CaCl2 solu­tion is
weakened.
What change takes place when the fish is made more resistant and why is
its normal resistance so great? The answer based on the writer’s experi­‐
ments seems to be as follows: Fundulus is comparatively resistant to sudden
changes in the concentra­tion of the sea water between m/80 and 9⁄8 m
because it possesses a comparatively impermeable skin whose permeability
is not seriously altered by sudden changes within these limits of concentra­‐
tion; while if these limits are exceeded and the fish are brought suddenly

into too high a concentra­tion the skin becomes permeable and the fish dies,
the gills becoming unfit for use or nerves being injured by the salt which
diffuses into the fish.
The fact, that by slowly raising the concentra­tion to 10⁄8 m the fish may
resist this limit, is in reality no adapta­tion. There is no sharp limit between
the injurious and non-injurious concentra­tion. We have seen that the fish is
naturally immune to a 9⁄8 m solu­tion. It is also naturally immune to a 10⁄8 m
or 11⁄8 m solu­tion if we give it time to compensate the injurious effects of a
10⁄8 m solu­tion by the repairing action of its blood or kidneys. Beyond this
no rise is possible. In reality adapta­tion does not exist in this case.
In former experiments the writer had shown that a pure NaCl solu­tion of
that concentra­tion in which this fish naturally lives kills it very rapidly,
while it lives in such a solu­tion indefinitely if a little CaCl2 is added. The
explana­tion of this fact is that the pure NaCl solu­tion is able to diffuse into
the tissues of the animal while the addi­tion of a trace of CaCl2 renders the
membrane practically impermeable to NaCl. The ques­tion then arose
whether it was possible to make the fish more resistant to a pure NaCl solu­‐
tion of sufficiently high concentra­tion and how this could be done. On the
basis of the idea of an adaptive effect of the environ­ment we should expect
that by gradually raising the concentra­tion of a pure NaCl solu­tion the latter
would gradually alter the animal and make it more resistant. The method of
procedure suggested was therefore to put the fish first in low and gradually
into increasing concentra­tions of NaCl. This method was tried and found
futile for the purpose. Fundulus when put from sea water (after having been
washed) into a 6⁄8 m NaCl solu­tion die in about four hours. When kept
previously in a weaker NaCl solu­tion they die if anything more quickly. But
it is possible to make them live longer in a 6⁄8 m solu­tion of NaCl; we have
to proceed, however, by a method which is in contrast with the ideas of the
adaptive influence of the environ­ment. When the fish are first treated with
sea water (or with a mixture of NaCl+KCl+CaCl2) of a higher concentra­tion
so that they become adapted to a 10⁄8 m solu­tion of NaCl+KCl+CaCl2 or to
10⁄8 m sea water, they become also more resistant to an otherwise toxic solu­‐

tion of NaCl. Fish taken directly from sea water were killed in less than four
hours when put into a 6⁄8 m NaCl solu­tion, while fish of the same lot
previously adapted to 10⁄8 m sea water in the manner described above lived
two or three days in a 6⁄8 m NaCl solu­tion. 282
It is not impossible that it was the high concentra­tion of calcium in the
10⁄8 m sea water which rendered the fish more immune to a subsequent
treatment with NaCl. We know why a pure NaCl solu­tion kills them and we
also know why the addi­tion of CaCl2 protects them against this pernicious
effect. It is rather strange that where the condi­tions of the experi­ments are
clear we find nothing to indicate an adaptive effect of the environ­ment.
4. Ehrlich’s work on trypanosomes seems to indicate a remarkable power of
adapta­tion on the part of organisms to certain poisons. If the writer
understands these experi­ments correctly they consisted in infecting a mouse
with a certain strain of trypanosomes, and treating it with a certain arsenic
compound, which inhibited somewhat the propaga­tion of the parasites but
did not kill them all. Four or five days later trypanosomes from this mouse
were transmitted to another mouse and after twenty-four hours this mouse
was treated with a stronger dose of the same arsenic compound; and this
process was repeated. After the third transmission or later, the trypanosomes
can resist considerably higher doses of the same poison than at first and this
resistance is retained for years. Ehrlich seems to have taken it for granted
that he had succeeded in trans­forming the surviving trypanosomes into a
type which is permanently more resistant to the arsenic compound than was
the original strain.
The writer is not entirely convinced that in these experi­ments a possibility
was sufficiently considered which is suggested by Johannsen’s experi­ments
on the importance of pure lines in work on heredity. According to this
author a strain of trypanosomes taken at random should, in all likelihood,
contain a popula­tion consisting of strains with different degrees of
resistance. If a high but not the maximal concentra­tion of an arsenic
compound is repeatedly injected into the infected mice the weaker popula­‐

tions of trypanosomes are killed and only the more resistant survive. These
of course continue to retain their resistance if transplanted to hosts of the
same species. According to this interpreta­tion the arsenic-fast strain may
possibly have existed before the experi­ments were made, and Ehrlich’s
treatment consisted only in eliminating the less resistant strains.
On the other hand, it has been shown that if an arsenic-fast strain of
trypanosomes is carried through a tsetse fly it loses its arsenic-fastness. This
fact may possibly eliminate the applicability of the pure line theory to a
discussion of the nature of the arsenic-fastness, but it seems that further
experi­ments are desirable.
5. Dallinger stated that he succeeded in adapting certain protozoans to a
temperature of 70° C. by gradually raising their temperature during several
years. It is desirable that this statement be verified; until this is done doubts
are justified. Schottelius found that colonies of Micrococcus prodigiosus
when transferred from a temperature of 22° to that of 38° no longer formed
pigment and trimethylamine. After the cocci had been cultivated for ten or
fifteen genera­tions at 38° they failed to form pigment even when transferred
back to 22° C. Dieudonné 283 used Bacillus fluorescens for similar purposes.
At 22° it forms a fluorescing pigment and trimethylamine, but not at 35°.
By constantly cultivating this bacillus at 35° Dieudonné found that after the
fifteenth genera­tion had been cultivated at 35° the bacillus produced
pigment and trimethylamine at 35°. Davenport and Castle 284 found that
tadpoles of a frog kept at 15° went into heat rigour at 40.3° C., while those
kept for twenty-eight days at 25° were not affected by this temperature but
went into heat rigour at 43.5°. When the latter tadpoles were put back for
seventeen days to a temperature of 15° they had lost their resistance to high
temperature partially, but not completely, since they went into heat rigour at
41.6°. The authors suggest that this adapta­tion to a higher temperature is
due to a loss of water on the part of protoplasm, whereby the latter becomes
more resistant to an increase in temperature. This idea was put to a test by

