The biological basis of individuality

Marine Biological Laboratory

Rece,ved_i^^J_„

Accession No.

58251

r. D Dr. Leo Loeb

Liiven oy

Place Washington University

I)

^^"

= ru

= 3-

— -=T

= tr

Os

— i-q

x==

= i-q

zM

-8 CO

> —

= CD

m—

2==

— i-q

=i D

sb m

= D

= °

THE

BIOLOGICAL BASIS
OF

INDIVIDUALITY

THE

BIOLOGICAL BASIS

OF

INDIVIDUALITY

By
LEO LOEB

Professor Emeritus of Pathology

Washington University

School of Medicine

Saint Louis

1945

CHARLES C THOMAS • PUBLISHER

SPRINGFIELD • ILLINOIS BALTIMORE • MARYLAND

Published by Charles C Thomas

at Bannerstone House

301-327 East Lawrence Avenue, Springfield, Illinois

Published simultaneously in Canada by
The Ryerson Press, Toronto

All rights in this book are reserved. No part may be re-
produced in any form whatsoever without permission in
writing from the publisher, except by a reviewer who
wishes to quote extremely brief passages in connection
with a critical review. Reproduction in whole or in part
in digests, in condensations of the literature, in lectures,
or in films; or by multigraphing, lithoprinting, or by any
other processes or devices, is reserved by the publisher.
For information, address Charles C Thomas.

Copyright, 1945, by Charles C Thomas

First Edition

Printed in the United States of America

To My Wife
Georgiana Sands Loeb

Preface

The study of individuality began when human beings observed others,
noted their structure and functions, their attitudes and actions. At a
later stage the physiologist and psychologist recognized that in the
individualities separate constituents can be distinguished and they extended
the concept of individuality to other organisms than man. In this book the
attempt has been made to distinguish between two types of individuality:

The first one is the mosaic type which represents the sum of the par-
ticular organ and tissue characteristics (organ and tissue differentials)
which determine structure, metabolism, motor and psychical activities and
the component parts of which differ in different individuals. These multiple
characteristics are combined into a composite or mosaic which is peculiar to
each individual.

The second type of individuality which may be designated as the essential
individuality is characterized by the presence of a chemical factor — the
individuality differential — which is common to the different organs and
tissues of each individual and which differs from the corresponding chemi-
cal characteristics of the organs and tissues of every other individual. This
concept emphasizes the oneness of the individual which depends upon the
presence of a common and unique factor in all of his essential parts.

In the same sense in which individuality differentials characterize individ-
uals, there are species, order and class differentials each possessing a specific
chemical constitution which characterizes the larger groups of organisms. All
these various differentials may be grouped together as organismal differentials
in contrast to the organ and tissue differentials which, as mentioned, constitute
the mosaic individuality. While it is thus possible to distinguish sharply be-
tween these two types of differentials and between the corresponding defini-
tions of individuality, various kinds of interactions take place between the
organismal and organ differentials and these interactions are required to make
of the individual an integrated whole.

In the following chapters these various aspects of individuality, including
the psychical, are analyzed, but only as far as the principles underlying these
phenomena are concerned and no attempt has been made to present a detailed
or complete account of all the data which may have a bearing on the problems
involved.

The starting point of this analysis was a series of investigations on the
transplantation of normal and of tumor tissues which the author and his col-
laborators have carried out in the course of about forty-eight years, some of
which, especially those dealing with inbred strains of mice, have not yet been
published. To make possible a unified account and interpretation of the various
aspects of individuality, it was necessary for one person to undertake this
work, rather than to edit a collective book written by specialists in the different

vii

viii THE BIOLOGICAL BASIS OF INDIVIDUALITY

sciences which contribute the data needed for this purpose. The method thus
chosen suffers from the difficulty that a single author may not be able to treat
with equal competence all the problems involved; but it is believed that the
unified presentation of these fields may, to a certain extent, compensate for
such a deficiency.

In the following chapters these types of individuality are analyzed as to
their evolution and their biological and psychical manifestations.

It is hoped that this presentation may be of interest to the biologist and to
the general pathologist and that certain parts of it may be helpful even to the
surgeon in the practice of tissue grafting, to the geneticist, to the student of
cancer and to the immunologist ; perhaps also to the psychologist and to some
philosophers.

Acknowledgments

This book was written in a provisional form in 1930 and in the follow-
ing years; however, it was not yet quite finished by 1937. In 1937 a
grant was received from the Josiah Macy Jr. Foundation for its com-
pletion ; this, as well as a revision, was accomplished between the latter date
and the present time. The writer wishes to express his appreciation to the
Josiah Macy Jr. Foundation for the assistance thus given.

To the International Cancer Foundation the author is indebted for grants
which enabled him to undertake additional experiments concerning a com-
parison between the individuality differentials of normal and cancerous tissues.
In this volume the results obtained have been incorporated.

Sincere appreciation is also due to the numerous collaborators who helped
to advance this field of research during the many years in which these in-
vestigations were carried out. Reference is made in the text to their contribu-
tions. The co-operation of Dr. Helen Dean King and Dr. Sewall Wright and
subsequently also of others was of very great help in making possible the
transplantation of tissues in closely inbred strains of rats and guinea pigs.
Later, there were added to these experiments those on closely inbred strains
of mice which were received from the New York State Institute for the Study
of Malignant Disease, from the Roscoe B. Jackson Laboratory, Bar Harbor,
and from other laboratories.

The aid given by the wife of the author, Georgiana Sands Loeb, in the re-
vision of this manuscript, and in other ways through many years, was of the
greatest value and to her this book is gratefully dedicated.

To Mr. Charles C Thomas, I wish to express my warm appreciation of the
great interest and helpfulness he has manifested in the publication of this book.

IX

Table of Contents

Preface vii

Acknowledgments ix

Introduction 3

PART I. Transplantation of Tissues in Higher Vertebrates, as a

Method for the Analysis of the Organisnial Differentials . . 27

Chapter 1. General considerations 27

Chapter 2. Autogenous and homoiogenous transplantations ... 37
Chapter 3. Transplantation of autogenous and homoiogenous tissues

in mice 54

Chapter 4. Autogenous, syngenesious, homoiogenous and interracial

transplantations in birds 59

Chapter 5. The mechanism of the reactions against homoiogenous in-
dividuality differentials; autogenous tissue regulators ... 66
Chapter 6. Syngenesiotransplantation,.transplantation in closely inbred

strains, and the individuality differentials of near relatives . . 72
Chapter 7. The individuality differentials of closely inbred animals . 83
Chapter 8. Individuality differentials in closely inbred guinea pigs . 89
Chapter 9. Individuality differentials in closely inbred strains of mice . 98
Chapter 10. Heterogenous transplantation of normal tissues and of

blood clots 116

Chapter 11. Exchange of tissues between different varieties or races

(subspecies) 131

Chapter 12. The problems and the criteria of success or failure in

transplantation of tissues and organs 136

Chapter 13. The effects of various extraneous factors on the activity

of the organismal differentials 140

Chapter 14. Hormones and individuality differentials 143

Chapter 15. Individuality differentials and blood groups .... 150
Chapter 16. The relations between processes of immunity and indi-
viduality differentials in transplantation 157

Chapter 17. The significance of the individuality differentials in trans-
plantation by means of blood vessel anastomosis and in parabiotic

states 166

Chapter 18. Modification of the reaction of the host against strange
individuality differentials by transplantation of tissues into the
allantois of chick embryos, into the brain or into the anterior

chamber of the eye 177

Chapter 19. The relations between age and individuality differentials . 184
Chapter 20. Individuality differentials and tissue culture .... 187

xii THE BIOLOGICAL BASIS OF INDIVIDUALITY

Chapter 21. The individuality differentials and potential immortality

of tissues 190

Chapter 22. The nature of the individuality differential and of the
reaction of an organism against a strange individuality differen-
tial 195

PART II. The Phylo genetic and Ontogenetic Development of Individu-
ality and Organismal Differentials 203

Chapter 1. Transplantation and individuality in coelenterates and pla-

narians 203

Chapter 2. Transplantation and individuality in higher invertebrates

and in amphibia 218

Chapter 3. Transplantation and individuality of embryonal tissues . 234

Chapter 4. The significance of organismal differentials in the trans-
plantation of pieces of embryonal tissue into embryos and into
adult organisms 244

Chapter 5. Organizers and tissue differentiation, and their relation to

organismal differentials 259

Chapter 6. Regeneration, transplantation and the autogenous tissue

equilibrium 275

PART III. The Significance of Organismal Differentials in the Inter-
action between Single Cells 287

Chapter 1. The role of organismal differentials in the union of free-
living cells 287

Chapter 2. Tissue formation and organismal differentials .... 298

Chapter 3. The role of organismal differentials in fertilization . . 307

Chapter 4. Self fertilization and autogenous transplantation . . . 315

Chapter 5. The relations between hybridization and transplantation . 326

PART IV. Tumors and Organismal Differentials 333

Introduction. The nature of tumors 333

Chapter 1. A comparison between the transplantation of tumors and

of normal tissues 338

Chapter 2. Heredity and transplantation of tumors 363

Chapter 3. The relation between growth energy, adaptive processes

and organismal differentials in the transplantation of tumors . 384
Chapter 4. Immunity and organismal differentials in tumor transplan-
tation 400

Chapter 5. Tumor growth and organismal differentials 432

PART V. Organismal and Organ Differentials and the Specificity of

Tissue Reactions 443

Chapter 1. The relative importance of substratum and of morpho-
genic substances in the specificity of tissue reactions, and the rela-
tion of these factors to organismal differentials 443

CONTENTS xiii

Chapter 2. Structure and function of organs and tissues as criteria of

individuality • 457

Chapter 3. Organismal differentials and specific adaptation of tissues

and their products 466

PART VI. Organismal Differentials and Organ Differentials as Anti-
gens 477

Introductory remarks 477

Chapter 1. Blood groups, heterogenetic (Forssman) antigens and

organismal differentials 478

Chapter 2. The demonstration of species differentials by serological

methods 498

Chapter 3. The demonstration of individuality differentials by sero-
logical methods 510

Chapter 4. The organismal differentials of hybrids between nearly re-
lated species 519

Chapter 5. On the differences between the reactions of foetal or new-
born organisms and of adult organisms against strange differen-
tials as established by serological methods 524

Chapter 6. Organ (tissue) differentials and their analysis by serological

methods , 530

Chapter 7. Idiosyncrasy and anaphylaxis and their relation to organ-
ismal differentials 550

Chapter 8. Toxins and organismal differentials 559

Chapter 9. The chemical nature of organismal differentials . . . 565

Chapter 10. Is it possible by experimental means to change organismal

differentials? 580

PART VII. Organismal Differentials, Organ Differentials and Evo-
lution 589

PART VIII. The Psychical-social Individuality 609

Chapter 1. The physiological basis of the psychical-social individuality 609

Chapter 2. Individuality and world 627

Chapter 3. The evolution of individuality 649

Bibliography 659

Index 697

THE

BIOLOGICAL BASIS
OF

INDIVIDUALITY

Introduction

We apply the term "individual" to a human being to emphasize the
distinctive unique features which such a person possesses. We note
his appearance, motor reactions, the expression of his face and his
psychical states, especially those which have a social significance. By this
designation we accentuate, in general, our impression that the different persons
we meet are more or less distinct from one another, although there may be
variations in the degree of these differences. Some persons appear to be more
like others, while other persons show marked peculiarities which differentiate
them sharply from the rest. Attention is given especially to the modes of
thinking, feeling, to the emotions, imagination, creativeness, to the behavior
in certain social constellations.

We apply the term "personality" to a human being, to state our reactions to
him in social intercourse, and our opinion as to whether we find him forceful
or weak, pleasant or unpleasant, serious or light.

Individuality is here used as the general term, while by personality is under-
stood that part of human individuality which manifests and maintains itself in
the social intercourse and struggle. We rnay define this distinction also some-
what differently. Individuality may be conceived of as the original physical
and psychical state of an organism, which has developed in accordance with
the genetic constitution of this organism with the co-operation of a sequence
of more or less fixed physical-chemical environmental conditions. In the course
of the natural and social struggle in which a human being is involved, tradi-
tions, suggestions, experiences of many kinds, mold this individuality in
various directions and thus determine the characteristics which the individual
takes on in becoming converted into the personality which develops in the
course of time and which alone we know. In this sense we are acquainted not
with individualities but only with personalities. The basic individuality is,
then, a mere mental construction, which we cannot know but some properties
of which we can surmise. However, secondarily, it is customary to express the
distinctive features or characteristics of a certain person, which differentiate
him from other persons, as his individual characteristics.

These are not sharply defined terms. Like all other beginnings of scientific
analysis, they express not yet fully correlated and analyzed experiences ; they
represent crude approximations to the understanding of reality.

The term "individual" is extended from man to other living organisms
which also show distinctive features, and it is applied even to non-living
things. In a literal sense, it signifies that an organism or a thing is an integrated
whole, which cannot be further divided without ceasing to be this particular
organism or thing, without losing its identity. Among the more primitive or-
ganisms it may be difficult to distinguish from one another individuals in a
given group, but it is possible to differentiate between the larger groups,
varieties, species, genera, orders and classes to which the individuals belong.

3

4 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Among the higher organisms we distinguish individuals the more readily, the
more varied the bodily features and the psychical reactions and the more
intimately we are acquainted with the peculiarities which each individual
possesses. In the phylogenetically higher organisms the differentiation between
the various parts, together with their functions, is greater, and likewise the
integration of the parts into one organism is more fixed and rigid. Here it is
evident that the individual, as a whole, is the unit in the biological and in the
social sense, and not the elements of which the individual is composed — the
cells, tissues and organs ; nor is a group of individuals, whether a family, clan,
nation or race, the real unit. Under natural conditions the smaller component
units depend upon the other constituents of the integrated individual for their
life and function, but the groups consist of individuals who, if necessary, are
able to live and function independently of the other units of the group. It is,
therefore, the effects which the actions and policies of the various groups
exert on the individual which is the ultimate test of their value. The wellbeing
of the group depends upon the wellbeing of the individuals of which it is com-
posed ; but conversely, social relationship to other individuals and a healthy
group life are conditions which promote the wellbeing of the individual, while
unfavorable social relations injure him.

All these individual characteristics in living organisms which we have men-
tioned so far, are localized in certain areas of the organism, in special organs
or tissues, and they are either structural or functional peculiarities of the
latter. If we conceive of the individual as a mosaic of many tissues and organs,
each one functioning and metabolizing in its own peculiar way, we may con-
sider this mosaic of separate parts as the biological basis of individuality, in-
cluding the psychical characteristics ; and in order to understand individuality
in this sense we would have to study the peculiarities of the units composing
such a mosaic in each individual. Also, the nervous system and the hormone
system which serve as means of communication between the various parts of
the body, represent special organs or products of organs and are therefore
parts of the mosaic. They are the properties of organisms, which are analyzed
as to their genetic basis by means of hybridizations according to Mendelian
methods.

There is, however, in addition to this mosaic basis of individuality, another
basis. There are properties which are not restricted to certain parts of the
organism, but which are common to all, or almost all, parts of the organism,
and which, although not visible, bind them together, make them into a unit and
differentiate one individual from every other individual ; also one species,
genus, order, class of organisms from every other species, genus, order and
class. There is inherent in every higher individual organism something which
differentiates him from every other individual, which can be discovered by
observing the reactions of certain cells and tissues belonging to one individual
towards the tissues and cells of another individual of the same species. These
reactions are indicative of a characteristic common to all the parts of one
organism, which differs from the analogous characteristic of all the parts in a
different organism of the same species. And not only do the cells and tissues

INTRODUCTION 5

of one individual recognize different individuals as such, they do more than
that, they recognize, to speak in a metaphorical way, the degree of difference
between two individuals in accordance with their genetic constitution.

It is not only the cells and tissues of one individual, however, which react
towards these elements of another individual in such a specific manner, but
there is also a substance in the bodyfluids of one individual which responds
towards all the cells and tissues of another individual in accordance with the
degree of the genetic difference between these two individuals. This again
indicates that there is a constituent common to all the tissues of an organism
which interacts with a constituent in the blood serum of another individual.

We may designate this particular characteristic distinguishing one indi-
vidual from another as his individuality differential; it is common to all the
various tissues and organs of an individual. In the same way, there are
characteristics common to all members of a species, genus, order and class,
which may be called species-genus-order-class differentials, and these may
be designated in their totality, together with the individuality differentials, as
organismal differentials, among which the individuality differential is the
highest and finest one. In contrast to these, in particular to the individuality
differentials, are the tissues and organ differentials, which differentiate from
one another the different tissues and organs, such as liver, kidney, thyroid,
carti'age, epidermis, in the same individual.

Theoretically it is of course conceivable that two individuals belonging to
the same species, other than unioval twins, possess exactly the same genetic
constitution and that accordingly their individuality differentials are identical ;
but considering the large number of genes which in all probability determine
this differential and considering also the possibility that mutations occur
spontaneously in the genetic constitution of individuals, such a state of
identity must be very rare indeed. Actually it has never been observed in the
course of our experiments which were numerous and which extended over
a long period of time, except possibly among brothers in a closely inbred
family of guinea pigs ; but even in this case the actual identity has not been
as yet definitely proven. However, as far as the identity of ordinary, non-
related individuals of the same species is concerned, the occurrence of such
an identity is so improbable that it has not been considered in the chapters
of this book, in which only the principles underlying the concept of individu-
ality are discussed.

There are two principal methods by means of which the organismal
differentials in general can be analyzed, namely, (1) by various types of
transplantation, and (2) by serological methods. As to transplantation, in a
wider sense we may include also parabiosis, the joining together of two fully
formed organisms and also the uniting of parts of embryos or of blastomeres ;
even the transfer of a spermatozoon into the egg during the process of
fertilization and the joining together of parts of free-living cells, such as
protozoa, may be considered as types of transplantation. Transplantation
and serological methods are not equally well adapted to the analysis of
organismal differentials; each has its own sphere in which it can be applied

6 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to the greatest advantage. While the serological tests are especially useful
in the analysis of the differentials of groups of animals, such as species,
genera, orders and classes, transplantation experiments are best suited for
the analysis of the differences between individuals as expressed in their indi-
viduality differentials. The study of transplantation among more primitive
organisms may contribute to our knowledge of the phylogenetic development
of the organismal differentials, and experiments in hybridization as well as
in transplantation of embryonal tissues may aid in the analysis of the onto-
genetic development of the organismal differentials.

We are concerned principally with the study of that type of organismal
differential which we have designated as the individuality differential, and here
the basic experiment is the following: Various organs or tissues are trans-
planted from one animal, e.g., a guinea pig, into two other guinea pigs not
directly related to the first guinea pig from which the tissues were taken ; this
is called homoiotransplantation. It is seen that the reactions of the hosts of
the multiple grafts toward the latter differ in accordance with the degree of
genetic relationship between host and donor, but the host behaves in approxi-
mately the same way toward the various tissues from the same donor. In one
animal the reactions are severe to all the tissues, in the other one they may be
very light. These reactions consist in the activity of the lymphocytes, the con-
nective tissue cells and blood vessels of the host towards the grafts ; in addi-
tion, tissues, especially the more sensitive ones, are also influenced by the
degree of their compatibility with certain constituents of the blood of the
host, and the degree of this sensitiveness again depends upon the genetic
relationship between host and transplant. In general, tissues are injured by
the bodyfluids of a strange host, and in some species this injurious action
plays a greater role than in others. However, in all the species which we have
studied so far it is the lymphocytes which sense or recognize the finest degrees
of similarity or difference in the constitution of the individuality differentials
between host and transplant. The distinctive reaction of the connective tissue
cells becomes noticeable if there is a slightly greater difference between these
differentials. The statement that all the tissues from the same donor elicit
the same intensity of reaction on the part of the same host is true in a relative,
but not in an absolute, sense. Different tissues have an unequal power to call
forth these reactions ; thus, for instance, thyroid gland usually induces a
stronger reaction than cartilage and perichondrium. This is evidently due to
the fact that a certain substance responsible for the reaction, the individuality
differential, is given off in sufficient quantities more readily by thyroid than
by cartilage, which latter has a more inert metabolism. However, notwith-
standing these differences between different tissues and organs, in all of them
the genetic relationship between host and transplant determines the intensity
of the reaction of the host against the individuality differentials of the trans-
plant.

There is a second type of experiment which brings out the meaning of the
individuality differential. This introduces variations in the relationship be-
tween host and transplant which are expressed by the terms : auto-, syn-

INTRODUCTION 7

genesio-, homoio- and heterotransplantation. The transplantation of various
kinds of tissues and organ pieces into the same animal from which they were
taken and to which, therefore, they belonged, is called autotrans plantation.
Here we find that lymphocytes are practically lacking around the graft; con-
nective tissue cells are attracted in only a moderate number and instead of
producing dense fibrous tissue, which is characteristic of their reaction against
a strange individuality differential, they form only a loose embryonal stroma
around the transplanted cells. The blood vessel supply is rich and in the course
of a relatively short time the transplant assumes about the condition of the
normal tissue or organ in the host. All tissues from the same organism behave
in this respect, in principle, in the same way, except that some tissues can
withstand the injury connected with the process of transplantation much
better than others. We may then conclude that it is not the organ or tissue
differentials which determine these injurious reactions of the host cells
towards the grafts, but the individuality differentials. The chemical consti-
tution of liver and of kidney is very different, but this difference has no effect
on the host cells — they react in about the same way towards liver and kidney,
provided these tissues possess the same individuality differential ; however, a
slight difference in the chemical constitution of the individuality differential
sets unfavorable reactions in motion ; and it makes little difference whether the
strange individuality differential is attached to organ differentials of kidney,
liver, skin, cartilage, uterus or thyroid. The various organ differentials all
behave in about the same way.

This, then, is the first important fact: the host cells recognize in a very
subtle way differences in individuality differentials. But they can do more
than this. As stated above, they are able to recognize the degree of difference
and to react accordingly. Thus, when a piece of tissue from brother to brother
is transplanted — a method designated as syngenesiotrans plantation — the cells
of the one which functions as host are not as much stimulated or excited by
the presence of a tissue so closely related to his own as by the tissues from a
non-related individual {hornoiotrans plantation) , the individuality differentials
being more similar in the first case. This observation holds good especially if
the parents belong to closely inbred strains ; otherwise brothers and sisters may
be genetically similar to each other to very different degrees and therefore, in
some instances, the reaction against a tissue of a brother may be about the
same as against that of a stranger, and if the strangeness exceeds a certain
limit, it is no longer the lymphocytes which are active, but the connective
tissue cells and the injurious substances of the bodyfluids. On the contrary,
in certain inbred strains the individuality differentials of all the animals
belonging to such a strain may have become so similar that no or only very
slight differences can be established between brothers and not directly related
individuals within the same strain.

On the other hand, if a piece of tissue is transplanted from one animal to
another which is genetically still further removed than in cases of homoio-
transplantation, as when animals from different species serve as host and
graft, the reactions are more severe. This procedure is called heterotrans-

8 THE BIOLOGICAL BASIS OF INDIVIDUALITY

plantation. In this instance the bodyfluids of the host are so different from
those to which the tissues of the transplant are adapted that they exert a
strongly injurious effect and kill the graft in a relatively short time; the
length of time in which this can be accomplished depends, among other factors,
upon the degree of resistance of the particular tissue. The reaction of the
connective tissue of the host is very strong in heterotransplantation ; besides,
it is the polymorphonuclear leucocytes which are attracted first, rather than
the lymphocytes, indicating the presence of a substance which acts as a
stronger poison, a heterotoxin. The reaction of the lymphocytes is the test for
the presence of a milder toxin, namely, homoio- or syngenesiotoxin. However,
in places where the toxin action is weaker or at a later period when the
acutely-acting toxins have been largely absorbed, lymphocytes may also be
attracted and collect in large masses around tissues derived from a strange
species. We see, then, that the host cells not only recognize a strange organis-
mal differential, but they also distinguish between different degrees of rela-
tionship or strangeness. But there is a limit to this power of discrimination. If
a certain threshold of strangeness has been reached, the reaction is maximal
and cannot be much increased if the tissues from individuals belonging
to still further removed classes are used. In this case serological tests are
better able to grade differences. The cellular reactions with which we have
to deal in transplantation are comparable to a very sensitive balance which
indicates small fractions of a milligram and which cannot be used for the
detection of differences which are measured by pounds. On the other hand,
serological tests are only under very restricted conditions serviceable in the
detection of finer differences. Thus, the experiments of Todd (to which we
shall refer later) show that under certain circumstances serological tests also
may indicate the presence of strange individuality differentials ; but only with
one particular kind of structure, the erythrocytes, has this test been used, and
even then it did not as a rule reveal the degree of relationship or strangeness
between the individuals which were compared.

Certain experiments show that the similarity or difference between two
individuality differentials corresponds to the similarity or difference in the
composition of the gene sets in the host and donor, and that the host cells
respond, so to speak, to genes which are strange to them. In reality, however,
it is not the genes as such to which the host cells react, but the organismal,
and in particular the individuality, differentials which develop in accordance
with the gene sets.

That it is the similarity or difference in the gene sets in two individuals
which primarily determines the kind of reaction which takes place between
host and transplant is also indicated by the fact that if, through close inbreed-
ing, we render their gene composition more similar, the individuality differen-
tials correspondingly become more and more similar in successive generations
and the severity of the reaction of the host against the graft is correspondingly
diminished. But it has been found very difficult to produce complete identity of
the individuality differentials even under these conditions. It seems, moreover,
that in different species closely inbred animals differ in respect to the readiness

INTRODUCTION 9

with which the stage of identity of the individuality differentials is approached
or becomes manifest, and the transplantation method can be applied in order
to test to what degree the gene composition in the individuals belonging to
a closely inbred family or strain has become similar, or, expressed differently,
the degree of homozygosity which has been reached in such a strain.

That it is the strange genes in the graft on which the reaction of the host
against the transplant depends is confirmed, also, by experiments in which two
inbred strains were hybridized and the reactions of individuals belonging to
the parent strains against tissues or organs of the hybrids were compared with
the reactions of the hybrids against transplants from the parent strains. In
the former case the reactions were more severe than in the latter case; this
corresponds to the fact that only one-half of the hybrid genes is represented
in the inbred parent strains, while the genes of parent strains are all present
in the gene sets of the hybrids.

In the course of phylogenetic evolution, gene sets which are characteristic
of the more highly differentiated species have gradually evolved from the
gene sets of other more primitive ancestor species, and the organismal
differentials have undergone a corresponding development. On the other hand,
in the fertilized ovum the chromosomes and gene sets are the same as in the
cells of the adult organism. Yet there are indications that in the fertilized tgg
the individuality differential is not yet fully formed, but that it develops from
a precursor substance in the course of embryonal life; it is certain that at least
the mechanism which makes the differences in the individuality differentials
of host and transplant manifest undergoes such an evolution. Even in very
young guinea pigs, before the age of sexual maturity, these mechanisms of
defense against a strange individuality differential are not yet fully developed,
.as is indicated by transplantation experiments of tissues into hosts of various
ages. The connective tissue reaction is diminished in intensity and the lympho-
cytes may have therefore a better chance to become active in these young
animals.

As to the number of genes which determine the nature of the individuality
differentials, no definite statement can be made. However, considering the
difficulty in eradicating reactions against other than autotransplants, even in
individuals belonging to strains closely inbred through a large number of
generations, and considering the improbability of ever obtaining an autoge-
nous reaction after homoiotransplantations in non-inbred strains, also in view
of the fact that the reactions are so very finely graded and that a homoio- or
syngenesio-reaction after transplantation of a piece of tissue belonging to
another individual may appear as late as several months following transplanta-
tion, it is very likely that the number of genes entering into the composition
of the individuality differential is great and that perhaps all the genes partici-
pate, although different ones possibly to a different degree. Both organismal
differentials and organ and tissue differentials depend entirely, or to a large
extent, on the constitutions of chromosomes and genes ; but the genes and
combinations of genes which preponderate as determiners of these two types
of differentials are evidently not the same and there are indications that it is

10 THE BIOLOGICAL BASIS OF INDIVIDUALITY

certain gene sets rather than individual genes which represent the precursors
of organismal differentials. While the individuality differential is therefore
determined by the gene composition, it is not identical with the gene sets
but differs from them in a way in which other characters of the adult organism
differ from the gene sets. Gene hormones may mediate the effects of the genes
on the organismal differentials; also, other factors which form part of the
environment in which the organism develops may conceivably modify the
development of the individuality differential from its precursor substances, and
there are indications that adaptive processes which may take place in the inter-
action between host and transplant may modify these differentials, or at least
their manifestation. Such adaptive processes are very prominent in serial
transplantations of tumors. Yet there remains constant the difference between
the individuality differentials and the organismal differentials in general on
the one hand, and the differentials of specific organs and tissues on the other
hand; the organismal, and in particular the individuality differentials are the
same in all the tissues and organs within the same organism, while each organ
and tissue has in addition its specific differential.

There exist, then, perhaps conditions which may complicate the direct
relation between organismal differentials and the gene sets which ultimately
determine the nature of these differentials. There are, in addition, several other
complicating factors. In no case is it possible to determine the organismal, and
in particular the individuality differentials directly, but we determine the
consequences of the interaction of the organismal differentials of host and
transplant; we observe their manifestation and this depends not only on the
nature of the organismal differentials but also on the amount of organismal
differences produced and given off by the host, and especially also by the
transplant, on the degree of reactivity of the host against strange differentials,
on the mode of attack on the part of the host, and on the ability of the graft
to resist these injurious conditions. A tissue that is readily injured will not
give off its individuality differentials for any length of time, because it will
be converted into a lifeless foreign body which has lost its specificity.

Notwithstanding these difficulties it is possible to analyze the nature of the
organismal differentials if we carry out a number of sufficiently varied experi-
ments, and by these means it is also possible to follow the formation of the
organismal differentials in the course of phylogenetic evolution and onto-
genetic development, and the gradual refinement of these differentials as indi-
cated by the appearance and increasing significance of the individuality
differentials. However, this phylogenetic and ontogenetic development is not
represented by a straight ascending line. There are various branches given
off by the main line which indicate the development of mechanisms closely
resembling the active individuality differentials, but- which may not be
identical with the latter ; in such instances it may not be possible to determine
whether we have to deal with real organismal differentials, to which the
criteria we have discussed apply. In particular, it is impossible to apply this
term in the strict sense to unicellular free-living organisms. Thus the attempt
to join together the main body of a rhizopod and a pseudopod, which has

INTRODUCTION 11

been cut off from either the same individual or from a different individual,
succeeds when there is an autogenous relationship between the remaining part
of the cell and the pseudopod, but it leads to abnormal reactions when there
is a homoiogenous relationship. The nature of the reaction seems to depend
on a specific sensitive state of the ectoplasmic layer of the cell protoplasm, and
also in part on the diffusion of certain substances into the surrounding
medium. In various species of Paramecium peculiar agglutination reactions
between different individuals belonging to a certain species, have been
observed, which are characteristic of each species. In general, cells belonging
to the same group do not agglutinate with one another, but individuals be-
longing to well defined, strange groups of the same species do agglutinate.
These reactions resemble those of organismal differentials insofar as rela-
tionship between different organisms is a factor which determines the reac-
tion, but they differ from organismal differential reactions in that the reaction
seems to depend upon the condition of a restricted portion of the unicellular
organism and that specific functions are accomplished by means of these
reactions, which are those of certain organs rather than of organismal differ-
entials. A similar problem arises in regard to the relations between sperma-
tozoa and eggs. These relations are in certain respects comparable to those
existing between graft and host; but while in the latter an autogenous rela-
tionship is most adequate, in the case of sperm and ova a homoiogenous
relationship seems in many instances to be as good, or even better, than an
autogenous condition. Indeed, in some organisms, plants as well as animals,
specific mechanisms exist which tend to prevent autofertilization. These
mechanisms depend apparently upon the reaction which takes place, perhaps
by means of contact substances, between certain somatic cells belonging to the
female organism and the spermatozoa or its analogue in plants, or in other
cases they depend upon the direct interaction between egg and spermatozoon.
In the adult organism the various organs and tissues may possess, in addi-
tion to the typical species and individuality differentials, structures and sub-
stances which are specific not only for this particular organ and tissue, but
also for the species to which the organism belongs. The organs and tissues
of related species as a rule resemble one another more closely than those of
more distant species. The substances which are the bearers of these character-
istics may, therefore, have something in common with the species differential
or even with the individuality differential substances. However, they differ
from the latter in that they are peculiar to a certain organ or tissue. They
are not identical with the typical species differentials ; this is indicated also by
the fact that their chemical reactions may differ in certain respects from
those of the typical species or individuality differentials. We may designate
these characters and substances as secondary or accessory organismal differ-
entials. In many cases it is not possible to determine to which of these two
classes a certain substance belongs and then we must be content to apply the
term organismal differential, and in particular, species and individuality
differential, in a general way, comprising both the primary and secondary or
accessory organismal differentials.

12 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Not every substance produced by tissues or accumulating in certain organs
possesses an individuality differential. Many hormones, and the vitamines,
do not have individuality differentials, while other hormones have at least
some of the coarser organismal differentials. It is especially the most complex
protein substances which act as bearers of organismal differentials. But there
are end-products of embryonal differentiation in which the cells, which give
origin to certain tissues, have been largely replaced by secondary paraplastic
substances, such as the lens fibers of the vertebrate eye. In these the finer
organismal differentials have apparently disappeared and only some of the
coarser ones have remained; instead, the organ differentials have become
more prominent. This is indicated if serological tests are used. However, if we
use finer tissue reactions as a test, the presence of individuality differentials
can be demonstrated even in tissues of this kind, as shown in the recent
experiments of H. T. Blumenthal. He has demonstrated that after homoio-
transplantation of a lobe of thyroid gland, and of pieces of liver or kidney,
from guinea pigs to other non-related guinea pigs, the number of lymphocytes
circulating in the blood rises, about five to seven days after transplantation,
by approximately 15 to 25 percent, and having reached this maximum it
begins to fall again. After transplantation of cartilage however, such a rise
is lacking entirely or almost entirely, because the amount of homoiodifferential
given off by this tissue is apparently insufficient to reach the threshold neces-
sary for the reaction. After syngenesiotransplantation the increase in lympho-
cytes begins, on the average, at a later date and remains lower. After hetero-
transplantation it is the polymorphonuclear leucocytes which show an increase
in the general circulation ; later they fall to the normal level and this phase is
followed by a second phase in which the lymphocytes rise ; after a few days
this latter rise is likewise followed by a fall. As far as we can judge, these
changes in the number and character of the blood cells are specific; inert
foreign bodies, for instance agar, do not bring about such a rise. The effects
produced by transplants on the lymphocytes and polymorphonuclear leuco-
cytes circulating in the blood are closely parallel to the effects which the trans-
plants exert locally on the lymphocytes and polymorphonuclear leucocytes, but
some of the effects of the strange organismal differentials are more readily
demonstrated by a study of the cell and tissue reaction taking place around
the grafts. By means of this general reaction it can be shown that the lens of the
eye also possesses an individuality differential, although, if serological tests are
used, it seems to be devoid of species and individuality differentials.

We see, then, that tissues give off substances which differ in their effects in
accordance with the genetic relationship of the tissues to the host organism. In
their own natural habitat these substances are of an autogenous character and
do not incite any abnormal reaction; but in accordance with the genetic
strangeness existing between transplant and host, they assume the character
of toxic substances, which call forth abnormal reactions in the host. In near
relatives these substances — the organismal differentials — act as syngenesio-
toxins ; in a strange individual of the same species they act as homoiotoxins,

INTRODUCTION 13

and in a different species, as heterotoxins. The chemical nature of the latter
is distinct from that of the syngenesio- and homoiotoxins.

Furthermore, these substances, the organismal differentials, diffuse not only
into the area directly surrounding the transplanted piece, but they also enter
the circulation and are carried by the blood and lymph to more distant organs.
This may be concluded from the observation, already stated, that transplanta-
tion of a normal piece of grafted tissue induces changes in the relative pro-
portions of the circulating blood cells, which are parallel to the degree of
relationship or strangeness between host and transplant and which depend
therefore on the nature of the organismal differentials of host and graft. Such
substances, corresponding to individuality and species differentials, enter the
blood and exert their effects in distant parts and thus resemble hormones in
their action.

When they have reached and are retained in certain organs, such as spleen
and bone marrow, they may, in addition, stimulate the formation of immune
substances, since they are strange to the individual or to the species in which
they circulate. It is especially the organismal differentials derived from a
different species, or even from a different individual, which initiate defensive
processes of immunity ; being strange to the new host they disturb his equilib-
rium, which is attuned to substances possessing his own specific organismal
differentials. These strange substances act, therefore, as antigens. Organ
differentials as such may not be strange to the host, in this sense, and as a rule
they function as antigens only in combination with a strange organismal
differential.

If, then, we may consider it an established fact that when tissues are trans-
planted from one to another individual of the same species, including even
nearly related individuals such as brother or sister, substances are given off by
these tissues which call forth noticeable reactions on the part of the host cells,
might it not be possible, or even probable, that such substances, acting on
nearby tissues as contact substances or on farther distant tissues as hormones,
are also given off in the animal's own organism ; but that, here, instead of
operating as disturbers of the tissue equilibrium, on the contrary, they serve
as instruments by means of which the tissue equilibrium is maintained and
regulated in such a manner that it is best adapted to the normal cooperation of
the various tissues in the interest of the entire organism, and thus to the
normal functioning of the organism as a whole? Such substances, represent-
ing the individuality differential, if discharged into an animal's own organism
may then be designated as autogenous substances. If two tissues, possessing
two different individuality differentials, adjoin each other, signs of disharmony
develop, which are partly or largely due to the action of disharmonious in-
dividuality differentials. This applies, for instance, to homoiogenous skin
transplants. Conversely, may we not assume that since the epithelial cells in
the normal skin remain at rest, this is due at least partly to the action of the
autogenous substances which keep the neighboring epithelial cells as well as
the underlying connective tissue and lymphocytes in a quiescent state?

14 THE BIOLOGICAL BASIS OF INDIVIDUALITY

However, a disequilibrated condition may occasionally be observed even
after allotransplantation, for instance, if pigmented skin is transplanted into
a defect in white skin of the same guinea pig. Notwithstanding the identity of
the individuality differential in this case, the transplanted pigmented epidermis
begins to infiltrate the neighboring white epidermis for a considerable time,
but ultimately a new tissue equilibrium is established and then the autogenous
tissues live harmoniously side by side. The pigmented epithelium is the more
active, vigorous tissue, and stimulated by the processes connected with and
following transplantation it asserts its superiority over the white epithelium
until this stimulation has died out ; yet neither connective tissue nor lympho-
cytes of the host are unduly activated under these conditions, because host and
graft possess the same individuality differential.

There exists, then, a mutual adaptation to one another of tissues bearing the
same organismal differential, and there exists, also, a mutual adaptation be-
tween the blood plasma and the various tissues belonging to the same in-
dividual. It is these harmonious interactions which make the unity of the
organism possible and which are perhaps the most characteristic feature of
the living organism as an individual. But not only are the substances charac-
teristic of each individual different from those characteristic of any other
individual and in this sense specific; there is, besides, a second type of speci-
ficity, which may be designated as specific adaptation. By specific adaptation
we mean that it is the individuality, species, order or class differentials, in
general the organismal differentials, attached to the various tissues or to sub-
stances derived from these tissues, which determine how suitable and effective
the interactions between the tissues and substances are in the performance of
certain functions. If the respective organismal differentials are the same in the
tissues or substances, the interaction is most perfect. This statement applies,
for instance, to the interaction between tissue extracts, blood plasma and
blood serum. The character of the organismal differentials attaching to these
various substances determines how effective the coagulating power of the
extract is, and how effective also the inhibiting action of the blood serum will
be.

We may then distinguish tivo types of adaptation within the organism. The
first one is well recognized; it is represented by the normal interaction of
various organs and of parts of organs, and by the transmission of stimuli
through the nervous system, through hormones, and through certain other
mechanisms. This is the basis of what might be called the mosaic type of in-
dividuality. The second type is the adaptation which depends on the identity
of the individuality differentials of tissues. The integrity of the organ func-
tions is largely based on this identity of the organismal differentials. But in
addition a number of chemical interactions in the organism, of which only
one example has been mentioned, depend specifically on the character of the
organismal differentials which are carried by these substances. This is the
basis of what might be called the essential individuality, in contrast to the
mosaic type.

Under some conditions normal tissues act as though they were abnormally

INTRODUCTION 15

stimulated ; they may assume increased growth and at the same time undergo
cerain structural and metabolic alterations. These characteristics may be main-
tained permanently and when this has occurred, then normal tissues have been
changed into cancerous tissues. It can be shown that the latter still possess
essentially the organismal differentials of the host from which they are de-
rived ; but they differ from the latter by an increase in the growth momentum
which enables them in certain cases to overcome, in a new host, injurious con-
ditions to which normal tissues would succumb ; they also seem to possess a
greater ability to adapt themselves to strange hosts and, moreover, they give
off more efficient antigens than do normal tissues.

It is essential for the completeness or fulfillment of the individuality in
higher organisms that the integrity of the individuality differentials be main-
tained. An intrusion of strange substances not bearing the same individuality
differential sets in motion reactions which lead to their splitting, their destruc-
tion, or their elimination, in some instances after they have been made innocu-
ous through conjugation with other substances. The primary local tissue reac-
tions, as well as the secondary local reactions of allergy and the general reac-
tions of immunity, serve this purpose. But the organism must also build up
his species and individuality differentials out of non-specific material or out
of material which carries unsuitable organismal differentials ; the processes of
splitting by means of digestion and those of syntheses lead to the production
of building stones endowed with the right type of specificity, and they bring
about the replacement of lost tissue and the addition of new material. The
specificity of enzymes plays an important part in these operations. There are
thus strong indications that the individuality differential has these functions :
(1) to co-ordinate and to equilibrate the mutual interaction of adjoining and
also of some distant tissues in such a way that the inner integrity of the in-
dividual is insured, and (2) to combat admixtures from strange organisms
and perhaps also to react against foreign bodies which are devoid of organis-
mal differentials.

The organism is, then, a harmonious whole, a combination of the mosaic
and of the essential type of individuality; in it, therefore, not only the organ
functions are adapted to one another, but also all the various tissues, though
apparently functionally unrelated, are specifically adapted to one another,
owing to the nature of their organismal differentials. This latter adaptation is,
above all, what characterises the individual. Such a harmonious relationship
must be based on resemblances or identities in certain chemical structures of
the most important and complex substances which enter into the building of
the organism, especially substances of a protein nature. Accordingly, it has
been established that the hemoglobins and hemocyanins, derived from various
species, or from still larger groups of animals, are the most nearly identical in
structure in the nearest related animals and are the more dissimilar in struc-
ture the farther distant the species are. In accordance with what we have
already stated, we may assume that the same chemical gradation in the struc-
ture of the organism in correspondence with phylogenetic relationship must
go still further, not only each species but each individual possessing its

16 THE BIOLOGICAL BASIS OF INDIVIDUALITY

chemical characteristics, which differ from those possessed by every other
individual of the same species.

Two possible schematic representations of the chemical constitutions of two
different individuals may be considered: (1) Individual A: Tla — T2a — T3a —
T4a. . . . Individual B: Tlb— T2b— T3b— T4b. (2) Individual A: Tla— T2b—
T3c — T4d. . . • Individual B: Tlm — T2n — T3o — T4p. Tx, T2, T3, T4 represent
organ and tissue differentials, such as those of liver, kidney, thyroid, cartilage
and ear. Provisionally they may be assumed to be identical in two individuals
belonging to the same species and variety, although this assumption may not be
entirely correct, a, b, c, d represent the individuality differentials which are
different in the corresponding organs and tissues of two individuals. In the
first mode of representation all the organs and tissues of individual A have
the factor a in common, while in individual B all organs and tissues have the
factor b in common ; a is the individuality differential of individual A ; b is
the individuality differential of individual B. In the second mode of represen-
tation each organ and tissue of individual A has its own specific factor; one
has a, the other b, a third one c, and so on, while the organs and tissues of
individual B also are distinguished from one another by specific factors, m, n,
o and p . . . but the factors in individual A differ from those of individual B ;
the factors a, b, c and d ... in their totality represent the individuality differ-
ential of individual A, while the factors m, n, o and p ... in their totality
represent the individuality differential of individual B. According to the
second mode of representation each organ and tissue differential of an in-
dividual possesses its own index of individuality, and every organ and tissue
would possess a secondary or accessory individuality differential. According
to the first mode of representation the individuality differential attached to
each organ and tissue of individual A would be the same, and those attached
to the individuality differentials of the organs and tissues of individual B
would be identical ; these individuality differentials would correspond to the
primary individuality differentials.

It will be necessary to decide between these two possibilities. If we adopt
the first mode of representation, the various tissue constituents, lymphocytes,
fibroblasts, blood vessels, polymorphonuclear leucocytes, would react against
all the constituent parts of individual A in about the same manner, because
these parts have the same factor in common. The same applies to constituent
parts of individual B. But if we adopt the second interpretation, each of these
tissue constituents would have to remember — to speak metaphorically — an
endless number of tissue and organ factors which are attached to the con-
stituents of its own body and would have to distinguish these from a multi-
plicity of tissue and organ factors possessed by a different individual. Corres-
pondingly, the blood serum of individual A would be favorable to all the con-
stituent parts of individual A, and would be less favorable to all the consti-
tuent parts of individual B, because the factor a, or a factor correlated with a,
in the blood serum of individual A would be adapted to the tissue and organ
factor a of individual A, and would be less favorable to factor b of individual
B. The second concept would only with great difficulty explain these specific

INTRODUCTION 17

reactions between the tissue constituents and the blood serum of the host and
the transplant. We may then conclude that each organ and tissue of individual
A has in common a chemical factor which differs from the corresponding
factor in individual B ; but in addition, certain organs and tissues may possess
accessory or secondary individuality differentials, which are peculiar to these
organs and tissues.

The individuals among the higher organisms possess, then, two kinds of
adaptive mechanisms : the first one is that represented by the functioning and
interaction of tissues and organs within the individual, and the second is based
on the fact that the tissues and organs in the same organism possess the same
individuality and species differential, and that other individuals or species
carry different organismal differentials which are graded according to the
phylogenetic relationship. In consequence of this functional and structural
constitution, very specific relationships have developed within the individual
organism and between the various inidviduals within the same species, genus,
order and class. These intricate and complex specificities of both the mosaic
and essential type in their totality constitute the characteristic feature of the
individual.

However, within the functioning organism, as well as in the relations be-
tween different individuals, the organ and tissue specificities are more obvious
than the individuality differentials, the effects of which are of a more subtle
nature. Also, in the sphere of social-psychical relations it is the function of
organs, above all, the nervous system and the endocrines, which appears as the
significant element. Yet, the individual organism is an integrated whole and
changes in one organ and tissue are followed as a rule by changes in other
organs and tissues. This applies also to those organ and tissue modifications
which occur during the process of ageing and disease, and also to interactions
between organs which concern primarily vegetative functions, as well as those
which control the psychical-social activities, and both of these two latter kinds
of processes are linked together. Ever}7 change in a part of an individual affects
the individual as a whole, although different types of interferences may differ
in their effects on other parts of the organism and on the individual as a whole.

Individuality, especially its social-psychical aspect, entered the experience
of man in very early periods of history; it helped to shape tradition and was
one of its important components, and as such it took part in orienting the rules
of conduct and of law. Gradually, under its influence, philosophical systems
and various metaphysical concepts arose. But it was only during the 19th.
century that the concept of individuality was fully dissociated from its prac-
tical social implications and that it began to be considered a biological problem;
from then on observations and experiments in various fields of biology have
contributed to its analysis and more definite problems concerning the in-
dividual and individuality were formulated. We shall here record a few of the
principal contributions concerning the biological aspect of individuality.

The botanist, Naegeli, conceived of a substance peculiar to each individual
or species and he distinguished it from other less important constituents of
the living matter as the idioplasm. It served as the carrier of the characteristics

18 THE BIOLOGICAL BASIS OF INDIVIDUALITY

which were inheritable and transmitted from generation to generation. The
botanist, Strassburger, and the zoologist, O. Hertwig, localized this hereditary
substance in the nucleus. Subsequently, based on the work of Mendel and of
those who rediscovered and continued his investigations, the idioplasm became
more sharply defined and transformed into sets of discrete units, the genes,
which are contained in the female and the male germ cells, and especially in
the chromosomes of the cell nucleus. But in addition to these genes located in
the chromosomes, also constituents of the egg cytoplasm were considered as
determiners of the distinctive features of the organism, and some geneticists
(Correns, v. Wettstein and Kuhn) have assumed that genes, equivalant to
those situated in the chromosomes, may also exist in the cytoplasm of the egg.

During the second half of the last century certain observations of surgeons,
who grafted tissues, pointed to a fargoing specificity and individualization in
the tissues comprising the higher organisms. The early experiments of the
French surgeon, Oilier, showed that only autotransplanted bone was able to
survive. Later experiments with skin and various other organs or tissues, such
as ovaries, and also with benign tumors, indicated that while homoiotrans-
plantation might perhaps succeed, autotransplantation was more favorable.
Yet, towards the end of the last century biologists found that the joining to-
gether of parts of embryos, as well as various kinds of homoiotransplantations
of invertebrate and lower vertebrate tissues, may give good results, and that
even heterotransplantations were successful under certain conditions. Not-
withstanding the experiences mentioned above, in the transplantation of
tissues in adult mammals no sharp distinction, as a rule, was made between
the results of auto- and homoiotransplantation. This was true even of the
work of Reverdin and Thiersch, who introduced skin-grafting into surgery
for therapeutic purposes. While, as stated, some of these observations sug-
gested that biochemical differences might exist between different individuals,
including those belonging to the same species, on the whole, the differences
between species were stressed rather than the differences between individuals,
and it was only within the last thirty-five or forty years that the distinctions
existing between the tissues of different individuals of the same species re-
ceived more attention.

In the meantime, discoveries in biochemistry, comparative anatomy and
embryology had led to a further analysis of the specific structure of organisms.
The biochemist, Huppert, in 1895, in a lecture on the persistence of species
characters, referred also to the differences which, according to Rollett, existed
between the hemoglobins of different species as regards their elementary
composition, solubility and shape of crystals. He concluded that not only the
chemical constitution of various substances differs in different species, but
also that the metabolism of these substances is distinct and characteristic of
these species. Four years later Rabl, apparently under the influence of Hup-
pert's suggestions, discussed the differences in the microscopic structure of
homologous tissues in different species. While the histologic structure of the
liver could not be distinguished, it was discovered that the lens of the eye
differed in different species. This difference was maintained during the various

INTRODUCTION 19

stages of development and also throughout life. Furthermore, the organ-
forming, germinal areas of His, and the cells which compose them, were ob-
served to be specific in their form and in the possession of organ-specific sub-
stances, and His traced this specificity back to the germ layers, to the blastula,
and, in the end, to the different parts of the unsegmented egg. It is this
specificity to which he attributed the differences in the embryonal develop-
ment of different species. Accordingly, Rabl and, in particular, Conklin were
able to follow the development of organs from the egg through the first seg-
mentations and through later stages to the complete organism ; protoplasmic
movements and the character of mitoses were found to correspond to the
specific structure of the species. Rabl concluded that the specific characteristics
of the organism, or rather of the species, as a whole, determine the specific
features of all the organism's component parts — its organs, tissues and in-
dividual cells. In the discussion of this investigator we find, therefore, already
a suggestion that besides the differences in the organs and tissues which dis-
tinguish different parts of the individuals as a species, and even different parts
in the unsegmented ova, there is something in the species as such which
determines its characteristic development in both the structural and chemical
aspects. This species peculiarity became manifest also in transplantations;
homoiotransplantations as a rule succeed, while heterotransplantations are
unsuccessful. It is evident also in blood transfusions, which may be considered
as modified transplantations.

Oscar Hertwig named the factor which made homoiotransplantation possi-
ble, but which caused incompatibility of heterogenous parts of organisms,
"vegetative" affinity, and contrasted it with "sexual" affinity which was re-
sponsible for successful fertilization. He believed that in plants as well as in
animals vegetative and sexual affinity are similar in their manifestation and
are due to the same underlying factors. These suggestions of Hertwig were
taken up later by W. Schultz, when he tried to prove the parallelism between
hybridizability and transplantability in the tissues of vertebrates. However,
as we shall see later, while a certain parallelism is noticeable between these two
processes, there are also some marked differences.

It is noteworthy that the concepts of Naegeli and Hertwig related mainly
to species, not to individuals. In the meantime, towards the end of the last
century, the development of the new science of immunology had set in, but it
was likewise primarily concerned with species differences, and only sec-
ondarily and somewhat later, with differences between individuals. But the
investigators in the field of transplantation and immunity influenced, also,
some biologists, as is noticeable in the writing of Fick, who in 1907 added to
the concept of the species plasma that of an individual plasma. The fertilized
egg of one individual was assumed to differ from those of all other individuals
of a certain species in regard to the character of its organ-forming substances ;
however, a distinction was made between the living protoplasm, in which
these specificities applied, and the trophoplasm, which represents merely food
and structural material, and which was less specific or nonspecific. It was
recognized that the living protoplasm consists essentially of protein. Each

20 THE BIOLOGICAL BASIS OF INDIVIDUALITY

organ-forming substance has individual peculiarities which depend upon the
presence of special chemical groups or on stereoisomeric groups in these pro-
teins, but it was not considered probable that this specificity was based on the
existence of giant protein molecules, which Pfliiger, and later Verworn,
identified with the living protoplasm. It may be added that Herbst subse-
quently attributed individual differences to sidechains or smaller radicles of
these complex substances rather than to the characteristic structure of giant
protein molecules as a whole. However, Fick did not interpret the individual
specificity of an egg as due to a single specific substance, but to the sum of
peculiarities in the different organ-forming substances in the egg, which latter
had been postulated as early as 1880 by the botanist Sachs. Similarly, the
individual plasmas of the spermatozoon and of the unfertilized ovum were
held to be united in the fertilized ovum, but this combination was thought to
lead not merely to a summation of the properties of these plasmas, but to a
new specificity. The individuality of the egg represented thus a mosaic of
individual peculiarities in the organ-forming substances, and the individual
plasma of Fick is therefore quite distinct from the concept of the individuality
differential. In the first place it refers to the constitution of the egg and not
to the differentiated and integrated individual, and, insofar, it might corre-
spond to precursor substances of the individuality differentials. But it differs
from the concept of the individuality differential in that it represents the
peculiarities of the mosaic of organs and tissues, or of their precursors, the
organ-forming substances of the individual rather than those of a substance
which is common to all of these organs and tissues. Subsequently Correns re-
stricted the meaning of the "individual plasma" of Fick and substituted for
it the specific plasma of pure lines in the sense of Johannsen. However, it
is clear that in the higher organisms which propagate by fortuitous cross-
fertilization such pure lines do not exist and transplantation experiments
indicate that among the higher classes of animals pieces of skin of different
individuals differ from one another. As far as we know now, the results of
homoiotransplantation are never quite the same as those of autotransplantation.

We see, then, that Fick's concept of "individual" referred to organ speci-
ficity, to inherited peculiarities of organs or their differentials. This appears
also to be the concept of G. Jaeger, who many years previously had postu-
lated differences in the chemical constitution of individuals belonging to the
same species on the basis of differences in scents, which may serve to dis-
tinguish individuals and species. This kind of specificity concerns individual
differences in certain tissues and not something which is the same in all the
tissues of an individual.

Likewise the term "homology," as used by the comparative anatomist
Gegenbaur, expresses the similarities in the phylogenetic evolution of corre-
sponding organ systems. Both comparative anatomy and paleontology con-
sider the similarity inherent in the organs in different species as an indicator
of their phylogenetic relationship, and they trace evolution by means of these
homologies found in fossils and in still existing species. In these instances we
have again to deal with organ specificities and therefore with something
distinct from the organismal differentials.

INTRODUCTION 21

To return to the individuality in the structure and chemical constitution of
the egg, the conceptions of Fick and others evidently do not localize these
characteristics in the nuclear genes, but in the cytoplasm. There can be no
doubt at the present time as to the significance of the chromosomes and genes,
or other subdivisions of chromosomes, and of the arrangement of the latter
in the chromosomes, for the determination of species and individual characters
although differences of interpretation exist as to the mode of their repre-
sentation in the chromosome. There is further no agreement, as yet, among
investigators as to the importance which must be attached to other factors
in addition to the chromosomes. We have referred already to the views of
Correns, von Wettstein and Kuhn, who assume that also the cytoplasm
carries genes which determine development ; this conclusion was based on the
results of species hybridizations in which reciprocal combinations gave differ-
ent results and in which an influence of the maternal germ cells was noticeable,
in accordance with the views of Jacques Loeb (1916), who had restricted the
Mendelian mode of heredity to certain individual characteristcs of organs
and tissues, while he believed that species characteristics are determined by
the cytoplasmic structure of the ovum. In a similar way von Wettstein assumes
that the hereditary substance which is localized in plasma differs in its signifi-
cance from that of the genes of the chromosomes. He suggests that it is the
former which is the real substratum of the developmental processes, whereas
chromosomal genes and environmental factors control and direct the processes
which are dependent upon the structure of the cytoplasm.

However, the majority of geneticists at the present time hold that the genes
are the substratum which determines the hereditary transmission not only of
the individual but also of the species, genus and class characteristics from
generation to generation, and that the genes impress upon the cytoplasm of
the ovum, by their interaction with the latter, the structure which is specific
for each species. We would, accordingly, have to assume that the individual,
species, genus, order and class differentials, in general the organismal differ-
entials, are preformed in both egg and spermatozoa and that, thus, precursors
of the organismal differentials exist in these germ cells, the nature of which
is determined by the genes of the egg and spermatozoon. However, whether
all the genes participate equally in the determination of the organismal differ-
entials, or whether some of the genes predominate in this function over others,
is not known. Inasmuch as no difference has been found between the male and
female sex in regard to the transmission and possession of the organismal
differentials or their precursors, it may be assumed that the Y chromosome,
which is concerned with the sex differentiation of the fertilized egg, does not
play an essential role in the determination of the constitution of these pre-
cursors. This would accord with the indications which exist that the Y chromo-
some does not as a rule carry demonstrable alleles of sexlinked genes, at least
not many of them. This interpretation of the nature of the precursors of the
organismal differentials is the most probable one, because egg and spermato-
zoon, as far as we know, contribute equally to the constitution of these pre-
cursors. In regard to the organ and tissue differentials, however, which
characterize and distinguish the various organs and tissues in the same indi-

22 THE BIOLOGICAL BASIS OF INDIVIDUALITY

vidual, species, and so on, these depend in all probability on the structure of
the egg and on organ- forming substances which are distributed in a definite
and characteristic manner in the egg of each species, and on the interaction
of the organ- forming substance with the nuclear genes, in accordance with
the fact that genes have a specific relation to organ peculiarities of individuals
or species.

There exist, then, in the fertilized egg not only the precursors of the organis-
mal differentials but also those of the various organ and tissue differentials,
which latter, singly or in their totality, likewise characterize an individual or
species and which constitute the mosaic parts which have served in the study
of Mendetlian heredity.

Comparative anatomy, embryology, genetics and biochemistry have thus
contributed to the analysis of what may now be designated as organismal and,
in particular, as individuality differentials on the one hand, and organ and
tissue differentials on the other hand. Furthermore, at about the time when
biochemists, anatomists and embryologists began to discuss the problem of the
chemical and structural basis of species differences, an important additional
stimulus to the analysis of this problem was given and new viewpoints were
revealed by the development of immunology. Following the discoveries of
Pasteur, Behring, Roux, Buchner, Ehrlich, Metchnikoff, Gruber, Kraus and
others concerning the production of an active and passive immunity against
microorganisms and their toxins, and the mechanisms underlying this im-
munity, it was found by Bordet, Tschistowitch and other investigators, that
similar immune reactions can be called forth against bodyfluids and cells of
organisms belonging to different species. As a result of this immunization
various kinds of antibodies, such as precipitins, agglutinins, hemolysins and
complement fixing substances are produced, corresponding to the antibacterial
and antitoxic substances which had previously been discovered. These find-
ings suggested the possibility of differentiating different species by means of
such antibodies. If blood sera or other substances of a protein nature from
various species were injected repeatedly into rabbits or other animals, immune
sera were obtained against the antigens used. The interactions of these immune
sera with the antigen and with other analogous substances obtained from
nearly related or more distant species were then compared and the results of
these tests served as indicators of the relationship between the various species
(Grunbaum, Nuttall).

In a similar way the interaction of performed bodyfluids and cells derived
from different species was tested directly (Friedenthal). Landsteiner (1901)
studied the interaction of individual human sera and erythrocytes in order to
find differences between different individuals; instead, he discovered the ex-
istence of four different blood, groups into which human beings can be ar-
ranged. Hamburger (1901), and later, Abderhalden, pointed out that proteins
derived from a foreign species are toxic if introduced parenterally and that it
is the function of the gastrointestinal organs to split these proteins into simpler
constituents, which are no longer characteristic of the species from which they
were derived and which at the same time have lost much of their toxic char-

INTRODUCTION 23

acter. The tissues of the intestines and various other organs then build up
from these split products new complex proteins which possess the specific
species character of the new host. Hamburger (1903) assumed that special
chemical groups characterize the different proteins of a certain species and
that these groups are common to the various tissues of the same organism.
Similar were the conceptions of Obermayer and Pick, who at this time had
begun their investigations into the chemical factors which determine the
species-specificity of proteins. Hamburger extended these ideas also to in-
dividuals and he held that the proteins of each individual have a chemical
characteristic in common, which differs from that of every other individual
belonging to the same species. Subsequently it was found that in addition to
the proteins, also carbohydrates and lipoids, as well as other simpler sub-
stances, if they are combined with foreign proteins (Landsteiner) can serve
as antigens which give rise to specific immune bodies, and that these non-
protein substances as such may interact in a specific way with these antibodies.
It had thus become possible to differentiate by means of immune reactions
between substances characteristic of different species and thus to obtain tests
for species differentials ; also, in a few cases, to differentiate by these means
even between different individuals belonging to the same species (Ehrlich and
Morgenroth, Todd).

Furthermore, a distinction can be made in this way, not only between species
differentials but also between the characteristic constituents of different
organs and tissues within the same organism (organ differentials) ; and it was
found that, as a rule, it is necessary to combine the organ differentials of one
species with a strange species differential in order to produce organ-specific,
immune substances ; these combined antigens are an expression of the intimate
relations which exist also embryologically and genetically between these two
types of differentials or their precursors. In certain protein substances both
species-specific and organ-, tissue-, or substance-specific groups may be
present.

It has been mentioned above that observations made in the grafting of
tissues led to the conclusion that constitutional differences may exist between
individuals of the same species ; we have referred already to the work of
Oilier, who in the second half of the last century found differences between
the readiness with which periosteum of one animal can be transplanted to the
same individual and to other individuals. Similar differences were noted also
in the transplantation of other organs, above all, in the skin-grafting which
Thiersch perfected ; according to Schoene, Thiersch had suggested biochemical
characteristics as the cause of these differences. Somewhat later, Knauer
found that also in the case of ovaries, autotransplantation was more successful
than homoiotransplantation. Between 1901 and 1907 we carried out, in rats
and dogs, several series of transplantations of mammary gland adenoma,
which were intermediate in character between normal and cancerous tissues,
and found that while autotransplanted pieces continued to live and in some
cases proliferated, homoiotransplanted pieces died.

We recognized three factors as responsible for this result: (1) the exist-

24 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ence of certain conditions in the bodyfluids of the host, which determine the
suitability of the animal's own autogenous bodyfluids and the unsuitability of
homoiogenous bodyfluids for the transplant. This conception implies a factor
in common to the bodyfluids and to the cells of each individual. In subsequent
investigations to which we have referred already also Todd (1913) recognized
the existence of a factor common to and characteristic of all the cells of an
individual ; but according to this investigator in near relatives this factor
might be the same. (2) Growth factors inherent in the transplant, and
(3) extraneous growth factors circulating in the bodyfluids of the host, similar
to those given off by the ovary under certain conditions. These observations
were subsequently confirmed by Borrel, Ribbert, and they were extended to
malignant tumors by Bashford and Tyzzer. In 1909, Borst and Enderlen re-
ferred the difference between auto- and homoiotransplantation of blood vessels
to "biochemical differences" between individuals of the same species. How-
ever, as we shall show later, these "biochemical differences" are not identical
with individuality and species differentials. With Addison, we extended our
investigations as to the effect of the phylogenetic relationship of tissues be-
longing to different species on the fate of the transplants, and Schoene studied
the influence of family relationship on transplantability. In the following
years, W. Schultz analyzed the relation between hybridizability and trans-
plantability of skin. In the meantime tumor transplantations had been carried
out on a large scale, and while at first, especially in the work of Jensen and
Ehrlich, problems of immunity played a prominent role in the analysis of con-
ditions which determine the result of transplantations, we and, subsequently,
Peyton Rous used the transplantation of tumors as a method for studying
tissue growth in general and we emphasized the close relations which exist
between the growth of normal tissues and of tumors.

The writer, in association with Addison, Myers, Hesselberg and others,
noted the significance of lymphocytes, and also of fibroblasts and vascular
endothelia, in the reaction of the host against the transplant. In the case of
tumors, it is especially the various investigations of Murphy and his collabora-
tors which subsequently showed the significance of lymphocytes in the re-
sistance of animals against inoculated pieces of cancers. In normal tissues we
found that the time of appearance and the intensity of the lymphocytic reac-
tion developing around a transplant in combination with connective-tissue and
blood-vessel reactions, could be used in testing quantitatively the genetic re-
lationship between host and donor. We formulated thus, in the following
years, the concept of organisnial differentials, and we analyzed the genetic
relationship between host and transplant and the fate of the latter. Qosely
inbred strains of mice were used for the analysis of the factors determining
the growth of transplanted tumors, especially by Little and his collaborators,
and we extended use of such strains to the analysis of the organismal differen-
tials of normal tissues. There developed hence, step by step, mainly as the
result of greatly varied transplantations of normal tissues in which simultane-
ous multiple and successive transplantations proved of special value, the con-
ceptions of various kinds of specificity in tissue and organ relations, of the
autogenous equilibrium of the organism and of tissue reactions as a test for

INTRODUCTION 25

individuality, of the contrast between mosaic and essential individuality, of the
phylogenetic and ontogenetic development of the organismal and, in particu-
lar, of the individuality differentials which we have mentioned in the first part
of this chapter, and which will be discussed in greater detail in the following
chapters.

At first various fields of investigations relating to the biological basis of
individuality, which have been enumerated in the preceding discussion, de-
veloped separately, but gradually an interaction between these diverse lines
of investigations was established and proved fertile. In the beginning of this
century it was mainly the concepts of immunology which greatly influenced
the study of the transplantation of tissues, but later a reciprocal influence be-
came noticeable and during the last fifteen years the analysis of individuality
by the method of transplantation has stimulated also the search for individ-
uality differentials in various antigens by immunological methods.

In the studies mentioned so far, the question of individuality and specificity
was considered from purely theoretical points of view. But the requirements
of social life and especially also the need to sustain the health of body and
mind of the individual members of a community and the harmonious relations
between those that compose a social group, made it necessary to face the
problem of individuality from a somewhat different viewpoint. This has led
to the concept of "constitution" as something which is peculiar to individuals
and allows the classification of certain groups of individuals according to
their reactions to various environmental conditions. It was observed that dif-
ferent individuals behaved differently in the same environment and under ap-
parently identical conditions. On this basis a distinction was made between
the environmental factors and the substratum on which the latter act. The
mode in which the substratum responded to conditions in the outer and also in
the inner environment, depended on and revealed the constitution of this sub-
stratum. While various characteristic features of a constitutional nature were
shared by a number of individuals, in the totality of these features each in-
dividual was unique and differed from every other one; and it was especially
the physician for whom these individual- and group-constitutional differences
were of practical importance. Thus the concept "constitution" developed in
response to the needs of daily life, and it accentuated, as does also the concept
"individual," the contrast between the organism and the outer world. The
analysis of constitution is therefore another step in the delineation of in-
dividuality and personality from the surrounding world. It is an attempt to
determine what in our interaction with the living and non-living world around
us is due to ourselves and what is due to the world outside ourselves. But here
great difficulties arise because of the great complexity which exists in the
interaction between the individual and the outer world, and between the outer
and inner milieu of a higher organism.

However, through experiment and observation it has been learned that
certain characteristics of an organism are fixed in the germ cells and give rise
to certain structural, metabolic and functional conditions in the individual.
These inherited features represent the core of his constitution; it is the un-
changeable part of it. But in actual life it is often very difficult or impossible

26 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to separate this core from effects produced by the environment. Therefore the
physician especially is forced to adopt as the definition of constitution not only
the genotype, the inherited part of the individual, but also those effects of the
environment which have modified his mode of response to environmental
factors in a more permanent way. But different environmental factors differ
greatly in their intensity and in the perpetuity of the constitutional changes
which they produce and in the number and imporance of the parts of the or-
ganism which they affect. All transitions exist in this respect and no sharp
line of demarcation can be found between various environmental factors. It is
particularly the nervous system which responds most readily to the environ-
ment in the mentally most plastic organism, man. Every thought and sugges-
tion which he has received produce an important change in his constellation
as far as his behavior is concerned. Constitution thus becomes identical with
the constellation of an organism produced by all kinds of inner and outer con-
ditions, which regulate future reactions; it depends upon the condition of
organs or organ systems and corresponds therefore to the mosaic type of in-
dividuality. But the term "constitution" has received a different content under
different circumstances ; it is not sharply defined, yet it may serve as a pro-
visional instrument in the analysis of the reactions of an individual.

In the following chapters we shall discuss more fully the different aspects
of individuality, to which we have referred in this introductory review. In
the various parts of this book the following problems will be discussed :

Part I. The transplantation of tissues in higher organisms which fur-
nishes the most delicate tests of individuality differentials and is the basis on
which further theoretical considerations have been built.

Part II. The phylogenetic and ontogenetic development of individuality
and organismal differentials, from the primitive to the highest organisms
and from the egg to the adult state.

Part III. Conditions suggesting or simulating the presence of individuali-
ty differentials which exist in certain unicellular organisms, either free-
living, such as certain protozoa; or representing parts of more complex
organisms and constituents of tissues, such as amoebocytes ; or cells inter-
mediate between these two types, as far as their independence is concerned,
namely, ova and spermatozoa.

Part IV. The organismal differentials of tumors, which represent modi-
fied tissues.

Part V . The role played by organismal differentials in the maintenance
of the harmony of the organism as a whole, and in the interaction of the
organs and tissues within the organism.

Part VI. Immune processes in their bearing on the interpretation of
organismal differentials. Organismal differentials as well as organ differ-
entials may function as antigens and give rise to the formation of immune
substances.

Part VII. The relationship between the evolution of species and organis-
mal differentials.

Part VIII. The significance of individuality differentials in the psychical-
social field; it is here that the concept of individuality had its origin.

Pi^rf T Transplantation of Tissues in Higher Vertebrates

as a Method for the Analysis of the Organismal
Differentials

Chapter I
General Considerations

Our analysis of individuality and organismal differentials is based
primarily on investigations into the fate of transplants of normal
tissues, and also of tumors, and their genetic relationship to the host
in which they live. In such an analysis it will therefore be necessary to discuss
in more detail the results we have obtained in these experiments, especially
in the ones on which a full report has not as yet been published. However,
before entering into a discussion of these results, the following questions,
which relate to these investigations in general, will be considered: (1) the aim
of these investigations; (2) the factors which have to be taken into account
in evaluating the conclusions, namely, a) the mode of interaction between host
and transplant and the various reactions of the host which are induced by the
transplant, b) the differences existing between different species, c) the differ-
ences existing between different strains and individuals, d) the differences
existing between different tissues serving as transplants; (3) the methods
which best serve our purposes and the variable factors which may complicate
the application of these methods, and (4) the possible errors which have to be
considered in these experiments.

1. The aim of these investigations is the analysis of the organismal differ-
entials of individuals, families, strains and species. We are not primarily con-
cerned with various other problems, as, for instance, the. conditions under
which tissues survive and the establishment of the methods most suitable to
accomplish their survival ; the analysis of polarity in the structure of various
organisms and tissues, and the question of the factors which determine the
growth of the grafts or the fate of pigmented tissues. Only in so far as such
problems aid in the analysis of the organismal differentials and, in particular,
of the individuality differentials, are they to be considered. But these investi-
gations, in addition to their primary objective, contribute also secondarily to
our knowledge of tissue reactions in general, of factors which are active in
pigment formation, and to our understanding of the potential immortality of
tissues. In a wider sense, our interest centers in the phylogenetic and onto-
genetic evolution of the organismal differentials, in the relation of these
differentials to organ and tissue differentials, and to the psychical differen-
tiation and the social life of individuals.

2. (a) As to the mode of interaction between host and transplant, the fol-
lowing factors have to be considered : ( 1 ) The effect which the bodyfluids of
the host exert on the transplanted tissues ; (2) the effect which the connective
tissue and blood vessels of the host have on the state of the graft; (3) the

27

28 THE BIOLOGICAL BASIS OF INDIVIDUALITY

significance of the lymphocytes and polymorphonuclear leucocytes for the fate
of the transplant; (4) the distant actions which, according to Blumenthal, the
individuality differentials exert on the host after these differential substances
have entered the host circulation. The connective-tissue and blood-vessel reac-
tions occur at an early phase following transplantation and the character of
these reactions is usually determined within the first two weeks. The lym-
phocytic reaction, as a rule, begins within the second week, but in some cases
it may exert its full effect only at subsequent periods, and in certain instances,
this reaction may appear and increase during the later phases of the inter-
action between host and transplant. The lymphocytes usually are indicative of
finer differences between the individuality differentials ; they are not found in
any considerable numbers if there is complete compatibility between host and
transplant, and they do not as a rule appear in very large masses if the incom-
patibility between host and graft is so great that the metabolism of the latter
is seriously affected within seven to ten days following transplantation. But
even in heterotransplantation these cells may accumulate after some time in
the periphery of the injured graft. Polymorphonuclear leucocytes are seen in
small numbers soon after the grafting of a piece of tissue, owing to circula-
tory disturbances and perhaps also to the presence of necrotic tissue, which is
found under these conditions ; but they accumulate in larger numbers usually
only around and inside of heterogenous transplants. In the distant reactions,
lymphocytes and polymorphonuclear leucocytes are activated in the circula-
tion, under the same conditions under which they are activated locally around
the transplant.

(b) Differences in the mode of reaction against strange individuality dif-
ferentials exhibited by different species. While the factors which are in-
volved in the struggle of an organism against strange individuality differen-
tials are in principle the same in all the species with which we have worked,
still, some quantitative variations exist in this respect. On the whole, rat and
guinea pig react in a similar manner, although there may be minor differences
in the intensity of the lymphocytic reaction in these species. There is, in addi-
tion, a stronger tendency on the part of the connective tissue to invade and
replace transplanted fat tissue in the guinea pig than in the rat. There are,
however, quite marked differences between the reactions in the guinea pig
and rat, on the one hand, and in the mouse, on the other. In the mouse, the
lymphocytic and connective-tissue reactions are in many cases less prominent
and consequently the direct injurious action of the body fluids becomes more
prominent. The amount of surviving tissue and the state of preservation of
the transplanted cells are therefore largely indicative of the degree of com-
patibility or incompatibility of the individuality (organismal) differentials in
this species. However, the lymphocytic and connective-tissue reactions may
here also participate in determining the fate of the transplants and under cer-
tain conditions this participation in the struggle is quite pronounced and
effective. In contrast to these species, in the chicken, in which the relative
proportion of lymphocytes in the circulating blood is higher than in other
species, the local lymphocytic reaction may be extremely strong even in cases

GENERAL CONSIDERATIONS 29

in which there is only a relatively slight divergence in the constitution of the
individuality differentials.

(c) There are also differences in the reactions of different strains, belonging
to the same species, against strange individuality differentials. Such differ-
ences might be expected in the reactions between individuals from strains
which have been inbred to different degrees. The less close the inbreeding, the
more severe will be the average reaction between different invididuals. Fur-
thermore, a strain whose genetic constitution differs markedly from that of
another strain may be expected to react strongly against individual mem-
bers of the latter strain. But in addition, there is some evidence that different
strains and also different individuals are able to react more strongly against
strange strains and individuals than are others. Thus, among rats it seems
that Busch strain rats reacted, on the average, more severely against individ-
uals belonging to various strains than did strains of a different origin.
Furthermore, among mice there is some indication that strain C57 tended to
react more readily with lymphocytic infiltration of a strange tissue than did
other about equally inbred strains. However, this observation is at present
only a preliminary one; it needs further study and confirmation. There are
also indications that certain individual animals exhibit a stronger reaction to
the tissues of various other individuals than do other animals of the same
strain. We must, therefore, in evaluating jthe significance of certain reactions
as tests for the constitution of individuality differentials, consider the possi-
bility that there exist some variations in the strength of the reactions which
are independent of the degree of difference in the constitution of these differ-
entials.

(d) As to the differences in the reactions against different tissues, all
derived from the same individual and transplanted into the same host, these
are quite marked. Tissues differ in respect to their resistance to injurious con-
ditions and therefore in their ability to survive following transplantation.
There are quantitative variations in this respect between different types of
tissues. Some, as for instance, adult ganglia cells, which are severely injured
by a short interruption of oxygen supply during and following the process of
transplantation, cannot be successfully transplanted. Under ordinary condi-
tions it is more difficult to graft, for any length of time, the adrenal cortex
into a homoiogenous individual than the anterior hypophysis. Cartilage and
perichondrium are very resistant to injuries associated with the process of
transplantation ; they withstand also relatively successfully an attempted in-
vasion by lymphocytes and connective tissue, although even in this respect
differences exist between very cellular cartilage and cartilage in which the
intercellular substance predominates. Dense fibrous hyaline tissue resembles
to some extent cartilage. Intermediate in their behavior following transplanta-
tion are kidney, fat tissue, salivary glands, and some glands with internal
secretion, such as ovary and thyroid ; and among each of these various organs
different constituents are graded in their power of resistance, thus the ex-
cretory ducts are usually more resistant than the specific functioning paren-
chyma.

30 THE BIOLOGICAL BASIS OF INDIVIDUALITY

In the ovary, the larger-sized follicles and corpora lutea are the most sensi-
tive constituents and they are therefore the first ones to be destroyed after
transplantation; in other cases, the small-sized follicles survive but do not
develop to a larger size if the individuality differentials of host and transplant
are not harmonious. Much more resistant than follicles is the germinal epi-
thelium, which covers the ovary and usually forms a cyst after transplantation.
Likewise, cortical spindle-cell connective tissue and medullary ducts, as well
as germinal epithelial ducts, and also the epithelium and unstriated mucosa of
the Fallopian tubes are more frequently able to withstand the injurious effects
of homoiotoxin than even the small follicles. Most often the tissue remaining
after destruction of all the others are strands of smaller and larger cuboidal
cells, which are probably derived directly from the interstitial gland, and in-
directly from the theca internal cells of atretic follicles ; and these cells may be
quite active as phagocytes and thus help in the removal of necrotic or hemor-
rhagic material. It may be remarked here that hemorrhages occur in certain
transplanted tissues and also in some non-transplanted organs, such as the
adrenal gland, probably more often than might be expected. The characteris-
tics of the ovary in the mouse, which we have described, make this organ very
suitable for the analysis of the individuality differentials.

Striated muscle tissue is fairly resistant and can be easily transplanted,
whereas bone marrow is a rather sensitive organ that readily perishes. In con-
trast to ovarian tissue, testicle is sensitive. However, the power of resistance
of analogous tissues may differ in different species ; thus it seems that ovarian
structures are more suitable for grafting in the rat and mouse than in the
guinea pig. Different tissues differ also in their ability to grow after trans-
plantation and also in their mode of regeneration, and these growth processes
are inhibited by incompatibilities between the individuality differentials of host
and transplant. Furthermore, there seem to be some differences in the quan-
tity of individuality differential substances produced or given off by various
tissues. Those possessing a very active metabolism, such as thyroid, produce
these substances apparently in larger quantities than does cartilage. This con-
clusion is suggested by the fact that different tissues differ in the readiness
with which they attract lymphocytes, and it may be assumed that the accumu-
lation of lymphocytes is an indicator of the amount of active individuality
differential substances.

^^r. As to the methods which are most useful in the analysis of the individu-
ality differentials, the place of transplantation is important. It is necessary
to select a place sufficiently large for the simultaneous insertion of multiple
grafts, or, in other cases, for the serial transplantation of pieces of tissue,
where, also, these operations can be done without serious interference with the
health of the animals and where, moreover, the transplants can be recovered
at the time of examination without much difficulty. Pockets in the subcutaneous
tissue seem to be most suitable for this purpose, and by using this site in the
majority of our experiments we avoided the introduction of unnecessary varia-
tions. In making the pocket it is important to avoid hemorrhages, which might
interfere with the nourishment of the transplant in the period following opera-

GENERAL CONSIDERATIONS 31

tion. In every case it is advisable first to study the sequence of events in the
struggle of the host against the transplant, which sets in following trans-
plantation and ends with the establishment of a new equilibrium of one or
another kind. Thereafter, the time of examination should be, as far as possible,
a constant factor in all the experiments. The time selected should be such that
the effects of the injury, due to the process of transplantation, have disap-
peared, but the reactions have not yet progressed so far that finer gradations
of the effects in different experiments have become impossible. The latter
condition is very important, but it has not received due consideration by some
investigators. As a rule, a period of 20 to 30 days following transplantation
will be found most suitable for a comparison of the various tissue reactions
and for the determination of relationship between the individuality differen-
tials of host and graft. If the degree of incompatibility between host and
transplant is only slight, a longer time may be required for the lymphocytic
accumulations and infiltrations around the graft to become manifest, and in
some cases collections of lymphocytes may appear even at a very long time
following transplantation. However, in certain transplanted tissues the lym-
phocytic infiltration does not increase with increasing length of time after
transplantation and there are some indications that in some instances it may
even decrease in strength with advancing time. Whether this decrease in the
effectiveness of the transplant with increasing time, which is especially
noticeable after transplantation of cartilage, is due to a diminution in the
amount of homoiotoxins produced or given off in the strange host, or whether
it is due to an adaptation of the host to the action of the homoiotoxins, needs
further study.

The choice of tissues to be used varies somewhat in different species. In
guinea pig and rat, the simultaneous transplantation of thyroid with adhering
parathyroid, of xiphoid cartilage together with the surrounding fat tissue,
striated muscle, and bone and bone marrow, will make possible a satisfactory
characterization of the relations of the individuality differentials of host and
transplant. It may be of advantage to add a separate piece of striated muscle,
thymus or salivary gland to the former tissues, all pieces to be implanted at
the same time.

In the case of the mouse, the thyroid is not quite so useful a test tissue as in
guinea pig and rat, because in the former species the reaction of the host
against the transplant may in some instances consist merely in a shrinking of
•the graft, unaccompanied by the lymphocytic reaction which is so fine a
reagent in the case of guinea pig and rat. But, also in the mouse a
lymphocytic reaction may develop around grafts if incomplete compatibility
exists and if the thyroid transplant remains, on the whole, well preserved.
However, a shrinking of the thyroid transplant may take place also under other
conditions, as when, for instance, the small thyroid of a very young mouse has
been used for grafting, or when a part of this organ was injured during the
process of transplantation. This multiplicity of factors, bringing about similar
results, may make the analysis of the relation of individuality differentials in
the mouse more difficult in some experiments. Therefore, in this species it is

32 THE BIOLOGICAL BASIS OF INDIVIDUALITY

advisable to transplant a larger number of tissues simultaneously, such as
thyroid, xiphoid cartilage with associated tissues, ovary and striated muscle.
A combination of this kind makes possible an accurate appraisal of the degree
of compatibility in the large majority of cases. As a general rule, applying to
all experiments of this kind, it is necessary to carry out the operations in a
sterile manner, whenever this can be done, and to inflict as little injury as
possible on the tissues. ■

4. In the evaluation of the results of the experiments various accidental
complicating factors must be considered. Very important in this connection is
infection with bacteria, which may occur notwithstanding the measures which
may have been taken to avoid such an accident. In the majority of instances it is
easy to recognize the effects of bacteria, with which the tissues were con-
taminated during the process of transplantation. The presence of localized
masses of polymorphonuclear leucocytes around or in the graft indicates
strongly the presence of extraneous microorganisms. However, in some ex-
periments it may be difficult to decide whether the leucocytes may not have
been attracted by sterile necrotic tissues. This difficulty is encountered espe-
cially in the mouse, where an infection may more readily take place, owing to
the small size of these animals. Here we may find, in or around the transplants,
either more scattered leucocytes or small accumulations of these cells, especial-
ly around the fat cells ; these changes seem to be, on the average, more wide-
spread and more intense if host and donor of the transplants are not nearly
related, whereas, they usually remain localized when the degree of incom-
patibility between the individuality differentials of host and transplant is only
slight; in cases of heterogenous transplantation, polymorphonuclear leucocytes
are quite commonly attracted. There are certain other conditions when doubt
may arise as to the significance of certain changes which have taken place in
the transplant, as for instance, in case of injury of the transplanted tissues.
Thus injury to fat tissue surrounding the xiphoid cartilage, caused by pressure
of the forceps during the process of grafting, may lead to localized necrosis of
fat tissue and cartilage ; subsequently, the necrotic fat tissue may be replaced
by fibrous tissue, and around the necrotic cartilage a plate of new perichondrial
cartilage may form.

Another difficulty may be encountered when the thyroid of the guinea pig
is transplanted. If this organ is surrounded by much fat tissue, the latter may
prevent the ready ingrowth of capillaries from the host into the graft and the
transplant may become necrotic over a smaller or wider area. Such a result is
obtained especially if well-nourished, older animals, in which considerable
amounts of fat tissue surround the thyroid, are used as donors and it will be
necessary to guard against this complication. Further obstacles to a correct
interpretation of the experiments may be due to the presence of adventitious
factors, which may accelerate, intensify or retard the lymphocytic reaction.
While the essential factor that determines the intensity of this reaction is the
degree of incompatibility existing between the individuality differentials of
host and transplant, certain tissues are more prone to call forth a strong reac-
tion than others. Thus in guinea pig and rat, thyroid tissue is usually more

GENERAL CONSIDERATIONS 33

effective in inciting a lymphocytic reaction than is cartilage with the surround-
ing fat tissue. Likewise, transplants of striated muscle tissue may be infiltrated
with lymphocytes, when in other tissues lymphocytes are absent or much less
numerous ; but as a rule, also in the muscle tissue they are present in larger
masses only if there is a definite antagonism between the individuality differ-
entials of host and transplant. But lymphocytes accumulate very readily even
around dead foreign bodies such as threads, especially if these foreign bodies
are situated in tissues possessing an individuality differential which is not
quite compatible with that of the host. In cases of infection in the fat tissue of
the mouse, there may be found in addition to the accumulations of poly-
morphonuclear leucocytes, collections of lymphocytes, an increase in connec-
tive tissue and an infiltration of the fat tissue with small vacuolated epithelioid
cells; but similar cellular changes may be noted in this animal also if the
homoiogenous differentials of host and donor are sufficiently strange to each
other. In such cases we have to deal either with a summation of the effects of
incompatible individuality and organ differentials, or of the combined effects
of the former and of bacterial infection or foreign body action. These com-
plications by no means diminish to any considerable extent the value of the
lymphocytic reaction as an indicator of the relation of the individuality differ-
entials to each other even in the mouse, just as little as the value of the agglu-
tination reaction in serological tests is destroyed by the fact that also changes
in ion concentration in the medium in which cells or particles are suspended
may cause agglutination ; but it will be necessary to take all these factors into
account in evaluating the results of such experiments.

In the large majority of our experiments we transplanted pieces of two or
more different tissues from the same donor into different places of the sub-
cutaneous tissue of the host and these pieces were subsequently removed at
the same time for examination. As a rule, it was then found that the kind and
intensity of the reaction of the host against these various tissues or organ
pieces were similar. In autotransplantation, injurious reactions were lacking
against all of them. In homoiotransplantation, if a severe reaction took place
against one of the pieces, all the others were likewise severely damaged; if
the homoiotoxins were less strong, the reactions in all pieces were equally mild.
In syngenesiotransplantation, corresponding reactions of a mild character
occurred in each case. In general, also the lymphocytic infiltration showed a
similar degree of intensity in the different grafts from the same donor into
the same host, provided the various complicating factors mentioned above
were taken into consideration. Likewise, the reaction against all types of
heterogenous tissues was of the same kind. In all these evaluations it is
necessary to make allowance for differences in the sensitiveness, the power of
resistance, the mode of growth of the tissues, and the amount of individuality
differential substances produced in the various types of transplants. We should
not expect the same reaction to take place against cartilage as against thyroid,
as each of these tissues has its own peculiar characteristics. Because of the
presence of so many variable factors present in investigations in which living
tissues enter into various kinds of relations, it is necessary to make in each

34 THE BIOLOGICAL BASIS OF INDIVIDUALITY

instance a large series of experiments in order to arrive at correct interpreta-
tions and to draw justified conclusions. Such experiments require, therefore,
much patience and experience on the part of the investigator, but the problems
are of sufficient importance to warrant these efforts. However, after all these
conditions have approximately been satisfied, there remain still a number of
variable factors in these experiments which have not yet been eliminated ;
therefore a complete solution of the problems involved is impossible at the
present time and must be left to future work.

Since multiple transplants of various kinds from the same donor into a host
behave in a corresponding manner, a grading of results can be made which
express the degree of compatibility between the individuality differentials of
donor and host, and thus a standard can be established with which to compare
the results obtained in different experiments. The grades chosen for this pur-
pose are arbitrary; they range between 1 and 3+ (3.25). In autotransplanta-
tion, the grades given are 3+ and 3. The tissues are well preserved and while
at first there may be some irregularities in the structure of the grafts, they
gradually assume more and more the characteristics of the normal organs,
provided some accidental factors do not prevent such a development. Marked
lymphocytic infiltration is lacking, but at early periods after transplantation
some very small collections of lymphocytes may be seen ; after some time,
these cells usually disappear. Likewise, the connective tissue ingrowth into
the autotransplant is restricted and an invasion of the fat tissue by small
vacuolated cells and by fibrous tissue is lacking. Grades 3— (2.75) and 2 +
(2.25) are given if the grafted tissues are, on the whole, well preserved, but
if a reaction of the host is definitely noticeable, consisting in various degrees
of lymphocytic infiltration and in a somewhat increased activity of the con-
nective tissue, which may cause a rather mild injury to the transplant ; reac-
tions of this kind may be seen if donor and host are related to each other. If
the reactions are somewhat more marked and tend to lead to a partial destruc-
tion of the transplant, grade 2 is given ; this indicates a somewhat greater
strangeness of the individuality differentials. In typical, more severe homoio-
reactions the grades range between 2— and 1. Grade 1 is applied in experi-
ments in rats and guinea pigs, in which the thyroid has been entirely destroyed
and the fat tissue largely replaced by fibrous tissue; grade 1+ signifies the
survival of only a small part of the thyroid gland ; the reaction in the fat tissue
is still very severe. Grade 2— (1.75) is given if the thyroid gland is strongly
invaded by fibrous tissue and a considerable part of it has been destroyed, but
if at least one-half of the organ has escaped destruction at the time of ex-
amination. There is usually, in these cases, a definite lymphocytic infiltration,
provided the injury to the tissues has not led to a marked diminution in the
amount of the individuality differential substance present in or produced by
the transplant. If in addition to thyroid, cartilage and fat tissue have been
transplanted, corresponding grades may be given in accordance with the degree
of survival of the tissues and the degree of lymphocytic infiltration. The addi-
tion of ovarian transplants may make possible a still finer grading : in the most
favorable cases large follicles and even corpora lutea are found in such grafts ;

GENERAL CONSIDERATIONS 35

if the results are somewhat less favorable, medium-sized or small follicles
develop, and a still less favorable reaction is indicated if merely primordial
follicles survive, without undergoing further growth processes; if the reac-
tions are more severe, no follicles are seen in the transplant, but there may be
only a cyst of the germinal epithelium, ducts, spindle-cell connective tissue
and interstitial gland, together with necrotic remnants of the transplanted
ovary; under the least favorable conditions, interstitial gland-like tissue may
be all that is found, or even this may be missing and necrotic material and
fibrous tissue alone may remain. However, it is always necessary to make
allowances for the occurrence of accidental injuries to the transplants ; but
even if it should be difficult to recognize the latter, errors in the interpretation
of the reactions can be avoided by performing a number of experiments, in-
stead of relying on a single one. While this method of grading can claim only
approximate exactness, still it is very helpful in comparing results obtained if
different types of individuality differentials are made to interact.

In some cases we have used a second type of grades, which were as follows :
Grade 6 is given to a typical autotransplant ; grade 5 to a favorable, and grade
4 to a less favorable syngenesiotransplant ; grade 3 to a milder and grade 2 to a
severe homoiotransplant ; grade 1 has the same meaning in both types of
grades. These two systems of grading correspond to each other about as
follows :

Type

of

Second Grades

Main Grades

6

=

3 +

5

=

3 or 3 —

4

=

2+ or 2

3

=

2 or 2 —

2

=

1 +

1

=.

1

Unless specifically so stated, the first type of grading was used. In a general
way, these series of reactions correspond to the spectrum of relationships ex-
tending from the autogenous through the syngenesious, first to the light and
then to the severe homoiogenous reactions. Certain features indicating a still
more severe injury are added in the case of heterogenous transplantations.

As to the terminology employed in distinguishing various types of trans-
plantation, very frequently the terms : autoplastic, homoio- or isoplastic, and
heteroplastic are used in the literature. However, the affix "plastic" accentu-
ates the practical use which is made of transplantation in surgical "plastic"
operations. But, transplantations may serve also as a method for the deter-
mination of the genetic relationship between the individuality differentials of
host and donor, and then it would be more appropriate to designate these
various types of transplantation as autogenous, syngenesious, homoiogenous
and heterogenous, in order to emphasize the importance of genetic factors in
such experiments.

Transplantations in which the relationships between host and transplant can

36 THE BIOLOGICAL BASIS OF INDIVIDUALITY

be graded and in which a variety of tissues can be chosen for grafting provide
the opportunity not only for the analysis of the organismal differentials of
host and transplant, but also for the study of the interaction of various types
of tissues and cells and of the factors which determine the tissue equilibria ;
they may therefore serve also as a method which may be of value in building
up a physiology of tissues, in contrast to the physiology of organs which has
been so extensively studied in the past. Accordingly, we shall emphasize this
aspect of our investigations in describing our results.

Chapter 2
Autogenous and Homoiogenous Transplantations

We shall now compare the reactions against autogenous and homoi-
ogenous transplants, first in rats and guinea pigs and then in mice
and chickens, and we shall consider the transplantation of thyroid,
cartilage and fat tissue, and later also that of striated muscle and a few other
tissues.

1. Autogenous transplantation of thyroid in rat and guinea pig. After auto-
transplantation of thyroid in rat, as well as in guinea pig, there remains at
first a ring of preserved acinar tissue around a central necrotic zone; the
latter is smaller in the rat. Blood vessels and connective tissue cells are at-
tracted by the transplant and the vessels and fibroblasts penetrate towards
the necrotic center, where they form a loose, vascularized connective tissue.
In the guinea pig, this takes the form of a distinct myxoid zone, situated be-
tween the necrotic center and the peripheral ring of living acini, whereas,
in the rat this ringlike myxoid area is not so distinct. The organization of
the center in the latter species is usually completed by the 15th day, when
also the necrotic center of the parathyroid has been replaced by connec-
tive tissue ; at this time, furthermore, accompanying the fibroblasts and vessels,
a few lymphocytes or very small groups of lymphocytes may be seen in
the central or peripheral connective tissue of the graft. In the first week
after transplantation the colloid may be lacking in the acini of the transplant
and phagocytes may contribute to the destruction of the latter, but after two
weeks this colloid has been replaced by newly-formed colloid wihin the acini,
the epithelium of which is rather low. The number of fibroblasts which move
towards the center is, on the whole, rather small, and the few lymphocytes
which may accompany these cells are probably attracted by non-specific fac-
tors, perhaps by the necrotic tissue ; in other cases, foreign bodies may attract
some lymphocytes. Around the 4th week, or somewhat earlier, the transplanted
thyroid shows a curved structure. At this time an interesting change takes
place, leading to the disappearance of the central connective issue which had
been formed by the organization of the central necrotic material. This con-
nective tissue, which may have become fibrous or hyaline, is either pushed out
of the transplant into the neighboring tissue or it is invaded and absorbed by
new fibroblasts of the host, although a small amount of hyaline material may
remain within the inner ring of acini. The acini are surrounded by well-formed
capillaries, not necessarily accompanied by fibroblasts. Towards the end of the
5th week, lymphocytes are either entirely lacking, or, in certain cases, are
present in small collections. Between the 40th and 60th day the transplant
begins to resemble the normal thyroid, but the epithelium is lower than in the
original acini and a very small amount of fibrous tissue may be found between

37

38 THE BIOLOGICAL BASIS OF INDIVIDUALITY

some of them. In the lymph vessels, no lymphocytes, or only a few, may be
seen. As in the rat, so too in the guinea pig the ingrowth of fibroblasts is
limited and a loose connective tissue forms in the center adjoining the thyroid;
but the latter formation, assuming the shape of a ring, is more pronounced
here than in the rat. Also in the guinea pig the central fibrous tissue is elimin-
ated after some time, and in both rat and guinea pig the blood vessels are at-
tracted by autogenous substance ; this conclusion is based on the fact that the
vascularization is more marked in autogenous than in homoiogenous trans-
plants ; in addition, in the former, lymphocytes are lacking or slight in number.
In rat as well as in guinea pig the injury to the acini and the destruction of
colloid are gradually repaired and the transplants assume more and more the
character of the normal gland. The activity of the connective tissue and
lymphocytes is, therefore, restrained around and in autogenous thyroid grafts
and this condition is best suited for the restoration of the normal tissue rela-
tions and of the normal structure of such transplants.

2. Homoiogenous transplantation of the thyroid in rat and guinea pig.
The intensity of this reaction depends largely on the relationship between host
and donor. In the rat, we carried out, therefore, three series of experiments, in
which the average relationship was somewhat varied; the probability that a
distant relationship existed between donor and host was greater in series B
than in series A; in both of these series white rats were used. In series C,
tissues of white rats were exchanged with those of cream and hooded rats. In
all of these series the same factors co-operated in inflicting damage on the
transplant, namely, (1) the action of the bodyfluids of the host, (2) the in-
creased invasion by fibroblasts and lymphocytes and the increased production
of fibrous or fibrous-hyaline tissue, which later interfered with the nutrition
of the transplant and injured it by exerting pressure on it, and (3) the dimin-
ished supply of blood and lymph vessels, which also diminished the nourish-
ment of the transplant. In series C the intensity of the reaction was greatest,
and in series A it was slightly greater than in series B. In both the latter series
the maximum of the reaction was obtained between the 20th and 30th day
after transplantation, but in series B, where there was probably, on the aver-
age, a nearer relationship between the different rats than in series A, an im-
provement in the average condition of the transplants was observed from then
on ; this was lacking in series A and C.

In series A and B, at first conditions were similar. Between the 1st and 8th
days, two or three layers of acini were preserved in a number of instances, but
in others they were less well preserved ; the acini were small and the colloid
had been lost in many of them, while in others it was still present. Some
capillaries grew through the ring of acini and mitoses were seen in the acinus
cells. The necrotic center was organized by not very dense, small-celled con-
nective tissue or by very dense fibrous tissue, or in certain cases some necrotic
material was still left and was at least partly taken up by phagocytes. Hemor-
rhages from the rupture of the newly-formed capillaries may have occurred.
From the 6th day on, lymphocytes appeared in series A, while in series B they
accumulated somewhat later. They were carried to the transplant first by way

TRANSPLANTATIONS 39

of the lymph vessels and they collected at the periphery of the center, or they
filled the center diffusely; moreover, lymphocytes and also some connective
tissue cells surrounded some acini. The central portion of the parathyroid was
necrotic and in process of organization. Mitoses were seen in both thyroid and
parathyroid.

In series A, between the 10th and 15th day, the thyroid transplant had dis-
appeared, only fibrous tissue with some lymphocytes was observed in a number
of cases. In other experiments there were some isolated acini or groups of
acini embedded in masses of lymphocytes, which had accumulated and which
gave to the transplant almost the appearance of a lymph gland. Lymphocytes
could be seen penetrating between and into certain acini and destroying them.
The center of the transplant was densely fibrous and blood vessels were here
less conspicuous. As a rule, the thyroid ring, if present at all, was incomplete.
After 16 and 17 days, variable amounts of thyroid tissue were found pre-
served; if the amount was small, the colloid was usually lost. Fibrous bands
separated acini or bundles of acini and lymphocytes separated acini in certain
areas; the center of the transplant and the lymph vessels were filled with
lymphocytes. There was some indication also in this series that the homoio-
reaction was especially marked after transplantation in certain strains of rats.

Series B differed from series A in that, in the former, the reactions were
on the average slightly less severe up to about 30 days after transplantation,
but from then on, a diminution in the intensity of the lymphocytic reaction
and in the destruction of thyroid issue set in, which was quite noticeable be-
tween the 40th and 85th days. While the lymphocytic reaction appeared some-
what later in series B, a marked lymphocytic infiltration did occur, and fibrous
bands surrounded the acini during the earlier periods. In both series, in ex-
ceptional cases, the grafts showed the character of typical syngenesiotrans-
plants, in which, instead of dense fibrous tissue, there was loose connective
tissue with blood vessels in the center ; here lymphocytes had accumulated as
well as in the periphery of the graft and they penetrated also between the
acini. But in other instances there was, in these cases, an intense destruction
of the thyroid by lymphocytes and connective tissue.

In series C, a complete or almost complete destruction of thyroid and para-
thyroid had occurred at about 20 days after transplantation, the reaction being
very severe, in accordance with the greater difference between the individuality
differentials of host and donor. There are, then, indications that the intensity
of the reactions against transplanted thyroid varies in accordance with the
relationship between host and transplant.

In homoiogenous transplantations of the thyroid gland in the guinea pig,
which were carried out with Hesselberg, the results were very similar to those
obtained in rats. Yet some differences between autogenous and homoiogenous
transplantations are brought out perhaps more clearly in the former than in the
latter species. In a first period, lasting about four to five days and representing
the earliest reaction to the injury, there is no marked difference between
transplantation of autogenous and homoiogenous thyroid. During this interval
the first mitoses appear and at the end of it some new acini may be produced.

40 THE BIOLOGICAL BASIS OF INDIVIDUALITY

There follows a second stage, one of transition, extending from the 5th to the
12th day, in which the formation of acini is less in homoiogenous than in
autogenous tissue; likewise, colloid is newly produced in lesser amounts in
homoiogenous than in autogenous grafts and this may perhaps be at least
partly due to injury inflicted by the homoiotoxins rather than by the lympho-
cytes of the host. During this period, and still more so during the third period,
beginning after 12 days, there is an increase in lymphocytes and connective
tissue in the homoiotransplants ; the fibroblasts tend to produce fibrous tissue,
which separates groups of acini as well as isolated acini and exerts pressure on
them ; the lymphocytes accumulate in increasing numbers in the homoiotrans-
plants and invade and destroy the acini. In the autotransplants, wider blood
capillaries grow through the thyroid ring into the center and here the zone of
myxoid connective tissue develops, which we have already mentioned, and it
surrounds the central fibrous tissue, which is either converted into loose con-
nective tissue by ingrowing capillaries and fibroblasts or is expelled into the
surrounding tissue. At the same time, fat tissue may be pushed into the center
of the thyroid from the outside and fat cells may be observed, although very
rarely, also in the lumen of an acinus. This distribution of thyroid acini in the
fat tissue is not found in homoiotransplants. At a later period, as, for instance,
five months after transplantation, the autotransplanted thyroid may be almost
like the normal, non-transplanted gland. Dense fibrous tissue separating the
acini, as well as collections of lymphocytes, is lacking. The center of the graft
consists merely of small amounts or strands of loose connective tissue. How-
ever, mitoses are not frequently seen in such transplants. The greatest number
of mitoses is found from 7 to 9 days following autotransplantation and some
mitoses may be found at this time even in homoiotransplants; they may still
be frequent in autogenous transplants during the later days of the second
week, but are lacking or very rare after 17 days.

In discussing the variable accidental factors which, apart from the nature
of the individuality differentials, may influence the result of transplantation
of various organs, we mentioned the fact that if together with the thyroid
gland much fat tissue is transplanted, a great part or even the whole of the
transplant may become necrotic. This seems to be true, however, only of
homoiotransplants. The same factor interferes with autogenous transplants
much less seriously ; it appears that in the latter a partial necrosis caused by
the fat tissue, may later disappear, as a further demonstration of the great
power of adjustment possessed by autogenous tissue.

We find, in guinea pigs, that younger hosts react on the average in a milder
way towards homoiogenous transplants than do older animals ; thus in grafts
made in hosts about 10 days old the preservation of the thyroid gland is, on
the average, somewhat better and the formation of fibrous tissue in the trans-
plant less extensive than in older hosts. Moreover, the lymphocytic reaction
may be less severe; but if the preservation of the thyroid tissue is relatively
good, the lymphocytic reaction may be quite intense in the young guinea pigs
as well. Some differences between younger and older hosts may be noticeable
between 11 and 17 days after transplantation. While as a rule also in younger

TRANSPLANTATIONS 41

animals there are typical homoiogenous reactions, occasionally reactions ap-
pear which are more characteristic of syngenesiotransplants, and even as late
as 20 to 25 days following transplantation the grade 3— was obtained in a
younger host, which signifies that the structure of the graft approached that
seen after autotransplantation. In older guinea pigs the reactions were more
severe. However, we found that in different series of experiments with guinea
pigs obtained from different breeders, the severity of the reactions differed
somewhat, in the same way as in transplantations in the rat.

The grades obtained between 20 and 25 days after homoiotransplantation
were 1,1 + , and 2—. Between 25 and 40 days, in the majority of cases, the
grade was 1 ; in only one-third of the cases the grade 1+ (1.25), and in no
case grade 2— (1.75), was reached. In younger guinea pigs the grades be-
tween 20 and 25 days were somewhat better; they varied between 1 and 2,
and even grade 3 — (2.75) was attained. Even after 50 and 60 days, while
the grade was mostly 1, in a few cases grades 2— /1+ (1.50), or even
2/2— (1.87), were obtained.

3. The effect of feeding thyroid substance to guinea pigs which are hosts of
thyroid transplants. If preparations of thyroid gland are added to the diet
of normal guinea pigs, the mitotic activity of these transplants decreases and
the colloid becomes hard, as an indication of the diminished function of this
gland. However, when we gave, by mouth, daily 0.1 grain of thyroid to
guinea pigs which received autotransplants of thyroid gland, the success of
the transplantation was not diminished thereby, although the height of the
acinar epithelium was low or medium to low. No increase in connective tissue
nor in lymphocytes took place. Likewise, in guinea pigs with homoiotrans-
plants of thyroid gland, thyroid feeding did not have any noticeable effect
on the reaction of the host against the transplant. The grade in one guinea
pig, after 30 days, was 1 ; after 20 days, the grades were : 1 in 6 guinea pigs ;
2— in 2 guinea pigs ; 2 in 3 guinea pigs, and in 2 additional guinea pigs it was
2 and 2— respectively. After 13 days, the grade was 1 — . In a second experi-
ment with younger guinea pigs the grades varied between 1 and 2. The effect
which administration of thyroid hormone exerts on the thyroid gland did
not, therefore, change the reaction of the host against transplants of this organ.

Autogenous and homoiogenous transplantation of cartilage and fat tissue
in rat and guinea pig.

4. Autotrans planted xiphoid cartilage in the rat, as a rule, remains well
preserved and the perichondrium is free of lymphocytes, in rat (as well
as in guinea pig) only when the cartilage has been injured as the result of
the operation, or is poorly nourished, owing to pressure or hemorrhage in
the surrounding tissue or other injurious factors, it becomes necrotic. Thus,
if the thick end of the cartilage near the bone is transplanted, the center of the
transplanted piece may be at a disadvantage because of the lack of nourishment
and may become necrotic and dissolved ; subsequently, connective tissue may
invade and replace the necrotic central areas. Necrotic pieces of cartilage may
be surrounded by connective tissue which has grown into and replaced the
transplanted fat tissue, or the perichondria! tissue may produce a new plate

42 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of cartilage around the necrotic area, and in some instances the newly- formed
cartilage may even infiltrate and take the place of the necrotic part. Corre-
spondingly, central necrosis and solution processes may be found even in
the normal, not transplanted xiphoid cartilage, in places where it is thick and
where the central parts are therefore not well nourished. Transplanted fat
tissue remains normal, but occasionally necrotic areas are found in it, pre-
sumably as the result of injury inflicted upon it during the transplantation ;
there may be at first very slight collections of lymphocytes, due probably
to the presence of necrotic areas or to other accidental alterations of the fat
tissue, but these disappear somewhat later.

5. Homoiogenous transplantation in the rat of cartilage and fat tissue pro-
duces the changes characteristic of homoiogenous individuality differentials.
The same three series of transplantations were made in the rat with cartilage,
bone and fat tissue as with thyroid. With thyroid, there was a grading of the
intensity of the reaction, corresponding to the average degree of similarity or
lack of similarity of the individuality differentials in these series. Upon this
condition depended the amount of tissue destroyed and replaced by fibrous
tissue and the intensity of the lymphocytic reaction. If we compare with these
gradations in thyroid, the gradations in cartilage, bone and fat tissue trans-
plants, we find in principle, in both kinds of grafts, the same condition, except
that the differences in the power of resistance of different tissues caused some
differences in the mode of reaction and in the absolute grades given. The
greater portion of the cartilage could remain alive permanently in all three
series of homoiotransplantations, but the fate of the fat tissue, epiphyseal
cartilage, bone and bone marrow, and the frequency and character of the
regenerative processes around necrotic parts of the cartilage served as indica-
tors of the severity of the reaction and of the degree of compatibility of the
individuality differentials of host and transplant.

Even in series C, in which host and donor of the transplant were least nearly
related, the cartilage remained alive, and if there was localized necrosis a
regeneration of perichondrial cartilage could take place, although this did
perhaps not occur as regularly as in series A and B, and in some cases it led
to the formation of a myxoid tissue instead of cartilage ; this occurred if the
intercellular cartilage substance was dissolved, while the cartilage cells re-
mained alive. Evidently the development of toxic substances could inhibit the
regeneration of cartilage. The epiphyseal cartilage and the transplanted bone
were completely or almost completely necrotic in this series. However, there is
some difficulty in the determination of the degree of necrosis of bone. If we
adopt the condition of the bone cells as a criterion of the life or death of this
tissue, then we encounter the difficulty that many of the apparently preserved
and living bone cells may in reality be connective tissue cells, that had moved
into the bone from the outside, in particular, from a zone of epithelioid cells
surrounding the bone-cartilage border and perhaps representing merely fibro-
blasts, which, under the influence of bone tissue, assumed the character of
epithelioid cells. But ordinary connective tissue cells may also invade and
replace necrotic bone and cartilage. There was extensive necrosis in the trans-

TRANSPLANTATIONS 43

planted fat tissue and replacement of the latter by fibrous tissue. Variable
amounts of fat tissue could remain preserved, but it might be invaded by
epithelioid and giant cells. Lymphocytic infiltration was usually marked in the
fibrous tissue around the cartilage as well as around the blood vessels which
supplied the fat tissue with blood, and also around the bone, but at other times
the infiltration was moderate. In one transplant, even remnants of striated
muscle tissue with nuclear chains were found. On the whole, the connective
tissue and lymphocytic reaction against the transplant was considerable in
series C, and more intense than in series A and B. Likewise, the bone marrow
became more rapidly and more completely necrotic and it was more exten-
sively replaced by fibrillar connective tissue than it was in the first two series.
In series A and B, the necrosis of the fat tissue was less marked than in series
C or it was lacking altogether, and there was often only localized ingrowth of
connective tissue into the fat tissue, together with a moderate invasion by
lymphocytes, which had a tendency to collect around the perichondrium.

As to the time relations in these reactions, they were about as follows : In the
first three days after transplantation there was noticeable a movement of some
polymorphonuclear leucocytes in the fat tissue, in the direction towards the
cartilage ; these cells disappeared in the following days. Between the 6th and
8th day, a new formation of cartilage could set in and a slight infiltration with
lymphocytes, varying in strength in different specimens, took place. The re-
action against the transplanted tissue usually was quite distinct on the 10th
day after transplantation and the maximum could be reached between the 20th
and 30th day. At this time, the average grade in series A was about 2— and
in series B it was intermediate between 2— and 2. Between the 30th and 85th
day a decrease in the average severity of the lymphocytic infiltration could
occur, while the connective tissue reaction remained in a quiescent state. In
some instances, at late stages the transplant even resembled an autotransplant,
perhaps on account of an adaptation of the host to the originally strange tissue,
a condition possibly akin to a state of active immunity.

In general there was, in the various experiments, a parallelism in the grades
of thyroid and cartilage-fat transplants. In rats, in which the homoiogenous
reaction was weak or lacking altogether in thyroid transplants, it was also as
a rule lacking or weak in cartilage-fat transplants ; but the destruction of the
tissue by lymphocytes and connective tissue was, on the whole, much greater
in the thyroid than in the cartilage; however, there were some instances in
which the thyroid transplant was so markedly invaded by lymphocytes that it
almost resembled a lymph gland, and then the cartilage-fat transplant likewise
was severely infiltrated. On the whole, then, the principles which applied to
the relationship between the individuality differentials of host and transplant
and the reactions towards the transplanted tissues were about the same in the
case of thyroid and cartilage-fat tissue.

6. Autogenous and homoiogenous transplantations in the guinea pig, of
cartilage-fat tissue with the associated tissues, are very similar to the corres-
ponding conditions in the rat. Again, in the first stages following transplanta-
tion there may be in both kinds of transplants, some polymorphonuclear leu-

44 THE BIOLOGICAL BASIS OF INDIVIDUALITY

oocytes, which later disappear. Fibroblasts and capillaries may grow into
blood clots and organize them, and connective tissue cells may penetrate also
into wounds or into necrotic areas in the cartilage. Some collections of lympho-
cytes around blood vessels or around the perichondrium and some increase in
the connective tissue in the transplanted fat tissue in autogenous transplants
may later disappear.

In the guinea pig as in the rat, homoiogenous cartilage may survive at least
for as long as almost six months, and probably permanently, although slight
degenerative changes or, in places, complete necrosis may take place in the
intercellular cartilage substance in the course of the first or second week.
During the second and third weeks, the lymphocytic infiltration may become
quite marked, although this varies in different cases and even in different
places in the same transplant. In some instances, towards the end of the third
week, the lymphocytes may be so numerous that the cartilage becomes se-
questered. During this time, also, the connective-tissue growth continues, lead-
ing either to a thickening of the septa in the fat tissue or to a substitution of
fat tissue by fibrous tissue. In the second week, epithelioid and giant cells
develop fairly often in the fat tissue and frequently perichondrial cartilage is
formed around necrotic cartilage. It is of interest that in all the species ex-
amined so far, mitoses are rarely found in perichondrial tissue and in young
cartilage cells, and only once was a mitosis seen in a perichondrial cell in the
guinea pig. During the fourth week the homoiogenous reaction is fully de-
veloped. Not only may newly-formed cartilage surround the necrotic area, but
also connective tissue with lymphocytes, with or without blood capillaries,
or lymphocytes without connective tissue may penetrate a necrotic area in
the cartilage and replace it. Lymphocytes may infiltrate and destroy part of
the perichondrium, but they penetrate the hyaline intercellular cartilage sub-
stance not at all, or merely for a short distance. They do not destroy healthy
cartilage to any large extent. On the other hand, cellular cartilage may more
readily be invaded by lymphocytes and, at least in part, be destroyed. But on the
whole the lymphocytic infiltration in cartilage- fat transplants is moderate and
it is found especially around the living cartilage, in places where dense fibrous
tissue surrounds cartilage or perichondrium ; but there may be much lympho-
cytic infiltration also in preserved fat and areolar tissue. During the second
month conditions are similar and lymphocytes may now also move lengthwise
in the direction of the fibrillation in the cartilaginous ground substance and
here they gradually perish. The injurious action of the lymphocytes makes it
occasionally possible for the blood vessels and connective tissue cells to pene-
trate for a short distance the marginal portion of the cartilage. Otherwise,
connective tissue cells push only into necrotic cartilage. After 5^2 months, the
reaction on the part of the host cells was not more intense than at earlier
periods and the lymphocytic reaction over wide areas could be mild ; likewise,
some fat and areolar tissue could still be preserved. The homoiogenous bone
marrow had become necrotic and was replaced by a loose fibrillar connective
tissue ; bone was surrounded in places by giant cells.

In general, in homoiogenous thyroid and fat tissue the activities of the con-

TRANSPLANTATIONS 45

nective tissue and lymphocytes set in at about the same time, and in the same
host the relative degree of the lymphocytic reaction was in many cases the
same in various tissues, despite the fact that cartilage and fat tissue give off a
smaller amount of homoiogenous substance than do thyroid and kidney. Al-
though it seems that lymph vessels grow more actively into the thyroid than
into fat tissue, it is not probable that this explains the difference in the degree
of lymphocytic reaction in these two tissues, especially in view of the observa-
tion that the lymph vessels which grow into the homoiogenous fat tissue are
less crowded with lymphocytes than are those in the thyroid gland.

Autogenous and homoiogenous transplants of cartilage-fat tissue differ,
then, not only in the greater ability of the former to survive and the great
injury inflicted on the latter by the homoiotoxins, as well as by various kinds of
host cells, but also in the greater regulative power in the autogenous tissues
which successfully overcomes the results of injuries caused by the experimen-
tal procedures used. However, also homoiogenous cartilage, perichondrium
and fat tissue possess to some extent still a certain regulative power, as indi-
cated by the new formation of perichondrial cartilage around an area of
necrotic cartilage. In autogenous and homoiogenous transplantations condi-
tions are therefore very similar in rat and guinea pig. A first period of injury
and degeneration is followed by a second period of recovery and regeneration,
which affects the same tissues. There are, however, some minor differences,
mainly of a quantitative nature, in these two species. In the rat the regenerative
activity of the perichondrial cells seems to be greater than in the guinea pig;
but in the latter the invasion of fat tissue by connective tissue, as a rule, is
more extensive than in the rat. On the other hand, in the rat the lymphocytic
reaction may be somewhat more intense.

We have, so far, discussed autogenous and homoiogenous transplantations
of thyroid, cartilage and fat tissue and associated tissues in rat and guinea
pig ; these were the tissues commonly used in our investigations. But in addi-
tion we have made use of a number of other organs or tissues ; from among
these we shall select striated muscle in the rat, and uterus and kidney in the
guinea pig, for a comparison of autogenous and homoiogenous reactions. Each
of these organs shows some peculiarities which are of interest in the analysis
of the common factors underlying the differences in the reactions against
autogenous and homoiogenous individuality differentials.

7. Autogenous and homoiogenous transplantation of striated muscle
tissue in the rat. Elson found that after autogenous transplantation of stri-
ated muscle tissue, the latter remains preserved for at least six months, and
probably indefinitely. During the first few days the greater portion of this
tissue became necrotic and was invaded by polymorphonuclear leucocytes,
which were attracted either by the necrotic material or by some accidental
bacterial products ; they disappeared again after a few days. After four days
a proliferation of the muscle nuclei set in, and this was quite marked after six
days, the nuclei lying in long slender muscle spindles, many of which developed
cross-striations. Gradually the latter became more definite, while some of the
nuclei disappeared and others assumed a more peripheral situation. At fifteen

46 THE BIOLOGICAL BASIS OF INDIVIDUALITY

days, the muscle tissue consisted chiefly of long slender fibers, with good
cross-striations and an increase of muscle nuclei as compared to the normal
number. By this time the lymphocytes, which at first were present in small
numbers, had almost or completely disappeared. At 28 days the muscle, except
for slight signs of degeneration in a few areas, appeared mature and normal
in almost every respect. Conditions were similar when the transplanted muscle
was about at the height of its development. Later on there was some invasion
by fibroblasts and the muscle fibers became small ; but there was still some in-
crease in nuclei and in connective tissue cells and lymphocytes. It was pre-
sumably the abnormal situation and the lack of the normal function of the
transplanted muscle which led to the slight pathological changes noticeable at
this time.

After homoiotransplantation of striated muscle tissue there were fewer
regenerative growth processes in the first period and much more degeneration,
on account of an invasion of the transplants by lymphocytes, and, to a less
extent, by connective tissue at subsequent periods. Thus homoiotransplanted
muscle disappeared much earlier than autotransplanted muscle, no well-
preserved tissue being present at 50 days. This result was due to the primary
action of the bodyfluids of the host, which were inadequate for the homoio-
genous graft, which injured it and interfered with its growth processes; and
it was secondarily the result of the activity of the host cells, which led to
further and, in the end, total destruction of the muscle tissue, at a time when
the autogenous muscle was well preserved. The growth processes, which take
place in the muscle following a primary degeneration of its major portion,
represent less true regenerative processes than those of compensatory hyper-
trophy, consisting in an increase in sarcoplasm and a multiplication of nuclei.

While in the autotransplanted muscle a nuclear proliferation was seen as
early as four days after transplantation, it was lacking at this time in the
homoiotransplanted muscle. In the latter there appeared at six days a slight
lymphocytic reaction and there were also fewer muscle fibers and a smaller
number of well developed nuclei in the homoiotransplants. At ten days the
lymphocytic reaction increased in intensity, some muscle fibers degenerated,
but other muscle fibers remained and underwent still a slight proliferation of
nuclei. There was thus, in the early periods after transplantation, a balancing
between growth processes and degenerative processes. Later, the invasion of
the muscle by lymphocytes and its destruction increased. At 32 days there was
an intense lymphocytic reaction, which more or less completely took the place
of the muscle transplant. However, there were a few small nucleated muscle
spindles or fibers with cross-striation. The invasion of lymphocytes continued
to increase and at the same time connective tissue cells of the host participated
in the process of destruction of the graft. At 50 days, only a few remnants of
muscle tissue were found, and at 70 days there was a maximum of lymphocytic
reaction coinciding with a minimum in the preservation of the muscle tissue.
At 118 days, no muscle tissue was seen; its place had been taken by lympho-
cytes, connective tissue and a few small blood vessels.

Hence, while the type of growth processes that occur in the muscle grafts is

TRANSPLANTATIONS 47

the same after homoio- and after allotransplantation, these growth processes
were less intense after homoiotransplantation and, instead, degenerative
processes predominated, largely due to the activity of lymphocytes and con-
nective tissue. But there was here also a primary injury of the transplant by
homoiotoxins carried to the graft by the bodyfluids, which corresponds to the
rinding of Hesselberg in the transplanted thyroid of the guinea pig, and which
has been observed by us also in this species in transplanted unstriated muscle
tissue of the uterus and in the placentoma formation in transplanted pieces of
uterus. The peculiarity of the growth processes in muscle grafts, which tend
to repair the degenerative processes, consists in the fact that they have to
contend with factors unfavorable to growth, similar to those which are found
in liver tissue or in those parts of the epidermis which are farther removed
from the source of nourishment, or in the connective tissue in the neighbor-
hood of foreign bodies.

8. In experiments carried out with Hesselberg and Kerwin, autogenous
and homoiogenous transplantations of the uterus were compared. Pieces of
uterus were transplanted either into subcutaneous pockets in the abdominal
wall or in the ear of the guinea pig. The latest period at which homoiogenous
pieces were found in pockets in the ear was after 16 days, and in the abdominal
wall, after 24 days. In the former, conditions for the survival of the transplant
are more unfavorable than in the latter;, at later periods, only hyaline tissue
with some clusters of lymphocytes were found as remnants of the homoio-
transplants. The autotransplants were well preserved after 35 days and would
presumably have lived indefinitely. At that time they showed good preservation
of the uterine surface epithelium and the glands, in both of which there was
mitotic proliferation; strands of connective tissue separated groups of glands,
without compressing them, because the connective tissue remained cellular-
fibrillar or myxoid near the epithelium, without becoming fibrous ; also, the
unstriated muscle tissue was well preserved and in connective tissue as well as
in unstriated muscle occasional mitoses were found.

Three periods can be distinguished as far as the fate of these transplants
is concerned. In the first five or six days there is no marked difference between
autogenous and homoiogenous transplants. During the second period, lasting
from the 6th to the 20th day, differences develop between the autogenous and
homoiogenous tissues, and in the third period the latter are in the process of
destruction, while the former are well preserved. In both auto- and homio-
transplants the tissue is shrunken during the first few days, owing to the in-
sufficient nourishment provided during this period ; they not only recover from
this condition later, but a new formation of tissue, as indicated by the occur-
rence of mitoses in various tissues, takes place. Also, the connective tissue
recovers ; it has a myxoid, cellular character near the epithelium and it shows
mitoses. A part of the connective tissue is derived from the transplant, but
other growing connective tissue has its origin in the host. The second period
begins at about the 6th day, and on the 7th day, when the transplanted uterine
epithelium forms a cyst with papillae, differences between the autogenous
and homoiogenous transplants set in. Mitoses are found in the cellular-myxoid

48 THE BIOLOGICAL BASIS OF INDIVIDUALITY

connective tissue in the autotransplant and, in general, there are many mitoses
here. In the homoiotransplant the epithelium is flatter, there are more lympho-
cytes and the connective tissue has a more fibrillar-cellular character. The
unstriated muscle tissue is either lacking or it is invaded by connective tissue
in the homoiotransplant. However, certain variations as to the differences be-
tween autogenous and homoiogenous transplants occur in individual cases ;
but on the whole, the recovery of the autogenous tissue is better and especially
the myxoid connective tissue and unstriated muscle are better preserved in
the autotransplant and there are here fewer lymphocytes. In the homoiotrans-
plant, the epithelial cyst remains incomplete and there is more necrotic tissue,
but even in this kind of graft the lymphocytes are not present in large masses
and they are not very injurious during the second week and first half of the
third week, but they may destroy the uterine glands and injure the surface
epithelium.

In the homoiotransplant the connective tissue still invades the unstriated
muscle tissue and gradually during the latter part of the third and the begin-
ning of the fourth week the lymphocytes become more frequent around and in
the graft, and very little myxoid connective tissue or muscle tissue is, at this
time, to be observed. The surface epithelium, some glands, and the peritoneal
epithelium are more resistant to the action of the homoiotoxins than are the
myxoid connective tissue and the unstriated muscle tissue. On the other hand,
the amount of hyaline connective tissue increases, at least partly on account
of the progressive organization of the necrotic material. In the middle of the
4th week, the latest period at which living homoiotransplanted tissue was
seen, few mitoses were found in the epithelium, although this epithelium and
the peritoneal endothelium were relatively best preserved, while the myxoid
connective tissue and the muscle tissue were replaced by fibrillar and hyaline
connective tissue.

It follows from these experiments that great parts of the homoiotransplanted
uterus are primarily damaged by the action of the homoiotoxins, that uterine
tissues attract the lymphocytes less strongly than do kidney and thyroid, and
that these cells are of less significance in uterus than in thyroid and kidney. In
uterus transplants the lymphocytes contribute only secondarily to the destruc-
tion of the graft and then chiefly through their action on the epithelial struc-
tures. Thyroid and kidney are largely epithelial structures, they are less
affected by the body fluids of the homoiogenous host, although a primary effect
of the strange bodyfluids may be exerted also on these organs; but, in the
main, their destruction is brought about by lymphocytes and connective tissue
cells. It is probable that without the injurious action of these cells of the host,
the homoiogenous thyroid and kidney would survive longer than the homoiog-
enous uterus transplants. The latter tissues cannot recover as well from the
primary injury caused by the process of transplantation, nor can their epi-
thelium induce or maintain the myxoid-cellular character of the stroma as well
as autogenous tissues. Furthermore, the tissues that have recovered cannot
maintain themselves permanently in the homoiotransplants because of the in-
adequacy of the bodyfluids. The changes produced in the stroma react un-

TRANSPLANTATIONS 49

favorably also on the epithelium and a vicious circle is thus established in the
epithelium-stroma relations. Also, the uterine epithelium is not seriously af-
fected by the homoiotoxins, if at all ; but secondarily, the epithelium is injured
by the lymphocytes. While the lymphocytes appear at about as early a time in
or around the homoiogenous uterine tissues as around the corresponding
thyroid and kidney tissues, in the latter the lymphocytic reaction becomes much
stronger than in the former. The resistance of the epithelial structures in the
homoiogenous uterus is indicated also by the fact that mitotic proliferation
continues actively in the transplanted uterine epithelium much longer than in
thyroid and kidney.

9. The effect of autogenous and homoiogenous bodyfluids on the devel-
opment of placentomata in the transplanted uterus. If the non-transplanted
uterus has been sensitized by the corpus luteum hormone about five to eight
days after estrus, incisions into the uterine horn or introduction of foreign
bodies into the uterus call forth the production of placentomata, which reach
their full development in about ten days, while at a still later period regression
of these newformations sets in. If instead of making incisions into the uterine
mucosa in situ, we autotransplant pieces of the sensitized uterus about six days
after estrus, the mechanical stimulation due to the process of transplantation
likewise leads to placentoma formation in the transplanted periglandular con-
nective tissue, which proliferates actively by means of mitoses. At the height
of the development, pearls and also giant nuclei may form in certain areas in
the placentoma; the other uterine tissues are well preserved and lymphocytes
are absent, but some spindle-cell connective tissue with mitoses may grow into
the placentoma and destroy parts of it.

If pieces of the uterus are homoiotransplanted instead of autotransplanted,
the results differ in accordance with the availability of corpus luteum hor-
mones in the host ; however, even under the most favorable hormonal condi-
tions the homoiotoxins always tend to exert an injurious effect on the trans-
plants. If the homoiotransplantation is made into guinea pigs, in which estrus
has taken place about six days previous to transplantation, in the large ma-
jority of the animals only traces of or very slight placentomata developed, or
none. Occasionally, large placentomata developed, but in this case there
seemed to be more necrosis in these homoiogenous than in the autogenous
structures; also, moderate or even marked lymphocytic infiltration could be
found about 10 or 11 days after transplantation in some of the connective
tissue of the transplant.

In five pregnant guinea pigs, pieces of uterus were homoiotransplanted. In
two animals no placentomata developed, while in three there were small
placentomatous areas. Lymphocytic infiltration in the surrounding tissue was
moderate, or, in places, more marked, and it was found also directly in the
placentomatous formations ; again, the ingrowth of spindle-cell connective
tissue could destroy and replace part of the placentomata. After transplanta-
tion of the uterus pieces into male or into sexually immature female guinea
pigs, no placentomata developed and the degree of lymphocytic infiltration
varied in different cases.

50 THE BIOLOGICAL BASIS OF INDIVIDUALITY

In the development of placentomata in the homoiogenous uterus of the
guinea pig we see another example of a direct injurious action of the homoio-
toxins present in the circulating bodyfluids, which damaged the mucosa of the
uterine transplant to such an extent that the formation of placentomata was
either prevented or much reduced under conditions in which normally the
sensitizing hormones would have made these growth processes possible. There
was, then, a struggle between the sensitizing hormones and the homoio-
toxins ; only in a few instances was the hormone action, in conjunction with
the mechanical stimulation due to the trauma, able to overcome the injurious
effect of the homoiotoxins. The lymphocytic infiltration was quantitatively so
weak that the reaction on the part of the host cells could not be held responsi-
ble for these growth-depressing effects.

10. Transplantation of autogenous and homoiogenous kidney tissue. The
process of transplantation initiates tissue reactions in the host and
changes in the transplant. These may be due to general factors common to
autogenous and homoiogenous tissue; in addition, there are the specific re-
actions due to the varying degrees of incompatibility of the individuality
differentials of host and transplant. These differences in individuality differ-
entials activate the formerly quiescent host tissues in accordance with the in-
herited, constitutional characteristics of the latter. Furthermore, by comparing
the reactions in tissues transplanted into different locations, the general injury
to the tissues is found to vary in degree; in a particularly unfavorable situa-
tion, with increasing injury to the transplant, the general, less specific reac-
tions of various tissues which are caused by the injury, may dominate over
the more specific reactions which are induced by incompatibility between the
individuality differentials of host and transplant. It is in order to analyze
still further these characteristics of tissues that we shall record the principal
observations as to the differences between autogenous and homoiogenous
transplants of kidney tissue in the guinea pig. Greater damage is suffered by
these grafts, for instance, after transfer into pockets in the ear of guinea
pig than into pockets in the subcutaneous tissues of the abdominal wall or of
the dorsum. This is true of both autogenous and homoiogenous tissue and both
may die after some time, although the latter is earlier destroyed; also, the
specific differences between these two types of transplantation are less evident
in ear transplants than in those in the subcutaneous tissue of the anterior or
posterior wall of the abdomen. Likewise, homoiotransplants of uterine tissue
are destroyed more rapidly in the ear than in the abdominal wall.

After transplantation into the ear of pieces of kidney, destruction of
homoiogenous tissue was complete after 21 days, while the autogenous tissue,
although injured by the ingrowing connective tissue, was not yet quite de-
stroyed at 38 days. Transplanted into the subcutaneous tissue of the abdominal
wall, both autogenous and homoiogenous kidney tissue was preserved for at
least 30 days, and it probably remained alive for a still longer period. These
differences were presumably due to the greater pressure exerted on the grafted
tissue in the ear and, perhaps, also to a less satisfactory blood vessel supply in
this region. The same factors caused also a much more marked lymphocytic

TRANSPLANTATIONS 51

infiltration of the homoiogenous tissue in the back of the abdominal wall than
in the ear. In the autogenous transplants there were occasional lymphocytes
around the tubules or in the capillaries of glomeruli, especially in places where
the connective tissue was increased around the tubules, but often they were
entirely absent, while they were very prominent in homoiogenous pieces, es-
pecially in those transplanted into the abdominal wall.

The lymphocytic infiltration is distinct after nine days in homoiotransplants,
after which period it increases gradually — this applies also to transplants in
the ear, although here it is less prominent. Lymphocytes collect around the
kidney transplant and penetrate into the lumen of the tubules as well as into
the glomeruli, isolating and helping to destroy and replace the tubules. The
destruction of tubules by these cells can be seen at ten days after transplanta-
tion and it persists from then on. In the central necrotic or organized area they
are present in smaller numbers. However, the intensity of the lymphocytic re-
action varies in different homoiotransplants ; it apparently is not prevented nor
even noticeably diminished by a loss of even as much as one-half of the weight
of the host. This reaction was similar in strength in thyroid and in kidney ; in
both these organs, after homoiotransplantation, it became noticeable at about
the same time and gradually progressed. If a bacterial infection takes place,
the tissue at some distance from the place of infection may remain preserved,
and the infection does not call forth a lymphocytic reaction in autogenous
transplants nor does it noticeably increase it in the case of homoiotransplants ;
but ordinarily already the lymphocytic reaction is marked around and in
homoiotransplanted kidney. As we have stated, in homoiotransplanted tissue
of the mouse it seems that bacterial infection may increase the intensity of
the lymphocytic reaction.

While the degree of compatibility between the individuality differentials of
host and transplant largely determines the reaction on the part of the lympho-
cytes, the less specific factors of injury sustained by the transplants during and
following the transplantation, the unfavorable conditions in the transplant,
caused by its strange situation, and the difficulty of entering into normal rela-
tions with the new tissues surrounding it are, to a greater extent, responsible
for the activity of the fibroblasts and the production of fibrous tissue. The
organismal differentials are of less significance in these latter changes, al-
though they are still important. In both autogenous and homoiogenous tissues
the connective tissue grows between the tubules and glomeruli of the peripheral
zone and progresses towards the central necrotic material. However, a larger
number of fibroblasts seem to grow into the homoiotransplants; this is es-
pecially clear following the first two weeks, when the injury due to the opera-
tion has in great part subsided. In the autogenous transplants the closely ap-
proximated tubules are arranged in lobules and it is the lobules which are
separated by connective tissue, whereas, in the homoiotransplants the individ-
ual tubules are separated by connective tissue; but strands of connective tissue
may surround some individual tubules also in autotransplants. Through the
exertion of pressure by this tissue the lumen of the central tubules is obliter-
ated or shrunken. But in addition there may be atrophy as a result of insuffi-

52 THE BIOLOGICAL BASIS OF INDIVIDUALITY

cient nourishment. The mechanism underlying these relations of the connective
tissue to various types or degrees of injury of the parenchyma is, as yet, very
little understood. Stereotropic reactions, movements in contact with strange
foreign bodies, perhaps chemotropic activity elicited by necrotic tissue, as well
as other altered relations between the more specific parenchymatous tissue and
the surrounding stroma, may form the stimulus for both movements and in-
crease in size and multiplication of cells in the surrounding connective tissue.
It is these factors which may ultimately lead also to the destruction of auto-
genous skin cysts in the guinea pig, which form after subcutaneous trans-
plantation of epidermis with the underlying connective tissue. Here the sur-
rounding connective tissue may grow stereotropically along the hairs of the
skin into the interior of the cyst, where it separates and surrounds the keratin
lamellae. Thus after some time the host connective tissue may bring about the
destruction of autogenous subcutaneous skin transplants ; but in addition there
develop specific lymphocytic reactions around homoiogenous skin grafts.

The size and character of the central necrotic area in transplanted kidney
varies in different animals ; the organizing fibroblasts grow first between and
along the necrotic tubules and then into the tubules. As the result of the organi-
zation of the fibroblasts the necrotic material becomes hyaline ; in addiion, the
latter is taken up by phagocytes, which thus aid in its removal. On the whole,
on account of the relative hardness of the necrotic kidney tissue, the organiza-
tion progresses slowly and with unequal rapidity in different hosts ; it may re-
quire 20 days or even longer for this process to be completed. Following or-
ganization of the autotransplanted thyroid, as we have stated, the central
necrotic part after some time becomes cellular and small in size, but the
homoiotransplanted thyroid is fibrous-hyaline and large. However, in the kid-
ney there is no marked difference between the condition of the central parts in
autogenous and homoiogenous transplants, because in both, the necrotic kid-
ney tissue is resistant to the action of the organizing host cells. The principal
difference between the two types of kidney transplants consists in the number
of lymphocytes and of fibroblasts and in the amount of connective tissue in the
peripheral living area.

The tubules in the transplanted kidney are simple and similar to the collect-
ing tubules. The glomeruli are small and tend to be hyaline. There are frequent
mitoses in the tubules between five and seven days ; at nine days a mitosis was
found in a glomerulus. From the 7th or 8th day on, a decrease in their num-
ber occurs, but they are found even after 27 days, although not after 30 days,
in both autogenous and homoiogenous transplants. The mitotic activity may,
at least for some time, be as great in the latter as in the former, or even greater.
As a result of the transplantation a chain of changes is initiated in the trans-
plant, irrespective of the character of the individuality differentials, and these
changes lead to mitotic cell proliferation; gradually this reaction curve de-
clines, and at last a new equilibrium is reached in which cell proliferation
ceases, although the original normal condition of the transplant has not been
restored. These curves of changes are similar in thyroid, kidney and uterus
transplants, although some differences exist. It is possible that in homoio-

TRANSPLANTATIONS 53

transplants, to the primary injury which initiates the regenerative processes
is added the secondary injury inflicted on the tubules by lymphocytes and con-
nective tissue cells; this second factor may cause increased mitotic prolifera-
tion, provided enough tubule tissue is left to respond with such activity.

We may then conclude that the difference between autogenous and homoio-
genous transplants of kidney pieces in the later stages is due to the more rapid
destruction of the regenerating tubules in the latter grafts, rather than to a
primary difference in the actual development and growth of kidney tissue,
which almost ceases on or about the 14th day after transplantation, although a
slight regenerative process may occur at a still later date. The damage to the
tissue begins on about the 9th day and in the homoiotransplant destruction is
almost complete 21 days after transplantation. The activity of the connective
tissue destroys also the autotransplant, which has been injured through the
abnormal conditions in which it lives, especially in the ear; this activity is
therefore, at least partly, an injury reaction, which may develop in autogenous
as well as in homoiogenous transplants. In contrast to the connective tissue
cells, the lymphocytes react more specifically to homoiotoxins which are
present in the bodyfluids of the host and in the transplanted tissue itself ; these
toxic substances are both involved, partly directly, partly indirectly, in the
activity of the lymphocytes, but, to a certain extent, also in that of the con-
nective tissue elements.

Chapter J

Transplantation of Autogenous and
Homoiogenous Tissues in Mice

The large majority of experiments which we carried out in mice were
done with closely inbred strains, and exchange of tissues between
members of the same strain would therefore not correspond to homoio-
genous transplantations but to something akin to autogenous or syngenesio-
transplantation. Which of these two types of transplantation it resembles more
would depend on the degree and effects of the inbreeding. However, experi-
ments in which tissues are transferred from one strain to another strain would
be more nearly comparable to homoiogenous transplantations, although there
is no absolute identity of inter-strain transplantation and ordinary homoio-
transplantation ; in the latter there may be a somewhat greater variability in
the relations between the individuality differentials of host and transplant. In
addition to the transplantation between different strains — inter-strain trans-
plantation— we have also made some experiments in which tissues were ex-
changed between ordinary non-inbred white mice obtained from various
dealers. As to autogenous transplantations, these should not be affected by the
inbreeding and should yield the same results in closely inbred, in less closely
inbred, and in non-inbred strains.

Autogenous transplantation in mice. Autogenous transplantation is in all
essential respects similar to this type of transplantation in rat and guinea pig.
The tissue remains preserved provided the injury connected with the process
of grafting and that due to the abnormal position of the graft have no long-
lasting, unfavorable effects. The changes which are observed after auto-
transplantation can not be due to incompatibility between the individuality
differentials of host and transplant, since these differentials are identical, but
they are due to mechanical or chemical factors of a non-specific kind, similar
to those which, under corresponding conditions, might also take place in non-
transplanted tissues. On account of vascular changes around the transplant
and of necrosis in the insufficiently nourished portion of the grafted tissues,
polymorphonuclear leucocytes may appear; lymphocytes may be attracted by
non-specific factors, such as foreign bodies, causing a mild degree of injury,
and epithelioid and giant cells may be produced. Injury or abnormal growth
processes in non-transplanted normal striated muscle tissue may call forth a
multiplication of muscle nuclei and the formation of thinner muscle fibers or
spindles. The same changes may take place in transplanted muscle. Dense
fibrous tissue tends to form around and sometimes between the living muscle
fibers, and, at first, some lymphocytes may accumulate between the muscle
fibers. But the lymphocytes were not numerous in the autotransplanted muscle
tissue ; they were still found at 20 days, but no longer after 30 days following

54

TRANSPLANTATION OF TISSUES IN MICE 55

transplantation. Hemorrhages were observed in the thyroid transplant at 12
days, therefore at early periods after the operation, but they also had disap-
peared at 30 days. In one autotransplant of thyroid gland an abscess, due to
bacterial infection, adjoined the graft in one place; the ring of acini was
interrupted at this point, but this condition did not destroy the autogenous
character of the transplant except locally. In early periods following auto-
transplantation the amount of fibrous tissue in the center of the graft may be
considerable, owing to the organization of the central necrotic tissue ; but this
decreases later. In the transplanted fat tissue, infiltration with lymphocytes, a
noticeable increase in connective tissue, and the presence of small vacuolated
phagocytic cells are lacking. Localized necrosis of the cartilage may here also
be followed by the formation of a plate of new cartilage through the regenera-
tive activity of the perichondrium. We have not examined autotransplanted
mouse tissue later than 30 days following transplantation, but there were al-
ready some indications at this period that the effects of the accidental factors
we have mentioned disappear in the course of time as a result of regulatory
activities of the tissues, which take place under autogenous conditions. By a
comparison of the results of autogenous and homoiogenous transplantation it
is thus possible to separate a variety of more or less accidental factors from
the specific ones caused by the disharmony of individuality differentials.

Homoiogenous transplantation. This 'consisted of two kinds of experi-
ments, namely, (1) an exchange of tissues between not closely related tame
mice or between non-inbred and inbred strains of mice, and (2) exchange
of tissues between closely inbred strains of mice. The second set of experi-
ments was first carried out, and in this type of homoiogenous transplantations
the connective-tissue as well as the lymphocytic reaction was definitely weaker
than in the corresponding transplantations in rats and guinea pigs. There was
the possibility that the relatively low intensity of these reactions was due to the
close inbreeding to which these mice had been subjected. We added, therefore,
to these transplantations, the first series; but here the results were similar,
indicating that these weak reactions are characteristic of the mouse and that
they are not due to the close inbreeding. If we make allowance for these differ-
ences, the grades in these transplantations in mice are otherwise in principle
the same as in the experiments with rats or guinea pigs. If the thyroid was
preserved, the relative incompatibility of the individuality differentials in host
and graft was indicated in many cases by the stunted condition of this trans-
planted organ; in addition, the organization of the central necrotic material
was, in some instances, as yet imperfect. There were a number of experiments
in which, particularly in the fat tissue, there were found either some scattered
polymorphonuclear leucocytes or even small collections of these cells. In such
transplants there were, as a rule, also an increased amount of fibrous tissue
and an increase in lymphocytes visible in addition to small vacuolated cells.
More rarely, a few polymorphonuclear leucocytes were found also in homoio-
genous thyroid or other homoiogenous transplants. As already mentioned,
there was often some doubt as to whether the presence of the leucocytes was
not due to accidental infections with bacteria, which could take place more

56 THE BIOLOGICAL BASIS OF INDIVIDUALITY

readily in mice than in rats or guinea pigs, because of the greater difficulty of
performing a perfectly sterile operation in the smaller animal.

In transplantations of pieces of thyroid, striated muscle, xiphoid cartilage
with fat tissue, and of ovaries between not closely inbred mice, obtained
from different dealers, or from inbred D or C57 mice to the former, after
20 and 30 days the grades ranged between 1 and 2—, except in one trans-
plantation, in which the grade was 2. With the exception of the latter, the
results were therefore characterisitc of severe homoio-reactions. In no case
was ovarian tissue preserved. When grade 1 was given, neither the muscle nor
the thyroid transplant was preserved; only cartilage and perichondrium had
survived and the fat tissue was partly infiltrated with small vacuolated or
epithelioid phagocytic cells and with varying amounts of fibrous tissue and
lymphocytes; however, these reactions in the fat tissue were always much
diminished as compared with those in rats and guinea pigs, except in some
transplants in which polymorphonuclear leucocytes were more pronounced.
In general, the amount of fat tissue preserved was greater in the mouse than
in the two other species. In the case in which grade 2 was given, the thyroid
transplant, while small, was in a relatively good condition ; the center was
filled with dense hyaline tissue and the surrounding ring of acini was incom-
plete; also, the parathyroid was preserved. In the cartilage-fat transplant the
fat tissue was fairly well preserved but there was here some increase in fibrous
tissue and there were collections of lymphocytes. Parts of the transplanted
muscle tissue were preserved and embedded in fibrous tissue.

In an additional series of experiments we exchanged thyroid, cartilage and
fat tissue, with or without bone or muscle tissue, between non-inbred mice and
inbred mice belonging to strains D, C57 and A. In these experiments the
grades also varied as a rule between 1 and 2— ; in a few cases, slightly better
grades (2/2—) were obtained. The reactions were usually more severe after
20 than after 12 days. Occasionally there was some lymphocytic infiltration in
the thyroid transplants ; in the fat tissue there was partial invasion by con-
nective tissue, vacuolated phagocytic cells and lymphocytes.

Among the many experiments in which tissues were exchanged between
different strains of inbred mice, we may mention one set in particular, in
which thyroid, cartilage and fat tissue, with associated tissues, as well as pieces
of striated muscle or ovary were transplanted into each host and examination
took place after 20 days. In ten transplantations to different hosts the grades
varied in the individual cases between 1 and 2—. When grade 1 was given,
only the cartilage or parts of cartilage were preserved, but perichondrial re-
generation of cartilage could take place around necrotic areas. The fat tissue
as a rule was, to a variable extent, invaded by small vacuolated phagocytic cells
and by connective tissue; infiltration with lymphocytes varied in different
cases ; also the amount of preserved fat tissue was variable, but on the average,
the amount was greater in these transplantations in mice than in rats and
guinea pigs. There were also some collections of polymorphonuclear leuco-
cytes, especially in the fat tissue, and more prominently around fat cells which
were enclosed in fibrous tissue. The thyroid was either entirely replaced by

TRANSPLANTATION OF TISSUES IN MICE 57

fibrous tissue in cases in which grade 1 was given, or variable parts were pre-
served ; in the latter case, the transplant was stunted, even if an almost com-
plete chain of acini was found in a fibrous nodule. Lymphocytes could be lack-
ing in such grafts, but in other instances some collections of lymphocytes
were found in certain places ; the dense masses of lymphocytes, which oc-
curred so often in rat and guinea pig, were as a rule absent in the mouse. The
transplanted striated muscle was either wholly necrotic or small numbers of
regenerated muscle fibers filled with nuclear chains could be seen. In the
muscle likewise, some lymphocytes could accumulate. The average grade in
these ten transplantations corresponded to 1 + .

We have carried out in addition, several other large series of experiments,
in which at different times, extending over a number of years, we determined
the mode of reaction in the reciprocal exchange of tissues between the fol-
lowing inbred strains of mice: A, D, C3H, CBA, C57, Old Buffalo, New
Buffalo, C, and AKA. A detailed discussion of these experiments will not be
undertaken, but a brief statement of the principal results may be made. The
examination took place, as a rule, between 12 and 30 days following trans-
plantation ; injurious effects, on the average, increased with increasing time
of exposure to the bodyfluids and cells of the host. The grades were changed
correspondingly. After 20 and 30 days, they varied in the majority of cases
between 1 and 2— ; but in some cases the grades were slightly higher than 2 — ,
without however definitely reaching 2. Intra-strain transplantations, which
were carried out at the same time, yielded higher grades. There was quite
generally a correspondence between the state of preservation or injury of the
various tissues in individual experiments. However, this did not necessarily
involve a correspondence in the degree of lymphocytic infiltration, because the
latter was often determined by local factors, among which, perhaps, local in-
fection with bacteria played a role in a number of cases. While lymphocytes
were by no means present in all homoiotransplants of cartilage and fat tissue,
some increase in connective tissue and infiltration of the fat tissue with small
vacuolated phagocytic cells was the most frequent indication of the incom-
patibility between the homoiogenous hosts and transplants. The lymphocytic
infiltration cannot serve, therefore, as an indicator of the relationship between
the individuality differentials of host and donor in the mouse to the same
extent as in guinea pig and rat.

We have, thus, in these inter-strain transplantations, to deal with marked
homoio-reactions similar to those found in transplantations of homoiogenous
tissues in rats and guinea pigs. They differ from the latter in the decidedly
decreased invasion of the grafts by lymphocytes and by connective tissue, in
the frequent preservation of a stunted thyroid, in which lymphocytic infiltra-
tion was absent, and in the usually much diminished organizing activity of the
connective tissue. As in the case of the rat, so also in the mouse the muscle
fibers which were transplanted with xiphoid cartilage and fat tissue were
relatively more resistant than the bone marrow, which was invariably de-
stroyed in these homoiotransplants. Also, in the mouse the perichondrium
was able to regenerate new cartilage, but the connective tissue cells seemed

58 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to penetrate less readily into necrotic areas in the cartilage than in the rat. On
the whole, it is evident that in the mouse the injury and destruction of homoio-
genous tissues by the bodyfluids preponderate over the damage inflicted by
lymphocytes and connective tissue, and that the activity of the latter may or
may not be added to the action of the homoiotoxins of the circulating body-
fluids.

From our observations, it follows that transplantation of thyroid gland,
cartilage and fat tissue, together with the associated tissues, cannot serve as
accurately as an indicator of the relationship between the individuality differ-
entials of host and transplant in mouse as in rat and guinea pig. It is ad-
visable wherever possible to use, in addition to these transplants, grafts of
ovaries and of striated muscle. A comparison of the effects of transplantation
on a combination of these various organs may then serve as a good indicator
of the degree of compatibility or incompatibility between the individuality
differentials of host and donor.

Chapter /J.

Autogenous, Syngenesious, Homoiogenous and
Interracial Transplantations in Birds

In our experiments with Addison, in which we compared the homoio-
transplantation of pigeon skin with the transplantation of this tissue into
chickens, into various mammalian species, and also into amphibia, we
found a marked difference between the results of homoio- and heterotrans-
plantation. In the former, the lymphocytes of the host were the principal
agent which injured and in the end destroyed the transplant, whereas, in the
latter it was the toxicity of the bodyfluids which injured the transplants,
caused a cessation of the proliferative power of the epidermis and, soon after-
wards, destroyed it altogether. After heterotransplantation, this destruction
was accomplished usually as early as during the first and second week, while
after homoiotransplantation it took place in some cases during the fourth
week, but in other cases transplants were found alive, at least partly, as late
as during the fifth week.

While thus the distinction between homoiogenous and heterogenous trans-
plants was quite sharp, and while there was also at least some indication that
among the various types of heterotransplants there was, under certain condi-
tions, a correspondence between compatibility of the organismal differentials
and the degree of genetic relationship between the species, which served as
hosts and donors, no attempt had been made in these experiments to analyze
the finer differences in birds, which might be expected to exist between autog-
enous, syngenesious, homoiogenous and interracial transplantations. Nor
did the subsequent experiments of Schultz, nor those of Danforth and Foster,
give any information in this respect, although the latter in particular were of
interest from other points of view. Danforth and Foster, in experiments with
Leghorn and Plymouth Rock chickens, transplanted skin flaps from recently
hatched chicks to other chicks of the same inbred race or to other races. In
many cases the pieces of skin healed in permanently in chicks belonging to
other races, although the best results were obtained in the exchange of skin
between members of the same inbred race; but this may have been due to
accidental factors rather than to a similarity of the organismal differentials
between host and transplant. Danforth and Foster concluded that individuality
differentials exist in birds in isolated instances. However, the fact that they
used recently hatched chicks rather than adult birds made the recognition of
differences between individuality differentials more difficult, because in these
very young animals the reaction against strange individuality differentials
should be milder or, under certain conditions, lacking altogether ; in addition,
in these long term experiments a gradual adaptation between host and graft
might take place. Furthermore, the use of healing-in or lack of healing-in of

59

60 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the skin flaps represents an "all or nothing" test, which cannot give any in-
dication of intermediate results which might be found by means of a micro-
scopic study of cellular reactions. Experiments in which we used microscopic
studies of the cellular reactions against transplants in adult birds showed that
there is no identity between individuality differentials even in brothers be-
longing to the same inbred race. Likewise, it may be found that in adult lizards
homoiotransplantation of skin does not succeed, whereas autotransplantation
is successful (May). By means of statistical analysis Kozelka found in skin
grafts in Leghorn fowl, within the first few months after hatching, strong
indications that the degree of relationship between donor and host, which
signifies also the relationship between the individuality differentials of host
and donor, is one of the factors which determines the success of the trans-
plantations. Thus he found a persistence of grafts between unrelated birds in
18 per cent, between half and full brothers and sisters in 27 per cent, between
full brothers and sisters in SO per cent, and between offspring from father
and daughter matings in 68 per cent of the transplantations. Similar to our
experiences, he noted a correspondence in the behavior of several transplants
from the same donor to the same host. However, also non-genetic factors,
such as size or age of the donor and of the host, helped to determine the fate
of the transplants. In accordance with expectation, transplantations between
adult birds gave less favorable results than those between very young chicks,
but in both instances the relationship between the individuality differentials
of host and graft was the essential factor that determined the result of the
transplantation.

In continuing our former experiments in birds, we made use first of inbred
races of chickens, which we obtained from the Mount Hope Farm in Williams-
town, Mass., through the kindness of Dr. Goodale. In these experiments we
observed that notwithstanding close inbreeding, there was a marked lympho-
cytic reaction present, even around transplants in nearly related adult animals
belonging to the same inbred race. This reaction was so strong that a definite
and very distinct differentiation between the degree of similarity of individ-
uality differentials in these animals seemed impossible and our investigations
remained, therefore, unpublished. According to information given me by Dr.
Goodale, these chickens had been inbred only for five or six generations of
consecutive brother-sister matings. Likewise in our more recent experiments
with guinea pigs, inbred for only a small number of generations of brother-
sister matings, we did not yet observe a definite approximation of the in-
dividuality differentials in the various members of these families. We may
therefore conclude that in order to achieve progress towards an autogenous
constitution of the individuality differentials, a larger number of consecutive
brother-sister matings is required than those which had been made in the
chickens in Williamstown. Resuming these investigations more recently with
W. J. Siebert, we confirmed the finding that also in the exchange of tissues be-
tween brothers of strains of chickens inbred to a limited extent, a very in-
tensive lymphocytic infiltration and destruction of the transplants take place,
and that syngenesio-, homoio-, and interracial transplantations in such chick-

TRANSPLANTATIONS IN BIRDS 61

ens all behave in about the same manner, although some very slight differences
may exist. Thus while in homoio- and interracial transplantations the intensive
lymphocytic infiltration set in about 10 to 11 days following transplantation,
in syngenesiotransplantations it appeared a few days later, namely, after 13
days. Similarly, follicle-like accumulations of large lymphoblast-like cells,
which were found in these grafts in chickens and which aided the smaller
lymphocytes in the destruction of the strange tissues, were seen in the first
two types of transplantations after 13 days, and in syngenesiotransplantations
only after 16 days. While these differences in the time of the appearance of
such cells are very small, still they are in agreement with the findings of H. T.
Blumenthal in regard to differences in the time when the lymphocytes are in-
creased in the circulating blood after subcutaneous transplantation of various
pieces of tissue. It might be expected that the rapidity with which these
changes in the lymphocytes and lymphoblast-like cells become manifest locally
and the rapidity with which the increase in the lymphocytes takes place in the
blood, should be greater in those cases where the individuality differentials,
diffusing into the surrounding tissue or into the blood vessels, showed a
greater degree of strangeness and therefore also a greater toxicity.

In contrast to these types of transplantations, after autogenous trans-
plantation of skin and xiphoid cartilage with the surrounding tendon-like
tissue, collections of lymphocytes are lacking altogether or only very small
clumps of these cells, arranged around the vessels, can be seen. If keratin
from the transplanted skin has been separated from the epidermis by the
connective tissue, a few lymphocytes quite commonly collect around such
foreign bodies. Lymphocytes are either absent or only very small collections
form around particles of fat tissue transplanted with the cartilage or around
some foreign bodies.

A very interesting occurrence is that sometimes around and in these autog-
enous transplants a disequilibration between the host connective tissue or
the transplanted tendon connective tissue and the cartilage takes place. Then
connective tissue cells move toward the piece of cartilage and surround it,
giving rise to a capsule. Often they penetrate also into the periphery of the
graft in the direction of the fibrillar structure of the long axis of the cartilage
cells. In some cases, turning approximately at right angles to the long axis
of the cartilage cells, they penetrate slightly into the interior of the cartilage.
Moreover, these connective tissue cells possess the power to split and dissolve
the cartilage, and in doing so, they sometimes become larger. Either in the
cartilage or in the surrounding dense fibrous tissue some cells, coming from
the connective tissue, may change into epithelioid and giant cells, especially
in places where an obstacle interferes with their progress. Connective tissue
cells also accompany certain vessels which grow into the cartilage. But on
the whole, the transplanted cartilage, as well as autotransplanted fat tissue
and bone marrow with myelocytes, is well preserved.

There is a remarkable correspondence between the reactions of the host
connective tissue towards autotransplanted cartilage and towards autogenous
epidermis transplants when the latter do not close to a cyst-like or to a flat

62 THE BIOLOGICAL BASIS OF INDIVIDUALITY

body. The keratin, and perhaps also remnants of feathers or other foreign
material, can in these cases act as non-specific stimulators for the host fibro-
blasts, or even for the transplanted fibroblasts, and this process can some-
times lead to the destruction of the transplants ; but in these instances, we
have to deal with non-specific reactions of connective tissue cells and not with
specific reactions on the part of lymphocytes induced by strange individuality
differentials. The great difficulty on the part of the chicken and pigeon skin
in forming a typical closed cyst, probably due to the low degree of growth
intensity of the avian epidermal cells, is an obstacle to the successful sub-
cutaneous transplantation of skin in this class of animals. But we must sharp-
ly distinguish between non-specific extraneous factors and specific factors
which can be used in the analysis of individuality differentials. In the former,
we have to deal with general tissue reactions, and these present important data
which can be used in the construction of a physiology of tissues.

Various difficulties, then, are encountered, which limit a successful analysis
of the individuality differentials in birds. They include : ( 1 ) the difficulty of
obtaining the organs and tissues most suitable for transplantation in living
animals; (2) the presence of complicating, non-specific factors which may
cover up the reactions characteristic of the individuality differentials, as, for
instance, the connective-tissue reactions which we have mentioned, and (3)
the preponderance of lymphocytes in the circulation of birds, with which is
associated an excessively strong reaction of lymphocytes against even very
slight differences in individuality differentials; the great intensity of this
reaction makes the discernment of smaller differences in individuality differ-
entials difficult. However, the experiments which we have discussed do prove
the presence of very fine differences in individuality differentials in birds,
inasmuch as they have shown that such differences exist also between brothers
in inbred strains or races of birds.

However, the great intensity of the lymphocytic reaction in this class of
animals makes possible the clearer recognition of the mode of action and of
the effects of the infiltration of a tissue with large masses of lymphocytes. In
the experiments with chickens it could be seen that these cells are able to
cause the disintegration of such structures as tendon-like fibrous tissue, car-
tilage, and even bone, resulting either in their complete solution or at least
very extensive destruction, and leaving behind a fine network of remnants of
these tissues. In mammalian transplantations it has not been possible to ob-
serve such marked effects ; this is due presumably to the usually less massive
invasion of mammalian tissues by lymphocytes, even in cases in which lympho-
cytes form lymph-gland-like accumulations in the tissues, such as we found
especially in rat and guinea pig. It appears doubtful whether mammalian and
avian lymphocytes otherwise differ markedly in their destructive power on
tissue, which is presumably due to the action of enzymes. In the mouse, for
instance, one can see in homoiogenous transplantations that lymphocytes as
well as connective tissue cells are able to penetrate into hyaline connective
tissue with ameboid processes ; they move, in the latter, in the direction of the
fibers and lymphocytes may likewise invade pieces of cartilage in the direction

TRANSPLANTATIONS IN BIRDS 63

of the preformed fibrillations of this tissue ; but under such unfavorable con-
ditions these cells may later perish.

The effect of the individuality differentials of autogenous, syngenesious
and homoiogenous transplants on the lymphocytes in the circulating blood.

Disharmony between the individuality differentials of the transplant and host
not only causes local reactions, owing to the diffusion of the individuality
differential substances into the area directly surrounding the transplant, but
according to the findings of Blumenthal, diffusion takes place also into the
blood vessels, and probably into the lymph vessels, from which points these
differentials are carried presumably to the blood-forming organs and here
stimulate an increased production or elimination of the white blood cells into
the capillaries. This occurs in birds as well as in mammals. There is, more-
over, a quantitative relation between the kinds of individuality differential
substances given off by the transplants and the kind and intensity of changes
induced. It may furthermore be assumed that even in the case of the local
reactions around the transplants these substances diffuse into the blood or
lymph stream and thereby contribute to the local accumulation of the white
blood cells ; at least the filling of the lymph vessels with lymphocytes and the
increased number of the latter in the blood capillaries around homoiotrans-
plants suggest such a process.

Investigation of the effect of homoiogenous and syngenesiotransplants by
Blumenthal gave the following results : A relative and absolute increase in the
number of lymphocytes in the peripheral blood took place after homoio- and
syngenesiotransplantation, in contrast to heterotransplantation, after which an
increase in polymorphonuclear leucocytes occurred. The general and local re-
actions were found at about the same time. After homoiotransplantation of
the thyroid gland the maximum in the increase in lymphocytes in the blood
was on about the 6th or 7th day ; this was also the time when the lymphocytes
began to collect locally around the graft; on the other hand, the maximum in-
crease in the polymorphonuclear leucocytes after heterotransplantation oc-
curred more rapidly, namely, on the 4th or 5th day. The time when the maxi-
mum in the response was attained depended also upon the consistency of the
different tissues; this factor seemed to determine the readiness with which
these specific substances, possessing the individuality differentials, were ex-
tracted and were able to diffuse into the adjoining areas and into the circulation
of the host. The relative increase in the percentage of lymphocytes after
homoiotransplantation of thyroid varied from 13.5 per cent in the pigeon, to
16.9 per cent in the rat, and to 16.6 per cent in the guinea pig, and in a number
of experiments it exceeded 25 per cent. After heterotransplantation the rela-
tive increase in the percentage of polymorphonuclear leucocytes ranged be-
tween about 12 per cent and 26 per cent. After autogenous transplantation of
different organs or tissues, the average maximum percentage increase of lym-
phocytes showed variations between 3.3 and 6.5 per cent in different species of
animals ; in the pigeon there was no increase. After subcutaneous transplanta-
tion of inert foreign bodies or after an incision the effect on the number of the
circulating lymphocytes was about the same as after autogenous transplanta-

64 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tion. The conclusion seems therefore justified that the increase after trans-
plantations in which host and donor are identical is a non-specific reaction.

Syngenesiotransplantation of the thyroid in guinea pigs caused an average
maximum percentage increase of lymphocytes amounting to 11.7 and the
average period of the maximum increase was 12.1 days after transplantation,
as compared with the corresponding figures in case of homoiotransplantation
of the guinea pig thyroid, which were respectively 16.6 per cent and 7.1 days.
The increase in the lymphocytes after syngenesiotransplantation was therefore
less than after homoiotransplantation and it appears later, indicating a milder
reaction in the former, a fact which harmonizes with the decreased disharmony
of the individuality differentials between nearly related individuals as com-
pared to not nearly related, homoiogenous individuals.

The conclusion that relationship between the individuality differentials of
host and donor is the decisive factor in the changes in the distribution of white
blood cells following various types of transplantation agrees also with the
results obtained in mice. After transplantation of tissues to a different strain,
the average lymphocytic increase was 17.7 per cent, and after transplantation
within the strain it was 12.1 per cent. However, after transplantation within
strain A, the most closely inbred strain, the increase in the lymphocytes was
only 10 per cent and the maximum increase appeared somewhat later, on the
average, after 13.6 days. These transplantations correspond therefore to the
syngenesiotransplantations in the guinea pig. The response of strain A mice to
heterogenous transplants from the rat was similar to that seen in other types of
heterogenous transplants ; the average increase in polymorphonuclear leuco-
cytes was 18.7 per cent ; it set in between the 2nd and 4th day and, as usual, was
followed by a secondary rise in lymphocytes. There was not only a relative in-
crease in the lymphocytes or leucocytes in the various types of transplantations,
but also an absolute increase, which was even more striking than the relative
increase. In the guinea pig the absolute increase in the number of lympho-
cytes amounted to about 78 per cent and in the rat to about 54 per cent, while
the average increase in polymorphonuclear leucocytes reached about 110 per
cent.

This method of analyzing the individuality differentials lent itself well to a
comparison between the individuality differentials in adult and in embryonal
tissues. It was found that tissues obtained from fully developed embryos near
the time of labor behaved after homoiogenous and heterogenous transplanta-
tion in the same way as the corresponding adult tissues. On the other hand,
very young embryonic tissues removed from an animal at about the conclusion
of the first third of pregnancy behaved differently ; here, after heterogenous,
as well as after homoiogenous transplantation, a lymphocytic response similar
to that noted after homoiogenous transplantation was observed, while an in-
crease in the number of polymorphonuclear leucocytes in the host was lacking
under these conditions. This indicates that the typical heterogenous organismal
differentials had not yet developed in these cases. But the lymphocytic reac-
tion may correspond to the increase in lymphocytes in the blood noted after
transplantation of various dead protein substances into the subcutaneous

TRANSPLANTATIONS IN BIRDS 65

tissue ; or it may represent a rudimentary heterogenous reaction, in which the
as yet imperfectly developed organismal differential is able to activate the
lymphocytes but is not yet strong enough to act on the polymorphonuclear
leucocytes.

In general, we may conclude from these data that the method used by Blu-
menthal is a very useful one if we wish to obtain comparable data of a
quantitative nature and that in this respect it surpasses the use of the local
reactions. But the latter give an insight into the effect of various types of in-
dividuality differentials on different kinds of host cells; it makes possible,
furthermore, the differentiation between the effects of the bodyfluids and of
the host cells on the transplant. There is, in addition, the possibility that the
reactions in the circulating blood are complicated by non-specific or less specific
substances which may be present in the transplanted tissues. Thus Blumenthal
found that also the introduction of certain non-living protein substances into
the subcutaneous tissue may cause an increase of lymphocytes in the blood,
similar to that noted after the introduction of living tissues. However, in this
case heating the protein substances does not lead to a loss of the general
lymphocytic reaction as does the heating of the tissues. Moreover, at least as
far as we know at present, the fine shading of the reactions in accordance with
the relationship between host and transplant, which is characteristic of the
introduction of pieces of living tissue, is lacking in the case of the protein
material. These complications are apparently absent in the case of the local
reaction. Considering all these facts, it seems that the combined use of these
two methods is preferable to the application of either of them alone.

Chapter J

The Mechanism of the Reactions Against

Homoiogenous Individuality Differentials;

Autogenous Tissue Regulators

1. Various phases which follow auto and hotnoio transplantation. It fol-
lows from the observations discussed in the preceding chapters, that after
transplantation there is a first phase in which there is no noticeable difference
between the conditions of autogenous and homoiogenous transplants. This
phase is dominated by the injury due to the process of transplantation and
by injurious conditions existing in the new location of the tissue. The damage
to the tissues is followed by regenerative reactions ; the homoiogenous tissues
are subjected subsequently, during the second phase, to further specific
injuries by the host and these may also call forth regenerative processes as
long as the injury has not progressed too far. These injuries, furthermore,
initiate the activity of the host connective tissue, which moves towards the
transplants. There originate, thus, general, partly non-specific changes, which
are based on attributes of the grafted tissues and of the host tissues.

This first phase is followed by a second one, in which differences develop
between the autogenous and the homoiogenous transplanted tissues. There is
a preponderance of regenerative growth processes and regulative processss
in the autogenous transplants, and there are injurious effects which the host
exerts on the graft under the influence of homoiogenous individuality differ-
entials. The latter tend to prevent a satisfactory recovery of the transplanted
homoiogenous tissue from the injuries received during the first phase, and
they cause additional damage to the homoiogenous transplant, which thus, in
many cases, cannot maintain itself and during the third phase is gradually
destroyed. These are the characteristic features of the second and third phases
following transplantation, in which differences between the conditions of the
autogenous and homoiogenous tissues become more and more marked. How-
ever, there occur, also, changes opposed to this outcome, namely, conditions
of adaptation between transplant and host, which in certain instances may
slowly lead to an improvement in the state of the homoiogenous transplant and
may make possible its survival in the strange host.

As to the mechanisms leading to the secondary injury of the homoiogenous
tissue, they consist, in the first place, in the action of the homoiotoxins of the
host, and secondly, in the activities of the host cells ; the most specific among
the latter are the reactions of the lymphocytes ; but also the behavior of the
connective tissue and blood vessels is influenced by the homoiogenous charac-
ter of the individuality differentials. Furthermore, the age of the host in-
fluences the action of the connective tissue ; the latter is diminished if the host
is very young. It seems that in every instance the homoiotoxins act on tissues

66

REACTIONS AGAINST INDIVIDUALITY DIFFERENTIALS 67

possessing strange individuality differentials and injure them ; but they do so
to a very different degree in different cases. The effect may be so slight that it
is hardly noticeable; but in other cases the direct injurious action of these
substances is quite marked and in different species the relative preponderance
of the influence of the host cells and of the bodyfluids varies, the latter being
relatively more important in the mouse than in the guinea pig and rat. The
fact that an interaction between transplanted tissues and the bodyfluids of the
host takes place in every instance makes it difficult to decide whether the host
cells are activated by the homoiogenous individuality differential of the trans-
plant directly, or only after the latter has combined with the homoiotoxins of
the host.

The growth processes, and in particular the mitotic cell multiplication, which
occur in the transplanted tissues are not entirely regenerative in character,
but they may be due partly to the continued function of a primary tendency
to mitotic proliferation, which is inherent to a very different degree in differ-
ent tissues. In tissues in which secondary differentiations have taken place, as
for instance, in cartilage and striated muscle tissue, or in epidermal cells at
some distance from the source of oxygen supply, the tendency to undergo
mitotic proliferation is replaced by amitotic processes. Certain unfavorable
environmental factors may likewise prevent mitotic proliferation and instead
cause formation of epithelioid and giant cells, and in general favor processes
of differentiation instead of mitotic proliferation.

2. The mechanism which leads to the specific reactions of the lymphocytes
of the host against the transplant. We have seen that different homoiogenous
tissues may attract the lymphocytes to a different degree, and we shall report
on particularly striking instances of such differences between different organs
in subsequent chapters when we discuss the transplantation of adrenal gland
and anterior hypophysis in mice. In addition, it was possible to demonstrate,
in the rat, the attraction which homoiogenous tissues exert on the lymphocytes
of a nearby lymph gland of the host, in experiments which Crossen carried
out in the guinea pig. He autotransplanted a lymph gland into the subcutaneous
tissue and then placed either a piece of autogenous or homoiogenous xiphoid
cartilage near the lymph gland, or into the lymph gland itself. While the
lymphocytes of the transplanted lymph gland were inactive towards the auto-
genous cartilage graft, they were actively attracted by the homoiogenous tissue
and they migrated into the homoiogenous transplant. This may be considered
as confirmatory evidence for the conclusion that the movement of the lympho-
cytes towards the homoiogenous transplants represents a chemotropic reac-
tion.

3. Differences in the intensity of the reaction against strange individuality
differentials observed in different families or strains of rats. If tissues are
homoiotransplanted from certain families or strains of rats into other families
or strains, different average degrees of severity in the reactions may be ob-
served. We have analyzed the factors which cause these differences in several
series of experiments carried out in rats. For this purpose we compared the
reactions in rats from various strains and families, obtained from different

68 THE BIOLOGICAL BASIS OF INDIVIDUALITY

breeders in different cities. Various combinations of donors and hosts were
tested, and in a number of experiments tissues from one donor were placed
into the left side, and those from another donor into the right side of a host;
in other cases, pieces of tissues from the same donor were transplanted into
two different hosts. In the majority of these experiments the examinations
took place 20 days after transplantation.

In order to compare the intensity of the reaction in different combinations
of hosts and transplants it is necessary to make equal the times at which the
examination takes place. With increasing time, the severity of the reactions as
a rule increases. If we consider all these experiments together, we may con-
clude that autotransplantation, where the individuality differentials of host and
transplants are identical, reactions which do occur are due to injury inflicted
on the grafted tissue during the operation or to the abnormal conditions under
which the transplants live in their new environment, and that these abnormal
conditions are, as a rule, overcome in the course of time. On the other hand, in
the case of homoiotransplantations the reactions are caused by the differences
in the individuality differentials between host and transplants, and in different
combinations of families or strains the severity of the reaction in the host and
the injury in the donor differ. While in some combinations the reactions are
severe, as indicated by grade 1, in others the grades range between 1 and 2— ;
in still others the average grade may be 2—, or even somewhat higher, and in
rare instances, grade 3 — , or even 3, may be reached in an animal. These grades
apply only for a certain length of time, during which the transplant was ex-
posed to the influence of the host ; this period was 20 days in this series of
experiments and there are indications that after 30 or 40 days the reactions
would have been more severe and the grades accordingly lower. Essentially
two factors are responsible for the grades thus obtained. In the first place,
these differences in the reactions are due to differences in the relationship be-
tween the individuality differentials of host and donor. This is indicated by the
fact that if various tissues are transplanted from one donor into the same
host, the severity of the reaction is the same in all the pieces, if we make
allowance for the peculiarities which distinguish different types of tissues.
This conclusion harmonizes with the many other transplantations which we
have carried out with homoiogenous tissues. Thus, in a certain experiment in
which grade 3 had been given, a great portion of the thyroid transplant was
preserved ; in the muscle transplant there were long parallel muscle fibers with
good cross-striations, and in one specimen of this kind even a mitosis seemed
to be present in a muscle cell. Likewise, the grafted fat tissue was well pre-
served. With grade 2 there was much lymphocytic infiltration in thyroid and
muscle and at least a large part of the fat tissue was preserved, while with
grade 1, neither thyroid nor muscle was preserved and the fat tissue was
mostly replaced by connective tissue, small vacuolated cells and lymphocytes.
Furthermore, it could be seen that the individuality differentials of both host
and donor determined the intensity of the reactions; this follows from ex-
periments in which either the donor or the host varied, while the other partner
which entered into the combination remained constant. The lymphocytic reac-

REACTIONS AGAINST INDIVIDUALITY DIFFERENTIALS 69

tions likewise, as a rule, were constant in pieces of tissue from the same
donor, transplanted into the same host, provided we consider that there are
various variable factors which complicate such experiments and, in particular,
that as a rule only in transplants in which there is a large amount of living
tissue left is the lymphocytic infiltration considerable.

However, there were strong indications that, in addition, another factor
played a role in certain instances. Thus we observed that in the same host the
reactions against various tissues from two different homoiogenous donors,
while not necessarily identical, were correlated with each other. Furthermore,
if tissues from two donors were each transplanted into two different hosts,
the reactions against both could be severe in one host and relatively mild in
the other host. It was especially the Bu rats which, in almost all cases, reacted
very severely against transplants from other families or strains of rats, the
grade being 1 in the large majority of cases, while the reciprocal transplan-
tations, in which Bu rats were the donors and other families the hosts, gave a
much greater number of milder reactions. The Bu rats, before being used for
transplantation, had been fed for some time on a riboflavin-deficient diet ; but
that this was not the essential cause of the strong reaction against strange
individuality differentials which these rats exhibited was shown in control
experiments, in which this same strain of rats had always been kept on a
normal diet, but the severity of the reaction was not diminished ; nor was the
age (weight) of the animals used, nor the season of the year when the experi-
ments were carried out of significance in this respect. Only in a single experi-
ment in which these rats served as hosts were the reactions somewhat milder.
While thus the Bu rats reacted in almost all instances very strongly against
homoiogenous differentials, the homoiogenous differentials of Wistar rats,
serving as donors, seemed to elicit less strong reactions on the part of the host
than did some of the other strains, although they still remained within the
homoiogenous range. There is, then, some strong experimental evidence for
the conclusion that certain strains of rats, and probably also other species,
have the peculiarity of reacting especially strongly against strange individuality
differentials, and it is furthermore possible that the grafted tissues from cer-
tain strains of rats, acting as donors, stimulate the host cells less actively than
do the tissues from other strains. A second set of factors exists therefore
besides the degree of strangeness between the individuality differentials of
host and transplant, which determines the severity of the reaction of the host
against the transplant, namely, a peculiar reactivity of the host tissues which
presumably has also a genetic basis. There is, besides, some evidence that not
only strains of animals have this peculiarity in their mode of reaction, but that
also various individuals may differ from one another in this respect.

4. The effect of heat on the homoiogenous individuality differentials in
rats. In these experiments we subjected thyroid and cartilage- fat tissue of
Bu rats to boiling temperatures for 5 minutes and then transplanted the pieces
into Chicago rats. Under these conditions the homoiotransplanted tissues
were entirely necrotic. After 12 days, the nuclei in the thyroid and parathyroid
were found dissolved in the peripheral, and shrunken in the central acini.

70 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Fibrous tissue grew around and into the transplant. Also, cartilage and fat
tissue were necrotic, but the peripheral portions of these pieces had been
fixed as a result of the boiling. Connective tissue and small vacuolated cells
grew into the fat tissue, but the lymphocytic reaction was lacking. After 20
days, the results were similar. In the thyroid, some balls of hard colloid, sur-
rounded by some giant cells and fibrous tissue, were seen. At this time also,
connective tissue grew into thyroid and into necrotic fat tissue, in which, in
addition, small vacuolated and epithelioid cells were seen. A few polymorpho-
nuclear leucocytes were likewise noted in the connective tissue, but a typical
lymphocytic reaction was absent, and the homoiogenous fat tissue did not
attract polymorphonuclear leucocytes. These experiments confirm, then, the
conclusion that in general, if we except reactions of a non-specific nature, such
as the ones elicited by certain dead foreign bodies, only living tissue calls forth
the lymphocytic reaction which is characteristic of transplants possessing
homoiogenous individuality differentials.

5. The autogenous tissue regulators. In the normal organism the various
types of cells have inherited those modes of interaction with other cells and
intercellular substances of different kinds, by means of which the mutual cell
and tissue relations are safeguarded. Hence, whenever the various types of
transplanted tissues possess the same autogenous chemical characteristics of
the individuality differential as the host, they tend to interact with the host
tissues as if they were a normal constituent of the host, even if at first a dis-
organization has taken place as the result of temporary accidental conditions.
The disappearance at later dates of factors disturbing the normal tissue rela-
tions directly following autogenous transplantation of thyroid, cartilage, fat
tissue and uterus, indicates the presence of autogenous regulators. However,
not in all organs do such regulators suffice to overcome the abnormalities
brought about by the operation ; for instance, in the transplants of kidney a
complete normality in the structure of the transplant does not need to be
achieved. A perfectly closed epithelial layer may survive permanently after
autotransplantation, but incompletely closed epithelial structures, such as
kidney tubules which have been cut at one end, and especially the more differ-
entiated convoluted tubules or epidermal cysts which are interrupted by hairs,
are at a disadvantage and may die even after autogenous transplantation.

After homoiogenous transplantation of various tissues and organs in a
number of species, the interaction of disharmonious individuality differentials
leads to abnormal relations between host cells and transplanted tissue. The
homoiogenous substances given off by the transplants stimulate and attract
lymphocytes and connective tissue cells, with graded intensities which exceed
the threshold of normality, and in addition, homoiogenous substances of the
host may injure directly the homoiogenous tissues, whose relation to stroma
cells and blood vessels and to lymphocytes in the adjoining areas of the host is
thus altered. In the end, in the large majority of cases the transplanted tissue
is either destroyed or at least its normal structure and relations to the neigh-
boring tissues are not completely re-established.

Regeneration may also be considered as a regulatory process in the relations

REACTIONS AGAINST INDIVIDUALITY DIFFERENTIALS 71

between tissues and it is based essentially on inherited properties of the tissues.
These inherited characteristics assert themselves in all instances, irrespective
of the autogenous or homoiogenous state of the transplants. In certain tissues,
which possess great resistance to injurious conditions and in which the re-
generative momentum is very strong, regenerative processes may take place
in a homoiogenous medium, but the homoiogenous relationship always tends
to act as an injurious factor, preventing or at least inhibiting regenerative
activities.

There enter, then, at least two factors in the creation and maintenance of the
autogenous tissue equilibrium, namely (1) the individuality differentials,
which diffuse from the tissues into the surrounding bodyfluids and which
are present also in the blood; (2) other factors inherent in the tissues, which
assert themselves under certain conditions, as, for instance during regenera-
tion. There exists the probability that the autogenous individuality differentials
as such function as these tissue equilibrizing substances ; but it is also con-
ceivable that there may exist special autogenous tissue-regulating substances,
which possess a chemical group characteristic of the individuality differential
of the host, or that there may be separate autogenous substances devoid of
the individuality differential but which could induce the tissues to react in the
normal manner only in an autogenous medium. However, the first interpreta-
tion seems to be the simpler and more ^probable one. Just as the homoio-
genous individuality differential exerts abnormal effects on various types of
cells, so the autogenous individuality differential may be expected to exert
the opposite functions, which in contrast to the homoiogenous substances
bring about and maintain a normal relation between the various tissues. These
substances, acting on adjoining tissues as contact substances which latter in a
wider sense may be included among the hormones, although not usually thus
classified, and acting also on distant tissues as hormones in the usual mean-
ing of this term, would thus possess a very important function in making
possible the harmonious interaction of the many constituent parts of the in-
dividual organism; however, they would be supported in this task by other
typical hormones produced in distant organs, which do not necessarily possess
the individuality differential, and also by specific elements of the nervous
system.

Chapter 6

Syngenesiotransplantation, Transplantation in

Closely Inbred Strains, and the Individuality

Differentials of Near Relatives

The average genetic relationship between near relatives, such as broth-
ers and sisters, parents and children, should be somewhere intermedi-
ate between the homoiogenous and autogenous relationship, and, ac-
cordingly, the average results of syngenesiotransplantation should likewise be
somewhere intermediate between those of autogenous and homoiogenous
transplantation. That this is the case is indicated by some experiments to
which we have already referred. However, there may be instances in which
such intermediate results are not evident, but in which the reactions obtained
in syngenesiotransplantation cannot be distinguished sharply from those ob-
tained in homoiogenous transplantation. Several conditions might account for
this occurrence: (1) It might be due to the fact that even in syngenesio-
relationship there may be such a degree of genetic difference between donor
and host of the transplant that the threshold determining a reaction charac-
teristic of a homoiogenous transplantation has been reached, although the in-
dividuality differentials of donor and host actually are more nearly related
than is the case in the average of homoiogenous individuals. (2) It might
also be due to the fact that when the threshold determining the homoiogenous
reaction is very close to the autogenous region in the spectrum of reactions,
the host cells are extremely active and efficient in discovering differences in
genetic relationship and therefore the transplants, whose individuality differ-
entials deviated only slightly from those of the host, are attacked with a
maximum intensity, a type of reaction which we have found to obtain in
birds. In those instances in which the individuality differentials of host and
donor in ordinary syngenesiotransplantation are so far removed from each
other that a mitigated reaction can not be demonstrated, an experimental in-
tensification of the brother-sister relationship, through inbreeding, may make
the genetic relationship closer than it is in ordinary brother-sister relationship.
In this event the threshold point separating homoiogenous and syngenesious
reactions may not yet have been passed and the difference in the reaction of
the host against the tissues from a brother and from a not so nearly related
individual belonging to the same inbred family or strain may then become
manifest. In all essential respects, transplantations in closely inbred strains
represent intensified brother-and-sister relationships, because the closely
inbred strains were obtained by brother-sister matings in consecutive gen-
erations. Theoretically, it would be expected that after a certain number
of consecutive brother-sister matings have been made, the relationships even
between individuals in the inbred strain other than brothers and sisters,

72

SYNGENESIOTRANSPLANTATION

73

should pass from the zone of syngenesio-relationship and reactions to the
autogenous zone; but in reality this does not seem to be fully accomplished.
A closely inbred strain is a strain of brothers and sisters, which are very
similar in genetic constitution.

After these introductory remarks, we shall consider the results of syn-
genesiotransplantation in the rat and in the guinea pig, and then we shall
analyze the interaction of the individuality differentials observed in trans-
plantations in closely inbred strains of rats, guinea pigs and mice.

(a) Syngenesiotrans plantation in rats. We have referred already to some
experiments in which the reactions against transplants from brothers or sisters
were, on the average, milder than the reactions against homoiogenous trans-
plants, but on the other hand there were some instances in which no sharp
distinctions between the individuality differentials of brothers and sisters and
those of not closely related individuals could be established. Thus in the mutant
Wistar rats, a special strain developed by Dr. Helen Dean King, the
syngenesio-reactions were milder than the reactions against transplants from
non-related rats of the same strain, if the examination of the grafts occurred
12 and 16 days after transplantation, but no difference was found after 20
days. Also in some other experiments the grades in syngenesiotransplantations
could approach closely the average grades in homoiotransplantations, although
their average reaction was still somewhat milder.

Two series of experiments will now be discussed — one made in 1918 (series
I), and the second made in 1927 (series II), in which we compared the fate
of various organs such as skin, ovary, uterus, spleen, liver and thyroid after
various types of syngenesiotransplantation and of homoiotransplantation.
More than one organ, as a rule, was transplanted into each host. The average
grades obtained in these series are given in the following table I.

TABLE I

Series I

Series II

Autogenous transplantation

3.15

Homoiogenous transplantation

1.24

Variations between
1 and 1 . 75

Brother or sister to brother or sister

2.08

2.50

Parents to children

2.28

2.06

Children to parents

2.11

2.25

Grandparents to grandchildren

2

Grandchildren to grandparents

2.60

In the second series it was thought unnecessary to carry out autogenous
transplantations, because these did not vary significantly in different experi-
ments. In both series the grades were better in the various kinds of syngenesio-
transplantations than in homoiogenous transplantations, and intermediate be-
tween those obtained in autogenous and homoiogenous transplantations. As to
various types of syngenesiotransplantations, no consistent differences were
found and those that were noted were not of the same kind in the first and
second series.

74 THE BIOLOGICAL BASIS OF INDIVIDUALITY

In earlier investigations, Schoene compared various types of transplanta-
tions of skin into defects in the skin ; he used as criterion of the results the
healing' in or the casting off of the transplants, which represents an all or
nothing effect and does not allow the recognition of intermediate degrees of
reactions. In young rats, autotransplantations of skin succeeded almost invari-
ably, while in older rats the pieces were entirely or partly cast off. In trans-
plantations between relatives, the most favorable results were obtained be-
tween brothers and sisters, provided the animals were young; but only in a
small minority of cases did the grafts in relatives behave like autotransplants ;
in the large majority, they were cast off like homoiotransplants. However,
altogether only eighteen transplantations between relatives were carried out, a
number which, considering the method used and the results obtained, was
hardly sufficient to differentiate between different types of transplantations.

If instead of considering merely the averages, also the intensity of the reac-
tions in the individual experiments are taken into account, it is found that in
the spectrum of relationships the grades of the syngenesiotransplants range
between those characteristic of homoiogenous transplants and those approach-
ing almost the grades characteristic of autogenous transplants, all transitions
in grades being found. These results indicate the presence of multiple factors
as the genetic determiners of the individuality differentials in the different
animals. We have not to deal with the simple proportions of alternating
Mendelian inheritance, such as we find if one or two factors are the hereditary
determiners. The results are similar to those noted in the hereditary trans-
mission of quantitative differences in the two parents, each quantity being
represented by multiple factors and one-half of the multiple factors of each
parent being united in the child ; this condition would lead to a series of inter-
mediate results in different matings and to the appearance of a blending in-
heritance. The combination of the multiple factors of the parents leads in the
offspring to the production of a chemical substance, the individuality differ-
ential, which is present in all, or almost all, the tissues and organs of the child.
The assumption of the presence of multiple factors as determiners of the
individuality differential is also in accordance with the gradations in the in-
tensity of the reactions against homoiogenous tissues which were found in the
numerous experiments carried out.

The effect of variations in the individuality differentials of host and donor
on transplanted organs and their constituent parts in the rat. We may here
digress from the consideration of syngenesiotransplantations and discuss the
manner in which different organs and tissues can be used in the analysis of the
character of the individuality differentials and of the organismal differentials.
Not only the reaction of the lymphocytes and of the connective tissue against
the transplant, but also the survival and preservation of the constituent parts
of the transplanted organs may be used in the standardization of the individual-
ity differentials, provided their comparative power of resistance is taken into
account, and, conversely, the various degrees of injury inflicted on these con-
stituent parts of organs may serve as a test of their sensitiveness. Conditions
prevailing in syngenesio-, homoio- and heterotransplantations cause different

SYNGENESIOTRANSPLANTATION 75

intensities of damage in different tissues, and they affect these tissues, there-
fore, in a graded manner. In general, only structures with an intermediate
degree of sensitiveness are suitable indicators in the analysis of the individual-
ity differentials. Tissues, such as cartilage, which are so little sensitive that
they react in about the same way after autogenous, syngenesious and homoiog-
enous transplantation, are not suitable for this purpose. Likewise, tissues
which are so sensitive that they are entirely or largely destroyed by the non-
specific injury connected with and following the process of transplantation,
such as adult testicle and brain of adult mammals, are not suitable test objects.
It is the simple constituents of various organs, those less differentiated as to
structure and function, which are usually more resistant and tend to survive
even if the conditions following transplantation are injurious. Unfavorable
conditions of nourishment, such as deficiency in oxygen, may cause the differ-
entiation of tissues — for instance, in the epidermis, in placentoma, in the large
follicles of the ovary — and differentiation may result in both increased sensi-
tiveness and a diminution or absence of proliferation, or in a proliferation of
an abnormal kind, in which mitoses are lacking and, instead, amitotic nuclear
multiplications occur; a production of epithelioid and giant cells, and
hypertrophy rather than hyperplasia, are then characteristic findings in
this condition. The most sensitive structures perish often after homoiotrans-
plantation but may remain alive after syngenesiotransplantation. We may now
briefly compare the relative sensitiveness of the various organ constituents
which we have used for transplantation in the rat and classify them approxi-
mately in accordance with the effect which the different types of individuality
differentials have on these constituents.

(1) Skin: In homoiogenous and syngenesious transplantation into the sub-
cutaneous tissue the skin, which here forms a cyst, is usually destroyed, not-
withstanding the fact that the epidermis as such is resistant. This destruction
takes place because in the skin, after transplantation, the injurious action of
the connective tissue elements is stimulated and strenghened in a non-specific
manner. It is especially the loss of the epithelial lining of the hair follicles
which may lead to the stereotropic ingrowth of the connective tissue and the
destruction of the cyst, even in autotransplantation. Furthermore, under un-
favorable conditions the whole epidermis of the cyst may become keratinized,
owing to insufficient nourishment or to mechanical pressure by hyaline con-
nective tissue, which may at times fill the cyst. Giant cells form around the
hair and the keratin particles. This non-specific action of the connective tissue,
and sometimes also of the lymphocytes, in co-operation with the homoio-,
or syngenesio-toxins of the host, usually leads to the destruction of the epi-
dermis after subcutaneous transplantation, owing to a summation of these
partly non-specific and partly specific effects. In some instances, however, the
action of the non-specific factors alone may lead to the destruction even of
the autogenous skin, although in other cases this may remain alive for a long
time or perhaps permanently. Mitoses are usually found in the hair follicles,
which are more protected than other structures.

(2) Ovary: The various constituents of the ovary show a graded power of

76 THE BIOLOGICAL BASIS OF INDIVIDUALITY

resistance, which diminishes in the following order: (1) Interstitial gland,
germinal epithelium and medullary ducts, both of which have a tendency to
form cysts; (2) primordial and small follicles; (3) medium-sized and large
follicles; (4) corpora lutea. For instance, six days after transplantation
interstitial gland may be seen ; it is derived from theca interna cells of atretic
follicles, and perhaps also surviving parts of the granulosa may participate
in its origin; these interstitial gland cells may give rise to larger cells, con-
taining yellow pigment, which constitute or resemble interstitial gland cells
and may act as phagocytes, taking up red blood cells in hemorrhagic areas
and thus producing pigment. Under somewhat more favorable conditions of
transplantation, primordial and small follicles may survive; and under still
more favorable circumstances these small follicles may grow to medium-sized
or large follicles. Under very favorable conditions of syngenesiotransplanta-
tion, the large follicles may rupture and give rise to corpora lutea; but the
corpora lutea, consisting of differentiated cells, are sensitive and usually
degeneration takes place if they are transplanted. In other instances the large
follicles do not rupture but, instead, develop into large cysts. Ovulation in
the transplanted ovary may occur synchronously with ovulation in the non-
transplanted ovary of the host, perhaps in response to a hormone given off
by the anterior hypophysis. In less than one-half of our transplants preserved,
medium-sized or large follicles were found; this is a frequency which is
somewhat less than that with which bile ducts were preserved in transplanted
pieces cf liver. If thyroid was transplanted simultaneously with the ovary, and
if the reaction against the homoiogenous thyroid was severe, only the more
resistant constituents of the ovary were preserved. On the other hand, in cases
of a syngenesio- reaction, with grade 3 or 3 — , in which therefore the individu-
ality differentials of host and transplant were relatively harmonious, primor-
dial and growing Graafian follicles as well as corpora lutea could be ob-
served. However, lymphocytes infiltrated even better preserved ovarian trans-
plants; they could appear first around vessels and then infiltrate also other
structures, but only in rather rare instances did they infiltrate preserved
follicles. Not only follicles, but even medullary ducts were found more fre-
quently in syngenesio- than in homoiotransplantations. Around follicles, which
after transplantation, underwent necrosis, giant cells could develop, which
functioned as phagocytes and helped in the removal of the necrotic material.
The removal of necrotic material proceeded very slowly and remained imper-
fect for a long time. On the whole there was, then, a great difference in the
power of resistance of the various ovarian structures and there was a definite
correlation between the types of transplantation and the kind of ovarian con-
stituents which survived after transplantation ; in general, the more resistant
ovarian structures were less prone, whereas the most sensitive constituents of
the ovary were more prone to injury than the acini in the thyroid gland trans-
planted simultaneously.

(3) The Fallopian tubes and fimbria belong to the most resistant and rela-
tively best preserved organs, comparable in this respect to the more resistant
constituents of the ovary and uterus and to the pelvis of the kidney; they

SYNGENESIOTRANSPLANTATION 77

tended to survive even under homoiogenous conditions of transplantation, but
were unfavorably affected by a marked disharmony of the homoiogenous
individuality differentials.

(4) The uterus is, on the whole, also a resistant organ, although certain of
its constituents may show less resistance. There was often necrotic material in
the lumen of the uterus and part of its wall could be destroyed. The epithelium
and the peritoneal endothelium were more resistant, while the unstriated
muscle tissue was more readily injured after homoiogenous transplantation,
and cellular, myxoid and predecidual connective tissue underneath the epithe-
lial structures continued to live only if the individuality differentials of host
and transplant manifested a high degree of compatibility.

(5) In kidney transplants the tubules and glomeruli, situated in the peri-
phery of the transplant, were most prone to survive; the collecting tubules,
with pelvis and ureter showing the least differentiation, were very resistant.
On the other hand, the convoluted tubules were very sensitive to the injurious
action of the unfavorable individuality differentials.

(6) After transplantation of pieces of liver, peripheral bile ducts remained
alive in about fifty per cent of our transplants for 1 or 1^ months; they
showed mitoses mainly in the earlier periods, as, for instance, 14 days after
transplantation, but some mitoses were visible at later periods. The bile ducts
corresponded, therefore, in their power ,of resistance to unfavorable indi-
viduality differentials, to the small follicles of the ovary or to spleen tissue.
New bile ducts could develop and these structures were able to survive for as
long as a month and a half, even under homoiogenous conditions, although
they were better preserved after syngenesiotransplantation. In 38 per cent of
the transplants in which bile ducts were preserved, or in a little more than
on-sixth of all our transplantations of liver, liver cells as well survived, which
is about the frequency with which megakaryocytes were preserved in the
spleen. However, liver cells did not survive if the individuality differentials of
the transplant were homoiogenous; but they could survive in favorable syn-
genesiotransplants, under conditions in which also mitoses were seen in the
bile ducts. In certain instances, a liver cell with two nuclei was noted, but only
in one case was a mitosis seen in such a cell. It may be remarked in this con-
nection that under exceptional conditions mitoses may appear in young carti-
lage cells, or even in transplanted cells of striated muscle tissue. As in ovary
and kidney transplants, so too in liver transplants the necrotic center could
remain partly unorganized for a long time.

(7) Spleen: Between 36 and 47 days following transplantation spleen tissue
was found preserved about as frequently as bile ducts in liver transplants or
small follicles in ovarian grafts. Here, again, homoiotoxins proved injurious
and the injury increased with increasing time following transplantation;
eventually, only fibrous tissue with blood pigment was found. Syngenesio-
transplants were more favorable and in these as well as in autogenous grafts
Malphigian bodies, blood sinuses containing erythrocytes, mononuclear, pha-
gocytic cells and trabeculae were seen, and at later stages megakaryocytes.

(8) Testicle: Testicle tubules as a rule perished, but a few peripheral ones,

78 THE BIOLOGICAL BASIS OF INDIVIDUALITY

lined merely with Sertoli cells, could survive. Testicle tubules were destroyed
also after autogenous transplantation; this effect is therefore due to a non-
specific injury, by which the more differentiated testicle cells are affected.

(9) Striated muscle tissue was relatively resistant to unfavorable individu-
ality differentials, and even under the action of strong homoiotoxins some
muscle fibers could survive and show amitotic nuclear proliferation.

(10) Fat tissue, at least in part, tended to survive even after homoiogenous
transplantation; but it was readily invaded by connective tissue and by cells
which acted as phagocytes, but which could in addition form giant cells, and in
some cases, by lymphocytes. The tendency to invasion by these cells differed
in different species ; it was greatest in the guinea pig, where there was also the
greatest tendency to the formation of giant cells, and it was least marked in
the mouse; rat tissue, with which we are here more directly concerned,
showed an intermediate position.

(11) Bone, bone marrow and cartilage: As stated previously, cartilage with
the surrounding perichondrium is a very resistant tissue, which could survive
and undergo regenerative growth processes even under very severe homoio-
genous conditions. In bone, the bone cells tend to die, especially in the central
parts, owing to a lack of nourishment. In the peripheral parts of transplanted
bone it was often difficult to decide whether the cells situated here had come
from the surrounding connective tissue, or whether they were actually pre-
served bone cells. Under certain conditions, new bone could be formed in
transplants around the cartilage as well as in the bone marrow. The bone mar-
row, as a rule, survived only under very favorable conditions of syngenesio-
transplantation.

In general, we may conclude that the results of transplantation of various
tissues depend upon inner and outer factors, the former situated in the trans-
plant and the latter in the host. Among the inner factors localized in the
transplant, (a) the most prominent is the constitution of the individuality
differential, which in its relation to the individuality differential of the host
largely determines the fate of the transplant ; (b) important too, is the degree
of sensitiveness to injury or the power of resistance of the transplant or its
various constituent parts to injurious conditions ; and (c) also influencing the
survival of the graft are certain accessory conditions, such as the presence of
hyaline tissue or other resistant tissues in the transplant, which protect the
more sensitive parts ; the thickness of the transplant, which affects the size of
the central, least nourished parts ; these latter tend to die, while the peripheral
parts remain alive. In addition, the age of the transplant may play a certain
role, as well as its possession of a peculiar tissue constitution, which influences
the activity of the lymphocytes of the host. Among the outer factors affecting
the results of transplantation are the constitution of the individuality differen-
tials of the host, the reactivity of the host against strange individuality differ-
entials, and the presence in the host of immune substances directed against the
transplant ; besides, the place of transplantation may be of significance.

If we make allowance for the variations caused by all these factors, our ex-
periments have shown that as a rule pieces of different tissues, transplanted

SYNGENESIOTRANSPLANTATION 79

from the same donor into the same host, behave in the same manner and have
a corresponding fate. There are hosts in which all pieces are well preserved,
others in which all transplants are destroyed, and still others in which the
transplants show an intermediate degree of preservation.

The behavior of lymphocytes towards different types of transplants. We
have discussed non-specific factors which influence the fate of transplants,
without any participation of lymphocytes or connective tissue cells being
necessary in this process ; we have also discussed non-specific reactions on the
part of connective tissue towards the transplants. Likewise, in the case of the
lymphocytes, factors other than the individuality differentials may be present
in or around the transplant, and may influence the activity of these cells
towards the graft. Thus foreign bodies around or in a transplant may cause
an accumulation of lymphocytes, as may also epidermal cysts, in some in-
stances even if the latter are autogenous in nature. Mildly inflammatory altera-
tions of a chemical nature, or more severe ones acting at a distance from the
exciting agent, may attract lymphocytes. But it seems that necrotic material
does not exert a direct attraction on these cells ; they do not usually invade
necrotic material unless it is invaded first and organized by growing connective
tissue; in the latter, some collections of lymphocytes are often found. But the
most characteristic feature of the lymphocytes is that they are attracted by
strange individuality differentials. The degree of this lymphocytic reaction
shows a curve which has its maximum at a point intermediate between the
autogenous and the severe homoiogenous zone of the relationship spectrum ;
the lymphocytic infiltration is frequently less marked in the latter zone, because
here the greater part of the transplant has become either necrotic or is replaced
by host tissue. The maximum of the curve may be in the syngenesious zone or
in the zone of mild homoiogenous reactions. In the different types of trans-
plantations lymphocytes move usually by way of the lymph vessels, but to a
lesser degree, also by way of the blood vessels, in the direction towards and
into the center of the transplant. To a certain extent they tend to accumulate in
different places in different kinds of transplanted tissues. It is of special inter-
est that they seem to prefer certain tissues to others. In the thyroid they may
first collect along the inner border of the ring of preserved acinar tissue. In
cartilage-fat transplants they accumulate in the fat tissue, where there is a
deposit of fibrous tissue containing vessels; but they also collect around the
perichondrium and cartilage and they may invade that portion of the cartilage
which consists almost entirely of cartilage cells. In the skin they often avoid
the sebaceous glands and the epithelium of the hair follicles when this is pre-
served. Of special interest is their behavior in the ovary ; here they infiltrate
first the fat and connective tissue surrounding the ovary ; they then accumu-
late in the interstitial gland, around the germinal epithelial cyst and in the
central connective tissue underneath this cyst, as well as around the medullary
ducts, and they may invade also corpora lutea. However, they avoid the pre-
served follicles and only quite late and rather rarely do they invade the latter.
In this case, the difference between their behavior towards different con-
stituents of the same organ is almost as great as the difference in their reaction

80 THE BIOLOGICAL BASIS OF INDIVIDUALITY

would be against two distinct transplants, one autogenous and the other
homoiogenous in nature. Two interpretations of this phenomenon are possible :
( 1 ) it may be assumed that different structures after transplantation produce
and give off different quantities of the individuality differential ; thus cartilage
and fat tissue attract the lymphocytes in rat and guinea pig much less actively
than does the thyroid gland. There is reason for assuming that the metabolical-
ly less active cartilage substance produces a smaller quantity of individuality
differential per unit of time than does the metabolically more active thyroid
gland. However, this interpretation probably does not apply to the ovarian
structures; preserved follicles can hardly be less active in the production of
individuality differentials than is interstitial gland tissue, or even corpus
luteum tissue; (2) it is more likely that, in this and in other similar or even
more striking cases, as for instance, in adrenal gland transplants in mouse, in
addition to the individuality differentials certain tissue-specific substances
attract the lymphocytes; but at the same time it is probable that, in this in-
stance, also the individuality differentials play a role, their action being much
re-inforced by that of substances given off by certain types of cells and tissues
and not identical with the individuality differentials. It is conceivable that these
two substances — the individuality differentials and the tissue-specific sub-
stances— are chemically linked to each other and that this combination exerts
its influence on the lymphocytes, either directly or in conjunction with the
individuality differentials1 circulating in the bodyfluids of the host. Such an
interpretation seems more probable than the assumption that the interaction of
the mutually not quite compatible individuality differentials of host and trans-
plant interfere more effectively with the metabolism of some types of cells
than with that of others, and that as the result of this interference, substances
are produced which attract the lymphocytes. In the transplant of the adrenal
gland of the mouse lymphocytes are attracted in large masses if certain re-
gressive, degenerative changes have taken place in the cortical cells, provided
this degenerative process does not exceed a certain limit. The rapidity and
frequency with which this regressive stage is reached in the cortical cells is
greatly influenced by the relationship between the individuality differentials of
host and donor. In addition to the interpretations mentioned already, after all
we cannot altogether exclude the possibility that in these cells larger amounts
of individuality differentials are produced than in the well preserved cortical
cells. Also to be considered is the possibility that in certain well preserved
tissues influences inhibiting the invasion of the lymphocytes may exist. These
are problems which still remain to be solved.

(b) Syngenesiotransplantation in guinea pigs. As in rats, so we compared
in guinea pigs transplantations between brothers and sisters, from parents to
children, and from children to parents. In addition, transplantations from
grandparents to grandchildren and from grandchildren to grandparents were
carried out. The guinea pigs were either very young, as yet sexually immature,
or they were young adults ; also, the rats used in the experiments already re-
ported had been young.

In the guinea pigs we carried out three series of experiments ; the largest

SYNGENESIOTRANSPLANTATION 81

number of transplantations was made in the third series. The time of ex-
amination varied between 7 and 40 days in the different experiments ; only
those transplants examined not earlier than 17 days after transplantation were
included in series III, while in series II some experiments are included in
which the examination took place at an earlier time.

TABLE II

Series I

Series II

Series III

Homoiogenous transplantations

1.85

Brother to brother or sister

2.34

2.78

2

Parents to children

1.97

2.47

1.55 (1+/2-)

Children to parents

3 (only 1
experiment)

1.84

1.70 (2-)

Grandparents to grandchildren

1.75 (2-)

Grandchildren to grandparents

1.55 (1+/2-)

The average results obtained are shown in the accompanying table II. There
is only one average figure for homoiotransplantation given ; it was obtained in
series I and it is probably too high ; this is due very likely to the fact that only
a rather small number of transplantations was made, and that among these
there were two grades which exceeded the usual range in homoiotransplanta-
tion, one of them closely approximating the results obtained in autogenous
transplantations. It is possible that in this instance we had to deal with related
guinea pigs. If we make allowance for this discrepancy, the table shows that
the grades in syngenesiotransplantations are higher than in homoiotransplan-
tations, but that they are nearer those characteristic of homoiogenous than of
autogenous transplantations. This was true also in the experiments with rats,
which we have already discussed.

Taking these grades as a whole, the results of the syngenesiotransplanta-
tions are intermediate between those obtained in autogenous and homoiogenous
transplants in either of two ways : (1) In a number of experiments the grades
in the individual experiments vary, approaching either the results in autoge-
nous or in homoiogenous transplantations. In these cases it is merely the aver-
ages which are intermediate. (2) In other transplantations the grades of the
individual experiments are intermediate. In order to understand the manner
in which such an intermediate condition may come about, we may distinguish
in the reaction against the transplants on the part of the host cells, two periods,
the first one tending from 6 to 12 days following transplantation, the second
one covering the time from the 12th day to the time of examination. The re-
actions in the thyroid gland may be cited as an example of varying results in
these two periods. During period I, the connective tissue reaction takes place.
If during this time the production and accumulation of injurious individuality
differential substances around and in the transplant has been strong, there
is an active ingrowth of connective tissue cells towards the center of the graft
and this tissue soon becomes transformed into hyaline substance; the ingrowth

82 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of blood vessels is very limited. But if there is no or only a slight accumula-
tion of injurious substances in this earlier period, then the connective tissue
cells form a myxoid connective tissue along the inner margin of the ring of
acinar tissue and there is here a good vascular supply. But in this case a
lymphocytic reaction may be expected to set in sometime during period II,
whenever toxic individuality differential substances produced have accumu-
lated in sufficient quantity to attract lymphocytes in larger numbers ; these
latter then invade the graft, perhaps together with a restricted amount of con-
nective tissue, which may move between and separate some of the acini. How-
ever, in general the severity of the reaction against the transplants increases
with increasing time following the grafting and the earlier syngenesio-reactions
may gradually become converted into severe homoio-reactions through
intensification of the fibrous-tissue reaction together with lymphocytic in-
filtration, both of these factors leading to an increasing destruction of the
transplanted thyroid. In cases in which paired organs from one donor were
transplanted to two brothers, or from a child to both parents, the reaction in
the two hosts was about the same in the majority of instances; this happened
especially in those instances in which the reaction was severe. Under these
conditions, a differentiation between results obtained in these hosts could not
very well be expected. However, sometimes the reaction differed in the two
hosts: there could be a severe lymphocytic reaction in the one and a slight
reaction in the other, and such a separation of the reactions occurred also when
the parents were derived from different strains of guinea pigs — one, for ex-
ample, being curly and the other smooth-haired. It was noted in such a case
that the reaction against tissues exchanged between parents and children was
severe, while on the contrary, there was some evidence that, when the parents
might have been related to each other, the reaction against the transplanted
tissues was relatively slight. In those instances in which two organs such as
thyroid and ovary were transplanted from the same donor into the same host,
the reactions against both organs corresponded to each other.

In a general way, the grades were highest in the brother-to-brother (sister)
transplantations, and there was no distinct difference between the two re-
ciprocal types of transplantations when tissues were exchanged between
parents and children. Such a result might be expected when random trans-
plantations between non-inbred families of guinea pigs were carried out. In
the rat, no definite difference between the three types of syngenesiotransplan-
tation was noticeable.

Chapter J

The Individuality Differentials of Closely

Inbred Animals

Closely inbred animals are those which have been bred by brother and
sister matings in a sufficiently large number of successive generations.
As the result of this procedure, these animals have a genetic composi-
tion which has become even more similar than that of ordinary brothers and
sisters; they exemplify an intensified brother and sister relationship. This
close relationship should exist even between animals which do not belong to
the same litter, but which have common ancestors in not far distant genera-
tions, and after very long-continued inbreeding, also between animals whose
common ancestors are somewhat farther removed.

Theoretically, after from eight to ten consecutive brother-sister matings, the
genetic composition of different individuals should be about the same (Sewall
Wright) ; their individuality differentials should then be almost as nearly
related as are those of different parts of' the same organism or of identical
twins. However, our transplantation experiments have shown that such an
identity of individuality differentials among different members of the same
closely inbred strain or family is approached with very much greater diffi-
culty than would have been anticipated. As factors which might prevent or
delay a homozygous state, we have, in the first place, to consider mutations in
the germ cells, which may be expected to take place spontaneously and with a
frequency which is not yet known. In the second place, a selection of the ani-
mals to be mated might influence the results. Thus Dr. Helen D. King, in her
inbreeding experiments, selected in every case the most vigorous rats for
breeding; this might imply a selection of the most heterozygous individuals,
those which differ most in their genetic constitution and in which the in-
dividuality differentials are most dissimilar from those of brothers and sisters.
Such a process of selection might delay the attainment of perfect homozygosity
in the closely inbred strains, but this retardation would probably not be of
very great consequence. A third factor involves the relationship between the
animals in the first brother-sister mating; if these two individuals are very
different in their genetic constitution, a greater number of consecutive genera-
tions of brother-sister matings will be required to produce homozygosity than
if they are very similar to each other, and lastly there exists the possibility
that a difference in the individuality differentials between host and donor of a
transplant will be found if a branching-off from the common line of descent
has taken place at a certain point and if the two individuals whose individuality
differentials we wish to compare belong to different branches ; the difference
thus developed should be greater the further back the branching-off from the
common line of descent occurred.

83

84

THE BIOLOGICAL BASIS OF INDIVIDUALITY

We carried out experiments ( 1 ) with rats closely inbred by Dr. Helen D.
King at the Wistar Institute; (2) with guinea pigs closely inbred at the De-
partment of Agriculture by Dr. Sewall Wright and Dr. Eaton, and later by
Dr. McPhee and Dr. Eaton, and lastly, (3) with various strains of mice closely
inbred by Mr. Marsh of the State Institute for Study of Malignant Diseases
in Buffalo, and others closely inbred by C. C. Little and L. C. Strong and their
associates at the Jackson Laboratory in Bar Harbor. A small series of experi-
ments with closely inbred chickens, obtained from Dr. H. D. Goodale in Wil-
liamstown, have already been mentioned.

(a) The individuality differentials in closely inbred rats. We shall now
discuss, first, investigations made with the closely inbred rats of Dr. Helen D.
King, who had developed two distinct inbred strains, A and B ; these had the
same origin but they had been bred separately for many generations and thus
had acquired in the end distinct genetic constitutions and individuality differ-
entials ; in addition, hybrids between strains A and B were obtained. Three
series of experiments were carried out with these animals. In the first one,
made mainly in 1926, rats from families A and B, belonging to generations 37

Donor and Host

TABLE III
(Series I)

Grades

Combined Grades

A to A (different litters)
B to B (different litters)
A to A (brothers and sisters)
B to B (brothers and sisters)
A to B
B to A

1.82 (24 rats)

1.92 (27 rats)

1.68 (12 rats)

2.55 (24 rats)

1.67 (18 rats)

1.57 (19 rats)

1.87 (51 rats)
2 . 26 (36 rats)
1.62 (37 rats)

TABLE IV
(Series II)

Donor and Host

Grades

Combined
Grades

A to A (different litters)

B to B (different litters)

A to A (brothers and sisters)

B to B (brothers and sisters)

A to B or B to A

Homoiotransplantation in non-inbred families

(AXB)F< (or F») to (AXB)F, (different litters)

(AXB)F4 (or Fs) to (AXB)Ft (brothers and sisters)

A or B to (AXB)F4

(AXB)F«to A or B

1.16 (16 rats) |
1 . 65 (33 rats) I
2.60 (17 rats) |
2.81 (19 rats) J
1.37 (32 rats)
1.36

1.29 (12 rats)
1.80 (26 rats)
1.50 (13 rats)
1.39 (13 rats)

1.49 (49 rats)
2.71 (36 rats)

and 38, 40 and 41, and also 46 and 47 were used ; in the second series made in
1930 and 1931, the rats belonged to the 60-67 generations, and in the third,
most recent series, made from the year 1939 to 1941, a smaller number of rats

DIFFERENTIALS OF CLOSELY INBRED ANIMALS 85

came from generations 91 and 92, and a larger number from generations 102
to 106. Somewhere between generations 92 and 102, family B died out and
from then on only strain A and hybrids between strains A and B were still
available. There was therefore a wide range of inbred generations, extending
from the 36th to the 106th, and a time span of about 15 years in the progressive
inbreeding of the rats, which were used in these experiments.

Series I (Table III). The grades in transplantations in different litters in
inbred strains are slightly better than the average grades in homoiogenous
transplantations in non-inbred rats and the grades are somewhat higher in
strain B than in strain A. The combined grade of the transplants between
brothers and sisters in strains A and B is higher than the grade of transplants
between different litters. This is quite definite in strain B, while in strain A
there is no marked difference between the two grades ; the reaction happens to
be even slightly less severe in transplants between rats belonging to different
litters. Transplants from family A to family B (grade 1.67), and from family
B to family A (grade 1.57) may serve as controls. Both these average grades
correspond about to the grades of ordinary homoiotransplants ; they are lower
than the average grades of transplanted tissues exchanged within family A
or family B. From these data we may conclude that as a result of close
inbreeding in rats for 37 to 47 generations in families A and B, only a very
slight progress towards a homozygous condition has been accomplished.

Series II (Table IV). A comparison of the grades in series I and II shows
that there is an improvement in the grades in transplantations between differ-
ent litters neither in family A nor in family B in series II over the corre-
sponding grades in series I. However, in the second series, in both families the
grades obtained in transplantations between litter mates are not only better
than the grades obtained in transplantations between different litters, but they
are also better than in the transplantations between litter mates in series I.
Also, the grades in transplantations between hybrids (AXB)F4 or F5 are
improved to a certain degree if litter mates are used. But in these transplan-
tations Ihe results are not so good as in transplantations between litter mates
in families A or B. Such a difference might be expected, because in hybrids
there is a greater chance for unlike genes to accumulate in brothers when
both A and B contribute to the genes of the fertilized germ cells. Trans-
plantations from parent to hybrid give somewhat better results than the
reciprocal transplantations, but both elicit severe homoiogenous reactions as
an indication that a homozygous genetic constitution has not yet been reached
in either family A or B. Exchange of tissues between families A and B like-
wise corresponds to a severe homoio-reaction, in accordance with expectations.

It is especially the results of transplantations between litter mates in inbred
strains A and B which suggest that some progress towards a greater homo-
geneity in the constitution of the individuality differentials has been made
through continued close inbreeding. In the exchange of tissues between broth-
ers and sisters of the same inbred family, the factor of a difference in the dis-
tance of relationship between different litters is eliminated. It is not probable
that the lack of a diminution in the severity of the reaction in the exchange of

86 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tissues between different litters of the same inbred family is entirely due to a
greater distance of relationship between these litters under these conditions,
although this factor may play a certain role, but that in exchange of tissues
between members of different litters the threshold required for a mitigated
reaction had not yet been reached in series I as well as in series II. In the case
of brothers and sisters it is probable that the decrease in the number and kind
of unlike genes which were present in different individuals helped to make the
individuality differentials so much alike that the reaction against the strange
individuality differentials was diminished. This increased similarity in the
constitution of the individuality differentials between brothers and sisters of
these inbred strains, which in many cases approached an autogenous state, was
brought out also in multiple simultaneous transplantations of various tissues
into the same host; here all the tissues behaved like autogenous transplants,
which is in accordance with the general rule that in transplantations from the
same donor to the same host, all tissues behave in the same way if we make
allowance for certain complicating factors, which we have discussed previous-
ly. Very instructive was also an experiment in which thyroids with adjoining
tissues were successfully grafted into brothers and sisters. After two successive
transplantations, and 50 days after the first transplantation, thyroid, para-
thyroid and fat tissue behaved like autotransplants ; but after the third trans-
plantation, the 73-day-old transplant showed a definite lymphocytic infiltration,
although otherwise it behaved like an autotransplant.

This experiment confirms the conclusion that in series II a complete autog-
enous state has not yet been reached between brothers and sisters ; but on the
other hand, it is probable that a further progress, although a not very consider-
able one, towards a homozygous condition in families A and B has been made
in continued propagation by brother-sister matings in the interval between the
37th to 47th generations and the 60th to 67th generations. However, in addi-
tion the strength of the reaction may depend not only on the genes of the
donor, which are strange to the host, but also on the genes of the host, which
differ from those in the donor, although the importance of the strange host
genes is presumably less than of those of the donor.

Series III. In this series, as a rule, thyroid, cartilage and fat tissue, as
well as pieces of striated muscle tissue, were transplanted and examination
took place 20 days later. Two groups of experiments were carried out. In the
first group ( 1 ) the hosts and donors were young rats, varying in age between
about one and three months. In the second group (2) the age of the animals
ranged between four and seven months. The results obtained in these experi-
ments are shown in table V.

If we compare the transplantations in young rats (group (1)) and in some-
what older rats (group (2)), we notice that grafts between brothers and
sisters, in family A in group ( 1 ) , behave about like autotransplants, while in
group (2), they behave like good syngenesiotransplants. The transplants be-
tween different litters of the inbred family have grades corresponding to those
between good syngenesiotransplants; again, the grades are slightly better in
group ( 1 ) . A comparison with series I shows that transplants between differ-

DIFFERENTIALS OF CLOSELY INBRED ANIMALS 87

ent litters as well as those between brothers and sisters elicit a much less an-
tagonistic reaction in series III than in series I. As compared with series II,
the grades are higher in series III in transplantations between different litters.

TABLE V

(Series III)

Group (1) Young

rats.

Group (2) Older rats.

Donor and Host

Grades

Grades

A to A (different litters)

2.82 ( 7 rats)

2.72 (10 rats)

A to A (brothers or sisters)

3.10 (22 rats)

2.77 ( 7 rats)

(AXB)F<and (BXA)F< (different

combinations, different litters)

3.12 ( 6 rats)

2.18 ( 2 rats)

(AXB)F<to (AXB)F,

brothers

or

or

3.12 ( 6 rats)

(BXA)F«to (BXA)F<

sisters

A to (AXB)F<

2.39 ( 4 rats)

(AXB)F«or (BXA)F4toA

2.87 (10 rats)

2.23 (4 rats)

B to A (91-92 generations)

1.48 ( 7 rats) 20 days

1.84 ( 7 rats) 12

days

In transplantations between brothers and sisters the results are better in young
rats of group (1) in series III than in series II, but about the same in the
older rats of group (2). We may then conclude that considerable progress has
been made in the direction towards a homozygous condition from series I to
series III, and that progress has also been made from series II to series III,
although even in series II the reactions between brothers and sisters were
much less antagonistic than in series I.

In all three series the reactions against transplants between different families
(A and B) were about alike and corresponded to homoiogenous relations of
the individuality differentials. The grades, both in the transplants between
different litters as well as between brothers and sisters of the hybrids (AXB),
corresponded to autogenous relations of the individuality differentials in group
1. In group 2, the grades of transplants between different litters of hybrids
were those of an average syngenesio-reaction ; they were much less favorable in
group 2 than in group 1. But the reactions in groups 1 and 2 of series III were
much better than the corresponding reactions in series II. Also, the reactions
in transplantations from Family A to the hybrid or from the hybrid to Family
A were much milder in series III than in series II. In series III these reactions
in young rats of group 1 corresponded to good syngenesiotransplantations,
while in the somewhat older rats of group 2 they corresponded to syngenesio-
reactions of medium intensity. The average was slightly, but not markedly,
higher in transplants from family A to the hybrid than in the reciprocal trans-
plantations. Similar results in this regard were obtained in series II, and this
might be expected if a completely autogenous condition of the individuality
differentials had not yet been attained in the families A and B.

Of interest in the third series is also the difference in the grades in the

88 THE BIOLOGICAL BASIS OF INDIVIDUALITY

groups of the young and the somewhat older rats, which agrees with the gen-
eral observation that when donors and hosts are very young, the reactions are
milder than in older animals. This difference cannot be due to a lack of in-
dividuality differentials in the former, because such differentials are present ;
but it is due rather to a lesser sensitiveness to strange individuality differen-
tials, or to a not yet fully developed mode of reaction in the younger animals.
In addition, the fact must be taken into account that younger tissues grow
more vigorously than older ones, and this condition is associated with a greater
ability to overcome the effect of the antagonistic reactions of the host ; it may
also be that tissues growing more rapidly do not give off individuality differen-
tial substances in as large amounts as the more differentiated tissues in which
the functional activity predominates. In accordance with these considerations,
we noticed that in the group of younger rats the grades are higher, even in
transplantations from hybrids to an inbred parent strain, where the derivatives
of strange genes are introduced into the host.

A comparison of the reactions observed in these three series of trans-
plantations shows that a continuous progress to a homozygous condition has
been made. In the first series there was only a slight indication of an improve-
ment in grades over the grades of ordinary homoiogenous and syngenesious
transplantations. A further slight progress was noted in series II, but the
greatest advance was made in the interval between series II and III. This
means that after about forty generations, there was only a very slight progress
towards an autogenous character of the individuality differentials ; some ad-
vance was made after 60 to 67 consecutive brother-sister transplantations ;
but the greatest advance had been made when the 102nd generation was
reached ; however, even at that time no completely homozygous condition had
as yet been attained. This finding is indicated especially by the transplanta-
tions into which the hybrids entered ; but it is noticeable also in the transplan-
tations within the inbred family A.

It seems most probable that the slow and imperfect progress in the direction
towards a homozygous condition in the inbred rats is due to the occurrence of
germinal mutations, leading to the introduction of strange genes into the con-
stitution of host and donor and opposing, therefore, the attainment of an
identity of the individuality differentials, which continued close inbreeding
would otherwise more readily have accomplished. But of these two counter-
acting factors, germinal mutations and close inbreeding, the effects of the
latter prove to be the more potent, and therefore the individuality differentials
continue to progress on their way towards increasing mutual similarity, with-
out, however, reaching this goal completely, even after as many as 106 con-
secutive brother-sister matings.

Chapter 8

Individuality Differentials in Closely
Inbred Guinea Pigs

Three series of experiments were carried out with guinea pigs. In the
first series (1927), the guinea pigs were closely inbred in the Depart-
ment of Agriculture in Washington, by Sewall Wright and O. N.
Eaton. In a second supplementary series (1931), these experiments were con-
tinued with guinea pigs inbred for a few additional generations, likewise in
the Department of Agriculture, by Hugh C. McPhee and O. N. Eaton ; and a
third, shorter and more recent series was carried out with guinea pigs closely
inbred for only five or six generations at the Caworth Farms. The guinea
pigs in the first series had been inbred by consecutive brother-sister matings
mostly for from 17 to 23 generations, while the large majority of those in the
second series had been inbred for from 20 to 25 generations. In the first series,
five inbred families were used, designated as 2, 13, 32, 35 and 39; 2N was a
line of family 2, selected for colored nose spots. This line was exceptional,
insofar as it was not strictly propagated by brother-sister matings, but mating
took place with a view of increasing the proportion of animals carrying this
characteristic nose spot, without regard to relationship. It happened, however,
that there were several brother-sister matings in this line, and in some in-
stances they were repeated for three or four successive generations, according
to information given me by Dr. O. N. Eaton. The degree of homogeneity in
the various families differed (Sewall Wright, Bull., U. S. Dept. Agriculture,
No. 1090). As controls, guinea pigs from a non-inbred B group and non-
inbred guinea pigs obtained from various dealers were used. In the second
series, only hybrids CY between families 2 and 13y, the latter an otocephalic
line of family 13, and hybrids CP between families 13y and 35 were used as
donors and hosts in the transplantation experiments. The figure following the
designation of the family indicates the number of consecutive brother-sister
matings. In the hybrids, the upper family represents the male and the lower
the female partner. The figure following CP or CY signifies the number of
generations of brother-sister inbreeding which the hybrids had undergone.
CP-0 and CY-0 represent the Flt CP-1 and CY-1 represent the F2 generations,
and so on. The guinea pigs in these experiments ranged in weight between 200
and 500 grams. The examinations usually took place between the 20th and 60th
day, but in some experiments they were made as late as about Zy2 and Sl/2
months following transplantation. We shall state the principal results obtained,
without distinguishing between series I and II.

A. (1) Transplantations in the same inbred family, host and donor not
being nearly related. In transplantations from 32-17 to 32-19 and in other
similar transplantations in family 32 the grade was 3 + . This indicates auto-

89

90 THE BIOLOGICAL BASIS OF INDIVIDUALITY

genous relationship between the individuality differentials of donor and host,
but in another experiment in family 32, after 37 days the grade was 3/3 — ,
corresponding to a very good syngenesio-reaction. In family 13, the grades
varied between 3— and 3— /2 + , even if both donor and host belonged to the
20th inbred generation. These grades correspond to good syngenesio-reactions,
indicating the existence of some differences in the constitution of the individu-
ality differentials. They may be due to the fact that, in family 13, there was a
greater possibility that the number of direct common ancestors of different
individuals was not so large as in the other families, and this may explain the
lack of autogenous conditions, at least in some cases. In family 2, one grade
was 3— (2-17 -> 2-17), in another experiment it was 3-/2+ (2-18 -» 2-16),
an indication of a lack of identity of the individuality differentials. These re-
sults were, on the whole, confirmed by some experiments in which the exam-
ination took place at a later date. Thus, in family 13, after 5 months and 12
days, the grade was 2 (unfavorable syngenesio-reaction) — after Zy2 months,
it was 3. In family 2 (or 2N), autogenous conditions were found in these
experiments.

These experiments indicate that in some families the autogenous condition
was closely approached but was not yet quite attained, while in other families
considerable progress had been made toward homozygosity, but the grades
corresponded still to good syngenesio-reactions. In different experiments the
results varied somewhat in various families. It is of special interest to note
that the lymphocytic reaction may appear only at a late stage following trans-
plantation, but that the lymphocytes may then exert a very destructive effect.
Together with the late lymphocytic reaction there may occur a secondary
slight proliferation of connective tissue in the transplant. However, the aver-
age grades in transplantations betwen guinea pigs belonging to different
litters in these inbred families were higher than the average grades in trans-
plantations between brothers or sisters in non-inbred families.

(2) Successive transplantations of thyroid into the same inbred family.
These gave similar results. In family 32 : First, transplantation for 37 days ;
second, transplantation to brother for 4 months, 9 days: grade 3-/3, which
closely approaches results in autogenous transplantations. In family 13 : First,
transplantation for 31 days; second, transplantation for 32 days: grade 2,
which corresponds to a severe syngenesiotransplantation ; but in this case,
donor and last host had only seven generations of brother- sister matings in
common.

(3) Multiple simultaneous transplantations. In four experiments with
families 13 and 32, several pieces either of thyroid gland alone, or of thyroid
and various other organs (spleen, liver, adrenal, pancreas) were transplanted
simultaneously : examination took place between 27 and 37 days. The grades
varied between 3/3— and 3 + , therefore between the reactions in favorable
syngenesious and in autogenous transplantations. The results here were as good
in family 13 as in family 32. In nine additional experiments with families 32,
2 and 13, in which the examination took place 4 months, 9 or 12 days after
transplantation, and in which thyroid, cartilage-fat tissue, bone and bone mar-

DIFFERENTIALS IN CLOSELY INBRED GUINEA PIGS 91

row, spleen, ovary, liver, adrenal gland, testicle and pancreas were trans-
planted, the grades were as follows : In two transplantations in family 32, and
in one case in family 13, the grades were 3 + , corresponding to autogenous
transplantations. In three cases in family 13 and family 32, the grades were
3— and 3— /2+, corresponding to favorable syngenesiotransplantations, and
in three experiments in family 2, the grades varied between 2+ and 2, cor-
responding to moderate or severe syngenesio-reactions. Liver and adrenal
gland were not preserved at this late period, while they were well preserved
after from 27 to 37 days ; likewise, spleen was not well preserved. Pancreas
was never recovered. Testicle tubules lined with Sertoli cells were seen. Again
it was observed that the lymphocytic infiltration can occur at a late period, and
that a fully homozygous condition has not yet been attained in the various
families. In two additional experiments in family 2, the donors were the off-
spring of parents which represented hybrids between two different individuals
belonging to family 2. For two generations this hybridization had taken the
place of the usual brother and sister matings. The hosts were the offspring of
continued brother-sister matings in family 2. The grades were 2 and 2.50,
which correspond to average grades in syngenesiotransplantations.

The average grades in the various subdivisions of group A were as follows :
2.91; 2.87; 2.56; 2.99; 2.66. The total average grade was 2.72, which cor-
responds to a favorable syngenesio-reactio'n. This confirms the conclusion that
a complete identity of the individuality differentials within the various closely
inbred families of these guinea pigs has not yet been reached.

B. Control experiments in which tissues were transplanted to non-related
guinea pigs. Examination took place 20 to 40 days later. (1) Transplanta-
tions from one inbred family to another inbred family : The grades varied be-
tween 2-/2 and 1. The average grade was 1.27, which corresponds to a severe
homoiogenous reaction. The most severe reactions were obtained in trans-
plantations in which family 13 was the host or was one of the constituents of
a hybrid. (2) Transplantations from non-inbred B to B stock, or from hybrids
between inbred families to B stock hosts: The average grade was 1.11.
(3) Similar results, with an average grade of 1.11, were obtained in trans-
plantations from B stock to St. Louis stock. In all these experiments the grades
were characteristic of homoiogenous transplantations.

C. Transplantations between brothers or sisters in inbred families. Families
35, 32, 2 (2N) and 13 were used in these experiments, in which examination
took place from 30 days to 5% months after transplantation. In the trans-
plantations in these various families, including family 13, the grade was 3 + ,
except in one case, in 13-9, where it was 3 — , corresponding to a favorable
syngenesio-reaction. The somewhat lower grade in this instance was presum-
ably due to the fact that here close inbreeding had not yet continued long
enough. In two cases, transplantations between brothers which were hybrids
of different generations within the same family were carried out, namely, in
family 13 and in family 32; in both, the grade was 3 + . As was to be ex-
pected, in the brother-to-brother transplantations autogenous reactions were
approached to a still higher degree than in the transplantations between differ-

92 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ent litters of inbred families. In 10 transplantations, brothers or sisters which
were hybrids between two individuals from families 32, 39, 35, 13 or 2 were
used. In six of these transplantations one of the parents belonged to family 13,
while the other parent belonged to families 32, 35 or 2. The grades were 3—,
3 — , 3 + , 3, 3, 3/3 — . In the remaining four transplantations, the parents that
entered into the hybrid composition belonged to families 39, 2, 32, or 35 ; the
grades were 3, 3 + , 3+, 3. In these two sets of transplantations, the average
grades were 2.94 and 3.12, respectively. While the difference between these
two averages is perhaps too small to be of much significance, both these grades
are slightly less favorable than those obtained in brother-to-brother trans-
plantations in the closely inbred strains. This is presumably due to the fact
that in hybrids a summation of the effects of strange genes takes place, which
latter may still be found in some individuals in inbred strains.

D. As controls, transplantations were carried out between brothers in non-
inbred stock. In former experiments of this kind, the average grade was 2/2—
(1.87). In 15 additional experiments in stock B guinea pigs, the average grade
was 1.91. These grades are better than those obtained in transplantations be-
tween non-related, non-inbred guinea pigs, in which the average grades were
1.27 and 1.11, but they are much lower than the average grades obtained in
transplantations between brothers in inbred strains.

E. Transplantation front a hybrid between two inbred families to one of
the parent families. 25 experiments were made; in each case an Fx hybrid
was used as the donor. In no case was one of the actual parents used as host,
but merely the families to which the parents belonged. Examination took place
between 21 and 37 days after transplantation. The average grade was 1.75,
which corresponds to a severe syngenesio-reaction, but is somewhat higher
than the average grade found in homoiogenous transplantations. Here, again,
it appeared that the severity of the reaction was strongest in transplantations
in which family 13 was a component part of the donor, even if the host be-
longed not to family 13, but to the other parent family which entered into the
hybrid. There were six transplantations in which family 13 entered as a parent
strain in the donor; in three of these, strain 13 was likewise the host. The
other parent family was 2. The grades in these six transplantations were as
follows: 1.25, 1, 1.12, 1.25, 1, 1.25. The average grade was 1.14, which cor-
responds to a severe homoiogenous reaction. There were 13 transplantations
in which family 32 entered into the hybrids, and in six of these it was also
host. The grades were as follows: 2.12, 2, 1.87, 1.87, 2, 2, 3.25, 1.87, 3, 1.12, 3,
1.87, 2.75, corresponding to an average grade of 1.98. The average grade of the
experiments in which strain 32 was also host was 2.5. The other component
families were 2, 35 and 39. There remain six transplantations in which families
2, 35 and 39 entered ; here the average grade was 1.65. There are, then, at least
strong indications that the presence of family 13 in the hybrid intensified the
reaction against the graft and that the presence of family 32 in the donor, and
especially also in the host, mitigated the severity of the reaction. It is not
probable that the strong reaction against family 13 is due actually to a lesser
effect of the long-continued inbreeding, but to a greater reactivity of family

DIFFERENTIALS IN CLOSELY INBRED GUINEA PIGS 93

13 as a host and to an increased injuriousness of its individuality differentials.
In family 32, the opposite conditions obtain.

F. Transplantations from a parent family to a hybrid. Also in this group
of experiments the actual parents of the hybrids were not used in these trans-
plantations, but other members of the corresponding families. 16 experiments
were carried out. Examination took place between 25 and 35 days. The reac-
tions were much milder in this series than in the reciprocal series E, except in
one case, in which 2N-52 was transplanted to a hybrid between families 2 and

(2-22
13y (CY-0 j . " _-. Here, the grade was 1. Whether in this instance the donor

2N happened to carry some genes strange to the family 2 component of the
host, or whether some error entered into this transplantation, is uncertain. The
fact may be recalled in this connection that the line 2N had not been propa-
gated by strict brother-sister matings. Omitting this last transplantation, the
average grade in the remaining 15 transplantations was 3.05, a grade similar
to those obtained in transplantations between brother hybrids in inbred fami-
lies, which were 2.94 and 3.12. If we include the transplantation with grade 1,
the average grade was 2.92. If we omit again this one transplantation, there
were six of 15 experiments in which the grades were below 3, namely, 2.87
and 2.75 ; these grades were characteristic of a favorable syngenesio-reaction,
while in the other cases the reaction approached closely the autogenous state.
Taken as a whole, the grades were very good in this series and they came near
to those characteristic of autogenous reactions, but a fully homozygous con-
dition had not yet been reached.

From these data, it may be concluded that transplantations from hybrids to
one of the parent families did not elicit homoiogenous reactions, but, instead,
severe syngenesio-reactions. It seems possible that in this case the presence of
gene sets common to donor and host mitigated the intensity of the reaction of
the parent- family serving as host against the strange component of the hybrid-
transplant. On the other hand, transplantation from a parent-family to the
hybrid-host did not give a perfect autogenous reaction, since some of the genes
of the parent may be strange to the corresponding constituent of the hybrid;
therefore, in a number of cases, syngenesio-reactions were obtained. Another
possible factor affecting the result in these experiments was the apparent
tendency of certain families to elicit a more severe reaction, or to respond
more aggressively themselves than others; thus the involvement of families
13 and 35 in the transplantation seemed to cause a relatively severe, and that
of family 32 a more mitigated reaction. As stated previously, there is some
indication that the reaction may be stronger in the presence of family 13, be-
cause in this family the various members may have a smaller number of
common brother-sister matings than in some other families; but such a con-
dition should not affect the severity of the reaction of a family other than 13
serving as host against a hybrid containing the gene set of family 13; in this
case, other conditions must be responsible for the severe effect.

G. Transplantations between hybrids, in which donor and host were com-
posed of the same two inbred families but were not brothers or sisters. 14

94 THE BIOLOGICAL BASIS OF INDIVIDUALITY

transplantations of this kind were carried out; but in one of these, the ex-
amination took place as early as 10 days after transplantation. Omitting this
case, there remain 13 experiments in which the examination took place between
20 and 40 days. In the large majority of these transplantations the hybrids
were composed of families 13y and 2, but in a few instances, families 35 and
32 were parents of the hybrids. We may arrange these transplantations accord-
ing to the similarity or difference in the generations of brother-sister matings
of the two component parents in donor and host. In one set the parent families,
13y and 2, which entered into the hybrids in donor and host, belonged to the

same generations: (Cy-0 j^J' 4 -^Cy-0 jl% (21 days) ; grade 3. In four
transplantations, the generations were the same in one inbred family but differ-
ent in the other family: CP-0 jj^"2^ -+CP-0 H^J5 (20 days) ; grade 2.75.

The grades in the other three transplantations of this kind were: 3, 3.25, 2.75 ;
the average grade was 2.94. In the remaining eight experiments, in each case
the parents composing the hybrids belonged to different generations. The
grades were: 1.75, 1.75, 1.75, 1.25, 1.75, 1 (hybrids between families 13y and
2), 2.75 (hybrids between families 2 and 35), and 3.25 (hybrids between
families 32 and 35). Again the presence of family 13 in the hybrids seemed to
intensify the severity of the reaction, while in the combination between fami-
lies 32 and 35, the result corresponded to that found after autogenous trans-
plantation. The average grade in the six transplantations into which family
13y entered was 1.54, which approached that of a homoiogenous transplanta-
tion.

H. Transplantation in hybrids in which one of the two parent families
was the same in donor and host, while the other parent family was different.
One hybrid was composed of families 2 and 13y, while the other hybrid, either
host or donor, was composed of families 13y and 35. Three transplantations
were carried out and examination took place after 19 to 21 days. The grades
were: 1.87, 2.12, 1, and the average grade was 1.69, which represents a mod-
erate homoiogenous reaction. The result is similar to that obtained in the
transplantations between hybrids 2 and 13y, in which both parent families be-
longed to different generations.

Series III. Transplantations between guinea pigs during early stages in
inbreeding.

Two short series of experiments were carried out with guinea pigs which
had been inbred for five to six generations by brother-sister matings at the
Caworth Farms in New York. We shall briefly mention*these transplanta-
tions, because they indicate that in contrast to the experiments with guinea
pigs which had been subjected to close inbreeding for from about 15 to 27
generations, no definite progress towards an autogenous condition of the
individuality differentials had as yet been made. Guinea pigs from two strains
(CP and Connaught), in each of which there were several inbred families,
were used. The initial weights varied between 225 and 310 grams and
examination took place after 30 days. Thyroid, cartilage, fat tissue and
muscle or thymus were transplanted.

DIFFERENTIALS IN CLOSELY INBRED GUINEA PIGS 95

In a few experiments of the first series, in which brother-to-brother
transplantations were carried out, the grade was slightly above 1 ; likewise,
in transplantations from one strain to another the average grade was 1. In a
second series of transplantations, made within the same strains, the average
grade was 1.85 in six experiments. In six other experiments, in which
transplantations were made between different strains from Caworth Farms
guinea pigs to St. Louis guinea pigs, the average grade was 1.33. We may
then conclude that there is perhaps a slight indication of a beginning homo-
zygous condition in these guinea pigs, as indicated by grade 1.85 in trans-
plantations within the same strain ; but in the first series, there is no indication
of such a tendency. Therefore, after five or six generations of inbreeding,
there is not yet any definite advance in the direction towards a homozygous
state among these animals.

The following are the principal conclusions suggested by all these experi-
ments with closely inbred guinea pigs. The difference between the relatively
rapid effect of inbreeding on the individuality differentials in guinea pigs as
compared to the effect in rats, which were studied in the preceding pages,
is striking. However, even in guinea pigs the ultimate goal of the inbreeding,
namely, a completely autogenous state of the individuality differentials, of
all the animals in an inbred family, has not yet been reached. The individuality
differentials of host and transplant were the more similar to one another the
larger the number of brother and sister matings which these individuals had
in common before the separation of these matings into different sidelines
took place, and the smaller the number of these separate and distinct brother-
sister matings had been in the preceding generation in host and donor. The
separation into side lines may cause an accumulation of unlike genes if a
perfect homozygous condition had not yet existed at the time of the separa-
tion; mutations may then add to the number of unlike genes. In family 2,
for instance, the grade was 2.50 in a case in which there had been six to
nine common ancestral matings, followed by 20 to 24 separate brother-sister
matings, while the grade was 3.25 with 12 and 16 brother-sister matings
in common and subsequent separation for only two or three generations.
Similar results were obtained in family 13. After 19 to 20 consecutive brother-
sister matings, there was usually an absence of any marked incompatibility
between the individuality differentials. Such individuals may behave like
identical twins, at least within the range of conditions which were used in
these tests ; however, a lengthening of the time during which the individuality
differentials of host and transplant had a chance to act on each other might
still have brought out a certain difference when a shorter period did not show
it, and some of our experiences indicate such an effect. Striking also is the
correspondence between the pedigree relationship of the various guinea pigs
and the degree of relationship of their individuality differentials as revealed
by transplantation ; this comes out especially in the brother-to-brother trans-
plantations and in the various types of hybrid transplantations. It is inter-
esting in this connection that in the experiments with inbred guinea pigs, as
well as in those with inbred rats, the greater similarity of the individuality

96 THE BIOLOGICAL BASIS OF INDIVIDUALITY

differentials in brothers and sisters, as compared to non-litter mates, was
very definite, in contrast to experiments in non-inbred animals, where these
differences between syngenesio- and homoiotransplantations are not always
definite. The correspondence between these two variables, pedigrees and
individuality differentials is, on the whole, very close, and this is one reason
why we thought it worth while to give some of the results obtained in these
transplantations with greater detail. Of further interest is the great difference
between the results of hybrid-to-parent and the reciprocal transplantations.
The former are not, however, identical with homoiogenous transplantations,
nor the latter with autogenous ones; but in both intermediate results were
obtained, suggesting that the presence in the hybrid of a gene set similar
to that in the host may have, beneficial effects, while the presence of unlike
factors in the host may intensify unfavorable reactions against the transplant.

It is conceivable that the presence in the host of a set of genes not present
in the donor might lead to differences between the metabolism of host and
transplant and that this might, to some degree, influence the aggressive
action of the host against the transplant. However, the intensity of the
reaction in these transplantations depends essentially upon the presence in
the donor of genetic factors not present in the host. In tumor transplantations,
Little and Tyzzer (1916) found that in transplantations from hybrids to
parent strain, no successful transplantations were obtained, while the
reciprocal transplantations gave 100 per cent takes ; they concluded that only
one dose of genes is required for successful transplantations. Subsequently
(1921/22), Little and Johnson noted that if pieces of spleen were trans-
planted from inbred Japanese mice to hybrids between the Japanese and
white mice, the results corresponded to those of autotransplantation, while
in reciprocal transplantations from hybrids to waltzing mice, the transplants
were destroyed in a short time, indicating a strong homoio-reaction. Similar
results were published more recently by Little and Bittner. But in these
experiments, conditions were selected which made the recognition of inter-
mediate results very difficult. This caused a lack of the finer means of measur-
ing existing differences between the individuality differentials of donor and
host, and led to the assumption of a genetic identity in one type of transplanta-
tion, and of a complete lack of similarity of the individuality differentials
of host and donor in the reciprocal type, whereas, in all probability, various
kinds of intermediate states existed.

And, lastly, there are at least indications that there exist constitutional
inherited differences between some of the inbred families, which determine
not only differences in the intensity of their reactions against strange indi-
viduality differentials in the transplant, but which also may perhaps influence
the degree of toxic action which the transplant exerts on various hosts. While
differences in the interaction between hosts and transplants in different
experiments may be partly explainable on the basis of differences in the
number of generations which have passed since the ancestries of two indi-
viduals, belonging to the same family, branched off from each other, it is
not probable that this is the only factor determining the differences observed

DIFFERENTIALS IN CLOSELY INBRED GUINEA PIGS 97

in the intensity of reactions of hosts against transplants. Although, as stated,
it is much easier to bring about a great similarity in the constitution of the
individuality differentials through continued close inbreeding of certain
families in guinea pigs than in rats, we have seen that even in guinea pigs,
after a considerable number of generations of brother-sister matings, a com-
plete identity of the individuality differentials has not yet been reached. In
accordance with this fact is the observation that, a small number of genera-
tions of brother-sister matings does not seem to cause a marked increase
in the similarity of the individuality differentials in guinea pigs, as shown
in series III of these experiments.

Chapter p

Individuality Differentials in Closely
Inbred Strains of Mice

We have already discussed the transplantations of tissues from one
closely inbred strain of mice to another, as well as some trans-
plantations in non-inbred mice, and we shall later analyze also
heterogenous transplantations between mice and some other species of ani-
mals. We shall now consider the transplantations within inbred strains —
intra-strain transplantations — the character of the individuality differentials
of mice belonging to such strains, and the effects of hybridization between
different inbred strains on the character of the individuality differentials of
the hybrids.

From among the large number of these types of transplantation carried
out, we shall first select a smaller representative group, in which, to a large
extent, some of the complicating factors, as indicated by the presence of
polymorphonuclear leucocytes in the transplants, have been avoided. We shall
then analyze the results of other groups of intra-strain transplantations, as
well as transplantations between hybrids, and some experiments in which
the analysis of the complicating factors mentioned, as well as of some addi-
tional ones, has been attempted.

In inter-strain transplantations between strains C57 and D, which we have
already discussed, the average grade of ten transplantations was 1.29. This
corresponds to a homoiogenous relationship of the individuality differentials.
In ten transplantations between not closely related mice belonging to the
same inbred strains C57 or D, the average grade was 2.26, which corresponds
to syngenesiotransplantation. The grades varied between 2 and 3.12, but
in one case the grade was as low as 1.75. In four transplantations within
inbred strain A, the average grade was somewhat higher, namely, 2.81. In
two New Buffalo mice the average grade was 2. These grades varied between
those characteristic of favorable and of average syngenesiotransplantations. In
eight transplantations between hybrids (DxC57)F1( belonging to different
litters, the average grade was 1.91, which, in accordance with expectation,
is below the grades obtained in grafts between members of inbred strains.
In 11 transplantations between hybrids (DxC57)F1; which were brothers,
the average grade was much higher, namely 3.04, a result which approaches
that found in autogenous conditions. In 21 transplantations from parents
D or C57 to their hybrid children (C57xD)F1, the average grade was
2.60, which corresponds to a favorable syngenesio-reaction. In case members
of the strains to which the parents belonged, but not the parents them-
selves were the donors, the average grade in six transplantations was
2.35, which is slightly less favorable than the transplantations from the

98

DIFFERENTIALS IN CLOSELY INBRED MICE 99

direct parents to the hybrids, although it still falls into the range of nearly
related individuality differentials. Decidedly more unfavorable were trans-
plantations from hybrids (C57xD)Fj to their own parents, with an average
grade of 1.42 in ten transplantations, or from such hybrids to members of
their parent strains, other than their actual parents, with an average grade
of 1.50 in five transplantations. Both of these reactions fall into the range
of homoiogenous relationship of the individuality differentials. In all these
experiments examination as a rule took place 20 days following trans-
plantation, and each mouse received transplants of thyroid, cartilage, fat
tissue and striated muscle ; whenever possible, also ovaries were trans-
planted. These grades indicate very strongly that neither in strains C57, D,
New Buffalo, nor even in strain A, has an autogenous condition of the
individuality differentials been reached ; but it has progressed farthest in
this direction in strain A. All these grades fall into the range of syn-
genesiotransplantation. However, the reactions are much milder in intra-
strain than in inter-strain transplantations, where they correspond to
homoiogenous transplantations. In accordance with expectation, the reactions
were more severe if instead of transplanting within the same inbred strain,
we transplanted between hybrids such as DxC57)F1, in which both parents
were from inbred strains. In this case the results were intermediate be-
tween those obtained in simple inter-strain and intrastrain transplantations,
corresponding to unfavorable types of syngenesiotransplantation. How-
ever, if the hybrids which served as donors and hosts were brothers and
sisters, then the results approached more closely those obtained in autog-
enous transplantations. As was to be anticipated, in transplantations from
parent strains to hybrids the grades were higher than in the reciprocal
transplantations. In the former, they corresponded about to the grades of
simple intra-strain transplantations, although they were slightly better
than the latter if the actual parents of the hybrids served as donors ; how-
ever, an autogenous condition had not yet been reached. The reciprocal
transplantations from hybrids to parent strains or to the actual parents
gave results which were only slightly better than those obtained in inter-
strain transplantations.

As stated on previous occasions, in the mouse the main reliance in the
grading must be placed on the state of preservation of the various tissues, on
the kind of structures which survive, and on the extent of the ingrowth of
connective tissue into the various transplants and the degree of replacement
of the latter by fibrous tissue. In the case of the fat tissue, also the number of
epithelioid phagocytic cells which separate the fat cells is significant. While
lymphocytic infiltration plays a certain role likewise in the mouse, and while
it may be very intense in some instances, it can not be relied upon as a quanti-
tative standard in the evaluation of the reactions to the same extent as in rat
and guinea pig; but in the mouse, also, there is a very good correspondence
beween the fate of various kinds of tissues transplanted from the same donor
into the same host, if we make allowance for peculiarities of different types
of tissues and for accidental variable factors which may complicate the results.

100 THE BIOLOGICAL BASIS OF INDIVIDUALITY

A comparison of the results of transplantations within various inbred
strains. In a further extensive series of experiments we have compared,
in a number of closely inbred strains, the reactions against transplants, when
donors and hosts belonged to the same inbred strain. (1) In strain A, pieces
were examined from 12 to 50 days after transplantation ; the age of the hosts
and donors varied, as a rule, between 2 months and 7 months, but in some
transplantations the hosts were as old as 16 months. These differences in age
did not affect noticeably the results of transplantation. In the large majority
of cases the transplants (thyroid, parathyroid, cartilage, fat tissue, bone and
bone marrow, and striated muscle tissue) behaved like autogenous transplants,
or they at least approached this condition. But in certain instances the thyroid
graft was stunted or there were some mild lymphocytic infiltrations in the
thyroid, muscle or cartilage-fat transplants. These changes were found as
early as 20 days after transplantation and also after 50 days ; but when pres-
ent, they were mild and they corresponded to favorable syngenesio-reactions.
There was a marked similarity in the condition of the various tissues trans-
planted from the same donor into the same host — they all showed the struc-
ture of autogenous transplants — although, as stated, there could develop a mild
lymphocytic infiltration in some instances. More severe reactions were noted
in experiments in which the presence of polymorphonuclear leucocytes, which
accumulated especially inside of fibrous nodules, indicated a probable infec-
tion. At some distance from the center of infection an increase in lymphocytes
in the fat tissue and infiltrations with small vacuolated phagocytic cells could
be noted; but even under such conditions the injurious changes, including
formation of fibrous tissue, as a rule were mostly localized and did not lead to
a general damage of the transplants. In the majority of these, as well as of the
following transplantations, examination took place after 20 or 30 days, but in
some cases it was as late as 50 days, as it was also in other strains than A.

In strain C3H, the results were similar to those found in strain A ; in the
majority of cases the pieces behaved like autogenous transplants; however,
there were occasionally some slight lymphocytic infiltrations, and if an infec-
tion had occurred, the reactions were more severe.

In strain D, a great variability of the reactions was noted; these ranged
from an autogenous to a severe homoiogenous type, in which a great part of
the thyroid was destroyed and the remaining acini were embedded in fibrous
tissue. There was also some lymphocytic infiltration; in the fat tissue an in-
crease in fibrous tissue had taken place, and epithelioid, small vacuolated
phagocytic cells, together with some accumulations of lymphocytes, were pres-
ent. In general, there was a correspondence between the behavior of different
tissues taken from one donor and transplanted into the same host. In an ex-
periment in which four pieces of thyroid had been transplanted from two
donors into the same host, two of the transplants behaved like autogenous,
and the other two like homoiogenous transplants. Strain D is then, it seems,
less homozygous than strains A and C3H.

In strain CBA the results corresponded mostly to those found in autog-
enous transplantations ; but in some instances there was an increase in fibrous

DIFFERENTIALS IN CLOSELY INBRED MICE 101

tissue and lymphocytes, a destruction of a part of the thyroid transplant, and
an infiltration of the fat tissue by connective tissue, lymphocytes and small
vacuolated phagocytic cells. However, the more severe reactions may have
been due to infection, as indicated by the presence of polymorphonuclear leu-
cocytes in or around the transplants.

In strain C57 we find, again, reactions varying between those seen in auto-
genous and those in homoiogenous transplantation. Besides the many experi-
ments in which the results resembled or approached those obtained in autog-
enous transplantations, there were a considerable number of syngenesio- and
homoiogenous reactions and, as a rule, a correspondence existed between the
behavior of different transplanted tissues. In some instances, the presence
of polymorphonuclear leucocytes made the interpretation of the results difficult.

In New Buffalo strain, in which donors and hosts were from 2 to 6 months
old, either almost autogenous reactions or syngenesio-reactions were obtained ;
in some instances, a stunting of transplanted thyroids and striated muscle
tissue was noted. The average grades were 2.84 in transplantations between
litter mates and 2.81 in those between non-litter mates, a difference which is
of no significance. In a few older mice belonging to strain Old Buffalo, a few
homoiogenous reactions were noted. There was, as a rule, a correspondence
in the type of reactions against different tissues in transplantations from the
same donor to the same host. On the whole, then, the individuality differen-
tials in strain New Buffalo approached identity, but this goal had not yet been
quite reached.

In strain AKA, there was usually a definite homoiogenous reaction against
thyroid as well as against cartilage and fat tissue. In some cases the thyroid
was destroyed, in others there was an incomplete ring of acini invaded by
fibrous tissue and with much lymphocytic infiltration, which helped to destroy
the acini. In such cases the fat tissue was usually invaded by fibrous tissue,
lymphocytes and phagocytic, vacuolated cells ; the bone marrow was necrotic.
In one instance, the thyroid transplant approached an autogenous condition,
and, correspondingly, there was very little connective tissue ingrowth or
lymphocytic infiltration in the fat tissue. In a few other cases there were
syngenesio-reactions ; but for the most part, a marked homoiogenous reaction
was found.

In strain C only a few transplantations were carried out ; the results were
good, approaching autogenous or syngenesious conditions.

Do variations in age of donors or hosts in inbred strains affect the reactions
against the individuality differentials? In further experiments we tested the
degree to which the individuality differentials, within the various inbred
strains, had become similar to one another or identical, by transplanting tissues
from relatively old donors to young hosts and vice versa. This procedure gave
us also an opportunity to study further the effect of the age of donors and
hosts on the reactions against individuality differentials, in experiments which
can be more readily carried out in mice than in other species, because mice
undergo old age changes and die earlier than do most other mammalian species
used in these experiments.

102 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Strain A. In experiments in which the donors were from 14 to 19 months
old and the hosts were young, the transplanted thyroid was found more or less
sclerosed, which means that the individual acini were surrounded and sep-
arated from one another by hyaline-fibrous tissue. However, in strain A, begin-
ning soon after the age of 12 months, the thyroid normally undergoes sclero-
sis, although not so frequently as in strain C57. The parathyroid showed cor-
responding pericapillary hyalinization. It follows that these local tissue changes
cannot be reversed by transplantation into young hosts, where the constitu-
tion of the bodyfluids differs in certain respects from that in older animals.
While in certain cases some of these transplants behaved like autogenous
tissues, in some others the transplants were invaded by lymphocytes, slightly
or even more extensively. The lymphocytic infiltration became greater, espe-
cially around the grafts which had been kept in the host for longer periods.
This observation seems to confirm the conclusion that even in strain A the
individuality differentials of different animals have not yet become identical.
But, as we have found in other cases, here also local factors may co-operate
with the effects of a certain degree of incompatibility between the individuality
differentials in calling forth lymphocytic infiltration ; thus we noticed in one
instance in which two thyroids from the same donor were transplanted into
the same host, one showed some lymphocytic infiltration while the other one
was as yet free from it. Such a result may have meant merely that in one graft
the threshold of stimulation for the host lymphocytes was reached somewhat
earlier than in the other one. In reciprocal experiments, tissues (thyroid,
cartilage and fat tissue, striated muscle) were transplanted from 2 or 2y2
months old mice to 18 or 19^ months old hosts. Here, all the tissues were
well preserved ; the transplants behaved on the whole like autogenous grafts ;
it is possible that the amount of preserved thyroid or muscle tissue was some-
what reduced, although this does not seem to be a necessary result of the old
age of the hosts. There was no sclerosis and no lymphocytic infiltration in the
old hosts.

We compared with these intra-strain transplantations, inter-strain trans-
plantations of the same kinds of tissues, in which both host and donor were
about 4 to 5 months old. Here the reactions were much more severe. In some
cases the thyroid transplant had been entirely replaced by fibrous tissue and
lymphocytes, in others, more or less tissue had been destroyed. The average
grades in these inter-strain transplantations were: Strain A to strain New
Buffalo— 1.06; strain New Buffalo to strain A— 1.90.

In strain D, in transplantations from young \y2 to 2y2 months old mice, to
mice ranging in age between 12 and 19 months, the grades varied between 3,
approaching grades given in autogenous transplantations, and 1+ ; usually
there was a partial fibrosis, due to increase of connective tissue between acini
and imperfect preservation of the transplants. In transplantations from 12
months old donors to 2 months old hosts the results were good, the grades
being mostly 3 and 3 — . In transplantations in which hosts and donors were
about 7 months old, the results were intermediate, lymphocytes invaded thyroid
and muscle and there were vacuolated phagocytic cells in the fat tissue. In

DIFFERENTIALS IN CLOSELY INBRED MICE 103

transplantations between 2 months old mice, the results approached those
found in autogenous reactions. These experiments confirm, then, our previous
findings, which indicated great variations in the transplantations in this strain
and the occurrence of autogenous as well as of homoiogenous reactions. We
noted furthermore that transplants into hosts as old as 18 months may remain
very well preserved, but in general the results were better in experiments in
which host and donor were young than in those in which they were older.

In strain C57, almost all mice older than 12 months are affected to a variable
extent with sclerosis of the thyroid gland. If the various organ pieces, includ-
ing thyroid gland, of mice ranging in age between \Sl/2 and 18 months, were
transplanted into young, 2 to 3 months old mice, the preservation of the grafts
was, on the whole, very good ; but in one-half of the transplanted thyroids
sclerosis was found, and in five out of six of these pieces there was much or
moderate lymphocytic infiltration. Therefore, the sclerosis of the thyroid,
which develops in older mice of this strain, may remain unchanged in young
hosts.

In strain C3H, tissues were transplanted from 13 to 13^ months old mice
to 35^2 to 4 months old animals. The results approached those of autogenous
transplantations and only rarely a slight lymphocytic infiltration was found.
As controls, transplantations were made from strain C3H to strain C57. The
donors ranged in age from 15 months and 13 days to 13 months and 20 days;
the hosts' age ranged from almost 3 to 4 months. The average grade was 1.37,
which corresponds to a marked homoiogenous reaction. In one instance the
thyroid was partly sclerosed. The relatively old age of the donor did not
modify noticeably the strength of the reaction of the host against the trans-
plants, and the marked difference between the severity of the reaction after
transplantation of tissues into different strains and into the same strain is
quite evident.

In one experiment, four thyroid glands were transplanted from two \]/2
months old CBA mice to a 19 months old CBA mouse. Two months later, at
autopsy, two thyroids were found. There was no lymphocytic infiltration and
the thyroid tissue was well preserved, but a small amount of hyaline tissue had
developed around certain acini. Also, in the parathyroid hyaline septa were
noted. This observation agrees with that made in some other instances in
which thyroid glands were transplanted from young into old mice. We are
inclined to interpret this condition as a partial sclerosis of the thyroid gland.
It seems, then, that after transplantation of the thyroid gland from young into
old mice of the same strain there may be, in some cases, relatively much de-
velopment of dense fibrous-hyaline connective tissue around certain acini.
The conditions usually present in the old hosts would favor sclerotic changes
in the thyroid tissue, and if this tendency is sufficiently strong, it may lead to
sclerosis even in the non-transplanted thyroid gland of the host; otherwise,
there was no indication of a specific reaction of the host against the individu-
ality differential of the transplant, and in some transplantations into old mice
the results may approach those found in autogenous grafts.

These experiments confirm, therefore, our former ones, in which it has been

104 THE BIOLOGICAL BASIS OF INDIVIDUALITY

shown that there are still disharmonies between the individuality differentials
of mice within the same inbred strains, but that the frequency with which the
resulting antagonism is found varies in different strains. They show also that,
essentially, old hosts react against transplants in a similar manner to young
hosts, except that there may possibly be a greater tendency in the old hosts to
the development of fibrosis around the transplanted thyroid acini ; but in ex-
periments in strain A, similar results were obtained in transplantations in
which the age of donors and hosts, brothers and sisters in these cases, was
1 or 2 months and in others in which it was 11 months. In addition, these
experiments show that if a sclerosed thyroid is transplanted to a young mouse
belonging to the same strain, the sclerosis may persist and that such a sclerosed
thyroid may also be invaded by lymphocytes.

Serial transplantation of thyroid gland in inbred strain A. From long-
continued transplantations of tumors, we concluded that various mammalian
tissues have the potentiality to immortal life, although the organism of which
they form a part is mortal. It is not possible to repeat this condition with
normal tissues through serial transplantations in the same way as with tumors,
because in the case of normal tissues the differences between the individuality
differentials of donor and host will, in all probability, be so great that the
toxicity of the bodyfluids of the host and the aggressive action of its lympho-
cytes and connective tissue will injure and destroy the transplants within a
relatively short time. On a former occasion we attempted to overcome this
difficulty by using for serial transplantations in the rat a very resistant tissue,
namely cartilage, and in this way it could be shown that parts of the cartilage,
originally taken from an old rat, after transplantation into younger hosts may
remain alive for so long a time that the total age of the transplant exceeds that
usually reached by rats.

Subsequently it occurred to us that this problem might perhaps be attacked
successfully in still another manner, namely, by serial transplantation in close-
ly inbred strains or families, in which the individuality differentials in all the
animals belonging to such a strain or famly had become identical or almost
identical. Here, the reactions against the transplants on the part of the hosts
should be lacking, or so slight that no serious damage would be inflicted. We
have already reported on short serial transplantations of this kind in guinea
pigs, but more favorable for this purpose seemed to be the inbred strain A
mice, because under natural conditions the life of this mouse is shorter than
that of a rat or guinea pig and because strain A was the one in which severe
reactions against transplants from donors belonging to strain A would be least
likely to occur. We selected for transplantation, the thyroid gland, with or
without the parathyroid. In this case, not only isolated tissues, such as fibro-
blasts or epidermal cells spreading out diffusely, but a complete organ would
be kept alive.

Ten experiments were carried out, in which one or two thyroid glands were
transplanted from a strain A mouse through a number of generations of A
mice, the donors in different experiments varying in age between Sy2 months
and 14 months. Three of the donors had reached the age of 14 months, one the

DIFFERENTIALS IN CLOSELY INBRED MICE 105

age of 13 months, and two the age of 12 months at the time the experiment
was started. The serial transplantations were continued for periods that varied
between 5^2 months and 34^ months. The youngest thyroid recovered after
completion of the serial transplantation was 11 months and 10 days old and
the oldest one was 41^ months old; the age of the others was intermediate
between these ages. The age of 41^2 months exceeds considerably the average
age of A mice and exceeds, probably, also the oldest age which mice belonging
to this strain reach. The number of serial transplantations made in these vari-
ous experiments ranged between three and seven, and the time during which a
transplant remained in a single host varied between 2j^ months and 6 months ;
but in several instances the transplant was left only 2^2 weeks in the last host.
On microscopic examination it was found that the thyroid was preserved, but
in four experiments it showed either slight or partial sclerosis, while in six
experiments it showed complete sclerosis. In the latter case, all the acini were
surrounded by rings of hyaline-fibrous tissue, which separated the acini from
one another. In the center, a number of acini had been reduced to thin cell
strands or had been lost entirely through pressure of the stroma, which injured
the epithelium, and, in addition, interfered with its nourishment. Several
capillaries were seen, however, in the stroma. These thyroid transplants, there-
fore, resembled closely the non-transplanted thyroids of older mice belonging
to strain C57. In four cases a limited number of acini were surrounded by
thin hyaline rings ; but over larger areas the acini were lying close together.
Lymphocytic infiltration was either lacking entirely, or it was slight. Probably
two factors are involved in the development of this sclerotic condition: (1)
The age of the donor. An age of the donor above 13 months favors complete
sclerosis. There was no sclerosis when the transplant was less than 12 months
old. (2) The length of time during which the transplant remained in the
strange hosts. Complete sclerosis was found in cases in which the donor was
only 6 or 12 months old ; here there is little doubt that the thyroid at the time
of transplantation was not yet sclerotic, but that it acquired the sclerosis in
the course of the serial transplantations. Therefore, if the transplanted thyroid
remained long enough in different hosts, or if it attained a certain age, it
tended to become completely sclerotic. This condition was especially marked
if the donor of the thyroid had reached the age of 14 months, in which event
the transplant either was already somewhat sclerotic or had a greater tendency
to become so. This interpretation agrees with our findings in the preceding
experiments, where there were likewise indications that both the factors men-
tioned here may play a role in producing thyroid sclerosis.

It follows from these experiments that by means of serial transplantations
in the same inbred strains, it will in all probability be possible to keep whole
organs alive up to an age which much exceeds that usually attained under
normal conditions, and that the reactions of the host against such transplants
may be lacking entirely. It may perhaps be possible even to keep such trans-
plants alive indefinitely by serial transplantation. However, it may be suggested
that in future experiments of this. kind, the transplant be allowed to remain for
longer periods of time in the same host and that, correspondingly, the number

106 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of repeated retransplantations be diminished; this may perhaps lead to a
diminution of the injury inflicted on the grafted tissue.

It is very probable that a sclerosed thyroid does not produce thyroxin and
is therefore functionally inactive, and it may be also that such a thyroid
produces a smaller amount of the individuality differential substance ; this con-
dition would tend to diminish the invasion of the transplant by lymphocytes.
Accordingly, we found the lymphocytic infiltration in these serial transplan-
tations of thyroid gland either lacking or slight; but, the fact that the indi-
viduality differentials in strain A approach, although they do not quite attain,
an autogenous state would in itself be sufficient to account for a lack of
lymphocytes. However, in the preceding experiments we noticed that after a
single transplantation of the thyroid gland, a sclerosed organ could be infil-
trated quite markedly with these cells. There is reason for assuming, then,
that in the case of the thyroid gland a deficiency in the amount of hormone
produced by the host thyroid is not required for a successful transplantation
of this organ, and, correspondingly, it is doubtful whether the diminution in
function of the sclerosed thyroid renders its transplantation easier.

Transplantation between nearly related individuals in inbred strains of mice.
If the inbreeding in mice had led to a completely autogenous condition of the
individuality differentials among all the members of a closely inbred strain,
there should be no difference between the results of transplantations between
nearly related mice — namely, those which belong to the same litter and their
own parents — and between other mice which belong to different litters. They
all should show autogenous reactions. We carried out, accordingly, a con-
siderable number of experiments in which we studied transplantations of
various tissues, but especially of thyroid, cartilage and fat tissue, between near
relatives, and those between brothers and sisters.

From these experiments it may be concluded that in brother-to-brother
transplantations, autogenous reactions predominated in all strains, and to the
highest degree in strains A, C3H and CBA ; but syngenesio-reactions did occur,
even in strain A, although they were more frequent in strains D and C57, and
in the latter strain even one homoiogenous reaction was noted, with some in-
crease in fibrous tissue. Variations in the age of the hosts within the range of
2 and 6 months did not seem noticeably to affect these results. The syngenesio-
transplants were characterized especially by an increase in lymphocytes, which
could destroy even otherwise autogenous tissue ; but there could be associated
with this reaction a slight increase of fibrous tissue. It was observed also that
transplantations from one donor to two hosts, or from two donors to one host,
might elicit somewhat different reactions. We note, then, that even in brother-
to-brother transplantations a complete identity of the individuality differentials
in these inbred strains has not yet been attained, and that again differences
exist in this respect between different strains. But there are indications that in
transplantations between litter mates the average of the reactions approaches
somewhat more completely the autogenous type than in transplantations be-
tween non-litter mates ; this seems to be the case, in particular, in strains D
and C57. In all these transplantations there was, as a rule, a correspondence

DIFFERENTIALS IN CLOSELY INBRED MICE 107

between the reactions against the different tissues transplanted from one single
donor into the same host. It was also of interest that in cases in which an
infection had taken place in a transplant between near relatives within an
inbred strain, this infection and the reaction against the transplant usually
remained localized and did not interfere with a good preservation of the tissue
at some distance from the place of infection.

In strain D, a number of transplantations were carried out in which tissues
were transplanted from parents to children, or from children to parents. In
these experiments, also, autogenous or almost autogenous results were ob-
tained, but the number of syngenesio-reactions, with marked lymphocytic in-
filtration, was distinctly greater than when tissues were exchanged between
brothers and sisters. In some instances, even homoiogenous reactions were
noted. On the whole, the reactions in transplantations from children to parents
were somewhat less favorable than the reciprocal ones. Also, in strain C57,
transplantations from parents to children and from children to parents gave,
in the majority of cases, autogenous reactions, but there were several marked
syngenesio-reactions. In seven transplantations from C57 children to C57
parents the average grade was 2.59. In strain A, autogenous reactions were
obtained in transplantations from parents to children. In a general way, it
seems that in these transplantations between mice in which the individuality
differentials were very similar but not yet identical, lymphocytic reactions were
more frequent than in transplantations between more distantly related mice.
This corresponds to the fact that a lymphocytic reaction is especially prone to
develop when the thyroid transplants are well developed, while in a stunted
thyroid, such as we find especially after transplantations between more dis-
tantly related mice, the lymphocytic reaction is either lacking entirely or at
least it is weaker.

Exchange of tissues between hybrids composed of two different inbred
strains and between hybrids and parents as a test for their individuality
differentials. In the beginning of this chapter experiments have already been
reported in which we transplanted tissue of hybrids (C57xD)F1 to mice be-
longing to different litters as well as to the same litter of the same kind of
hybrid, and other experiments in which we exchanged tissues between hybrids
and parents, and vice versa. A few experiments were also considered in which
we transplanted tissues from hybrids, not to their direct parents but to other
members of their parent strains.

In earlier investigations we had carried out, on a somewhat larger scale,
similar transplantations in which we used hybrid strains (C57xA)F1, (tan
C57xA)Fx and F2, and (C57xC)Fx, as well as the reciprocal hybrids. It will
not be necessary to describe these experiments in detail, because they gave
essentially the same results as the transplantations already discussed. We shall,
therefore, merely state the main results obtained.

In the following table, the results of transplantations discussed in the be-
ginning of this chapter (Group I) and of this group (Group II) are shown.
There may be added to the data contained in this table the fact that in control
experiments, in which transplantations of tissues (thyroid, cartilage and fat

1.29

2-2.26-2.81

1.50

1.44

1.42

1.48

2.60

2.54

2.35

3.04

3

or 2 . 75

1.91

108 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tissue) to strange strains (AKA, Old Buffalo and C) were made, as usual
severe homoiogenous reactions approaching grade 1 were obtained.

The data in table I show a very good correspondence in group I and group
II, and their significance is thereby increased. In addition to the conclusions
already discussed, it may furthermore be stated that transplantations from
parents to hybrids do not correspond to autogenous but to syngenesiotrans-

TABLE I

Group I Group II

Inter-strain transplantations

Intra-strain transplantations

From hybrid Fi to parent strains

From hybrids Fi to actual parents

From parents to hybrids Fi (children)

From parents to hybrids Fi (not actual children)

From hybrids Fi to brothers

From hybrids Fx to other hybrids Fi (not brothers)

plantations, and that transplantations from hybrids to parents seem to give
somewhat higher grades than the average homoiotransplantations in not inbred
strains, and inter-strain transplantations in inbred strains. These facts, to-
gether with the better results obtained in transplantations between hybrid Fx
brothers than in those between parents and hybrid Flf suggest the presence of
a considerable number of genetic factors as determiners of the individuality
differentials, and they also confirm the conclusion that the strains which were
used for hybridization had not yet attained a completely homozygous condi-
tion.

Besides these transplantations between parents and hybrids F1 into which
two inbred strains had entered, we carried out some experiments in which
transplantations were made from the second generation of hybrids (black
C57xA)F2 and (tan C57xA)F2 to their parents, which were hybrids Flt and
to their grandparents, C57 and A, and also the reciprocal transplantations;
in addition we grafted tissues from some F2 hybrids to their brothers. The
results obtained may be summarized as follows :

(1) From (black or tan C57xA)F2 to parent hybrids F1 : mostly syngenesio-
reactions.

(2) From (black or tan C57xA)F2 to grandparents (C57 or A) : mostly
homoio-reactions.

(3) From (black or tan C57xA)F! to hybrid F2 children : mostly syngenesio-
reactions (somewhat less favorable than those in 1). The reactions in (1) and
(3) are intermediate between those from parents to Fx hybrids and from F1
hybrids to parents.

(4) From (tan C57xA)F2 to brothers: results intermediate between
syngenesio- and homoiogenous reactions (average grade 2.05). These are less
favorable than those obtained in transplantations from hybrids F1 to brothers.
In general, the results in these various transplantations in which hybrids F2

DIFFERENTIALS IN CLOSELY INBRED MICE 109

enter, are in accordance with expectations, considering the fact that, in con-
trast to the homogeneous genetic constitution in the Fx generation, in the F2
hybrids, different individuals may differ in their genetic constitution.

Transplantation of ovaries in inbred mice and interaction between endocrine
factors and individuality differentials. We have carried out a larger series
of transplantations of the ovary in inbred mice for two reasons : 1 ) the ovary
in the mouse offers certain advantages over other organs for the study of the
relations between transplantation-reactions and the character of the individu-
ality differentials, since this organ contains a variety of structures which differ
greatly in sensitiveness and thus in their ability to survive ; it presents a grada-
tion in the degree of reactions between the individuality differentials of host
and donor, without regard to the cellular response of the host against the
transplant. The corpora lutea and large follicles are the most sensitive struc-
tures ; they are followed in order of decreasing sensitivity, or of increasing
resistance, by the medium, small and primordial follicles, by germinal epi-
thelium and ducts derived from it, by medullary ducts, by cortical spindle cell
connective tissue, and by interstitial gland. The Fallopian tubes, situated near
the ovaries, are also rather resistant structures. By noting the survival or lack
of survival of these different constituents of the ovary, we can grade the
degree of similarity between the individuality differentials of host and donor ;
(2) the ovary, also on account of its structure, is a good test organ for the
evaluation of the importance of endocrine factors, of age of donor and host,
as well as of the sex of the host in the results of transplantation. We are espe-
cially concerned with the question as to how far the endocrine influences,
which originate in the host ovaries, may affect the fate of the transplants. The
associated structures of the ovary, such as germinal epithelial cysts and ducts,
medullary ducts and interstitial gland, together with the Fallopian tubes, are
comparable in their power of resistance to thyroid gland, striated muscle
tissue and some other organs, since they are at least partially preserved under
conditions in which the various types of follicles are in a graded manner
destroyed. Because the transplantation of the ovary of the mouse has thus
many advantages over that of many other organs in the analysis of the in-
dividuality differentials, we have carried out a large number of ovarian trans-
plantations in various inbred strains of mice, but this account will be limited
to a brief statement of some of the principal conclusions at which we have
arrived.

In grafting the ovaries in strains AKA, Old Buffalo, and to some extent
also in strain New Buffalo, the follicles are much more injured than are the
associated structures of the ovary and the constituents of other organs usually
used in our transplantations, indicating a difference in the constitution of the
individuality differentials in the animals composing each of these strains. In
the other strains, A, C3H, CBA, C57 and D, the disharmony between the in-
dividuality differentials is not so great that it affects the state of the follicles
very considerably, although it may affect especially the formation of large-
sized follicles and corpora lutea under conditions in which the preservation of
small-sized follicles is not yet interfered with. In these latter strains, in

110 THE BIOLOGICAL BASIS OF INDIVIDUALITY

which the individuality differentials have become more similar although not
yet completely identical, accumulations of lymphocytes may still allow a grad-
ing of the different degrees of homozygosity which have been attained. The
lymphocytes invade first the tissues adjoining the ovaries, and only later the
ovary proper. Within the ovary the lymphocytes invade the granulosa of
preserved follicles last; they seem to be especially attracted by the yellow
vacuolated interstitial gland tissue, which corresponds closely, in some re-
spects, to certain cell complexes found in the cortex of the adrenal gland in
mice. In both of these organs vacuolated cells may act as phagocytes, neigh-
boring cells may coalesce, or the nuclei may form central rosettes. By the
combined use of the lymphocytic reaction and of the survival of the various
types of follicles as tests for the individuality differentials, the strains can be
arranged in the following order of decreasing homozygosity: (1) strain A;
(2) strains C3H and CBA; (3) strains C57 and D; (4) strain New Buffalo;
(5) strain Old Buffalo, and (6) strain AKA. In strain Old Buffalo, the best
results were obtained if the ovaries were transplanted into ovariectomized sis-
ters, but neither ovariectomy nor the close relationship between donor and host
alone was sufficient to insure a good preservation of the follicles. However, in
general there are conditions in which, with the aid of a hormone constellation
that is very favorable for the survival or growth of the transplanted ovaries,
the latter may be preserved and the follicles may grow even in transplants
from different litters. This was the case after transplantations, for long
periods of time, into castrated males ; such mice offer, perhaps, the most favor-
able hormone-constellation, which may overcome the damage caused by a
certain degree of incompatibility between the individuality differentials of
host and transplant. Likewise in strain A, in which there is also a difference in
the constitution of the individuality differentials between mice belonging to
the same and to different litters, the removal of the ovaries somewhat im-
proved the results.

While in strains New Buffalo and AKA transplantations into sisters seemed
to have an advantage over transplantations into different litters, ovariectomy
did not appear to be of much significance, the improvement, at best, being only
slight. Transplantation into males gave at least as good results as transplanta-
tion into female mice, and after transplantation into older mice there was in
quite a number of cases a survival of the ovarian structures. Furthermore,
given favorable relations between the individuality differentials of host and
donor, ovarian transplants may remain alive in the host for a length of time
which is so great that the age of the ovary, or of some of its surviving struc-
tures, may exceed the average age of the individuals belonging to a certain
strain. Thus, in a nonovariectomized mouse, young corpora lutea were found
in a transplanted ovary which had remained in the host for about 18 months;
here, lymphocytic infiltration had occurred. Also in strain A it was not diffi-
cult to recover well preserved ovaries which had been transplanted for half a
year or longer. Moreover, in strains A and C57, ovaries were successfully
transplanted into 12 to 20 months old female mice. In strain C57, donor and
host belonged to different litters and the hosts had not been ovariectomized. In

DIFFERENTIALS IN CLOSELY INBRED MICE 111

a 15 months old host, 2^ months after transplantation, good, large follicles
and many well preserved corpora lutea were found and there was only a slight
lymphocytic infiltration ; likewise in a 19 months old host, large follicles
were noted, but here there was too some lymphocytic infiltration around the
ovary. We have found indications also that a lymphocytic infiltration may set
in late, and further, that a number of successive transplantations may lead to
injury of the transplant.

Such serial transplantations were carried out in strain A. The transplanted
ovaries remained in each host for 4 to 6 months, after which time they were
re-transplanted into another host. Altogether, the ovaries were thus kept in
successive hosts for periods ranging between 14 and 24 months and the age
of these ovarian grafts varied between 24 and 36 months. Only in four of
eleven of these serial transplants was living transplanted tissue found at the
end of the experiment ; and only associated structures were recovered, such as
germinal epithelium lining a cyst, ducts consisting of germinal epithelium, and
interstitial gland tissue ; in one instance, also a Fallopian tube with preserved
epithelium, connective tissue and muscle tissue was found. Lymphocytic in-
filtrations were observed in some cases around or near surrounding parts.
These experiments prove that only the most resistant tissues were able to
survive, and they also indicate that the ovary is less suitable for such serial
transplantations than the thyroid gland.

Transplantation of anterior pituitary glands as indicators of individuality
differentials in inbred strains of mice. We have shown previously that anterior
pituitary glands may be transplanted successfully and that such transplants
may exert effects on the ovaries, which, under certain conditions, increase the
incidence of mammary gland carcinoma in the inbred strain A. Additional ex-
periments have now been made, in which we compared the reactions against
these transplants in various inbred strains differing in regard to the homozy-
gous state which they had attained. In most cases, between two and six pitui-
tary glands from sisters and brothers were transplanted subcutaneously.

In this series of transplantations, the transplants of anterior pituitary glands
survived readily for long periods of time in most of the inbred strains, espe-
cially if the glands were taken from brothers and sisters. However, in the Old
Buffalo strain, the transplants had apparently been destroyed at the time of
examination ; whether this was an accidental occurrence or is an indication of
a more destructive action of the host against the transplant, perhaps caused by
a greater dissimilarity of the individuality differentials, an effect similar to that
seen after transplantation of the ovaries in this strain, needs further investiga-
tion. The most interesting observation from our point of view is the fact that
under the conditions of these experiments, lymphocytic infiltration around or
in the transplant was, on the whole, rare, and if it occurred at all it usually
remained slight. In this respect the results differ from those obtained after
long-term transplantation of thyroid gland, ovaries and adrenal gland, where
as a rule the lymphocytic infiltration was more marked. On the basis of these
experiments we may also conclude that the transplantation of anterior pitui-
tary glands is less suited for the analysis of individuality differentials than that

112 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of some other organs, because they elicit so weak a reaction on the part of the
host and do not, therefore, make possible finer gradations of the individuality
differentials in the various strains.

Transplantation of the adrenal gland and the analysis of the individuality
differentials. While some of the principles concerning the nature of the
individuality differentials have been established through the experiments on
transplantation, which we have already discussed, still, it may be expected
that an extension of the type of organs and tissues subjected to transplanta-
tion may give additional data. Such further information was obtained by
means of transplantation of the adrenal gland.

As far as the analysis of the individuality differentials is concerned, the
most important observation in these experiments concerns the lymphocytic in-
filtration, which was found to occur with increasing intensity around degener-
ating cortical tissue as late as eight or ten months after transplantation, while,
on the contrary, well preserved areas of cortical tissue were not invaded
by lymphocytes. This condition corresponds to the action of the lymphocytes of
the host towards ovarian transplants from donors whose individuality differ-
entials differed from those of the host. Here, also, the lymphocytes invaded
mainly degenerating interstitial gland tissue and not at all, or only very rarely,
the preserved granulosa of well developed follicles. Therefore, certain struc-
tures within several types of transplanted organs behaved not unlike auto-
genous transplants, while other structures, especially those undergoing a cer-
tain kind of degenerative change, behaved like homoiotransplanted tissue. We
have already discussed the possible causes for these peculiar responses of
different structures; the possibility exists that certain tissue differential sub-
stances may combine with strange individuality differentials to form sub-
stances whch attract the lymphocytes ; or some types of growing or well pre-
served tissues may give off substances which protect them against an invasion
by lymphocytes, which might otherwise occur if disharmonious individuality
differentials interact; or lastly, it is conceivable that individuality differen-
tials are produced or set free in larger quantity in certain stages of regression
in various tissues. However, such a behavior of the lymphocytes is not usual.
Thus, we have found very strong indications that well preserved thyroid tissue
can be invaded and destroyed by masses of lymphocytes, if there is a slight
divergence between the individuality differentials of host and transplant. In
autotransplanted organs we have not observed, thus far, a marked invasion by
lymphocytes of the degenerating cells, but this point is being investigated still
further at the present time in the case of adrenal glands. In non-transplanted,
autogenous adrenals frequently degenerative changes occur, similar to those
which attract the lymphocytes in transplants, but they do not lead to intensive
accumulation of these cells. The time at which accumulations of lymphocytes
occur seems to vary in different inbred strains; it apparently takes place
earlier in strains in which the differences between the individuality differen-
tials of the various members of the inbred strains are as yet considerable. It is
also of interest that pronounced infiltration with lymphocytes may be seen in
transplants from sisters or brothers in closely inbred strains, but they occurred

DIFFERENTIALS IN CLOSELY INBRED MICE 113

here at very late periods. This fact again seems to confirm the conclusion
that the individuality differentials in these inbred strains have not yet reached
an autogenous condition.

Transplantation of the thyroid and parathyroid glands for longer periods
of time in various strains of mice and the analysis of the individuality differ-
entials. These experiments were made in addition to earlier transplantations
of the thyroid gland, which we have reported in the preceding pages, and in the
large majority of which the examination took place at earlier periods, usually
between 12 and 30 days following transplantation.

In strain A, seven transplantations of thyroid and parathyroid, either alone
or in combination with other organs, were made ; examination took place
between 9 and 15 months, mostly between 10 and 11 months, following trans-
plantation. The thyroid and parathyroid glands were well preserved, although
there was in some instances a small amount of fibrous tissue around some
acini. In or around all transplants, except one, there was definite lymphocytic
infiltration, which was moderate in some cases and marked in others. This
also occurred in a case in which donor and host belonged to the same litter. We
may then conclude that an autogenous relationship between the individuality
differentials has not yet been reached and that the absence of lymphocytic
infiltration at a given time, indicating apparent compatibility between the
individuality differentials of host and transplant, does not actually prove such
a harmonious condition ; it merely indicates a lack of incompatibility great
enough to cause a lymphocytic reaction at a particular time, but does not ex-
clude the possibility that if the transplants had remained in the host for longer
periods, such a reaction would have occurred.

In strain D, thirteen transplantations of thyroid and parathyroid were made ;
in all but four cases the organs from brothers and sisters were used. In two of
the animals from different litters no transplants were found 9 months after
transplantation. In the two remaining animals from different litters, 8 months
and 20 days, and 4 months after transplantation respectively, the structure
of the transplants was not like that of autogenous grafts and here was much
lymphocytic infiltration. In the nine cases in which donors and hosts belonged
to the same litter, the examination took place in most instances about 9 and
11 months after transplantation; in one, the time of examination was about
4 months, and in another it was 1 month and 3 weeks. In only two of these
transplants, namely in those examined after 9 months, was the lymphocytic
infiltration lacking; in seven grafts it was moderate or marked, but in every
case quite definite. These experiments confirm then again the conclusion, that
a homozygous condition did not exist in strain D. We may add that this is due
not merely to an early branching-off of sublines from the main line, because
late reactions occurred also between brothers and sisters, therefore between
members of this strain, which have been propagated continuously and directly
by brother and sister matings. In both strain A and strain D, antagonistic
reactions of the hosts may thus develop against tissues which had been trans-
planted a considerable number of months previously.

In strain C57 the grafts remained, in eight cases, from 2 to 8>2 months in

114 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the hosts. The outcome of these experiments also indicates that there was
a lack of a completely homozygous condition.

In strain New Buffalo, only those grafts in which donors and hosts were
litter mates survived for greater lengths of time; lymphocytic infiltration
occurred in these transplants .

In strain Old Buffalo the transplantations carried out were fewer in number
than in the other strains. As far as we can judge from these experiments,
the individuality differentials in this strain are farther removed from the
autogenous state than those in strains A, C3H, D, C57, and CBA. This con-
clusion would be in harmony with our findings in the related New Buffalo
strain, although in the latter the reactions against transplants from other
individuals, belonging to the same strain, was less severe than in the Old Buffalo
strain.

On the whole our previous findings concerning differences or similarities
between the individuality differentials in the various inbred strains of mice
are therefore confirmed in these experiments.

In general, we may conclude from all our experiments with closely inbred
strains of mice that, as with inbred rats and even with inbred guinea pigs, an
autogenous state of the individuality differentials has not yet been reached,
and that the degree to which this state has been approached differs in different
strains. However, it is probable that the differences in the severity of reactions
against transplants from other members of the same inbred strains are not
entirely due to the different degree to which the genetic constitutions have
become similar in the various individuals belonging to a strain ; it may be due
also to the differing intensity of the reactions of different hosts against a
similar degree of disharmony between the individuality differentials in a given
strain. Yet, after all, it is principally the differences in the genetic constitution
between the various members of a strain and therefore also the differences in
the individuality differentials of these animals, which determine the character
of the reactions against transplanted tissues and organs. All these experiments
add then new evidence for the conclusion that multiple factors determine the
nature of the individuality differentials and that the time of the appearance
of a reaction may be an indicator of the degree of disharmony between the
individuality differentials of different hosts and donors; if the disharmony is
relatively slight, the reaction may appear at a late date following transplantation.

A complication may be caused by the fact that various organs and tissues
may differ very much in the intensity of the cellular reactions which they
induce in the host. We observed formerly that cartilage is relatively inert
and we attributed this characteristic to the relatively inactive metabolism in
this tissue. We have now found that also anterior hypophysis is a tissue that
remains relatively well preserved after transplantation and that calls forth
no lymphocytic reaction, or only a slight one. This organ is therefore not
well suited for the analysis of fine differences in the individuality differentials.
Furthermore, we see that different structures in the ovary induce the lympho-
cytic reaction to a very different degree; the yellow interstitial gland tissue
and also the corpus luteum tissue are quite active in this respect, while the

DIFFERENTIALS IN CLOSELY INBRED MICE 115

preserved granulosa of follicles is not readily invaded by lymphocytes. An even
more striking example of such differences is to be noted in the activity of differ-
ent structures within the adrenal gland. Here, the degenerating yellow cortical
tissue attracts lymphocytes in large masses, although this reaction in its full
strength may occur only very late after transplantation ; on the other hand,
preserved strands of glomerulosa or fasciculata cells are not invaded by
lymphocytes. Such peculiar differences in the attraction which various tissues
exert on lymphocytes and which must be connected with peculiarities in the
metabolism of these various tissues, may prevent a complete correspondence
between reactions against different kinds of tissues which have been trans-
planted at the same time, from the same donor into the same host.

Chapter 10

Heterogenous Transplantation of Normal
Tissues and of Blood Clots

We shall now discuss the characteristic features of heterotrans-
plantation. The marked toxicity of the bodyfluids, causes early
injury and necrosis of the transplants, without the co-operation
necessarily of cellular elements of the host. This necrosis affects different
organs and different tissues with unequal rapidity in accordance with the
degree of resistance of these structures, and even within the same organ or
tissue there may be differences in the rapidity of necrosis, inasmuch as those
parts which are in general more resistant in their constitution, or which,
owing to their situation, are more protected against various kinds of injurious
factors, succumb less quickly to the action of the heterotoxins. Organs or
tissues which have a low degree of resistance, such as bone marrow, or a
medium degree of resistance, such as thyroid, kidney, fat tissue, striated
muscle tissue or epidermis, are destroyed by the heterotoxins within one or
two weeks. In the skin, the hair follicles are more resistant than the epidermis
proper, a fact which agrees with the observation that under certain conditions,
for instance, after painting the skin with the carcinogenic hydrocarbon
methylcholanthrene, the epithelium of the hair follicles shows a higher degree
of resistance than other parts of the epidermis. Cartilage may survive for
four weeks or somewhat longer, although in some instances it may undergo
necrosis sooner. Thus, in transplantation from rat to guinea pig, necrosis of
cartilage and perichondrium may be found after 20 days or even as early
as after 12 days. Likewise, in the exchange of tissues between rat and mouse
the greater part of the cartilage in one case was preserved as late as 25 days
after transplantation, while in some other animals cartilage and perichondrium
soon became entirely necrotic. Fat tissue as a rule was found necrotic very
early, as for instance, after 6 days, and it was usually invaded by connective
tissue cells and by small vacuolated cells, the latter evidently representing
phagocytes, which took up fat in the form of small droplets. Some lymphocytes
were observed admixed to the connective tissue and polymorphonuclear
leucocytes were found frequently, sometimes in large quantities, sometimes
only as scattered cells. There were certain heterotransplants in which no
leucocytes were to be seen at the time of examination. After homoiogenous
transplantation the necrosis of the fat tissue is, as a rule, less extensive than
after heterotransplantation, the necrotic tissue is less actively invaded by
connective tissue, and furthermore, under sterile conditions of operation
the polymorphonuclear leucocytes are usually entirely lacking, except in the
first few days after operation.

116

HETEROTRANSPLANTATION 117

The connective-tissue reaction around the heterotransplants is in general
very strong; there is a tendency for the connective tissue soon to become
transformed into fibrous-hyaline tissue, which latter encapsulates the trans-
plant and may surround some of its constituent parts and injure it through
the exertion of mechanical pressure; but in certain heterotransplants, such
as those of thyroid or kidney, where the tissues early become entirely necrotic,
the ingrowth of the connective tissue cells was at first less marked than it is in
those homoiotransplants where the reactions are severe ; it seems that a heter-
ogenous tissue, which is either completely necrotic or is near death, and in
which the metabolism is therefore very weak or wholly suspended, may
attract fibroblasts less actively than a more energetically metabolizing tissue
which is giving off homoiotoxins.

In syngenesiotransplants and in some homoiotransplants large and dense
masses of lymphocytes may invade and destroy the grafted tissue independ-
ently of a preceding activity of the connective tissue. Such a condition we do
not find in heterotransplants. Here, lymphocytes may invade the graft usually
only in association with the connective tissue of the host. This invasion of
lymphocytes may, in the course of time, be quite marked; it may, however,
remain slight or be lacking altogether if the heterotransplant becomes entirely
necrotic at an early date, as often occurs when thyroid or kidney is trans-
planted ; but even in these cases a considerable lymphocytic infiltration
may later take place in the fibrous capsule surrounding the graft, or in the
fibrous tissue adjoining it, or sometimes also in the fibrous-hyaline tissue that
has replaced the graft, where it may exceed, in density, the infiltration found
in the majority of homoiotransplants.

As stated, the appearance of larger numbers of polymorphonuclear leuco-
cytes distinguishes heterogenous transplants from homoio- and syngenesio-
transplants; these cells accumulate in and around the capsule, they may
pentrate into the transplant and be found around or in the necrotic tissue;
they may either be scattered or may form small accumulations, or even dense
masses, in certain areas. Necrotic material seems to be their chief point of
attraction. In and around homoiotransplants, on the other hand, leucocytes as
a rule are noted only in the first three days following the operation when
necrosis and changes in the circulation and in the permeability of vessels may
be responsible for their appearance; they occur in these, and even in syn-
genesiotransplants of the mouse, more frequently in places where much fibrous
tissue has been produced, and, above all, in fibrous tissue that has invaded and
replaced fat tissue. The possibility exists that in the mouse we may have to
deal with bacterial infection in those homoiotransplants in which leucocytes
appear in larger numbers', and this raises the question as to whether also
in heterotransplants the accumulation of polymorphonuclear leucocytes may
not at least in part be due to contamination with bacteria. The presence of
bacteria and their responsibility for the accumulation of polymorphonuclear
leucocytes is suggested particularly also by the development, in some instances,
of localized, abscess-like masses of these cells in or around the heterotrans-
plants. Furthermore, the fact that if a piece of mammalian tissue is trans-

118 THE BIOLOGICAL BASIS OF INDIVIDUALITY

planted into a frog for only a few hours and then re-transplanted into a
mammalian host, large collections of polymorphonuclear leucocytes are at-
tracted by it and then destroy the transplant, likewise suggests this interpre-
tation. Similar is the result if pigeon skin is transplanted for various periods
into the frog and then re-transplanted into the guinea pig. That necrosis as
such, even necrosis of fat tissue, cannot be responsible for the accumulation
of such cells in or around the transplant is shown by the observation that
in rat and guinea pig, as well as in pigeon and chicken, necrotic areas do not
noticeably attract polymorphonuclear leucocytes if the necrosis develops in
homoiotransplanted tissues. And even in the mouse there are many homoio-
transplants entirely free from leucocytic infiltration.

Various considerations, however, make it seem more likely that these cell
accumulations are due to heterotoxins, which are given off by the graft and
which diffuse into the surrounding tissue, especially after the graft has
become necrotic. We must then assume that there are chemical differences
between the necrotic areas in homoiogenous and in heterogenous tissues,
which are responsible for the different modes of reaction of the polymorpho-
nuclear leucocytes, and that the latter are attracted by either necrotic or living
tissue, in contrast to homoiogenous tissues, which do not attract them, although
a few isolated leucocytes may be found here also in the first few days follow-
ing transplantation ; however, the possibility cannot as yet be entirely excluded
that the growth of microorganisms is promoted by conditions present in the
heterotransplants, as compared to those in auto- and homoiotransplants, or
that both these factors — microorganisms and heterotoxins — may be active.
That a greater strangeness of the individuality differentials of host and graft
may favor the accumulation of bacteria is shown especially in mice; when
transplants come from nearly related donors, the collections of polymorpho-
nuclear leucocytes usually remain localized at one spot, while similar collec-
tions in transplants from further distant donors often affect the transplanted
piece as a whole, or at least over wider areas. As we have seen in the preceding
chapter, together with the leucocytes, also connective tissue, lymphocytes,
and, in the case of the fat tissue, small-vacuolated phagocytic cells, invade the
homoiotransplanted mouse tissue. In our laboratory several experiments have
been made for the purpose of deciding between the various possibilities re-
garding the appearance of polymorphonuclear leucocytes and some associated
conditions.

1. Siebert exposed, in the water bath, the thyroid and cartilage, with ad-
joining fat tissue, of rats to temperatures ranging from 43° to 51°, for from
15 to 45 minutes, and then transplanted these pieces into guinea pigs; exami-
nation took place after 20 days. The activity of lymphocytes and polymorpho-
nuclear leucocytes was only slightly decreased and the connective tissue reac-
tion was even somewhat increased as compared with that observed in tissues
not previously heated. We interpret these results as indicating that heteroge-
nous tissues, even if they are killed through heating previous to transplanta-
tion, still possess and give off their specific heterotoxins to almost the same
extent as the unheated tissues. When the same procedure was used with

HETEROTRANSPLANTATION 119

homoiotransplanted tissues, the latter, when killed by heating, no longer
elicited the typical homoio-reaction. There was a marked lessening of the
lymphocytic reaction normally called forth by homoiotransplanted thyroid or
cartilage together with the adjoining fat tissue, but again the connective tissue
reaction was not markedly diminished in such a thyroid transplant ; it could
even be slightly increased. The reaction of the connective tissue is partly
directed against necrotic tissue; it is, therefore, not seriously affected by the
heating. But, the much more specific lymphocytic reaction in case of homoio-
transplantation depends upon the presence of actively metabolizing tissue,
because homoiotoxins are produced and given off mainly by functioning
homoiogenous tissue. This interpretation is supported also by other observa-
tions and experiments, to which we shall refer later. Of interest is also the
finding of Siebert, that heating homoiogenous cartilage and perichondrium at
47° for 30 minutes seemed to increase the regeneration of cartilage by the
perichondrium around necrotic injured cartilage. On the other hand, it might
be argued that the heterotoxic action remains almost as strong after heating
as it was in the case of unheated tissues, because the exposure to moderate
heat did not seriously injure the contaminating bacteria ; but against this
interpretation may be cited experiments in which the heterogenous tissues
were exposed to the temperature of boiling water. In these experiments, to
which we have already referred, the thyroid and cartilage, with adjoining fat
tissue, of rats, were boiled for 5 minutes in normal NaCl solution and then
transplanted to guinea pigs. In the examination, which took place after 12
and 20 days, the reactions were found to be essentially the same as after
heterotransplantation of the unboiled tissues, except that in the boiled thyroid
the colloid of the acini remained preserved in the grafts, while, as was to be
expected, the acinus tissue, as well as cartilage and fat tissue, was necrotic.
The essential point in such experiments is that the boiled heterogenous tissues
still attracted the polymorphonuclear leucocytes in large numbers, and that the
infiltration with the latter was almost as strong as in the transplants of non-
boiled rat tissues in the guinea pig ; lymphocytes were in evidence in or around
these tissues after 12 days, but they were no longer found after 20 days,
although they were seen in the unboiled grafts at this time. It is very difficult
to believe that under the conditions of these experiments bacterial infection
was the cause of the accumulation of polymorphonuclear leucocytes in cr
around the transplants.

2. In further support of these conclusions, there may be cited experiments
carried out by Blumenthal, to which we have already referred. When he
transplanted small pieces of autogenous, homoiogenous or heterogenous tis-
sues under the skin in various species, changes in the absolute number and
distribution of lymphocytes and polymorphonuclear leucocytes took place in
the circulating blood, which in principle corresponded to those occurring
locally around such transplants. In the case of homoiotransplantation there
was an increase in lymphocytes, which began in the first few days following
transplantation and reached a maximum between about the third and tenth
days. The exact time of the maximum varied with different tissues, according

120 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to the consistency of the pieces, which evidently determined the readiness
with which the individuality differential substances were extracted from the
tissues. After syngenesiotransplantation, the reactions appeared somewhat
later, in accordance with the diminished toxicity of the substances given off
by transplants of this type. The reactions to heterogenous grafts consisted
in a primary increase in polymorphonuclear leucocytes in the circulating blood,
which tended to appear a few days earlier than the reactions to homoiogenous
transplants. After heterotransplantation of thyroid tissue, the maximum in
the count of polymorphonuclear leucocytes was reached on about the fifth
day, approximately two days earlier than the maximum observed after
homoiotransplantation ; however, the reaction sets in as early as on the 2nd
or 3rd day after the operation, but then a regression in the number of leuco-
cytes begins and on about the 10th day a normal count has again been
reached. This is followed by a secondary reaction consisting in a relative and
absolute increase in lymphocytes, which usually reaches a maximum between
the 14th and 16th days and likewise is followed by a regression to normal. These
reactions occurred in the guinea pig, rat and mouse with equal regularity.
That they were caused by contamination with bacteria can be excluded, since,
as a rule, no infection was found, and even where after homoiotransplantation
a slight infection with bacteria had taken place, this did not call forth a notice-
able increase in the number of polymorphonuclear leucocytes in the blood ;
such an increase was observed only in cases in which pus from an abscess,
that had formed in and around the graft, had ruptured and escaped into the
surrounding tissue. A small number of microorganisms did not therefore
cause alterations in the number and distribution of blood cells, such as is
seen after transplantation of heterogenous tissues. In these experiments as
well as in those in which the local reactions around transplants were studied
the results were, on the whole, constant and this fact again could not very
well be reconciled with the assumption that bacterial contamination and sub-
sequent growth of the bacteria — occurrences which are of an accidental char-
acter and therefore necessarily variable — were responsible for these changes.
3. A direct attempt was made to follow the fate of bacteria normally ad-
hering to pieces of skin after its transplantation, in order to determine their
possible role in the attraction of leucocytes. In these experiments, Ermatinger,
Queen and Parker transplanted autogenous as well as heterogenous earskin
pieces into the subcutaneous tissues; after 1, 2 or 3 days, they were removed
for bacterial examination. Autotransplants of skin in guinea pigs, rats and
rabbits were studied, as well as heterotransplants from guinea pigs to rats
and rabbits, and also the reciprocal transplants. A progressive decrease in the
number of bacteria in the skin pieces was found on successive days. The large
majority of the microorganisms were destroyed within the first 24 hours,
while after 48 hours nearly 25 per cent of the plates were sterile ; after 3 days,
sterile plates were found in 62 per cent of the cases and in the rest of the
pieces the number of colonies was very small. Staphylococci survived longest.
However, during the very hot season a considerable increase in the number
of bacteria was observed in the first three days in several instances and the

HETEROTRANSPLANTATION 121

count of bacteria living on the normal skin seemed to be higher during the
hot summer weather than during other seasons. There was also some indica-
tion that the destruction of the bacteria proceeded more actively after hetero-
transplantation than after autotransplantation of the skin.

The results in all these experiments make it probable that the poly-
morphonuclear leucocytes were attracted to heterotransplanted tissue not
mainly by bacteria attached to these tissues, but by the action of heterotoxins.
While it seems that this is, in general, the correct interpretation, still, under
certain conditions, and especially in transplantations carried out in the mouse,
it may well be that slight infections with microorganisms play a certain role ;
but it is probable that even if microorganisms should be involved, they act in
conjunction with toxins derived from the tissues and that they exert a greater
effect when the individuality differentials of host and transplant differ greatly
from each other than when they are closely related.

We may further conclude that while the typical reaction against syngenesio-
and homoiotransplants occurs only if these tissues are alive and presumably
actively metabolizing, the heterotoxins are present and active also in dead
tissues. Additional evidence in favor of this conclusion is furnished by the
results of experiments in which the reactions of a host against autogenous,
homoiogenous and heterogenous blood clots were compared. If autogenous
and homoiogenous blood clots are transplanted into the guinea pig, the charac-
teristic differences that are found between the reactions of the host against
autotransplants and homoiotransplants of living tissues, such as thyroid, kid-
ney, epidermis, or cartilage and fat tissue, are almost or entirely lacking. This
seems to be due to the fact that the cellular elements enmeshed in the net of
fibrin soon die and no longer give off the autogenous and homoiogenous sub-
stances which bear the individuality differential. These clots are merely organ-
ized by the connective tissue and the blood vessels of the host like inert foreign
bodies, no noticeable amount of homoiotoxins being given off after trans-
plantation into another individual of the same species. As a result of the
invasion by the fibroblasts of the autogenous or homoiogenous host, first a
provisional organization takes place, representing a mixture of blood coagu-
lum and of the cytoplasmic substances of the fibroblasts; subsequently, a
definite organization is effected by continued ingrowth of fibroblasts. A few
lymphocytes may be admixed to the capillaries and fibroblasts, which move
into the clot, but they are not frequent. As stated, there are no definite differ-
ences between the autogenous and homoiogenous blood clots under these con-
ditions. While phagocytes may, to a limited extent, be seen in homoiogenous
blood clots, they are not a prominent feature in the process of organization.
The phagocytic cells distintegrate into granula, which later help to form a
hyaline material. Polymorphonuclear leucocytes are, on the whole, not con-
spicuous in these transplanted blood clots. It seems, then, that the non-
nucleated erythrocytes included in the network of fibrin do not give off
homoiotoxins to any noticeable degree. Much more pronounced was the re-
action against heterogenous blood clots, such as that observed if clots were
exchanged between rat, guinea pig and rabbit. In these cases, accompanying the

122 THE BIOLOGICAL BASIS OF INDIVIDUALITY

connective tissue cells surrounding and invading the clot, were many lympho-
cytes and the capsule of the heterogenous clot was thicker than that of the
homoiogenous clot. However, the thickness of the connective tissue capsule
and the number of lymphocytes varied in different instances and even in
different places in the clot. Areas of partial solution also were visible and a
larger number of phagocytic cells was present in such heterogenous clots.
The latter cells, which may show a xanthoma-like tissue arrangement, are able
to dissolve particles of fibrin as well as the erythrocytes. Furthermore, the
hemolysin present in the serum of the host and active against the blood cells
of strange species may help in the solution of parts of the coagulum. Also,
polymorphonuclear leucocytes, which again are much more prominent in
heterogenous than in homoiogenous transplants, invade the clot and may aid
in its destruction. These differences in reaction against different types of clots
are quite definite, although the same technique was used in these various trans-
plantations. In principle, the reaction against all kinds of heterogenous clots is
about the same, although some minor quantitative differences may exist in
different species; thus, in the guinea pig the solution of the clot proceeded
somewhat more actively than in the rat and likewise the number of polymorpho-
nuclear leucocytes in and around the clots was somewhat greater than in the rat.
These experiments indicate, then, a noticeable similarity between the behavior
of heterogenous blood clots and heterogenous tissues. In both cases, lympho-
cytes as well as polymorphonuclear leucocytes participate in the reaction in
addition to the connective tissue, and heterotoxins are given off by nOn-living
material in both types of heterotransplants ; on the other hand, homiotoxins,
are given off only by living tissue transplants, but not to any marked degree
by the necrotic homoiogenous blood clots.

By measuring the lymphocytic and leucocytic reaction in the circulating
blood, Blumenthal discovered not only differences between the reactions
against homoiogenous and heterogenous blood clots, but he found also differ-
ences between the reactions against autogenous and homoiogenous clots, cor-
responding to those found against the corresponding normal tissues, in par-
ticular, he noticed an early increase in lymphocytes after homoiogenous trans-
plantation of blood coagula. By means of this method he could show, further-
more, that also homoiogenous and heterogenous plasma clots may elicit the
typical blood cell reactions, although they appeared somewhat later than the
reactions following transplantation of the whole blood clot. It appears, then,
that the individuality differential substances are present also in fibrin, although
they may perhaps not be of the same kind as those present in the cells. The
reactions affecting the white cells in the circulating blood seem to indicate the
presence of substances in the blood which are carriers of the individuality
differentials, although they do not elicit the local homoiogenous reactions.
These reactions, which are called forth by fibrin and which presumably are
present also in fibrinogen, are not induced by injections of blood serum ; the
latter does not apparently possess these individuality differential substances.
However, it is possible that the individuality differential substances in cells
included in whole blood clots are the same as those present in the fibrin, but

HETEROTRANSPLANTATION 123

that the differences in the local reaction and the reaction in the circulating
blood is due to a greater sensitiveness of the latter, which allows the recogni-
tion of homoiogenous differentials in material in which these differential sub-
stances are present in so small a quantity that they can not be discovered by
the local reaction. But in this instance we have again to consider the possibility
that less specific reactions against non-living protein material may participate
in these general reactions and that this factor may introduce a complication
which is absent in the local reaction.

There are some additional questions concerning heterogenous transplanta-
tions which are of more general interest and which we shall now consider :
(1) Does a relationship exist between the time of survival and the growth
processes in heterotransplants and the reactions of the host tissue against the
latter, on the one hand, and the phylogenetic relationship between host and
transplant on the other? (2) What are the relations between growth processes
in heterotransplants and time of survival? To what extent do regenerative
growth processes take place in heterotransplants? (3) What differences occur
in heterotransplantation of different organs and tissues? (4) Do the results of
reciprocal heterogenetic transplantations differ and what is the reason for
this difference? In order to answer these questions we may discuss briefly the
principal results obtained in some of our series of heterotransplantations,
while we omit a description of others. *

Heterotransplantation of guinea pig skin. In association with W. H. F.
Addison, we observed that after transplantation of guinea pig skin into other
species the epithelial cells grew less actively than after homoiotransplantation,
but the growth continued for some time, as indicated by the presence of
mitoses in the epidermal cells. Mitoses were found in the rabbit as late as 8
days, in the dog, 7 days, and in the pigeon 5 days following transplantation.
However, the mitoses were less numerous than after homoiotransplantation
and the difference between the activity in the homoio- and heterotransplanted
tissue increased with increasing time after transplantation. In heterotrans-
plants the mitotic activity usually ceased a few days before the tissue became
entirely necrotic ; but, it happened that a mitosis could be seen near the time
of death. The hair follicles, which are burrowed deep in the tissue and are
surrounded by a connective tissue capsule, thus being most effectively pro-
tected, remained alive longest and showed the greatest number of mitoses.
Also, the cells of the surface epidermis lived for some time and continued to
produce keratin; the connective tissue of the host surrounded the trans-
planted epidermis ; yet the growth energy of the epithelium was too weak to
cause a cystic distention of the transplant from pressure of the newly pro-
duced keratin, in contrast to the finding after homoiotransplantation, where the
epidermis does, as a rule, form a cyst. However, even the homoiotransplanted
tissue may lose this ability if its growth energy has been weakened, as for in-
stance, by previous serial transplantation. Lymphocytes migrated into the
heterotransplanted epidermis from the surrounding host tissue and they, to-
gether with the pressure exerted by the fibrous capsule, helped to destroy the
epithelium which had already been injured by the action of the heterotoxins.

124 THE BIOLOGICAL BASIS OF INDIVIDUALITY

After re-transplantation of the guinea pig epidermis from the foreign
species back to the guinea pig, the epithelial cells grew only very weakly and,
on the whole, the farther removed the first host species was from the guinea
pig, the shorter was the interval after re-transplantation during which mitoses
appeared. No growth took place in the guinea pig skin after transplantation
into the frog, which is so unfavorable a soil that a piece remaining longer than
3^2 hours in this distant species, did not grow after subsequent re-transplanta-
tion into the original donor. Guinea pig skin which had been kept in the rabbit
for 2 days was able to grow after re-transplantation into its own species, but
pieces that had been longer in the rabbit died after re-transplantation; in the
pigeon, pieces that remained less than 5 days could be successfully re-trans-
planted into the guinea pig, but not if they were left in the former species for
a longer time. If we consider merely the duration of mitotic activity and sur-
vival after a single heterotransplantation, the order of compatibility for guinea
pig skin was approximately as follows: (1) rabbit, (2) dog, (3) pigeon,
(4) frog. But in general the differences between these species in these respects
were not great, with the exception perhaps of the frog, which had a very
injurious effect on the transplanted guinea pig skin. However, this order does
not obtain in regard to readiness of re-transplantation of this tissue, because
a primary transplantation from guinea pig to pigeon was less injurious to the
graft than a primary transplantation to rabbit.

Heterotransplantation of pigeon skin. In principle, the results were similar
after homoio- and heterotransplantation of pigeon skin to those found in the
case of guinea pig skin, but there were also some interesting differences. Even
after homoiotransplantation of pigeon epidermis the epithelial proliferation
was found to be very slight, although epidermis and connective tissue re-
mained largely preserved. While the homoiotransplanted guinea pig skin
formed a cyst because of its continued proliferative activity and keratin
formation, and while, for the same reason, a necrotic area in the guinea pig
skin was rapidly replaced by new tissue, the pigeon skin did not give rise to
the formation of such a cyst and reparation of necrotic tissue did not take
place on account of the lesser growth energy in the transplanted pigeon epi-
dermis.

Heterotransplantation of thyroid gland. Cora Hesselberg and the writer
studied transplantation of the thyroid gland in various species, (a) Thyroid of
guinea pig to rat: The heterotransplanted thyroid succumbed readily to the
action of heterotoxins, remaining preserved for a short time only under the
best of conditions. The primary injury of the graft by the bodyfluids of the
host was quite noticeable as early as 3 to 5 days after transplantation. The
number of mitoses was much diminished, but they still could be seen as late
as 9 days after operation ; this was also the latest time at which living tissue
could be found. The epithelium was best preserved in the neighborhood of
growing fibroblastic tissue and, conversely, growing epithelium seemed to
attract the fibroblasts. The latter penetrated also between acini and had a
tendency to form dense fibrous tissue, which compressed the acini and con-
tributed to their destruction. The vascularization of the graft was very poor,

HETEROTRANSPLANTATION

125

but some capillaries were noted between some of the acini. Lymphocytes were
seen only occasionally in these places, being found especially where fibro-
blasts had invaded the transplant or were active around it, as well as in the
capsule of the graft surrounding blood vessels. On the whole, heterotrans-
planted thyroid as such did not attract lymphocytes to any marked extent;
indeed, these cells and the connective tissue contributed only secondarily and
to a minor degree to the destruction of the graft.

In general, the connective tissue of the heterotransplanted thyroid became
fibrous during the second week. The number of lymphocytes in the transplant
itself was small, but in the course of the second week a marked accumulation
of lymphocytes could take place in the surrounding capsule and at some dis-
tance from the thyroid proper; lymphocytes collected also in the fibrous tissue
resulting from the organization of the necrotic material.

Heterotransplantation of kidney tissue into various species, studied in
association with M. H. Myers, on the whole gave results similar to those
found after heterotransplantation of skin and thyroid, but the duration of
mitotic activity and the survival seemed to be slightly longer in the case of
thyroid and kidney than of skin. A comparison of the period of survival and
of mitotic activity in these various series of experiments is shown in the fol-
lowing tables.

TABLE I

Transplantation
of Skin

Latest Time at

Which Mitoses

Were Seen

Time of Survival of

Transplanted Skin

Tissue

Pigeon
Pigeon
Pigeon
Pigeon
Guinea
Guinea
Guinea
Guinea

to chicken
to guinea pig
to rabbit
to frog
pig to rabbit
pig to dog
pig to pigeon
pig to frog

7 days

10-11 days

0 days

10 days

(little tissue surviving)

5 days

5 day:

; (one piece 10 days)

0 days

5 hrs.

7-8 days

10 days

6-7 days

7 days

5 days

10 days

0 days

1 day

TABLE II

Transplantation of
Thyroid

Latest Time at
Which Mitoses
Were Seen

Time of Survival of

Transplanted Thyroid

Tissue

Guinea pig to rat
Rabbit to rat
Rabbit to guinea pig
Cat to rat

9 days

9 days

6 days

1 1 days (a few mitoses)

9 days
11 days (in 1 of 3 pieces)
8 days
14 (18?) days

Heterotransplantation of cartilage. After heterotransplantation of cartilage
together with the adjoining fat tissue, connective tissue of the host invaded
and largely replaced the fat tissue, but it was also able to invade the cartilage,

126 THE BIOLOGICAL BASIS OF INDIVIDUALITY

especially the necrotic areas. Fibrous tissue formed in larger quantity around
the heterotransplant of cartilage than around that of thyroid or of kidney,
probably because cartilage was less rapidly destroyed and its effect on the
host tissue extended therefore over a longer period of time ; however, a similar
reaction could take place also around heterotransplanted thyroid and kidney

TABLE III

Latest Time at

Time

of Survival of

Transplantation of

Which Mitoses

Transplanted Kidney

Kidney

Were Se£n

Tissue

Mouse to rat

9 days

11 days

Rabbit to rat

11 days

11 days

Rabbit to guinea pig

5 days

6 days

Guinea pig to rabbit

12 days

20 days

Guinea pig to cat

7 days

12 days

Cat to guinea pig

0 days

0 days

Guinea pig to pigeon

6 days

10 days

Pigeon to guinea pig

0 days

3f days

Pigeon to rat

0 days

0 days

in the course of the second week. In accordance with the large amount of
fibrous tissue produced especially around heterotransplanted cartilage and fat
tissue, large masses of lymphocytes accumulated in the surrounding connective
tissue at some distance from the graft; a similar reaction could also occur
around other kinds of grafts, but it was observed more rarely in such tissues
as thyroid, skin and kidney, as a rule, probably because these were destroyed
by the heterotoxins more rapidly than cartilage.

Exchange of tissues between rat and mouse. In addition to the transplan-
tations mentioned above, we carried out also heterotransplantations of tissues
from rat to mouse and from mouse to rat, on the assumption that between
these relatively nearly related species the reactions against heterogenous grafts
might be less severe. However, we found that the reactions did not differ in
severity essentially from those obtained in transplantations between the other
species which we had tested. Transplantations from rat to mouse and recipro-
cal transplantations caused much more severe injury than homoio- and even
inter-racial transplantations. Not only was the damage greater if we consid-
ered the average results obtained in a number of individuals, but in each in-
dividual case it was very great. Moreover, the individual variations which we
have found between different homoio- and inter-racial transplants were almost
absent in this series and this lack of variation applied to heterotransplantations
in other species as well. Only the time of survival of the cartilage hetero-
transplanted into mouse or rat showed more marked differences ; in some cases
it became necrotic at an early period following the transfer into the hetero-
genous host, while in other cases it could survive for almost four weeks, or
even somewhat longer. But the degree of this variability was more apparent
than real, inasmuch as even under the best conditions the new formation of
cartilage by perichondrium, which is found around necrotic or damaged car-

HETEROTRANSPLANTATION 127

tilage in cases of homoiogenous and even inter-racial transplantation, is lacking
in this type of heterotransplantation. There was seen only one instance of
heterotransplanted cartilage in which at an early period a slight attempt at
regeneration was apparently observed ; but in this instance the interpretation
was not certain. These findings indicate that even in cases in which struc-
tural appearances indicate the survival of the cartilage and perichondrium,
these tissues are functionally and metabolically no longer normal or com-
parable to the corresponding homoiotransplanted tissues. Similarly, the nu-
clear multiplication, which is a sign of an abortive regeneration in injured
areas of homoiotransplanted striated muscle fibers, is lacking in heterotrans-
plantations ; here, again, there was one possible exception observed at an early
period following exchange of tissues between rat and mouse, and in this
instance, likewise, the interpretation was doubtful.

Of special interest in these experiments were some differences which we
observed between reciprocal transplantations in mouse and rat. The number
of polymorphonuclear leucocytes, as a rule, was greater in the rat to mouse
transplants than in the mouse to rat transplants ; this corresponds to the fre-
quent appearance of leucocytes in the mouse also in many cases of homoio-
transplantation, especially in the fat tissue. On the other hand, in the mouse to
rat transplants the fibrous tissue formation was more advanced, which may
perhaps be due to the greater reactivity of connective tissue cells in the rat
than in the mouse, which we had noticed likewise in homoiotransplantations.
Similarly, the lymphocytic reaction was stronger in the rat than in the mouse ;
again this corresponds to findings in homoiotransplants. In the circumference
of these heterotransplants the lymphocytic infiltration was in some instances
even more pronounced than around homoiotransplants, although the invasion
of the heterotransplant itself by lymphocytes was usually less than that found
in many homoio- and even in some syngenesiotransplants.

Heterotransplantations from Peromyscus maniculatus to mice of strain C57
and the reciprocal transplantations. Although the number of experiments we
could carry out in this series was much more limited than in other series of
heterotransplantations, nevertheless the results were concordant and we are
therefore able to draw some additional conclusions regarding heterotrans-
plantations. The difference in reactions against the grafts taking place in
reciprocal transplantations was evident again in these experiments. The
results are of special interest also on account of the somewhat diminished
severity, in certain cases, of the heteroreactions. In transplantations from
C57 to Peromyscus there was almost complete destruction of the transplanted
thyroid, the cartilage with adjoining fat tissue, and the striated muscle; this
was noted as early as 8 days and was observed thereafter up to 20 days
following the operation. Parts of cartilage were occasionally found preserved,
and after 12 days even a mitosis was seen in a peripheral cartilage cell. Lym-
phocytes as well as scattered polymorphonuclear leucocytes were noted fre-
quently in these transplants, and sometimes there were, instead of scattered
cells, collections or even masses of leucocytes. The fat tissue was largely or
entirely replaced by fibrous tissue. The grades were 1 throughout this series.

128 THE BIOLOGICAL BASIS OF INDIVIDUALITY

The reactions were less severe against the transplants from Peromyscus to
strain C57. Here the grades were better, especially in early periods after
transplantation. At 8 days, the grades were 2— ; at 12 days, they varied be-
tween 2— and 1+ ; at 15 days, the grades were 1 and 1 + , and at 20 days,
they were 1 in three cases and 1 + in one case. At 8 and 12 days, some pres-
ervation of thyroid tissue and also of muscle tissue was found and in the
latter there was some nuclear proliferation; also at 15 days a small part of the
thyroid was preserved, and, in one case, even at 20 days. The fat tissue was
replaced by fibrous tissue or invaded by small vacuolated tissue. At 15 and
20 days the muscle tissue was necrotic and more or less organized by connec-
tive tissue. At 8 and 12 days, no. lymphocytes but scattered polymorphonuclear
leucocytes were seen in certain instances. At 15 days, besides variable num-
bers of leucocytes in one transplant, also some lymphocytes were present,
whereas at 20 days, only leucocytes, but no lymphocytes, were noted.

We find, then, a definitely less severe reaction in cases in which C57 mice
were hosts and Peromyscus were donors, than in the reciprocal transplanta-
tions. Lymphocytic infiltration in general was more common in the former
experiments than in the latter. These findings bring, therefore, additional con-
firmation of the conclusion, that in addition to the relations of the individu-
ality differentials of host and transplant to each other, the strength and mode
of the reaction of the host against the transplant is also a factor which has to
be taken into account and which may influence the results obtained. The type
of reaction which a certain species or strain shows is also, in all probability,
due to the inherited genetic constitution. It is furthermore of great interest
that in strain C57, the reaction against heterotransplants of Peromyscus may
not be stronger than those seen in a type of homoiotransplantations in which
the individuality differentials of host and donor are very dissimilar.

On the basis of these observations, and of others which we cannot describe
in detail, we may answer the questions raised in the beginning of this dis-
cussion. (1) As to a possible corespondence between the severity of hetero-
genous reactions in different combinations of species and the phylogenetic
relationship of these species, the data given in tables 1, 2 and 3 indicate a
relatively great similarity in all these species as to time of survival
and mitotic activity. Both periods were relatively short and, in general, there
was no very definite correspondence between phylogenetic relationship of
donors and hosts and the fate of the transplants. There was very little differ-
ence between the results of experiments in which tissues of rodents were
transplanted to other rodents and in those experiments in which tissues were
exchanged between rodents and cats; in some instances, transplantations in
the latter gave even better results than in the former.

Even exchange of tissues between mammals and birds, which represent
two different classes, could give results not unlike those observed in trans-
plantations between species as near as rat and mouse. Only in certain cases
was there an indication of a shorter time of survival and mitotic activity
after transplantation into different classes. Thus, pigeon skin fared better
when grafted into chicken than into a mammalian species. Transplantation of

HETEROTRANSPLANTATION 129

mammalian or avian tissues into the frog was very injurious, but it is doubt-
ful whether this result was entirely due to distance of phylogenetic relation-
ship; it is possible that bacterial infection played a role in this instance.

Evidently the heterotoxic action in general is so strong that all hetero-
transplanted tissues are near the threshold of destruction and the factor of
phylogenetic relationship becomes thus of minor importance; under these
conditions, a little more or a little less intense heterotoxic action may be of
less importance than some other factor of a secondary nature. Thus there is
some indication that the guinea pig may represent a host more unfavorable
to certain heterogenous tissues than the rat or rabbit.

(2) As to growth processes in the heterotransplants, these were very slight,
as might be expected in view of the injurious action of the heterotoxins. The
mitotic activity usually ceased from one to a few days before the complete
necrosis of the transplant occurred. The continuous destruction of the hetero-
transplant is not therefore compensated by a marked new formation of tissue.
Heterotoxin prevents the full recovery of the tissues after transplantation
and causes their death after a relatively short time. Correspondingly, certain
regenerative processes which are found quite normally in cases of homoio-,
and even in inter-racial transplantations, are lacking after heterotransplanta-
tion ; this includes, for instance, the new formation of cartilage from the peri-
chondrium, as well as the multiplication of nuclei in striated muscle tissue.
In a few exceptional cases, at early periods, there were possibly some indi-
cations of weak regenerative processes, but the interpretation in these in-
stances was doubtful. Only in transplantation from Peromyscus to mice of
strain C57, restricted regenerative growth was noted within the first two
weeks after grafting; in one case, even a mitosis was seen in a young car-
tilage cell, but here, also, the growth soon ceased. It seems that for the
same reasons, namely, the interference of active heterotoxins, it is difficult
for the host capillaries to make connection with the capillaries in the trans-
planted tissue and to use these preformed channels for the establishment of
blood circulation in the transplant, the grafted vessels presumably dying soon
after transplantation; furthermore, this factor may be responsible for en-
gorgement of the surrounding vessels and for hemorrhages into and around
the transplant. (3) The difference in the fate of different heterogenous tis-
sues used, such as thyroid, skin and kidney, was very slight; they all be-
haved in almost the same manner after heterotransplantation ; only cartilage
was definitely more resistant, as it was also in homoiotransplantation. It fol-
lows from these observations that the method of heterotransplantation is not
suited for the determination of species differences ; serological tests are pref-
erable for this purpose. In this respect, heterotransplantation differs from
homoio- and syngenesiotransplantation, in which latter, especially the cellu-
lar reactions as a rule are very fine indicators of the degree of relationship
between individuality differentials of host and donor and in this respect
are superior to serological tests. Transplantation as a method for the deter-
mination of individuality differentials may be compared to a delicate balance,
able to distinguish between fractions of a milligram but ill-adapted to the

130 THE BIOLOGICAL BASIS OF INDIVIDUALITY

determination of differences in weight amounting to pounds; similarly,
homoio- and syngenesiotransplantations distinguish between the finer degrees
of relationship of individuality differentials, whereas, heterotransplantation is
not quite adequate for the finer and more general distinction of species dif-
ferentials.

(4) The data given also demonstrate that reciprocal transplantations, in
which the role of donor and host are reversed, may differ as far as the fate
of the transplant is concerned. We have referred already to the greater
severity of reactions found in some instances in the guinea pig than in the
rat, and we have also shown the difference in reactions in reciprocal rat-
mouse and C57-Peromyscus transplantations. Similar differences in reciprocal
transplantations may be found also in some instances in homoio- and in
syngenesiotransplantations. It is the host which reacts against the graft, but
the latter does not seriously affect the condition in the host ; the ability to re-
act strongly against a strange tissue differs in different species, strains, and
probably even individuals.

There is one last conclusion which is of more general interest. In the case
of syngenesio- and homoiotransplantations we find a relatively wide range of
reactions in different individual experiments, in accordance with the great
range of variations in the combinations between different individuality dif-
ferentials of host and graft. In contrast to these, the range in the results of
heterotransplantations is rather narrow ; this is due, at least partly, to the
great severity of the reactions in heterogenous transplantations, which ap-
proaches a threshold already in the relations between nearly related species,
but it may also be due to the fact that the range of variation in the genetic
constitution of the species differentials is much smaller than that of the
homoiogenous differentials.

Chapter II

Exchange of Tissues Between Different
Varieties or Races (Subspecies)

The reactions against heterogenous transplants, on the whole, are
sharply denned and distinct from those against homoiogenous trans-
plants ; a transition to the latter is seen, however, in the grafts from
Peromyscus to mice of strain C57. If we pass from transplantations of tis-
sues between different species to transplantations between different varieties,
races or subspecies, the results are different ; these correspond to severe
homoiogenous reactions. Such experiments were carried out with Gray
Norway rats and two mutant races derived from them, mutant albino and
Curly Coat ; these mutations were discovered and their bearers propagated
by Helen Dean King, at the Wistar Institute in Philadelphia. Five series of
transplantations were made, each one representing a different type. I. Autog-
enous transplantation of thyroid and cartilage and adjoining tissues in Gray
Norway rats; II. Syngenesiotransplantation between brothers and sisters in
Gray Norway and the two mutant races; III. Intrarace transplantations be-
tween not nearly related individuals in each one of these three races; IV.
Interrace transplantations from one of these races to another; V. Exchange
of tissues between these three races and tame albino and hooded rats. Exam-
ination took place at 9, 12, 16 and 20 days following transplantation ; however,
at 20 days the number of experiments available for grading was not as large
as at 16 days.

In the grading of the reactions in these experiments, the second set of
grades was used. In autogenous transplantations in the Gray Norway rat
the grade was 6. The average grades in the other experiments, together with
the range of variations, are shown in table 1. The highest and lowest grades
in each case represent the separate grades for thyroid only, because these
grades are sharper than those for cartilage transplants.

From these results we may draw the following conclusions: (1) After
autogenous transplantation in the wild Gray Norway rat, an injurious reac-

TABLE I

. „ ^ Range of t , _ Range of „„ ^ Range of

12 Days X1 16 Days ,, 20 Days ,r

Variation Variation Variation

Series II 4.42 5.5-3.4 3.3 5.2-2.3 2.05 3.6-1

Series III 3.15 5.5-1 2.55 4.8-1 2.20 3.9-1

Series IV 2.60 4.3-1 2.15 3.5-1 1.80 3.8-1

Series V 2.30 4.2-1 2. 3-1 2.15 3-1

131

132 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tion against the transplant was absent. (2) In series II-V with increasing
length of time during which the grafts were kept in the hosts, the damage
inflicted on the transplants became greater ; this might be expected, provided
a discrepancy in the individuality differentials existed between hosts and
donors ; it did not occur in autogenous transplantations where, on the contrary,
signs of injury due to the operation became less and disappeared in the course
of time. (3) If we consider the different series, we find that the intensity of
the reactions on the whole increased with increasing distance of relationship
between host and donor. This is most clearly indicated by comparing the
grades at 12. and 16 days, and especially also by comparing the combined
grades at 12 and 16 days. The latter were as follows: series II, 3.9; series
III, 2.9; series IV, 2.4; series V, 2.2. At 20 days, the difference between these
four series had almost disappeared, either because at that time the injury had
become very marked in all of them, or because of the smaller number of
experiments that were available for the determination of the average grade.
The combined grades for thyroid at 20 and at 16 days also suggest an increas-
ing deterioration in the preservation of the transplants with increasing dis-
tance of relationship. In these series, and especially in series III, IV, and
V, the reactions were relatively severe and accordingly, grade 1 was fre-
quent in individual transplantations. The reactions were not so strong
in some instances in intrarace transplantations, although in other cases they
also were severe. This is especially interesting in view of the fact that some
of these strains had been inbred for a considerable number of generations,
although not necessarily by brother-to-sister breeding; strain Gray Norway,
for instance, having been inbred for 45 generations. Although the rats
belonging to the same strain were closely related, still, even in series II and
III the reactions were, on the whole, severe. (4) While the differences be-
tween the grades in the different series seem to be real, they were much less
than one might have expected, considering the great differences in relationship
between the rats in these different series. It is noteworthy that the reactions
even between brothers and sisters were very marked and that they approached
much more closely the reactions against distant donors than those against
autogenous transplants. We must assume that the individuality differentials
even in brothers and sisters showed quite definite differences and that these
were great enough to cause injurious reactions against the grafts. At the
same time, it appears probable that the sensitiveness of the host and his
ability to react against even relatively slight differences in the constitution
of the individuality differentials were great. (5) The transplantations within
the mutant albino race showed less severe reactions than those within the
other mutant race. It is possible that the mutant albino rats reacted less
strongly than other mutant races against the individuality differentials of
rats belonging to their own strain. (6) There were definite indications that
also in rats the bodyfluids reacted on the transplants in accordance with the
relationship between transplant and host, and that the reactions of the host
cells were superimposed upon the effect of the bodyfluids. However, in many
cases the damage done to the graft by the latter was very slight, or not mani-

EXCHANGE OF TISSUES BETWEEN VARIETIES 133

fest, the principal injurious effect being that exerted by the cells of the host.
If the bodyfluid was injurious in a given host, it acted on the various organs
and tissues from the same donor in a corresponding manner. These various
tissues from the same donor must therefore all have possessed the same
individuality differential ; otherwise the bodyfluid from the same host could
not have acted on all of them in this way. If we consider in a general way the
cellular reactions of the host against the transplants and the structural changes
in the latter, in these various series, we find that the degree of necrosis in the
grafts and the degree of the substitution of the necrotic tissue, by fibrous tissue
as well as the extent of the invasion of living tissue by fibrous tissue, became
greater with increasing distance in relationship between host and donor. Like-
wise, the lymphocytic infiltration was the more marked the greater the distance
in relationship between host and graft, provided the difference between the or-
ganismal differentials was not so great that it led to extensive necrosis of the
graft and largely to the replacement of the necrotic issue by fibrous tissue.
Such a graded replacement by connective tissue and also by lymphocytes could
be followed especially clearly in the transplanted fat tissue ; but on the whole,
the lymphocytic infiltration was more marked around and in the thyroid than
in the cartilage-fat tissue transplants, and as a rule there was a correspondence
between the reactions against the thyroid and cartilage- fat tissue. In autog-
enous transplantation of the thyroid in Gray Norway rats the connective
tissue tended to be loose, fibrillar-cellular rather than fibrous-hyaline, the
blood and lymph vessels were prominent in the center of the transplant and
marked lymphocytic infiltration was lacking.