Kryž 285, who found that the coagula­tion temperature of their muscle plasm
is not altered by keeping cold-blooded animals at different temperatures.
Loeb and Wasteneys 286 found that Fundulus taken from a low temperature
of 10° C. die in less than two hours when suddenly transferred to sea water
of 29° C.; and in a few minutes if suddenly transferred to a temperature of
35° C. If, however, the fish were transferred to a temperature of 27° C. for
forty hours they could live indefinitely in sea water of 35°. By exposing the
fish each day two hours to a gradually rising temperature they could render
them resistant to a temperature of 39°. The remarkable fact was that fish if
once made resistant to a high temperature (35°) did not lose this resistance
when kept for four weeks at from 10° to 14° C. Control fish taken from the
same temperature died in from two to four minutes; immunized fish taken
from 10° and put directly to 35° C. lived for many hours or indefinitely.
They will even retain this immunity when kept for two weeks at a
temperature of 0.4° C.
Why is it that an animal can in general resist a high temperature better if the
latter is raised gradually than when it is raised suddenly? Physics offers us
an analogy to this phenomenon in the experience that glass vessels which
burst easily when their temperature is raised suddenly, remain intact when
the temperature is raised gradually. Glass is a poor conductor of heat and
when the temperature is raised suddenly inside a glass cylinder the inner
layer of the cylinder expands while the outer layer on account of the
slowness of conduc­tion of heat does not expand equally and the cylinder
may burst. We might assume that the sudden increase in temperature brings
about certain changes in the cells (e. g., an increase in permeability or
destruc­tion of the surface layer?). If the rise of temperature occurs gradually
the blood or lymph or the cell sap may have time to repair the damage, and
this repair seems to be irreversible, at least for some time, as the experi­‐
ments on Fundulus seem to indicate. If the temperature rises too rapidly the
damage cannot be repaired quickly enough by the cell or body liquids.

It is also to be considered that substances might be formed in the body at a
higher temperature which do not exist at a lower temperature, and vice
versa, and this might explain results like those of Schottelius or Dieudonné
and many others.
6. The theory of an adapting effect of the environ­ment has often been linked
with the assump­tion of the inheritance of acquired characters. The older
claims of the hereditary transmission of acquired characters, such as
Brown-Séquard’s epilepsy in guinea pigs after the cutting of the sciatic
nerve, have been shown to be unjustified or have found a different and more
rational explana­tion. Recently P. Kammerer has claimed to have proven by
new experi­ments that by environ­mental changes, hereditary changes can be
produced.
It has been mentioned already that the mature male frogs and toads possess
during the breeding season lumps on the thumbs or arms which are
pigmented and which bear numerous minute horny black spines; these
secondary sexual characters serve the male frog in holding the females in
the water during copula­tion. There is one species which does not possess
this sexual character, namely the male of the so-called midwife toad (Alytes
obstetricans). In this species the animals copulate on land, and it is natural
to connect the lack of this secondary sexual character in the male with its
different breeding habit. Kammerer now forced such toads to copulate in
water instead of on land (by keeping the animals in a terrarium with a high
temperature). He makes the statement that by forcing the parents to lay their
eggs during successive spawning periods in water he finally obtained
offspring which under normal temperature condi­tions lay their eggs
naturally in water; in other words, they have changed their habits. We will
not discuss this part of his statement since the breeding habits of animals in
captivity are liable to be abnormal. But Kammerer makes the further
important statement 287 that the male offspring of such couples will in the
third genera­tion produce the swelling on the thumb and the usual
roughness, and in the fourth genera­tion black pads and hypertrophy of the
muscles of the forearm will appear. In other words, he reports having

succeeded in producing an inheritance of an acquired morpho­logical
character which has never been known to occur in this species. Bateson, on
account of the importance of the case, wished to examine it more closely
and I will quote his report.
The systematists who have made a special study of Batrachia
appear to be agreed that Alytes in nature does not have these
structures; and when individuals possessing them can be produced
for inspec­tion it will, I think, be time to examine the evidence for
the inheritance of acquired characters more seriously. I wrote to Dr.
Kammerer in July, 1910, asking him for the loan of such a specimen
and on visiting the Biologische Versuchsanstalt in September of the
same year I made the same request, but hitherto none has been
produced. In matters of this kind much generally depends on
interpreta­tions made at the time of observa­tion; here, however, is an
example which could readily be attested by preserved material. 288
More recently the same author has reported another hereditary morpho­‐
logical change brought about by outside condi­tions. 289 A certain salamander
(Salamandra maculosa) has yellow spots on a generally dark skin.
Kammerer states that if such salamanders are kept on a yellow ground they
become more yellow, not by an extension of the chromatophores (which
would not be surprising) but by actual multiplica­tion and growth of the
yellow pigment cells; while the black skin is inhibited in its growth. The
reverse is true if these salamanders are kept on black soil; in this case
according to Kammerer the growth of the yellow cells of the skin is
inhibited while the black part of the skin grows. Curiously enough,
according to him, these induced changes are hereditary. Here again we are
dealing with the inheritance of an acquired morpho­logical character.
Megusar 290 has repeated Kammerer’s experi­ments on salamanders but
contradicts him by stating that the colour of the soil has no influence on the
coloura­tion of salamanders. Of course, we know the phenomenon of colour
adapta­tion in which the animal changes its colour pattern according to the