While the reactions in transplantations between different races in rats
varied in intensity in individual cases, they still fell within that part of the
spectrum of reactions which characterizes homoiogenous relationship ; but
within the homoiogenous range of the spectrum they were situated at the
end farthest removed from autogenous relationship. Notwithstanding the con-
siderable degree of individual variations in the intensity of the reactions, the
best grades attained in the interracial series did not equal the highest grades
reached in typical homoiotransplantations ; but there is no sharp break in
these cases between the character of homoiotransplantations and of inter-
racial transplantations, such as is found if we pass from homoiogenous or
interracial transplantations to transplantations between nearly related mam-
malian species.

In a former smaller series VI in which thyroid, cartilage, fat tissue
and bone were transplanted from white rats to cream or hooded rats and the
examination took place after the grafts had been kept in the host for 20 and
21 days, the transplants of the thyroid gland were all destroyed or only a few
acini were found, and these were compressed by connective tissue and in
process of destruction by lymphocytes; likewise in the fibrous tissue as well,
that had replaced the destroyed thyroid, there was still some lymphocytic in-
filtration. In the cartilage transplants the fat tissue was infiltrated or mostly re-
placed by fibrous tissue and there were variable amounts of lymphocytic infil-
tration. Perichondria! regeneration of cartilage around necrotic cartilage was

134 THE BIOLOGICAL BASIS OF INDIVIDUALITY

only rarely seen. If we use the second type of grades, the average grades in
these two last named series was 1.75 and 1.5, respectively. In ordinary trans-
plantations among white rats, carried out at the same time, the average reaction
was 2.8. In this series of interracial transplantations, also, there was a corre-
spondence between the degree of genetic relationship between donor and host
and the degree of the reactions against the transplants. Regeneration of
cartilage by perichondrium was inhibited, but not entirely prevented. The bone
marrow became necrotic and was replaced by fibrous tissue at an early date,
while in homoio- and syngenesiotransplantations the marrow could remain
preserved for a longer time; in agreement with the findings in other experi-
ments, cartilage remained as a .rule preserved, at least in part.

In series VII in the mouse, we carried out transplantations of thyroid,
cartilage and fat tissue from wild gray mice to mice belonging to the inbred
A and Old Buffalo strains. In general, the results corresponded to homoio-
genous reactions, which were more severe in the series in which Old Buffalo
mice were the hosts. In this series the thyroid transplant had been destroyed
in animals examined later than 12 days. In the fat tisssue there was more and
more ingrowth of connective tissue, as well as of vacuolated phagocytes, and
after 16 and 25 days there was much infiltration with lymphocytes. In the
mice from the A strain the thyroid was present up to 20 days, but it was
stunted or incomplete and the organization of the necrotic center proceeded
only slowly. Here, also, more and more connective tissue and vacuolated cells
grew into the fat tissue, and, in some cases, the lymphocytic infiltration was
quite marked. The transplanted bone marrow became replaced by connective
tissue in all instances. However, in several animals some muscle fibers with
nuclear chains were found in both strains of mice. There is, then, no sharp
demarcation between these experiments and others in which homoiogenous
tissues elicited severe reactions; the grades varied between 2— and 1, and the
latter grade was obtained in the mice examined at the later dates. On the
whole, there was a remarkable correspondence in the reactions against differ-
ent tissues from the same donor in the same host. This applies to all of these
transplantations and it comes out clearly, for instance, in series III, the
intraracial transplantations. Polymorphonuclear leucocytes were not found,
as a rule, in these experiments ; if seen at all, they appeared especially in the
fat tissue.

The main result which emerges from these investigations is, then, the dem-
onstration that the reactions against tissues from different races or subspecies
correspond to very severe homoiogenous reactions, and that they differ from
heterogenous reactions in several respects. Furthermore, inasmuch as the race,
Curly Coat, differs from Gray Norway in one single mutation, it may be con-
cluded that such a mutation may have a definite effect on the individuality
differential.

If we compare these transplantations between individuals belonging to
different races with those in which donor and host belong to different species,
the grades applied do not completely correspond to each other. This is par-
ticularly true of grade 1, the severest grade. In both of these types of trans-

EXCHANGE OF TISSUES BETWEEN VARIETIES 135

plantation, grade 1 signifies the complete destruction of a tissue of medium
sensitiveness, such as the thyroid gland, and the complete or at least very-
extensive substitution of fat tissue by fibrous tissue, the cartilage being pre-
served entirely or in part. But while in heterotransplantation the tissues are
injured to such an extent that regenerative growth does not as a rule occur,
this may take place in interracial transplantation. The reactions designated
by grade 1 have, thus, a certain latitude, signifying both the less severe and
the very severe injury inflicted, respectively, by interracial and by interspecies
(hetero) transplantations.

Chapter 12

The Problems and the Criteria of Success or

Failure in Transplantation of

Tissues and Organs

jk fter having stated the principal experimental data relating to the in-
l\ dividuality and species differentials in higher organisms, obtained by
jl JL means of transplantation of tissues, we shall now add some brief
considerations concerning various problems which arose in the course of these
investigations and the criteria of success or failure used in the evaluation of
such experiments by various authors.

In the later period of the last, and at the beginning of this century, it was
noted by some clinicians and pathologists that autotransplantations of certain
organs may succeed better than transplantations into other animals belonging
to the same species. Thus Knauer, Ribbert and others obtained more favorable
results after autogenous than after homoiogenous transplantations of the
ovaries, but Ribbert believed that in some instances also homoiotransplanta-
tions of organs may succeed. We found that tumors could be successfully auto-
transplanted in cases in which homoiotransplantations failed. We carried out
successful autotransplantations of pigmented skin in guinea pigs into defects
in white skin, but Carnot and Deflandres, who had obtained similar results,
thought that homoiotransplantations succeeded equally well. However, Sale
who compared the results of auto- and homoiotransplantations of pigmented
skin in the guinea pig in our laboratory found that only autogenous transplants
healed in permanently while homoiogenous grafts were as a rule cast off after
some time and that during this preliminary period lymphocytes collected under-
neath the transplant. Christiani (1900-1905) believed that the thyroid gland
in various species can be transplanted successfully into the same animal, as
well as into other animals of the same species, and even into different races
and varieties. Yet, the experimental immunological and serological studies,
which began to develop actively during this period, had already exerted a
certain influence on the interpretation of experiments in transplantation, and,
accordingly, Christiani noted that transplantation into different families, or-
ders and classes of animals did not succeed, with the exception of transplanta-
tions between guinea pig and rabbit, which were successful. But, some-
what later it was more generally recognized that homoiotransplants of organs
did not, as a rule, survive. Halsted, for instance, obtained negative results
with homoiotransplantation of parathyroid in dogs. In many cases at this time
and also for some time afterwards, investigators did not definitely distinguish
between homoio- and syngenesiotransplantation, although in other cases such
a distinction was made, as for instance, by Goodale, who carried out ovarian

136

CRITERIA OF SUCCESS OR FAILURE 137

transplantations in fowl. But in all these experiments, as well as in subsequent
ones, the principal problem was the study of the conditions which permit
successful transplantation and of those which prevent it. However, a second
problem soon became prominent: transplantations of organs with internal
secretion were used also in order to determine the effects of certain hormones
on the growth and functions of various tissues and organs. As examples of
transplantations of the latter kind, the experiments of Steinach on the fem-
inization of male guinea pigs and rats, by implantation of ovaries into cas-
trated males, and on the masculinization of female guinea pigs by the grafting
of testes, and those of C. A. Pfeiffer on the effect of transplantation of testes
on the endocrine function of the anterior pituitary gland may be mentioned.
Both of these investigators carried out transplantations into litter mates and
into very young animals. Steinach used castrated guinea pigs, and Pfeiffer,
non-castrated rats, as hosts. In the latter experiments, the proportion of
testicles in which the tubules survived was relatively great. In both series of
investigations we have therefore to deal with syngenesio- rather than with
homoiotransplantations. The analysis of individuality was not the principal
objective in the large majority of these experiments. A further consideration
of all the numerous experiments in transplantations which have been made
during the last fifty or sixty years would therefore not contribute much to a
fruitful analysis of individuality, and it is not needed because resumes of
these investigations have already been given by various authors.

However, we shall here attempt, if possible, to find the main factors which
caused the differences in the results in transplantations of tissues obtained by
various investigators, and in particular the differences in their interpretation
of these results. One of the principal differences concerns the question as to
whether transplants may survive after homoiotransplantation, and whether
they survive as well after homoiotransplantation as after autotransplantation.
As already mentioned, especially in earlier investigations the view is fre-
quently expressed that various homoiotransplanted tissues or organs survive
as well as autotransplanted ones ; but this view occurs also even in the more
recent literature. This may be due (1) to the lack of differentiation between
real homoiogenous and syngenesious transplantations, the latter succeeding
better than the former; (2) to the disregard of the age of the transplants; it
seems that organs from newborn donors can be more readily transplanted than
organs from older donors, and likewise, that the reactions may be milder after
transplantations into very young than into older hosts; (3) often to the lack
of a complete microscopical examination of the transplants. The smaller
transplants should be cut into serial sections and many sections should be
available for study from the larger transplants. It is necessary that all im-
portant stages, from the beginning of transplantation until the reaction is
definite, be examined in succession, and that the various modes of reactions
on the part of the host — cellular as well as bodyfluid reactions — be considered
and evaluated in as quantitative a manner as possible; and lastly, it is im-
portant, if there is a limit to the periods when examinations can be made, that
such stages be selected as would permit the recognition of the presence of

138 THE BIOLOGICAL BASIS OF INDIVIDUALITY

intermediate stages between success and complete failure of transplantation.
If too late a stage is chosen for examination, the impression of an all or
nothing result is obtained, when actually intermediate stages of reaction exist.
The different degrees to which these rules were adhered to can explain, for
instance, differences between the conclusions at which Little and Bittner
arrived, and those obtained by us. In contrast to the findings of some other
investigators, in the experiments of Appel, who made careful studies of the
intermediate stages in the reactions and who considered also the cellular
response of the host, the quantitative differences between the results ob-
tained in syngenesio- and autotransplantations of testes in fowl came out
very clearly. Likewise Perthes, in careful experiments on skin grafting in
man, had noted the difference between the results of autogenous and syn-
genesiotransplantation, the marked advantage of the former over the latter
being quite definite. In these investigations the same host was used for both
types of transplants and the experiments were made at the same time;
in addition, multiple grafts were used and the method of transplantation
being the same in each case, variable factors were excluded as much as possi-
ble. The results agree with those in our experiments in non-inbred animals,
which show that the reaction against syngenesiotransplants resembles much
more closely that noted in homoiogenous than that in autogenous transplanta-
tions. It is also possible, in certain cases, to determine in an approximately
quantitative manner the differences in the outcome of transplantations by
making a large series of skin grafts into many hosts, which are alike in all
but a single distinctive factor. In this manner, valid conclusions may be drawn
by means of the statistical method, even without the aid of microscopic ex-
aminations ; as an example of this kind of experiments, we might refer to the
investigation of Kozelka in fowl.

In some instances the differences between the results obtained by various
investigators are apparent only and do not really exist. -Thus, from the ex-
periments of Browman the impression might be obtained that heterotransplan-
tation of testicles in mice and rats may succeed to a limited extent, although
it is in fact always negative. This interpretation was given because the author
accentuates the staining of central portions of the testicular graft, which may
sometimes be observed, in contrast to the peripheral portions, which are en-
tirely necrotic. In the case of a successful graft, it is the peripheral parts
which live, while the central parts die. We have observed similar specimens in
which apparently the central parts survived. These findings seem to be
due to the fact that the heterotoxins act first on the periphery of the trans-
plants, which latter, as a result, are destroyed ; the central parts being with-
out nourishment, have already died and no longer function, but they have
retained some of their staining characteristics. Browman himself recognized,
through functional endocrine tests, that these central parts did not exert any
vital activities.

The experiments of Richter and Jaffe on transplantations of thymus into
bone marrow and into the subcutaneous tissue, and of lymph glands into the
latter area, are of interest because they contribute a further example of the

CRITERIA OF SUCCESS OR FAILURE 139

gradual destruction of autogenous tissue under certain unfavorable condi-
tions. Autogenous transplants of thymus may remain permanently preserved
in the subcutaneous tissue. Here, at first, it is mainly the reticular tissue which
withstands the injury of transplantation; but other cells which soon after
transplantation degenerate, subsequently regenerate. In a first stage, these
processes occur in transplants also in the bone marrow ; however in the latter
location the preservation of the grafts is merely temporary, because the bony
capsule which, after some time, surrounds them, interferes with their proper
nourishment ; they then atrophy and a gradual absorption of the thymus tissue
takes place. We have previously discussed another example of destruction of
autogenous skin transplants, due to the ingrowth of the host connective tissue
into the epidermal cyst, especially along channels prepared by hairs devoid of
complete epithelial covering. In this way, secondary factors not connected
with the individuality differentials may determine the fate of transplants, as
do under some circumstances, growth stimuli, such as those of certain hor-
mones, acting on a transplant, which may to some extent counteract more or
less accidental, injurious factors, as well as other unfavorable conditions.

The experiments of Marine and Manley, in which they compared auto-
genous and homoiogenous transplantations of various organs in the rabbit, are
of interest because they confirm not only the fact that usually the destruction
of homoiogenous tissues takes place wifhin 20 to 30 days, but also because
they show that in some rare cases such tissues may remain alive for longer
periods. Still, their experiments did not reveal the existence of the finer
differences in the reactions of the host against the transplants, in accordance
with the relations of the individuality differentials of host and donor. These
authors recognize the relatively great power of resistance of lipoid cells in
ovary and adrenal gland, but they underestimate the injury which lympho-
cytes can inflict on the transplant. However, the injurious effects exerted by
lymphocytes differ much under different circumstances, as the experiments
which we have already reported show. As to the causes of the unfavorable
results of homoiotransplantation, Marine and Manley attribute them to the
antigenic properties of the transplants; and the differences in the power
of resistance of various organs following transplantation they apparently re-
gard as being due to the differences in the antigenic capacities of different
tissues. Their conclusions were based not only on theoretical grounds but
also on the results of successive transplantations, in which they found that
a second homoiotransplant is always more rapidly destroyed than a first one.
However, these observations and interpretations are not in accord with our
own, as we shall discuss still further in a subsequent chapter.

Chapter I J

The Effects of Various Extraneous Factors on the
Activity of the Organismal Differentials

The reactions of hosts against transplants possessing individuality
differentials which show various and graded degrees of similarity
or difference from those of the hosts, have been described; also
the differences in the reactions noted in different kinds of tissues, these dif-
ferences depending upon an interaction between tissue differentials and in-
dividuality differentials. Furthermore the differences in the action of hosts
belonging to different species have also been analyzed and we have seen
that such species differences may affect the reactions which take place in the
host against strange individuality differentials. In the course of these discus-
sions, various problems of wider biological significance have been intro-
duced and these will now receive further consideration.

(I) The interaction between tissues possessing different individuality dif-
ferentials, and the interaction between tissues possessing the same individuality
differentials but different tissue differentials. We have seen that organisms
react against strange individuality differentials by means of their bodyfluids
as well as of certain cells and tissues, or the latter may be the predominant
reacting agents. The reaction of the bodyfluids is the more specific one of
these two types. The tissue reactions as such are not entirely specific, but
they may become so if we take into account also the quantitative factors in
their activity, in particular the intensity and time of their action, and also the
interaction between different types of tissues and cells involved. The con-
nective tissue in general reacts very readily against various kinds of changes
in its environment. It reacts wherever cells and tissues in the neighboring
area are injured or killed; also against dead foreign bodies and it is influenced
in its behavior by variations in the activity of neighboring epithelial structures ;
but in addition, connective tissue reacts very finely to differences in the
individuality differentials in the adjoining tissues, discerning here the slight-
est differences and responding in accordance with a definite time curve. With
advancing age the connective tissue stroma undergoes changes similar to
those induced by strange individuality differentials. The lymphocytes too re-
act primarily in a non-specific manner against foreign bodies and against
injured tissues, provided these changes do not exceed a certain intensity.
It is the polymorphonuclear leucocytes which are activated whenever acute
changes of a relatively great intensity occur ; these cells become prominent as
soon as the difference between organismal differentials has attained such a
degree that the tissues are markedly injured, as, for instance, when tissues
possessing different species differentials adjoin each other, or when species

140

EFFECTS OF VARIOUS EXTRANEOUS FACTORS 141

differential substances are given off into the circulation. Blood vessels re-
spond to changes in the environment in certain respects similarly to the con-
nective tissue. With the latter, they move into necrotic tissue or into foreign
bodies soft enough to permit penetration by capillaries. But while the con-
nective tissue is stimulated more by homoiogenous than by autogenous dif-
ferentials, the blood capillaries are inhibited by the former and attracted
more actively by the latter. On the other hand, contact with autogenous tissue
tends to prevent the change of cellular connective tissue into fibrous tissue.

However, tissue reactions can occur also between adjoining tissues of autog-
enous constitution and these reactions may be altered if a homoiogenous,
takes the place of the autogenous differential. Thus we have referred to the
changes which are seen when pigmented skin is autotransplanted into de-
fects in white skin in the guinea pig, or conversely, if white skin is trans-
planted into a defect in pigmented skin; the pigmented epidermis grows
into the unpigmented epidermis and this process continues for a cer-
tain time until new boundaries are produced between these tissues. In the
normal quiescent state of the tissues, each adjoins the other without re-
action; but whenever a tissue disturbance takes place, such as is caused
by the injury connected with transplantation, a struggle ensues between
the two adjacent types of epithelium. The pigmented epidermis is the stronger
one, but under normal conditions its superiority is merely potential ; it be-
comes activated under certain conditions which disturb the tissue equilib-
rium, and then a reaction occurs against tissue elements possessing the same
individuality differentials. If a syngenesio- or a homoiogenous differential
takes the place of the autogenous differential, this reaction is suppressed
The strange individuality differentials injure the tissue metabolism, as indi-
cated by the loss of pigment, which may occur in homoiogenous or syngenesi-
ous pigmented epidermis. The degree of inferiority of the unpigmented
epidermis and the mode of reaction of the tissues towards each other, if dis-
turbances take place, may vary in different species, even in nearly related
ones. In some instances, changes in the tissue equilibrium between pigmented
and white skin in the guinea pig may apparently arise spontaneously in non-
transplanted skin. Such an effect was observed by Saxton, Schmeckebier and
Kelley, presumably under conditions in which a disturbance of the tissue
equilibrium was due to some hidden metabolic change.

As stated, the reactions above described were found in the guinea pig.
In the mouse, the transplanted pigmented skin does not extend into the
adjacent tissue, probably because the chromatophores here are not epidermal.
Also, in the tadpole conditions are, in certain respects, different. Thus Rand
and Pierce noted that while white transplants of ventral tadpole skin to pig-
mented dorsal skin were invaded by the adjoining pigmented host epidermis,
this could occur in autogenous as well as in homoiogenous transplants, yet,
an individuality differential was also involved in this reaction, as is indicated
by the fact that in many instances in autogenous grafts the desequilibration
was not sufficient to cause an invasion. An injury by homoiotoxins may then
have to be added, in order to overcome the inertia of the pigmented epidermis

142 THE BIOLOGICAL BASIS OF INDIVIDUALITY

and to make its potential superiority actual. In adult rana pipiens, after
transplantation of autogenous white skin to a pigmented dorsal area, no
change in the condition of the transplant takes place, but following homoio-
transplantation, the pigmented epidermis invades the white epidermis after
about two weeks (H. H. Vogel).

A related process may take place at the border between the squamous
epithelium of the cervix and the cylindrical epithelium of the uterine horns.
This is especially noticeable in the mouse under the influence of stimulation
of the vagina-cervix-uterus by estrogen. Under these conditions the squa-
mous epithelium dominates over the cylindrical epithelium and begins to in-
vade and replace it ; it may also push into uterine gland ducts and here un-
dermine or exert pressure on the cylindrical epithelium. This invasion may
extend to various distances. There are indications that such changes may take
place to a slight extent even without the hormone stimulation, but it is the
latter which greatly intensifies the potential superiority of the squamous epi-
thelium of the cervix over the cylindrical epithelium of the uterus.

In certain respects, also, cancerous growth may be considered as a related
phenomenon. In this condition one tissue, as a result of long-continued stim-
ulation, gains the ascendancy over adjoining tissues of the same or of a
different kind and then begins to invade them. But in cancer such a change is
not temporary, as in the examples previously mentioned; it is a permanent
change, leading ultimately to the destruction of the whole organism. The
mode of stimulation of one tissue which brings about this result in cancer
may be of various kinds, but this is the less important factor ; it is the reac-
tion of the stimulated tissue which is characteristic. Thus we may conceive
of an organism as an equilibrized system, composed of many mosaic parts,
which function in harmony with one another. Various kinds of changes may
disturb their equilibrium and then a potential tissue superiority may become
actual. Tissue differentials, without the co-operation of individuality dif-
ferentials, may condition such disharmonious reactions, but antagonistic, dis-
equilibrizing reactions may be induced also by individuality differentials,
and in some cases they are brought about by an interaction between tissue
and individuality differentials.

Chapter I//.
Hormones and Individuality Differentials

The organism is an approximately equilibrized mechanism in which
the maintenance of the structural autonomy of the various parts and
the integrity of the whole organism depend upon the inherited char-
acteristics inherent in these parts, in particular upon the nature of the inter-
acting tissues and their individuality differentials; furthermore upon their
state of sensitization, and upon the degree of stimulation these structural
units receive especially by hormones. Interaction of all these factors with one
another takes place, including the interaction between individuality differ-
entials and the hormones, and it is this last type of interaction which is of
interest also in our analysis of the individuality differentials. In this interac-
tion the endocrine function may be considered as the primary factor and we
may inquire how this function would be affected by changes in the individual-
ity differentials, or, on the other hand, .the individuality differentials may be
considered as the primary factor and we may inquire into the effect which
changes in hormone action may have on the activity and efficiency of the in-
dividuality differentials, especially under conditions in which two different
individuality differentials oppose each other.

Hormones as such, within a wide range of their action do not possess in-
dividuality differentials and are independent of the latter, but the organs
in which they are produced and the tissues upon which they act carry these
differentials, and the new formation of tissues which takes place as the
result of the function of certain hormones, may be greatly influenced by the
nature of the individuality differentials of these tissues and organs; these
effects may be unfavorably affected by the presence of other than autogenous
individuality differentials. Thus we have seen that the formation of placento-
mata, which is controlled by the interaction between the corpus luteum hor-
mone and mechanical stimulation, requires the presence of autogenous in-
dividuality differentials if the maximum effects are to be achieved, whereas,
the presence of a homoiogenous differential has an inhibiting action on such
processes. Likewise, the grafts of endocrine glands, such as ovaries and thy-
roid, develop and function best in a perfect autogenous environment.

On the other hand, under some conditions the presence or absence of cer-
tain hormones may affect the function and growth of organs and tissues in an
environment in which the individuality differentials are not entirely adequate ;
or the action of hormones, also, may be of significance even in the survival of
autogenous transplants. However, in this respect different organs seem to
differ as to the degree to which they are influenced by the activity of certain
hormones. In the organs which we have studied, the ability of hormones to
prevent altogether the injurious effects of not quite adequate individuality

143

144 THE BIOLOGICAL BASIS OF INDIVIDUALITY

differentials was not very striking; if such power existed at all, it was
usually slight and in other cases it was lacking. Thus we observed that if
ovaries were transplanted in certain inbred strains of mice, the unfavorable
effects of relatively slight deviations from the optimum conditions of the in-
dividuality differentials could to some extent be remedied by using ovariec-
tomized or castrated hosts; but in other strains, these improvements, due to
the removal of the hormones secreted by the sex glands of the host, were
lacking ; in no instance were the effects very striking. We saw, furthermore,
that multiple transplantations of anterior hypophysis succeeded in mice in
which the host's own hypophysis was present and functioning, and that
these transplants could exert certain hormonal functions and remain alive for
considerable periods of time. This result was obtained in cases in which the
disharmony between the individuality differentials of host and donor was
only very slight; but there were some indications that when the differences
between individuality differentials were greater, the transplants did not long
survive. Likewise in experiments with thyroid and parathyroid glands, it was
possible to transplant these organs successfully into hosts whose individuality
differentials differed only to a slight degree, without first removing the hosts'
own thyroid and parathyroid glands, and even several glands transplanted
simultaneously in such hosts could survive. In the case of the adrenal gland
of the mouse, such transplants degenerated to a large extent; but in many
instances some part of the cortex survived for a long time if there was no
marked disharmony between the individuality differentials of host and donor.
It is possible to test the interaction between endocrine effects and individ-
uality differentials in still another way, namely, by experimental administra-
tion to the host of an excess of certain hormones, in order to determine
whether this counteracts or accentuates the effects of not quite adequate in-
dividuality differentials. Christiani, it seems, was the first to express the opin-
ion that the need of thyroid tissue on the part of the host organism deter-
mined the fate of the thyroid transplants. In thyroidectomized animals the
grafts healed in better than in those possessing their own thyroids. On the
other hand, administration of thyroid substance caused an atrophy of the
thyroid transplants. We were unable to observe any marked effect of the oral
administration of thyroid tablets on the fate of thyroid transplants; it cer-
tainly did not prevent their survival in transplantations which otherwise
would have been successful. At most, this procedure may perhaps have re-
duced the functional and mitotic activity of the thyroid transplant, as well
as that of the host's thyroid, without, however, interfering very noticeably
with the action of the individuality differentials, which latter determined
essentially the success or lack of success of these transplantations.

Likewise, Carroll Smith did not notice that administration of potassium
iodide had any marked effect on the fate of autogenous or homoiogenous
thyroid transplants in guinea pigs. Also, experiments in which injections of
extracts of cattle anterior pituitary were made into guinea pigs carrying
thyroid transplants should have some bearing on this problem. Such extracts
contain the hormone which causes a very marked growth and functional

HORMONES AND INDIVIDUALITY DIFFERENTIALS 145

stimulation of the thyroid gland in the guinea pig ; they should therefore pro-
mote the growth of thyroid transplants and help the latter to overcome the
injurious effects which a disharmony between the individuality differentials
of host and transplant exert on the survival and growth of the latter. How-
ever, Martin Silberberg, who carried out such experiments, noticed that the
hypertrophy of the transplanted organ is less readily accomplished than that
of the non-transplanted thyroid gland, a finding with which our own is in
agreement and which can be understood if we consider the less favorable
circulatory conditions in a transplanted organ and a certain inadequacy in
the relations between stroma and transplanted parenchyma whenever a dis-
harmony exists between the individuality differentials of host and transplant.
Silberberg furthermore made the interesting observation that a thyroid
gland, rendered hypertrophic previous to transplantation by injections of
anterior pituitary extracts, can be less readily successfully transplanted than
a non-hypertrophic gland. Apparently the state of hypertrophy corresponds
to an increased differentiation of the tissue, which makes the organ less
resistant to the injury inflicted during the process of grafting. But on the
whole, this investigator found favorable effects of injections of anterior
pituitary extract on the homoiogenous thyroid if the injections were begun
after the thyroid had been transferred to the new host. However, the results of
the experiments of Silberberg, as well as our own in similar experiments,
showed a certain variability, and on the whole, in the large majority of trans-
plantations the action of the thyroid-stimulating hormone was not able to
overcome the unfavorable results of homoiogenous transplantation of the
thyroid gland in the guinea pig. These results agree with those of Bayer and
Wense, who showed that injections of pregnancy urine, containing prolan,
did not exert a beneficial effect on intra-ocular, homoiogenous transplants of
testicle in the rabbit.

There is another condition in which hormones might possibly affect the
fate of the transplant, namely pregnancy. In pregnant guinea pigs the reac-
tions against homoiogenous transplants of thyroid, cartilage and fat tissue
were severe in the majority of cases, even during early pregnancy of the host,
but in some animals the reaction was relatively mild. It was conceivable that
pregnancy exerts its effects by causing undernourishment of the transplants.
However, in control experiments, in which young guinea pigs with an initial
weight of 195-225 grams were underfed for a period of 18 days, so that the
end weight was between 160-185 grams, the grades of the homoiogenous
thyroid transplants were similar to those in well-fed animals, or they were
even somewhat better in the underfed guinea pigs.

As already mentioned on the basis of experiments with transplantations of
the thyroid gland, Christiani (1900-1905) stated that an endocrine deficiency
is needed for the successful transplantation of an endocrine organ. He attrib-
uted this favorable result of a diminution in the amount of the endocrine
organ, in particular the thyroid present in the host to the improvement in the
vascularization of the graft in animals deficient in the production of the
thyroid hormone. However, he actually observed merely an increased size and

146 THE BIOLOGICAL BASIS OF INDIVIDUALITY

hyperemia in transplants in completely thyroidectomized hosts, as compared
to animals in which a part of their own thyroid glands had been left intact.
Haberer and Salzer (1909), in rabbits, and more recently, Ingle and Cragy,
in rats, likewise noted a better vascularization and better growth of the acini
in completely thyroidectomized animals than in those in which a part of the
thyroid had remained. Halsted (1909), in the case of the parathyroid gland,
found in dogs a better growth of autogenous parathyroids in animals in which
their own glands had been completely extirpated ; he believed that an endocrine
deficiency is necessary not only for the better development, but also for the
survival of an autogenous graft. However, this opinion is based apparently
on a relatively small number of cases, in which the autogenous parathyroid
transplants were recovered in parathyroidectomized dogs, and this investiga-
tor is very cautious in stating his conclusion.

There are, however, experiments with transplantation of other endocrine
organs, in which the effect of an endocrine deficiency on the survival of
transplants of such organs is greater. Thus the experiments on the grafting of
adrenal cortex by Wyman and Turn Suden, by Ingle, Nilson, Higgins and
Kendall, as well as those of Lux, Higgins and Mann, showed that successful
transplantation of the adrenal cortex depends, in the first place, upon the
genetic relationship between donor and host, better results being obtained in
inbred rats in litter mates than in less nearly related animals. Furthermore,
transplants from newborn rats are more favorable than those from older
donors, but in addition, a deficiency in adrenal hormone production in the
host stimulates the growth of the transplanted gland very much. The influence
of the hormone consists primarily in an enhancement of the growth processes
in the transplant, but in addition there is strong evidence that this factor may
favor also the survival of the graft ; and again, as a result of the stimulation
of the transplant by the specific hormone, the vascularization of the graft is
improved.

We may add here some related observations concerning the influence of
hormones on the transplantation of non-endocrine organs. In our earlier
transplantations of the uterus in various stages of the sexual cycle in guinea
pigs, we found a favorable effect of hormones given off by the host on the
survival of the transplanted decidual cells. Jacobson, in autotransplanting the
endometrium of rabbits into the pelvic cavity, observed that the different
periods of the sexual cycle in the animal may affect favorably or unfavorably
the fate of the transplant and that ovariectomy carried out at the time of the
transplantation does not prevent the formation of endometrial cysts, but that
it diminishes the size of the cysts and the thickness of their walls. Neumann
noted that intra-peritoneal autotransplantation of endometrium succeeds if
the animals possess their own ovaries, but that it is unsuccessful in previously
ovariectomized rabbits, which indicates that the atrophic uterine mucosa can-
not maintain itself in the host. Likewise, while transplantation of the uterine
mucosa into sisters is successful, it does not succeed in brothers for the same
reason. In these experiments we have to deal chiefly with autotransplantation.

Corresponding investigations concerning autotransplantation of the Fal-

HORMONES AND INDIVIDUALITY DIFFERENTIALS 147

lopian tube in rabbits (Guerriero), and of vagina in guinea pigs (Reynaud),
show that stimulating hormones influence here, also, the growth processes
and size of the transplants, without being needed, however, for the survival
of the latter. In regard to the transplantation of ovaries, according to Lip-
schiitz the total number of preserved follicles in the transplants is greater in
ovariectomized than in non-ovariectomized animals, an effect which was ob-
served however only under certain conditions and not as a general rule in our
experiments ; moreover, the interaction between individuality differentials
and hormones were not considered by this investigator. Numerous experi-
ments have demonstrated the effects of the anterior hypophysis on the ovaries
and testicles, demonstrating the significance of the hormones given off by this
organ for the growth and for the functioning of various constituents of the
sex glands, and these influences extend also to the transplanted sex glands
(Engle, Moore and Price, Takewaki, Bayer and Wense, and others). If we
consider the results of these investigations as well as of our own, on which
we have already reported, and those of Pfeiffer, we may conclude that the
following conditions are involved in the survival and growth of transplanted
sex glands: (1) The relation between the individuality differentials of host
and transplant (genetic factors) ; (2) The age of the transplant; the trans-
plantation of the sex glands of newborn animals seems to succeed better than
that of older animals, at least in the case of the testes; (3) The removal of
the sex glands of the host; this favors, in the first place, the growth and
function of the transplant, and it may, secondarily, affect also its survival ; it
seems to be a more important factor when the hosts are older animals ;
(4) Transplantation to the opposite sex ; there are some indications that under
certain circumstances this may be a more favorable procedure than trans-
plantation to the sex of the donor. The order in which these factors are cited
indicates probably also their relative importance, the first one being the most
important.

The following are the principal conclusions concerning the relation of varia-
tions in hormone actions to the fate of transplants. The effects of administra-
tion of hormones to the host, or of a diminution in the amount of hormones
in the host on the fate of transplanted organs varied in different organ trans-
plants and perhaps also in analogous organ transplants in different species.
They were moderate, slight, or perhaps entirely lacking in some experiments
with thyroid, parathyroid and ovarian grafts, or they were quite pronounced,
especially in the case of adrenal grafts. They were found in transplants of
endocrine organs, as well as in transplants of other organs or tissues on which
hormones may exert a certain influence. Such effects may be noticeable after
autotransplantation as well as after homoiotransplantation. In the former, it
may be assumed that continued hormone stimulation prevents the gradual
atrophy which might ensue due to the combined effect of lack of function of
the transplanted organ and of injurious conditions existing at the site of
transplantation. Homoiotransplanted organs, as a result of the increase in
growth momentum acquired with the aid of hormone action, are enabled, to
some extent, to overcome the unfavorable conditions caused by disharmonious

148 THE BIOLOGICAL BASIS OF INDIVIDUALITY

individuality differentials. But in all these experiments, the degree of strange-
ness of the individuality differential of the host was a factor in determining
the effectiveness of the hormonal stimulation on the survival and growth of
the transplant; if the disharmony between the individuality differentials of
host and transplant was diminished, the results were better. The increase in
growth momentum acts in these instances in principle in the same way as this
factor acts in tumors, which thereby also are enabled, to a certain extent, to
overcome the injurious action of non-adequate individuality differentials by
an increased growth momentum. In some organ transplants, factors inherent
in the transplanted cells seem to predominate over the endocrine factors, and
such transplants are largely unaffected by an increase in hormone stimulation ;
or a minimal amount of such stimulation may be sufficient and its effectiveness
cannot be increased by additional amounts of hormones. As stated already, in
addition to these factors, the age of the host, and especially of the transplant
may affect the results.

In earlier investigations concerning these problems emphasis was laid on the
importance of the creation of a deficiency in the amount of the corresponding
endocrine organ of the host, as far as the success of the fate of the graft was
concerned. But in reality, there is hidden behind this diminution in the amount
of the host endocrine organ an increase in the stimulation of the transplant by
an increased function or an increased production of the effective hormone in
the host. We may illustrate this interpretation by a reference to the condi-
tions noted by us in the development of compensatory hypertrophy of the
thyroid gland in the guinea pig. We found that this depends upon the balanc-
ing of two hormone effects. In the first place, the administration of thyroid
hormone tends to diminish the growth and hormone production of the normal
thyroid gland of the treated animal. The thyroid hormone given off by the
intact thyroid gland, correspondingly tends to limit these activities. On the
other hand, the thyroid-stimulating hormone of the anterior pituitary gland
opposes this effect by stimulating the thyroid gland and by causing hyper-
trophy. The normal condition of the thyroid gland is the consequence of a
certain equilibrium between these two opposing tendencies, and this equilibri-
um can be changed by suppressing or enhancing one of the two factors in-
volved. By excising a considerable portion of the thyroid gland, the amount
of thyroid hormone given off is diminished and, correspondingly, the stimu-
lating activity of the anterior pituitary gains the upper hand; on the other
hand, an increased activity of the thyroid causing a depression in the func-
tion of the anterior pituitary has the opposite effect. Somewhat similar con-
siderations apply to the equilibrium in the thyroid gland, ovary, and perhaps
also the islands of the pancreas and some other organs with internal secretions.
It is not certain in these cases whether the intrinsic hormone, as for instance,
the thyroid hormone, acts directly on the organ in which it originates or
whether it acts on the controlling endocrine gland, the anterior pituitary. In
the case of the ovary, estrogen exerts its effects evidently by way of the
anterior pituitary. We may therefore conclude that the results of extirpation
of an endocrine organ depend on the consequent surplus function of another

HORMONES AND INDIVIDUALITY DIFFERENTIALS 149

hormone which is able to stimulate the transplant. These hormones act pri-
marily on the parenchyma of the graft, stimulating its increased growth and
function, and such increased activity of the glandular tissue may secondarily
stimulate the activity of the stroma and especially also its vascularization,
which then further aids the growth and power of survival of the graft.

It may therefore be stated that hormones may influence in various ways
the effects of the individuality differentials on the fate of a transplant. By
stimulating growth processes in the latter, hormones tend to neutralize the
damaging action of strange differentials, and by depressing these growth
processes they may intensify the effect of unfavorable differentials.

Chapter 1$
Individuality Differentials and Blood Groups

Towards the end of the last century and in the beginning of this,
serological methods had been established which made possible the
distinction of species and wider groups of organisms. It was natural
that the question should have been raised as to whether it might not be possible
to distinguish races and even individuals belonging to the same species by
these means. Thus Bruck believed that by the use of the complement fixation
method it was possible to distinguish between different human races. Land-
steiner, in order to find individual differences, studied the interaction of
blood serum and erythrocytes in man and thus discovered the existence of
four primary blood groups, which are based on the possession or lack of
possession of the agglutinogens A and B in the red blood corpuscles and of
specific agglutinins for the four types of erythrocytes. Subsequently it was
found that also certain animal species possess similar blood groups and that
there may even be an identity of some of these antigenic factors in the eryth-
rocytes of different species, as for instance, of man and certain apes. A
comparison of the distribution of these blood groups in different human
races showed that the proportions of the four blood groups differed in differ-
ent races, but that the blood groups which did occur were always the same.
It was furthermore established that the interaction between the agglutinins
in the blood plasma or serum and the blood-group factors is responsible for
thrombi which form in the blood if blood transfusions are made in case the
donor and recipient belonged to different blood groups. There was a definite
analogy between the blood, with its cells and the complex protein-containing
medium surrounding these cells, and a tissue in which the cells were sep-
arated by intercellular substances.

Previous to the serological investigations which led to these discoveries,
surgeons had noticed a difference in the results of tissue grafting, in par-
ticular of skin grafting, if the latter was made into the person from whom
the skin flap was taken, or into other individuals, and this observation sug-
gested the presence of chemical differences in the constitution of these tissues
in different individuals. Similar differences were found in experimental trans-
plantations in animals and also, as we observed, in the transplantations of
tumors; we interpreted these differences as being due to the specific bio-
chemical relationships between the bodyfluids and the tissues in donors and
hosts. In continuation of this work, begun in 1909, finer methods were de-
veloped for the investigation of the relationship between such tissues. These
depended largely upon the study of the cellular interactions between tissues of
the host and of transplants. On the basis of these investigations, gradually the
theory of the individuality differentials developed, according to which all

150

INDIVIDUALITY DIFFERENTIALS AND BLOOD GROUPS 151

tissues or organs in the same organism have in common a chemical charac-
teristic, which differs from those present in every other organism. These
differences are genetic in origin and are therefore proportional to the genetic
relationship between different individuals, but they are not identical with the
genes. Such individuality differentials must be distinguished from the tissue
differentials, which are the same in the corresponding tissues in different in-
dividuals, but which differ in different tissues of the same individual. Also,
the red blood corpuscles possess these individuality differentials. At first, by
means of the study of the fate of transplanted blood clots, and especially of
the cellular reactions of the host against them, merely the presence of heterog-
enous, but not of homoiogenous, individuality differentials could be definitely
established, but subsequently, by the use of the white blood cell reaction,
Blumenthal could demonstrate also the presence of homoiogenous differentials
in blood clots, and correspondingly, in the erythrocytes included in these
clots, or at least reactions were found similar to those elicited by homoiog-
enous differentials present in the various tissues.

Following the experiments of Ehrlich and Morgenroth, who succeeded in
producing hemolysins for homoiogenous erythrocytes in goats, Todd extended
these investigations and obtained similar hemolysins for homoiogenous red
corpuscles in cattle and sheep. In 1911, he found differences between red
blood corpuscles of individuals in certain species by using the differential
absorption method. These antigenic differences between the erythrocytes of
individual animals could be readily demonstrated, except in cases where there
was a close relationship between two individuals. In 1930 and 1931, this in-
vestigator prepared polyvalent homoio-(iso) agglutinating immune sera
against fowl erythrocytes, and again, by using the differential absorption
method, he found that the red blood cells of each individual examined differed
from those of every other individual. Also, members of the same family
differed from one another in the agglutinogens of their blood corpuscles, the
degree of difference varying very much in individual cases. The investiga-
tions of Todd on antigens present in the erythrocytes of cattle were recently
confirmed and extended by Ferguson, Stormont and Irwin, who, by repeated
injections of one individual with the erythrocytes of another individual of
this species, prepared homoiogenous hemolytic sera, or by injecting a rabbit
with such erythrocytes, they prepared heterogenous hemolytic sera ; they
furthermore analyzed the antigens present in the erythrocytes in an indi-
vidual animal by means of these two kinds of sera. These tests were refined
by absorption of the antibodies from the immune sera by the erythrocytes of
individual animals. Thus, these investigators found thirty different antigens
giving origin to immune hemolysins. Each individual differed from all other
individuals tested in the combination of the antigens present in its red cor-
puscles. There were indications that other antigens might be added to this
number. There were moreover, strong indications that each separate antigenic
substance was determined by a single dominant gene and that correspondingly
many multiple genes determined the set of antigens in a certain individual. It
is very likely that by using for immunization other species in addition to the

152 THE BIOLOGICAL BASIS OF INDIVIDUALITY

rabbit, and by testing erythrocytes of various cattle with the normal sera of
individuals from different species, a considerable number of additional anti-
gens may be found in cattle erythrocytes. There is therefore no basis for the
suggestion made by these authors that each one of the thirty genes, corre-
sponding to the thirty antigenic substances found so far, might be located in
one of the thirty chromosome pairs which the cells of cattle are supposed to
possess. Inasmuch as these antigenic (individuality differential) substances
are genetically determined, it is to be assumed that, considering the relatively
large number of these substances, on the average there should be a greater
similarity between the sets present in parents and offspring than between the
sets of less closely related individuals. Experiments were in agreement with
this postulate. And there is thus, in this respect, a correspondence between the
effects of these multiple factors present in erythrocytes and the individuality
differentials of tissues in general.

In the meantime, Landsteiner and others, by studying further the agglutina-
tion reactions in blood of man and of other species, had added several addi-
tional factors (P.M.N., Rh., Ax and A2) to the original A and B which were
found in erythrocytes; accordingly, the number of factors which have to be
considered in selecting compatible donors and receivers in transfusions of
blood has also increased, and it seems very probable that this number will be
still further increased in the future. As to the different agglutinogens which
are present in and distinguish the red corpuscles of fowl, Kozelka, who also
extended the work of Todd, believes it possible that their number is small,
notwithstanding the infinite number of individuals which all differ in the
character of their erythrocytes. This opinion is based on the fact to which
Landsteiner and Wiener have repeatedly drawn attention, namely, that there
are a great many possible combinations of relatively few factors. On the other
hand, it must also be remembered that the greater the number is of different
rabbit immune sera and of natural sera from different species which are used
for testing the agglutination and hemolysis of the corpuscles of individual
fowl or mammals, the greater will become the number of factors which dis-
tinguish the erythrocytes of individual organisms. While it is true that the-
oretically a limited number of factors would suffice to account for a large
number of differences between different individuals of a certain species, this
does not necessarily prove that the number is actually very small.

As far as the individuality differentials are concerned, there are strong
indications that the number of distinguishing factors is very great. We have
referred already to some experimental data which strongly support this con-
clusion, such as the many fine gradations found in the strength of the reac-
tions against syngenesious and homoiogenous tissues, in accordance with the
relationship of donor and host, and the fact that no autogenous reaction is
found against homoiogenous or syngenesious tissues except when we weaken
artificially the ability of the host to attack the strange transplant, but that
autogenous reactions occur only if the host and transplant possess the same
genetic constitution. Furthermore, marked differences between the individu-
ality differentials of host and graft lead to rapid and strong reactions, and

INDIVIDUALITY DIFFERENTIALS AND BLOOD GROUPS 153

slight differences may lead to weak and often long delayed reactions. Especial-
ly significant in this connection are transplantations within closely inbred
strains; here the great difficulty in making the genetic constitution, which
determines the nature of the individuality differentials, identical, is clearly
demonstrated ; it is also shown that the reactions against the latter are parallel
to the differences in the genetic constitutions of host and donor and that these
differences show all kinds of gradations. Taking all of these facts together,
the only conclusion possible seems to be that many genes take part in the de-
termination of the nature of the individuality differentials.

It seems therefore most probable that a further anlysis of the antigens pres-
ent in erythrocytes will show that they are either identical with or are a part
of the factors which call forth the individuality differential reactions against
all kinds of strange tissues. The peculiar character of the erythrocytes makes
it possible to obtain for the analysis of the constitution of these cellular ele-
ments, special hemolytic and agglutination reactions, which cannot be applied
generally in the study of the reactions against strange individuality differen-
tials ; but even in the case of the erythrocytes, as a rule it is not possible to dem-
onstrate the existence in the serum of the host of preformed hemolysins or ag-
glutinins for the red blood cells of the donor. Other characteristics which we
have discussed repeatedly make it possible to distinguish the individuality
differentials of cells and tissues in general, and there is, therefore, no reason
why the individuality differentials, which were established by entirely differ-
ent methods and which are common to all tissues, should be subordinated to
the factors which determine the agglutination and hemolysis of erythrocytes,
which latter represent very specialized modes of reaction between particular
kinds of cells and particular constituents of the blood serum.

These conclusions as to the relations between the antigenic constitution of
the erythrocytes and the individuality differential do not necessarily apply if
instead of the numerous antigens of the erythrocytes, we consider merely the
four primary blood groups. By means of these it is possible to distinguish be-
tween certain individuals, and it is the identity or lack of identity of the blood
groups to which two individuals belong that determines the compatibility of
their blood in transfusions ; as stated the blood shows some analogies to
tissues ; therefore the compatibility of the blood might be taken as an indication
of the compatibility of the tissues comprising an individual. In pursuing this
trend of thought, several investigators went still further and considered the
blood group characters of an individual as the most significant features of his
constitution.

The experimental data on which the evaluation of the correctness of this
interpretation has been based were obtained in a comparative study of the
results of skin grafting, in cases in which donor and host of the graft belonged
to the same or to different blood groups. The number of skin graftings in
man, in which the blood group relations between donors and hosts have been
considered, is great, but the conclusions arrived at by various investigators
differ very much. There are those who believe that the success of homoiog-
enous skin transplantations is determined by the blood group relations be-

154 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tween donor and host ; there are others, as, for instance, Lexer and Holman,
who were unable to discover a relation between the compatibility of blood of
donor and host and the result of grafting, and there are still others who do not
hold that identity of the blood groups makes the homoiogenous transplantation
of skin fully successful, but who still find indications that the sameness of the
blood groups at least delays the destruction of the homoiogenous grafts.

In appraising the value to be attached to these divergent results, it seems
that surgeons, with the largest experience in skin grafting, and among them
those who have carried out these transplantations more recently, have ob-
tained as a rule entirely negative results, while especially some earlier work-
ers, with more limited experience, who did not follow the fate of the trans-
plants over longer periods of time, believed that they had obtained confirma-
tory results; as to the latter, however, there always remains a doubt as to
whether the definite healing-in of the transplants was actually seen, or whether
the transplants were not gradually replaced by the adjoining skin of the host in
cases in which there was compatibility between the blood groups of donor
and host of the graft. More convincing then these earlier experiments are the
experiments of transplantations in animals ; especially the very careful in-
vestigations of Kozelka, in which skin of fowl was used for transplantation,
are significant in this respect ; no relation between the agglutinogens present in
the erythrocytes of host and donor and the success of the transplantation was
noted. Likewise in the work of Ingbrigtsen, who transplanted segments of
arteries in cats, and that of Haddow, who transplanted sarcoma in fowl, the
findings were independent of the agglutination reactions between the blood of
donor and host. We believe, therefore, that the evidence available at present
makes very improbable a direct relationship between the four primary blood
groups and the individuality differentials of host and donor. Correspondingly,
we must conclude that there is no definite correlation between the results of
transfusion of blood and those of homoiogenous grafting of skin. There seems
to be no more reason for assuming that the particular genes determining the
four blood groups determine also the fate of homoiogenous transplants than
for believing that the identity of heterophile antigens, among different classes
of animals, makes heterotransplantation between these classes possible.

However, in recent experiments, Sandstrom made some observations of a
different nature, which suggest to him a relation between organismal differ-
entials and blood group antigens. Implantation of a piece of macerated meta-
nephric tissue of the duck on the chorio-allantoic membrane of the chick
caused the death of the chick, provided the donor of the implanted tissue was
near the stage of hatching or had hatched. Neither implantation of non-
macerated tissue nor of macerated chick kidney to the chorio-allantoic mem-
brane of the duck had this effect. Other kinds of macerated duck tissue have
apparently not yet been tested. Sandstrom believes that the death of the chick
in this experiment was caused by an agglutination of erythrocytes within the
blood vessels. However, it is not certain from his report whether the occlusion
of the vessels was due to a pure agglutination process or whether coagulation
processes had been involved in this effect; it seems possible that it was due

INDIVIDUALITY DIFFERENTIALS AND BLOOD GROUPS 155

to the action of tissue coagulins extracted from the macerated kidney tissue.
The further possibility has to be considered that in this case toxic substances
which were peculiar to the duck kidney or also to other duck tissue were ex-
tracted from the implanted material ; such toxins would in certain respects be
comparable to special poisons which are present in some amphibian tissues.
But substances of this kind are distinct from the species differentials. Con-
sidering all these data, there is no reason to attribute the effect observed by
Sandstrom to the organismal differentials of the duck, but the substances
responsible for it may represent a special kind of tissue differential.

Returning to the consideration of the blood groups, the conclusions stated
above apply directly to the four primary blood groups ; they probably apply
also to the secondary factors (A and Ax, P.M.N., Rh.) more recently found.
All these factors determine the agglutination in vitro of blood corpuscles of
one individual by the serum of another, as well as the results of transfusions
of whole blood or of plasma. But as stated, it is very likely that additional
factors will be discovered in the future also in human blood, and that the
human erythrocytes contain individuality differential constituents. It is con-
ceivable therefore that in some cases, in which transfusion of blood or of
plasma has led to injurious reactions, strange individuality differentials may
have been involved.

It may then be concluded that the greater the number of factors which are
found as determiners of the agglutination and hemolysis of the erythrocytes,
the greater will be the probability that some, or even all. of these factors may
also be constituents of the individuality differentials and thus may be the same
as the factors which determine the interaction of tissues from different
individuals. However, if we restrict ourselves to a consideration of the four
original blood groups, which at first were the only ones known and analyzed
from this point of view, these cannot, in all probability, be identified with the
individuality differentials. This conclusion is in agreement with the experi-
ments which we have already cited, as well as with some other data which
may briefly be mentioned: (1) Brother and sisters may belong to different
blood groups, whereas, many entirely unrelated individuals of the same
species, and even members of different species, may belong to the same blood
group. This identity of blood groups in members of different species does not
improve the outcome of the corresponding heterotransplantations, which de-
pends on the character of organismal differentials. The individuality differ-
entials are graded according to the genetic similarity between the bearers of
these individuality differentials. (2) There is much evidence that homoiog-
enous individuality differentials in no case have become, through inbreed-
ing, absolutely identical with antogenous differentials. Even after many gen-
erations of brother-sister inbreeding there is still no complete identity of the
individuality differentials in members of the closely inbred strains, and there
are strong indications that reactions against slight disharmonies of grafts may
appear in the hosts a long time after the transplantation has taken place.
Furthermore, the strength of the response of the host against different organs
and tissues differs and by selecting an active organ and the proper time for

156 THE BIOLOGICAL BASIS OF INDIVIDUALITY

examination, a reaction of the host may be demonstrated, which otherwise
would not have become manifest. In these respects, the primary blood group
antigens and individuality differentials differ from each other. (3) While in-
dividuality differentials have been found in all vertebrates so far studied, and
at least as far down in the phylogenetic series as the anuran amphibia, there
seem to be great variations among different species and classes in regard to
the presence, number and character of the blood groups. (4) While the
reactions against individuality differentials manifest very fine gradations in
response in accordance with the genetic relationship between host and trans-
plant, the blood group reactions are sharply defined into essentially two
classes, namely, those of compatible or incompatible individuals.

In certain respects the blood group factors of primates have an intermediate
position between the organismal and tissue differentials, having certain fea-
tures in common with both. As far as the organismal differentials are con-
cerned, we shall discuss later their phylogenetic evolution ; it would be of in-
terest to trace in a similar manner also the evolution of the blood group anti-
gens. Such a study might help to clear up still further the relationship between
the blood group factors and the organismal or individuality differentials.

Chapter 16

The Relations Between Processes of Immunity and
Individuality Differentials in Transplantation

The observations made by surgeons and by experimental biologists,
which showed that in man and in higher animals autotransplantation
succeeds much better than homoiotransplantation of various organs
and tissues and that heterotransplantation never succeeds, gave rise to various
interpretations as to the cause of these differences. In tracing the develop-
ment of these interpretations it is interesting to note that they depend largely
on two factors. In the first place, the discoveries made and the systems of
thought built up in different fields of science are seen to be related to par-
ticular problems certain analogies are observed or are assumed to exist be-
tween two different series of investigations and the conclusions of the one are
applied, with some modifications, to the other. Secondly, new experiments
are carried out in order to analyze a problem by a direct approach, but here,
also, the interpretation may be influenced by analogies with conclusions ar-
rived at in the related science. These two factors are clearly discernible in the
search for an answer to the question as to why homoiogenous transplanta-
tions do not as a rule succeed. Towards the end of the last and in the be-
ginning of this century, the thoughts of pathologists, in their analysis of
transplantations of organs and tissues in higher animals, were influenced by
the investigations of experimental biologists, who grafted tissues in lower
animals and plants and who found polarity in the structure of the organisms
to be a factor in transplantation, and who also observed that the character of
the tissues adjoining each other in host and transplant was of great signifi-
cance in determining the compatibility of grafts and hosts, and it was main-
ly for the purpose of discovering polarity and other related factors as deter-
miners of normal structures that biologists carried out experiments in graft-
ing. Such an influence is noticeable in the work of the pathologist Marchand
on transplantation in higher animals and in man, in the writings of Lubarsch,
and also to some extent, in those of Schoene. Then in the beginning of this
century, the differences between the results of autogenous and homoiogenous
transplantations of tissues and tumors in higher vertebrates were inter-
preted as due to the various degrees of compatibility or incompatibility be-
tween the chemical composition of the bodyfluids of the host and of the
transplanted tissues. This interpretation was suggested by us, and the im-
portance of the biochemical constitution of host and graft was also empha-
sized by Borst, who believed that inadequate biological systems may cause
atrophy and loss of function of transplanted organs; Borst considered, in
addition, the effect of cytolysins and anaphylaxis, assuming that such factors

157

158 THE BIOLOGICAL BASIS OF INDIVIDUALITY

may explain, as well, the occasional lack of success in autogenous trans-
plantations, while we held that the controlling factors are identical in hosts
and in autogenous grafts.

It was at this point in the history of transplantations that the viewpoints
developed in immunology and serology began to be applied. It was believed,
with some justification, that these differences in the chemical constitution of
host and transplant might be due to differences in the structure of proteins or
of a certain protein in host and transplant, and that after transplantation of a
tissue into a different host, such a protein might give rise to antibodies, com-
parable to hemolysins or agglutinins. Furthermore, anaphylactic phenomena
were used in explaining the destruction of the transplants in unfavorable
hosts. While we stressed the concept that the primary incompatibility between
bodyfluids and tissues of host and transplant, as such, may lead to toxic in-
jury of the transplant, the large majority of investigators thought at that time
that immune processes, taking place in the host against the graft, were the
principal factors that produced the injury and destruction of the graft after
homoiogenous and heterogenous transplantation, although it was considered
possible that a primary toxicity of the bodyfluids might play a minor role.
This point of view was presented especially by Schoene, a collaborator of
Ehrlich, and there was some direct experimental evidence in favor of this
interpretation. In the case of tumor transplantation it had been possible to
demonstrate an active immunization of the host as the result of the growth
and regression of a primary tumor and of various other conditions, and
Russell went so far as to maintain that in every case the lack of success in
transplantation of tumors as well as the regression of transplanted tumors
was due to the development of an active immunity against the tumors. The
reaction of the host towards the transplanted tumor was assumed to be the
consequence of the development of immunity in the host and the period
necessary for the appearance of a reaction should accordingly correspond to
the time required for the production of an immune state. This view was
accepted also by Tyzzer and Burgess, and by various other investigators, and
Tyzzer applied this conception to the reaction on the part of the lymphocytes.

In the case of normal tissues, Schoene found it possible to immunize a rat
actively against mouse organs ; such an immunized rat reacted more rapidly
against a subsequently transplanted piece of mouse skin. It was more difficult
to elicit immunity against homoiogenous skin. But Schoene succeeded, by pre-
liminary treatments with embryo skin, kidney or liver of rabbit, in immuniz-
ing another rabbit against homoiogenous tissues, so that, 24 days after graft-
ing, a homoiogenous skin transplant was more rapidly destroyed while autog-
enous skin was not affected. The more closely donor and host were related,
the more difficult it was to produce such an immunity. Accordingly, skin
grafts between brothers and sisters were more successful than those between
distant members of the species ; yet Schoene did not recognize the significance
of genetic factors in transplantation. Also, the observation that skin grafts
could apparently heal in for two or three weeks and that only then were they
cast off, was interpreted as indicating that a certain time had to elapse before

PROCESSES OF IMMUNITY 159

the active immunity could establish itself. There were, in addition, the experi-
ments of Fichera, who showed that it was possible to immunize rats against
grafts of rat embryo by successive transplantations of the tissues of rat
embryos, and those of Peyton Rous, who obtained similar results with mouse
embryos. Likewise, repeated transplantation of adult skin seemed to lead to a
more active destruction of the last transplant. There may be cited, besides,
the finding of von Dungern, that rabbits could be immunized against the
tracheal epithelium of cattle, which was then more rapidly destroyed by the
bodyfluids of rabbits. Subsequent investigators, as for instance Lehmann and
Tammann, as well as Fischer, assumed that the development of an active im-
munity was the cause of the lack of success in homoiotransplantation. The
former conceded, however, that with a heterogenous serum a primary toxicity
may play a certain role, but that this would be of slight importance in homoiog-
enous transplantation.

In addition to the active immunity, some other factors were thought to cause
the destruction of homoiogenous transplants. Ehrlich had observed that
growth of a first tumor could prevent the growth of a second tumor in certain
cases, and he also noted that transplantation of a tumor piece into a pregnant
animal did not succeed well : he interpreted these effects as being due to a com-
petition for specific foodstuffs, in which an established tumor or a growing
embryo had the advantage over a recently transplanted tumor, which thus,
suffered from athrepsia. To this factor, starvation, Ehrlich attributed also
the slow death which a mouse tumor underwent when it was transplanted to a
rat. In a similar way Schoene explained the fact that homoio- or heterotrans-
planted skin could be successfully re-transplanted to the original donor after
it had been in the new host for three days, whereas, after a period of four days
the injury of the skin graft was so severe that a successful retransplantation
was no longer possible.

Among still other factors considered as responsible for the death of homoio-
transplanted tissues, may be mentioned lack of function. The importance of
this factor was especially indicated by an experiment of Jores, which showed
that electric stimulation exerts a beneficial effect on transplants of striated
muscle. Also, deficient nourishment and older age of the host resulted in less
successful transplantation, as did also, according to Ribbert, differences in the
composition of the inorganic salts of host and donor. Schoene accordingly be-
lieved that factors, such as favorable conditions for function and nourishment
in the host, may make possible a successful homoiotransplantation. However,
less significance was attached to these factors by later investigators, who, as
stated previously, stressed above all the importance of an active immunization
of the host against the transplant as the cause of the destruction of homoiog-
enous and heterogenous grafts. That so little importance was attributed to
the primary incompatibility between the bodyfluids and tissues of host and
transplant seems to have been due largely to two factors. In the first place, the
reactions taking place between the hemolysins and bacteriolysins, the agglu-
tinins and precipitins, which were considered as types of primary toxins,
and the cells providing the antigens occur very rapidly and inasmuch as so

160 THE BIOLOGICAL BASIS OF INDIVIDUALITY

rapid an injurious effect was not observed in the case of transplanted tissues,
the importance of such toxins in transplantation was ruled out. The possi-
bility that in homoiogenous transplantation we may have to deal with primary
toxins of a different kind, acting less acutely but rather slowly in a gradually
cumulative manner, was not sufficiently taken into account. In the second
place the conclusion of these investigators, were based to a large extent, on
naked-eye observations of skin grafts and not on the microscopical examina-
tion of successive stages in the process of transplantation. The latter would
have revealed the fact that a reaction of the host may set in at a much earlier
stage than would have been otherwise expected ; the specific cellular reactions
of the host could begin as soon as the transplant had sufficiently recovered from
the injuries inflicted by the operation and by the transfer into a strange soil.

The cellular reactions of the host against the transplant were likewise
attributed to immune processes which develop in the host. In the case of tumor
transplantations, cellular infiltrations were observed by Da Fano in various
places in the host ; these cells were lymphocytes, plasma cells and macrophages,
and they were interpreted by Da Fano as indicators of, as well as instruments
in the production of an active immunity against the transplanted tumor, and
also the numerous observations of Murphy as to the significance of lympho-
cytes around transplanted tumors were in harmony with this view. On the
other hand, we interpreted cellular infiltrations, principally of lymphocytes,
around and in the homoiogenous transplants as being caused by the difference
in the individuality differentials of host and transplants, these cells being at-
tracted by the strange individuality differentials of the grafted tissue; their
presence indicates the existence of variable degrees of incompatibility be-
tween tissues and the action of a mild rather than that of a severe, acutely
acting toxin.

We tested, partly in collaboration with Cora Hesselberg, the effect of a
first transplant on a second transplant in several series of experiments in
guinea pigs and rats of different ages. The first transplants remained in the
host for periods varying from two to twelve days. Control experiments were
made for the first as well as for the second transplants. Single instead of
double transplants served as controls in some instances ; in others, a piece of
paraffin was inserted instead of a first transplant. In general, it may be stated
that no definite effect of the first on the second transplant was noticeable in
these experiments, the condition of both transplants varying within the same
range as those in the controls. If we assume that it was the development of an
immune state in the host which caused the reactions against the graft, we
should have expected that about eight to twelve days after transplantation of
the first pieces an immunity was established and that, accordingly, the lympho-
cytes were ready to attack the strange homoiogenous tissue. A definite lympho-
cytic reaction should therefore have developed around a second transplant
within the first five days after transplantation. This, however, was in no case
observed ; instead, the reaction occurred at about the usual time and as usual
there were considerable variations in the strength of the reactions against the

PROCESSES OF IMMUNITY 161

transplants and in the preservation of the latter ; under these circumstances it
was very difficult to recognize the possible presence of slight effects of a first
on a second graft. However, as a rule, in accordance with expectations, the
reactions against the first and older graft were more severe, on the average,
than the reactions against the second graft. Furthermore, thyroid gland and
cartilage and fat tissue, which were the tissues transplanted in the majority of
cases, again behaved in a corresponding manner in the individual experiments.
It was likewise noticeable that the same host reacted with different degrees of
severity against homoiogenous transplants which had originated in different
donors, and different hosts seemed to differ in the severity of the reactions
against the same donor. There was in a number of instances, in the same host,
a correlation between the fate of the first transplant examined 33 days after
transplantation and of a second transplant examined after 12 days. When the
first transplant was relatively well preserved, or when the reaction against it
was severe, also when there was much lymphocytic infiltration in the first
transplant, similar conditions were found in the second transplant. This indi-
cates that the degree or reactivity of the host against homoiogenous differen-
tials was one of the factors that determined the results of the transplantations.
From these experiments we may therefore conclude that immune reactions in
all probability are not of paramount importance in determining the reactions
against homoiogenous transplants, but on the other hand, we cannot exclude
the possibility that slight immunizing effects may be exerted by a first on a
second homoiogenous transplant.

The primary factors determining the fate of transplants are, then, the
differences in the individuality differentials of host and transplant, these
differentials being preformed and giving rise to relatively slow and mild, but,
in many instances, gradually accumulating primary reactions against the
transplants. The reactions of the host against the transplant set in as soon as
the latter has entered into organic connections with the host and as soon as the
individuality differentials have had a chance to diffuse from the transplant
into the host and here to set in motion a response on the part of the various
tissues.

The investigations of M. S. Fleisher agree with our conclusions. He found
that immunization of an animal by homoiogenous tissues did not in any definite
way modify the course of the typical reaction against homoiogenous trans-
plants. Conditions were different in the case of heterogenous grafts ; here as a
result of immunization there was an increased accumulation of polymorpho-
nuclear leucocytes around the graft in the first few days following transplanta-
tion, as well as a delay in the ingrowth of fibroblasts into it, and furthermore,
a reduction in the slight growth processes which may take place in a heterog-
enous host; but these differences between immunized and normal hosts were
only transitory ; they soon subsided. These experiments are furthermore in
agreement with the view that heterogenous tissues are more efficient sources of
antigens than are homoiogenous ones, because the former are more strange
and are therefore more prone to initiate immune reactions. However, it seems

162 THE BIOLOGICAL BASIS OF INDIVIDUALITY

that also in the case of heterogenous tissues the primary reactions due to the
preformed organismal differentials are the more essential factors on which
depend the fate of the transplants.

The data so far discussed suggest, then, the interpretation that the reactions
of the host against both homoiogenous and heterogenous tissues are due largely
to the direct, primary action of the individuality differentials given off by the
transplants, but that, secondarily, these differentials may also act as antigens
and induce the formation of immune substances, which then may secondarily
intensify the strength of the reactions. However, it is apparent also that by
means of successive transplantations it is difficult to decide the question as to
how far such immune processes participate in these reactions. This method
suffers from the disadvantages that each transplant can be examined only at
the end of the experiment and that it is necessary to study the tissue in stained
section. The examination of the white blood cells as a method for the analysis
of the individuality differentials obviates these disadvantages, although in
certain respects the study of the local reactions around the transplanted tissues
is preferable. By determining the effects of two successive transplantations on
the white blood cells circulating in the peripheral blood, Blumenthal demon-
strated the existence of immune reactions also against transplanted tissues.
In these experiments, the interval between the two transplantations was 10 or
21 days. In the case of successive transplantations of homoiogenous tissues,
the second transplant called forth an accelerated increase in the lymphocytes
in the blood. The maximum number of these cells appeared from two to four
days earlier than after transplantation, but the maximum number of cells
counted after the second transplantation was not so high as after the first
transplantation in the large majority of cases. This effect of a second trans-
plantation was noted only if both the first and second transplant were homoi-
ogenous, but not if one of the two grafts was of a heterogenous nature.

If successive heterogenous transplantations were made, the maximum in
the increase of polymorphonuclear leucocytes, as well as of lymphocytes,
which took place as the second phase of the reaction of the host against the
transplant, was accelerated to about the same extent as after successful
homoiogenous transplantations. But, again, the maximum number of cells
found in the blood after the second transplantation was lower than that found
after the first transplantation. In order to obtain this effect, both the first and
second transplant had to be heterogenous ; again a combination of a heterog-
enous and a homoiogenous graft did not produce this effect. The immuniz-
ing effect of homoiogenous and heterogenous tissue on the lymphocytes and
polymorphonuclear leucocytes in the circulating blood is therefore a specific
one. Immunization against the growth of transplanted homoiogenous and
heterogenous pieces of tumors may, to a certain degree, be accomplished by a
first transplantation of normal tissues, and here, also, both the first trans-
plant of normal tissue and the second transplant of tumor must be either
homoiogenous or heterogenous. We may conclude from these experiments:
(1) that the reactions against homoiogenous and heterogenous tissues differ
not only quantitatively but also in kind, and (2) that also normal homoiog-

PROCESSES OF IMMUNITY 163

enous and heterogenous tissue may induce immunity reactions against tumor
as well as against normal tissue. (3) These secondary immune reactions also
are relatively slight as compared with the primary reactions occurring as the
direct result of the diffusion of the individuality differentials from a trans-
plant into the circulation of the host. The primary individuality differentials
are therefore responsible for the major portion of the reaction of the host
against homoiogenous tissues ; but secondary, immune reactions may also par-
ticipate in this reaction, although only to a lesser extent.

These investigations as to the nature of the reactions against homoiogenous
and heterogenous tissues suggested a second problem, one which was of
practical importance and which therefore interested surgeons especially,
because its solution might be an aid in the grafting of homoiogenous tissues
in human beings. This problem concerned the possibility of improving the
results of homoiotransplantations by experimental means. It was thought
possible that in animals, through a preliminary treatment of the host with
blood serum or plasma, or with tissue extract of the donor, the former
might become desensitized to the effect of the homoiogenous tissues. These
experiments were, however, unsuccessful. Likewise, the treatment of the
transplants with similar substances from the host previous to the grafting
did not cause an accommodation of the 'homoiogenous tissue of the donor
to the conditions found in the host. Nor was it possible by means of para-
biosis between donor and host to prolong noticeably the life of the homoiog-
enous tissue, although under these conditions the graft was supplied with
some of the blood to which it was adapted. The observation of Murphy and
his collaborators, that by the application of Roentgen rays to the host, and
by other means which tended to reduce the number of available lymphocytes,
a more favorable outcome in the transplantation of homoiogenous tumors
could be obtained, induced surgeons to apply the same methods to the
homoiotransplantation of normal tissues, but no real improvement was
attained.

In some of the papers of earlier investigators, in which the question as
to the causes of the usual failure of homoiogenous transplantations was
discussed, frequent reference is made to a state of anaphylaxis, resulting
from grafting of tissues, as one of the principal factors involved in this
process. However, a statement as to the nature of such an anaphylactic state
and its distinction from a condition of immunity against the transplant in
the host is not usually made. In order to test this assumption regarding the
presence of anaphylaxis in transplantation, experiments were made by us in
which conditions were favorable for the development of a state of sensitiza-
tion and thus also for a subsequent state of anaphylaxis in the transplant.
We sensitized guinea pigs by injecting them with horse serum and after-
wards transplanted pieces of uterus, thyroid or ovaries of the sensitized
animal into other guinea pigs, which had not previously been injected with
horse serum but which were injected sometime after they had received
the transplants. In other experiments we transplanted corresponding tissues
from non-injected guinea pigs into animals which received an injection of

164 THE BIOLOGICAL BASIS OF INDIVIDUALITY

horse serum during the period following the transplantation, and in a third
type of experiments, injections were given to the host, both prior to and
following transplantation. It was conceivable that the transplanted tissues
in some of these instances had been sensitized to horse serum and that a
second injection of horse serum would cause an anaphylactic reaction in the
transplant, which would alter the state of preservation and the lymphocytic,
connective-tissue and blood-vessel reaction of the host towards the transplant.
However, this was not the case ; the reactions of the host tissues against the
graft were not essentially altered by these procedures. Only in a few cases,
in which the general health of the guinea pig serving as host had been
affected by the injection of horse serum, was a definite effect on the trans-
plant noticeable, but it is not probable that in the last named experiments
we had to deal with a specific condition of anaphylaxis in the transplant.
As far as our experiments make possible a decision in this respect, it may
then be concluded that a state of true anaphylaxis is not one of the factors
which underlies the reaction of the host against homoiogenous transplants.
As to a possible improvement in the results of homoiogenous transplantation,
only one method appeared to be able to exert such an effect, and this was
the inactivation of the reticulo-endothelial system by means of injection of
trypan blue into the host previous to the transplantation. In the experiments
of Lehmann and Tammann, such a procedure seemed to prolong the life of
the transplanted piece of skin to a moderate degree. In 16 out of 28 mice so
treated, the skin grafts were better preserved after having been in the hosts
for four weeks than in controls; also, the staining of the skin to be trans-
planted by trypan blue seemed to protect it to some extent against the
antagonistic processes which as a rule take place in the host after trans-
plantation. Trypan blue was effective presumably because, temporarily, it
diminished the cellular response in organs where the lymphocytes are acti-
vated by the homoiogenous tissue, and also it may, perhaps, have neutralized
primary antagonistic constituents of the bodyfluids which otherwise would
have acted on the strange grafts; furthermore, it is possible that the
individuality differentials of transplanted skin infiltrated with this dye are
rendered ineffective for a certain period. But on the whole, these effects
are weak and temporary. The use of trypan blue proved to be ineffective
in similar experiments in rabbits, and Villata also obtained negative results
with this method when applied to transplantation of bones and joints in
rabbits. In similar experiments by Blumenthal with guinea pigs, into which
trypan blue was injected, the rise in the number of white blood cells other-
wise caused by the implantation of homoiogenous and heterogenous tissues
was prevented ; but he noticed that when tryan blue exerted such an effect, the
transplant was surrounded by a peripheral ring in which this dye was
deposited. He concluded, therefore, that it must be left undecided whether
the deposit of the dye in the periphery of the transplant inhibited the diffusion
of the organismal differentials into the host, or whether the trypan blue
inhibited the reaction on the part of the leucocytes through a blockade of
the reticulo-endothelial system.

PROCESSES OF IMMUNITY 165

In accordance with the relatively slight effectiveness of this method, if
applied to homoiogenous skin grafts, it was found that splenectomy, which
causes a partial elimination of the reticulo-endothelial system, was ineffective
as far as improvement in the results of homoiogenous transplantation was
concerned. Also, in our experiments splenectomy did not weaken noticeably
the reactions of the host against homoiogenous transplants of thyroid and
other tissues. There still remains the method used by Rhoda Erdmann for
this purpose in amphibians, in experiments which we shall discuss subse-
quently. In general, as was to be expected on theoretical grounds, we may
then conclude that it has not been possible to change experimentally the
individuality differentials of tissues, although it may be possible to influence
the reactions of the host against strange differentials by certain experimental
procedures. As to the reason why the local reaction around transplanted
normal tissues does not reveal definite processes of immunity, under condi-
tions in which such effects can be demonstrated in the case of transplanted
embryonal or cancerous tissues, this may be due to the fact that both pieces
of embryonal and of tumor tissue, as a rule, grow much more rapidly after
transplantation and metabolize more actively than normal tissues and that
in all probability the former correspondingly give off larger amounts of
effective antigen.

Chapter IJ

The Significance of the Individuality Differen-
tials in Transplantation by Means of Blood Vessel
Anastomosis and in Parabiotic States

So far, the interaction of the individuality differentials of host and
transplant and the effect of various factors on this interaction have
been considered under conditions of a complete primary separation of
the grafts from the surrounding tissues, only later a union taking place
between the transplant and the tissues of the host. Such a transplant lives
under unfavorable conditions of nourishment during the first few days
following the transplantation and the central parts of the graft, which suffer
most from insufficient nourishment, undergo necrosis. This disadvantage is
eliminated if directly after separation of an organ or of a part of an animal,
the large blood vessels, and perhaps even the nerves, of the transplant are
connected with the corresponding structures of the host at the site of trans-
plantation. Thus the blood of the host is carried at once to all parts of the
transplant, which does not then suffer from lack of nourishment and the
central necrosis is prevented. The homoiogenous or heterogenous indi-
viduality differentials act, therefore, in this case, on tissues which are well
provided with food and should be better able to resist the unfavorable action
of the host. Moreover, the individuality differential substances produced in
the transplant, instead of diffusing slowly into the adjoining area, have a
chance to be carried directly by vessels into the general circulation of the
host, where they are much diluted. It may therefore be expected that the
local reaction around the transplant, which is so prominent a feature in the
ordinary kind of transplantation, is lacking around transplants which are
joined to the host by means of blood vessels.

In parabiosis — a method of transplantation which was first conceived and
applied by Paul Bert, but was technically developed in its present form by
Sauerbruch and Heyde — two individuals, usually belonging to the same
species, but sometimes also to different species, are united by establishing
by means of incisions and sutures a connection between the peritoneal cavities
as well as between the skins of the two animals. In parabiosis, two indi-
viduals are therefore incompletely joined together; essentially, both partners
continue their individual metabolism and functions of organs and live their
own life, but at the same time some substances, including individuality dif-
ferentials, have a chance to pass continuously — although at a slow rate —
from one partner to the other; this takes place mainly by way of capillary
anastomoses, connections which gradually develop at the site of the peritoneal-

166

BLOOD VESSEL ANASTOMOSIS 167

skin junctions, but in some cases there may be, in addition, connections
through large omental blood vessels. To the peritoneal-skin union there is
usually added, in parabiosis, a union by skin flaps, which increases the size
of the area of vascular connection between the two animals. Characteristic
of parabiosis is, then, the combined action of two systems of bodyfluids and
of two kinds of individuality differentials in the same individual; however,
there is a great quantitative predominance of the animal's own constituents
over the strange ones carried to him from his partner. There are some
related parabiotic states which differ in various respects from the typical
parabiosis just described. Thus it is possible to transplant skin and certain
other organs to a strange individual by means of a pedicle containing blood
vessels, which keeps the transplant united with the original donor ; it then
received blood from the latter, while at the same time it receives bodyfluids
from the new host, and is accessible, to a limited extent, to the action of the
host cells. The union between child and mother in the uterus, by means of
the placenta, may also be considered as a modified state of parabiosis, in
which both organisms lead largely an independent life and in which both
carry on their own metabolism, but in which to a certain degree an exchange
of substances may take place through the placenta. In a still wider sense,
the condition of symbiosis, or of parasitism, may be considered a state of
parabiosis, in which host and symbiont or parasite carry on essentially their
own metabolism and function, each in its own peculiar manner, but in
which substances may be exchanged between the two organisms. We are
concerned here with these various conditions only in so far as the action of
individuality differentials on strange tissues, organs, or whole individuals
comes into play.

Transplantation by blood vessel anastomosis. Hoepfner (1903) first car-
ried out the retransplantation of an amputated leg in a dog by uniting blood
vessels, muscles and skin. The dog died as a result of an accident after
eleven days ; the vessels were found free from thrombosis ; skin and muscles
at the place of union between host and transplant showed satisfactory healing
and there was a tendency of the bones to unite. Several years later, Carrel
and Guthrie, Carrel, as well as Lexer and Giani, made similar experiments ;
but Carrel improved the method of blood vessel anastomosis and in addition
extended transplantation by this method to kidney, thyroid, adrenal gland
and ovaries. He believed that not only autotransplantation but also homoio-
transplantation of arteries may succeed. After a few months, the micro-
scopical structure of the transplanted vessels was almost, although not
entirely, normal. Both Carrel and Guthrie found that even after hetero-
transplantation of carotid from dog to cat, the vessels were normal after
more than one year. When rabbit vessels were grafted to a dog, the function
of the artery was maintained for a long time, but only the connective tissue
constituents of the arteries remained preserved. Not only autotransplantation,
but also homoiotransplantation, of kidney, thyroid, adrenal and ovary suc-
ceeded. The kidney functioned, although hydronephrosis and interstitial
nephritis were observed in some cases in the transplanted organ. Likewise,

168 THE BIOLOGICAL BASIS OF INDIVIDUALITY

homoiotransplantation of a leg from one fox terrier to another was successful.
The animal lived 22 days after the operation, all the tissues had healed,
there was no ulceration, and even regeneration had taken place when a toe in
the grafted limb was injured. A callus united the bone ends. In later experi-
ments, Carrel observed, in a homoiotransplanted kidney, secretion of urine
for 8 days, but the animal died after ten days. After heterotransplantation
of kidney, the transplant was absorbed a few weeks later. Lexer did not
find it possible to keep a transplanted leg in a dog alive for longer than
three weeks, and thrombi were found to develop in the transplanted tissues.
Giani however was more successful and a leg autotransplanted by him lived
for three months; there was good union but no active motion.

However, the results of careful microscopical studies made by Borst and
Enderlen on transplanted blood vessels showed that only autogenous trans-
plants survive for any length of time; homoiogenous and also heterogenous
transplants gradually die and are replaced by the tissues growing into the
transplant from the adjoining host tissues and wandering cells of the host
may accumulate at the point of union. In this place thrombi form more
frequently after homoio-, and especially after heterotransplantation, than
after autotransplantation. Autotransplantation of thyroid and kidney by
means of blood vessel anastomosis may succeed ; but after homoiotransplanta-
tion, hemorrhagic infarction, necrosis, or atrophy and fibrosis of the grafted
organ occur. Likewise Williamson found that the homoiotransplanted kidney
functioned only for a few days, while autotransplantation was successful,
except that atresia of the ureter could cause hydronephrosis and infection of
the graft. In case of syngenesiotransplantation of kidney within the same
litter of dogs, kidney function was maintained for 26 days. As to the length
of time during which homoiotransplantation of blood vessels may succeed,
Ingbrigtsen observed, in cats, that the carotids may remain alive for three
months; among 14 experiments, 8 satisfactory results were obtained. There
was no thrombosis in these latter cases, but this did occur in the other six.
Elastic fibers of media were normal, likewise muscle cells were well pre-
served, while intima and adventitia were thickened.

The interpretation of these investigations, as far as they are of interest in
the analysis of the individuality differentials, suffers from a lack of distinc-
tion, in the reports of the authors, between strict homoiogenous and
syngenesious (brother-sister) relationship in many of the experiments. Also,
too great a reliance was placed on a mere macroscopic examination of the
transplant, while careful microscopic studies of successive stages in such
transplantations were omitted. Furthermore, these experiments were made
largely from the viewpoint of the surgeon, who is interested in the possibility
of using such methods of transplantation in patients. Notwithstanding the
difficulties involved in a correct interpretation of the results of these investi-
gations, and of other similar ones, which need not be discussed, it may be
concluded that there is a marked difference between the fate of autogenous,
homoiogenous and heterogenous parabiotic transplants. The former may live
indefinitely if unfavorable conditions of a more or less accidental kind can be
avoided, whereas, the two other types of transplants in all probability die as a

BLOOD VESSEL ANASTOMOSIS 169

rule. Difficulties arise in the latter two, at the place of junction between the
vessels of donor and host because of tissue and bodyfluid incompatibility, and
thrombi often develop, but even without such thrombi, other than autogenous
tissues are injured and ultimately succumb. This applies also to homoio- and
heterotransplanted organs, which apparently regress relatively soon after
transplantation. There is some difference of opinion as to the length of
time during which transplanted pieces of arteries can remain alive, but this
seems to be a point of less importance. Certain connective tissue structures
may live presumably longer than the more sensitive constituents of these
transplants.

From a theoretical point of view, these transplantations by blood vessel
anastomosis are of special interest, because they make possible a separation
of the effects of the bodyfluids on transplanted tissues from those of the
host cells. The latter effects are, in all probability, as far as the incomplete
reports on the results of microscopical examination make an evaluation of
this factor possible, either entirely lacking or very slight under the given
conditions of experimentation. It is essentially the injurious action of body-
fluids, carrying disharmonious individuality and species differentials from
the host to the grafted tissues, which accomplishes the destruction of
homoiogenous and heterogenous tissues and organs. However, those investi-
gators who express an opinion as to the cause of the lack of success of
homoio- and heterotransplantations, as, for instance, Borst and Lexer, stress
two specific factors. In the first place, it is assumed that the homoiogenous
and heterogenous transplants cannot make use of the specific foodstuffs of
the host and, therefore, after using up their own reserve material, they
starve, and that secondly, cytolysins or related immune substances develop
as a result of processes of immunization taking place in the host. Even
Borst, who emphasizes the biochemical differences between host and trans-
plant as the primary cause of the state of athrepsia and immunization, has
in mind specificities inherent in various organs and tissues, which require
not only the adequate nourishment but also the normal function of these
structures in order to overcome adverse conditions. Biochemical differences,
in the way he applies this term, refer largely to or include the tissue
differentials. This concept differs therefore from that which holds the
differences in individuality and organismal differentials as primarily re-
sponsible for the changes characteristic of the various types of transplantation.

Transplantation by pedicled flaps. It is especially in skin transplantation
that pedicled flaps are used. This method of grafting tissue resembles trans-
plantation by blood vessel anastomosis, in so far as the transplant has, from
the beginning, a satisfactory blood supply, reaching it in this instance through
the vessels of the pedicle, which originate in the donor of the skin graft.
Secondarily, the skin flap makes connection with the vessels of the host, from
whom it then also receives blood. Thus its own blood vessels carry to the
transplant substances bearing autogenous individuality differentials, while
the blood vessels coming from the host carry to it substances bearing strange
individuality differentials. The pedicle-flap mode of transplantation, there-
fore, differs from that by blood vessel anastomosis, which has just been

170 THE BIOLOGICAL BASIS OF INDIVIDUALITY

discussed, in that in the latter case the transplant is supplied exclusively
with the blood of the host. However, in addition experiments have been
carried out in which, first, two animals were united by parabiosis and then
various organs were transplanted by blood vessel anastomosis from one
partner to the other. Likewise, skin has been quite commonly transplanted by
means of pedicled flaps to a parabiotic partner. Indeed, the transplantation
of pedicled skin flaps from one animal to another represents a rudimentary
parabiosis. If a pedicled skin flap is transplanted to another region in the
same individual, and the pedicle is cut after healing has taken place, the
transplant may continue to live during the lifetime of the person or animal.
In the case of homoiogenous transplantation the skin graft remains pre-
served usually as long as the skin is united by the pedicle with the circulation
of the donor and the transplanted tissue receives, through the blood, sub-
stances carrying its own individuality differentials. During that period it
is sufficiently under the influence of autogenous substances to be able to
resist the action of homoiotoxins which are active at the point of union.
But if, after healing has taken place, the pedicle is cut, the transplant is
fully exposed to the antagonistic reaction of the host cells, as well as to the
homoiotoxins of the bodyfluids of the host, and its fate does not differ from
that of the ordinary homoiogenous transplant, the advantage gained by the
flap method being merely temporary. It seems that, as in skin transplantation
by the ordinary method, so also by the pedicle-flap method, after the pedicle
is cut, the transplant may, at least in some cases, survive for a longer time,
perhaps even permanently, provided the individuality differentials of host
and graft are relatively harmonious, which may be expected especially if
syngenesiotransplantations are carried out. Thus Lexer succeeded in keeping
alive for eight weeks a skin-flap transplant from daughter to father. In
this case, the father received daily injections of blood serum from the
donor; when these injections were interrupted, the skin flap no longer re-
mained preserved but was cast off by the host. Lexer attributed this result
to the favorable action of the injections of donor serum, supplying suitable
foodstuffs for the transplant; but later experiments in animals by Lexer
and Keysser showed that such serum injections do not exert a beneficial
effect on the transplant and it may be assumed that the near relationship
of the individuality differentials of transplant and host was responsible for
the favorable results obtained.

Transplants of organs by blood vessel pedicles to a parabiotic partner
do not behave differently from corresponding pedicled skin transplants ; the
grafted organs undergo the fate of ordinary homoiogenous transplants and
die after the pedicle has been cut. We see, then, that it is essentially the
relationship of the individuality differentials which determines the outcome
in these transplantations, as it does in those of the ordinary type. However,
it seems that in man, not only strange individuality differentials but also
blood group antigens (A) may pass from one partner through the vessels
connecting the skin flap to the other partner, causing in the latter the pro-
duction of antibodies and leading here to the destruction of the blood cor-
puscles possessing the antigen A. This occurrence was observed by Lauer.

BLOOD VESSEL ANASTOMOSIS 171

But it is doubtful whether such an occurrence would take place in rodents,
in which experiments of this kind are carried out most frequently; here,
apparently, the actions of the individuality differentials greatly predominate
over blood group antigens, if the latter play any significant role at all in
these animals. The same considerations would apply also as far as the
interaction of the partners in typical parabiosis is concerned; here, too, it
is very doubtful whether in experiments in organisms other than man and
monkeys, blood group antigens would be of any importance. But in the
latter, they may be effective, and in man also the stage of pregnancy may
be of importance. In women it has been observed that especially the antigen
Rh may pass from the fetus to the mother, causing the production of anti-
bodies which then may lead to changes in the fetus (Wiener, P. Levine).

Parabiosis and individuality differentials. Parabiosis is an extension of the
method of transplantation by pedicle flaps, in which, in addition, union
usually takes place between two individual organisms by the joining together
of small areas of the peritoneal wall, and, in some cases, also of the intestines.
However, it is a method devised primarily for the purpose of joining to-
gether or transplanting on each other, two organisms which are able to live
independently, and which, in certain respects, continue to live independently
even after the union has been accomplished. Each organism takes its own
food and maintains its own metabolism ; each is united with its partner
mainly by means of capillary anastomoses, which gradually increase up to
about two weeks after operation, after which time there may be again a
diminution in the number of anastomosing capillaries owing to the pressure
exerted by the developing scar at the site of junction. It has been found that
the connection by lymph vessels is richer than that by blood capillaries ;
occasionally, though, there may be an additional connection by large vessels
in the omentum. The partners, corresponding to host and transplant, continue
therefore to be perfused largely by their own blood supply; but, at the
same time a not very intense, but continuous, inflow of strange body fluids
occurs, thus transferring to one partner products of the intermediary metab-
olism from the other partner, and above all, transferring also substances
carrying the individuality differentials of the other partner.

Locally, at the point of union, at first a large amount of granulation
tissue develops, consisting largely of fiibroblasts but containing also various
kinds of leucocytes; it is uncertain whether this abundant tissue formation
represents merely the sum of that which would normally be furnished by
each partner in the course of wound healing, or whether in addition the in-
fluence of substances strange to each partner exerts a special stimulation on
the granulation tissue. In contrast to the blood vessels of the two organisms
which communicate with each other and may grow from one animal into the
territory of the other, no spontaneous ingrowth of peripheral nerves takes
place, the nerves of each organism remaining separate. This is probably the
reason why diseases like rabies or tetanus, which are propagated mainly by
way of peripheral nerves, do not in parabiosis progress spontaneously from
one partner to the other. However, as Morpurgo has shown, it is possible to
establish experimentally a union of a nerve of one partner with a nerve of

172 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the second partner, and then an ingrowth of a peripheral nerve into the second
animal may take place and cross-reflexes between the two partners can be
established. Apart from these data, the sequence of events taking place in the
tissues adjoining the area of union has not yet been sufficiently examined
microscopically to determine whether at this point accumulations of lympho-
cytes occur comparable to those which are found around and in the ordinary
transplants of homoiogenous tissues. However, it is conceivable that the
constant supply of its own bodyfluids to the tissue of each partner alters the
reaction of the lymphocytes to the strange tissue of the parabiotic partner,
which would otherwise be found.

The general changes occurring at the site of union may vary greatly in dif-
ferent cases. In some instances, the tissues of the two partners may not unite
well and may separate soon after the operation ; or a temporary union may oc-
cur, which is followed before very long by a separation ; again, there may be
a long-continued union, which still may ultimately be succeeded by a shrink-
ing of the skin flaps and a separation. In the majority of experiments the
union seems to last not longer than a few weeks, but Morpurgo succeeded in
keeping a pair of parabiotic rats united for 9-12 months, and one case is
known in which the union between two rats continued for as long as two
years and five months (Goto). Rats are apparently best suited, and rabbits
next best, for parabiotic union, and it seems that union between other
species, such as cats or dogs, and perhaps even mice, can be established only
with greater difficulty. The results of parabiosis are most favorable between
young litter mates of about the same weight and sex; however, a union
between rats not belonging to the same litter nor to the same sex also may
succeed, but for technical reasons it is advisable to choose partners of about
the same age. As stated, the establishment of a syngenesio-parabiosis, where
the partners are brothers or sisters, is most favorable, although a homoi-
ogenous parabiosis may also succeed, but on the average less readily. Still
more difficult are unions between different races; but Irwin joined success-
fully different races of doves. A parabiotic union between individuals be-
longing to different species (heterogenous parabiosis) may, in rare instances,
succeed for a very short time; thus Lambert joined a rat and a mouse for a
maximum period of eight days, and even a union between a guinea pig and
rat succeeded for as long as eight days. However, under these conditions
no real wound healing occurred at the point of union and afterwards the
skin flaps separated as in cases of disharmonious homoiogenous union.

In parabiosis, a small amount of blood, of peritoneal fluid, of lymph and
interstitial fluid constantly passes from one partner into the other and here
it is mixed with a much larger quantity of the animal's own fluids. There is
reason, therefore, for assuming that the fluids of one animal reach, the cells
of the strange organism, but only in very great dilution, and before they come
into actual contact with the cells of the partner, they meet a current of fluid
from the latter passing in the opposite direction, namely, from the cells to-
wards the capillaries. The tissues thus constantly create their own indi-
viduality differentials, which move towards and mix with the very dilute
strange differentials in such a way that a gradient of these differentials de-

BLOOD VESSEL ANASTOMOSIS 173

velops. Hence the action of the bodyfluids of one partner on the other
is very imperfect. We notice, accordingly, that substances which have a
relatively low molecular weight and are not colloidal, such as KI, also prod-
ucts of the intermediary metabolism and certain toxins pass readily from one
partner to the other. Other substances which have presumably larger mole-
cules, with more colloidal properties, or substances such as some hormones
which have strong affinities for organs in their own body and are here held
back more readily, pass with greater difficulty and only under favorable
conditions from one partner to the other. For instance, following extirpa-
tion of the kidneys of one partner, it is this partner which is primarily af-
fected by the lack of these excretory organs ; it suffers therefore from
edema, also, in some cases, from hypertrophy of the left ventricle of the
heart, and only under favorable circumstances can the compensatory hyper-
trophy which may occur in this animal save it from death by uremia
(Morpurgo).

Similarly the interaction between the sex hormones takes place only im-
perfectly between the two partners, but castration of one partner may exert
a stimulating effect on the sex organs of the other partner through the
intermediation of the hypophysis (P. E. Smith, Matsuyama. Kellars, Mar-
tins, and others). If a pregnant and a pon-pregnant rat are united, a growth
may set in also in the mammary gland of the non-pregnant partner, but
the reaction in the latter is weaker and delayed, indicating that some inhibi-
tion exists in the transmission of this effect. A passive immunity can be readily
transferred from one partner to the other, but an active immunity can be
induced in one animal through injections of the antigen into his partner only
with greater difficulty; larger quantities of antigen must be used for this
purpose. Likewise, if an animal susceptible to leukemia is united by means
of parabiosis with a partner not susceptible to this disease, both individuals
retain their specific degree of resistance to it, the leukemia being transmitted
only to the susceptible individual ; but transmission is more readily effected
by injecting the leukemic blood cells into the susceptible animal directly
than by injecting them into the non-susceptible partner. Also, in the case of
a difference in susceptibility to transplanted tumors between two partners,
as a rule each partner retains its specific state of susceptibility or lack of
susceptibility; only in the case of Jensen rat sarcoma Zakrzewski observed
that a Wistar rat, not susceptible to this tumor, can be made susceptible to
it by the parabiotic union with a susceptible Warsaw rat. According to
Simonnet and Pretresco, if a normally faster growing male rat and a more
slowly growing female rat are joined in parabiosis, the growth rate of the
partners is intermediate between the normal developmental rates of the two
partners; an effect is thus transmitted in this case from each partner to the
other.

As to the general effect of two parabiotic partners on each other, it is
possible, in many instances, to distinguish two successive phases. As a rule
there is at first a harmonious phase, in which both animals are relatively
strong ; this is followed sooner or later by a disharmonious phase, in which one
of them becomes weak and atrophic, and eventually may die; but also the

174 THE BIOLOGICAL BASIS OF INDIVIDUALITY

surviving, dominating animal is usually not quite so well as it would have
been in the free state. In this disharmonious phase the tone of the blood
vessels is gradually lowered, especially in the weaker partner and towards
the end of its life, consequently the stronger partner pumps a considerable
part of its blood into the weaker one, which thus becomes hyperemic and
polycythemic, while the dominating partner is made anemic. The diminished
erythrocyte-destroying function of the spleen of the weaker animal has also
been held responsible for the developing polycythemia. In this animal there
are, in addition, atrophic changes in the inner organs and at last a fibrosis
of the bone marrow may occur ; in the stronger partner there occurs, on the
contrary, a stimulation of the various lymphatic organs and of the bone
marrow, with corresponding changes in the circulating cellular elements
originating in the bone marrow. Nodules consisting of reticular-endothelial
tissue may develop and accumulations of plasma cells may appear in the
connective tissue. As a rule, the weaker hyperemic partner, whose heart is
overloaded with blood, dies first, but occasionally the dominating though
anemic partner may succumb earlier.

As to the cause of the disharmony which may develop, as early as in the
second or third week after the union has been established, but much later
in other cases, various suggestions have been made. Which of the two
partners will be the less resistant one and will be ultimately suppressed
seems usually to be determined by accidental factors, such as the presence
of some inferiority, as for instance, lack of a kidney, at the time when
parabiosis was established. The fact that disharmony develops at all has
been attributed by some investigators to a state of undernourishment, on
the assumption that the stronger partner deprives the weaker one of food-
stuffs ; however, the weaker partner often consumes a large amount of food
and, also, the stronger partner may lose somewhat in weight. According to
Hermannsdorfer, disharmony arises from the passing of intermediary
metabolic products from one animal to the other. The increased toxicity of
the urine in parabiotic animals, as indicated by the production of convul-
sions in other animals injected with such urine, has been considered as due
to these substances. However, it is not probable that such metabolic products,
which are present and are about the same in all normal individuals of the
same species, are the essential cause of the disharmonious state.

Another view as to the underlying factor in this condition is held by a
number of authors, who believe that a state of chronic anaphylaxis exists,
due to the constitutional biochemical differences between the two partners,
such differences arising from inherited differences in various organs. The
dilatation of the vessels which is observed in the weaker partner is often
cited as an important argument in favor of this view ; but, this condition of
the vascular system may be the result of general weakness rather than of
specific anaphylaxis. Furthermore, if the two partners during the phase of
disharmony are separated, a recovery of both may take place, and if subse-
quently, parabiosis is re-established, no sign of hypersensitiveness becomes
noticeable. Moreover, the production of the well-known immune substances,
such as hemolysins, agglutinins, or precipitins, can not usually be demon-

BLOOD VESSEL ANASTOMOSIS 175

strated in parabiosis, although it seems that under special conditions hemol-
ysins may develop. Thus Irwin found that in two different races of doves,
in which no blood groups can be shown to exist, hemolysins may be pro-
duced ; but in this case we have to deal not with a homoiogenous parabiosis,
but with one approaching a heterogenous type. Also, Majeda states that he
has observed the presence of hemolysins in a few cases. But the other
investigators who have searched for hemolysins in parabiosis did not find
them ; or in those instances in which they were present, they had, in all
probability, not been produced in response to the action of blood group
antigens in the other partner, the existence of which could not be established,
but they may have been due to the antigenic action of certain heterogenous
or homoiogenous gene sets or their derivatives. The usual absence of the
ordinary immune substances in parabiosis renders improbable also the exist-
ence of antibodies responsible for a state of anaphylaxis.

We suggested (1930) the possibility that substances which carry the
individuality differentials are given off in small quantities by various organs
of one partner and enter the circulation of the other, and that these may
account for the gradually developing disharmony, the increasing atrophy of
organs, and the weakness in the partner which was inferior from the be-
ginning. Such substances may be expected to stimulate the lymphocytic and
also the reticulo-endothelial system of tKe other partner, in accordance with
the usual stimulation of lymphocytes in ordinary homoiogenous transplanta-
tion. These homoiogenous substances may thus conceivably function as very
slowly acting toxins and secondarily may give origin also, although only
feebly, to immune substances specifically directed against the individuality
differentials of the partner.

In favor of this view, several facts may be cited : in the first place there
is a parallelism between the genetic relationship of the parabionts and the
rapidity with which disharmony is established and the intensity of the latter.
As we have mentioned, the success of parabiosis essentially parallels the
relationship of host and donor, in the same sense in which success of trans-
plantation depends upon this factor; as in syngenesiotransplantation, es-
pecially in inbred strains, where the reaction against the transplant may
become manifest only after a long period of latency, so also under favorable
conditions of parabiosis the stage of disharmony may develop only after a
long preceding harmonious state. Furthermore, the healing of the skin flap
at the site of union of the parabionts behaves in a way which approximately
corresponds to the genetic or pedigree relationship of the two partners ; the
healing-in succeeds the better the more compatible the two partners are
with each other and the longer the harmonious phase lasts (Gohrbandt).
During the disharmonious state it is especially the stronger partner which
reacts more markedly against the skin flap. Of special interest in this respect
are also the experiments of Majeda, who transplanted skin from one rat
to another preceding and following the establishment of parabiosis. He found
that those animals between which skin could readily be exchanged and re-
main preserved for some time were better adapted for parabiosis experi-
ments, than were other animals in which skin transplants did not heal in a

176 THE BIOLOGICAL BASIS OF INDIVIDUALITY

satisfactory manner; if animals of the latter type were used, disharmony
appeared earlier. Inasmuch as the conclusion is justified that the local re-
actions affecting transplanted skin are due to the action of strange individu-
ality differentials, it seems also justifiable to conclude that, essentially, dif-
ferences in individuality differentials are the cause of the disharmony which
develops sooner or later in parabionts. Schoene, Majeda, and others, found
furthermore that instead of improving the outcome of homoiogenous trans-
plantation of skin, parabiosis, on the contrary, seemed to make the results
more unfavorable, and similar observations were made also in autotrans-
plantation. It is possible that the intensified injury, inflicted upon homoi-
ogenous transplants as a result of parabiosis, is caused by an increase in the
immune reactions against strange individuality differentials taking place
under homoiogenous conditions. As to the injurious effect on autogenous
grafts, we must consider the fact that a real autogenous transplantation in
parabiotic animals is not possible, inasmuch as homoiogenous individuality
differentials, even if much diluted, are continuously given off by the partner
and must, to some extent, affect the condition of the autotransplant.

We may then conclude that in all probability strange individuality differen-
tials are responsible for the injurious general as well as local reactions affect-
ing partners in parabiosis, as for instance, for the damage inflicted on
transplanted pieces of skin or of other organs, but that in addition to these
primary direct actions of the strange individuality differentials, also immune
reactions against these antigens may be active.

We have referred already to the analogy which exists between the state of
pregnancy and that of parabiosis. However, pregnancy differs from true
parabiosis in three respects : ( 1 ) In pregnancy, we have not to deal with the
union of two formerly independent partners, able to sustain themselves in a
free state, but with the development of an embryo and fetus inside the
mother's organism; (2) the blood vessel connections between fetus and
mother, by way of the placenta, are much more extensive than those exist-
ing between true parabiotic partners, and (3) the embryo and fetus receive
essential foodstuffs from the mother. During pregnancy there is no indication
that strange individuality differentials injure fetus or mother. Perhaps an
enlargement of the lymphatic organs which may appear in the fetus might
point to a late effect of strange individuality differentials, but this inter-
pretation appears uncertain at present. On the other hand, it has been shown
that in some rare cases antibodies may develop in the mother against blood
group differentials present in the fetus, a point which has already been dis-
cussed. It is probable that during embryonic and fetal development an adap-
tation takes place against strange individuality differentials in both mother
and fetus.

Also, parasitism may be considered as a condition resembling parabiosis.
But this condition differs from true parabiosis in the very great inequality
distinguishing host and parasite. The parasite lives at the expense of the host
and is adapted in a peculiar manner to the host and to one or more of its
organs. A further discussion of this relationship will be taken up in a later
chapter.

Chapter l8

Modification of the Reaction of the Host Against
Strange Individuality Differentials by Transplan-
tation of Tissues Into the Allantois of Chick
Embryos, Into the Brain, or Into the
AnteriorlChamber of the Eye

It has not been possible to prevent the injury or destruction of homoi-
ogenous or heterogenous transplants by immunization of the host with
blood or tissue extracts of the donor, or, conversely, by treating the
donor with similar substances obtained from the prospective host. On the
other hand, in a limited way, it was possible to protect the transplant against
aggression by the host by inactivating the reticulo-endothelial system of the
latter by means of injections of trypan blue. Previous to the last mentioned
observations it had been shown that heterogenous mammalian tumors were
able to grow in the chorio-allantois of the developing chick (Rous and Mur-
phy), and subsequently the mechanism of this condition was analyzed by
Murphy and his collaborators in a series of investigations. Murphy could
show that after transplantation of a piece of spleen, and to some extent also
of bone marrow, previous to or simultaneously with the transplantation of
heterogenous tumor or of heterogenous embryonic tissue into the chorio-
allantois, the transplants were destroyed in the same way as they were in adult
hosts. The spleen tissue initiated the reactions of the embryo-host which, in
the fully developed adult host, prevent the growth of heterogenous tumors
and embryonal tissues, and correspondingly, the chicken embryo spontaneous-
ly became resistant to these strange transplants as soon as the embryonic
development had reached the stage when the organs of defense could function.
According to Murphy, these defense mechanisms consist largely in the ac-
tivity of the lymphocytes, which call forth a state of immunity in the host.
The immune processes thus produced acted not only against strange tumors,
but they could also inhibit the growth of autogenous tumors and they were
the same as those which protected the organism against pathogenic micro-
organisms, such as tubercle bacilli. All the means which injure or destroy the
lymphocytes, weaken or remove the immune processes in the host and allow,
therefore, tumors to grow or tuberculosis to spread, while those mechanisms
which tend to stimulate the multiplication and activity of the lymphocyes, tend
to intensify the immune processes and to protect the organism. By the applica-
tion to the host of X-rays, dry heat, benzene, and certain other means which
injure the lymphocytes, it is therefore possible to enhance the growth of
malignant tumors in the organism.

177

178 THE BIOLOGICAL BASIS OF INDIVIDUALITY

As mentioned already, it is only at a certain stage in the embryonic develop-
ment that organismal differentials are fully developed, and there is every
reason to assume that the development of the mechanisms which are directed
against strange organismal differentials takes place only subsequent to the
complete formation of the organismal, and, in particular, of the individual-
ity differentials. As we shall discuss more fully later, even in the very
young guinea pig not long after birth the reactions against homoiogenous
tissues are weaker than in older animals. The experiments of Murphy suggest
very strongly that the spleen and the reticulo-endothelial system in general are
the tissues which originate these mechanisms of defense, or at least aid in
their development. We have furthermore seen that the lymphocytes are at-
tracted by strange individuality differentials and that they may help in the
destruction of homoiogenous tissues ; but it is possible that also the individu-
ality and species differentials, which are attached to certain substances in the
bodyfluids and which exert a primary toxic effect on homoiogenous and
heterogenous tissues, may develop with the aid of the reticulo-endothelial
system. These considerations concerning the lack of individuality differentials
and of the mechanisms of reaction against the latter in early embryos, would
then explain why the chorio-allantois of the chick and, according to Murphy,
also the chick embryo as such, do not oppose the preservation of heterogenous,
actively-growing tissues, such as malignant tumors and embryonal tissues.
According to Taylor, Thacker and Pennington, it seems that mammalian
tumors grow very well also in the yolk sac of the chick embryo.

There are also, in adult animals, at least two sites where heterogenous
tumor transplants may survive, namely, the brain and the anterior chamber of
the eye. Shirai found that heterogenous tumors, which cannot be successfully
transplanted elsewhere, may grow when transplanted into the brain. Murphy,
who obtained similar results, observed that around such heterogenous trans-
plants in the brain the usual lymphocytic reaction is absent; but, as in the
case of transplantation into the allantois, a lymphocytic reaction can be called
forth if simultaneously with the grafting of the tumor a piece of spleen is
transplanted into the brain. However, when Harde transplanted homoiogenous
tumors to the brain, no differences in results between the brain and the usual
sites of transplantations were noted. Siebert compared with the reactions
against tumor tissue, those against homoiogenous thyroid transplants in the
guinea pig, the time of the examination of the graft varying between 20 and
120 days after transplantation. He found the amount of homoiogenous thyroid
gland that was preserved in the brain less than that of autogenous transplants.
Much fibrous-hyaline tissue developed in or around the homoiogenous graft.
After 20 to 30 days, only a few small acini were preserved in the hyaline
stroma. Lymphocytic infiltration appeared in the fibrous tissue invading the
transplant and some scattered lymphocytes also surrounded the brain tissue,
but on the whole, the lymphocytic infiltration was much less intense than after
transplantation into subcutaneous pockets. The homoiogenous thyroid tissue
remained longer preserved in the brain than it is usually in the subcutaneous

MODIFICATION OF REACTION OF THE HOST 179

tissue, and it is possible that at a later period a moderate newformation of
acini may have taken place in the graft in this site. We may then conclude
that while in and around transplants of normal homoiogenous tissue the
lymphocytic infiltration is diminished in the brain, the connective-tissue re-
action is at least as marked as after subcutaneous transplantation. The mech-
anism which exerts a certain protective influence on homoiogenous grafts in
the brain is therefore exactly the reverse of that which is active in young, as
compared to older hosts. In young hosts the connective-tissue reaction is
diminished, whereas the lymphocytic infiltration may be very marked; in the
brain, the connective-tissue reaction may be quite pronounced, whereas the
lymphocytic infiltration is weak. As to the difference in the mode of reaction
in brain and in subcutaneous tissue of young animals, it seems improbable that
this is caused by a lack of individuality differentials in the brain ; it is more
probable that the blood-brain barrier (L. Stern) prevents the homoio-toxin
from reaching the brain in full strength, or at least diminishes its effective-
ness. However, the possibility cannot be excluded that also other factors may
be involved in this process.

Likewise in the anterior chamber of the eye transplantations, especially of
organs with internal secretion, have been shown to succeed better than those
made subcutaneously or intraperitoneally. Of considerable interest are the
intra-ocular transplantations of testicle. As a rule, the testes of newborn
animals, in particular those of rats, were used in these experiments, for in-
stance, in the work of Pfeiffer, which we have already mentioned, and in the
extensive investigations of G. D. Turner; furthermore, in rabbits (Bayer and
Wense) conditions seem to be similar. The functioning of these transplants
is greatly influenced by hormones ; their presence exerts a stimulation favor-
able to spermatogenesis and their absence appears to cause degenerative
changes in the more sensitive cells, so that only Sertoli cells survive. In all
probability, stimulation by certain hormones is necessary to ensure the survival
and function of the most differentiated cellular constituents of endocrine
organs, particularly if these organs are under environmental conditions which
are not quite adequate. Because the function of the sex organs may inhibit the
formation of such stimulating hormones, these transplants may be more suc-
cessful in castrated than in normal hosts, and in younger, sexually immature
hosts than in older ones. However, it must be mentioned that the very favor-
able results of Turner were due to the fact that in addition to the very young
age of the donors, donors and hosts were litter mates and the rats belonged to
an inbred strain. These conditions eliminated to a great extent the action of
unfavorable individuality differentials. But, it seems that after all, the in-
dividuality differentials of hosts and transplants were not entirely com-
patible in these experiments, and that under less favorable hormonal condi-
tions these differences between the differentials could assert themselves and
cause an invasion of the transplant by connective tissue and lymphocytes ; at
least this is the interpretation which might be given to some of Turner's ex-
periments. That the organismal differentials do assert themselves also in the

180 THE BIOLOGICAL BASIS OF INDIVIDUALITY

anterior chamber of the eye is indicated by the fact that heterogenous testes
and ovaries survived only up to 20 days, and that at a later date only fibrous

tissue was found.

The ovary seems to behave after intra-ocular transplantation in a similar
way to the testis (Goodman, as well as Lane and Markee) ; however, the
various constituents of this organ are, on the whole, more resistant than those
of the testis. In the case of both of these organs, hormones may affect not only
the transplants, but the latter also give off hormones which may leave the eye
and affect distant organs. In intra-ocular transplants of seminal vesicles and
prostate of the rabbit, R. A. Moore and his collaborators have found that the
effects of repeated stimulation of the transplants by hormones follow a definite
curve; the growth response is strongest in the beginning and then soon

declines.

In intra-ocular transplantations of the adrenal gland, conditions are in
principle similar to those of the testicle, as a comparison of the results of
adrenal transplantations into the eye (Turner) and elsewhere (Wyman and
Turn Suden, Atwell, Ingle and Higgins) indicate. Here also, stimulation by
the specific anterior pituitary hormone which occurs especially in adrenal-
ectomized animals, is important. However, under the more favorable condi-
tions existing in the anterior chamber of the eye, cortical glomerulosa tissue
may grow, differentiate, and survive for a long time, even in non-adrenalec-
tomized animals ; in these experiments, also, the organs of very young animals
were used for grafting. But the stimulation by the pituitary hormone in
adrenalectomized animals, or the repeated transplantation of pituitary lobes,
enhanced the growth and the percentage of survivals.

Likewise, after intra-ocular transplantation of the hypophysis the grafts
remain well preserved. The different types of hypophyseal cells are affected
in the usual way by various hormones, and, conversely, transplants of the
hypophysis through their own hormones may affect other organs (R. M.
May, Haterius, Schweizer and Charipper, Martins) ; but as mentioned pre-
viously, pituitary transplants survive for a long time also after subcutaneous
transplantation in mice, if the individuality differentials of host and donor
are relatively harmonious.

So far, we have studied only the fate of intra-ocular transplants of tissues
which were very young or were derived from litter mates and which had,
therefore, special advantages. However, in order to differentiate between the
factors which distinguish the reactions against strange individuality differen-
tials in the anterior chamber of the eye and in the subcutaneous tissue, it is
necessary to transplant into the eye adult tissue and, preferably, thyroid gland.
We carried out heterogenous as well as homoiogenous transplantations of rat
thyroid, into the eye of the guinea pig. Living homoiogenous thyroid tissue
was found at various times from 20 to 50 days after transplantation. There
was a diminution of both the intensity of the connective-tissue and the lympho-
cytic reaction against the transplant, which for this reason may have shown a
slightly better preservation. But neither invasion by fibrous tissue nor lympho-
cytic infiltration was entirely lacking in and around these transplants. After

MODIFICATION OF REACTION OF THE HOST 181

heterogenous transplantation of thyroid from rat to guinea pig, living acinar
tissue was found in two cases 10 days, and in two other cases, 18 days after
transplantation; there was formation of hyaline connective tissue in and
around these heterogenous transplants, and in some instances polymorpho-
nuclear leucocytes collected around them. At dates later than 18 days, the
transplants had disappeared. In this case, also, the results were somewhat
better than in heterogenous transplantations into the subcutaneous tissue.

If we compare with these results, those obtained after intra-ocular trans-
plantations of malignant tumors, the latter are much more striking. In a
number of instances it has been possible to obtain active, continued growth in
the anterior chamber of the eye, where none was found subcutaneously, and
even heterogenous tumors, including human tumors, grew, in contrast to the
subcutaneous grafts of this tissue. The difference between the growth of
tumors obtained in these two sites is much greater than that of normal adult
tissue. Results of this kind have been recorded by Smirnova, by Greene, by
Greene and Saxton, by Appel, Saphir, Janota and Strauss, and by Cheever
and Morgan; but Greene found that not all heterogenous tumors could be
successfully transplanted into the eye; and the degree of success seemed to
depend upon the original growth energy of the tumor used for transplantation.
In some instances, also serial transplantations in the eye were successful.
After retransplantation to the subcutaneous tissue, of tumors that had grown
in the eye, the tumor cells died. The greater power of survival and growth of
tumors in the anterior chamber of the eye as compared to that of ordinary
tissues is in part probably due to the greater growth momentum inherent in
tumors, which leads to a multiplication of the advantages offered by conditions
in this site as compared with those present in the subcutaneous tissue. How-
ever it is possible that still another factor is active, namely, the diminution
or lack of immune substances in this region. Tumors, as a result of their
growth in hosts bearing different individuality differentials, as a rule seem to
give rise to immune processes to a higher degree than do normal tissues, per-
haps at least partly on account of their increase in mass, which takes place
with relatively great rapidity, and tumors are very sensitive to the injurious
action of such substances, especially during the first period following trans-
plantation. In the case of ordinary tissues, as we have seen, the primary
homoio- and heterotoxins are apparently very much more important in the
determination of their fate after transplantation than are the immune sub-
stances, although the latter may play some role also ; however, in the case of
tumors there is evidence that though the primary homoio- and heterotoxins
likewise help to determine the result after transplantation, the immune sub-
stances are of much greater consequence. But it has been shown by Becht
and Greer, and by Hektoen and Carlson, that the titer of immune substances
is much less in the fluids of the anterior chamber of the eye than in the
blood, or it may be lacking altogether in the former when it is present in
the latter region; and more recently, Appel, Saphir, Janota and Strauss
have stated this to hold good also for immune substances produced by
the growth of the Brown-Pearce tumor in rabbits. This condition would help

182 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to explain the special advantage which the eye offers for the growth of certain
transplanted tumors, as compared with the subcutaneous tissue or other sites.
Against such an interpretation are the recent experiments of Greene, as well
as those of Cheever and Morgan, which indicate that a transmission of im-
mune processes may take place between the aqueous humor of the eye and the
circulating blood, although again, the results of these investigators, working
with different types of tumors, differ as to the degree to which such an ex-
change may occur. Moreover, as Greene points out, the growth of tumors is
enhanced if the testicle is used as the site of transplantation, and in this organ
such a barrier between blood and organ constituents does not, in all proba-
bility, exist. Also, in other kinds of transplantations the testicle has been
found to be a favorable site ; thus, according to Stockard, homoiotranspJanta-
tion of the ovary in the salamander Diemyctylus, succeeds only in the testicle ;
likewise, the Pearce-Brown rabbit tumor is advantageously propagated by
grafting it into the testicle. The most probable conclusion in regard to im-
mune substances, at the present time, seems to be that a certain degree of
interference with the exchange of these substances between blood and the
fluids of the eye may play some part in favoring the growth of tumors in the
anterior chamber of the eye, but it may not be the only factor concerned.
However, it is possible also that the primary homoio- and heterotoxic sub-
stances may pass only with greater difficulty from the circulating blood or
lymph into the fluid of the anterior chamber, and that this condition may
contribute to the advantage which transplantation of tumors into the eye has
as compared to the subcutaneous tissue; furthermore, fluid in this site sur-
rounds a part of the periphery of the transplant and this may favor a continu-
ous removal of individuality differential substances functioning as homoio-
or heterotoxins, from the transplant. But, as stated, there exists the further
possibility that still other, as yet unknown, factors may cause a mitigation of
the injurious reaction of the host against transplants in special locations, in-
cluding the anterior chamber of the eye.

Transplantations into the eye have contributed additional information as to
the effect of hormones on the survival and growth of transplanted endocrine
organs. By means of these transplantations, more evidence has been obtained
for the conclusion that various secreting cells living under unfavorable con-
ditions, may not be able to sustain themselves without receiving stimulation
by specific hormones; a certain degree of disharmony between the individu-
ality differentials of host and transplant may be one of these unfavorable con-
ditions. Strange individuality differentials bringing about degenerative effects
in the transplant, as, for instance, in the ovary and adrenal cortex may help
to induce connective tissue cells as well as lymphocytes to react very strongly
against tissues bearing these strange individuality differentials, in the man-
ner already indicated in the discussion of transplantations of ovary and
adrenal gland in the mouse. By inhibiting or preventing these degenerative
alterations, hormones may protect the transplanted tissues against these in-
tensified reactions, especially of lymphocytes. It has likewise been shown
that the activity of the connective tissue providing the stroma of organs is

MODIFICATION OF REACTION OF THE HOST 183

partly conditioned by the activity of the epithelial tissues. The latter therefore
help to determine whether the stroma shall be cellular or fibrous in charac-
ter ; by stimulating the function of the parenchymatous tissues, hormones may
thus indirectly also affect the character of the stroma. It may then be stated
again that one of the factors which aids in the survival and function of certain
differentiated and therefore sensitive endocrine tissues, is not so much a de-
ficiency in function of the corresponding host organ, as a stimulation of the
transplant by the effective hormone of the host. The deficiency required may
be merely a means of accomplishing a stimulation of the transplant by the
hormone.

In conclusion, it follows from the data discussed in this chapter that in
certain organs of the adult host, or in embryonic structures, various special
conditions exist, which protect at least, to some extent tissues possessing
strange individuality or species differentials from the injurious action of the
bodyfluids and cells of the host, but that the nature of these mechanisms is,
at the present time, only imperfectly understood.

Chapter Ip

The Relations Between Age and Individuality

Differentials

The French surgeon, Oilier, observed, during the latter half of the
last century, that autotransplants of skin and periosteum grew much
better in young than in older individuals, where they grew only
temporarily. Also, Schoene noticed that old age is unfavorable for trans-
plantation of skin and that in old rats even autotransplantation may yield
bad results. Kozelka found, in transplantation of skin into fowl, that the
adult host had greater resistance to grafts of strange skin than the chick
and that also the adult tissue is less able to adapt itself to an adult host
than the young tissue to a very young host, and furthermore, that young
grafts in young hosts remain alive or regress only slightly when the host
becomes older. He assumed that the milder form of tissue antagonism present
in the host enabled it to eliminate the incompatible elements, without totally
destroying the tissue. According to Pfeiffer, the gonads of immature animals,
and especially those of immature rats, take more readily than those of adult
rats. On various occasions we have compared the reaction against strange
grafts in young and in older rats and guinea pigs. In the young, inbred
King rats the reaction against transplants of various tissues was milder than
in older rats, and not only against transplants within the inbred strain, but
also against those from hybrids, in which latter a constituent had entered
which was strange to the member of the inbred parent strain serving as
host. In experiments in mice we had observed that in somewhat older mice
the reaction against the transplant was, in certain cases, stronger than in
very young mice, although this did not need to be the case in all experiments.
In older mice, from 10 months to 20 months old, transplants of various
tissues from younger animals could be as well preserved as in younger hosts,
and the reaction was not noticeably more severe in these old mice than in
younger adult mice.

There remains the problem as to the mechanism by means of which age
affects the transplants and in this respect experimental evidence is as yet
slight; it will be necessary especially to consider separately the effect of age
on the host and on the transplanted tissue. If even in autotransplantations,
skin and bone grafting is less favorable in older than in younger individuals,
this is possibly due to the better vascularization and to the greater tendency
of the connective tissue to remain more cellular and less fibrillar in younger
organisms. This condition seems to be independent of the reaction of the
individuals serving as donors and as hosts against strange individuality dif-
ferentials ; it is related, in all probability, to the fibrous changes in the stroma,

184

AGE AND INDIVIDUALITY DIFFERENTIALS 185

which are characteristic of older age in various organs. Carrel has found
that the blood serum of older animals is less suitable as a medium in which
tissues grow in vitro than is that of younger individuals. However, it is not
certain that this factor plays a significant role in the living organism.

We approached this problem by means of transplantation of the thyroid
gland in guinea pigs. Our observations showed that within the first 10 days of
extrauterine life of the host the connective-tissue and lymphocytic reactions
against homoiogenous thyroid gland are less intense than in adult hosts.
Tureen then compared, in our laboratory, transplantations of thyroid glands
in which adult guinea pigs were the donors and in which the donor-age was
therefore constant, while the age of the host varied. In the group of young
hosts the age varied between 4 days and 5 weeks, while in the group of older
hosts variations in weight between 500 and 800 grams indicated corresponding
variations in age. In the first 4 or 5 days the reaction was about the same in
both groups. But from then on a difference developed : in the older guinea pigs
there was a more marked formation of fibrous tissue, which destroyed a con-
siderable part of the transplant, and, in the majority of cases, destroyed it en-
tirely after 20 days or more had elapsed. In the younger animals the formation
of the fibrous tissue was considerably less in most of the animals and the
thyroid tissue was therefore better preserved. But in a certain number of
instances there was a marked fibrous reaction also in the younger guinea pigs.
However, because in the majority of the younger group the preservation of
the gland was so much better, the homoiogenous individuality differentials
were here subsequently given off in larger quantities ; these then attracted the
lymphocytes, which, somewhat later, surrounded and invaded the transplant in
considerable numbers and, secondarily injured it. In younger animals, as a
rule, there is therefore a tendency for the homoiogenous tissue to elicit a syn-
genesio rather than a severe homoiogenous reaction. A combination of homoiog-
enous individuality differentials, and a relatively older age of the host, led
thus to an early increase in the formation of fibrous tissue in or around the
transplant. Under the influence of not well compatible individuality differen-
tials the stroma developing in the transplants in adult animals is inclined to as-
sume prematurely the fibrous character which is so characteristic of the bodily
structures in old age. Because of these injurious effects grafts in older hosts
were, then, less liable to attract lymphocytes than the better preserved tissues
of younger animals. But when in older guinea pigs the preservation of the
thyroid tissue happened to be better, in such animals, also, a larger number
of lymphocytes were attracted ; hence it is the strong connective-tissue reac-
tion in the older animals which in these instances caused the difference in
the fate of the graft in the old and in the young guinea pigs. Whether an
increased toxicity of the bodyfluids in older hosts contributed to the ac-
celerated and intensified injury of the graft is difficult to determine, because
the injury by the connective tissue was so marked that it might have obscured
a damaging effect of the bodyfluids. We have already remarked that in old
mice, transplants of thyroid and cartilage and fat tissue could do as well as
in younger animals.

186 THE BIOLOGICAL BASIS OF INDIVIDUALITY

As to the reason why transplantations from very young donors may succeed
better than those from older ones, our knowledge is still less definite. How-
ever, by means of the white blood cell reaction Blumenthal could show that
both tissues from early as well as from later stages of rat embryos elicited a
lymphocytic reaction after transplantation into adult rats; but rat or mouse
embryos obtained during the first half of pregnancy called forth, in a
heterogenous host, merely an increase in lymphocytes, as an indication that
the organismal differentials were not yet fully formed at this period ; a short
time before the end of pregnancy the typical heterogenous reaction did
develop. In this connection, the fact must be recalled that also implantation
of non-living protein substances, may call forth a lymphocytic reaction and
it is therefore possible that a non-specific or at least a less specific, factor
caused the effect which very young embryonic tissue exerted on the lympho-
cytes of the host. It may then be concluded from these experiments that the
organismal differentials are fully developed in newborn animals, and if tissues
from very young donors survive better in homoiogenous hosts than those
from older ones, this must be due to other factors than lack of differentials.
In this regard we have to consider, in the first place, the greater growth
momentum of the younger tissues, and perhaps also their greater adaptability
to inadequate environmental conditions. The increased growth momentum
may be able to overcome injurious conditions, which more slowly growing,
adult tissues cannot overcome so readily. This view would be in harmony with
the experience that transplanted rapidly growing tumors which possess a
strong growth momentum may be more resistant to the action of unfavorable
individuality differentials than normal tissues, and, similarly, embryonic
tissue may be more independent of the action of such differentials.

There is still a further point to be considered. Certain organs from old
animals show changes which make them less suited for transplantation than
the corresponding organs from younger ones; thus the ovaries of older mice
and of other species contain few follicles, and the thyroid gland in certain
strains of mice undergoes sclerosis ; these are conditions not favorable to a
good development and function of the essential constituents of the organs
when transplanted.

We have attempted in this analysis to separate the various factors which
may cause the difference in the results in carrying out transplantation experi-
ments, using young and old animals as hosts and donors, and we have found
that the individuality differentials are fully developed in young donors and
that a lack of the differentials is not one of the factors that causes the
difference in the results of homoiotransplantation in animals of different
ages. The greater tendency to the formation of fibrous tissue in older,
homoiogenous hosts and the greater growth energy of younger tissues may
explain at least some of these differences.

Chapter 20
Individuality Differentials and Tissue Culture

In the living organism, tissues bearing strange individuality differ-
entials are injured by the homoio- or heterotoxins circulating in the
bodyfluids of the host, as well as by the cells of the host. The relative
importance of these two injurious factors differs in different species and
with different tissues. In higher organisms, the reactions against tissues
bearing homoiogenous individuality differentials are, as a rule, severe;
however, if tissues are grown in tissue culture, no special difference in the
effect of autogenous and homoiogenous serum or plasma serving as media
is noticeable. This follows from the observations of I. T. Genther and the
writer, which showed that the number of mitoses in the guinea pig thyroid
was about the same in vitro in autogenous and homoiogenous serum, when
it might be expected that quantitative differences in mitotic activity would
serve as a delicate indicator of the injurious influence of homoiotoxins. Like-
wise, the differences between the effects of homoiogenous and heterogenous
plasma or serum on tissue growing in vitro are much less than are the
corresponding differences between the effects of homoiogenous and heterog-
enous hosts on tissues transplanted into living animals. Thus Lambert and
Hanes noted that rat sarcoma cells may grow in guinea pig plasma for 30
days, in rabbit plasma for about 12 days, in dog plasma for 2-3 days, and in
pigeon plasma for 4-5 days, but no growth of rat or mouse tumor cells took
place in goat plasma. Also, motile cells of the spleen could grow out in
heterogenous plasma, and both rat sarcoma and rat spleen produced giant
cells in such a medium ; a culture of fibroblasts remained active, for a certain
time at least, in a heterogenous medium, but the injurious effect of hetero-
toxins became manifest more readily in normal fibroblasts than in certain
tumor cells (A. Fischer). There may be active in these cases, both the
strange organismal differentials, whose effect is graded in accordance with
phylogenetic relationship, and special toxic substances, whose action does
not correspond directly to this relationship.

The same two factors play a role also in amphibian tissues growing in
vitro. Thus, Rhoda Erdmann cultivated skin of Bufo first in Bufo plasma
and Bufo spleen extract, next in Bufo plasma and frog spleen extract, and
in the end in frog plasma and frog spleen extract; by these means a gradual
adaptation of tissues to strange organismal differentials was achieved. The
skin of another amphibian species could likewise be cultivated in combina-
tions of heterogenous plasma and tissue extracts. Hitchcock found that frog
skin of a certain species grew equally well in autogenous and in homoiogenous
plasma or serum, and also in the bodyfluids of heterogenous species of
Rana. However, frog skin was rapidly killed in vitro by Necturus plasma

187

188 THE BIOLOGICAL BASIS OF INDIVIDUALITY

and Necturus skin was similarly affected by frog plasma. But skin of
Necturus, as well as of Triturus, grew well in plasma and serum of Necturus.
It may then be concluded that the differences in the reactions against other
than autogenous tissues are much less when the tissues are grown in homoi-
ogenous or heterogenous serum or plasma, than when they are placed in
homoiogenous or heterogenous living hosts. However, it must not be con-
cluded from these and other similar experiments that no differences exist,
as far as tissues growing in vitro are concerned, between the effect of
homoiogenous and heterogenous media; results obtained by Hitchcock al-
ready suggest that such differences do exist. Likewise, experiments with
mammalian tissues indicate that homoiogenous plasmas and sera are pre-
ferable to heterogenous ones, although the admixture of heterogenous tissue
extracts to such media seems not to interfere seriously with the life and
growth of tissues under these conditions. Thus it has been possible for fibro-
blasts from the subcutaneous tissue of the adult mouse to grow actively for
many successive generations in a culture medium of chickenplasma, chick
embryo extract and horseserum without serious interference with the pro-
liferation, motility and structural potentialities of these cells.

There exist various differences between tissues living in their normal
environment, tissues transplanted into other living organisms, and tissues
cultivated in vitro. In tissue culture, the aggressive action of host cells which
attack the grafts is eliminated; in vitro the tissues are exposed merely to
the action of homoiogenous or heterogenous organismal differentials, con-
tained in the bodyfluids, and the toxic effect produced on them by the latter
is less than when they are transplanted into living hosts.

As to the conditions which render these bodyfluids less injurious in tissue
culture: (1) One factor is probably the small amount of blood plasma or
serum present in the culture media, which contains the toxins, as compared
to the continuous current of fluid carrying fresh supplies of homoio- and
heterotoxins to the transplant in the living body. Such a condition may be
active also when the homoiogenous plasma of an animal which had proved
to be immune to the growth of a certain tumor, is used as a culture medium
for a piece from the same tumor growing in vitro; it does not prevent the
growth of the tumor; under these circumstances, the amount of homoio-
toxins present at a certain time is presumably insufficient. (2) A second factor
concerns the growth momentum of cells in vitro. Cells growing in vitro are not
components of an ordinary, relatively resting tissue; they are very actively
growing and are either of embryonal origin or are derived from adult cells,
or, they may be cancer cells. Both embryonal cells and cancer cells are under
the influence of factors which stimulate them to grow continuously, while
cells derived from adult cells, being separated from their normal environ-
ment, are continuously regenerating. In all these types of cells the growth
momentum is increased, and furthermore, it is possible that in the case of
the embryonal cells the individuality differentials may not yet be completely
developed. Such an increase in growth momentum makes it possible for
these cells to overcome difficulties to which other cells might succumb; in

TISSUE CULTURE 189

addition, they may lack certain products of differentiation which might serve
as an effective point of attack for injurious substances present in the
circulating blood ; this is suggested by the fact that in actively growing cells,
whether they are embryonal, regenerating adult, or tumor cells, there is less
tendency to differentiation and a full development of the tissue or organ
differentials is lacking — a condition noted apparently also in plant cells
growing in vitro, as the experiments of White indicate. On the other hand,
if factors capable of inflicting a limited degree of injury, act on these stimu-
lated, actively-growing cells, either normal or abnormal processes of dif-
ferentiation may occur, which, as an endstage, may lead to cell death. It
seems that with this diminution in the development of tissue differentials and
in tissue differentiation, as well as with the increase in growth momentum,
there is perhaps associated also a diminution in the sensitiveness to not quite
adequate individuality differentials. These factors, taken together, might then
explain why tissues growing in tissue cultures are less affected by not quite
harmonious individuality differentials than normal adult, relatively resting,
differentiated tissues.

Chapter 21

The Individuality Differentials and Potential
Immortality of Tissues

In the preceding chapter we have analyzed the significance of individual-
ity differentials in the life of tissues growing in vitro and have tried
to explain the relative independence of the cells living under these con-
ditions from the nature of the individuality differentials and the diminution
in the significance of the species differentials of the surrounding media. The
same factors which are active under these conditions enable the cells to live
and propagate indefinitely, provided definite experimental requirements are
fulfilled. It could be shown that some cells and tissues of mammalian
organisms are potentially immortal. This holds good, with the reservation
that the term "immortality" is applied here in a relative, not in an absolute
sense, the immortality being limited by the need of the existence of certain en-
vironmental factors, which in all probability will come to an end in some dis-
tant future.

However, the potential immortality of various mammalian tissues was first
recognized in the case of tumors. In 1901, we showed that it is possible to
transplant tumors through many consecutive generations of animals of the
species or strain in which the tumor originated. There seemed to be no
limit to the continuous life inherent in the propagated cells, inasmuch as the
termination of these long continued serial transplantations depended solely
upon accidental, unfavorable factors which could be avoided. Furthermore,
since it was evident that tumor cells are merely ordinary tissue cells which
could be transformed into tumor cells at will under well-defined experi-
mental conditions, the conclusion was justified that also the normal cells
from which the tumor cells were derived, have the potentiality to immortal
life.

Subsequently, a second method, already mentioned, was used by Carrel
and Ebeling, who transferred embryonic connective tissue cells serially from
generation to generation in tissue culture. Here the embryonic cells are
stimulated to multiply indefinitely by the conditions which have been pre-
pared for them experimentally; when transferred serially to fresh culture
media, they may be kept alive indefinitely. But while it is mainly embryonic
fibroblasts which have been propagated in this way from generation to
generation, there are a considerable number of types of normal cells which,
after transformation into tumor cells, have acquired the ability to propagate
indefinitely. This is true not only of different types of connective tissue cells,
but of mammary gland tissue and various other epithelial cells; also of
endothelial and cartilage cells ; indeed, it is in principle true probably of all
cells which constitute transplanted malignant as well as some benign tumors.

190

POTENTIAL IMMORTALITY OF TISSUES 191

While, therefore, on theoretical grounds it is justifiable to extend the
conclusion as to the potential immortality of cells to ordinary tissue cells,
actually it has not been possible to demonstrate this characteristic by the same
method in normal tissues as in tumors, on account of the more severe injurious
effects produced by strange individuality differentials on normal tissues,
as compared to tumors, after their transplantation into new hosts. Our
attempts to transplant epidermis serially succeeded for only a relatively short
period. Normal cartilage seemed to be a much more favorable tissue for long-
continued transplantation, inasmuch as it is more resistant to injurious condi-
tions than are most tissues, and better able to withstand the unfavorable
effects of the homoiotoxins of the bodyfluids of the host and of the aggressive
host cells, especially the connective tissue cells and lymphocytes. In addition,
there is some reason for believing that transplanted cartilage gives off a
smaller amount of homoiogenous substance than do other more actively
metabolizing tissues. It was thus possible to transplant cartilage serially for
several years, and not only into young rats but also into very old animals
which were approaching the end of their life. In these experiments it was
the xiphoid cartilage of rats which was transplanted into dorsal subcutaneous
pockets of other rats. The length of time elapsing between consecutive
transplantations of a piece of cartilage, to a series of hosts varied between
one month and one year. On the average, a new transplantation was carried
out every five to six months. It was thus possible to keep the transplant
alive for several years, since at the time of the first transplantation the
cartilage had already reached an age varying between two and three years
and it could be transplanted serially for more than three years ; at the end
of the experiment the cartilage had reached an age of five to six years, a
period considerably exceeding the average length of life of the rat, which is
usually not more than three years.

This relative success in the serial transplantation of cartilage is due to the
factors mentioned above. The lymphocytes of the host accumulate around
the transplant in smaller numbers, and, as stated previously, the lympho-
cytic reaction may even decrease in the course of time. The lymphocytes
were found in the largest number in the fourth week, and from then on
their number gradually decreased, until after five months the transplant
showed usually only a very weak or no lymphocytic reaction; but 20 days
after re-transplantation the lymphocytic reaction could again become distinct.
In the course of these transplantations the perichondrium may regenerate
and form new cartilage around a piece of this tissue, that had become
necrotic as a result of transplantation. Groups of very young perichondrial
cartilage cells may be found at the time of examination, but the new
cartilage does not penetrate into the surrounding tissue. The perichondrium
produces cartilage towards the inside, ensheathing or replacing the old
cartilage, but towards the outside it seems to produce a tissue that is transi-
tional between cartilage and fibrous tissue, and that resembles at the outer-
most border typical fibrous tissue. However, if the transplanted cartilage
becomes thick as the result of the growth activity of the perichondrium —

192 THE BIOLOGICAL BASIS OF INDIVIDUALITY

and this is true even if normal, not transplanted cartilage has reached a
certain thickness— the central parts may shrink and become necrotic, due
to their distance from the blood vessels which carry nourishment to the
perichondrium and to the outer layers of the cartilage. It is probably also the
deficiency in oxygen and other food material that causes the small, relatively
undifferentiated perichondrial cells to change into the large and fully dif-
ferentiated cartilage cells. Only in one case had a piece of cartilage, after a
period of serial transplantations extending over two years and ten months,
produced bone; bone plates were lying along the cartilage and in the bone
there was a development of marrow containing fat cells.

It is the connective tissue which is active in the destruction of serially
transplanted cartilage. This forms a capsule around the transplant and it
invades, dissolves and gradually replaces the necrotic parts ; occasionally,
blood capillaries and some lymphocytes may penetrate with the connective
tissue into the areas of necrosis. But under certain conditions the connective
tissue may push its way also into that part of the living cartilage where
the cells are separated by a relatively large amount of hyaline intercellular
substance or by a very thick capsule. On the other hand, the connective
tissue is apparently unable to penetrate into living perichondrium or into
young perichondrial cartilage, where the cells are placed close to one another.
It is therefore the fargoing differentiation, the marked formation of inter-
cellular substance or of capsule meterial, which gives the connective tissue
an opportunity to exert its invasive, constrictive, and therefore injurious
action. Healthy young cartilage cells are safe from the attack by the host
connective tissue, although, as we have seen previously, they are exposed to
the invasion by lymphocytes. Thus a vicious circle is established: certain
unfavorable conditions, such as deficient nourishment, lead to the production
of the differentiated cellular and intercellular paraplastic substances, and
then the resulting ingrowth of connective tissue tends to divide the trans-
plant into small partitions and otherwise injure it, decreasing still further
its normal oxygen and food supply and preventing its normal proliferation.
To ensure the survival of the cartilage transplant, it is necessary to keep the
perichondrium surrounding it alive. The tissue equilibrium is best main-
tained if the resting connective tissue of the host surrounds the perichondrium
of the transplanted resting cartilage. But at the same time it is necessary to
prevent the impairment of the nourishment of the transplant by the con-
nective tissue capsule. If there is a deficiency in the nourishment of the
transplant, a necrosis in its center occurs, the tissue equilibrium is disturbed,
and in consequence the new formation of the perichondrial cartilage cells
takes place, which subsequently differentiate and produce intercellular sub-
stance. Thus both (1) primary injurious conditions which affect directly
the transplant, and (2) the activity of the host connective tissue and lympho-
cytes, taking place under the influence of homoiogenous individuality dif-
ferentials, may play a part in shortening the life of the transplant. In old
age, changes similar to those seen after homoiogenous transplantation occur
in organs, namely, a decrease in the parenchyma and an increase in the

POTENTIAL IMMORTALITY OF TISSUES 193

fibrous stroma. The primary degenerative changes in the parenchyma may
stimulate the connective tissue or glia to increased activity. These changes in
the stroma impair still more the preservation and functioning of the
parenchyma, which then may undergo further degeneration.

However, if we select very closely inbred strains of mice, where all the
individuality differentials approach the character of autogenous differentials —
although this state has not yet been completely attained — the prospects of a
successful serial transplantation even of whole organs such as thyroid gland
are greatly improved. Moreover, in the mouse the host cells, whose function
it is to attack the tissues possessing strange differentials, are often less active
than they are in rat and guinea pig. Hence it has been possible in our experi-
ments to prolong the life of serially transplanted organs beyond the usual
length of life of the mouse, and there are indications that it may be possible,
by carrying out serial transplantations in closely inbred strains, to keep alive
and growing indefinitely not only cells which are more or less independent of
each other, such as connective tissue cells, but also whole organs.

The potential immortality of mammalian cells has then so far been demon-
strated by two methods, in both of which the cells are subjected to unceasing,
intensified growth stimulation — namely (1) the serial transplantation of
tumors and (2) the continued transfer of cells in tissue culture. In the first
method specific tumor stimuli, and in the latter stimuli characteristic of
regenerative and embryonal growth are active. The constant renewal of the
cells by mitosis, under the influence of these stimuli, prevents undue dif-
ferentiation and production of paraplastic substances, which would injure the
cells and in the end prematurely destroy them. Cells which have gained in
differentiation beyond a certain limit and, correspondingly, lost in the power
of propagation, such as ganglia cells or certain leucocytes, either slowly
undergo gradual atrophy or degenerative processes or they die at an early pe-
riod. Cells which, as a result of processes of differentiation, have lost, not yet
entirely but to a certain degree, their power of propagation, undergo abnormal
changes of further differentiation when acted upon by growth stimuli origi-
nating from the outside or within the cells themselves. The same process
may therefore function both as growth stimulator and, in a certain sense, also
as differentiator of cells, if it acts on a cellular substratum in which an in-
termediate degree of differentiation has taken place. Eut, as stated, if the
differentiation has reached a further advanced stage, growth stimuli may
induce alterations in the cell equilibrium so great that they lead to cell death,
which thus represents the endstage of the differentiating process.

While both methods, which have been used so far for the demonstration
of the potential immortality of tissues of higher organisms, require the
constant action of growth-promoting factors, there remains the possibility
that certain organs, such as the thyroid gland, in which the units composing
the organ are closed cell complexes, forming acini or similar structures,
may through well-timed serial transplantation be kept alive indefinitely,
without a very active cell proliferation taking place. This can, however, be
accomplished only if the individuality differentials of the host and transplant

194 THE BIOLOGICAL BASIS OF INDIVIDUALITY

are very similar. Homoiogenous and heterogeneous individuality differentials
represent one of the most important injurious factors opposing the perpetual
life of tissues if separated from their normal connections. However, even
within the animal's own body, where the individuality differentials are autog-
enous, the return to the original tissue equilibrium after a disequilibration
has been established may be incomplete, owing to the fact that the various
tissues live under environmental conditions to which they are not fully
adapted and which, under some circumstances may become injurious. These
factors, step by step, cause the old age changes and, finally the death
of the tissues and of the individual in which, for a time, they have func-
tioned. The cells have to live under such injurious conditions because they
exert functions which concern the organism as a whole, and they are
acted upon by cells and substances which likewise function in the interest
of the whole organism; it is this condition which causes their ultimate
destruction. Hence potential immortality does not apply to the higher organ-
ism as a whole, but only to certain types of cells or organs which constitute
parts of this organism. The individual as such, as far as is known at present,
cannot avoid death.

Chapter 22

The Nature of the Individuality Differentials and

of the Reaction of an Organism Against a

Strange Individuality Differential

We have discussed the reactions of the host against the various
types of individuality differentials in various species of animals,
but in every case we have dealt with reactions against tissues con-
taining an individuality differential mixed with other substances, and not
with the reaction of cells and tissues against an individuality differential
isolated in a pure state. No direct attempt has been made so far to determine
the chemical structure of this substance. However, by subjecting the tissues
to various procedures, it has been possible to draw certain general conclusions
as to the chemical constitution of the individuality differentials. We have used
for this purpose (1) the effect of graded exposure of tissues to higher
temperatures, and (2) the effect of different chemical substances on the
individuality differentials present in various tissues. Tissues thus treated
were then tested by means of transplantation into different types of hosts
in the same way as normal tissues.

(1) The effect of heat on the organismal differentials in (a) homoiogenous
and (b) heterogenous tissues. In experiments by Siebert, to which we have
referred already, it was shown that by in vitro exposure of thyroid and
cartilage of the guinea pig to temperatures varying between 43 and 51 °C
for half an hour and then by transplantation of these pieces into homoiogenous
animals, it is possible to diminish very much the lymphocytic reaction
of the host against the transplants. These results indicate that the heating
at very moderate temperatures reduced markedly the quantity of homoiogenous
individuality differentials which diffused from the graft into the surrounding
host tissue. It is not certain whether in this case a definite injury of the
individuality differentials had taken place in the transplanted tissues, or
whether merely the diffusion of these differential substances into the sur-
rounding tissue had been made more difficult.

It is more probable that the first explanation is the correct one, because a
short delay in diffusion should not have affected so much the strength of
the lymphocytic reaction, but should only have delayed its appearance for a
short time. The heating of the tissues at the same temperature affected the
reactions of a heterogenous host much less than those of a homoiogenous
host; in the former there was only a slight diminution in the number of
polymorphonuclear leucocytes and lymphocytes. This effect must have been
due to a not very marked injury inflicted on the heterogenous differentials

195

196 THE BIOLOGICAL BASIS OF INDIVIDUALITY

through the heating. Blumenthal subsequently tested the effect of heating of
both homoiogenous and heterogenous tissues on the organismal differentials
by means of white blood cell counts. In these experiments, also, the tissues
were exposed to heat for 30 minutes in a test tube previous to transplanta-
tion. A temperature of from 45° to 50°C hardly affected the individuality
differential of guinea pig or rat thyroid, nor was the individuality differen-
tial of pigeon skin, which normally shows a weak reaction, much affected
thereby. The same negative result was obtained when rat skin was heated at
52°C, but the individuality differential of pigeon thyroid, heated at 54°C,
was weakened or destroyed in one-half of the experiments. This temperature
seems to represent the critical point ; but if the temperature reached 56°C,
the individuality differential of thyroid in various species was destroyed,
but that of the guinea pig kidney was merely weakened; presumably the
denser texture of the kidney affords a better protection against the effect of
the heat.

To test the heterogenous organismal differentials (species differentials),
tissues were exchanged between rat and guinea pig. Heating at 56° C de-
stroyed the heterogenous differentials of thyroid tissue of rat and guinea pig,
but left those of cartilage and kidney unaffected. In kidney tissue, heating at
60°C destroyed the differentials in seven out of eight experiments, and in
cartilage this temperature injured or destroyed the differentials in one-half
of the cases, but heating at 65°C destroyed also the species differential in
cartilage. In the experiments of Siebert, as well as in those of Blumenthal,
the heterogenous differentials were somewhat more resistant to heat than
the homoiogenous differentials. However, the temperatures needed for the
injury of both types of differentials were somewhat lower in the experi-
ments of Siebert, who used the local reactions as a test, than in those of
Blumenthal, who made use of the blood-cell reaction. Furthermore, in the
latter series the tissues possessing a denser texture were more resistant to
the destructive effects of heat than those possessing a looser structure. While
the differentials in thyroid were more sensitive than those in kidney, the latter
were more sensitive than those in cartilage. This again corresponds to the
gradation of sensitiveness of the various tissues to the action of strange
differentials. The injury of the tissues takes a course parallel to that of the
organismal differentials, which they contain. In general, we may conclude
that the homoiogenous and heterogenous differentials possess marked sen-
sitiveness to the injurious effects of heat, corresponding approximately to the
heat sensitiveness of the organs of which they form a part and this sensitive-
ness may be attributed to the labile proteins which are the most characteristic
constituent of living tissues. It seems probable therefore that the differentials
themselves are proteins, or combinations of proteins with certain chemical
groups of a different kind.

This conclusion is supported by experiments in which Blumenthal ex-
posed tissues to the action of various chemicals and then tested their effect on
homoiogenous differentials by the alterations induced by these differentials in
the white blood counts of the host. Least injurious for the individuality differ-

NATURE OF THE INDIVIDUALITY DIFFERENTIALS 197

entials was glycerine or a 0.9% solution of sodium chloride, saturated with
thymol. In the latter, the individuality differentials were active in the majority
of cases after immersion for 24 hours, and in the former, after immersion for
12 hours. In acetone and in half molar sodium benzoate, the transplants in
most cases were inactive after immersion for one hour, but some remained
active; after 12 or 24 hours immersion, they all had become inactive. In 95%
alcohol, 37% formaldehyde, and one-half saturated solution of ammonium
sulfate, all the pieces were inactive after immersion for one hour. Treated
with 50% urea, less than one-half of the pieces were active after immersion
for one hour; with one-half molar ferrous chloride and with 1/200 molar
ferrous chloride for six hours, all the pieces had become inactive.

The substances used in these experiments may act in either of two ways :
(1) some may extract the homoiogenous differentials, and (2) others, espe-
cially those which affect the proteins, probably injure or destroy the homoiog-
enous differentials. Among the latter, most effective are those substances
which actively denature protein. In general, the homoiogenous differentials
proved to be very sensitive to chemical substances of various kinds and par-
ticularly to substances which alter proteins. There is reason for assuming that
these differentials are produced only in living tissues, inasmuch as the ma-
jority of the pieces of tissues which had become ineffective, after having been
subjected to the action of such a chemical, had been killed or severely injured.
If, under these conditions, merely a newformation of the individuality
differentials had been prevented, it should have been possible at least for the
differentials preformed in the tissues to be potent. However, as stated, it
seems that the majority of the chemicals used injured also these individuality
differential substances as such.

It is of interest to compare with these reactions, those in which Blumen-
thal introduced various proteins, carbohydrates, fats, or lipoids subcutaneous-
ly. Substances which were liquid were injected subcutaneously on successive
days. The proteins caused a reaction in the peripheral blood, similar to that
induced by homoiogenous differentials. But it differed from the latter reaction
in that the response of blood cells was not destroyed by a preliminary ex-
posure of these protein substances to heat. Heterogenous rabbit serum and
heterogenous embryonic tissue behaved like these protein substances ; they
elicited merely an increase of lymphocytes in the blood, which appeared
between the second and fourth day after implantation of the foreign protein.
None of the non-protein substances gave rise to this reaction.

From these experiments, it follows that as far as the effects of strange sub-
stances on the white blood cells circulating in the blood vessels indicate there
is a definite order in which these substances can be arranged. (1) The finest
gradations in the reactions are found if substances possessing strange indi-
viduality or species differentials are introduced. The reactions here correspond
to the genetic reationship between host and donor. (2) Next come substances
of a protein nature, which cause reactions not unlike those produced by
homoiogenous differentials ; the former elicit more marked reactions than those
brought about by autogenous individuality differentials, which themselves

198 THE BIOLOGICAL BASIS OF INDIVIDUALITY

induce no changes, the changes noted being due merely to the operation on the
animal. But these protein substances continue to exert their effects after they
have been subjected to treatments which deprive homoiogenous differentials of
their characteristic influence. (3) Likewise, protein substances, such as those
present in blood serum of strange species, exert a homoiogenous effect; (4)
on the other hand, blood plasma of a different species exhibits the effects of
true heterogenous differentials, probably because of the presence of fibrinogen.
(5) Lastly, there are strange substances of a non-protein nature; these are de-
void of any specific action and behave like autogenous substances. But again,
in contrast to autogenous substances, non-protein substances are non-specific.

It might be of interest also to compare the local reaction elicited by ordinary
foreign bodies with that induced by substances carrying autogenous, homoiog-
enous or heterogenous organismal differentials. The material which possesses
individuality or species differentials, after introduction into the subcutaneous
tissue, exerts a combination of two effects: (1) non-specific foreign body
effects and (2) specific effects elicited by the individuality and species differ-
entials

It will therefore be necessary to analyze the differences between the reac-
tions against a foreign body and the more specific reactions against living tis-
sue. The reactions of the host cells against the foreign body do not show those
fine gradations which are elicited by the individuality and species differentials.
Variations observed in the reactions against foreign bodies depend largely
upon mechanical factors which distinguish different kinds of material, but
there are also some slight differences in the mode of reaction shown by differ-
ent host species. Common to all these foreign body reactions is the prominent
part played by the connective tissue cells of the host; they move towards the
strange material and attempt to invade and to make it into a part of the host
by transforming it into fibrous tissue. They first surround the periphery and
then turning at a right angle invade it, branching off in tree-like fashion ; they
act as though they were stimulated and activated by the foreign material. In
contrast to the farther distant connective tissue, which tends to assume a
resting condition, forming collagen fibers, the connective tissue directly ad-
joining the foreign body remains cellular. However, the soil into which these
host cells have penetrated is injurious to them and after a certain time they
are apt to perish ; their fibroplasm and nuclei become admixed to the foreign
material, such as 1% agar, and thus a new substratum consisting of a com-
bination of disintegrating cellular material and the fibroplasm-agar-mixture is
produced; into this other host cells penetrate and ultimately accomplish its
organization. In the peripherpy of the foreign body and also in its fissures
there may also collect giant cells of various sizes, and mononuclear cells, the
nature of which is uncertain, but which may perhaps represent either modified
connective tissue cells or monocytes. It seems that giant cells with their ac-
cumulation of nuclei and their increase in cytoplasm form especially in
those places in which there is an obstacle to the progress of the host cells, as
in furrows in the foreign body. All those cells, the giant cells as well as the
mononuclear cells, or cells transitional between these two, possessing two

NATURE OF THE INDIVIDUALITY DIFFERENTIALS 199

nuclei, may act as ameboid cells and as phagocytes ; they send pseudopods into
the foreign material, take small particles of it into their cell-body and if
possible digest them, as indicated by the intracellular vacuoles to which they
give rise. The cytoplasm of the giant cells may become quite vacuolated and
in the end, the latter perish. Small particles of the foreign body, detached
from these aggressive cells, may be found also between the connective tissue
fibers surrounding the agar or filling the fissure in the agar which they had
produced. In certain cases, but not very frequently, also lymphocytes accumu-
late round the piece or in its fissures ; they were found more often in rat and
guinea pig than in pigeon, although lymphocytes occur in the circulation in
larger proportion in birds than in rodents and although they were more numer-
ous around and in homoiogenous tissues in the pigeon than in guinea pig or
rat. Their presence around foreign bodies is due to non-specific irritations
which the foreign material exerts and perhaps to some as yet unknown acci-
dental factors. Occasionally also polymorphonuclear leucocytes penetrate,
likewise in tree-like fashion, into the agar and dissolve it readily; here they
perish after some time and the dissolved material is ultimately replaced by
ingrowing connective tissue. It is not certain whether invasion by these leuco-
cytes is the result of an accidental infection by bacteria or whether it is due
to other factors. If coagulated egg-white instead of agar is implanted into the
subcutaneous tissue, the reactions of the host cells are, in principle, the same
as with agar ; but on account of the greater hardness of this substance, it is
much more difficult for the cells to penetrate it and the reactions, therefore,
take place for the most part in the periphery of the egg-white, but, to some
extent, cells do invade it. Formation of fibrillar connective tissue capsules
around the pieces seems to be relatively the more prominent the harder the
material.

We see, then, that the same elements participate in these reactions against
foreign bodies as against living tissues possessing individuality differentials
and species differentials. But as stated, the local reactions against foreign
bodies do not show the fine gradations in activity of the host cells which the
homoiogenous and heterogenous tissues call forth. There is, here, on the
whole, a marked rigidity noticeable, although the degree of participation of
lymphocytes and polymorphonuclear leucocytes is very irregular and appar-
ently due to factors which cannot be foreseen or are unknown, in contrast
to the definite orderly manner in which these cells react against the autoge-
nous, homoiogenous and heterogenous differentials of living tissues.

In contrast to these non-living substances and to tissues that have been
killed by heat or by chemical substances, living tissues possess individuality
and species differentials which call forth definite graded reactions on the part
of the host cells and bodyfluids. However, as we have seen, indirectly also the
tissue differentials of the grafts may under certain conditions partake in these
specific reactions, either intensifying or weakening them. The character of
different tissues belonging to the same donor may affect the reaction against
strange individuality differentials : ( 1 ) by variations in the amounts of in-
dividuality differentials which they give off; (2) by the differences in the

200 THE BIOLOGICAL BASIS OF INDIVIDUALITY

strength of resistance which different transplanted tissues oppose to the in-
jurious actions of the bodyfluids and cells of a host possessing different in-
dividuality differentials : (3) by the production of certain degenerative changes
in the tissue, which may increase very much the strength of the lymphocytic
reaction of the host; such an effect we have observed especially with trans-
plants of ovarian and adrenal-cortical tissue ; in addition, certain specific reac-
tions may take place between two adjoining autogenous tissues within the
same organism, if the equilibrium between these tissues is disturbed. Such
reactions may, for instance, take place between autogenous grafts of pig-
mented skin into defects of white skin in the guinea pig, and similar reactions
may occur between the squamous epithelium of the cervix and the cylindrical
epithelium of the uterus, particularly under the influence of estrogenic stimu-
lation.

Other factors of a secondary nature exist, which may affect the strength
and character of the reactions of the host against organismal differentials, such
as age of host or donor and stimulation leading to an increase in the growth
momentum of the transplanted tissue. This increase enables the graft to over-
come various obstacles present in the host and especially also an unfavorable
constitution of the individuality differentials. In particular, hormones which
stimulate the transplanted cells to grow may enable them better to withstand
the attacks of the host. There may be associated with this increase in growth
momentum a diminished differentiation of the transplanted tissue, which may
also indirectly contribute to the decrease in the severity of the reaction of the
host against the transplant. We have seen furthermore that there are loca-
tions in the host where the transplants are, to some extent, protected against
the host reactions, and different mechanisms of these various kinds may be
active in different places.

As to the character of these organismal differentials, they are essentially
genetically determined, but they are not identical with the genes; they are
gene derivatives which lead to the production of the chemical substances
characteristic of these differentials. While the genes in the donor of the graft
strange to the host are mainly responsible for the intensity of the host reac-
tion, there are some indications that also genes in the host which are not
present in the transplant, may play a certain role in this reaction. However,
it seems that in addition the ability of the host to react against strange indi-
viduality differentials may vary. The mechanism underlying this difference
between different hosts has not been determined, and it cannot be excluded at
present that the function of certain organs or tissues, such as the reticulo-
endothelial system, is involved. Besides, different species to which the hosts
belong differ quite distinctly in the mode of their reactions against a strange
individuality differential.

The character of the individuality and species differentials directly or in-
directly determines the mutual compatibility or incompatibility of two differ-
ent organisms; but there does not exist a simple reciprocal relation between
the reactions of individual or species A to individual or species B or vice
versa, but it follows from what has been stated, that A may differ from B in

NATURE OF THE INDIVIDUALITY DIFFERENTIALS 201

its functions as host or donor. Furthermore, while the organismal differen-
tials exert primarily a direct effect, in determining the reactions of the host
against the transplant, secondarily they may function also as antigens and
call forth immune reactions, which may contribute to the intensity of the re-
actions, although to an unlike degree in different tissues. As to the number of
genes which are involved in these reactions, it is in all probability very large,
as especially the experiments with closely inbred strains suggest. There is no
indication that the genes determining the four primary blood-group differen-
tials are the genes which determine the nature of the individuality differen-
tials ; however, if we consider also the large number of additional differentials
already found in erythrocytes by means of agglutination or hemolysin reac-
tions,— a number which will probably increase still more in the future — , it
appears possible that the gene sets from which the blood cell antigens de-
velop and the individuality differentials will more and more tend to approxi-
mate each other.

In this connection it may be stated that a distinction should be made between
the terms "individual differential" and "individuality differential." The for-
mer may be regarded as the more general term, including many characteristics,
which differentiate one individual from another, such as color of skin, hair,
eyes, size, shape of body and its parts, psychical attributes and which com-
prise thus the organ and tissue differentials. In contrast to these, "individuality
differential" is a more specific term, designating a definite characteristic
which is common to all or most parts of one individual and which differen-
tiates him from the common characteristic denominator in another individual.

There has evolved, as the result of a long-continued series of experiments,
the concept of individuality and species differentials, and, in general, of
organismal differentials, in their interactions with tissue differentials and
various other factors characterizing the organism. This evolution was a
gradual one, taking place step by step, in close connection with concepts which
were prominent at certain periods in the development of biology and patholo-
gy. We may distinguish essentially four periods in this development: (1) In
the first period transplantations among more primitive invertebrates had
proved the importance of the polarity of tissues and of other structural pecu-
liarities affecting the harmony between grafted parts and the host, and these
observations were generalized and applied also to transplantations in higher
vertebrates; (2) In a second period the discoveries concerning active im-
munity and anaphylaxis, and especially those concerning agglutinins, hemoly-
sins and precipitins, very strongly influenced the interpretation of all subse-
quent experiments in transplantation ; (3) Later Mendelian concepts of hered-
ity, following the revival of the study of genetics at the beginning of this cen-
tury, suggested that the results of grafting were determined by the presence or
absence, in the host, of genes which the grafted tissue needed for survival ; (4)
The foregoing data, as far as they were found valid, and the addition of new
experimental data gave then origin to the concept of the various types of
organismal differentials as determiners of the mode and intensity of inter-
action between different organisms and their parts.

202 THE BIOLOGICAL BASIS OF INDIVIDUALITY

The means which the animal organism possesses for the regulation of dis-
turbances, initiating reactions tending to reestablish a state of equilibrium
between the parts of an individual, are relatively limited. Against a great
variety of interferences which may affect an organism, the latter reacts in a
very similar manner making use of the small number of reaction patterns
which are at its disposal, in accordance with its inherited constitution. The
variations in the environmental agents which act on the organism are very
much greater than the various modes of reaction which the affected indi-
vidual can initiate, but a gradation in the kind and intensity in the individu-
ality differential reactions which may take place against these interfering ele-
ments can be noted. No reaction occurs against living parts of the animal's
own body, to which a complete adaptation exists. Likewise, against non-living
constituents of the environment, other than protein substances, no general
or specific local reaction occurs. Against dead protein substances the lympho-
cytes in the circulation, and presumably those of the lymphatic organs, react
in about the same way as against homoiogenous individuality differentials, al-
though locally there is a distinction between the reactions against living
homoiogenous tissues and against dead material. The local reaction against
all foreign bodies, whether of protein or non-protein nature, is in principle
the same, tending to destroy, to transform and to incorporate the strange ma-
terial into the body in a way which is least injurious to the organism. However,
certain heterogenous material, non-living but containing formerly living ele-
ments such as blood clots, if introduced into the organism may call forth a
local reaction corresponding to that seen after implantation of heterogenous
living tissues. Also, the general blood-cell reaction is stronger against more
complex heterogenous proteins than against the simpler ones. Thus injections
of heterogenous blood sera elicit merely a lymphocytic reaction, whereas, sub-
cutaneous implantation of more complex proteins, such as heterogenous fibrin-
ogen induce a typical heterogenous blood-cell reaction.

There are thus increasing intensities and specificities of reactions noted if
non-living substances of different degrees of chemical complexity are intro-
duced into the body; but the maximal specificity in reaction is attained only
if living tissues, bearing strange organismal differentials, are transplanted. It
is therefore those substances which are most nearly related to the characteris-
tic constituents of living tissues namely the most complex proteins which call
forth reactions most similar to those elicited by the tissues themselves.

We see, then, that the reactions against strange individuality and species
differentials are not entirely disconnected and newly created responses of the
organism against interferences, but they represent the endstage of a series of
interactions which are graded in specificity in accordance with the increasing
complexity in the structure of the strange environmental elements, and in ac-
cordance with the increasing similarity between their constitution and the
constitution of living tissues.

IDorf" The Phylogenetic and Ontogenetic Development

of Individuality and Organismal Differentials

Chapter I

Transplantation and Individuality in Coelenterates

and Planarians

In the foregoing part we have discussed the organismal differentials
and their relations to organ and tissue differentials in the very complex,
phylogenetically higher organisms ; in a subsequent part we shall discuss
these differentials also in certain pathological growths, which develop in
vertebrates under abnormal conditions of stimulation. We now intend to
undertake the same analysis in normal invertebrates and lower vertebrates.
In each class of animals we wish to determine how far transplantation of
parts of organisms indicates the presence of organismal differentials and
what the relations of the organismal differentials are to the organ and tissue
differentials.

In adult birds and mammals there is a very strong reaction against strange
individuality differentials, and against strange organismal differentials in
general ; the normal equilibrium is strictly autogenous ; it depends upon the
presence of the same individuality differential in all the important tissues
and organs, and it is disturbed and leads to notable reactions if small parts
of tissues possessing a strange individuality differential are introduced into
the animal body. The strong cellular reactions of the organism against inter-
ferences with its structural integrity indicate that this tissue equilibrium is
relatively fixed and rigid. The replacement of lost parts by the organism
is very much restricted and the reactions which take place, ultimately tend
to maintain or restore the characteristic structural pattern of the individual.
Associated with this fixity is the great complexity and differentiation in the
tissues of each individual, which does not allow fargoing adaptations to new
environmental conditions or a nevvformation of lost parts. The individual
represents, therefore, a rigid autogenous equilibrium between its constituent
parts.

It was of interest to determine whether this association between the degree
of sensitiveness to and of reactivity against strange organismal differentials,
and the degree of structural fixity and rigidity of an organism extends through
the whole phylogenetic development. Such a parallelism would suggest that
a causal relation exists between these two sets of factors.

The special conditions confronting investigations in these more primitive
organisms have made necessary in many cases different methods of experi-
mentation. Instead of transplanting small pieces of tissues or organs, a method

203

204 THE BIOLOGICAL BASIS OF INDIVIDUALITY

commonly used in the case of higher organisms, in the more primitive ani-
mals, as a rule, larger parts are joined together. In some instances they are
so large that the procedure is comparable to parabiosis rather than to ordinary
tissue transplantation, except that in the typical parabiosis the size of the
area of union between the two partners is usually much smaller than in
transplantation as practiced in lower organisms. However, it is not only the
size of the pieces joined together which suggests a comparison with parabio-
sis, but also the fact that in invertebrates parts of organisms have, on the
whole, a much greater capacity to carry on an independent life and to restitute
the whole organism than the corresponding pieces in vertebrates. The pieces
to be joined together are therefore usually more independent of each other
and more self-sufficient than is the case in ordinary transplantation in higher
organisms. We might also express these differences by distinguishing be-
tween organismal transplantations in which organisms or parts of organisms
capable of independent life and of restitution into whole organisms are joined
together, and tissue or organ transplantations in which the transplants are
devoid of such capabilities.

It is not our aim to survey the whole field of transplantations in inverte-
brates and lower vertebrate classes as such, but to use these experiments
merely as a means for the study of the organismal differences in their func-
tion of sustaining the tissue and organ equilibrium, and making thereby pos-
sible the maintenance of the individual organism. It is especially the experi-
ments on coelenterates and planarians of Jacques Loeb, T. H. and L. V.
Morgan, Wetzel, Peebles, H. D. King, E. N. Browne, Rand, Issayew, Child,
Goetsch, Burt, Mutz and Santos on which our conclusions are based.

A. Organismal Differentials and Organ and Tissue Equilibria

in Coelenterates

In a general way it can be stated that two sets of factors determine in
coelenterates the kind of organ which is to be formed and its localization,
namely (1) a more or less rudimentary preformed differentiation of the
various parts of the body of an organism, and (2) the ability of parts of the
organism to undergo structural changes and to restitute a whole organism
from parts under varied conditions of the inner or outer environment. Instead
of the relative fixity in the structural relations between the various tissues
and organs which is characteristic of higher organisms, we find here a
primitive and very incomplete differentiation, associated with a great degree
of plasticity in the modes of response to altered conditions. It seems that
each part of the organism has a tendency to produce a certain area of the
organism or a certain organ system (pole) rather than another one, but often
this tendency can be overcome; moreover, the readiness with which organs,
other than those normally occurring in a given area, can be induced to form
by experimental means (heteromorphosis) differs in different parts of the
organism, the resistance being greater in those areas where the preformed
organization, rudimentary though it is, tends to the formation of a more or
less well differentiated organ area.

COELENTERATES AND PLANARIANS 205

The existence of a rudimentary differentiation in coelenterates is well
exemplified in the experiment of Burt, who showed that rings taken from
the anterior pole have, after transplantation, a greater tendency to form heads
than have foot pieces, which latter have a greater tendency to form a foot,
although in exceptional cases here, also, a rudimentary head formation with
tentacles can be induced. This predifferentiation can be overcome under cer-
tain conditions : ( 1 ) By the application of various external factors. In this
way Jacques Loeb first produced heteromorphosis in Tubularia. (2) Also
by the action of factors present within the organism; namely, when certain
differentiated areas, in some cases strange organs, introduced by means of
transplantation, extend their influence to other areas. Here we must again
distinguish two sets of factors: (a) The action of contact substances, or —
to use a more general term — contact mechanisms. Through contact with a
differentiated transplant, as, for instance, with the head of a Hydra, the
anterior pole or the foot region of the host can be induced to form, at or near
the place of contact, an organ corresponding to the transplanted head. In this
case we must assume that contact mechanisms (contact substances) induce
a heteromorphosis, inasmuch as a new formation takes place at a point where
normally another part of the organism would have developed. Thus, a head
may be induced to form in a place where normally a foot had been, or it may
form in the middle zone. The resistance to such a head formation is greater
at the aboral part than at the oral part, owing to the predifferentiation of the
host organism. We have, here, to deal with an organizer action comparable
to that which plays so important a role during embryonal development. It is
especially transplantation of a regenerating hydranth, but also of other kinds
of tissues, such as parts of Hydra buds and peristome, which in a specific
manner induces the formation of hydranths in Hydra viridis (E. N. Browne,
Goldsmith). In addition to these factors which thus lead to the formation of
supplementary organs, there may be active another factor, which consists
in the tendency of an organ to inhibit the formation of an organ of the same
kind, especially in its close proximity. From such a near point this inhibiting
influence may be transmitted to more distant parts, but apparently with
decreasing intensity, (b) Factors of a regenerative or restitutive character.
These may tend to supplement a part of an organism which has been separated
from the rest, in such a way that the formation of a whole organism results.
In this latter interaction a more differentiated tissue again is generally more
potent in determining what organs shall be produced, than one less differen-
tiated— it is the dominating, directing constituent of the organism. Moreover,
a larger part usually prevails over a smaller part, other conditions being
equal. While the organizer action in coelenterates mentioned above may lead
to the reproduction of the same organs as are present in the organism, the
regenerative tendency on the other hand leads to the newformation of sup-
plementary, therefore of different, organs or areas. There is another, more
definite difference between the mode of action of such an organizer and of
the integrative restitutive or regenerative factors. The former acts, as stated,
presumably through contact substances or contact mechanisms, while the

206 THE BIOLOGICAL BASIS OF INDIVIDUALITY

latter extend their sphere of influence to distant parts, perhaps through diffu-
sion of contact substances into distant areas of the body. Thus a well dif-
ferentiated organ may be able to force a distant part of a transplant to form
a heteromorphic organ, counter to its normal rudimentary differentiation.
In this case, the size of the transplant becomes one of the determining factors.
If the transplant exceeds a certain size, then its rudimentary preformed
differentiation is able to control the regenerative, heteromorphic tendency of
the host organ. Such a predifferentiation in the transplant may determine the
mode in which the whole organism shall be formed, its integrative action
inducing the formation of oral and aboral organs in accordance with the
structure of the transplant, which may thus dominate over the integrative
tendencies in the host. If a small piece is transplanted, there is evidently not
enough material present to allow its predifferentiation to assert itself, because
its opposite poles are very near to each other; the host, which is the larger
partner, then dominates and apparently induces degenerative processes in
the transplant, leading to its absorption. Perhaps the amount of active sub-
stance produced by short pieces is too small to overcome the opposing tend-
encies inherent in a larger piece.

A lack of a sufficient degree of predifferentiation in the transplant may
be the reason why, under certain conditions, it cannot maintain itself in
competition with the host and, instead, is absorbed by the latter. This applies
especially to pieces from the middle zone; and, correspondingly, the middle
zone of the host, by not inducing differentiation in a transplant, may lead to
its absorption. On the other hand, if, as a result of the combined organizer
and regenerative action, a part of an organism has been duplicated, the
restitutive tendency can lead to a separation of the duplications, which may
be followed by the formation of two independent organisms.

The tendency to supplement by regeneration a part of an organism in such
a way that a whole predifferentiated organism develops has a counterpart in
the tendency to form a normal whole from an organism, in which, through
transplantation, a surplus of certain organs, for instance, tentacles, has been
produced. The disequilibrium thus induced leads either to certain degenerative
processes, presumably agglutination and reduction, or it may act as a stimulus
to the production of certain organs, an effect which indirectly brings about the
loss of excessive parts. The predifferentiated organism represents an equili-
brated system, and disturbances in this system initiate various reactions aiming
at the restitution of its equilibrium. It is remarkable how varied and different
the mechanisms are which in the end all lead to the same result, the integrative
newformation of an equilibrated whole.

In the experiments on which these conclusions are based transplants influ-
enced the host and induced in it the newformation of organs, thus acting as
organizers, or in other cases the transplants influenced the restitutive, regen-
erative activities of the host by actions at a distance; conversely, the host in-
fluenced, under certain conditions, also the regenerative or restitutive activity
of the transplant. In these instances, as stated, certain organs, usually the
more differentiated ones, are dominant over others and force those parts of

COELENTERATES AND PLANARIANS 207

the organism which are not yet fully differentiated, to differentiate in such a
way that the dominating directing organ is supplemented and that a complete
organism develops. There are indications that the greatest potency of a certain
part is required if it is to function as an organizer and this is an attribute
mainly of the head, while apparently less potency is required for the regenera-
tive, integrative function of inducing supplementary organ formation and of
attaining in this way the formation of a whole organism by regenerative
means. Those parts which are functionally and structurally indifferent, such
as the middle piece, cannot act as organizers, nor can they induce regeneration.
The potential growth energy which is present in so marked a degree in these
primitive organisms, as exemplified in their response to inductive regenerative
influences and to organizer action, lies dormant in the normal organism ; the
mechanisms which cause induction of complementary parts and inhibit forma-
tion of similar parts are not ordinarily manifest. At each point the normal
contact mechanisms are active and keep the various parts in a quiescent state ;
but as soon as (through a cut or otherwise) this normal action of contact sub-
stances is disturbed, local growth processes set in, which are determined in
their character by a localized rudimentary differentiation, by regenerative
and integrative processes, such as induction and inhibition at a distance, by
organizer effects, and by environmental factors, all interacting with each
other. This interaction leads to the establishment of a new equilibrium which
takes the place of the previous disturbed equilibrium, and the most stable
equilibrium is reached when complete individuals are integrated. Within these
individuals the component parts are again equilibrized.

However, a wound not only disturbs the regulating and inhibiting influences
which originate in the remaining parts of the organism and which would
normally act on the wounded area, but it exerts also a direct stimulating effect
on the tissues thus affected and its influence seems to extend even over a
relatively great distance, accelerating the formation of a hydranth on removal
of the inhibition existing normally. Through wound stimulation the organism
or parts of it are transformed in such a way that they resemble, in their be-
havior and reactions, organisms during the budding, reproductive state, when
they are very plastic and possess a greater growth momentum. We find here a
condition analogous to the autogenous regulating mechanisms which deter-
mine tissue equilibrium also in higher organisms and the kind of disturbance
in this equilibrium which follows injury. However, the relative importance of
the various factors which become potent following the making of a wound
cannot be exactly determined at the present time.

Predifferentiation and coordinated integrative actions not only manifest
themselves through mechanisms which cause completion of incomplete or-
ganisms, but there must exist in addition, mechanisms which lead to degenera-
tion of excess tissues or organs ; we have referred to the resorption of small
parts which do not possess a pronounced differentiation. There may occur also
a coalescence of two small partners to form a single organism.

We may then conclude from these data that what corresponds to the fixed
organ differentials of higher organisms, is, in the coelenterates, still in a very

208 THE BIOLOGICAL BASIS OF INDIVIDUALITY

plastic, modifiable condition. It is due to this plasticity of organ differentials
and to the readiness with which transformations and newformations of organ
systems and parts of the body take place that individuals are restituted from
parts. But this factor alone would not insure the ready restitution of in-
dividuality. There must be added to it a certain autogenous state in which
organ systems interact perfectly in such a manner that a relatively stable
equilibrium is maintained. Some of the mechanisms which participate in the
maintenance of this equilibrium we have analyzed in the preceding pages.
Any disturbance in this autogenous equilibrium, consisting in the balancing
of these organ systems, activates mechanisms which result in the integration
of the organism. It is the relative lack of fixity in organ differentials, their
ability to change within certain limits, that make possible the integrative activity
of the mechanisms leading to the restoration of the individual.

So far, we have analyzed the interaction of organs and organ differentials
and their significance in the maintenance of the equilibrium which makes
possible the integration of parts into the individual organism. We shall now
compare with the nature of this equilibrium, the mode of action of the or-
ganismal differentials in this class of animals. Here we notice that the plas-
ticity of the organ differentials is somehow bound up with a relative lack of
fixity of the organismal differentials, or at least of the effects which differ-
ences in organismal differentials would induce in higher organisms.

We find, accordingly, that in Hydra auto- and homoiotransplantations seem
to succeed equally well ; similarly, there seems to be no difference in the results
when several autogenous or homoiogenous pieces are joined together, the
integrative as well as the organizer impulses being transmitted in a normal
manner from one piece to the other. At the point of union corresponding
tissues of homoiotransplants and host may unite perfectly in Hydra, without
any scar remaining visible. Homoiotransplantation in Hydra succeeds very
well, even if the two partners have been made unequal in their contents in
algae. However, we must not necessarily conclude from these experiments that
homoiodifferentials do not exist in these organisms. While this may per-
haps be the case, there still remains the possibility that they do exist in a
rudimentary form, but that they are not strongly enough developed to lead
to noticeable reactions and that the tissues have a power of resistance suffi-
cient to overcome unfavorable conditions caused by a difference in organismal
differentials. With this conclusion harmonizes also the observation that while
in organisms like Tubularia homoiotransplantation may apparently be per-
fect, yet in some cases separation between host and transplant takes place
after a time.

The results of heterotransplantation differ noticeably from those of homoio-
transplantation. Even if the transplantation succeeds, the differences in race
or species differentials may cause the union to take place more slowly and the
resulting combination may only be temporary, separation occurring perhaps
at a later date. On the other hand, it seems that union of different species may
permanently succeed in certain instances. In Hydra the union of heterografts
may, however, not be so firm as that of homoiograf ts ; the surface of contact
between the species may at first become smaller, until at last some mechanical

COELENTERATES AND PLANARIANS 209

factor, such as a pull, can produce separation. Furthermore, nerve stimulation
may fail to be transmitted from one partner to the other. This incompatibility
between adjoining surfaces is also evident in the experiments of Peebles in
Hydractinia. When a piece of Pennaria was grafted on Tubularia, the
coenosarc united temporarily, but no union of the perisarc took place, and
after formation of the hydranths the pieces disintegrated. Similarly, the union
between Eudendrium and Pennaria was only imperfect and temporary. While
here homoiotransplantation may, at least in some cases, be perfect, in hetero-
transplantation the union of the coenosarc does not last, and if farther distant
species are used, injurious effects become still more noticeable.

In general, buds develop, as H. D. King has shown, at the point of union
of two different kinds of organisms; these represent a mixture of the con-
stituents of both partners and thus constitute a chimaera. When the organis-
mal differentials of the two partners are markedly similar, the mixture is more
complete and the character of the tissue interaction differs from that seen
when the organismal differentials have less similarity. In the latter instance
parts of one organism have a tendency to penetrate as a connected mass into
the other, the constituents of both partners remaining more separate and dis-
tinct than when the organismal differentials are very much alike. In a very
interesting way the domination of one organism over the other, when they
differ in the constitution of their organismal differentials, has been shown in
the experiments of Goetsch and Issayew, who found that when two individuals
belonging to different species are united into one organism, budding often takes
place, the buds representing chimaerae of various kinds in which, however,
the constituents from one of the two species predominate. Issayew obtained
chimaerae also by cutting individuals from two different species into small
particles, which, when mixed, united to form one complete organism repre-
senting a mosaic of both partners. The union of Pelmatohydra oligactis and
Hydra vulgaris into a chimaera leads to a struggle between the constituents of
the two partners, in which the former gradually infiltrates and almost replaces
the latter; Pelmatohydra dominates and apparently only certain interstitial
cells of Hydra vulgaris remain preserved. The buds from such chimaerae may
be either Pelmatohydra or a mixture of both species. The remaining inter-
stitial cells of Hydra vulgaris are totipotent and may give rise to whole
organisms.

The dominance of one species over another in heterotransplantation may
also become manifest in another way. If an excess of tentacles has been pro-
duced as a result of transplantations, the dominant species may determine
the number of tentacles which shall be absorbed and, in the end, the number
which is characteristic of the dominant species remains. We see that even in
this case of heterotransplantation the integrative factors, tending towards the
reestablishment of an organ equilibrium which accords with the predifferen-
tiation of the dominant species, are active. As a rule, that species which, in the
separate state is the more vigorous one dominates. We shall find also in
amphibians joined together in embryonal stages, a dominance of one partner
over the other, in accordance with the more rapid growth and greater size of
one of these species in the free-living stage.

210 THE BIOLOGICAL BASIS OF INDIVIDUALITY

While thus the difference in race- and speciesdifferentials in the pieces
joined together may lead to antagonistic actions between the tissue consti-
tuents of the different grafts, yet to a certain extent it is possible for the
tissues in such buds and chimaerae to live and grow side by side without the
manifestation of a hostile reaction. Somewhat comparable results can be ob-
tained, as we shall see later, in the transplantation of regenerative buds of
extremities in amphibia, in the ingrowing of sidelines from one partner into
the other in heterotransplanted amphiban larvae, or, as we have mentioned
already, in the ingrowth of a nerve from one partner into the other in para-
biosis in rats. In all of these conditions there is a lack of manifest reaction on
the part of tissues which are in close contact with each other, although they
differ in their organismal differentials. In such cases we have to deal either
with ontogenetically or phylogenetically very primitive forms, or with re-
generating tissue which does not yet possess the fully developed organismal
differentials, or at least the mechanism of reaction against such differentials.
In the case of parabiosis in rats we may have to deal with relatively slight
differences in organismal differentials.

In accordance with the experiments mentioned above, Mutz found that
pieces of Hydra and Pelmatohydra can be joined together in the long axis of
the body, the different constituents retaining the character of their own
species. However, the growing together takes place with much greater diffi-
culty than in homoiotransplantations and for a long time the place of union
remains visible; but in the end a uniform, apparently normal Hydra, though
in reality representing a chimaera, may result from this transplantation. On
the other hand, the green Chloro hydra cannot be joined to the brown Pelma-
tohydra, to Hydra vulgaris or Hydra attenuata, separation taking place within
eight days. It seems that in this case the presence of algae in Chlorohydra
intensifies the difficulties of heterotransplantation. While in the case of
homoiotransplantation algae do not interfere seriously with the result, this is
not so if distinct races or species of Hydra are combined; then, the presence
of Algae increases the incompatibility between the partners, as the experi-
ments of Goetsch have shown. But even if the number of algae is approximate-
ly the same in different partners, there still remains noticeable the difference
in race or species constitution. If the head of Hydra vulgaris or attenuata is
transplanted to Pelmatohydra, the union between transplant and host is only
a temporary one, lasting usually from three to five days, or, at most, two
weeks. In this instance, the transplant is not able to act as readily as an or-
ganizer, inducing a head formation in the host, as it would have been if the
transplant and host had been homoiogenous. There forms, instead, at first a
bridge of tissue, growing from the host in the direction towards the transplant.
This bridge represents a somewhat indifferent kind of tissue in which tenta-
cles are lacking; but after separation of the transplanted head and host has
taken place, it may develop in some cases into a small head, while in others it
is drawn into the host and absorbed. The organizer action is therefore inter-
fered with in such a heterotransplantation. However, when reciprocal or-
ganismal transplantations of pieces of Pelmatohydra and Hydra attenuata
are made, the two pieces may remain united long enough to make possible the

COELENTERATES AND PLANARIANS 211

restitution of a head in the headless part, although also in this type of hetero-
transplantation certain disturbances appear ; thus, distance actions which take
place in cases of homoiotransplantation, leading to reversal of polarity
(heteromorphosis) in the transplant or to the formation of buds in the host
under the influence of the transplant, do not occur. There is, therefore, under
these conditions an interference with the transmission of the regenerative or
organizer influence, which under other circumstances would have passed from
host to partner, or vice versa. For the most part, either an absorption of the
transplant takes place in these heterotransplantations, or the grafted head
separates from the host. We may then conclude that after heterotransplanta-
tion incompatibilities develop between the partners or between a transplanted
organ and the host at the point of union. This often leads to early separation
and, in addition, difficulties may possibly develop in the passage of active sub-
stances from one organism into the other.

We must now inquire how far the reactions which have been observed when
we unite organisms belonging to different species or races in hydrozoa, can be
considered as due to differences in organismal differentials. There are two
circumstances which favor this interpretation: (1) The severity of these in-
compatibilities corresponds approximately to the distance of relationship be-
tween the parts which are joined together, and (2) the reactions after hetero-
transplantation seem to occur irrespective of the place where the two strange
organisms are united ; this fact suggests the presence of the same organismal
differential in all parts of the same individual.

As stated above, while in general only heterodifferentials lead to noticeable
incompatibilities in hydrozoa, we cannot therefore conclude that individuality
differentials do not exist in these primitive forms. We must consider the
possibility that each individual within a race or species has its own individu-
ality differential, which differs from that of every other individual, but that
the incompatibilities which result from these differences between differentials
in the lower types of animals are too slight, in proportion to the resistance of
the affected tissues, for injurious agencies to become manifest. It is this rela-
tion between the degree of incompatibility, the resulting injurious reaction on
the one hand, and the resistance of the transplant, which might be expected to
determine the degree of disequilibrium arising from differences in the differ-
entials. If the individuality differentials are as yet only very slightly developed,
the incompatibility resulting from the union of parts of different individuals
may not become evident. On the other hand, it is possible, after all, that in-
dividuality differentials are not yet present in these primitive organisms. The
second alternative might even be the more probable one, because there is
reason for assuming that in young vertebrate embryos fully developed indi-
viduality differentials do not as yet exist. By analogy we may extend this con-
clusion also to adult individuals belonging to very primitive vertebrates.

We must now return to a discussion of the conditions which maintain the
normal organism in a definite formative and functional equilibrium, and of
the similarities or the differences observed between higher and lower organ-
isms in this respect. In higher organisms such a formative equilibrium de-
pends, in part at least, on local conditions affecting the tissues; interactions

212 THE BIOLOGICAL BASIS OF INDIVIDUALITY

take place between adjoining tissues which are of a regulatory character and
keep the animal equilibrated. However, distance substances, in the form of
hormones, may also participate in this equilibrium as secondary factors,
though their action is less important and more specialized. In the case of
hydrozoa, conditions are in some essential respects similar to those of higher
organisms ; the equilibrium depends on local and distant factors and it can be
disturbed through local as well as through distant changes ; also, there is reason
for assuming that in both instances definite substances mediate these effects.
Furthermore, in these primitive organisms the organismal differentials, as well
as what corresponds to organ and tissue differentials in higher organisms, par-
ticipate in the maintenance of an equilibrium; but the particular structure
and function of adjoining autogenous parts of the organisms seem to be better
able to induce growth processes of various kinds in hydrozoa than in higher
organisms, on account of the greater plasticity of the tissues and organs in
the former. Important also in these lower forms are specific distance sub-
stances, which, acting in a stimulating or an inhibiting manner, are able to
modify the structure of the organism. There is a third difference between
higher organisms and hydrozoa in the stabilization of the equilibrium. In
higher organisms the equilibria depend upon the local interaction of tissues
bearing the same individuality differential and they are therefore essentially
autogenous in character. In hydrozoa, on the contrary, parts of an organism
differing in the character of their individuality differentials may, in general,
substitute for each other; incompatibilities, with resulting disturbance of the
formative equilibria, as a rule become manifest only if distinct differences in
species differentials exist between adjoining tissues. We cannot therefore con-
sider this equilibrium in lower forms as strictly autogenous in character ; it is
of a homoiogenous, as well as of an autogenous nature.

The next problem to be considered concerns the incompatibilities and dis-
turbances of equilibrium which may take place, in organisms bearing heterog-
enous differentials, after a primary union and an apparently complete forma-
tive equilibrium have been established. These changes may be due to two
different causes: (1) The primary incompatibility of the organismal differ-
entials may gradually increase, the resulting disturbance of the equilibrium
becoming manifest in the appearance of growth processes in whole organ-
isms, which otherwise would occur only in isolated parts; or (2) the original
incompatibility of the organismal differentials may lead to a primary separa-
tion of the adjoining surfaces of the heterogenous parts and this process may
be followed by regenerative changes. We believe that the* first interpretation
is the more probable one for several reasons: (1) In certain cases, when the
union between adjoining homoiogenous pieces was apparently perfect, sec-
ondarily a separation also took place. Presumably a formative change at the
point of union was here the primary process, which was followed by separa-
tion; (2) the separation may occur in some classes of animals not exactly at
the junction of the two surfaces, but at a neighboring point. This indicates
that either growth processes or changes of a degenerative character induced
the separation; (3) one of the mechanisms which help to reestablish a stable

COELENTERATES AND PLANARIANS 213

equilibrium may, in certain instances, in hydroids as well as in planarians,
lead to the separation of autogenous parts of an individual which have been
present in excess, and which have become superfluous. Here it is evident that
regulatory, integrative mechanisms of an unknown nature constitute the
primary process, and this is followed by the creation of a wound surface as a
secondary effect ; the latter is, therefore, caused by the action of these integra-
tive mechanisms ; (4) there are indications that the mechanisms mediating the
maintenance of an individual as an equilibrated system are not so well trans-
mitted at the points of union between heterogenous partners. We may expect
in this case regulatory processes to be set in motion, leading to attempts at new
integrations of individuals, with the resulting separation of the incompatible
parts.

We have seen that an individual hydrozoon can be divided, and that each
part can give origin to a complete organism. The degree to which divisibility
can be carried depends on whether such particles are kept in their normal
medium free from contact with other individuals, or whether they are trans-
planted to another organism ; if transplanted, the antagonistic influences which
the host may exert on the transplant may make it necessary for the transplant
to have a minimum optimal size before it is able to restitute the whole. We
may again refer in this connection to the experiments of Issayew, which
have shown that particles from different individuals may be joined together
in such a way that they form a whole organism, which represents the mosaic
of a chimaera. In this case each particle forms part of one whole, at the
same time still retaining its own organismal differential.

In hydrozoa, as has been noted, the tendency exists to produce single
individuals through processes of coalescence, as well as of splitting leading
to supplementary newformations. Correspondingly, stolons of hydroids
belonging to the same colony, and even stolons from adjoining colonies,
may coalesce. Also, larvae of coelenterates may unite among themselves and
give origin to a new colony, or they may join a part of an already existing
colony and help to enlarge it. However, the mechanism which usually leads
to colony formation is that of budding. The question may be raised whether
it is the individual polyp or the colony of polyps which shall be considered
as the bearer of the individuality. As far as the individuality differentials
are concerned, we may assume that, provided they exist at all, they are the
same in all component parts of a colony. Even strange colonies belonging
to the same species may have identical individuality differentials if they
have developed from buds given off by the same colony. But differences in
conditions analogous to individuality differentials in such colonies might pos-
sibly have originated under the influence of different environmental factors,
which were able to modify the different colonies ; furthermore, it is con-
ceivable that somatic mutations might occur and lead to such changes. In
higher individuals, differences in individuality differentials are, as a rule,
due to processes which take place during the formation of the germ cells
and during fertilization. We may therefore expect less sharp differences in
the nature of the individuality differentials in organisms propagating by

214 THE BIOLOGICAL BASIS OF INDIVIDUALITY

asexual budding or having the power to restitute the whole organism from a
part, than in those propagating only by sexual mechanisms.

If we consider individuality from the functional point of view and attribute
it to an organism able to live and function independently as an equilibrated
mechanism, to which different parts of the whole contribute in a distinctive
manner, then we can attribute individuality to the single hydrozoon as well
as to a colony, in which certain constituent parts may exert different func-
tions. However, this seems to be a problem of minor importance, because
the term "individuality" is not rigidly defined ; it is used in reference to or-
ganisms merely in order to describe certain of their characteristics. On the
other hand, it may be worth while to inquire whether a connection exists
between the lack of a manifestation of finer differentials in these primitive
organisms and their great plasticity, as exemplified in their readiness to form
organs under the influence of external and internal environmental factors
and propagate asexually. All the evidence tends to the conclusion that such
a connection does exist, although the underlying mechanism is not yet un-
derstood. It is presumably also these latter characteristics which provide
such organisms with the potentiality of immortal life, which higher organ-
isms no longer possess; in the higher organisms at best, certain tissues and
cells may possess such a potential immortality.

B. Transplantation and Individuality in Planarians

In many respects conditions in planarians are very similar to those found
in hydrozoa. In planarians we have also to deal with a very plastic living
substance in which, however, again a definite state of rudimentary preformed
differentiation exists; within a certain range it is possible to change the po-
larity of organs and thus to produce heteromorphosis. However, there are in-
dications that in proportion to the greater differentiation which exists in
planarians external factors do not quite, to the same extent, influence organ
formation and change the polarity in these organisms as they do in Hydra.
In order to evaluate the relation of organ differentials and of the equilibrium
between the parts of an organism, on which its existence as an individual de-
pends, to organismal differentials, we shall also in this instance first discuss
very briefly the factors that determine polarity, fixity and transformability
of parts of the body and its various organ systems.

The existence of a predifferentiation in this class of animals is indicated
by the fact that the anterior pole has a greater head-forming tendency than
the posterior pole. Thus, while the posterior (aboral) pole has the power
to regenerate a head, its ability to do so is less than that of the anterior (oral)
pole. Furthermore, in the region where the sex organs form, proliferation
in the host tissue may, according to Gebhardt, readily lead to the casting off
or resorption of the transplant. The existence of a rudimentary differentia-
tion comes out also in the specific inhibition in organ formation; thus, the
proximity of a head inhibits head formation (Rand, Goldsmith) and that of
a tail inhibits tail formation (Rand). It is also indicated by the fact that if
Planaria is split lengthwise into halves, each half may regenerate into a

COELENTERATES AND PLANARIANS 215

complete organism. In the latter case there must be a local factor active, which
causes the various organs to reproduce each its own kind, although even under
these conditions inducting factors acting in the direction of the long axis may
play a certain part. Likewise the fact observed by Child, that even in the
absence of a head an isolated piece of Planaria is able to regenerate all parts
representing the levels posterior to its situation in the organism, points to the
existence of a predifferentiation in these parts, and there are some indications
that it is the nervous system which plays, here, an important role in deter-
mining the rudimentary differentiation.

In Planaria, as in a similar manner in hydrozoa, it is possible to demon-
strate the existence of organizers. In both classes of organisms it is especially
the most differentiated organ area, the anterior pole or head, which not only
dominates the structure of the organism, but may also act as organizer (Child,
Goetsch, Santos). Furthermore, both classes show the same types of induc-
tion, and the inducting organ gives origin to its own kind of organ in the
material acted upon; in hydrozoa a transplanted head gives rise to a new
head, and in Planaria, according to Gebhardt, the eyes of the host may induce
eye formation in a bud from the posterior part, which has been transplanted
into the head region. In addition, a second type of induction has been estab-
lished in Planaria, especially by Morettj, Goetsch and Santos. Goetsch ob-
served that a transplanted head can induce in the host a reorganization, which
leads to the development of a postcephalic region. Santos grafted a piece from
the ganglion region of Planaria into the prepharyngeal levels of the host. If
the transplant was of a sufficient size, it gave rise to a head and determined
in the host a postcephalic outgrowth. If implanted into postpharyngeal levels
of the host, the transplant not only determined postcephalic outgrowth in the
host, but, besides, it caused a further reorganization, with the development
of a pharynx and postpharyngeal region. But the reorganizing influence of
the grafted piece extended in the host also in an anterior direction and in
this way it could determine a reversal of the polarity. However, the host. too
may exert an influence on the grafted part. This was indicated by the fact
that when the union between host and transplant was complete, the host
inhibited the perfect development of a head from the graft, while an incom-
plete union gave the transplant a chance to develop in accordance with its
own potentialities.

As Rand has found, the inhibiting influence which a graft exerts on a
wound, in a more or less specialized region in the host, varies somehow in
an inverse relation to the distance of the inhibiting material from the wound
surface. This suggests that we may have to deal with a diffusible contact
substance, which decreases in concentration with the distance between graft
and wound. Besides such inhibiting effects, we have then to deal here, as in
coelenterates, with two kinds of actions. One leads to the reproduction of the
same organ as that which acts as an organizer and the second represents a
complementary, integrative mechanism, which causes the completion of a
whole organism from a part.

We may assume that the inducting action of the transplanted head region

216 THE BIOLOGICAL BASIS OF INDIVIDUALITY

which Moretti, Goetsch and Santos observed, is effective also in the normal
organism and here helps to maintain its polarity, a conception emphasized
especially by Child in his axial gradient theory. There are two mechanisms
through which such an effect could be accomplished: (1) Through contact
action the dominant, most differentiated part could transmit an inductive
effect to the adjoining posterior part and this part in sequence could exert
a similar inductive effect on the nearest adjoining region in the antero-
posterior direction ; in this way a distance action could be brought about, in
which the inductive effect becomes gradually weaker; or (2) substances could
be produced by the dominant part, from which they pass to neighboring and
to distant regions in gradually decreasing concentration. But there is reason
for assuming that such actions do not affect an indifferent material, but one
which, while plastic within a definite range, still possesses a certain pre-
differentiation which varies in different parts in fixity.

It is possible that parts, other than the dominant part, also exert an induc-
tive distance effect. Thus L. V. Morgan has shown that when a head is cut
off in Planaria and a small piece is placed on the wound in an inverted direc-
tion, so that the oral pole of the graft joins the oral pole of the host, a distance
action is exerted by the larger piece, representing the host, which causes
the aboral pole of the transplant to form a head. Such an interpretation of
the experimental findings would apply if we assume that the head formation
in the transplant was not the result of unknown external factors, but was
caused by an integrative type of induction.

As in the case of hydroids, so also in planarians, the mechanisms under-
lying the change of abnormal structures to a normal organism may lead to
the absorption of excess organs. In other cases the mechanism underlying
integration may lead to a duplication of an organism, as when two complete
organisms form following the production of two heads and two tails through
partial lengthwise incisions in the anterior and posterior parts.

According to Goetsch, a transformation of one organ into another, a coa-
lescence of two organs, or a newformation of an organ, takes place by means
of an intermediate stage, in which, at first, under the influence of various
stimuli, an indifferent tissue develops, which secondarily undergoes the
specific differentiation. Fully differentiated organs cannot be directly trans-
formed. The less marked the differentiation is in a certain organism, the less
fargoing need be the preliminary changes, as well as the later differentiations,
which make possible the transformation of one organ into a different one.
In hydroids the regeneration following removal of a part of an organism
can be prevented by grafting another piece of a hydroid on the cut surface.
In the same way it is possible to prevent regenerative action also in Planaria.

The facts to which we have referred indicate that the normal Planaria
represents an equilibrated system in which there are various mechanisms of
induction acting on the neighboring tissue, as well as at a distance. It is the
removal of these influences, as well as the direct effect of a new medium
surrounding the injured tissue and the altered mechanical conditions in the

COELENTERATES AND PLANARIANS 217

latter, which have to be considered as possible factors responsible for the
regenerative and integrative changes setting in after an injury.

Homoiogenous tissues can bring about such an equilibration, whereas after
transplantation of pieces belonging to a different species or genus, this result
is only temporary and after some time regenerative, integrative activity sets
in at the point of union, so that, as Goetsch observed, the two parts of two
organisms previously joined together separate again. This fact makes it rea-
sonable to assume that contact substances whose organismal differentials are
not too distant are needed for equilibration. Also, the inductive action, which
a transplant exerts on the mesenchymatous tissue of the host, takes place,
according to Gebhardt, only if transplant and host are homoiogenous ; if the
adjoining tissues carry heterodifferentials no induction is noted. On the other
hand, the organizing action of ganglionic material, studied by Santos, is
effective not only when both graft and host belong to the same species, but
also when they belong to different species; when the graft belongs, for in-
stance, to Planaria dorotocephala and the host to Planaria maculata, or vice
versa.

As in hydroids, so also in planarians homoiotransplantations succeed readily
and distinct differences between the effects of auto- and of homoiotransplan-
tation have not been established; we have therefore no indications of the
existence of distinctive homoiodifferentials, though the existence of hetero-
differentials has been definitely demonstrated. As stated, in certain favorable
cases heterotransplants act like homoiotransplants ; but it seems, as a rule,
that contact and distance mechanisms active at the point of union between
two homoiogenous pieces are ineffective in heterogenous combinations. Hetero-
transplantation of small pieces seems not to lead to a complete union of the
graft with the surrounding host tissue.

So far as the plasticity of organs and the lack of manifestation of finer
organismal differentials are concerned, there is thus a fargoing likeness in
hydroids and planarians, and the same general conclusions apply in these two
groups of animals as to the similarity of the mechanisms which maintain the
intraorganismal equilibrium and the absence of distinctions between autog-
enous and homoiogenous tissues in this equilibrium. Various types of organ-
izer and regenerative, integrative influences play a role in determining the
mutual relations of organs and tissues in these lower organisms, all tending
to reestablish the original equilibrium when it is disturbed. It is this autog-
enous equilibrium, as we have studied it in higher organisms and as it exists
in a wider sense also in these primitive organisms, which determines the
maintenance of individuality. However, here the type of interactions between
organs and tissues which helps to sustain the normal equilibrium, or to re-
establish a disturbed equilibrium, is in some respects more accessible to
analysis than are the corresponding mechanisms in the higher organisms. In
the latter, accompanying the greater refinement in individuality, the means of
restoring an unbalanced equilibrium, in the sense in which it can be accom-
plished in these very primitive organisms, are lacking.

Chapter 2

Transplantation and Individuality in Higher
Invertebrates and in Amphibia

In this chapter we shall analyze individuality first in lumbricidae, which
represent a transitional form between the very primitive invertebrates,
already discussed, and the more differentiated echinoderms and arthro-
pods. These latter will then be considered, and lastly, amphibia, as representing
a less highly developed type of vertebrate.

A. Transplantation and Individuality in Annelids

The lumbricidae differ from the planarians in a considerably greater fixity
of their organs and presumably in a correspondingly greater specificity and
fixity of the substances on which the differences between organs depend
(organ differentials). While the organs have not yet become entirely rigid,
still the differentiation between head and tail parts is more fixed than in
planarians. In accordance with this change in the organs we find a greater
differentiation in the organismal differentials, as is indicated in the trans-
plantation experiments on lumbricidae which have been carried out especially
by Korschelt and his associates, Joest, Rutloff, Leypoldt, Harms, Rabes, and
more recently by Mutscheller. The earlier of these experiments antedated the
majority of the investigations on coelenterates and planarians. At that time
attention was focused on problems which have since receded into the back-
ground. Thus the problem as to the significance of a reversion of polarity in
transplantation, which had been introduced largely through the investigations
of Voechting in plants, dominated research to a large extent at this earlier
period, and even much later we find Schoene studying polarity in transplan-
tation of vertebrate skin.

As to polarity, two questions might be asked: (1) Is there inherent in
these organisms an orientation of their constituent parts comparable to the
organization of a magnet, and is it therefore necessary that the transplant be
inserted into the host in a definite direction if transplant and host are to be
mutually compatible? As far as is known, this does not hold good in the
animal series. (2) Do the actions of contact substances and of distant sub-
stances exert different influences on regenerative processes, and in particular
on wound healing, in a normal and a reversed orientation of the transplanted
piece? This may be the case in the more primitive organisms, where regenera-
tive processes of an integrative character play a much greater role than in
the higher organisms, and where the organ differentials are not yet so rigid
as to prevent heteromorphosis. However, in some instances certain subsidiary
factors may differ at the two poles of a transplant and then such factors may
play a role also in higher organisms.

218

HIGHER INVERTEBRATES AND AMPHIBIA 219

A second problem prominent in the earlier experiments concerned the
possibility of changing species characters of parts of organisms by means of
heterotransplantation. Is the host able to impress his own organismal differ-
ential on the transplant? We now know that species, as well as individuality
differentials are gene derivatives and are therefore essentially fixed, although
their manifestations may be modifiable within certain limits.

If we now consider the investigations in lumbricidae which have a bearing
on the problems with which we are especially concerned, namely, the evolu-
tion of the organismal differentials and their relation to the degree of plasticity
of the organism in its response to environmental changes, it has been shown
that, as a general rule, homoiotransplantation of pieces which are viable
succeeds readily, host and transplant remaining permanently united. Follow-
ing transplantation, a union of the corresponding organs, such as integument,
vessels, intestines and nerve strands, takes place, and movements as well as
mitotic divisions in the tissues play a role in this process ; thus one harmonious
individual is produced in which the organ systems derived from different
individuals function well, and it is only by means of differences in pigmen-
tation that the homoiogenous constituents of such individuals can, in some
cases, be distinguished. It seems that especially the union of the nerves of the
two partners is important in homoio- as well as in autotransplantation ; if
the nerves do not properly unite, then regeneration may occur at the point
of junction of the pieces and a new head may grow out, or the partners
separate, even if outwardly the union between the partners has been perfect.
Apparently the nerves play, here, an important part in determining regenera-
tion, and we may recall the fact that also in Planaria Santos found indica-
tions that the cephalic ganglia may determine head formation. It is apparently
the contact with corresponding living nerve tissue which keeps the nerves in
a quiescent state, preventing their regenerative outgrowth and thus their
stimulating effect on the growth of other surrounding tissues. However, the
evidence as to the significance of nerve tissue in regenerative and integrative
growth processes, especially in cells in planarians, is still contradictory, and
in lumbricidae even a defect in the union of the body walls of the two pieces
may lead to a newformation of a head, irrespective of the presence of nerve
fibers.

While, then, in this class of animals there are apparently no differences
between auto- and homoiotransplantation, yet by means of certain experi-
mental procedures it is possible to bring out such differences ; thus, if three
pieces are joined together, the middle piece being inserted in an inverse
direction, this combination remains alive permanently only in autotransplan-
tations, while in homoiotransplantations some difficulties appear. But, there
remains the possibility that the superiority of autotransplantation may be due
to the fact that in this instance the pieces fit together better mechanically and
that individuality differentials are not concerned in this result. Similar obser-
vations were made in Hydra by H. D. King in joining together more than
two homoiogenous pieces.

In lumbricidae, the differentiation of the organism is farther advanced

220 THE BIOLOGICAL BASIS OF INDIVIDUALITY

than in planarians and the relative importance of inductive factors, acting
by means of distance substances given off by transplanted pieces, is dimin-
ished as compared with the more primitive organisms, although it is not yet
entirely lost. Likewise, the action of external environmental factors on organ
formation is not evident in lumbricidae in the sense in which it exists in the
case of hydroids. Korschelt and Mutscheller have shown that the ability to
form a head is limited to the most anterior part of the body, and that the
farther back the segments are, the greater is their tendency to form a tail.
The gradient in organization in Lumbricus is thus quite definite. If one
transplants to the anterior pole of an animal, whose head has been cut off,
a posterior part (tail) of a worm in the inverse direction and then cuts off
the end segments of the transplanted tail, the inductive action of the large
posterior piece, which would tend to call forth the production of a hetero-
morphic head at the end of the graft, cannot overcome the strong organ-
specialization of the tail segments which have the inherent tendency to produce
a tail. But if a still larger number of the posterior segments of the tail piece
are removed before a remaining piece of the tail is grafted inversely on the
anterior cut surface of the host, then the inductive, integrative action of the
larger partner can overcome the less specialized organ differentials which
exist in the graft, at a somewhat greater distance from the posterior end of
the animal, and formation of a head may take place at the free cut surface.
There exists, thus, a competitive struggle between the inductive action of
substances or mechanisms, which act from a distance and which may tend to
produce a heteromorphosis, and the fixity of the organ differentials in the
transplant, which, when unopposed, would lead to the reproduction of a tail
organ. In this struggle the larger partner has an advantage over the smaller,
a condition applying similarly in hydroids and in planarians. A corresponding
experiment which L. V. Morgan carried out in Planaria, leading to the
heteromorphic development of a head at an aboral cut surface grafted in-
versely on the anterior cut surface of a larger piece, succeeded more readily,
because in planarians the organ differentials are not yet fixed to the same
degree as in lumbricidae. The more pronounced differentiation of organs in
these latter animals diminishes the plasticity of the organism and the ready
transformation of polar organs, as well as the importance of integrative
induction.

More recent experiments of Julian Huxley and Gross with the polychaete
worm, Sabella, indicate that the making of a wound as such may exert a
stimulus which acts not only locally in an area adjoining the wound, but
which may also act at a distance and influence the character of the structural
changes which shall take place. Thus the cutting off of a regenerated head
may not only influence a transformation of abdominal segments into thoracic
segments near the head pole of the animal, but it may also cause, under
certain conditions, a further transformation of regenerating abdominal seg-
ments situated at the tail pole of the animal into thoracic segments. Also,
small lateral wounds may influence the changes which take place in adjoining,
and even in more distantly situated segments ; these changes may consist either

HIGHER INVERTEBRATES AND AMPHIBIA 221

in a loss of certain structures, followed by the formation of new structures,
or, in some instances, in the direct transformation of organs, without the
previous loss of other structures. These observations point to the existence
of a somewhat furthergoing plasticity in the structure of annelids, which
permits the transformation of regenerating abdominal segments into segments
with the character of thoracic segments. On the other hand, experimentally
produced duplications of considerable size may persist unchanged under
conditions in which, in the more primitive and plastic organisms, various
regulative mechanisms would have eventuated in the formation of normal
individuals. As far as the organismal differentials are concerned, homoioge-
nous combinations are possible in lumbricidae, without leading to disharmonies
which, as we have seen, take place in parabiotic partners in mammals, owing
to the greater refinement of organismal differentials in the latter.

We see, then, that in general the differentiation and fixity of the organism
is much more advanced in lumbricidae than in hydroids and planarians ;
correspondingly, the inductive distant action has decreased in effectiveness
in the former, and it is likewise due to their relative fixity in organization
that an organizer action, in which a differentiated part grafted on a host
induces here the development of its own kind of an organ, seems not to have
been observed in this class of animals. Such an organizer would probably be
unable to act effectively with this less plastic material. On the other hand,
there is reason for assuming that the second kind of inductive action leading
to integrative regeneration is still, though to a much diminished extent, potent
even in lumbricidae.

Heterotransplantation succeeds in lumbricidae with much greater difficulty
than homoiotransplantation. In the large majority of cases heterogenous
pieces remain united only for a few days, then separate or degenerate. In
other cases there may be a better union by means of scar tissue covered by
epithelium ; secondarily, muscle, nerves and vessels may grow through it and
into the heterogenous tissue. Thus also in heterotransplantation blood vessels
as well as other organs may unite with the corresponding organs of the partner
and a common circulation be established. But even under these conditions
while there is, at first, an apparently perfect union of the two heterogenous
pieces, a separation may take place subsequently and as late as after five
weeks. As a result of changes occurring at or near the place of union, the
latter becomes looser and a mere mechanical pull may readily separate the
two partners. However, in one instance Korschelt succeeded in keeping a
combination of Lumbricus rubellus and Allophora terrestris alive for a period
of eight to nine months. In pieces thus temporarily united, in which a smaller
heterogenous piece has been grafted in an inverse direction on a larger host
whose head has been cut off, the host may induce the beginning formation
of a heteromorphic head in the smaller anteriorly situated graft; but usually
at the point of union a new head develops and then the pieces separate. The
heterogenous contact substances, or, more generally expressed, contact
mechanisms, which are active at the cut surfaces do not keep the adjoining
parts in an equilibrated, quiescent state and can not therefore prevent regen-

THE BIOLOGICAL BASIS OF INDIVIDUALITY

eration. The attachment of a heterotransplant to the adjoining host tissue is
from the beginning less complete than it would be in case of homoiotrans-
plantation and gradually degenerative changes occur in the transplant.

Similar are the results if, instead of larger heterogenous transplants, small
pieces are grafted on defects in larger pieces. If small pieces of skin together
with the adjoining muscle are thus heterotransplanted into wounds in lum-
bricidae, they remain as a rule preserved only for a certain time; but in
exceptional cases the transplant may maintain itself apparently without change
for as long as nine months. Leypoldt used in experiments of this nature,
regenerating, heterogenous skin which was not yet fully developed; but in
most instances it was either soon discarded or it was gradually absorbed
through the activity of the adjoining tissue of the host. Even after the pieces
had healed in, in an apparently perfect condition, subsequently degenerative
changes took place in the transplants and led to their gradual absorption. On
the other hand, homoiogenous pieces of skin usually were much more readily
preserved for a long period of time, or even permanently. When ovaries were
heterotransplanted, in a small minority of cases the grafts remained in good
condition as long as for three months or even for one year, provided the
species were nearly related; but if they were farther distant, the transplants
were injured and were much more quickly absorbed. It is of interest that it
was also possible to obtain heterofertilization of the eggs which developed
in the heterotransplanted ovaries. The F1 generation of such hybrids possessed
characteristics of both parents, but they were sterile and soon died.

We may then conclude that heterotransplantation may succeed, although
usually with some difficulty, in lumbricidae as well as in the more primitive
hydroids and planarians, provided the species used are nearly related ; other-
wise the incompatibility of the organismal differentials leads to an early
separation or destruction of the transplant.

Somewhat similar are the factors which are active in transplantation in the
oligochaeta Criodilus, as we may conclude from the experiments of Tiara.
In this organism certain kinds of heterotransplantation succeed, while others
do not. We have here, likewise, a limited degree of organ differentiation, the
anterior segment having the tendency to form a head, the posterior segment
a tail ; but as in lumbricidae, heteromorphosis may occur as a result of certain
mechanisms acting in such a way as to force upon a smaller piece, from a
distance, the formation of an organ contrary to the rudimentary differentiation
existing in the smaller piece. Thus a larger sized partner may gain dominance
over a smaller one.

In this case also, the nervous system may perhaps determine whether or
not a head formation shall take place at the point of union between two
pieces. A head forms at the anterior cut surface if the nerve strands of the
partners do not unite. Under these conditions the regenerative activity of the
cut nerve seems to furnish the stimulus for a head formation. That in these
organisms a certain plasticity of organ formation still exists follows also
from the fact that the epidermis of the adult animal has the power to regen-
erate the nervous system.

HIGHER INVERTEBRATES AND AMPHIBIA 223

We may conclude from the principal facts relating to organ and organ-
ismal differentials in the relatively primitive classes which we have considered
so far, that while with the progress in phylogenetic development the differen-
tiation of the organs advances, their plasticity decreases and, correspondingly,
the effectiveness of the inductive processes leading to the reestablishment of
normal individuals is diminished ; however, there is not a proportional advance
noticeable in the differentiation of the organismal differentials, or at least in
their manifestation. In all these classes heterotransplantation between nearly
related species seems to succeed, although as a rule with greater difficulty than
between homoiogenous organisms, while between farther distant species it
does not succeed. But, it is possible that the greater regenerative power of the
hydroids and also of the planarians, as compared with that possessed by
lumbricidae, — a regenerative power which leads to integration of defective
organisms, — may serve to cover up the fact that they actually do possess less
differentiation of the organismal differentials than the lumbricidae and less
sensitiveness to strange differentials. The greater regenerative power of the
hydroids may lead to a more ready outgrowth from a cut surface and to
subsequent separation of the partners in case the organismal differentials
are not quite compatible, and this condition may make it appear as though the
reactions against differences in organismal differentials were more severe in
the more primitive organisms than they actually are.

B. Transplantation and Individuality in Arthropods and Echinoderms

In general, the regenerative power is very limited in insects and moths,
especially after metamorphosis has taken place, and this condition interferes
with transplantability to a certain extent. It also seems to be associated with
an increase in the rigidity of organization.

In moths, experiments in transplantation were carried out by Crampton
as early as 1899. At that time, as we stated in reference to experiments in
lumbricidae, the problems of polarity and of the preservation of the species
characters in transplant and host were prominent; also, the question as to
the behavior of the various organs of host and transplant to each other had
been introduced through the experiments of Born with embryos of amphibia.
On the other hand, the problem as to the effects of variations in relationship
between the partners, or between donor and host, on transplantation played
an unimportant role at that time. In Crampton's experiments parts of pupae
were used ; on account of their low regenerative power only the skins or other
organs situated near the surface, but not the internal organs, united after
transplantation, and positive results were obtained therefore only in a minority
of cases. While homoiotransplantation of small pieces of tissue was successful
in a number of instances, heterotransplantation succeeded not at all, or at
best only exceptionally. However, if instead of grafting small pieces of tissue,
whole segments of the animals were transplanted, a procedure which does
not exactly correspond to parabiosis because of the inability of the isolated
segments to lead an independent existence, both homoio- and heterotrans-
plantation succeeded, but the former apparently somewhat better than the

224 THE BIOLOGICAL BASIS OF INDIVIDUALITY

latter. In all probability we have therefore in these cases to deal with a result
similar to that found in lumbricidae ; heterotransplantation may succeed, yet
heterodifferentials do exist and exert a certain influence, on the fate of the
transplants. On the other hand, we must always consider the possibility that
whenever negative results were obtained in heterotransplantations, this may
have been due not to a primary incompatibility of the organismal differentials,
but to secondary factors, as for instance, to differences in the size of the
pieces to be united and to similar more or less accidental conditions.

The subsequent experiments of Meisenheimer also make it probable that
heterodifferentials may play a role in these transplantations. In Lymantria
this investigator succeeded in. transplanting ovaries into individuals of the
same, as well as of different species, provided the latter were nearly related.
We might then conclude that heterodifferentials become manifest only in the
case of more distant species, either because in more nearly related species the
less marked differences in genetic constitution do not lead to the production
of antagonistic mechanisms to the same extent as greater differences, or be-
cause the sensitiveness and reactivity to the injurious action of the correspond-
ing heterodifferentials are less pronounced in these lower forms than in
higher organisms. However, the experiments of Kopec, which followed those
of Meisenheimer, indicate that heterodifferentials are well developed in
moths; he found that, while homoiotransplantation of sex glands succeeds,
heterotransplantation does not. Of interest is also his observation that differ-
ent tissues show different degrees of resistance to the manifestation of
heterodifferentials ; thus the germ cells are the most sensitive ; these die earliest
after heterotransplantation, while transplanted connective tissue grows at first
and is only secondarily destroyed. Furthermore, he also notes that the destruc-
tion of the transplants takes place the more rapidly, the more distant the
heterogenous species are from each other. It seems, then, that in these cases
we have to deal with a direct injurious action of heterotoxins ; but in addition
cellular mechanisms participate in these processes, inasmuch as phagocytic
cells of the host may destroy isolated heterogenous germ cells.

In insects, according to E. Ries, it is possible to transplant larval fat tissue
which has been transformed into a mycetoma, into larvae of different orders.
Accordingly, if transplanted from Periplaneta into the peritoneal cavity of
Tenebrio, or from Psylla to Tenebrio, the grafted fat tissue remains alive
throughout the life of the larva; however, as a result of the strangeness of
the transplant, lymphocytes soon begin to collect around it. The transplanted
tissue can even survive the metamorphosis of the host into a pupa without
being affected by the general changes, and not even by the histolytic processes
which occur during this period. In evaluating these observations we must,
however, consider the fact that in all the transplantations in insects discussed
so far, we have to deal with transplantations not in adult forms, but in cater-
pillars and pupae.

Some remarkable successes in transplantation have been reported by W.
Finkler. According to this author, it is possible in the insect species Hydro-
philus to replace the head which has been cut off, by grafting the head of

HIGHER INVERTEBRATES AND AMPHIBIA 225

another individual of the same species; this kind of transplantation appar-
ently succeeded also between different species if they were nearly related
(Hydrophilus and Dytiscus), but not between farther distant species. Finkler
states that the head thus transplanted determines to a large extent the sexual
reflexes and the color of the body in the host. But other investigators were
not successful in repeating these experiments, and according to Przibram no
connection takes place between the nerve strands of the grafted head and the
body.

As to echinoderms, these organisms are very unfavorable for transplan-
tation experiments on account of their rigid integument, and very few
investigations have been reported. However, Przibram succeeded in homoio-
transplantation of the disc in crinoids ; also in transplanting this organ into
other varieties differing from each other in their color; and even in the
starfish H. D. King accomplished, in one exceptional case, a homoiotrans-
plantation, in which however the ectoderm of host and transplant was the only
tissue which underwent union.

As far as we can judge from the relatively limited number of experiments
in arthropods and echinoderms, these organisms seem to behave in a similar
way to lumbricidae as far as manifestation of organismal differentials is
concerned, provided we disregard more or less accidental difficulties in trans-
plantation due to peculiarities in the structure of these animals. On the other
hand, the difference between the results of homoiotransplantation and hetero-
transplantation of ovaries in the experiments of Kopec indicates that, after
all, the sensitiveness to heterodifferentials may be greater in this class than in
lumbricidae, and that the reactions of the host against the strange transplant
may be more complex. We have furthermore to consider the possibility that
the relatively low degree of regenerative power which these organisms possess
may render the manifestation of a reaction against transplants possessing a
different organismal differential more difficult than in lower organisms.

In evaluating the relative significance of organismal differentials in the
various classes of animals which we have analyzed so far, we must in addition
to the complications already mentioned, take account of the fact that our
estimates as to reactions against strange differentials are based largely on a
gross study of the grafts. A study of the finer cellular reactions, which may
have occurred, is lacking, and if undertaken it might have made possible a
finer gradation of the organismal differentials. As stated, auto- and homoio-
transplantation show no marked differences in results in these various classes
of animals, and even heterotransplantation succeeded in a number of cases
between more nearly related species. In these respects the different classes
so far considered have behaved in a similar manner.

Much more pronounced were the differences in the rigidity of organization
and in the possibility of inducing new organ formation or of transforming
one organ into another in these types of animals. As regards these reactions,
we find a definitely graded series, beginning with the hydroids and ascending
by way of planarians to the annelids and then to the arthropods. In the latter,
only small parts of the body can undergo far reaching changes; we refer in

226 THE BIOLOGICAL BASIS OF INDIVIDUALITY

particular to the changes in the head appendages which may be induced
in certain crustaceans and in which the activity of the nervous system is of
importance ; here, also, regeneration is on the whole limited to the extremities
and other appendages.

In general, the transformation from one part of the body into another, or
from one organ into another, seems as a rule not to be a direct one, but this
change is apparently accomplished by the return of the part of the body or
of the organ involved to a more indifferent state, which subsequently assumes
the characteristics of the new part or organ. Furthermore, it appears that
with increasing phylogenetic development, cells with relatively great poten-
tialities of further differentiation may take over the newformation of organs.

C. Transplantation and Individuality in Adult Amphibia

In our discussion of organismal differentials in amphibia, we shall omit,
for the present, transplantations in which host and transplant, or host and
partner, are embryonal; these we shall consider later. Furthermore, some
transplantations in amphibia were used for the analysis of the factors under-
lying metamorphosis, and these investigations will also be considered sep-
arately. There remain for our present purpose a number of transplantations
in adult urodeles and anurans, two groups in which the results differ in
certain respects. Of special interest are the transplantations of pigmented to
white skin and vice versa, because the behavior of the pigment may serve
as an additional indicator of the reaction of the host against the graft.

In the urodele, Triton alpestris, homoiotransplantation of skin succeeded
well, as did likewise heterotransplantation of skin from Triton alpestris to
Triton cristatus, but in the latter type the healing took place more slowly than
in homoiotransplants. The white transplant assumed gradually the dark color
of the host skin. On the other hand, Triton salaratus did not, as a rule, tolerate
transplants from Triton alpestris but casted them off (Taube). In the sala-
mander, Diemictylus viridescens, Collins and Adolph did not observe a differ-
ence between the results of autogenous and homoiogenous transplantation of
skin; both remained preserved, but in both, a re-organization of the pigmen-
tation took place.

In anurans, the differences between the results of auto-, homoio- and
heterotransplantation of skin were more pronounced. We may here refer also
to transplantations in frog tadpoles, where autogenous transplants of white
skin to pigmented areas remained preserved, but very slowly, pigmentation
could occur in the graft, caused apparently by changes which took place in
the transplanted epidermis itself. After homoiotransplantation, the skin healed
in more slowly, a relatively rapid invasion of the white skin by the pigmented
cells of the host occurred, and lymphocytes accumulated underneath the
transplant (Cole). In adult Rana pipiens, according to Hadley, autogenous
surface epithelium and glands healed in well, whereas homoiotransplantation
of skin succeeded not as readily, the number of unsuccessful grafts being
greater and the pigmented cells of the host growing into the graft. Still less
favorable were heterotransplantations from Rana pipiens to Rana clamitans.

HIGHER INVERTEBRATES AND AMPHIBIA 227

The healing-in took place with greater difficulty and pigmented grafts that
remained attached to the host for more than 15 days became progressively
lighter, whereas the unpigmented grafts were invaded by the pigmented host
skin; degenerative changes took place in the transplant and large masses of
leucocytes collected underneath it. There were then, in anurans, graded
differences in the tolerance of the host to autogenous, homoiogenous and
heterogenous transplants, and the reactions against strange organismal dif-
ferentials were, here, more definite than in urodeles. It is of interest that
heterotransplantation into the lymph-sac succeeded, and this suggests that it
was the action of the tissues rather than that of the bodyfluids which caused
the injury of the heterogenous graft.

We may mention in this connection also similar experiments of May in
reptiles. In chameleon, May found that autotransplantation of skin succeeded
very readily, without any change in the pigmentation of the transplants. On
the other hand, homoiotransplants were absorbed after they had healed in,
the total absorption taking place between the 61st and 90th day. Usually no
change in pigmentation occurred here, except in one case, where the trans-
plant became lighter. Conditions were then, in this case, similar to those seen
in birds and mammals, except that the reactions occurred more slowly;
whether or not lymphocytes participated' in these experiments in reptiles is
not stated.

The results of transplantations of other organs are in essential agreement
with those we have mentioned. Thus, in the salamander, Diemictylus viri-
descens, Stockard found that homoiotransplanted pieces of the ovary can be
maintained alive in a satisfactory condition in the testicle, but not in other
organs. However, in other urodeles, Harms showed that not only homoio-
transplantation, but even heterotransplantation, of the ovaries may succeed
within a certain range of relationship, and that in general there seems to be a
parallelism in the transplantability of tissues and the possibility of hybridiza-
tion between certain species. In this connection, Harms made the interesting
observation that in urodeles blood vessels of heterogenous origin supply the
circulation in these transplants, and that the peritoneal cells lining the grafted
ovaries may swell, send out processes in the direction towards the lining
peritoneal cells of the host, and that both may then meet and coalesce. In adult
urodeles, therefore, heterogenous cells may enter into close contact with each
other, or may coalesce apparently without the development of any antagonistic
reaction. Meyns noted a similar coalescence of cells also in anurans, but it
occurred in homoiogenous transplantations. In case a destruction of the
heterotransplanted ovary did take place, this may not have been altogether a
direct effect of heterotoxins, inasmuch as connective tissue and phagocytic
cells of the host took part in the disintegration and elimination of those trans-
planted ova which had escaped the direct toxic action of the bodyfluids of the
host. It seems, therefore, that ova which, under the influence of the strange
organismal differential were changed in their metabolism, secondarily were
exposed to the injurious action of host cells.

In mammals we observed in certain cases that reciprocal transplantations

228 THE BIOLOGICAL BASIS OF INDIVIDUALITY

did not behave in the same way ; similarly, in urodeles some differences have
been noted; thus, transplantations of the ovaries from Triton alpestris to
Amblystoma tigrinum succeeded, while in the reciprocal transplantation the
graft exerted a toxic effect on the host. However, it is possible that in this
instance we have to deal not with the direct effect of the organismal differen-
tials, but with specific toxic substances, the production of which is limited
to certain organs.

Also, heterotransplantations of testicle were successful in some species of
Triton (Koppanyi). But if certain organs are grafted with greater difficulty,
then it is possible to make homoio- and auto-, but not heterotransplantations.
Thus, according to Kurz, limbs can be homoiotransplanted in adult Triton
and even regeneration may take place in autogenous as well as in homoiogenous
grafts of this kind ; but heterotransplantation does not succeed. Similar obser-
vations have been made by Mathey in the case of transplantation of the eyes
in Salamander larvae and in adult Tritons. Under these conditions even
autotransplantation succeeds only in a small minority of cases, and still greater
difficulties are encountered in the case of homoiotransplantation. In Triton,
the presence of a functioning spleen, or of substances given off by this organ,
may be an unfavorable factor in the transplantation of this tissue. Ehrenpreis
accomplished, therefore, a homoiotransplantation of spleen only in urodeles
in which the spleen had previously been extirpated; but even in this case
autotransplantation seems to have been preferable to homoiotransplantation
(Jolly and Lieure).

If we compare the range in which transplantations are possible in anurans
and in urodeles, we find a greater restriction in the former. Welti succeeded
in homoiotransplantation of the ovaries in Bufo vulgaris, while transplanta-
tions into different races failed. The successfully transplanted ovaries gave
off hormones which modified certain secondary sex characters in the host.
Meyns observed that the testicle is readily homoiotransplanted in immature
frogs, but can be heterotransplanted only in exceptional cases. In adult frogs
even homoiotransplantation does not produce as favorable results as autotrans-
plantation, an observation which indicates that also homoiodifferentials may
exert here an injurious effect on tissues. Furthermore, this investigator noted,
in accordance with the findings in the case of mammalian organs, that different
constituents of an organ may differ in the degree of sensitiveness which they
manifest; the efferent ducts of the testicle were less sensitive to the injurious
effects of transplantation than the generative cells proper. As in Tritons,
so also in anurans a specific hormone may inhibit the successful transplantation
of an organ with an internal secretion. Thus transplantation of the testicle was
possible neither in normal males nor in normal females, but only in castrated
animals. Which phase in the process of transplantation is here affected by the
internal secretion, whether it is the healing-in of the graft or its subsequent
preservation, is not clear from the data on hand; nor do we know whether
the destruction of the transplant takes place directly under the influence of
the injurious bodyfluids of the host, or through the mediation of the host
lymphocytes and connective tissue cells.

HIGHER INVERTEBRATES AND AMPHIBIA 229

An internal secretion is also active after homoiotransplantation of thumb-
pads of the frog; however, in this case the testicular hormone affects only the
further growth processes in the organ after it has healed in; and according
to Harms, it accomplishes this effect largely by means other than variations
in the circulatory condition and blood supply received by the transplant.

Rhoda Erdmann noted that in the adult Rana autotransplantation of skin
succeeded well; but homoiotransplantation succeeded only for periods of
from two to four months, and skin glands did not develop in the latter kind
of transplants. But even after heterotransplantation from Rana temporaria
to Rana arvalis the graft could remain attached to the host for as long as
eighty days, when it was cast off. Similar to the observations of Harms as to
toxic effects exerted by ovaries transplanted into Triton, and to those of
Diirken in the transplantation of parts of neurulae into larvae of Rana, Erd-
mann noted after transplantation of skin of Hyla to Rana, the occurrence of
hemorrhages and other toxic symptoms in the host. These results agree also
with those of Schultz, who found that after transplantation of skin from Bufo
viridis to Bufo vulgaris, the host died, while the reciprocal transplantations
were successful. It is evident that specific toxins given off by such transplants
complicate the results of grafting in these amphibia, and that we have not
merely to deal with the effects of organismal differentials. As stated above,
similar effects have also been observed after transplantation in certain
urodeles.

We may then conclude that heterotransplantations succeed with greater
difficulty in urodeles than in lower classes of animals, and with still greater
difficulty in anurans. In the latter class some differences have been recorded
even between the results of homoio- and autotransplantation, and we may then
conclude that a furthergoing stage in specialization of these differentials has
been reached in amphibia, and that within the amphibia there is seen a graded
advance in the refinement of the organismal differentials in the transition from
urodeles to anurans. However, as we pointed out previously, the lack of an
unfavorable reaction of a host against a certain kind of transplant does not
exclude the presence of the finer grades of organismal differentials. Thus we
cannot exclude the possibility that in urodeles, as well, individuality differen-
tials may exist; indeed, certain observations indicate that here, also, auto-
transplantation may succeed better than homoiotransplantation.

The interpretation of the results of transplantations in the more primitive
organisms which we have discussed so far, is based largely on the gross
examination of the transplants ; however, in the case of grafting in the urodele
Triturus, Anderson and Horowitz have carried out microscopical examina-
tions, in which they compared the reactions in auto-, homoio-, and hetero-
transplantations of skin (Anderson), and muscle tissue (Horowitz). Horo-
witz has described a reaction of the fibroblasts and lymphocytes of the host,
which invaded the transplant the more actively, the stranger the organismal
differentials were between host and transplant. In the case of heterotrans-
plants, also polymorphonuclear leucocytes participated in this reaction. These
various cells succeeded in destroying tissues possessing organismal differ-

230 THE BIOLOGICAL BASIS OF INDIVIDUALITY

entials incompatible with those of the host. In principle, conditions are
therefore similar to those found by us in the case of mammalian tissues; a
difference exists only in that the reactions in urodeles were slower than in
rodents, and also in that lymphocytes and fibroblasts later destroyed parts
of the autotransplants, while other parts remained preserved ; these reactions
against autogenous tissues were presumably due to necrobiotic changes which
occurred in certain areas of the grafts. In both urodeles and mammals the
vascularization of autotransplants was better than that of homoio- and hetero-
transplants.

Also, Hitchcock finds that frog skin autotransplanted into the lymph sac
of frogs remains preserved much longer than heterotransplanted skin. Ulti-
mately, however, it is destroyed through the ingrowth of fibroblasts ; but this
result is due merely to accidental factors and not to factors inherent in
amphibian tissues, as is evidenced by the fact that skin autotransplanted into
a defect of skin remains preserved indefinitely. Similar results may be obtained
in mammals and birds, for example, when skin is injured after autotrans-
plantation into the subcutaneous tissue. Following heterotransplantation of
frog skin, the transplant is destroyed much more rapidly than after autotrans-
plantation and the destruction takes place the more rapidly the farther distant
phylogenetically the species of host and transplant; frog skin dies very
quickly after transplantation into Triturus and Triturus skin becomes necrotic
within a very short time after transplantation into the frog. After trans-
plantation into urodele species, it is the heterotoxin of the bodyfluids which
kills the transplants, while after heterotransplantation into Rana, the injury
is due, above all, to the action of leucocytes. In the tissue surrounding the
graft, lymphocytes accumulate. Conditions here are therefore, in principle,
similar to those after heterotransplantation of mammalian and avian tissues;
only in the latter the injurious action of the bodyfluids is evident in every
instance, while, according to Hitchcock, this effect is not noticeable after
transplantation of frog skin into more nearly related species. Presumably we
have, in the case of frog skin, to deal merely with quantitative differences
in the effects of toxins and of cellular reactions, such as were observed also
in the case of mammalian tissue, where we noted that heterotransplantation
of cartilage produced cellular reactions which were much more prominent than
those following heterotransplantation of such very sensitive tissues as thyroid
and kidney, which are destroyed by strange bodyfluids within a very short
time. We have found also other instances of quantitative differences between
the respective importance of toxic serum and cellular reactions in different
species of mammals. It has been assumed in the case of tumor transplantation
that necrosis primarily attacks the center of the pieces and not the peripheral
parts, which indicates that an injurious action of the bodyfluids on the trans-
plant is lacking. Hitchcock uses the same argument in order to prove the
absence of an injurious action of the bodyfluids after transplantation of skin
of Rana into strange species of Rana. Nevertheless, homoiotoxic action does
exist in the case of tumors as well as of normal mammalian tissues; and we
may draw the same conclusion in regard to heterotoxic action in heterotrans-

HIGHER INVERTEBRATES AND AMPHIBIA 231

plantation among anuran species. The center of the graft degenerates first
because it is injured by the lack of foodstuffs; it succumbs therefore before
the peripheral parts do, which resist the injurious action of the bodyfluids
better, since they are near the source of oxygen and the foodstuffs. Careful
microscopic studies of grafts in amphibians tend to prove, therefore, that
here, in principle, already a fargoing specialization of the organismal differ-
entials has taken place and that this specialization manifests itself in a similar
manner in amphibia and in mammals.

In progressing from the urodeles to the anurans there is thus noted an
advance in the specificity of the reaction on the part of the host against a
strange organismal differential. Furthermore, parallel to this progression in
specificity a reverse change takes place in the regenerative and integrative
power of these classes of animals. While this is very much more restricted
in urodeles than in the primitive invertebrates, still a certain degree of the
power of regeneration has been retained by them, as indicated by their ability
to regenerate extremities. In the anurans, on the other hand, only the rudi-
ments of this integrative power are left, consisting merely in the ability of a
number of individual tissues to undergo, to a moderate degree, proliferative
processes, which may lead to the filling-out of certain defects and to wound
healing in the skin. In accordance with' our previous conclusions we find,
therefore, also in this instance a parallelism between the degree of plasticity
in the organ-forming potencies of organisms and the development of the
finer organismal differentials. The greater the trans formability of organs and
the greater the restitutive and integrative power of organisms, the more
undifferentiated appear to be the organismal differentials and the less specific
are their effects.

From this brief survey of the behavior of organismal differentials during
phylogenetic development we may conclude that already in the most primitive
organisms certain reactions against tissues from strange species are present,
and that these reactions become more refined and specific with the advance
to groups of animals whose structure is more complex. But we observe also
that with progressing evolution the differentiation of organs and tissues, their
decreasing plasticity and increasing fixity are much more clearly graded than
is the refinement of the organismal differentials. No definite advance was
observable in the individualization of organismal differentials within the most
primitive classes of animals ; they all seemed to behave in a similar manner.
However, this lack of steady progression is perhaps only apparent and not
real. It may be at least due partly to the method used for the demonstration
of the organismal differentials, namely, observation of the reactions which
take place in an animal against a strange transplant, or between two partners
differing in their organismal differentials; now, in the lowest organisms the
tendency to integration is very great and there is the danger that the integra-
tive reactions which follow various kinds of disturbances may be interpreted
as reactions against strange organismal differentials. Furthermore, we may
recall the great complexity of the factors which enter into the reactions against
strange organismal differentials, and the fact that the intensity of these reac-

232 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tions is determined not only by the presence of the finely differentiated sub-
stances, which represent the organismal differentials in tissues and organs,
but also by the rate at which such substances are produced, given off by the
cells and allowed to diffuse into the strange organism ; finally, the results of
the reactions vary with the sensitiveness of the tissues involved. As far as the
injurious effects of incompatible bodyfluids are concerned, our ability to
discern these depends mainly on the sensitiveness of the tissues on which they
act; on the other hand, the strength of the cellular reactions against tissues
with strange organismal differentials is, to a certain extent, susceptible to
measurement, even if the tissues are more resistant.

We see, thus, that we have to deal with a considerable number of factors
if we wish to grade the degree of compatibility of the organismal differentials
of different organisms. With regard to the higher organisms, only a beginning
has been made in the approximate quantitative grading of these incompati-
bilities; in the case of the more primitive organisms the observations which
bear on this question are more or less casual and are based largely on gross
aspects of the changes following transplantation. The introduction of micro-
scopical methods for the study of cellular reactions against strange differen-
tials, methods similar to those used in the case of mammalian tissues, has only
recently been undertaken in the study of transplantations in urodeles. The
results already indicate that reactions against strange tissues, endowed with
strange individuality differentials, are present in classes of animals where the
methods formerly used were not adequate for their demonstration. In addi-
tion, there are the immunological studies of the relationship of the bodyfluids
of various organisms ; these are based on the ability of bodyfluids to serve as
antigens and to call forth the production of antibodies, which latter, in their
interactions with antigens, indicate the relationship between various species
of animals. These investigations will be discussed in a subsequent chapter.

We may then conclude that in the most primitive classes of animals the
substances which represent the organismal differentials or at least the reactions
against these differentials are as yet less finely differentiated than in higher
organisms, and that in general there is a correspondence between the lack of a
finer differentiation of organismal differentials and the lack in the finer differ-
entiation of organs and tissues, and an inverse correspondence between the
degree of development of organismal differentials and the degree of plasticity
of these organs.

As stated above, the graded progression towards an increase in the speci-
ficity and fixity of organs and tissues in the course of evolution are clearly
discernible. With advancing phylogenetic development the various parts of
the body differentiate more and more into a variety of organs, tissues and
cells, interacting with each other according to patterns which are specific and
rigid. Hand in hand with this change from the relatively simple structures of
such primitive organisms as the hydrozoa, to the greatly differentiated types
of organs, tissues and cells of the anuran amphibia, there takes place a change
also in the kind of substances which regulate the interaction of the different
parts of the individual. In hydrozoa we must assume that substances repre-

HIGHER INVERTEBRATES AND AMPHIBIA 233

senting various kinds of inductors exist and are transferred from one part
of the body to another; these, acting on a specific substratum of a very plastic
nature, are presumably responsible for the production and growth of the
organ systems which are characteristic of the different regions of the body.
In arthropods such transformations are limited to certain appendages, and
also in urodele amphibia integrative processes are possible only within a very
limited range; but in anuran amphibia they are lacking altogether. There
develop in insects and in the higher organisms, in accordance with their more
finely differentiated organs and tissues, hormones and neuro-hormones which
affect certain organs and cells in a very specific manner. Such hormones may
also affect the life and growth of transplanted organs with which they have
specific relations. Perhaps a corresponding increasing differentiation exists
also in the case of various other substances, such as vitamins and enzymes,
which regulate maintenance, growth and metabolism of organs and tissues;
but we have as yet no definite knowledge as to the phylogenetic development
of the latter types of substances.

Chapter J

Transplantation and Individuality of
Embryonal Tissues

We have studied the phylogenetic development of organismal dif-
ferentials and their manifestations in animals, using transplantation
of adult tissues as indicator. In this and the following chapter we
shall study the ontogenetic development of the organismal differentials and
for this purpose we shall make use of the data supplied by the transplantation
of embryonal tissues. In these experiments either parts of developing organ-
isms were joined together, each of which was capable of independent life, or
relatively small, not independently viable pieces of embryonal tissues or organs
were transplanted into embryonal or adult organisms. The union of inde-
pendently viable parts bears some resemblance to parabiosis especially if the
size of the surface, by means of which the partners are joined together, is
relatively small in comparison with the diameters of the grafts.

I. Transplantation in Amphibia. It was in amphibia that the possibility of
uniting parts of two different embryos into one organism was discovered in
1897 by Born, whose work thus introduced a problem which subsequently
suggested many similar investigations in amphibia as well as in other classes
of animals.

Born used in his experiments larvae of anuran amphibia. In these as in
other transplantations, besides the organismal differentials, other factors, some
of which were non-specific, helped to determine the results, and it is im-
portant, as far as feasible, to separate these factors. Thus, the rapidity of
growth of larvae of Rana esculenta is greater than that of larvae of Rana
fusca or arvalis, and in the union of parts of the former with parts of one
of the two latter larvae, components of Rana esculenta tend to dominate over
the other components and cause their atrophy. It is necessary to distinguish
such secondary effects from the direct manifestations of organismal differ-
entials, although the growth rate is, of course, as well as all other character-
istics of tissues and organs, at least in part, determined also by the genetic
constitution of the organism.

As a direct effect of the organismal differentials, we may consider the
readiness with which autotransplantation of embryonal constituents succeeds :
two parts can be readily united into a single organism, in which the corre-
sponding organs form so perfect a connection that, subsequently, the place
of junction can, as a rule, no longer be recognized; however, difficulty may
be experienced in the joining together of the components of the chorda dor-
salis, especially in older larvae. As in adult annelids, so also in amphibian
embryos analogous organs of the partners usually find each other and unite.

The results of homoiotransplantation are about the same as those of auto-

234

INDIVIDUALITY OF EMBRYONAL TISSUES 235

transplantation. Here, too, all kinds of combinations succeed, including the
union of smaller parts, which as such would not be capable of independent
life, with larger parts of larvae; in these experiments abnormalities, such as
organisms possessing two heads, may develop under certain conditions. Also,
in homoiotransplantation analogous organs tend to find and join each other
and usually it is impossible to recognize later the original line of demarcation.
No incompatibilities due to differences in individuality differentials develop,
and such combinations of organisms may even pass through metamorphosis.
If difficulties do arise, they are of a non-specific nature.

Similar were the results in heterotransplantation if the partners belonged
to nearly related species. In this case also the analogous organs of the two
partners had the tendency to unite and thus the two partners developed into
one homogeneous organism, in which no scar could be recognized at the point
of union; but when non-analogous organs of embryonal partners happened
to join, a scar did form, or else the organs separated after some time. As we
have noted previously, in the joining-together of pieces of adult lumbricidae
there developed at first a scar, which only secondarily was replaced by the
specific tissues. While the rates of growth in the two partners could be
independent of each other, the rates of differentiation were about the same,
substances circulating in both partners determining presumably the latter
effect. As we shall see later, Uhlenhuth, in transplanting eyes in salamander
larvae, found a similar correspondence in the rate of differentiation and in
the time of metamorphosis of host and graft. There resulted, thus, not only
a harmonious union of the two embryos belonging to different species, but in
certain cases even the blood vessels of one partner could grow into the other
partner apparently without causing any incompatibility.

We find, then, that heterodifferentials do not need to prevent the direct
union of the specific tissues in analogous organs without interference by
connective tissue; this was true also of parts of the nervous system, even in
cases in which the diameters of the components differed in the partners. On
the other hand, if non-analogous organs happened to meet, as stated, the
union took place by means of connective tissue, except in the case of ecto-
dermal and entodermal epithelia. These observations suggest that under these
conditions tissue differentials functioning as contact substances regulate the
interaction of tissues from analogous organs at the point of junction, although
the species differentials of the corresponding tissues differ in the two partners.

While after union of embryos from different species of Rana, the results
were similar to those obtained in homoiotransplantation, such combinations
were not able to maintain themselves for longer than two to three weeks when
species as distant as Rana esculenta and Bombinator igneus were united.
Although for some time in the beginning the partners could develop normally
and the double organisms begin to feed themselves, after awhile they became
sickly and progress ceased. Therefore, in the case of transplantation of more
distant species, heterotoxins apparently led to various abnormal conditions
in the animals. In Born's experiments circulatory disturbances became mani-
fest after about fourteen to sixteen days; there was either edema or no

236 THE BIOLOGICAL BASIS OF INDIVIDUALITY

circulation at all and death followed. Also in the subsequent experiments of
Braus, who showed that under favorable conditions the life of such combina-
tions could be prolonged for as long as five weeks, ultimately serious incom-
patibilities developed. However, union between members of different orders
(urodeles and anurans) did not succeed for longer than one or two days.

When thus heterotransplantations between nearly related species succeed
well, this does not necessarily mean that heterodifferentials do not exist in
their tissues, but merely that the intensity of the reaction against the strange
organismal differentials does not preclude a successful transplantation. How-
ever, if the conditions under which such heterotransplantations take place
are less favorable, then the existence of incompatibilities between the heterog-
enous organisms may become manifest. Hence, while the parabiosis-like
union between different species of Rana could be readily accomplished, ex-
change of pieces of skin between the larvae of different species of Rana did
not succeed; within a few days the grafts became smaller and then disap-
peared. As for the raising of such combinations of embryos to a stage further
than metamorphosis, Born succeeded only in the case of homoiogenous graft-
ing of embryos of Rana esculenta. He did not succeed in reaching this stage
with heterogenous combinations, although in other respects, as noted above,
heterotransplantations between nearly related species behaved about like
homoiotransplantations.

The experiments of Born were continued by Harrison, who in one instance
kept alive a heterogenous combination (Rana virescens and Rana palustris)
through the period of metamorphosis and was able to observe that each of the
two constituents in this combination retained its characteristic species features.
But the size of a whole animal of this kind was much smaller than that of a
normal frog. In general, such heterogenous combinations, although able to
eat and shift for themselves, became weak in the course of time, they de-
creased considerably in size and finally died ; at most, they could be kept alive
for three or four months, while in Born's experiments similar heterotrans-
plantations succeeded only for a period of three weeks. But even in Harrison's
experiments atrophy and degeneration in the large majority of cases set in
after a few weeks. This investigator also observed that if a tail had been
grafted to an individual of a different species, there was noticeable an early
interference not only with the growth, but also with the life of the grafted
tail, parts of which, however, could remain viable for a longer time.

Harrison furthermore noted that in some instances reciprocal transplanta-
tions behaved in an unlike manner, an effect which has been found also in
other kinds of transplantations and to which we have previously referred. Of
interest also is his observation that the lateral organs of one partner could
grow into the other, although the partners belonged to different species, as
happened when the tail portion of Rana palustris was joined to the anterior
part of Rana sylvatica; in this case the lateral line organs extended from
Rana palustris into Rana sylvatica. Evidently there was here no very marked
incompatibility between parts of organs possessing, each one, its own species
differential ; if antagonistic reactions did occur under these conditions, they

INDIVIDUALITY OF EMBRYONAL TISSUES 237

were presumably of a subtle nature and proceeded more slowly. Even indi-
viduals belonging to different genera and families could be temporarily joined
together.

On the whole, these experiments bear certain similarities to mammalian
parabiosis; apparently heterotoxins are active in both. Inasmuch as in these
transplantations of parts of embryos we have to deal, not with the peculiarities
of some of their constituent tissues or organs, but with conditions common
to all the tissues, which are affected the more unfavorably the greater the
distance in relationship between the two partners, we are justified in attribut-
ing the incompatibilities which may develop between them to differences in
their organismal differentials. These embryonal organisms show a sensitive-
ness to heterogenous differentials similar to that noted in certain invertebrates,
as for instance, the lumbricidae; in both cases incompatibilities arise if the
species of the partners are far removed from each other phylogenetically. The
mutual tolerance of heterogenous constituents seems to be greater in the
embryonal than in the adult anuran amphibia, which latter, as we have seen,
are on the whole very sensitive to the effects of heterotransplantation. We
have seen, in a preceding chapter, that in adult amphibia restitution processes
are restricted to the appendages of urodeles. On the other hand, in amphibian
larvae of Rana, Harrison has shown that it is possible to obtain furthergoing
integrations. When pieces of tail were grafted so that their aboral poles were
in contact with the oral poles of the host and the oral surfaces of the grafts
were cut off, the influence of the larger piece induced processes of adaptation
in the grafts, which made them part of the host. In this respect a larva of an
anuran amphibian resembles, therefore, a hydrozoon or a pianarian; but in
other respects the integrative ability of these larvae is much less pronounced
than that of the more primitive adult invertebrate organisms. As a rule, in
amphibian larvae abnormal combinations of several pieces do not undergo
those various regulative processes leading to the reestablishment of normal
individuals, which take place so readily in primitive adult animals ; the larvae
of amphibia correspond in this respect rather to adult lumbricidae.

II. Transplantation of Embryos and Eggs in Invertebrates. The experi-
ments of Born in amphibia were soon afterwards extended to invertebrates.
It is especially the eggs and embryos of echinoderms, of Ascaris and Chae-
topterus, which were used in these investigations, in which Driesch, Morgan,
zur Strassen, Jacques Loeb, de Haan, Goldfarb, and others participated.
Although these experiments were not undertaken primarily for the sake of
the study of organismal differentials, still some valuable data in this regard
were obtained.

Two cells or cell complexes may be joined together in two ways : (a)
Through agglutination, a process which will be more fully discussed in a
later chapter, dealing with tissue formation and organismal differentials ; (b)
through coalescence of agglutinated cells, due to solution processes which
take place in the ectoplasmic cell-layer, especially of eggs or their very early
cleavage stages. If the union consists merely in an agglutination process, sev-
eral further possibilities exist. Either the two organisms remain distinct and

238 THE BIOLOGICAL BASIS OF INDIVIDUALITY

develop as separate embryos, or they become secondarily integrated into a
single organism through the action of regulating mechanisms,— presumably
similar to those which are effective as contact and distance substances, — on
cells derived from the same embryo, and then an orderly development may fol-
low. In addition there may be observed certain intermediate conditions in
which the greater parts of the two embryonal structures remain distinct, but
some organs unite and become common to both organisms. Furthermore, under
certain conditions the joined organisms may separate again secondarily, the re-
sult of a process which may be designated as disagglutination. Structures rep-
resenting various stages of embryonal development can thus be united, un-
fertilized or fertilized eggs as well as early cleavage stages up to blastulae, and
perhaps even still farther advanced embryos.

If two embryos have in this way been joined together by means of agglu-
tination into a single organism, giant individuals may develop, in which the
number of cells composing the embryo is approximately doubled, but in which
the size of the cells remains unchanged. However, in other cases in which,
at a very early stage, coalescence takes place between the two partners, an
organism with the same number but with double the size of cells results.
Under certain conditions it may happen that one of the two organisms
becomes atrophic and then the remaining parts of it may be dominated by
the larger partner. Such a dominance of a larger over a smaller partner has
been noticed repeatedly in cases of transplantation in lower invertebrates, as
well as in parabiosis in mammals. Whether the two embryos will form one
single organism or separate into two organisms depends upon several factors :
(1) The degree of development of the embryos and the rigidity of their tissue
and organ differentials at the time of union ; in general, the further the
embryonal development has progressed, the more the original plasticity of
tissues and organs has been lost, the less will be the chance that one single
individual will result from the union. (2) The orientation of the two surfaces
which unite the two partners; if this orientation is favorable then the union,
whether by means of agglutination or of coalescence, can be more readily
accomplished and a secondary separation becomes more improbable. This
conclusion agrees with observations in lower adult invertebrates, where the
covering of wound surfaces in the right orientation prevents regeneration at
the cut ends, but where the joining together of two unsuitable poles may
lead to budding or regenerative outgrowth and subsequent separation of the
component parts. It agrees in general also with the changes which take place
at the point of union between tissues in higher animals, where certain contact
differentials determine whether a stable or an unstable equilibrium will be
reached. (3) The result also depends upon the organismal differentials of the
two partners. Syngenesious and homoiogenous combinations apparently suc-
ceed. However, in many cases it is impossible from the reports of the investi-
gators to determine whether, in a certain experiment, a syngenesio- or a
homoiotransplantation was carried out, and we can therefore not be sure
whether any difference existed between the results of these two types of
transplantation; but some investigators, and in particular Bierens de Haan,

INDIVIDUALITY OF EMBRYONAL TISSUES 239

have given consideration to the influence of organismal differentials in their
transplantations.

More definite is the difference in effects which is seen between homoio-
and heterotransplantation. After the latter, there may take place neither a
primary nor a secondary unification of the two organisms. The incompati-
bility may manifest itself at the surfaces where the organisms are joined
together and thus a separation, due to disagglutination, may occur after
apparently a primary union of the organisms had taken place. If we unite two
distant species, either this latter process occurs or there may be from the
beginning a lack of union. If, however, we combine more nearly related
species, the two organisms may remain united for a longer period of time,
but secondarily also here abnormalities occur, such as a slowing-up of the
developmental processes, until they cease in the end altogether. In still other
cases more localized abnormalities in development take place, affecting either
one or both of the partners ; or on the other hand, disintegration or atrophy
of tissues has been observed and at last one partner may be destroyed or
incorporated into the dominating one. In these instances we have, therefore,
presumably to deal with heterotoxins injuring especially the weaker organism.
However, the difficulties experienced in transplantations between different
species may depend not entirely on the incompatibilities between the organis-
mal differentials as such, but also on secondary factors of a less specific
character, such as differences in the size and rate of development of the two
partners; factors of this kind may determine the readiness with which two
relatively nearly related species can be joined together.

Of great interest is the observation that in heterotransplantation, if a part
of one of the two component organisms disintegrates, the remaining part of
this organism may be changed in its development under the influence of cer-
tain organs of the other partner, which has now become the dominating factor.
Thus, a line of ciliated cells may form in the injured component of the com-
bination, when similar developmental processes take place in the dominating
component. In such a case we have apparently to deal with an organizer action
similar to those actions which are potent during the normal development of
embryos, or which may be produced experimentally through implantation
of certain specific parts of another embryo, which function as organizers.
Evidently the presence of heterodifferentials does not necessarily prevent
organizer action.

We see, then, that in the case of invertebrate embryos a distinct sensitive-
ness to heterogenous organismal differentials exists, while a like sensitiveness
to homoiogenous organismal differentials is apparently lacking, and in this
respect eggs and embryos behave in a similar way to parts of adult inverte-
brates when they are joined together. However, as stated above, it may be that
what has been interpreted in these experiments as homoiotransplantations,
really represented syngenesiotransplantations, since this distinction was not
always made by the investigator.

We shall cite a few experiments which will illustrate some of the general
conclusions at which we have arrived and which will bring out some addi-

240 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tional points of interest. In certain instances ova were joined together and
agglutinated with each other, as in the experiments of de Haan and zur Stras-
sen; in others, early embryonal stages were combined (Driesch, Goldfarb).

Driesch united two blastulae of Echinidae and observed that they were able
to form one organism with twice the number of cells, but the individual cells
did not coalesce. A single organism developed presumably if contact mecha-
nisms or contact substances acting as regulators were favorable to such a
union ; otherwise, separate organisms resulted. Apparently the stage at which
the joining together of the component parts took place and the size of the
surfaces which agglutinated (Goldfarb), and probably also the degree of
specificity of tissue and organ differentials, determined the outcome of the
operation. The further the differentiation had progressed, the more pro-
nounced was the tendency on the part of the partners to separate again and
to give origin to two distinct organisms. If one organism had been produced,
the inner organs appeared to be double or they had united into single organs.
In some cases two larvae formed, which had certain organs, such as gut,
skeleton or body cavity, in common, while in other cases these organs re-
mained separate. When one partner dominated, as so often occurs in mam-
malian parabiosis, distintegration of the skeleton could take place in the
weaker partner, and as a result of such degenerative processes a single larva
developed, in which the gut of the dominant larva supplied the remnants of
the other partner with food ; furthermore, it was observed that even mesen-
chyme cells could move from one larva into the other. Agglutination was, in
these experiments, preliminary to coalescence and we may assume that it took
place readily if the consistency of the cells was suitable for this process.
According to Herbst and Driesch, lack of Ca and a certain degree of alka-
linity or low temperature in the surrounding medium caused stickiness and
favored agglutination of the cell surfaces. In Driesch's experiments it is not
indicated whether he had to deal with syngenesious or homoiogenous relations
between the partners ; but in Goldfarb's experiments, both syngenesious and
homoiogenous unions succeeded. In the investigations of Morgan in Echini-
dae, parts of brothers were successfully joined together in syngenesious
transplantations. He observed that processes of degeneration or atrophy in
one of the partners could precede the transformation of the combination into
a single larva, but there were also found all transitions between a single
homoiogenous organism and double organisms. Goldfarb, as well as Bierens
de Haan, showed in Echinidae that as many as forty eggs could be made to
agglutinate with one another, but that a combination of more than two eggs
rarely developed beyond an early embryonal stage. Thus an incompatibility
became noticeable, comparable to that observed in transplantation of primitive
adult invertebrate organisms, where likewise the difficulty in the integration
of the parts into one whole seemed to increase the more the greater the number
of pieces which were joined together.

Of general interest are also the experiments of zur Strassen, who showed
that in Ascaris two unfertilized eggs could coalesce, and that there was present

INDIVIDUALITY OF EMBRYONAL TISSUES 241

under these conditions a double set of chromosomes as well as twice the
amount of egg substances. Such eggs could then be fertilized and could de-
velop into one individual. In case two already fertilized eggs were united, the
two female and also the two male nuclei, respectively, united with each other,
and either twins or single embryos resulted from such combinations. If, instead
of eggs, early embryonal stages were combined, they tended to agglutinate
rather than to undergo coalescence, the protoplasm of the individual cells
remaining separate. However, the direction of the axes of the two organisms
was found to be of significance; if there was correspondence of direction,
one complete organism developed, otherwise two separate individuals. In
general, the two factors which above all others seem to be of importance in
such combinations and which determine whether one or two organisms shall
be formed from two young embryos are : (1) The developmental stages of the
embryonal structures, and (2) the direction of the axes of the organisms.

As to the effects of the organismal differentials, Bierens de Haan found
that different combinations succeeded unequally well, it being easier to unite
certain species than others. Heterogenous fusions succeeded only rarely, and
if they did succeed, the resulting fusion was less complete. In this case there
was a chance for a secondary separation of the partners, similar to the separa-
tion which had been observed if two more distant species were joined together
in primitive invertebrate adult organisms and in amphibian embryos. Separa-
tion could still occur as late as after eighteen hours ; but if in other cases these
heterogenous combinations developed, the development was not quite typical
and it was slower than normal. Unified, single giant plutei never resulted from
such heterogenous unions. Some combinations of this kind, however, succeeded
better than others and in these successful experiments the intestines were seen
to grow from one into the other partner. But even in relatively successful
heterogenous transplantations, such as those between Parechinus and Para-
centrotus, the organ formation was rudimentary and development soon ceased ;
perhaps substances which were produced as the result of incompatibilities
between the two organisms acted as poisons. In a combination between Pare-
chinus and Paracentrotus the dominant Parechinus could call forth the de-
velopment of a line of cilia at the expense of the rudimentary Paracentrotus,
and in this case parts of the skeleton seemed to act as organizers. In general
it was found that heterogenous combinations never led to the formation of
really uniform organisms, but that at best merely sectorial chimaerae were
produced. Under the most favorable conditions each component of these com-
binations could develop to the stage of a normal pluteus, otherwise regulative
processes occurred which led to separation ; in other cases, both heterogenous
partners became sickly. As far as unfertilized ova are concerned, it was ob-
served that while a homoiogenous union could be accomplished, heterogenous
unions did not succeed. From the latter, unified single giant plutei never
formed; in some instances cytolysis, in others a temporary agglutination oc-
curred, but a real coalescence did not take place. However, even twin larvae
which developed from a homoiogenous union often showed some defects. We

242 THE BIOLOGICAL BASIS OF INDIVIDUALITY

must therefore consider the possibility that specific toxic substances distinct
from the organismal differentials were responsible for some of the results fol-
lowing heterogenous, and even homoiogenous combinations.

When we review this entire series we come to the conclusion that there is
no very definite gradation noticeable in the joining together of different in-
dividuals, if we ascend from the ontogenetically lower to the more adult
forms. However, there develops in every case an incompatibility between
farther distant heterogenous parts of an artificial combination, and it is often
noticeable also between more nearly related heterogenous partners; on the
other hand, there is usually no definite incompatibility between homoiogenous
partners, although even here some abnormalities may be found.

However, there are several difficulties in interpreting these findings. In the
first place, as stated above, these investigations were not carried out with a
view of analyzing the organismal differentials and therefore the experimental
data which would make possible such an analysis are very incomplete. Sys-
tematic comparisons between auto-, syngenesio- and homoiotransplantations
were in no case made. Secondly, it is possible that in some instances factors
of secondary importance came into play, such as the more or less accidental
differences in the size of the surfaces which were to be joined together.
Thirdly, there are some indications that organ differentiations and the inter-
actions of organs that adjoined each other played a definite role in determin-
ing compatibility; this is suggested by the importance of the orientation of
the surfaces of contact. In addition, there may have been active, specific
toxic actions, which were referable not to the whole organism as such and to
its organismal differentials, but to specific metabolic processes of certain
organs, and which were comparable to the toxins produced in the glands of
some amphibia and reptiles.

Notwithstanding these difficulties of interpretation, there is very little doubt
that essentially the results of the joining together of two ontogenetically
primitive organisms depend upon the compatibility of their protoplasms, and
in particular, of their ectoplasmic layers, which presumably form around
wound surfaces of cells. But, while a coalescence takes place only between
homoiogenous individuals, or possibly between individuals belonging to very
nearly related species, the primary agglutination process seems to be less
specific, although specificity is not lost entirely. Furthermore, we find here,
opposed to the tendency to coalesce and to form one unified organism, a
tendency towards regeneration and the development of two distinct organ-
isms similar to that which we observed in transplantations among phylo-
genetically primitive organisms. This applies especially to heterotransplanta-
tions. The more suited to each other the character of both the protoplasms
and the surfaces of contact, the less this regenerative tendency will assert
itself. Instead, integrative mechanisms, which tend to make one single organ-
ism out of the two, dominate. While it is impossible to form a definite
concept as to the relative importance of physical and chemical factors which
may assert themselves at the place of union, still it is evident that the degree
of relationship between two embryonal organisms is one of the factors

INDIVIDUALITY OF EMBRYONAL TISSUES 243

which helps to determine the compatibility of the partners in experiments in
which different species are joined together.

There is reason for assuming that regulative substances of a similar
character to those present in the morphogenic interaction between parts of
a natural individual, regulate also the interaction between coalesced and
secondarily unified organisms. This tendency to form more or less normal
individuals out of abnormal combinations may lead to the production of a
single organism from two partners, or to the later separation of the two
joined-together parts, each of which then gives origin to a single individual,
or to the domination of one partner over the other, which latter undergoes
various degrees of degeneration. These observations apply both to trans-
plantations in phylogenetically primitive classes of animals and to fusions
of early ontogenetic stages. However, notwithstanding these similarities, one
has the impression that the regulative and integrative mechanisms, which
are so pronounced in the case of the phylogenetically most primitive adult
organisms, are perhaps not effective to quite the same degree in embryonal
forms of phylogenetically more advanced organisms, although here, also,
various fargoing regulations may take place. The typical organizer actions
which may be observed in transplantation of very primitive adult organisms,
and which are so important during embryonal development, are only very
rarely evident under the conditions prevailing in these combinations between
ontogenetically primitive organisms.

In experiments with eggs and young embryos we have not to deal with the
same organismal differentials which are active in adult organisms. There
are indications that neither the specific organismal differentials which charac-
terize the adult individual, nor the mechanisms which react against strange
differentials are as yet fully developed ; still, protoplasmic specificities which
distinguish different species evidently exist even in such ontogenetically early
forms. Some of these specificities presumably represent stages in the develop-
ment of the organismal differentials and their means of manifestation, and
all intermediate gradations between the precursors present in the fertilized
egg and the fully formed substances and mechanisms in the adult form may
be found. Furthermore, as in phylogeny, so also in ontogeny there is notice-
able an inverse parallelism between the degree of plasticity of organs and of
the integrative potentialities active in an organism, on the one hand, and the
the degree of development of the organismal differentials, on the other hand.

Chapter 4.

The Significance of Organismal Differentials in

the Transplantation of Pieces of Embryonal

Tissue into Embryos and into Adult

Organisms

In the preceding chapter we have discussed transplantation of parts of
organisms, each of which had the ability to live and develop inde-
pendently, in invertebrate and amphibian embryos. We shall now con-
sider experiments in which smaller pieces of tissue, which under ordinary
conditions are not able to live separately or to develop, were grafted into
embryos or into adult individuals. Transplantations of this kind in amphibia
have been used, especially by Spemann and his associates, in the study of the
effects of organizers and their role in embryonal development. This motive
rather than the intention of analyzing organismal differentials dominated a
large series of such experiments. We shall analyze first, transplantations which
were undertaken previous to the full development of the organizer concept,
and then in a subsequent chapter we shall discuss transplantations which
were carried out with the problem of organizers in view, as far as such
experiments are of interest in the analysis of individuality.

The experiments of Lewis, Filatov and others, have shown that homoio-
as well as heterotransplantation of skin can be readily carried out in amphibian
larvae, and that in contact with the optic disc the transplant in either case is
able to produce the lens of the eye. But the conditions under which the
formation of the lens takes place vary in different species. In some species,
such as Rana fusca, the skin from all regions of the organism retains up to a
relatively late stage of development the ability to produce the lens in contact
with the optic vesicle. In Rana esculenta, on the other hand, only the skin
of the eye region is able to form the lens, though the transformation of the
epithelium of the skin into lens apparently proceeds, through self-differentia-
tion, independently of a previous contact with the optic disc. Skin from other
areas is not able to produce lens in this species, but the optic disc has the
same power to act as an organizer in contact with epidermis as that of other
species. Bombinator behaves in a somewhat intermediate manner; certain
areas of skin are able to produce lens tissue without contact with the eye
vesicle, but the optic vesicle also has the power to induce lens formation in
skin with which it is in contact. We have to deal in these cases probably with
differences of a quantitative kind, and they seem to depend upon the stage
of differentiation which the skin of the various species has attained at certain
periods. In principle, there exists in all these species the potentiality of inde-

244

TRANSPLANTATION OF PIECES OF TISSUE 245

pendent transformation of skin into lens tissues, as well as the production
of lens under the influence of the eye vesicle.

As to the length of time during which such homoio- and heterotransplants
of skin remain alive, no systematic studies seem to have been made. However,
that the heterodifferential may after all assert itself is indicated by the
experiments of Filatov, in which larval skin of Bufo was grafted over the
eye of Rana esculenta. The lens developed from the transplant but subse-
quently it degenerated. Perhaps a certain length of time was required for the
cumulative action of the heterodifferential to become apparent.

Somewhat analogous conditions exist also in other instances. Thus, Ekman
found that in larvae of Bombinator the ectoderm from the heart and kidney
regions, but not from other parts of the body, if transplanted to the gill region
is able to produce gills. There appears to exist a varying degree of rigidity
of the tissue differentials in analogous tissues at corresponding periods of
embryonal development in different species, and in addition, the tissue or
organ differentials may be specialized to a different degree in different areas
of the same individual.

Whether these differences in the degree of plasticity of the skin are in any
way related to its transplantability and sensitiveness to strange organismal
differentials seems not to have been determined. But it is quite obvious from
these investigations that the tissue differentials may be graded in a much
finer way than is apparent from the manifest structural characteristics of the
tissues. That this is true also of tissues of the adult organism follows, for
instance, from our studies of the varying ability of connective tissue in dif-
ferent parts of the sex tract to produce placenta.

In general, evidence is lacking that in transplantation in amphibian larvae
the individuality differential plays any particular role. In urodele, as well as
in anuran larvae, skin, extremities, tailbuds, eyes and other organs can be
readily homoiotransplanted. However, under certain conditions individuality
differentials may, after all, produce a certain effect ; thus, according to Hell-
mich, in anuran larvae a homoiotransplanted limb may heal in, but subse-
quently the transplant, ceasing to grow, shrinks and becomes necrotic. Other
effects of the individuality differential on transplantation in anuran larvae
will be discussed later.

In urodele larvae heterotransplantation succeeds more readily than in
anuran larvae. For instance, between Amblystoma punctatum and Amblys-
toma tigrinum extremities can be readily exchanged. Likewise, transplantation
of extremities from larvae of Triton taeniatus to Salamandra maculata, and
other similar heterotransplantations, may be successful. However, this is true
only of transplantations in larvae. In metamorphosed urodeles, even after
autotransplantation the transplanted limbs are readily cast off, an effect which
must be due, however, to other factors than organismal differentials. Simi-
larly when, according to Detwiler, autotransplantation of a limb in larvae of
the urodele Amblystoma succeeds better than homoiotransplantation, this
difference in all probability does not arise from the direct injurious influence
of strange individuality differentials on the grafted tissue, but from secondary

246 THE BIOLOGICAL BASIS OF INDIVIDUALITY

effects, involved, perhaps, in the establishment of connections between the
transplants and the central nervous system.

Graper and Alverdes, on the other hand, find that transplantations of ex-
tremity buds from larvae of Rana palustris to Rana sylvatica succeed only
temporarily; they retrogress within four to five weeks. Similarly, in earlier
experiments Born had observed that transplantation of skin from larvae of
Bombinator to Rana did not succeed very well. Likewise, Ekman had noticed
that after exchange of gill ectoderm between these organisms the transplants
were soon destroyed or cast off. Among amphibian larvae, and especially also
in urodele larvae, the transplantations become more difficult if the species
used are more distantly related. Thus, Harrison found that the balancer
anlage can be readily transplanted from Amblystoma punctatum to Amblys-
toma tigrinum, but if this organ is grafted from Amblystoma punctatum to a
larva of Rana sylvatica, only a short appendage develops. Similarly, the
induction of the balancer in Triton by means of frog material gives only
doubtful results (Mangold). An ear vesicle transplanted from a larva of
Rana esculenta to Triton taeniatus remained alive at most for twenty-nine
days, and in the majority of cases it disappeared even earlier; yet the trans-
planted organ, while it lived, was able to induce the formation of cartilage
in the host (Balinski). In the tailbud stage of Amblystoma punctatum and
tigrinum, pieces of spinal cord can be exchanged between these two species
and may remain alive, the brachial plexus growing out from the transplant
into the host. However, subsequently irregularities do develop ; there is a
greater mortality and metamorphosis does not take place in the bearers of the
grafts (Wieman and Nussman). In urodele larvae heterotransplants from
nearly related species may not only remain alive, but the tissues from both
species may intermingle with each other, so that chimaerae develop. Thus
Schaxel grafted parts of regenerative blastemas of extremities of white
axolotls into autogenous blastemas of black axolotls, and vice versa.
Although these tissues differed in their race differentials, they could be mixed
in various ways without any resulting incompatibilities.

As to the manner in which unfavorable heterodifferentials may in the course
of time injure the transplant, older observations of Braus gave no indica-
tions of differences between the results of auto- and homoiotransplantations
of buds of extremities in anuran larvae; the transplants survived even
through the period of metamorphosis, and extremities of host and donor
metamorphosed at the same time. But, transplantations of buds of Bombinator
larvae to larvae of Rana esculenta were only temporarily successful. The
transplants began to develop and then, when a certain stage had been reached,
growth and development ceased. Growth seems, thus, to be a more delicate
indicator of incompatibility of organismal differentials than the life of the
transplant; the former may stop under the influence of injurious factors
of a heterogenous nature at a time when life still continues. As to the cause
of cessation of growth at a certain stage, Braus believes that the critical time
coincides with the period when the circulation is established in the host. This
would suggest that heterotoxins are carried from the host to the transplant

TRANSPLANTATION OF PIECES OF TISSUE 247

by means of the circulation. However, we have already seen that incom-
patibilities between organismal differentials may become manifest even with-
out injurious effects being transmitted through the blood. In Harrison's
heterotransplantations of tails of anuran amphibians, atrophy and degenera-
tion often set in within a few weeks after grafting, although some parts of the
transplant could survive. But it is possible that vascular changes, interfering
with the circulation of the blood, and caused presumably by the incompati-
bility of the organismal differentials of host and graft, were at least partly
responsible for the degenerative conditions that occurred in the experiments
of Braus.

It is of interest to compare with these transplantations of small pieces the
results obtained in the joining together of larger parts of larvae of Rana
esculenta and Bombinator. In Born's experiments such combinations lived
only for three weeks, but, according to Braus, they may persist longer under
favorable conditions. It seems, then, that in both cases after heterotrans-
plantation incompatibilities developed, which caused a cessation of growth.
We may conclude that certain, not well defined, growth factors may be potent
even in heterotransplantations between amphibian larvae, and that the sub-
stances circulating in the body fluids of the host which regulate the growth
processes, may be independent of organismal differentials, as are also other
growth-regulating substances, such as certain hormones, which apparently
do not carry organismal differentials. As in the case of tumors, we must dis-
tinguish from these hormone-like, growth-regulating substances, other growth-
determining factors which are inherent in the transplanted tissue itself, and
which continue to assert themselves even in a heterogenous soil, provided the
heterotransplantation does not preclude the life of the transplanted tissues.

As to the relation of these inherent growth substances to the organismal
differentials, these experiments do not give any indication. As stated above,
between Amblystoma tigrinum and Amblystoma punctatum, limb, and also
eye, can be readily exchanged, and both of these organs may then continue
to live. Normally, Amblystoma tigrinum reaches a greater size than Amblys-
toma punctatum and the experiments of Twitty and Schwind indicate that the
transplanted extremities retain essentially the characteristics, as to growth
energy, of the species or race from which they are derived. This may per-
haps be due to the fact that the growth factors inherent in the transplanted
tissues dominate over extraneous growth factors, which are transmitted to
them through the circulation of the host. Similarly, Burns and Burns found
that heterotransplantation between larvae in these two species of Amblystoma
succeeds if young stages are used for this purpose, and that under these
conditions both partners retain their intrinsic growth momentum. Likewise,
the specific stimulus to metamorphosis is not transmitted from one partner
to the other, or if transmitted, is ineffective in these transplantations, but the
sexual characters of one partner may be influenced by those of the other.
Also, in the case of heterotransplantation of eyes the transplanted organ
retains the growth energy inherent in the donor tissues. In some cases the
inherent growth energy of the donor tissue may be the deciding factor only

248 THE BIOLOGICAL BASIS OF INDIVIDUALITY

in the first period of transplantation, while subsequently the transplant adapts
itself to the growth rate of the host; this was observed after transplantation
of the heart primordium from Ambly stoma tigrinum to Ambly stoma punc-
tatum; moreover, here the more rapid growth of the transplant in the first
period was accopanied by a more rapid differentiation.

On the other hand, it has been observed by Detwiler that when parts of
spinal cord are transplanted from Amblystoma tigrinum to Amblystoma
punctatum, the transplant not only grows better than the corresponding
organs in the host tissue, but even better than the non-transplanted donor
organ in Amblystoma tigrinum. Similar observations were made in the case
of limb transplantations. It is possible that in this instance differences in the
organismal differentials between host and transplant exerted a stimulating
effect on the graft. However, this stimulation of growth following hetero-
transplantation of cord tissue again applies only to an early period; subse-
quently, an adaptation takes place between the size of the transplant and the
corresponding organs in the host. The experiments of Detwiller regarding
the factors regulating the growth of the nervous system prove that the out-
growth of nerves was not determined by species-specific substances.

The age of the host affects the transplant in a characteristic way. If an
eye of a young organism is transplanted to an older host, its growth is accel-
erated, so that its stage of development after some time is equal to that of
the host, while an older eye, having attained a more advanced stage of de-
velopment, after transplantation to a younger host grows more slowly, so
that the eye of the host, after some time, reaches the same stage of develop-
ment as the transplant. Twitty explains these phenomena on the basis of
Robb's specific partition coefficients for foodstuffs which different tissues
possess, a theory related to the conception of athrepsia of Ehrlich. However,
if differences in partition co-efficients, inherent in different tissues and chang-
ing in accordance with the ontogenetic stage of development, should be
responsible for these results, this would presumably be a factor of only
secondary importance, the primary factor consisting in differences in the
inherent growth energy of various tissues, upon which would depend the
amount of foodstuffs which the various tissues attract and use. The influence
of age on the growth energy of the transplant appears to be similar to the
effect which the time of metamorphosis has on the growth of transplants in
urodele larvae and which will be discussed later.

In these more primitive organisms, such as larvae of urodele and anuran
amphibia, there is some indication that relatively undifferentiated cells remain
preserved through certain periods of larval life and that it is these cells
which in ontogenetically more primitive organisms give origin to a blastema
endowed with great regenerative potency. The presence of such cells would
also account for the transformability of relatively primitive transplants under
the influence of host tissues acting as organizers in a certain "action field"
of the host. It may perhaps be assumed that in urodeles such less differentiated
cells remain preserved longer than in anuran larvae and in this way the
greater regenerative power of the former may be explained. These cells are,

TRANSPLANTATION OF PIECES OF TISSUE 249

as Hellmich points out, comparable to the totipotent cells which have been
found in sponges (archeocytes), hydrozoa (interstitial cells), vermes (neo-
blasts), and tunicates (amoebocytes). Corresponding to the relatively un-
differentiated character of such cells, their organismal differentials are pre-
sumably also as yet relatively little developed and they can therefore be
successfully heterotransplanted, while this is impossible in ontogenetically
further developed stages.

However, differences in the degree of differentiation of the organismal
differentials do not depend merely on the presence or lack of certain un-
differentiated cells, which, under ordinary circumstances, remain more or
less dormant, but such differences must also exist in the ordinary tissues
composing an embryo or a larva in various types of animals. It is presumably
due to this inverse parallelism between the prospective potency of embryonal
tissues and the degree of specificity of their organismal differentials, that in
larvae of urodele amphibia extremities can be successfully homoiotransplanted
under conditions which make such a result impossible in anuran larvae ;
in contrast with what is found in urodeles, in anuran larvae homoiotrans-
planted extremities placed in close proximity to a developing extremity of
the host heal in only temporarily; they then cease to grow and undergo
shrinking and necrosis. But so far a systematic comparison of auto- and
homoiotransplantation of limbs has not, apparently, been undertaken, and
this would be necessary before more definite statements can be made as to
the development of organismal differentials in these embryos and as to the
parallelism between the degree of organ and tissue differentiation and the
fixity of the organismal differentials during different stages of embryonal
life.

The stage of differentiation of the transplant seems to influence its fate in
a graded way. We have seen that fully differentiated extremities of amphibia
cannot be successfully transplanted into the skin or subcutaneous tissues.
If somewhat younger extremities are used, only the less differentiated parts
like perichondrium and other mesenchyme cells remain alive, become a part
of the host and continue to differentiate. Also, after transplantation into the
interior of the host the fully differentiated cells die and only the less dif-
ferentiated cells remain alive. However, when very early stages of extremity
buds are transplanted, although no further development takes place, necrosis
does not occur and the mesenchyme cells of the transplant dissociate from
one another and migrate into the host tissue (Hellmich) ; but in other cases,
if an early embryonal bud is able to maintain itself in the host, it is more
accessible to the organizer action of the surrounding host tissue than older
tissues, and accordingly, it is modified in its development by the host tissue,
whereas somewhat further differentiated transplants develop through self-
differentiation. Correspondingly, several authors have stated that in trans-
plantation of avian embryonal tissues the results are not favorable if very
early stages are used, and similarly, Goetsch has observed that if in Hydra
very early regenerative buds of the oral region are transplanted into the
lateral zone of other polyps, the transplants are resorbed, whereas older re-

250 THE BIOLOGICAL BASIS OF INDIVIDUALITY

generative tissues can develop in accordance with the potentialities of the
transplants. It seems, then, that too slight a differentiation of the trans-
planted tissue favors its complete adaptation to the host and is responsible for
the lack of a growth momentum, which would otherwise have led the trans-
plant to develop in its own way.

We shall consider transplantations in their relations to organismal and
organ differentials still further in the following chapter, in which we analyze
organizer actions and their connection with organismal differentials. But the
data which we have already discussed lead to the conclusion that the outcome
of transplantations in amphibia depends primarily upon two sets of consti-
tutional factors, namely, (1) the phylogenetic stage of development; this, in
urodeles, is more primitive, the precursors of the organismal differentials are,
as yet, less differentiated and, therefore, the range of relationship in which
transplantation of embryonal material succeeds is wider than it is in anuran
amphibia. (2) The ontogenetic stage of development of the organismal differ-
entials ; the genes from which the organismal differentials develop are fixed
for each species and individual, and they remain unchanged in all the tissues
throughout embryonal development. In contrast to this fixity of the genes, the
degree of differentiation which the organismal differentials have reached in
successive stages of embryonal development differs; the greater the tissue
and organ differentiation, the further advanced is also the differentiation of
the organismal differentials, and correspondingly, the narrower will be the
range of relationship within which the transplantations succeed. Besides, in the
same embryonal stage different tissues and cells may differ as to the degree
of differentiation they have attained, and, correspondingly, they may differ
also as to the stage of transformation of the gene-precursors into the actual
organismal differentials, which are localized in these tissues. Since organismal
and also organ differentials are further differentiated and more fixed in
anuran larvae than in urodeles at corresponding stages of embryonal de-
velopment, the transplantability of the former will be less than that of the
latter at any given period.

Furthermore, during regenerative newformation of limbs, conditions exist
which in certain respects resemble those present during embryonal develop-
ment (Schaxel) ; a graded differentiation of the regenerating tissues and a
corresponding maturation of the organismal differentials take place. There-
fore, if buds of extremities representing early stages of regeneration are
transplanted, they may give origin to mixtures of various tissues ; but if
somewhat later stages are transplanted the tissues are fixed in their poten-
tialities and in the localization of the regenerating material and under these
conditions typical limbs develop. The great plasticity of the blastema of limb
or tail of an amphibian is demonstrated in a remarkable experiment of
Schotte, in which he showed that after transplantation into the eye of frog
larvae, from which the lens had previously been removed, the blastema
changed into lens tissue under the influence of organizers located in the
eye of the host.

Durken and Kusche diminished the effect of the host tissue on the trans-

TRANSPLANTATION OF PIECES OF TISSUE 251

plant by grafting embryonal tissues into the eye socket of amphibia after
its contents had been removed. However, even under these conditions the
transplant did not develop as a mosaic, but underwent various irregular
transformations into other tissues, presumably under the influence of the
host ; thus ectoderm could differentiate here into neural or mesodermal parts,
in contrast with what happened in salt solutions in vitro, where ectoderm
merely proliferated and formed epidermis. This result applied to tissues
transplanted at early stages of their development; if farther advanced tissues
were used, the more fixed the organ differentials were at the time of trans-
plantation, the more frequently normal organs were produced. Diirken called
this method "interplantation" ; it represents a condition intermediate between
the ordinary transplantation and tissue culture in vitro. Such experiments
were carried out in anurans as well as in urodeles, but there was an interest-
ing difference between the interplantation in the anuran Rana and the
urodele Triton, in the former the homoiogenous material being toxic for
the host. Such toxic effects, consisting in hemorrhages and necrosis, were not
observed in case of syngenesiotransplantation. In urodeles, toxic effects were
lacking. It is noteworthy that in these experiments individuals were apparently
sensitive to toxic substances produced in their own species, although as a
rule a high degree of immunity exists in a species against its own poisons.
Kusche could successfully interplant early embryonal tissues which belonged
to different genera in urodeles; for example, Triton cells continued to dif-
ferentiate after transfer into larvae of Salamandra and Amblystoma; but if
the interplantation took place between different orders, such as between
Triton tissue and larvae of Rana fusca, or between cells of Amblystoma and
larvae of Hyla, the interplants were destroyed. We may assume that under
these conditions the bodyfluids of the host were toxic for the transplant,
owing to the divergence between the organismal differentials in host and graft.

A number of investigators, beginning with Belogolowy, transplanted seg-
mented eggs, blastulae, gastrulae or neurulae, into the peritoneal cavity of
adult amphibia; or in other experiments the freshly fertilized eggs of
Axolotls were transplanted into larvae of the same kind, measuring 13 to
15 mm. in length. The transplants were able in certain cases to undergo
development, but this was abnormal, even after homoiotransplantation. How-
ever, if the relationship between host and transplant was very distant the
transplants usually died. Belogolowy did not observe a difference between
the results of homoiotransplantations and transplantations from Rana to
Pelobates and vice versa; but transplants from Rana to Triton were found
alive after one month only in exceptional cases.

In two instances Janda observed that in axolotls fertilized eggs, when
transplanted to the peritoneal cavity of the same species, led, after three or
four months, to the development of embryonal formations, which were very
incomplete and structurally quite abnormal. Especially prominent in these
formations were epidermal cysts, masses of cartilage and nerve tissue pro-
ducing cysts; also, intestinal structures with glands and rudimentary kidney
and eyes were found. As in Diirken's interplantations into the eye socket,

252 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the surrounding host tissues did not show a marked activity. However, in
the majority of cases the implanted material, it seems, was absorbed without
having led to the formation of these embryomata.

In such transplantations, certain substances in the host may be toxic for
the transplant, and, conversely, there is a tendency also for the hosts to be
injured by the transplants and they may die within a few months. The toxic
substances in the peritoneal cavity were found by A. Weber to be identical
with substances present in the blood or lymph. Especially the eggs of Triton
appear to be killed within a few minutes by such substances in an adult
Triton. On the other hand, eggs of Bufo and Bombinator develop in the
peritoneal cavity, or in the lymph sacs of adult animals of their own species,
without being injured by toxins. But if Triton eggs, which would have died
within five minutes in the peritoneal cavity of adult Tritons, are transplanted
into the lymph sac of Bufo, they develop, although abnormally. Anuran
eggs live for several hours in the peritoneal cavity of Triton. It seems, then,
that it is particularly the eggs of Triton which are sensitive to these toxic
substances.

It is not sufficiently clear in these experiments what role organismal differ-
entials may play in producing such toxic effects. However, according to Weber
the eggs survive longer in the peritoneal cavity of the parents than in
homoiogenous individuals. While this indicates that organismal differentials
may in some way be concerned in these processes, it is probable that
essentially we have in these experiments to deal with the presence of special
toxins, distinct from the heterodifferentials, which affect injuriously the
transplants after ordinary transplantations.

Transplantation of avian embryonal tissues into adult birds. In the ma-
jority of experiments avian embryonal tissues were homoiotransplanted into
the subcutaneous tissue, muscle of the chest, peritoneal cavity, or anterior
chamber of the eye of adult birds (Fere, Wilms, Tiesenhausen and Skubis-
rewski). One-day-old embryos were not found suitable for transplantation;
experiments with young embryos, about five days old, appeared most suc-
cessful. The gross observation indicated that in the majority of cases the
transplants did not grow, or growth disappeared within a month or two. In
some instances, however, masses of irregularly arranged embryonal tissues,
embryomata, developed, which grew to larger size and remained alive for a
year or more; but in the end they also diminished again in size and were
absorbed. Certain tissues, such as bone, cartilage, smooth muscle and
squamous epithelium, were especially resistant. There was apparently no
difference between the results, irrespective of whether the embryonal material
was transplanted into the mother or into non-related individuals of the same
species. However, considering the great variability in the results obtained in
these experiments, definite conclusions cannot be drawn as to the effects
of the relationship between transplant and host, although it seems that hetero-
transplantations, such as those of chick embryo to duck or pigeon, of duck
embryo to chicken or pigeon, or also of mammalian embryo to chicken, resulted
in an early degeneration of the transplants.

TRANSPLANTATION OF PIECES OF TISSUE 253

Transplantation of embryonal material into the allantoic of chick embryos.

The first transplantations on the chorio-allantoic membrane of the chick were
made with thin pieces of mammalian tumors, and these experiments indicated
the great tolerance for heterogenous tissues which this organ exhibits. How-
ever, the chorio-allantoic membrane was used also for transplantation of
embryonal material and a survival of the grafts was here observed when
transplantation into the adult chicken would have been followed by the rapid
destruction of the grafts. Thus Hoadley, Murray and others, found that
sense organs and extremities of very young, one or a few days old chick
embryos develop well, although apparently not always quite normally or
completely, on the chorio-allantoic membrane of eight- to nine-day-old chick
embryos. However, the time during which the transplants continue to grow
under these conditions is not longer than about nine days ; even heterotrans-
planted tisue can develop during this short period. Hiraiwa and Willier
observed that parts of eleven-day-old rat embryos grew well for nine days
on the chorioallantoic membrane of the chick; epidermis, hair follicles, car-
tilage and bone, were used and grew as well here as in rat embryos of the
same age, but the entodermal and nerve structures did not continue to grow
and differentiate in this strange host, or at least they developed less well. The
age of the embryonal graft seems to influence the fate of the transplant to
some extent. Sandstrom noted that kidney tissue from nine-day-old duck
embryos healed in on the chick chorio-allantoic membrane without any part
of it becoming necrotic. Older embryonal kidney tissue underwent partial
necrosis and the necrotic areas persisted the longer in the host the older the
embryo was from which the graft was taken; moreover, the activity of host
lymphocytes also increased with increasing age of the grafted embryonal
tissue.

The relatively favorable results of heterotransplantations on the chorio-
allantoic membrane of the chick are probably due to the fact that the defense
mechanisms, the sensitiveness to strange differentials of the host, and the
organismal differentials, factors acting in combination or singly, are not yet
fully developed in the placental structures of the early embryo.

Inoculation of mammalian embryonal material into adult mammals of the
same species. Here a growth may take place, which at first may be quite rapid,
but which then slows up, comes to a standstill, and finally is followed by
retrogressive processes. In different species the tendency to active growth
and persistence apparently varies. It seems to be very great in the rat, where
the transplant may persist for months and even a year, although in most
cases the proliferation may continue only from one to four months, when a
cessation occurs followed by retrogression. The period of growth is relatively
brief in the mouse, retrogression beginning usually after one week (Rous).
In the rabbit, after transplantation into the uterus, it appears that only
cartilage survives as long as twenty days (Hammond). However, in all of
these experiments with homoiogenous tissues there is a great diversity in the
results in different experiments, and even in the rat it is only in exceptional
animals that the grafted tissues remain active for very long periods. It is

254 THE BIOLOGICAL BASIS OF INDIVIDUALITY

always cartilage, and, to a lesser extent, bone, osteoid tissue and bone mar-
row, and perhaps also smooth muscle tissue, squamous epithelium with its
appendages, the hair follicles and sebaceous glands, which have the best
chance to survive; to a lesser extent, entodermal (intestinal) and lymphoid
tissue, and much more rarely, nerve tissue and rudimentary formations of
sense organs, as well as glands such as liver, may be found in these embryo-
mata.

Mammalian embryonal tissues give evidence of possessing species differen-
tials and, consequently, do not withstand much better than adult tissues the
injurious effects of heterotransplantation. Thus Rous observed that embryonal
tissue of the mouse may grow in the rat for a few days, but then it dies.
However, as to the individuality differential, there seems to be less selective-
ness here, after homoiotransplantation, than in adult tissues ; but this may be
at least partly due to the fact that the original growth momenium is greater
in embryonal than in adult tisues, and hence the former may be carried
over some of the difficulties to which the latter succumb. Yet we find, also,
in transplantation of embryonal tissues, great differences in the results
obtained in different hosts of the same species. This indicates that individuality
differentials may, after all, play a certain role in determining the fate likewise
of the embryonal grafts. But in transplantation of mammalian tissue the
age and developmental stage of the embryo, too, may be of some importance
in the differentiation of the organismal differentials; in very early stages
even species differentials are not yet fully developed.

That in transplantations of both normal adult and embryonal tissues the
genetic relationship between transplant and host is a very essential factor in
determining the outcome is further indicated by the fact that lymphocytic
infiltration takes place around grafted living embryonal tissue. Two weeks
after transplantation of embryonal tissue into the stomach wall of rats,
Askanazy found an accumulation of lymphocytes around the transplant, and
W. P. Neilson noted the same occurrence more recently in our laboratory.
However, the interpretation of these observations is complicated by the
fact that transplanted embryonal tissue not only grows, but also differentiates,
and thus in the course of time becomes more like an adult tissue, and we
cannot therefore be certain how much the maturation of the embryonal
tissues had to do with the accumulation of lymphocytes.

Rous, in making two grafts of the same embryonal tissue into different
places in the same host, observed that both transplants behaved in the same
manner ; either both did well or both retrogressed at an early date, or neither
took, a finding analogous to ours in the case of tumors. This might be in-
terpreted as indicating the importance of the individuality differentials of
host and transplants in determining the result. But, Rous also found that
mouse tumor tissue and mouse embryonal tissue transplanted simultaneously
into the same mouse had a similar fate. Inasmuch as the individuality differ-
entials of the embryonal and tumor grafts in this case were not identical,
it appears that the sensitiveness and intensity of the reaction of a host
towards strange individuality differentials in general likewise were determin-

TRANSPLANTATION OF PIECES OF TISSUE 255

ing factors in these experiments. Similar effects may be observed also after
homoiotransplantation of several pieces of adult mammalian tissue into the
same host, as we have pointed out in a previous chapter.

In a relatively small number of experiments, various investigators trans-
planted embryonal material into the mother from which the embryo had been
obtained ; in some of these cases pregnancy continued, while in others it was
interrupted. Freund found no difference in the rat between syngenesio-
transplantation, that is, grafting of the embryo to its own mother, designated
by this author as autoplastic transplantation, and homoiotransplantation,
grafting of embryonal tissue to a strange host; but, considering the wide
range of variations which has normally been found after homoiotransplanta-
tion of embryonal material, the number of experiments of this kind was not
sufficiently large for definite conclusions. In contradistinction to Freund,
Fichera noted that in rats the embryonal transplants persisted longer and
more tissues developed in the own mother than in homoiogenous hosts. A
similar result was obtained by Rous in the mouse. While the growth of the
embryonal material was not more rapid in the mother than in favorable
homoiogenous animals, in the former it persisted longer and led to the
development of a greater variety of tissues. Thus it seems that even in the
case of embryonal material the individuality differential, or its precursor,
plays a certain role. Nicholas attempted to transplant embryonal limb or eye
from brother to brother in the uterus, but technical difficulties made a suc-
cessful transplantation only exceptional, and the effect of a close relationship
between host and transplant in these experiments remained, therefore, un-
certain. Likewise, reports as to the part played by pregnancy in the host on
the fate of transplanted embryonal material are contradictory. Freund be-
lieved that such tissue grows better in pregnant than in non-pregnant hosts.
However, according to Peyton Rous, in the mouse pregnancy inhibits the
growth of transplanted embryonal material in a similar manner to that of
tumor transplants.

Through repeated implantation of the embryonal tissue a relative immunity
against the growth of subsequently inoculated embryonal tissue can readily
be demonstrated, while in adult tissue such an immunity cannot be recognized
with the same degree of definiteness. Both Peyton Rous and F. Fichera noted
the development of this type of immunity; Rous produced a relative im-
munity in the mouse by means of a single inoculation of homoiogenous
embryonal material, while Fichera made a series of injections of embryonal
rat tissues into the adult rat; after each additional injection the immunity
of the host became more pronounced. On the other hand, Paula Freund
noted that a first unsuccessful subcutaneous inoculation of embryonal tissue
in the rat did not need to prevent the growth of a second intraperitoneal graft.
As in the case of active tumor immunity, we have not, in these experiments
with embryonal tissue, to deal with a specific immunity to the particular
homoiodifferential of the tissue which was used for immunization, since an
immunity to all embryonal tissues of the same species seem to have resulted
from the repeated injections. However, there is still the possibility that in

256 THE BIOLOGICAL BASIS OF INDIVIDUALITY

addition to this general reaction against homoiogenous tissue, a specific im-
munity against the particular individuality differential, which was used as
antigen, may also have developed.

Rous believes that this acquired immunity manifests itself in the lack of
a stroma reaction in the immunized mouse towards the transplant; an in-
growth of capillaries and connective tissue from the host into the transplant
does not take place and the transplant dies as a result of this deficiency in
blood supply. A lack of stroma reaction has also been observed by Rous
in natural immunity, if a single transplantation of embryonal tissues is
made into an unfavorable host. Rous does not mention the appearance of
lymphocytes around the transplants in the immune hosts. A similar immune
reaction has been described by Russell and Bashford in the case of grafted
pieces of tumors, a mode of reaction which we shall discuss in a subsequent
chapter.

If we wish to draw definite conclusions concerning the relations which
exist between the state of the organismal differentials and the degree of
differentiation and fixity of organs and tissues in various types of organisms,
we again suffer from the difficulty that transplantations of embryonal ma-
terial were not usually undertaken with this problem in mind. However, if
allowance is made for a certain degree of inadequateness in the data, we
may conclude that the range of transplantability in general is wider in the
phylogenetically more primitive classes of animals, and that among the latter,
in particular, it is wider in the more primitive urodele than in the anuran
amphibia ; that within certain limits in the ontogenetically earlier stages there
is found both a lesser degree of organ and tissue differentiation and fixity
and a lesser differentiation of the organismal differentials, and lastly, that
the range of transplantability decreases with advancing embryonal develop-
ment and differentiation. Furthermore, regenerating tissues in adult urodele
amphibia have been shown to behave in certain respects like embryonal
tissues; and corresponding to the increasing degree of organ and tissue
differentiation, which is attained with advancing regeneration, transplantabil-
ity of regenerating tissues likewise decreases. The earlier, less differentiated
tissues are still more plastic and amenable to environmental factors, while
the father advanced stages in embryonal development are more fixed in their
organ and tissue differentials and thus have a greater tendency to develop by
way of self-differentiation. This latter conclusion applies also to the regenerat-
ing tissue in the adult urodele. We find again, therefore, a relation between
the differentiation and fixity of organ and tissue differentials on the one hand,
and organismal differentials on the other hand, and in certain respects also
a parallelism between the development of organ and tissue differentials and
organismal differentials in the phylogenetic and in the ontogenetic series; but
this parallelism exists only in a general way. As stated above, gradations in
refinement of differentiation with advancing phylogenetic and ontogenetic
development can be more clearly recognized in the case of organs and tissues
than in the case of the organismal differentials.

TRANSPLANTATION OF PIECES OF TISSUE 257

However, while thus a great similarity exists between the successive changes
in the phylogenetic and ontogenetic series as far as the development of the
organismal and organ differentials is concerned, there are also some very
important differences in these two series. In phylogenetic evolution we have
to deal with changes in the genetic constitution of the organisms as the basis
for the corresponding changes in organismal differentials and in individuality,
and in differentiation and fixity of organs and tissues. On the whole, we can
trace the relationship between different species of animals, one species de-
veloping from the other in an apparently connected series and each possessing
its own kind of organismal differentials; the later species show a greater
complexity and fixity in the organismal differentials than the preceding ones
and, accordingly, also a greater differentiation and fixity of the organ and
tissue differentials.

This same relationship obtains also if we compare the corresponding
ontogenetic stages in the different classes and species of animals; but in
ontogenetic development there is, as far as we know at present, in the con-
secutive stages of development throughout, an identity in the genetic consti-
tution of cells and tissues in the same individual and species. And if in the
series of ontogenetic stages likewise a development of the organismal differ-
entials takes place, it is one from the precursor predifferential stage in the
fertilized egg to the mature organismal differentials in the adult organism.
The genetic basis of the organismal differentials remains unchanged in all
these successive stages. We have then to deal, during embyronal life, with a
development of the organismal differentials that is parallel to the develop-
ment of organ and tissue differentials. In both, the genetic basis is already
present in the egg, and notwithstanding this sameness of the genetic consti-
tution throughout the series of successive ontogenetic stages, the constitution
of the tissues as well as of the organismal differentials changes progressively.
With this increasing development of organismal differentials out of their
precursor stages or predifferentials, the mutual compatibility of tissues pos-
sessing different organismal differentials decreases. In testing by means of
transplantation the effect of the increasing differentiation of tissues and
organs and their differentials on the plasticity of organs, the adaptability of
the organs and tissues to new environments, and the mutual interactions
between the grafts and host tissues, we introduce at the same time a second
variable in this experiment, namely, a change in the character of the organis-
mal differentials which also have progressed in the direction from their
precursors to more mature differentials in the course of embryonal develop-
ment. In observing the effects of the new environment on organs and tissues
we may thus have to deal with a summation of effects of both the changes
in organ and in organismal differentials. It is conceivable that likewise during
the process of regeneration in the earliest stages the precursors of organismal
differentials are present in the regenerating tissues, and that with progressive
regeneration the precursors of the organismal differentials present in ordinary
tissues and in totipotent cells, mature into the fully adult organismal differen-

258 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tials. This would not apply however to the highest organisms, where regen-
erative processes are much reduced in extent and where totipotent or even
pluripotent cells no longer are present in the regenerating substratum.

In regard to the evolution of organismal differentials, and of the individu-
ality which depends upon these differentials, there is, therefore, as far as we
know at the present time, a radical difference between phylogenetic and onto-
genetic development ; and this difference is present notwithstanding the many
structural and functional analogies which have been shown to exist between
the various stages of phylogenetic and ontogenetic evolution, as far as the
differentiation of tissues and organs is concerned. Furthermore, while the
basic constitution of the organismal, and, in particular, also the individuality
differentials corresponds closely to the genetic constitution of the various
organisms, the subsequent differentiation of these organismal differentials
depends not alone on these genetic complexes, but also on the progressive
changes in organs and tissues which occur in the course of ontogenetic de-
velopment within the same organism ; a combination of both genetic and non-
genetic factors is needed for the differentiation of the organismal differentials.
We may assume that although both during phylogenetic and ontogenetic
evolution a development and differentiation of the organismal differentials
take place, the precursors of the organismal differentials must differ
in these two series as widely as does the constitution of the egg protoplasm
in a mammal and the cytoplasm in an ameba or in a coelenterate.

Chapter $

Organizers and Tissue Differentiation, and Their
Relation to Organismal Differentials

In our discussion of the factors which cause organ formation in primi-
tive organisms, we have referred to organizers localized in certain organs,
which are able to induce the production of these same organs in another
animal of the same species into which they have been transplanted. How-
ever, the "organizer" concept was not used originally in the analysis of organ
formation in phylogenetically primitive species, but rather in embryos of
less primitive organisms. The transplantation of pieces of organs may lead
to the development of organs or of embryonal tissues other than those which
function as organizers, and, in particular, the latter may induce the formation
of parts of an organism normally adjoining the organizer tissue. It has been
possible to trace this potentiality to the formation of organs and tissues and
the distribution of organ-forming substances from the ovum through the first
segments, through blastula and gastrula, to the more complex organisms.
Associated with these changes is a parallel development of organismal differen-
tials from their precursors, which also proceeds in the direction from less
specific to more specific substances and mechanisms. It is this parallelism in
these two processes and the possibility of a relationship between them which
we wish to analyze in this chapter.

As stated, tissue and organ formation during embryonal life is brought
about partly by substances which function as organizers in association with
inherent, genetically determined characteristics of the tissues, which are the
substratum on which the organizers act. The organizers may be defined as
morphogenic contact substances, which serve as tissue transformers, or
rather, as inductors, causing the tissues with which they come in contact to
undergo certain changes, which, within a definite range of variability, are
fixed by the constitution of the tissues upon which they act. In the earlier
stages of embryonal development, when the plasticity and range of variability
of the tissues are still very great, these substances may determine which of
their potential differentiations the tissues will actually undergo. When in
later stages the structure of the organism has become more stabilized, the
organizers may exert quantitative rather than qualitative effects; they may
determine not what kind of organs are to be produced, but what their size
and position shall be and how many of them shall be formed; or they may
stimulate the tissues to develop in a certain direction rather than to stand still
or to undergo only relatively slight further differentiation. But this difference
between the effects exerted in earlier and later embryonal stages is not a radical
one ; it is rather a difference of degree. As might be expected, during embryonal
development we may have to deal not only with single inductions by or-

259

260 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ganizers, but with chains of such transformations. An organizer induces a
certain tissue and organ formation ; there is associated with this transforma-
tion the production of a new organizer, which, on its part, induces a specific
differentiation in the surrounding tissue and this again may lead to the forma-
tion of an additional organizer exerting a specific function.

There are, then, two sets of factors which fix the structure, chemical con-
stitution, metabolism and function of tissues and organs: (1) The inherent
characteristics of tissues and their range of modifiability, which may lead
to development by "self-differentiation," and (2) the character of the or-
ganizers which are parts of the inner environment of the tissues. There is
reason for assuming that, in general, without the action of the organizers the
development of the early embryonal tissues would be very imperfect and
rudimentary. This is indicated by the behavior of isolated embryonal tissues
made to grow in vitro; even here, differentiation of tissues seems to depend
largely upon the interaction between adjoining tissues and their organizers,
and if this interaction is lacking, further differentiation does not take place.
However, the artificial growth stimuli as such, acting in vitro, tend to prevent
further differentiation. The less evident the action of the organizers is in the
differentiation of tissues, the more the tissues appear to develop as the result
of inherent conditions by way of self -differentiation. Development by self-
differentiation usually leads to a more restricted formation of organs than
that which takes place under the influence of organizers. In general, with
advancing differentiation and increasing fixity of tissues in the course of
embryonal life, self-differentiation comes to play a greater role and the
tissue will depend less upon specific environmental organizer effects.

Furthermore, with the increasing development and differentiation of the
organizer tissue, the organizer may change or the organizer effect may be lost,
although even tissues in an advanced stage of differentiation, such as retina
or brain, may still exert some of the organizer action which the more primi-
tive precursors of these tissues exerted. Likewise, with increasing differen-
tiation, different parts of the organizer tissue may begin to undergo modifica-
tions in respect to the organizer functions they exert.

Both organizer and conditions inherent in the recipient tissue or substratum
are then of importance in embryonal development; therefore a tissue may
develop by self-differentiation in the absence of an organizer and it may be
modified in its development by the presence of an organizer. Of course, there
may be always hidden in the apparent process of self-differentiation some
previously exerted effects of organizers. Now, this interaction between these
two sets of factors may assume the character of a competitive struggle between
the inertia of the substratum, with its varying potentialities, and the inductive
activity of the organizers. Thus the same organizer may be able to accomplish
a certain transformation with one tissue with which it comes in contact,
but not with another. Or the difference may be of a quantitative character
rather than an absolute one; the organizer may be able to induce a certain
change more readily in one organ than in another; or in one tissue the or-
ganizer may readily induce newformation of a certain kind, while in another

ORGANIZERS AND TISSUE DIFFERENTIATION 261

the same organizer may induce only quantitative changes in number, velocity
and intensity of developmental processes. Furthermore, quantitative relations
between the tissue acting as organizer and the tissue representing the sub-
stratum may play a certain role. Hence, if the substratum tissue is very
extensive, it may offer an effective resistance to the activity of the organizer
and appear inert; on the other hand, if the organizer tissue is very large,
it may induce in the substratum changes which are greater from a quantitative
point of view, although they may be of the same character as those effected
by smaller pieces of organizer tissue. There seems to be active here, a quan-
titative relationship not unlike that characteristic of certain chemical inter-
actions which determine the ultimate kind of equilibrium to be attained. We
noted similar effects of the relative size of host and graft in transplantations
in phylogenetically primitive organisms.

This struggle between the inductive activity of the organizer and the re-
sistance of the substratum is also exemplified in the interaction between the
organizer belonging to one species or order of animals and the substratum
belonging to another species or order. In this case, the direction in which
the differentiation of the affected tissue shall take place may be determined
by the organismal differentials or their precursors in the substratum, rather
than by the precursors of the organismal ^differentials in the organizer tissue.
The organizer may transmit merely the impulse to further differentiation of
the tissue in the direction of certain organ formations ; but the character of
these organs is modified by the characteristics of the species or order to which
the substratum tissue belongs. The organismal differentials or their pre-
cursors do not exhibit a modifiability under the influence of organizers com-
parable to that which the specific substances of the various organs and tissues,
the organ and tissue differentials, display.

Thus in the analysis of the organizer action use was made, especially by
Spemann, Zeinitz and Schotte, of transplantations into different species and
orders, either the organizer tissue being transplanted into a distant host, or
the tissue serving as substratum being grafted into a different species in such
a way that it came in contact with the organizer of the host. In both these
instances the inductions expected took place. These experiments furnished at
the same time further data as to the transplantability of tissues representing
early embryonal stages. It was in this way possible to graft successfully tissues
belonging not only to different species, but even to different orders, and the
latter type was called xenotransplantation. But in xenotransplantations there
was sometimes noticeable on the part of the grafts a tendency not to enter
into perfect union with the adjoining host tissue; however, the time during
which the strange tissues were kept under observation in these experiments
was short, because the main aim was the analysis of the organizers rather
than of the organismal differentials or their precursors. Nevertheless, as far
as such investigations make conclusions possible, they seem to confirm the
view expressed in the preceding chapters, that in early embryonal tissues the
organismal differentials, or rather the mechanisms through which their
existence becomes manifest, are not yet fully developed and the range of

262 THE BIOLOGICAL BASIS OF INDIVIDUALITY

transplantability in these early embryonal states is, therefore, still greater
than in the later ones.

While it was possible to keep embryonal tissues alive, at least for a short
time, after hetero- or xenotransplantation and to obtain organizer effects,
it has been found more recently that it is not necessary to transplant living
tissue in order to obtain induction. In these experiments the dorsal lip of the
blastopore from urodele gastrulae, which had been found to contain especially
efficient organizer material, was used primarily, but also other material, such
as medullary plate, with the underlying mesodermal structures, showed marked
organizer effects. In contact with ectoderm of the gastrula, this material
caused the transformation of the ectoderm into a medullary plate. Thus
Spemann, Bautzmann, Holtfreter and Mangold could show that tissue which
had been killed by exposure to heat or cold, by drying or by mechanical
means, could still function as an active organizer. Likewise tissues treated
with alcohol, ether, acetone, glacial acetic, hydrochloric acid or xylol, or
infiltrated with paraffine, were still effective. Moreover, tissues which, in the
living state, lacked the ability to act as inductors, acquired this property after
they had been killed by drying (Holtfreter), or following treatment with
acetone and alcohol. Thus entoderm or ectoderm of gastrulae acquired the
ability to induce medullary plate formation after they had been exposed to
such treatment. Even the unsegmented egg could, under these conditions,
induce the development of very differentiated organs, such as the lens of the
eye, whole eyes, optic vesicles, and parts of the brain. Spemann has suggested
that the manifestation of organizer action in material formerly devoid of
such effects may be due to the removal, by means of solvents, of inhibiting
substances which had been present in the living, inactive tissues, or the
changes which take place during the denaturation of protein may set free
the active organizer. As to the chemical nature of the substances which act
as organizers, the evidence obtained so far appears to be contradictory; the
effects have been attributed to various substances, glycogen, proteins, and
simpler hydrocarbons. It is possible that proteins in combination with glycogen
or with certain non-specific lipoid substances may act as organizers ; also
estrogens and carcinogenic hydrocarbons may perhaps exert organizer func-
tion (Needham and Waddington). Some investigators have found that injury
of embryonal tissue may activate the organizer.

Considering the fact that dead tissues of amphibian embryos and certain
extracts from such tissues may serve as organizers, it is not surprising to learn
further that a great number of organs of embryos or adult forms of verte-
brates as well as of invertebrates may act as organizers in gastrulae of Triton.
In some instances adult tissue from distant species has first to be killed by
heat before it will thus act ; but in other cases, strange adult living tissues
exert this function after transplantation.

These results apparently are contradictory to the great specificity of the
factors which are evident during embryonal life, where only definite organs
and not others can act as organizers at given periods of embryonal develop-
ment and in definite areas of the embryo if certain results are to be obtained.

ORGANIZERS AND TISSUE DIFFERENTIATION 263

However, the injured or killed material does not behave exactly like living
tissues from the same or related species or orders of animals ; the former
seems to be less specific, as shown by the fact that it induces a smaller number
of transformations in the tissues on which it acts, and the fine differences
between different parts of a certain organ used as organizer are lost under
these conditions. Thus, while in the normal medullary plate of Triton different
portions are differentiated — the anterior portion inducing formation of brain,
eyes, nose, ear vesicles and balancer, the posterior portion inducing formation
of spinal cord and tail — in the medullary plate produced by killed material
these specific differences between anterior and posterior portions are no
longer present, the different parts acting alike. It is especially the development
of neural tube from ectoderm of the gastrula which can be induced by dead
organizer material. The production of certain mesodermal structures, such
as kidney, musculature, bone and extremities, can only barely be initiated
by killed organizer tissue, and at best these organs and tissues are formed only
in small quantities. But coagulated embryo extract of the chick may call forth
not only the development of nerve tissue in gastrula ectoderm, but even
of chorda and musculature. It seems, after all, that there is no absolute, but
only a graded difference in the ability of dead tissue to function as organizer
and in the specificity of the transformations brought about by it, as compared
with the effects of living tissues of the same kind. Needham and Waddington
distinguish two types of actions of organizers: (1) The organizer reproduces
or tends to reproduce the axis of the embryo and, ultimately, a more or less
whole, early embryonal stage of the organism, which furnishes the sub-
stratum for its operation. This process is designated as "evocation" and the
organizer involved is called an "evocator." It is a relatively non-specific action,
which may be shown also by dead material, and it represents a much more
simple chemical effect than that exerted by (2) the individuator which pro-
duces certain subdivisions of the axis. The latter type of action is exhibited
only by living tissue. Somewhat related views have also been expressed by
Weiss.

The ability of xenoplastic tissues to act as organizers suggests that the
organizers are either entirely devoid of organismal differentials, or bear
organismal differentials with a very slight degree of differentiation. This en-
ables the transplanted tissues which contain the organizer to exert their func-
tion in the host, notwithstanding the great difference in organismal differen-
tials; or their precursors, in host and transplant; likewise, the experiments
with dead organizer material suggest that the organizers, at least those possess-
ing the more restricted, the evocator functions of the killed tissues, are devoid
of organismal differentials. In contrast to the lack of organismal differentials
in the inducting and transforming substances, the living substratum on which
they act does possess organismal differentials.

We may enlarge somewhat on these more general statements by citing
some specific experiments. If we transplant prospective medullary plate into
regions where the ectoderm normally develops into epidermis, the transplant
may, in its new location, merely form skin. Conversely, prospective epidermis

264 THE BIOLOGICAL BASIS OF INDIVIDUALITY

transplanted into a defect in the region of the presumptive medullary plate,
is able to develop into parts of the central nervous system and it may give
rise to the formation of an eye. On the other hand, if a differentiated medul-
lary plate, together with adjoining mesodermal tissue, which will give rise
to chorda formation, is transplanted into a gastrula, it may induce in the
overlying ectoderm the formation of a medullary plate. We see, then, that
an organizer may induce in the recipient tissue either structures of the same
kind as the organized tissue, a process we may designate as "isoinduction,"
or it may induce structures of another kind, "alloinduction," as when archen-
teron induces formation of medullary plates. Similar differences in organizer
action we mentioned in our analysis of the factors which are potent in trans-
plantation in lower adult vertebrates.

The isoinduction which we mentioned, may be of a very specific character.
As Mangold has shown, the medullary plate of the neurula may be divided
into four parts in the direction from head to tail, and each part is then
found to induce in the host the formation of those organs into which that
particular segment of the medulla itself would have developed, although to
some extent the effects of the different segments are overlapping. However,
the various parts of the underlying mesodermal tissue may also exert corre-
sponding specific formative effects, cephalic parts of the roof of the archenteron
tending to induce the nervous structures characteristic of the head, the
posterior portions tending to induce the tail parts.

While in some cases the ability of a tissue to act as an organizer may be
retained with further development, or may become specifically localized in
certain portions of the organizer area, in other cases this power is lost. Thus
not only the medullary plate, but also the fully developed brain tissue may
function as an organizer for the transformation of ectoderm into medullary
plate. Similarly, the embryonal optic disc, as stated above, can call forth in
the overlying ectoderm the formation of lens tissue. With further differentia-
tion of the optic disc, such action has apparently been transferred to the fully
differentiated retina of the Triton eye, which now has gained the power to
induce in the iris of the eye the formation of a lens. On the other hand, under
certain conditions, with increasing differentiation a diminution or a specific
limitation in the capacity to serve as an organizer may be noted. From the
dorsal lip of the Triton gastrula, which, as we have seen, acts as a very
effective organizer, there develops chorda as well as mesodermal structures;
but Mangold has demonstrated that it is only the chorda which preserves for
some time the ability to induce the production of a medullary plate from the
presumptive epidermis, while the mesodermal structures have lost this func-
tion.

During embryonal development we may have to deal with chain reactions
induced by successive organizers. Certain mesodermal structures may induce
the formation of the optic disc, and the optic disc in contact with ectoderm
induces the formation of a lens ; but here the chain reaction ends, the lens not
being able further to act as an organizer. Another chain reaction is the fol-
lowing: ectoderm, which under normal conditions would differentiate into

ORGANIZERS AND TISSUE DIFFERENTIATION 265

epidermis, may be transformed into mesoderm if it is transplanted into a
place in the embryo where normally mesodermal structures develop. After
further transplantation, these mesodermal tissues, if they are brought into
contact with other ectoderm, are able to induce the formation of a medullary
plate, and the medullary plate can induce the formation of medullary plate
and other nerve structures from ectoderm.

As stated above, in addition to organizer actions induced from the outside,
there are active processes inherent in the tissues themselves, leading to self-
differentiation ; during normal embryonal development these two processes
seem to cooperate in various combinations, in which the relative importance
of each factor may differ quantitatively. Various kinds of interaction may
thus be produced experimentally. We have referred previously to an instance
in which an organ, although much differentiated, still retains its ability to act
as an organizer. The optic disc in certain stages of embryonal development
can induce lens formation in some species only in the cephalic ectoderm, while
in other species at a certain stage of differentiation, also ectoderm of the rest
of the body can be made to develop into lens. Now, Mangold has found that
the eye-forming substances are determined in the ectoderm a short time after
the mesodermal tissues and the chorda, constituting the roof of the archen-
teron, have formed and have been able to act on the ectoderm ; it is therefore
possible that this contact induces the ability of the overlying ectoderm to
differentiate into an eye. However that may be, it can be shown that, from
a certain period in embryonal development on, there is manifested in the
overlying neural plate, as a result of increasing self-differentiation, an inherent
tendency to produce optic vesicles independently of any organizer action. Yet
even then, according to Adelman, an organizer action may be associated in
its effects with this process of self-differentiation. The roof of the archen-
teron of Amblystoma not only tends to reinforce the inherent tendency of the
ectoderm to form eyes, but it also modifies the place in the neural plate where
the eyes develop. Inherently the median portion of the neural plate has a
greater tendency to form eyes by self-differentiation than the lateral parts;
but the underlying roof of the archenteron acquires a marked bilateral polarity
in the course of embryonal development, and this condition influences the
organizer action of this tissue ; the lateral parts of the underlying tissue now
gain a greater tendency to induce or to intensify eye formation than its median
part, the organizer action dominating over the forces inherent in the neural
plates and causing the production of lateral eyes.

These interferences between self-differentiation tendencies and organizer
action can be shown in still another way. If the lateral parts of the neural
plates are transplanted together with the underlying organizer tissues, more
eyes are formed than would develop without the latter. If, on the other hand,
the median parts of the neural plate are transplanted without the underlying
tissues, they form eyes just as well ; however, median parts of the underlying
tissue, when transplanted with the median neural plate, frequently cause the
separation of the eye-forming material into two eyes, while without this
tissue, more often only one eye forms. In this case the organizer exerts effects

266 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of a quantitative rather than of a qualitative character. We have here to deal,
as in all vital phenomena, with a quantitatively varying interaction between
genetically determined, inherent factors and inner or outer environmental
factors. It must be borne in mind that inner environmental factors may also
be genetically determined.

The relations between inductor and recipient substratum may vary in dif-
ferent cases. As Mangold points out, ordinarily an organizer transforms the
substratum in such a way that both organizer and substratum form one whole,
which tends to reproduce the organism in which this transformation occurs.
This condition Mangold designates as "complementary induction." But, in
other cases the organizer gives rise in the host tissue to the formation of
structures which do not fit into such an organization, as when double or other
abnormal structures develop. Such an occurrence Mangold calls "autonomous
induction." This is found only under abnormal conditions ; for instance, when
the age and stage of differentiation differ very much in inductor and sub-
stratum, so that the typical sequence of interactions is disturbed. Or, in other
cases an autonomous induction may take place in case of xenoplastic trans-
plantation when the organismal differentials of host and transplant are so
strange to each other that a complementary result becomes impossible.

These observations present an interesting parallelism to those found after
transplantation of adult pieces of organs or tissues in primitive classes of
animals. Here also the transplant may unite with the host in an integrated
manner, leading in the end to the formation of a normal individual. We may
assume that under these conditions a tissue acting as organizer causes com-
plementary induction ; but if the surfaces of contact do not fit each other,
or if the organismal differentials are too far removed from each other, then
an autonomous induction takes place in the embryo, while in the adult the
transplant becomes absorbed or is cast off and the host tissue may undergo
regenerative growth processes.

As to the effect of the relative size of organizer and recipient tissue,
Bytinski-Salz has observed that within a certain range the larger the organizer
piece the greater its effectiveness, other conditions being equal. Quite recently
Schotte carried out some experiments which, while made for other purposes,
also have some bearing on this question. He transplanted large portions of
the ectoderm, including the presumptive medullary plate, from young gastrulae
of Hyla crucifer to the face region of Amblystoma punctatum, the former a
relatively small and the latter a relatively large organism. Under the influence
of the large quantity of organizer for mouth organs which was present in the
face region of the Amblystoma host, mouth organs formed in Hyla skin,
which were typical suckers with Hyla character, but they were three times
as large as they normally are in Hyla. The number of cells which entered into
these suckers was likewise about three times greater than is normally observed
in Hyla embryos. Similar results were obtained with the induction of other
organs, such as lenses, nasal placodes, ear vesicles and mouth organs. We may
assume that the larger quantity of organizer material present in certain regions
of Amblystoma induces formation of correspondingly larger organs in the

ORGANIZERS AND TISSUE DIFFERENTIATION 267

recipient transplanted tissue, although the latter belongs to a different order.
While, therefore, the organismal differentials inherent in the ectoderm of
Hyla influnced the type of organ which would develop, the organizer modified
the size and cell number in the developing organ.

We have seen that in early phylogenetic stages the character of the organ-
ismal differentials carried by the parts which are joined together is of im-
portance in determining the mode of interaction between the different tissues
of the two partners. Similarly, we may inquire how a gastrula and a piece of
tissue to be grafted into it, one or the other of which is the carrier of an
effective organizer, will interact when the transplantations are of a heterog-
enous or xenogenous character.

Some important observations which have a bearing on this problem were
made many years ago by Lewis, who found that the optic vesicle was able to
induce in embryonal skin the production of cornea, even if skin and optic
vesicle belonged to different species. Spemann transplanted ectoderm, repre-
senting presumptive abdominal skin, from Triton taeniatus into the anterior,
the brain portion of the developing nervous system of Triton cristatus. The
latter acted as inductor and transformed the skin into central nervous tissue,
which retained, however, the original species characteristics of Triton taenia-
tus. Similarly, after heterotransplantation of ectodermal tissues from Triton
taeniatus into the gill region of Triton cristatus, the gill which developed from
the taeniatus tissue under the influence of cristatus organizers retained the
characteristics of the taeniatus species.

More recently, Mangold showed that the mesodermal structures and chorda
of the host could act as organizers even towards heterogenous presumptive
ectoderm transplanted into different species of Triton (cristatus, alpestris and
taeniatus). The differentiation of the transplant under the influence of the
heterogenous organizer tissue proceeded in the same way as after homoio-
transplantation ; the rudimentary embryos consisted of constituents of two
different species, which, uniting harmoniously, thus represented chimaeras.
More extensive investigations of organizer functions following transplanta-
tion into different species with varying degrees of relationship were made,
especially by Zeinitz, Bytinski-Salz, and Schotte. While in the majority of
such experiments tissues from different species were transplanted into Triton
taeniatus, Bytinski-Salz carried out also the reciprocal transplantation of parts
of Triton taeniatus into a number of nearly or distantly related species. In
these experiments either the organizer tissue was transplanted into the bearer
of the recipient substratum, or the recipient tissue of a strange organism was
transplanted into the carrier of the organizer tissue. If in this way tissues from
a more distant species were made to act on each other, difficulties arose irl
certain instances, although even after transplantation of anuran tissues into
Triton, organizer effects could occasionally be observed.

Whether under such conditions an organizer effect occurs depends essen-
tially upon three sets of factors : ( 1 ) The relationship between host and trans-
plant and the influence of organismal differentials; (2) the effect of toxic
substances. While to a certain extent the degree of toxicity may be influenced

268 THE BIOLOGICAL BASIS OF INDIVIDUALITY

by the taxonomic relationship between host and transplant, the correspond-
ence between toxicity and taxonomic relationship is not perfect. There are
some species which are especially poisonous for Triton, although they may
not be farther removed in relationship than other less poisonous species. (3)
The relative rapidity of embryonal development in host and transplant. If in
the transplant the development takes place very rapidly, then sufficient time
may not be available for the organizer action to become effective.

In general, under the best of conditions xenogenous transplantations are
difficult. In many cases the transplant is expelled or absorbed after it has been
lying for some time in the deeper parts of the host as an apparently inert,
though living tissue ; but it may be possible to transplant presumptive epidermis
of Bombinator into the ectoderm of Triton and have it develop here into skin;
but such skin soon becomes thinner and gradually it disappears. After trans-
plantation into deeper parts of the host it is either discarded or gradually
absorbed, although in this position the graft may at first act like an interplant.
For a short time it may develop and possibly even be effected by the organ-
izers of the host, producing mesodermal structures. But union does not take
place between host and transplant and chimaerae do not form.

If presumptive medullary plate is transplanted from Bombinator into
Triton, two medullary tubes may develop in the host ; one is from the trans-
plant itself, the other, originating in the host, is determined by the transplant
acting as an organizer. But under these conditions interesting differences may
appear in the further fate of these new formations, from those observed after
heterotransplantation, owing to incompatibilities between the organismal
differentials of the two tissues. While the medullary tubes arising after hetero-
transplantation may coalesce into one single organ, those arising after xeno-
transplantation are unable to do so ; at best there may be a temporary union
between the two medullary formations, which is followed secondarily by a
separation. A difference between the behavior of hetero- and xenogenous
structures was found also in mesodermal formations. Here the difficulties in
the union of xenogenous structures may be still greater than those observed
in ectodermal tissues. While two medullary plates or tubes of xenogenous
origin may exist side by side, with mesodermal tissues single organs develop
either from the host or from the transplant, the one which develops first
apparently suppressing the other. In the case of mesodermal chordae, hetero-
transplanted organs may not unite with the analogous host organs. Here we
find, then, incompatibilities similar to those which are observed in the union
of distantly related eggs or young embryos in echinidae and Ascaris, or in
heterotransplantations in adult hydrozoa and planarians. In all these instances
the character of contact mechanisms, which presumably is contingent upon
the mutual suitability of contact substances, primarily determines the possi-
bility and durability of coalescence. As we have seen previously, the com-
pleteness of the union depends, at least in some instances, upon the lack of
regenerative growth processes at or near the point of contact, and this again
is determined by the relationship of the two organismal differentials which
interact.

ORGANIZERS AND TISSUE DIFFERENTIATION 269

An organizer effect in case of xenotransplantation may even be demon-
strable if the organizer action takes place at somewhat later stages of em-
bryonal development. Thus the ectoderm of the gill area can, to a certain
extent, transform ectoderm from other than the gill region of a xenogenous
gastrula into gill tissue.

We may then conclude that the organizer can, in some instances, continue
to function, but usually only in a very limited way, if very distant organismal
differentials interact with each other. Moreover, it can be shown that also
the factors which determine self-differentiation leading to further develop-
ment may still act after xenotransplantation of an embryonal piece of tissue.
Thus, according to Bytinski-Salz, anuran presumptive mesoderm after
xenotransplantation, may differentiate into chorda and musculature, presump-
tive epidermis into epithelium of the skin.

Mangold and Seidel succeeded in joining together early stages of segmen-
tation of Triton eggs belonging to the same species; in some cases a single
homoiogenous organism resulted from this combination, in other cases two
or more organisms developed. Mangold found that also union of heterogenous
Triton eggs in the two-cell stage of segmentation may succeed, but the number
of single organisms which resulted was smaller than after homoiotransplanta-
tion. After heterogenous union various organs which developed could contain
constituents of both species, which functioned without any antagonistic reac-
tions becoming manifest. However, as stated above, even under these condi-
tions various abnormalities developed in the case of chorda. It is these abnor-
malities observed in heterogenous early embryonal combinations, which sug-
gest that noticeable differences exist also in the character of the precursors
of heterogenous organismal differentials, and although such differences usually
do not become evident, they may lead to incompatibilities under certain un-
favorable conditions.

In combining heterogenous parts in adult individuals belonging to different
species in primitive classes of invertebrates, we have noticed that it is usually
the larger piece which dominates over the smaller piece. Similarly after trans-
plantation of small parts of embryos it is the larger host which is usually the
dominating partner, the xenotransplant being, in most cases, either discarded
or destroyed ; but if the transplant belongs to a species particularly toxic for
the host, the latter may be injured and ultimately killed by the transplant.

If thus xenogenous transplantations may succeed in amphibia and organizer
effects be exerted, these effects become manifest after a relatively short time
of interaction between the two strange tissues, a period too short perhaps for
the manifestation of incompatibilities between the organismal differentials.

We have already referred to experiments of Spemann which showed that
under the influence of heterogenous inductors the receptive tissues undergo
differentiations into organs which are in accordance with the specific organ-
forming potencies of the organizers ; yet at the same time the organs and
tissues which do develop show the species characteristics of the recipient
tissues.

Some very instructive experiments of a similar nature, illustrating the

270 THE BIOLOGICAL BASIS OF INDIVIDUALITY

specific effects of the organismal differentials of the recipient tissue, were
reported by Schotte. He transplanted presumptive skin from the abdomen of
anuran Rana or Bombinator gastrula into the mouth region of urodele Triton
or Amblystoma embryos. In the transplants there developed mouth organs
under the influence of the organizers of Triton and Amblystoma; however,
whereas in the latter species a balancer would have formed, in the anuran
transplants anuran mouth organs, such as suckers, horny jaws and teeth, as
well as operculum, developed, each one in its characteristic place. We must
therefore conclude that the organizers in the mouth organs of Triton or
Amblystoma tend to induce amphibian mouth organs in general, but not the
specific urodele mouth organs. The character of the recipient tissues, and in
particular the characteristics determined by the organismal differentials or
their precursors inherent in the transplant, determine what species charac-
teristics these organs shall possess. It is, of course, possible, although not very
probable, that in addition to the organizer substances, other less specific factors
localized and inherent in the mouth region, participate in bringing about this

result.

These findings again show the intimate connection which exists between
the organizers, whose functioning leads to the development of specific tissues
and organs, and the organismal differentials. A similar connection was noted
in the case of inductions produced in the transplant by the host tissues, or in
the host tissues by the transplant, in phylogenetically primitive classes of
animals. Here, also, we observed that the species characteristics of the strange
tissues were fixed, but that the determination of the kind of organ which was
to develop was influenced by the inducting substances which asserted them-
selves, notwithstanding the strangeness of the organismal differentials.

While we have so far reviewed only experiments in amphibia, in principle,
similar conclusions hold good also in other classes of animals. Thus in the
chick embryo at the stage of the primitive streak formation, the potentiality
of embryonal parts to form various tissues and organs is greater than is
indicated by the tissues and organs which actually are produced during normal
embryonal development. This fact has been established by means of trans-
plantation of parts of the embryo into the chorio-allantois of the chick embryo.
In this way it has been found, for instance, that heart can be produced at three
different levels, and gut may develop from all levels of the primitive streak.
The portion anterior to the pit can produce liver and mesonephros and the
portion posterior to the pit can produce adrenal (Hunt). In the normal
embryo substances are presumably given off by tissues, which inhibit the
development of certain neighboring tissues and organs in a similar manner to
that noted in the two-cell stage of echinoderm eggs, when one blastomere
inhibits the other from developing into a whole embryo. But other tissues which
normally develop in the embryo in a certain place, may not develop if isolated
parts of the embryos are transplanted, perhaps because under the conditions
of isolation needed organizer substances may be lacking. Furthermore, we may
assume that the ability of the embryo to form tissues varies in the direction
from the oral to the aboral pole of the primitive streak and also in a lateral

ORGANIZERS AND TISSUE DIFFERENTIATION 271

direction. The more anteriorly a tissue is situated, the greater is the variety
of tissues which it is able to produce ; in the posterior direction the frequency
and completeness in the production of such a variety of tissue are, step by
step, decreased. We have evidently to deal with a multiplicity of factors
which determine the formation of these structures and which also bring about
in the course of embryonal development a gradually diminishing receptiveness
of the tissues to the stimuli of the organizers.

In some respects we observe here, in principle, the same conditions which
we found in the cervix of the guinea pig, where there is a gradual decrease
in the potency of the tissues in one direction to form uterine structures, and
in the other direction to form vaginal structures under the influence of hor-
mones. We may consider uterus and vagina as representing two opposite
poles. In passing from one pole to the other, or in the opposite direction, there
is a graded change in structure and in mode of reaction to hormones.

Thus it is seen that there is a close correspondence between the action of
organizers and that of well known hormones, which occur in invertebrates
as well as in vertebrates, but which have best been studied in mammals. The
organizers represent hormones which are present and act locally in contact
with the recipient tissue, in contradistinction to distance hormones, which act
after being carried to a distant recipient organ; the former are contact hor-
mones produced in the cells and causing cytoplasmic differentiations in certain
responsive tissues with which they are in contact. These organizers are devoid
of the finer organismal differentials and there are indications that they may
not possess any organismal differentials.

Further instances of correspondence in the action of contact and distance
substances may be cited : In the case of the corpus luteum it has been shown,
in the guinea pig, that a very interesting correlation exists between the time
during which the hormone produces the maximum effect on the recipient
tissue, namely, the uterine mucosa, and the period during which such a hor-
mone effect is needed for the embedding of the fertilized ovum. It is only at
a time when the hormone is produced in full strength that the tissue exhibits
its full responsiveness. After the period has passed during which the egg nor-
mally attaches itself, the recipient tissue loses its responsiveness to less specific
stimuli to which it was formerly responsive, presumably because the quantity
of hormone necessary for sensitization of the tissue is diminished, or because
a refractory state develops in the uterine mucosa.

A somewhat similar condition exists in the relation between organizer and
recipient embryonal tissue. Here, as Lehmann has pointed out, the time during
which the organizer is produced in maximal quantity in the upper lip of the
gastrula of a certain species corresponds to the time when the ectoderm of the
gastrula, which is the recipient embryonal tissue, is responsive to the action
of the organizer. This correspondence applies, however, only if organizer
and recipient tissue belong to the same species ; it does not apply if organizer
and recipient tissue are derived from distantly related species ; in the latter
case, abnormalities may result.