environ­ment. This is an effect of the retina image on the skin and has been
interpreted by the writer as a case of colour telephotography, for which no
physical explana­tion has yet been found. 291 This phenomenon, however,
does not lead to any hereditary change of colour.
Kammerer makes many statements on the heredity of acquired modifica­‐
tions of instinct; indeed he claims that an interest in music on the part of
parents produces offspring with musical talent. In such claims much
depends upon the subjective interpreta­tion of the observer.
The writer is not aware that there is at present on record a single adequate
proof of the heredity of an acquired character. We have records of changes
in the offspring by poisoning the germ plasm by alcohol given to parents—
as in Stockard’s well-known experi­ments—or by exposing butterflies to
extreme temperatures, but in these cases the germ cells were poisoned or
altered by the alcohol or by chemical compounds produced at very low or
very high temperatures. This is of course an entirely different thing from
stating that by inducing the midwife toad to lay its eggs in the water the
male offspring acquires the pads and horns of other species of frogs on its
thumb; or that by keeping black salamanders on yellow paper the offspring
is more yellow. Yet if there is an inheritance of acquired characters which
can in any way throw light on the so-called phenomena of adapta­tion it
must consist in results such as Kammerer claims to have obtained.
While the writer does not decline to accept Ehrlich’s interpreta­tion of the
arsenic-fast strains of trypanosomes or Kammerer’s statements in regard to
the inheritance of acquired character, he feels that more work should be
done before they can be used for our problem.
7. This attitude leaves us in a quandary. The whole animated world is
seemingly a symphony of adapta­tion. We have mentioned already the eye
with its refractive media so well curved and placed that a more or less
perfect image of the outside objects is focussed exactly on the retina; and
this in spite of the fact that lens and retina develop independently; we have
mentioned and discussed the cases of instincts or automatic arrangements

which are required to perpetuate life—the attrac­tion of the two sexes and
the automatic mechanisms by which sperm and egg are brought together;
the maternal instincts by which the young are taken care of; and all those
adapta­tions by which animals get their food and the suitable condi­tions of
preserva­tion. Can we understand all these adapta­tions, without a belief in
the heredity of acquired characters? As a matter of fact the tenacity with
which some authors cling to such a belief is dictated by the idea that this is
the only alternative to the supra-naturalistic or vitalistic ideas. The writer is
of the opinion that we do not need to depend upon the assump­tion of the
heredity of acquired characters, but that physio­logical chemistry is adequate
for this purpose.
The earlier writers explained the growth of the legs in the tadpole of the
frog or toad as a case of an adapta­tion to life on land. We know through
Gudernatsch that the growth of the legs can be produced at any time even in
the youngest tadpole, which is unable to live on the land, by feeding the
animal with the thyroid gland. As we have stated in Chapter VII, it is quite
possible that in nature the legs of the tadpole begin to grow when enough of
the thyroid or a similar compound has been formed or is circulating in the
animal.
It might justly be claimed as a case of adapta­tion that the egg attaches itself
to the wall of the uterus and calls forth the forma­tion of the decidua. We
have mentioned the observa­tion of Leo Loeb that the corpus luteum of the
ovary gives off a substance to the blood which alters the tissues in the
uterus in such a way that contact with any foreign body (e. g., the egg)
induces this decidua forma­tion. Again what appeared as adapta­tion when
unknown turns out to be a result of the action of a definite chemical
substance circulating in the body.
It appears as a case of adaptation that the eggs of the majority of animals
cannot develop without a spermato­zoön, and yet we can imitate the
activating effect of a spermato­zoön on the egg by definite chemical
compounds, which leads to the sugges­tion that the activating effect of the

spermato­zoön on the egg might be due to the fact that it carries such a
compound.
The wonderful adaptations exhibited in the mating instincts seem to be due
to definite substances secreted by the sex glands, as was shown by Steinach
(Chapter VII). Here, again, the process as popularly conceived, is the
reverse of the truth; those survive that have the equipment,—they did not
acquire the equipment under the influence of environ­ment.
It is absolutely imperative for green plants that their stems and leaves be
exposed to the light since only in this way are they able to form
carbohydrates; and it is equally essential that the roots should grow into the
soil so that the plant may get the nitrates and phosphates required to build
up its proteins and nucleins. This result is, in the language of adapta­tionists,
brought about by an adaptive response of the plant to the light. In reality
this adaptive response is due (Chapter X) to the presence of a photo­‐
sensitive substance present in almost all green plants.
Lewis has shown that if the optic cup is transplanted under the skin of a
young larva into any part of the body the skin in contact with the optic cup
will form a lens; it looks as if a chemical substance from the optic cup were
responsible for the forma­tion of the lens.
These examples might be multiplied indefinitely. They all indicate that
apparent morpho­logical and instinctive adapta­tions are merely caused by
chemical substances formed in the organism and that there is no reason for
postulating the inheritance of acquired characters. We must not forget that
there are just as many cases where chemical substances circulating in the
body lead to indifferent or harmful results. As an example of the first type,
we may mention the existence of helio­tropism in animals living in the dark,
of the latter type, the inheritance of deficiencies like colour-blindness or
glaucoma.
While it is possible for forms with moderate disharmonies to survive, those
with gross disharmonies cannot exist and we are not reminded of their

possible existence. As a consequence the cases of apparent adapta­tion
prevail in nature.
The following observa­tion may serve to give an idea how small is the
number of existing or durable forms compared with the number of forms
incapable of existence. We have mentioned the fact observed by
Moenkhouse, the writer, and Newman, that it is possible to fertilize the eggs
of each marine bony fish with the sperm of practically every other marine
bony fish. The number of teleosts at present in existence is about ten
thousand. If we accomplish all possible hybridiza­tions, one hundred million
different crosses will result. Of these only a small fraction of one per cent.
can live (see Chapter I), and it is generally the lack of a proper circula­tion
which inhibits them from reaching maturity. It is, therefore, no exaggera­tion
to state that the number of species existing today is only an extremely small
fraction of those which can and possibly do originate, but which escape our
notice and disappear because they cannot live or reproduce. If we consider
these facts we realize that the mere laws of chance are adequate to account
for the fact of the apparently purposeful adapta­tions; as they are adequate to
account for the Mendelian numbers.