There are, however, other cases in which a hormone is still produced at a

272 THE BIOLOGICAL BASIS OF INDIVIDUALITY

time when the recipient tissue has already lost its ability to interact with this
hormone. Thus the anterior pituitary may continue to produce follicle-stimu-
lating hormone in old persons, at a time when the ovary no longer possesses
the structures which are able to react with this hormone. In a comparable
manner, according to Mangold, the epidermis of axolotls is unable to respond
with the production of a balancer at a time when the adequate organizer is
present in the archenteron and medullary plate; but in other urodeles the
recipient organ may actively respond to the presence of this organizer.

In recent years it has been discovered that there are hormones which medi-
ate some effects of genes on those tissues which are under the control of these
genes (Kiihn, Ephrussi, Beadle). Such hormones develop, therefore, not
under the influence of cytoplasmic, but of nuclear constituents. They may
transmit to distant places, for instance, the effects of genes which distinguish
the dominant characteristic of a wild race from the recessive characteristics
of a mutant race. These gene-hormones have been found in various orders
of insects, such as Ephestia, Bombyx, Habrobracon and Drosophila ; they may
occur in certain organs (ovary, testis, brain), or in the body fluids, and they
can be conveyed to other organisms either by implantation of these organs
or by injections of the bodyfluids. If the hormone is transmitted in this manner
to a mutant individual which lacks the gene that causes the development of
a certain eye pigment, it acquires now the ability to produce the eye color of
the dominant race. Such genes thus seem to exert their effects on the recipient
tissues by means of hormone-like substances to which certain tissues have a
specific affinity. These gene-hormones are not species-specific; they may be
effective even in different orders of animals. Ephestia as well as Habrobracon
hormones are effective in Drosophila, and conversely, Drosophila hormones
exert typical effects in Habrobracon pupae. It is, in all these cases, the wild
dark-eyed type which possesses a hormone which is lacking in the mutant
form. As to the chemical constitution of such hormones, they seem to be
neither protein nor lipoid; they, as well as the organizers, apparently lack
organismal differentials.

We see, then, that the organizers, on which the organ formation in the
embryo depends to a large extent, and the substances, by means of which the
genes produce their effects during embryonal or larval life, are both hormone-
like and do not possess the organismal differentials; whereas the substances
from which they are derived, the cytoplasm of embryonal tissues and organs
and the genes of the chromosomes, have a complex structure and do possess
organismal differentials or their precursors. Likewise, the substratum on
which they act are bearers of organismal differentials or their precursors.
The cytoplasm is the more specific material which has the potentiality to
develop and differentiate within certain limits under the influence of these
hormone-like inductor substances. The latter induce the development of organ
systems in an orderly fashion, in accordance with the organismal differentials
of the species and the individual in which they act. Both the precursors of the
organizers and the organismal differentials are presumably present in the
fertilized ovum. In the course of embryonal life the organ precursors and the

ORGANIZERS AND TISSUE DIFFERENTIATION 273

organizers which they contain develop step by step ; they become distinct for
each organ, until in the end the complete set of organs and organ differentials
has fully developed. At the same time, also, the precursor substances of the
organismal differentials develop and differentiate into finer differentials, until
in the end the structures characteristic of the individuality have fully formed
in the substratum. It may be assumed that the coarser organ differentials,
organizers and organismal differentials develop first and that only at later
periods of ontogenesis the finer chemical structures differentiate in the case
of both the organ and organismal differentials. While these two sets of dif-
ferentials have thus certain important characteristics in common, they differ
in their chemical constitution as well as in their distribution. Whereas the
organ differentials and their precursors differ in every organ and tissue, the
organismal differentials are the same in all parts of an organism. We may
perhaps tentatively assume that on a common chemical basis, which is the
bearer of the organismal differentials, there are superimposed in various
places chemical structures which correspond to the various organ differentials.
While the general design of the latter is similar in nearly related organisms,
differences develop corresponding to the distance in relationship between the
organismal differentials. The finest, the least noticeable differences are found
between the organs and tissues of nearly related individuals. Yet, the wider
pattern of the embryonal development' of the organs and organ differential
substances, which takes place by means of self-differentiation and with the
aid of organizers, is similar throughout the whole animal series ; this applies
especially to the coarser, more basic organ and tissue structures, while with
progressing ontogenetic development a greater differentiation sets in in the
development of organs. These developmental similarities are maintained, not-
withstanding the differences which exist as to the precursor substances char-
acterizing the germ cells of the various classes, species and individuals. The
organs and their differentials undergo graded changes during embryonal life
and they are readily accessible to modification within a certain range, under
the influence of alterations in the inner or outer environment. The organismal
differentials, on the other hand, although they also differentiate in the course
of embryonal development, are, as far as is known, much more stable and
much less readily accessible to environmental influences ; however, during this
period the character of the organismal differentials limits also the variability
of the organs which may occur. Differences in organismal differentials which
the organizer tissue and the recipient tissue may possess do not preclude the
effective action of organizers, but the tissue and organ differentials can de-
velop only within the range prescribed by the nature of the organismal dif-
ferentials of the recipient tissue.

We have seen that in the adult mammalian organism a tissue equilibrium
is established, which is strictly autogenous ; the integrity of tissue boundaries,
the normal interaction of tissues, depend upon the presence of the same
autogenous differential in all the adjoining tissues. On this autogenous char-
acter depends the maintenance of the normal tissue equilibrium and the normal
function of tissues. There is a good deal of evidence that in the adult mam-

274 THE BIOLOGICAL BASIS OF INDIVIDUALITY

malian organism, also, some special substances are given off by tissues which
influence the state of adjoining tissues. They may be contact substances,
comparable in certain respects to the organizers of embryonal tissues. Thus,
the egg in the ovary may stimulate the growth of the surrounding follicular
granulosa and the state of the parenchyma may change the condition of the
surrounding stroma; but also, the blood vessels and their permeability may
affect the stroma in which they are embedded, and by way of the stroma they
may affect even the parenchyma. Local defects may alter the tissue equilibrium,
inducing tissue growth, and even without such defects neighboring pigmented
epidermis may, under certain conditions, invade unpigmented epidermis. In a
similar maner the squamous epithelium of the cervix, which develops under
the influence of hormones, may act towards the neighboring cylindrical epi-
thelium of the uterus. These exists, in all probability, other local mechanisms
which maintain the tissue equilibrium in addition to the action of hormones
originating in distant places. We may then conclude that the normal tissue
equilibrium depends (1) upon the action of autogenous differentials, which
all tissues possess, and (2) upon a variety of other effects, among which the
action of some special hormone-like contact substances as well as typical
hormones play a prominent role. There is thus a certain correspondence be-
tween the factors which determine the interaction of embryonal tissues and
those which determine the autogenous equilibrium of the adult higher or-
ganisms.

Chapter 6

Regeneration, Transplantation, and the
Autogenous Tissue Equilibrium

IN earlier periods of the experimental study of transplantation a dis-
cussion arose between two French biologists, Yves Delage and Giard,
as to the relation which exists between transplantation and regeneration.
Yves Delage maintained that there is an antagonism between these two proc-
esses. He based this conclusion on the very great regenerative potency in
lower organisms, such as planarians and lumbricidae, which renders trans-
plantation difficult, because the new tissue developing in or near the surface,
which separates host and transplant, tends to push off the transplant. Plants,
on the other hand, in which the tendency to regeneration is very slight, are
very suitable for grafting. However, according to Giard, such an antagonism
does not exist. He cited the fact that in tunicates, sponges and corals, where
the regenerative power is great, transplantation can readily be accomplished.
In previous chapters we have mentioned the importance of regenerative
processes in the fate of transplants; we shall now consider these facts in a
connected way, because they have an important bearing on the establishment
of the autogenous equilibrium in higher organisms, which holds together the
various organs and tissues, as well as different parts, in the same organ or
tissue, and unites them into one individual. This equilibrium is autogenous in
higher organisms, because adjoining tissues need to possess the same individu-
ality differential. The proof of the existence of such an equilibrium is based
largely on the absence of regenerative growth phenomena whenever adjoining
autogenous tissues or constituents of the same tissue balance one another in
such a way that there is a relative state of rest and a lack of interference with
the neighboring tissues. To such a state of formative equilibrium there must
correspond a similar equilibrized state of metabolic and functional interactions
of tissues; whenever a replacement of the autogenous tissue constituents by
homoiogenous constituents alters this equilibrium, regenerative movements
and growth tend to take place, and thus antagonisms between adjoining tissues
may become manifest ; these changes may be taken as an indication that an
autogenous equilibrium has existed before the disturbances became manifest.
As the following discussion will show, in certain respects there does exist an
antagonism between the regenerative activity of the host and the successful
outcome of transplantation. There are conditions in which the tendency of
the host to regenerate may be responsible for the casting off or the resorption
of the transplant; but, on the other hand, there are also conditions in which
the transplant may prevent regenerative processes in the host ; this it may do
if, owing to the nature of the organismal and organ differentials of host and
transplant, the contact mechanisms at the point of junction between the

275

276 THE BIOLOGICAL BASIS OF INDIVIDUALITY

partners are adequate and exert a mutually balancing effect. As stated pre-
viously, there is reason for assuming that the normal contact mechanisms
depend at least partly on the interaction of adequate contact substances.

The conditions prevailing at the point of junction may influence the occur-
rence or non-occurrence of regeneration in one of three ways: (1) The
presence of adequate contact mechanisms or contact substances may prevent
regeneration directly by insuring a relative state of rest; conversely, the
absence of such mechanisms or substances may directly cause regenerative
processes to set in; (2) the absence of adequate contact mechanisms may
lead primarily to the loosening of the connection between transplant and host,
and this may be followed by regeneration. In both of these cases we have
presumably to deal with specific actions of a chemical nature; (3) the ap-
proximation of the surfaces of contact may directly inhibit regeneration in a
simple mechanical way by exerting pressure. In addition, we have to consider
the growth momentum of both host tissue and transplant; the greater the
growth momentum, the greater must be the forces that tend to repress regen-
eration, other conditions being equal.

While actual experience has proven the mutual antagonism between re-
generative activity and successful transplantation, other factors tend to make
regenerative processes favorable to transplantation. Thus a slight degree of
regenerative activity in many instances is needed for and makes possible the
joining together of host and transplant. There may exist, besides, an indirect
relation between the degree of transplantability and the degree of regenera-
tive activity which host and transplant exhibit; it depends upon the frequent
association of great regenerative power of organisms and their constituent
parts, with a primitive, less complex constitution and a correspondingly lower
degree of sensitiveness to differences in organismal differentials. There is
noticeable, therefore, particularly in phylogenetically and ontogenetically more
primitive organisms, a greater mutual adaptability between transplant and
host, and a greater ability of the transplant to withstand the injuries con-
nected with the process of grafting, especially during the first critical period
following transplantation when the nourishment of the grafts may as yet be
inadequate. But where the opposite conditions prevail, where there is a lack
of regenerative ability associated with a great sensitiveness of the tissues to
injuries, transplantation may be impossible, as, for example, in the case of
the adult mammalian ganglia cells of the central nervous system.

It was presumably the difference in point of view between Yves Delage
and Giard which, more recently, suggested to Weiss the analysis of the factors
on which the antagonism between regeneration and transplantation depends.
In Salamander larvae, amputation of an extremity is followed by regeneration
of a new extremity; but if, according to Weiss, another extremity of such
a larva is transplanted onto the wound, regeneration is completely prevented,
provided the new extremity fits the defect anatomically as well as functionally ;
however, if the covering of the wound by the surface of the transplant is
incomplete, wound healing may take place at first, but then regeneration may
set in, and even if it is rudimentary or retarded, the transplant is cast off.

REGENERATION AND TISSUE EQUILIBRIUM 277

These observations agree with those of Morgan, who previously noted that
if, in tadpoles, a tail is cut off and the cut-off tail of another larva is grafted
onto the wound, regeneration does not occur on the cut surfaces, although
both the stump and the grafted tail have the power to regenerate.

Similar results were obtained in anuran amphibia by Graper. Transplanta-
tion of extremity buds on stumps of limbs succeeded, but regeneration was
prevented thereby only if the orientation of the cut surfaces of host and
transplant to each other was correct. If the two surfaces were not adequate,
the transplant either changed in such a way that it became secondarily ad-
justed to the host and was transformed into the right kind of extremity, or,
if this did not take place, there was a regeneration of the original limb, not-
withstanding the presence of the graft. Of special interest is the fact that in
case of a disharmonious character of the cut surfaces a regenerative growth
occurred, which did not need to be restricted to the cut surfaces but which
took place even at some distance in the transplanted limb. We have already
referred to similar results when we discussed regeneration in primitive adult
invertebrates, where likewise an outgrowth may take place at some distance
from the place of union of the two pieces, a contact effect apparently having
been propagated from the directly affected area to nearby parts. Therefore,
according to Graper and Weiss, a satisfactory axial orientation between trans-
plant and host is essential if regeneration is to be suppressed. An arm can
inhibit the regeneration of a posterior extremity, provided the axes in host
and transplant have an analogous orientation. If the transplantation occurred
not directly at the point where a part of the limb had been cut off, but at some
distance from it, in the direction towards the head in the branchial region, the
tendency to regeneration was greater, but in principle the same competitive
struggle took place between the prospective or early regenerate and the trans-
plant, and in certain cases both pieces, regenerate and transplant, coalesced.
The transplant, even if it did not succeed in suppressing the regeneration, was
able in some instances to make it less perfect.

In many other experiments, also, especially those of Harrison, success in
the grafting of extremities in amphibian larvae depended largely upon the
fulfillment of the condition that the transplant satisfy the tendency of the host
to form a certain type of extremity ; unless the transplant conformed to this
condition, the reaction of the host tissue was unfavorable to a permanent union.
In these cases we have, it seems, to deal with specific interactions between
host and transplant at the point of contact. But homoiogenous tissue of a
different kind, such as transplanted living skin, may also exert an inhibiting
effect on the regeneration of extremities. Thus Harrison and Detwiler found
in embryos of Amblystoma that the regeneration of limbs which had been
excised, can, to some extent, be inhibited if the wound is covered with
homoiogenous skin, and it can be entirely prevented if the wound and the size
of the skin subsequently grafted onto the wound are very extensive.

However, there are several investigations which make it very probable that
in addition to these specific contact actions, also purely mechanical, non-
specific factors may play a part in preventing regeneration. Thus Schaxel

278 THE BIOLOGICAL BASIS OF INDIVIDUALITY

observed that the covering of a wound in Siredon pisciformis not only with
transplanted living skin, which heals on rapidly, but also with dead material,
may prevent regeneration. In this case purely mechanical factors are probably
responsible for the result and we might even conclude that if the organismal
or organ differentials are active after transplantation of extremities, their
effect is only an indirect one, permitting the graft to remain in perfect apposi-
tion to the wound and thus to exert the needed mechanical pressure; but if
the differentials are not compatible with each other and the right contact
substances do not interact in the area of the wound, then the transplant is not
able to exert the required mechanical pressure on the wound surface and
regeneration takes place. But, there is reason for assuming that the type of
inhibition of the regenerative process which occurred in Schaxel's experiment
is different from that caused by the transplantation of an extremity bud. In
the former case regeneration was not actually prevented ; it began to take
place and then the pressure of the scar-tissue apparently did not allow the
regenerating extremity to break through. Therefore, in this instance the
regenerative processes were presumably merely inhibited and made abnormal
by the mechanical pressure of the overlying skin. Perhaps the inhibition of
the development of transplanted buds of extremities was also a pressure
effect of the overlying skin, although here the homoiogenous nature of the
transplanted skin may also have played a role. On the other hand, if two
well-fitting surfaces of extremities or tails are joined together, even the
beginning of regeneration can be obviated. In this case we have probably to
deal with specific contact effects rather than with non-specific mechanical
pressure.

In accordance with this interpretation, and somewhat different from the
conclusions suggested by the experiments of Schaxel, are the results obtained
by Godlewski, who noted that only living tissue, especially skin with the
underlying cutis, was able to prevent regeneration of a tail in axolotl ; further-
more, only auto- and homoiotransplants, or transplants belonging to different
races but to the same species, were effective. Thus, according to Godlewski,
skin of the white axolotl grafted onto wounds in the black axolotl prevented
regeneration of the tail in the latter, which would otherwise have followed
an amputation. Godlewski assumes that this result is due to the specific effect
of the cutis, which remains alive after transplantation and which prevents the
epidermis from growing down into the underlying coagulum and initiating
the regenerative process. As usual, under similar conditions the inhibition of
regeneration is complete only if the wound has been covered in an exact man-
ner. If certain small areas have been left uncovered, finger-like, thin, prolifer-
ative buds may grow out.

However, there is considerable difference in the conclusions of various
investigators as to the manner in which the regeneration of the extremity
takes place. We may cite the more recent experiments of Harrison, who be-
lieves that the extremity is produced by the mesenchyme of the extremity bud
and not by the ectoderm. Still, the ectoderm may exert some influence on the
formation of the limb and different types of ectoderm may vary in the effects

REGENERATION AND TISSUE EQUILIBRIUM 279

which they produce. While ectoderm taken from the area covering the devel-
oping extremities may favor the regenerative growth of embryonal buds, or
at least does not inhibit it, ectoderm taken from the head region does inhibit
it, but only if this ectoderm has reached a certain stage of development.
Similarly, Mangold observed that the epidermis of Axolotl, which does not
possess the ability to produce a balancer, may exert an inhibiting effect on skin
which otherwise would be able to produce this organ. We would have, then,
in this case, to deal with specific effects of the transplanted epidermis on the
regenerative process and not with non-specific pressure effects; but while
these relations between epidermis and underlying cutis are specific and not
purely mechanical in their action, they are specific in a particular way and
not exactly identical with the effects observed by Weiss and others. There
are involved, here, tissue equilibria of a special nature. According to the
observations of Weiss, a transplant inhibits even the onset of regeneration
if the two surfaces joining transplant and host are mutually perfectly ade-
quate. Under these circumstances a very rapid union between the two pieces
takes place. We may assume that the transplant brings about the same condi-
tion at the point of junction which would prevent regenerative growth proc-
esses in this area in the normal intact organism ; in the latter, the normal
neighboring tissue exerts presumably the same kind of inhibiting contact
effects as does the grafted, strange tissue under experimental conditions.
Inasmuch as in many of these experiments there are successful homoiotrans-
plantations, we may furthermore conclude that even homoiogenous differen-
tials make possible these normal interactions of equilibrating contact mecha-
nisms in amphibia, and also that a very brief interruption of the contact action,
such as occurs during the excision of a piece of tissue and the grafting of
another piece in its place, is not sufficient to initiate growth processes. But
if these contact actions are not completely adequate, graded differences in
incompatibility may exist in different cases between transplant and host and
then it is possible for the regenerative outgrowth of the host tissue to take
place even at a time when the union with the transplant has become already
so firm that this outgrowth is unable to induce the casting off of the trans-
plant ; instead, a struggle may develop between the two tissues and the trans-
plant may be pushed sidewise by the regenerating host tissue, so that in the
end it forms an appendage to the regenerated extremity and a double forma-
tion is produced. In this case the mutual antagonism between host and trans-
plant manifests itself in an inhibition of growth of the transplant; but the
more subtle mechanisms of attack by means of specialized cells of the host,
which we can observe in mammalian transplantation, are, as yet, apparently
lacking in these more primitive organisms.

Similarly in the experiments of Milojevich, who used Triton extremities
directly after metamorphosis, the surface of an extremity was partly, but not
entirely, inhibited from growing out by grafting onto it the regenerative bud
of another Triton limb. If the latter was at such an early stage of development
that the tissue differentials had not yet fully formed, then the outgrowing
part of the remnant of the host bud and the grafted bud united to form one

280 THE BIOLOGICAL BASIS OF INDIVIDUALITY

extremity, but at the sides where the grafted limb did not fully cover the
remnant, new extremities grew out. In this instance, therefore, the inhibition
exerted by the graft was strictly limited to the place of contact. If, instead of
grafting another bud onto the exposed surface of the regenerative bud, it was
completely covered with a piece of skin or with a layer of muscle and skin,
the regeneration was entirely prevented. Possibly here mechanical factors
also played a role, as they apparently did in the experiments of Schaxel.

Another interesting example of the antagonistic action between transplant
and host, and the latter's tendency to grow or regenerate, is the inhibiting
effect shown, in various degrees, by the morphogenic gill field on the de-
velopment of transplanted limbs. In the presumptive gill region ectoderm and
mesoderm have the tendency to produce gill structures, a tendency which
is graded in intensity in different areas (Ekman, Detwiler) ; this inhibiting
effect is evidently of a specific nature and it leads to a struggle between the
transplant and the host tissues, which mutually antagonize each other in the
realization of their morphogenic tendencies. These effects consist presumably
in contact actions. Very fine differentiations which take place during em-
bryonal development in this area are made manifest by means of transplan-
tation, and they determine the character of the contact actions. Thus, in
general, the nearer the ectoderm used for transplantation is situated to the gill
region in the donor, the more it is forced to conform to the influences exerted
by the underlying tissues in this area, which tend to convert the transplant
into gill structures and at the same time to suppress limb formation.

The specificity of the factors which are active in the inhibition of regenera-
tion is, perhaps, most convincingly demonstrated in some experiments of
Harrison, which concern the production of heteromorphic tails in larvae of
Rana. Two anterior parts of these larvae were united, each with the aboral
pole of the other. If a piece was cut off from one of the combined anterior
parts a tail regenerated, in which the medulla of the head part, which had
been left intact — the new host — and that of the second partner — the graft —
and its regenerate were united, but in which the chordae were not united.
Under these conditions the free end of the chorda of the dominating host
stimulated regeneration of an additional tail, which possessed chorda but in
which the medulla was lacking. Evidently the surface of the medulla in the
graft, which fitted the surface of the medulla in the host and regenerate,
prevented a new regenerative outgrowth of the medulla of the host into the
additional tail. On the other hand, the surface of the chorda, not being in-
hibited by contact with a suitable surface of chorda tissue, regenerated and
gave rise to the newformation of a tail. In this case, also, the inhibition must
have been of a specific character ; medulla inhibited medulla, but the chorda,
not being specifically inhibited by an adequate surface of chorda, grew out
and gave rise to regeneration. Here we can therefore exclude simple mechani-
cal factors as inhibitors of regeneration.

Whether there will be compatibility or lack of compatibility between host
and transplant depends also upon the degree of self-differentiation which has
been reached in the development of both host and transplanted tissues. As

REGENERATION AND TISSUE EQUILIBRIUM 281

long as the material entering into these reactions is still plastic, adaptable, and
not yet definitely fixed and differentiated, especially in the transplant, there
is less likelihood that incompatibilities will develop, than at later stages when
differentiation into the more rigid structures has already occurred.

We find, therefore, very complex interactions between transplant and ad-
joining host tissue, and the effects exerted by neighboring tissues upon each
other depend not only on the kind of tissues which are brought into contact
with each other, but also on the stage of development and differentiation of
these interacting tissues. Thus the inhibiting action of a transplant on the
regeneration of an extremity is effective only in the first phase of the process
of regeneration ; it is ineffective if the transplantation is carried out at a later
stage, when regeneration is already under way. On the other hand, if in some
manner, as for instance through a purely mechanical factor, we prevent the
regeneration from being initiated, all subsequent outgrowth has, by these
means, been made impossible. Perhaps the ability to regenerate depends upon
the presence and activity of a sensitizing substance, which may be lost or
neutralized after a definite time has elapsed. This would represent a condition
analogous to that observed in mammalian organisms, where a placentoma can
develop only at the stage of the sexual cycle when the sensitizing substance
given off by the corpus luteum has become active. The effect of certain contact
actions would then perhaps consist in a neutralization of the influence of
sensitizing and stimulating substances.

It follows from our previous discussions that these contact mechanisms
between adjoining tissues may consist in the giving-off of various specific
substances corresponding to organizers, to sensitizing, or, under some con-
ditions, also to inhibiting substances in the place of union. In addition, the
physical-chemical structure of the cut surfaces of transplant and host may
be of importance, in accordance with Graper's comparison of these surfaces
with electro-magnetic fields.

The importance of contact effects in determining the fate of tissues is
indicated also in some experiments of Schaxel with transplantation of ex-
tremities in Axolotl. If buds at very early stages of regeneration are trans-
planted into a further developed body wall, the transplant is not able to form
an extremity through self-differentiation; it is prevented from doing so by
the organizer action of the strange surrounding host. Instead, the transplants
may form irregular masses, which later disappear; but further differentiated
regenerative buds transplanted under the same conditions are able to form
extremities. However, if an early regenerating bud is transplanted together
with the surrounding skin, then it may differentiate into the typical extremity ;
apparently its own skin can supply the needed kind of contact action, which
allows it to differentiate normally and to maintain itself after transplantation.

We can understand the way in which neighboring tissues exert contact
actions upon each other, presumably through the giving-off of certain sub-
stances, if we consider what happens at certain stages of metamorphosis. In
anuran amphibia the gills at definite periods of metamorphosis secrete a sub-
stance which dissolves the overlying skin. Also, transplanted gills exercise

282 THE BIOLOGICAL BASIS OF INDIVIDUALITY

this function, but later on they lose it. In these instances there may be active
the secretion of an acid or of a proteolytic enzyme possessing the power of
dissolving the skin and serving as a contact substance. In a corresponding
manner, Helff has shown that it is due to absorption processes taking place
in the gills, which must be in direct contact with the integument, that histolysis
in the overlying integument is initiated. The histolytic influence of the atro-
phying gills increases at first as metamorphosis proceeds, reaching a maximum
just prior to the release of the forelimb; and then gradually it subsides as the
gills undergo the final stage of atrophy.

As stated previously, we think it justifiable to transfer these conceptions,
derived from what has been observed under experimental conditions, espe-
cially those prevailing after transplantation, to the equilibrium, which exists
normally in an organism, between adjoining tissues; here contact substances,
in addition to hormones, presumably determine the tissue equilibrium, and
disturbances of this equilibrium may lead to extensive regenerative processes
in phylogenetically or ontogenetically more primitive organisms, and to simple
wound healing in the more differentiated organisms. Among these contact
substances the organismal as well as organ differentials may play a part, the
organismal differentials gaining in importance with increasing phylogenetic
and ontogenetic development.

Certain kinds of transplantation in the more primitive classes of inverte-
brates similarly contribute to the understanding of the significance and origin
of regenerative processes at or near the point of junction of graft and host
and to the interpretation of the factors that maintain the tissue equilibrium
within the same individual. We have seen that organismal differentials are
of importance in this process, as are also correct axis orientation and polar
direction of joined parts. This is true especially in the case of the more primi-
tive invertebrates as well as of plants. If the cut surfaces do not fit each other
completely, a regenerative outgrowth may take place from an uncovered point.
Moreover, in vertebrates as well as in invertebrates, regenerative processes
may proceed not only directly from the free surfaces of injured organisms,
or from surfaces exposed after incompatible pieces have separated, but also
from totipotent cells which migrate to the exposed surfaces. Such observa-
tions have been made, for instance, in amphibia by Hellmich, and by Spek
and others in the ascidian Clavelina. In the latter case, under various condi-
tions leading to budding, certain totipotent cells are attracted from the deeper
tissues to that point of the body where the growth processes are to take place.
It may be assumed here, too, that certain substances rather than purely
mechanical factors direct the movement of these cells. It seems that the sep-
aration of the transplanted parts may in some cases constitute the primary
process, which subsequently is followed by regeneration ; but in other cases,
as we have previously pointed out, it is very probable that incompatibilities
between the joined pieces lead to regenerative processes, which are thus pri-
mary, and that these are followed only secondarily by a separation of the parts.

Cell equilibria which depend upon contact influences exerted by adjoining
cells upon each other, determine whether one or more embryos shall develop

REGENERATION AND TISSUE EQUILIBRIUM 283

from the blastomeres ; this is a problem which we have already discussed in
a previous chapter. Developmental processes which might lead to the forma-
tion of two embryos are prevented if the surfaces of the blastomeres, either
derived from the same or from different eggs, are oriented to each other in
the right direction and if the organismal differentials of the joined parts are
mutually compatible. Under these conditions adjoining cells, even if they were
obtained from different organisms, may restrain each other from carrying
out movements and from undergoing cell divisions, such as would give rise
to the formation of a whole organism from one of the partners; instead, the
blastomeres may coordinate the activities of the neighboring cells with their
own.

However, if the organismal differentials of the partners are unsuitable, or
if the axes of the adjoining segments do not fit each other, then the neighbor-
ing segmented cells no longer exert this regulating effect. When unsuitable
heterodifferentials cause the duplication of organisms, the two partners may
still remain united in a mechanical sense; but sometimes a complete separa-
tion occurs. Conversely, in the normally segmented ovum each blastomere may
develop into a separate individual if the surfaces through which the blasto-
meres are joined are altered, or if the substances lying at the surfaces of the
cells are made to move. The same conditions in the surrounding medium which
prevent the spontaneous separation of joined together blastomeres and the
subsequent initiation of abnormal growth processes, may also bring about the
union of two organisms into one. In regeneration in both adult and in em-
bryonal tissues the character of the organismal differentials, the nature, and
in particular, in certain cases, also the orientation of the parts of cells or
tissues adjoining each other, determine whether or not movements of cells,
as well as cell multiplications, shall be initiated, which may lead to the forma-
tion of separate organisms; in the case of the ovum, movements of special
substances also play a role in this regard.

In general, transplantation of suitable tissues onto remnants of embryonal
tissues prevents regeneration of the host embryonal tissue, and conversely,
the latter may prevent such growth in the transplant; but if various incom-
patibilities exist, these act as stimuli which may cause an outgrowth from the
host or a duplication of the transplant. Such incompatibility may consist in
differences in organismal differentials or in the contact of otherwise unsuit-
able tissues; even the turning around of a longitudinal axis of one of two,
ordinarily suitable, tissues may bring into contact unsuitable tissues. But, an
embryonal bud does not tend to reduplication if the strangeness of the soil
onto which it is transplanted exceeds a certain limit of unfavorableness. Thus,
if limb buds are transplanted to the head or medulla of larvae of salamander,
conditions which favor duplication are lacking.

We find, therefore, that very early embryonal buds of amphibia behave in
a similar manner to adult organisms of very primitive classes of animals ;
also, that very young embryonal material and early regenerative stages in
adult primitive animals behave very much alike. In all these cases, we have
to deal with plastic material, where a certain degree of unsuitability between

284 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the part of an organism and the environment may lead to growth processes
tending to the reduplication of the tissues. In such a finely equilibrated sys-
tem the normally present factors must cooperate to keep an organ, or a part
of an organism, at rest. Furthermore, a normal, non-transplanted part of an
organism which still tends to grow, may be induced by the presence of an
otherwise indifferent foreign body to produce an additional extremity, pro-
vided the necessary material for such an outgrowth is present. Or in very
primitive organisms, such as planarians, disturbance of the equilibrium by
mechanical means may lead to fargoing transformations in the individual,
and in coelenterates changes in the oxygen content in the surrounding me-
dium, or perhaps also diffusion of growth inhibiting substances out of the
animal may be followed by the formation of multiple growth centers. It may
be assumed that the contact with suitable tissues maintains an equilibrium in
which all parts of the organism are correlated in such a way that abnormal
growth processes are excluded ; distance substances also play a role in main-
taining this equilibrium. If these normal contact actions are interfered with,
outgrowths, which may lead to reduplication in some cases, take place in very
plastic material, while simple wound healing follows in higher, more differen-
tiated organisms. In all these instances the alteration in the environmental con-
dition represents the first link which sets in motion a chain of events leading
to the abnormal growth. It is of great interest to note the apparent similarity
in the initial factors, as well as in the subsequent links of the reaction chains,
which play a role in embryonal development, in budding, in the regenerative
newformation of organisms, and in the more simple wound healing as we
know it in higher organisms.

Whether an outgrowth occurs from a tissue surface which is not adequately
covered by other tissue, depends also on the growth momentum inherent in the
substratum. The greater this momentum is, the greater the restraining action
of the transplant must be to become effective. The growth momentum is high-
est in the more primitive organisms. Here, too, transplantation of tissues suc-
ceeds better and differences in organismal differentials between host and
transplant play a less important part than in higher organisms. In the latter the
transplants have to overcome greater difficulties in holding their own, but they
have not to overcome as great a growth momentum in the host as do the trans-
plants in the more primitive organisms. Tissue transformers in the form of
organizers are lacking here, where the substratum has lost its plasticity.

As to the character of the contact mechanisms, we have, as stated above,
presumably to deal with substances or chemical groups transmitted from one
surface to an adjoining one; conditions here seem to be analogous to those
observed in the case of the organizers, where effects exerted by chemical
substances are involved. Grafting experiments in embryonal and very primi-
tive adult organisms confirm and extend, therefore, our conceptions as to the
part which contact mechanisms play in higher and fully developed organisms.
There takes place a gradual transformation of the embryonal system of regu-
lation into the system of regulation of the higher adult organism, which,
because of the prominence of the organismal differentials, becomes an autog-
enous regulating system. This regulating system functions in higher organ-

REGENERATION AND TISSUE EQUILIBRIUM 285

isms through the tissues, which are the carriers of finely graded organismal
differentials.

In the highest organisms, the adult mammal, the same factors which are
active in the lower organisms play a role in the maintenance of the equilibrium
which makes possible the existence of an individual. But in contradistinction
to the findings in more primitive organisms, this equilibrium is an autogenous
one. The various tissues composing the individual must have the same in-
dividuality differential, otherwise disturbances take place. In addition, also
mechanical factors, like cuts, the presence of foreign bodies, may lead to dis-
equilibrations in these organisms, which are, however, usually readily re-
paired. Only under certain conditions of sensitization may mechanical factors
lead to furthergoing growth processes, such as the formation of placentomata.
But even without the action of mechanical factors the autogenous equilibrium
may be disturbed if growth stimuli act on adjoining tissues of a different
kind ; thus, changes connected with transplantation of pigmented skin into
defects in white skin in the guinea pig may give to the pigmented skin, or
some of its constituents, a growth momentum which causes it to invade the
adjoining white epidermis. Similarly, if in the vagina-cervix-uterus sex tract
a marked and long-continued stimulation of the surface epithelium is pro-
duced by the injection of estrogen, the growth momentum of the epithelium
of the cervix, which has the power to produce squamous epithelium, is in-
creased more than that of the cylindrical epithelium of the uterus, and in
consequence of this disequilibrium the squamous epithelium may invade and
replace the cylindrical epithelium over long distances. The equilibrium in
the normal individual depends, therefore, also upon the maintenance of the
mutual normal growth momentum of adjoining tissues. A long-continued dis-
turbance of this equilibrium by a variety of factors may ultimately lead to the
initiation of localized cancerous growth.

In general, we may then conclude that a finely equilibrated state exists be-
tween neighboring tissues, the disturbance of which may lead to growth proc-
esses which, in some cases, succeed in restoring the same, or, in other cases,
a new stable equilibrium. Transplantation prevents regeneration when it
supplies the missing regulatory factors, which in the higher organisms are of
an autogenous character ; but in principle, conditions are the same in this re-
spect in the furthest differentiated adult organisms as in the more primitive
and embryonal ones. In the latter, regeneration can be prevented by tissues
which differ within a certain range in their organismal differentials, and which
also may differ in their tissue differentials. We can here distinguish ( 1 ) a
specific inhibition exerted by tissues of the same kind, such as, for instance,
medulla restraining adjoining medulla, or chorda restraining chorda, in their
respective regenerative tendencies (isoregulation), and (2) an inhibition by
tissues of another kind, such as gill tissues inhibiting leg growth, or skin pre-
venting the growth of a tail or limb (alloregulation). It is necessary, besides,
that transplant and host, or adjoining tissues in general, should be in close
contact if the specific interactions between neighboring tissues are to become
effective; otherwise these interactions are interfered with and growth and

286 THE BIOLOGICAL BASIS OF INDIVIDUALITY

movements may set in. Hence inadequate mechanical factors may be the
primary link which leads to these reaction chains.

The results of these various sets of experiments so far discussed harmonize
with each other and also with the conception of the role that autogenous
morphogenic contact substances play in determining the tissue equilibrium.
Again, in this instance the reactions which take place if incompatible organis-
mal differentials are joined together, are due not merely to mechanical factors,
although mechanical factors are involved too in the maintenance of the
autogenous tissue equilibrium, but to the interplay of chemical contact fac-
tors of a more specific character which reside in the tissues. The effect of
unsuitable contact substances may be transmitted to neighboring areas.

The higher developed the organism, the finer and more differentiated are
the organismal differentials which keep the various parts of the body in
equilibrium; this applies to the relation between neighboring parts of the
same type of tissue, as well as to the relation between neighboring tissues
which differ in type. In the more primitive organisms the individuality or
species differentials do not yet possess the same fineness as in higher organ-
isms ; at least the more delicate reactions, which would allow their manifesta-
tion, are lacking. Correspondingly, in these organisms embryonal or regenera-
tive organ and tissue formation is still possible and here, too, organismal
transplantations can be made.

We now have analyzed two sets of facts in connection with the develop-
ment of the more primitive into the higher organisms. In the first place we
have noted the importance of organizer actions, which are very potent in
early embryonal stages, and their replacement with advancing embryonal life
by very complex systems of contact substances, functioning between adjoin-
ing parts of tissues and organs. Involved in this process, also, is the action
of distance substances or hormones, and, moreover, a step-by-step diminution
in growth potentialities and growth momenta, as well as in tolerance to strange
organismal differentials, as tissues and organisms progress from primitive to
more differentiated types.

Furthermore, through transplantation experiments we have arrived at the
recognition of the relatively rigid character of the adult higher organisms.
Reactions of growth and differentiation are here very much diminished, except
in cancer growth, where the growth momentum of tissues may be very great.
Not only are the reactions against strange organismal differentials very
strong, but there exist, besides, some reactions against strange tissue differen-
tials. While in the more primitive organisms the organismal differentials play
a relatively less significant role and the interactions of tissues and organs and
the transformations which they undergo are very prominent, in the higher
organisms, concurrently with the diminution in potentialities of growth and
differentiation, and in morphogenic effects in tissues and organs, the reactions
against organismal differentials become very pronounced. There are found
in the higher organisms a marked fixity and strict regulation of tissues and
organs, which latter is maintained by the interaction of contact substances.
Thus an autogenous tissue equilibrium, which makes possible the existence
of integrated individuals, is established.

P^irf TTT ^e Significance of Organismal Differentials in

the Interaction Between Single Cells

Chapter I

The Role of Organismal Differentials in the
Union of Free-living Cells

We have so far considered the significance of organismal differen-
tials in the grafting of pieces of tissues or organs, or of whole
organs, to embryonal or adult organisms, as well as in the union of
larger parts of primitive organisms and in parabiosis. As a further step in
the analysis of individuality, we shall now study the role which genetic rela-
tionship and the organismal differentials play in the joining together of parts
of cells or of whole cells, which latter may function as independent, free-
living organisms. In these experiments we have not to deal with transplan-
tations in the usual restricted meaning of the term, but with related processes.
The methods used and the problems considered in this part are similar to
those studied in the previous parts. We should naturally have to include in
these chapters also experiments in which unsegmented eggs or ova in early
stages of segmentation were joined together; however, these have already
been discussed in earlier chapters, in which in experiments with the eggs of
Ascaris distinct effects of the organismal differentials or their percursors
were noted, and this was true also in the experiments of Mangold on the
combinations of eggs in amphibia. We have also reported already on investiga-
tions in which early embryos or parts of embryos were united.

In this chapter analogous phenomena in certain protozoa and unicellular
plants will be analyzed.

1. The union of free-living protozoa or of parts of protozoa. As early as
1863, Max Schultze observed that pseudopods from different individual
protozoa belonging to the same species did not unite when they were brought
into close contact with each other; but it was only in 1897 that Jensen noted
a difference in the behavior towards each other of protoplasmic particles from
the same and from other protozoan individuals. In experiments especially
with the polythalamous rhizopod Orbitholites, he observed that two pseudo-
pods from the same individual readily joined each other at the point of con-
tact to form one single organ, and in particular, adjoining small pseudopods
could unite into a single larger one by the flowing together of the protoplasm
at the points of contact; furthermore, a pseudopod of large size could in-
corporate a smaller one. In these cases we have to deal with autogenous
reactions. On the other hand, if two pseudopods which belonged to two differ-

287

288 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ent but homoiogenous individuals touched each other, the pseudopods, instead
of coalescing, contracted and disintegrated into small balls, which could be
taken into the body of the individual from which they were derived. These
observations were made primarily on pseudopods which were still connected
with the body of the rhizopod. But even pseudopods which had been cut off
from the main body behaved in principle in the same manner; they readily
coalesced only with the pseudopods derived from the same individual. If, on
the other hand, a cut-off pseudopod was first allowed to degenerate and then
to come in contact with another individual of the same species, it could be
eaten by the latter. This observation suggests that during the process of
degeneration the protoplasm loses its individuality differential and becomes
converted into inert material that may serve as foodstuff.

If we bring into contact with each other, instead of autogenous or homoiog-
enous parts, pieces belonging to different species of polythalamous rhizopods,
the initial reaction of repulsion, which characterizes homoiogenous contacts,
is lacking. Such pseudopods behave to each other in the beginning as they
would to foreign material, such as various foodstuffs, with which they first
agglutinate and which they then incorporate into their body. But in the case
of heterogenous contacts this initial agglutination reaction is followed soon
afterwards by a contraction similar to that observed when two protoplasmic
particles of homoiogenous origin come into contact, and a secondary separa-
tion of the two strange pseudopods takes place. The response to heterogenous
protoplasm represents, therefore, a combination of the reactions which take
place against a foreign body and of those that occur in contact with homoiog-
enous protoplasm. But in addition there may be an effect which suggests the
action of a toxic substance; for instance, in some cases if a rhizopod touches
the pseudopod of a foraminifera belonging to a different species, the rhizopod
may be paralyzed and drawn into the body of the latter organism, although
it may subsequently be able to free itself again.

It is furthermore of great interest that, to judge from the data available
regarding Orbitholites, the reactions of nearly related, syngenesious organ-
isms towards each other may be like those of autogenous parts of a single
individual. Thus different individuals may fuse and form a colony. Jensen
considered the early age of the individuals which unite as the principal factor
underlying this reaction, but it seems probable that the close relationship
between the organisms and the great similarity of their individuality differen-
tials are of greater importance than the age. This interpretation is supported
by the observation that also in Arcella syngenesious pieces may behave in
a similar way to autogenous parts of an organism.

In other organisms, such as Difflugia, somewhat related but less sharply
differentiated effects are noted. While here, again, two autogenous frag-
ments of protoplasm may coalesce, homoiogenous particles as a rule react
differently towards each other, although occasionally the homoiogenous and
autogenous parts behaved alike. In the case of Arcella polyposa, the more
recent experiments of Reynolds confirm the earlier observations, according
to which autogenous pseudopods which come in contact with each other

UNION OF FREE-LIVING CELLS 289

readily coalesce ; on the other hand, homoiogenous pseudopods which contact
each other shatter into small particles or droplets ; but this does not apply to
the main bodies of these organisms, which are more resistant. Shattering
apparently represents a characteristic homoio-reaction and it is lacking if
heterogenous individuals come in contact. On the other hand, heterogenous
protoplasms do not fuse with each other as readily as autogenous ones. The
heterogenous reaction resembles, in certain respects, that noted towards
foreign material ; however, these heterogenous particles, in contrast to food-
stuffs, are not incorporated into the main body of the protozoa.

The dependence of the reactions of individual protozoa on relationship is
evident also in the subsequent investigations of Reynolds. He started with a
single individual in Arcella, which, in the course of time, underwent fissions,
and this process was continued through several generations ; a comparison
was then made between the behavior of the individuals towards each other
in the later and in the earlier generations of such cultures. Reynolds found
that although all these individuals were originally derived from a single cell,
after some time they began to react towards each other as if they were ho-
moiogenous organisms, and shattering occurred if two such individuals be-
longing to later generations met. Such a change from an autogenous into a
homoiogenous reaction took place after about twenty-two consecutive fissions,
even in cells which had been kept under the same environmental conditions, in
the same culture fluid. However, if individuals developing through fission
of the same protozoon were separated from each other at once and kept in
different culture fluids, representing a somewhat different chemical environ-
ment, then the homoio-reaction was attained sooner.

But Reynolds was also able to obtain the reverse transformation. For this
purpose he proceeded in the following way : after he had changed syngenesious
individuals into homoiogenous ones, he succeeded by means of daily ex-
change of the culture fluid — placing Arcella A into the fluid in which Arcella
B had lived — in transforming the homoiogenous reaction back into a syn-
genesious or an autogenous one. If such individuals were kept together in the
same culture dish, the return to the autogenous reaction could be obtained even
sooner. It appears then, that we have, under these conditions, not to deal with
rigid, mutation-like changes in the protoplasm, but with changes of a more
labile nature, which occur in response to environmental factors and that these
changes are reversible. This holds good provided the genetic constitutions of
the individuals were closely related to each other from the beginning, as is
the case if the organisms are derived through fission from a single individual.

Such experiments suggest that into the culture fluid substances diffuse
which are characteristic of the individual organism and with which presum-
ably their surface layers become impregnated. These substances would then
be responsible for the type of reactions that follow the meeting of two indi-
viduals, or at least be one of the factors involved. It must further be assumed
that the protoplasm of these organisms is readily modifiable and that in the
course of continued fissions a change gradually takes place, leading to a cor-
responding modification in the character of the substances which they give

290 THE BIOLOGICAL BASIS OF INDIVIDUALITY

off. The experiments also suggest that it is the chemical character of the
surrounding medium which is responsible for the changes taking place in the
constitution of the individual. It is known that protozoa can become adapted
to certain toxic substances and to higher temperatures; here likewise, the
alterations of the individuals may be reversible. Do we have to deal in these
cases with functional, phenotypic changes in these unicellular organisms or
in certain parts of them, or do we have to deal with changes in their genetic
constitution?

The observations of Reynolds in Arcella bear some resemblance to reactions
noted in certain of the higher vertebrates, by means of which the latter are
able to distinguish not only between species, but also between individuals or
related groups of individuals within the same species ; as an instance, we may
cite the recognition by dogs of individual scents. In the latter phenomenon
true individuality differentials are not involved, but the characteristics used
for differentiation between individuals are localized in certain organs and
tissues.

However, one important feature these reactions in protozoa have in com-
mon with the reactions due to individuality differentials in higher organisms,
namely a graded differentiation between different organisms in accordance
with their relationship ; this similarity may be taken as an indication that also
in certain protozoa differences exist in the constitution of individuals as
well as of different species. We may then provisionally hold that the reactions
which we have studied in this chapter are due to substances analogous to but
not identical with organismal differentials, substances in particular analogous
to individuality differentials. It may furthermore be assumed that in protozoa,
too, a differentiation of cytoplasmic constituents and also of genetic substances
has taken place in the course of evolution, which has made the production of
such substances and the manifestation of these mechanisms possible. It seems
that a finely adjusted constitution of the surface layer of these protozoa has
made possible the individuality, race and species reactions, which take place
when two individuals or parts of individuals come in contact with each other.
However, in addition to contact actions, the organisms seem to exert upon
each other also some distance actions. Thus, according to Reynolds, Arcella
moves in the direction towards detached autogenous or syngenesious pieces of
Arcella, but it is not attracted by fragments of individuals belonging to the
species Difflugia. The distance reactions and the substances on which they
depend are apparently not so finely graded as the contact reactions. We may
perhaps interpret, in this sense, the observation that parts of an Arcella, which
in the course of generations has lost an autogenous or syngenesious contact
reaction, the latter having been changed into a homoiogenous reaction, may
still retain an autogenous reaction towards Arcella if it is not in direct con-
tact with it. While the contact action may depend upon sessile or only slightly
diffusible substances, the distance reactions in all probability are mediated by
diffusible substances.

But, not in all unicellular organisms have such finely graded reactions,
indicating the relationship between individuals, been observed. Thus in As-

UNION OF FREE-LIVING CELLS 291

trorhiza, a foraminifera, E. Schultz found that the pseudopods of two sepa-
rate individuals can fuse with each other, but it is not certain whether this
represented a syngenesio- or a homoio-reaction. Similarly in Radiolaria,
Verworn (1892) succeeded in exchanging the nuclei between different, non-
related individuals of the same species. Such organisms remained apparently
normal and were protected by the possession of a nucleus of homoiogenous
character against the injurious effects which otherwise would have followed
loss of the nucleus.

The extensive studies of Jennings, Sonneborn, and others, make it very
probable that genetic factors play a role in the mating reactions in Para-
maecium bursaria and aurelia, and similar conditions have been observed in
the green algae, Chlamydomonas, and other flagellates, by Moevus. In Para-
maecium bursaria, Jennings observed that conjugating pairs can be obtained
from mixtures of two appropriate clones, but not from either culture sepa-
rately. Within a few seconds after mixture the individuals have agglutinated
into small groups. If pairs of two agglutinated individuals form, the partners
in each pair are derived one from each of the two clones. These mating re-
actions occur provided certain physiological conditions, such as temperature,
light and state of nourishment of the Paramaecium are suitable, and the
agglutination takes place if two clones of, different reaction types are mixed.
But in certain clones, isolated pairs may be observed even between members
of the same clone, if the clone is left for a long time in a state of declining
nutrition ; the latter favors agglutination and this environmental factor may
overcome conditions inherent in the constitution of the different individuals.
A segregation into two different mating types may occur in some cases at
the first division after conjugation; in other cases, all clones descended from
the same pairs may represent at first the same reaction type and a segrega-
tion may take place only at later fissions. The meeting of two mates is acci-
dental, but an effective agglutination occurs only if the organisms belong to
different and suitable mating types. These two individuals remain united for
24 to 30 hours and during this time they exchange half of their chromosomes ;
however, there is no distinction between males and females in the sense that
one family would consist of males and the other family of females. After
separation, each parent multiplies by fission. The offspring is at first immature
and has not yet acquired the ability to undergo an effective agglutination with
an appropriate mate, but in the course of months they become mature. The
offspring of two parents that mated are all of the same type, which is usually
one to which one of the parents belonged ; but in some instances, they may
belong to another type. It seems, then, that it is not solely the genetic constitu-
tion which determines the mating type.

Likewise, in experiments of Sonneborn, which preceded the ones just
mentioned, inheritable differences in mating types were observed in Para-
maecium aurelia. Here, in various stocks, collected in different localities, six
mating types could be distinguished, namely, types I, II, III, IV, V and VI.
Mating occurred only between types I and II, between III and IV, and
between V and VI. These three mating groups do not mate with one another ;

292 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the organisms belonging to these groups differ also in other characteristics
and represent, therefore, three physiologically distinct varieties. Certain
races belonging to variety 2 produce toxic substances, which may be the
same or different in different races. One of these substances is strongly
toxic for all the races belonging to varieties 1 and 3, and only weakly toxic
for races belonging to their own variety, namely, 2. This toxic substance
affects, markedly, also certain other species of Paramaecium. Similarly, the
toxic substance produced by another race of variety 2 exerts marked dele-
terious effects on all the races of varieties 1 and 3, but is very injurious only
for certain races of its own variety, whereas others are more resistant or
completely immune. This toxic substance also acts strongly on certain strange
species, but not on others. In these cases we have evidently to deal with a
reaction type, which we have designated as "specific adaptation," the specific
adaptation depending in this instance presumably upon the specific chemi-
cal nature of the toxic substances and of certain receptor substances in
the different varieties, which insures a decreased toxicity of a substance se-
creted by Paramaecium aurelia for nearly related organisms. Sonneborn made
it probable that Mendelian rules of inheritance are applicable in the trans-
mission of the characteristics determining reaction types to successive gen-
erations of the various races. The determining factors were contained in the
micronucleus, but exerted their influence by way of the macronucleus and
cytoplasm. However, these genetic factors were accessible to environmental
conditions, and, in particular, the temperature prevailing at the time when
the macronucleus is formed from the micronucleus could influence the
proportion of individuals belonging to certain types. After this sensitive
period has passed the mating type is inherited by all subsequent macronuclei
produced at later fissions without further interference by the temperature. In
other organisms studied by Moevus, light is able to suppress the mating
reaction and in certain cases the mating types seem to be determined entirely
by environmental factors.

We see, then, that in interactions of certain protozoa, comparable to ferti-
lization reactions in higher organisms, factors play a role which tend to
prevent fertilization with nearly related organisms and favor fertilization
with selected, more distant groups of the same species, and that differences in
reactions may have to be attributed to genetic differences in the constitution of
clones ; there are, furthermore, indications that also in these protozoa changes
in the constitution of the genetic substance may take place and thus increase
the diversification of various stocks. In contradistinction to these genetic dif-
ferences between various stocks of Paramaecia just discussed, certain struc-
tural abnormalities, which may be found in some individual Paramaecia raised
in cultures, do not seem to affect the mating reactions, inasmuch as such
abnormal individuals can be made to fuse with normal ones under the same
conditions as can other normal individuals.

Is it correct to attribute these reactions between different groups of Para-
maecium to mechanisms comparable to those occurring in higher organisms
under the influence of organismal differentials? There are some apparent

UNION OF FREE-LIVING CELLS 293

similarities between the reactions noted in Protozoa and in higher organisms,
but there exist also marked differences. The characteristic feature of organis-
mal differentials that they are the same in the various tissues of the same
organism and are different in the analogous tissues of different individuals
does not apply to unicellular organisms. Furthermore, it is very probable
that many genes enter into the constitution of the individuality differentials
and of the organismal differentials. In Paramaecia, on the other hand, there
are strong indications that the difference in agglutination reactions depends
upon single or a few selected genes. It seems then that the reactions between
different mating groups of Paramaecia are analogous to the fertilization re-
actions in higher organisms and this is also implied in the term "mating re-
actions" given to this condition, or they may be compared to the agglutination
reactions between different blood cells belonging to different blood groups in
higher organisms.

Reactions similar to those studied in protozoa have also been observed in
algae and myxomycetae. In the phycomycetous fungus Achlya, the sexual
reaction between male and female mycelia seems to depend upon the action
of hormone-like contact or distance substances. Such a substance given off
by the female vegetative hyphae induces in the male the formation of antherid-
ial branches and the oogonial initials attract the antheridial branches, causing
the delimitation of the antheridia. The antheridial branches on their part act
on the female vegetative hyphae and here induce the formation of oogonial
initials, and furthermore, the antheridia cause the delimitation of the oogonia
through the formation of a basal wall. These reactions take a normal course
if the male and female organisms belong to the same species, but if male and
female belong to different species of Achlya, the reaction sets in but remains
imperfect. It stops either at the time of the differentiation of the antheridia,
or the female fails to produce oogonial initials in response to the substances
produced by the numerous antheridial branches. This indicates a specific
adaptation between these distance substances, which transmit the stimuli from
male to female, or vice versa, and the mycelial substratum on which these
substances act. If the latter and the substratum are derived from different,
though related, species, the reaction will be incomplete.

We may refer here, also, to the very interesting recent investigations of
Moevus concerning the motility, chemotaxis and copulation of the gametes
of certain green algae. There exist a number of races or species of Chlamy-
domonas which show inheritable differences in the mode of reactions of their
gametes and the conditions which determine these hereditary differences are
localized in the chromosomes of the various races. As a result of these genetic
differences race specific substances are produced, which direct the motile
gametes in the dark. The extract from individuals of each race or species
acts most efficiently on the gametes of their own race or species, and more
weakly on the gametes of other races. These specific substances are caroti-
noids ; the filtrates contain transcrocetin sugar esters which are responsible
for these effects. Also, the sugars which combine with crocetin seem to be
specific in the different races.

294 THE BIOLOGICAL BASIS OF INDIVIDUALITY

The copulation-determining substances are, or at least act like different
combinations of cis- and transcrocetin methyl esters and the proportions of
these two esters differ in the different races of Chlamydomonas eugametos
and also in certain other species of Chlamydomonas. These proportions are
hereditarily fixed for the gametes of these races and species ; copulation occurs
between those gametes of races and species in which the difference in the
proportions of these two esters exceeds a certain threshold value. This same
difference in the proportions of the esters determines also the degree of
chemotactic action which must precede copulation and which leads to group
formation in the various gametes, processes of agglutination being presumably
involved in these relations. The interactions between certain cells are thus
determined by substances which cause distance as well as contact effects and
they are graded in accordance with the genetic relationship of the different
races, and the combinations of the effective substances are likewise thus graded.

In the alga Bryopsis, Prowazek (1907) has apparently observed, if we
interpret his short description correctly, that when protoplasmic particles,
which are surrounded by haptogen membranes, come into close contact with
each other, the membrane dissolves and the particles coalesce, in case we have
to deal with substances derived from homoiogenous organisms ; but if the
particles belong to different races or species, such a solution of the membrane
and fusion of the protoplasms do not take place.

Similarly, in the formation of plasmodia of myxomycetae, individual
myxomycetae or small plasmodia first stick together and then coalesce into
one large Plasmodium. Occasionally such a coalescence may take place even
between a large active plasmodium and a small resting round plasmodium,
which had previously been taken into the body of the larger individual (Cela-
kowsky, 1892). However, as Cienkowski (1863) had found previously, only
plasmodia or myxamoebae of the same species can coalesce. If heterogenous
individuals meet, they may flow around each other but do not unite, even
individuals belonging to nearly related species differing in this way from
individuals of the same species. Whether only syngenesious or also actual
homoiogenous individuals coalesce with each other is not stated by these
authors, but it appears probable that all individuals belonging to the same
species can thus unite. Nevertheless, there have been observed instances in
which even separate parts of the same cell could not join each other; this was
the case when haptogen membranes developed on the surfaces of the particles.

The tendency to react adversely to contact with the protoplasm of other
individuals of the same species, which has been found in certain rhizopods
and which we have discussed already, must have the consequence that such
organisms, even when not surrounded by a shell or cuticle, remain separate.
But if a syngenesious reaction should become identical or almost identical
with an autogenous reaction, then the formation of larger plasmodia or colonies
would not be impossible. Conversely, it may be expected that in organisms
which tend to form plasmodia or colonies, this sensitiveness to homoiogenous
protoplasm is lacking and an antagonistic reaction takes place only if more
pronounced differences between the organismal differentials of two individu-

UNION OF FREE-LIVING CELLS 295

als exist. It would be of interest to compare, from this point of view, the
protoplasmic reactions in different colony- and plasmodia-forming organisms
with the corresponding reactions in types of organisms which live as isolated
individuals.

We have seen that genetic relationship may determine not only the char-
acter of contact reactions, but may control also the movements of two organ-
isms which are at some distance from each other. Analogous reactions occur
likewise in cells of metazoa. The cytotropic reactions described by Roux
(1895) may possibly be of a similar nature. Roux found that cells of morulae
or blastulae of Rana, when separated from each other at no greater distance
than the diameter of a cell, may send out processes and move towards each
other. However, in this case reactions between homoiogenous cells were found
to be apparently of the same character as autogenous reactions. Cell move-
ments, which probably depend upon substances active at a distance, seem to
play a role also in embryonal development. For instance, in urodele larvae
certain mesoderm cells are attracted by and move towards the developing eye
vesicle ; in this case the organismal differentials have not yet reached a stage
of marked specificity, and accordingly a lack of individual specificity is noted
in the movements of these embryonal cells towards a transplanted eye vesicle.
As we have seen, in higher organisms the organismal differentials regulating
the interaction between cells and tissues are more finely graded. In addition
to the examples discussed already, we may mention the following observation
recorded by A. Fischer. If parts of two homoiogenous chick embryo hearts are
combined in vitro, cellular anastomoses between contractile elements of such
fragments are produced and synchronous pulsations of the two parts take
place ; but this reaction does not occur if the embryonal heart fragments,
placed in contact with each other under otherwise the same conditions, belong
to two different avian species. In a like manner, as we have already pointed
out, there is reason for attributing to autogenous morphogenic contact sub-
stances the function of maintaining in mammals the normal inter-relation and
balance between the different tissues of the same organism, the autogenous
tissue equilibrium.

It seems then that reactions occur in unicellular organisms, which in some
respects correspond to those which, in higher organisms, we attribute to
organismal and especially also to individuality differentials. But as we have
seen, the same criteria as to organismal differentials which we applied in
higher organisms cannot, in a strict sense, be used in protozoa and unicellular
plants, because by definition the organismal differentials, and in particular the
individuality differentials, are substances present in all, or almost all of the
cells and tissues of a given individual and differentiate this individual from
all other individuals. It is clear that in a unicellular organism such a defini-
tion cannot apply. Still, we may at least conclude that certain protozoa and
flagellated gametes of algae possess structures and substances which function
in a somewhat similar manner to the organismal differentials of higher organ-
isms, inasmuch as they determine in a graded manner the reactions of these
cells to other cells in accordance with the genetic relationships. Also, the male

296 THE BIOLOGICAL BASIS OF INDIVIDUALITY

and female mycelia of certain fungi may behave in an analogous manner.
However, we have also pointed out some important differences between the
mechanisms underlying apparently analogous reactions in these primitive
organisms and in vertebrates. It is possible that not all the reactions in these
primitive organisms are of the same kind, and in some of those which we
have described the probability that individuality differentials are involved is
greater than in others.

We may find even in some of these unicellular, apparently primitive organ-
isms, much finer differentiations between individuals than those which are
noted in relatively simple adult metazoan invertebrates, such as Hydra and
Planaria, or in the embryos of vertebrates. Although protozoa and the gametes
of algae belong to classes of organisms which are considered primitive, it
seems that within these classes there have developed, in the course of evolu-
tion, very fine differentiations between single cells, which cannot as yet be
observed in the organisms from which they are presumably derived. It is
therefore possible that in these classes of unicellular organisms mechanisms
or substances have evolved, in certain respects analogous to but probably not
identical with individuality differentials. The reactions which they manifest
are at least partly localized in the ectoplasmic structures of these cells ; but
inasmuch as the latter may be newly formed by the rest of the protoplasm in
a protozoon temporarily deprived of them, we must assume that also other
parts of these cells, including perhaps their nuclear substance, have the power
to give origin to their own specific individuality differential-like substances.

As we have already mentioned, the observations discussed in this chapter
may be of significance also in the analysis of the conditions underlying the
formation of colonies which, in some instances, develop from unicellular
organisms. Individuality differential-like mechanisms in unicellular organisms
tend to keep the individuals separate from other individuals of the same species
and thus to insure to those organisms the maintenance of a separate existence.
Conversely, it may be concluded that whenever colony formation occurs,
reactions characteristic of individuality differential-like substances, such as
we have here described, are lacking.

As to the interpretation of the mechanism underlying contact reactions be-
tween unicellular organisms, possessing their own individuality or species
differential-like mechanisms, Jensen and Verworn started with the assump-
tion that the protoplasm of these cells is liquid throughout. However, from
what has been learned since about the constitution of amoeboid cells in pro-
tozoa, in amoebocytes of Limulus, and even in cells of higher organisms, it
appears that the consistency of the ectoplasmic layer of isolated cells is gen-
erally more or less solid, although readily undergoing changes, and that under
different conditions its consistency may vary between the extremes of a com-
pletely solid and a liquid state. In the case of the organisms under discussion,
the contact between the surface layers of two unicellular animals or plants,
which latter differ in what in higher organisms would correspond to organis-
mal differentials, may, under certain conditions, act as an abnormal stimulus
initiating a softening of the surface layer; this change may be followed by

UNION OF FREE-LIVING CELLS 297

agglutination and coalescence of the cells, while under other conditions a more
complete liquefaction and a subsequent shattering reaction may occur, result-
ing in the disintegration of the protoplasm into separate droplets in accordance
with the alterations in surface tension of the liquids concerned in these reac-
tions.

In the case of the amoebocytes of Limulus it can be shown that numerous
environmental changes may produce variations in the consistency of the outer
layer of the protoplasm, which in some instances cause agglutination, and in
others amoeboid movement. It is therefore conceivable that in other unicellular
organisms stimuli, which sometimes lead to agglutination and coalescence,
may under different circumstances initiate amoeboid movements of cells in a
direction towards each other, influenced in this process by substances which
are hormone-like and which may not, themselves, possess organismal differ-
entials. Also, the movements of embryonal cells in the direction towards other
tissues may be explained as due to surface reactions similar to those which
lead to agglutination, coalescence, or migration in unicellular organisms.

Chapter 2
Tissue Formation and Organismal Differentials

We have seen that incompatibilities between the organismal differ-
entials or their precursors, or between substances analogous to
these differentials, but not identical with them, which are present
in adjoining cells may prevent the union of the latter and lead to the separa-
tion of cells or parts of cells at or near the point where the bearers of the
incompatible differentials come in contact. This applies to the union of ova
and of embryos, or parts of embryos, in very early stages of development,
as well as to the union of free-living, unicellular organisms or parts of them.
In other cases it may merely modify the nature of their union. There is a
related phenomenon of great biological interest, namely, the formation of
tissues through the union of single cells. Here apparently similar factors to
those which we have discussed in the preceding chapters are active and it may
therefore perhaps be possible to analyze the conditions on which the union of
various cells into tissues depends, and to determine whether there is any
indication that in this process, also, organismal differentials or related sub-
stances play a part.

1. A very simple and primitive type of tissue results from the agglutina-
tion of amoebocytes of Limulus, which takes place spontaneously whenever
the blood of this animal leaves the body under natural conditions. Because of
the primitive nature of this process, it exemplifies, perhaps, some of the prin-
ciples underlying tissue formation in general, and moreover, it is more readily
accessible to experimental analysis than the more complex processes leading
to the formation of the fixed tissues in organisms. In contrast to the latter,
the amoebocyte tissue is merely an experimental tissue, but the analysis of the
factors underlying its formation has served as the starting point for similar
studies in the case of the more complex natural tissues.

The essential factor underlying the formation of this amoebocyte tissue is
an agglutination process, and the agglutination is due to a change in the
environment of these cells, which acts as a stimulus. The stronger the stimulus
within a certain range, the greater are the changes in the amoebocytes and the
more intense is the agglutination which takes place. Thus, if we make an
incision into a Limulus and allow the blood to flow out through such a narrow
opening, it will come in contact with the rough surface of the wound and
subsequently with the chitinous body covering; under these conditions the
amoebocytes send out pseudopods and some of the cells may even change into
a diffuse gelatinous material. If the altered cells and the material flowing out
from the injured amoebocytes come in contact with one another they stick
together, so that they form one jelly-like mass, which gradually retracts into
a small firm clot, in this respect behaving therefore not unlike a blood coagu-
lum. But if, instead of using this simple process, we collect the blood by means

298

TISSUE FORMATION 299

of a smooth, oiled cannula, in glass dishes kept at a temperature near the
freezing point of water, the changes which the cells undergo are much less
pronounced, and although under these conditions the cells still agglutinate
with one another, the agglutination is less firm, the cells remain preserved
much better and gradually sink down to the bottom of the dish, where they
form a connected, relatively thin layer of tissue.

However, whether we use the first or second method, in principle we have
to deal with the same change in the constitution of the cells. Within the blood-
channels of the animal the amoebocyte represents a flat elliptic transparent
disc, which is carried along by the blood-lymph current and is not sticky ; but
under the influence of mechanical and various kinds of chemical stimuli the
amoebocyte seems to take up some fluid from the surrounding medium and
becomes a round or oval cell with larger granules which are separated by a
considerable amount of intergranular substance. As a result of this change in
consistency, especially of the outer ectoplasmic layer of the protoplasm, the
cells become sticky and adhere to one another as well as to the more or less
solid surface of the dish with which they come in contact, or they sink down ;
furthermore, associated with this change there is a tendency of the amoebo-
cytes to send out pseudopods and to manifest amoeboid movement. These
observations suggest that agglutination - and amoeboid movement may be
related processes. Conditions which tend to increase the consistency of the
protoplasm within a certain range, also tend to decrease the stickiness and
agglutinability of the cells and to diminish their amoeboid movement. Under
the action of these factors the pseudopods become fine, more or less shred-
like, and the amoeboid movement is slowed down. Such effects are produced,
for instance, by the use of hypertonic salt solutions, by addition of a slight
amount of acid to a sodium chloride solution isotonic with sea-water, by an
increase in certain ions, as for instance, Na and S04, in the surrounding
medium, and by exposing the cells to cold. In a limited way, a temporary result
of this kind is also brought about by a relatively strongly alkaline NaCl solu-
tion. On the other hand, a softening of the cells increases agglutination and,
to a certain extent, amoeboid movement; a moderate amount of alkali in an
isotonic NaCl solution, hypotonic solutions, an increase in certain ions (K,
NH4, N03), and a slight rise in temperature, exert the latter effects. The
blood serum of Limulus and extracts of Limulus tissue act in a similar way,
and they likewise have a tendency to cause an extension and spreading-out of
the amoebocytes on the surface of a glass on which these cells rest. This
spreading-out is due to a softening of the cells ; it represents a modified type
of amoeboid movement, and furthermore, together with the processes which
take place during amoeboid movement, it explains the tissue-stereotropism
which is common to amoebocyte tissue and to mammalian epidermal and other
tissues. In general, all these different modes of reaction of the amoebocytes
correspond to variations in the consistency of the protoplasm, and such
variations explain the diverse structural types which the cells, singly or com-
bined into tissues, may assume ; in addition they explain the modifications in
the character of amoeboid movement which may be observed. Moreover,

300 THE BIOLOGICAL BASIS OF INDIVIDUALITY

certain agencies, as for instance, acid dissolved in isotonic NaCl solution
within a certain range of concentration, not only diminish agglutination, but
may even cause a separation of agglutinated amoebocytes from one another
and thus change a tissue-like formation back into a suspension of isolated
cells. The agglutination and resulting tissue formation represent, therefore,
to a certain extent, reversible processes. A similar reversibility we find also
in some of the tissues of the most differentiated vertebrates.

2. With amoebocyte tissue we can imitate and analyze certain phenomena
of wound healing which takes place in the normal epidermis of higher organ-
isms. Embedded in this tissue the amoebocytes are at rest, but as soon as an
incision is made and a piece cut out, the cells adjoining the wound become
active and migrate into the wound, thus tending to cover it. There is a differ-
ence in the environment of different parts of the cells adjoining the wound,
these cells being in contact with other amoebocytes, on the side away from the
wound and with a fluid medium and a glass surface on the side of the defect ;
and this condition acts as a stimulus, causing amoeboid movement in the
direction towards the wound and away from contact with the cells. Similarly,
we can excise small pieces of such a tissue, place them on a cover glass, and
treat them as we do pieces of higher tissues according to the tissue culture
method. Through secondary processes which, under certain conditions, may
become degenerative, the character of various higher tissues, especially those
of a mesenchymatous nature, may be imitated, and also pictures corresponding
to outgrowing fibroblastic tissue may be readily obtained with this experi-
mental amoebocyte tissue. The same factors which are responsible for the
movement into the wound of cells and groups of cells adjoining a defect,
cause also the active movement of cells in tissue culture. During this process
of migration the moving cells meet fresh amoebocytes which are likewise
migrating through the culture medium; if they come in contact with one
another, they stick together and form small clumps of cells, from which the
individual amoebocytes tend to detach themselves again; in this way cell
movement takes place, both in tissue culture and in wound healing, in a
centrifugal direction, similar to the cell behavior of higher vertebrate tissues
under analogous conditions. There is no indication that the movement is
otherwise an oriented one; on the contrary, we may consider it as more or
less a chance phenomenon.

As stated, it is the physical and chemical changes in the environment which
bring about the agglutination of cells and, therefore, those reactions which
transform the cells from free-living, isolated cellular organisms into com-
ponents of tissues. If a corresponding condition existed within the blood
channels, as a result for instance of the introduction of a foreign body into
the blood, an agglutination would take place here also, which would lead to
the formation of an agglutination thrombus consisting of amoebocytes and
comparable to thrombus formation in higher organisms, where analogous
cells or blood platelets, representing parts of cells, furnish the substratum of
the thrombus. Tissue formation and thrombus formation are thus essentially
related processes.

TISSUE FORMATION 301

While in certain respects amoebocytes and free-living protozoa differ from
each other in their behavior as far as amoeboid movement is concerned, there
are also some important similarities in these cell types ; to mention only one
feature common to both : the primary and principal change in the consistency
of the protoplasm occurs especially at the point where the pseudopod forma-
tion takes place, which is the leading and most active and sensitive part of the
cell. Connected presumably in some way with the characteristics of the pseu-
dopods are their fine reactions to individual and species differences, which
have been observed in certain protozoa and which we have already discussed.
These reactions also depend on changes in the consistency of the protoplasm,
especially of the surface of the cells, which take place in accordance with the
degree of compatibility or lack of compatibility between the cells which meet ;
and as we have seen, similar changes are also the principal factors leading to
pseudopod formation.

There are, however, also some important differences between amoebocytes
and protozoa. In the case of amoebocytes, their behavior, and in particular the
degenerative processes they undergo, vary greatly in different media and
under different physical conditions. Characteristic of these cells also is their
need of a protein medium. The free-living protozoa, on the other hand, are
adapted to a medium free of protein. Associated with this difference in the
protein requirement of these organisms there is a further difference in their
reaction towards certain ions.

As to the possible role substances corresponding to organismal differentials
play in the behavior of amoebocytes, there are individual variations observed
in the reactions of the cells and consequently also of the amoebocyte tissue
derived from different Limuli. Such variations are as a rule, however, mani-
festations of the quantitatively different tendency on the part of amoebocytes
to contract and of associated differences in the consistency of these cells;
these result mainly from environmental conditions to which the Limuli have
been previously subjected. There seems to be no difference in the behavior of
amoebocytes to one another, homoiogenous and autogenous amoebocytes
behaving in the same way. Therefore there is no manifestation of an indi-
viduality differential or a similar substance noticeable in these cells, as far
as their mutual reactions are concerned. They differ in this respect from the
protozoa, which we have discussed in the preceding chapter.

The behavior of amoebocytes and the agglutination process leading to a
joining together of cells have been considered somewhat more in detail because,
as stated, the analysis of experimental amoebocyte tissue shows clearly the
principles underlying tissue formation in general, and the union of cells in
tissues is the basis of the formation of multicellular organisms. But our con-
clusions apply only to the granular amoebocytes, such as those of Limulus.
The so-called hyaline amoebocytes which have been studied in recent years,
especially by Faure-Fremiet, behave somewhat differently and do not lend
themselves to experiments with tissue formation in the same way as the
amoebocytes of Limulus.

In certain respects related to tissue formation is the process which leads

302 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to the development of colonies out of isolated cells. Such colonies are observed,
for instance, in the ciliate Zoothamnium alternans ; but here, in contrast to
the most primitive tissues, a differentiation in function has taken place between
different members of the colonies, as Summers has shown. The apical cell
exerts an inhibiting effect on neighboring cells. When the apical cell is cut
away, a formerly subordinate cell becomes dominant and assumes the genera-
tive function of the apical cell. But the latter may also exert a stimulating
effect on the other members of the colony. If it becomes an exconjugant, it
induces the first three or four branches below its own level to divide pre-
cociously and so actively that each branch develops almost as an individual
colony. In such a colony evidently a complex tissue equilibrium exists, but
whether this equilibrium requires a strictly autogenous relationship between
the various members of the colony is not certain.

3. The next higher type of tissue formation is found in sponges. Some
complications are added here to the primary factors observed in amoebocytes.
H. V. Wilson, who first separated sponge cells experimentally, was able to
observe that these cells later united again with one another, forming aggregates
from which, under favorable conditions, complete sponge organisms devel-
oped. More recently Galtsoff noted that it is the archaeocytes which play the
principal role in the agglutination of sponge cells, and that they resemble very
much in their behavior the amoebocytes of Limulus. As in amoebocytes, so
also in sponges the migrating cells happen to meet other cells of the same kind
in the course of their movements, and whenever such a chance meeting takes
place the cells stick together. In both cases there is the same lack of an orient-
ing force which leads to the tissue-like agglutination of cells. However, sub-
sequently some differences develop between the behavior of amoebocyte tissue
and sponge-cell aggregations. In the latter, a secondary detachment and
migration of cells in a centrifugal direction does not occur as it does so often
in the former; instead, they now spread out on the surface on which they
are resting, in a way comparable to the extension which is such a common
occurrence and which we have analyzed in amoebocyte tissue. In both these
types of cells the process of extension can be considered as a pathological
modification of amoeboid movement. However, subsequently, the aggregates
of sponge cells, provided they are sufficiently large and contain cells of a
certain type, may change into normal proliferating sponges, while from
amoebocyte tissue more complex formations may develop merely as a result
of secondary, often degenerative changes which lead to the production of
paraplastic structures. The mechanisms, in both instances, underlying the
primary agglutination and the development of stickiness in the hyaline ecto-
plasm, which latter precedes the agglutination process, are related to the factors
concerned in the production of pseudopods and in the extension of the cells.
Temperature, osmotic pressure and hydrogen ion concentration seem to affect
amoebocytes and archaeocytes in a similar manner; for instance, alkali in-
creases the tendency of both kinds of cells to agglutinate. But as far as the
effect of salts, and of ions composing them, on tissue formation is concerned,
the reactions of archaeocytes apparently correspond more closely to those

TISSUE FORMATION 303

observed in free-living protozoa than to those observed in the amoebocytes,
which latter are adapted to a protein-containing environment, while the pro-
tozoa and sponges are adapted essentially to a medium which consists of a
mixture of salts. We may therefore regard the experimental amoebocyte tissue
as representing the most primitive and rudimentary type of tissue, and the
sponges as the next higher type, in which a further differentiation of the
component cells and their power to proliferate are added to the primitive mode
of agglutination and tissue formation.

More recently the agglutinated sponge cells have been studied by Faure-
Fremiet in tissue culture in a similar manner to the amoebocyte tissue, and
he has shown that the archaeocytes behave, here, in about the same way as
the amoebocytes ; they move out of the peripheral piece of tissue in a centrifu-
gal direction and flatten out. It seems, also, according to this investigator, that
a further development of such a tissue culture into a typical sponge takes
place only if the archaeocyte tissue has become agglutinated to the surface
on which it has been placed. In both cases the processes leading to agglutina-
tion depend on changes in the ectoplasmic layer, which make it sticky, prob-
ably as a result of the taking-up of a certain amount of fluid by the stimulated
cell. In addition to the archaeocytes, the collencytes and the choanocytes take
part in the formation of the complete sponge, while the other structures are
produced through differentiation of these primary cells. It seems that the
excretory canals are the central organ around which the other structures are
built up.

If the amoeboid cells of two different species of sponges, such as Micro-
ciona and Ciona, are mixed, two types of reaction may be noted: (a) When
separate archaeocytes of Microciona and Ciona come into contact the outer
hyaline layers of the protoplasm of the cells belonging to the different species
fail to coalesce, the cells of each species remaining separate and forming
aggregates of their own kind. Such a segregation is evidently caused by
differences in the physical properties of the outer protoplasmic layers of the
cells of these two species, and possibly, as in the case of pseudopods of certain
protozoa, by specific changes which take place in the consistency of the
protoplasm when cells possessing different species characteristics meet. There
may also be involved in this effect of foreign cells, either sessile contact
substances or substances secreted by these cells, or substances liberated from
the cells when they are injured in the preparation of the suspension. We may
have, in this case, to deal chiefly with the action of contact substances, which
lead to separation of cells if they are heterogenous ; in addition there may be,
as stated, direct physical differences in the cell membranes, which prevent
agglutination and normal tissue formation. In this connection it is of interest
to note that, according to Galtsoff and Pertzoff, the cells of Ciona and Micro-
ciona differ also in the pH of their cell content, (b) But there may take place
a second type of interaction between cells of different species. As a result of
the unfavorable effect of substances extracted from a suspension of heterog-
enous sponge cells, the archaeocytes are injured; rapid cytolysis take place
and the outflowing cytoplasm of the degenerating cells agglutinates to form

304 THE BIOLOGICAL BASIS OF INDIVIDUALITY

a floccular material which likewise gradually becomes dissolved. There is,
however, no perfect correspondence between the phylogenetic relationship
of the two species and the way in which these heterogenous cells act on each
other; furthermore, the results obtained with reciprocal combinations may
vary. Whether the cytolytic substances involved in this process differ only in
quantity, or also in kind, from the contact substances mentioned above is
uncertain. It may be added here that in arthropods we have observed that
a precipitation takes place if the sera belonging to different species are mixed
with each other; this may be a related phenomenon to the cytolytic effect of
heterogenous substances seen in sponges.

4. A still higher type of tissue formation has been described by Spek in
the tunicate Clavelina. Within this organism amoebocytes are found carrying
special cell inclusions and wandering to places where, owing to the presence
of a wound, regenerative or reduction processes occur, such as are associated
with bud formation. These amoebocytes migrate in great numbers and either
go to the area of new-growth or accumulate in the body cavity. Here they
agglutinate to form clumps or masses, arranging themselves in a tissue-like
manner, and according to Spek, subsequently giving rise to the formation of
the new tissues and organs. Under normal conditions when instead of other
amoebocytes they meet cells of a different kind, or if they migrate through
other tissue layers, they do not agglutinate with one another nor do they
agglutinate with the other kind of cells. But as soon as their environment
becomes abnormal, as for instance, near a wound, or when during the re-
duction processes in the animal they are exposed to conditions under which
abnormal products of disintegration act upon them, or when the preformed
tissues in these tunicates are unable to undertake the necessary regenerative
functions, then these cells become sticky and agglutination occurs. Preceding
the formation of clumps under such abnormal conditions, the amoebocytes
migrate in masses to areas which presumably have undergone pathological
changes, either to the aboral pole in dying animals or into the body cavity
prior to the formation of winter buds. In case of regeneration of special
organs they may first form epithelium-like surfaces, a process which likewise
presupposes agglutination. Smaller groups may then agglutinate with one
another, so that larger or sausage-like masses result, but the agglutination
processes are always preceded by active amoeboid movement, and this is an
oriented one, directed apparently by substances produced in regions where
pathological processes take place. These movements and agglutination proc-
esses are followed by organ formation.

Thus we note here a close parallelism to the reaction of amoebocytes of
Limulus, where likewise abnormal environmental factors cause changes in
the surface layer of the cells leading to agglutination and formation of tissue-
like layers, but in Clavelina, as well as in sponges, these primary processes
are followed by the development of differentiated tissues and organs. There
is an additional point of similarity between amoebocytes of Limulus and the
amoebocytes of Clavelina ; for both of these types of cells sea-water or solu-
tions of inorganic constituents, as such, are toxic, and a salt solution which

TISSUE FORMATION 305

is balanced, as far as these cells are concerned, cannot be produced, since
they need a protective colloid in the form of protein, as has already been
stated in the case of Limulus. However, subsequent investigators (Brian,
Ries) attribute the tissue formation during the process of budding, not to
these amoeboid cells, but to special cells which resemble more closely lympho-
cytes and which have a tendency to divide mitotically. Ries assumes that the
packages of amoeboid cells which are seen, serve merely as foodstuffs during
the process of tissue formation ; but even if this view should be correct, still,
the amoeboid cells of Clavelina do produce tissue-like formations during or
preceding the process of budding and migrate towards the regions where
active tissue formation occurs, and in this respect they resemble in their
mode of reaction the amoebocytes of Limulus and the archaeocytes of
sponges under injurious conditions.

There is some indication that also in other instances the blastema from
which regenerative processes proceed, takes its origin from cells migrating
to a wound from distant parts of the organism. Observations of this kind
have been made by Balinsky and Hellmich, and we have referred to them in
a previous chapter. There is, however, some doubt at present as to whether
we have to deal in these processes with the migration of more or less un-
differentiated mesenchymatous cells possessing great developmental poten-
tialities, or with the migration of already more or less differentiated cells
giving rise to the new tissue. If the migration of undifferentiated wandering
cells should actually play so great a part in regenerative processes as is as-
sumed by Hellmich, it is quite probable that here, also, agglutination and
possibly coalescence of these cells precede tissue formation.

5. Tissue formation which takes place during embryonal life begins with
the segmentation of fertilized or parthenogenetically developing ova; but in
this case, underlying the union of the cells is a more complicated mechanism.
This depends, above all, on the presence of membranes surrounding the
ovum and the early embryo, and furthermore, on certain special structures
which connect the individual segments. However, the methods which are
successful in accomplishing the union of different ova or blastomeres, or in
separating normally united blastomeres from each other — both processes
being influenced by changes in alkalinity, in Ca content, and in the tempera-
ture of the surrounding medium — indicate that also in these cases we may
primarily have to deal with agglutination processes due to changes in the
consistency of the ectoplasm of ova or blastomeres. These primary changes
may then be secondarily followed either by coalescence or by fargoing cell
and tissue differentiations. It may be assumed, therefore, that also in the first
stages of the formation of multicellular embryos, agglutination processes,
not unlike those which occur between amoebocytes of Limulus, may play a
significant role.

With this conclusion harmonize also the experiments relating to the
agglutination and coalescence of ova and blastomeres in various classes of
animals, to which we have referred in a preceding chapter. The organismal
differentials or their precursors were found to be an essential factor in de-

306 THE BIOLOGICAL BASIS OF INDIVIDUALITY

termining whether such an agglutination will or will not take place and
whether the union will be temporary or permanent. Similar factors, and in
particular agglutination processes, may perhaps be concerned also in the
joining together of parts of more primitive adult organisms, such as Hyla,
Planaria, Lumbricus, and even in the transplantation of extremity buds in
Triton, or of extremities in the larvae of Salamander, although the processes
underlying these latter phenomena have not yet been analyzed from this point
of view.

6. Even in still higher organisms, as, for instance, in mammals, when a
wound is made in the epidermis, reactions follow, not unlike those observed
in experimental amoebocyte tissue, and in all probability the factors under-
lying both these phenomena are likewise similar. However in the more dif-
ferentiated tissues more complex structures, which connect neighboring
cells or tissues to one another, have developed, and these may vary in the
different tissues ; but even in the mammalian skin these complex structures
disappear during wound healing, at least temporarily, and then the primitive
reactions, which are common to so many organisms and which we have
analyzed in this chapter, have a chance to set in. In addition, we have reason
for assuming that in the tissues of higher animals there are at work finely
graded substances carrying individuality differentials and regulating the
interaction of tissues of the same type, as well as of different types adjoining
each other within the same organism. These autogenous morphogenic regu-
lators have already been discussed.

It may therefore be assumed that also tissue cells of higher organisms still
possess the fundamental properties of amoebocytes, at least potentially, and
that only secondarily other, more complicated structures and functions are
superimposed upon these primary characteristics and that especially in certain
artificial or pathological conditions, such as those leading to wound healing,
these primary modes of reaction come again into play. But there are found
even in higher organisms certain types of cells which, within the normal
organisms, remain isolated; among them are the erythrocytes, especially the
nucleated ones, the various types of leucocytes and the spindle cells, which as
far as their function is concerned, take the place of mammalian blood plate-
lets in other vertebrates. These, as well as the blood platelets, possess in
various degrees the characteristics of the amoebocytes. The tendency to
agglutinate is most markedly developed in the avian spindle cells of the
blood and in the mammalian blood platelets, but it is to a lesser degree also
found in the other types of cells. In all these elements, and particularly in
the spindles and blood platelets, the stickiness of the outer cell layer is lack-
ing under normal conditions within the blood channels. It is only under the
influence of abnormal stimulation that their protoplasm undergoes changes
which, in principle, are presumably similar to those we have analyzed in the
case of amoebocytes, and which lead to agglutination and thrombus forma-
tion, or to tissue or cell reactions of a so-called inflammatory kind. As to the
role which organismal differentials play in these latter processes, no definite
knowledge exists.

Chapter J

The Role of Organismal Differentials
in Fertilization

In preceding chapters we have considered the joining together of proto-
zoa, ova, blastomeres, amoebocytes, and more differentiated tissue cells,
in their relation to organismal differentials, and we found that in general
agglutination processes play a significant part under these various conditions.
A somewhat similar process takes place when two cells unite in the fertiliza-
tion of an ovum by a spermatozoon, although the interaction between these
two cells is of a more complicated nature.

It was O. Hertwig who first drew attention to the similarity which exists
between the process of fertilization and transplantation, fertilization being
considered as the transplantation of a spermatozoon into an ovum. He desig-
nated the relationship between these cells, upon which their mutual com-
patibility depends and which may vary in different combinations, as sexual
affinity, and distinguished it from the vegetative affinity which determines
the relationship between somatic transplants and hosts. Later, W. Schultz,
who, within a limited range, carried out investigations concerning the rela-
tionship between transplantability and genetic conditions, tested experimen-
tally the question as to whether a parallelism exists between transplantability
of parts of heterogenous individuals and the feasibility of hybridization be-
tween the same host and donor species.

However, although in certain respects transplantation and fertilization are
analogous processes, there are also some essential differences which had not
yet been clearly recognized by Hertwig. While in both processes the result
depends upon the relationship between two organisms or parts of organisms,
the kind of genetic relationship which is normal or optimal is not the same in
both cases. Whereas the relationship between spermatozoon and egg is usually
homoiogenous, and this is the one best suited for a successful fertilization,
such is not the case in transplantation of adult tissues in higher organisms.
Here a homoiogenous relationship between the organismal differentials of
host and graft leads, as a rule, to severe reactions and to injury of the trans-
plant. Furthermore, in transplantation of differentiated tissues in higher
adult hosts we have to deal with the interaction of two fully developed
organismal differentials, whereas in fertilization we have to deal, in the main,
with the transplantation of nuclear material, and especially of the chromo-
somes of the spermatozoon, into a cell which likewise does not yet possess a
fully developed organismal differential, nor the mechanism by means of
which differentiated organisms react against strange organismal differentials.
Ovum and spermatozoon each carry a substance or substances which later in
the course of embryonal development will give origin to a fully formed

307

308 THE BIOLOGICAL BASIS OF INDIVIDUALITY

organismal differential, identical in various organs and tissues of the same
individual and species.

In many instances where, in plants and animals, both male and female
germ cells are produced in the same organism, mechanisms of a special kind
have developed, tending to prevent auto fertilization, which otherwise would
have been the simplest mode of fertilization but which might have injurious
consequences. Even syngenesio-fertilization occurring in succession through
many generations leads in many cases to a gradual deterioration of the
organism.

On the other hand, if heterofertilization takes place, incompatibilities also
develop, as a rule, sooner or later, even if spermatozoon and egg belong to
relatively nearly related species; but these incompatibilities may in certain
respects be less marked than those in heterotransplantation and the spermato-
zoon may even, under such conditions, remain alive and apparently unharmed
in the strange ovum, whereas, after transplantation of differentiated tissues
between the corresponding two species in mammals the host reacts very
strongly against the transplant, which is severely injured and, as a rule,
destroyed within a relatively short time. Thus in Echinoderms, by means of
fertilization between different orders it is possible to produce hybrid plutei,
which in certain of their characteristics are intermediate between the two
parent orders. In some instances, a slight increase in the constitutional differ-
ences between spermatozoon and egg above those characteristic of the average
homoiogenous relationship between the organisms which carry the sex cells,
may even have a stimulating effect on the developmental processes resulting
from fertilization and may thus prove favorable at least in the first generation.
But in the case of transplantation the incompatibilities between transplant
and host, and the resulting injury of the transplant, increase rapidly with
increasing strangeness of the organismal differentials.

However, notwithstanding these differences between fertilization and
transplantation, there is one very essential similarity; after heterogenous
fertilization as well as after heterogenous transplantation incompatibilities
do, as a rule, develop, which to a certain extent are the greater, the greater
the differences in the constitution of the organismal differentials or of their
precursors in the cells or tissues which are joined together. A markedly heterog-
enous character of the precursor substances of the organismal differentials
in egg and spermatozoon is associated with an abnormal interaction, causing
an interference with the development of the resulting hybrid; but with less
incompatible precursors of organismal differentials the development may
continue long enough for a specific organismal differential to form in the
hybrid, which thus acquires its own mechanism of reaction against strange
organismal differentials.

As to incompatibilities developing between spermatozoa and ova, which
are sufficiently distant genetically from each other, these, in general, may be
caused by two factors: (a) an incompatibility between the spermatozoon
and the surface layer of the strange ovum; (b) incompatibilities between the
nuclei of these two cells, and in particular between their chromosomes, or

DIFFERENTIALS IN FERTILIZATION 309

between the sperm nucleus and the cytoplasm of the ovum. The second type
of abnormal interaction represents, on the whole, much the finer test for the
mutual fitness of the interacting cells. Thus the spermatozoon may readily
enter the ovum when the distance of the two partners in the spectrum of
relationship is not too great, but subsequently, incompatibilities between the
cells, and especially between their nuclear constituents, may manifest them-
selves, or the spermatozoon may be entirely inactivated or eliminated from
the ovum, so that a parthenogenetic development of the stimulated egg takes
place.

But there exists within certain limits, in addition, a proportionality between
the difficulty which the spermatozoon experiences in entering the egg and
the distance in relationship between these two cells. If the distance is very
great, for example, when ovum and spermatozoon belong to different classes,
it is necessary to make the surface of the egg more sticky by treating it with
alkali, according to the method of Jacques Loeb, or by allowing the egg to
become stale in order to effect the entrance of the spermatozoon into the
ovum. In certain echinoderms, making a dense suspension of eggs, without
first washing them in sea water, seems to improve the results in heterofertili-
zation (E. Browne Harvey). It is, then, only after this difficulty has been
successfully overcome that the more serious antagonism between the con-
stituents of the male and female germ cells becomes manifest. If the distance
in relationship between egg and spermatozoon is very great, the paternal
chromatin is prevented from orderly interaction with the egg chromatin;
instead, it is pushed aside into the cytoplasm of the ovum. This reaction may
take place almost at once, or it may occur later, during the process of seg-
mentation. The subsequent development is, under these conditions, partheno-
genetic. However, even such a development is not normal; it appears as
though the mere presence of the strange chromatin in the ovum exerts an
injurious effect on the latter. Either the development of the embryo may be
merely retarded, or certain abnormalities in differentiation may occur and
the resulting organism may therefore be less viable than a normal one. Fur-
thermore, such organisms, if they should reach the larval stage, do not usually
undergo normal metamorphosis.

From conditions of marked incompatibility between egg and spermatozoon,
we find all degrees of transition, to an almost complete harmony between
these cells. If in an intermediate stage there is a mild degree of disharmony,
only a part of the paternal chromosomes may be eliminated and in the re-
sulting embryo the maternal characteristics may predominate over the pa-
ternal. As Baltzer and Tennent have shown, elimination of chromosomes
may occur at different stages of development: as early as during the first
segmentation or later in the blastula stage. According to Tennent, not only
paternal but also maternal chromosomes may be eliminated. On the other
hand, if sperm and egg are so far removed from each other as to belong to
different classes, the paternal chromatin may in some cases be cast out even
before the first segmentation. All kinds of irregularities or monstrosities can
be observed under these conditions, and in general they are the more severe,

310 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the less compatible the interacting germ cells. As an example of a slight de-
gree of disharmony, we may cite the observation of Doncaster and Gray in
crosses between different species in echinidae, who found, as the only ab-
normality, a vesicle formation on the part of a few chromosomes.

Disharmonies between the chromatin of egg and spermatozoon can also be
produced experimentally. Thus as a result of injury to the chromatin of
spermatozoon or ovum, caused by the exposure of these cells to radiations or
to certain dyes preceding fertilization, the result of homoiofertilization can
be made to resemble that of heterofertilization. Incompatibilities develop
here between the precursors of the organismal differentials of the two germ
cells, or between the carriers of these precursors. These incompatibilities may
be so severe that the injured nucleus no longer participates in the develop-
ment and parthenogenesis results, similar to that found in hybridization be-
tween different classes. However, in case the injury of the chromatin has
been less pronounced, the radiated nuclear substance may cause merely ab-
normalities in embryonal development.

There exist certain critical periods in embryonal life when difficulties in
the formation of some tissues and organs are especially prone to arise, as
for instance, during the process of gastrulation ; in addition, it is conceivable
that a summation of injurious effects takes place gradually as development
proceeds. Furthermore, the incompatibility may affect either growth and
differentiation or viability, or both jointly, and there may be a parallelism
between the retardation in growth and in the abnormalities in differentiation
of the embryo as a whole, or of its individual organs, resulting from heterog-
enous fertilization.

The following list of the results of heterofertilization in echinoids, which
Tennent gives, may show the gradation of injurious effects in a certain order
of animals.

1. Elimination of no chromosomes and dominance of one species with
inactivation of incompatible chromosomes :

Toxopneustes 9 X Hipponoe $ (different genera)
Echinus 9 X Antedon $ (different families?)
Strongylocentrotus 9 X Antedon $ (different families?)

2. Elimination of part of chromosomes and dominance of one species over
the other:

Hipponoe 9 X Toxopneustes $ medium incompatibility (different

genera)

Echinus 9 X Sphaerechinus $ (different families)

Strongylocentrotus 9 X Sphaerechinus $ (different genera)

3. Elimination of no chromosomes and intermediate plutei :
Sphaerechinus 9 X Strongylocentrotus $ (different genera)
Sphaerechinus 9 X Arbacia $ : most compatible (different suborders)

4. Elimination of part of chromosomes and intermediate plutei :
Toxopneustes 9 X Hipponoe $ (different genera)
Arbacia 9 X Echinus $ (different suborders)

DIFFERENTIALS IN FERTILIZATION 311

5. There may be elimination of part of both maternal and paternal chromo-
somes and inhibition of development. Unfavorable.
Arbacia 9 X Toxopneustes $ (different suborders)
Toxopneustes 9 X Arbacia S : fairly compatible (different suborders)

There is, here, at least an indication of a parallelism, although not a com-
plete one, between relationship and the results of heterofertilization. The
best results were obtained in the case of hybridization of suborders. In these
experiments we notice differences between the reactions in reciprocal hetero-
fertilizations. Differences in reciprocal hybridizations were noted also in
fertilization between different orders of echinoderms ( Echinocyanus and
Parechinus), when plutei, in some way intermediate between both parents,
could be obtained if certain combinations were used. Similar differences we
have observed also in the case of transplantation; even in this respect there
is thus a correspondence between transplantation and hybridization.

Of special interest are the hybridizations between Drosophila melanogaster
and Drosophila simulans, because in these insects the genetic constitution of
the two parent species has been analyzed very carefully, primarily by genetic
methods, and more recently by a cytological study of the chromosomes.
Sturtevant found that in both these species, the second and X chromosomes
contain the same genes and that the latter are arranged in the same order, but
D. simulans has a long inversion in the right limb of chromosome 3, as com-
pared to melanogaster. Certain variations between these two species pertain
to the different distances between the genes in the corresponding chromosome,
also to the different lengths of the Y chromosomes and to the relative amounts
of heterochromatin in the X chromosomes.

Examination of somatic cells in the hybrids between Drosophila melano-
gaster and Drosophila simulans suggests the possibility that differences in
certain genes prevent, here, the normal union of homoiogenous chromo-
somes. Even such slight differences in gene composition as exist between
these two species and the resulting incomplete union of chromosomes, lead
to sterility in the hybrid. Other species of Drosophila cannot be hybridized,
presumably because of the greater differences in gene constitution. If, how-
ever, crosses are made between still more nearly related organisms, as for
instance in the experiments of Lancefield, who hybridized two races of
Drosophila pseudoobscura, abnormalities of a lesser degree may arise, espe-
cially during the process of crossing over, but sterility results if in certain
chromosomal loci the alleles are derived from the two races.

In the hybridization between species as nearly related as horse and donkey,
incompatibilities occur during meiosis in the male sex cells of the hybrid, and
in the primary spermatocytes of the Ft generation abnormal mitoses appear.
A lack of coordination in the action of chromosomes derived from these dif-
ferent species leads to disturbances. Under certain conditions even lympho-
cytes may be attracted by the abnormal substances which are presumably
present at later stages of the development of tissues in such hybrids.

Differences in the results of reciprocal fertilization are very evident in the

312 THE BIOLOGICAL BASIS OF INDIVIDUALITY

experiments of Montalenti, who crossed Bufo viridis and Bufo vulgaris. In
this case the combination Bufo viridis ? X Bufo vulgaris $ was much more
unfavorable than the reciprocal combination, Bufo vulgaris 9 X Bufo
viridis $ . In the former type of hybrids retardation in development and
abnormal morphogenesis may affect early cleavages and gastrulations ; sub-
sequently, malformations appear, especially in the development of the ner-
vous system and of the heart. In the reciprocal crosses, alterations in early
stages of development, resulting in the death of the embryos, are very rare.
The large majority of these embryos develop like the controls, although at
first there may be some delay in development. The tadpoles seem to be about
normal, but later on, during metamorphosis, there is a considerable mortality.

This difference in the results of reciprocal hybridization, as in those of
transplantation, may be attributed to the dissimilar role which host and donor
play in these processes ; in hybridization it is the ovum which acts as host to
the spermatozoon which it receives into its body. The dissimilarities in the
significance of egg and spermatozoon may be taken to indicate that it is not
only the chromosomes of these two cells which interact with each other, but
that the chromosomes of the male germ cells interact also with the cytoplasm
of the egg.

In accordance with the more complex and delicate chemical differentiation
of cells and tissues, which progressively takes place during the development
of the embryo, the interaction of the chromosomes derived from the two
parents evidently becomes, correspondingly, a process of increasing delicacy,
and finer differences in the relationship between sperm and ovum may there-
fore, as a general rule, manifest themselves only during the later develop-
mental periods, while coarser differences may result in abnormalities at
much earlier embryonal stages.

It appears that in some of these incompatibilities processes of a purely
mechanical character may be involved, as, for instance, maladjustment in the
size and shape of male and female chromosomes, or in the movements of the
asters and chromosomes, and, somewhat later, disturbances in the rhythms
of mitotic divisions and in the developmental rhythms characteristic of the
paternal and maternal species in general may interfere. However, there is
reason for believing that in hybridization interactions of a chemical nature
between substances derived from the male and female germ cells may also be of
importance; and in this respect, again, the mechanisms active in transplanta-
tion and in fertilization would then resemble each other. These chemical
interactions may be of a toxic nature, if the two individuals from which the
germ cells are derived do not belong to the same species ; toxic effects of this
kind have been suggested by Jacques Loeb and Moenkhaus. But it seems that
in some cases, in which the distance in relationship between the male and
female cells is very slight, the offspring may not only not be defective, but
embryonal development may, on the contrary, be accelerated ; observations
of this kind we shall discuss in the next chapter. Also in the hybrids, Bufo
vulgaris 9 X Bufo viridis $ , to which we have referred above, it was found
by Montalenti that there were some tadpoles, a few weeks old, which ac-

DIFFERENTIALS IN FERTILIZATION 313

quired a larger size, underwent metamorphosis earlier and exhibited lower
mortality than the controls. In such instances of heterofertilization conditions
apparently exist comparable to those characteristic of homoiogenous fertili-
zation ; but, in addition, certain differences between the germ cells may exert
a stimulating effect which is favorable instead of being injurious.

While, then, within certain limits there is presumably a proportionality
between the incompatibilities which develop in hybridization and the distance
in relationship between egg and spermatozoon, exceptions to this rule do
occur and may be very striking. They are most likely due to the presence of
secondary factors superimposed upon the primary ones, which latter would
act in accordance with the greater nearness or distance of relationship be-
tween spermatozoon and egg. Thus the degree of resistance to injurious con-
ditions on the part of these cells belonging to two different species may vary
in different cases, irrespective of phylogenetic factors.

There is another fact indicating the lack of complete correlation which
may be present, in certain respects, between readily effected hybridizations in
different species and the phylogenetic relationship between egg and spermato-
zoon. It seems that in certain cases heterogenous fertilization may succeed
as well in teleosts as in echinoderms, although the latter stand much lower
in the phylogenetic scale than the former. Conditions are different in trans-
plantations ; here we find, as a general rule, that transplantability becomes
more and more restricted with increasing phylogenetic development. In
plants, on the other hand, transplantations seem to succeed over a wider
range of phylogenetic relationships than hybridizations.

It may then be concluded that while there exist distinct similarities be-
tween transplantation and fertilization, there are also notable differences. To
recapitulate some essential facts : In both these processes we have to deal with
what may be considered a host-donor relation, the ovum representing the
host and the spermatozoon the donor cell in the case of fertilization. In both
processes the host has a function which differs from that of the donor and in
both the reactions of the host preponderate ; however, on the whole the con-
stitution and function of the spermatozoon are of a relatively greater sig-
nificance for the fate of the host, in the case of fertilization, than is the piece
of grafted tissue or organ for the recipient organism in the case of trans-
plantation. While in transplantation in adult mammals it is the character of
the organismal differentials in host and donor which is the most important
factor determining the fate of the transplant, in the interaction between
ovum and spermatozoon we have to deal with the precursors of organismal
differentials ; while in transplantation it is the autogenous relationship between
the organismal differentials which is most favorable for a satisfactory inter-
action between transplant and host, in fertilization it is the homoiogenous
relationship which may be considered normal and, as a rule, conducive to the
best results. But, if we compare fertilization with transplantation between
embryonal organisms, the difference between these two processes is less
pronounced, inasmuch as also in embryonal grafting we have to deal with
precursors of organismal differentials and not with fully developed organ-

314 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ismal differentials. However, in these embryonal transplantations it is again
the autogenous relationship between host and graft which, on the whole,
results most readily in a harmonious combination, although in many cases
no distinct difference between an autogenous and a homoiogenous relation-
ship can be noticed. In certain respects the analogy between fertilization and
transplantation between single cells, or parts of single cells, such as the graft-
ing of pseudopods in protozoa, would seem to be greater than that between
fertilization and transplantation of tissues in higher organisms, but again,
comparisons show a very striking difference, insofar as here, also, only an
autogenous relationship between cells or parts of cells leads to a satisfactory
union, while, as stated, the homoiogenous relationship is, as a rule, the
normal one in fertilization.

In addition to other similarities between transplantation and fertilization
there is the observation that a reciprocal relationship between the individuals
or species serving as host and transplant, and between male and female
gametes, may lead to very different results ; the latter are due to the differ-
ences which exist in these processes between the function of the host and the
ovum, on the one hand, and the donor tissue and spermatozoon, on the other
hand. In both these processes the phylogenetic relationship between the
interacting cells or tissues is a factor which helps to determine the outcome,
but the parallelism between such a relationship and the results is, on the
whole, much less evident in fertilization than in transplantation.

Moreover, the reactions between the sex cells depend on very special
mechanisms which regulate the interaction between spermatozoon and egg,
and which are lacking in other primitive cells. Such mechanisms consist in
the specific functioning of the chromosomes of male and female sex cells, in
the relation of chromosomes to each other and to the cytoplasm of the ovum
and in the interaction of certain genes. As a rule, these interactions are
optimal in case of homoiofertilization and there may even exist in certain
instances means for preventing autofertilization. However, as in transplan-
tation, so also in fertilization, heterogenous relationships between the chromo-
somes of two parent strains lead to incompatibilities, which are greater if
distant species, than if nearly related species, or different races of the same
species, are combined.

Chapter £

Self Fertilization and Autogenous
Transplantation

In the preceding chapter we have compared the effects of heterogenous
and homoiogenous fertilization and transplantation. We shall now con-
sider the significance of self-fertilization, which, if continued through
successive generations, may lead in the end to a very great similarity or to iden-
tity in the genetic composition of spermatozoa and ova ; we shall also con-
sider the influence of close inbreeding, a process which may have a similar
effect as far as the genetic composition of egg and spermatozoa are con-
cerned. In order to indicate the analogy between these two processes and the
corresponding types of transplantation, self fertilization may be designated
as autogenous fertilization, because in this case the two germ cells have de-
veloped in the same individual, and fertilization between nearly related indi-
viduals may be designated as syngenesiofertilization. Close inbreeding im-
plies serial syngenesious fertilization, and through such brother-and-sister
matings a relationship may be attained between members of the inbred group,
which, while still in the syngenesious region of the spectrum of relationships,
may at last approach an autogenous condition.

As we have seen, genetic factors largely determine the character of the
precursors of the organismal differentials in the embryo, as well as of the
fully developed organismal differentials, which latter control the interaction
between adult tissues; genetic factors play a part also in the interaction be-
tween egg and spermatozoon. In addition to these two kinds of interaction
there exists a third type, which, while not identical with these, possesses
some of the characteristics of both. This third type is represented in the
fertilization process in some higher plants. Here we have to deal neither
with the direct interaction of spermatozoon and egg, nor with that of two
different tissues, but with the interaction of a structure associated with or
containing the male germ cell, the pollen, with a specialized tissue which
surrounds the egg, and ultimately, with the egg itself. During this process,
mechanisms may be active which prevent self-fertilization, when both ovum
and spermatozoon originate in the same individual. In plants, incompatibility
between pollen-tube and tissues which surround the female sex cell may like-
wise prevent a successful fertilization if ovum and pollen belong to differ-
ent species or to different varieties. However, in the case of heterofertiliza-
tion the pollen-tube may, in some instances actually reach the eggule, but even
then a successful fertilization may be prevented, owing to incompatibilities
between nuclear or cytoplasmic constituents of the germ cells. We must then
consider the spectrum of compatibilities and incompatibilities under the fol-
lowing three conditions, (1) in the interaction of tissues after transplantation,

315

316 THE BIOLOGICAL BASIS OF INDIVIDUALITY

(2) in the interaction of germ cells with each other, and (3) in the interactions
of germ cells and of structures associated with the germ cells.

I. In higher plants, Jost (1907) assumed that the retardation in the growth
of the pollen-tube into the style, which is observed in certain cases of self-
fertilization, was controlled by substances given off by the tissues along which
the pollen-tube grew on its way towards the ovary, and which he assumed to
be specific for each individual. But, according to Jost, it was not necessarily
differences in the chemical constitution of these substances, but differences
in the concentration of the latter, which distinguished the different individuals
and might suffice to explain their specific effects.

Subsequently, Correns (1912) interpreted the observed facts in accordance
with the concepts of Mendelian heredity, and in particular, with the concepts
of the pure lines of Johannsen. He investigated self-sterility in Cardamine
pratensis and concluded that the inhibiting substances, which in this case
do not permit the pollen-tube to penetrate into the style and which thus pre-
vent auto fertilization, are not characteristic of the individuals as such. Ac-
cording to this investigator, it would not be correct to assume that a certain
substance is unique and occurs only in one particular individual and that
it is lost when this individual dies, but he believes that there are substances
characteristic of certain pure lines, which are dependent upon the inherited
genetic constitution of these lines. However, the individuals in Cardamine
do not represent members of pure lines, because each individual is the result
of preceding fertilizations in which members of different lines entered. A
special combination of substances rather than one particular substance is
therefore characteristic of each individual. But according to the law of chance,
it is possible even for different nonrelated individuals to possess the same
combination of substances. These conclusions of Correns are based on the
analysis of the behavior of individuals belonging to the Fx generation, which
develops after fertilization between two homoiogenous individuals of
Cardamine pratensis. He carried out back-cross fertilizations between the
F1 hybrids and each of the two parents and thus he could establish the ex-
istence of four classes of individuals according to the character of the sub-
stances retarding the growth of the pollen-tube, which each one of these
individuals possessed. When the father had the factors Bb and the mother
the factors Gg, these multiple allelomorphs were transmitted to the offspring
according to the rules of Mendelian inheritance. Whenever either B or G,
or both together, are present in the pollen and in the female tissues, the pollen-
tube is inhibited in its downgrowth. Accordingly, there is only one of the four
classes of F1 hybrids which is fertile with both parents, and it has the factors
Bg-

The genetic constitution which causes self-sterility has been subsequently
analyzed by East in Nicotiana. East assumes that within the same organism,
in the male as well as in the female apparatus, which latter corresponds
genetically to the sporophyte and represents therefore diploid somatic tissue,
two characteristic substances, Sa and S2, exist. In the female the stigma and
style retain both these substances, because their segregation is effected only

SELF FERTILIZATION 317

at the time of the reduction division ; but in the male the pollen-tube corresponds
not to a diploid somatic tissue, but to a gamete in which there has occurred a
reduction division, causing a segregation, and some pollen-tubes possess,
therefore, S1? while others possess S2. In other plants S3 and S4, or Sx and
S3, may substitute for Sx and S2. Now, fertilization is possible if the substance
which characterizes the pollen-tube is not present in the female style, other-
wise an inhibition in the downgrowth of the pollen-tube takes place and
fertilization is prevented ; in other words, fertilization cannot follow if the
stimulating effect on the pollen-tube, which is due to a difference in the sub-
stances characterizing pollen-tube and style, is lacking.

The fertilization experiments which East carried out yielded results which
were in agreement with his assumption. There are involved in this case,
conditions in which the response of certain tissues to each other depends upon
the presence of the same, or of two different substances, in the interacting
cells and tissues ; when these substances are identical the outcome of the re-
action is unfavorable.

If a very large number of various kinds of homoiogenous fertilization ex-
periments are carried out, many different factors can be made to interact with
each other and a variety of combinations occurs. It is thus found that if two
individuals which differ in a factor are crossed, the F1 hybrids are fertile with
each of the parents. As far as the behavior of the Fx hybrids towards one
another is concerned, they can be placed in four groups, the members of each
group being sterile with the other individuals of the same group, and fertile
with all members of the other groups.

However, in some species of Nicotiana self-fertilization leads to fertile
progeny; this is so in Nicotiana Langsdorfh. Here, possession of the same
factors by style and pollen-tube does not interfere with the rapidity of down-
growth, while in Nicotiana alata it leads to sterility.

As to the mechanisms underlying self -sterility, in Medicago sativa, after
self-pollination, not only does the pollen-tube grow into the ovary more slowly,
but also the number of eggs which are fertilized is smaller; in a number of
instances the pollen-tube does not enter the micropyle of the ovulum, and if
fertilization should take place, abortion occurs rather frequently. More recent
investigations indicate that in certain instances, as presumably also in some
other plants, self-sterility is genetically determined and depends upon the
presence in pollen and ovule of two recessive genes, which must be present
in double dose in order to insure self-sterility. These genetic factors determine
the mechanism which causes a very slow rate of downgrowth of the pollen-
tube into the style; in the latter, it may also induce the formation of a separat-
ing wall, preventing the further movement of the pollen-tube towards the
ovule. According to Yasuda, an ovarian secretion diffuses into the style and
has this inhibiting effect on the pollen-tube ; in addition, this substance may
inhibit the germination of the pollen. The ovarian product may also exert
an inhibition on otherwise non-self -sterile pollen. According to Eysh, spray-
ing of the flowers of self-sterile plants with alpha naphthalene acetamide di-
rectly before or after self-pollination neutralizes this ovarian secretion and

318 THE BIOLOGICAL BASIS OF INDIVIDUALITY

thus makes self-fertilization possible. There are also other methods which
have such an effect ; the most interesting one of these is, perhaps, the induction
of polyploidy by means of colchicine treatment of some branches in Petunia
axillaris (Stout and Chandler). Self-compatibility was procured for all seed-
lings obtained from the self- fertilized flowers of tetraploid branches. More-
over, these seedlings could be cross-fertilized ; likewise, backcrosses to parents
were fertile, except the combination of a tetraploid female seedling and a
diploid male parent. The genetic balance is presumably changed in these
tetraploid plants in such a way that the mechanism controlling the movement
of the pollen-tube towards the ovule is no longer inhibited. How many genes
are involved in this process in polyploid organs is not known.

If we compare conditions in transplantation of mammalian tissues with
those in pollination experiments, we find certain analogies. The results in
both processes depend upon whether certain substances are the same or are
different in the two interacting cells or cell complexes. This determines the
relations between host and transplant, as well as those between spermatozoon
and female sex apparatus. In both cases the reactions are more intense in
a homoiogenous than in an autogenous or syngenesious relationship, but
homoiogenous reactions injure a transplant, whereas they are as a rule bene-
ficial in pollination. Furthermore, in transplantation we noticed in certain
instances marked differences in the types of reaction resulting from a reversal
of the relationship between transplant and host, and in a similar way, dif-
ferences were observed in certain plants in the case of reciprocal fertilization.
There is another observation which is of special interest because it corresponds
to certain findings in transplantation. If the same plant is pollinated by two
different types of pollen, each one behaves in its own way, uninfluenced by
the presence of the other. In a similar way we have found that in case of simul-
taneous transplantation of pieces of tissues from two different donors into
the same host, the specific reactions, as determined by the mutual relation-
ships between the individuality differentials of the various transplants and
the host, take place around each transplant in their characteristic manner,
without any influence of the other transplant being noticeable.

However, there are also important differences between transplantation and
pollination. While in transplantation an autogenous condition is the most
favorable one for a satisfactory union between host and graft, in fertilization
identity of the specific substances which come into play is in many cases
unfavorable for the production of a fertilized ovum. There is an additional
difference in that in the former all degrees of gradations in the results occur,
whereas, in fertilization we find either compatibility or non-compatibility, the
latter leading to sterility; no inter-grades exist as far as the end result con-
sisting in the fertilization of a single ovum by a spermatozoon is concerned.
In the pollination process, itself, it is nevertheless possible to recognize certain
gradations in the degree of compatibility between the male and female cells,
as is indicated by the varying rapidity of the downgrowth of the pollen-tube,
and in some cases, by the number of eggs which are fertilized and of embryos
which develop in a normal manner.

SELF FERTILIZATION 319

As to the causes of these differences between transplantation and fertiliza-
tion, we may consider the following facts : Correns as well as East, in their
analysis of self-sterility, compared the results of various combinations, some
of which correspond to a syngenesious, others to a homoiogenous relation-
ship. They observed the behavior of sperm and tgg, or of pollen-tube and
style, toward each other in individuals closely related, as well as in those not
closely related though belonging to the same species. In the case of fertiliza-
tion, the individuals belonging to the same family could be arranged in a few
groups in such a way that all the members of the same group behaved in an
identical manner, whereas in the case of transplantation various gradations
could be found in syngenesious reactions, ranging from those seen in autog-
enous, to those seen in homoiogenous transplantations.

There remains still to be considered a third difference between transplanta-
tion and fertilization. While after autotransplantation antagonistic reactions
between host and transplant in higher organisms are lacking, in syngenesio-
transplantation they occur sooner or later if sensitive tissues are used. On
the other hand, in some experiments in plants fertilization between members
of the same group (syngenesious fertilization) and self-fertilization were
equally unsuccessful, while fertilization between individuals belonging to
different groups did succeed. However, a condition corresponding to what
we find in auto- and syngenesiotransplantation in mammalian tissues, has
been observed by Correns also in the case of fertilization in a plant, namely,
in Tolemiea Menziesii. Here, individuals of the Fx generation can be readily
fertilized by one another, as well as with both parents, whereas self-
fertilization is impossible. This may be considered as another type of self-
sterility and it corresponds to what we find in transplantation if we choose,
for instance, the thyroid gland as a test object, and the presence or absence of
a reaction as the standard for measurement. In transplantation as well as in
the case of fertilization in Tolemiea, it appears that a greater number of factors
is required than in the other instances of pollination, mentioned above, in order
to explain the results in accordance with the rules of Mendelian heredity.

In hetero-pollination, including pollination between different varieties as
well as between different species, there may develop disharmonies of various
kinds, which may be similar to those observed in attempted self-fertilization.
Thus, lack of germination of the pollen-grain and inhibition in the down-
growth of the pollen-tube into the style may be noted in both cases; like-
wise, in hetero-pollination there may be in addition an interference with
those mechanisms which direct the movement of the pollen-tube through the
micropyle toward the ovulum. It seems, therefore, that the specific chemo-
tropically active substances, which function under these conditions, are not
interacting in a normal manner with the pollen-tube. The relationship between
substances of this kind and the pollen-tube is evidently a specific one, which
is graded in accordance with the genetic relationship between the interacting
organisms, and these substances behave, therefore, in this respect, in a manner
similar to the organismal differentials of the tissues in higher organisms.

But if hetero-fertilization should actually take place, leading to the produc-

320 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tion of hybrids, the germ cells in the latter may have abnormal numbers of
chromosomes. Besides, abnormalities in the reduction division and, further-
more, a non-disjunction of chromosomes may be observed. Still later, in-
compatibilities may become manifest between the nuclei of the male and
female germ cells if fertilization between hybrids should be attempted. Con-
ditions are, then, in these respects, analogous in plants and in animals; in
both, a homoiogenous relationship between the substances produced in cells
belonging to the male or female organism, as well as between the cytoplasm
and the nuclei of the gametes, is most conducive to the normal development
of a new organism.

II. While in higher plants the prevention of self-fertilization occurs in
many species, in hermaphroditic animals it has been observed so far only in
several ascidians, and especially in Ciona. In other animals, for instance,
the oligochaetae, self-fertilization may occur and lead to the normal de-
velopment of the ovum, and even self-copulation may take place in certain
species.

The fact of self-sterility in Ciona was first observed by Castle, and its
mechanism has been studied especially by T. H. Morgan. According to Mor-
gan self -sterility in this species depends on a condition in the egg membranes,
which prevents the entrance of spermatozoa derived from the same individual,
whereas spermatozoa from individuals which were not the bearers of the
eggs were able to penetrate through the membranes. A short treatment of the
egg membrane with acid makes the latter permeable also for the spermato-
zoa from the same individual; likewise, the use of dense sperm suspensions
renders the chances of self-fertilization better. However, it has not been
possible to extract substances from the eggs or sperm which noticeably in-
fluenced the results of self- or cross-fertilization. In different ascidian species,
the readiness with which self-fertilization succeeds varies; it is greatest in
Molgula, intermediate in Styela, and very rare in Ciona. It is the sameness
in the genetic constitution of the spermatozoon and the ovum which tends
to prevent fertilization and a difference in this constitution which makes
possible self-fertilization. Morgan suggests that self-fertilization may be-
come possible as a result of a mutation, which alters the genetic constitution
of a spermatozoon and makes it unlike that of the egg. It is not known how
many genetic factors are involved in this process of self-sterility.

It seems then that the mechanism which prevents self-fertilization in
Nicotiana, Petunia and some other plants, and in ascidians, is not the same,
inasmuch as in the latter it depends on the relations between spermatozoon
and egg membrane, whereas, in the former, it depends largely on the inter-
action between ovary and pollen-tube; but also in plants, self-fertilization
may be inhibited in certain instances by incompatibility between the fertilizing
element in the pollen-tube and the ovum, as well as by the usual mechanisms.
The processes which prevent self-fertilization in these plants and in ascidians
agree, in so far as in both, genetic factors determine primarily whether or
not self-fertilization can take place; but the effects exerted by these genetic
factors differ. As to the number of genetic factors involved in these processes,

SELF FERTILIZATION 321

in plants it is assumed that this is very small, but there is the possibility
that, actually, also a larger number may control this mechanism. In ascidians,
it is at least possible that the number of determining genes may be consider-
able and that in this respect the latter resemble the factors which determine
the individuality differentials in the somatic cells of higher organisms.

In conclusion it may then be stated that while in transplantation of tissues
in higher adult organisms incompatibilities in the interaction of host and
transplant are avoided only when autogenous relations exist, in fertilization,
in general, a homoiogenous relationship produces the most adequate results
and the subsequent perfect development of the embryo, although in various
plants and animals autogenous fertilization occurs normally, without injurious
consequences. As to heterogenous fertilization, this leads, as a rule, to in-
jurious results in plants as well as in animals, but in different instances the
distance in relationship between spermatozoon and egg, which results in
abnormalities, varies. Thus in the case of Zea Mays, Demerec observed that
in the variety "everta", homoiogenous as well as autogenous fertilization
was successful, but that fertilization with other varieties of Mays did not
succeed. Usually we must assume that species differences between male and
female plants produce an injurious effect greater than that characteristic of
variety differences. On the other hand', certain heterogenous fertilizations in
Echinoderms may lead to the formation of normal organisms as far as somatic
differentiation is concerned, although the parents belong to different genera or
even to different orders.

In general, homoio- fertilization is the normal process most conducive in
plants and animals to an undisturbed development of the embryo and the
chromosomes and cytoplasm of the germ cells are not adversely affected by
such a relationship. We find, then, in the interaction between spermatozoon
or pollen-tube and egg or ovary, reactions which presuppose the presence
of individual and species substances or of mechanisms which are characterized
by a great sensitiveness to these individual and species differences. The
individuality differentials of higher adult animal organisms are not yet de-
veloped in these less developed cells and tissues, but there is reason for assum-
ing that the latter possess the precursors of organismal differentials. It is pos-
sible that such precursor substances are involved in the individual reactions
noted in these cells and tissues, at least in some instances ; on the other hand, it
is also possible that substances of a special kind are concerned in these re-
actions. Such substances and mechanisms of a special kind are present in
certain protozoa, and the terms "organismal and individuality differentials"
apply to these cases only in a wider sense. In a specific sense, they refer only
to the adult tissues of higher vertebrates.

Inbreeding: There is a condition intermediate between self-fertilization and
homoiogenous fertilization, namely, syngenesio-fertilization. This is a process
which corresponds to inbreeding. In higher organisms, close inbreeding is
effected by means of successive, long-continued brother and sister mating.
As a result of this procedure the genetic constitution of such inbred individ-
uals becomes gradually more and more similar, until in the end, syngenesio-

322 THE BIOLOGICAL BASIS OF INDIVIDUALITY

fertilization may approach auto-fertilization. Thus a homozygous constitution
may be nearly attained in both the germ cells as well as in the somatic cells
of the adult forms, in constrast to the heterozygous condition which char-
acterizes, as a general rule, individuals belonging to the same species but to
different families or lines, which are not closely related to one another in their
genetic constitution and whose germ cells unite in the process of homoio-
fertilization. As the outcome of continued inbreeding, individual differences
are more and more lost.

As stated, the individuals of higher species of animals are, usually, in
accordance with accepted terminology, heterozygous as far as their genetic
constitution is concerned. However, in order to indicate the relationship which
exists between the different types of fertilization, on the one hand, and of
transplantation and organismal differentials, on the other, it might be ad-
vantageous to designate as homoiozygosis the normal condition resulting
from homoio-fertilization, which, as we have seen, corresponds to a homoio-
transplantation. As a consequence of close inbreeding the normal homoio-
zygosis passes, then, into a state which might be designated as syngenesio-
zygosis, until at last a condition is approached corresponding to autozygosis,
but generally designated as homozygosis. By adopting the term "autozygosis",
we would express the genetic relationship to one another of the gene sets
which have been brought together in the fertilized ovum and in the individual
developing therefrom, in cases in which self-fertilization is the normal
process, or a genetic relationship which may be approached in cases in which
long-continued close inbreeding through many generations has preceded the
mating of the germ cells. Heterozygosis, in the sense in which this term is
used by geneticists, would then correspond to homoiozygosis, and the homo-
zygous condition of the geneticist would correspond to autozygosis, in the
sense in which the corresponding terms would be applied in transplantation.
In the genetic analysis of the effects of inbreeding and of transplantation,
we have to deal with closely related problems ; but this relationship is some-
what obscured by the terminology used, and, in particular, by attributing to
the terms "hetero" and "homoio" different meanings in the case of fertiliza-
tion and transplantation. The term "heterozygosis", as it is used in breeding,
is really meant to designate a dissimilarity in the gene sets of the different
individuals which are mated. In order to accentuate the mutual strangeness
of the gene sets or genes combined in zygotes, this condition might be desig-
nated as "allozygous", in contrast to the "isozygous" condition, which would
correspond to the homozygous state in the ordinary meaning of this term.

In our discussion of transplantation we have analyzed the effects of close
inbreeding on the fate of the graft. It may therefore be of interest to com-
pare with the latter, the effects of close inbreeding on the character of the
offspring. It has been observed that in many instances the individuals of the
first generation, Flf derived from two parents possessing genetic constitutions
differing within a certain range, show an increase in size, fertility and,
strength, as compared with the parents, but in continuing the breeding of

SELF FERTILIZATION 323

this strain by brother and sister mating no further improvement occurs, and
very often deterioration finally takes place as a result of close inbreeding.

East and Jones explained the results of inbreeding in accordance with the
rules of Mendelian heredity. The parents belonging to two different inbred
strains possess genetic constituents which differ from each other. In fertilized
ova, giving rise to the Fx generation, a large number of the dominant factors
from both parents are brought together, and this combination may cause
an increase in size, fertility and strength of the F1 hybrids. This is per-
haps due to the fact that mutations are mostly recessive and injurious and
that these injurious effects become manifest if two recessive alleles are com-
bined in the offspring. In the F1 generation, the chances that these injurious
recessive factors become manifest are slight as compared to the genetic
constitution in inbred strains. If the Fx hybrids are inbred the advantages
gained in Fx disappear again. In the F2 and following generations, these
dominant factors again become segregated in the large majority of the in-
dividuals and a loss of the advantages gained in the Fx generation may take
place, until, as the result of continued inbreeding, the individuals have again
reached a condition in which they all have acquired essentially the same, or
at least a very similar genetic composition, and then no further deterioration
needs to take place. The increased vigor In the F2 generation of hybrids, due
to the bringing together in the same individual of factors which are derived
from different lines, and especially of dominant favorable genes which pre-
vent the injurious effects of recessive mutants from becoming manifest, is a
condition called "heterosis". In accordance with what we have stated above,
inasmuch as in inbreeding in the beginning two individuals are united, belong-
ing not to two different species but to the same species, although to two
different lines or perhaps to different varieties, it would be preferable to
designate this stimulated state in the Fx hybrids as homoiosis, depending on
a "homoiozygous" in contrast to an "autozygous" condition of the gene sets.
Such a state of homoiosis would then, in the course of further inbreeding
be followed by a state of syngeniosis and ultimately by one approaching
autosis. In some instances, even a certain stimulation may result from fertili-
zation, when the two germ cells belong to different though closely related
species. In the latter case we would have to deal with a true heterosis. How-
ever, according to common usage the term "heterosis" is meant to signify
the beneficial effects derived from the fact that unlike genes derived from
unlike parents are combined in the same individual, and furthermore, it
attributes to this unlikeness of the genes certain effects without regard as to
whether the relationship of the genes is a heterogenous or a homoiogenous
one. If it is desired to express merely the mutual strangeness of the genes
derived from the two different parents, we might apply the term "allosis" to
the condition usually designated as heterosis.

According to East and Jones, the injurious effects of inbreeding are then
due to combinations of certain recessive allelomorph genes in the same in-
dividual; injurious conditions which had existed previously in a potential

324 THE BIOLOGICAL BASIS OF INDIVIDUALITY

state, but which had been hidden, thus become manifest. The inbreeding as
such is not necessarily injurious, provided the genetic constitution of both
parents is a very favorable one.

The deterioration caused by inbreeding in animals can, perhaps, to a certain
extent be mitigated and delayed through continuous selection of the most
vigorous individuals of the inbred strain for breeding purposes ; such a selec-
tion was made in the breeding experiments in rats by H. D. King and it is
possible that by these means a severe deterioration was avoided, at least for
a long time. We may assume that presumably in using the strongest in-
dividuals, in most cases also the most allozygous (or heterozygous, according
to the usual terminology) individuals were chosen, and thus the approach
to an autozygous condition was delayed. Evidently a homoiogenous com-
bination of genes in a zygote and in the individual subsequently formed is
most favorable for the best development of a higher animal organism ; con-
versely, a condition of autosis in fertilization may lead to deterioration. In
this respect gene combinations in the fertilized ovum differ from the com-
binations of gene derivatives, the individuality differentials, as they are accom-
plished in transplantation of tissues. Here, as we have seen, the autogenous
combination is the most favorable one; a syngenesio-, and still more so,
a homoio- and a hetero-combination are injurious. However, it is possible
also that a combination of genes derived from two unlike parents may lead
to a summation of two beneficial conditions and that this summation may
produce favorable physiological conditions in the hybrid. Such an effect
seems to have been observed by Robbins in two races of tomatoes in which
the hybrid Fx presumably possessed the combined ability of both parents to
synthesize certain vitamines B.

From a physiological point of view, it has also been suggested that a
combination of genes which differ within a certain range of intensity in the
Fj generation, leads to the development in the embryo of a substance or of
substances, which are slightly different from those to which the fertilized
ovum and the developing embryo are adapted, and that this condition if
present within a certain range of concentration exerts a stimulating effect,
while a substance which exceeds a certain degree of strangeness may cause
injurious effects. This formulation recalls the so-called Arndt-Schultz rule,
according to which very small doses of toxic substances, instead of having
an injurious effect, on the contrary, may exert a stimulating effect. It was
especially Lohner who, in comparing the effects of inbreeding and of fer-
tilization of ova by less nearly related sperm, applied the Arndt-Schultz rule
to their analysis. We should then attribute the advantage of homoio-fertiliza-
tion over close inbreeding to the stimulation caused by a greater mutual
strangeness of the genes in the former process, as compared with the great
similarity of the genes in the latter. Furthermore, cross-fertilization between
different subspecies, or between certain very nearly related species, on ac-
count of the still greater mutual dissimilarities of the combining genes, might
be even more beneficial and exert also the effects characteristic of heterosis
(allosis) ; however, if the dissimilarities between the genes exceed a certain

SELF FERTILIZATION 325

limit, toxic effects would predominate and disharmonies would occur in the
process of fertilization or in the development of the embryos. If we accept
this mode of interpretation, we should have to assume that in homoiogenous
fertilization, which represents the normal process, the injurious effects of in-
breeding are avoided, because in the former case there is provided the stimu-
lation which slightly toxic substances exert on the developing ovum. We
would then have to deal with substances, the character of which depends
upon the relationship between the male and female germ cells, a certain
distance of relationship, but one not exceeding a definite limit, giving the best
results.

Of interest in this connection are also the experiments of Demoll, who
found that the injurious results of inbreeding in mice can apparently be
neutralized by administration of small doses of arsenic to the breeding in-
dividuals. It seems, however, that in the deterioration caused by inbreeding
we have essentially to deal with genetic reactions and that arsenic, if it should
be potent at all, merely prevents some of the injurious results from becom-
ing manifest, without essentially changing the underlying causes of the
deterioration. Such a method would therefore represent merely a symptomatic
treatment, and with this interpretation agrees the fact mentioned by Demoll,
although not interpreted by him in this way, that following the cessation of
the arsenic administration the injurious consequences of inbreeding again
became manifest.

Demoll furthermore attributed the favorable effect of homoiogenous com-
binations of sperm and egg to the formation of antibodies, the strange sper-
matozoon acting as an antigen in the egg and eliciting here, or in the develop-
ing embryo, the production of antibodies, which interact with the antigen.
However, the production of antibodies presupposes the presence of mecha-
nisms which, to our knowledge, form only during the later embryonal, or even
post-embryonal life. Within the same organism all the constituent normal
parts have, as far as their mutual relations are concerned, an autogenous
character and they are therefore not able to function as antigens. Thus it is
hardly conceivable that in mechanisms so well regulated as are those of
embryonal development, abnormal processes of a variable character, such
as the formation of antibodies, should play a role.

We mention these physiological viewpoints, although the interpretation of
East and Jones, as to the mechanisms by means of which inbreeding exerts
its injurious effects, seems to have been generally accepted by geneticists.
However, genetic and physiological modes of interpretation are not neces-
sarily mutually exclusive.

Chapter $

The Relations Between Hybridization
and Transplantation

In the preceding two chapters we have analyzed the relationship which
connects fertilization and hybridization with the organismal differen-
tials of the organisms which play a part in these processes, the term
"organismal differentials" being used in the wider sense. We have stated that
in fertilization and hybridization the interaction between the male germ cells
and certain somatic tissues in the female, the interaction between the chromo-
somes of spermatozoon and egg, and between the genes they contain, and
also the interaction between the cytoplasm of the ovum and the male and
female nuclear substances, as well as the action of certain substances which
develop during embryonal development, have to be taken into account. It
was considered at least possible that some of the substances involved in these
processes are the precursors of the individuality differentials of the adult
organisms. In transplantation of adult tissues we are concerned with the
relations to each other of fully developed organismal and organ differentials
in host and transplant. It is certain that the results in both transplantation and
hybridization depend upon the genetic relationship between the two inter-
acting organisms. While, thus, transplantation and fertilization, and in par-
ticular hybridization, have certain important factors in common, they differ
in other features, and we should therefore expect, in addition to certain paral-
lelisms between the feasibility of hybridization and transplantation, the oc-
currence of definite differences between these two processes. These have
been discussed from general points of view in the preceding chapters, when
we analyzed and compared transplantation in higher adult and in phyloge-
netically and ontogenetically more primitive organisms and the relations which
exist between transplantation and fertilization.

There still remains the question as to whether actual experiments in trans-
plantation support the assumption that a parallelism exists between the
ability to make successful transplantations between different species and the
ability to hybridize these species. Schoene suggested, in 1912, that hetero-
transplantation might be possible between hybridizable species, but he also
pointed out that while hybridization can take place between rat and mouse,
transplantation of skin from rat to mouse, and vice versa, does not succeed ;
however, it is doubtful whether hybridization between rat and mouse can
actually be accomplished either.

As stated previously, the most extensive experiments in which the existence
of a parallelism between transplantability and hybridization was tested were
carried out by W. Schultz. He attempted to prove that these two conditions
follow a parallel course and that a wide cleft exists between hybridizable and
non-hybridizable animals as far as the mutual transplantability of their tissues

326

HYBRIDIZATION AND TRANSPLANTATION 327

is concerned. He made still finer gradations in accordance with Poll's ter-
minology, distinguishing between tokonoth hybrids, which are fertile, and
steironoth hybrids, which are sterile ; the disharmony in the constitution of
the parent strains giving rise to the former, should be less than that giving
rise to the latter. Accordingly, he finds that exchange of tissues between
species with tokonoth hybrids gives the better results. We shall first cite
certain examples of Schultz's observations and then discuss some of the
factors complicating his transplantations. Such a discussion will provide an
opportunity to state also some of the principles which apply to transplantation
in general.

I. Experiments in Amphibia. Skin of Bufo vulgaris transplanted to Bufo
viridis remained alive one hundred days, and the reciprocal transplant, fifteen
to thirty days ; these two species can be hybridized. Skin grafted from Rana
temporaria to Rana arvalis lived eighty days, the reciprocal transplant, one
hundred days. In these cases in which the skin was exchanged between hy-
bridizable species the results were therefore relatively good. On the other
hand, skin transplanted from Hyla arborea to Rana esculenta remained alive
only ten to twenty days. These two species not being hybridizable, the life
of the transplant was shorter. However, also transplantation of skin from
Rana temporaria to Rana esculenta may give very good results and the graft
may remain alive for more than one hundred days, although these two species
are not hybridizable. Exchange of tissues between urodele and anuran am-
phibia was unsuccessful.

The principal results obtained by Schultz in the heterotransplantation of
amphibian skin may be summarized as follows : Length of time during which
transplants remained alive after: (a) Transplantation of skin between hybrid-
izable species.
Exchange of tissues between Rana temporaria and Rana arvalis :

70 to 105 days.
Transplantation from Bufo vulgaris to Bufo viridis : 100 days.

From Bufo viridis to Bufo vulgaris : 15 to 30 days.
(b) Transplantation of skin between non-hybridicable species.

From Bufo viridis to Rana esculenta : 10 to 20 days.

From Hyla to Rana: early death of host as well as of transplant.

From Rana esculenta to Rana temporaria : 40 days.

From Rana temporaria to Rana esculenta: 130 days.

From Salamander to Rana esculenta : 8 to 10 days.
It is evident that there is no complete correspondence between compatibility
of host and transplant and hybridizability. It is furthermore probable that
toxic actions, due to other factors than organismal differentials, play a role,
at least in some of these transplantations.

II. Experiments in Birds. Schultz finds that the skin of the canary when
transplanted to hybridizable species remains alive up to twenty-five days and
during that time shows mitoses, whereas after transplantation to the pigeon,
with which the canary is not hybridizable, the skin is found necrotic after
seventeen days. Skin exchanged between pigeon and laughing dove, which
are hybridizable, remains alive up to thirty days, during which time mitoses

328 THE BIOLOGICAL BASIS OF INDIVIDUALITY

are found, while in non-hybridizable forms the results are not so good.
Pheasant and chicken give steironoth hybrids; skin transplanted from the
former to the latter species shows mitoses after fourteen days. In skin trans-
planted from chicken to pigeon, which are non-hybridizable, mitoses may be
found after twelve days. After transplantation of skin from the domestic to
the musk duck, which are likewise non-hybridizable, necrosis is found from
the eleventh day on.

Exchange of skin between hybrids of Pharaniamus and another species
gives good results, the skin remaining alive for twenty-eight days, while skin
transplanted from such a hybrid to one of the parents was found living after
eighteen days. However, in these transplantations the exact relationship be-
tween donor and host was not definitely known; the hybrids may have been
brothers and sisters and therefore Schultz may actually have carried out
syngenesiotransplantations in exchanging pieces of skin between them.

III. Experiments in Mammals. After transplantation from rabbit to hare,
which are hybridizable, skin was found preserved after thirty-five days, but
grafts from a wild to a domestic rabbit were necrotic after thirty days. Skin
of cat transplanted to rabbit was still alive and showed mitoses after eleven
days ; the beginning of necrosis was observed after fourteen days. But skin
of rat transplanted to mouse and the reciprocal graft showed necrosis from
the eleventh day on and there was marked lymphocytic reaction.

In case of transplantation of skin from one variety to another belonging
to the same species, the results were good. Thus, after transplantation from
albino to hooded rat the graft was found preserved after thirty days and
showed mitoses at that time. Similarly, when skin from an albino Angora
rabbit was transplanted to a French grey rabhit, the results were satisfactory.

However, the findings of Schultz, that transplants between different varie-
ties, such as those mentioned in the case of the rat, behave exactly like
ordinary homoiotransplants within the same species, do not quite agree with
our own. Furthermore, Schultz (1915) assumed that no differences existed
in the results of auto- and homoiotransplantation of skin, although marked
differences between these two types of transplantation had already been well
established.

In addition, Schultz carried out transplantations also of ovaries. Previ-
ously, he had found that within the same species (rabbits or guinea pigs)
ovaries can be transplanted to males as well as to females. In the former, they
remain alive for at least four months and he concluded therefore that trans-
plantations between different sexes are less injurious than those between
different species. Furthermore, the exchange of ovaries between different
varieties is successful ; thus, ovaries transplanted from one variety of guinea
pigs to another may survive for longer than one hundred and fifty-eight days.
However, regeneration of ovarian tissue takes place only after homoiotrans-
plantation. He believes that ova, follicles, and other ovarian structures behave
after transplantation in a parallel way, and assumes, therefore, that the same
factors dominate the fate of the germ cells and of the surrounding ovarian
tissue. After heterotransplantation the results were unfavorable, even in nearly
related species; exchange of ovaries between dog and fox soon led to the

HYBRIDIZATION AND TRANSPLANTATION 329

death of the transplant. Similarly, after transplantation of cat ovary to rabbit
there was early degeneration, although at first there may still have been
noticeable some mitotic activity.

As we have seen, in a general way a parallelism may be expected to exist
between the transplantability of tissues of certain organisms and the possi-
bility of hybridizing them, and, on the whole, the experiments of Schultz
indicate the actual existence of such a parallelism; but there are quite a num-
ber of exceptions to this rule and to some of them we have already drawn
attention. Thus reciprocal hybridizations may give different results and such
results may not correspond to those which are found in the case of corre-
sponding reciprocal transplantations. We have pointed out the differences
which exist in the significance of autogenous, syngenesious and homoiogenous
relationships in hybridization and in transplantation. While the results of
heterogenous relationships are more similar in hybridization and transplanta-
tion, a perfect correspondence is lacking even here. But a strict parallelism
should not be expected, because hybridization and transplantation, as pre-
ceding chapters have shown, represent in some very important respects very
dissimilar processes.

To mention some of these differences : The chromosomes of horse and
donkey meet in the somatic cells of the mule without any apparent injury to
cells resulting from this heterogenous combination. On the other hand, skin
of the horse cannot be grafted successfully to the donkey, nor does the re-
ciprocal transplantation succeed. Furthermore, the fact that although hybrids
between two species may be well formed and strong, yet the eggs of the female
hybrid may not be fertilized by the spermatozoon of a male hybrid, can be
readily understood if we consider that the function of the male and female
chromosomes is not the same in the germ cells and in the specialized somatic
cells of the hybrids. The chromosomes of the germ cells undergo synapsis and
reduction divisions, which are very complex processes. Before reduction divi-
sion has taken place, the sex cells and the surrounding somatic cells have the
same set of genes, but they differ following this occurrence. During reduction
division in the hybrids, abnormalities may arise, which prevent the formation
of healthy spermatozoa and ova and thus lead to sterility.

Schultz, in general, seems however to assume that the mutual interaction
of sex cells and of somatic cells is of the same kind, and that the germ cells
are more differentiated than the somatic cells, because they have the poten-
tiality of reproducing the whole organism. But early ontogenetic stages of
tissues do not yet show the same degree of differentiation of organismal
differentials as do adult tissues. Likewise, there is evidence for a phylogenetic
evolution of organismal differentials. Because homoio- and even heterotrans-
plantation may succeed in certain amphibia, it does not necessarily follow
that such transplantations must succeed also in mammalian organisms.

If two animals of the same species differing in certain characteristics, as
for instance, in the pigmentation of certain parts of the skin, are mated, then
in the F2 generation a segregation of these allelomorphs may take place. Two
individuals, A and B, belonging to the same litter, may therefore differ in the
color of a certain part of their skin. Schultz holds that it should be more

330 THE BIOLOGICAL BASIS OF INDIVIDUALITY

difficult to exchange skin from areas in A to B, which differ in color, than
from areas where the color is the same in host and donor. According to the
concept of organismal differentials, on the other hand, the same individuality
differential should attach to the black and to the white skin in the same animal,
and it should make no difference as far as the reaction of the host against the
transplant is concerned, which part of the skin of A is grafted to B. Of course,
the tissue differentials of these two parts of the skin might differ and it might
thus be easier to transplant pigmented than unpigmented skin, but this dif-
ference would apply also to transplantation of white and pigmented skin in
the same individual. We must assume that the tissues in the same individual
possess the same organismal differentials and that these alone determine the
specific reaction of a particular host against a transplant, while tissue and
organ differentials would call forth the same reaction in all hosts, irrespective
of the character of the organismal differentials in host and transplant. When
differences in tissue or organ differentials are superimposed, in a certain
individual, upon those in organismal differentials, the former do not call forth
reactions specific for an individual in the same sense in which the latter do.
This holds good in general, although in some cases the character of the tissues
may help to determine the reaction of the host against individuality differentials.

Both Schoene and Schultz stress the importance of athrepsia in transplan-
tation, by which is understood a condition in the graft caused by lack of
foodstuffs, mainly of a protein nature, but also of salts which are specifically
needed by tissues transplanted into certain hosts ; furthermore, importance is
attributed to anaphylactic reactions. Although in a general way both these
authors regard the presence of toxic substances as a possible additional factor
in determining the fate of heterotransplants, the existence of heterotoxins
affecting interspecies transplantation is denied by them, because it can be
observed that the margin of a transplant may be better preserved than its
central parts. They assume that if a heterotoxin were active in such cases
it should first show its injurious effects in the peripheral part of the graft.
However, as we have seen, the better oxygen supply in the periphery as com-
pared to the center of the graft, may overbalance and obscure the effect of
specific heterotoxins.

There are still other secondary factors which have to be considered and
which may explain some difficulties in transplantation : for instance, the un-
equal sensitiveness of different tissues to the lack of a sufficient amount of
oxygen during the process of grafting, or directly following it, may play a
role also in the transplantation of the fertilized ovum; differences in the
structure of tissues, such as the density of the cutis, may be of some im-
portance in skin grafting; and lastly, the different effects of hormones in
different hosts and in the same hosts under varying conditions, may affect the
fate of the transplanted sex organ.

On account of the difficulty in obtaining a sufficient number of suitable
animals for certain transplantations, the conclusions of Schultz are based on
a very limited number of experiments, but they, as well as our earlier ones,
indicate that within certain limits a parallelism exists between transplant-
ability and the phylogenetic relationship between heterogenous hosts and
transplants, and the experiments of Schultz in addition suggest, with certain

HYBRIDIZATION AND TRANSPLANTATION 331

restrictions, the existence of a parallelism between the transplantability of
tissues and the hybridizability of the organisms from which the tissues are
derived.

A much more complete correspondence between the effects of hybridization
and transplantation was observed in the more recent experiments of von
Ubisch, who used, however, not adult organisms for transplantation, but early
embryonal stages of echinoderms. When he transplanted the micromeres,
which give origin to the skeleton, from one species, or even from one order,
into another one in which the character of the skeleton was different from
that of the first species or order, he observed the formation of an intermediate
skeleton in the plutei derived from these chimaerae ; this intermediate condi-
tion may represent either a mosaic of the skeletons of host and donor, or a
still more perfect combination. If hybrids were produced between the same
orders or species which were used for grafting, the hybrids developed a skele-
ton which was similar to that which developed in the corresponding chimaerae
following transplantation. It may be assumed that the nuclei of the two indi-
viduals which give origin to the third individual largely determine the results
in both hybridization and in the formation of chimaerae through transplanta-
tion; and although in the hybrid every nucleus contains both maternal and
paternal material, while in the chimaerae some cells have only nuclei of the
host and others only nuclei of the donor, still, in hybrids and chimaerae the
nuclear material from both parents, or from both host and donor is present.
This might explain the similarity in the results of transplantation and hybridi-
zation. However, whereas the chimaerae contain cytoplasm of both species,
the hybrid contains only the maternal cytoplasm. Therefore the results of
reciprocal hybridization may differ greatly, because the cytoplasm, which is
present only in the female sex cell, differs in reciprocal crosses, whereas in
the case of chimaerae, since both parents contribute cytoplasm, the cytoplasm
and therefore also the results of reciprocal transplantations are the same. But
this explanation may hold good only for transplantation of very early em-
bryonal material ; we have seen that in further developed organisms the results
of reciprocal transplantations may differ.

In the primitive organisms employed in von Ubisch's experiments, the cells
and tissues were still very plastic and they possessed the precursors of, rather
than the fully developed organismal differentials, facts which may account
for the fargoing parallelism found in this instance between the results of
hybridization and transplantation, while such a parallelism is very much less
complete in experiments in which adult tissues are used.

Concluding Remarks

From the experiments on which we have so far reported, it seems to follow
that organisms in general represent organismal equilibria which in the case
of the most differentiated organisms may be autogenous; this means that all
the various constituent parts of organisms possess in common certain chemical
characteristics, which differ from those of all, or almost all, the other organ-
isms, and which prevent a tolerance for contacts between tissues derived from
strange organisms and, instead, cause reactions of aggression or defense.
This applies not only to complex metazoa, but also to certain free-living cells.

332 THE BIOLOGICAL BASIS OF INDIVIDUALITY

The degree to which this type of specificity between different members of the
same group exists varies according to the difference in the genetic constitution
of different individuals of such groups, as well as according to the phylo-
genetic and ontogenetic stages of development which these organisms have
reached. It is very difficult, or perhaps impossible to eliminate entirely these
differences between different members of the same group through long-con-
tinued, close inbreeding, which starts with two different individuals; but by
these means these differences can at least be very much mitigated in the course
of time, the length of which varies in the case of different species. These
specificities have reached their, most fargoing development in the highest
organisms, which otherwise are the most rigid and the least modifiable as far
as their tissue and organ constitutions and the interrelation between the latter
are concerned. They are at the lowest stage of development in the phylo-
genetically and ontogenetically most primitive organisms, especially as far as
the manifestation of these reactions is concerned. The mechanisms which
underlie such specificities under different conditions vary in different stages
of the phylogenetic and ontogenetic evolution. In the course of the former,
these specificities, or at least their manifestations, are newly created step by
step, while in ontogenetic development they are present in the form of pre-
cursor substances and mechanisms, which in the end lead to the complete
formation of systems of the individuality differentials of the higher organ-
isms. The substances and the mechanisms on which the maintenance of these
equilibria depends may accordingly vary to a certain extent under different
conditions.

Thus, in some free-living single cells such specificities may exist; but the
substances or mechanisms underlying them, and the reactions which reveal
their existence may differ, here, in certain respects from those found in higher
organisms, and such differences probably exist also in regard to the genetic
constitution which determines these specificities. On the other hand, the results
achieved by these various modes of interaction of different species are very
similar in unicellular and the more complex organisms. As far as the indi-
viduality differential reactions are concerned, some very finely developed
mechanisms, indicative of autogenous equilibria, are found in certain in-
fusoria among the protozoa and also in some primitive plants; however, in
these unicellular organisms also, environmental conditions, in addition to the
genetic factors, seem to enter into the determination of these interactions to
a greater extent than they do in higher animals. Moreover, in unicellular
organisms there seems to be superimposed upon these autogenous equilibria,
a second type of mechanism, corresponding to the fertilization process; it
resembles the types of interaction which occurs between the eggs and sperma-
tozoa in higher organisms. In the latter, the point of equilibrium is situated
in the homoiogenous rather than in the autogenous zone in the spectrum of
relationships. Different genetic and phenotypic mechanisms underlie these
processes of interaction in transplantation and fertilization and these mech-
anisms may vary also in different organisms, as for instance, in ascidians and
in some plants. However, there are indications that even in fertilization
genetic constellations, similar to those which determine the individuality dif-
ferentials, may also play a part.

P^rt" l"V Tumors and Organismal Differentials

Introduction
The Nature of Tumors

In a preceding part we have discussed the organismal differentials and,
in particular, the individuality differentials of normal tissues and the
reactions they call forth in the host. Under certain conditions normal
tissues become transformed into cancerous or so-called malignant tissues,
which possess characteristics differing in certain respects from those of normal
tissues. It will be of interest to inquire whether in this cancerous transforma-
tion the individuality differentials and the organismal differentials, in general,
also undergo changes ; but first, we shall state briefly ( 1 ) wherein some of
the differences between normal and cancerous tissues consist, and (2) what
causes this transformation of normal into malignant tissue.

In cancerous tissues the growth energy is increased, at first usually in a
localized area; but this increase in growth energy differs from the increase
observed in embryonal tissue, in that it is not accompanied by progressive
differentiation and in that often irregularities in the structure of cells and
their nuclei and in cell multiplications take place. Mitoses may be abnormal,
amitoses and giant-cell formation may be found. In the actively dividing cells
the normal differentiation of cells and tissues may be incomplete, but there
are all degrees of this incomplete differentiation. The stimulated cells fre-
quently undergo more active movement ; during these movements the normal
organization of the tissues may partly be lost. The cells usually penetrate into
adjoining tissues, into blood and lymph vessels, and through the circulation
they may be carried to distant places and here develop in the form of metas-
tases. Cancerous growth is a dissociated growth, in which some of the regu-
lative factors normally controlling tissues are no longer effective. To these
structural changes correspond certain chemical changes. In the carbohydrate
metabolism, enzymatic splitting processes (glycolysis) may predominate over
oxidative processes, especially under anaerobic, but also under aerobic condi-
tions, and substances such as lactic acid may then be produced in excess.
There may be quantitative changes in the distribution of enzymes and vita-
mins found in various tumors, on the one hand, and in the normal tissues
from which they developed, on the other; but these alterations may vary in
direction, or at least quantitatively, in different types of cancer and in dif-
ferent species of animals. There may be still other changes, chemical or struc-
tural ; however, it is not certain whether these modifications are primary and
causal, or whether they are not, rather, the consequences of the cancerous
growth. Metabolic or structural abnormalities of a related kind, although

333

334 THE BIOLOGICAL BASIS OF INDIVIDUALITY

usually differing in certain respects from those noted in cancers, may be
found also in other types of abnormal growth, as, for instance, in certain
types of regenerative or of the so-called inflammatory growth, or even in
certain instances, of excessive hormonal-correlative growth. Cancerous tissue
behaves essentially like an originally normal tissue stimulated to grow and
to move under more and more abnormal conditions.

However, essentially cancerous growth differs from other types of ab-
normal growth in that it is an irreversible process, whereas regenerative,
hormonal and inflammatory growth ceases whenever the causes which in-
duced these proliferations are removed. Once a normal cell has become can-
cerous, it may die, but as far as is known at the present time, it will not
return to the normal state. All kinds of tissues which have the ability to grow
may become cancerous; cancerous epithelial tissue is called carcinoma and
cancerous mesenchymatous tissue is called sarcoma. Also, embryonal tis-
sues may become cancerous and parthenogenetically developing eggs may
give origin to teratomas, in which many varieties of tissues may be repre-
sented. Cancerous growths developing from tissues of the adult organism
are classified in accordance with the character of the tissue from which they
are derived. In addition to the fully cancerous, malignant tissues, there exist
others which are in a transitional state. They form the so-called benign
tumors, in which the growth is increased and abnormal but slower than in
the typical cancers, and in which it takes place not by infiltration of the
neighboring tissues but by concentric extension, the differentiation of the
affected tissues usually occurring in a more normal manner than it does in
cancerous tissues. However, all kinds of gradations exist between normal
tissue, benign tumors and cancer, and while in the majority of cases a benign
tumor remains benign throughout the life of the individual, it may change
into a malignant one. When cancer particles are transplanted into other
animals of the same species, they may, in the new host, maintain their
malignant growth or they may become necrotic, and are then absorbed. The
readiness with which different tumors can be transplanted into different
hosts and individuals differs greatly.

As to the factors which induce this transformation of normal into can-
cerous tissue, three main sets of conditions can be recognized : ( 1 ) a stimu-
lation of growth which usually extends over long periods of time and may
show various degrees of intensity, (2) genetic factors, and (3) viruses or
virus-like substances. 1. Stimulating factors: Hormones may function as
stimulators of the cancerous transformation and they elicit cancerous growth
in those tissues in which they induce, also, under normal conditions, growth
processes. Then there are special chemical, so-called carcinogenic substances,
tar and some substances which are constituents of tar or related compounds;
they are very efficient in causing cancer, but are not as selective in regard
to the tissues which they affect as are hormones. Dibenzanthracene, benz-
pyrene and methylcholanthrene are the best known among these substances.
Also, various injuries, inducing long-continued, regenerative growth, may
have similar effects. Ultraviolet light, X-rays and radium may in the end,

THE NATURE OF TUMORS 335

change normal into cancerous tissues. Lastly, certain metazoan parasites, such
as Bilharzia (Schistosoma), acting on the urinary bladder, the nematode
Spiroptera neoplastica, affecting the fore-stomach of rats and mice, and
Taenia crassicollis, causing sarcoma in the liver of rats, may function as
cancer-producing agents.

All these stimulating factors have in common that they initiate and main-
tain long-continued growth processes. But hormones are the only natural
physiological agents known so far, which in this way induce cancerous proc-
esses through their normal function. All others are abnormal agents. Struc-
turally estrogenic substances may or may not be related to the carcinogenic
polycyclic hydrocarbons. Under the influence of these stimulating factors
the growth processes, in the tissues on which they act, become step-by-step
more intense, until they end in irreversible cancerous proliferations. Some-
where during this preparatory process a state of sensitization of the tissue
is reached, so that from this point on, without as yet being cancerous, the
tissue will continue in its progression to cancer as a result of normal meta-
bolic or mechanical factors and without the further aid of the specific cancer-
producing agent. While the various stimuli wdiich initiate these growth proc-
esses are important in the analysis of cancerous changes, the growth proc-
esses which they all set in motion are probably the most characteristic and
the most important factor in the origin of cancer. It has been tentatively
suggested by us that during this preparatory growth period, an autokatalytic
growth substance is produced or increased in amount step by step and that
this effects in the end the irreversible cancerous state.

(2) Hereditary genetic factors may co-operate with the stimulating fac-
tors in inducing cancer. In general, the genetic factors, as far as they relate
to the development of cancer, are limited to a specific organ or tissue and
the mechanism of the hereditary transmission of cancer in a certain organ
may differ from that in another organ. Different tumors are, therefore, in-
dependent of one another as far as their genetic determination is concerned.
These hereditary factors may be of diverse kinds ; they may consist in in-
herited malformations of tissues or in certain diseases which cause abnormal
stimulation of tissues in localized areas. In the case of mammary gland
carcinoma of the mouse, which is a very common type of cancer in that
species, it has been found that, in the main, differences in the hereditary
tendency to mammary carcinoma in various strains corresponds to the graded
ability of the mammary gland tissue to respond with growth processes to
the action of ovarian hormones. These differences in the responsiveness to
growth stimuli is the essential factor underlying the hereditary tendency to
the development of mammary gland carcinoma, and the same factor is pre-
sumably active also in other types of cancer. In addition, a virus-like sub-
stance, transmitted to the nursing child with the milk of the mother, but
present also in certain organs and in the blood, participate in the production
of mammary gland carcinoma. The frequency of mammary gland carcinoma
in some strains may be zero and in others 100 per cent; normally it affects,
almost exclusively, females, because the hormone, estrogen, which in this

336 THE BIOLOGICAL BASIS OF INDIVIDUALITY

instance represents the stimulating factor, is present mainly in the female
sex. It has furthermore been observed in this kind of cancer that in hybrids
the mother strain is much more potent than the father strain in determining
the cancer rate, and this is due to the factor transmitted with the milk from
the nursing mother to the offspring. An inverse relation seems to exist be-
tween the intensity of stimulating factors and the strength of the genetic
factors needed for the transformation of normal tissues into cancer. Either
of these two sets of factors alone may be effective in certain cases, if it
reaches a given intensity. This relation can be expressed by the equation:
H (hereditary constitution) X S (stimulation) = C (cancer).

(3) In the main, three kinds of viruses or virus-like substances are known
as causative factors in cancer, namely, (a) the virus of cottontail rabbits,
which may give origin to papilloma, but under certain conditions, also to
epidermal cancer. It probably acts as a stimulating factor, comparable to
the other stimulating factors already mentioned, (b) The milk factor, which
participates in the origin of mammary gland carcinoma in mice and acts in
association with hormonal and genetic factors. It may have also a slight
effect in mouse leukemia. Its mode of action is not definitely known, but
there is some indication that it also may act as a sensitizing factor, (c) In
avian sarcomas, agents can be separated from the tumor cells by filtration
and certain other means. These agents seem to cause this type of cancer
directly, without inducing first a preparatory growth period. They are largely
but not entirely species- and organ-specific. They represent a carcinogenic
substance in the strict sense, while the other factors apparently are growth
promoters. A similar agent is, perhaps, present in renal carcinoma of the
frog.

It is believed by some investigators that somatic mutations in tissue cells
may be responsible for the origin of cancer; however, there are a number
of facts which make this interpretation very improbable. On the other hand,
mutations which affect the germ cells may determine the degree of hereditary
tendency to the development of a certain type of cancer in individuals, strains
or species. Three theories concerning the origin of cancer are under con-
sideration at the present time : ( 1 ) The somatic mutation theory assumes
that all the other factors mentioned cause cancer by inducing changes in the
genes of a certain cell, which then becomes cancerous and gives origin to
the other cancer cells. There are very serious objections to this theory, which
is, therefore, in all probability not correct. (2) The virus theory assumes
that viruses are the essential causes of all cancers, and that all other factors
are effective only if they make it possible for viruses to invade cells and to
activate their growth. While the possibility of such a function of viruses is
indicated, especially in the case of avian sarcoma, there are some difficulties
also to the application of this theory in many other cancerous states. (3)
The theory that step-by-step increases in growth momentum of tissues lead
to intermediate stages of sensitization, and ultimately to irreversible, can-
cerous proliferation, perhaps through the mediation of an autokatalytic
growth substance. This seems at present the most likely general explanation

THE NATURE OF TUMORS 337

of the cancerous process, although we cannot rule out the possibility that a
virus or virus-like substance may be a hidden cause of all cancers.

Given these fargoing changes in the reactions which normal tissues un-
dergo in becoming cancerous, the problem arises whether these remarkable
changes at the same time induce alterations in the character of the individu-
ality differentials of the tissues or in the reactions of the host against the
abnormal transplants. To answer these questions, we present in the follow-
ing chapters the data which are relevant in this regard.

Chapter I

A Comparison between the Transplantation
of Tumors and of Normal Tissues

We have analyzed by means of transplantation the organismal and
organ differentials of the normal tissues, and we shall now proceed
to the study of the corresponding differentials in tumors, which
latter differ in their behavior, after transplantation, in certain respects from
normal tissues. In the introductory statement we have discussed the essential
characteristics of tumors, especially of cancers, and wherein they differ from
normal tissues. We then inquired into the factors which caused the trans-
formation of normal into cancerous tissues. We shall now study the various
types of transplantation of tumors and compare the essential results with
those obtained after the grafting of normal tissues ; there are some very
marked similarities, as well as some differences. In tumors, we shall find
certain complications which did not occur in normal tissues, such as an in-
creased growth energy, which to some extent may overcome the antagonistic
reactions of the host to the transplant; also, there are indications that the
tumor cells themselves can undergo changes of an adaptive character during
the course of transplantation, and that, in particular, they may acquire re-
sistance to certain injurious conditions to which they are exposed in the new
hosts. On the other hand, cancerous tissues may call forth in the new hosts,
states of immunity or allergic reactions, which tend to injure the transplant;
but there are strong indications that against these the cancer tissue may find
protection to some extent, by its ability to absorb and to neutralize substances
antagonistic to its growth. There exist in addition, the same problems which
we had to face also in normal tissues, namely, that of distinguishing between
the presence or lack of the various organismal differentials in the tumor cells,
and of the manifestation of these differentials, which may depend on the
rapidity of the production and discharge of the organismal differentials by
the transplanted tumors or host, and on the power of resistance of the
tumor cells to the injurious effects of the host. There is still a further com-
plication : while in normal tissues we can readily follow the reactions of the
host against the transplant and, with certain precautions, use these reactions
as a standard with which to gauge the differences in the organismal differ-
entials between host and graft, in the case of tumor transplants such an
analysis is very difficult on account of the relatively rapid growth of the
tumor tissue. Thus the finer reactions, which we used as indicators in the
analysis of the organismal differentials, and especially of the individuality
differentials, in normal tissues, cannot very well be used in tumors, at least,
not in many cases. Instead, most investigators employ as the standard, the
growth or lack of growth of the grafted tumors. This is a less finely graded

338

TUMORS AND NORMAL TISSUES 339

method of measuring the individuality differentials; what is measured in
this way is not necessarily the degree of similarity or dissimilarity of the
individuality differentials of host and transplant, but the ability or lack of
ability of the tumor to overcome a limiting factor for the growth of the
transplanted tumor tissue in a certain host. It may be regarded, therefore,
as doubtful whether the data obtained in tumor transplantation can be directly
applied to the analysis of the individuality differentials of tumors; notwith-
standing these difficulties, there is much evidence that the organismal, and
in particular, the individuality differentials, are essentially the same in normal
tissues and in tumor tissues, and that the specific characteristics of cancer
tissues, which differentiate them from normal tissues, are not so much due
to changes in the organismal differentials as to certain other conditions.

As has been said, in tumor transplantation the main concern is to deter-
mine whether or not a transplanted piece of tumor shows continued growth,
and it is customary to record the percentage of successful transplantations,
of "takes," as they are obtained under various circumstances. However, be-
sides the transplantability there are two other variable factors which should
be considered in evaluating the result of transplantation, namely, (1) the
growth energy of a tumor, by which is meant the rapidity of its growth,
and (2) the latent period intervening between the time of transplantation
and the first definite manifestation of an expansive growth of the grafted
piece. These data are obtained by measuring at certain periods the diameters
of the tumor, or better still, by determining, in addition, its weight at the
conclusion of the experiment. In some of our early transplantations, we gave
attention, also, to these last named factors. But as mentioned, only the per-
centage of "takes" was recorded by the majority of investigators, and the
lack of fineness of this test was not felt as a serious difficulty, especially in
the earlier period of tumor research in which the peculiar properties of
tumors were analyzed largely by means of transplantation. As a rule, the
growth of transplanted tumors was considered as something distinct from
the growth of various normal tissues. Only gradually, step by step, was the
great similarity in the behavior of normal and tumor tissues after transplan-
tation established, and at the same time the factors which differentiate tumor
and tissue growth were analyzed.

The first successful transplantations of tumors in animals were carried
out by Hanau, Morau, Velich, Eiselsberg and Firket. They used for this
purpose, carcinoma of rat and mouse as well as sarcoma of rat. These ex-
periments established the fact that certain tumors can be transplanted to
other animals of the same species, at least for a limited number of genera-
tions. Incidentally also, some interesting observations concerning the factors
on which transplantation depended were made, especially by Morau in his
experiments with carcinoma of the mammary gland in the mouse. A new
motive was introduced into the experimental study of tumors in the begin-
ning of this century, in a series of consecutive transplantations of sarcoma
of the thyroid gland of rats by the writer (1901) and of a mammary gland
adenocarcinoma of the mouse by Jensen (1902). In these experiments, which

340 THE BIOLOGICAL BASIS OF INDIVIDUALITY

extended through many more generations than previous ones, transplanta-
tion was used as a method for analyzing the characteristics of the tumor
cells and the interaction between tumors and hosts; there was thus initiated
the subsequent large number of investigations into the biology and causes
of cancer, which has continued with increasing intensity until the present
day and which has contributed much to the solution of these problems.

The objective of the writer was the study of the characteristics of tumor
cells, of the factors which made them behave in their own peculiar way, of
the possibility of separating a living agent responsible for the tumor growth
from the transplanted cells ; in addition, there was the analysis of the causes
and mechanism of the transformation of normal into tumor cells, and, above
all, the comparison between the behavior of transplanted normal and can-
cerous cells, which made possible a critical examination of what we now call
the organismal differentials of tumors. Jensen approached these investiga-
tions primarily from the point of view of bacteriology and immunology, his
central problem being the possibility of obtaining an active and passive im-
munity against tumor growth, similar to that which can be obtained against
bacteria and their toxins. In a similar way, the subsequent investigations of
Ehrlich and Apolant, Gaylord and Clowes, Bashford and Murray and their
collaborators, and many other well known workers, were largely concerned
with the problem of immunity, but gradually these studies have led back
again to a comparison between the behavior of normal and tumor tissues,
since it became more and more evident that some of the most important
characteristics of tumor cells are shared with normal cells. Thus, in the end
both these series of investigations contributed also to the analysis of or-
ganismal differentials in general.

We shall now compare the various types of transplantation of tumors
with those of normal tissues and determine wherein they resemble each other
and wherein they differ.

Auto- and Hotnoio trans plantation of Tumors

We have seen that normal tissues behave very differently after auto- and
after homoiotransplantation. In the former, the individuality differentials
of host and transplant are identical, while in the latter they are different.
One of the marked differences between normal tissues and tumors consists
in the fact that some tumors can be homoiotransplanted from generation to
generation into a percentage of animals of the same species, which varies in
the case of different tumors, whereas, such a serial homoiogenous trans-
plantation does not succeed with normal tissues. But this is not true of the
majority of tumors ; while there are some which can be readily transplanted
into animals belonging to the same species, irrespective of family or strain,
the large majority grow only in animals belonging to the same closely inbred
strain, and very much less or not at all in other strains; again, others grow
in a certain percentage of mice from mixed strains of the same country in
which they had developed, but do not grow in strains bred in distant coun-
tries. To cite an example: a carcinoma of the mammary gland which had

TUMORS AND NORMAL TISSUES 341

originated in a white American mouse, and which we used in many of our
experiments, could be transplanted into the large majority of American
white mice, but into a much smaller percentage of German or English mice.
We find, therefore, all kinds of transitions between transplantable and non-
transplantable tumors. The larger the number of animals which are tested
for their suitability as hosts, the greater becomes the chance that in the end
we shall find an animal in a mixed strain in which the tumor will take ; which
means that the cells remaining alive after transplantation will continue to
multiply. And between this condition of relative non-transplantability and a
perfect transplantability in 100 per cent of all animals of the same species,
we find all intermediate grades. However, the more closely inbred a strain
is, in which a tumor originated, the larger becomes the number of animals
belonging to this strain into which, as a rule, the tumor can be successfully
transplanted, whereas, the tumor may not grow after transplantation into
other strains.

There are, in a general way, two factors which determine the degree of
transplantability of a tumor, as expressed by the average number of takes,
namely, (1) the relation of the individuality differential of the host to that
of the transplant, and (2) certain factors which differentiate normal tissues
from tumor tissues, and which may vary quantitatively in the case of dif-
ferent tumors ; among these are variations in growth energy and processes
of adaptation, which may take place between tumor and host. In all cases
the individuality differentials in host and transplant seem to assert them-
selves, even in those tumors in which the transplantability is 100 per cent,
for here, also, a transplanted tumor differs in its relation to the host from
a spontaneous tumor developing in the same animal. We had already noted,
in our earlier transplantations, this difference between spontaneous autog-
enous tumors and transplanted homoiogenous tumors. While spontaneous
tumors have a tendency to recur after extirpation, transplanted tumors are,
as a rule, more sharply separated from the host tissue and can much more
readily be completely removed ; they behave like strange organisms implanted
in the host, from which they draw their nourishment but from which they
often remain separated by a capsule; their vascularization is less adequate,
and not rarely they grow even more rapidly in the host than do spontaneous
autogenous tumors. Notwithstanding such a rapid growth of the homoiog-
enous tumors, it is, after all, a precarious existence which they lead in the
strange host, as shown by the fact that they are usually more readily dam-
aged by the injection of certain unsuitable substances into the host than are
autogenous spontaneous tumors. These various differences in the behavior
of spontaneous and homoiogenous transplanted tumors are, perhaps, partly
due to the process of transplantation as such, but they are largely caused by
the difference in individuality differentials of host and transplant; an in-
jurious reaction against the transplant takes place in the strange host, and
such an injurious effect is the more evident the greater the dissimilarity
between organismal differentials of host and transplant. In a general way,
it may be stated that these primary reactions are similar to those which are

342 THE BIOLOGICAL BASIS OF INDIVIDUALITY

noted in the case of normal homoiotransplanted tissues; but added to these
primary reactions are secondary immune reactions, which are much less
evident in the case of normal tissues than of tumors. However, at the time
when these observations were made, very closely inbred strains approaching
homozygosity were not yet available; if transplantations are carried out in
such almost homozygous strains, the differences in the individuality differen-
tials between host and transplant may be much reduced, or almost entirely
eliminated, and if there are still some differences to be found in the behavior
of spontaneous and transplanted tumors under these conditions, these must
essentially be due to changes which took place in the tumor cells in the course
of transplantation. Also, normal tissues grow very much better after trans-
plantation into individuals belonging to the same inbred strain than into those
belonging to different strains, and this fact again proves the similarity of
the role of the individuality differentials in the behavior of tumors and of
normal tissues after transplantation.

We see, then, that even when tumors grow well in homoiogenous animals,
differences which exist in the constitution of analogous tissues in different
individual hosts assert themselves ; but this fact was appreciated only after
it had been shown that the relative readiness with which auto- and homoio-
transplantation can be carried out in the case of tumors is the same as in the
case of normal tissues. The first systematic investigations concerning such
differences in the behavior of tumors after auto- and homoiotransplantation
were made in 1901 and 1902, when we studied for this purpose a mammary
adenoma of the rat, and subsequently, with S. Leopold, a mixed tumor of
the breast in a dog. After autotransplantation the tumors — their epithelial
as well as their connective tissue constituents — remained alive, while after
homoiotransplantation they died. As to the rate of growth, the autotrans-
plants showed the slow rate of the original tumors; but if, under the influ-
ence of pregnancy, the original tumor grew more rapidly, the autotransplants
likewise assumed a rapid growth, which ceased after the conclusion of preg-
nancy. We drew, then, the conclusion that the composition of the body-
fluids in the individual in which the tumor originated differs in some respects
from that in other individuals of the same species, and that in the former it
is much more favorable for the life and growth of transplanted cells. This
conception we have applied to tissue transplantation in general and as far as
this conception holds good we have considered tumor transplantation merely
as a special kind of tissue transplantation. We would now attribute these
individual differences in the composition of the bodyfluids to the primary
differences in the individuality differentials which are present in the cells of
these animals, and these cellular differences are associated with secondary
differences in the constitution of the bodyfluids. From such individual spe-
cific substances we distinguished growth substances of an intrinsic character,
inherent in the tumor cells, and representing the essential stimulus to tumor
growth, and lastly, extraneous growth substances, especially certain hor-
mones, such as those given off by ovarian structures, and other similar sub-
stances, which were able to influence tumor growth as well as the growth

TUMORS AND NORMAL TISSUES 343

of certain tissues. We concluded further that when the intrinsic factor,
which represents the essential stimulus to tumor growth, is very strong,
then the substances which determine to what extent tumor cells are able to
live in other individuals — the individuality differentials — may become less
important in determining the fate of the transplanted tumor. However, there
is a limit as to the differences between the individuality differentials of host
and transplant if the intrinsic growth stimuli shall be able to assert them-
selves. This would represent a special instance of the more general rule that
the action of efficient growth stimuli, or expressed differently, a strong
growth momentum, may make it possible for tissues to overcome conditions
which are unfavorable, not only to the growth but also to the life of these
tissues.

Subsequent experiments of others have confirmed these observations and
conclusions. Thus Borrel and Petit, Ribbert and Mann, obtained similar
results in horse, dog and cat, respectively, and Tyzzer, Apolant and Haaland
found the same differences between auto- and homoiotransplantation in
mammary carcinoma of the mouse. While only a relatively small number of
spontaneous mouse carcinomata can be readily homoiotransplanted, auto-
transplantation almost always succeeds. In accordance with these concep-
tions also, were the subsequent findings of Haaland (1910) that inoculation
of a transplantable tumor in a mouse did not prevent the later development
of a spontaneous tumor in this animal ; nor did the growth of the trans-
plantable tumor affect metastasis formation or a subsequent autotransplan-
tation of a spontaneous autogenous tumor. Conversely, Haaland observed
that the presence of a spontaneous tumor did not noticeably influence the
take or the secondary retrogression of a transplantable tumor. Bashford
interpreted these differences between the behavior of the transplantable
tumors and of spontaneous tumors as an indication that the conditions of
transplantation differ from those which determine the origin of a spon-
taneous tumor; he did not attribute them to differences in the individuality
differentials of host and transplant. While it is true that the conditions deter-
mining the first origin of a tumor and its transplantability are different, the
essential factor is that a spontaneous tumor represents an autogenous tissue,
possessing essentially the same individuality differential as the other tissues
of the indvidual in which the tumor originated, whereas the tumor trans-
planted into another individual of the same species represents a homoiog-
enous tissue with an individuality differential which differs to a greater
or lesser degree from that of the host.

While the growth of a homoiotransplanted tumor does not need to affect
the autotransplantation of a spontaneous tumor, there are some observations
which indicate that a spontaneous (autogenous) tumor may, under certain
conditions, influence the growth of a homoiotransplanted tumor. Thus it
seems that spontaneous mouse tumors, which, as we have seen, in the ma-
jority of cases are very difficult to transplant into other individuals, can
apparently be more readily homoiotransplanted when the host is also the
bearer of a spontaneous tumor (Loeb, 1907; and Loeb and Fleisher, 1913

344 THE BIOLOGICAL BASIS OF INDIVIDUALITY

and 1916). A similar but more casual observation has been made also by
Apolant. In recent experiments from our laboratory, Blumenthal confirmed
this difference between the transplantability of spontaneous tumors into
normal mice of different strains and into mice which are bearers of other
spontaneous tumors. However, this condition was found only if the hosts
were below the age of 12 months, while in older mice, the growth of a
spontaneous tumor did not enhance the result of homoiotransplantation.

The importance of the relations between the individuality differentials
of host and tumor was quite definite in experiments in which we compared
the effects of the extirpation of a spontaneous autogenous and of a homoio-
transplanted tumor on the growth of a second homoiogenus tumor. In this
connection we must first refer to the important experiment of Uhlenhuth,
Haendel and Steffenhagen, who found that if they inoculated a trans-
plantable rat tumor into a rat and the transplant took, it was possible to
inoculate the same rat successfully with a second homoiogenous tumor. But
if previous to the second inoculation the first homoiogenous tumor had
been extirpated, the animal was immune and the second inoculation was
unsuccessful. However, if the extirpation of the first tumor had been in-
complete and the part which had been left behind grew again, then a second
inoculation with the homoiogenous tumor was successful. These observa-
tions were controverted by some investigators; especially by Russell, and
also by Woglom. The effect of the extirpation of the first tumor, if present
at all, was attributed by these authors to the non-specific effects of the
operation, and the immunity following the extirpation of the first tumor
was accordingly designated as an "operative immunity". But, the experi-
ments of Fleisher and the writer showed that the observations of Uhlenhuth
and his collaborators were essentially correct, at least as far as certain
types of tumors are concerned, among which may be included our trans-
plantable mouse carcinoma IX. We found that extirpation of this tumor,
when growing in a homoiogenous mouse, prevented the successful second
inoculation with this tumor. Evidently the growth of the first tumor had pro-
duced an immunity, which became noticeable only after the first tumor had
been removed. Furthermore, it could be shown that if pieces of carcinoma IX
were transplanted, not into a normal mouse but into a mouse which, in ad-
dition to a first inoculated tumor, was also the bearer of an autogenous
spontaneous tumor, the Uhlenhuth effect was also readily demonstrated as far
as the influence of the transplanted tumor was concerned; but if we extir-
pated instead of the first homoiogenous tumor, the autogenous spontaneous
tumor, no immunity was conferred on the mouse against a second inocula-
tion with homoiogenous mouse carcinoma IX. This proves that the immunity
conferred by the extirpation of the first tumor is not a non-specific "opera-
tive immunity", but must be due to a specific relation between the individuality
differentials of the growing tumor and of the host. The individuality dif-
ferential of the transplant differs from that of the host and of the spon-
taneous autogenous tumor, the autogenous tumor and the normal tissues of

TUMORS AND NORMAL TISSUES 345

the host possessing in all probability the same or almost the same individuality
differential.

The most probable interpretation of this experiment seems to be that the
growth of the first homoiogenous tumor causes the production of an im-
mune substance, injurious to the growth of this tumor. However, this in-
jurious substance is, to a large extent, absorbed and neutralized by the growing
homoiogenous tumor itself. If now this tumor is extirpated, the immune sub-
stance is no longer neutralized and it is thus able to prevent the growth of a
second homoiogenous tumor. Besides, this immune body must carry a differen-
tial able to combine with the homoiogenous differential of the transplanted tu-
mors, while the tissues of the host animal, as well as those composing the
autogenous tumor, being the bearers of an autogenous differential, are not able
to remove and to neutralize this substance. Substances which carry a homoiog-
enous individuality differential may then induce in the host immune re-
actions antagonistic to the growth of homoiogenous tumors, but they are
not absorbed and neutralized by autogenous tissues. It would be of interest
to determine whether the immunity procured in the Uhlenhuth phenomenon
is a specific one, directed only against a certain homoiogenous tumor, or
whether it also protects against other types which carry different homoiog-
enous individuality differentials. In accordance with this interpretation
it may then be concluded that antibodies are produced by growing homoiog-
enous, but not by autogenous tumors, and furthermore, that such antibodies
are neutralized by homoiogenous but not by autogenous tissues ; but at any
given time, the amount of such antibodies circulating in the bodyfluids may be
too small for direct demonstration by the ordinary serological methods.

There is another set of experimental data which confirms and further
extends these conclusions as to the importance to be attached to the difference
between autogenous and homoiogenous differentials. It has been found possible
(Schoene, Bashford) to immunize mice, although only to a limited extent,
against the growth of a homoiogenous, transplantable mammary carcinoma
by a previous inoculation of normal tissues, such as erythrocytes, embry-
onal material, liver and spleen. As a matter of routine, the tissue used for
immunization was taken from other animals of the same species. Woglom
however, tested the immunizing power of a piece of the animal's own spleen.
At first he believed that the inoculations of such autogenous tissue also pro-
duced a positive result, but the subsequent experiments of Apolant and
Marks, as well as of Woglom himself, showed that neither the animal's
own spleen tissue nor its erythrocytes had any demonstrable immunizing
action, while inoculation of the tissue of other animals of the same species
was effective. We may then state that a difference in individuality differen-
tials is a prerequisite for the production of immunity, that it is presumably
the strange differential itself which is concerned in this process of immuni-
zation, and that identity of organismal differentials, in the immunizing ma-
terial and in the animal which is to be immunized, precludes an effective
immunization ; this observation is in harmony with the fact that a transplant

346 THE BIOLOGICAL BASIS OF INDIVIDUALITY

possessing the same organismal differential as the host, does not elicit an
antagonistic reaction ; it does not act as a stimulus.

There are on record, however, some observations which apparently do not
agree with these conclusions. (1) According to Murphy, it is possible to
influence the growth of transplanted homoiogenous or heterogenous tumors
through the application of a method which affects the number and activity
of lymphocytes of the host; an increase of the latter is believed to initiate
or to intensify the mechanism of defense against the transplanted piece of
tumor, while a diminution in the number of lymphocytes makes possible
the growth of tumors, which otherwise would not have occurred. But of
special interest is the additional finding that the change in lymphocytes is
effective not only against homoio- and heterotumors, but also against pieces
of autotransplanted tumors. An experimentally produced increase in the
number of lymphocytes was found to diminish markedly the ability of the
autotransplanted tumors to grow and to develop. However, in this case we
may have to deal with a non-specific effect exerted on the tumor cells by
lymphocytes without the intervention of organismal differentials. (2) Fibiger
and Miller, in the course of experiments, in which they produced carcinomas
through often repeated applications of tar to the skin of mice, found in a
certain number of instances that metastases of these cutaneous cancers took
place spontaneously in the lung and elsewhere. Now if these animals, during
the period when the tar was applied, were inoculated several times with
mouse embryo-skin, the number of metastases was thereby diminished. There
would then be involved, in these experiments, apparently an effect of homoiog-
enous material on autogenous tissue. If these observations should be correct,
we would have to assume that also in this case we had to deal with conditions
of a non-specific nature, which affected unfavorably the growth of the
transplant. In this connection we may recall the more recent findings of
Murphy and Sturm, who showed that in embryo-skin substances are present
which inhibit tumor growth and may cause the regression even of spontaneous
tumors. (3) Lumsden found that when he made repeated injections of the
euglobulins from the serum of sheep, which had been immunized against
either human, rat or mouse tumors, into or around a spontaneous mouse
tumor and then extirpated the tumor and autotransplanted a part of it, the
autotransplants did not grow in the large majority of cases, although homoio-
transplantation of these tumors into other mice would succeed ; furthermore,
as a rule the tumor did not recur after excision. He attributed this result
to the development of an immunity against its own tumor in the mouse, and
believed that this immunity was due to the absorption of tumor material. But,
this type of imunity has apparently not yet been tested by inoculating one
of the transplantable tumors in such a mouse. In accordance with such an
interpretation, it would be necessary to believe that there is present in the
autogenous tumor, in addition to the organismal differentials, still another
constituent which calls forth this reaction. This constituent might be an
organ differential or it might be a specific stimulus to tumor growth, in the
latter case an "antimalignancy" constituent, in the sense of Lumsden.

TUMORS AND NORMAL TISSUES 347

However, according to this investigator the serum of rats immunized against
a rat tumor does not affect autogenous macrophages of the immunized animal
or those of another immunized rat, although it may injure macrophages of
the rat spleen, which are homoiogenous in nature.

The analysis of the individuality differentials will be continued in the next
chapters, where we shall further discuss immunity against tumors and
hereditary factors as they apply to tumor transplantation.

Transplantation of Heterogenous Tumors and the
Species Differential

In heterotransplantation of normal tissues we observed not only survival
of the transplants, but also growth phenomena in some of the tissues, but
both of these processes had a very limited duration, and growth, if it took
place, was much weaker than after homoiotransplantation of the correspond-
ing tissues ; furthermore, the proliferative processes ceased sometime previous
to the death of the grafts. We also noted that different kinds of tissues showed
different degrees of resistance to the injurious action of the primary, pre-
formed heterotoxins. While more sensitive tissues, such as thyroid, kidney,
and also skin, were destroyed so rapidly that a pronounced cellular (lympho-
cytic) reaction on the part of the host tissue against the transplant could not
develop, or was much diminished in intensity, heterotransplanted cartilage
proved more resistant, and it lived long enough to allow a very marked
connective-tissue reaction as well as an accumulation of polymorphonuclear
leucocytes and lymphocytes around the graft.

If instead of using normal tissues, we carry out heterotransplantation of
tumors, the results are in principle the same, although there exist some
quantitative differences, which are due at least partly to the greater prolifera-
tive momentum inherent in tumors. In addition, the possibility must be con-
sidered that tumors manifest a greater power of adaptation to certain injurious
conditions than normal tissues, and, as we have seen, they may be able
to neutralize, in some way, substances which tend to inhibit their growth.

Under these circumstances, it is to be expected that the range of condi-
tions under which tumors can grow should be somewhat wider than that of
normal tissues after homoiotransplantation as well as after heterotransplan-
tation, though as a rule, tumors are about as sensitive to heterotoxins as are
normal tissues. After heterotransplantation of tumors there may be a pre-
liminary period during which the growth may be quite active; but soon it
ceases, degenerative processes set in, and the tumors are destroyed. The
degree of growth and the duration of this preliminary period depend upon
the inherent proliferative momentum of the tumor, the sensitiveness of the
tissues of which it is composed, and the degree of difference between the
species differentials of host and of transplant. Only if the species of donor
and host are very nearly related may the growth be more intense and the
growth period of greater duration. Thus heterotransplantations between rats
and mice may succeed relatively well, temporarily ; but the results are much
more unfavorable if less nearly related species are used. Also, in the case

348 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of normal tissues we found that the degree of species-relationship between
host and donor may influence to some extent the result of heterotransplanta-
tion. Furthermore, especially those tumors which grow rapidly after homoio-
transplantation may be expected to grow actively also after heterotransplan-
tation ; therefore, a rapidly growing sarcoma may be especially well suited for
heterotransplantation. There may perhaps be in addition some special condi-
tions which may enable cancer tissues to overcome more readily than normal
tissues the unfavorable effects of heterogenous transplantation.

However, in general, the injurious effects which take place in strange
species are cumulative and lead gradually to the death of the transplant.
By re-transplanting the tumor into an individual belonging to the species in
which it originated, such a cumulative action may be prevented, or at least
delayed, and the tumor given a chance to recover to some extent from the
injury received by the hetero toxins. After such a recovery has taken place, it
may be possible to transplant the tumor again into the strange species, and
this process may be repeated a number of times. Such a procedure was used
by Ehrlich in heterotransplantation of mouse tumor to rat and he called it
zigzag transplantation. The conditions are here, to a certain extent, com-
parable to those prevailing after injuring the tumor by exposure to graded
degrees of heat; then, also, a recovery may take place after transplantation
into a new host. But there are indications that even after transplantation into
relatively nearly related species a gradual and slowly cumulative injury does,
as a rule, take place eventually; while after transplantation into more dis-
tantly related species, as for instance, from mouse to guinea pig, a repeated
heterotransplantation, with intermediate recovery periods, in the original
species would in all probability be impossible.

However, it is not only the cumulative action of the preformed heterotoxins
which prevents the continued growth of a tumor in a strange species, but in
addition, it is the active immunity developing in the host against the heterog-
enous differential which helps to injure and destroy the transplant. Such an
immunity against heterogenous tissues can be elicited much more readily and
effectively than against homoiogenous tissues, and when it is well established,
the critical period sets in. It might therefore be expected that if the injurious
action of these immune heterotoxins were avoided by re-transplantation of
the heterogenous tissue into a new, not yet immunized individual of the
strange species, the results might be improved, provided we had to deal with
relatively resistant and rapidly growing tumors. Such a condition apparently
has been realized in more recent experiments by Ito in transplantation into
rats of a squamous cell tar carcinoma experimentally produced in a mouse.
This mouse carcinoma could be transplanted for many generations into rats
if a re-transplantation into a new host was carried out every five or six days.
But if the transplant was allowed to remain as long as ten days in the
heterogenous host, it became entirely necrotic. It must be assumed either that
an increased growth momentum, acquired during their transformation into
cancer, made it possible for these cells to overcome the injurious action of
the natural heterotoxins better than normal tissues, or that a diminished sensi-

TUMORS AND NORMAL TISSUES 349

tiveness to these substances, or a greater power to absorb and neutralize them
was responsible for the increased resistance. That these tar cancer cells, how-
ever, still possessed the species differential of the mouse is indicated by the
fact that it was possible to elicit an active immunity against them by a previous
immunization of a rat with mouse liver serving as an antigen. But the best
known experiments of this kind are those of Putnoky, who has been able
to propagate an Ehrlich mouse carcinoma continuously in rats since 1929
by re-transplanting it every ten days. This mouse tumor grew very rapidly in
rats for from ten to fourteen days, during which time many rats were killed
by its growth. Following this period, necrosis and death of the tumor set in in
animals which survived. In other series of heterotransplantations, various
investigators have succeeded in keeping mouse tumors alive in rats and in
inducing temporary growth, but invariably the growth energy has decreased
after a number of successive rat to rat transplantations and then the tumors
died out, although after re-transplantation to the mouse, if the tumor had not
been too seriously injured, it could be propagated indefinitely.

Why is it that in these few instances it has been possible to propagate
indefinitely, under the conditions mentioned, the mouse tumor in rats? Pre-
sumably the various factors enumerated above were responsible for its
successful development in heterogenous hosts. The tumor chosen by Putnoky,
being a very rapidly growing one, the growth momentum of the cells could
overcome injurious conditions up to a certain limit. This marked growth
intensity found a morphological expression in the small amount of stroma
present in this carcinoma. It was to be expected that such a rapidly growing
tumor would be able to absorb and neutralize a larger quantity of either
natural or immune heterotoxins than would a slowly growing tumor. Addi-
tional factors to be considered in these heterogenous tumor growths are the
greater power of resistance of the tumor cells and, furthermore, the strain of
rats into which the transplantations are made. Putnoky found that the constant
propagation of the Ehrlich mouse carcinoma in rats succeeded only if a Hun-
garian strain of rats was used ; in English rats the tumor regressed spontane-
ously after about ten or fourteen days. This explains why several other investi-
gators, who used other than Hungarian strains of rats, were unable to obtain
equally favorable results. However, more recently de Baloghi succeeded in
repeating Putnoky's experiments with another strain of Ehrlich mouse carci-
noma. This tumor behaved biologically and structurally in a similar way to
Putnoky's tumor; but de Baloghi obtained long-continued heterogenous
growth in diverse races of white and gray rats. The favorable results noted
in these experiments were therefore not primarily due to racial factors in the
host, but apparently to the selection of the most vigorous tumors possessing
a great growth momentum.

There remains the question as to whether the differences in the growth
of different mouse tumors in the rat are due to a change in the genetic con-
stitution of these tumors, implying a difference in their organismal (species)
differentials. There is no definite reason for assuming such a change. These
rat tumors can readily be re-transplanted into mice, where they grow in the

350 THE BIOLOGICAL BASIS OF INDIVIDUALITY

usual active way without undergoing regression. This conclusion is also con-
firmed by the fact that regression of a Walker rat carcinoma or a Jensen rat
sarcoma did not cause immunity against the growth of the Ehrlich-Putnoky
tumor. If the carcinomatous cells had assumed, at least partly, the species
differential of the rat, the immunity against the growth of a rat tumor caused
by the previous retrogression of a rat tumor in rats should have affected also
the Putnoky tumor. On the other hand, the growth of the Ehrlich-Putnoky
rat-strain tumor in rats can be prevented by previous inoculation of mouse
embryo-skin into the rats. This again indicates that the tumor cells still pos-
sessed the species differential of the mouse. If inoculation of mouse embryo-
skin induces only a slight retardation of the growth of the Ehrlich-Putnoky
tumor in the mouse, this is presumably due to the very strong growth mo-
mentum which this tumor possesses in mice. In a similar way, Purdy found
in heterotransplantation of fowl tumors into ducks, ducks were made immune
to the fowl tumors by a previous implantation of chick embryo, but not of
duck embryo.

However, there is one observation which might suggest that an actual
change in the species differential of the Ehrlich-Putnoky tumor growing in
rats has taken place. After regression of such a rat-propagated tumor in rats,
the latter have acquired an active immunity against the growth of subsequently
inoculated Walker and Jensen rat tumors ; rat-propagated Putnoky tumors
are more effective in this respect than are Ehrlich mouse-strain carcinomas.
But this difference may perhaps be due to the fact that the Ehrlich-Putnoky
rat-strain tumors grow much more vigorously in rats than do mouse-strain
tumors ; they may therefore be expected to induce a higher degree of im-
munity. While there is no reason for assuming that the genetic constitution
of the mouse carcinoma cells has been transformed into the genetic constitu-
tion of the rat, or that the better growth of these cells in the rat was made pos-
sible through a gene mutation or chromosomal change in these somatic cells,
still it is possible that certain adaptive changes have gradually taken place in
the Ehrlich-Putnoky tumors, which make them more able to overcome the
injurious conditions existing in the rat after long-continued propagation in
this strange species. Also, in other series of heterotransplantations, adaptive
changes of this kind seem to have occurred. These may consist in a gradually
increasing growth energy of the tumors in the rat, or in an increasing resist-
ance to the injurious rat substances, perhaps caused by a more active absorp-
tion and neutralization of such substances by the growing tumor cells. That
such an adaptation may take place after heterotransplantation is indicated,
also, by the fact that at first the temporary growth of the Ehrlich-Putnoky
mouse tumor was accomplished only in very young rats, in which the reac-
tion against strange differentials is less marked than in adult animals, and
that only in the course of continued transplantations in the rat did the tumor
begin to grow well, at least for some time, also in young adult rats. In addi-
tion to these adaptive changes, it is conceivable that in the course of continued
re-transplantations into rats those metabolic cell activities which lead to the
production of the organismal differential, and which in the last analysis

TUMORS AND NORMAL TISSUES 351

depend upon the genetic constitution, may perhaps have been slightly modified,
and that such a modification may have facilitated the growth of the mouse
tumor in the rat ; but we do not possess any definite knowledge as to wherein
such adaptive processes consist.

There can be little doubt that even under the most favorable conditions a
heterotransplantation of a mouse tumor into rats, which would lead to a
permanent growth in the latter, cannot be accomplished. There remains a
difference between the growth of these tumors in the rat and in the mouse,
and there also remains a difference between the growth of rat-adapted mouse
tumors and real rat tumors in the rat. It is therefore not possible to conclude
that a heterotransplantation has been fully successful in these experiments.
Furthermore, we must not identify mouse-to-rat transplantation with hetero-
transplantation in general. There can be no doubt that transplantation of
mouse tumors into the subcutaneous tissue or into the peritoneal cavity of
farther distant species would have a much more unfavorable outcome and that
such tumors would undergo rapid necrosis.

While the data concerning the degree to which transplantation of tumors
from mouse to rat is possible may be considered as well established, and
while these data are not in conflict with the conclusion that the concept of
organismal differentials applies also to the transplantation of tumors, there
have been recorded, from time to time, observations which make it appear
that cancers can be successfully transferred also into widely distant species.
If this were a fact, it would be contradictory to what is known about the
significance of organismal differentials in determining the fate of transplants.
Thus it has been stated that human tumors can be transplanted to dog, rabbit
or rat; however, should a tumor develop in the new host following such a
transplantation, there is the possibility that it may have been a spontaneous
growth ; it is very improbable that the growth was derived from the heteorog-
enous cells. In the case reported by C. Lewin many years ago, the transplant-
able tumor, which formed in the rat following transplantation of pieces of
human cancer, was of a very low degree of specificity and was apparently
constituted of cells which usually take a prominent part in inflammatory
reactions.

In heterotransplantations of normal tissues we have seen that the toxic
action of the bodyfluids of the host is much more evident in the destruction
of the transplant than in homoiotransplantations. Although in the latter the
toxicity of the bodyfluids does injure the transplant, the cellular and vascular
reactions of the host are, here, relatively more important. Likewise, hetero-
transplanted tumors are primarily injured by the heterotoxins of the body-
fluids of the host, although cellular reactions may secondarily participate in
the destruction of the graft.

Since, after homoiotransplantation of a tumor, even in an animal im-
munized against it, it is usually the central part of the graft which dies first,
while after heterotransplantation in an immunized animal the peripheral, as
well as the central, part shows signs of injury, it has been assumed that im-
mune substances exert their injurious action only on heterotransplants, and

352 THE BIOLOGICAL BASIS OF INDIVIDUALITY

not on homoiotransplants. However, the primary degeneration of the more
central parts of a homoiotransplant is due to the more unfavorable condition
of these areas, involving a deficiency of oxygen and possibly also of other
foodstuffs during the period directly following transplantation; the central
portions of the tumor may therefore be more accessible to the action of the
injurious homoiotoxins, while in the peripheral parts these toxins are not
strong enough to destroy tissues which live under relatively favorable condi-
tions. On the other hand, the more active heterotoxins, especially the immune
heterotoxins, may accomplish a direct injury also of the peripheral parts.

The reaction against homoiogenous tumor transplants depends, at least in
part, on the development of an active acquired immunity in the host ; whereas,
in the case of normal homoiogenous tissue transplants, the injurious effect
seems to be due largely to the action of primary homoiotoxins and to the
direct response on the part of the host tissues. Similarly, while in the case
of heterotransplanted normal tissues the preformed heterotoxins and the
activity of the cells of the host play the principal role, and immune hetero-
toxins seem to enter into the reaction only secondarily, in the case of hetero-
transplanted tumors the effect of active immunization can be more readily
demonstrated. Through a previous inoculation with normal tissues from
the heterogenous species to which the tumor belongs, immunization of the
host can be accomplished and the destruction of the tumor transplant can
be much accelerated. While under these circumstances the action of the im-
mune heterotoxins is the most important agency that causes the rapid destruc-
tion of the transplant, an intensified reaction on the part of the lymphocytes
may play a part here, as well as after homoiotransplantation of tumors into
actively immunized animals ; it is by means of this accumulation of cells
around the graft, rather than by a lack of ingrowth of connective tissue and
blood vessels from the host into the transplant, that the incompatibility
between the differentials of the host and transplant may become manifest.

We may then conclude that in the case of tumors, as well as of normal
tissues, it is primarily the primary, performed heterodifferentials which call
forth the reaction of he host tissue against the transplant, and that it is these
heterotoxins which injure the transplanted tumor. Secondarily, such hetero-
differentials may act as antigens and call forth the production of immune
heterotoxins, which are especially effective in the case of tumor transplants;
associated with this process may be an intensification of the cellular reaction.
Tumors are the descendents of normal tissues; they have retained the or-
ganismal differentials of the latter in all essential respects ,and they call forth,
therefore, the same primary reaction in the hosts. But some changes take
place in the normal tissues during their transformation into tumors and it is
in consequence of these changes that tumor tissues differ in certain respects
from normal tissues in their transplantability and in the reactions they call
forth in the host.

That, however, notwithstanding these modifications the organismal differ-
entials of the tumors play a significant role in transplantation, is also made
evident by the fact that in order to accomplish an immunization against a

TUMORS AND NORMAL TISSUES 353

heterogenous tumor, one must use heterogenous tissue of the same species as
that in which the tumor originated. For instance, if one wishes to immunize
a rat against a mouse carcinoma, the rat must be inoculated with normal
mouse tissue, and such an immunization cannot be accomplished by inoculating
rat or guinea pig tissues into the rat. Correspondingly, an immunity against
a homoiogenous tumor can be attained only by the inoculation of tissues
from the same species : a mouse can be actively immunized against a mouse
tumor only by means of mouse tissues. Now we know that in the tissues used
for heteroimmunization there are present in addition to the heterodifferentials,
homoiodifferentials ; but evidently the presence of the heterogenous differen-
tials in some way prevents the homoiodifferentials from becoming effective un-
der these conditions. We see, then, that the organismal differentials play a role
in immunization against heterogenous as well as against homoiogenous tumors.

The direct action of heterotoxins, and especially of immune heterotoxins —
but not of homoiotoxins — on tumor tissue, can also be demonstrated in tissue
culture. While, as Lambert and Hanes have found, rat sarcoma grows in
vitro as vigorously in plasma from immune rats as in the plasma from normal
or tumor-bearing, non-immunized rats, the immune heterogenous serum from
guinea pigs immunized against rat sarcoma has a toxic action on this tumor
in tissue culture. It also exerts such an effect on rat-embryo skin. Other
authors, such as Gussio, Mottram and Rous, likewise were unable to demon-
strate the injurious action of homoiotoxins in tissue culture. Furthermore,
Rous, and subsequently Kross, did not succeed in demonstrating the existence
of homoiotoxins by means of parabiosis, in which substances produced in
one animal are supposed to be transferred directly to the circulation and thus
to the tissues of its partner. However, as shown in a previous chapter, factors
which complicate parabiosis and tissue culture make it necessary to accept
negative results obtained by means of these methods with certain reservations.
In the case of chicken sarcoma growing in vitro, A. Fischer found that not
only plasma from naturally resistant fowl was without any inhibiting effect,
but even the serum of geese, ducks and rabbits immunized with chicken
sarcoma did not prevent the proliferation of this tissue in vitro. However,
the lack of effects of homoiotoxins in tissue cultures may, at least partly, be
due to the fact that while in the living vertebrate organism the bodyfluids are
constantly circulating and new substances of a specific character are carried
to the transplanted tissue, in vitro the amount of such an injurious substance
which is able to act on the tissue is very limited, and the tissue can presumably
neutralize it to some extent; the results obtained in vitro are, therefore, not
comparable in every respect to those obtained in the living animal.

In a preceding part it could be shown that the homoiotoxins in the blood
stream of a homoiogenous animal may injure directly the transplanted normal
cells. This is more noticeable in some species than in others, and especially it
is noticeable if the difference between the individuality differentials of host
and graft is relatively great and if the transplanted tissue is sensitive. There
are indications that immune substances may be formed as a result of a first
transplantation, which cause an acceleration of the reaction against the

354 THE BIOLOGICAL BASIS OF INDIVIDUALITY

transplanted tissues. More marked than the injurious effect of the homoio-
toxins is that of heterogenous bodyfluids, containing heterotoxins, on trans-
planted tissues; these heterotoxins damage all transplanted tissues without
the cooperation of host cells. The action of sera on tumor cells has been
studied particularly by Lumsden and his coworkers. They distinguish: (1)
homoiotoxins which develop, for instance, in a rat after immunization with
Jensen rat sarcoma and rat spleen. They injure cancer and normal wandering
cells from the same species in tissue culture, but not other kinds of normal
tissue cells. These substances are heat-labile and are contained in the euglobu-
lin fraction of the serum; (2) normal heterotoxins which are injurious for
cells of all other species. They are very heat-labile and are also contained in
the euglobulin fraction ; they can be increased in quantity through immuniza-
tion; (3) immune heterotoxins which are directed specifically against the
species which has been used for immunization. These are stable, heat-resistant,
and are contained in the pseudoglobulin fraction; (4) and possibly in addition
to the species-specific antibodies, tissue- or organ-specific immune substances.
Lumsden believes that there is evidence as well that "anti-malignant" immune
substances develop in response to inoculation of cancer tissue into animals
of the same species in which the cancer originated, for instances, in response
to inoculation of the Jensen rat sarcoma into rats. These sera would act not
only on the kind of cancer which was used for immunization, but also on
various other types of cancer, irrespective of the species in which they
originated. However, other investigators (Phelps) find that such sera are
not specific for cancer cells, but contain heterotoxins which act equally well
on normal cells of the species to which the antigen belonged. Lumsden,
Macrea and Skipper themselves noted that such "anti-malignancy" sera kill
also young, not as yet much differentiated macrophages emerging from spleen
cultures; however, these sera do not affect the macrophages of the producer
of the antiserum. This is presumably due to the fact that in the latter case we
have to deal with autogenous cells, while the ordinary "anti-malignancy"
sera act either on homoiogenous or heterogenous cells. At present it appears
doubtful whether such anticancer sera exist. However, it is very probable
that heterogenous, and also homoiogenous cancer growth in an animal may
call forth the production of immune substances much more actively than do
normal adult tissues; but strange embryonal tissues likewise produce im-
munity, and it is very probable that the more active growth of cancerous
tissue as compared with inoculated adult normal tissue is at least one of the
factors that is responsible for the difference in the effectiveness of these
various tissues serving as antigens.

By a different method Woglom attempted to prove the existence of im-
mune substances in the serum of rats inoculated with rat sarcoma 39, after
the spontaneous retrogression of these tumors. He absorbed the immune
substances which were present in the blood of these rats by means of a
mash of sarcoma 39. After subsequent extraction of the immune substances
from the sarcoma mash with Locke solution, this extract inhibited the growth

TUMORS AND NORMAL TISSUES 355

of a sarcoma emulsion on which it had acted for a few hours. Similar extract,
in which serum of normal rats had been used, was ineffective.

The experiments of Lumsden are in accordance with the conclusions at
which we arrived in our experiments with normal tissues, namely, that
primary (natural or preformed) heterotoxins in the host exert a direct
injurious effect on the transplant; the presence of the heterodifferential in
the transplanted tissues is responsible for the accumulation of lymphocytes
and polymorphonuclear leucocytes and for the marked development of fibrous
tissue around the graft. Various observations have made it probable that
secondarily there is superimposed upon the natural preformed heterotoxin,
a secondary immune heterotoxin, which is especially readily demonstrable
in the case of tumor grafts. There is reason for assuming that the hetero-
differentials may act as antigens, which lead to the production of the immune
heterotoxins.

Experiments in heterotransplantation into related species have been carried
out, not only with mammalian tumors, but also with certain of the filterable
chicken sarcomata and related fowl tumors which can be transmitted to other
birds by the inoculation of tumor cells as well as by means of an agent
separable from cells. Fujinami transferred -his chicken myxosarcoma to ducks
and propagated it here serially through forty generations. Gye, by means of
filtrates or of cell suspensions, could transmit the same tumor serially to
ducklings, but in half-grown or adult ducks the tumor could grow only for
some time and it later regressed. But Purdy succeeded in transmitting it
serially to ducklings as well as to adult ducks by injecting very large amounts
of minced tumor tissue. There is some reason for believing that the chicken
tumor cells, as such, were able to grow in the heterogenous host, because it
has been found possible to elicit a certain degree of immunity against the
fowl tumor by a previous injection of minced fowl-embryo into the ducklings.
It is of interest that a chick in which a Fujinami tumor happened to regress,
had thereby acquired an immunity against a Fujinami sarcoma but not
against a Rous tumor.

As to the heterogenous transfer of Rous chicken sarcoma, Purdy was not
able to accomplish this in adult ducks by injection of large amounts of virus-
containing extracts, but by transmitting large quantities of minced tumor
tissue he could transfer Rous sarcoma through several generations of very
young ducklings ; he was unsuccessful in similar experiments with adult ducks.
Des Ligneris likewise had negative results when he used adult ducks and also
geese, but he succeeded in transferring the tumor to turkeys and guinea fowls.
Not all such chicken tumors, however, can be transferred into foreign species ;
growth did not take place with Begg's endothelioma. If it is then probable
that at least in some of these instances we have actually to deal with a success-
ful transplantation of tumor cells into heterogenous hosts, we must not lose
sight of the fact that host and donor belonged to relatively nearly related
species, and furthermore, that it is not ordinary tissue cells which developed,
but cells stimulated to grow by an agent which has invaded them ; moreover,

356 THE BIOLOGICAL BASIS OF INDIVIDUALITY

it is of importance to note in this connection that cells of a less differentiated
nature composed these tumors. Moreover, different types of fowl tumors
differed in their ability to grow in heterogenous hosts and, likewise, different
races of certain avian species differed in their suitability as hosts. The transfer
of the tumor by large amounts of tumor cells was, on the whole, more suc-
cessful than the transfer by means of virus-containing tumor extracts. In
general, fowl sarcoma could be transmitted much more readily to newly
hatched heterogenous birds than to somewhat older ones.

According to the quite recent experiments of Duran-Reynals it can be
shown that if we transfer Rous fowl sarcoma I to ducklings, at first the un-
changed chicken tumor virus or cells cause the tumor development in these
ducklings, as indicated by the fact that the tumors thus produced have not
only the same morphological characteristics as the original chicken tumor, but
they also possess the same tissue affinities and the same tendency to develop
in certain regions of the host. However, after the tumors have lived for some
time in ducklings, they may change their characteristics, the chicken-adapted
virus becoming duck-adapted virus; it tends to cause sarcomas in organs,
different from those in which it grew at first, growing now in bones or
lymph glands, calling forth a lymphosarcoma in the latter organ. Further-
more, this changed tumor tends to become generalized. A similar adaptation
seems to occur if tumor cells are inoculated ; these also cause the same kind of
tumors as the duck-adapted virus. Such a duck-adapted virus or cell suspen-
sion induced not only tumor formation in ducklings, but also in adult ducks.
Cells and viruses are now no longer heterogenous but homoiogenous elements
for the duck. If such duck-adapted virus or cells suspension is transferred
back into chicken, it seems at first to behave like material heterogenous for the
chicken, but after some time, the duck-adapted virus or cell suspension can
again become chicken-adapted, being thus converted into a homoiogenous
virus for the chicken. However, it should not be concluded from these ex-
periments that a chicken cell was actually transformed into a duck cell, but it
seems, merely, that the changed virus altered secondarily the tumor-producing
characteristics of the chicken cells in which the virus lived.

We have seen that it is possible to a certain extent to protect transplanted
normal tissues against the injurious reactions which ordinarily take place in
the host, and by various means to diminish the reactions in the host which
follow as a rule transplantation of strange tissues. Thus homoiotransplants
induced less active reactions when younger hosts were used ; also when they
were made into the anterior chamber of the eye, into the brain, or after pre-
ceding injections of trypan blue. More striking differences have been observed
when similar methods were employed in the case of transplanted tumors, and,
indeed, experiments with tumor transplants preceded experiments of a like
nature with normal tissues. It has been found by Murphy that transplanted
heterogenous tumors, even if host and tumor were phylogenetically far distant,
grew for some time on the chorio-allantoic membrane of the chick; an ex-
periment with heterogenous embryonal tissue also succeeded; but as soon as
the development of the chick embryo had reached the stage at which the

TUMORS AND NORMAL TISSUES 357

spleen and other organs were fully differentiated, the growth ceased and the
transplant died. From more recent experiments, it appears that not only the
allantoic membrane, but also the yolk-sac of the chick embryo, is suitable for
the growth of the heterogenous tumors (Taylor, Thacker and Pennington).
Shirai and Murphy noted a better growth of heterogenous tumors in the
brain than in the subcutaneous tissue ; the lymphocytic reaction was diminished
in these instances if contact with the meninges was avoided. Greene and Saxton
succeeded in transplanting into the anterior chamber of the eye of- rabbits,
homoiogenous tumors which failed to grow when the usual modes of trans-
plantation were tried. In 1937, a Russian investigator, Smirnova, observed
that human and mouse tumors grew from four to six months in the anterior
chamber of the eye of rats. Greene carried out successful serial transplanta-
tions of rabbit tumors in the anterior chamber of the eye of guinea pigs; a
human fibrosarcoma, and even a human scirrhous cancer of the mammary
gland, grew in this organ. The chick chorio-allantoic membrane, the brain and
the anterior chamber of the eye represent places where the aggressive reactions
on the part of the host are diminished. In a previous chapter we have dis-
cussed already, to some extent, the factors which make possible a better
growth of heterogenous embryonal and tumor tissues in these places and we
shall return to this problem later, when we' analyze the processes of immunity
which develop againts transplanted tumors. In this connection we may refer
also to long-continued growth of benign and malignant tumors in roller-tube
tissue cultures, in which the medium consisted of coagulated chicken plasma
covered by human serum (Gey, Coman).

Also by other means it was possible to improve the growth of tumors in
hosts bearing strange individuality or species differentials. Thus it was found
that after previous irradiation of the host by a sufficient dose of X-rays the
resistance of the latter against the growth of homoiogenous as well as of
heterogenous tumors was diminished (Murphy, Clemmensen and others).
Moreover, the transfer of mouse leucosis to otherwise unfavorable hosts
could be promoted by these means (Krebs, Furth). Not only tumor and
leukemic cells could thus be transferred more successfully, but also Shope's
rabbit fibroma virus, when injected into X-rayed or tarred rabbits, caused
generalized fibromatosis, the tumors showed a prolonged growth in these
animals and in one case the fibroma assumed a sarcomatous character (An-
drewes). According to Maisin and Masse, also minced embryonal chick tissue
develops, in chickens previously treated with tar, into larger embryomata,
which persist for a longer time. Injections of trypan blue and of other
colloidal substances (Lignac, Ludford, Andervont) diminish the resistance
to the growth of tumors in homoiogenous hosts, and in addition, trypan blue
inhibits the development of some types of immunity (Andervont).

These various agents, X-rays, colloidal dyes and tarring, act presumably on
the reticulo-endothelial system, the usual place for the production of general-
ized immune reactions. On the other hand, the possibility must be considered
that also the primary reactions against strange normal tissue, tumor or virus,
due to the presence of preformed substances, may depend upon the reticulo-

358 THE BIOLOGICAL BASIS OF INDIVIDUALITY

endothelial system. This is perhaps indicated by the fact that the lymphocytes
and leucocytes of the blood may react as early as within the first few days
against a homoio- or heterotransplant of normal tissue or tumor.

But there are several observations which indicate that the application of
X-rays, injections of tar, or perhaps even of trypan blue, may have results of
a quite different kind ; they may promote the induction of autogenous cancers
elsewhere in mice under the influence of tar or other carcinogenic substances
(Mayngord and Parsons, Maisin and Masse, Andervont). A related phenom-
enon is probably the effect of X-rays or tar on the development of rabbit
fibroma following the injection of virus mentioned above. In addition, Rous
and his collaborators produced carcinomata in rabbits through intravenous
injection of rabbit papilloma virus, in places where the skin had been irritated
through previous applications of tar. These effects cannot be due to an inhibi-
tion of immune processes developing against strange tissues or tumors and
their organismal differentials, but mechanisms of a different kind must be
active in these experiment.

Taken altogether, these experiments add further data in support of the
conclusion that in principle the host reacts in a similar way against normal
tissues and against tumors, but that secondary factors may be added in the
case of tumors, which may induce certain modifications in the types of reaction
which occur; and furthermore, that it is the organismal differentials which
normal tissues and tumors have in common.

Transplantation of Benign Tumors

We have, so far, analyzed some of the principal factors which determine
the growth of transplanted malignant tumors, with particular regard to the
significance of organismal differentials of host and transplant. It will be of
interest, now, to compare with the growth of cancerous tissue, that of benign
tumors. In experiments beginning in 1901, and continuing at various periods
during the course of the following thirteen years, we transplanted, at various
times, altogether four mammary fibroadenomata and two mammary fibromata
of the rat, and, with S. Leopold, a mixed mammary tumor, a chondromyx-
adenoma of a dog. Similar experiments were subsequently reported by Rib-
bert, Borrel and Petit, and more recently, by Mann, Robinson and Grauer,
Heiman, Heiman and Krehbiehl, Umehara, Picco, Oberling, and the Guerins,
Emge and Wulff, as well as by Wolfe, Burack and Wright.

From our investigations the following conclusions may be drawn : Benign
tumors show a reaction in certain respects intermediate between that of
normal tissues, which after serial transplantation manifest at most only a
very limited and transitory regenerative growth, and that of malignant tumors.
If they grow at all, they usually do so only very slowly and after a relatively
long preceding latent period, during which, however, mitotic proliferation may
occur. In the majority of cases we had to deal with tumors of the mammary
gland, which were composed of adenomatous as well as of fibrous constit-
uents, and both could take part in the subsequent proliferation; the fibrous
portion evidently did not represent merely the stroma of the epithelial struc-

TUMORS AND NORMAL TISSUES 359

tures, but a part of the tumor itself. The tumors grew, as a rule, only in the
same animal in which they originated and not in other animals of the same
species. The individuality differential, therefore, asserted itself under these
conditions. This was observed in some of our experiments, as well as in those
of Ribbert and Mann, but we, as well as subsequent investigators, found that
different benign tumors may differ in their power of resistance to homoio-
toxins, it being possible to transplant certain of them serially into other in-
dividuals of the same species. We observed, furthermore, that while after
transplantation of carcinoma or sarcoma, the greater part of the transplant
became necrotic and only a small peripheral zone remained alive, in the case
of these benign tumors of the mammary gland a greater portion of the pe-
ripheral tissue could be preserved, and in some autotransplanted tumors even
almost the whole of the transplant; evidently some of the constituent parts of
the tumors, especially the fibrous ones, were more resistant than very cellu-
lar and rapidly dividing malignant cells. In addition, while with malignant
tumors as a rule, an increase in growth energy occurred in the course of the
first few transplantations, such an increase was lacking with these adenofibro-
mata. In our experiments there was a gradual decline in the growth energy
after successive transplantations. Another difference between these two types
of tumors consisted in the different effects which hormones exerted on their
growth. Cancerous tissues, in particular carcinomas of the mammary gland,
are no longer accessible to the action of ovarian hormones, whereas a positive
effect was quite evident in the case of benign tumors of the mammary gland ;
such tumors retained the ability to respond with marked growth processes to
the action of hormones, which determine the growth processes in the normal
breast tissue during pregnancy. The cells of these adenofibromata evidently
had not changed their physiological characteristics to the same extent as the
cells of malignant mammary gland tumors. Moreover, while in our experi-
ments the tumors were propagated mainly in female rats they were able, also
to grow in male rats.

It may therefore be concluded that the fate of the transplanted benign
tumor depends not only on the organismal differentials, but also on its mode
of growth and some other factors, which are localized either in the tumor
cells themselves or are circulating in the bodyfluids of the host. Some of the
factors localized in the tumor cells correspond to those present also in normal
tissues, in particular, the organ or tissue differentials, which help to determine
whether a tissue is able to withstand the injury connected with autotrans-
plantation.

A further factor in determining transplantability is the increase in growth
energy acquired by normal tissues during their transformation into benign
tumors. This additionl growth is relatively slight, although it varies in different
benign tumors. Correspondingly, the morphological and biochemical modi-
fications, which the normal tissues undergo during their change into benign
tumors, are less marked than those which take place during their change into
malignant tumors. In this respect again, different benign tumors may behave
somewhat differently, and it should therefore be expected that they show a

360 THE BIOLOGICAL BASIS OF INDIVIDUALITY

different degree of transplantability. This is indeed a fact, as our own experi-
ments have already indicated and as the subsequent, more extensive experi-
ments of various investigators, especially those of Heiman, Emge and Wolfe,
and their collaborators, have shown. Thus certain benign tumors cannot even
be autotransplanted, while some others can be homoiotransplanted through
a number of generations. But when homoiotransplantation does succeed, the
latent period is usually long and the subsequent growth very slow.

Fibrous tissue was a relatively prominent constituent in many of the benign
tumors which so far have been used by various investigators for homoiotrans-
plantation ; it surrounds and protects the epithelial structures. It is very prob-
able that homoiotoxins are not given off to any considerable extent by tissues
of this kind, and hence accumulations of lymphocytes are not prominent after
homoiotransplantation of such tumors.

Subsequent experiments, especially those of Heiman, of Emge, and of
Wright and Wolfe, have contributed further data as to the influence of
hormones on the growth of these tumors. Castration of the host had a
marked effect, in the investigations of Heiman, and Heiman and Krehbiehl,
castration of female rats lowering, and castration of male rats improving the
transplantability. Furthermore, gonadotropic hormones, and still more so,
combinations of these hormones with estrogen, and also estrogen alone, could
promote very noticeably proliferative processes in these tumors, especially in
castrated female and male, as well as in normal male rats. However, while
application of these hormones was thus effective in intensifying growth ac-
tivity in these tumors, and in some instances especially in their adenomatous
constituents, it has not been possible so far to increase thereby the growth
energy to such an extent that a definite transformation into a carcinoma took
place. However, it seems that Wright and Wolfe succeeded, by means of
estrogen injections for as long as 50 days or more, in producing proliferations
in the epithelial parts of a fibroadenoma in rats, which seemed to be pre-
cancerous or perhaps represented beginning cancerous changes. On the other
hand, both Heiman and Emge were able, in some tumors, to stimulate the
growth of the connective-tissue constituent so markedly that a fibroma became
converted into a spindle-cell sarcoma; it seems that this stimulation was the
result of continued serial transplantations, but there are some indications that
in some cases also stimulation by pituitary-like hormones exerted similar
effects. The beneficial effect of gonadotropic hormones on the growth of the
tumors also in castrated females suggests a direct action on the tumor rather
than an action mediated by the sex glands. Androgenic hormones, on the other
hand, tended on the whole to diminish the number of successful transplanta-
tions of fibroadenomata of the mammary gland; an action which is in agree-
ment with the fact that castration in male rats, which means removel of the sex
hormones, raises the number of takes of these tumors. According to Heiman,
also progesterone inhibited the growth of the epithelial portion of the fibro-
adenoma, and it reduced the number of takes; still more effective in this
respect was a combination of testosterone and progesterone.

It may be assumed that the intensification of the growth energy of some

TUMORS AND NORMAL TISSUES 361

of these fibroadenomas of the mammary gland under the influence of cer-
tain hormones may enable them to overcome the resistance to their growth,
caused by unfavorable individuality differentials of hosts, and to grow, there-
fore, after homoiotransplantation. There were also some indications that there
exist strain differences, a certain tumor growing better in one strain of rats
than in another; presumably strains in which the individuality differentials of
the rats were similar to that of the tumor were more suitable than strains
with more strange individuality differentials.

While as the result of the growth or of the retrogression of transplanted
malignant tumors the bearers of the transplant may become immune against a
second transplantation, such an immunity has not been observed in the case of
benign tumors; the latter behaved in this respect, as well as in the lack of
adaptive processes and in their responsiveness to hormones, similar to normal
tissues, while as far as the growth energy and abnormal mode of growth is
concerned, they are intermediate between normal tissues and cancers. In
cancerous tissue the inner growth factor (Gi) has become so strong and
provides so stable a growth momentum to the tumor cells that extrinsic fac-
tors (Ge), such as hormones, have no longer any chance to affect the growth
to any marked extent. In normal tissues and benign tumors the relation be-
tween Gi and Ge differs in favor of Ge, whereas in cancerous growth Gi
predominates ; in addition, other changes may have taken place in the tissues
during their cancerous transformation, which tend to diminish the effective-
ness of regulatory processes. It is then the strength of Gi (endogenous growth
factor) which is one of the factors enabling a cancerous tumor to overcome
difficulties in transplantation, and especially in serial transplantation, and per-
haps the main difficulties in the way of the transplanted cells consist in differ-
ences in the individuality and species differentials between host and trans-
plant. In tumors in which Gi has not yet reached sufficient strength, there is
therefore need for the additional and longer continued action of Ge
(exogenous growth factor) and this applies especially to certain benign
tumors, where hormones may affect favorably the growth of transplanted
fibroadenomas. Also, in certain other tumors which have not yet reached a
fully cancerous state, the effect of Ge, acting on the host of the graft, may be
required for a successful growth of the tumor in the strange host; thus
Gardner noted that estrogen administration in male mice could make possible
the development of transplanted tumors of the interstitial gland of the tes-
ticle. Although such tumors could occasionally metastasize, on the whole they
had reached only a very low degree of growth momentum, or, expressed
differently, they had not yet progressed very far in the process of cancela-
tion. They therefore could be transplanted successfully only if the host re-
ceived, at the same time, estrogen. The same factor, Ge, which helped to
cause in the normal tissue the increase in Gi and thus the transformation into
cancer, was needed in order to add to the growth momentum of the trans-
plant and aid it in surviving and growing under otherwise not quite adequate
conditions. There seemed to exist a somewhat similar action of Ge in the
transmission of leukemia from hybrids between mice belonging to a leukemic

362 THE BIOLOGICAL BASIS OF INDIVIDUALITY

and to a non-leukemic strain to the parent strains ; this transmission could be
accomplished only in the parent belonging to the leukemic strain, perhaps
because here a factor favorable to the development of leukemia was active.

All the data which have been considered so far lead, then, to the conclusion
that in normal tissues and benign tumors, as well as in cancers, the organismal
differentials are present and affect the results of transplantation, but that in
cancers the increase in inner growth momentum and perhaps other changes
which make possible an increased adaptation to environmental conditions in
the host, may help to overcome the unfavorable effects of strange organismal
differentials.

The essential similarity between the organismal differentials of tumors and
normal tissues, and the similar significance which both of these differentials
have in determining the reactions of the host against transplants have been
made evident also by the recent investigations of H. T. Blumenthal, who
studied the effects of various types of transplants on the character of the
white blood cells in the circulating blood. We shall discuss his findings more
fully in the fourth chapter of this part, where we analyze the cellular reactions
in the bodyfluids which develop against tumors.

Chapter 2
Heredity and Transplantation of Tumors

In the preceding chapter it has been shown that the results of autogenous,
homoiogenous and heterogenous transplantations of tumors differ great-
ly and that the differences are very similar to those found in correspond-
ing transplantations of normal tissues. In both tumors and normal tissues the
organismal differentials are identical, or almost identical, in host and graft
in case of autotransplantation ; they are different in case of homoiotransplanta-
tion, and still more unlike in case of heterotransplantation. While these inves-
tigations have established, in a definite way, the importance of organismal
differentials, and therefore also of heredity in the transplantation of tumors,
there were already some earlier observations which pointed to the significance
of constitutional hereditary factors. Thus Morau, in his transplantations of
mouse carcinoma, believed that in the offspring of mice in which the tumors
could be transplanted successfully, the chances for the growth of the trans-
planted tumor were better than in not directly related mice. At an early
stage in our first series of transplantations of rat sarcoma, we found that this
tumor did not grow in a strange species, even in one nearly related to the rat ;
neither did it grow in some white rats; but it did grow in a hybrid between
a gray and a white rat. At that time we decided, therefore, to study the finer
differences within white rats which determine their suitability or lack of
suitability as hosts for these tumors. The presence of a constitutional element
in tumor transplantation was also indicted by our observations that in the
same individual in the case of multiple simultaneous transplantations of the
same kind of tumor, either all or none of them took ; and that if a transplanted
tissue did not take in an individual rat, subsequent transplantations proved
usually likewise negative, although some exceptions to this rule occurred, in-
dicating that certain accidental, variable factors complicated these experi-
ments. Similar observations were made by Jensen in his serial transplanta-
tions of mouse carcinoma. Subsequently, Michaelis, as well as Bashford and
Murray and others, found that white mice obtained from different localities
differed in the number of takes which followed inoculation with mouse car-
cinoma. In the meantime, we had successfully transplanted a carcinoma, origi-
nating in a Japanese waltzing mouse, in about 100% of all Japanese waltzers,
although the growth in the first generation of transplants was slow. This
indicated that here we had to deal with a very favorable soil of a homozygous
character. A few years later, Tyzzer (1909) studied the differences in the
number of takes of another carcinoma, which had developed spontaneously
in a Japanese waltzing mouse, after transplantation into Japanese, into com-
mon white mice, and into hybrids between these two species or subspecies.
Tyzzer expressed the view that hereditary factors determine the differences in

363

364 THE BIOLOGICAL BASIS OF INDIVIDUALITY

suitability of the hosts for the tumor he used ; however, in his experiments he
had to deal with mice which belonged to different subspecies. Cuenot and
Mercier separated, through breeding of white mice from their locality, fam-
ilies in each of which the degree of transplantability was a fixed quantity
which was inheritable ; they believed that, through breeding, they had been
able to sort out what corresponded to Johannsen's pure lines. But such in-
vestigators as O. Hertwig and Poll, and C. Lewin, denied the existence of
these differences of susceptibility to tumor transplantation between different
families or strains within the same species, and it was especially an experi-
ment of Haaland which was responsible for the assumption, subsequently
made, that adaptive variations in the animals, taking place in response to
changes in the environment, rather than fixed constitutional characteristics
were the cause of these differences between different strains. Haaland ob-
served that mice bred in or near Frankfurt, which were suitable as hosts for
Ehrlich's mouse sarcoma, became unsuitable after they had been transferred
to Norway and bred there for a short time. He attributed this change to the
difference in the kind of food given to the mice in these two localities and
concluded, therefore, that the suitability of hosts for a certain tumor de-
pended on variable environmental, rather than on fixed inheritable conditions.
Other investigators confirmed Haaland's observations and accepted his con-
clusions as to the effect of various kinds of food on the number of takes of
a certain tumor.

On the other hand, our investigations, made in conjunction with M. S.
Fleisher (1912), showed that the differences in transplantability occurring in
different strains of mice depend upon fixed hereditary conditions, which are in-
dependent of environmental factors. American and different types of European
white mice, all fed in the same way and bred separately under identical en-
vironmental conditions, each maintained its characteristic transplantability in-
dex for a carcinoma which had developed spontaneously in an American
mouse. Subsequently Morpurgo, and also Roffo, made similar observations.
The change which Haaland found in his mice after transfer to Norway was
interpreted by us in a different manner, because we noted that in one of our
European strains a change in its suitability as host took place as a result of a
disease which eliminated a number of families. Evidently a selection had
occurred, causing the survival of a family which differed genetically from
the rest, and which now began to predominate over the other mice. As a
result of this selection process, the transplantability rose considerably in this
strain. However, the results of transplantation depend not only on the host,
but also on the kind of tumors which are used for inoculation. Thus Haaland
noted that if each mouse is inoculated with two different types of tumor, the
receptivity of different strains of mice differed for each tumor. As we may
now express it, the transplantability depends upon the relation of the in-
dividuality or organismal differentials of the host to those of the transplant.
But we must make the reservation that, within a certain range, adaptive
changes may take place in the tumor cells and that thereby the results may be
modified.

HEREDITY AND TRANSPLANTATION OF TUMORS 365

The transition from the ordinary strains of animals to closely inbred, homo-
zygous strains is a gradual one ; it takes place step by step. The guinea pigs
and rats which we used at first in our transplantations of normal tissues did
not belong to inbred strains. We determined the organismal differentials by
comparing the effects of auto-, various kinds of syngenesio-, homoio- and
heterotransplantations. Because we did not have to deal with closely inbred
strains, variability in the results within certain limits in the syngenesious-
homoiogenous range of the spectrum of relationships may therefore be ex-
pected, and this was actually observed. But this difficulty could be over-
come by increasing the number of experiments in which we tested the effects
of relationship on the fate of the transplants. The greater the number of un-
known factors, the greater must be the number of equations. The conclu-
sions reached in these earlier experiments concerning the significance of the
relations between organismal differentials of host and transplant on the fate
of the latter were confirmed in our subsequent investigations with closely in-
bred strains of guinea pigs and rats. However, a fully homozygous condition
had not yet been reached in the case of the inbred guinea pigs ; in the case of
the rats, the heterozygous condition had only very slightly been diminished
after as many as forty generations of' close sister-brother inbreeding. As
stated, our early observations on the transplantation and spontaneous develop-
ment of tumors in mice were made in partly inbred strains. The same limita-
tions applied here as in the earlier transplantations of normal tissues in
guinea pigs and rats. In both instances, the difficulties due to the larger num-
ber of variable factors present made necessary a larger number of experi-
ments. Likewise, in the case of tumor transplantations subsequent experiments
by various investigators and also by ourselves with more fully homozygous
strains confirmed essentially the earlier conclusions. It must, however, be
emphasized that even these closely inbred strains had, in all probability,
not yet reached a completely homozygous condition. There is therefore only
a quantitative difference in the nature of the strains used in the earlier and
in the later investigations, and both lead to the same results provided a suffi-
cient number of experiments are made.

All these observations and experiments point to the conclusion that the
transplantability of tumors depends largely on the relations between the
genetic constitutions of host and donor and the character of the organismal
differentials, which is the expression of these constitutions. But there is one
finding which seems contradictory to these conclusions. Rous and Long dis-
covered that their third chicken sarcoma, which had originated in a Leghorn,
grew, on the average, better after transplantation into Plymouth Rock chickens
than in Leghorns. Presumably factors of a secondary character complicated
the relationship between tumor and host in this case, or this condition may
possibly have been due to peculiarities of the agent present in these tumors
rather than to those of the tumor cells. But before entering into a further
discussion of genetic factors in the transplanted tumors, we must again con-
sider the difficulty which we experience if we analyze tumor growth by means
of transplantation of the ordinary transplantable tumors.

366 THE BIOLOGICAL BASIS OF INDIVIDUALITY

In the case of normal tissues we used as criteria of the suitability of the
transplant for the host, or of that of the host for the transplant, the changes
which the graft underwent in the host and the reactions of the host tissues,
especially the lymphocytes, connective tissue and blood vessels, against the
transplant. In this way we could show that there is a close correspondence be-
tween transplantability and the individuality differentials of host and trans-
plant, as determined by the genetic constitution of host and donor. In the case
of tumors, conditions are somewhat different. In general, in these experiments
tumors are used which are easily transplantable, which means that they grow
readily in a large number of individuals of the same species. Finer individual
differences in relationship, such as those between parents and children, and be-
tween brothers, and even between somewhat farther distant relatives such
as those tested by us in the case of normal tissues, cannot be distinguished if
such transplantable tumors are used. The behavior of the latter towards dif-
ferent individuals belonging to species and strains in which they are readily
transplantable, is to all appearances about the same. For this reason, only
very marked differences between different hosts can be discovered in this
way; they represent either strain differences or even differences as great as
those between subspecies, or those obtaining between hybrids which result
from the mating of two different strains. Furthermore, the standards used
for the determination of the degree of transplantability are different for
tumors and for normal tissues. For the latter, a more delicate grading of the
suitability of the individuality differentials of host and transplant is made
possible by the evaluation of the histologic changes which take place in the
cellular reactions of the host against the graft. These criteria are not com-
monly used or available in the case of tumor transplantations; instead, the
number of growing tumors (takes) and, less frequently, the growth energy
of the tumors are employed as criteria of the differences in individuality differ-
entials. In the investigations of M. S. Fleisher and the writer, a comparison
was made between the averages of growth energy and number of takes as
criteria of transplantability; in addition, we noted the duration of the latent
period, that is, the length of time which intervenes between the date of trans-
plantation and the appearance of the tumor visible to the naked eye. The
length of the latent period measures the growth energy in the first and most
critical period following grafting. It was found that the conditions deter-
mining the number of takes are in certain respects distinct from those de-
termining growth energy, while in other respects they are correlated with
each other. Both these factors depend primarily upon the relations of the
organismal differentials of host and transplant, and secondarily, upon the
growth energy of the graft and upon the adaptability of the transplant to
different hosts or of the host to different transplants. However, tumors which
may all be classed as transplantable, may still differ as to their growth energy ;
thus, in two parallel series of experiments, all inoculations may be followed
by growth of the graft and therefore be considered as takes ; yet, in one set
of hosts the growth energy may be greater than in the other. In general, differ-
ences in growth energy in a certain host represent finer gradations of the

HEREDITY AND TRANSPLANTATION OF TUMORS 367

mutual suitability of hosts and grafts than do differences in the number of
takes. This was quite evident, for instance, in some of our experiments in
which mouse carcinoma IX, in the beginning, grew in all the mice inoculated
and the number of takes was, therefore, 100 per cent; for a time following
transplantation, also the growth energy was approximately the same, or at
least similar ; but after a certain size had been reached by the transplants the
growth energy diminished in some of the animals, the tumors retrogressed and
finally disappeared, while in others they continued to grow. The main distin-
guishing feature between the tumors in the different hosts was the develop-
ment or accumulation in some of the animals of certain unfavorable factors,
which caused a slowing of the growth or even a retrogression of the tumors,
while in others, conditions were more favorable and the growth energy was
not markedly diminished.

To return now to the study of the conditions which determine the results in
transplantation of tumors, Tyzzer (1909) hybridized two strains of animals,
one of which was very favorable and the other very unfavorable to the trans-
plantation of a certain tumor. In a Japanese waltzing mouse a tumor developed,
which grew in 100 per cent of Japanese mice but not at all in white mice. As
stated above, the Japanese waltzing mice have apparently become a relatively
homozygous strain or subspecies. Tyzzer found that in the Fx hybrids between
the Japanese and white mice the tumor grew as well or even better than in
the Japanese mice, whereas in the F2 and F3 hybrid generations no growth took
place. As we have already stated, it is not possible to analyze the individuality
differentials if we use one of the readily transplantable tumors, because these
tumors grow in many animals of the same species, without regard to differ-
ences in the individuality differentials ; there may, however, be some differ-
ences in the average number of takes in different kinds of strains, in which
the averages of individuality differentials are different. However, Tyzzer in
his series of transplantations did not actually study strain differentials, but
something akin to subspecies differentials. He concluded from his experi-
ments that the inheritance of factors which determined the transplantability
of tumors did not take place in accordance with Mendelian principles.

In the following year (1910) Cuenot and Mercier, to whose investigations
we have already referred, were concerned with the inheritance of the factors
influencing tumor transplantability in white mice. They believed that it was
possible to sort out, in these animals, pure lines in which the average trans-
plantability of a certain tumor was a fixed quantity; furthermore, they be-
lieved that the extent of the deviation from this mean was likewise a charac-
teristic feature for a pure line. The pure line to which a mouse belongs
determines the percentage of cases in which a tumor can be transplanted;
on the other hand, the character of the parents does not necessarily indicate
whether a transplanted tumor piece will grow in a child; this may depend
on phenotypic rather than on genetic conditions. However, in the light^of what
we now know, it is more difficult to obtain pure, fully homozygous strains
even through long-continued close inbreeding, than should be assumed on
theoretical grounds, and it is therefore improbable that Cuenot and Mercier

368 THE BIOLOGICAL BASIS OF INDIVIDUALITY

worked with pure lines. Levin and Sittenfield soon afterwards noted that the
offspring of non-susceptible rats were less susceptible to the growth of a
sarcoma than the offspring of susceptible rats.

In experiments with mouse carcinoma IX it was shown by Fleisher and
the writer (1912) that this tumor could be successfully transplanted into a
strain of American mice in 80 per cent of the cases, into a first strain of Euro-
pean mice in 23 per cent, and into a second strain of European mice in 3 per
cent of the animals. However, in the early period following transplantation
the tumors grew as well in European as in American mice, namely, in 85 to
95 per cent in both ; but after twelve days a large proportion of the tumors
became stationary and retrogressed in the European mice, while in the Ameri-
can mice the proportion of retrogressing tumors was small. In the ¥1 hybrids
between American and European mice the tumor grew as well or almost as
well as in the American mice ; but in the F2 and F3 generations there was a
sharp fall in takes, which was followed again by a rise in the F4 and F5
hybrids. Except for the partial recovery in F4 and F5 and the results in back-
crossing, our results and Tyzzer's were therefore similar. We concluded that
these findings were compatible with Mendelian principles if we assumed that
the susceptibility for growth in Tyzzer's, as well as in our experiments, de-
pended on multiple factors. In this connection we applied the term multiple
factors in the usual sense of the Mendelian theory, and in the same way in
which we applied this term in our transplantations of normal tissues and in
our analysis of the origin of tumors. In this sense we also explained subse-
quently the difference in the results obtained between transplantations of nor-
mal tissues from children to parents and in reciprocal transplantations from
parents to children. In the former case, the number of genes which are present
in the transplant but not in the host, should, on the average, be greater, and, on
the average, the reaction should accordingly be more severe than in the
reciprocal transplantations.*

In continuation of our experiments (1916), we extended our study to a
number of other strains of mice. Again we found that American and various
imported strains did not differ in respect to the number of original takes, but
that they differed greatly in regard to the number of subsequent retrogres-
sions. No marked individual differences in the growth energy could be estab-
lished by the standards used at that time, either in that group of mice in which
the tumor grew definitely, or in the other group in which it retrogressed.
However, the marked differences which we had observed formerly in the
number of takes or growth energy between different hybrid generations were
no longer found ; the growth throughout was about intermediate between that
observed in the American and in the imported strains. Likewise, in hybrids

* In a paper by the writer on "The individuality differential and its mode of inherit-
ance," in the American Naturalist, Vol. IV, Jan.-Feb. 1920, there occurs in the last
paragraph of page 58, the sentence : "In the case of transplantation from child to mother,
on the other hand, the graft would lack one-half the chromosomes — ." It is quite evident
that this is a misprint and that instead of "graft" it should read "host." This correction
is made here, because this misprint has led to an erroneous interpretation of the views
of the writer.

HEREDITY AND TRANSPLANTATION OF TUMORS 369

between American white and gray wild mice the differences between successive
generations noted in our first series did not occur.

Subsequently Tyzzer and Little, and Little and Tyzer, found that a Japa-
nese mouse sarcoma, as well as a carcinoma, grew in Fx hybrids between
Japanese and white mice as well as in pure Japanese mice, whereas in white
mice the tumors grew in only a small minority of the animals. The growth
of carcinoma and sarcoma behaved in these respects almost alike, but the
growth of sarcoma was somewhat better. Also, Tyzzer and Little interpreted
now, these variations in the percentage of takes in different generations of
hybrids as due to the action of multiple factors. They assumed that the con-
tinued growth of both the sarcoma and carcinoma depended upon the presence
of a complex of independently inherited factors, and this factor-complex was
supposed to be present in a nearly homozygous condition in the Japanese
waltzing mice. Since Fx hybrids had Japanese mice as one of their parents,
they possessed the factors comprising the Japanese complex in a single dose,
and since this single dose allowed tumors to grow, it followed that a single
representation of these factors was all that was required for the establishment
of susceptibility to tumor implantation. Also, in his more recent investigations
Little assumed that the transplant must have double representation and the
host single representation of the genes required for continuous growth of the
grafted tumor. It was furthermore necessary to hold that inasmuch as there
was associated with the single complex of genes inducing susceptibility a set
of unlike genes in the host, the set of genes determining susceptibility was
dominant over the other set. Susceptibility was therefore supposed to be
dominant over non-susceptibility or resistance to the growth of transplanted
tumors. In addition, Tyzzer and Little assumed that the percentage of in-
dividuals in which the tumor grew in the F2 generation could be used as an
index of the number of factors necessary for continued growth. The larger
the number of F2 hybrids in which the tumor takes, the fewer the number of
genetic factors required. For instance, these authors concluded that twelve
factors were necessary in the case of a carcinoma, and from five to seven in
the case of a more readily growing sarcoma.

In subsequent investigations into the transplantability of tumors, Little and
Strong made use of strains which had been rendered more or less homogene-
ous (homozygous) by means of long-continued sister-brother inbreeding. In
transplanting a melanotic tumor, which originated in strain dba, into hybrids
between dba and A, Spangler, Murray and Little noted that transplantations
succeeded in a larger percentage in colored than in albino hosts, and they
assumed that one "susceptibility factor" is required for a successful trans-
plantation in colored mice, while in albino mice there is needed, in addition, a
second factor, which would be necessary also for melanin production in non-
colored individuals but would function in this way only in the presence of the
color factor. The use of closely inbred strains meant, in certain respects, a
great simplification of the analysis of the growth of transplanted tumors and
led to the establishment of some important facts in a more definite manner
than had been previously possible. To mention only one example : Bittner, by

370 THE BIOLOGICAL BASIS OF INDIVIDUALITY

means of this method, could show that if multiple inoculations of pieces from
the same tumor were made into different individuals belonging to such a
closely inbred strain, almost all of the inoculated pieces behaved alike in
the same individual. Thus there was proved definitely the view the writer
had expressed previously (1902), that all transplants from the same donor
into the same host should elicit about the same reaction in the latter, the re-
actions depending, as we expressed it subsequently, on the relations of the
individually differentials of host and transplants. Bittner furthermore found
that if a closely inbred strain is used, the growth rhythms, described by Bash-
ford as inherent in the character of tumor cells, do not occur. This agreed
with the findings of Fleisher, who also had arrived at the conclusion that
such rhythms do not exist.

Little, L. C. Strong, Bittner and Cloudman, noted that if a tumor originates
in one of the inbred parent strains, it can be transplanted into all the individ-
uals of this strain, but not, as a rule, into the individuals of another inbred
strain. These observations are in agreement with the theory of the organismal
differentials and accord with the earlier data established in experiments in
which less closely inbred strains had been used. If two inbred strains are
hybridized, a tumor which had developed in an animal belonging to one of
the two parent strains grows well in all or almost all of the F1 hybrids, while
in the F2 hybrids only a certain percentage of individuals is susceptible to the
growth of the transplants in accordance with the rules of Mendelian segrega-
tion, and as mentioned above, this percentage figure, according to these in-
vestigators, can be used as an indicator of the number of factors which must
be present in the hosts if the tumor shall take. The percentage of successful
transplantations of the tumor into backcrosses between F1 hybrids and each of
the two parent strains indicates how many of the required growth factors in
the hybrids have been contributed by each one of the two parent strains. As
should be expected, according to the theory of the organismal differentials,
a tumor which originates in an Fx hybrid takes readily in all the F1 hybrids,
but not at all or very poorly in the parent strains, and it grows in a certain
percentage of mice of the F2 generation ; this observation is also in agreement
with the finding of Tyzzer that a tumor originating in a hybrid Fx between
Japanese and white mice, could not be transplanted into either of the parent
strains. Strong compared the growth of two adenocarcinomata developing in
two individuals belonging to the same inbred strain of mice. Because of the
close inbreeding of this strain, we should have expected the tissues of the two
adenomata to possess approximately the same individuality differentials;
but Strong found that these two tumors behaved in a different way after in-
oculation into F2 generations of hybrids between a strain of mice which was
susceptible to the tumors and another strain which was non-susceptible. There-
fore he concluded that the two tumors, although they had developed in in-
dividuals which should be expected to be genetically identical, differed from
each other in their genetic constitution, and further, that two tumors struc-
turally indistinguishable from each other may differ in their physiological
behavior, an observation which in certain respects agrees with our own that

HEREDITY AND TRANSPLANTATION OF TUMORS 371

several spontaneous sarcomata which developed in the thyroids of different
rats, differed very much in their behavior after inoculation into other rats,
although these tumors were very much alike in their structure.

Continuing these experiments, Strong, as well as Bittner, studied two
tumors which developed spontaneously in the same mouse of an inbred
strain. These two tumors likewise were found to behave differently after
transplantation into the same and into other inbred strains and into differ-
ent generations of hybrids, and it was therefore believed that they differed in
the number of genetic factors required for their continued growth in a strange
host. Also, Cloudman, who transplanted three tumors originating in a mouse
of the inbred A strain, and Bittner, who compared the growth of multiple
tumors which developed spontaneously in an Fx hybrid between the A and D
strains, obtained similar results when the individual tumors were transplanted
into A and D strains and into the different hybrid generations between A and
D. But, although one of Strong's tumors grew in a larger number of individ-
uals belonging to another strain and in hybrids between its own and the strange
strains, otherwise the two tumors behaved in a parallel way as far as the rela-
tive percentages of their takes in these different kinds of mice were con-
cerned. Both tumors were also affected in the same way by sex differences of
the hosts after transplantation into Fx ^hybrids, the females being the more
favorable hosts.

Previously, Little had assumed that in female mice at the time of sexual
maturity a change in the receptiveness to transplants occurs. He attributed the
difference which he observed in the percentage of takes in newborn female
mice and in mice three weeks old, to the sexual maturity which takes place
during this period and to corresponding changes in the individuality differ-
entials ; this would represent a linkage between susceptibility and sex factors.
But only in certain hybrid strains did the number of takes increase at the time
of sexual maturity, while in the white and dilute brown parent-strains the re-
verse relation was noted. Furthermore, the differences between these age
classes with which Little dealt were only slight.

More recently Bittner described another case of what he interpreted as
linkage, namely, one between the factors determining transplantability of a
certain tumor and the color of the skin ; but in this case also, the differences
in the percentage of takes in different groups of white mice differing in their
hair color were slight. As to the effect of sex on transplantability of tumors, it
is conceivable that sex hormones may, under exceptional conditions, favor the
growth of certain mammary gland carcinomata in the same way as, in accord-
ance with our previous observations, they may do in benign tumors of the
mammary gland; however, such an action is not likely to affect fully devel-
oped carcinomas ; they no longer respond, as a rule, to hormones. We, as well
as Strong, Cloudman and Bittner, assumed that differences in the percentages
of takes of tumors originating in the same animal, in hosts with a similar
genetic constitution, depend upon differences in the characteristics of these
tumors, but we do not agree in our interpretation as to the nature of such
differences.

372 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Before attempting to evaluate the results of these investigations, we may
consider some earlier findings of a related nature. The study of multiple
spontaneous tumors developing in the same individual was begun as early as
1907, when the writer, working with mice, noted that the structure of multiple
carcinomata originating in the same animal was very similar, although not
identical. At that time we suggested that it might be possible through trans-
plantation of such tumors to determine whether the characteristic behavior
of different carcinomata in strange hosts was due to factors inherent in the
tumors or in the hosts. Woglom (1919), who had carried out such transplanta-
tions, found that the large majority of multiple tumors arising spontaneously
in the same animal, behaved similarly after transplantation into the same
strain of mice, but in a minority of cases differences did occur. Especially
striking in this respect was the transplantation of three spontaneous tumors
which had developed in the same mouse. One of these was readily trans-
plantable into other mice, while the other two retrogressed following a tem-
porary period of growth, and one tumor retrogressed more readily than the
other. However, in these experiments Woglom wished to determine whether
the behavior of tumors after transplantation depended upon adaptation of the
tumors to the environment as it existed in the animal in which they had
originated, or whether it depended upon the growth energy of the tumor
at the time of transplantation. In the former case all the transplants should
behave in a similar manner, since all these tumor cells had been reared in
the same environment, while in the latter case the tumors should behave
differently from one another because the growth energy is a variable factor,
which, according to Bashford, differs at different times even in the same tumor.

The basic assumption underlying the interpretation of Strong and his col-
laborators is that the difference in the behavior of two tumors arising spon-
taneously in the same mouse is due to differences in the mutations of genes
in somatic cells and, therefore, to the differences in the gene sets of these
two tumors resulting from these mutations. But this, it seems, is not the
only possible interpretation of this finding. We know that various normal
and also embryonal tissues show different degrees of transplantability ; thus,
cartilage may be homoiotransplanted successfully in cases in which thyroid
cannot, although both tissues can be autotransplanted equally well. These two
tissues, when taken from the same individual, possess the same individuality
differential but differ in the constitution of their organ and tissue differentials,
and this latter difference may cause variations in their sensitiveness and trans-
plantability. We also know that normal tissues differ much in the growth
momentum which they possess ; for instance, the normal and sensitized uterine
mucosa may exhibit quite a different degree of proliferative activity after
homoiotransplantation. Now, if we assume that during the transformation
of normal tissues into cancerous tissues a graded increase in growth energy
occurs and a concomitant change takes place also in the resistance to the
injurious effects of transplantation, and if we furthermore assume that in
two tumors, developing spontaneously in the same individual, this transfor-
mation has progressed to a different degree, then we could explain the ob-

HEREDITY AND TRANSPLANTATION OF TUMORS 373

servations of Strong without having recourse to the assumption of different
genetic mutations in different somatic cells of the same individual.

However, there are certain other conditions which may correctly be at-
tributed to genetic conditions. Thus Strong and Bittner observed in the course
of their transplantations that in the closely inbred strain, "dilute brown,"
a change suddenly took place in the transplantability of a certain tumor and
they attributed this change to a selection within the larger strain of a certain
substrain or family, which thus evidently differed in genetic composition
from that of the main strain. This agrees with our previous observations,
in which we had found a similar change in the transplantability of tumors and
also in the percentage of spontaneous tumors developing in a strain of mice,
due to the splitting off of certain families possessing a somewhat different
genetic composition.

From our findings after transplantations of normal tissues and of several
tumors, we concluded that in a general way the outcome of transplantation
depends upon the relation between the organismal differentials of host and
transplant; and this means that it depends, essentially, upon the genetic con-
stitution of the tumor cells as well as of the host cells, and that the reaction of
the latter takes place in response to the strange genes carried by the transplant.
In the strict sense the reaction does not, however, occur against the genes as
such, but against certain physiological and biochemical mechanisms developing
in transplant and host on a genetic basis. Strong expressed more recently the
same idea that the result of tumor transplantation is a function of the genetic
composition of both host and transplant. In this respect, then, the various
investigators are in agreement.

There still remains to be discussed the relation between the hereditary pre-
disposition to cancer and the change which takes place in normal cells during
their transformation into cancer cells. These two conditions are distinct from
each other. A comparison between the transplantation of normal tissues and
of tumors which arise from normal tissues makes possible an analysis of the
constitution of the individuality differentials of both, and we studied tumor
transplantation largely from this point of view. Tyzzer, on the other hand,
in common with Ehrlich, and also to some extent in common with Bashford,
considered tumors as essentially different from ordinary tissues, as an abnormal
condition which called forth an immunity peculiar to cancer, although certain
exceptions to this rule were admitted. Thus Tyzzer assumed that the genetic
study underlying transplantation of tumors might furnish an insight into the
character of cancer and into the conditions which cause its development. Simi-
larly, Little, Strong and Bittner infer a similar connection between the
hereditary factors determining transplantability of tumors and the origin of
tumors, and in this sense, Bittner intimates that the same dominant multiple
factors which determine the transplantability of tumors may determine, also,
the origin of cancer.

We shall now attempt to analyse still further the various data which we
have discussed, and to determine, if possible, the significance of genes in the
transplantation of tumors. For this purpose it will first be necessary to consider

374 THE BIOLOGICAL BASIS OF INDIVIDUALITY

again the principal factors which may enter into the transplantation of normal
tissues and of tumors. There is (1) the relation between the individuality dif-
ferentials or species differentials of host and transplant. This, as we have
seen, plays a role in cancers as well as in normal tissues, numerous data
confirming such a conclusion. (2) Variable factors relating to the mode of
inoculation or transplantation may greatly influence the number of successful
transplantations ; these are non-genetic in nature. To mention an example :
the usual figures for takes relate to experiments in which the transplant is
placed into the subcutaneous tissue. Intracutaneous or intraperitoneal in-
oculation may alter these figures considerably. As we have seen, transplanta-
tion into the brain, and especially into the anterior chamber of the eye, may
make possible a tumor growth, which would not take place after subcutaneous
transplantation. And, as various investigators have shown, even heterogenous
cancers may grow in the chorio-allantoic membrane or in the anterior cham-
ber of the eye. Likewise, the amount of material inoculated is of importance.
In many instances, transplantation of a larger quantity increases the number
of successful transplantations. But if the quantity exceeds a certain optimum,
the number of definite takes may decrease again in certain cases, because
the added tissue may increase the amount of material which may serve as
antigen and call forth the production of injurious immune substances. Also,
in the case of mouse leukemia the quantity of injected leukemic cells helps to
determine the result. While, as Furth has shown, a single leukemic cell may
be able to transfer the new formation to another host, on the whole, prospects
of a successful transplantation are greater and this tumor-like condition de-
velops and kills the inoculated mouse more rapidly if the number of inoculated
cells is greater. Also experimentally it is possible to diminish the virulence or
growth energy of tumor cells by the application of various physical and
chemical agents. (3) Certain extraneous, non-genetic factors which alter the
susceptibility or the power of resistance of the host tissue to transplanted
material. Application of X-rays, injection of colloidal dyes or other material,
may diminish the resistance of the host, presumably by affecting the reticulo-
endothelial system. There is good reason for assuming that also without the
use of these experimental means, differences exist in different individuals
and strains in the intensity of the reaction against transplants bearing a dif-
ferent organismal differential. (4) Differences in the resistance of different
tissues, of which the tumors are composed, to injurious influences which may
prevail in the host. These differences we have found in normal tissues, such as
thyroid and cartilage, and there is evidence that they exist also in tumors. Thus
the malignant chondroma of a mouse observed by Ehrlich could readily be
transplanted into other mice, irrespective of their genetic constitution. The
tumor grew slowly but was able to resist unfavorable conditions. When a
piece of cartilage becomes permanently endowed with greater growth energy
and thus assumes the characteristics of a tumor, it still retains some of the
essential characteristics of cartilage, such as its relatively great resistance to
the action of injurious body fluids and antagonistic cells. On the other hand,
if thyroid becomes endowed with great growth potentiality, it likewise still

HEREDITY AND TRANSPLANTATION OF TUMORS 375

retains some of the essential characteristics of thyroid tissue and is, therefore,
more susceptible to injurious influences. There is good reason for assuming
that different tissues, such as cartilage and thyroid, and cancers derived from
them which develop in the same host, possess the same genetic constitution
and the same individuality differential, and that differences which such tissues
and cancers show, are therefore, in all probability, directly non-genetic, al-
though ultimately they depend also on the constitution of the germinal gene
sets. (5) There are certain factors of an environmental nature which may
also, under some conditions, influence the number of successful transplanta-
tions. Severe undernourishment may diminish it ; hormones may affect the
transplantability. Thus according to the recent experiments of Gross, trans-
plantation of a mouse sarcoma succeeded more readily in sexually mature
male than in female mice. He could make it very probable that the ovary gives
off a substance, presumably a hormone, which had this inhibiting effect on the
growth of the transplanted tumor. This is of importance, because it has been
taken for granted by some investigators that slight differences in the effect of
sex on the number of takes observed at a certain time of life were of genetic
origin. However, it must be noted that Gross carried out intracutaneous trans-
plantations and that under these conditions the existence of the tumors is a
very labile and rather precarious one, in which slight interferences, which in
transplants growing under more favorable conditions would hardly be notice-
able, may affect quite definitely the fate of the tumor. The effect of the hor-
mone in this case is presumably an indirect one. (6) Other intrinsic factors
such as growth momentum, immunizing power, and adaptability of tissue to
the condition of the host, all of which are greater in tumors than in normal
tissues.

As far as the growth momentum is concerned, its constant increase in
cancer tissue over that in the normal tissue from which it originated, is per-
haps the most characteristic feature of tumor tissue. This increase in growth
momentum makes it possible for cancer tissues to resist injurious influences
to which normal tissues would succumb, the rapid cell multiplication probably
increasing the ability of the transplant to absorb and neutralize injurious sub-
stances circulating in the host. Associated with this greater growth momentum
there is usually a diminution in differentiation of the cancerous cells, which
may likewise diminish the sensitiveness of the transplant to injurious factors
under certain circumstances. However, the growth momentum is not a sta-
tionary condition ; in a very large number of instances it has been observed
that during the first transplantations of a tumor, whether a carcinoma or a
sarcoma, the growth energy increases. Such an effect is typical, as we found
about forty years ago in the course of our first transplantations of sarcoma of
the thyroid gland in rats, and it has since been noted by many other investi-
gators. There is no justification for assuming that so regular an occurrence,
which does not depend upon a single tumor cell but may be noted after
transplantation of various parts of the tumor, is due to a haphazard somatic
mutation. It is presumably due to the stimulation exerted by incisions into the
tumor and by the process of transplantation. A similar stimulation has been

376 THE BIOLOGICAL BASIS OF INDIVIDUALITY

noted also in the transfer of leukemic blood cells into other susceptible individ-
uals. In the mammary gland, where the development of cancer out of normal
tissue under the influence of hormones can be followed very well, it can be
seen that, step by step, the growth energy of the tissue on which the hormone
acts increases, and that as soon as a certain stage of intensity in this stimula-
tion has been reached, the transition into abnormal growth takes place, pro-
vided the conditions transmitted by the germ cells make the gland tissue
responsive to the action of the hormones. Furthermore, it is not a single cell
which is altered, but more complex structural units, the acini and ducts
of the mammary gland, undergo this cancerous change ; and the latter does not
depend upon the amount of newly formed tissue, but on the intensity of the
growth stimulation which the gland structures have undergone. There is,
thus, no indication that this process is caused by the occurrence of somatic
mutations and that the cancer-producing stimuli in general are effective be-
cause the right kind of somatic mutations are produced. Although, therefore,
the facts do not warrant the conclusion that this process of stimulation acts
by way of the genes, on the other hand, the conditions which determine the
degree of responsiveness of the tissues to the stimuli are transmitted by genes,
but by genes of the germ cells and not of somatic cells. Eisen found that in the
course of serial transplantations of a mammary carcinoma, which arose spon-
taneously in a rat belonging to a closely inbred strain, noticeable variations
in the growth energy were lacking in the different generations of transplants ;
he attributes the constancy in the slow growth rate in the course of serial
transplantations to the homozygous constitution of this strain and believes
that when an increase in growth energy is noted in the course of the first
generations of grafts, this is due to differences in the genetic constitution of
different members of the strain. However, it can be shown that this increase
in growth energy has in many cases been observed also in closely inbred
strains. It is certain that this phenomenon is not due to selective processes in
an impure strain of animals. But it is not observed in the case of all the
tumors; to some extent, it seems to depend upon differences in the stability
of the tumors used for serial transplantations.

As already stated, the primary condition required for the development of
malignant tumors is an augmented growth momentum, and this augmentation
may continue to take place in the course of transplantations of the cancerous
tissue ; it is one of the principal causes for the additional number of successful
transplantations or "takes" which may take place during serial transplanta-
tion, and which accompanies the increase in growth momentum. But, omitting
here from consideration, differences in the receptiveness of the host for the
transplant, there are still other variable factors involved in the number of
takes, which are situated in the tumor cells; among such factors we have
referred above to differences in the resistance of the tissues to injurious condi-
tions, which is likewise not directly genetic in character; and a third factor
consists in the changes of an adaptive nature which can be seen sometimes
after continued transplantation of tumors, changes which also occur after
successive inoculations of bacteria and after longer continued exposure of

HEREDITY AND TRANSPLANTATION OF TUMORS 377

certain protozoa to various injurious conditions. In all these cases we may
perhaps have to deal with alterations in cytoplasmic or nuclear-cytoplasmic
mechanisms corresponding to the persisting modifications of Jollos ("Dauer
modifikationen"). Such processes of adaptation have been observed under
various circumstances; for instance, leukemic cells, which at first could be
transferred only to X-rayed individuals belonging to an unfavorable strain
of mice, could subsequently be transferred, also, to other individuals belong-
ing to the unfavorable strain which had not previously been X-rayed. We
shall discuss these processes of adaptation more fully in the next chapter.

In accordance with this interpretation of apparently spontaneous changes in
growth momentum and takes which, as a rule, occur in the course of serial
transplantations of cancerous tissues, we may likewise interpret the differ-
ences in growth momentum and transplantability which have been observed
between spontaneous tumors originating in different mice of the same inbred
strains, or even in the same mouse, and which we have already mentioned
in this chapter. It should be expected that some differences may develop during
the process of cancerization of normal tissues. This process may be somewhat
farther advanced in some beginning tumors than in others, and there is no
reason for attributing such differences to somatic mutations. Changes of the
opposite kind take place during embryonal development ; here, associated with
a greater differentiation of the tissues, a gradual diminution in growth mo-
mentum and, correspondingly, in transplantability occurs; and these changes
taking place during embryonal life are irreversible. Bat they are not due to a
series of successive somatic mutations ; nor should we be justified in attribut-
ing typical changes in growth and differentiation in the granulosa of follicles,
previous to and during the process of maturation and corpus luteum forma-
tion, to a continuous series of somatic mutations. All these considerations
make it improbable that either the transformation of normal tissues into
cancers or the variations in growth momentum and transplantability of fully
developed cancers are due to somatic mutations. However, as stated, the
organismal differentials, and therefore also the genetic constitution of tu-
mors, are important factors in their transplantability, as well as in the produc-
tion of immunity against tumor transplants.

After transplantation of tumors, as well as after transplantation of em-
bryonal tissues, processes of immunity can be more readily demonstrated in
the host than after transplantation of normal tissues. We shall discuss these
processes of immunity in tumor transplantation somewhat more in detail in
a succeeding chapter. Here, it may be stated merely that the genes in the
piece of tumor, which are strange to the host, are the precursors of those
constituents of the organismal differentials in the tumor, which may function
as antigens. The difference between the individuality and species differentials
of host and transplant not only gives rise to the primary local defense reaction
of the host against the tumor, but it also subsequently causes the transforma-
tion of these strange constituents into antigens and thus leads to the production
of immunity. It is especially when a tumor, following a period of growth in a
host, retrogresses that the host becomes immune against a second transplant

378 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of the same kind of tumor, or of a tumor resembling the first one, as far as
the constitution of their organismal differentials is concerned.

Gorer has observed that when a transplanted tumor has retrogressed, hemag-
glutinins appear in the blood of the host, which are directed against the
erythrocytes of the donor of the tumor. He could show that when certain
strains of mice and certain tumors were used, there were several kinds of
hemagglutinogens present in the red corpuscles of the donor of the tumor
which gave rise to the formation of hemagglutinins, and the number of these
agglutinogens seemed to be approximately the same as the number of "sus-
ceptibility factors" for the growth of the tumors, as determined by the propor-
tion of takes in the F2 and backcross generations of hybrids between two
strains varying in their susceptibility to the tumor, in accordance with the
theory of Tyzzer and Little. He concludes, therefore, that it is the hemag-
glutinogens which represent the genetic factors needed for the growth of a
transplanted tumor. Lumsden also noted in rats, in which tumors had
retrogressed, the presence of hemagglutinins for the erythrocytes of the donor
of the tumor. As we shall see later, it is unlikely that the number of factors
needed for the growth of a transplanted tumor can be determined in a valid
manner by the method mentioned. However, it is probable that differences in
the constitution of the individuality or species differentials of cells and tissues
in different individuals or species extend also to the erythrocytes, and that
here they may be represented by agglutinogens, and that the constituents of
the individuality and species differentials in the tumor cells, which are strange
to the host, give rise to several kinds of immune substances, one of which
consists of hemagglutinins. As stated, we believe that it is the genes of the
tumor, which are not represented in the host, which are the precursors of
strange constituents of the individuality and species differentials in the tumor,
and which thus, indirectly acting through the organismal differentials, may
give origin to processes of immunity and thus help to determine the fate of
the transplanted tumor.

As to the determination of the "susceptibility factors" necessary for the
growth of a tumor in a host by counting the number of takes in the F2 hybrids
between a favorable and an unfavorable strain, this is in principle the method
which is used for establishing the number of multiple factors required for the
appearance of a character in an individual, in case the father and mother
strain differ in the number of the genes, needed for this purpose, which they
contribute to the fertilized egg. In regard to the number of "susceptibility fac-
tors" found by using this method of determination, this differs in each kind
of tumor; by making a sufficiently large number of assumptions as to the
number of factors directly concerned and by having recourse to modifying
factors, it will be possible, approximately, to fit all ratios found in the F2
generation of hybrids into a certain formula; but it is difficult to see the
advantages gained by establishing such a formula applying only to one
particular tumor. However, the growth of a tumor depends not only upon
certain genes in the host,, but, as we have already indicated, various factors
of a primarily non-genetic nature help to determine the number of successful

HEREDITY AND TRANSPLANTATION OF TUMORS 379

transplantations in the F2 generation of hybrids between susceptible and
non-susceptible strains, such as the different degrees of resistance, the growth
momentum, and the mode of inoculation of a tumor. The number of success-
ful takes in the F2 generation depends, therefore, not only on the relations of
the organismal differentials of host and transplant, but also on various sec-
ondary factors, and the number of takes in F2 hybrids might be quite different
if these secondary conditions were altered. Moreover, if we use the percentage
of takes of tumors as the criterion for the presence of genes in the tumor, which
are compatible with those of the host, we apply a relatively coarse standard of
measurement. There is no intergrade between take and non-take ; the tumor
either grows continuously after transplantation, or it does not grow ; it may
grow for a while, then retrogress and ultimately disappear. But there exist
various finer kinds of distinction between degrees of compatibility or non-
compatibility of host and graft, such as variations in growth energy, in the
length of the latent period, and in the number of cells or size of a piece of
tumor tissue which permits a successful transplantation. If these variables
should also be considered, the gradations in the fate of tumor transplants in the
F2 generation would be much greater, and correspondingly, the number of
factors which are supposed to determine the compatibility between host and
transplant would likewise be found to be much greater. By taking merely into
account the proportion of the number of takes to the number of non-takes in
the F2 generation, a threshold value is determined, namely, a slight excess or
deficit in the sum of the large number of variables which decide the continuous
growth or lack of growth of the transplanted tumor. Such a determination
is not identical with the study of the differences between the individuality
and species differentials of host and transplant.

In transplantation of normal tissues, much finer standards of measurement
are used in the evaluation of the compatibility between host and transplant than
in transplantation of tumors, where the percentage of successful transplanta-
tions alone is considered, and consequently the number of genetic factors on
which this compatibility depends has been found to be great in the case of the
former.

Although the non-genetic factors which we have discussed play a certain
role in the transplantation of cancerous tissues, and, to a less extent, also of
normal tissues, still, in both it is essentially the genes which fix the con-
stitution of the organismal differentials, and therefore the result of trans-
plantation depends largely on the relation of the individuality and species
differentials in transplant and host. We have already referred to some of the
essential facts which prove this conclusion. Autotransplantation succeeds as a
rule, and autotransplantation means transfer under conditions in which the
individuality differentials and their precursors, the genes, are the same in
host and graft. Conditions might be different if somatic mutations were char-
acteristic of tumors. In this case, an incompatibility might arise even between
autotransplant and host; but this has not been observed. More or less ap-
proaching autotransplantation is transplantation into closely inbred strains ;
but it must again be stated very definitely that even the inbred mouse strains

380 THE' BIOLOGICAL BASIS OF INDIVIDUALITY

D, C57 and others are not homozygous; not even the A strain, which ap-
proaches homozygosity more than other strains, is completely homozygous.
But such inbred strains come near to this state to a degree which enables
cancerous tissues to pass the threshold point which makes possible the con-
tinued growth of the transplants in other individuals of such a strain;
whereas in individuals of different strains this threshold point has not yet
been reached. On the other hand, normal tissues transplanted within these
inbred strains quite frequently reveal the lack of a perfect identity between
the individuality differentials of host and transplant. Analogous conditions
are found if we compare transplantations of cancerous and of normal tissues
from hybrids between two different inbred strains to parents, and vice versa,
in cases in which the donors of the transplants belong to one of the two inbred
strains. Tumor transplants, owing to the largely non-genetic characteristics
which they have acquired, are able to pass the threshold point separating non-
growth from growth in the new host, if parent tissue is grafted to the hybrids ;
whereas normal tissues, although they also do not evoke marked signs of in-
compatibility in the hybrids, still in many instances, call forth some reactions
on the part of the host and may undergo a moderate degree of injury. How-
ever, in transplantations from hybrids to parents, tumors as a rule have not yet
passed the point of threshold which allows them to grow, while normal tissues
are injured in such a host to a higher degree than in the reciprocal transplanta-
tions, but because of the use of finer criteria the results are not considered,
to the same degree, to be completely unfavorable or negative as they are when
tumors are used in this type of transplantation. These differences between
normal tissues and tumors are then not caused essentially by differences in
the genetic constitution, but either by non-genetic factors, or by the methods
applied in the evaluation of the results. If we deal with other strains which
have not yet reached so high a degree of homozygosity, we should find various
averages in the number of takes; the less the strain has been made homo-
zygous by close inbreeding, the greater should be the number of animals
which need to be examined in order to arrive at valid figures indicating the
connection existing between compatibility of tumor and host and the genetic
relationship between donor and host.

Additional data which prove the significance of the individuality and species
differentials for the successful transplantation of tumors are furnished by
experiments in immunization against tumor grafts. It is possible, although
only to a limited degree, to immunize an animal by a previous transplantation
of normal, and especially of embryonal tissue or by injection of red blood
cells against a tumor transplant. In order to accomplish such an immunization
against the individuality differential of a tumor, the tissue serving as antigen
must belong to the same species as the tumor to be inoculated subsequently, but
it must differ in the genes which determine individuality from those of the
host. Such genes; which occur in the antigen but not in the host, give rise to the
immune mechanism, and, in all probability, to the formation of antibodies.
If antigen and host are heterogenous in their constitution, then the developing
immune mechanisms are directed only against heterogenous, but not against

HEREDITY AND TRANSPLANTATION OF TUMORS 381

homoiogenous constituents of the antigens. Correspondingly, the immunity
which is found in animals in which a homoiogenous tumor has retrogressed is
directed only against the same or against related homoiogenous tumors.

In accordance with the theory that the organismal differentials are pri-
marily responsible for the compatibility between tissues, we have assumed that
it is the genes, or rather their derivatives, in the tumors which are strange to
the host which call forth and determine the intensity of the reactions of the
host against the transplant ; and that the genes and their derivatives which are
identical in host and transplant do not enter into these reactions, or do so
only to a slight degree. We thus define in a more exact manner the cause of
the reactions between host and graft. According to the terms of Mendelian
heredity, the genes, which differ in host and transplant, are dominant over
the genes which are identical, the latter being recessive, although as we have
seen in our discussion of the transplantation of normal tissues, there is the
possibility that also the latter may exert a certain effect.

In agreement with the interpretation given here are the results which Eisen
and Woglom obtained in immunizing rats against the growth of a trans-
planted mammary gland adenocarcinoma, which had developed in a rat be-
longing to the inbred August strain; this strain was the offspring of a cross
between two inbred strains (990 and 1561). The mammary gland tumor could
be transplanted successfully into 100% of the August strain rats and into
78% of the 990 strain rats. Previous inoculation of embryo skin derived
from August strain rats was not able to immunize August strain rats; nor
was it possible to immunize 990 rats against the growth of the adenocarcinoma
by means of strain 990 embryo skin ; but embryo skin of August strain rats
was very effective in immunizing animals belonging to strain 990. This is a
good illustration of the fact that it is the strange genes which make possible
the development of efficient antigens, and that it is the degree of strangeness
of the individuality differentials in host and transplant which determines
the degree of the antigenic effectiveness of the normal tissues or tumors.

Another difference between normal tissues and tumors or tumor-like tissues
has been noted by Furth in his experiments concerning the transmission of
leukemia in mice. He observed that in certain inbred strains a large propor-
tion of the animals become affected by this disease. If leucocytes from a
leukemic mouse were injected into other normal mice of this inbred strain,
leukemia developed in all the animals, but leukemia could not be transferred
to another strain in which spontaneous leukemia did not occur or was rare ; it
developed in 100% of Fx hybrids between these two strains which had been
inoculated with the leukemic cells. There was a decrease in transplantability
in the F2, and still more so in the F3 generation. In backcrosses from hybrids
F1 to the susceptible parents leukemia developed in 100%, while in the back-
crosses from Fx hybrids to the non-susceptible parents it took in 50%.
Leukemia arising in a hybrid F1 could be transferred to all mice belonging
to the susceptible parent strain ; this is contrary to what should be expected
according to the theory of the organismal differentials and to what is actually
found in normal tissues and in mouse carcinoma. On the other hand, leu-

382 THE BIOLOGICAL BASIS OF INDIVIDUALITY

kemia could not be transferred to any individuals belonging to the non-
susceptible parent strain. The results were variable in F2 hybrids ; leukemia
could be transferred in 50% of F3 hybrids.

These results could perhaps be explained if we assume that in addition
to the gene sets derived from both parents, which determine the organismal
differentials of these leukemic cells, there is present in the Fx cells an intrinsic
stimulus (Gi), derived from the parent which is susceptible to the develop-
ment of spontaneous leukemia. The possession of this intrinsic stimulus
converts the lymphoid cell into a leukemic cell and makes it possible for this
cell to proliferate in an abnormal manner.

In the inbred strain of mice in which leukemia occurs spontaneously in a
high percentage of cases, a factor (Ge) is present which stimulates or
otherwise makes it possible for the leukemic cells to multiply and thus to
transfer the disease, while in other strains this auxiliary factor is lacking.
The activity of both the intrinsic factor within the leukemic cells and the
auxiliary factor would enable the cells to overcome the resistance to the
growth which is due to the presence of a combination of a set of strange
genes and a set of genes identical with those of the host. We have referred
to a similar condition already in the preceding chapter, when we discussed
the effect of the continued action of Ge (hormones) on transplantation of
not yet full cancerous tumors.

Further complications may be due to the fact that long-continued trans-
plantations may modify the immunological characteristics of tumor cells and,
according to MacDowell, also of leukemic cells. However, not all leukemic
cells arising in F1 hybrids of two strains, one of which has a high and the
other a low incidence of spontaneous leukemia, behave in the manner ob-
served by Furth and Barnes. Kirschbaum and L. C. Strong found that the
leukemic cells from F1 hybrids between the CBA and F strains behaved in
the same way as typical carcinoma cells originating in such hybrids, while
the leukemic cells from other kinds of Fx hybrids in which leukemia had
been produced experimentally could behave in an entirely different manner.
But notwithstanding the existence of such complications which may arise, in
general, it may be concluded that it is the organismal differentials in host
and transplanted tumor and the genetic factors of which these differentials
are the expression which primarily determine the fate of the transplant in a
given host.

The genetic constitution of an individual influences the receptivity or
resistance to the inoculation of a tumor by way of the individuality and
species differentials of which the genes are the precursor elements. Further-
more, there are indications that special growth promoting substances may
aid in the growth of transplanted cancer cells in certain cases, and it is
probable that these growth promoting substances (Ge) which may be either
hormone-like or virus-like, are also ultimately determined genetically.
Organismal or individuality differential substances may be fixed in tissues as
well as be present in the circulating bodyfluids. In certain respects they

HEREDITY AND TRANSPLANTATION OF TUMORS 383

represent gene hormones through which in the course of embryonal develop-
ment gene effects may be transmitted to the recipient tissues and organs.

There are two experiments which indicate that substances of this kind
may be transmitted by means of parabiosis from one animal which is
genetically receptive to the growth of a transplanted tumor to the partner
which is genetically resistant to such a tumor. Thus Zakrzewski observed that
a Wistar rat, a strain not susceptible to the growth of the Jensen sarcoma,
could be made susceptible by the parabiotic union with a susceptible Warsaw
rat. Similarly Cloudman found that a hepatoma which originated in the C57
leaden strain, and which could readly be transplanted into mice belonging to
this strain, but which could not be transplanted as a rule into black C57
strain mice could be made to grow in the C57 black if the latter was united
by parabiosis with a C57 leaden strain mouse.

However, as a rule it does not seem to be possible to change the inherited
strain receptivity or resistance of an animal by parabiotic union with an
individual belonging to a strain differing in these respects from the first
strain. Each of the two partners retains its own specific mode of reaction
against the transplant. It is perhaps necessary that the differences in the
constitution of the individuality differentials of the two parabiotic partners
do not exceed a certain limit if a differential favorable to tumor growth
shall exert its characteristic effects in the second partner. But as stated it is
possible that in addition special substances favoring the growth of certain
cancer cells may be involved in this effect.

Chapter J

The Relation Between Growth Energy, Adaptive

Processes and Organismal Differentials in

the Transplantation of Tumors

In order to evaluate the role which organismal differentials play in the
growth and transplantability of tumors, it will be necessary to consider
separately certain variable factors which, in their interaction with
organismal differentials, may influence the results of transplantation. Among
these the most important ones are changes in growth energy and adaptive
processes which may take place in the tumor in the course of serial trans-
plantation in response to conditions present in the host; processes of im-
munity may also be considered as adaptive changes, but they occur in the
host as a reaction to the growth of the tumor. Adaptive processes in the
tumor may consist in changes in the readiness with which organismal (indi-
viduality) differential substances are produced and given off into the circu-
lation of the host; likewise, the sensitiveness of the tumor and its power of
resistance to injurious substances of the host may be modified; this would be
added to primary differences in the sensitiveness which distinguish different
types of tumors.

However, the degree of adaptability of a tumor to a new environment
may be determined, in addition, by variations in growth energy which may
take place in the course of serial transplantation. The growth energy of
tumors was considered by us (1905) as one of the factors on which depends
their transplantability, a low degree of growth energy rendering transplanta-
tion more difficult. In addition, we recognized in the host, as significant for
the fate of the graft, a factor corresponding to what we later defined as
individuality and species differentials. Among the growth factors we dif-
ferentiated those inherent in the tumor cells (Gi) from others circulating
in the bodyfluids of the host (Ge), and furthermore, we differentiated factors
which permit a tumor to live, without necessarily enabling it to grow, from
other conditions which enable it to grow. The growth energy was measured
by the duration of the period of latency as well as by the rapidity of growth
of the visible tumor. Different tumors were seen to differ very much in their
growth energy and in their ability to withstand the injurious conditions
associated with the process of transplantation, and among the latter there
were some tumors which did not grow even after autotransplantation. We
distinguished, therefore, between weakly and rapidly growing tumors, be-
tween temporarily and permanently growing tumors, and between transplant-
able and non-transplantable tumors; also between stable and labile tumors,
the former retaining their growth energy unaltered, the latter, as a result of

384

TRANSPLANTATION OF TUMORS 385

various stimuli, showing an increase in growth energy, especially in the
course of the first transplantations. If the constitutional factors in host or
transplant, in particular the relations between organismal differentials of
host and transplant, are unfavorable, the various kinds of growth stimuli
may not be able to overcome the obstacles to transplantation, but on the
other hand, if the inherent specific tumor stimulus (Gi) is very strong, the
tumor may be able to overcome a not quite adequate constitutional condition
and may dispense with growth hormones or other growth promoting sub-
stances (Ge) circulating in the bodyfluids. The less favorable the constitu-
tional condition of the organismal differentials, the stronger must be the
growth factors, those present in the host as well as those residing in the
transplanted tumor cells, if a continuous growth of the tumor shall be
accomplished.

Because of the action of these variables, including the relationship be-
tween the individuality differentials of host and transplant, growth energy
and transplantability of a tumor do not need to follow a parallel course. The
difference between these two sets of conditions was especially marked in the
case of a carcinoma originating in a Japanese waltzing mouse studied by us;
all the transplants grew, but the growth energy of the developing tumors
was, at least in the first generation, not great. Here the constitutional factors,
the individuality differentials, in the host and graft were well adapted to
each other. The distinction between growth energy and transplantability was
subsequently emphasized also by Apolant, and it still is useful at the present
time.

I. Changes in Growth Energy

Of the two sets of factors, the constitutional factors residing in the host
and those determining the growth energy of the tumor cells, the latter were
more readily accessible to experimental analysis and the first attempts we're
therefore directed towards their modification by exposing the tumor cells
to certain physical and chemical conditions. These experiments revealed the
degree of what may be termed the elasticity of the tumor cells, their ability
to recover from injury and to regain the growth energy which had been
diminished by their exposure to injurious factors. Such reactions on the
part of the tumor cells also represent adaptive processes ; but they are
temporary, not permanent adaptations. In the early period of experimental
cancer investigations, the writer determined the intensity of heat required to
cause the death of the rat sarcoma cells, and Jensen, independently, made
similar determinations in mouse carcinoma. While the methods used in these
two cases were different, the results were of the same kind. We found, also,
the conditions under which certain chemical substances, such as glycerin
and KCN, kill the tumor cells. It could be shown (1903) by the use of inter-
mediate intensities in physical and chemical actions that between the full
virulence and the death point of the tumor cells there exists an intermediate
stage, in which the latter are still alive though growing with a much
diminished energy. In certain cases, tumors grew temporarily; then the

386 THE BIOLOGICAL BASIS OF INDIVIDUALITY

growth ceased and a retrogression took place. It is therefore possible to
diminish experimentally the growth energy of cancers. These results applied
equally to sarcoma of the rat and to adenocarcinoma of the mouse. In some
instances a very interesting phenomenon was observed; after heating the
tumor in vitro for twenty to twenty-six minutes at 44°C, the growth energy
of pieces, after transplantation into a living animal, decreased, but following
this early period of slowed growth a certain degree of recovery set in. While
usually this recovery was incomplete and the tumors which developed re-
mained smaller than is normal for unheated tumors, in some instances the
recovery was complete. However, in other cases the growth energy remained
weak and at last the resulting tumors became stationary or retrogressed. This
was especially noticeable after heating pieces for fifty-five to sixty minutes,
when there was a great decrease in growth and recovery was rare. But even
under these conditions recovery sometimes occurred and a period of more
rapid growth followed. Some tumors showed what we called an oscillating
growth, in which a weak growth or a stationary condition, or even an
incomplete retrogression, was followed by a definite but slow growth, and
this again by a cessation of growth and retrogression. On the whole, the
effects of the intensity of heat on the latency period, the growth energy
of the tumors, and the number of retrogressions took a parallel course.

Inasmuch as the change in growth energy of tumors produced by an
injurious external agent could persist for a number of cell generations, it
became of interest to determine whether repeated applications of heat, in
successive transplantations, would lead to a summation of the injurious
effects, or whether in the course of subsequent transplantations a recovery
might still take place. There was noted such tendency of the tumor cells to
recover from these injurious effects and this process seemed to be aided
by an intervening transplantation into a new host. However, the restitution
of the full growth energy in previously heated tumors was delayed after
transplantation under these conditions. There occurs then, after all, in these
cases, a summation of injuries caused by the heating and the process of
transplantation, but this condition may be followed after some time by
recovery. Such a recovery may also take place in tumors which have been
injured by other means than heat; a heterotoxin injures the tumor trans-
planted into a strange species, but recovery may occur after return into
the same species, as Ehrlich has shown. Chambers, Scott and Russ noted the
injurious effect of the action of X-rays on rat sarcoma. In this case, also, a
gradual recovery was seen after successive transplantations. And inasmuch
as the process of transplantation as such is an injurious one, we may con-
clude that this faculty to recover from injurious effects is one of the condi-
tions that makes possible the continued transplantation into successive gen-
erations of strange individuals of the same species. While thus in most
instances a summation of the injuries caused by heat, leading to irreversible
changes, does not take place in successive generations, but instead recovery
follows, the opposite effect, a state of increased resistance to heating as a
result of repeated exposures to higher temperatures, is likewise lacking.

TRANSPLANTATION OF TUMORS 387

If, following exposure to a sufficiently intense heat the tumor cells are
injured, they may no longer be able to resist to the same degree as normal
cancer, the activity of the connective tissue of the host, which thus begins
to envelope the tumor with a fibrous capsule and to restrict its expansive
growth. But following transplantation into a new host, a recovery of the
tumor again may be accomplished and the tumor cells may now predominate
over the stroma cells of the host. Furthermore, in accordance with the
diminution in growth energy following the heating, we found that the
number of cells undergoing mitotic division is distinctly diminished, although
mitoses are not quite suspended ; however, mitotic proliferation may occur,
as we have shown formerly, even in retrogressing tumors. Lastly, we noted
that as the result of the depression in growth energy following heating, cer-
tain reparative processes, which otherwise could take place in the tumor, are
inhibited ; thus the growth of active tumor cells into the central necrotic areas
and the replacement of the latter by these cells are retarded. As these experi-
ments show, we are able to produce through experimental interference,
depressions in the growth energy of tumors, with or without subsequent
complete recovery, or with only a temporary recovery. A similar diminution
in growth energy, number of mitoses and, oxygen intake, has been observed
by Maus, Craig and Salter after transplantation of mouse sarcoma 180 into
immunized mice; as a result of the immune processes, conditions injurious
for the tumor cells had been created.

The experiments to which we have referred so far, concern sarcoma, but
similar results can be obtained also in experiments with carcinoma. Thus,
the writer and E. P. Corson-White observed that if the growth energy has
been depressed, either through graded heating of the pieces of carcinoma
preceding transplantation or through transplantation of the tumor into
unfavorable strains of mice bearing a different strain differential, transplanta-
tion of the injured tumor cells into other more favorable mice might lead
to the development of tumors which grew much more actively than the
injured tumor which had been used for transplantation, although as a
general rule the tumors developing under these conditions showed less
growth energy than the average normal carcinoma No. IX. It was possible
through continued serial transplantation of depressed tumors to raise still
further their growth energy. In this manner, tumor tissue which otherwise
would have perished, could be saved. But also in this series, as in the
preceding one, grafted pieces of tumor failed to develop when once a certain
stage of retrogression had been reached. Certain types of tumors which are
presumably very sensitive to injury may therefore not respond to these
procedures with a resumption of their growth energy. It seems, moreover,
that in different types of tumors the inherent potential growth energy differs
and the behavior of retrogressing or stationary tumors may depend also
upon this factor. There is a constant balancing between the inherent growth
energy and antagonistic factors, such as marked differences between the
organismal differentials of host and transplant, or direct injury of the tumor
caused by the graded application of heat or of certain chemicals, or, in some

388 THE BIOLOGICAL BASIS OF INDIVIDUALITY

cases, also by microorganisms. In principle, all these and still other more or
less accidental factors act in a similar way. Thus we can understand that
under certain circumstances these two sets of factors may approximately
balance each other and thus the oscillating growth which we have described
may be brought about.

However, not only a depression in growth energy of tumor cells, but also
the opposite effect, can be obtained experimentally, namely, an increase in
growth energy in cells which possess either a normal or a very low level of
growth energy, or which may be retrogressing. Clowes and Baeslack observed
that in not very virulent tumors the growth energy may be stimulated through
a very mild exposure to heat; after subjecting tumor material for one hour
to a temperature of 40°-41°C, they noted a certain stimulation. Michaelis
also found such a stimulation under similar conditions, as well as after the
use of very low concentrations of otherwise poisonous substances. But, pre-
vious to these experiments, in our early serial transplantations of rat sarcoma,
we had produced stimulation in tumors in which, as a result of injurious
factors, the growth energy had been lowered, leading to a stationary state
or to retrogression. In a number of such tumors it was possible, by mechanical
means, such as pulling a thread through the cancer, making an incision into it,
or excising a piece of the tumor, to bring about a resumption of growth,
which occurred in certain cases even when transplantation of a tumor nodule
to a different place in the same animal had no or only a slight effect. But in
another experiment, transplantation of a stationary tumor into a second
animal led to a complete restoration of the growth energy of the tumor, which
subsequently could be further transplanted into other animals. Such a stimu-
lation was accomplished in stationary and retrogressing tumors only if
mitotic activity was still present in the tumor cells; if this had ceased, the
results were unsatisfactory. Thus it is seen that certain mechanical factors,
such as incisions, extirpation of pieces of tumor, removal of pressure exerted
by a fibrous capsule, or the process of transplantation, may stimulate growth
energy; but it may also be that, in some transplantations, the transfer to
hosts with strange individuality differentials may have had an additional
growth-stimulating effect.

We have referred already to the increase in growth energy which occurs
quite commonly after transplantation of spontaneous tumors into other indi-
viduals of the same species and strains ; this was noticeable in our first trans-
plantations of rat sarcoma; it was very definite also in our transplantations
of a tumor which had developed spontaneously in a Japanese waltzing mouse,
and which could be successfully transplanted into all other Japanese mice.
Although in this instance the individuality differentials in tumor and waltzing
mice serving as hosts were sufficiently similar to allow takes in 100% of the
transplantations, still there was a marked increase in the growth energy of
the grafts in the early generations. This may therefore be attributed to a
stimulation of the tumor cells resulting from the process of transplantation,
as such. Similar effects of transplantation were observable also in the sub-
sequent transplantations of chicken sarcoma by Rous and Murphy. Here it

TRANSPLANTATION OF TUMORS 389

was apparent, furthermore, that the more actively the tumor grew, the greater
was the number of individuals in which it took. Likewise, in the experiments
of Chambers, Scott and Russ with a rat carcinoma which had been injured
through radiation, there was a parallelism noticeable between the change in
growth energy and number of takes. It was also found in the transplantation
of leukemic cells into individuals of the strain in which the leukemia had
originated.

There was, moreover, in our experiments a correlation between the
growth energy of spontaneous tumors and their transplantability into other
individuals, and Woglom, too, noted a parallelism between the number of
successful transplantations of spontaneous tumors into other mice and the
growth energy of these tumors. However, Woglom also observed that even
very slow-growing tumors may yield a high percentage of takes, an observa-
tion which corresponds with our above mentioned experiments with the
Japanese mouse, and which may be explained essentially by the great simi-
larity of the organismal differentials of host and graft. But, in general, a
tumor with greater growth energy will be better able to overcome the re-
sistance which relatively unfavorable constellations of the individuality
differentials present, than a tumor with a lesser growth energy. In addition
to this factor, also variations in the resistance of various tumors to injurious
conditions and in the rapidity with which organismal differential substances
are produced by tumor and host may interfere with the proportionality be-
tween growth energy and transplantability.

The increase in growth energy which so often follows the first trans-
plantation of a tumor is limited ; it usually reaches a maximum in the first or
in one of the following generations of tumors and from then on remains
approximately constant. But, on the other hand, there can be no doubt as to
the reality of this change and the great frequency of its occurrence. On the
contrary, the rhythmic variations in growth and transplantability of tumors,
which, as Bashford, Murray and Cramer assumed, take^f place in successive
generations of a transplanted tumor and which they attributed to conditions
inherent in the tumor, were probably caused by changes in environmental
factors affecting the growth energy of the tumor cells. Bashford believed,
furthermore, that through selective transplantation, a tumor may be divided
into substrains, which differ in certain characteristics and vary independently
of each other in regard to growth rhythms. He held that a tumor represents
a conglomeration of cells endowed with different characteristics. These
rhythmic changes were not found by Fleisher in the case of carcinoma No.
IX, nor by Bittner in his series of transplantations. Bittner holds that varia-
tions in the individuality differentials of the hosts, due to the use of mixed
strains of animals, are responsible for these apparent rhythms.

II. Adaptation of Tumor Cells to Environmental Conditions

In addition to the factors mentioned, we have to consider some special
adaptive changes which take place between transplant and host in the course
of transplantations, as an occurrence which may influence the transplanta-

390 THE BIOLOGICAL BASIS OF INDIVIDUALITY

bility of tumors and complicate the analysis of the organismal differentials.
However, it is necessary to distinguish from real adaptive processes a condi-
tion which may lead perhaps to similar changes, but is different. As a result
of selective transplantation, lines of tumors, differing in certain character-
istics, may be separated from the original tumor. By always selecting the
most actively growing tumors for transplantation it was thought possible
to separate from the tumors with ordinary growth energy and transplanta-
bility, a line which exceeded this average tendency. In these instances we
would have to deal not with adaptive changes in the tumor — the character-
istics of the tumor cells remaining the same throughout — but with a selection
of certain types among several already in existence. In the case of true
adaptation, on the other hand, actual changes in the characteristics of tumor
cells would occur. Ehrlich used such a method of selection in order to obtain
readily transplantable tumors. He compared this procedure with that em-
ployed in order to increase the virulence of bacteria, where, in serial inocu-
lations of certain microorganisms into susceptible animals, the most virulent
strain of bacteria was selected for each inoculation. However, Ehrlich
believes that at the same time changes take place in the tumor cells in the
course of transplantation.

In contradistinction to the increase in growth energy in successive genera-
tions of transplantations which we had observed, Ehrlich stressed the increase
in percentage of takes in successive generations of transplanted tumors, and
in accordance with his conception of athrepsia, as the main factor which
determines the life and growth of cells, he explained the increase in trans-
plantability in the course of serial transplantations as due to a new produc-
tion of "nutriceptors" in tumor cells, which, according to his views, took
place under the unfavorable conditions following transplantations into new
hosts. Thus, the behavior of tumor cells was explained in the same way as
the origin of strains of trypanosomes resistant to trypanicidal substances.
Ehrlich operated therefore, essentially with one variable factor, namely, the
difference in the ability of different cells to attract foodstuffs to themselves,
and he assumed that a selection takes place in cells which differ in their
power to respond to unfavorable conditions with changes in their nutriceptor
apparatus. However, it would be difficult to explain on this basis the fact
that the variations in growth energy and transplantability which do occur
do not always take a parallel course ; Ehrlich did not take into account the
differences which exist in the individuality differentials of different hosts, and
he also failed to consider the effects of separating strains of hosts. Further-
more, he did not consider the relations which exist between growth energy
and transplantability.

Various observations make it very probable that adaptive changes in the
constitution of tumors can actually take place. The considerable increase in
the number of takes, which has been noted by different investigators in the
course of serial transplantation of spontaneous tumors into strains of animals
in which they at first grew only with difficulty, is probably at least partly due
to certain adaptive changes which have arisen in the tumors in the new host.

TRANSPLANTATION OF TUMORS 391

Thus Bashford and Murray found that the Jensen mouse carcinoma, which
grew readily in Danish mice, but only with difficulty in English mice, began
to grow at last also in the latter in the course of continued transplantations.
Similarly, the first Rous chicken sarcoma which, according to Rous and
Murphy, at first took only in blood relatives of the animal in which it had
originated, after further transplantation grew well also in non-related
chickens of the same variety, and after still further propagation it became
adapted even to growth in different varieties of fowl. On the other hand, the
second Rous sarcoma, an osteochondroma, grew from the start in all varieties
of fowl, in conformity perhaps with the relatively low degree of sensitiveness
of cartilage to differences in individuality differentials. Rous and Murphy
observed also a selective process, which led to the opposite effect ; by
selecting weakly growing tumors for further transplantation, a line of
tumors was propagated which tended to undergo retrogression. In this case
evidently the tumor cells had been injured through unfavorable organismal
differentials of the host, or through certain secondary factors — an injury
similar to that obtained by heating — and after successive transplantations
these injuries accumulated. We have already referred to the experiments of
Duran-Reynals, in which marked adaptive changes were observed in Rous
chicken sarcoma cells after transplantation into ducks ; these changes affected
primarily the agent situated in the cells, but secondarily, the cells themselves
seemed to undergo corresponding adaptive changes, presumably under the
influence of the agent they contained.

Similar in certain respects were the adaptations which Roffo noted in a
transplantable rat tumor. Through continuous selective tranplantation he
succeeded in adapting this tumor to growth in different varieties of rats. At
last it could be successfully transplanted in 70 per cent of wild rats, in which
it had not been able to grow at all in the beginning. It was of interest that
also in these experiments there was a parallelism between the increase in
transplantability and growth energy of the tumors, indicating that we may
not have had to deal solely with an increase in transplantability due to special
adaptive processes, but also to an increase in growth energy. Similar adaptive
changes were apparently observed by Gheorgiu when he transplanted mouse
tumors into very young rats. With successive passages the process of complete
retrogression in the heterogenous animals became more and more delayed,
until at last growth extended as long as to the twenty-seventh day following
transplantation. After several passages in newly-born rats, in which presum-
ably the mechanisms of reaction against strange organismal differentials are
not yet fully developed, the tumors could be transplanted also into older suck-
lings, but here the tumor did not live as long as in the very young animals. The
retrogression and absorption in these young animals seemed to follow without
the aid of leucocytes (lymphocytes). After reinoculation into mice the tumors
grew with increased intensity. There are still additional experiences which
point to adaptations taking place in tumors in the course of serial trans-
plantations and causing an increase in their transplantability. Furth and others
observed that also leukemic cells after continued serial transplantations be-

392 THE BIOLOGICAL BASIS OF INDIVIDUALITY

came more virulent, which means that they multiplied more rapidly in the host ;
at the same time, certain structural and other changes occured and these cells
acquired the ability to propagate in alien strains into which they could not be
transplanted in the beginning. However, in such experiments it is difficult to
determine how far the increase in transplantability of the leukemic cells is due
to the increase in growth momentum and how far it is due to actual adaptive
processes to strange individuality differentials. In some cases, on the other
hand, the contrary effect, namely, a greater sensitiveness to strange individu-
ality differentials, has been observed in the course of continued transfers.

We have referred above to the experiments of Gheorgiu, in which adaptive
processes, arising in mouse tumors, gradually increased the ability of these
tumors to grow also in heterogenous, although nearly related species. Similar
observations have been made in the Putnoky experiments, in which a mouse
carcinoma could be serially transplanted into rats ; but these we have discussed
in an earlier chapter. We may, however, add here that in the early passages
there was more necrosis than in later ones, in which the tumors were able to
maintain themselves also in somewhat older rats. There was, moreover, a
diminution in the amount of stroma in the rat-adapted mouse tumors. In these
heterotransplantations, as well as in the transplantation of leukemic cells into
different strains, certain structural changes took place in the course of con-
tinued transplantations; furthermore, rat-adapted tumors, when transplanted
back to mice, showed a marked growth energy.

In a considerable number of experiments it was possible to make tumor or
leukemic cells grow in unfavorable strains, if the aggressive power of the hosts
had first been depressed by some experimental means. Preliminary treatment
of the host animals with X-ray or with trypan blue had this effect. Cancerous
or leukemic cells, which had been propagated for some time in such specially
prepared hosts, were afterwards able to propagate in otherwise unsuitable
strains, even without a preceding experimental depression of the aggressive
power of the host animals. Another method, which led to similar results, was
used by Margaret R. Lewis, who inoculated mouse sarcoma into mice belong-
ing to strains which were genetically unsuitable for the growth of this tumor.
The first inoculations of this kind were unsuccessful; but after repeated
inoculation of pieces of this sarcoma into the same individual mice, the sar-
coma grew in the end, and after the tumors had once succeeded in growing in
alien strains they could be further propagated in these strains without much
difficulty. Several investigators have found that tumors which did not grow
after subcutaneous, intramuscular or intraperitoneal transplantations, grew
successfully in the brain or in the anterior chamber of the eye. Such tumors
could subsequently be successfully transplanted, also, by subcutaneous or
intramuscular inoculation into animals in which originally they would not have
grown in these places. But such an increase in the capacity of tumors to grow
elsewhere after they had first been transplanted into the anterior chamber of
the eye was not noted in some recent experiments which Greene carried out
with rabbit tumors.

As to the mechanism underlying these adaptive changes, it might be assumed

TRANSPLANTATION OF TUMORS 393

that these are due to somatic mutations in the tumor cells, rendering the organ-
ismal differentials of tumor and host organisms more similar; thus the differ-
ential substances in the tumor, which act as toxins for the host, would be di-
minished, and the reaction of the latter, causing an injury to the tumor, would
be lessened or prevented. According to this interpretation, mutations would
make the tumor better able to resist injurious conditions. Thus Warner and
Reinhard interpreted certain changes which they recently observed in tumors
following treatment with X-rays as due to somatic mutations. They exposed
two spontaneous adenocarcinomas, which originated in the dba strain and in
the New Buffalo strain of mice-, to 100 Roentgen units in vivo, or to 50 Roent-
gen units in vitro. The non-radiated tumors grew in 100% of its own strains,
but not in strange strains. After radiation the tumors continued to grow
in 100% of the mice belonging to the strain in which the tumors originated,
but they now grew, also, in about 40% of mice belonging to strange
strains. They concluded that this result was due to somatic mutations in the
tumor cells. This is, however, improbable, because the genetic change, which
would have been required to produce the adaptation of the tumor to the strange
strain, should have lowered the successful transplantations to its own strain.
Moreover, it does not appear likely that a random somatic mutation which
had such an effect, producing the same percentage of takes in strange strains,
should have occurred independently in two different tumors belonging to two
different strains. Lastly, the Roentgen dose necessary for inducing mutations
in germ cells is much greater than the one used in these experiments. It appears
more probable that the X-rays affected a cytoplasmic mechanism, which
caused, perhaps, a diminution in the production of the organismal (individu-
ality) differentials in the tumor, and which therefore elicited a less active
reaction of the strange strain against the transplant ; this cytoplasmic change
was then transmitted to successive generations of tumor cells. In general, the
same objeections which can be raised against the opinion that cancers arise as
the result of somatic mutations in normal cells, or that variations in the growth
energy and in the number of takes, which occur in the course of the first
transplantations, have such an origin, apply also to the assumption that adap-
tive changes are due to somatic mutations. The adaptive changes, consisting in
an increase in growth momentum, and the gradual increase in takes in at first
unfavorable hosts are again due, in all probability, to changes in cellular metab-
olism which are independent of somatic mutations. There is no indication that
noticeable changes in the constitution of the organismal differentials are con-
cerned in these adaptive processes.

This applies also to the Ehrlich-Putnoky carcinoma, to which we have re-
ferred previously. The behavior of this tumor suggests that no definite change
in the species differentials of the tumor has taken place as the result of the
serial transplantation of tumor cells into rats. This is true although the rat-
adapted strain induces in the rats, in which it has grown and subsequently
regressed, immunity against Walker rat carcinoma and Jensen rat sarcoma;
but the mouse-adapted Putnoky tumor also has some immunizing effect,
although it is less effective in this respect. However, it is significant that this

394 THE BIOLOGICAL BASIS OF INDIVIDUALITY

rat-adapted mouse carcinoma could not be transplanted in rats previously
treated with normal or cancerous mouse tissues, while a previous treatment
of rats with rat tissue did not prevent transplantation. We may therefore as-
sume that the rat-adapted strain of the Putnoky mouse tumor bears essentially
the species differentials of the mouse and it is possible that its apparently in-
creased effectiveness in the production of immunity in rats may be due to its
growth momentum, which is greater in the rat-adapted strain than in the
mouse-adapted strain. Yet, even if the increase in immunizing power which
distinguishes the rat-adapted strain from the mouse-adapted strain should
not be due to the increased growth momentum, it still would not be necessary
to attribute such changes to somatic gene mutations ; instead, it might be at-
tributed with greater justification to metabolic changes taking place in the
tumor cells, independently of constitutional modifications of the organismal
differentials. The same considerations apply to the alterations in the specific
immunizing action which, according to MacDowell and his associates, leukemic
cells undergo in the course of serial inoculation ; properties are acquired
which make these propagated lines of leukemic cells different in various as-
pects from the original leukemic cells from which they were derived; and
similar observations have been made by Dmochowsky in the case of ordinary
cancerous tissues.

Somewhat related to the experiments with the Putnoky tumor are those of
Lumsden, which also indicate that a certain adaptation may take place between
a tumor and a heterogenous host of a nearly related species, as indicated by the
reaction of the tumor cells in tissue cultures. Lumsden finds that if a mouse
carcinoma has been developing in a rat for a week, pieces of this tumor grow-
ing in vitro are not injured by the serum of the rat which was the host of the
tumor, and in which, therefore, immune bodies have developed against the
mouse carcinoma cells ; but such a serum rapidly kills mouse carcinoma cells
which have previously been growing in a mouse. Likewise, serum of a rat in
which a rat sarcoma has grown is not injurious to mouse tumor cells which
have been growing previously in a rat, but it is injurious to mouse carcinoma
cells which have been growing in a mouse. Yet such tumor cells, which have
become resistant to the effects of heterogenous immune serum acting in vitro,
retain their specific sensitiveness to transplantation into a heterogenous or-
ganism. A mouse tumor is injured after transplantation into a rat, even if it
has been growing previously in a rat. Lumsden assumes, therefore, that the
immunity thus acquired by the tumor cells is active only against constituents of
the blood and, moreover, that the tumor cells growing in a heterogenous host
acquire the ability to use the amino-acids specific for the latter as building
stones for proteins, which are no longer characteristic of their own but of the
foreign species ; this would imply that the species differential of the tumor
cells changes into that of the foreign species. However, all the data known so
far point to the conclusion that the animal organism transforms amino-acids
into protein of its own kind. The adaptation occurring in the tumors growing
in heterogenous hosts must therefore be due to processes of a different nature.

There have thus been established certain variable factors which affect the

TRANSPLANTATION OF TUMORS 395

transplantability of tumors into different kinds of hosts, such as the growth
energy of tumors and their power to adapt themselves to conditions present
in the hosts. These characteristics, or the potentiality to develop them, were
acquired during the process of the transformation of normal tissue cells into
cancer cells, and this transformation is due to the interaction of genetic factors,
transmitted by the germ cells, with variable stimulating factors ; both these sets
of factors, the intrinsic genetic and the extrinsic stimulating ones, are active
in the organism in which the transformation to cancer occurs. Such a process
is a graded one, which takes place step by step, and it is probable that to the
stage which has been reached in this transformation there correspond different
degrees of those characteristics which distinguish tumors from normal tissues.
Prominent among these characteristics is the increase in growth momentum
and the range of variations which the growth momentum may undergo, and
it is probable also that the ability to undergo adaptive changes was acquired, or
at least intensified, during the cancerous transformation.

That adaptive changes to conditions otherwise injurious may be effected in
tumor cells has been shown in a more direct way in experiments by Fleisher
and the writer. We observed that intravenous injections of solutions of
colloidal copper into mice diminish the growth-rapidity of a mammary gland
carcinoma in these animals; but if tumors that have been subjected to the
influence of colloidal copper for some time, are then transplanted into other
mice which subsequently were injected with solutions of this substance, the
developing tumors were found to be more resistant to the action of colloidal
copper than a line of transplanted carcinomas which had not previously been
treated in this way. Similar effects were noted when hirudin was substituted
for colloidal copper. Both of these substances immunized the tumor cells in a
specific manner. A corresponding decrease in the effectiveness of these tumor
growth-inhibiting agencies could be observed if mice bearing adenocarcinoma
No. IX were injected with either of these two substances from the second to
the sixth day following transplantation, and again from the ninth to the thir-
teenth day; the effect of the second series of injections was diminished
as the result of the immunizing influence of the early injections. This
immunization affected the bearer of the tumor as well as the tumor itself.
Likewise, some more recent experiments of Lignac suggest that the cells of a
mouse sarcoma may adapt themselves to the action of trypan blue injected into
mice ; here, also, it seems that we have to deal with an immunization of tumor
cells. Apparently, then, tumor cells may behave in a similar manner to try-
panosomes, which also may become adapted to various injurious substances,
such as trypanicidal preparations of arsenic.

We may then conclude that the increase which in many instances takes place
in the growth energy and in the number of growing tumors following trans-
plantation of spontaneous tumors, is due to different factors which have to be
kept distinct. In the first place, the process of transplantation as such produces
an augmented growth energy ; this may be due to mechanical stimulations
similar to those which induce regenerative growth. In addition there may,
under certain conditions, come into play perhaps a direct stimulating effect of

396 THE BIOLOGICAL BASIS OF INDIVIDUALITY

a strange individuality differential. This increase in growth energy, other
factors being equal, must lead to an increase in the number of developing
tumors, and indeed, under these conditions there can be observed a paral-
lelism between increase in growth energy and number of takes. Secondly,
there may take place in the tumor more specific changes of an adaptive
character ; the strange individuality differential of the host seems to alter the
tumor in such a way that it becomes less sensitive to the injurious action of
the strange differential. In diminishing the injurious effects of the host this
change itself also may, under certain circumstances, secondarily cause an
increase in the growth energy of the transplant. Whether a strange differential
will act merely injuriously on a tumor, whether it will also have a stimulating
effect, or whether, in the end, it will produce adaptive changes, depends pre-
sumably upon quantitative relations between the degree of strangeness of the
individuality differentials and the inherited power of resistance and other in-
herited characteristics, such as a certain modifiability of the tumor cells.

It may then be stated that transplantability, as judged by the number of
takes of a tumor, is contingent largely on the relation between the organismal
differentials in host and transplant, and on the ability of the tumor cells to with-
stand injurious influences of not well suited organismal differentials. The
latter factor depends, among other conditions, also on the actual or potential
growth energy of a tumor and on the ability of the tumor cells to undergo
adaptive changes in different environments. The organismal differentials in
host and tumor are determined directly by their genetic constitution, but the
range of the potentiality of adaptation, the increased growth momentum,
and the ability to undergo variations in growth energy are only indirectly de-
termined by genetic factors transmitted by the germ cells ; directly, they are
determined by environmental factors which are active during the transforma-
tion of normal into cancerous tissues.

This relatively high degree of adaptability to different environmental condi-
tions which we observed in tumors, distinguishes them from normal tissues,
in which such an adaptive, plastic character of the cells cannot be demon-
strated. For instance, attempts to overcome the action of unfavorable individu-
ality differentials in the host by serial transplantation of normal tissues did
not succeed. Thus, in our serial transplantations of epidermis the transplants
soon died and while we found that cartilage cells could be transplanted
serially and live for a long time — much longer than the animal in which this
tissue originated — in the end they also died and the serial transplantation
ended. It is possible that this difference between normal and tumor tissues is
due to the difference in the growth energy which exists between these types of
tissues. The greater growth energy which cancers possess makes it possible
for them to resist difficulties which would destroy normal tissues, and gives
the former a chance to react to a new environment with adaptive changes. But
there is also the probability that the changes which take place in normal tissues
when they are transformed into tumor tissues, introduce at the same time a
new type of adaptability to strange organismal differentials, which normal
cells do not yet possess ; this power of adaptation would then represent a newly

TRANSPLANTATION OF TUMORS 397

acquired characteristic of tumors which distinguishes them from normal
tissues.

However, there are some indications that also in normal tissues of higher
organisms some processes of adaptation may take place. If we stimulate the
thyroid gland of the guinea pig by means of iodine or anterior hypophyseal
extracts, the stimulating effect ceases after some time and at last, after con-
tinued applications of these substances, a refractory state with less than the
normal reactivity ensues. It is probable that in this case adaptive changes which
occur in the cells exposed to such stimulating substances are responsible, at
least in part, for the condition of tolerance attained. Similarly, if a piece of
homoiotransplanted cartilage is left for a long time in the host, the reactions on
the part of the host tissue against the transplant, instead of increasing or
showing a cumulative effect with increasing length of time, seem, as a rule,
to diminish in intensity. But, here, it is not certain how far the diminution
in reaction is due to adaptive changes in the host or in the transplant.

Reference has also been made in an earlier chapter to the observations of
Rhoda Erdman and Gassul, that a gradual adaptation of anuran amphibian
skin to heterogenous amphibian anuran hosts may be accomplished by cultivat-
ing the former for some time in vitro in culture media, which were rendered
more unsuitable through step-by-step addition of the foreign plasma from the
species to which it was desired to adapt the skin. But in these experiments
it is not certain that adaptive changes had actually taken place in the trans-
planted tissue.

Somewhat related investigations were carried out subsequently by Kimura,
who cultivated chicken tissue in vitro in duck plasma and tissue extract. The
chicken tissue thus prepared was used as antigen for the production of
precipitins. These precipitins reacted with duck instead of with chicken
antigens. Kimura concluded therefore that chicken tissue had assumed the
characteristics of duck tissue as a result of adaptive changes taking place in the
new heterogenous environment. However, instead of assuming so fargoing a
change in the species differential of the chicken tissue within a relatively short
period, the possibility may be considered that some duck plasma was admixed
to the chicken tissue serving as antigen and that the adhering duck plasma was
responsible for the production of the precipitins. That such a transformation
of the individuality differential does not actually take place is also indicated
by an experiment of A. Fischer, in which he showed that rat fibroblasts, which
had been cultivated for more then twenty-three years in chicken plasma, still
remained rat cells ; they retained their species differential and cytotoxic im-
mune serum directed against rat tissues injured the rat cells that had pre-
viously grown in chicken plasma in the same specific way as it injured fresh
rat cells. In both the case of tumor tissues and of normal tissues we arrive,
therefore, at the conclusion that in all probability definite changes in the species
differential do not take place in the course of serial transplantation, and that
the adaptive changes occurring in transplanted tumors under certain condi-
tions are not due to somatic mutations.

In the experiments which we have discussed so far, an adaptation of tumor

398 THE BIOLOGICAL BASIS OF INDIVIDUALITY

cells to a different type of host was produced experimentally, or in other cases,
the reactivity of the host against the cancerous transplants was diminished
through injection of substances which in all probability inactivated the
reticulo-endothelial system of the host. We have also referred to experiments
in which the reactions of the host against transplanted cartilage became
weaker in the course of time, thus indicating possible processes of adaptation
which took place in the host under the influence of the transplant. Quite
recently, Cloudman has published some experiments which point perhaps in
the same direction. He found that an osteogenic sarcoma, which had originated
in the tail of a C57 mouse and grew in 100 per cent of C57 mice inoculated
with this tumor but grew in a much smaller percentage in D mice, took in a
somewhat larger percentage of D mice which had been transferred at the
beginning of their embryonal development into the uterus of C57 mice and had
undergone further developments here instead of in the uterus of their real
mother. While this treatment increased the number of successful inocula-
tions and also the rapidity of growth of the transplanted tumors, the
growth of the sarcoma was not decreased thereby in C57 mice which had
developed in the uterus of D mice. Corresponding results were obtained
in experiments with a malignant melanoma which had originated in the
tail of a D mouse, and perhaps also in experiments in which Law increased
by means of foster-nursing the number of successful transplantations of
leukemic cells in mice belonging to a subline of the D strain, which differed
from the one in which the leukemia had originated and which was less favor-
able for the transplantation of the leukemic cells possessing a different
individuality differential. It is possible that the transfer of substances possess-
ing a different individuality differential by way of the uterus or by way of the
milk of the mother caused an adaptation of the host against these substances,
which was thus rendered more tolerant against the strange individuality differ-
ential of the tumor cells. But it is also possible that the substance thus trans-
ferred into the mice serving as hosts supplied the latter with a carrier of the
individuality differential more closely related to that of the tumor cells which
the latter needed for a successful growth, or that substances introduced into
the future hosts by way of the uterus or with the milk of the nursing mother
supplied the hosts with an agent which stimulated the growth of the sub-
sequently transplanted cells. There are indications that the effect observed in
these experiments is only a temporary one ; mice which were inoculated with
the tumor several months after they had received the strange substance no
longer reacted favorably to the transplanted tumor. However, it is not yet
certain whether this loss of tolerance was due to the older age of the mice
under these conditions, or whether it was due to the fact that the strange sub-
stance was gradually eliminated. All these experiments taken together do not,
therefore, suggest that variations in the growth energy or in the percentage
of successful transplantations of a tumor are due to changes in the organismal
differentials in the host or in the transplant; but they point to the presence
of factors, which, when added to the action of these differentials, may modify
the mode of the reaction of the host against the transplant.

TRANSPLANTATION OF TUMORS 399

In comparing the conditions which influence the transplantation of normal
tissues and of tumor tissues, we conclude that in both of these processes the
relations between organismal differentials of host and transplant play a similar
role, but that various factors of a secondary nature may obscure the signifi-
cance of the organismal differentials, and this applies particularly to tumor
growth. The conditions determining the growth of transplanted tumors include
the factors which control the growth of normal tissues, as well as other
factors which are specific for tumor tissue, such as the intensified growth
momentum, the possibility of increasing this growth momentum still further,
and the potentiality to undergo special adaptations in the course of serial trans-
plantations. In the analysis of tumor growth and tumor transplantations, it
is necessary to separate these various factors as much as is possible at the
present time.

Chapter 4.

Immunity and Organismal Differentials
in Tumor Transplantation

In the preceding chapters we have analyzed the relation between the
transplantability of tumors and the genetic constitution of the organisms
in which the tumors originated, as well as of the hosts, and the indi-
viduality and species differentials of these organisms. It has been stated
already that also immunity against cancer grafts may be an expression of
the organismal differentials and from this point of view various aspects
of this type of immunity will now be considered. We shall study, therefore,
mainly those phenomena in immunity which have a bearing on the role
which organismal differentials play in tumor growth, in particular, the con-
stituents of strange organismal differentials which may readily function as
antigens and thus induce immunity against grafted tumors.

Early investigators in this field, Jensen, Ehrlich and Apolant, Bashford
and Murray, applied the principles established in the study of immunity
against microorganisms, animal cells and proteins to the study of immunity
against transplanted cancer. At an early stage of these investigations, a nat-
ural immunity and an acquired immunity to microorganisms and their
toxins were distinguished. By natural immunity is understood a preformed
constitutional resistance. The development of an active immunity, on the
other hand, presupposes a previous interaction between the host organism
and the strange cells or substances against which the immunity is acquired.
In active immunity, substances (immune substances, antibodies) may be
produced, which circulate in the bodyfluids of the host and tend to injure the
strange cells or to neutralize those substances (antigens) which elicited the
immune reaction. By injecting these bodyfluids of the actively immunized
animals into other animals it is possible to transfer the immunity to the
latter, which thus acquires a passive immunity. We have already discussed
some of the conditions on which depends the existence or lack of natural
immunity to the growth of transplanted tumors, namely, the relations be-
tween the constitutional genetic factors in the tumors, which are to be
transplanted, and in the hosts, into which they are to be transferred; the
latter may be individuals of the same strain or species in which the tumors
originated, or individuals of different strains or species. The resistance to
homoiogenous or heterogenous transplantation may thus be considered pri-
marily as a manifestation of natural immunity, which depends on the relation
between the individuality and species differentials of the host and transplant.
Especially striking in this connection are the differences between the results
of auto- and homoiotransplantation. Here, reference may again be made to
the experiment in which Fleisher and the writer showed that the immunity

400

IMMUNITY IN TUMOR TRANSPLANTATION 401

which becomes manifest after extirpation of a homoiogenous tumor does not
affect an autogenous tumor growing at the same time in the bearer of the
homoiogenous tumor, nor is the extirpation of an autogenous tumor followed
by immunity against inoculation with a homoiogenous tumor.

The observation of the writer and of Jensen, that in animals in which
a first inoculation of a homoiogenous piece of tumor was not followed by
tumor formation, a second inoculation of a homoiogenous piece was also
unsuccessful, suggested to Jensen the idea that as a result of the first inocu-
lation immune bodies developed in the animal, which protected it against a
second inoculation, and that the phenomena apparently attributable to natural
immunity did in reality represent an acquired immunity. Subsequently, it was
observed however that under the conditions of Jensen's experiments immune
bodies cannot be demonstrated in the blood of the inoculated animal. Jensen's
work was the starting point for the investigations of Ehrlich and Bashford,
and their collaborators. Ehrlich and Apolant, extending to natural immunity
against transplanted tumors their conception of natural immunity against
microorganisms, assumed that specific X substances are needed to allow, in
a certain host, the growth of bacteria as well as of tumor cells. If there is
an insufficient amount of such an X substance present, a state of athrepsia
exists in the host as far as the microorganisms or cancer cells are concerned
and they are therefore prevented from growing in this host. Other investiga-
tors have attributed the natural immunity against transplanted tumors to the
action of lymphocytes, and this factor they held responsible also for the de-
velopment of an active acquired immunity against canter. Thus, in the case of
the Rous chicken sarcoma it was observed that in naturally immune fowl
lymphocytes collected around the tumor transplant ; it resembled in this respect
transplanted normal tissue, where likewise lymphocytes play a significant role.

When it was found that it is possible in a certain percentage of animals,
which varies in different cases in accordance with the kind of tumor or host
used, to produce an active immunity through inoculation of normal tissues
or of certain kinds of tumor tissue, the view was expressed by Russell that
all natural immunity against tumor grafts is in reality a manifestation of
active immunity, due to the absorption of a certain amount of the inoculated
piece, which thus acts at the same time as an antigen. Whether an animal
proved to be naturally resistant (immune) or not depended therefore upon
its ability to develop an active immunity. This conclusion of Russell, which
represents an extension of Jensen's view, was very widely accepted and has
found expression even in recent literature. However, while active immunity
undoubtedly plays an important role in determining the fate of transplanted
tumors, this interpretation does not explain why certain individuals should
develop an active immunity, whereas others are not able to do so, and this is
the important point which needs to be elucidated. In the case of normal tissues
we have seen that such an interpretation would be inadequate. Here, the
primary relation between the organismal differentials of host and transplant
is the determining factor, and tumor tissue has retained in many essential
respects the characteristics of normal tissues, with the addition of certain

402 THE BIOLOGICAL BASIS OF INDIVIDUALITY

peculiarities secondarily acquired. Also, in the case of transplanted tumors
an active immunity develops only if there exists a primary incompatibility
of the organismal differentials of host and transplant, although such a primary
incompatibility between the organismal differentials of host and transplant
may in certain cases be insufficient to prevent the growth of implanted tumors.
But, as we have stated already, with tumors an active immunity seems to be
of much greater importance in preventing the growth of the transplant than
with normal tissues.

In the majority of cases it seems to be the strange organismal differentials,
and in particular the strange individuality differentials, which serve as antigens
in the production of an active immunity. Therefore, under normal conditions
no immunity develops in mammals against autogenous spontaneous tumors;
they are not antigenic. Conversely, because autogenous tumor tissue does not
elicit immunity against itself in the bearer of the tumor, it may be assumed
that the tumor tissue has essentially the same individuality differential as the
other cells of the same organism. However, it has been shown that avian
sarcomata and related tumors, produced by means of injections of tumor
filtrates, may give origin to antibodies which are active against the autogenous
tumor cells ; but these antibodies are directed against the agent and not against
the tumor cells. Furthermore, there has accumulated more recently some
evidence which proves that in mammalian tumor tissue there may be present
in addition to the organismal differentials, some antigens which are specific
for a certain kind of tumor and not for the corresponding normal tissue, and
perhaps others which are common to many different types of cancer. In these
cases, special substances may serve as antigens.

There has been a certain reluctance on the part of some investigators,
especially Bashford and his associates, to apply the term "immunity" to the
mechanisms underlying the reactions against tumors developing in animals
inoculated with the latter. They preferred the term "resistance," because in
the course of time they began to doubt that a typical immunity, comparable
to antibacterial immunity, develops at all against cancer cells. This doubt was
based on the impossibility of demonstrating immune substances in the host
inoculated with homoiogenous tumors and of transferring antibodies to other
animals, which thus would be protected against the growth of a second
homoiogenous tumor. However, this difficulty has disappeared in recent years,
since it has become possible in various ways to demonstrate that such protec-
tive substances are formed. We therefore need not hesitate to consider these
reactions against tumor grafts as evidence of an active immunity. The
processes of active immunity are of special importance as far as the reactions
against homoiogenous tumors are concerned. In heterogenous tumors the
primary incompatibilities between host and graft become so strong, particu-
larly with increasing distance between the species of the host and the bearer,
that preformed processes may be sufficient to injure and kill the transplants.

An active immunity against inoculated tumors may be obtained under the
following conditions : ( 1 ) When a transplanted tumor grows in an animal ;
the developing immunity is known as "concomitant immunity"; (2) in cer-
tain cases following the extirpation of a growing homoiogenous tumor; here

IMMUNITY IN TUMOR TRANSPLANTATION 403

an active immunity which had not been demonstrated previously may become
manifest, but there is reason for assuming that it was actually present already
while the tumor was growing in the host; (3) after regression of a homoiog-
enous or heterogenous tumor, when an animal as a rule is found to be
immune to a second inoculation of the same or of a similar kind of tumor;
(4) after inoculation of normal tissues or of pieces of tumor unable to give
rise to the formation of tumors ; to a certain extent, animals thus treated are
immune to the growth of a piece of tumor subsequently inoculated. We shall
now describe the essential characteristics of each of these types of active
acquired immunity, and shall also discuss (5) the presence of immune sub-
stances in the bodyfluids or tissue extracts of an animal which has acquired
an active immunity against a tumor, as well as (6) the significance for im-
munity of cellular reactions in the host against tumor transplants and lastly
(7) the presence in tumor cells of antigens other than organismal differ-
entials.

(1) Concomitant immunity. From a theoretical point of view, this is per-
haps the most important and most generally occurring type of active acquired
immunity. It can be tested by inoculating animals, which already are the
bearers of such transplanted tumors, a second time with tumor pieces and
comparing the number of takes and the' growth energy of the second tumors
with those of the first. This immunity is elicited only if the organismal differ-
entials of host and transplant differ, and is demonstrated the more readily,
the greater the difference between the organismal differentials. It is very
marked when a tumor grows for some time in a heterogenous host ; homoiog-
enous tumors also give rise to immunity, but the growth of an autogenous
tumor graft does not have this effect, nor is it observed if a spontaneous tumor
is propagated through transplantation in the same closely inbred, homozygous
strain in which it originated.

As we have seen in a preceding chapter, the experiments of Fleisher and
the writer, as well as those of Haaland, prove that the growth of an autogenous
spontaneous tumor does not influence the subsequent development of a
homoiogenous inoculated tumor; conversely, the growth of a homoiogenous
tumor does not affect the growth of autogenous tumor transplants and of
metastases from the autogenous tumor.

However, in addition to differences in organismal differentials between
host and transplant, other factors may enter into the production of con-
comitant immunity. This is clear if we compare the varying conditions under
which this type of immunity has been observed. Strieker noted that at a cer-
tain period in the growth of a homoiogenous lymphosarcoma in a dog, im-
munity against a second inoculation developed, and Ehrlich found that the
growth of a rapidly growing tumor inhibited the growth of a tumor of the
same kind subsequently inoculated. According to Ehrlich and Schoene, the
extirpation of the first tumor suspends this immunity and makes possible an
inoculation with a second tumor. Ehrlich held that the first actively growing
tumor used for its own growth all available growth-substances specifically
required for the multiplication of tumor cells, and thus prevented the growth
of a second tumor (athreptic immunity). That this interpretation does not

404 THE BIOLOGICAL BASIS OF INDIVIDUALITY

apply generally is indicated by the fact that the writer, as well as Jensen,
observed that successive inoculation of tumors into the same animal led in
some cases to the growth of both tumors; and Russell, as well as Tyzzer,
found that there are actively growing tumor grafts which apparently do not
produce immunity in the host. Russell distinguished, therefore, tumors which
as a result of their growth, conferred concomitant immunity, and others which
did not confer such an immunity. In addition, there were tumors which
showed an intermediate behavior. However, there is reason for assuming
that all growing homoiogenous tumors are able to induce active immunity
against secondarily transplanted homoiogenous tumors, but that the degree of
this immunity varies in different cases and that the presence of such an im-
munity may not always become manifest. If a tumor originates in a strain of
animals in which, as the result of long-continued, very close inbreeding, the
individuality differentials in the various animals have become very similar,
then the individuality differentials of tumors which originate in such a strain
are about the same as those of the animals constituting this strain, and such
tumors after transplantation into members of this homozygous strain behave,
therefore, about like autogenous tumors, which have no antigenic power.

After transplantation into a strange, closely inbred strain, the large ma-
jority of tumors do not show continued growth ; they may grow for a short
time and then retrogress and disappear, or may show a slightly longer initial
growth. Similarly after transplantation into only partly inbred strains, not
yet approaching homozygosity, the majority of primary (spontaneous) tumors
do not take. But as we have discussed already in the preceding chapters, dif-
ferent tumors differ very much in this respect. There are some tumors which
can be transplanted into almost all homoiogenous animals and others which
may be transplanted in various proportions into such animals. Furthermore,
there exist differences between different strains of animals serving as hosts ; a
certain tumor which originated in an American mouse may be transplanted
into a considerable number of American mice, but not at all or only into a very
small number of some European strains. These differences in transplantability
depend partly on the relations and the degrees of mutual strangeness between
the individuality differentials of hosts and transplants; but there enter also
other factors, such as the growth momentum of the tumors, variations in their
sensitiveness and power of resistance to injurious substances, and lastly, in
their ability to adapt themselves to new hosts bearing individuality differen-
tials of different degrees of strangeness. Moreover, different strains of hosts
and different individual animals may not have the same ability to react against
and to injure a transplant carrying a strange individuality differential. While
the significance of these factors has not yet been analyzed sufficiently in the
recorded series of transplantations, and while it is not yet possible to determine
in most cases how much importance is to be attributed to one or the other of
these factors, there is enough evidence at hand to warrant the conclusion that
they play a role under various conditions.

To return now to the discussion of concomitant immunity. We have seen
that the prerequisite for the development of this type of immunity is a differ-

IMMUNITY IN TUMOR TRANSPLANTATION 405

ence in the individuality differentials of host and transplant, which makes it
possible for constituents of the transplant to act as antigens in the host. Inas-
much as the constitution of the individuality differential depends upon the
genetic constitution of the organism which is the bearer of the individuality
differential, it may also be stated that certain genetic differences between host
and transplant make it possible for constituents of the latter to act as antigens
and to call forth processes of immunity in the host which become manifest if
repeated transplantations of homoiogenous tumors are made. It should then be
possible to demonstrate the presence of concomitant immunity in all cases in
which a tumor grows in an animal whose individuality differential differs to a
sufficient degree from its own. Experience, however, indicates that only in
certain cases in which a homoiogenous tumor grows in an animal bearing a
different individuality differential, can such a concomitant immunity be
shown. In other cases, the presence of immune processes becomes apparent in
an animal only after the successfully growing tumor has been completely ex-
tirpated, and in still others, only when the tumor growth comes to a standstill
and, in the end, the tumor retrogresses. In the latter instance, after such a
retrogression has taken place, immunity against a second homoiogenous trans-
plant can be shown to exist. It does not appear probable that in these different
types of immune reactions we have to deal with entirely different processes ;
it is much more likely that they are merely quantitative variations of the same
fundamental process. It is possible that when a concomitant immunity be-
comes manifest, the amount of immune substances produced as a result of the
action of the strange antigens is sufficiently great to make possible the dem-
onstration of these immune processes, notwithstanding the presence of a grow-
ing tumor, which seems to have the tendency to absorb a certain quantity of
immune substances and to make them innocuous. We may also assume that
another type of tumor may absorb so great a proportion of the immune sub-
stances that the immune bodies remaining free in the circulation of the host
are unable to prevent the growth of a second homoiogenous tumor trans-
planted at a time when the first one is already growing. Extirpation of the first
growing tumor would then make immune substances available for the attack
on the second tumor. In some instances, in which the individuality differentials
of host and transplant possess a sufficient degree of strangeness, the amount
of immune substance produced in response to the first homoiogenous growing
tumor may become so large that it gradually begins to inhibit and prevent the
further development of the first graft, which then ceases to grow and may
even retrogress. The absorption of this tumor material would still further
increase the strength of the immune processes, so that after retrogression of
this tumor the animal has become completely immune against a further trans-
plant of a homoiogenous tumor. But there are other cases in which, after
extirpation of a tumor with its antigens, the production of immune substances
becomes so weak that the latter are unable to prevent a subsequent successful
transplantation of a homoiogenous tumor. In this way it might be possible to
interpret the various types of immunity which can be distinguished as mani-
festations of the same basic process ; the differences noted would then be due

406 THE BIOLOGICAL BASIS OF INDIVIDUALITY

merely to quantitative differences in the intensity of the immune reactions in
various animals or strains, in the ability of different kinds of tumors to neu-
tralize the immune substances, and in the power of resistance of different
tumors to the injurious action of such substances. The immunity found after
extirpation of a growing tumor or after retrogression of a formerly growing
tumor would then represent merely quantitative variants of the same type of
immunity.

There exist certain other experimental procedures which may make it possi-
ble to prove the existence of immunity against a tumor graft. This may in
some cases be accomplished by experimentally weakening the second tumor in
vitro, previous to inoculation. Also, by artificially weakening a first tumor it
may be possible to demonstrate the development of an active immunity, be-
cause under these conditions the absorbing and neutralizing function of the
tumor may be markedly diminished. Through experimental weakening of the
second tumor by means of graded application of heat previous to transplan-
tation, Fleisher, Corson-White and the writer demonstrated the inhibiting
effect of the first tumor on the development of a subsequently transplanted
tumor, in mouse carcinoma No. IX, in which, in successive transplantations
of fully active, unheated tumor pieces, immune processes are not manifest.
Thus it could be shown that a first unheated tumor possessing its full growth
energy prevents the growth of a second tumor which has been exposed to a
temperature of 44° for a period of from thirty-five to forty minutes. It does
not entirely suppress, but it weakens the growth of a second tumor which has
been exposed to a temperature of 44° for thirty minutes. If the growth energy
of the first tumor has also been slightly reduced through heating, the develop-
ment of a second tumor is prevented only if its growth energy has been dimin-
ished quite markedly through heating for forty minutes. But if the first tumor
had been injured through heating as much as the second tumor, or even more,
we then observed in several instances the opposite phenomenon, namely, an
increase in the growth energy of the second tumor. Thus one tumor may, under
certain conditions, have a beneficial influence on the growth of a second tumor,
perhaps owing to a neutralizing effect on substances antagonistic to tumor
growth which a first, weakly-growing tumor may exert.