CHAPTER XIII
EVOLUTION

Darwin’s work has been compared to that of Copernicus and Galileo
inasmuch as all these men freed the mind from the incubus of Aristotelian
philosophy which, with the efficient co-opera­tion of the church and the
predatory system of economics, caused the stagna­tion, squalor, immorality,
and misery of the Middle Ages. Copernicus and Galileo were the first to
deliver the intellect from the idea of a universe created for the purpose of
man; and Darwin rendered a similar service by his insistence that accidental
and not purposeful varia­tions gave rise to the variety of organisms. In this
struggle for intellectual freedom the names of Huxley and Haeckel must be
gratefully remembered, since without them Darwin’s idea would not have
conquered humanity.
Darwin assumed that the small fluctuating varia­tions could accumulate to
larger varia­tions and thus cause new forms to originate.
It was the merit of de Vries 292 to have pointed out that fluctuating varia­tions
are not hereditary and hence could not have played the rôle assigned to
them by Darwin, while discontinuous varia­tions as they appear in the so-
called “sports” or muta­tions are inherited. This was an important step in the
history of the theory of evolu­tion. It did not touch the founda­tion of
Darwin’s work, namely the substitu­tion of the idea of an accidental evolu­‐
tion for that of a purposeful crea­tion; it only modified the concep­tion of the
possible mechanism of evolu­tion. According to de Vries, there are special
species or groups of species which are in a state of muta­tion. He considers
the evening primrose on which he made his observa­tions as one of these
forms. Morgan and his pupils have observed over 130 muta­tions in a fly
Drosophila. From our present limited knowledge we must admit the
possibility that the tendency toward the produc­tion of mutants is not equally

strong in different forms. Whether this part of de Vries’s idea is or is not
correct there can be no doubt that varia­tions occur which consist in the loss
and apparently, though in rarer cases, in the gain or a modifica­tion of a
Mendelian factor. If we wish to visualize the basis of such a change we may
do so by imagining well-defined chemical constituents in one or more of
the chromomeres undergoing a chemical change.
This way of looking at the origin of varia­tion has had the effect of putting
an end to the vague specula­tions concerning the evolu­tion of one form from
another. We demand today the experi­mental test when such a statement is
made and as a consequence the amount of mere specula­tion in this field has
diminished considerably.
It is possible that any further progress concerning evolu­tion must come by
experi­mental attempts to bring about at will definite muta­tions. Such
attempts have been reported but they are not all beyond the possibility of
error. 293 The most remarkable among them are those by Tower who by a
very complicated combina­tion of effects of temperature and moisture
claims to have produced definite muta­tions in the potato beetle. The condi­‐
tions for these experi­ments are so expensive and complicated that a repeti­‐
tion by other investigators has not yet been possible.
It is, however, still uncertain whether the mere addi­tion or loss of
Mendelian characters can lead to the origin of new species. Species
specificity is determined by specific proteins (Chapter III.), while some
Mendelian characters at least seem to be determined by hormones or
substances which need neither be proteins nor specific for the species.

CHAPTER XIV
DEATH AND DISSOLUTION OF THE ORGANISM

1. It is an old saying that we cannot understand life unless we understand
death. The dead body, if its temperature is not too low and if it contains
enough water, undergoes rapid disintegra­tion. It was natural to argue that
life is that which resists this tendency to disintegra­tion. The older observers
thought that the forces of nature determined the decay, while the vital force
resisted it. This idea found its tersest expression in the defini­tion of Bichat,
that “life is the sum total of the forces which resist death.” Science is not
the field of defini­tions, but of predic­tion and control. The problem is: first,
how does it happen that as soon as respira­tion has ceased only for a few
minutes the human body is dead, that is to say, will commence to undergo
disintegra­tion, and second, what protects the body against this decay while
the respira­tion goes on, although temperature and moisture are such as to
favour decay?
The earlier biologists had already raised the question why it was that the
stomach and intestine did not digest themselves. The hydrochloric acid and
the pepsin in the stomach and the trypsin in the intestine digest proteins
taken in in the form of food; why do they not digest the proteins of the cells
of the stomach and the intestine? They will promptly digest the stomach as
soon as the individual is dead, but not during life. A self-diges­tion may also
be caused if the arteries of the stomach are ligatured. Claude Bernard and
others suggested that the layer of mucus protected the cells of the stomach
and of the intestine from the digestive enzymes; or that the epithelial layer
had a protective effect. Pavy suggested that the alkali of the blood had a
protective action. All these theories became untenable when Fermi showed
that all kinds of living organisms, protozoans, worms, arthropods, are not
digested in solu­tions of trypsin as long as they are alive, while they are

promptly digested in the same solu­tion when dead. 294 This is in harmony
with the fact that many parasites live in the intestine without being digested
as long as they are alive. Fermi concluded that the living cell cannot be
attacked by the digestive ferments, while with death a change occurs by
which they can be attacked. But what is this change? Fermi seems to be
inclined to think that the “living molecule” of protein is not hydrolysable
(perhaps because the enzyme cannot attach itself to it?), while a change in
the constitu­tion or configura­tion of the proteins takes place after respira­tion
has ceased. The fact that the living cell resists the digestive action of trypsin
and pepsin has found two other modes of explana­tion, first, that the cells are
surrounded by a membrane or envelope through which the enzyme cannot
diffuse, and second, that the living cells possess antiferments. But the so-
called antiferments are also said to exist after the death of the cell, whereas
after death the cell is promptly digested. Frédéricq, as well as Klug, has
shown that worms which are not attacked by trypsin are digested by this
enzyme when they are cut into small pieces; although the pieces of course
contain the antienzyme. The other sugges­tion that a membrane impermeable
for trypsin protects the cells would explain why living protozoa are not
digested by trypsin, but it leaves another fact unexplained, namely, the
autodiges­tion of all the cells after death by enzymes contained in the cells
themselves.
2. The disintegration of the body after death is not caused exclusively or
even chiefly by the digestive enzymes of the intestinal tract or the micro-
organisms entering the dead body from the outside, but by the enzymes
contained in the cells themselves. This phenomenon of autolysis 295 was first
characterized by Hoppe-Seyler. 296

All organs suffering death within the organism, in the absence of
oxygen, undergo softening and dissolu­tion in a manner resembling
that of putrefac­tion. In the course of that process, albuminous matter
gives rise to leucin and tyrosin, fat to free acids and soaps. This
macera­tion, identical with the pathological concep­tion of softening,

is accomplished without giving rise to ill odour and is a process
similar to the one resulting from the action of water, acids, and
digestive enzymes.
In work of this kind, rigid asepsis is required to exclude the possibility of
bacterial infec­tion and this was first done by Salkowski, who showed that in
aseptically kept tissues like liver and muscle the amount of substances that
can be extracted with hot water increases considerably. By the work of
others, especially Martin Jacoby and Levene, it was established that the
power of self-diges­tion is shared by all organs. Analysis of the products of
the autodiges­tion of tissues shows that, e. g., the amino acids, which
constitute the proteins, are produced. Dakin, Jones, and Levene
demonstrated the hydrolytic products of the nucleins, in the case of the self-
diges­tion of tissues. 297

Again the ques­tion arises: Why do the tissues not undergo autolysis during
lifetime and what protects them, and the answer is that self-diges­tion is a
consequence of the lack of oxida­tions. The presence of antiferments must
continue after death and cannot be the cause which prevents the self-diges­‐
tion during life, since nothing indicates the destruc­tion of the hypothetical
antidigestive enzymes through lack of oxygen. The recent work of Bradley
and Morse 298 and of Bradley 299 has thrown some light on the problem.
These authors found that proteins of the liver which are indigestible can be
made digestible by the liver enzymes if an acid salt or a trace of acid is
added to the mixture. A m/200 HCl solu­tion gives marked accelera­tion of
the autodiges­tion of the liver. This would explain why autodiges­tion takes
place after oxida­tions cease. In many if not all the cells, acids are constantly
formed during lifetime, e. g., lactic acid, which through oxida­tion are turned
to CO2, and this diffuses into the blood so that the H ion concentra­tion in
the cells does not rise materially. If, however, the oxida­tions cease, as is the
case after death, the forma­tion of lactic acid continues, but the acid is not
oxidized to CO2 and thus removed, and as a consequence the H ion
concentra­tion increases in the cells and the self-diges­tion of proteins, which
the digestive enzymes contained in the cells themselves could not attack

formerly, becomes possible. Acid increases the digestibility of a protein,
probably by salt forma­tion. Theoretically we should not be surprised that
while in the liver an increase in the CH favours autolysis in other tissues the
same result is produced by the reverse effect. We might say that the
preserva­tion of a certain CH probably at or near the point of neutrality
during life prevents self-diges­tion, while the gross altera­tion of the CH in
either direc­tion after death (or after the cessa­tion of oxida­tions in the
tissues) induces autolysis. Bradley indeed suggests that many of the
phenomena of autolysis during lifetime, such as atrophy, necrosis, involu­‐
tion, might be due to an increase in the CH in the tissues.
These facts agree with the suggestion of Fermi that in the living cell the
proteins cannot be attacked by the digestive enzymes but relieves us of the
necessity of making the monstrous assump­tion of a “living molecule” of
proteins as distinct from a “dead” molecule. The difference between life and
death is not one between living and dead molecules, but more likely
between the excess of synthetic over hydrolytic processes.
In the second chapter we mentioned the interesting idea of Armstrong that
when a synthesis is brought about by a digestive enzyme (e. g., maltase) not
the original substrate is formed (e. g., maltose) but an isomer, in this case
isomaltose; and this isomer is not attacked by the enzyme maltase. We thus
get a ra­tional understanding of the statement which Claude Bernard used to
make but which remained at his time mysterious: la vie, c’est la créa­tion.
During life, when nutritive material is abundant, through the reversible
action of certain enzymes, synthetic compounds are formed from the
building stones furnished by the blood. These synthetic isomers cannot be
hydrolyzed by the enzymes by which they are formed and hence on account
of the isomeric structure are immune against destruc­tion. It is not
impossible that the increase of the concentra­tion of acid in the cells after
death trans­forms the isomers into that form in which they can be digested
by the enzymes contained in the cell. Another possibility is that the increase
in digestibility brought about by an increase in CH in the cell is due to the
hydrating effect of acids on proteins with a subsequent increase in

digestibility. Whatever the answer may be, the work done since Claude
Bernard has removed that cloud of obscurity which in his days surrounded
the prevalence of synthetic action in the living and of disintegra­tion in the
dead tissues.
3. We have already referred to the connection between the lack of oxygen
and the onset of autolysis and disintegra­tion of tissues in the body. It is of
interest that there are cells in which the disintegra­tion under the influence of
lack of oxygen is so rapid that it can be followed under the microscope. The
writer has observed that certain cells undergo complete irreversible dissolu­‐
tion in a very short time under the influence of lack of oxygen, e. g., the
first segmenta­tion cells of the egg of a teleost fish Ctenolabrus. 300
When these eggs are
deprived of oxygen at the
time they reach the eight- or
sixteen-cell stage, it can be
noticed that the membranes
of the blasto­meres are trans­‐
formed into small droplets
Fig. 48 Fig. 49
within half an hour or more,
according to the
temperature. These droplets
begin to flow together,
forming larger drops.
[Figures 48 to 51 show the
successive stages of this
Fig. 50 Fig. 51
process.] When the eggs are
exposed to the air in time, segmenta­tion can begin again; but if a
slightly longer time is allowed to elapse, the process becomes
irreversible and life becomes extinct. Such clear structural changes
cannot often be observed in the eggs of other animals under the
same condi­tions. Are these changes of structure (apparently
liquefac­tion of solid elements) responsible for death under such