It seems that the antigenic function of a tumor graft bears some relation to
the intensity of its metabolic activity, or to the presence of substances which
are readily injured by heat even of a moderate intensity. The influence which
the second tumor exerts on the first is less marked, but an enhancing effect of
a second, less inhibited tumor on a first, weakened tumor has been observed
also by Andervont in the case of sarcoma 180. Under other circumstances,
however, a second tumor whose growth energy has been only moderately
diminished through heating may be victorious in competition with a first, more
markedly depressed tumor ; and it is further possible to produce experimental-
ly a balancing between a first and a second tumor. Apparently the interaction
of two mutually antagonistic processes may play a role in bringing about this
effect, namely, (1) the production of immune substances in the host, and
(2) their absorption and neutralization by the tumor, or perhaps by organismal

IMMUNITY IN TUMOR TRANSPLANTATION 407

differentials which have been given off by the tumor into the circulation and
which act as antigens. Also, Seelig and Fleisher observed such a balancing
between the growth energy of the first and second tumors and they noted that
the tumor with the greater growth energy has the advantage over a weaker
tumor. In addition, they found that intraperitoneal inoculation with tumor ma-
terial may exert a greater immunizing power than a subcutaneous inoculation,
although the intraperitoneal inoculation may not be followed by actual growth
of the carcinomatous tissue. In this case we may have to deal with an immunity
similar to that which is caused by inoculation of normal or tumor tissues which
do not noticeably grow.

This method of using an originally active, virulent tumor, after its growth
energy has been experimentally reduced, for the demonstration of immune
processes which otherwise would not be manifest, was subsequently employed
also by Tsurumi, as well as by Rohdenburg and Bullock, and in a modified
way by Caspari and his collaborators, Schwarz and Ascoli. Besides grading
the growth energy by means of heat, they accomplished the same purpose also
by exposing the tumors to the action of radiation or of various chemicals. Only
when the inoculated tumor material was living did they find an immunizing
effect. Presumably the injured tumor grew temporarily to a slight extent, but
it soon retrogressed, and it is possible that the immunization was accomplished
by living but not growing material. However, the essential point is that a
balancing may take place between the first and second tumor pieces in ac-
cordance with the degree of potential growth energy which each inoculated
piece possesses; and Caspari and Ascoli also observed such an effect. The
greater the growth energy of the first piece, the more it tends to diminish the
growth energy of the tumor developing from the second piece ; furthermore,
the influence of the first piece is inversely proportional to the growth energy
of the second. In a similar manner Lumsden has recently demonstrated that
by weakening the growth of a second transplanted piece of cancerous tissue
in various other ways, such as by inoculation in unfavorable places, constric-
tion of the blood vessels leading to the tumor, by means of ligatures, and in-
jection of formalin into the transplant, it is possible to prove that tumors like
the Twort mouse carcinoma or mouse carcinoma 63, which, according to Rus-
sell, belong to the type of tumors which do not elicit concomitant immunity,
may give rise to such an immunity. Of interest is the observation of Foulds that
parallel to changes in their growth energy, tumors in the course of continued
transplantations may undergo variations in their power to elicit concomitant
immunity. The effects which a first growing tumor exerts on a second one
may further depend also on the kind of tumors used. For instance, the growth
of a secondarily transplanted mouse chondroma, a very slow-growing tumor,
was apparently not affected by a first tumor of the same kind, because these
cartilage tumors are very resistant to injurious influences.

We may therefore conclude that even tumors whose growth apparently
does not lead to the development of immune processes, may actually have this
effect provided their individuality differential differs from that of the host.
The existence of concomitant immunity may then, in general, be ascribed to

408 THE BIOLOGICAL BASIS OF INDIVIDUALITY

differences between the individuality differentials of the host and transplant.
On the other hand, Caspari and Schwarz believe that concomitant immunity
is due to necro-hormones given off by the growing tumor and that the greater
immunizing power of a rapidly growing tumor is dependent on the more ex-
tensive necrosis which occurs in the central portions of such tumors.

(2) Immunity following extirpation of a tumor. We have already referred
to this kind of immunity as representing a variety of concomitant immunity,
which becomes manifest only after extirpation of the first tumor. Uhlenhuth,
Haendal and Steffenhagen have shown that when homoiogenous rat sarcomata
growing in rats were excised, the rats were thereby rendered immune to re-
inoculation with this type of tumor. But, if the operation was incomplete and
the tumor recurred, a second inoculation was successful. There has been
much discussion concerning this experiment ; some have denied its significance,
or even its occurrence. However, Fleisher and the writer were able to confirm
the findings of Uhlenhuth and his collaborators ; after extirpation of a homoiog-
enous mouse carcinoma No. IX, the animal became immune against reinocu-
lation with this tumor. It is to be noted, however, that the growth of this type
of carcinoma did not, under normal conditions, lead to the manifestation of a
distinct concomitant immunity, presumably because the immune substances
are absorbed by the growing tumor. In addition, it must be assumed that the
production of immune bodies continues for some time after the source of the
antigens has been removed. The absorptive or neutralizing function of a first
tumor is not exercised by an autogenous, so-called spontaneous tumor, the
extirpation of which does not elicit processes of immunity either against re-
inoculation with autogenous or with homoiogenous tumors. We may therefore
conclude that the organismal differentials are involved also in these neutraliz-
ing mechanisms and that, in particular, homoiogenous individuality differen-
tials are able to neutralize homoiogenous immune substances.

(3) Immunity following retrogression of tumors. Homoiogenous tumors may
grow for some time and then retrogress apparently spontaneously; if the
tumor pieces used for inoculation have been subjected to chemical or physical
injuries previous to transplantation, such a retrogression is particularly apt to
occur. In all these cases retrogression takes place because conditions injurious
to the tumor cells have had a depressive effect on the tumor growth. We
described a spontaneous retrogression of transplanted tumors in 1901. We
observed also that during the first stages of retrogression mitotic cell prolif-
eration may still proceed quite actively in the tumor cells and that tumors in
the early stages of retrogression may be transplanted successfully and may
subseqently recover their full vigor of growth ; but at later stages of retro-
gression mitotic proliferation is much reduced or it ceases altogether, and
from then on the ability of the tumor to recover after renewed transplantation
is very much decreased. These observations were subsequently confirmed and
extended by Woglom, and in 1905 Clowes and Baeslack established the inter-
esting fact that mice, in which a homoiogenous mouse carcinoma had retro-
gressed, had become immune against re-inoculation with a homoiogenous
tumor. In the case of heterotransplantation, for instance, if a mouse tumor

IMMUNITY IN TUMOR TRANSPLANTATION 409

is grafted into a rat, the tumor, as a rule, after a temporary growth retro-
gresses, and then a second inoculation of a similar tumor into the same host
does not lead even to the limited growth shown by the first transplant. The
animal has become immune as the result of the growth and retrogression of
the first tumor. In accordance with what we know as to the inability of autog-
enous tumors to elicit immunity of this kind, is the great infrequency with
which spontaneous tumors retrogress; but if they do retrogress, this is pre-
sumably brought about by factors other than immunity, or by an immunity
not directed against the organismal differentials but against other substances.

As stated above, we must conceive of the immunity following retrogression
of a tumor as a variety of concomitant immunity, which primarily is due to
the dissimilarity and incompatibility of the organismal differentials of tumor
and host. As the result of this incompatibility the primary, preformed homoio-
or heterotoxins of the host injure the transplant and the strange individu-
ality or species differentials of the grafted tumor may act as antigen, eliciting
the production of immune bodies, which then support and complete the effect
of the primary homoio- or heterotoxins ; and it is probable that these immune
substances are mainly responsible for the injury of the transplant and the
subsequent cessation of its growth and its retrogression. In addition, during
retrogression of the tumor, tumor material is being absorbed, which also may
serve as antigen and cause additional formation of antibodies.

The retrogression immunity is very effective and may cause the shrinking
and the ultimate disappearance of tumors which had already been established
in the host, and which had successfully passed through the early, dangerous
stages following transplantation. As a result of this immunity the tumor it-
self, which has given rise to the production of the immunity, experiences the
effect of its own activity and undergoes complete retrogression. A subsequent
second inoculation of a tumor piece is then unsuccessful. After the tumor
has once been absorbed, the animal organism is no longer able to neutralize
the immune substances which may still continue to be produced. We believe,
therefore, that also this type of immunity, against the growth of a transplanted
tumor, is not merely caused by the retrogression of a tumor, but that it already
sets in some time preceding the retrogression and continues during this
process, and that it is intensified through the absorption of material from the
retrogressing tumor. There follows then a struggle between the host, which
produces substances injurious to the tumor, and the inherent growth energy
of the tumor combined with its power to neutralize injurious substances; in
addition, there may perhaps come into play also certain adaptive processes in
the cancer cells.

The increase in immunity which takes place during the retrogression of
the tumor must in some way depend on the activity of the living, metabolically
still potent tumor cells. This is indicated by the fact that when we produced
retrogression of a first mouse carcinoma IX by exposing the tumor, previous
to transplantation, to a degree of heat sufficient to injure the tumor cells
markedly and thus experimentally to induce the subsequent retrogression
of the grafted tumor, the immunity resulting from this retrogression was

410 THE BIOLOGICAL BASIS OF INDIVIDUALITY

less pronounced than that following a spontaneous retrogression of a larger
tumor which at first grew well. Lumsden similarly observed that the im-
munity is greater after retrogression of large than of small tumors. It may
be assumed that in order to accomplish the retrogression of an actively grow-
ing large tumor, a higher degree of immunity will be required than for the
retrogression of a weak tumor, and more immune substances will therefore
subsequently be available for combating the growth of a second tumor. As
stated, this high degree of immunity necessary for the absorption of large
tumors is achieved only if the individuality differentials of host and trans-
plant are sufficiently different to cause a primary incompatibility, which
must, however, not be so great that it prevents growth of a tumor during the
early periods following transplantation. Subsequently, it must be assumed,
the quantity of immune substances increases at a rate too rapid for the
neutralizing power of the tumor. However, we have seen that also the im-
munity induced by a growing tumor is greater if the first tumor grows
vigorously, than if it has been weakened in its growth intensity.

That immune substances are produced under these circumstances and may
be present in the spleen of the tumor-bearing animals is indicated by the
experiments of Mottram and Russ, as well as of Woglom, who show that
in the spleen of animals in which tumors had retrogressed, substances are
present which injure the cells of a similar tumor. As mentioned previously,
Woglom's recent investigations suggest the possibility that the antibodies
circulating in the bodyfluids of an immune animal can be absorbed by
tumor mash. These substances, then, are able to injure in vitro a piece of
tumor and prevent its successful transplantation ; and likewise Lumsden has
found that substances circulating in the blood of rats, rendered immune against
rat sarcoma, succeeded in killing cancer cells as well as spleen cells of the
same species growing in vitro. As stated in a preceding chapter, Lumsden
attributes these effects to "antimalignancy" immune bodies, devoted as
a result of the growth of a homoiogenous sarcoma ; but Phelps and others
interpret them as due to cytotoxins, which form in response to the presence
of strange species or individuality differentials, since these reactions occur
also with normal spleen cells and may be elicited by antigens present in normal
spleen.

In addition to cytotoxins, there may be found in the bearers of retrogressed
tumors hemagglutinins, which may, however, affect not only erythrocytes,
but also other kinds of cells (Gorer, Lumsden). Lumsden has made it probable
that these cytotoxins and hemagglutinins are distinct and develop independ-
ently of each other; he also observed a definite relation between the strength
of such antibodies and the retrogressive changes which take place in the
tumor; this would indicate that retrogression is due to the action of immune
substances. However, while it is quite probable that the latter aid in the
injury of the tumor, it is probable also that primary mechanisms are involved,
and that the immune substances originate as a reaction against primary
incompatibilities between organismal differentials.

Lumsden noted that the erythrocytes of a rat may possess an agglutinogen,

IMMUNITY IN TUMOR TRANSPLANTATION 411

which is present also in rat sarcoma cells, as demonstrated by the agglutina-
tion of these rat red corpuscles when mixed with the serum of a rat made
immune against a rat sarcoma. If pieces of rat sarcoma are transplanted
into such a rat, immune substances would not be produced, because of the
presence of a common antigen in the sarcoma cells and in the host cells, and
hence an inoculated piece of rat sarcoma would grow. In this case an agglu-
tinogen present would, therefore, make possible the growth of a transplanted
tumor and would actually function as a susceptibility factor for this tumor.
We have discussed these observations already in a preceding chapter.

The histological changes which are observed around retrogressing tumors
do not explain the character of the immunity noted in these animals. Thus
Gaylord and Clowes, and others, found necrosis and hemorrhages, as well
as collections of lymphocytes in or around such retrogressing tumors ; the
presence of lymphocytes may be taken to indicate an active reaction on the
part of the host against the transplant. However, Ishii and the writer, in
examining tumors that retrogressed following an in vitro exposure to heat,
did not observe such collections of lymphocytes ; there was merely a connec-
tive tissue capsule around the tumor and a replacement of parts of the tumor
by fibrous tissue.

It is an interesting problem as to whether the immunity thus produced is
specific for the tumor which has retrogressed, or whether it applies also to
other types of tumors. Bashford assumed it to be specific, because he noticed
that mice in which an immunity had developed after retrogression of a car-
cinoma were immune against a re-inoculated carcinoma, but not against a
sarcoma. However, as Caspari and others have pointed out, this result is
probably to be explained by the difference between the growth energy of the
mouse sarcoma and that of the carcinoma ; an immunity sufficient to prevent
the growth of a carcinoma, may not have been sufficient to prevent that of a
much more active sarcoma. In general, the specific immunity which has been
acquired is directed against strange individuality differentials in case of
retrogression of a homoiogenous tumor, and against a particular species
differential after retrogression of a heterogenous tumor. The "retrogression"
immunity is therefore essentially an immunity directed against organismal
differentials which are common to various kinds of tissues and tumors belong-
ing to the same species ; it represents what Ehrlich called "pan-immunity,"
by which he meant an immunity directed not only against a tumor composed
of a certain kind of tissue, but also against a tumor composed of another kind
of tissue of the same species. Nevertheless, the immunity may be greater
to tumors composed of the same kind of tissues than to another kind of tumor
belonging to the same species ; such a partial specificity was observed by
Greene after a primary transplantation of homoiogenous tumors of the rabbit
into the anterior chamber of the eye, and a second transplantation of the same
or of another kind of tumor into the other eye or into the testicle. Under
these conditions a growing first tumor seems to act similarly to a retrogressed
tumor. In addition to the "pan-immunity" directed against all the individuality
differentials of a species, there may exist, therefore, an immunity directed

412 THE BIOLOGICAL BASIS OF INDIVIDUALITY

against the individuality differential of a particular tumor. This is indicated
also by the observations of Rous and Murphy that the immunity noted after
retrogression of three types of chicken sarcoma, namely, a spindle-cell sar-
coma, an osteochondroma, and a rifted sarcoma, was directed mainly against
the special kind of tumor that had retrogressed. It appears moreover that
different types of tumors differ quantitatively in the degree of immunity they
produce, and the effectiveness of the immunization seems also to depend
on the place where the first and second tumors were inoculated. Thus, in
the rabbit each tumor of the uterus and mammary gland seemed to differ
in certain respects from the Brown-Pearce rabbit tumor, in experiments
reported by Appel, Saphir and their collaborators, and by Cheever and
Morgan, and by Greene. Furthermore, there is even the possibility that
immunity against a tumor of a different species is not absolutely specific, but
that it may extend also, although to a lesser extent, to individuals belonging
to a nearly related species.

(4) Immunity produced through inoculation of pieces of normal tissue or
of tumor tissue unable to induce tumor formation.

Ehrlich obtained immunization against a mouse carcinoma by first inocu-
lating mice with pieces of a hemorrhagic mouse carcinoma, which itself
did not give rise to tumor formation because the tumor cells were injured.
This experiment suggested the use of normal tissues for purposes of immuni-
zation. Bashford, by injection of homoiogenous defibrinated blood, obtained
active immunity against subsequent inoculations with homoiogenous tumor,
and Schoene found that other living tissues, in particular, embryonal tissues,
were similarly effective. These observations were subsequently confirmed
and extended by many investigators. The results obtained may be summarized
as follows: (a) Only living tissue is effective in inducing immunity; dead
cells do not immunize, (b) It is the organismal differentials of the inoculated
pieces which give rise to this type of immunity. There must be a definite
relation between the organismal differential of the piece of tissue serving
as antigen (vaccine) and that of the host; furthermore, the organismal
differential of the antigen must bear a definite relation to the differentials
of the tumors against which the immunization is directed. Autogenous
tissues do not, therefore, act as an efficient antigen (Apolant, Woglom).
Tissues which possess homoiogenous differentials in reference to the host
animals, immunize against homoiogenous tumors, and heterogenous tissues
immunize against tumors possessing the same heterogenous differential.
However, it is possible that an immunization may in certain instances be
produced also by the use of tissues from nearly related species, mouse
tissue immunizing against a rat tumor and vice versa; but this immunity,
if successful at all, is much weaker than that produced by tissues with
identical organismal differentials, (c) Different types of tissues differ as
to their effectiveness as antigens ; embryo skin is very effective, whereas
cartilage, bone, muscle tissue, lens and brain are not. Other tissues range
between these extremes. That cartilage, bone and muscle are relatively
unfavorable may be due to the predominance, in these tissues, of inter-

IMMUNITY IN TUMOR TRANSPLANTATION 413

cellular substances, and we have every reason to believe that it is the
cytoplasmic elements which produce most actively the individuality differ-
entials rather than the paraplastic parts, although there is some evidence
that also the latter are not devoid of individuality differentials. Correspond-
ingly, we have found that normal cartilage elicits a weaker antagonistic
reaction of the host than does thyroid, which is rich in cells. As to the
inefficiency of lens and brain, this might be expected, because they do not
furnish very effective homoiogenous antigens in immunization experiments,
although as we have seen in an earlier chapter, they do contain homoio-
differentials. (d) There is, then, ample reason for the conclusion that it is
the organismal differentials, and in particular, the individuality differentials,
of the normal tissues acting as antigens, which call forth immunity against
the organismal differentials of the tumor.

However, it is not necessarily the specific individuality differential of a
certain individual which serves as antigen against the identical individuality
differential in the tumor; but any individuality differential of the normal
tissue, which differs from the differential of the host animal and is therefore
strange to the latter, may function as antigen for the tumor. It may then
be assumed that any strange individuality differential activates, in the host,
reactions which are directed against all other strange individuality differen-
tials, provided both host and donor belong to the same species.

We have seen that autogenous tissues cannot serve as antigens against a
subsequently transplanted homoiogenous tumor; likewise, it may be safely
assumed that tissues fom an animal belonging to a closely inbred strain cannot
function as an effective antigen in another animal of the same inbred strain.
The experiments of Eisen and Woglom on transplantation of a mammary
gland carcinoma in inbred strains of rats, to which we have already referred
in a preceding chapter, as well as certain experiments in which the production
of immunity was attempted against transplanted leukemic cells, are in agree-
ment with this conclusion. Rhoads and Miller observed that implantation of
normal mouse tissues may immunize mice against inoculation of mouse
leukemia; but while, according to MacDowell, embryo-skin of the inbred
strain Sto Li can produce resistance in strain C58 to leukemic cells of line I,
embryo-skin of strain C58 is not able to serve as an efficient antigen. However,
embryo-skin from hybrid (C58 x Sto Li)Fx may call forth immunity in
strain C58. Evidently a single gene set of Sto Li present in the hybrid enables
the tissue of the latter to function as antigen and the presence of the gene
set of C58 in the hybrid does not interfere with the antigenic action of the
strange Sto Li gene set. In a similar manner, it seems that the agglutinogens
of the F1 hybrid between two closely inbred strains, which has inherited a
gene set from each of the parents, possess the ability to produce antibodies
(agglutinins) in certain hosts and to absorb these agglutinins; in this case,
also, one strange gene set is sufficient for this purpose and the double gene
set is not required, (e) While a strange individuality differential of normal
tissue may call forth immunity against a transplanted tumor, the immunity
thus produced is not so strong as that following retrogression of a tumor. It

414 THE BIOLOGICAL BASIS OF INDIVIDUALITY

is even less than the usual concomitant immunity and the degree of resistance
following extirpation of mouse carcinoma IX. (f) Considering the relative
weakness of the immunity obtained by inoculation of normal tissue, it might
be foreseen that this type of immunization is ineffective against a tumor
possessing a great growth energy, or one as resistant to injurious conditions
as the chondroma of Ehrlich. Rous and Murphy were not able, therefore,
to produce immunity by inoculation of normal tissues against the Rous
chicken sarcoma, although during retrogression of these tumors there devel-
oped spontaneously an immunity which seemed to be directly against the
agent.

(5) The demonstration of immune substances in the body fluids or tissue
extracts of animals which have been inoculated with cancerous material or
in which cancer has grown.

In the blood of an animal which has become immune against certain
bacteria, either by recovering from the disease caused by them or by vaccina-
tion with the microorganisms or certain parts of them, the presence or anti-
bodies directed against these bacteria can in many cases be demonstrated.
Similarly, antibodies have been produced against proteins and against cells
belonging to a different species, and in some instances even against certain
cells belonging to the same species but to different individuals, or against
certain kinds of tissues and organs characteristic of a species. It is natural
that following the proof that an active immunity can be produced against
transplanted tumors, the question should have been raised as to whether there
are indications in this case, also, of the presence of antibodies circulating
in the blood or retained in the tissues. The existence of such antibodies against
heterogenous tumors can be shown, but it has been impossible, at least until
more recently, to demonstrate antibodies which developed against homoioge-
nous tumors.

In the large majority of cases, attempts to reveal the presence of antibodies
in the blood of immune animals directly, by injecting such blood into sus-
ceptible animals of the same species and thereby inhibiting the growth of a
tumor graft, did not succeed, although a few investigators (Clowes, Beebe
and Gay lord, and C. Lewin) have reported positive results. In subsequent
experiments, Lumsden believed he had obtained some positive results by
injecting serum of heterogenous animals, immunized against a tumor, into
the tumor itself growing in homoiogenous animals, but under conditions
which were not favorable to a rapid proliferation of the cancerous tissue.

By the use of in vitro cultures of tumor cells, Lambert and Hanes found
antibodies against cancer cells in the serum of heterogenous, but not of
homoiogenous, animals immunized against this tumor. Likewise, Yamagiwa
believed he had demonstrated antibodies against mouse tumors in the extract
of spleen of rabbits immunized against such tumors. Also, in experiments of
Tyzzer there was some indication of an immune substance in the serum of
hybrid F2, F3, and F4 mice, between Japanese susceptible and white mice
non-susceptible to a tumor which had originated in a Japanese mouse. The
hybrids were non-susceptible to this tumor. If a piece of this tumor was

IMMUNITY IN TUMOR TRANSPLANTATION 415

inoculated into a susceptible Japanese mouse and serum from the hybrid
injected into the same mouse, but not directly into the tumor tissue, necrosis
increased in the graft, the mitoses were diminished, and polymorphonuclear
leucocytes infiltrated the transplant. These changes indicated an injurious
effect of the serum, which was, however, only transitory; subsequently the
transplanted piece began to grow.

However, in animals belonging to the same species as the tumor transplant
it has not been possible to demonstrate the existence of such antibodies until
recently. Older experiments of Lambert and Hanes had been negative; also
the work of Peyton Rous with parabiotic rats — a susceptible rat joined
to a rat naturally immune to a rat tumor — failed to reveal immune
bodies in the susceptible animals, while other investigators were unable to
find that homoiogenous blood serum of actively immune animals affected the
growth of tumors, even if the serum was injected previous to or soon after
the implantation of the tumor pieces. Contrary to these results are those of
Lumsden, who noted indications of the presence of antibodies against rat
sarcoma in rats actively immunized against this sarcoma, or in which the
tumor had retrogressed. We have referred already to these experiments in
which the serum was added to tissue cultures of rat sarcoma and rat spleen,
and we have likewise discussed the experiments of Woglom, which strongly
suggested that in serum of a rat, in which a tumor had retrogressed, sub-
stances are found which injure the tumor cells and may prevent their growth
after inoculation into a homoiogenous animal.

Furthermore, substances injurious to Rous chicken sarcoma were obtained,
not only in geese, ducks, rabbits and goats actively immunized against this
tumor, but also in fowls bearing a slowly growing fibrosarcoma, immune sub-
stances developed very gradually which neutralized in vitro not only the agent
of the fibrosarcoma but also the agent of the more rapidly proliferating Rous
chicken sarcoma. However, these latter manifestations of tumor immunity are
different from those observed in the case of mammalian tumors, because this
immunity in avian tumors was primarily directed not against the tumor cells
as such, but against the agent which causes the sarcoma to grow.

If we compare the reactions of a host against normal tissues and against
tumors, both possessing organismal differentials differing from those of the
host, the bodyfluids are found to contain substances which are injurious to
both kinds of grafts. There are strong indications that preformed substances
as well as newly formed, immune substances, directed against the individuality
or species differentials of these transplants, are active, and that the substances
directed against the strange species differentials are stronger than those
directed against strange individuality differentials. But whereas in the case of
normal tissues the immune substances are apparently of minor importance, in
the case of tumors they appear to play the major role in determining the fate of
the transplants ; still, even in the latter it is primarily the divergence between
the organismal differentials of host and transplant which makes it possible for
the differentials of the tumor grafts to function as antigens.

In principle, there do not seem to be significant differences in the antigenic

416 THE BIOLOGICAL BASIS OF INDIVIDUALITY

function of transplanted tumor cells and normal cells and of injected eryth-
rocytes, which latter elicit the formation of hemagglutinins and hemolysins.
The differences which do exist seem to be mainly of a quantitative nature, the
immune substances, which are formed after transplantation of living normal
tissues, being weaker. There is, perhaps, the additional difference that the
growing tumor seems to be able to absorb and to neutralize very effectively
the immune substances circulating in the host, while normal tissues and eryth-
rocytes do not do so. The proportion of neutralized and non-neutralized
immune substances and the power of resistance of the tumor tissue to the ab-
sorbed immune substances seem to vary in the case of different tumors, and it
is largely these variations which are probably responsible for the differences
in the types of immunity which develop after transplantation of tumors into
hosts whose organismal differentials differ from those of the tumor. However,
as we have stated already, there are indications that not only the organismal
differentials, but also other constituents of the tumor cells, may give rise to
states of immunity and to the production of immune substances ; some of these
data we shall discuss in the last part of this chapter.

The presence of immune substances in the circulating bodyfluids of an ani-
mal actively immunized against a transplanted tumor is perhaps suggested also
by the demonstration of the presence of substances in the circulating body-
fluids which enable a tumor graft to grow in an animal belonging to a strain
unfavorable to the growth of a particular type of tumor. This has been dem-
onstrated by means of parabiosis, if an individual belonging to a strain favor-
able to the growth of the transplanted tumor was joined to an individual
normally resistant to the growth of the inoculated tumor. Substances supplied
by the first partner enabled the tumor to grow in the second otherwise unsuit-
able partner. We have referred already to experiments of this kind by
Zakrzewski and of Cloudman in a preceding chapter, when we discussed
factors in the growth of transplanted tumors. However in this case we have to
deal with substances favoring tumor growth while here we are concerned with
substances inhibiting tumor growth.

(6) Cellular reactions of the host against the tumor transplants. We have
discussed evidence which tends to prove that under various conditions immune
substances directed against the individuality or species differential of the
transplanted tumor may develop in the host. But, in addition, certain types of
host cells react against the transplant, and these reactions manifest themselves
locally around the graft as well as in the circulation of the host. The local
reactions consist, above all, in the accumulation of lymphocytes, but also
polymorphonuclear leucocytes, connective tissue and blood vessels may take
part in these processes.

Simultaneously with the early studies of the role of lymphocytes in trans-
plantation of normal tissues there began the study of the role of various types
of leucocytes, including lymphocytes, in the reactions of the host against a
tumor. But the cellular changes against transplanted tumors were interpreted
as the local manifestations of a general immunity against the tumor growth.
This immunity was considered as distinct from other types of immunity,

IMMUNITY IN TUMOR TRANSPLANTATION 417

although it was conceded by some authors that also immune reactions, which
were analogous to those developing against embryonal tissues, may participate
in this process. Other investigators believed that the acquired resistance or
immunity against tumor transplants led to a deficiency in the ingrowth of
stroma from the host into the tumor. Under normal conditions the surrounding
host tissue supplies the tumor with blood vessels and a connective tissue
stroma ; but it was assumed that if the host has been made resistant or immune
against the transplant, it fails to provide this stroma.

As to the lymphocytes, in the case of normal tissue transplants we found a
double significance of these cells: (1) Under certain conditions the strength
of the lymphocytic accumulation could be used as a quantitative measure of
the intensity of the reaction of the host against a strange individuality differ-
ential ; it served therefore as a standard with which to measure the difference
between the individuality differentials of host and donor, and, accordingly,
also of their degree of relationship or strangeness. (2) The lymphocytes, in
collecting around the transplant and invading it, were able to injure it if they
penetrated into it in dense masses. On the other hand, we did not find any
evidence for the further conclusion that the lymphocytes give off substances
which diffuse into the transplant and thereby damage it, an assumption that
was made by some investigators in the' case of tumor transplants.

The role which lymphocytes play in the growth and retrogression of trans-
planted tumors seems to be similar to that seen in the case of transplanted
normal tissues. There is, however, one significant difference. While the marked
accumulation of lymphocytes around normal tissues and their invasion of these
tissues may lead to the injury and destruction of a considerable part of the
graft, in the case of a growing tumor the multiplication and expansive growth
of the tumor cells may be so active that the lymphocytes cannot overcome the
graft. Also, around retrogressing tumors the local accumulation of lympho-
cytes does not need to be very conspicuous. This condition accounts perhaps
for the fact that in the transplantation of tumors several investigators did not
attribute to the lymphocytes the role which we did in the grafting of normal
tissues, but they considered them, rather, as important agents in the production
of the general immunity which develops under various circumstances against
tumor transplants. This latter interpretation seemed also to be supported by
the observation that while an accumulation of lymphocytes may become
noticeable already after a first inoculation of a piece of tumor, it is more
accentuated and it appears more rapidly after a second inoculation, because
here the inoculation takes place in an animal in which immunization processes
have set in already as the result of the first inoculation.

As stated, the activity of lymphocytes around a piece of tumor does not
need to be pronounced; this is true especially if the first transplanted piece
begins to grow actively soon after transplantation. An accumulation of lym-
phocytes was more marked in the early experiments of Burgess and Tyzzer;
however, these investigators did not study the local reaction around homoiog-
enous tumors, but around pieces of tumor which approached a heterogenous
character; and here polymorphonuclear leucocytes were as prominent as

418 THE BIOLOGICAL BASIS OF INDIVIDUALITY

lymphocytes, an observation which agrees with our findings that polymorpho-
nuclear leucocytes tend to collect around heterogenous transplants of normal
tissues. Burgess and Tyzzer noted that if the tumor was not destroyed too
rapidly through the accumulation of these wandering cells, dense scar-like
fibrous tissue was produced in the transplant. Likewise, in a later analysis of
these phenomena, Tyzzer (1916) did not interpret these primary cellular
reactions as due to and directed against incompatible organismal differentials,
which secondarily call forth an immunization, but he adopted Russell's view
that natural resistance against tumors is merely the ability of the host to
acquire an active immunity against the tumor, while susceptibility means the
lack of this ability. Tyzzer assumed, therefore, that in every case the local
cellular reaction was due to an active immunity produced against the trans-
plant, and it was considered as a phenomenon specific for tumors.

As to the mechanism underlying this reaction, Tyzzer assumed that in com-
bination with an immune body the tumor products become strongly chemo-
tatic for leucocytes and at the same time stimulate the surrounding fibro-
blastic tissue. In animals already immunized, the reaction not only sets in more
promptly, but here also the polymorphonuclear leucocytes are more numerous,
while in as yet untreated animals, in which the immunity develops only gradu-
ally following the first inoculation, the reaction takes place more slowly and
the lymphocytes are found in relatively larger numbers; the preponderance of
lymphocytes signifies a milder reaction on the part of the host. In addition to
the movements of lymphocytes and polymorphonuclear leucocytes, an increase
in the number of fibroblasts occurs in the surrounding tissue, and this he com-
pared with the formation of granulation tissue in inflammatory processes.
Tyzzer concluded, then, that immunization leads to the production of sensitiz-
ing antibodies in the host, and these combine with a substance given off by the
tumor to form an injurious substance (anaphylatoxin), which injures the host
tissue surrounding the tumor. As a result of such injury, inflammation sets
in and lymphocytes, polymorphonuclear leucocytes or monocytes appear. In
general, it is the presence of this antigen-antibody combination (anaphyla-
toxin) which causes the accumulation of the leucocytes of the host in and
around the graft.

Also, in the case of other tumors cellular reactions around the "transplants
were noted and the resistance of the host to transplanted homoiogenous tumors
was attributed especially to the lymphocytes. Thus, when chicken sarcoma was
transplanted into a naturally immune fowl, Rous and Murphy observed on
the fifth day following transplantation the appearance of masses of lympho-
cytes around the graft, which then degenerated. In other instances it seemed,
however, that the tumor was already seriously injured at an earlier period
following transplantation, owing to the failure of the surrounding tissue to
provide a stroma for the graft. Similarly, Mottram and Russ, studying im-
munity against Jensen rat sarcoma, found that when a piece of tumor was
inoculated into non-immunized rats, the lymphocytic reaction which developed
around the transplant was very slight and did not seriously interfere with the
growth of the tumor. But if, following a first inoculation with experimentally

IMMUNITY IN TUMOR TRANSPLANTATION 419

weakened tumor pieces, a second non- weakened piece was inoculated, there
occurred on the second and on the third day a marked accumulation of lympho-
cytes, the sarcoma cells disappeared rapidly, fibrous tissue formed subsequent-
ly, and also plasma cells were seen. With the disappearance of the sarcomatous
tissue the lymphocytic reaction came to a standstill.

However, preceding these latter investigations Da Fano, in 1910, had
emphasized the significance of lymphocytes and plasma cells in tumor im-
munity, but his interpretation of the function of the lymphocytes differed
from that of Tyzzer and also from our conception. Da Fano noted an ac-
cumulation of lymphocytes not only around transplanted pieces of tumor, but
these cells as well as plasma cells were seen also in various other places as for
instance in the connective tissue underneath the skin of the animal during the
process of immunization. Only living tumor tissue elicited this reaction;
furthermore, it was lacking around a second piece of tumor inoculated in an
animal in which immunity had already developed. Da Fano attributed, there-
fore, to the lymphocytes and plasma cells the function of initiating the general
state of immunity which follows the inoculation of a piece of homoiogenous
normal tissue or tumor. Somewhat later, Baeslack observed in addition to the
localized reaction, a general reaction of the lymphocytes to tumor growth ;
the active growth of a homoiogenous tumor was accompanied by a decrease
in the number of lymphocytes and by an increase in the number of poly-
morphonuclear leucocytes, whereas the retrogression of a tumor was associ-
ated with an increase in the number of lymphocytes as an indication of the
development of immunity against the transplanted tumor. Quite recently,
Lewis has confirmed the increase in the number of polymorphonuclear leuco-
cytes in the peripheral circulation in mice in which the transplanted tumor
grows.

The most extensive and ingeniously varied investigations concerning the
relations between tumor immunity and activity of lymphocytes were carried
out by Murphy and his associates. They noted both a local accumulation of
lymphocytes around the tumor graft as well as a general increase of lympho-
cytes in the circulation following transplantation; an injurious effect re-
sulted, however, from an increase in the number and activity of lymphocytes,
not only in homoiogenous and heterogenous, but also in autogenous tumor
grafts. After heterotransplantation of a piece of tumor, the lymphocytic re-
action played the principal role in the destruction of the transplant. These
investigators concluded, furthermore, that immunity against a tumor can be
elicited not only through inoculation with a piece of tissue or of tumor be-
longing to the same species, but that any non-specific agency which increases
the number and activity of lymphocytes, increases thereby the defensive reac-
tions of the host against the transplant, and conversely, any agency that de-
creases the number and activity of lymphocytes increases thereby the sus-
ceptibility of the host to the tumor transplants. Small doses of Roentgen rays
stimulate and strong doses injure the lymphocytes ; exposure of mice to
graded intensities of dry heat and injections of certain oils or unsaturated
fatty acids stimulate the lymphocytes. The effects of these various agencies on

420 THE BIOLOGICAL BASIS OF INDIVIDUALITY

resistance and susceptibility to tumor growth can be gauged by their effects
on the lymphocytes. In accordance with the views expressed by Da Fano,
Murphy believes that the lymphocytic reaction which develops around a tumor
graft in an immunized animal is the local manifestation of a general reaction
which takes place in the animal. When mice are naturally immune against a
tumor graft, or when they have been made immune by experimental means,
they show an immediate and very marked increase in the number of circulat-
ing lymphocytes following inoculation with a piece of tumor against which
they are immune, whereas, the other blood cells show no change. Similarly, in
the lymph glands of a mouse which has been immunized experimentally, or in
which immune processes set in following absorption of its tumor, the mitotic
proliferation of the lymphocytes is much increased, and it is still further in-
creased after a second inoculation of a tumor piece. From all these observa-
tions Murphy concluded that the general, as well as the localized lymphocytic
reaction is not merely a condition accompanying tumor immunity, but that it
is responsible for the development of this immunity, and as stated above, he
found that even an otherwise successful autogenous transplantation of spon-
taneous tumors can be prevented through an increase in the activity of
lymphocytes.

There were various other experiments which seemed to support this inter-
pretation. Thus Murphy found that if pieces of heterogenous (mammalian)
tumors or embryonal tissues were transplanted on the chick allantoic mem-
brane, they grew for some time. However, if he transplanted simultaneously
with the mammalian tumor small pieces of chicken spleen or bone marrow,
the tumor did not grow, presumably because of the injurious action of the
lymphocytes contained in the latter organs. Accordingly, growth of the tumor
ceased at the time when, in the eighteen or twenty-day-old chick embryo, the
spleen begins normally to function. But, Danchakoff maintains that it is not
the lymphocytes of the transplanted spleen or bone marrow which grow out
towards the tumor and injure it, but monocytes or reticuloendothelial cells.

There are other regions in the body where the resistance offered to the
growth of homoiogenous or heterogenous tumors is distinctly lessened. Ref-
rence has been made to the diminution in the intensity of the lymphocytic
reaction after homoiotransplantation of normal tissues into the brain. Ebeling
( 1914) had found indications that in mice which are immune to subcutaneous
inoculation of mouse carcinoma, transplantation into the brain might still be
successful. According to the subsequent observation of Shirai, it was possible
to transplant mammalian tumors into the brain of a strange species. Murphy
likewise noted that heterotransplantation of tumors into the brain may be
more successful than transplantation into other parts of the mammalian or-
ganisms, and moreover, that the lymphocytic reaction is lacking here pro-
vided the transplant has not been in contact with the meninges or with the
choroid plexus. Active immunization which was sufficient to prevent tumor
growth subcutaneously, was ineffective against a tumor grafted into the brain ;
but again, a simultaneous transplantation of a piece of spleen tissue into the
brain caused the mechanisms of defense against the heterogenous tumor to

IMMUNITY IN TUMOR TRANSPLANTATION 421

become active. E. Harde also observed that heterotransplantation of mouse
tumors succeeds better in the brain than in the subcutaneous tissue, but this
applies only if nearly related species are used as hosts ; transplantation of
human tumors into the brain of rodents did not succeed, nor did the trans-
plantation of mouse tumors into the brain of guinea pigs. It seems that in this
organ the organismal differentials are less well developed than in most other
parts of the body. In this respect the brain behaves somewhat like the testicle,
where, according to Gheorgiu, heterogenous tumors can also be transplanted
successfully, and even more readily than into the brain. A further favorable
site is the anterior chamber of the eye (Smirnova, Greene and Saxton,
Greene) ; however, as to the behavior of the lymphocytes under these condi-
tions, no observations have been recorded so far.

The views of different investigators concerning the role which lymphocytes
play in the immunization against transplanted tumors are, to some extent, still
contradictory. However, from a review of the results obtained and from our
own experiments, we conclude that in the growth of tumors the lymphocytes
play a part similar to that which we ascribed to them in the case of grafts of
normal tissues. Under certain conditions they may serve as indicators of a dis-
cordance between the individuality differentials of host and transplant. If host
and transplant belong to different species, polymorphonuclear leucocytes ap-
pear around the tumor and invade it, in addition to or instead of the lympho-
cytes. But, while with normal tissues the accumulation of lymphocytes and
their invasive activity may in certain cases become so pronounced that it leads
to the destruction of a great part of the transplant, with tumors this effect
seems to be much less marked. According to Woglom, the retrogression of
tumors is not necessarily associated with an increased activity of the lymph
glands, and in our early work on the retrogression of tumors in homoiogenous
organisms, whose individuality differentials differed markedly from those of
the hosts, we found no reason to attribute the retrogression to the activity of
the lymphocytes ; furthermore, Ishii and the writer, in a study of tumors which
had been weakened by heat previous to transplantation and which subsequently
retrogressed, did not observe an accumulation of lymphocytes around or in the
transplant sufficient to account for the retrogression ; we did find, however,
the formation of a strong connective tissue capsule around such tumors, which
may very well have helped to produce an inhibiting effect on the weakened
tissue. As in transplanted normal tissue, so also in transplanted tumors the
bodyfluids of the host may, to a large extent, determine the fate of the graft,
and they may be the principal factor concerned in this effect in the case of
tumors.

It is, then, essentially the discrepancy in the individuality differentials of
host and transplant which causes the accumulation of lymphocytes, and which
may also increase the activity of connective tissue around the transplant ; and
it is likewise on the basis of a discrepancy between the organismal differentials
that immunity develops, which then may perhaps intensify the lymphocytic
reaction. If this interpretation is correct, we should expect a distinct accumu-
lation of lymphocytes to be lacking around autotransplants of spontaneous

422 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tumors, and this seems to be the case ; it likewise has been found impossible to
immunize against a tumor with autogenous tissue. However, there is an ex-
periment by Murphy which does not seem in accordance with this interpreta-
tion. He found it possible to prevent the growth of autogenous carcinoma
transplants by the local application of erythema-producing X-ray doses to the
skin ; but in this case we have probably to deal not with an effect on the lympho-
cytes but with a condition of a different nature. Through radiation the tissue
has presumably been made into an unfavorable soil for the development of
the graft. The incorporation of the latter into the host and its nourishment
are inhibited under these circumstances, which are non-specific and would
therefore affect tissues, irrespective of their relationship to the host.

However, lymphocytes are attracted not only locally to a tumor possessing
a strange individuality differential, but they are increased also in the general
circulation, due to the fact that the homoiodifferentials enter also the blood
vessels and various organs. This is another instance of the resemblance of
tumors to normal tissues possessing a strong individuality differential. But no
proof has been given for the view that it is on account of these lymphocytic
changes in the whole organism that immunity develops. The production of
antibodies probably depends on the stimulation of the reticulo-endothelial
tissue.

The great similarity in the behavior of lymphocytes after transplantation of
tumors and of normal tissues, and the significance of the relations of the
organismal differentials of host and transplant in determining the nature and
intensity of these reactions, has been further confirmed by the recent investi-
gations of Blumenthal, concerning the alterations which take place in the
blood cells of animals into which pieces of tumors have been transplanted.
There is a complete analogy between such alterations and those which occur
after transplantation of normal tissues ; differences which do exist are due to
secondary conditions. Homoiotransplantation of rat carcinoma and sarcoma
into rats brings about an increase in lymphocytes in the blood, which begins
on the fourth or fifth day following transplantation and persists for eight to
ten days, or sometimes longer, the maximum being reached between the
seventh and ninth days. Quantitatively, the reaction is of about the same order
as the one following transplantation of homoiogenous normal tissues, and it
may occur whether the tumor grows or not. The same results were obtained
in mice after homoiotransplantation of tumors, either into the same inbred
strain or into strange strains. In these two types of transplantation the
changes in the blood were similar, although the tumors grew in the same
strain, while they did not grow in strange animals. Still, the increase in the
number of lymphocytes in the first type was not quite as rapid as that in the
second type, although it tended to persist for a somewhat longer period; in
transplantations between different strains, the curve representing the variations
in the lymphocyte counts showed a steeper ascent as well as a steeper descent.

Homoiotransplantation of a benign rat tumor, an adenofibroma of the
mammary gland, likewise caused an increase in lymphocytes, but it was a little
lower than that observed after transplantation of cancerous tissues and there

IMMUNITY IN TUMOR TRANSPLANTATION 423

was a somewhat greater variation as to the time of maximum increase. When
in rats and mice with growing homoiotransplanted tumors the period of obser-
vation was extended until the tumors had reached a considerable size and the
animals had become debilitated, the number of erythrocytes decreased and at
the same time the number of polymorphonuclear leucocytes increased in the
peripheral blood. A similar parallelism in the changes in erythrocytes and
leucocytes occurred in mice with growing autogenous (spontaneous) tumors.
There were no significant changes in the number and relative distribution of
lymphocytes and polymorphonuclear leucocytes until the tumors became moder-
ately large. From that time on there was a gradual increase in the total white
cell count and in the relative number of polymorphonuclear leucocytes. At the
same time a decrease in the total number of red cells and an increase in
reticulocytes occurred ; also, normoblasts appeared in the peripheral blood
when the later stages of the anemia were reached. When the tumors became
large, the average erythrocyte count fell to 4.12 million cells per cmm.
(Blumenthal). In the bone marrow the newformation of the red cells was
intensified and it appears probable that the increase in the number of poly-
morphonuclear leucocytes in the peripheral blood was caused by the stimula-
tion which occurred in the bone marrow as the result of the very marked
anemia.

Heterotransplantation of rat and mouse tumors to guinea pig, mouse and
rat led in principle to the same changes as those observed after heterotrans-
plantation of normal tissues. There was an increase in polymorphonuclear
leucocytes in the peripheral blood, which set in between the second and fourth
day after transplantation and which reached a maximum between the sixth and
tenth day. It persisted somewhat longer than the increase observed after
heterotransplantation of normal tissues, but the degree of increase was about
the same in each. In each also the return of the number of polymorphonuclear
leucocytes to normal was followed by an increase in lymphocytes, which
reached a maximum usually between the sixteenth and eighteenth day after
transplantation and then dropped to the usual level. This rise in the number
of polymorphonuclear leucocytes following heterotransplantation of tumors
and of normal tissues was not associated with anemia and increased erythro-
poiesis in the bone marrow; it was presumably due to a direct effect of the
organismal differentials on the leucocytes or their precursor cells in the bone
marrow.

If, twelve or twenty days following the homoiotransplantation of a piece of
normal tissue, a second homoiotransplantation of a similar piece is carried out,
a lymphocytic reaction follows also this transplantation as well, but in this
case the reaction occurs somewhat more rapidly, although the rise is not quite
so great in the majority of animals as after the first transplantation. The same
effect is obtained if in the first homoiotransplantation a piece of cancerous
tissue is used instead of normal tissue and if normal homoiogenous tissue is
then transplanted twenty days after the first transplantation. In principle, the
same results were obtained if two successive homoiotransplantations of
tumors were made; even if the second transplantation was delayed so long

424 THE BIOLOGICAL BASIS OF INDIVIDUALITY

that the first homoiotransplant had elicited an increase in polymorphonuclear
leucocytes, a second homoiotransplantation of tumor was again followed by
a rise in the lymphocytes.

Furthermore, a like sequence of events was noted when in a first homoio-
transplantation normal tissue was used and, sometime later, a piece of homoiog-
enous tumor. But if instead of homoiogenous tissue, heterogenous tissue was
transplanted and this was followed by a second transplant of homoiogenous
tumor, the reaction which followed the second transplantation was not modi-
fied by the first transplant. It is apparently only a first homoiotransplantation
which influences a second homoiotransplantation. The character of the or-
ganismal differentials of both the first and second grafts determines the mode
of reaction in the blood, but the tissue or organ differential, or the differences
between the differentials of normal and tumor tissue belonging to the same
species, is of no importance as far as this reaction is concerned. These very
interesting experiments of Blumenthal confirm, therefore, the conclusion that
in transplantation of both normal tissues and tumors the organismal differ-
entials are a very important factor in determining the kind of reaction of the
host against the graft, and the behavior of the lymphocytes and of the
polymorphonuclear leucocytes can be used as an indicator of the relationship
between hosts and transplants. It may then be concluded that as far as the
reactions in the cellular constituents of the blood are concerned, transplants of
various kinds of tumors, as well as autogenous tumors, behave like the corre-
sponding transplants of normal tissues, and that the reactions in both instances
depend on the relationship of the organismal, and in particular, of the indi-
viduality differentials of host and transplant, the differentials of the tumor
being essentially the same as those of normal tissues from which they are
derived. There is reason for connecting the increase in the number of polymor-
phonuclear leucocytes in the circulating blood which occurs during a later
period in the growth of transplanted as well as of spontaneous autogenous
tumors, with the same factors which were responsible for the anemic changes
which are noted in the bone marrow.

In the case of normal tissues we have seen that differences in the constitu-
tion of the individuality differentials between host and transplant may cause
not only the invasion of the transplant by lymphocytes, but may also induce
a more active reaction of the connective tissue cells of the host against the
graft, and may tend to diminish the ingrowth of capillaries into the transplant.
The experiments of Burgess and Tyzzer indicate that also around a graft,
whose organismal differential differs markedly from that of the host, connec-
tive tissue growth may be quite active, and the resulting increase in the forma-
tion of fibrous tissue may still further contribute to the injury of the trans-
plant. But it is exactly the opposite condition, namely, a lack of ingrowth of
connective tissue, accompanied by a lack of ingrowth of blood vessels into
the graft, a lack of "stroma reaction" on the part of the host tissue, which,
according to Russell and Bashford, may result in the destruction of homoiog-
enous tumor transplants in immunized animals, and they believe the lack of
this reaction to be the mechanism through which the active immunity of the

IMMUNITY IN TUMOR TRANSPLANTATION 425

host against the transplant becomes effective. They applied this conception
also to animals which had become immune following the retrogression of
their tumors. In some way immunization was supposed to interfere with the
chemotatic attraction which tumor transplants exerted on the surrounding
tissues of the host. Russell and Bashford held that the mechanism of an active
immunity, or rather, of an active resistance against transplanted tumors, com-
bined with the apparent lack immune bodies in the bodyfluids of the host,
constituted a condition distinct from any other known kind of immunity. On
the other hand, natural immunity and active immunity against heterogenous
tumors did not depend, in their opinion, upon a lack of stroma reaction, the
immunity against heterogenous tumors in particular being due, rather, to the
cytolytic effect exerted by the injurious bodyfluids on the peripheral tumor
cells, a phenomena related to the formation and action of agglutinins, precipi-
tins and hemolysins which affect certain normal cells or proteins. Similar
observations to those of Russell concerning the significance of the stroma re-
action, were subsequently reported by Woglom in the immunity against rat
tumors, and by Rous in the transplantation of embryonal tissues in mice which
had been previously immunized against embryonal mouse tissue. According
to Rous and Murphy, in the transplantation of chicken sarcoma into naturally
immune fowl, especially into those in which previously retrogression of such
a tumor had taken place, the successful inoculation with a second tumor may
be prevented either through lack of a stroma reaction or through the subse-
quent accumulation of lymphocytes. However, later investigations did
not confirm the theory of a lack of a stroma reaction as the mechanism under-
lying the destruction of the grafts in immunized mice (Mottram and Russ,
Murphy, Tyzzer and Levin). We and our associates likewise have failed to
observe a phenomenon corresponding to it in the case of normal tissues, al-
though Cora Hesselberg and the writer noticed a diminished vascularization
of homoiogenous as compared with autogenous grafts.

Russell and Bashford, believing that active immunity depends upon a lack
of stroma reaction, assumed that this immunity can manifest itself directly
after transplantation only, before the tumor has been incorporated in the host
tissue and has begun to grow, However, there is every reason for believing
that a retrogression of homoiogenous tumors may be caused by an active immu-
nity which develops in the host during the period of growth of the transplant.
In this case there is then an active immunity which does not depend upon a
lack of stroma reaction. Moreover, Russell himself noted that in actively
immunized animals a small tumor nodule may occasionally grow for some time,
but subsequently retrogress. Here, too, the active immunity causing the retro-
gression does not depend upon the stroma reaction for its manifestation. It is
known that under certain conditions homoiogenous and even heterogenous
tumors are able to remain alive and even to grow for some time without
possessing a stroma. We may then conclude that the lack of a stroma reaction
does not play a significant role in the active immunity against homoiogenous
tumors.

In a somewhat different way, also, Greene attributes to the stroma a promi-

426 THE BIOLOGICAL BASIS OF INDIVIDUALITY

nent role in the mechanism through which immunity affects the tumor. He
believes that immune processes may act on a tumor injuriously by interfering
with the formation of the specific stroma which the tumor needs, and that in
this way the growth of a carcinoma may be prevented in immune animals.
However, it is much more probable that in his experiments the immune proc-
esses acted primarily on the tumor cells directly, diminishing their growth
energy, and that as a result of this interference the relations between the tumor
parenchyma and the ingrowing connective tissue were changed. We have found
in other instances definite correlations between the parenchyma and stroma,
in which the condition of the. former was the primary and decisive factor
which determined the condition of the latter.

In the case of microorganisms there is good reason for assuming that the
reticulo-endothelial tissue is the seat of the production of immune bodies,
and there are strong indications that also the immunity against tumor trans-
plants, as far as it is caused by differences in the organismal differentials be-
tween host and transplant, is due to a stimulation of the reticulo-endothelial
system ; the activity of the lymphocytes and polymorphonuclear leucocytes
are apparently factors of secondary importance in the mechanism underlying
this immunity ; they function mainly as indicators of the relationship between
the organismal differentials of host and transplant. Various investigators,
Apolant, Uhlenhuth, Vorlander, Caspari, have assumed that it is the reticulo-
endothelial system which gives origin to tissue immunity. In the reticulo-
endothelial tissues abnormal cells or strange colloidal substances circulating in
the bodyfluids are held back and phagocytosed, and here, especially in the
spleen and bone marrow, they set in motion the mechanisms leading to the
production of immunity. The main evidence for the conclusion that this applies
also to immunity against transplanted tumors consists in the demonstration
that different types of this immunity, such as concomitant and retrogression
immunity, and probably also certain instances of natural immunity, can be
abolished by inactivation (blockade) of the reticulo-endothelial system, either
by injection of substances such as India ink, colloidal metals or dyes (Roskin,
Lignac and van de Borne), or by means of strong doses of X-rays. Weak doses
of X-rays, or certain other procedures, such as stimulation of the spleen
through ultraviolet rays (Roskin), may stimulate the reticulo-endothelial cells
and thus produce an opposite effect, leading to an increase in immunity against
tumor transplants. There is the possibility that in addition to the formation of
the immune substances the reticulo-endothelial cells may be concerned in the
production of the primary preformed substances circulating in the bodyfluids
which act on organismal differentials, although such a function has not yet
been demonstrated. Quite recently Ehrich and Harris have found evidence
that also local lymph glands may participate in the production of antibacterial
immune substances and of immune hemolysins and they noted that such lymph
glands show a hyperplasia of the lymphocytic tissue. This observation sug-
gests the possibility that it may be the lymphocytes rather than the reticulo-
endothelial cells which produce these substances. We would then have to
assume that the lymphocytes react to strange differentials in a twofold way,
namely by movements and by the production in immune substances.

IMMUNITY IN TUMOR TRANSPLANTATION 427

We have discussed those aspects of immunity against transplanted tumors,
in which organismal differentials function as antigens. It may be further
stated that the organismal differentials in tumors, are essentially the same
as those of the normal tissues from which the tumors are derived. There are,
however, indications that other substances present in tumors, besides the
organismal differentials, may be antigenic. A brief outline of some of the
principal data which point to the presence of these secondary antigens will
now be given.

(7) The presence of antigens other than organismal differentials in tumor
cells. By serological tests the same types of antigenic constituents have been
found in certain cancers, which normal cells in corresponding organs of the
same species possess, namely, species-specific, organ-specific, blood-group
and heterophilic Forssman antigens ; also alcohol soluble substances corre-
sponding to Wassermann antigens not characteristic of either organ or species
may occur. Thus the cells of a carcinoma developing in individuals belonging
to blood group A may contain these same blood-group antigens and the partial
Forssman antigens which are associated with blood group A. Mouse carcinoma
may contain Forssman antigen, in accordance with the fact that the mouse
belongs to the group of those species which possess heterophilic antigens.
However, there are apparently some exceptions to this parallelism between
normal tissues and tumors. According to Kritchewski and Rubinstein, also
the Flexner-Jobling rat tumor contains Forssman antigens, although normal
rat organs do not contain them ; this would constitute a difference between
cancerous and the corresponding normal tissues. Moreover, while human
carcinoma cells of individuals belonging to blood group II, like some normal
cells, may possess the A differential, it has been stated that it is never found
in sarcoma cells; but it is not certain that normal connective tissue cells of
such individuals contain it. Hence we find in cancer cells a complex condi-
tion, which makes the search for constituents characteristic of carcinomatous
cells, and not present in normal cells, difficult, and this may explain at least
in part the contradictory nature of some of the results obtained by various
investigators. Some of these obstacles to the discovery of specific tumor anti-
gens were overcome by using for immunization carcinomatous material from
persons belonging to blood group I, which is free of antigens A and B, or by
first extracting the blood group antibodies by means of erythrocytes possessing
group A. Furthermore, the attempt was made to modify the material to be used
for immunization by destroying or eliminating the species and normal organ
antigens before injecting the antigen. Hirszfeld and his collaborators found
that by immunizing rabbits with human carcinoma of a certain organ, immune
sera developed in a small minority of the rabbits which reacted with different
types of human carcinomas, irrespective of the organs in which they origi-
nated. Witebsky and Lehmann-Facius, by using boiled, instead of fresh,
unheated carcinoma suspensions as antigens, obtained antibodies which were
specific for carcinoma, and not merely for the species or the organ in which
the cancer occurred. Witebsky, in addition, used boiled globulins of cancer
tissue in these tests. According to Lehmann-Facius, the complement fixation

428 THE BIOLOGICAL BASIS OF INDIVIDUALITY

which takes place when antigen and immune substances interact, can be
made still more specific if the test is carried out at a temperature near the
freezing point. But, while Witebsky assumes that the immune serum obtained
against the carcinoma of a certain organ as a rule reacts specifically with the
antigens prepared from a carcinoma of the same organ, and only exceptionally
with cancers from other organs, Lehmann-Facius maintains that the antisera
show a positive complement fixation reaction with all kinds of human cancers,
and even with cancers of other species.

But, in addition, Witebsky and Morelli found that if in rabbits immune
substances are produced against human sarcoma, these immune substances
react with alcohol extracts not only of human sarcoma, but also of carcinoma
and even of various normal human organs ; but these substances are species-
specific and do not react with rat or chicken sarcoma. However, it is possible
to absorb from such immune serum the quota reacting with normal organs
and to leave behind the anti-tumor fraction ; also the anti-carcinoma fraction
can be specifically absorbed with carcinoma extract, so that in the end only
the sarcoma antibody is left in the immune serum. It seems, then, from these
and other experiments, that antibodies can be produced against constituents
which are specific for cancers in general, but that antigenic differences exist
between the various kinds of tumors. These antibodies, and therefore also
the antigens producing them, may or may not carry species differentials.
However, somewhat different are the more recent results of Lehmann-Facius
(1932), who finds that ether extracts of mouse intestines may induce the
formation of antisera, which react with cancer extracts of a lipoid nature;
lipoid antigens which are present in cancer do not need, therefore, to be
specific for the latter, but may occur also in normal organs.

It is possible to obtain anti-cancer sera under conditions in which species-
specific immune bodies do not develop, as for instance, when boiled antigens
are injected ; but such methods do not exclude the production of organ-specific
immune sera. Some of these observations suggest that the antibodies which
are common to various anti-carcinoma sera are organ-specific constituents, and
that, correspondingly, the change in the constitution of normal cells, which
leads to their transformation into cancer cells, represents a change in the
organ rather than in the organismal differentials, which latter seem to be
essentially the same in cancer and in normal cells. Accordingly, Witebsky's
method of injecting cancer globulins for preparing immune sera against can-
cer, can be readily used also for the preparation of organ-specific immune
sera if, instead of cancer globulins, globulins from various organs are taken
as antigens.

But, there are still further differences between antigens obtained from cancer
and from normal tissues. According to Witebsky, in carcinoma cells the lipoids
may exist in a state which makes them readily available as antigens, while
in normal organs they are less available, perhaps because they are bound to
other cell constituents.

There are some additional indications of the presence of specific cancer
antigens. Hirszfeld and Halber, assuming that there are immune substances

IMMUNITY IN TUMOR TRANSPLANTATION 429

against cancer antigens in the serum of cancer patients, mixed alcohol extracts
from a human carcinoma with the blood serum of patients suspected of cancer
and observed a specific complement fixation. A positive reaction was obtained
irrespective of the organ in which the carcinoma had arisen. However, other
investigators consider this test as non-specific, or at best, as successful in
only a small number of instances. Lehmann-Facius, in order to demonstrate
the presence of specific immune substances in the serum of cancer patients,
used the euglobulin fraction of the serum and the phosphatid fraction of
tumor extracts. Also, the diagnostic cancer reactions of Freund and Kaminer,
of Willheim and Stern, and of Fuchs, are based on the assumption that in
the serum of cancer patients substances are circulating which are specific
for all kinds of human cancer, which develop in response to antigens charac-
teristic of cancer, and which interact with these antigens in a specific manner.
The substances present in the cancer sera may be either proteolytic or lipolytic.
Moreover, not only human cancers, but also animal cancers, may contain
these antigens. But there is still some difference of opinion as to the degree
of specificity attaching to these various tests.

We have already referred to the experiments of Lumsden, who believes
that besides preformed natural and experimentally produced immune sub-
stances which are species-specific, there exist in the serum constituents which
act in a specific manner on various kinds of cancer cells growing in vitro,
although they are able to injure, also, reticuloendothelial cells growing out
from pieces of spleen in tissue culture. As stated, it is not certain at present
whether these reactions are due to the species differentials present in cancer
and in spleen tissue, or whether they are due to "antimalignancy" antigens,
calling forth the production of the corresponding antibodies. On the whole,
the evidence seems to point to the conclusion that the reactions which Lumsden
observed were caused by species differentials, therefore, by organismal differ-
entials, and not by a special kind of antigen, designated by this investigator
as "antimalignancy" antigens. More recently, Mann and Welker produced
in rabbits, injected with preparations from various types of human cancer,
antisera which contained precipitins for the proteins present in autolysed
carcinoma, but not as a rule for proteins from normal human tissues ; these
immune substances reacted also with the blood serum from cancer patients,
and most strongly with the serum of patients that were bearers of the same
kind of carcinoma as the one from which the antigens that were used in the
preparation of the precipitins had been obtained. This suggests that the specific
carcinomatous proteins are present also in the blood of cancer patients. Such
serum is species-specific; it reacts only with human sera, not with those of
various animal species. These precipitins were therefore, specific for protein
from carcinoma and at the same time they were species-specific.

There is, furthermore, noticeable in some of the diagnostic tests for cancer
mentioned above, a similarity between the reactions of cancer sera and of
embryonal or pregnancy sera; embryonal cells may be affected by these sera
in a similar manner to cancer cells, and in embryonal tissue, antigens similar
to cancer antigens may be present. Moreover, Hirszfeld and Dmochowski

430 THE BIOLOGICAL BASIS OF INDIVIDUALITY

have shown that spontaneous as well as long-transplanted tumors, and also
rapidly growing embryonal tissues, contain antigens which are also present
in dying leucocytes (pus) and in necrotic tissue. Antigens which are common
to long-transplanted tumors and pus are species-specific; for instance, the
Brown-Pearce rabbit carcinoma has an antigen in common with rabbit pus,
and the guinea pig liposarcoma has an antigen in common with guinea pig pus.

We have already mentioned the fact that in the sera of animals which bear
virus-induced cancers antibodies may be demonstrable, which are directed
against the virus. Such sera may contain substances which neutralize the virus,
or in combining with a virus antigen, call forth complement fixation or lead to
the formation of precipitates. Thus the filtrable Rous fowl sarcoma contains
virus antigen which may induce in the blood of geese, injected with the tumor
extract, antibodies against this virus (Rous, Robertson and Oliver). Similar
immune substances may be demonstrated in the serum of chickens in which
such tumors have retrogressed (Rous, Mottram). They may also develop in
bearers of slowly growing tumors of this kind (Andrewes) and one kind of
tumor may elicit the production of antibodies which interact also with the
virus of a different type of fowl sarcoma. According to Peyton Rous and
Kidd, the growth of the rabbit papilloma, which is caused by a virus, as well
as carcinoma which develops from this papilloma, may give rise to specific
immune substances circulating in the serum of the bearer of this newformation.
In saline extracts of the cottontail rabbit papillomas, a serologically specific
substance can be demonstrated, which probably is identical with the Shope
papilloma virus. It is of special importance that, according to Rous, if a
papilloma virus-induced carcinoma develops in domestic rabbits, the virus is
no longer demonstrable in the tumor extracts; but the presence of such a
virus can be made very probable, because specific antibodies against the
papilloma virus are demonstrable in the blood serum of these rabbits. Similarly,
Andrewes has shown that when sarcoma is produced in fowl by injection of
carcinogenic substances and a filtrable agent cannot be shown to exist in this
tumor by direct methods, the presence of a hidden agent in the tumor may be
made probable by means of immune substances which can be shown to exist
in the blood serum of the fowl. Kidd found, with the aid of the complement
fixation method, an antigen in the extract of the Brown-Pearce rabbit car-
cinoma ; this antigen was not of the same type as the antigens present in
normal rabbit organs, nor was such an antigen noted in tumors occurring in
the uterus of the rabbit ; but this antigen was also distinct from the rabbit
papilloma antigen and the presence of a virus has not so far been demonstrated
in the Brown-Pearce rabbit carcinoma.

In this connection it may also be of interest to recall the experiments of
Furth on transplantation of leukemic cells from a case of leukosis which arose
in Fx hybrids between two strains of mice differing markedly in their tendency
to become leukemic. The results of transplantations from Ft hybrids to both
parent strains could not be interpreted merely as due to differences in the
relationships of the individuality differentials of the two parent strains and
the hybrids. We suggested that exogenous growth stimuli (Ge), acting spe-

IMMUNITY IN TUMOR TRANSPLANTATION 431

cifically on the transplanted leucocytes, might be responsible for the peculiari-
ties noted.

There exist, then, tumors in which an extraneous growth stimulus (virus)
determines the reaction of the host against the transplant and the specificity of
the immune sera. In other cases the reaction may be determined by growth
stimuli intrinsic in the cancerous cells (Gi). These stimuli may perhaps be
similar to factors active in embryonal tissue, although in some very essential
respects conditions prevailing in tumors and embryonal tissues differ. In still
other instances, perhaps, substances related to tissue and organ differentials,
such as those present in pus and necrotic tissue, may give rise to immune sub-
stances. However, definite data as to the nature of some of the antigenic sub-
stances found in these cancers, and also in leukemia, which would differentiate
them from normal tissues, are as yet lacking. Moreover, some characteristics
of tumors may change in the course of serial transplantations ; we have dis-
cussed the probable nature of these changes in a preceding chapter. Dmochow-
ski, in the case of some mammalian tumors, found indications that also the
antigens may change as the result of long-continued serial transplantations.
Similar are the recent observations of MacDowell and his associates in mouse
leukemia. Mice belonging to strain C58 clevelop leukemia in a very large per-
centage of cases. Leukemic cells from a C58 animal with spontaneous leukemia
can readily be transplanted into other C58 mice, where they proliferate and
so transfer their disease to the hosts. When several lines of leukemic cells
were propagated through a large number of generations of C58 mice, in the
course of these passages the cells gained in proliferative power and transmitted
the disease more readily to other C58 mice. MacDowell found that, through
graded inoculation with increasing doses of such leukemic cells, C58 mice can
be immunized against these various propagated lines, so that in the end the
transfer of such cells no longer calls forth leukemia in mice thus treated. But,
if a C58 mouse, immunized against these special lines of C58 leukemic cells,
is inoculated with cells taken directly from a case of leukemia arising spon-
taneously in a C58 mouse, then the inoculated mouse succumbs to the disease.
The immunization with the serially propagated leukemic cells from strain C58
protects only against these special propagated lines, but not against new
leukemic cells which have not yet been propagated in passages. It appears
therefore, as if, as a result of the serial propagation, not only did the leukemic
cells acquire a greater growth energy and become therefore more virulent,
but there must also have taken place in all the serially propagated lines the
same type of modification of the antigen, which made this antigen different
from that present in the leukemic cells from primary spontaneous cases. As
to the nature of this antigen, it may represent an intrinsic stimulus or an
extrinsic virus, or something akin to a tissue or organ differential ; but for
the reasons stated, it is not probable that this antigen or any of the special
tumor antigens originate as a result of somatic mutations occurring in the
cells. There occurs then, in cancer cells, in addition to the organismal differen-
tials, various other kinds of antigens, but there remains some doubt at the
present time as to the nature of some of these antigens of the second type.

Chapter $
Tumor Growth and Organismal Differentials

In the preceding chapters the principal facts concerning the significance of
organismal differentials for the growth of transplanted tumors have been
analyzed. The concept of organismal differentials has contributed in
various ways to the understanding of tumor transplantation and of the im-
munity against transplanted tumors; and conversely, the analysis of tumor
growth has contributed to the understanding of the organismal differentials.
It is for these reasons that we have discussed also the various factors which
interact with the organismal differentials in tumor growth. In concluding, it
will be of interest to trace the development of the various concepts and theories
relating to the factors which are of importance in the transplantation of
tumors. Some of the most prominent investigators in the field of cancer have
contributed to these studies, and while certain of their interpretations have
been modified in the course of time, the conclusions they expressed and the
experiments they carried out in support of them helped greatly to advance our
knowledge of the nature of cancer and of the factors active in transplantation.

Jensen in his transplantations of mouse carcinoma approached the facts he
discovered from the point of view of the bacteriologist and immunologist.
It had been found possible to induce immunity against various diseases caused
by microorganisms. By using as a vaccine, in a weakened form or in a very
small quantity, the microorganisms that caused the disease or certain of their
derivatives, or by introducing related organisms less virulent for the host but
sufficiently related to the causative agent, an active immunity was produced.
These studies gave direction to and supplied the problems for Jensen's work
as well as for the following investigations of Ehrlich and Apolant, and also
of Bashford, Murray, Haaland, Russell and Cramer. In the beginning it was
assumed that cancer cells differ in various ways from ordinary tissue cells
and that the laws relating to the transplantation of tumors differ in some
essential respects from those governing ordinary tissue cells. Thus Ehrlich
applied the same principles in explaining immunity against cancer and im-
munity against microorganisms ; he explained both on the basis of his nutri-
ceptor and athrepsia concepts. However, Bashford and his associates, Murray,
Russell and Cramer, soon recognized important differences between these two
types of immunity, and one of the most essential was the fact that a formation
of antibodies against the ordinary transplantable tumor could not be demon-
strated in the case of tumor immunity; they substituted therefore the term
"resistance" for that of "immunity." But even these investigators considered
the problem of immunity or induced resistance against tumor growth as the
principal problem of tumor growth.

Although soon some facts were established, which proved certain similari-
ties between the behavior of tumors and of normal tissues, still the immunity

432

TUMOR GROWTH 433

against tumors retained distinctive features and there was the expectation and
hope that a study of immunity against transplanted tumors might lead to the
discovery of methods of immunization also against spontaneous tumors, which
would prevent their development or cause the retrogression of tumors which
had already developed. Similar views were held, also, by subsequent in-
vestigators, Tyzzer, Woglom, Uhlenhuth, Chambers and Scott, Caspari,
Lewin and Lumsden.

We approached the problem of tumor transplantation essentially from the
point of view of the experimental analysis of tissue growth, and from the
beginning we emphasized the parallelism between the behavior of tumors and
normal tissues after transplantation. The favorable results of autotransplanta-
tion were attributed to the similarity in the constitution of host and spon-
taneous tumor, and the reactions in homoiotransplantation, and the still
stronger reactions in heterotransplantation, were correspondingly interpreted
as due to the relative strangeness of the constitution of host and transplanted
tumor. In this sense we explained also the experimentally produced variations
in growth energy of tumor cells which we had observed under various condi-
tions, and the conclusion was drawn by us that the potential immortality of
tumor cells which the serial transplantation of tumors had revealed was not
peculiar to tumors, but was shared by the majority of normal tissues, at least
by all of those that could give origin to tumors. A comparison of the struc-
tural changes of normal tissues and tumors after transplantation and of
cellular reactions taking place around them revealed additional similarities,
and it was possible to distinguish between the constitutional factors, which
would permit the tumor cells to live in the host, and the increased proliferative
tendency inherent in the tumor cells, which enabled them to grow after
transplantation. A distinction was made also between transplantability and
the factors determining the growth energy of tumors and at the same time
the analysis of the constitutional factors underlying these conditions was
further developed. There was noticeable a great similarity in the behavior of
normal tissues and tumors after auto-, homoio- and heterotransplantation.

These points of view were extended by Peyton Rous, who (1910) compared
the immunity against embryonal tissues and against tumor tissues, when both
tissues grew side by side in the same host. He found that immunization against
embryonal tissue, and that against tumor tissue, took a similar course. A few
years later (1916) we further compared the reactions of the host against
transplanted normal and tumor tissue, and we observed in both instances a
parallel reaction of the lymphocytes and connective tissue of the host against
the transplant. Thus there was formed gradually on the basis of these com-
parative studies of tissue and tumor transplantation, the concept of organismal
differentials as the essential factors underlying both of these processes.

A definite divergence existed, therefore, between these two tendencies in the
development of cancer research, and especially in the study of the transplanta-
tion of tumors ; in the one, the immunity against tumors was the central prob-
lem, in the other, it was the comparative behavior of normal and tumor tissues.
However, this distinction was not quite so complete as it might appear. Thus,

434 THE BIOLOGICAL BASIS OF INDIVIDUALITY

in our early analysis of tumor transplantation we admitted the possibility that
extraneous agents might be concerned in the growth of tumors, and this sug-
gested a possible difference in the behavior of normal tissues and of tumors.
Our findings regarding the difference between the results of auto- and
homoiotransplantation of tumors, the observations of Schoene and Bashford
that an immunity against tumors could be produced by inoculation of normal
tissues, but that it was impossible to immunize with autogenous tissues
(Apolant, Woglom), as well as the behavior of heterotransplanted tumors,
suggested also to Ehrlich and Bashford that in tumor immunity there may be
a component directed against the tumor as a tissue and not as a tumor. Ehrlich
even went so far as to state that tumors showed in this respect a greater
specificity than normal tissues, inasmuch as he assumed that the latter could
be successfully transplanted between individuals belonging to different but
hybridizable varieties, while it was difficult to transplant tumors even to dif-
ferent strains within the same species ; and Bashford, Murray and Cramer in-
terpreted the condition following retrogression of a tumor, which was desig-
nated as panimmunity by Ehrlich, not as due to a specific tumor immunity but
as directed against the tissues of which the tumor was composed. In a similar
manner Bashford and Russell (1910) explained the immunity produced
against a second heterogenous tumor through a first inoculation with the same
heterogenous tumor; in this case, too, they assumed that the immunity was'
directed not against the tumor but against the tissues. Some years later
Murphy transplanted not only heterogenous tumors, but also heterogenous
embryonal tissue, into the chick allantois and found that both tumor and
embryonal cells behaved similarly under these conditions, although he stressed
the results obtained with tumors rather than those obtained with embryonal
tissues. Little also, in 1922, using more closely inbred strains of mice, com-
pared the genetic factors underlying the transplantation of tumor tissues
with those effective in the transplantation of normal spleen from points of
view similar to our own.

Yet notwithstanding these analogies between the growth of tumors and
normal tissues, which began to accumulate more and more, the large majority
of authors still conceived tumor growth and tumor immunity as essentially
distinct from the growth and immunity of normal tissues. This was true, as
mentioned, of Ehrlich as well as of Bashford and his associates. The latter
saw one of the characteristic features of tumor immunity in the lack of stroma
reaction, as first defined by Russell. Moreover, they attributed all the reac-
tions of the host against tumors to an induced active immunity against tumors
(Russell), in contradistinction to the writer's subsequently defined concept of
preformed individuality differentials, to which the primary reaction against the
homoiogenous transplant, in the case of normal as well as of tumor tissues, was
attributed ; also, the active immunity against tumors was considered by us as
resulting from differences in organismal differentials between host and tumor.
Tyzzer, who recognized the importance of hereditary constitutional factors in
the immunity against tumors, likewise accepted Russell's interpretation; in
estimating the factors which determine the transplantability of tumors and

TUMOR GROWTH 435

in fixing the number of genes for this purpose, he assumed that these factors
were specific determinants of tumor immunity, and that they did not apply to
tissues in general.

These differences in the theories of various investigators are shown more
clearly in additional investigations. Jensen (1908-1909) compared tumors
growing after transplantation into other individuals with metastases of spon-
taneous tumors, an interpretation subsequently expressed by various other
authors. He believed, furthermore, that if a change in diet can affect trans-
plantability of tumors — as it apparently did in Haaland's experiments — it
might equally influence metastasis formation. No distinction is recognized
here between the conditions in auto- and in homoiotransplantation. On the
other hand, Bashford, Murray and Cramer made a sharp distinction between
the conditions that cause the formation of a spontaneous tumor and those
determining the growth of a tumor once it has formed ; they were led to this
distinction by the observation that an animal unsuccessfully inoculated with
a transplantable homoiogenous tumor, subsequently could develop a spon-
taneous tumor. They did not, however, distinguish in these cases between the
development of a spontaneous tumor possessing the same or almost the same
individuality differentials as the host and the growth of homoiogenous (trans-
planted) tumors, in which the individuality differentials of tumor and host
differ; this can be seen from their statement that they observed — evidently
contrary to their expectations — that animals affected by spontaneous cancers
are not greatly more susceptible to inoculation with cancerous tissue than are
normal animals. They believed that spontaneous tumors which do not grow
in other animals of the same species not affected by cancerous growth, rarely
grow when transplanted to other parts of the animal's own body, and not
at all in other animals bearing spontaneous tumors ; there was no need, there-
fore, for any subsidiary assumption as to the importance of a constitutional
condition inherent in the normal cells of the animal in which the tumor origi-
nated and in the fully developed tumor cells for the growth of spontaneous
cancer after transplantation. What these authors called "individuality" of
tumors was not the chemical constitution of the tumor cells as determined by
genetic factors; identity of individuality did not mean identity in chemical
composition of cells due to genetic factors, but it was considered to be the
result of identity of the sum total of changes which had taken place in the
tumor cells, in consequence of past experiences in the life of the organism.
According to this conception, every individual mouse was therefore different
from all the others, and this difference would increase with the increasing
length of life of the animal. This point of view is expressed in a paper by
Bashford, Murray and Cramer on the resistance of mice to the growth of
cancer (1907).

Bashford and his collaborators attributed differences in transplantability
of tumors to factors inherent in the host as well as to variable factors which
distinguish different tumors. Among the latter they also recognized the sig-
nificance of the growth energy of the tumor, and they insisted especially on
the great significance of growth rhythms in tumor cells which occur spon-

436 THE BIOLOGICAL BASIS OF INDIVIDUALITY

taneously and in which periods of depression and of great intensity of growth
alternate; tumor cells which are in the phase of depression offer great diffi-
culty to transplantation. There were two facts known at that time which
demonstrated the dependence of the fate of the transplant on factors which
are present also in normal tissues, namely, the difference in the results of
auto- and homoiotransplantation of tumors, and the species-specificity of the
antigens in normal tissues which immunized a host against the growth of a
transplant, the latter indicating a parallelism between immune reactions against
tumors and against normal tissues and their proteins. Bash ford, Murray and
Cramer pointed out the species-specific factors in the production of immunity
against tumors and in the production of hemolysins and precipitins. Yet, they
considered the immunity against transplanted homoiogenous tumors as due
to a lack of the stroma reaction, a special phenomenon not heretofore de-
scribed in the transplantation of normal tissues. Moreover, as stated, they
did not attribute the specificity of the tumor tissue to its genetic constitution,
but to environmental factors which induce processes of adaptation in the
tumor to the organism in which it develops. These investigators conclude that
the "influence of individuality, i.e., the sum total of changes due to the past
life of the organism, will be to make any mouse different from all the others
and these differences will increase the longer the animal lives." In the new
host the environment is so strange that the cells cannot survive the interrup-
tion of their nutrition. Their failure to grow does not necessarily imply that
they would fail to proliferate in their new hosts if the conditions to which
they had been accustomed would be immediately supplied in the experiment.
"Cells which have lived and have become accustomed to the bodyfluids of one
mouse for, say, two years, may easily die or fail to adapt themselves when
transferred to the bodies of new animals." Autogenous tissues would then
differ from homoiogenous tissues in that the former have had a chance to
adapt themselves to the bodyfluids of the host, while homoiogenous tissues
have not had such an opportunity. It is evident that this conception differs
in some very essential respects from the conception of the organismal differen-
tials. The organismal differentials are the derivatives, the phenotypic mani-
festations of the genetic constitution of the fertilized germ cells and of the
tissues. The organismal differentials in host and transplant and their mutual
relationship represent the constitutional factors which determine transplanta-
bility of normal tissues and also of tumors ; other factors also enter into this
process.

Bash ford, Haaland, Woglom, and more recently, Lumsden, attributed
therefore the transplantability of a tumor, in the main, to secondary processes
of adaptation which take place between the tumor and the host in which it
originated, or into which it had been transplanted. The origin as well as the
transplantability of tumors would therefore depend upon variable, fluctuating
factors. It is especially the older experiments of Haaland which suggested
this point of view. Haaland believed that he had shown the apparent influence
of environmental, and especially of nutritional, conditions on the character of
the animals and their ability to serve as hosts of transplanted tumors. But

TUMOR GROWTH 437

also the more recent work of Lumsden concerning the adaptation of tumors to
the action of heterogenous serum, resulting from a temporary growth in a
strange species, was in conformity with this view. While there is much evi-
dence for the conclusion that tumor cells may display a remarkable ability of
adaptation to new environments, the transplantability of tumors is determined
above all by the relation of their organismal differentials to those of their
hosts. Haaland and Woglom were struck by the observation that in the same
individual one tumor, a spontaneous cancer, may continue to grow, while
another, a transplanted tumor, retrogresses. However, such an occurrence
is to be expected if we consider the great similarity or identity of the in-
dividuality differentials in the host tissues and in the spontaneous tumors and
their differences from those of the strange transplanted tumors. The impor-
tance of the relation between the individuality differentials of host and
transplant had not yet been recognized by Haaland, who attributed the dif-
ference in the fate of the two tumors to local conditions residing in the
tumor cells. Indeed, the sharp distinction between autogenous and homoiog-
enous tumors which the theory of the individuality differentials implies
had not yet been made by the majority of authors. Thus as late as 1916,
Tyzzer applied the findings concerning the growth of homoiogenous tumors
to the explanation of the origin of spontaneous tumors. He compared the lack
of development of a spontaneous tumor with the non-take of a homoiogenous
tumor and defined the factors which prevent a spontaneous tumor from
developing or from expanding as immunity; the means for regulating the
growth of autogenous tissues were considered analogous to those which de-
termine immunity against transplanted tumors. He further concluded that
spontaneous tumors must have feeble antigenic power and offer effective
resistance to the normal influences which inhibit undue tissue growth ; in this
way the continuous growth of a tumor is made possible in the animal in which
it originates. Otherwise reactions sufficient to destroy spontaneous cancerous
growths would occur more frequently. A spontaneous tumor, according to
this investigator, is therefore a parasite strange to the host and it owes its
origin to a somatic mutation. Similarly, L. C. Strong and his associates ex-
pressed the opinion that a genetic analysis of the factors underlying tumor
transplantation will explain also the origin of spontaneous tumors. Inasmuch
as according to these authors it is possible by means of transplantation to
determine the specific number of factors (genes) which each tumor requires
for its growth in a strange host, it was perhaps tacitly assumed that the
number and character of these genes explain also the development and peculi-
arities of a spontaneous tumor.

However, it follows from the concept of organismal differentials that an
analysis of the factors underlying transplantability of tumors can give an
insight only into the difference between the genetic constitution of the host and
the tumor graft, and that there is no reason for assuming that the hereditary
conditions which favor the development of a spontaneous tumor are identical
with the genetic factors which would be required for the growth of a trans-
planted tumor, when these factors are determined according to the procedure

438 THE BIOLOGICAL BASIS OF INDIVIDUALITY

used by Tyzzer, Little and Strong. Also, Uhlenhuth, who recognized the
species-specific characteristics of tumors, has not apparently considered the
relations between the individuality differentials of the tumor and the tissues
of the host. He explained the low degree of immunity against spontaneous
tumors by the assumption that the defense mechanism against parenterally
introduced cells may not be of a high degree of efficiency. Therefore, pieces of
spontaneous tumors, even if they possess only a low virulence, can be re-
inoculated into the animal in which they originate. Likewise, Caspari assumed
that the factors, in particular necro-hormones, which induce immunity against
homoiogenous tumors, would be equally effective in the case of autogenous
spontaneous tumors. Chambers and Scott ( 1924) regarded immunity against
cancer as analogous to immunity against bacteria. They believed a substance
is given off during the early stages of autolysis of tumor cells, which acts as
antigen and elicits immunity against the cancerous tssue. The reason why
spontaneous tumors, and especially human spontaneous tumors, do not call
forth immunity in the bearer, in contrast to transplanted tumors, is that in
spontaneous tumors the cells are healthy, the implication being that for this
reason they do not give off the immunizing substances ; yet, there can be no
doubt that autolysing and necrotic areas are frequently found also in spon-
taneous tumors. Similar views were expressed also by Woglom (1919). The
ready growth of spontaneous tumors in the animals in which they originate
is due to an adaptation which has taken place between the tumor cells and
the bodyfluids; but there is a general resistance against the growth of spon-
taneous tumors as well as against transplanted tumors (1923), and further-
more, it needs to be explained why resistance cannot be established in all
transplanted tumors (1922). C. Lewin assumed that during the development
of a spontaneous tumor, which means, during the transformation of normal
tissue cells into tumor cells, the former lose the characteristics which make
them constituent parts of the host organism; they behave like foreign cells.
He therefore concluded that it should be possible to elicit an immunity reac-
tion against a spontaneous, as well as against a transplanted tumor. A cure
of a spontaneous tumor would depend therefore on conditions similar to those
which determine the retrogression of a transplanted tumor.

This analysis shows the difference between the views which have been ex-
pressed by some of the most prominent investigators concerning the distin-
guishing features of tumor growth, the relations between the factors which
determine the growth of transplanted tumors and the origin and further
growth of spontaneous tumors ; it also presents the interpretations which
have gradually developed in conformity with the theory of the organismal
differentials. These views are based on some of the earlier observations on
tumor growth, which we have discussed already, and on a comparison of the
fate of transplanted normal and tumor tissues. All these experiments, as well
as those of Tyzzer and Little, and especially the extensive investigations of
Little and Strong and their associates on the transplantation of tumors in
closely inbred strains, showed the importance of genetic factors in tumor
transplantations. Nevertheless, certain differences have developed between

TUMOR GROWTH 439

the theory of organismal differentials, based on the comparative studies of
transplantation of normal tissues and of tumors, and the concepts of Little
and Strong. These authors, did not determine differences which existed be-
tween the individuality differentials of tumors and their hosts, but they dealt
instead with certain factors which they believed were needed in a specific
manner for the growth of transplanted tumors.

As we have shown in the foregoing pages, there is good reason for assuming
that the problem of the transplantability of tumors is complicated by a number
of variable factors, including changes in growth energy of the tumor, adapta-
tion of the tumor cells to the hosts, different degrees of sensitiveness of differ-
ent tissues or cells to injurious conditions, and lastly, processes of immunity,
which again depend upon complex conditions, such as the ability of the tumor
to give off antigens and to absorb and neutralize antibodies. While genetic
factors enter also into these conditions in conformity with the fact that the
organismal differentials may act as antigens and that the range of reactivity
of an organism to environmental conditions is limited by constitutional fac-
tors, still, the fact that also external factors are involved in these processes
makes it impossible to account for the transplantability of tumors entirely on
the basis of Mendelian heredity, and to refer modifications of transplantability
entirely to genetic mutations, either in the host or in the tumor cells them-
selves. These difficulties have been discussed in the preceding chapters.

As to the relations between the origin of spontaneous tumors and the fate
of transplanted tumors, it is certain that tumor cells even more than regenerat-
ing cells have properties which differ from those of normal cells. As the
result of acquired characteristics, tumor cells may be more readily accessible
to certain injuries than some types of normal cells. Various physical and
chemical agencies affect the former somewhat differently from the latter, but
the changes which have taken place during the cancerous transformation are
in all probability not specific, in the sense that they depend upon alterations in
the constitution of the organismal differentials of the affected tissues, as the
result of which it would be possible for antibodies to develop against the in-
dividuality differentials of the tumor cells in the host in which they originate.

It is especially the recent investigations of Blumenthal, in which the effects
of transplanted normal tissues and transplanted tumors on the distribution
of the leucocytes in the circulating blood were compared, which again con-
firmed in a very convincing manner the essential similarity in the principles
underlying the transplantation of both normal and tumor tissues, and which
again demonstrated the fact that in both instances it is the nature of the
organismal differentials in the host and transplant which primarily determines
the outcome of these transplantations. However, in addition to the organismal
differentials which normal tissues and tumors have in common, there occur
other substances which are also the same in both and which likewise may
function as antigens, and lastly there are at least indications that various
types of tumors may possess specific antigenic substances which distinguish
them from normal tissues.

Qrganismal differentials and in particular individuality differentials are

440 THE BIOLOGICAL BASIS OF INDIVIDUALITY

then the same in tumors and in the normal tissues in which the tumors
originate and these differentials are among those substances which may func-
tion as antigens and call forth immune processes against transplanted tumors.
This interpretation is not invalidated by the recent experiments of L. Gross in
which it has been shown that, if in the inbred strain C3H after transplantation
of a tumor originating in another mouse belonging to this strain, this tumor
undergoes complete regression, after a preliminary period of growth, the
inoculated mouse has acquired thereby, at least in a number of cases, an
immunity against a second transplanted tumor of the same type.

Inasmuch as Gross assumes in accordance with the widely prevalent opinion
that in strain C3H all individuals are genetically homozygous, he concludes
that tissue constituents as such of one mouse, if inoculated into another in-
dividual belonging to this strain, are not able to call forth immune processes in
this mouse and that the immunity demonstrated under these conditions must
be due to factors other than constituents which normal tissues and tumors
have in common. However actually a fully homozygous condition has not
been achieved in any of these closely inbred strains and the genetic constitu-
tion of all the different C3H individuals is therefore not identical ; and inas-
much as the method used by Gross makes possible the demonstration of very
fine degrees of immunity, it might be expected that in a number of mice
belonging to this inbred strain an immunity can be shown to exist under the
conditions of these experiments. If the interpretation of Gross were correct,
it should be possible by similar means to call forth an immunity against an
autogenous tumor, in the mouse in which the tumor originated. But even if
such an experiment should succeed, which is not very probable, it would not
be permissible to conclude on this basis that the individuality differentials can-
not function as antigens in such instances, but it would indicate merely that
under these experimental conditions constituents of the tumor cells other
than the individuality differentials which they have in common with normal
tissues, acted as antigens.

We believe that the organismal differentials in tumors and in normal tissues
from which they have developed are identical, or at least very similar, and
that the transformation of normal tissues into tumors does not depend
upon changes in the genes which determine the organismal differentials,
but upon conditions which are comparable to changes in organ and tissue
differentials, although they are not necessarily identical with these. The dif-
ferences between various tumors, arising in different individuals and in dif-
ferent organs, depend upon the original differences in the organismal and
organ differentials of the individuals and of the tissues in which they develop,
and in addition, upon certain changes of a special character, among which
the production of specific intrinsic growth factors or the invasion of cells by
extrinsic agents or viruses may play a role. Additional alterations may take
place during the life of a tumor, and in particular during serial transplanta-
tions, such as variations in growth energy or adaptations to the constitution of
new hosts. Future investigations must determine more accurately wherein
these changes of a chemical nature, which occur during the transformation of

TUMOR GROWTH 441

normal into cancerous tissue, consist, and what the chemical factors are which
different tumors have in common.

By means of transplantation of tumors a considerable plasticity in certain
functions of the cells composing tumors has been revealed ; this plasticity of
function is superimposed upon and interacts with the constancy of the in-
dividuality differentials of these tumors. In the case of normal tissues, adap-
tive processes are either lacking or they are very much weaker than in tumors,
and by comparison with the latter, normal adult tissues appear relatively rigid.
Because of the complexity and the relatively great plasticity in the reactions
of tumors, the behavior of tumors presents problems of great biological in-
terest, especially in view of the fact that tumors are transformed normal tis-
sues, and that various attributes applying to tumors apply, therefore poten-
tially, also to normal tissues. But these attributes become manifest only when
normal cells, undergoing transformation into tumors, have reached the
equilibrium of cancer cells.

Piirf "\7" Organismal and Organ Differentials and the

Specificity of Tissue Reactions

Chapter I

The Relative Importance of Substratum and of

Morphogenic Substances in the Specificity of

Tissue Reactions, and the Relation of These

Factors to Organismal Differentials

IN preceding chapters we have referred to the relations which exist be-
tween organismal and organ differentials, and the role which morpho-
genic contact substances play in the differentiation of tissues, organs,
and in the development of organ differentials. We have also referred to the
action of morphogenic substances affecting tissues at a distance from the place
of origin of these substances, and to the importance of gene-hormones in the
realization of genetic determinations. In this chapter we shall continue this dis-
cussion and analyze additional conditions of an analogous kind — some of which
are effective also in the adult organism — in which the specificity in structure
and function depends upon and also manifests itself in an interaction between
hormones and factors inherent in certain tissues. Transplantation of tissues,
which act either as carriers of the stimuli or represent the substratum, was
used as a method for the analysis of these relationships in a number of in-
vestigations. This specificity may, in certain cases, manifest itself also in the
differences in the reactions to stimulating or inhibiting factors which are
observed when these factors act on the tissues of different individuals, species,
orders or classes of animals. We may designate the latter kind of relation as
an organismal specificity ; and if this organismal specificity is of such a nature
that the stimulating or inhibiting factor originating in a certain individual,
species, order or class of animals, is more effective when acting on tissues of
the same kind of individual, species, order or class, than when acting on
tissues of another kind of organisms, then we have to deal with what may
be designated as specific organismal adaptation between the stimulating or
inhibiting factor and the recipient tissue. We may therefore distinguish three
kinds of specificities: (a) simple organ or tissue specificity; (b) organismal
specificity; (c) organismal specific adaptation.

The problem may arise as to the seat of the specificity of the reactions in
such cases, whether it is the hormones and other distance substances or the
organs in which they originate, or the tissues on which they act. What factor
determines the differences in the behavior of analogous tissues or substances in
different individuals, species, orders or classes, or the differences in the behavior

443

444 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of different tissues or substances, or even of apparently the same kind of tissues
at different localities within the same individual? Do the organismal differen-
tials cause variations in the hormones and the tissues in which they originate
or in the recipient tissues? As the following analysis will show, as a rule the
specificity in the reactions in these cases seems to reside in the recipient tissues
rather than in the morphogenic agents.. This conclusion is in accordance with
what is known as to the lack of organismal differentials in hormones in the
large majority of cases and their presence in the tissues, in which latter,
therefore, the individuality of the organism predominantly resides.

A simple specificity of the first type exists, for instance, in the structure
of the different parts of the uterine cervix and in the graded interaction of
this organ with two kinds of hormones. We shall return, here, somewhat more
fully to this condition, to which we have already referred in a different con-
nection in a preceding chapter.

In the genital tract of the female guinea pig there exists a graded change in
structure in the direction from the vagina through the different portions of
the cervix to the uterus, and correspondingly, there can be demonstrated
experimentally a graded responsiveness of these tissues to the two ovarian
hormones, the follicular hormone and the corpus luteum hormone. The grada-
tion in the action of the lutein substance is in an opposite direction to that of
the follicular hormone. Thus in the system consisting of vagina, cervix and
uterus, the response to the follicular hormone is strongest in the vagina and
shows a graded decrease in the various portions of the cervix. It has still a
definite effect of its own in the uterus, but one that is different from the
effect observed in vagina and cervix. Through increasing the amount of
follicular hormone the reaction in the middle portion of the cervix, which
normally is much less responsive to this substance than the vagina, can be
made more distinct; but the same quantity of hormone exerts, then, a still
stronger stimulating effect on the vagina. In general, the greater the amount of
hormone which is allowed to act, the greater the proportional response of the
various tissues, this response being always relatively greater in the vagina
than higher up, and decreasing the more the nearer the tissue is to the uterus.
The reverse relation is noted in the case of the lutein hormone. This exerts a
very strong effect on the uterus, which extends only to the directly adjoining
part of the cervix, while in the vagina and presumably also in the lower
portion of the cervix it exerts mainly an antagonistic and inhibiting influence
on the follicular hormone, thus favoring a resting condition in these organs,
which otherwise would be stimulated by the latter substance. The most in-
teresting feature in this connection is the graded character of these reactions.
Apparently we have to deal with a graded difference in the state of sensitiza-
tion of these tissues, which either leads to the binding of a graded amount of
hormone by the various tissues and thus to a gradation of the reactions, or
causes a difference in the responsiveness of the tissues after they have com-
binca with the same amount of hormone. In this case there is thus a specificity
in the interactions of adjoining tissues in the same organism with two hor-
mones and a corresponding specificity in the structure of these tissues. We

SUBSTRATUM AND MORPHOGENIC SUBSTANCES 445

have therefore to deal directly with organ and tissue differential substances
and structures, and only indirectly with organismal differentials, the signifi-
cance of which is indicated by the fact that in certain other species these
tissue reactions may slightly differ.

There is another condition of morphogenic character, in which likewise
quantitative relations seem to exist between hormones and specific activities of
tissues ; namely, in the origin of mammary carcinoma of mice. It can be
shown that in individual mice and in different strains of mice there exists a
quantitatively graded tendency to acquire carcinoma of the mammary gland.
It can furthermore be shown that through a quantitatively graded diminution
in the activity of the ovarian hormones, which normally set in motion the
growth of the mammary gland, the frequency in the development of carcinoma
and the intensity of the reaction, as measured by the length of the latent period
preceding the appearance of the tumor, can be reduced in a graded manner ;
or expressed differently, the length of the time during which the hormone
must act in order to produce the carcinoma varies in different individual mice
and strains of mice and can be altered experimentally. There is some evidence
for the conclusion that here, also, quantitative differences in the response
of the recipient tissue, namely the mammary gland of different individuals,
depend upon different degrees of sensitization of the reacting tissues rather
than on differences in the quantities of the hormones acting in different in-
dividuals and strains, and that these differences in the responsiveness of the
mammary gland tissue determine the relative incidence of mammary gland
cancer in mice.

It is likewise by means of hormone action that it has been possible to dem-
onstrate the fact that in different parts of the body, differences exist in the
constitution of the same type of recipient tissues, which morphologically seem
to be identical, and that therefore a much greater individualization of tissue
differentials within the same organism exists than could have been foreseen.
It can be shown that the action of the corpus luteum hormone on the con-
nective tissue in the mucosa of the genital tract of the guinea pig is very selec-
tive ; it is only the connective tissue of the uterus, but not that of the central
or of the vaginal portion of the cervix, nor that of the fallopian tube and
vagina, which in the guinea pig responds to the stimulation of this hormone
with the formation of decidual tissue, and this is true equally of the tissue in
situ, as well as of transplanted tissue. The connective tissue of the uterine
cervix responds to the lutein hormone, but with a decreased intensity as com-
pared with the response of the uterine mucosa. We may therefore conclude
that the chemical structure and function of the ordinary fibrillar connective
tissue differ in adjoining and related organs.

Even adjoining parts of the ordinary epidermis of amphibian anuran larvae
are differently constituted, as is shown in a graded response to certain hor-
mone-like substances. Thus the skin covering the root of the tail is more
resistant to the injurious effects of substances which induce metamorphosis
than the skin at the tip of the tail, the former behaving more like the skin of
the trunk of the larva ; we shall refer again in a later chapter to this difference

446 THE BIOLOGICAL BASIS OF INDIVIDUALITY

in the reactions of epidermal tissues. Another instance of differences in the
constitution of an apparently homogeneous tissue has already been noted;
it was shown that different areas of skin of amphibian embryos exhibited dif-
ferent degrees of responsiveness to the contact action of the optic disc, some
areas possessing, others lacking the ability to form a lens.

In agreement with these conclusions is the observation that fibroblasts ob-
tained from the connective tissue of different areas of the embryo may behave
differently when cultivated in vitro (R. C. Parker). They differed in their ra-
pidity of growth, in the amount of acid produced, and in their power of resist-
ance to injurious conditions, and these differences were permanent in certain
strains of fibroblasts and seemed to be inherent in the cells. Not only were
variations found in these respects between periosteal, perichondral and ordi-
nary connective tissue cells, but even between connective tissue cells taken
from the stroma of various organs. Although in these cases we have to deal
with lower organisms and with not yet fully differentiated embryonal or
larval instead of with adult tissues, it is evident from our findings in the
uterus that in principle the same condition holds good also in the case of
adult mammalian organisms.

We may then conclude that the differentiation of tissues is in reality much
furthergoing than has been assumed on purely morphological grounds. Fur-
thermore, the possibility must be considered that the contact substances, and
in certain cases perhaps also the hormones, given off by tissues which are
morphologically indistinguishable from one another, may correspondingly
differ.

More recent studies of various authors prove the still wider applicability
of this mode of experimental analysis of the specific character of certain
tissues in embryonal development, as well as in adult organisms. By these
means Ritter and Blacher have studied the cause of the differences in pig-
mentation which are observed in two races of urodele amphibia, the black
and white Axolotl, and in different areas of the skin of the same individual
Axolotl.

The white and black races of Axolotl differ in the proportion of the pig-
mented and unpigmented parts of their skin; in the former the white, and
in the latter the black color predominates. Now, it is known that in the
hypophysis there is produced a hormone which causes a black coloration of
amphibian skin by inducing the expansion of the chromatophore pigment and
also by increasing the number of these pigment cells. The question arose,
therefore, as to whether the inherited difference in the behavior of the skin
of the white and black Axolotls might be due to inherited differences in the
amount of hormone produced by the pituitary glands of these two races, or
whether it was due to differences in the recipient skin. Experiments by E.
Ritter have shown that the second interpretation is correct, no difference being
noticeable between the hypophysis and its pigment-regulating hormone of
the black and the white Axolotls. The difference between these two races con-
sists not only in the greater number of pigmented cells in the black as com-
pared with the white race, but also in the reactivity of these two kinds of

SUBSTRATUM AND MORPHOGENIC SUBSTANCES 447

skin. If through extirpation of the pituitary gland the number of chromato-
phores has been diminished, and if subsequently the pituitary hormone is
experimentally again introduced into such an animal, either through trans-
plantation of hypophyseal gland tissue or through injection of the active sub-
stance, the skin of the black race responds more readily with the new forma-
tion of pigment cells than the skin of the white race. But under these conditions
injection of hormone or transplantation of hypophyseal tissues does not en-
tirely restore the normal characteristics of the skin, the number of new pig-
mented spots remaining smaller in the hypophysectomized than in the normal
individuals of the black race of Axolotls. The essential point, however, is
that there is no noticeable difference between the action of hypophysis of the
white and of the black race, both being about equally effective. The dis-
tinguishing features in the pigmentation of these two races depend upon
conditions inherent in the structure of the skin; after transplantation of
skin from the white to the black Axolotls, and vice versa, the transplants
retain their race characteristics. Therefore, factors inherent in the substratum
on which the hormone acts primarily determine the pigmentation of the skin.
On the other hand, if through transplantation of an excess of hypophyseal
tissue into an Axolotl belonging to the white race the quantity of hormone
action on the substratum is much increased, then also the skin of the white
race can be converted into black skin. The conclusion may then be drawn that
the threshold of hormone action necessary to call forth production of pigment
cells is greater in the white race than in the black race, and that correspond-
ingly more hormone is needed in the skin of the former to obtain the same
amount of pigmentation as in the black race. In this case we have to deal
with an example of the second type of specificity, the organismal specificity.

In various classes of animals the skin of the same individual may be white
in certain areas, while in others it is black ; here, also, the coloration depends
not upon differences in the activity of the hypophysis but upon differences
inherent in the skin ; and again, the threshold in the reaction to pituitary hor-
mone differs in the pigment cells in different areas of the skin. Thus Blacher
has shown that after extirpation of the hypophysis the pigment contracts first
in the chromatophores of the abdominal skin, next in the chromatophores of
the tail and dorsal skin, and lastly, in the corresponding cells in the skin of
the head. As a result of the contraction a whitening of the skin takes place.
Corresponding to this difference in the reactivity of the chromatophores is the
greater tendency of the skin of the head to be black, than of the skin else-
where ; the same difference between the different areas of the skin is found in
the black as well as in the white races ; also in the latter the skin of the head
has the greatest tendency to assume a black color under the influence of
the hypophyseal hormone. While thus the differences in the behavior of
pigment cells in different areas of the body are of the same type in the
white and black races, the threshold of hormone action necessary to cause
expansion of the pigment and call forth a new formation of chromatophores
differs in the two races.

Blacher and Ritter assume that the differences in the reaction of these cells

448 THE BIOLOGICAL BASIS OF INDIVIDUALITY

depend upon different threshold reactions of the pigment cells to the hor-
mone, the amount of hormone needed in order to obtain an effect being differ-
ent in the pigment cells in different races, as well as in different areas within
the same individual. There remains, however, the possibility that different
cells may vary primarily in their ability to attract and to bind a certain amount
of the hormone, rather than in the amounts necessary to call forth a reaction.
As to the causes of the differences in the behavior of these different types of
cells, nothing definite is known, but it may be suggested that a substance is
produced within the cell which increases the sensitiveness of the latter to the
hormone, a condition analogous to the sensitization to mechanical stimuli
which is produced in the uterine mucosa by the lutein hormone.

We see, then, that the same mechanism applies to a condition of pure
organ- or tissue-specificity, and to a condition of combined organismal- and
tissue-specificity.

Analogous are certain findings in adult mammals. Here in women past the
menopause the ovary no longer reacts to the stimulating action of pituitary
gonadotropic hormones with maturation of follicles and corpus luteum for-
mation, although the human anterior hypophysis is still potent (Saxton and
Loeb) ; the lack of ovarian responsiveness must, in such instances, be due
to changes which have taken place in the recipient organ, the ovary.

In mammals differences in the reaction of analogous organs to the same
kind of hormones have been observed in different species. Thus, for instance,
the ovary of the guinea pig, rat and rabbit react quite differently to the same
gonadotropic hormones of the pituitary gland and to changes in the constitu-
tion of hormones which follow hysterectomy. These differences depend on
the structure of the ovaries in these species and in particular on the power
of resistance of follicles and corpora lutea to injurious conditions and on the
ability of the theca interna to undergo luteinization. In these instances we
have to deal with organismal specificities in the reaction of tissues to the
same kind of hormones.

A similar problem as to the relative significance of substratum and stimulus
in determining the specificity of the reaction arises in the field of regeneration.
Triton is able to regenerate tail as well as anterior and posterior extremities ;
anuran amphibia, such as toads, do not possess this regenerative power. In
the lizard the condition is intermediate; the tail is able to regenerate, while
the posterior extremities regenerate only in a rudimentary way, and the
anterior extremities not at all. Weiss transplanted in Triton the regenerative
bud from a tail to a cut surface in the anterior extremity, a piece of which
had previously been excised. It seemed that the grafted tail material became
transformed into a leg under the influence of the leg stump, which thus acted
as an organizer and caused the transformation of potential tail material into
a limb. In this case evidently the stimulating tissue and not the recipient tissue
determined the fate of the tail bud. However, when a similar experiment was
carried out in the lizard, where the tail still has the power to regenerate but
the anterior extremity lacks it, the transplanted tail bud was not transformed
into a leg, because the wound surface of the limb to which it was attached

SUBSTRATUM AND MORPHOGENIC SUBSTANCES 449

was not able to restitute lost parts. Weiss concludes therefore that the leg has
lost the ability to act as an organizer. However, the interpretation of these
experiments suffers from the difficulty that there is some uncertainty as to
whether, in Triton, a real transformation of the grafted tail into leg took
place, or whether, instead, a regeneration may not have proceeded from
the remaining stump of the limb.

On the other hand, Guyenot had shown previously that if, following
metamorphosis, an extremity of Bufo vulgaris, which no longer possesses the
ability to regenerate lost parts, is grafted to a larva of Salamandra maculosa,
which latter is able to regenerate extremities, the transplant heals in but has
not gained thereby the power to regenerate lost parts when a portion of the
transplanted limb is amputated. This indicates that the lack of regeneration
depends upon conditions inherent in the transplanted Bufo tissue, and that
the presence in Salamander of substances able to stimulate the growth of a
leg, if such substances should exist, is of no avail. In these instances we have
to deal with examples of organ rather than of organismal specificity.

Axolotl does not possess a balancer, while Triton does have this organ.
But notwithstanding the lack of a balancer in Axolotl, the medullary plate of
this species contains an inductor substance able to cause the formation of this
structure in the kind of tissue which has the potentiality to produce this organ.
Therefore, if the anterior portion of the medullary plate is transplanted from
Axolotl to a later gastrula, or to an early neurula stage of Triton, the trans-
plant may induce in the host epidermis the formation of a balancer, while
this effect is lacking if the medullary plate is in contact with the Amblystoma
epidermis. The reason then why Amblystoma does not possess a balancer is
not due to the lack of the proper stimulus, but to the inability of the tissue to
respond to such a stimulus in an adequate manner.

The analogy between this condition and the findings of Schotte, to which
we have referred in a preceding chapter, is evident. After transplantation
of Rana tissue to Triton the oral region of the host supplied an organizer
substance, which induced the formation of mouth organs in the transplant ; but
the potentiality of the transplanted tissue itself determined the specific kind of
mouth organs which actually developed under the influence of the inductor
tissue. In both of these cases we have to deal with examples of organismal
specificities inherent in the reacting tissues, whereas the organizer substance
does not manifest an organismal specificity.

There exist, however, conditions in which the lack of reaction is due not
to the specificity of the recipient tissue but to the lack of a hormone. Thus
Wigglesworth, Piepho, and others, have demonstrated that in the larvae of
insects changes leading to pupation are induced by a hormone which is local-
ized in certain parts of the brain — or rather in the ring gland situated be-
tween the hemispheres of the larval brain (Hadorn and Bodenstein) — and
which may circulate also in the bodyfluids. Now, it can be shown that changes
characteristic of the pupa may be induced even in the skin of the imago if the
larval pupation hormone is supplied. This hormone does not possess finer
organismal differentials and presumably lacks them altogether; therefore it

450 THE BIOLOGICAL BASIS OF INDIVIDUALITY

may be active also in distantly related species of insects. However, while in
this case the skin of the distantly related imago, if properly stimulated, still
possesses the ability to produce a cuticula, which ordinarily is produced only
by the larva, the kind of changes which take place in the skin under the in-
fluence of this hormone, the structure and pigmentation of the newly formed
cuticula, possess the characteristics of the imago skin. The modifiability of
this tissue under the influence of a specific hormone, obtained from a distant
species, is therefore restricted. However, if the skin of the imago undergoes
regeneration, its potentiality to react like larval skin is restored to it and
now the typical changes in the cuticula may be produced by the hormone.

Similarly, Piepho has shown that a larval hormone may induce the normal
skin of a pupa to form the cuticula characteristic of the pupa, while regenerat-
ing skin regains the ability to produce larval cuticula. In the latter instance
the initiation of growth processes in the skin enlarges the range of reactivity
of this tissue to specific hormones ; when it has reached a more advanced
stage of regeneration it behaves like tissues of earlier embryonal stages, which
are as yet less differentiated; it returns to a more plastic condition in which
the equilibrium is more labile and in which certain changes in the inner or
outer environment may cause fargoing transformations. But it seems that
the effects of regeneration in increasing the range of reactivity of tissues de-
creases with increasing phylogenetic evolution, being much less in mammals
than in invertebrates. We have seen that the very plastic material of phylo-
genetically primitive organisms, such as planarians, reacts readily to environ-
mental changes with modifications of organs, whereas the reestablishment
of the original set of environmental conditions may lead again to the restora-
tion of the original tissue structures and tissue equilibrium, as the recent
experiments of Child have shown. In the very primitive and very plastic
material of certain coelenterates the tissue equilibrium may be determined
by a set of relatively simple conditions in which mechanical factors and
oxygen supply (Barth) may play a significant role.

Also, in the early ontogenetic stages the as yet less differentiated tissue
may react to stimulation by specific hormones with tissue changes which
correspond more to the specificity of the hormone than of the tissue. Thus
in sufficiently early embryonal stages of birds (Willier) and mammals (Ivy)
male and female sex hormones can determine in which direction, female or
male, the sex glands of the embryo shall develop.

In our experiments on the production of maternal placenta and placentoma
in the uterus of the guinea pig, we analyzed by means of transplantation of
pieces of uterus, the interaction between certain morphogenic distance sub-
stances and organismal differentials. We found that the formation of
placentomata depended upon the amount of lutein substance which has had a
chance to act on the uterus previous to, as well as following transplantation,
and action at both these periods was necessary in order to obtain the develop-
ment of large-sized placentomata. There entered into these reactions, further-
more, a mechanical, stimulating factor, which was introduced during the
process of transplantation. But in addition the effect depended also upon

SUBSTRATUM AND MORPHOGENIC SUBSTANCES 451

the organismal differentials of host and transplant, the transplant showing a
marked sensitiveness to the injurious action of homoiotoxins. In this case
the morphogenic substance, the lutein hormone, does not bear an organismal
differential and the injurious action of the homoiotoxin is due to the sensitive-
ness of the tissue on which the hormone acts.

Somewhat related conditions were found in the compensatory hyper-
trophy of the thyroid gland, a process which in all probability is caused by a
change in the normal balance between the thyroid-stimulating hormone of the
anterior hypophysis and thyroxin, the hormone of the thyroid gland, the for-
mer inducing, the latter inhibiting hypertrophy. If we diminish the quantity of
the thyroid hormone by extirpating a part of the gland which produces it,
hypertrophy takes place; if we increase the quantity of thyroid hormone,
hypertrophy is prevented. Although these hormones do not carry homoiodif-
ferentials, still, homoiotransplantation of thyroid tissue interferes with the
development of hypertrophy, because the homoiotoxins have an unfavorable
effect on the graft.

Similar problems arise in the analysis of the factors underlying meta-
morphosis. How far do the conditions initiating metamorphosis reside in the
tissues and depend upon the organ and organismal differentials of the latter,
and how far are they due to the action of stimulating or regulating substances
circulating in the bodyfluids and comparable to hormones ? It is again largely
by means of transplantation experiments that the analysis of metamorphosis
has been carried out. In his early experiments of joining together parts of
frog larvae, Born had observed that the two partial larvae, when they were
combined, metamorphosed at the same time, irrespective of the state of nour-
ishment of the two partners; this may be taken as an indication that one
partner influenced the time of metamorphosis of the other. Such an influence
was also noticeable in the more recent experiments of Burns, who accom-
plished a union between larvae of Amblystoma tigrinum, which normally
metamorphose very slowly, and those of Amblystoma punctatum, which
metamorphose more rapidly; under these conditions Amblystoma punctatum
caused a definite acceleration of the metamorphosis of the tigrinum larva.

A furthergoing analysis of the factors underlying metamorphosis has been
accomplished through transplantation of pieces of amphibian skin and of the
iris of the eye, in which, normally, characteristic color changes take place
during metamorphosis. In this way it has been possible, within certain limits,
to determine how far organismal differentials influence these processes, and
in particular, whether an interaction takes place between the factors determin-
ing metamorphosis and the homoio- and heterotoxins which may act on the
grafted tissues. From the older experiments of Uhlenhuth on the eye, of
Weigl on skin, of Kornfeld on the gills of urodeles, and from the more
recent experiments of Lindemann on the skin of frog larvae, we may, in
general, draw the conclusion that a chemical factor, a substance circulating
in the bodyfluids of an amphibian, initiates metamorphosis synchronously in
all the tissues which are sensitive to the effect of such a substance and which
are subject to metamorphosis. Furthermore, this substance is able to act not

452 THE BIOLOGICAL BASIS OF INDIVIDUALITY

only on the tissues of the same individual, but also on tissues transplanted
from another individual of the same, or even of a different species ; if it is
present at the time just preceding transplantation in a larger quantity in the
host than in the donor, the metamorphosis of the transplant tends to be ac-
celerated ; but if present in a larger quantity in the donor than in the host,
then a relative retardation in the metamorphosis of the transplant, as compared
with the metamorphosis which would have taken place in the donor, is apt to
occur.

However, in addition to these factors, others which are present in the
transplant influence the character and time of metamorphosis. Among these
latter, primary factors inherent in the structure of the tissues, and secondary
ones depending on variable environmental conditions, can be distinguished.
Thus, the iris of the eye in salamander and also the gills in urodeles undergo
certain changes apparently under the influence of specific substances, which
become potent some time previous to the onset of metamorphosis, but the
mode of action is influenced by specific characteristics of the tissues. Even
skin from different surface areas of the same animal may differ as to its
reactivity to these substances. According to Lindemann, the skin of the tail
of frog larvae will undergo absorption during metamorphosis, and this takes
place irrespective of whether the skin has been left in its normal place or
whether it has been transplanted into other parts of the body surface. On the
other hand, dorsal skin will remain unchanged, even if transplanted into a
place which undergoes retrogressive changes during metamorphosis. The con-
dition of the tissues of the donor may modify the metamorphosis in still an-
other way : if the donor organism at the time of transplantation has reached
a stage nearer to metamorphosis than the host, the transplant has a tendency
to metamorphose at an earlier date than the host; if, on the contrary, the
donor is still farther removed from the stage of metamorphosis, the trans-
plant tends to require a longer time before metamorphosis can take place. It
seems therefore that preceding the processes occurring during metamorphosis
there are preliminary changes in the tissues, which make the latter more re-
sponsive and gradually sensitize it to the substances causing metamorphosis,
and this process of sensitization requires a certain time. It is possible that the
sensitizing substance is identical with the metamorphosis-inducing substance.
We may then assume that this substance gradually accumulates in the organ-
ism, combines with the responsive tissues and thereby makes them ready for
metamorphosis, which takes place after a certain point of tissue saturation has
been reached and after the hormone has had a chance to act on the tissues for
a sufficient length of time. The possibility also exists that the sensitizing sub-
stance differs from the metamorphosing substance and merely makes the tis-
sues receptive to the action of the latter substance. However that may be,
a tissue thus sufficiently prepared undergoes metamorphosis after transplanta-
tion, even without the presence of the active metamorphosing substance in
the host, whereas a tissue not fully prepared or sensitized is not sufficiently
responsive even if the metamorphosing substance of the host is fully active.
Such a transplant will, therefore, not metamorphose synchronously with the

SUBSTRATUM AND MORPHOGENIC SUBSTANCES 453

host organism, but at an earlier or later date, in accordance with its sufficient
or insufficient sensitization. Yet, within a certain range of sensitization the
hormone active in the host at the time of metamorphosis tends to induce
metamorphosis in the transplant synchronously with that of the host tissues.

As to the significance of organismal differentials in the process of meta-
morphosis, in urodele amphibia the effects described can be noted after auto-
and homoio-, as well as after heterotransplantation of the respective tissues,
but in anuran amphibia W. Schultz observed that only auto-, but not homoio-
transplanted skin takes part in metamorphosis. With the progress in phylo-
genetic development, the tissues become more and more specialized and the
organismal differentials more selective, so that only if the latter are nearly
related in the host and the transplant is the metabolism of the transplanted
tissue such that the graft is able to respond effectively to the metamorphosing
substances.

In the experiments cited in this chapter certain tissue reactions may depend
upon the interaction between several sets of factors: namely, (a) conditions
inherent in the tissues and determining their ability to undergo certain
changes ; (b) the action of hormone-like distance substances circulating in
the bodyfluids of the host, combining with the transplanted tissues and thus
causing their specific effects; (c) the time when these hormone-like sub-
stances act on the tissues. In some cases substances of this kind must act
not only following but also previous to transplantation, and thus sensitize the
tissues; (d) the action of organismal differentials affecting, as a rule, the
transplanted tissues and, much less or not at all, the hormone-like substances,
although in some cases hormones may possess some of the less specific or-
ganismal differentials ; (e) mechanical factors acting as stimuli in combination
with sensitizing agents; as in the formation of maternal placentomata ; (f)
a balancing action between conditions inherent in the tissues and the effects
of the hormone-like distance substances.

A balancing action, similar to the last mentioned factor, may take place in
ordinary transplantation of tissues. In this case we have in all probability to
deal with an antagonism between factors inherent in the transplant and con-
tact substances residing in the tissues of the host which serve as a soil for
the transplant. Thus in the experiments of Milojevitch, with transplantation
of regenerative buds of extremities, the surrounding host tissues apparently
determined what kind of limb was to develop, their influence dominating over
the conditions inherent in the transplants ; on the contrary, in the experiments
of Ruud, with transplantation of embryonal limb buds, factors inherent in the
transplants determined the result.

In this connection we may also refer to Goldschmidt's theory of the
mechanisms underlying Mendelian heredity, and in particular to his interpreta-
tion of the sex-intergrades which result from hybridization of different races
of Lymantria. In the various types of hybridizations there takes place a
mutual interaction of germ cells possessing different genetic constitutions and
therefore also different precursors of organismal differentials. Goldschmidt
attributes different potencies to various allelomorph genes or gene combina-

454 THE BIOLOGICAL BASIS OF INDIVIDUALITY

tions in the fertilized ovum. The greater the potency, the greater and the
more rapidly reached will be that amount of a hormone-like substance suffi-
cient to direct the development of the egg into certain channels. The earlier
the threshold is reached at which this substance becomes active, the earlier
and more extensive will be its influence on the embryonal development and
the more fundamental will be the changes produced, while a substance devel-
oping late and in small quantities will affect only the latest phases of embryonal
development and its action therefore will be less far reaching. Hence, the
effect of such a substance depends upon its potency, quantity, and time of
appearance, and also upon the character of the substratum on which it acts
and on the intensity and rapidity of the processes which it influences. In a
preceding chapter it has been pointed out that the time-factor plays a role
also in the interaction between organizer and recipient tissues and that these
time-relations may differ in the case of homoiogenous and heterogenous
tissues. In heterotransplantation, therefore, incompatibilities may develop
between the action of the organizer contained in the transplant and in the
recipient tissues in the host, or vice versa. There is, here, an additional
interesting analogy between the processes of fertilization and transplantation.

In a somewhat similar manner, according to F. R. Lillie, the gynandro-
morphism which is occasionally found in birds depends upon certain quanti-
tative variations in the interaction between factors residing in the tissues and
the hormone acting upon the latter. In gynandromorphic individuals one side
of the animal has male and the other side female plumage, and at the same
time the quantity of the female sex hormone which is produced by the
ovary is diminished. Lillie assumes that the female sex hormone, under these
conditions, is able to impress upon the feathers the female characteristics
only if the growth rate of the feathers during their development is sufficiently
slow to allow the female sex hormone to become effective, otherwise the
feathers assume the male characteristics. Lillie observed also that the side on
which the male feathers developed in some birds was often hypertrophic,
and he assumes therefore that the rate of growth was too rapid on this side
to give the female sex hormone a chance to endow these feathers with
female characteristics. Thus they remained male on the hypertrophied side,
since here the threshold of reaction for the female sex hormone would need
to be higher on account of the more rapid tissue growth. In this case there
would be an interaction between intrinsic and external factors, the latter
being represented by hormones which, in combination with the inherent
properties of the recipient tissue, determine the character of the developing
plumage.

Cell and tissue differentiation and loss of differentiation (dedifferentiation),
as well as metaplasia, present the problem as to how far factors inherent in
the tissues and how far environmental factors, including the inner environ-
ment, and, in particular, contact substances and hormones, play a role in
these processes. There is a strong indication that as a rule both intrinsic and
environmental factors are active, but in varying proportions in different
areas, and that with advancing development the intrinsic factors of the

SUBSTRATUM AND MORPHOGENIC SUBSTANCES 455

substratum begin to predominate more and more over the environmental
stimulating factors, although some general conditions, such as the action of
more specific hormone-like substances and the state of nourishment and
oxygen supply, remain of importance. In regard to the latter factors, the
degree of differentiation may depend, in some instances, upon the influence
which relatively unfavorable conditions of nourishment exert on the tissues.
To cite an example : there can be little doubt that the keratinization of the
epidermis is due to the distance of epidermal cells, undergoing this change,
from the capillaries, a distance which increases in proportion to the intensity
of proliferation of these cells. The same factors may also affect the rapidity
and character of cell division ; a certain degree of unfavorableness in a
constellation of factors may act as a stimulus, initiating cell division, but at
the same time the unfavorable conditions may make the cell division thus
induced irregular. On the other hand, conditions which induce rapid normal
cell division may thereby inhibit a complete differentiation of the resulting
tissues.

Experimental analysis of tissues by the use of hormones, as well as by
other means, has made it possible to establish the existence of a much greater
differentiation and individualization of , tissues in different areas than had
previously been assumed to exist, when observation of the structure of
tissues seemed to indicate their identity. Furthermore, the characteristics of
tissues and organs of an organism are determined by factors inherent in the
recipient tissues as well as by stimuli acting on them. While in different cases
the relative importance of these two sets of factors varies, in many instances
the former preponderate. This is true at least when the more differentiated,
phylogenetically and ontogenetically mature stages have been reached, while
in the more primitive stages the stimulating and transforming effects of
contact and distance hormone-like substances play a prominent role.

There must be added to these morphogenic substances, certain vitamins
which also can be shown to have specific morphogenic effects under some
conditions ; this holds good, for instance, in the case of vitamin A, the
absence of which may produce a transformation of cylindrical into squamous
epithelium in some epithelial membranes ; also of vitamin D, which affects in
a specific manner the bony structures. With furthergoing phylogenetic and
ontogenetic development certain tissue differentiations take place, requiring
the presence of definite vitamins for the maintenance of normal structure
and function.

The problem which we have discussed in this chapter is a part of the
wider problem as to the relative significance of living substratum and
environment in the development and function of living matter, whether of
individuals, species, or wider classes of organisms. The tissues which are the
bearers of the organismal and the organ and tissue differentials and their
precursors represent the substratum, and in this substratum the organismal
differentials and their precursors are the most constant constituents, while
the organ differentials seem to be more modifiable; the contact substances
and hormones represent a part of the inner environment, which however, can

456 THE BIOLOGICAL BASIS OF INDIVIDUALITY

be experimentally introduced also from the outside. In all the cases discussed
we notice the relative preponderance of the character of the substratum over
the environmental factors. Nevertheless, in the course of investigation, it has
been found in many cases that what had hitherto been assumed to be deter-
mined solely by conditions inherent in the substratum, is determined in part
also by environmental factors, the latter thus growing in importance. The
further extension of the conscious control of life processes depends on the
discovery of additional extrinsic factors influencing tissue reactions, and the
possibility of modifying these experimentally.

Chapter 2

Structure and Function of Organs and Tissues
as Criteria of Individuality

Our recognition of and distinction between different human indi-
| viduals depends on many factors, particularly on their facial features,
the color of hair and eyes, the height and outlines of their bodies, the
character of their movements, especially their way of walking, the quality of
their voices and modes of speech, thinking and feeling, in general on their
reactions under varying conditions. By these means we can distinguish be-
tween individuals and we conclude that no two persons whom we meet are
exactly alike ; this holds good even of identical twins. But a certain experience
is necessary in the use of these different signs. We can best differentiate
individuals who, in the most essential features, are similar to those we meet
daily in the greatest number, and we have more difficulty in differentiating
between classes of individuals with which we are less well acquainted ; for
instance, it is more difficult for most of us to distinguish between individual
monkeys and dogs, than between human beings, although persons who are
studying monkeys and dogs very closely can, here, also quite readily distin-
guish different individuals. We use the combination of a large number of
organ and tissue peculiarities and the general body build as distinguishing
marks between individuals, each individual thus representing to us a mosaic,
which, as a rule, leaves in us a composite impression rather than a memory of
the separate elements constituting the mosaic. These separate features are
determined largely by inheritance, although variable environmental factors
may greatly influence their ultimate character, and different kinds of charac-
teristics are unequally affected by the genetic constitution of the individual
and by environmental factors, the experiences through which the individual
has passed.

We shall discuss here, in particular, two characteristic features which
distinguish human individuals and which are especially striking as to their
fineness of individualization, namely, the skin patterns, which are employed
for the identification of individuals, and the scents which dogs use in tracing
the movements of and in recognizing individuals.

I. The palmar and plantar skin patterns as criteria of individuality. The
patterns due to the arrangements of the ridges in the skin of the palms of
the hand and the plantar surfaces of the foot differ, but are constant in each
individual; in the form of finger prints they are used to distinguish indi-
viduals from one another. These peculiarities are distinct from the indi-
viduality differential, inasmuch as they are limited to one particular organ
and do not represent a characteristic shared by all or the majority of the
organs or tissues of the body. In this respect they resemble therefore other

457

458 THE BIOLOGICAL BASIS OF INDIVIDUALITY

individual peculiarities, such as the color of hair and of iris, the cephalic
index, or similar characteristics, which, all combined, represent the mosaic
structure of the organism, in contrast to the essential individuality, which is
based on the organismal differentials. However, while many persons have
brown hair or blue eyes, the pattern of the skin ridges, as stated, is specific
in every individual. The ridge patterns of the skin, together with other mosaic
characters, differ as to the frequency with which certain peculiarities are
present in different races, the difference between races being, therefore,
largely statistical, the same structural elements as a rule occurring in all of
them. The papillary skin patterns have this statistical characteristic in
common also with the factors on which blood grouping depends, certain
blood groups being found more often in some races than in others. But, like
the individuality differentials, the skin patterns represent individual character-
istics, while the features distinguishing the four original blood groups do not,
to the same degree, allow the differentiation of individuals; they represent
group characters, as their name implies.

In the case of monkeys, the parts of the skin where these ridges are found
serve as instruments with which to hold fast to trunks of trees and other
objects of a similar character, and those types of ridges which may be of use
in this function have been designated as "friction ridges." According to the
description given by Wilder and Wentworth, the ridges run, in general, in an
approximately parallel direction over the greater part of the friction skin,
more or less across the longitudinal axes of hand and foot, but in certain
definite places where the surface rises slightly, to come into fuller contact
with external objects, there occur some departures from the usual course
and the ridges form loops, typical concentric whorls and spiral whorls or
spirals. These patterns are arranged about a central core which corresponds
to the center or summit of the mound. At the point of origin of certain ridges
of the patterns, formations may be found which resemble the letter delta and
are therefore called "deltas." In addition there are distinguished some ridges
which connect the bases of adjoining whorls, and according to the mode in
which these ridges end, they are designated as inner and outer melting
whorls. Furthermore, there can be recognized the socalled "details" first
described by Galton : the forks, ends, islands and enclosures, signifying the
length and shape of certain interrupted portions of ridges.

Pairs of symmetric fingers in both hands may have their own peculiarities.
In one finger pair one pattern may predominate, and in another pair, another
pattern. The number of ridges may differ in certain areas of the skin in
different individuals, and this quantitative factor behaves in a corresponding
manner in each finger pair in the same individual. Taking all these peculiari-
ties together, it is impossible to duplicate the character even of a relatively
small area of friction skin in two individuals. The ridges are a permanent
bodily mark, never changing throughout life; they originate in the embryo
and even after injury they form again in the same manner, unless the injury
has led to the destruction of the entire epidermis over a given area.

As stated above, the average frequency with which certain patterns occur

ORGANS AND TISSUES AS CRITERIA 459

differs in individuals belonging to different races. However, the relative
frequency of these patterns in different finger pairs is similar in all races.
The ramifications of the cutaneous nerves seem to determine the situation of
the cores of the patterns and the distribution of the nerves apparently deter-
mines also the number and frequency of ridges in a unit area. In addition,
the differences in the shape of embryonal fingers, and especially in their
surface radius, influence the character of the patterns. These determining
factors underlying the formation of the patterns, which are thus complex in
nature and, to some extent, separate and independent of one another, are
largely transmitted hereditarily from parents to offspring in the same way
as other characteristics constituting the bodily and psychical mosaic.

Of special interest, therefore, is the study of the skin patterns in so-called
identical twins, and here it has been found that the number of ridges com-
posing a pattern are much more similar than in bi-oval twins. But even in
identical twins certain variations in the patterns develop. It is therefore
assumed that these variations are phenotypic in nature, that is, they are
partly determined by environmental factors which are different in each twin,
and these latter variations are superimposed upon the genetic factors, which
are identical in both.

There exist, also, sex differences in the skin patterns, but these disappear
in old age with the cessation of sexual function; they may therefore be
considered as constituting secondary or tertiary sex characters.

The correlation, noted by Poll in human beings, between skin patterns and
certain characteristics of parts of the nervous system, especially conditions
which lead to insanity, is of interest. This investigator finds that certain
patterns predominate more in normal, and other types in insane persons, but
only in the male. However, as in the case of race characteristics, we have
here also to deal merely with statistical differences, the frequency with which
certain characteristics of skin ridges occur differing in normal and in certain
insane persons. Poll holds that this correlation is due to the fact that both the
nervous system and the skin are of ectodermal origin, an interpretation not
borne out by the findings of Kretschmer, that correlations exist also between
the character of the structure of the osseous system and of the panniculus
adiposus on the one hand, and the tendency to the development of certain
temperaments and of certain types of insanity on the other hand. In a similar
way, Graves has observed a certain correlation between the shape of the
scapula in a man and his power of resistance to injurious conditions. It may
therefore be assumed that the total skin pattern, as well as its single features,
depends upon genetic factors in the same way as the structures and function
of other systems depend upon genetic factors, and there exist, probably, on
this basis correlations between various organ systems, irrespective of their
embryonal relationship.

II. Scents as criteria of individuality. Distinctive scents emanating from
animal organisms originate in the metabolic changes in certain organs; they
may therefore be classed among organ characteristics of the kind with which
we have to deal in this chapter.

460 THE BIOLOGICAL BASIS OF INDIVIDUALITY

It is well known that the reactions of many animals towards other animals
are determined mainly by the sense of smell, which is very much more finely
developed in them than in man. This sense of smell plays evidently a great
role in the social-psychical relationships of certain insects. It is also appar-
ently by means of individual or family scents attaching to their young that
certain animals, for instance, a guinea pig mother, can distinguish their own
children from the children of others, and it is this factor which determines
the difference in their reactions towards their own offspring. In human
beings, this faculty is lost ; mothers no longer possess the ability to distinguish
babies from each other by the sense of smell. That human beings, too, possess
characteristic scents, however, is shown by the fact that dogs can thus readily
distinguish different individuals.

As early as in 1879, Gustav Jaeger drew attention to the distinctive scents
differentiating human beings as well as human races. He maintained, further-
more, that different species, genera and classes of animals, each have their
own characteristic scents, different from those of other groups of animals.
As to the origin of scents, some of his conclusions were erroneous. He
believed, for instance, that the substances responsible for specific smells were
preformed already in the germ plasm ; similarly, he assumed that the sub-
stances, on which the specific sense of taste depends in various species of
animals, are present in their germplasm, and that these substances, together
with certain pigments which distinguish different races and species, represent
the specific constitution of the germplasm. However, it is not these substances,
themselves, which are preformed in the germplasm, but rather certain other
substances which, in the course of embryonal development, make possible
the formation of organs, whose metabolism is of such a nature that the
specific scents, tastes and pigments are produced. While, thus, the character
of specific scents is ultimately determined by the constitution of the germ
cells, the scents as such, represent derivatives of germ cell constituents. Jaeger
erred in still another direction. He did not differentiate between the inherited
individual or racial scents and others which are due to accidental, social
conditions. Traditional suggestions leading to emotional attitudes, the result
of certain phases in the social struggle, obscured, in this respect, his judgment.

Subsequently, Correns drew attention to the importance of individual
differences in the scent of human beings, but it is especially Lohner who,
more recently, has analyzed experimentally the character of individual scents
and the reaction of dogs to them. According to Lohner, in human beings there
are regional smells distinctive of certain areas of the body, which are mainly
seated in the skin and which originate especially in the secretions given off
by the sebaceous glands. The different regional smells in the same individual
differ very much from one another, from a quantitative as well as from a
qualitative point of view, and these differences may be so pronounced that
even the human olfactory organ can differentiate them in the same individual.
On the other hand, a human being cannot recognize the scent of an individual
as a whole, while dogs, especially police dogs, can do so very readily. Accord-
ing to Lohner, such dogs, in addition, are able to recognize even individual

ORGANS AND TISSUES AS CRITERIA 461

differences in the corresponding regional smells, although it is not certain
from Lohner's report that this fact has been experimentally established.
However, if this view should be correct, then it would follow that the scent
of an individual is not only a composite effect of his multiple regional scents,
but there is, besides, a specific feature attached to each regional scent of a
given individual. It is of interest also that, secondarily, these scents are
influenced by the functioning of the sex organs and that they become quanti-
tatively more pronounced at the time of puberty. It has been found, more-
over, that likewise the distribution of the openings of the sweat glands are
individual characteristics in man.

We see, then, that in the case of individual scents, as in the case of skin
patterns, we have to deal with complex effects which represent the result of
the composite actions of more elementary units. Organismal differentials are
not involved in either instance, but rather special substances or structures
inherent in certain tissues or organs; these localized characteristics are not
inherent equally in all, or even almost all, the tissues of an individual, but
they are specific for each individual. They must therefore be included among
the mosaic characters which distinguish individuals.

III. We have discussed more in deta-il two inherited conditions in man as
examples of individual differences of organs, or tissues, their structures and
chemical characteristics. But similar differences are found also between the
other analogous organs and tissues in different individuals and species. On
the other hand, analogous organs have essential features as to metabolism
and function in common in different species, especially in more nearly
related ones; the differences which they show become individualized the
more, the further advanced these species are in the phylogenetic and onto-
genetic scale.

In mice it can be demonstrated that in different, closely inbred strains,
various organs such as thyroid and corpus luteum, differ in their structural
and, therefore, also functional age curve; likewise, notwithstanding the
essential similarity in structure of vagina and uterus, the structure of the
maternal placenta in nearly related species shows some notable differences.
Furthermore, different species of fresh-water fishes present characteristic
differences in their reaction to differences in C02 pressure in the water in
which they live (Irving). The structure and physiologic reactions of the red
corpuscles, the crystalline forms of hemoglobin differ in different species,
and these differences are, to a certain extent, correlated with the phylogenetic
relationship of the species from which they are derived (Reichert and
Brown).

As a further example of this type of specificity, we might mention the
manner in which various species or classes of animals react against phenyl-
acetic acid when it is introduced into their bodies. In the majority of mam-
mals, including monkeys, this substance combines with the aminoacetic acid
(glycin), and it leaves the body in the form of phenaceturic acid. In man
and in anthropoid ape (chimpanzee) phenylacetic acid combines with glut-
amine, the amide of glutamic acid, a dicarboxy acid, to form phenylacetyl

462 THE BIOLOGICAL BASIS OF INDIVIDUALITY

glutamine. In birds, and presumably also in reptiles, it combines with
diaminovaleric acid (ornithin), the principal endproduct of protein metabo-
lism in these classes of animals. Or, to mention another example : while in
man and mammals in general, in amphibia and fish the principal endproduct
of amino acid metabolism is urea, in birds and reptiles the principal end-
product of protein breakdown is uric acid.

Individual differences in the electric potential of the grey matter of the
brain, originating presumably in the structure and function of the ganglia
cells, are found when electric currents are obtained with electrodes placed on
different parts of the skull or brain surface (Hallowell Davis). A similar
individualization in electric potentials also exists in different parts of the
eye, and the totality of such potential gradients in the adult and in the
embryo seems to be characteristic of different species. Similar findings may
be obtained presumably in every organ and every tissue, and we may assume
that at least in the higher organisms it might be possible not only to discover
species and strain differences in all the organs and their functions, but also
individual differences, in accordance with inherited constitutional character-
istics, if only we had fine enough methods to recognize them.

In a general way, such organ and tissue differences parallel, in their de-
velopment, the phylogenetic evolution of these species, but there are many
exceptions to this rule. Two examples in which a strict parallelism does not
exist may be mentioned, namely ( 1 ) the substances which control the expan-
sion and contraction of the melanophores of the skin, become effective in
some classes of animals mainly through the nervous system, when they
function as neurohormones ; in other classes, through the blood, when they
function as ordinary hormones. Sex determination depends, in part, on the
distribution of two chromosomes in male and female in two possible ways ; in
vertebrates as well as in insects, these two modes of distribution are found
irregularly present, without reference to phylogenetic relationship ; likewise
the means of control of the state of contraction of the chromatophores are
irregularly distributed.

The organism consists therefore of a mosaic of organs and tissues; but
the units in this mosaic are subdivided again into smaller units and thus the
mosaic is really much finer than it might appear if only gross methods of dif-
ferentiation are used. It is by means of a more detailed microscopic examina-
tion and a study of the mode of reactions, of different tissues to various
hormones that very fine subdivisions are revealed, as for instance, in vagina,
cervix and uterus of the guinea pig ; and this is true of connective tissue as well
of epithelial structures. As mentioned already, in tissue cultures of various
embryonal structures R. C. Parker has shown that fibroblasts derived from
different organs behave differently in regard to rapidity of growth, produc-
tion of acid, as well as solution of fibrin, and these characteristics remain
constant in vitro, although, on the whole, they may change with advancing
development. The existence of definite units constituting the organism is also
indicated by the study of inheritance of organ characteristics in accordance
with Mendelian principles. Furthermore, those factors whose development is
controlled by gene-hormones in various insects represent mosaic character-

ORGANS AND TISSUES AS CRITERIA 463

istics, such as the color of the eye. However, structural and functional sub-
divisions in the living adult organism do not need to be sharply separated,
but transitional areas may gradually lead from one unit to the adjoining one.
And all these organ and tissue units, which make up the mosaic of the
organism, are connected into one functionally unified whole by means of
hormones, including contact substances, and the nervous system.

Accompanying the structure of organs and tissues are their functions.
As they are actually studied, they are essentially the functions of species
and not of individuals; they are therefore those which are shared by the
individuals of a species ; they bear the character of species differentials. Of
this nature is the tendency to maintain a constant osmotic pressure and fluid
content in the bodyfluids, termed by us homoiotonia and homoiohydria, to
which might be added homoioproteinemia, the tendency to keep the protein
content of the blood constant, and, in general, the condition called by Cannon,
homoiostasis, which comprises the sum of all the mechanisms which tend to
keep the constitution of the bodyfluids, the milieu interne, within narrow
limits constant. However, within these functional mechanisms characteristic
of species there are those due to the variations of individuals, of which the
species type merely represents the average. In different individuals the func-
tions of different organs may show independent primary variations, which
secondarily may lead to adjustments which concern the individual as a whole.
These individual differences in organ functions, associated as they are with
visible or invisible structural differences, may also be used for the character-
ization and distinction of individuals.

Besides regulating function, the hormones present in endocrine organs,
and similar substances present in other organs, such as bone marrow, liver
and kidney, may, in an organ-specific way, regulate also growth, promoting or
inhibiting it, and some of these substances may to some extent control the
organ in which they originated. But the organs where the hormones are
produced, and the various constituents of the nervous system which are
endowed with the function of controlling and coordinating other organs, are
merely parts of the mosaic organ system. They function by means of their
organ characteristics, and the hormones which they produce are not, as a
rule, endowed with the organismal differentials which are however present
in these organs. But there are indications that some hormones, as for instance,
the gonadotropic hormones of the pituitary gland, possess species or class
differentials. This specificity applies presumably only to those hormones
which chemically have a more complex structure, and which consist of or
are combined with proteins. During ontogenetic development, organizers,
which at very early stages may induce the reproduction of approximately the
whole embryonal organism, but gradually, with the increasing differentiation
and specialization of the parts of the organism, become more specialized,
exert a controlling, unifying influence in cooperation with the specific
substratum on which they act. However, it will be necessary ultimately to
trace backward these specific substrata and organizers to simpler structures
which represent the precursors of such specific formations.

Combined with the mosaic individuality is the system of organismal dif-

464 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ferentials which help to produce the autogenous or, more generally, the
organismal tissue equilibrium, and which are present throughout the various
parts of the organism. They represent a second unity and are the foundation
of another type of individuality which, in contrast to the mosaic type, might
be designated as the essential individuality. From a genetic point of view,
tissue and organ characteristics, as well as individuality and species differ-
entials, ultimately depend upon the genetic constitution of individuals and
species and there is therefore a close relation between these two factors ;
however, the number of genes determining them, and perhaps also the
character of the individual genes which enter into their composition, differ,
and there is therefore no complete parallelism between organ characteristics
and organismal differentials.

From the point of view of chemical structure, we may conceive of the
organ and tissue units as essentially consisting of a base of proteins which
have undergone phylogenetic and ontogenetic development. These proteins
may be assumed to be the bearers of characteristics common to all living
protoplasm ; but on this foundation there are built protein characteristics, first
of the largest animal group, to which the organism bearing these organs
belongs, and gradually there are added to these in sequence, constellations in
the protein, which are characteristic of class, order, family, genus, species,
strain and individual. These represent the organismal differentials. There
develops also in association with this basic protein structure, phylogenetically
and ontogenetically, a subdivision of each organism into a mosaic of organ
and tissue units, in which there are added to this protein base, new protein
constellations differing in different organs and tissues ; or looser associations
of the proteins with other, at first presumably very complex, substances of a
carbohydrate or lipoid character are acquired. In this case, likewise in
sequence, an increasing differentiation of these mosaic organ and tissue units
occurs, until in the end the most complex individual is established. Being
built upon the foundation of organismal differentials, these units contain the
class, order, species and individual characteristics which all parts of the
organism have in common; but there develop also in these chemical struc-
tures, smaller units which may become detached from the main substance,
and which as a rule show less or none of these organismal differentials ;
these function as enzymes, hormones, and certain other substances. In study-
ing the factors which bind the cellular constituents into the organ and tissue
units and which cause the interaction of different organs and tissues within
the same individual, specificities characteristic of class, order, species or
individual, may be present or may be lacking. In the latter case we can
exclude participation of the various organismal differentials in the reaction
or function of these organs and tissues. But if a function or reaction does
show such an organismal specificity, then the further question arises as to
whether this specificity is to be attributed to the organismal differential
chemical groups as such, or to other structural peculiarities of the organ
and tissue units, which presumably originally developed under the influence
of the organismal differentials, but which secondarily assumed a constitution

ORGANS AND TISSUES AS CRITERIA 465

distinct from that of the latter. It may be impossible in many cases to answer
such a question. These difficulties arise especially if there are found chemical
characteristics in a certain group or tissue of an organism and if these are
lacking in other organs. In such a case class or species specificities, which in
other instances are due to the existence of organismal differentials, may be
due to chemical structures of a different kind in which the organismal dif-
ferentials are not involved. This question may arise also if we have to deal
with characteristics of organs and tissues which distinguish one species, or
one individual, from another, but in which these organ differentials do not
show the gradations corresponding to the degrees of phylogenetic relationship.

While skin patterns as well as scents are characteristic of individuals and
may differentiate one from another, it has not been shown that these
structural and biochemical characteristics can be used for determining the
relationships between organisms belonging to the same species in the same
sense in which individuality differentials can be used for this purpose. This
fact does not exclude the possibility that as a result of close inbreeding,
continued through successive generations, we might approach a homogeneous
population, in which all component individuals would presumably have very
nearly the same skin patterns and scents. There are other tissue and cell
characters which show a certain group distribution, which is largely inde-
pendent of individual and species relationship. This is true, for instance, of
the agglutinability of the red corpuscles according to which individuals can
be assigned to one of the four primary blood groups ; although these char-
acteristics may be similar in related species such as men and certain apes.
There are other tissue or cell characters, such as the heterophile differentials,
which are distributed quite irregularly among different species, without
regard to relationship. Some substances show variations in constitution, which,
within a definite range, correspond to relationships of species ; this seems to
be true of the hemoglobins, and there is some reason for assuming that it is
true of other kinds of proteins.

However, the larger the number of tissue and organ characteristics of
individuals, families and species which we use for identification, the more
probably will become the chance that, in their totality, their distribution will
correspond to relationships between these individuals, families and species.
Thus, if we study various organ systems in different species, a correspond-
ence is found, at least in a general way, between these structures and the
phylogenetic relationship of these species ; comparative anatomy and bio-
chemistry can help thus in the tracing of phylogenetic relationships, and more
intricate studies of the evolution of organ systems may likewise reveal
individual and family relationships. We may therefore conclude that various
kinds of tissue and organ differentials, whether structural, biochemical, or
functional, may serve to distinguish between individuals, and insofar as
these characteristics have a genetic basis, they might, in a limited way, even
indicate certain relationships between individuals; but they would not there-
fore become identical with individuality differentials.

Chapter J

Organismal Differentials and Specific Adaptation
of Tissues and Their Products

In the preceding chapters we have used the interactions between whole
organisms or parts of organisms, between organisms and tissues or
organs, as indicators of organismal relationship; which means the rela-
tionship of organisms or of parts of organisms, in accordance with the data
of phylogeny; and it is the organismal differentials which express these
relationships ; but in addition the interaction between certain substances
which are produced by organisms, or the interaction of such substances with
cells or tissues, may likewise indicate these relationships. If a tissue or such
a substance interacts more efficiently with an organ and its products derived
from the same phylogenetic group than with an organ or its products derived
from a strange phylogenetic group, then these substances or tissues may be
designated as "specifically adapted" to each other, especially if the degree of
efficiency in this interaction is the greater the nearer the phylogenetic rela-
tionship. We have previously discussed various interactions of tissues which
are mediated by substances which, as a rule, do not carry the organismal
differentials, such as hormones and organizers, the latter functioning as
organ- and tissuespecific substances. We also have given some reasons for
assuming that certain substances bearing individuality differentials may
function as autogenous regulators, which maintain the equilibrium between
adjoining tissues ; the localized substitution of a homoiogenous for an autog-
enous tissue may alter the normal activity and relationship of tissues, and
there are good reasons for believing that these changes are caused by the
character of the substances given off by homoiogenous tissues. However,
before we enter into a discussion of such substances, in which organismal
differentials determine the specific adaptation of tissues to each other, it
might be well to define again the different meanings which may be attached
to the terms specificity and specific adaptation, as far as they refer to
organisms.

1. The term "specificity" may be applied solely to organs or tissues inter-
acting within an organism, without reference to the organism as a whole;
such a condition may be designated as organ, tissue or function specificity.
The term "specific" may thus accentuate differences between different organs
and tissues within the same kind of organisms. It may include the most
important organ and tissue differentials, as well as others of secondary
importance; and, furthermore, structural and functional peculiarities which
depend presumably on the presence of such differential substances. We have
discussed these organ and tissue specificities in the preceding chapter. In a
wider sense, this term may also include enzymes and hormones produced by

466

ADAPTATION OF TISSUES AND THEIR PRODUCTS 467

certain tissues or organs within an organism, because they differ from
substances produced by other related tissues in the same organism.

The term "specific" in this sense may refer to a relation between two
kinds of substances, or between a substance and an organ or tissue, or
between the function and structure of various organs within the same
organism, or between an organ or tissue and environmental factors. Such
specific relations exist, for instance, between an enzyme and its substratum,
between a hormone and the organ on which it acts, between an environ-
mental factor and a particular sense organ, and between various organs and
organ systems within the same organism. We have here to deal with intra-
organismal tissue, organ and substance adaptations. Specific in this sense are
also the relations obtaining in general between parasites and hosts, as well
as the relations between man and domesticated animals. These may also
depend on tissue or organ specificities but in these adaptations there may
participate, secondarily, also the organismal differentials, and these specifici-
ties are therefore organismal in character and may be classed with type 2.
In general if these organ characteristics are specific of individuals or species
they become organismal specificities, and such organ or tissue specificities
characteristic of species are used largely in determining the systematic posi-
tion of plants and animals.

2. The term "specific" may be used in order to express the fact that a
certain structure, substance or function is limited to and characteristic of a
certain class or species of organisms, or a certain individual. This is
organismal specificity. There is no reference made, in this case to a particular
adaptation which this structure, substance or function may bear to others in
the same organism. Thus, in certain tropical nymphaeaceae, the pollen-tube
grows out and fertilization can occur if the surrounding medium contains a
very small amount of boric acid. This is apparently a specific characteristic
of these plants and is not known to apply to other plants. In this sense the
chitinous integument is specific for certain classes of animals. Limulus and
other arthropods have respiratory blood pigments, which are peculiar to
these types of organisms. In the metabolism of birds, allantoin plays a specific
role. Different hemoglobins are specific for species, and in certain respects,
for individuals. We have referred to other similar examples of this kind of
specificity in the preceding chapter. While these specific structures, substances
or functions may actually enter into relationship with others bearing a corres-
ponding organismal differential, we leave this possibility out of consideration
under present conditions. A certain combination of structural, metabolic and
functional peculiarities is characteristic of a given individual or species. Also,
in the realm of psychical-nervous functions there exist specificities of a
similar kind. Thus a certain event calls forth in one individual, but not in
another, a peculiar reaction, often depending upon a preceding experience of
the first individual, which was peculiar to him and not shared by certain other
individuals. While these two types of specificity represent distinct character-
istics of organs and tissues, still they appear as a rule associated with each
other.

468 THE BIOLOGICAL BASIS OF INDIVIDUALITY

3. The term "specific adaptation" may be used to designate the difference
between the results of the interactions of two substances or tissues if they
take place on the one hand between individuals A and B, and on the other
hand between individuals A and C ; and likewise between species S and T and
species S and R. These differences in the results of interaction depend upon
the character of the organismal differentials of the different individuals or
species, and the degree of these differences should then be graded in corres-
pondence with the degree of genetic relationship between these organisms,
since the organs or substances involved find, in more nearly related organisms,
receptors to which they are better fitted than to those in less nearly related
organisms. It is the correspondence between the organismal differentials of
organs, tissues or substances in one organism and the receptors of organs,
tissues or substances in another organism, which characterizes the specific
adaptation in the reaction between them.

Such a specific adaptation can be demonstrated most readily if we have to
deal with class and generic differentials. The finer the differentials are which
come into play, the more difficult it is to demonstrate a mutual adaptation.
Thus, a specific adaptation between substances carrying species differentials
can be demonstrated less readily than an adaptation between substances
carrying class or generic differentials ; and still greater is the difficulty when
individuality differentials interact. This increasing difficulty in recognizing the
presence of finer organismal differentials may be due to deficiencies in the case
of the very finely graded reactions by means of which finer organismal differen-
tials are tested. We would have, therefore, to face in this case the same
problem which arose when, in joining together more primitive tissues or
organisms, it was possible to demonstrate the presence of the coarser, but not
of the finer, organismal differentials.

In all the instances considered so far, we have to deal with the interaction
of specifically adapted substances or tissues which are preformed. However,
a similar specific adaptation can also arise through active immunization, when
one substance serving as antigen, enters the system of an organism belonging
to another species ; immune substances may then develop, which react with
the antigens in a specific and graded manner, corresponding to the relation-
ship of the organisms or tissues and organs involved in these processes. We
have here, then, to deal (1) with a specific adaptation between an antigen
and an antibody, and in addition (2) with a gradation in specificity in the
interaction between antigen and antibody in the sense that other substances
may take their place the more readily, the more nearly related organs and
tissues, or the organisms are which substitute for the primary antigens or
antibodies. Conversely the degree of specific adaptation between these sub-
stituted antigens or antibodies may serve as the indicator of the degree of
relationship between the primary substance and the substitutes.

In this discussion we have attributed the organismal reactions exhibiting
a specific adaptation to the presence of organismal differentials, with which
organ-specific substances may be combined in certain cases. However in
preceding chapters we have found instances in which specific reactions be-

ADAPTATION OF TISSUES AND THEIR PRODUCTS 469

tween organisms graded in accordance with their relationship depended on
substances which were not identical with the primary organismal and individu-
ality differentials. We have encountered reactions of this latter kind for instance
in transplantations among embryos which do not possess organismal differen-
tials in the strict sense, but instead possess precursors of these differentials ; we
have encountered examples of this kind also among unicellular organisms and
among algae; but there is reason for assuming that also in other cases the
equilibrium between the parts of an organism and its graded interaction with
other organisms may depend on substances other than the typical fully
developed organismal differentials. We have seen that the characteristics of
certain organs and tissues may also be used in the classification of organisms
and that the development of the organs and tissues and their differentials
from simple structures and substances to more complex, differentiated ones
has taken place in association with the corresponding development of the
organismal differentials. Substances other than organismal differentials may
be involved in the reactions which exhibit specific adaptations between organ-
isms. Some of the substances which are the bearers of these specifically
adapted relations seem to be relatively simple, heat resistant substances, of
neither a protein nor of a complex carbohydrate or lipoid nature, therefore
quite distinct from the organismal differential substances in the strict sense,
although the possibility exists that they are derived from the latter type of
differentials. Our present limited knowledge does not make it possible, in
many instances, to distinguish between these different types of substances and
the specific reactions which they cause. We may then apply in these cases the
term organismal differentials in a wider sense, which includes substances
which are concerned with the production of specific adaptations.

We may now cite some examples of specific adaptations in the interaction
of preformed substances which may or may not carry organismal differentials.
It can be shown that there exist in the blood sera of various classes or species
of vertebrates, substances which in combination with certain other substances,
the tissue coagulins present in tissue extracts may cause either an acceleration
or an inhibition of blood coagulation, in accordance with the kind of animals
from which the sera or extracts were obtained, and in accordance with the
length of time during which these two kinds of substances were allowed to
act on each other before they were added to the blood plasma which served
as test material. Now, there is evidence that the substances in tissue extracts
and sera which act together or perhaps combine to form agents accelerating
the coagulation of the blood are specifically adapted to each other, and there
is likewise a probability that also the inhibiting substances are, in the same
sense, specifically adapted to each other. This would mean that the accelerat-
ing, and perhaps also the inhibiting, precursor substances in serum and
extract carry class or species differentials, and that when substances carry-
ing the same or related differentials interact, the effect on coagulation is greater
than when substances carrying disharmonious differentials interact. A specific
adaptation is also noticed between tissue extract and blood plasma, the tissue
extract of the same class as that from which the plasma has been obtained,

470 THE BIOLOGICAL BASIS OF INDIVIDUALITY

presumably in combination with a factor in the blood plasma, causing
coagulation of the fibrinogen more rapidly than that of another class.

A similar type of specific adaptation between substances may influence
also the behavior of cells ; thus, according to Mudd, Lucke, McCutcheon and
Strumia, the macrophages and polymorphonuclear leucocytes of rabbits act as
phagocytes towards bacteria, and also towards erythrocytes and protein-
coated collodion particles, more efficiently if rabbits sera are used as the
carrier of bacteriotropin than when human sera are used. The same specific
relation is seen if immune serum is used instead of normal serum. The serum
with the tropin which it contains, or the globulin fraction of the immune
serum, is supposed to spread over and to attach itself to the surface of the
antigenic material. As a result of this effect the spreading-out and phagocytic
activity of the leucocytes are stimulated. Under these conditions the leucocytes
behave as if they were able to differentiate between the sensitizing substances
in the sera of two different mammalian species.

Tillett and Garner, and subsequently Madison and Van Deventer, ob-
served that a filterable, heat-stable substance can be extracted from strepto-
coccus hemolyticus, which fibrinolyzes plasma. Substances from strepocccci
isolated from inner human organs dissolve human plasma and, slightly,
monkey plasma ; cultures of this kind are inactive towards the plasma clots of
other animal species, such as the rabbit. In streptococci isolated from horses
there is a fibrinolysin that is specific for horse plasma and the same applies
to swine streptococci and swine plasma. Addition of serum from the same
species, especially of anti-streptococci immune serum, inhibits the action of
the fibrinolysin in a specific way. By serial passage of a human streptococcus
through rabbits it is possible, according to Reich, to cause in the streptococcus
a loss of the human carbohydrate A and a loss of the fibrinolysin for human
plasma; instead, a carbohydrate characteristic of animals appears. By sub-
sequent serial cultures of the streptococcus on human blood agar plates, the
original characteristerics of this streptococcus are restored.

In a somewhat related way, Duhey finds that the action of serum is
specifically adapted to red corpuscles of a certain kind.Thus the venom of
Synancya horrida is hemotoxic as well as neurotoxic. The hemotoxic action
against the red blood corpuscles of a given species of animals is much more
readily prevented through the addition of serum of the same species than by
that of the serum of a different species. Thus rabbit serum protects rabbit
corpuscles, while human serum protects human corpuscles; a species differ-
ential seems therefore to be attached to an inhibiting substance.

A further analogous condition is noted in the interaction between blood
sera and the venom of heloderma; sera which do not activate the hemolytic
effect of this venom, inhibit it. Now in some cases hemolysis of the erythro-
cytes of a certain species seems to be especially inhibited by the blood serum
of the same species. Likewise, Besredka observed that sheep serum protects
sheep corpuscles, but not the corpuscles of another species, in a specific
manner against the hemolytic action of rabbit serum.

In general, the blood serum of an individual is specifically adapted to its

ADAPTATION OF TISSUES AND THEIR PRODUCTS 471

own red corpuscles and the serum of a species is likewise specifically adapted
to the red blood corpuscles of this species, although the adaptation between
the serum and cells within a certain species is not so perfect as that between
serum and cells within the same individual. Therefore autohemolysins do
not occur under ordinary conditions and, as a rule, cannot be produced
experimentally. Much more common, however, is the appearance of heter-
olysins. Examples of such a specific adaptation between blood serum and
erythrocytes may also be found in invertebrates; amoebocyte tissue which,
under certain conditions, results from the agglutination of the amoebocytes of
Limulus, remains better preserved in Limulus serum than in the sera of other
kinds of arthropods.

Another example of the specific adaptation between the various constituent
parts of an individual is the following. Fresh serum or heparinized plasma
from normal dogs as a rule causes a local reaction in capillary permeability
when injected intradermally into other dogs, but this does not usually occur
when the injection takes place into the dog from which it had been obtained
(Freeman and Schecter). This is a further demonstration of an autogenous
equilibrium. On the other hand, the presence of a species equilibrium is
indicated, when, according to Togawa, injection of autogenous and homoioge-
nous serum causes an early increase in the amount of fibrinogen in the blood
of the injected animal, while heterogenous serum usually does not have this
effect.

All these observations have one characteristic in common : they illustrate a
species or class or an autogenous equilibrium which latter we have analyzed
previously. The various constituent parts of an individual organism are
adapted to one another. Similarly the various components in the organiza-
tion of a species or class are adapted to one another. In a previous chapter
we have mentioned the fact that in more primitive organisms where it is not
possible to demonstrate the existence of individuality differentials, species or
class equilibria, indicating specific adaptations between the component parts
of these organisms, may be present.

There exists a certain analogy between these specific adapations and the
specific adaptation between the red corpuscles and presumably other cells
belonging to a certain blood group and the serum of this group. In the latter
case, the specific adaptation manifests itself by the lack of an agglutinating
effect of the serum on the cells of the group to which both belong, although
such a serum agglutinates the cells of individuals belonging to other blood
groups which possess the necessary agglutinogen. But in this instance the
specific adaptation is not due to a real species differential but to a special
substance of a somewhat different nature. This relationship between serum
and erythrocytes serves to maintain the autogenous equilibrium. Bernstein,
however, interprets this phenomenon in a different manner; he assumes that
the antigen (agglutinogen) of a certain group, circulating in the blood unites
with the corresponding agglutinin and thus prevents it from becoming mani-
fest, while agglutinins which are able to combine with a strange agglutinogen,
not being bound by this antigen, remain active. However, if this explanation

472 THE BIOLOGICAL BASIS OF INDIVIDUALITY

were correct, it would be difficult to understand why the equilibrum between
antigen and agglutinin should be always balanced in such a way that no free
agglutinin can be demonstrated in the blood. We know that in the case of
toxin-antitoxin combinations such a perfect inactivation of either toxin or anti-
toxin is not possible. Moveover, a condition similar to that found in the case
of the blood groups applies also to the Forssman antigens and the corre-
sponding hemolysins. The blood sera of those species which belong
to the heterophilic guinea pig group do not contain the hemolysin re-
quired for this reaction, while the sera of the species belonging to the non-
heterophilic rabbit group do carry it. Now, in the case of the Forssman anti-
gen, it can be shown that only animals belonging to the rabbit group can be
immunized against the heterophilic antigen, while such antibodies cannot be
produced experimentally in the heterophilic group. There must, therefore,
be some mechanism which prevents the immunizing effect of antigen in the
latter. These findings seem to be analogous to what we observe in the case of
autogenous substances ; they are not able to serve as antigens. Constituents
of tissues are adapted in such a manner to the organism to which they belong
that they cannot, here, call forth the production of antibodies ; it seems, then,
that the possession of the same individuality (or species) differentials on the
part of antigen and receptive organs prevents the disequilibrium which is
necessary for the production of artificial immunity. It is probable that this
mechanism depends on the identity of the organismal differential proteins in
an individual or species ; in the latter, the species differential-proteins are the
same, and in an individual the individual differential proteins are the same.
Associated with and presumably superimposed upon these organismal
differentials are the organ and tissue differential substances, which differ
everywhere within the same individual. However in addition to the typical or-
ganismal differentials also other substances which help to maintain or play
a role in the autogenous or species equilibrium may be adapted to the other
parts of the organism in such a way that they cannot call forth the production
of antibodies in the body to which they belong.

A species equilibrium can be recognized as mentioned already in a pre-
vious chapter in the observations of F. R. Lillie, who found that substances
can be extracted from the eggs of various species, which possess an agglutinat-
ing power for the spermatozoa of their own species, but not for those of
another species. Thus the egg extract of Nereis aggultinates the spermatozoa
of Nereis, but not the spermatozoa of Arbacia. Similarly, the extract of eggs
of Strongylocentrotus fransiscanus agglutinates the spermatozoa of the
same species, but not those of Strongylocentrotus purpuratus, though the
latter are agglutinated by the extracts of eggs of Strongylocentrotus pur-
puratus. However, such homoiogenous agglutinins cannot be demonstrated
in the ova of all species, as Miss Sampson has shown. Heterogenous agglu-
tinations may occur, but if this is the case, it is probable that the heterogenous
agglutinins causing them are distinct from the typical homoiogenous agglu-
tinins. There is another difference between the heterogenous and homoiog-
enous agglutinins ; the agglutination produced by the former may be irrevers-

ADAPTATION OF TISSUES AND THEIR PRODUCTS 473

ible, and moreover, the heteroagglutinins may be toxic for the spermatozoa,
whereas the agglutinations caused by homoioagglutinations are reversible and
non-toxic for the spermatozoa (Little and Just). In addition, there has been
found a more direct specific adaptation between eggs and spermatozoa, inas-
much as a smaller number of spermatozoa suffices for the fertilization of eggs
of the same species than for that of eggs of other species (Jacques Loeb,
R. F. Lillie).

A specifically adapted substance, which seems to be a protein, has been
extracted from the sperm of the giant Keyhole limpet ; it is able to dissolve
the membrane of eggs of the same species. Correspondingly Abalone (Haliotis)
sperm yields a lysin which acts on the eggs of Abalone ; cross-lysis between
limpet and Abalone does not occur (Tyler). In addition sperm extracts of
Arbacia seem to agglutinate eggs of the same species, and this egg-agglutinating
substance resists boiling for hours. Tyler has found that in certain echinoderms
and worms there may occur in a watery extract of egg, a substance, fertilizin,
which combines in a specific manner with the homoiogenous sperm, but with-
out causing a noticeable agglutination of the spermatozoa. Such fertilizin he
calls "univalent." There may be extracted from spermatozoa a similar species-
specific substance, an antifertilizin, which combines with the fertilizin, neutral-
izes its sperm agglutinating power, and agglutinates the eggs from which the
fertilizin can be extracted. Tyler noted moreover a certain relationship between
fertilizin and the fourth component of complement which is present in normal
guinea pigs serum. Complement is fixed by fertilizin, but is released from
this combination by the action of antifertilizin; there exists thus a certain
analogy between the action of complement and antifertilizin.

In a previous chapter we have referred to hormone-like substances which
accelerate or induce metamorphosis in insects ; also in amphibia there are indi-
cations of the existence of substances accelerating metamorphosis. In a similar
way, Caswell Grave prepared from the larvae of two ascidian species,
Polyandrocarpa and Phallusia, extracts which induce metamorphosis in their
own but not of the other species. These substances are therefore species-
specific, yet they are neither proteins nor lipids ; perhaps they are amino-acids ;
but their chemical nature has not been established.

According to F. B. Turck, a substance developing in autolysed muscle, or
also in other tissues, has on certain cells very characteristic effects, which are
either stimulating or injurious, according to the quantities used. This sub-
stance, which Turck names "cytost," seems to be species-specific. Thus,
cytost from chicken acts specifically on chicken cells in tissue culture, and
human cytost on human cells. Similarly, extract of dried paramaecia appar-
ently stimulates the multiplication of paramaecia, while extracts from chicken,
rat or human tissues do not have such an effect. Corresponding observations
were made with bacteria. In immunization experiments it was shown that
injection of autolysed muscle of the cat called forth active immunization
only against cytost from the cat, but not against that prepared from other
animals.

Specific adaptation may be found, furthermore, in the case of enzyme

474 THE BIOLOGICAL BASIS OF INDIVIDUALITY

action. There exist not only the first kinds of specificity, which imply that
one enzyme is different from another one and is peculiar to a certain species
or series of species and to a certain organ or tissue, but there has been
demonstrated, also, a specific adaptation in the sense here defined. Thus ac-
cording to E. N. Harvey, luciferin, the substance which, in being oxidized,
gives rise to luminescence, if acted on by the oxydation accelerating enzyme
luciferase, shows a specific adaptation to this enzyme. Only the enzymes
from the same species, or from species very closely related to the species
from which luciferin was obtained, seem to cause luminescence; if solutions
of luciferin and luciferase are prepared from Cypridina and Systellaspis,
the mixing of luciferin from one organism with the luciferase from the same
species leads to a marked production of light; but if the solutions of luciferin
from one species are mixed with the luciferase from the other species, the
results are negative.