condi­tions? In order to obtain an answer to this ques­tion, the writer
investigated the effect of the lack of oxygen upon the heart-beat of
the embryo of the same fish Ctenolabrus. This egg is perfectly
transparent and the heart-beat can easily be watched. When these
eggs are put into an Engelmann gas chamber and a current of pure
hydrogen is sent through, the heart may cease to beat in fifteen or
twenty minutes; it stops beating suddenly, before the number of
heart-beats has diminished noticeably, and ceases beating before all
the free oxygen can have had time to diffuse from the egg. In one
case the heart beat ninety times per minute before the hydrogen was
sent through; four minutes after the current of hydrogen had passed
through the gas chamber, the rate of the heart-beat was eighty-seven
per minute, three minutes later it was seventy-seven, and then the
beats stopped suddenly. It is hard to believe that this cessa­tion could
have been caused by lack of energy. Hydrolytic processes alone
could furnish sufficient energy to maintain the heart-beat for some
time, even if all the oxygen had been used up. The suddenness of
the standstill at a time when the rate had hardly diminished seems to
be more easily explained by a sudden collapse of the machine; it
might be that liquefac­tion or some other change of structure occurs
in the heart or its ganglion cells, comparable to that which we
mentioned before. In another fish Fundulus, where the cleavage
cells undergo no visible changes in the case of lack of oxygen, the
heart of the embryo can continue to beat for about twelve hours in a
current of hydrogen. In this case the rate of the heart-beat sinks
during the first hour in the hydrogen current from about one
hundred to twenty or ten per minute; then it continues to beat at this
rate for ten hours or more. In this case one might believe that during
the period of steady diminu­tion of the tension of oxygen in the heart
(during the first hour), the heart-beat sinks steadily while it keeps up
at a low but steady rate as long as the energy for the beat is supplied
solely by hydrolytic processes; but there is certainly no change in

the physical structure of the cells noticeable in Fundulus, and
consequently there is no sudden standstill of the heart.
Budgett has observed that in many infusorians visible changes of
structure occur in the case of lack of oxygen 301; as a rule the
membrane of the infusorian bursts or breaks at one point, whereby
the liquid contents flow out. Hardesty and the writer found that
Paramœcium becomes more strongly vacuolized when deprived of
oxygen, and at last bursts. Amœbæ likewise become vacuolized and
burst under these condi­tions. Budgett found that a number of
poisons, such as potassium cyanide, morphine, quinine, antipyrine,
nicotine, and atropine, produce structural changes of the same
character as those described for lack of oxygen. As far as KCN is
concerned, Schoenbein had already observed that it retards the
oxida­tion in the tissues, and Claude Bernard and Geppert confirmed
this observa­tion. For the alkaloids, W. S. Young has shown that they
are capable of retarding certain processes of autoxida­tion. This
accounts for the fact that the above-men­tioned poisons produce
changes similar to those observed in the case of lack of oxygen. 302
The phenomenon of rapid disintegra­tion when deprived of oxygen (or in the
presence of KCN) seems to be general as Child 303 has shown in extensive
experi­ments. Child has used it to show that younger animals disintegrate
more rapidly than older or larger ones, and he uses this fact for a theory of
senescence. He connects the more rapid disintegra­tion of the young animal
with a greater metabolism. 304 Without wishing to doubt Child’s interesting
observa­tions the writer is not quite certain whether the more rapid
disintegra­tion of the younger forms is not a result of the fact that the walls
of membranes in the young are softer than those of the older animals, and
hence are more readily liquefied. Such a difference could be due to mere
chemical constitu­tion, e. g., the increase in Ca in the membrane with the
increase in age. In old age in man the deposit of Ca in the blood-vessels is a
frequent occurrence.

These facts may help us to understand the nature of death and dissolu­tion of
the body in higher animals. Death in these animals is due to cessa­tion of
oxida­tions, but the surprising fact is that if the oxida­tions have been
interrupted but a few minutes life cannot be restored even by artificial
respira­tion. This suggests that the respiratory ganglia in the medulla
oblongata suffer an irreparable injury or an irreversible change (comparable
to that just described in the cells of Ctenolabrus) even when deprived of
oxygen for only a short time. As a consequence of the irreversible injury to
the medulla the respira­tions cease permanently, the heart-beat must also
cease, and gradually the different tissues must undergo the dissolu­tion
characteristic of death. While all the cells may be immortal they are only so
in the presence of oxygen and the nutritive solu­tion which the circulating
blood furnishes. With the proper supply of oxygen cut off they can no
longer live.
4. It is an unques­tionable fact that each form has a quite definite dura­tion of
life. Unicellular organisms are immortal; but for the higher organisms with
sexual reproduc­tion the dura­tion of life is almost as characteristic as any
morpho­logical peculiarity of a species. No species can exist unless the
natural life of its individuals outlasts the period of sexual maturity; and
unless the average dura­tion of life is long enough to allow as many
offspring to be brought into the world as will compensate for loss by death.
The male bee dies before it is a year old, while the queen may live several
years. In a certain species of butterflies, the Psychidæ, the partheno­genetic
female lays its eggs while still in the cocoon and then dies without ever
leaving the cocoon. The imago of the ephemera leaves the water in the
evening, copulates, lets its eggs fall into the water, and is dead the next
morning. The imperfect condi­tion of their mandibles and alimentary canal
makes them unfit for a long dura­tion of life. The males of the rotifers which
are devoid of organs of diges­tion live but a few days.
In the Zoölogical Station at Naples in 1906, an actinian, Actinia equina, was
alive after having been in captivity fifteen years, and another one,
Cerianthus, had been observed for twenty-four years. Korschelt kept

earthworms for as long as ten years. The fresh-water mussel may reach the
age of sixty years or more and crayfish may live for over twenty years. The
differences in the dura­tion of life of mammals are too well known to need
discussion. If the cells and tissues are immortal, how does it happen that the
dura­tion of life is so characteristic for each species?
Metchnikoff 305 has recently investigated the cause of “natural” death in the
butterfly of the silkworm. The butterfly in this species lacks the organs
necessary for taking up food, like the male rotifer or the ephemeridæ and
hence is already, by this fact, condemned to a short life. Metchnikoff
observed that these butterflies could live twenty-three days, but the average
dura­tion of life was 15.6 for the males and 16.6 days for the females; and
that seventy-five per cent. of them contained no parasitic fauna or flora in
their intestine. They lose considerably in weight during their lives, but the
males still contain the fat body at the time of death. None of the changes
accompanying “old age” in man are found in the tissues of these butterflies
before death. Metchnikoff is inclined to believe that the animal is poisoned
by some excre­tion retained in the body; namely, the urine, and that this
poison also causes the symptoms of weakness which characterize the
animal. He could prove the toxic character of their urine on other animals.
This combined with starva­tion could sufficiently account for the short dura­‐
tion of life. The facts of the case show that it is due to an imperfec­tion in the
construc­tion of the organism such as one would expect to find more or less
in each animal if one discards the idea of purposefulness and divine wisdom
in nature. Only a slight, perhaps an infinitesimal, fraction, of those species
which are theoretically possible and which at one time or another arise can
survive. Those which are durable show all transi­tions from the grossest
disharmonies to an apparent lack of such shortcomings.
5. Minot had tried to prove that the death of metazoa is due to the greater
differentia­tion and specializa­tion of their tissues. Admitting the immortality
of the unicellular organisms he argues that death is the price metazoa pay
for the higher differentia­tion of their cells. This is of course purely
metaphorical, but we may put it into a form in which it is capable of

discussion in physico­chemical terms, by assuming that death is a necessary
stage in the development of a species. We are inclined, however, to follow
Metchnikoff and suspect some poison accidentally or unavoidably formed
in the body or some structural shortcoming as the cause of “natural” death.
An unusually favourable object for the study of natural death is the animal
egg. The egg of the starfish Asterias forbesii when taken out of the body is
usually immature, but in the spawning season it ripens in sea water. The
writer 306 observed that eggs which ripen disintegrate very rapidly when not
fertilized. This disintegra­tion may be due to a process of autolysis, which
sets in only after the egg has extruded the two polar bodies. The writer
found that by preventing the matura­tion of the egg either by withdrawing
the oxygen or by replacing the alkaline sea water by a neutral solu­tion or by
exposing the eggs for some time to acidulated sea water, the disintegra­tion
could also be prevented.
Further experi­ments showed that even in the mature egg rapid disintegra­‐
tion could be prevented by lack of oxygen, and similar results were
obtained by Mathews. When the egg is fertilized it does not disintegrate in
the presence of oxygen but it gradually dies in the absence of oxygen. One
is almost tempted to say that while the fertilized egg is a strict aërobe the
mature unfertilized egg is an anaërobe. This latter statement, however,
becomes doubtful since the presence of oxygen may help the disintegra­tion
only indirectly by allowing certain changes to go on in the egg. The
important points for us are that dura­tion of life in the mature unfertilized
egg is comparatively short and that the entrance of a spermato­zoön or the
process of artificial parthenogenesis saves the life of the egg. Loeb and
Lewis found that the life of the unfertilized sea-urchin egg (which is usually
mature when removed from the ovaries) can also be prolonged when its
oxida­tions are suppressed. The decay of the unfertilized egg seems to be
due to the fact that those altera­tions in the cortical layer which underlie the
membrane forma­tion and which are responsible for the starting of
development gradually take place. In such a condi­tion the egg will die
quickly unless deprived of oxygen. This view is supported by the observa­‐

tion of Wasteneys that unfertilized eggs of Arbacia show an increased rate
of oxida­tions when allowed to remain for some time in sea water; we have
seen in Chapter V that such an increase also accompanies artificial
membrane forma­tion.
6. If the limited dura­tion of life of an organism is determined by one or
more definite harmful chemical processes, we should expect to find a
temperature coefficient for the dura­tion of life or at least be able to show
that if all other condi­tions are the same the dura­tion of life is for a given
organism a func­tion of temperature. The writer 307 investigated the dura­tion
of life of fertilized and unfertilized eggs of Strongylo­centrotus purpuratus
for the upper temperature limits.
TABLE XX

Duration of life of the eggs of S. purpuratus
Temperature
Unfertilized Fertilized
°C. Minutes Minutes
> 1 1⁄ 6
32 11⁄2
<2
> 2 1⁄ 4
31
<3
>3 >4
30
<5 <5
>6
29
<7
>8 > 11
28
< 10 < 13
> 20
27 about 18
< 22

> 35 > 35
26
< 40 < 40
> 76
25
< 81
> 168 > 192
24
< 200 < 209
Hours
22 101⁄5
21 24
20 72

These observa­tions show a very high temperature coefficient near the upper
temperature limit, and this may account at least partly for the fact that in
tropical seas the pelagic fauna is so much more limited than in polar seas. 308
It is quite probable that the high temperature coefficients at the utmost
limits are only an expression of the coagula­tion time of certain proteins.
P. and N. Rau state that in the cold certain butterflies live longer, and similar
statements exist for the silkworm, but these statements are not based on
exact experi­ments, which are difficult. Dr. Northrop and the writer have
started experi­ments on the influence of temperature on the dura­tion of life
of the fly Drosophila. Newly hatched flies were kept first without food
except water and air at 34°, 28°, 24°, 19°, 14°, and 10°, and second with
cane sugar. The average dura­tion of life was as follows:
With water days With cane sugar days
34° . . . . . . . 2.1 . . . . . . . . . . 6.2
28° . . . . . . . 2.4 . . . . . . . . . . 7.2
24° . . . . . . . 2.4 . . . . . . . . . . 9.4
19° . . . . . . . 4.1 . . . . . . . . . . 12.3
14° . . . . . . . 8.3
10° . . . . . . . 11.9

These experi­ments show that there is a definite temperature coefficient for
the dura­tion of life and that this coefficient is of the order of magnitude of
that of a chemical reac­tion. We are continuing these experi­ments with
animals in the presence of food. It should, however, be remembered that the
fly carries with it a good deal of reserve material from the larval period. We
have carried on simultaneously determina­tions of the temperature
coefficients of the dura­tion of the larval and pupa stage of these organisms
at the same temperatures and found ratios similar to those given above for
the dura­tion of life with water only.
7. Metchnikoff 309 has furnished the scientific facts for our understanding of
senescence. He has demonstrated that the changes in tissue which give rise
to phenomena of senility are due to the action of phagocytes. Thus the
ganglion cells are altered (digested?) and destroyed by “neuronophags” and
this is the main cause of mental senility. Definite phagocytic cells, the
osteoclasts, slowly dissolve the bones (by the excre­tion of an acid?) and this
leads to the known fragility of the bones in old age. The whiteness of the
hair is due to the action of phagocytes; in the muscles in old age the
contractile elements are destroyed by the sarcoplasm, and so on. It agrees
with these facts that where organs are absorbed in the embryonic
development of an animal, as e. g., the tail of the tadpole in metamorphosis,
the phenomenon is due to a process of phagocytosis (and autolysis). We
have men­tioned the fact that in the larva of the Amblystoma the absorp­tion
of the gills and of the tail occurs simultaneously and that both must be
caused by a constituent of the blood. Such a constituent may be responsible
for phagocytosis and autolysis in the organs undergoing absorp­tion.
Metchnikoff calls atten­tion to the fact that certain infectious diseases, e. g.,
syphilis, may bring about precocious senility; and he men­tions also the
senile appearance of young cretins which is due to the diseased thyroid. “It
is no mere analogy to suppose that human senescence is the result of a slow
but chronic poisoning of the organism.” He assumes that in man this
poisoning is caused by the products of fermenta­tion in the large intestine
and that the micro-organisms responsible for these fermenta­tions may

therefore be regarded as the real cause of senility in man. Parrots which are
long-lived birds have a limited flora of microbes in their intestine, while
cows and horses which are short-lived in comparison with man possess an
extraordinary richness of the intestinal flora. But, needless to say, it is not
the quantity of microbes alone which is to be considered, the nature of the
microbes is of much greater importance.
Certain plants like the Californian Sequoia gigantea may be considered as
practically immortal since they live several thousands of years; other plants,
the annuals, die after fructifica­tion. Metchnikoff quotes from a letter by de
Vries that this author prolonged the life of Œnotheras by cutting the flowers
before fertiliza­tion.
Under ordinary condi­tions the stem dies after producing from forty
to fifty flowers, but if cutting be practised new flowers are produced
until the winter cold intervenes. By cutting the stem sufficiently
early the plants are induced to develop new buds at the base and
these buds survive winter and resume growth in the following
spring.
Metchnikoff suggests that it is a poison formed in the plant (in connec­tion
with fructifica­tion?) which kills the annuals, while it is not formed or is less
harmful in the perennials. He compares the situa­tion to the death of the
lactic acid bacilli if the lactic acid is allowed to accumulate. This hypothesis
is certainly worthy of considera­tion, and it is quite possible that in addi­tion
to structural shortcomings poisons formed by certain organs of the body as
well as poisons formed by bacteria account for the phenomenon of death in
metazoa.

INDEX
Abraxas, 203, 238, 241
Acquired characters, inheritance of, 337 ff.
Actinia equina, 361
Adaptation, 12, 318 ff.;
to life in caves, 319 ff.;
fresh and salt water, 327 ff.;
poisons, 332 ff.;
temperature, 334 ff.;
caused by hormones, 342
Addison, W. H. F., 188
Agglutination, of corpuscles by sera, 67 ff.;
of sperm, 78, 82 ff.
Allolobophora terrestris, 46
Alpheus, 176
Alytes obstetricans, 337, 338
Amanita phalloides, 63
Amblystoma, 157, 368
Amelung, 184
Amphipyra, 283
Analogies between living and dead matter, 14 ff.
Anaphylaxis reaction, 61 ff.
Ancel, 158, 225 ff.
Antagonistic salt action. See Balanced salt solutions.
Antennularia antennina, 194, 196
Apes, blood relationship to man, 54, 56 ff.
Apolant, 45
Arbacia, 75 ff., 96, 99, 101, 111, 114, 150, 190 ff., 293 ff., 298, 299, 364
Arenicola, 277
Armstrong, E. F., 26, 28, 354

Arrhenius, S., 33 ff., 88, 290, 296
Arrhenoidy, 218, 225
Artificial parthenogenesis, 95 ff.;
in sea urchins, 95 ff.;
new method of, 98, 99;
by blood, 101 ff.;
by sperm extract, 103;
by acids, 105;
by mechanical agitation, 107;
in starfish, 110;
rôle of hypertonic solution, 112, 115, 116;
and oxidation, 116, 117, 118;
and permeability, 119 ff.;
in frogs, 124;
and determination of sex, 125
Artificial production of life, 38–39
Assimilation of CO2 without chlorophyll, 17 ff.
Asterias, 49, 81, 110, 363;
ochracea, 73 ff.;
capitata, 74
Asterina, 75, 81, 110
Astrospheres, 115 ff., 192
Auer, J., 315
Autolysis, 351 ff.
Avena, 263

B. coli communis, 36;
typhosus, 36;
fluorescens, 334
Bacteria, growth of, 15 ff., 29, 71 ff.;
specificity in, 41 ff.
“Bacterio-purpurin,” 41
Balanced salt solutions, 307–317;

theory of, 317;
and adaptation, 331 ff.
Balanus, 259
Baltzer, F., 215 ff.
Bancroft, F. W., 70, 125, 127, 264, 269 ff.
Bang, 63
Bardeen, C. R., 174 ff.
Barnacle, larvæ of, 313 ff.
Bataillon, 124
Bateson, W., 230, 240 ff., 338, 348
Batrachia, 338
Baur, E., 48, 246
Bayliss, 63
Becquerel, P., 36 ff.
Beggiatoa, 19
Beijerinck, M., 20
Berkeley, Lord, 111
Bernard, Claude, 2 ff., 26, 159, 350, 354, 355, 358
Berthelot, 290
Bertrand, G., 248 ff.
Beutner, R., 140
Bichat, 2, 349
Bickford, E. E., 169
Blaauw, H. A., 263
Blackman, F. F., 302
Blastomeres, 141 ff.
Blind animals, 319 ff.
Blood, transfusion of, 53 ff.
Blood relationship, established by transfusion, 53, 54 ff.;
precipitin reaction, 55 ff.;
anaphylaxis reaction, 61 ff.;
hemoglobin crystals, 64 ff.
Blood serum, precipitin reaction of, 54 ff.;