Another example from the field of enzyme activity is presented by certain
older observations of Hedin. There occurs in the gastric mucosa of various
vertebrates not only the milk-curdling enzyme rennet, but, according to Hedin,
also a substance inhibiting the enzymatic action of rennet, which can be
obtained if the enzyme is treated with NH4OH. This inhibiting agent is
specifically adapted to the enzyme of the same species, both of these sub-
stances, the enzyme as well as the inhibiting substance, carrying species dif-
ferentials. However, certain other substances, such as egg albumin and blood
serum, may also contain inhibiting substances for rennet, but they are non-
specific; charcoal, likewise, may act in a non-specific manner. The species
differential which is present in rennet participates in the antigenic function
of this substance and calls forth in the animal, immunized against the rennet,
the development of an anti-rennet, which is specifically adapted to rennet in
a way similar to the natural anti-rennet. However, these investigations may
perhaps have to be reconsidered in the light of more recent studies on
proteinolytic enzymes of the gastro-intestinal tract. As far as the various
enzymes and their precursors in the gastro-intestinal tract, which have been
separated in recent years by Northrop and Kunitz, are concerned, it has been
shown that their constitution differs in different species. Similarly, catalase
seems to differ somewhat in different species (Sumner); also the urease
which has been found in various tissues and in the blood serum of Limulus
seems to be specific for this animal (Loeb and Bodansky). However, no
instance of specific adaptation has been observed so far in these substances.
Considerably more readily demonstrable than the species-specificity is the
organ or "substance" specificity of these enzymes; each one is adapted to a
definite type of substratum.

A specific adaptation is characteristic of many antigens and immune sub-
stances. In order to produce an antibody it is necessary to introduce into the
organism which is to be immunized, a substance sufficiently strange to it to
cause a certain disequilibrium. In many cases it is the introduction of a strange
organismal differential which serves as antigen and makes possible the pro-
duction of an antibody carrying the corresponding organismal differential.

ADAPTATION OF TISSUES AND THEIR PRODUCTS 475

It seems that specific adaptations of the kind mentioned here may underlie
also some types of parasitism, the parasite becoming adapted to certain sub-
stances of the host which carry the species differential of the host, or at least
differentiate one type of host from other types of hosts. Thus, according to J.
H. Welsh, the freshwater mussel, Anodonta cataracta Say, is infested with
parasitic water mites (Unionicola Ypsilophorus), which live between the gills
of their host. In the free-living state these mites are positively heliotropic, but
if to the water in which a positive heliotropic reaction would otherwise take
place, an extract of the gills of the host or water from the mantle cavity of
the host is added, they become negatively heliotropic, thus assuming the
characteristic behavior they show in their parasitic life. It is interesting to
note that in the case of Unionicola, which parasitizes on Anodonta, only
material from this particular host will bring about such a change in be-
havior, whereas corresponding substances from other species, such as Ellipho
or Lampsilis, have no effect on the parasite. In this instance we have to deal
evidently with a specific adaptation between host and parasite, which depends
upon the interaction of certain specific substances. However, whether the
substances, which play the decisive role in these and certain other cases,
actually carry the organismal differentials, or are merely derivatives of or
otherwise related to these differentials, cannot be decided without further tests.
But it could be made probable that the substances concerned in these reactions
are at least nearly related to the organismal differentials of the parasite and
host if, after immunization with these substances, the antibodies produced
were found to react not only with the material which served as antigen, but
also with other substances obtained from the same host species, but not from
distant species; or, if it could be shown that there is a graded response of
the parasite to analogous substances from different species, the response being
the stronger the more nearly related the species from which the test substance
is obtained, to the host species of that particular parasite.

In the examples which we have cited, we have to deal primarily with pre-
formed relations between two substances, or between a substance and a tissue,
the reaction depending upon the genetic relationship between the organismal
differentials of the organisms concerned, although primarily, organs and tis-
sues and organ-specific substances are involved in the majority of these reac-
tions rather than purely individual and species-specific substances. The great
structural and functional specificity which is characteristic especially of the
higher, more differentiated organisms, depends largely upon this interaction
of organismal differentials or of substances derived from them, or also of
substances originating in organs which are specific for a species in a similar
manner in which the organismal differentials are specific, but which differ
otherwise from the latter. In addition, we have cited some instances in which,
by means of artificial immunization, the same specific relations between differ-
ent organisms, or between the substances derived from them, can be demon-
strated in case one of the substances involved served as antigen.

These data may then be interpreted as indicating the presence of autoge-
nous species or class equilibria, in which the various organs and substances

476 THE BIOLOGICAL BASIS OF INDIVIDUALITY

which are concerned in the function of these organs are specifically adapted to
one another because they carry the same organismal differentials, and in which
tissues or substances bearing strange organismal differentials call forth antago-
nistic reactions on the part of the host. However, in addition there may be
active in this correlation between the phylogenetic relationship of animal
species and the interaction of tissues and organs and of substances concerned
in the functions of organs and tissues, other functions of tissues and organs,
in which the organismal differentials are not involved and in which the active
compounds may be of a less complex nature. However the finest and most varied
examples of specific adaptations are furnished by the interactions between
transplanted tissues and hosts which we have discussed in the chapters of the
first part of this book. These experiments furnished also the basic data from
which the concepts of organismal and individuality differentials and of autoge-
nous tissue equilibria have developed.

P^rf "Y/n Organismal Differentials and Organ Differentials

as Antigens

Introductory Remarks

When pieces of organisms, organs or tissues, or when cells or parts
of cells are transferred to or united with other organisms or parts
of them, there are initiated those reactions which we have discussed
in the preceding chapters, and which may serve as indicators of the nature
of organismal and organ or tissue differentials. But in addition, the introduc-
tion of these tissues and cells, or of substances which are derived from them,
may lead to the production of new substances and mechanisms which are
specifically directed against the bearers of the organismal and organ differ-
entials. These latter kinds of reactions represent immune processes and the
altered state resulting in the strange organism is that of immunity ; the specific
substances formed in these reactions are immune substances or antibodies,
and the substances which initiate these immune processes and lead to the de-
velopment of immunity are antigens. Antigens and the corresponding anti-
bodies may be considered as specifically adapted substances, which may either
develop spontaneously or are produced experimentally.

In this part we shall discuss the relations between organismal and organ
differentials and antigens. We shall also include in the discussion some sub-
stances which have certain characteristics in common with organismal or
organ differentials, but which differ from them in some respects. There are,
in addition, substances which are able to react in a specific way with antibodies,
although unaided by proteins they may not be able to initiate immune proc-
esses, and therefore to act as complete antigens.

In the first chapter, we shall consider the differentials of blood groups and
the heterogenetic (Forssman) antigens, which while differing in certain re-
spects from the typical organismal and organ differentials, in some ways re-
semble them.

477

Chapter I

Blood Groups, Heterogenetic (Forssman) Anti-
gens and Organismal Differentials

Iandsteiner discovered, about forty years ago, that there can be distin-
guished in the human blood four groups of red corpuscles, according
-i to the type of human serum which agglutinates them. Under normal
conditions the serum of a person does not agglutinate the blood corpuscles of
another person belonging to the same group, but the serum of individuals
belonging to other groups has this power, except the serum of one group,
which does not possess such agglutinating substances (agglutinins) for any of
the blood groups. The red corpuscles of this latter group, on the other hand,
contain both kinds of substances (agglutinogens) which are responsible for
the agglutination of corpuscles under the influence of the specific group ag-
glutinins in two of the groups. If the serum of this group possessed an active
agglutinin, it would agglutinate its own blood corpuscles. There exists another
group of individuals whose corpuscles cannot be agglutinated by the serum
of any of the other groups, because their corpuscles lack both kinds of ag-
glutinable substances (agglutinogens) ; correspondingly, their blood serum
has agglutinins for all the other groups. Such agglutinogens, according to the
terminology of Ehrlich's sidechain theory, are considered as receptors, which
combine with the agglutinin to which they are specifically adapted and such
a combination leads to the process of agglutination of the erythrocytes. Inas-
much as these agglutinogens, if injected parenterally into animals of a dif-
ferent species — e.g., the rabbit — may give rise to the formation of antibodies
(immune agglutinins), acting specifically on the type of corpuscles which
possess that particular agglutinogen which was injected, they may act also as
antigens. In general, they represent the blood-group differentials.

We can thus distinguish four human blood groups, which differ according
to the character of agglutinogens in their erythrocytes as well as according to
the character of the agglutinins in their serum. In Group I, the corpuscles do
not have any agglutinogens and in the serum there are found agglutinins
alpha and beta. Agglutinin alpha has the power to agglutinate the corpuscles
of Group II, and agglutinin beta agglutinates the corpuscles of Group III.
In Group II, the corpuscles carry agglutinogen A and the serum agglutinin
beta. In Group III, the corpuscles have agglutinogen B and the serum pos-
sesses agglutinin alpha. In Group IV the corpuscles have both agglutinogens
A and B and, correspondingly, their serum lacks agglutinin alpha as well as
beta.

As to the heterogenetic (Forssman) antigens or differentials, these are
characterized by their ability to call forth the production of hemolysins for
sheep corpuscles if they are injected into the rabbit. As a rule, only the injec-

478

BLOOD GROUPS, HETEROGENETIC ANTIGENS 479

tion of the red corpuscles of a certain species into a rabbit induces in the
latter the formation of hemolysins specifically directed against the corpuscles
of that particular species. But it has been found by Forssman that it is possible
to produce hemolysins which dissolve sheep corpuscles not only by the intro-
duction of sheep erythrocytes into a rabbit, but also by the use of kidney of
the guinea pig or of the horse, or of the blood corpuscles of chicken, as anti-
gens; if extracts of such cells or tissues are injected into rabbits, hemolysins
for sheep corpuscles will be found to circulate in the rabbit blood. Similar
differentials which may induce the formation of hemolysins for sheep cor-
puscles have been found in the tissues of the most diverse species of animals,
and even in certain bacteria, without any reference to the relationship of these
organisms with the sheep ; but the organs of certain other species, such as the
rabbit, do not usually possess such antigens. Accordingly, two classes of or-
ganisms are distinguished, namely those which, like the guinea pig, possess
Forssman heterogenetic or heterophile differentials, and others which, like the
rabbit, usually do not possess such differentials. The term "heterogenetic" is
applied, because they are found in species and classes of animals far distant
in relationship from the sheep, and even in bacteria. Evidently these sub-
stances behave in a very different way from organismal differentials; there
is no specific connection between the systematic relationship of these organisms
and the presence of the heterogenetic differentials in their cells, although the
possession of Forssman antigens may be characteristic of whole genera and
families. In addition to the Forssman antigens there exists still another system
of heterogenetic antigens, which is shared by bacteria of the hemorrhagic
septicemia group and the erythrocytes of many species of birds (Buchbinder),
and presumably many other non-related groups have certain chemical charac-
teristics in common. In this connection the fact may be recalled that also
estrogenic substances occur in the most diverse classes of organisms.

In order to analyze the relationship of the blood-group and Forssman dif-
ferentials to the organismal and organ differentials the following questions
must be considered: (1) By what methods is the presence of the blood-group
and Forssman differentials determined? (2) In which organs and tissues do
these differentials occur? (3) What is the distribution of these differentials
among animals and bacteria? and (4) What is the relationship of the blood-
group differentials in various animal species to those in man?

Let us state once more the characteristic features of the organismal and,
in particular, of the individuality differentials. In contradistinction to the
structure and function of tissues and organs, which differ from one another,
there is something common to all these different organs and tissues in the
same individual, at least in the higher classes of animals, which differs from
the corresponding characteristics in all other individuals. If we consider in
addition, classes, orders, genera and species, and strains and family relation-
ships, we then find that the various kinds of organismal differentials, includ-
ing the individuality differentials, correspond in their graded properties to
the graded phylogenetic relationships of these various types of organisms.
This latter characteristic is very important in the definition of the organismal

480 THE BIOLOGICAL BASIS OF INDIVIDUALITY

differentials ; it is not sufficient that certain structural or functional peculiari-
ties should serve as distinguishing marks between different individuals or
species, but a correspondence between the constitution of the organismal
differentials and the genetic relationship of the organisms is required in
addition. As we have seen, the sum of certain organ or tissue differentials, or
even a single characteristic feature of a certain kind, may serve to distinguish
different species as well as different individuals, but these individual organ
and tissue differentials do not become thereby organismal and individuality
differentials. Thus the ridge patterns of the skin, the scents and many other
peculiarities, which are not individuality differentials, allow the differentiation
between different individuals.

If we keep these criteria of the organismal differentials, and in particular
of the individuality differentials, in mind, the differences which exist between
blood-group differentials, their agglutinogens, and the organismal differen-
tials are obvious. The primary blood-group differentials allow the separation of
individuals into four groups, irrespective of their relationship. Two brothers,
members of the white race, may belong to different blood groups, while one of
the brothers and a member of an African race, or even an anthropoid ape,
may belong to the same group. Thus the difference between individuality
differentials and the differentials of blood groups is evident. Even the differen-
tiation of individuals by means of the four primary blood groups is impossible
as a general rule, although in certain cases they may help in identifying per-
sons and even in establishing relationships to other persons ; they resemble
in this respect other hereditary organ characteristics, which may also be used
for this purpose.

For the identification of the blood-group differentials we have at our dis-
posal : ( 1 ) The various specific agglutinins normally present in human sera ;
and (2) the specific immune agglutinins which are produced by injecting,
into rabbits, human blood corpuscles possessing a certain group differential,
these immune agglutinins being absorbed in a specific manner by the ag-
glutinogens (group differentials) to which they are adapted. Either the cor-
puscles as such, or alcohol extracts of the particular group of erythrocytes
which contain the specific group differentials, are used for absorption. By these
means we can determine also the occurrence of similar differentials which
function as agglutinogens in blood corpuscles of various species of animals, or
we may study the relationship of the blood-group differentials to other differ-
entials, as for instance, the Forssman differentials.

The same principle applies to the analysis of the Forssman heterogenetic
differentials, although in this case hemolysins, and in particular those dis-
solving sheep corpuscles, are used instead of agglutinins. Guinea pig or horse
kidney, as bearers of the Forssman differentials, serves as tissue with which
other material may be compared. In using these methods for the analysis of
the identity or lack of identity between different kinds of differentials, we find
that while certain differentials behave in every respect like the typical blood-
group differentials, other differentials do so only in an imperfect manner. Re-
sults of this divergent kind are obtained especially when we study the blood-

BLOOD GROUPS, HETEROGENETIC ANTIGENS 481

group differentials in various species, or when we analyze the relationship
between Forssman and blood-group differentials, and these results are inter-
preted as indicating that the various differentials have certain sidechains in
common, while they differ in respect to others ; or it is assumed that antigens
with a blood-group, Forssman, species or organ differential, which are unlike
in different individuals, are associated with other differentials (antigens)
which are the same in two individuals and which explain the partial con-
cordance in the results obtained in the testing of the antigens.

It is a very characteristic feature of the individuality differentials, and of
the organismal differentials in general, that they occur in all or almost all of
the various tissues and organs of a certain individual or species and are not
restricted to one particular type of cell or tissue. At first it appeared as if the
blood-group differentials were limited to the erythrocytes, but subsequently
they have been found also in other cells, and according to Kritschewsky and
Schwarzmann, they occur in all the organs of an individual, except the lens
of the eye. The blood serum also seems to contain blood-group differentials,
but here they are present in only a small quantity and are apparently covered
up by other substances. They gained access to the body-fluid, presumably
secondarily, perhaps as the result of the destruction of certain cells. As we
have seen, also individuality-specific substances are present in the blood
serum. In addition to the blood serum, various secretions, such as saliva and
urine, may contain blood-group differentials. Landsteiner and Levine demon-
strated "blood-group specific substances" in human spermatozoa, which had
been freed from the sperm fluid through centrifugation and subsequent wash-
ing with salt solution. This observation suggests that germ cells contain pre-
formed blood-group differentials ; otherwise we should have to assume that
some of the constituents of the sperm fluid may have adhered to the sperma-
tozoa, or that a precursor substance of the fully developed differentials, rather
than the latter themselves, was responsible for the group antigen reaction.

In regard to their general distribution among various tissues, blood-group
antigens and organismal differentials behave, then, in a similar manner. As to
the Forssman differentials, in one species they may occur only in the erythro-
cytes, in another species in the kidney, and perhaps also in the liver ; in still
others they may be found in the erythrocytes as well as in the kidney, and
in the guinea pig they are present in the kidney, but only in the erythrocytes
of certain individuals. In man, according to Schiff and Adelsberger, the
Forssman differential is present in those corpuscles which possess the blood-
group differential A ; according to Kritschewsky, it is present also in various
organs, but not in the brain. However, it is possible that blood-group A and
the Forssman antigen have certain chemical characteristics in common, while
they differ in respect to others ; or there may be perhaps not even an identity
of certain chemical groups, but merely a chemical similarity in these two
antigens. This similarity in chemical structure may lead to an overlapping
in the action of the resulting antibodies. In their wide distribution in human
tissues the blood-group differentials would then differ from the typical organ
differentials which, on the whole, are limited to one organ, although different

482 THE BIOLOGICAL BASIS OF INDIVIDUALITY

organs, such as liver and kidney, may have certain receptors in common; in
this respect the blood-group differentials resemble the organismal differen-
tials.

From what has been stated, it follows that by means of the four primary
blood groups it is not possible, as a rule, to differentiate one individual from
another, nor to indicate the degree of relationship between individuals. The
behavior of transplanted tissues, on the other hand, does show not only the
distinctiveness, but also the relationship of individuals in an approximately
quantitative manner. All degrees of relationship are revealed by transplanta-
tion. This difference between the factors determining the results of transplan-
tation and the differentials of blood groups among individuals belonging to
the same, as well as to different species, is also emphasized by the lack of
parallelism between the results of transplantation and blood-grouping. We
have seen previously that the results of skin transplantation among human
beings are not noticeably influenced by the blood groups to which these
individuals belong. In animals transplantation reveals individual differences,
although blood-group differences may be lacking here altogether. Furthermore,
the presence of similar group differentials in different species of animals does
not affect noticeably the severity of the reaction following heterotransplanta-
tion in these species.

What applies to the relations between the organismal differentials, as ana-
lysed by means of transplantation, and the human blood groups applies also,
and to a still greater extent, to the relations between the heterogenetic dif-
ferentials of Forssman and the organismal differentials. The Forssman differ-
entials are in some respects the opposites of the organismal differentials ; the
latter correspond to and express the systematic relationship of organisms,
whereas the Forssman differentials disregard these relationships; as stated
they are factors held in common by the most varied and often distant kinds of
organisms, without regard to systematic relationship. We may, perhaps, com-
pare them in part with certain pigments which are present in the epidermis of
the most varied species, without reference to their systematic position.

In many species of animals there occur in the blood corpuscles, species-
specific agglutinogens, and in the blood serum, species-specific agglutinins,
which latter cause agglutination of the blood corpuscles of foreign species,
without reference to the blood-group to which they may belong. Inasmuch as
these agglutinins are directed against heterogenous species, they are called
heteroagglutinins ; they are not, at least in some cases, experimentally or
accidentally produced immune substances, but are preformed substances.
At present it is not possible to establish a direct relationship between pre-
formed heteroagglutinins and the organismal differentials, except that in
some cases, when two species are relatively nearly related, heteroagglutinins
seem to be lacking, as in the case of rat and mouse, or of buffalo and cattle ;
however, human serum may contain heteroagglutinins for the erythrocytes
of nearly related anthropoid apes. In addition, there may occur in the serum
of these species, hemolysins which are similar. Distinct from these preformed
heteroagglutinins in the sera of various animal species are immune agglutinins

BLOOD GROUPS, HETEROGENETIC ANTIGENS 483

and hemolysins, which may be produced by injection of red corpuscles of one
species into a strange species. These immune agglutinins and hemolysins also
possess a species-specific character; the presence of such species-specific sub-
stances may obscure the existence of the group differentials, and in the case
of immune agglutinins which are directed against human erythrocytes it may
be necessary first to absorb the species-specific heteroagglutinins by human
corpuscles of Group I, which possess neither the A nor the B group differen-
tials, if a test is to be made of the presence of group agglutinins in this serum.

There exist, then, marked differences between the individuality differentials
demonstrable by means of transplantation and the differentials of the four
primary blood groups. It seems that it was the proof that very fine differences
between individual constitutions can be established by means of transplanta-
tion which led immunologists to seek likewise for methods making possible
finer differentiations between individuals by means of blood grouping. Ac-
cordingly, in recent years, by the use of immune agglutinins in addition to
the natural blood-group agglutinins, Landsteiner succeeded in adding new
groups to the four primary blood groups. Thus within the Group A, Land-
steiner distinguished between two subgroups, Ax and A2 ; these differ in the
way they unite with two subagglutinins; alpha! and alpha2. In a somewhat
related way Thomsen distinguished between the original Group A and the
subgroup of the latter, Ax. Ax corpuscles are less intensely agglutinated by
antisera than are the typical A corpuscles. Thomsen thus adds to the differen-
tials A, B and A+B, a fourth one, Ax. To these subgroups correspond sub-
groups among the agglutinins of the normal human sera.

Also, the B differential in human erythrocytes has recently been further
differentiated into a Bx component, which so far seems to be peculiar to human
cells, and into B2 and B3, which occur, besides, in the blood corpuscles of
certain animals, such as the rabbit. Correspondingly, anti-B of human sera
may contain a mixture of anti-Bx and anti-B2; however, not all human sera
contain the anti-B! component.

In addition, Landsteiner and his associates established three further sub-
groups carrying the agglutinogens M, N and P, respectively. No preformed
agglutinins corresponding to the agglutinins M and N exist in normal human
sera, but they can be produced through immunization of rabbits with these
antigens. Moreover, in contradistinction to the primary blood-group antigens,
M and N have not been found in cells other than the erythrocytes. These
additional agglutinogens occur probably in all of the four primary blood
groups and they, together with the ordinary blood groups and subgroups Ax
and A2 differentials, make possible the differentiation between thirty-six
classes of individuals. In this way the ability to differentiate between different
individuals is much increased.

More recently, Schiff, through immunization of a sheep with the blood of a
person belonging to Group O and possessing M, N and P differentials, estab-
lished the existence of still another differential in human corpuscles, which
he designates as H, and which may be present in any of the four primary
human blood groups ; it seems to be transmitted to the offspring by means of

484 THE BIOLOGICAL BASIS OF INDIVIDUALITY

a single dominant gene. Thus seventy-two classes of individuals can now
be distinguished if one considers all these factors, and there is little doubt that
the number of such differentials could be increased still further. Still more
recently, the agglutinogen Rh, which is common to man and the Rhesus mon-
key, has been added to the list of blood-group antigens.

Notwithstanding the possibility of finer differentiations of individuals by
such means, these blood-group differentials are not identical with the in-
dividuality differentials, according to the evidence which is available at the
present time. The fact that two individuals belong to the same primary blood
group does not seem to have any relation to the reaction which takes place if a
piece of skin is transplanted from the one to the other. Furthermore, inasmuch
as Aj and A2 represent subgroups of A, the same objection applies to the
identification of these subgroups with the individuality differentials as to the
primary group A. In regard to the M, N and P differentials, they are appar-
ently inherited in a similar manner to the four primary blood groups ; neither
they nor H, as such, would make possible a differentiation between different
individuals. But even if it should be possible to distinguish individuals by
means of these additional blood groups, it has not been shown that the mode
of distribution of blood-group differentials among the different individuals
corresponds to their degree of relationship, and even if contrary to expectation
there should be found such a parallelism, it would still remain improbable
that these differentials are identical with the individuality differentials so
generally found among all kinds of species and animals, including those in
which these particular blood-group differentials are lacking.

In addition to the secondary blood group or subgroup differentials, there
occur other unusual agglutinogens and agglutinins in the blood of various
individuals, or in certain classes of individuals. Several authors — Guthrie
and Huck, Ottenberg and Johnson, and others — have already drawn attention
to such occurrences. Thus it seems that especially in cases of insanity abnormal
agglutination reactions have been observed. Furthermore, if the union between
agglutinogen and agglutinin takes place at a low temperature, abnormal ag-
glutinations may result, which are not found at ordinary temperature. Other
complications are due to an apparent linkage which has been noted between
certain types of agglutinogens or agglutinins. Thus an agglutinin for A2
usually causes an agglutination also of blood corpuscles which belong to
the primary blood group I, possessing neither A nor B. Agglutinin alphax of
human sera from groups I and III can be removed by blood cells of Group A,
which lack the Ax receptor. It is possible that with the agglutinogens N and
P, there may be associated other agglutinogens which increase the agglutina-
tion effect normally produced by the union of N and P and their respective
agglutinins ; perhaps anti-human species agglutinins may be active in anti-N
or anti-P rabbit immune sera and cause agglutination in addition to the
specific agglutination of the N and P corpuscles. Agglutinins for human P
agglutinogen have been observed also in sera of horses, hogs and rabbits. An-
other indication of the complexity of this mosaic of antigens is the existence

BLOOD GROUPS, HETEROGENETIC ANTIGENS 485

of a common partial antigen in human corpuscles, and in other cells, without
respect to the group to which they belong, as well as in certain Shiga bacilli ;
and in the latter, in addition, the Forssman antigen is present. There are a
number of other differentials which are found in cells of various species,
irrespective of their systematic relationship. Thus human corpuscles of Group
A have a certain factor in common with erythrocytes of hog, sheep and cattle.
Besides, common differentials are present in hog erythrocytes and in the
erythrocytes of man, regardless of the blood-grouping of the latter. There are
known still other differentials, which different, not phylogenetically related,
species have in common, and in all probability a still larger number, unknown
as yet, could be added to those which have so far been established.

All these observations exclude the possibility of identification of these
agglutinable factors with organismal differentials, but not the possibility that
these various factors, or some of them, may be present among the individuality
differentials, or, rather, that the genes representing these factors may be a
component part of the gene sets which determine the individuality differentials.
This conclusion holds good even if it should be feasible to distinguish all
individuals by a study of their blood-group antigens. If we consider that
besides the differences already established between human corpuscles, or
between the blood sera of human groups, and of certain individuals in these
groups, additional differences might be discovered between the red corpuscles
of individuals if their reactions with different animal sera were studied, then
we can conceive the possibility that, as Landsteiner suggests, in this way the
corpuscles of all, or at least a large number of individuals, might be identified
and distinguished from one another. Yet, as stated, it would not follow there-
fore that the sum of these factors constitutes the individuality differential.
This would require that there should be found the same graded relationship
between these regular or irregular, often heterogenous group differentials
and the genetic constitution of individuals, as can be shown to exist in the
case of the individuality differentials. That an individual can be distinguished
from other individuals by means of certain characteristics does not, by itself,
prove that these characters represent the individuality differentials. We may
be able to identify an individual by means of the combination of certain
characteristics which are a part of the Mendelian mosaic of this individual,
or even by a single characteristic belonging to the Mendelian mosaic. It is the
organismal differentials which determine the graded compatibility in the
biological sense between two organisms, and especially between two individ-
uals of the same species or race, whereas the blood groups and the immune
reactions based on such group differentials, which may be common to man
and nearly, or even more distantly, related species of animals, do not exert
this function as far as known at the present time. We have discussed these
problems already in a preceding chapter, where we considered the relation
between natural and experimentally produced immune hemolysins in cattle
and fowl and organismal differentials, and we concluded that certain relations
may exist between these types of substances. However, it may be assumed that

486 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the greater the number of additional antigens which will be found in the
erythrocytes, the less will be the difference remaining between the totality of
these antigens in the erythrocytes and in the individuality differentials.

Investigations as to the distribution of blood groups in different human
races we owe especially to Hirszfeld and his collaborators. In general, it may
be stated that the different primary blood groups are found in all races, but
the frequency with which the different groups occur differs in different popu-
lations and races. In general, in Western Europe A predominates ; the farther
we progress in the direction of India, the greater the frequency of B. In
certain more primitive races, such as the American Indian and the Eskimo,
O is the most common blood group ; but among the Black Feet Indians, Mat-
son and Schrader found a marked preponderance of Group A. As a rule,
among whites and negroes a certain agglutinogen may occur with varying
frequency.

From these facts it may be concluded that the differences even between
supposedly pure races are essentially statistical as far as their blood-group
differentials are concerned. On the other hand, as stated above, different
species may possess the same kinds of blood groups. Conditions are different
in transplantation. Here a large number of very fine gradations in reactions
occurs in accordance with the relationship of donor and host. If we compare,
for instance, the results of transplantations of thyroid from rat to mouse,
or of the reciprocal transplantations, with those of syngenesio- and homoio-
transplantations in rats, we do not find in the former, in a single instance, the
excellent state of preservation of the thyroid transplant which may be ob-
served in a favorable syngenesiotransplantation from rat to rat ; we have here
to deal with absolute differences in the distribution of a large number of
factors, not merely with statistical differences in the distribution of a limited
number of factors as in the case of the four blood groups. In homoio- and
inter-racial transplantations we may find an overlapping of the results; but
the most favorable ones obtained in some syngenesiotransplantations are not
observed in inter-racial transplantations ; the differences in the results of dif-
ferent kinds of transplantation are therefore not merely of a statistical nature,
such as those obtained in comparing the blood groups in different populations.

In order to analyze further the relations between blood-group differentials
and organismal differentials, we shall consider the occurrence of the former
in the cells and of agglutinins in the blood serum in different species of ani-
mals. However, some of the evidence concerning this subject is still contra-
dictory and the data on hand must, therefore, be used with caution.

There can be no doubt that in certain anthropoid apes, as Landsteiner and
Miller have shown, there are group differentials which are identical with those
in man. Thus A and O corpuscles occur in chimpanzees, and A, B and AB
corpuscles in orang-utangs. In a Gibbon, A corpuscles were found. In the
blood serum of these species there are present agglutinins which react with
those differentials not present in their own erythrocytes. The agglutinogens
and agglutinins in these anthropoid apes behave exactly like the corresponding

BLOOD GROUPS, HETEROGENETIC ANTIGENS 487

human group differentials and agglutinins. This relationship of the group
differentials corresponds to the close relationship existing between the or-
ganismal differentials of man and these apes. However, notwithstanding the
identity of group differentials in these organisms, a very marked difference
exists as far as the organismal differentials in man and anthropoid apes are
concerned. Injection of human red corpuscles into chimpanzees leads to the
production of species-specific antibodies, which allow the differentiation be-
tween human and chimpanzee blood (Landsteiner and Levine), although
both of these may possess the same blood-group differentials. This fact again
demonstrates the distinction between organismal and the original blood-group
differentials. The combination of blood-group antigens M and N has been de-
tected so far only in the blood of primates, but the M differential seems to
occur also in the Macacus Rhesus erythrocytes.

If we turn to the lower monkeys, Landsteiner and Miller found among
Old World monkeys no blood-group differentials which correspond to human
isoagglutinogens, while New World monkeys, which are less nearly related to
anthropoids than Old World monkeys, have a differential analogous to human
differential B, although B of man and monkey are not identical in this instance.
Among the Old World monkeys it is especially Macacus Rhesus that has been
studied very extensively. According to Buchbinder, the erythrocytes of
Macacus do not possess a differential corresponding to the human blood-group
differentials, but in the blood serum of this species there is found the iso-
agglutinin alpha, which agglutinates human corpuscles A. However, more
recently it has been observed that antigen Rh is common to human and
Macacus Rhesus erythrocytes. No Forssman differential exists in Macacus
erythrocytes or kidney, but there is a hemolysin for sheep corpuscles in
Macacus serum ; however, this hemolysin seems not to behave in the ex-
pected way towards the corpuscles of other species which contain Forssman
differentials. Macacus erythrocytes do not contain blood-group differentials
A and B, and no classification of Macacus blood into groups is possible. As
Eisler has found, human corpuscles have also a differential distinct from the
Forssman differential, in common with Shiga bacilli.

We see, then, that to a certain extent the blood-group distribution is con-
nected with the phylogenetic relationship of animals ; the anthropoid apes have
blood groups more similar to those of man than the lower monkeys and other
animals. However, this is a condition which is not restricted to blood groups,
but which is observed likewise in other organ characteristics ; thus the shape
of the skull and brain, and many other features, are in apes, more similar to
those of man than are those of other animals. On the other hand, this paral-
lelism between relationship and blood-group distribution is not general and,
moreover, we find quite similar characters shown equally by very diverse
organisms, without respect to their relationship.

The investigations in apes and monkeys were preceded by those concerning
the blood groups in other mammals. At first the same methods which had led
to their establishment in man were used also in the case of various animal

488 THE BIOLOGICAL BASIS OF INDIVIDUALITY

blood corpuscles and sera. Employing these methods Hektoen obtained nega-
tive results, but von Dungern and Hirszfeld reported some which were posi-
tive, although the reactions in these animals were weaker and more irregular
than in man. The conclusions became more definite when not only blood
corpuscles and sera from individuals belonging to a certain species of animals
were compared, but when, in addition, the interactions between sera and
blood corpuscles of these animals with the well defined human agglutinogens
and agglutinins were studied ; and furthermore, when use was made of im-
mune sera, obtained in rabbits by injection of human or animal blood cor-
puscles, and when comparative absorptions of the antibodies, present in the
immune sera, by human as well as by animal erythrocytes or their alcohol
extracts were also considered. By these means the identity of certain group
agglutinogens in human erythrocytes and in the erythrocytes of more remote
animal species has apparently been demonstrated, as well as the identity of
certain agglutinins in animal and human sera, while other blood-group dif-
ferentials and agglutinins have been found to be limited to man or to various
species of animals.

However, in some instances it has been possible to establish the presence
of blood groups in animal species by the same methods which have been used
for this purpose in man. Thus Hirszfeld and Przesmycki, and also Schermer
and Hofferber, have shown that in the horse four groups exist, which are
analogous to those in man, namely, O-alpha, beta, A-beta, B-alpha, and AB-oo.
The similarity between the blood groups of man and horse goes still further.
Thus in both of these species, analogous subgroups Ax and A2, and two
agglutinins, alphax and alpha2, can be recognized ; in both instances the differ-
ences between these subgroups are presumably of a quantitative rather than
a qualitative character. Furthermore, in addition to the primary four blood
groups, four additional blood groups, X, Y, Z and N, comparable to the
additional blood groups M, N, P and H in man, are demonstrable in horses
(Schermer and Kaempffer).

Similarly, by means of injections of rabbits with the erythrocytes from other
rabbits, Fischer and Klinckhard prepared immune sera which agglutinated
blood corpuscles from certain groups of rabbits. They believed they were
able in this way to establish the existence of two agglutinogens and two ag-
glutinins, and they divided therefore these animals into four groups, corre-
sponding to the four groups found in man, although neither agglutinogens nor
agglutinins were identical with those of man. However, Levine and Land-
steiner, by immunizing rabbits with the hemolyzed blood corpuscles of other
rabbits, obtained a larger number of agglutinins, and they assume therefore
the occurrence of individual blood differences in rabbits similar to those which
have been established in goats, cattle and chickens, and which we shall discuss
in a subsequent chapter. But there occurs in certain rabbits a condition which
differs from the usual findings in man and in other animals. There may be
observed in these particular animals a peculiar distribution of the A differen-
tial ; it is lacking in their erythrocytes but is present in their organs, and some

BLOOD GROUPS, HETEROGENETIC ANTIGENS 489

of this substance may pass from the organs into the serum. In those rabbits
which contain the A differential, the anti-A agglutinin is lacking in the serum ;
on the other hand, the anti-A agglutinin can be demonstrated in the serum of
those individuals in which the A differential is not present in their organs
(W. Treibman). The latter type of animals can be immunized against the
human A differential, which is strange to them ; while the former type, which
possesses the differential, cannot thus be immunized. These observations
indicate very strongly that the A differential occurring in the organs and
serum of certain individual rabbits, is essentially the same as that occurring in
the erythrocytes of man.

In a corresponding manner, according to Hirszfeld and Halber (1928), the
isoagglutinable substance of sheep and hog is serologically identical with the
isoagglutinable substance A of human blood. The isoagglutinable blood cor-
puscles of certain sheep and hogs absorb all the anti-serum A antibodies
obtained through immunization, whereas the non-agglutinable blood cor-
puscles of other sheep and hogs do not possess this property. Therefore, ac-
cording to these investigators, we must conclude that sheep and hogs actually
possess an A differential identical with that of man.

Still, certain differences seem to exist between the A differential in human
corpuscles of blood-group II and in those sheep corpuscles which also possess
A. While by means of absorption with A-containing sheep corpuscles it is
possible to absorb more antibodies from the serum of rabbits immunized
against the human A differential, than by using for this purpose sheep cor-
puscles which do not contain the A differential, on the other hand, if the
sera of rabbits immunized against A-containing sheep corpuscles are absorbed
with A sheep corpuscles, then all antibodies against the A differential of
sheep corpuscles are entirely removed, but only a part of the antibodies against
human corpuscles of group A is removed. Similarly, from serum of rabbits
immunized against human differential A, the antibody against the A differen-
tial of sheep corpuscles can be entirely removed through absorption with
sheep corpuscles containing A, but there remains, then, still a reaction against
an alcohol extract from human A corpuscles. These observations have led to
the conclusion that there exists not a complete, but only a partial identity
between the A differential in the erythrocytes of man and of sheep; but we
may possibly have to deal merely with quantitative differences between the
A differential as it occurs in man and in certain animal species.

While no isoagglutinable substance was found by direct test in Polish
cattle, indirectly a grouping could be demonstrated in these cattle erythrocytes.
Cattle and sheep corpuscles have a receptor in common, as is shown by the
fact that the amboceptor in the serum of rabbits immunized against sheep
corpuscles hemolyzes not only sheep but also cattle corpuscles, whereas the
anti-Forssman serum, obtained through injection of guinea pig kidney into
rabbit, which also hemolyzes sheep corpuscles, does not affect cattle corpuscles.
Therefore the antigen in sheep corpuscles which gives rise to the formation
of antibodies able to act on certain cattle corpuscles, is not identical with the

490 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Forssman differential, which likewise occurs in sheep corpuscles. But the
antigen common to sheep and cattle corpuscles which gives rise to this
hemolytic amboceptor is not possessed by all cattle, but only by some indi-
viduals. Thus the presence of groups can be demonstrated also in the case of
cattle corpuscles. Cattle contain Bx and B2 receptors. Bx is the differential of
those blood corpuscles which are not hemolyzed by anti-sheep-rabbit serum,
while B2 cattle corpuscles are hemolyzed by anti-sheep-rabbit serum.

In general, in lower animals the agglutinogen B apparently is more fre-
quent than A. Thus in the dog, in the rabbit, and, as mentioned above, also
in New World monkeys, B is .present, and correspondingly the agglutinin
alpha is found in the serum of such individuals ; also in the guinea pig a very
weak B has been noted. More recently the occurrence of B differentials in
erythrocytes and of anti-B in sera has been further analyzed by Friedenreich
and With. It was found that among the B differentials, different subgroups can
be distinguished, namely Bx, B2 and B3. The separation of these fractions was
accomplished by means of absorptions of normal human and animal sera by
human B corpuscles, as well as by B corpuscles from various animal species.
Rabbit corpuscles were observed to contain B2 and B3 differentials, but not
Blf which is peculiar to man. The guinea pig erythrocyte has a weak B dif-
ferential ; also, dog, rat and hog have B components. The same facts apply to
cattle, sheep and goats, although their erythrocytes are not agglutinated by
anti-B serum. In conformity with the lack of Bx in the erythrocytes of these
various species, the sera of the latter possess anti-Bx substance ; only the
chicken serum shows anti-B substance, and correspondingly, the chicken
erythrocytes are free of the B differential. That different kinds of B differen-
tial may be distinguished explains also the occurrence, in some species, of B
in the red blood corpuscles and of agglutinin beta in the serum of the same
individual ; in such cases, B and beta represent different fractions, as for in-
stance, B2 in the corpuscles and anti-Bx in the serum. In this way auto-
agglutination would be avoided.

In Polish chickens the sera of many individuals strongly agglutinate hu-
man erythrocytes O and B, but not A. Conversely, according to Karshner,
human serum belonging to blood-group B-alpha gives the greatest number of
positive agglutinations with chicken erythrocytes, while human sera of blood-
group A, containing anti-B agglutinin, give the least. Dunn and Landsteiner,
by means of anti-chicken-rabbit sera found in several chicken families an
agglutinogen, the hereditary transmission of which was apparently deter-
mined by a single dominant gene. Karshner, by means of isoagglutination
reactions, distinguished three blood groups in chickens, the largest group
consisting of individuals in which neither agglutinogens nor agglutinins
could be demonstrated. On the other hand, Shimidzu did not find that the
weak isoagglutinations which occur in chickens permit the differentiation of
different groups. However, if the agglutination of the erythrocytes of in-
dividual chickens is tested with rabbit-anti-chicken immune sera' or with
various heterogenous sera, individual differences in the majority of all in-
dividuals examined could be found. Such experiments were carried out by

BLOOD GROUPS, HETEROGENETIC ANTIGENS 491

Landsteiner, Miller and Levine, and we shall refer to them again in a later
chapter, where we shall discuss the use of serological methods in the estab-
lishment of individual differences in several species of animals.

Various phases may be distinguished in these investigations into the oc-
currence of blood-group differentials and agglutinins in human and animal
cells and sera. At first it appeared as though the blood-group differentials in
man and in certain animals were identical ; then certain differences were
found and doubts arose as to whether the identity was complete. Thus von
Dungern and Hirszfeld observed that human beta sera are not only absorbed
by human B corpuscles, but also by B corpuscles of various animal species.
But subsequently it was discovered that the beta agglutinin of these animal
sera cannot be absorbed in a corresponding manner by B human and animal
corpuscles. Moreover, from human anti-B immune rabbit serum only B of
human origin and B from some anthropoid apes can absorb the B agglutinin ;
whereas the B corpuscles from other animal species cannot do so. Further
investigations made it then very probable that the agglutinogens A and B
can be subdivided into various fractions and that, correspondingly, the dif-
ferent serum agglutinins can be subdivided ; also, that certain of these second-
ary differentials may be common to human blood and that of various animal
species, while others are peculiar to single species. The question now arises
as to how far it is possible to proceed with this process of subdividing cor-
puscles and sera; it is not improbable that by increasing the number of tests
between corpuscles and sera of man and those of different types of immune
sera against a greater variety of blood corpuscles, employing other species
than the rabbit as donor of the immune sera, the number of subdivisions
may be still further augmented. In addition the question suggests itself as to
whether experiments of this type actually prove the existence of multiple
differentials and agglutinins, or whether we have to deal merely with quantita-
tive differences in the strength of different differentials and agglutinins and
with the presence of substances which may interfere with the absorption
processes in different types of blood.

We have seen, then, that various species of animals, including the human
species, have certain differentials in common, without regard to the relation-
ship of these species. In addition, a connection has been established between
blood-group differentials and differentials of different kinds. Thus a relation
has been noted between the human blood-group differential A and the
Forssman differential of sheep erythrocytes, guinea pig kidney, and certain
cells of other heterogenetic species, and even of some bacteria. Schiff and
Adelsberger first found that through immunization of rabbits with human
erythrocytes A, hemolysins for sheep corpuscles are produced, as well as im-
mune agglutinins for the human corpuscles of Group A. As to whether dif-
ferential A and the Forssman differential are identical, or whether they occur
side by side in the same human corpuscles, it seems, according to investiga-
tions of Sachs and Witebsky, that the second alternative holds good. It can
be shown that some sheep corpuscles which possess Forssman antigen — as
well as other sheep corpuscles which do not possess it — have no human A

492 THE BIOLOGICAL BASIS OF INDIVIDUALITY

antigen ; they absorb only traces of the human anti-A substance preformed in
human serum. This indicates that the Forssman differential and the human
A differential are not identical.

In anti-human A rabbit immune serum which, as stated, contains also
Forssman antibodies, it is possible to remove the latter by absorption with
sheep corpuscles which contain the Forssman differential but do not contain
the human A differential; at the same time the ability of the immune serum
to react with alcohol extract from human corpuscles A is also diminished
by the removal of the Forssman antibodies. Forssman antibodies and anti-
bodies against human A differentials are perhaps in some loose manner linked,
and a certain constituent of the Forssman differential may occur in human
corpuscles belonging to group A. However, it may also be that the common
reactions of group A and Forssman differentials depend merely upon a
similarity in their chemical structure.

In the case of the organismal differentials we have seen that the reactions
against strange differentials are not yet fully formed in very young organisms.
The development of the human blood-group differentials seems to set in at
about six or seven months of embryonal life and to be completed at the time of
birth. But it has been maintained that the full development of the A differen-
tial occurs only at the age of fifteen to twenty years.

As to the agglutinins A and B which circulate in the blood serum, these
originate within the last two months of pregnancy; they develop therefore
later than the differentials present in the cells. In some cases they seem to be
lacking at the time of birth and to be formed only in the first few months of
extrauterine life. According to Thomsen, they reach their full development
only in children between five and ten years of age, and a decrease in the
quantity of these agglutinins may occur in old age; but this age involution
may take place fairly early and may therefore be found even in relatively
young individuals (Schiff and Mendlowitsch).

If agglutinins are found in the blood of the newborn child, they may have
been derived from the mother, having reached the foetus by way of the
placenta. But in case mother and child belong to different blood groups, no
pathological effects seem to result from the combination of agglutinins in the
blood serum and the agglutinogens in the erythrocytes, which, theoretically,
should be expected to act on each other. It is assumed that mechanisms exist
which, as a rule, prevent the passing through the placenta of maternal ag-
glutinins capable of agglutinating the erythrocytes of the child. Von Oettingen
and Witebsky believed that the occurrence of the blood-group differentials
could not be demonstrated in the embryonal part of the placenta, although
they are found in the maternal decidua. According to Kritschewsky, it is the
Forssman differential which is present in the decidua and not the blood-group
differential, while the embryonal placenta is free of the latter. However,
Levine has found that the Rh antigen may pass in the uterusr from the child
to the mother. If the latter does not possess this antigen, antibodies may be
produced against it, which then pass in the opposite direction from the
mother to the child and here may cause erythroblastosis foetalis.

BLOOD GROUPS, HETEROGENETIC ANTIGENS 493

In regard to the time of development of the blood-group differentials and
of the corresponding agglutinins in the blood serum, this shows some paral-
lelism to the time of origin of the organismal differentials. The experiments of
Blumenthal have shown that the latter are not yet fully developed during the
first stages of embryonal development, but can be demonstrated during the
second half of the intrauterine life of the embryo. From Murphy's experiments
on the transplantation of heterogenous tissues to the allantois, and from
similar experiments of various embryologists, we may conclude that in early
embryos the species differentials, or rather certain mechanisms of reaction
against such differentials, are not yet developed, and also that the bodyfluids
are not yet injurious to the strange transplant, but that not very much later
the harmful mechanisms develop in the embryo. However, as we have seen,
even during post-embryonal life the reactions against strange individuality
differentials are not as strong in very* young animals as in adults. In all these
cases it is necessary to distinguish between the presence of the organismal
differentials and of the reactions against the latter on the part of the strange
organism. The reactions may not yet be fully active at a time when the dif-
ferentials have already been completely formed.

One of the characteristic features oi individuality differentials, and or-
ganismal differentials in general, is the lack of an injurious reaction of the
bodyfluids as well as of the cells of the host against cells or tissues which are
derived from the same organism, and which possess therefore the same in-
dividuality and the various other organismal differentials. This fact is ex-
pressed in our definition of individuality and organismal differentials. Simi-
larly, it is well known that, as a rule, it is not possible to produce antibodies
against autogenous normal cells, or against substances which represent a
normal constituent of the animal to be immunized, especially if it is accessible
to his bodyfluids. This applies also to the Forssman differentials, against which
antibodies can be produced only in those species which do not possess this
differential ; and the same holds good presumably in the case of the blood-
group differentials. It is a very interesting fact that if the blood cells of an
individual contain a certain agglutinogen, his blood serum lacks that particular
agglutinin which would interact with its own blood corpuscles and cause their
agglutination, and that thus the formation of agglutination thrombi and
emboli is avoided (Landsteiner). As we have discussed in an earlier chapter
Bernstein assumes that in every individual, to whatever blood group he may
belong, all the agglutinins are produced, including those which are able to
agglutinate his own corpuscles; but the latter kind of agglutinins are made
innocuous by union with the corresponding agglutinogens present in the
erythrocytes of the same organism, and only agglutinins which would act on
corpuscles belonging to other groups are left intact. Against this interpretation
may be cited the observation that injection of rabbits with human blood cor-
puscles of group A seems to cause the formation of anti-A immune agglutinins
only if the serum of these rabbits contains normally some anti-A antibodies,
which implies that the cells of this animal do not contain A receptors. But
if actually the A agglutinin was able to develop in a rabbit which possesses A

494 THE BIOLOGICAL BASIS OF INDIVIDUALITY

agglutinogens and it was merely hidden by its union with these agglutinogens,
then it should be possible by means of an intense immunization to produce
enough anti-A agglutinin to overbalance the slight amount of A receptor pres-
ent in the blood plasma. Or if it is assumed that the red blood corpuscles
themselves can bind and inactivate this immune agglutinin, then an ag-
glutination of the erythrocytes should take place in the immunized animal.
Such an effect however seems not to have been observed. Similarly, as men-
tioned already, antibodies for the Forssman antigen cannot be produced in
animals which belong to a Forssman positive species, although in this case
erythrocytes do not need to contain the heterophile differential.

Taking these various considerations together, we think it much more
probable that in the case of the blood groups we have to deal with the same
phenomenon as in the case of the organismal differentials, namely, that in the
same organism mutually incompatible constituents do not develop, and that
the normal constituents within the body, especially if they are present also
in the bodyfluids, cannot serve as antigens, and that this is due to the fact
that in the same organism the analogous proteins and, in particular, certain
globulins possess some essential similarity in chemical structure irrespective
of their situation in the individual. The production of antibodies can take
place, as a rule, only when these differentials show a definite divergence in
chemical constitution in host and donor.

Organismal differentials, primary blood-group differentials, the more re-
cently discovered accessory differentials occurring in human and also in
certain animal erythrocytes, as well as the heterophile Forssman differentials,
all have this characteristic in common, that they are genetically fixed con-
stituents of the various organisms and do not owe their origin to environ-
mental factors. As to the mode of inheritance, there are differences between
the organismal, and in particular, the individuality differentials and the pri-
mary as well as the accessory blood-group differentials. The individuality dif-
ferentials depend, as we have discussed previously, upon the presence of
multiple factors, the number of which must be considerable. On the other
hand, the inheritance of the primary blood-group differentials seems to de-
pend upon three allelomorph factors, according to the analysis of human
inheritance by Bernstein, whose interpretation has now been almost generally
accepted. The inheritance of the primary blood-group differentials follows
therefore a much simpler scheme than the inheritance of the individuality
differentials. Among the latter many fine gradations exist, while among the
former there is only a small number of variables. According to Landsteiner,
Schiff, and other investigators, the inheritance of the accessory factors M and
N is contingent on the presence of an allelomorph pair of genes. The possible
combinations of these two genes are M M, N N and M N. The factor P also
seems to be fixed by heredity. It has been observed that when neither of the
parents contains P, none of the children contain it. The factor H is believed
to be represented by a single dominant gene. We may then conclude that
the mode of inheritance of the primary blood-group differentials differs not

BLOOD GROUPS, HETEROGENETIC ANTIGENS 495

only from that of the individuality differentials, but also from that of the
accessory blood-group differentials.

There are found, thus, in human erythrocytes, a number of different differ-
entials. We have mentioned the occurrence of species differentials, of the
typical blood-group differentials, of the accessory blood-group differentials,
of the Forssman differentials, and of certain special differentials which human
erythrocytes and erythrocytes of some distant animal species have in com-
mon. In addition, we must consider the possibility of the occurrence of organ
differentials in various types of human cells. In this connection the observa-
tions of Jacobs are of interest. He compared the ability of the erythrocytes
of many different species to absorb various kinds of chemicals and he found,
on the whole, that the corpuscles of related species resemble each other more
in their permeability to and absorbing powers of certain substances than do
the erythrocytes from animals more distant phylogenetically, although a
strict grading according to phylogenetic relationship is not possible. The red
blood corpuscles behave in this respect like some blood-group differentials
and characteristics of organs which may show a certain correspondence to the
phylogenetic development of these cells and organs. But a gradation in the
organismal differentials present in the erythrocytes according to the relation-
ship of the various species would also explain this phenomenon.

This is in all probability a very incomplete list of the differentials oc-
curring in erythrocytes and we may assume that besides those named, there
occur other differentials. Of special interest for us is the question whether
also individuality differentials are present in human erythrocytes. Experiments
which we have discussed in an earlier chapter make this very probable. Do
transfusion experiments give any indication of their presence? There are some
observations concerning injurious results following transfusions of apparently
compatible blood which suggest such a possibility ; but other interpretations
of these occurrences, such as the presence of an agglutinogen common to
man and Rhesus monkey in the blood of the donor, or of an immune ag-
glutinin in the blood of the person which received the transfusion, or the
presence of agglutinogens A and B in human blood plasma used for intra-
venous injection (M. Levine and D. State), cannot be excluded.

We shall now briefly summarize our conclusions concerning (1) the rela-
tions between blood groups and organismal and, in particular, individuality
differentials; (2) the relations between blood groups and what is designated
as "constitution," and (3) the general significance of the antigens discussed in
this chapter.

(1) The primary blood-group differentials do not make possible a dis-
tinction between different individuals in general, but only between some
individuals ; they do not indicate the degree of relationship between individuals ;
they differ in these and in other respects from the individuality differentials.

However, if in addition to the primary blood-group differentials, we con-
sider other types of differentials which may be found in erythrocytes, such as
the accessory blood-group differentials, the Forssman and accessory hetero-

496 THE BIOLOGICAL BASIS OF INDIVIDUALITY

genetic antigens, it is possible that all of them combined, or even a certain
number of them, might suffice to distinguish individuals, but they would
not in all probability indicate the relationship of these individuals. But there
is reason for assuming that also a combination of various organ differentials
might differentiate between different individuals, although they would not
be identical with the individuality differentials. To demonstrate the identity
of the former with the individuality differentials, the proof would first have
to be given that they are qualitatively the same in all the essential tissues of
the same individual, and different in all other individuals ; furthermore, that
these sets of blood-group differentials are actually the ones which function
in the various individuals as individuality differentials, or that they are an
important constituent of the individuality and species differentials. This is very
improbable as far as the primary blood groups are concerned, because, as
we have seen, the results of homoiotransplantations are independent of the
distribution of these differentials; besides, the presence of similar blood-
group differentials in different species of animals does not affect noticeably
the severity of the reaction following heterotransplantation in such species.
The Forssman antigens, which are characteristic of very diverse species, can
be removed or neutralized by means of specific absorption without the species
differentials being affected by this procedure. However, as already stated, if
the number of blood-group differentials serving as agglutinogens or able to
give rise to the production of hemolysins is greatly increased in the individ-
uals belonging to a certain species, then it is possible that such sets of poten-
tial antigens may more and more coincide with the factors composing the in-
dividuality differentials.

To recapitulate : There are at least four requirements which have to be
satisfied before a set of differentials can be accepted as representing the
individuality differentials : (a) they must make possible the distinction be-
tween individuals; (b) they must occur in all or almost all the tissues of an
individual and thus allow the distinction of the tissues of one individual from
the different tissues of another individual ; (c) they must indicate the relation-
ship of a particular individual to another individual, and (d) their inheritance
must not depend upon a very small number of factors which are transmitted
in accordance with simple Mendelian rules of alternate inheritance. The pri-
mary blood groups, and even the accessory blood-group differentials, as well
as the various heterogenetic antigens have not, so far, been shown fully to
satisfy these requirements. However, the possibility cannot be excluded that
blood-group differentials may be a constituent part of the individuality dif-
ferentials. It seems that a comparison of the ability of the erythrocytes to
absorb various chemicals, and presumably also other physiological or phar-
macological tests, indicate better the phylogenetic relationship of the species
from which the red cells to be tested are derived, than the study of the relations
between blood-group differentials and blood sera of various species of animals.
As we have stated in a preceding chapter, various tissue and organ differentials,
whether their significance is due to structural, biochemical or functional con-

BLOOD GROUPS, HETEROGENETIC ANTIGENS 497

ditions, may serve to distinguish between individuals, and inasmuch as these
characteristics have a genetic basis, they might in a limited way even indicate
certain relationships between individuals. But they would not, therefore,
become identical with individuality differentials. The four primary blood-
group differentials are essentially tissue differentials, which have however
certain characteristics in common with the individuality differentials while
they differ from the latter in other respects; but the larger the number of
accessory blood-group differentials which are added to the primary group, the
greater will, in all probability, become the similarity between blood-group
and individuality differentials.

(2) Some authors have identified the blood-group differentials with the
constitutional characteristics of a certain individual. The constitution of an
individual means an inherited or acquired constellation of structures which de-
termine his characteristic modes of reaction or tendencies, including those of
an abnormal kind. These inherited or acquired modes of reaction or tendencies,
as a rule, become manifest only in their interaction with variable factors of the
inner and outer environment. The emphasis is laid in this definition of con-
stitution on the reaction-modes ; but constitution may also mean that a certain
reaction-mode of an organism is associated with a specific inherited habitus or
structural feature, and in this case tne emphasis is laid on the structural
aspect. Only in the sense that the blood-group differentials are an inherited
characteristic may they be considered as part of the constitution, without,
however, representing the whole or even the essential features of the con-
stitution. Probably because of the readiness and sharpness with which the
blood-group differentials .can usually be determined in human beings, and
because of the role they play in blood transfusion and because of the in-
herited differences in their distribution among different individuals were they
considered as specially representative of the constitution of individuals or
races. However, there is more justification for the belief that the various
kinds of organismal differentials represent to a much higher degree the con-
stitution of an individual, or a race, or of a species, than do the blood-group
differentials.

(3) Individuals and species may have special genes or gene combinations in
common which determine the formation of special differentials and antigens
as revealed by serological methods. The latter indicate particular relation-
ships between these individuals and species or they can be used as a means
of distinguishing between these individuals and species. The main problem
which we have discussed in this chapter concerns the connection between
such special differentials and the organismal and in particular the individual-
ity differentials and the relationships which the various differentials have to
one another which may render them significant in the analysis of individuality.

Chapter 2

The Demonstration of Species Differentials by

Serological Methods

At the end of the last and in the beginning of this century, when our
knowledge of experimental immunity began to develop and it was
^ found that immune bodies could be produced not only against bac-
teria but also against cells, which are normal constituents of the body of
higher animals, and against proteins, such as those of the blood, the problem
arose more definitely as to the chemical basis for the differences and the rela-
tionships between various animal species and as to the possibility of ap-
proaching this problem by the methods of immunology. It was important to
know whether the relationship between different species and classes of ani-
mals, which so far had been studied mainly by the morphological methods
of comparative anatomy and embryology, could be measured also by sero-
logical methods and whether the results obtained by these two methods
agreed with each other. The chemical constitution of the cells and proteins
serving as antigens, and the antibodies produced by the injection of these
antigens into other animals should then correspond to the systematic relation-
ship of the various species and they should show similar gradations.

Friedenthal in 1900 first studied the relationship of animal species by testing
the compatibility between the transfused blood of a foreign species and the
blood of the host species. Hemoglobinuria resulting from hemolysis of the
strange blood corpuscles would signify incompatibility between the blood
sera and the red blood cells of the two species. He also found in in vitro tests
that only the erythrocytes of anthropoid apes resist solution by human sera,
while the blood corpuscles of lower monkeys are dissolved. In these investiga-
tions the relation between preformed constituents of sera and erythrocytes was
used as a test, rather than the reactions between an antigen and the immune
substances resulting from injection of the antigens into a foreign species.
Gruenbaum, in 1902, first used the precipitin test in analyzing relationships
between species. This method depends upon the production, in an animal
injected with blood serum from another species, of substances (precipitins)
which have the power to precipitate specifically certain constituents of the
serum used for injection. Neither Gruenbaum nor subsequent investigators
were able to differentiate between man and anthropoid apes in this way. Two
years later, Nuttall published the results of very extensive systematic studies,
in which by means of precipitins he tested the relationship of many species,
not only of vertebrates but also of invertebrates. In general, his findings con-
firmed the conclusions of zoologists as to the phylogenetic relationship of ani-
mals, which were based on morphological criteria. This method was

498

DEMONSTRATION OF SPECIES DIFFERENTIALS 499

subsequently employed for similar experiments by Uhlenhuth and his col-
laborators. They introduced a refinement in the precipitin test by obtaining
the precipitins from animals belonging to one of the species whose blood was
to be tested or from a related species. For this purpose, cross-immunization
was used between two species, the relationship of which was to be studied
by the precipitin test, each of the two species being injected with the blood
serum of the other species. This method eliminated the coarser reactions
which led to the production of less specific precipitins in farther distantly
related animals which had been immunized against blood serum. Thus, by
immunizing rabbits with hare serum Uhlenhuth could obtain specific precipi-
tins for hare blood, although it was not possible to distinguish between in-
dividual rabbits. Similarly, through a slight modification of the same method,
Black succeeded in differentiating Negro chickens from Italian chickens,
individuals belonging to a third chicken species being immunized against
Negro and Italian chickens. Subsequently, further refinements were intro-
duced by Boyden, Hektoen, Wolfe, and Wilhelmi. The specificity of the
precipitin test was enhanced by limiting the amount of protein injected into
animals to be immunized, by dilution of the anti-sera, by using reciprocal tests
and quantitative methods of determination, by removing the lipids from the
antigens and in addition also by employing a nephelometric method of meas-
urement. In some instances it was possible to distinguish between the serum
proteins of such closely related animal species as ox, sheep and goat, and in
some cases even between the proteins of buffalo and ox serum. With these
improved methods it was also possible to differentiate between nearly related
species of birds and of reptiles, classes of animals which had not been found
very suitable in the experiments of Nuttall. By considering also the results of
cross-reactions and of absorption or exhaustion tests of immune sera against
egg albumins of various species of birds, differentiation between these species
was possible (Hooker and Boyd, Landsteiner and van der Scheer). In using
these precautions, the ring-test for the detection of precipitates permits not
only the determination of relationships, but also the degrees of relationship
between various species.

Still, it was found impossible to distinguish in every case by the ordinary
precipitin method between man and anthropoid apes, and between horse and
donkey. On the other hand, certain differences were more readily found
between man and lower monkeys, and the Old World monkeys were shown
to be more nearly related to man than the New World monkeys. It was also
possible to distinguish between rat and mouse, and in recent experiments
Landsteiner and Levine observed, in one case, that by the use of Uhlenhuth's
method precipitins could be produced which differentiate the blood sera of
man and chimpanzee. These investigators immunized a chimpanzee with
human serum proteins and thus obtained an immune serum which precipitated
only human serum but not chimpanzee serum. However, this differentiation
could be much better accomplished by applying the Uhlenhuth method to the
production of hemagglutinins. Furthermore, Hicks and Little traced, by
means of the precipitin test, the relationship and origin of different species

500 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of mice. By immunizing rabbits, they believe that they succeeded in differen-
tiating between Mus musculus and Mus bactrianus ; however, Mus musculus
could not be differentiated from Mus farvensis and Mus bactrianus behaved
like the Japanese waltzing mouse. These investigators concluded, therefore,
that Mus musculus is closely related to Mus farvensis, and Mus bactrianus to
the Japanese waltzing mouse. But, as Boyden remarks, this serological differ-
entiation of two so nearly related species is unusual and needs confirmation.
By reducing very much the quantities of antigen used for immunization Wolfe
was able to distinguish, by means of the precipitin reaction, between gray
squirrel and red squirrel, and also between ox and sheep, but not between
goat and sheep.

By means of reciprocal immunization Boyden found the dog to be more
closely related to the pig than to the horse; still further distant from dog
were beef and sheep ; beef was nearest related to sheep, then followed horse
and pig and dog. However, Boyden is careful to state that these tests merely
indicate the relationship of these animals as they are constituted at present, and
that they do not necessarily correspond exactly to the phylogenetic evolution
of these species. Greater are the difficulties of distinguishing, by means of
the precipitin reactions, species among reptiles and amphibia, if rabbits are
used for immunization, although to some extent this, too, can be accomplished.
This method, supplemented by absorption tests, made it also possible to dif-
ferentiate between the hemocyanins present in the blood of various arthropods.
Within a certain range there existed a relation between the strength of
the precipitin reaction and the phylogenetic nearness or distance of the species
used.

Different species of birds could be especially well differentiated serologically
(Defalco), more readily than mammals, amphibians or fishes; it is therefore
believed that birds represent a very homogeneous group. Blood serum, crystal-
lized egg albumin and lens of the eye, or hemoglobin, when used as antigens,
gave essentially similar results, except that in serum several proteins were
present, which introduced certain complications, while egg albumin and
hemoglobin represented essentially single proteins. Among invertebrates sharp
differentiations could be made between species belonging to different genera
as well as between others which belonged to the same genus. On the strength
of his tests of helminth species, Wilhelmi believed that it was possible to
define quantitatively the dilution of the antigen in the precipitin reaction
which was characteristic of species differences. The results obtained with the
precipitin reaction were also in conformity with the conclusion that echino-
derms, and especially holothurians, were more closely related to prochordates
than were annelids. In general, then, serological tests confirmed and made
more secure earlier conclusions based mainly on structural studies.

The relationships of plants have been studied very extensively, by Mez
and others, by means of precipitin tests, and they have thus traced the
phylogenetic evolution of the vegetable kingdom. In contrast to the experi-
ments in animals, where usually body fluids or some of their constituents were
used as antigens, Mez employed for his determination, extracts of young,

DEMONSTRATION OF SPECIES DIFFERENTIALS 501

growing parts of plants, in which storage of proteins, and possibly also of
other substances, is as yet less prominent than in fully developed parts, and
especially less prominent than in seeds. Before using material from growing
parts as antigen he freed it from its fatty constituents through extraction
with alcohol and ether, and this procedure greatly increased the specificity of
the reaction, which, as in the case of animal serum reactions, depends pri-
marily upon the proteins contained in the antigen solutions. Mez assumed
that the increase in specificity of the reaction, caused by previous absorption of
the lipids from the tissue furnishing the antigen, is due to the lack of species-
specificity of these lipid substances. By means of this method, Mez attempted
to trace the development of plants from bacteria to algae and mosses, and
from these to the higher organisms. More recently, Steinecke has extended
these investigations. According to Boyden, these phytoserological studies have
yielded data of crudely quantitative nature which support the concepts of
plant phylogeny advanced already on the basis of morphological studies. In
a similar way Wilhelmi found that the previous extraction of lipids from the
antigens increased the value of the precipitin reaction as a method for deter-
mining phylogenetic relationships of helminths. After the lipids had been
removed, the proteins acted as potent species-specific antigens, whereas the
presence of lipids interfered with this reaction, because these substances by
combining with a protein could function as haptens, which are less effectively
species-specific and may be organ-specific.

In general, we may then conclude that substances of protein character,
which differ in their constitution in different, not too nearly related species,
may serve as antigens and lead to the production of precipitins which react
specifically with the antigen by the formation of precipitates. If we compare
the interactions of different antigens with the same immune serum, we notice
that the strength of these reactions indicates the graded relationship of these
antigens and of the animals from which they were obtained. By the introduc-
tion of certain refinements in the methods used, distinction may be made in
this way also between more nearly related species, although as a general
rule it is possible by the ordinary precipitin methods to distinguish only be-
tween species belonging to different orders, and it may be difficult to estab-
lish fine gradations even between different orders. In principle, then, these
antigens behave like the coarser types of organismal differentials.

Soon after the precipitin test had been introduced as a serological test for
phylogenetic relationship, Marshall, in the laboratory of Ehrlich, used for the
same purpose, hemolysis, the solution of red corpuscles by means of pre-
formed or of immune sera. Thus he found a close relationship between the
antigens present in the erythrocytes of man and of Macacus monkeys. How-
ever, certain differences were observed in the hemolyzing power of active
monkey serum for human and monkey erythrocytes, respectively, and differ-
ences between these two kinds of blood were established also by absorption
tests, in which different antibodies present in the same immune serum could be
separated from each other by specific absorption with erythrocytes from
different species, to which these antibody fractions had specific affinities.

502 THE BIOLOGICAL BASIS OF INDIVIDUALITY

More recently, Landsteiner and Miller were able to differentiate between
the blood of man, of chimpanzee and orang-utan by means of immune hemag-
glutinins, which they produced in rabbits, against these various types of
erythrocytes, but it was necessary first to remove, by specific absorption, the
non-specific agglutinins which these species had in common. These investi-
gators found that the differences between the blood of man and chimpanzee
or orang-utan are less marked than those between these species and the
lower monkeys. As mentioned above, Landsteiner and Levine furthermore
succeeded in obtaining hemagglutinins which agglutinated only human but
not chimpanzee erythrocytes, by injecting a chimpanzee with human erythro-
cytes, in this manner applying Uhlenhuth's method to the hemagglutinin test.
In still another and more simple way they were able to differentiate between
human and chimpanzee blood by the use of the preformed heteroagglutinins
which occur in ox serum. After absorption with chimpanzee erythrocytes, ox
serum still agglutinated human corpuscles very strongly and, conversely, after
absorption with human corpuscles it was still active towards chimpanzee
blood.

Certain additional methods were employed for the purpose of grading the
relationship of antigens derived from different species. Thus alcohol extracts
of various types of blood corpuscles in combination with a foreign serum,
the protein of which served as carrier, could be used as antigens for the
production of hemolysins. When these alcohol soluble, partial antigens were
acted upon by the specific, heat-inactivated hemolytic immune sera, a floccula-
tion and also a fixation of complement occurred, which were specific. Specific
complement fixation has been employed for the testing of graded relationships
of antigens by various investigators. Many years ago, Bruck believed that it
was possible to demonstrate, through complement fixation, differences even
between the blood of different human races, such as European, Malay, Arab
and Chinese. However, this observation could not be confirmed by Marshall
and Teague, nor by Fitzgerald ; nor were Landsteiner and Miller able by
serological methods to demonstrate differences between the blood cells of the
white race and the Negro.

A further test for the specificity of antigens, especially of haptens which
are non-protein components of antigens, was introduced by Landsteiner. Such
haptens, which when injected alone into an animal belonging to a foreign
species do not call forth the production of antibodies, do so if they are
combined with a foreign protein acting as the carrier of the specific substance.
But even without the aid of a carrier they may be able to inhibit in a specific
manner the reaction between the antigen and the specific immune serum,
irrespective of whether this reaction consists in precipitation, hemolysis, or
hemagglutination.

Also, anaphylactic reactions have been used, especially by Wells and Os-
borne, for the testing of the organismal specificity of certain substances. These
investigators worked with alcohol soluble proteins from various seeds, such
as gliadin from wheat and rye, hordein from barley, zein from maize. First
they showed that the occurrence of anaphylactic shock in sensitized guinea

DEMONSTRATION OF SPECIES DIFFERENTIALS 503

pigs depended upon the chemical relationship between the substances used
for sensitization and for reinjection, irrespective of the species of the plant
from which the substances had been obtained. Thus, for instance, gliadin
and hordein, although they occur in seeds of different species, could not be
differentiated by means of anaphylaxis, because their chemical structure was
similar. Corresponding results were obtained with other substances resem-
bling albumoses in their reactions, which likewise were isolated from seeds ;
however, these substances were not, in all probability, split products of pro-
teins, because real albumoses or peptones seem to lose their power to sensitize
the guinea pig. With these materials from seeds, bcause of their solubility
in water, anaphylactic reactions could be obtained much more readily than
with the above mentioned alcohol soluble substances. The tests indicated that
these albumose-like substances are quite distinct immunologically from the
alcohol soluble substances, although both occur in the same kinds of seeds.
A relative overlapping of reactions in experiments was apparently due to
impurities, it being impossible to separate completely the first and the second
type of substances.

Wells and Osborne concluded, then, that the specificity in the anaphylactic
reaction depends primarily not on the biologic origin, but on the chemical con-
stitution of the substances used for sensitization and the production of shock.
But, the chemical constitution furnishes the basis for the biological specificity,
and biological specificity depends upon the constitution of tissue constituents,
and there should therefore be expected a correlation between the chemical
constitution of plant proteins and the systematic position of the plants in
which these substances originated. When, in the case of these plants substance-
specificity was prominent, whereas species-specificity was not manifest, it
may be assumed that besides the biologically important seed proteins, which
could not be differentiated, there were other chemically distinct substances
present in the embryo proper, which were not indicative of organismal dif-
ferentials. In experiments with proteoses there was a slight interaction be-
tween those of pea and soy bean, two nearly related substances, and in more
recent investigations Lewis and Wells found more definite evidence of a
correlation between chemical constitution and systematic relationship.

By means of various anaphylactic methods, such as the uterus strip method
of Dale, the bronchospasm method and the production of shock, as well as by
the use of the complement fixation tests, these investigators observed that
the alcohol soluble proteins from certain cereal grains can be separated into a
wheat group and a corn group. The various proteins of the wheat group could
not be differentiated from one another by immunological methods, nor could
the members of the corn group be thus distinguished. On the other hand,
there were sharp distinctions and a lack of cross reactions between two
proteins which belonged to different groups ; analogous proteins in related
species behaved immunologically in the same way, but they were distinct
from the proteins of further removed species. These results agree with the
chemical analysis of these substances by Gortner and Hoffman, which showed
the great chemical resemblance of the analogous alcohol soluble substances

504 THE BIOLOGICAL BASIS OF INDIVIDUALITY

in the various species of the wheat group and their differences from those
belonging to the corn group. However, Gortner also refers to differences in
the number of chromosome sets which exist between different members of the
wheat group and to corresponding differences in hybridizability between these
species. It seems, then, that here cytological differentiations and the mode of
interaction of spermatozoa and ova of various species during fertilization are
much finer tests for the constitution of organismal differentials than the
chemical analysis of the alcohol soluble proteins, or the serological methods,
such as anaphylaxis or complement fixation.

In the case of some animal substances, Dakin and Dale, using the uterus
strip method for the diagnosis of an anaphylactic state, were able to differen-
tiate between the crystalline egg albumens of hen and duck. The specificity of
this reaction could also be shown by means of specific desensitization. In more
recent years, Landsteiner's demonstration that certain antigens are complex
and consist of a combination of non-protein hapten and a foreign protein
which acts as a carrier, was followed by attempted immunization against these
complex antigens, and in this connection use was made also of anaphylaxis
as a test for the specificity of various antigens and of the relative significance
of these two component parts of the antigen.

In such experiments, in order to sensitize a guinea pig against a hapten, it
was necessary to inject the latter in association with a foreign protein, the
hapten alone not being able to cause sensitization. As to the means of produc-
ing shock in actively or passively sensitized guinea pigs through a second
injection of the antigen, somewhat divergent results were obtained. Land-
steiner could, in some cases, but not in all, produce anaphylactic shock in
guinea pigs sensitized with an azodye-protein combination by injecting the
azodye alone. It has even been maintained that it is possible to sensitize
guinea pigs by injection of diazotized atoxyl alone and, moreover, to cause
shock in animals thus sensitized by injection of the same substance; it was
further assumed that under these conditions the injected animal's own serum
may act as carrier. In guinea pigs sensitized against the polysaccharides,
which are responsible for the type-specificity of pneumococci, it was necessary
to inject the animal with the same kind of polysaccharide, in combination with
a protein, for the production of shock. On the other hand, intradermal injec-
tion of the type-specific pneumococcus polysaccharide alone could bring about
a specific inflammatory skin reaction.

However, a specific glucoside, which itself was not able to produce shock
nor, correspondingly, to cause precipitation with antisera, inhibited in a specific
manner the condition of shock, which otherwise would have resulted in
sensitized guinea pigs, by the injection of the glucoside in association with a
protein (Tillet, Avery and Goebel). Similarly, the hapten inhibited precipita-
tion, which would ordinarily have resulted from the precipitin-antigen com-
bination.

In the case of streptococci the specific carbohydrate, without the addition of
foreign protein, could induce shock in passively sensitized guinea pigs, pro-
vided the immune serum used for passive immunization had been very effec-

DEMONSTRATION OF SPECIES DIFFERENTIALS 505

tive (Lance field). Also, specific nucleo-proteins isolated from streptococci
could readily serve as sensitizers and likewise induce shock.

In general, it seems then that the specificity of the anaphylactic reactions
is of about the same order as that of the ordinary precipitin and complement
fixation tests. There is no indication that by means of the anaphylactic
reaction it may be possible to differentiate between individuality differentials,
although this reaction may very well serve for the demonstration of species
differentials and of chemical substance-specificity.

Wells and Osborne were able to find in every case in which two sub-
stances were specific, as far as the anaphylactic test indicated such specificity,
a definite chemical, in contrast to a mere stereoisomeric constitutional differ-
ence between these two substances ; and this was true not only of the alcohol
soluble plant proteins, but also of five substances derived from ovomucoid.
From former data it might have been expected that also stereoisomeric dif-
ferences between substances might give rise to specific serological reactions,
and, as we shall see later, Landsteiner subsequently succeeded in demonstrat-
ing effective stereoisomeric differences in haptens by means of the precipitin
reaction.

There still remains one point to be discussed. We have noticed that in the
experiments of Wells and Osborne, and in those of Lewis and Wells, the
specificity of the reactions was either absolute, one substance sensitizing
exclusively against the substance used for the production of anaphylactic
shock, or the reaction did not make possible the distinction between analogous
substances from related plants. The quantitative gradations in the reactions
corresponding to the gradations in phylogenetic relationship seemed to be
lacking entirely in the earlier experiments, although there was an indication of
such gradations observed in the later work. Wells, Osborne and Lewis used
in their experiments purified substances rather than mixtures of substances
as they occur in ordinary extracts from blood or organs. Their findings might
suggest that the gradations which are so commonly observed in the case of im-
mune reactions, result from the use of mixtures of antigens as they are present
in the tissues and bodyfluids of organisms ; from this point of view the graded
relationships of different species would depend upon differently constituted,
quantitatively graded mixtures of various substances which are characteristic
of these species, and not on gradations in the structure of a complex protein
or on a combination of a specific hapten of a non-protein nature, which
differs in a graded way in different species, with the same or a similar protein
serving as carrier. However, this conclusion would not be in agreement with
some other well established facts. Thus we may recall the immunological
differences between the whites of chicken and duck eggs, as shown in the
anaphylaxis experiments of Dakin and Dale. Such differences are graded,
although these investigators used crystalline substances in their experiments ;
in this case, therefore, the gradation in the reactions must have depended
in all probability on graded differences in the chemical structure of single
substances.

We have seen that by means of immunization it is possible to demonstrate

506 THE BIOLOGICAL BASIS OF INDIVIDUALITY

in the sera of the immunized organism the presence of immune substances
which react specifically with the antigens used for their production, but which
also react more weakly with analogous substances from related species in a
graded manner, in accordance with the graded relationships of the various
species. How do preformed agglutinins and hemolysins behave in this respect ?
Do they show the same degree of specificity as do the immune substances?
There are present in the sera preformed antibodies which react with group
antigens in the erythrocytes. The question now arises whether there exists a
specific adaptation between preformed antibodies in sera, on the one hand,
and erythrocytes and other cells, on the other, in accordance with the system-
atic relationship of the organisms from which the sera and cells are derived.
Such a specific adaptation would be comparable to that which obtains be-
tween constituents of the plasma and tissue coagulins, and which becomes
manifest in the coagulation of the blood. We have already discussed the fact
that a specifically graded relationship between blood sera and erythrocytes of
various species, corresponding to the phylogenetic relationship, has not yet
been demonstrated by means of hemagglutination. Marshall likewise found
that normal heterogenous sera of goat, sheep, goose, or rabbit were equally
hemolytic for human and Macacus blood. Landsteiner observed that normal
hemagglutinins absorbed by certain erythrocytes and then dissociated from
this combination by elution, are active with the red corpuscles from numerous
near and distant species. Thus solutions of agglutinin obtained by washing
rabbit erythrocytes, which had previously been agglutinated by beef serum,
acted intensely with both rabbit and frog erythrocytes. Landsteiner concluded
therefore that agglutination or failure of agglutination of erythrocytes by the
normal serum of another species is almost independent of the systematic re-
lationship of those species. As far as agglutination of erythrocytes is con-
cerned, this lack of agreement is understandable, since within the same species
corpuscles from different individuals differ from each other as regards their
agglutinability by the sera of other individuals of the same species, and since
not only agglutinins exist in the sera of various species which agglutinate
human red corpuscles, but heterogenous sera in general may agglutinate
corpuscles from other species, irrespective of systematic relationship. Like-
wise, the presence of Forssman differentials and of other antigens of a similar
kind, which, as we have seen, do not conform to the laws of systematic re-
lationship, may interfere with and prevent a parallelism between the reactions
of sera on cells of a heterogenous nature and the systematic relationship of
the various species, genera, orders and classes of animals from which the
sera and cells are derived. Thus, according to Klopstock and Lehmann-
Facius, the sera of species possessing Forssman antigens dissolve cells of
various species, irrespective of whether they belong to the heterogenetic or
the non-heterogenetic series ; on the other hand, sera from non-heterogenetic
species dissolve only cells from heterogenetic species. But in addition, another
factor may interfere with the manifestation of a parallelism between the
toxicity of heterogenous sera and the systematic relationship of two species.
There seem to occur in the same serum multiple constituents, each one directed

DEMONSTRATION OF SPECIES DIFFERENTIALS 507

against the erythrocytes — and presumably also against other cells — of a
certain species. Thus specificities, if they exist, may be obscured by the ex-
istence of a multiplicity of preformed antibodies which may interfere with
one another. Accordingly, Landsteiner and Levine found, as stated above,
that a serum after absorption with chimpanzee erythrocytes, acted much less
on chimpanzee than on human blood, and the converse effect was seen after
absorption with human blood cells. Also, in other instances when sera and
cells of sheep, goat, fox and dog were used, it has been possible through
absorption with erythrocytes, or in some cases, with other cells of a certain
species, to remove from a serum, in a specific way, the agglutinins acting on
the cells of this species, while leaving behind the agglutinins for the erythro-
cytes of another species. In some instances however, this absorption did not
act in such a specific manner, but with the specific agglutinins for the cells
of one species there were removed also those acting on the cells of a different
species.

Furthermore, when once a definite threshold of strangeness has been
reached, a finer differentiation among the strange species, as to the degree of
toxicity of substances present in their sera or cells, will hardly be possible.
This applies as far as preformed substances in sera and cells are concerned,
but not in the case of immune sera. In a similar way, we found that in
heterotransplantation the conditions existing in the host are so intensely in-
jurious for the transplant that finer gradations in the degree of injuriousness
of different species, in accordance with the systematic relationship between
host and transplant, are very difficult or even impossible to accomplish.

As to the effects of the injection of foreign sera into the circulation of
rabbits, we noticed that these animals succumb readily when a certain amount
of the heterogenous serum has been injected with a given rapidity. But again,
different factors may be responsible for such a fatal outcome in the case of
sera from different species and this diversity of factors precludes a strict
parallelism between the systematic relationship of the various species used
and the toxicity of their sera. Thus, according to Strickler, Tuttle and Loeb,
intravenous injection of dog serum kills the rabbit, essentially, by the hemoly-
sis it produces in the blood vessels of the rabbit. The products of hemolysis
cause coagulation of the blood in the living animal in the same way as in
vitro. Accordingly, the pulmonary vessels and the vena cava become filled
with blood clots and the animal dies from asphyxiation. If the formation of
blood clots is prevented by injection of hirudin or heparin into a vein previous
to the injection of the serum, the latter does not kill the rabbit. The heparin
diminishes hemolysis as well as the coagulation of the blood (Rabinovitch).
Beef serum, on the other hand, causes, in vitro as well as in vivo, agglutination
of the erythrocytes ; the clumps of red corpuscles formed occlude the pulmo-
nary vessels and death results. Directly after the death of the animal these
agglutination thrombi may be demonstrated by exerting pressure on the
pulmonary vessels, which forces the thrombi out of the cut vessels (Rabin-
ovitch). It is possible that in addition to these toxic effects of dog and beef
serum, other factors are involved in some instances; thus Zinsser maintains

508 THE BIOLOGICAL BASIS OF INDIVIDUALITY

that goat serum may, in certain cases, kill rabbits by a mechanism comparable
to that which is effective in anaphylaxis.

While these facts make understandable the lack of a strict quantitative
correlation between the systematic relationship of animals and the action
of heterogenous blood serum on cellular constituents, still, a specific adapta-
tion between sera and the cellular elements does exist. This is evident from
the fact that, as a rule, autogenous and homoiogenous blood sera are much
more favorable for the preservation of the cellular constituents of the blood
than are heterogenous sera. This is true also of man and of certain animal
species in which blood groups occur, if the group agglutinins are first removed
from the blood. There are indications that similar conditions hold good in the
case of the blood of invertebrates as well. Thus we found the blood serum
of Limulus on the whole more suited for the normal activities of experimental
amoebocyte tissue of Limulus, than the blood serum of decapode arthropods,
such as the lobster. However, through previous heating of lobster serum the
latter can be converted into a favorable medium. Furthermore, Limulus serum
on being mixed with the serum of other Limuli remains clear, but after mixing
it with the sera of various crustaceans, precipitates usually develop.

While thus, in general, no very strict quantitative parallelism can be dem-
onstrated between the action of normal sera on heterogenous cells and the
relationship of the organismal differentials of the species used, such a specific
relationship is demonstrable in the case of immune sera, produced through
injection of sera or cells into an animal possessing different organismal dif-
ferentials. As a rule, the antigenic activity of the species differentials pre-
dominates under these conditions over that of other antigens contained in
the cells.

We may then conclude that not only in the cells of an organism, but also in
its blood serum, there are present species differentials which can function as
antigens, and which, by means of experimentally produced immune sub-
stances, can readily be demonstrated ; also, that these differentials show a
gradation corresponding to the systematic relationship of the organisms.
Moreover, we have found that the cells of an organism and its normal blood
plasma contain species differentials which are mutually adapted to each
other; but a graded relationship between the organismal differentials of the
cells and bodyfluids belonging to different species and orders of animals, which
would correspond to the systematic relationship of the animals, cannot as a
general rule be demonstrated in the interaction between sera and cells.

In these investigations, which concern the differentiation of different species
by serological methods in animals, substances and cells, which are constituents
of the blood, have been used in most experiments. While in plants substances
which are present in young tissues may also serve as species-specific antigens,
it seems to have been difficult, so far, to extract from organs of higher
animal species antigens which, after injection into other species, would give
rise to the production of precipitins or of complement-fixing substances. Such
antigens, if present at all, are found only in very small quantities and show
only a slight degree of specificity. But, it may be suspected that these

DEMONSTRATION OF SPECIES DIFFERENTIALS 509

largely negative results are due not so much to the lack of these species differ-
entials in the respective tissues, as to the difficulty experienced in extracting
them in a potent form, and there are indications that, by injecting organ
suspensions into rabbits, species-specific antibodies may be obtained. In the
preparation of antigens from invertebrates for the production of precipitins,
it is customary to make extracts from the whole animal after it has been
frozen, dehydrated and ground to a fine powder; however, this material con-
tained tissues as well as bodyfluids.

As we have stated previously, heterotransplantation of various tissues and
organs shows the presence of heterodifferentials, which are not limited to one
kind of tissue but which are distributed throughout the body similarly to the
individuality differentials. But the gradations in the results of transplantations
are not as delicate and as definite in the case of species differentials as in the
case of individuality differentials. In that part of the spectrum of relation-
ships which represents the heterodifferentials, the analysis by means of sero-
logical methods is at least equal, and probably superior, to the analysis by
means of transplantation. In the individuality differentials, on the other hand,
we have to deal evidently with much more delicate and specific substances than
in the species differentials, and here serological analysis is the less refined
method. And yet, each species has its characteristic species differential. Is
this species differential attached to a particular substance, which is the same
in all organs of a species, or do different substances assume these functions
in different organs? There is no doubt that different substances, present in
different organs or tissues, may possess species differentials exhibiting the
specific effects. The evidence so far points strongly to the conclusion that
there is one chemical feature which characterizes a species and that this may
be attached to various substances, which are thus the bearers of the species
differential ; and, as a rule, the demonstration of serological differences in the
experiments discussed in this chapter depended upon the presence in the
proteins of this species differential which served as an antigen. However, it
seems that in some instances in which certain plant proteins were used for the
sensitization of animal, tissue- or substance-specific material may have called
forth sensitization and the subsequent anaphylactic reaction, and it is probable
that also in animals a combination of tissue and organ differentials may to a
certain extent, and with certain limitations, substitute for the real species
differentials.

Chapter J

The Demonstration of Individuality Differentials

by Serological Methods

IN the preceding chapter we have discussed various investigations which
tended to prove the existence of species, generic and class differentials
by means of serological methods. We have seen that the precipitin test
in general permits only the distinction of relatively far distant species, but
certain refinements in technique may make it possible to distinguish also be-
tween more nearly related species. At an early period of these investigations,
it was especially Hamburger who suggested that not only species differed in
their chemical constitution, but that also individuals might differ. It was
therefore natural that the attempt should be made to demonstrate differences
between the proteins of different individuals by means of methods similar to
those used for the demonstration of species differentials. Weichardt seems to
have been the first to make experiments of this kind. He believed that he was
able to demonstrate individual differences in the degree of precipitation taking
place on mixing the blood proteins of two individuals with their respective
antisera, after previous saturation of the antiserum of one with the serum of
the other individual. The sera then appeared to react more strongly with the
individual antigen used for immunization. Weichardt used heterogenous im-
mune bodies in his investigations and in the light of what we have since
learned concerning the limitations of the precipitin test, it is very improbable
that individuality differentials can be demonstrated by these means.

However, a few years previous to this work Ehrlich and Morgenroth,
using a different technique, had actually shown the existence of individual
differences between antigens, in experiments to which we have referred
already. But it seems that these investigators were not primarily interested in
the analysis of what we now would designate as individuality differentials;
they wished, rather, to determine whether immune substances could be pro-
duced only against heterogenous substances, and whether a condition which
Ehrlich had named "Horror autotoxicus" would prevent the formation of
antibodies in an animal of the same species. They therefore injected massive
doses of hemolyzed blood corpuscles of thirteen goats into other goats and
obtained thirteen hemolysins for the blood corpuscles of the individuals which
had served as donors of the antigens. A comparison of the effects of the
different immune sera on the blood corpuscles of the various individuals
showed that the sera were not all alike, but that each one behaved in a dis-
tinctive manner. It could furthermore be shown that the differences depended
not only on the kind of corpuscles injected, but also on the animal which had
produced the hemolysins. Thus two different goats, injected with the same
goat blood, gave different hemolysins. This corresponds with the results

510

DEMONSTRATION OF INDIVIDUALITY DIFFERENTIALS 511

which are obtained in the analysis of individuality differentials by means of
transplantation, the reaction depending here not merely on the nature of the
transplant, but on the relation between the individuality differential of the
donor and of the host. While it was thus possible to produce substances which
Ehrlich and Morgenroth called "isolysins" — but which would, perhaps, better
be called "homoiolysins" — in no case did such a homoiohemolysin dissolve the
erythrocytes of the animal which had produced that particular hemolysin.
Autohemolysins did not develop under these conditions. However, in some
goats it was not possible to elicit the production of homoiohemolysins in this
way; here the injected homoiogenous red corpuscles behaved like autogenous
cells. Another difficulty was that the antisera not only reacted with the red
corpuscles of the goat which had furnished the antigen, but also with the
erythrocytes of a number of other goats. These facts suggested to von Dun-
gern and Hirschfeld, as well as to Witebsky, the interpretation that Ehrlich
and Morgenroth had in reality not to deal with individual hemolysins, but with
group isolysins corresponding to the group hemagglutinins, the occurrence of
which in certain animal species had been demonstrated by von Dungern and
Hirschfeld. Also, Zinsser assumed that while Ehrlich and Morgenroth had
actually discovered individual differences, between the red corpuscles of differ-
ent goats, these individual differences were identical with blood-group differ-
ences.

As discussed previously, it is necessary to distinguish between at least four
different kinds of substances: (1) The typical group differentials, which are
represented in man by the agglutinogens A and B; (2) accessory blood-group
differentials, such as M, N, P, Rh and H; (3) substances which allow the
distinction of individuals, as for instance, individual scents, and also certain
tissue or organ differentials, or combinations of the latter. While a combina-
tion of a sufficiently large number of accessory blood-group or organ differen-
tials might permit the distinction between individuals, this would not make
these individual differences necessarily identical with (4) the individuality
differentials. It is difficult to determine whether Ehrlich and Morgenroth had
to deal with substances enumerated under 2, 3, or 4.

However this may be, the desire of Ehrlich and Morgenroth to determine
the possibility of the formation of "isohemolysins" suggested to them the
use of a method which allowed a much finer differentiation between in-
dividuals than had been possible previously by means of serological methods,
in particular, those in which the ordinary heterogenous immune sera were
employed. These investigators anticipated the essential feature of the method
of cross immunization, subsequently introduced by Uhlenhuth with a view
of refining the precipitin test. Furthermore, the use of cells instead of blood
proteins as antigens may have been a favorable factor which made possible
the demonstration of individual differences by serological methods.

The fact that homoio (iso) hemolysins can be produced experimentally was
subsequently confirmed by Ascoli and by various other investigators. But the
most extensive and important studies concerning the demonstration of in-
dividual differences between the red blood corpuscles of different individuals,

512 THE BIOLOGICAL BASIS OF INDIVIDUALITY

belonging to the same species, were carried out by Todd and White, and later
by Todd alone. We have referred already to their work and we shall now
again discuss these investigations. There can be little doubt that these latter
investigators had to deal with individual and not with group differentials in
their investigations. Todd and White, and Todd, in preparing immune serum
against cattle plague, injected different cattle with the blood of other cattle.
Out of one hundred and six cattle injected, seventy-six furnished active sera
containing homoio (iso) hemolysins for normal cattle, which were active in
combination with guinea pig complement. Each immune serum thus obtained
was able to hemolyze the red corpuscles of certain other individual cattle, and
this action differed from that of the immune serum obtained from another
animal. Thus a particular serum was very hemolytic for some kinds of
erythrocytes and only weakly hemolytic for others, and each serum acted
in its own specific way on the various kinds of corpuscles. The order in which
two different sera affected a series of corpuscles from different individuals was
different in each case.

These individual variations between the antigens present in the corpuscles
of different cattle were brought out still more strikingly in specific absorption
experiments. If a certain serum was exhausted by the addition of the red
corpuscles of an individual animal, it lost thereby not only the ability to
hemolyze the kind of corpuscles which had been used for absorption, but
also the erythrocytes of some other individuals ; moreover, a gradation be-
tween the erythrocytes of different individuals according to genetic relation-
ship, such as had been observed in transplantation experiments, did not ap-
parently exist here; it seemed, rather, that "an all or nothing" law obtained.
But if several immune sera were pooled, the absorption tests became more
specific, in so far as now absorption with the corpuscles of one particular
animal removed, primarily, the hemolysins of this individual, leaving the
others as a rule intact. Still it might happen here also, that not only the
hemolysins for those individuals whose corpuscles were used for specific
absorption were removed, but also the hemolysins for some other individuals.
It appears that if the relationship between two individuals did not exceed
a certain degree of remoteness, their erythrocytes behaved alike in the ab-
sorption test, a finer quantitative gradation in the intensity of the reaction,
such as can readily be accomplished by means of transplantation, being im-
possible in this case. However, in an indirect manner, by comparing the be-
havior of the corpuscles of various individuals to different immune sera it
might perhaps have been possible to establish the mutual relationship of the
corpuscles of the various individual cattle, at least in an approximate manner.

The same lack of gradation was also apparent in the analysis of the relation-
ships of the members of certain families by means of the hemolysis test. Thus
the blood corpuscles of a cow and her calf were compared as to their specific
ability to absorb the individual hemolysins. It was found that absorption with
the corpuscles of the mother removed also the hemolysins for the calf, but
absorption with the corpuscles of the calf left the hemolysins of the mother
intact, while removing those for its own corpuscles. In this case we have to

DEMONSTRATION OF INDIVIDUALITY DIFFERENTIALS 513

consider the possibility that in the corpuscles of the calf the antigens were
quantitatively not yet as fully developed as in the corpuscles of the mother.
Examination of a family of sheep, consisting of father, mother and three
lambs, showed that the corpuscles of one lamb behaved in an almost identical
manner with those of the mother, while the corpuscles of the other two lambs
had the character of the father. Here, too, there is a lack of gradation, and
there is again reason for assuming that under similar conditions transplanta-
tion would in all probability have revealed graded differences between the
constitution of the cells of the various children and of father and mother. An-
other peculiarity in these experiments needs particular mention, namely, the
importance of the race to which the individual cattle belonged. We should have
expected the erythrocytes of a certain individual to resemble more the cor-
puscles of an individual belonging to the same strain than the corpuscles of
an individual from a different strain, but this was apparently not the case. In
transplantation experiments, on the other hand, the differences existing be-
tween different strains, such as white, yellow and piebald strains of rats, and
also those between inbred strains of guinea pigs and mice, have a distinct
effect on the reaction of the host against the grafts.

In more recent experiments Todd analyzed in a similar manner, individual
relationships in fowl by means of immune hemagglutinins. Here, too, it was
found that by absorption tests the red corpuscles of each individual animal
could be distinguished from those of others. Some erythrocytes resembled
each other more than others ; but certain members of the family could not
be distinguished from one another by this method. In these experiments poly-
valent sera were used. If they were absorbed with the corpuscles of one
individual, only immune substances directed against this individual and
against some near relatives were thereby removed ; but if the polyvalent serum
was exhausted with the red corpuscles of several individuals, the number of
immune substances removed was greater. Also, in this case we find a lack
of a furthergoing gradation in the relationship of the various individuals. In
analyzing the relationship between parents and children, Todd found, again,
the corpuscles of some children behaving like those of the father, others like
those of the mother; but in two instances the antigens of the children pos-
sessed components of both father and mother. If a polyvalent serum is ab-
sorbed with the erythrocytes of both parents successively, it has of course,
lost also the agglutinins for the cells of the child completely. Theoretically,
the red corpuscles of the child should have components of the parents to an
unequal degree in the large majority of cases. This is found in transplanta-
tion experiments and they suggest that there does not, as a rule, exist an
identity between the structure of the differentials of a child and of one of the
parents.

An indication that it is perhaps the differentials which serve to distinguish
the erythrocytes of various individuals, and that they also function as antigens
in immunization, was obtained in experiments in which the production of
agglutinins against the blood corpuscles of brothers and sisters was tested. In
each instance, Todd injected a chicken with the blood of a brother. Several

514 THE BIOLOGICAL BASIS OF INDIVIDUALITY

pairs of this kind were tested in this manner ; in two of them antibodies were
readily produced, whereas in two other pairs immunization was obtained
with greater difficulty. In the latter cases, in testing the agglutinating power
of the sera for the blood corpuscles of the two partners, almost no distinction
was found ; correspondingly, each had very weak antigenic potency in the
partner. On the other hand, the partners in the first two pairs could be readily
differentiated from each other and, accordingly, distinct effects were obtained.
The agglutinating sera resulting from immunization with the erythrocytes of
brothers were highly specific and acted only on corpuscles of birds very similar
to those whose erythrocytes had been used for injection ; but towards these
cells they appeared to be as active as the sera prepared by injection of non-
related fowls ; there was again a lack of gradation.

In chickens, individual differences were found also by Landsteiner and
Miller, who immunized rabbits with chicken blood. The immune agglutinins
in the rabbit serum could be absorbed with the red blood corpuscles from a
certain chicken. The remaining rabbit serum was still able to agglutinate the
erythrocytes from other chickens but not those from the animal used for
absorption; only in two pairs of chickens were the agglutinins found identical
in these tests. Similarly in natural ox serum multiple substances seem to exist,
which are able to agglutinate the red corpuscles of individual chickens.
Through absorption with the erythrocytes of a chicken these substances could
be specifically removed. Ox serum thus treated no longer agglutinated the
chicken corpuscles used for absorption, although it had retained the ability to
agglutinate the corpuscles from other chickens (Landsteiner and Levine).
Likewise, by injecting chimpanzees with human erythrocytes, Landsteiner
and Levine were able to find some differences between individual human
red corpuscles. However, in the case of turkey and guinea fowl blood, in-
dividual differences could not be established by these means.

In the experiments of Todd, and in similar investigations of others, as
well as in the earlier experiments of Ehrlich and Morgenroth, the question
arose as to whether we have not to deal with group antigens rather than with
individual antigens. Thomoff, in experiments on the formation of homoio-
hemolysins or homoioagglutinins in horses, suggested that reactions occur
only if the donor of the antigen and the producer of the immune substances
belong to different blood groups. However, even in these experiments the
hemolysins or agglutinins were not primarily antibodies against the group
antigens of horses, but they were individual agglutinins and hemolysins, al-
though secondarily the group differentials may have entered as a factor in these
reactions. Similarly, it may be possible that also in Todd's experiments the
group differentials may have played a secondary role, but essentially these
experiments concern differentials distinguishing individuals.

In comparing these serological tests for individuality with the analysis of
the individuality differential by means of transplantation, we see that in the
former use is made of the antigen of one type of cell only, the erythrocytes,
and the conclusions likewise relate merely to the differences between the
antigens in various kinds of red blood cells. In transplantation experiments,

DEMONSTRATION OF INDIVIDUALITY DIFFERENTIALS 515

on the other hand, the character of various tissues and organs of one in-
dividual is contrasted with that in another individual ; this is possible because
the individuality differential is not merely an attribute of one particular kind
of cells, such as the erythrocytes, but is present in the various tissues and
organs of an individual.

We find, in general, in the serological tests a lack of those fine gradations
between intensities of reaction, which correspond to the degrees of relation-
ship of the partners, observed in cases of transplantation. In transplantation
experiments the cells and tissues transferred to a strange environment set in
motion finely graded cellular mechanisms of attack in the host and the trans-
plants are also acted upon by the graded injurious actions of the host body-
fluids. In the experiments of Ehrlich and Morgenroth, as well as in those
of Todd, the antigens of the red corpuscles initiated the production of im-
mune hemolysins or immune agglutinins. On the whole, these latter reactions
resembled either autogenous or fully developed homoiogenous reactions, al-
though in the hemolysis tests certain gradations in the intensity of hemolysis
were found in different combinations of corpuscles and immune sera in some
instances, and such gradations were apparently in accordance with the rela-
tionship between the animal whose blood corpuscles were tested and the
animal serving as the immune-body producer. Is this difference between the
reactions following transplantation and the effects of immune sera due to a
difference in the differentials or antigens which participate in these two tests?
Presumably it depends largely on the more finely graded reactions exhibited
by living tissues, as compared with the in vitro reactions between antigen
and antibody.

The antigens present in the erythrocytes are substances which can be
partly or wholly neutralized or removed through absorption with the corre-
sponding antisera. When a certain degree of relationship exists between the
donors of the erythrocytes and the various animals to be injected with these
cells, the correspondence between the immune bodies and the antigens may be
sufficiently great to make possible the complete removal of these immune sub-
stances by the erythrocytes of the donor. These differences between antigens
may conceivably depend upon chemical groups forming part of one complex
substance, or perhaps we may have to deal with distinct substances. These
antigens, which ultimately are derived from genes situated in the nucleus, are
themselves situated outside the nucleus; at least this is the case in the non-
nucleated erythrocytes.

We have seen that the individuality differentials are preformed and there is
reason for assuming that they elicit homoioreactions in transplantation di-
rectly, at least to a large extent, and that these reactions do not primarily
depend upon the formation of immune bodies, although secondarily, immune
reactions may occur. Similarly, the solution of the foreign blood corpuscles,
after intravenous injection into homoiogenous hosts, depends primarily upon
the incompatibility between the strange individuality differentials of the
erythrocytes and the bodyfluids of the host, and the formation of immune
substances is a process caused by this primary incompatibility. While it has

516 THE BIOLOGICAL BASIS OF INDIVIDUALITY

been possible to produce homoiogenous immune hemolysins or immune hemag-
glutinins in goats, cattle, chickens, and perhaps in some other species, accord-
ing to Todd it is not possible to obtain a corresponding formation of homoiog-
enous immune bodies in guinea pigs and rats; but these are exactly the
species which, above all, have been used in transplantation experiments and
this is an additional reason for assuming that in the case of homoiogenous
transplantation we have primarily to deal with incompatibilities between host
and transplant, and with primary reactions of attack or defense, and only
secondarily with immune reactions.

As we have pointed out above, in those experiments in which individual
differences between cells could be demonstrated by serological methods,
homoio-immunization was used in the preparation of the immune sera in the
majority of the experiments, and in all cases erythrocytes or their derivatives
served as antigens. There is, however, at least one instance on record in which
apparently hetero-immunization with another type of cells also led to the
demonstration of individual differences. According to Dervieux, by means
of repeated injections of fresh human sperm into rabbits, antisperm precipitins
can be produced, which have the strongest effect on the individual sperm of
the donor; here they are effective in the greatest dilution. Dervieux found,
furthermore, that the immune serum thus obtained had a stronger precipitating
power for strange human sera than immune sera produced by injection of
human serum; also, it allowed the distinction between individuals, and even
between men and women. However, the spermatic fluid used by Dervieux, and
also in the subsequent investigations of Siissman, contained not only sperma-
tozoa but also other material, among which were admixed proteins. Therefore,
the immune substances elicited by the injection of sperm may readily have
been directed against these admixtures rather than against the spermatozoa as
such. These experiments were apparently confirmed by Siissman as far as the
individual specificity of the sperm antigens, but not of the blood protein
antigens, is concerned. But it seems that Siissman carried out only a small
number of experiments and not all of these were confirmatory of Dervieux's
conclusions, It will therefore be necessary to wait for a confirmation of
Dervieux's investigations before his results can be fully accepted.

More recently, Zangemeister indicated another method by means of which
he thought it possible to differentiate between the blood sera even of nearly
related individuals. He assumed that following fertilization of the ovum by
a spermatozoon and the subsequent formation of the embryo, there develop,
as the result of the entrance of sperm material into the blood serum of the
mother and of the child, substances which cause a change in the state of
dispersion of the serum proteins if the serum of the father is mixed with the
serum of the mother, or if the serum of one of the parents is mixed with
that of the child. This change in the state of the serum proteins was thought
to indicate the relationship between the individuals whose sera were allowed
to act on each other. However, these experiments could not be confirmed
by Lattes.

We may then conclude that it is possible to produce specific immune sub-

DEMONSTRATION OF INDIVIDUALITY DIFFERENTIALS 517

stances through immunization with homoiogenous erythrocytes, but that a
hemolytic immune serum thus obtained does not hemolyze the red corpuscles
of the individual in which the immune serum developed. It is therefore im-
possible to elicit a reaction against autogenous cells. Similarly, Ehrlich and
Morgenroth have shown that antihemolysins cannot be made to appear by
injecting isohemolysins into a goat in which the hemolysins had originated.
Likewise in the case of tumor immunity, we have seen that an active im-
munity against the growth of a transplanted tumor will not result from
inoculating an animal with pieces of its own organs.

However, it has been held that in certain cases autogenous antibodies may
actually be formed, but not all the authors distinguish sharply between sub-
stances and reactions of an autogenous and homoiogenous nature, and it is
thus difficult to determine whether we have actually to deal with autogenous
rather than with homoiogenous reactions. To mention some examples :
According to Guyer, an injury to the eye-lens of a rabbit elicits in this animal
the production of antibodies against lens tissue which enters the blood serum;
these antibodies can be demonstrated by the formation of a precipitate on
mixing the serum of the animal which has been injured with homoiogenous
lens substance. Similarly, according to Henshaw, antibodies develop against
autogenous antigens after exposure of the skin to ultraviolet rays ; either by
means of anaphylactic shock or by the precipitin reaction with corresponding
homoiogenous skin material, the development of antibodies could apparently
be demonstrated. In these cases we may perhaps have to deal with tissues,
which, as a result of injury, had undergone chemical changes of a kind which
seem to have made possible the formation of auto-antibodies. This applies
also to the experiment of Letterer, who, by injection of autogenous venous
blood, sensitized a guinea pig against its own blood, which caused a reaction
when injected parenterally. Apparently the normal circulating blood does not
cause such a sensitization.

In the case of paroxysmal hemoglobinuria, pathological changes of a specific
kind have evidently taken place in the blood of certain individuals. As a
consequence of these changes, it seems that autohemolysins develop, and the
union between erythrocytes and autohemolysin which follows depends on an
exposure of the erythrocytes to a low temperature. But it is not certain that
in this instance there is actually involved an antibody formation against
autogenous cells. Certain non-specific procedures, such as injection of boiled
milk, apparently intensify the autohemagglutination in some rabbits, but
injection of erythrocytes, normal or injured, does not have a corresponding
effect.

In general, it may therefore be assumed that the body does not react against
its own normal cells with the production of immune substances, while it is
able to do so against homoiogenous substances. However, we cannot exclude
the possibility that if a body is injected with its own injured cells, in certain
cases a reaction may be elicited, but that such a reaction is less strong than one
produced by means of injections of homoiogenous, or better still, of heterog-
enous material; furthermore, it is possible that substances of an autogenous

518 THE BIOLOGICAL BASIS OF INDIVIDUALITY

nature, not normally circulating in the bodyfluids, may call forth the produc-
tion of immune substances if they gain access to the circulation.

It may then be concluded that in the erythrocytes of several species the
presence of differentials of an individual character has been established by
means of immune sera, but it has not yet been definitely proved that these
differentials are identical with the individuality differentials. Even in some
preformed sera, such as ox serum, multiple agglutinins seem to exist, which
can be specifically absorbed by the erythrocytes of certain individuals. This
fact may be interpreted as indicating that complexities in the structure of
blood proteins exist, which have not yet been amenable to a purely chemical
analysis.

Chapter 4.

The Organismal Differentials of Hybrids
Between Nearly Related Species

In all conditions which we have studied so far, in which serological
methods have been used for the analysis of relationship, we were able
to compare the results with those obtained by means of transplantation.
There is, however, one type of relationship in which such a comparison
between these two methods of investigation is not feasible at present. The
mutual relations of hybrids between nearly related species, as well as
the relations between the hybrids themselves and their parents, have been
analyzed by serological methods, but only in a rudimentary manner by
transplantation methods; the number of experiments representing the latter,
made by Schultz, is very small. As Jacques Loeb has pointed out, a comparison
of the species characteristics of an Fx hybrid with those of the father and
mother species should give an indication as to whether the rules of Men-
delian heredity apply to the transmission of species characters, or whether
hereditary transmission in this case takes place through the cytoplasm of the
egg. If it takes place through the cytoplasm, the hybrid should resemble the
mother species, but not the father species. Jacques Loeb suggested that it
might also be possible to determine this question by comparing the characteris-
tics of hemoglobin crystals of mule with those of horse and donkey. But the
measurements of Brown showed that the mule crystals were outside the
range of figures found for horse as well as for donkey, although they were
somewhat more nearly related to those of the donkey. Thus crystallography
did not help in solving this problem.

I. In order to test the relationship between horse, donkey, and the hybrid
between these two species, the mule, use was made by Walsh of the presence
of preformed hemolysins and hemagglutinins in these three types of sera
acting on the various kinds of erythrocytes, while Landsteiner employed for
this purpose immune agglutinins. The findings of Walsh were as follows :
(a) Horse serum does not hemolyze horse, donkey or mule erythrocytes. Don-
key serum hemolyzes both horse and mule erythrocytes in a large percentage
of cases. Mule serum does not hemolyze horse or mule erythrocytes, (b)
Horse serum agglutinates neither horse nor mule erythrocytes. Donkey serum
agglutinates the erythrocytes of the horse in a high percentage of cases, but
does not agglutinate the erythrocytes of the mule. Mule serum does not ag-
glutinate horse or mule erythrocytes. From these observations it may be con-
cluded that mule serum behaves like horse serum, and mule corpuscles behave
like horse corpuscles rather than like donkey corpuscles, except as far as
the agglutinating action of donkey serum is concerned. However, according

519

520 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to Landsteiner, donkey serum does agglutinate mule corpuscles, although not
to the same degree as horse corpuscles. Agglutination tests indicate, therefore,
that mule blood behaves essentially like horse blood, but in some respects
it shows the influence of the donkey. It seems, then, that in this species hybrid
the characteristics of the female parent predominate, suggesting the possi-
bility that we may have to deal at least with a partial cytoplasmic inheritance.

Landsteiner wished to determine whether the blood groups which are pres-
ent in the horse, and lacking in the donkey, are transmitted to the mule. Von
Dungern and Hirschfeld had previously observed that the isoagglutinins of
the horse are transmitted to the mule. In the donkey, isoagglutinins are
not demonstrable. By means of immune sera and absorption tests Land-
steiner and Van der Scheer found in the erythrocytes of the horse more than
three kinds of isoagglutinable substances. The mule inherits from the horse
isoagglutinable groups, but not all the blood groups are equally transmitted
from horse to mule. The blood of the majority of mules belongs to the class in
which the serum contains agglutinins, and the corpuscles are not, or only
slightly, agglutinable. Not as many mules contain the isoagglutinable sub-
stances as do horses; this agrees with the fact that donkey blood contains no
blood groups with isoagglutinable erythrocytes. There is therefore, again,
an influence of the genetic constitution of the donkey noticeable in the mule
so far as the inheritance of the blood groups is concerned. But horse ag-
glutinogens are transmitted to mule corpuscles, which lead to heteroagglutina-
tion of mule corpuscles by donkey serum. Donkey serum behaves therefore in
the same way to a certain group of horse and mule corpuscles ; however, it
does not cause the agglutination of mule corpuscles to the same degree as it
does that of horse corpuscles, and there are more individual differences in
the erythrocytes of the mule than in those of the horse. Likewise, there are
differences between different donkey sera, but a given serum behaves in a
similar manner to horse and mule corpuscles.

We find thus, that also in this instance mule blood resembles, on the whole,
horse blood ; but to a certain degree an influence of the donkey is noticeable
and it modifies the inheritance in the mule. We may furthermore conclude
that there are differences in individual mules. Of two mules, the one inherits a
characteristic from the horse, while another inherits the corresponding char-
acteristic from the donkey ; yet both are equally mules. The hybrid character
"mule" is therefore distinct from and independent of those individual char-
acteristics which differ in different mules, some of which resemble, as far as
this particular characteristic is concerned, more the horse, while others re-
semble more the donkey. The species differentials that distinguish horse,
donkey and mule are definite, although some of the mosaic characteristics
of individual horses and donkeys may vary, and the composite of these
characteristics also differs in individual mules.

As to the analysis of mule blood by means of immune sera, Landsteiner
and Van der Scheer found that while it might be possible to use the precipitin
and complement fixation tests for the differentiation of the serum proteins
of these three types of animals, the differences established by such methods

ORGANISMAL DIFFERENTIALS OF HYBRIDS 521

were relatively slight and these investigators preferred therefore the use of
immune agglutinins, which they produced in rabbits by injection of the dif-
ferent types of red corpuscles. They tested the immune sera thus obtained as
to their action on the erythrocytes of horse, donkey and mule, either directly
or after previous absorption of the immune sera by the various types of
erythrocytes. All of these tests showed that the mule erythrocytes contained
agglutinogens of both horse and donkey. However, in the mule red corpuscles,
either not all of the donkey and horse agglutinogens were present, or they were
present in smaller amounts. As a rule, the immune serum prepared in rabbits
by injection of mule erythrocytes behaved more like anti-horse-corpuscle im-
mune serum than like anti-donkey immune serum, notwithstanding the fact
that the mule red corpuscles contain both kinds of agglutinogens. Horse as well
as mule erythrocytes could bind the immune agglutinins from immune serum
against mule corpuscles, including also the agglutinins which act on donkey
erythrocytes; but after a previous absorption of such sera by donkey red
corpuscles, a high agglutinin titer for horse and mule erythrocytes still
remained in the serum, while the donkey agglutinins had been removed. It
may therefore be concluded that as far as the production of immune sera can
be used as an indicator, the horse agglutinogens predominate in the red cor-
puscles of the mule.

II. More recently Landsteiner studied, by means of immune hemolysins
and immune hemagglutinins, the relations of the blood of hybrids between
the domestic guinea pig (Cavia rufescens) and the wild Brazilian guinea pig
(Cavia porcellus) to the blood of the parent species. In this case Landsteiner
made use of homoio-immunization in order to eliminate the complication
which the strangeness between the donor of the blood and the animal to be
immunized would have introduced. Normally, no hemolysins or hemag-
glutinins are present in the blood serum of guinea pigs belonging to one
species or race for the erythrocytes of the other. But by injecting the blood
corpuscles of Cavia porcellus into Cavia rufescens it is possible to produce
immune hemolysins and immune agglutinins in the serum of the latter, which
act on the erythrocytes of Cavia porcellus, but not, as a rule, on the red cor-
puscles of Cavia rufescens. It was found that the red corpuscles of the hy-
brid behaved in an intermediate way; they contained characteristics of both
parents. This result corresponds to our findings in the analysis of hybrids
between different families in rats and in guinea pigs by means of transplanta-
tion.

III. Irwin tested, by means of immune hemagglutinins, the relations be-
tween the domestic Ring dove ( Streptopelia risoria), the Asiatic Pearlneck
(Spilopelia chinensis), and the hybrids between these two genera. Rabbits
were immunized separately against the red corpuscles of the two parents and
of the hybrid and use was made of the absorption of the specific antibodies
by the various kinds of erythrocytes. It was found that the agglutinogens
of both parents were present in the erythrocytes of the hybrid, and that also
in the immune serum against the corpuscles of the hybrid, agglutinins against
the corpuscles of both parents could be demonstrated. However, the erythro-

522 THE BIOLOGICAL BASIS OF INDIVIDUALITY

cytes of the hybrid either did not possess all the antigens of the parental
genera, or they did not possess them in the same quantity as the corpuscles
of the parents. An additional interesting observation was the following:
when the anti-hybrid rabbit serum was absorbed by the erythrocytes of both
parents in succession there still remained in the immune serum a remnant
of agglutinin, which could not be removed by such absorption ; and further-
more, after absorption of the anti-hybrid immune serum by the red corpuscles
of one of the parents, there still remained a greater amount of agglutinin
against the erythrocytes of the hybrid than against those of the other parental
genus. Irwin concludes that a new antigen (agglutinogen) must have devel-
oped in the erythrocytes of the hybrid as a result of fertilization, and that a
new agglutinin may thus be produced in the immune serum. A combination
of the gene sets belonging to the two parent genera would, therefore, give
rise to something different from both component sets. Furthermore, it may be
stated that the haploid number of chromosomes present in the germ cells of
each of the parents is evidently able to produce in the hybrid almost the
same amount of antigenic substance as the diploid number does in each of the
parents.

Subsequently, Irwin and Cole investigated, by similar methods, the ag-
glutinogens in the backcross generation from hybrid F1 (Ring dove X
Pearlneck) to Ring dove parent ("one-fourth Pearlneck"). In addition, the
"one-eighth Pearlneck" backcross generation was studied ; these were obtained
by mating the one-fourth Pearlneck backcross a second time to a Ring dove
parent. In these backcross hybrids a separation of the pearlneck genes took
place, so that all possible random combinations were found, according to
the rules of Mendelian segregation. The presence or absence of Pearlneck
agglutinogens in the two backcross generations was tested as usual by the
anti-hybrid Fx rabbit serum which had been exhausted once or twice by
various types of erythrocytes. The results showed that in the Pearlneck
erythrocytes multiple, and at least ten, agglutinogens are present, which are
distributed in a specific way in the backcross birds, so that each individual
can be differentiated from the others, if a sufficient number of agglutination
tests are made with anti-Fx hybrid (Ring dove X Pearlneck) rabbit serum,
after certain agglutinins have been absorbed with various kinds of erythro-
cytes. Besides, there was present in many, but not in all, of the backcross in-
dividuals the newly formed hybridL agglutinogen, which did not exist in the
erythrocytes of either parent, but formed as a result of the union of the genes
of both parents in the Fx generation.

However, these results were obtained only if immune serum from a certain
rabbit was used for these tests. An immune serum from another rabbit might
have given different results, and it is conceivable that if the immune sera had
been used from a different species, additional differentiations would have
appeared and the number of agglutinogens found in the Pearlneck erythro-
cytes would have been still further increased. Moreover, the question may
be asked as to whether these species-specific multiple agglutinogens which
were present in the erythrocytes were peculiar to these cells, or whether they

ORGANISMAL DIFFERENTIALS OF HYBRIDS 523

were found also in the cells of other tissues and organs. In the first named
possibility we would have to deal with species-specific organ or tissue differen-
tials. However, of special interest is the formation, in the hybrids, of a new
agglutinogen, which is not present in the erythrocytes of either parent. This
would indicate that new combinations of genes may give rise not only to
corresponding combinations of substances which are present in the parents,
but also to new substances which are not represented by any of the genes
as such, but which depend upon the way in which the genes are sorted out.

In these various experiments we have to deal with different generic or
species (or race) differentials in the parents and with combinations of such
differentials in the hybrids. In the hybrids we note in all instances characteris-
tics transmitted from both of the parents. In the mule, as well as in the
hybrids between Ring dove and Pearlneck dove, it was observed that the
hybrid red corpuscles contained combinations of the parental characters,
either in smaller amounts or in the same complete assortment as the erythro-
cytes of the parent species. On the other hand, it may be recalled that by
means of serological methods Todd found that the individuality differentials
of children within the same race and species resembled either those of the
father or those of the mother.

Furthermore, it would seem that some characteristics of the hybrids are
constant and common to all individuals of the hybrid generation, while others
are variable and may differ in different hybrids derived from the same parents.
To the latter class belong, for instance, the blood-group characteristics ;
neither these nor their precursors can, as such, constitute or be a significant
part of the species or hybrid differential. Also, the individual hybrids between
domestic and wild Brazilian guinea pigs varied greatly in certain characteris-
tics other than in those determining species or race, and behaved in this respect
similar to the hybrids between inbred families of rats and guinea pigs when
they were analyzed by means of transplantation ; here also, all kinds of
quantitatively graded, intermediate conditions could be established in the trans-
mission of the individuality differentials.

An experiment similar to those reported in this chapter and dealing with
animal species has more recently been performed by O. Moritz with plant
species. He crossed Berberis empetri folia with Berberis Darwinii and thus
obtained the species hybrid, Berberis stenophylla. He then sensitized animals
by injecting extracts from the leaves and young shoots of these three kinds of
plants and by means of the anaphylaxis reaction he could show that the hybrid
antigen contained constituents of both parent species. This experiment repre-
sents only a beginning in the analysis of plant hybrids by serological methods,
but the results so far indicate that similar modes of distribution of the parent
differentials in species hybrids will probably be found in plants and in
animals.

Chapter 5

On the Differences between the Reactions of

Foetal or Newborn Organisms and of Adult

Organisms Against Strange Differentials as

Established by Serological Methods

In a preceding chapter we have discussed the differences in reactions
between very young and older guinea pigs or of embryonal organisms
against various homoiotransplanted tissues. The reactions against foetal
or embryonal tissues have also been studied. In general, the reactions on
the part of very young organisms were definitely diminished in intensity.
As far as those of young guinea pigs towards homoiotransplants are con-
cerned, this difference is due especially to a diminished intensity of the host
connective tissue response towards the graft. The lymphocytic reaction may
be quite pronounced, although it may appear at a relatively late date ; this may
be due to the fact that the transplant, being less injured by connective tissue,
is able to exert a more marked effect on the lymphocytes. We have also re-
ferred to the transplantations of heterogenous tumors into the allantois of
developing chick embryos, where at early stages the reactions against hetero-
differentials are lacking. Similarly, it has been shown by various investigators
that the reactions against transplanted tumors may not be so great in newborn
animals and in early life as later. Blumenthal has shown that early stages
of embryos do not yet contain fully developed organismal differentials.

It is of interest to compare with these findings the data supplied by sero-
logical methods. Roessle immunized rabbits with mammalian and avian em-
bryonal tissues and found that these tissues were just as effective as antigens
as were red corpuscles of adult animals in the production of hemolysins and
also of agglutinins ; there was no difference in this respect between embryonal
and adult tissues. On the other hand, injection of pig embryo did not lead
to the production of precipitins. The subsequent experiments of Braus also
showed that injection of larval and embryonal amphibian tissues into rabbits
did not lead to precipitin formation for either foetal or adult tissues, while
injection of adult tissue produced precipitins which reacted with adult but not
with embryonal tissue. He showed furthermore, that even tissue from an
advanced stage of embryonal development which, when serving as host, no
longer permitted a heterotransplant to grow, did not yet elicit the production of
precipitin. We see, then, that while embryonal tissue may not possess antigen
sufficient for precipitin formation, it may possess antigen which is able to
call forth the production of hemolysins and agglutinins. Similarly, Uhlenhuth
found that while serum of adult chickens gave a positive reaction with anti-

524

REACTIONS OF NEWBORN AND ADULT ORGANISMS 525

chicken serum, the blood of young chickens did not contain an active antigen
which, when mixed with the precipitin of the immune serum, induced forma-
tion of a precipitate. Kritschewski noted that a substance obtained from nine-
week-old tadpoles of Rana esculenta can be differentiated in its antigenic
function from the substance of adult frogs by means of the complement fixa-
tion test, and he likewise observed that the Forssman antigen, which is present
in the erythrocytes and organs of adult chickens, is not yet present in the tgg
and in very young embryos, but that it forms four days after the beginning of
segmentation, when a more advanced embryonal stage has been reached.

These experiments, indicating that antigens develop only gradually during
embryonal life, agree with the findings mentioned previously concerning the
blood-group differentials, which seem to begin to form prior to the sixth
month of pregnancy, but reach their full development only at about the time
of puberty. It is necessary to select an especially active isoagglutinin in order
to effect the agglutination of young as compared with older blood corpuscles.
Likewise, the two different varieties of the A differential, A and A1 (Thorn-
sen), or Ax and A2 (Landsteiner), which differ in their binding power for
isoagglutinin, gain their full strength only gradually with advancing childhood.
While thus, in the course of time, the' blood corpuscles acquire properties
which enable them to bind a greater quantity of isoagglutinin, the difference
in the ability of the A and Ax corpuscles to combine with isoagglutinin re-
mains preserved also at later periods.

Similarly, according to Thomsen, the full development of the isoagglutinin
occurs only sometime between the fifth and tenth year of life, while in old
age it may decrease again (Schiff and Mendlovitsch). Also, the natural
amboceptor and complement of hemolysin, as well as the corresponding sub-
stances acting with bacterial substances, are not yet present in the earliest
embryos, but form as embryonal life progresses in chicken and cattle (Sachs,
Rywosch). In the chicken embryo, antibodies first appear after the twenty-
first day. In very young swine embryos only very small amounts of comple-
ment, hemolysin-amboceptor and opsonin are found ; these increase during
embryonal development (Sherman). In this connection we may also cite the
observation that while in the Freund-Kaminer test normal adult human sera
are able to dissolve cancer cells, the sera of human fetuses do not yet possess
this ability, and resemble in this respect the sera of persons afflicted with
cancer.

It is well known that different species of animals differ very much in their
power of resistance to certain bacteria and toxins. Similarly, the reactivity of
young organisms to various toxins and bacteria may differ from that shown
by adult organisms. Thus, according to Camus and Gley, the erythrocytes of
newly-born rabbits are more resistant to eel serum than those of older in-
dividuals. Newly-born chicks and rabbits are not sensitive to arachnolysins
and are less sensitive to cobra toxin. Heterohemolysins may be found in
smaller quantity in younger than in older individuals, the amount of ambocep-
tor as well as of complement being less in younger organisms. These observa-
tions agree with the findings in other experiments of Sachs, in which he

526 THE BIOLOGICAL BASIS OF INDIVIDUALITY

showed that immune hemolysins produced against erythrocytes of adult
chickens, beef, rabbits and guinea pigs are without injurious effect if they
are injected into the circulation of embryos or of newly-born animals of these
species. Similarly, very young children often prove negative to the Schick
and Dick tests, their blood being free from antitoxin. On the contrary, we
may find in young organisms a lack of resistance to certain bacteria and
viruses, to which adult organisms may be definitely resistant. Thus there seems
to be an increase in the resistance to poliomyelitis with advancing age, as
manifested by the fall in morbidity and the rising level in the therapeutic
efficiency of blood serum. In the serum of adult Rhesus monkeys a substance
neutralizing the poliomyelitis virus may be observed, while it is lacking in
immature monkeys. Such increased resistance has been attributed by some
investigators to a preceding latent or very mild infection with this disease. But
Jungeblut and Engle could show that such a change may occur even in
monkeys which have been kept isolated and that it is therefore probably
not due to a previous infection.

Likewise, young rats are much more susceptible than are adult rats to
inoculation with pneumococci. The blood of almost all humans is destructive
for pneumococci of type II, while that of very few persons possesses the
power to destroy type I. The blood of an intermediate number of individuals
destroys type III. In the blood of young children, one to fifteen months old,
this ability of a mixture of serum and leucocytes to kill pneumococci is rarely
observed (Robertson and Sia) ; with advancing age its frequency increases,
but in the aged it is again rarely present. As in the case of poliomyelitis, some
investigators attribute also this increase in resistance with advancing age to a
preceding latent or mild infection with the specific organism, but recently the
suggestion has been made that an infection with a different and perhaps non-
virulent organism which has certain antigens in common with the pathogenic
one, may be responsible for such an effect. But this interpretation is not
sufficient to explain all observations, although it may apply in some instances.
Other investigators, Friedberger, Hirszfeld, Jungeblut and Engle, assume
therefore that a gradual physiological ripening, due to a biochemical change
in cells or tissues, is the cause of this altered mode of reaction in older age.
On the whole, this explanation appears more probable and it seems to hold
good, for instance, in the case of the blood-group differentials and in other
instances already mentioned. A maturation immunity develops in mice, with
advancing age, to the virus of vesicular stomatitis. Mice two weeks of age,
succumb to intramuscular injection of this virus in almost 100 per cent. With
increasing age, the resistance gradually increases. Mice older than six weeks
are completely resistant to intramuscular injection, but not to intracerebral
administration of this virus (Olitsky, Sabin and Cox). A barrier to the
further progression of the virus seems to develop at the myoneural junction.
In favor of the theory of a maturation resistance of tissues, it may also be
stated that an active immunity is very difficult to produce against certain
cells and toxins in very young animals. This fact has been demonstrated by
the experiments of Famulener, who found that young kids did not respond

REACTIONS OF NEWBORN AND ADULT ORGANISMS 527

to any extent with the production of hemolysins following subcutaneous in-
jections of sheep red blood corpuscles. In more recent investigations Jules
Freund as well as Leona Baumgartner noted that production of agglutinin,
hemolysin and precipitin, interacting with bacteria, erythrocytes or proteins,
is less intense in very young rabbits, and according to Baumgartner, the avidity
of immune sera for antigenic bacteria may be diminished. Furthermore, the
skin in very young rabbits is less sensitive than in adult ones, and in young
guinea pigs the skin likewise reacts less actively to tuberculin. However, as
stated, at present we cannot entirely exclude the possibility that in some cases
a previous infection with a homologous or heterologous microorganism may
have caused an increased resistance against certain viruses or bacteria.

As to the mode in which a physiological maturation of cells leads to an
increased resistance, Hirszfeld is inclined to attribute it to an increase in
affinity of cells for certain toxins, taking place either during a normal bio-
chemical maturation process or as the result of the previous activity ojf
microorganisms and their toxins. Such an increase in affinity of cells for a
certain antigen is also assumed to be the factor causing anaphylactic reactions.
Thus during the process of immunization there may exist, side by side with
the production of antibodies, an increased sensitiveness to the action of toxins.
If children, negative to the Schick or Dick tests, who are allergic to the toxins
of diphtheria bacilli or of streptococci, are actively immunized by the injection
of these respective microorganisms or their toxins, their skin may for some
time react positively to the local injection of the toxins and thus a change may
take place, which is apparently due to an increase in the affinity of certain cells
for the products of these bacteria.

From a purely chemical point of view, very little is known as to the changes
occurring in cells with increasing age, although it has been shown that there
are alterations in the water content and in the amount of calcium and
cholesterin or its esters held by certain tissues during the process of ageing.
Furthermore, Kossel has shown that during maturation of the sperm cells
their constituent proteins undergo definite variations as far as the quantitative
distribution of the amino-acids and diamino-bases (histidin, lysin, arginin)
is concerned. According to Schenk, the character of the globin in the hemo-
globin changes during the ageing of the erythrocytes or in persons affected by
pernicious anemia. Thus it becomes conceivable that the mode of reaction of
certain cells to homoiogenous sera or to toxins may differ under various
conditions, and especially at different ages and during the process of im-
munization; but the chemical character of the factors underlying the change
in the mode of reaction is not definitely known.

It may then be concluded that the differences in reaction towards homoiog-
enous or heterogenous tissues which organisms show at different stages of
development and at different ages are not an isolated phenomenon, but are
the expression of changes in reactivity to various types of foreign substances,
especially to those of a toxic character. In general, both the reactivity of cells
against foreign substances and the ability of tissues to produce immune sub-
stances against them is lacking or diminished in young organisms. Presumably

528 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the production of immune substances presupposes the power of the tissues
to respond with primary reactions against the foreign material. The chemical
differentiation is not yet completed in fetal or newly-born organisms, as is
evidenced by their diminished power to act as antigens. Perhaps this lack
of available antigen in certain cells may be responsible for a diminution in
their binding power for toxic substances and in their ability to react against
the latter. Moreover, it seems that, as we have seen in the case of the blood-
group agglutinogens, differentials may develop in certain cells before the
mechanisms have developed which lead to the production in the serum of
specific substances interacting with those differentials. Such observations
permit the conclusion that in the embryo and fetus some substances, which
are present in the adult organism and which may function as antigen, are
lacking, and likewise, that the earlier ontogenetic states have not yet acquired
the full power to react against and to neutralize strange and toxic substances.
In agreement with this interpretation are certain experiments of Theobald
Smith and R. B. Little, who noted that newborn calves are prone to acquire a
generalized infection with colon bacilli; this can be prevented if the calves
are fed colostrum or receive the serum of a lactating cow. The deficiency in
globulin in the blood of newborn calves prevents the production of agglutinins
in these animals (Orcutt and Howe). P. Cannon suggests that the availa-
bility of globulin for the production of immune substances is the essential
factor on which depends the ability of an animal to respond with immune
processes to injurious interferences. Globulin is relatively deficient in very
young, and again in old individuals and also under unfavorable conditions of
nutrition. While this factor may play an important role in determining the
degree of resistance of an animal to an injurious condition, it is probably not
the only one which is active.

But there exists, on the other hand, also some evidence which indicates that
the embryo and fetus, and even the organism at the time of birth, may pos-
sess substances which are able to act as antigens and which are not possessed
by the adult organism. Thus Lockemann and Thies, and Graefenberg and
Thies, found that it is possible to sensitize adult rabbits with the serum of
rabbit fetuses, and that a second injection of such serum causes anaphylactic
shock in the sensitized animals ; even the mother can thus be sensitized against
the blood serum of its own fetuses. It appears, furthermore, that during the
later stages of pregnancy, rabbits as well as guinea pigs become naturally
sensitized against a substance in the blood of their fetuses, the pregnant rabbit
and guinea pig being sensitive to the injection of the blood of newborn ani-
mals belonging to the same species. However, in addition to these effects, toxic
substances of another kind may apparently be active in pregnant animals ; it
has been stated that the latter are sensitive also to the injection of the blood
serum of pregnant animals belonging to the same or different species, while
normal guinea pigs seem to be more sensitive to the serum of puerperal than
to that of pregnant animals.

We do not need to conclude, as have some investigators, that the earlier
ontogenetic stages represent different and phylogenetically more primitive

REACTIONS OF NEWBORN AND ADULT ORGANISMS 529

stages, but merely that the ontogenetic structural development is accompanied
by a parallel chemical development and that therefore different stages of the
developing organisms possess their own characteristic substances, which under
certain conditions may function as antigens. Furthermore, the organs and
tissues of embryos of phylogenetically higher, more differentiated organisms
may resemble the organs and tissues of embryonal, and, perhaps, even of
adult, phylogenetically more primitive forms. But, the embryonal organs and
tissues of the higher organisms differ from those of phylogenetically less
developed species, in that the former possess specific precursor substances
of the organismal differentials present in the corresponding adult forms,
which are lacking in the phylogenetically lower embryonal or adult
organisms.

Chapter 6

Organ (Tissue) Differentials and Their Analysis

by Serological Methods

We have discussed the difference existing between the organismal
differentials and the mosaic characters which compose the indi-
vidual. It is the latter with which Mendelian heredity and also
embryology have so far been almost exclusively concerned. The organismal
differentials are common to all parts of an individual, except perhaps certain
paraplastic structures ; they thus differ from the mosaic characters which
distinguish the various organs and tissues in the same individual, and which
are about the same in organs and tissues of the same type in two different
individuals with distinct individuality differentials. As we have seen, it is
possible to analyze the organismal differentials not only by means of trans-
plantation but also by means of serological experiments, one of these two
methods being preferable in certain ranges of the spectrum of relationship,
the other in other ranges. Similarly, it is possible to analyze by serological
methods the organ differentials, those chemical factors which are the same
in analogous organs in different individuals, but which differ in the different
organs within the same individual. Moreover, it has been found that there
are a few organs or tissues in which, under certain conditions of experi-
mentation, species differentials cannot be demonstrated by serological meth-
ods, but in which organ differentials can be distinguished by these means.
The first example of this kind observed and the one best known is the lens
of the eye. Uhlenhuth found that this organ can function as antigen and
lead to the production of anti-sera, which, however, react about equally
against the lens substance of mammals, birds, reptiles and amphibia, while
they do not affect other organs of the species whose lens was used for
immunization.

Organ differentials are, therefore, factors inherent in organs or tissues;
they are very similar in the corresponding organs and tissues of different
individuals and species and represent the structural and functional char-
acteristics of these organs and tissues, while the organismal differentials are
the substances which distinguish organisms as such from one another, and
are the same in different organs and tissues of the same individual. The
organ differentials represent what is different and distinct in different parts
of the same organism, while the organismal differentials represent what is
common to different parts of the same organism but differs in analogous
organs and tissues of different individuals and species.

Potentially, both organismal and organ differentials are present in the
fertilized egg in the form of precursor substances. These differentials are in

530

ORGAN (TISSUE) DIFFERENTIALS 531

some way connected with each other, differences in organismal differentials,
which distinguish individuals or species, being associated in a graded way with
differences in organ differentials and, in general, with differences in the mosaic
structure of the organism of which these organ differentials form a part. In
the embryo, the organismal differentials, as well as the organ differentials, are
not yet fully specialized ; in both cases only the more fundamental differentials,
the precursor substances of the finer differentials, exist. Thus the organ dif-
ferentials at a certain embryonal stage may be represented by the differentials
of the germ layers. Furthermore, the organizer (inductor or evocator)
substances in their origin are intimately connected with the mosaic characters
of the individual ; they are produced in differentiating organs or tissues and
initiate further differentiation in other organs or tissues. The organ differ-
entials represent, therefore, the specific structures and functions of the
tissues and organs within an organism ; they are intraorganismal differentials.
As we have stated previously, in this strict sense the organ differentials
represent the specific factors which are common to the same types of organs
in individuals belonging to the same species and in species belonging to the
same order or class; but in making these distinctions between homologous
organs and tissues, it must be understood that finer differences exist between
tissues in the same organism than is usually assumed. When we differentiate
between certain organs and tissues in an organism we use for this purpose,
as a rule, very obvious anatomical and histological peculiarities. Thus we
distinguish between organs, such as liver and kidney, and between tissues,
such as epithelium and connective tissue; among the epithelial tissues we
distinguish still further between stratified and glandular epithelium, and
among the connective tissues, between the ordinary collagenous and the
cartilage and bone-forming connective tissues. However, further analysis
shows that these are rather crude distinctions, that in reality much finer ones
exist between different tissues, which, on the basis of morphological criteria,
we are accustumed to consider as possessing essentially the same character.
As we have mentioned on previous occasions, biochemically the connective
tissue of the uterine mucosa differs from that of the Fallopian tube and
vagina, and even within the different parts of the cervix there are graded
differences in the connective tissue, as is shown by the response of these
tissues to the lutein and follicular hormones. Fibroblasts differ biochemically
in different areas of the embryo as to the amounts of acid they produce and
also in their resistance to acid and in their proliferative power. Furthermore,
Huggins has shown that the regenerating epithelium of the bladder has the
power to transform the fibroblasts of certain organs, but not those of others,
into osteoblasts, which are then able to produce bone. Apparently the
epithelium of the bladder gives off a contact substance, which acts as an
organizer and transforms only connective tissue cells of some organs into
osteoblasts. As these examples show, the differentiation of various tissues
is a much finer one than is assumed on the basis of ordinary morphological
criteria; but such finer differentiations have not yet been subjected to
serological tests and these would presumably be unsuccessful on account of

532 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the present lack of satisfactory serological methods for the detection of these
organ or tissue differentials.

The organ differentials develop in the embryo and undergo a predetermined
sequence of transformations. As a rule, the organismal differentials, or their
precursors, are present in the developing organs and tissues ; however, certain
endproducts of these transformations of organ-forming substances may lose
a part, or even all, of their organismal specificity, as occurs for instance in
the case of some enzymes and many hormones and related substances. Also,
the endproducts of tissue differentiation, such as keratin and lens fibers, may
lose entirely or in part the finer organismal differentials, while the organ
differentials retain their full strength ; this applies only when certain serologi-
cal tests are used as indicators for the organismal differentials. Because of
the relative predominance of the organ differentials and the diminution in
the significance of the organismal differentials in certain organs or tissues,
it is possible to demonstrate by serological tests, organ specificity against
tissues and substances derived from the same species when it is difficult to
demonstrate individuality and species differentials. Homoiogenous lens,
spermatozoa, keratin, thyreoglobulin, fibrinogen, and even insulin, may
function thus as organ, tissue or substance antigens. Likewise casein from
goats' milk and the albumin of chicken egg may serve as such antigens in
goats and chickens, respectively. In a similar way, Schwentker and Rivers
produced antibodies against rabbit brains in rabbits, not only by the use of a
combination of rabbit brain extract and pig serum, but also autolyzed or other-
wise pathologically altered brain as such could serve as antigen. Substances
of a homoiogenous nature may function in serological tests as antigens if
they are abnormal or if they do not occur in the circulation under ordinary
circumstances.

Both organismal and organ differentials develop thus by a chemical epi-
genesis in the course of phylogenetic and ontogenetic development. However,
while the organ differentials or their precursors not only undergo very far-
going, specific changes during embryonal development, but are also readily
accessible to experimental modifications, the organismal differentials or their
precursors seem to be fixed; so far it has not been possible by experimental
means to transform one organismal differential into another, at least in
higher organisms, while it has been possible to change, experimentally, the
mode of development and the transformations of organs and tissues.

We are here concerned only with the serological methods employed for
the analysis of organ differentials. As to the criteria that can be used for
this purpose, we assume the presence of organ differentials, in contrast to
organismal differentials, under the following conditions:

(1) If an immune serum, e.g., one against fowl egg, differs in its reaction
qualitatively or quantitatively from one against blood serum of fowl, or
against other organs, tissues or substances derived from the same individual
or species, we conclude that an organ differential was involved in the
antigenic action which gave rise to the formation of the immune serum. The

ORGAN (TISSUE) DIFFERENTIALS 533

precipitation method, especially in combination with specific absorption, has
been used most commonly in the analysis of such antigens.

(2) If the immune serum directed against a certain organ, or against a
characteristic substance derived from this organ, reacts with the analogous
organ or substance not only from the species which served as the donor of
the antigen, but also from other species more nearly related to or even
farther distant from the donor species, then we assume that these immune sera
and the corresponding antigens are organ-specific. Thus, as stated, the immune
serum directed against the lens of mammals may react about equally well
with lens material from birds, reptiles and amphibia, and even, although not
quite so well, with lens substance of fishes ; in this case we have therefore
predominantly to deal with organ differentials.

(3) If the immune serum, directed against a certain organ, should react
also with blood serum or some of its constituents, or with other organs of
the donor species, the latter reaction must at least be weaker than the one
which takes place with the organ which served as antigen for the immune
serum. In some cases the reactions are graded in accordance with the
graded relationships obtaining between the antigen-furnishing organ or
tissue and the other organs or tissues 'of the donor species. Thus immune
serum against guinea pig erythrocytes may react not only with erythrocytes,
but also with leucocytes and spleen tissue of the guinea pig, but not with
other organs of the guinea pig, nor with the corresponding rat cells; and
the immune serum against brain may react also with testis, but not with
other organs. If an immune serum reacts not only with constituents of an
organ which served as antigen but also with a certain constituent of the
blood, it does not necessarily mean, therefore, that an organismal differential
served as antigen — although it may have this meaning — but it may mean in
some instances that the splitting of very complex material, characteristic of
an organ, into somewhat more elementary substances may lead to a relative
organ-specificity, which allows for the presence of similar substances in
certain other organs or tissues, or in the blood of the same species. The
chemical constituent common to two or more organs and, perhaps, to blood,
which is responsible for the joint reaction of these organs or of the blood with
the immune serum primarily directed against one particular organ, would not,
in this case, be a part of the organismal (species) differential, but of the
differential of the organ used for immunization, as well as of the differentials
of certain other organs or tissues.

It is possible in some cases to increase the specificity of the immune serum
against an organ differential and to diminish or destroy entirely its reaction
with organismal differentials by boiling the antigen before injecting it. In
this way the organismal differentials, which concomitantly with the organ
differentials might serve as antigens, are injured in their antigenic power to
a much higher degree than are the organ differentials. Furthermore, if the
test reaction is carried out with an alcohol extract of the organ which served
as antigen, instead of with native or boiled antigen, the organ-specificity is

534 THE BIOLOGICAL BASIS OF INDIVIDUALITY

intensified in certain instances. Serologically, organ differentials have been
tested in vitro mainly by means of the precipitin or complement fixation
reactions ; organ differentials have also been tested in the living animal by
means of specific cytotoxic effects following injection of immune serum
against a certain organ, or by means of anaphylactic reactions.

In the large majority of cases where an organ differential has been shown
to exist, the simultaneous presence of the organismal differential in the
material serving as antigen could likewise be established, or at least made
probable. A combination of these two antigens is indicated under the
following conditions :

a. If an immune serum reacts not only with the organ or the substance
used as antigen, but also with other organs or fluids of the same species,
although to a lesser degree, this might be due to the presence of an organismal
differential in the antigen; but, as stated above, this is not necessarily the
case.

b. The conclusion that also an organismal differential is involved in the
reaction is strengthened if the immune serum reacts with the analogous
organs of other species in such a way that the reaction is the more intense,
the nearer the species providing the antigen and the second species to be
tested are related to each other.

c. If the immune serum reacts only with the organ of the donor species
which served as antigen, but not with other organs or with the blood of the
donor species, and if it does not react with the analogous organs of other
species, then such an immune serum may or may not be directed also against
the organismal differential. We may possibly have to deal with an immune
serum specific for a certain substance which does not possess an organismal
differential. But if the immune serum, while reacting most intensely with the
antigenic organ of the donor species, reacts likewise, although more weakly,
with other organs of the same species, but does not react with the correspond-
ing organs of other species, then the material which served as antigen contains
in all probability both organ and organismal differentials. The lack of a
reaction with any other species in such a case may represent the end-stage
in a series of reactions, in which the intensity of the reaction decreases more
and more with the increasing distance in relationship between the antigen-
providing species and the other species which are to be compared with the
former.

Various organs, and substances derived from these organs, differ very
much as to the degree of their organ- and substance-specificity. According
to Fleisher, who used in vitro tests, the simultaneous presence of species-
specific substances and of substances of a non-specific character in various
organs complicates the demonstration of the organ- and tissue-specific sub-
stances which they contain. But quite apart from these complications, different
organs actually seem to vary considerably in the readiness with which
these organ-specific substances can be demonstrated. Thus, Fleisher states
that it is very difficult to demonstrate them in the spleen, but that this can be
more easily done in liver and kidney. We have referred to the marked

ORGAN (TISSUE) DIFFERENTIALS 535

specificity of the lens of the eye ; from the lens substance, partial antigens, two
crystallins, may be separated, and also against these specific precipitins can
be produced, which are the same irrespective of the species from which the
antigens are derived (Hektoen and Schulhof ) ; this is an observation which
is in accordance with what has been found in the case of the precipitins
against the lens as a whole. However, these two crystallins are related to each
other, because cross-immune reactions between them do occur. We see, then,
that in this instance the organ specificity can be reduced to the specificity of
certain substances derived from these organs. But in a preceding chapter we
have seen that according to Defalco it is possible, by means of the precipitin
reaction, to demonstrate in the lens of birds the presence of species
differentials.

The brain behaves in a similar manner to the lens ; it also shows a very
pronounced organ specificity, which may or may not be associated with
species specificity. However, as stated, immune serum against brain reacts
equally well with testis (J. H. Lewis). Also, vitellin obtained from egg yolk,
as well as casein and thyreoglobulin (Hektoen) are organ- or rather
substance-specific material. Anti-thyreoglobulin sera do not react with
globulins from other organs.

In other cases a more graded specificity exists. Thus immune serum
against egg albumin reacts also with albumin from fowl serum ; yet both
these albumins can be distinguished by means of quantitative tests. Fibrinogen
and the globulins of chicken plasma are immunologically nearly related to
each other; but they can be distinguished by means of quantitative tests with
immune sera; they are very different from the albumins of fowl's egg or
fowl serum. Similar relationships are found between serum globulins of
mammalian organisms (Hektoen and Welker). As Dale and Hartley, as
well as Doerr and Berger, have shown, the serum proteins exhibit two kinds
of specificities: (a) The species-specificity, which depends upon the char-
acter of the organismal differentials ; this is the same in the various plasma
proteins from the same blood, (b) The fraction-specificity, so-called by
Doerr, which corresponds to organ-specificity. Each mammalian serum protein
can be distinguished from another serum protein derived from the same
individual or species by means of the anaphylactic reaction. Likewise, Bence-
Jones protein, which occurs in the urine under certain pathological conditions
(multiple myeloma), is serologically quite different from the normal serum
or plasma proteins. Immune sera against hemoglobin react with hemoglobin
but not with serum proteins. Furthermore, the antihemoglobin sera are quite
distinct in their reactions from immune sera against the stroma of erythro-
cytes ; the latter contain hemolysin and hemagglutinin, in contrast to the anti-
hemoglobin sera, which do not contain these two antibodies. In general, the
organ proteins are distinct from the proteins of the bodyfluids, although the
latter may be derived from certain organs. On the other hand, we have men-
tioned the close relation which exists between albumin from egg and from
serum.

In lens and brain, lipoid substances seem to be at least partly responsible

536 THE BIOLOGICAL BASIS OF INDIVIDUALITY

for the organ-specificity displayed by these organs. According to Witebsky,
organ-specific lipoids are present also in kidney and liver. In seeds of plants
there occur alcohol soluble prolamins which are identical in very nearly
related species and somewhat different in more distant groups (Wells and
Osborne, Gortner). These may be considered organ-specific substances. We
have referred to these investigations in a preceding chapter, but may discuss
here certain points which relate to the problem under consideration. Wells
and Osborne found that, as evidenced by the anaphylactic reaction, hordenin
from barley and gliadin from wheat are similar to each other; likewise,
gliadin and glutenin from wheat behave much alike immunologically. How-
ever, a guinea pig sensitized with gliadin reacts somewhat more strongly with
gliadin than with hordenin. On the other hand, hordenin and glutenin are
quite different, as far as their immunological reactions are concerned ; it may
provisionally be concluded that glutenin and gliadin are distinct substances
and that the common reaction shown by them is due to a common radicle
which they possess. But hordenin does not seem to have this common group,
which may correspond to an organismal differential, though it possesses
some radicle in common with gliadin, which is not shared by glutenin. This
is an interpretation of the facts which would seem more probable than the
assumption that we have to deal, in gliadin, hordenin and glutenin, with
mixtures of different proteins.

Also, in the case of animals evidence has been found that the analogous
proteins in different organs may contain different radicles which determine
the organ-specificity and are associated with certain other characteristics of
the protein which determine the organismal differentials. However, as to the
character of these gradations in structure, interpretations may differ; it
might, for instance, be assumed that the character of the radicle is approxi-
mately the same in nearly related species, but differs more strongly in more
distant species, although some similarity may still exist in the structure of
this radicle even in remote species. It is also conceivable that finer chemical
groups are the same, or only very slightly different, in all nearly related
species, but that the common basic radicle on which they have been super-
imposed is the same in nearly related species, but differs in more remote
classes of animals.

The investigations we have mentioned may serve as examples of organ-
specificity, the latter being due to substances contained in these organs and
tissues; these substances are evidently the bearers of the organ specificities.
It is of interest that these organ-specific substances apparently represent
either reserve foodstuffs or secondary cell constituents not exhibiting the
most characteristic features of living matter, but constituting end-products
of cell differentiation and specialization. Other substances of this kind are
pathological in origin. How far the more labile constituents of living cells,
as for instance certain nucleo-proteins, possess organ-specificity is as yet
unknown.

We shall now take up somewhat more in detail the question as to what
extent organ differentials may be associated with organismal differentials,

ORGAN (TISSUE) DIFFERENTIALS 537

either in the extracts or suspensions of certain organs or in chemically
defined substances obtained from and characteristic of such organs. We
shall consider only certain of those substances concerning which there are
on hand data sufficient for this analysis.

1. It is known that a comparison of the blood sera of various groups of
animals, when tested by means of the precipitin reaction, indicates the degree
of relationship of these animals within a somewhat limited range of specificity.
We have furthermore seen that different serum proteins show a definite
substance-specificity when tested with precipitin containing immune sera;
but a specific reaction takes place in the latter case only if the antigen and
the corresponding substance with which it is to be compared belong to the
same or to nearly related species (Hektoen and Welker). Thus, immune
serum directed against the serum globulin prepared from human serum
reacts only with the globulin prepared from human or from monkey blood.
Immune serum against fibrinogen prepared from mammalian blood reacts
strongly with mammalian but only weakly with chicken fibrinogen, while con-
versely, anti-chicken fibrinogen serum reacts strongly with chicken and but
little with mammalian fibrinogen. By means of absorption of the immune
serum by the principal antigen, all the antibodies can be removed from the
immune serum, but absorption with the corresponding antigens from other
species removes only the special antibodies which are adjusted to the latter
kinds of antigen, while the principal antibody, namely that which is directed
against the fibrinogen of the species which was used for immunization,
remains in the serum. Much finer are the differences between the albumins
from the egg of different species. Here the investigations of Dale and Hartley,
who used the anaphylactic method, at first seemed to indicate an identity
between the crystallized albumins of fowl and duck eggs, but by the use of
more refined methods Dale succeeded in distinguishing between these two
substances also immunologically. Such a result suggests that in other cases
as well, when apparently no immunological differences exist between two
corresponding proteins from two species, such differences after all may exist.

These observations show that we may have to deal in these instances not
only with organ differentials, but also with organismal differentials. Like-
wise with casein, it seems possible that a combination between a substance-
(organ) and an organismal-specificity exists, although by means of immune
reactions apparently no differences between the antigenic effects of different
mammalian caseins can be established.

2. Hemoglobin possesses a distinct substance-specificity, corresponding to
a tissue- or organ-specificity ; the immune serum against this substance con-
tains specific precipitins. However, an immune serum against hemoglobin
of a given species reacts not only with the hemoglobin from this species,
but also with the hemoglobin from nearly related species, but not with
that derived from a distant species. Thus immune serum against cattle
hemoglobin may react also with a solution of sheep hemoglobin, but not
with a solution of hemoglobin from farther distant species; exceptionally,
this immune serum reacts with human hemoglobin, but only if it is used in

538 THE BIOLOGICAL BASIS OF INDIVIDUALITY

stronger concentrations. Likewise sheep and goat hemoglobins react with
the immune sera against hemoglobin from either of these two species and
immune serum for human hemoglobin reacts also with monkey (Macacus
rhesus) hemoglobin. Immune serum directed against chicken hemoglobin may
react with hemoglobin from turkey, duck and pigeon, although not with
hemoglobin from goose. If immune serum against cattle hemoglobin is
exhausted with cattle erythrocytes, all the antibodies against any kind of
hemoglobin are removed, but if such cattle immune serum is exhausted with
sheep or human corpuscles, only the antibodies against sheep and human
hemoglobin, respectively, are removed. In this instance we have to deal with
a phenomenon similar to that observed in the case of fibrinogen.

Heidelberger and Landsteiner demonstrated the specificity also of crystal-
line hemoglobin and were able to show that the precipitate which forms,
when hemoglobin and its immune serum are mixed, is due to hemoglobin
as such acting as an antigen and not to an adhering impurity. They further-
more found the specificity of hemoglobins derived from different species to
be very great ; thus horse hemoglobin immune serum reacts much more
strongly with horse hemoglobin than with that of the donkey. In addition,
the reaction was found to be substance-specific, the immune serum against
horse hemoglobin reacting not at all or only very weakly with serum albumin
from horse. However, according to Higashi, immune serum against chicken
hemoglobin gives a reaction of equal or nearly equal intensity with hemo-
globin of pigeon or sparrow; this, then, would indicate a restriction of the
species-specificity of hemoglobin. Hemoglobin has, therefore, a marked organ-
specificity and a definite although somewhat less marked organismal-specificity,
comparable to that of serum proteins.

According to Ottensooser and Strauss, globin, which can be split off from
hemoglobin, also has a similar organ- and species-specificity. Immune sera
against horse globin and against horse serum do not give cross-reactions if
the complement fixation is used as a test, but if precipitation is the test method,
immune serum against globin from horse reacts also with horse serum as a
whole, but not with albumin from horse serum, while immune serum against
horse serum does not give a precipitate with globin. By preparing amino-
and nitroglobin further structural specificities are produced. Anti-globin sera
reacted with anti-nitro- and anti-aminoglobin sera, but the reciprocal reac-
tions did not take place ; anti-amino- and anti-nitroglobin sera reacted only
with their respective antigens, but not with globin.

In these experiments the relationships of hemoglobins of various species
were tested by means of immune sera and a substance- (tissue) specificity,
as well as an organismal-specificity, was found ; the antigens, within a certain
range of accuracy, behaved in accordance with the relationships of the various
species. Reichert and Brown had previously observed that also the structure
of the hemoglobin crystals corresponded to the phylogenetic relationships of
the species from which they were derived. These criteria did not, however,
suffice for the differentiation of horse, donkey and mule hemoglobin. How-

ORGAN (TISSUE) DIFFERENTIALS 539

ever, the characteristic crystal forms of the hemoglobins, which were studied
by Reichert and Brown, correspond to primary differentials in transplantation
and not to antigens which call forth immune reactions, with which we are
here principally concerned.

There are other characteristics of hemoglobin which may serve to dif-
ferentiate the species of animals and even individuals, but no definite cor-
respondence has been shown to exist between these characteristics and the
relationships of the species or individuals tested. In this regard, according to
Anson, Bancroft and Mirsky, there are differences in the maximum spectro-
graphic intensity of the bands of oxyhemoglobin in different species, but the
distribution of these bands does not correspond to the relationships of the
species. Measurements of the distances between the maximum intensities of
the A bands of oxygen and carboxyhemoglobin showed individual as well as
species differences, but the individual differences could be greater than those
between species. In these respects these characteristics behaved therefore to
some extent like the blood-group differentials, which are quite unlike the
individuality differentials in their distribution.

3. Thyreoglobulin immune serum reacts specifically with thyreoglobulin,
but not with globulins from pancreas and adrenal glands, and the immune
sera against the latter substances react specifically only with the globulins
from their respective organs. But it seems that in the case of thyreoglobulin
the organ-specificity is not an absolute one and that this substance may react
also with certain other proteins from the same species. There is an organismal
differential present in thyreoglobulin, in addition to its organ- or substance-
specificity. The immune serum against thyreoglobulin reacts in a graded way
also with the thyreoglobulin from other species and in this case the range of
associated secondary reactions is wider than in the case of serum proteins
and of hemoglobins. Thus immune serum against thyreoglobulin of one
mammalian species reacts in the greatest dilution with thyreoglobulin from
the same species, but in stronger concentrations it reacts also with many
other mammalian thyreoglobulins ; however, the relative specificity, as mani-
fested by the graded character of the reaction, does not seem to be present
in every instance, probably owing to an organ- or substance-specificity, which
the thyreoglobulins from many species have in common and which may
sometimes cover up the organismal-specificity. Still, a species-specificity does
exist, as is shown by the fact that immune serum against chicken thyreo-
globulin reacts with chicken thyreoglobulin, but not with mammalian thyreo-
globulin. As with hemoglobins and serum proteins, so too with thyreoglobulin,
absorption of the immune serum by the thyreoglobulin which served as
antigen removes also the antibodies against the associated secondary thyreo-
globulins, while absorption with an associated thyreoglobulin removes only
this secondary thyreoglobulin, but leaves the antibody against the principal
thyreoglobulin intact. If for immunization heated thyreoglobulins are used
as antigens, the resulting sera contain only organ-specific antibodies, but not
antibodies against the organismal differentials (Witebsky). Similarly,

540 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Witebsky found that the globulin of adrenal glands and pancreas lose their
organismal differentials as the result of the heating but retain their organ
differentials.

4. If we use whole cells or pieces of organs for immunization, we find
again a combination of organ and organismal differentials present in the
material serving as antigens. If rat leucocytes are injected into an animal
belonging to a different species, the immune serum reacts most strongly with
rat leucocytes and more weakly with kidney and liver of rat. This indicates
a relative organ-specificity ; but in addition there is noticeable also a reaction
with guinea pig and rabbit leucocytes, which is weaker, however, than the
reaction against rat leucocytes. This graded character in the reactions indicates
the presence of organismal differentials. Forssman differentials are also
found in leucocytes (Witebsky).

5. In the lens there seem to be only organ-specific differentials, yet a
closer analysis indicates the presence also of organismal differentials. This
was shown by the transplantation experiments of Fleisher, and the recent
experiments of Blumenthal indicate even the presence of individuality dif-
ferentials. Serological tests also suggest the presence of organismal differ-
entials, at least of the very coarse ones. Thus immune serum against mam-
malian lens manifests a weaker reaction against fish lens, or the reaction
against the latter may even be lacking altogether. Conversely, the anti-fish
lens serum reacts more strongly with fish lens than with mammalian lens
(Hektoen and Schulhof). By means of absorption tests it can be shown
that each type of lens, fish as well as mammalian, binds its own immune
serum quota in a specific manner and leaves the other fraction behind in the
serum.

According to Krusius, a guinea pig sensitized against a mammalian lens
reacts only very weakly against fish lens, and not at all against the lens of
the eye of cephalopods. Likewise, the observation of Krusius, that if animals
are sensitized with the complete lens of a certain species, there may take
place a slight reaction also with the serum from this species, indicates the
presence of organismal differentials. As Krusius points out, this reaction is
probably due to the effect of the outer layer of the lens, which shows as yet a
less fargoing tissue differentiation than the inner lens fiber material. With
increasing tissue differentiation of this, as well as of other organs, the
organismal differentials seem to become less marked or to disappear in the
end, while the organ differentials become more pronounced, at least as far
as the serological tests indicate. It is the transformation of the capsular
epithelium into lens fibers which brings about this change. A similar change
takes place, according to Krusius, when the epidermis undergoes keratiniza-
tion. The species-specificity depends, therefore, apparently upon the presence
of primary tissue proteins, while the organ-specificity depends upon a modi-
fication of the primary tissue proteins comparable to the introduction of a
N02 group into the protein molecule in the experiments of Obermayer and
Pick. The keratin of horse hoof and of human hair shows accordingly, in
anaphylaxis experiments, an organ-specificity in addition to a species-

ORGAN (TISSUE) DIFFERENTIALS 541

specificity. This interpretation agrees with the findings of v. Szily, to which
we shall soon refer.

However, that organismal differentials are still present in the lens is also
indicated by the fact that injection of homoiogenous lens material in the
rabbit does not, as a rule, lead to the production of antisera, but it is neces-
sary for this purpose to use heterogenous lens substance, and conversely, in
a rabbit sensitized with strange lens material its own lens cannot call forth
an anaphylactic reaction. This observation is in agreement with the demon-
stration of individuality differentials in lens tissue by means of cellular
reactions. Still, according to Guyer, it seems that a guinea pig can be
sensitized to strange lens material by injuring the animal's own lens. It is
possible that in the case of the lens a very pronounced organ specificity
covers up the more finely graded organismal differentials and allows only
the very coarse ones to become manifest. In agreement with this interpre-
tation would be the experiments of Defalco, who obtained species-specific
precipitins for the avian lens.

6. Two different types of organ-specific constituents have been demon-
strated in the brain by Witebsky and his collaborators. Witebsky and
Steinfeld showed that there are (1) alcohol soluble, coctostable substances.
The antigen, or rather hapten, present in an alcohol extract from the brain
of a given mammalian species, reacts not only with the immune serum
produced against the brain extract from this particular species, but also with
those of all other mammalian species. It is therefore to a very high degree
organ-specific, and to a much lower degree, or not at all, species-specific.
Similar organ-specific, alcohol soluble differentials can be shown to exist in
the posterior lobe of the hypophysis and in the medulla of the adrenal gland.
(2) In addition, there are demonstrable in brain suspensions, heat-sensitive
substances, which are not soluble in alcohol and which react only with the
immune serum against the brain of the species from which this organ was
derived; hence, beef brain suspensions react only with immune serum
against non-heated beef brain suspensions. These differentials, which are
presumably of a protein nature, are therefore not only organ-specific, but
also, to a high degree, species-specific. The immune serum prepared against
non-heated brain suspensions reacted in some instances also with alcohol
soluble antigens; but such a reaction did not take place if the corresponding
immune serum against certain other organs, such as the epiphysis, were tested
in a similar manner.

While in some cases, according to Witebsky and Lehmann-Facius, boiled
or alcohol soluble organ extracts seem to be better suited than watery, non-
heated extracts for the demonstration of organ-specific constituents, this
apparently is not true in all cases. Thus it is possible to distinguish by means
of complement fixation between brain and epiphysis, if we use immune sera
prepared against the unheated, water soluble antigens; but immune sera
against the heat stable, alcohol soluble substances in epiphysis and brain do
not make possible the distinction between these two organs. The alcohol
soluble substances in brain and epiphysis are evidently identical, or at least

542 THE BIOLOGICAL BASIS OF INDIVIDUALITY

so similar that they cannot give origin to organ-specific immune substances.
On the other hand, certain water soluble, heat sensitive substances, pre-
sumably of protein nature, in brain and epiphysis represent organ differ-
entials which do permit the distinction between these two organs. However,
while these two kinds of immune sera react most strongly with the
homologous organ extract, a weaker reaction takes place also with the other
organ suspension. This is probably due at least partly to the presence of
common organismal (species) differentials in brain and epiphysis, as is
indicated likewise by the fact that the immune sera against unheated beef
brain and epiphysis suspensions react also with beef serum.

7. Fleisher showed that in liver and kidney there exist species- specific as
well as organ-specific substances ; in addition to strictly organ-specific sub-
stances there are others which are similar to or identical with substances
present in certain other organs. He used the complement fixation test, but
before making the latter he determined the presence of specific and other not
strictly specific substances in the immune sera by means of absorption.
Also, according to Witebsky, immunization with suspensions of kidney and
liver leads as a rule to the production of both species- and organ-specific
antibodies, but the former predominate. It is also of interest that precipitins
and hemolysins do not develop as readily after injection of these organ
suspensions as after injections of serum proteins and erythrocytes; they are
found only in some of the immune sera against these suspensions.

In recent experiments Henle and Chambers showed that if rabbits are
immunized with particles 0.1-0.3 micra in diameter, obtained through centrif-
ugation of various organ suspensions of the mouse, organ-specific agglu-
tinins can be obtained from brain, liver, kidney and testicle ; negative or
doubtful results were obtained from muscle, lung, pancreas and spleen. Liver
and brain particles from ferret reacted likewise in an organ-specific manner
with the corresponding anti-mouse sera, whereas ferret kidney and muscle
particles behaved differently. These experiments indicate therefore a very
marked organ-specificity of several organs of the mouse, which may have
been associated with a species specificity. These particles consisted of nucleo-
proteins as well as other extractable substances (lipids). Claude had formerly
shown that similar particles behave tinctorially and chemically like mito-
chondria. It is therefore possible that in these experiments mitochondria
were the substratum which yielded the organ-specific reaction, but it is more
probable that these particles corresponded to the "particulates" which Bensley
described in the liver of guinea pigs; these particulates are similar in their
chemical constitution to mitochondria, but they are smaller in size.

8. In this connection we may also refer again to the experiments of Mann
and Welker, who found that it is possible to produce in rabbits precipitins
for the proteins of human and rat carcinoma. The immune sera against
human cancer reacted with autolysates of human cancer, but not with those
of rat cancer, and the immune sera against rat cancer reacted with autolysates
of rat cancer, but not with those of human cancer. There was some indica-
tion that the number of positive results was greater if the cancerous tissue,

ORGAN (TISSUE) DIFFERENTIALS 543

which was tested with the immune serum, was derived from cancer of the
same organ as that which served as antigen for the preparation of the
immune serum, than if cancer of a different organ was used; but positive
results were obtained in many cases also with autolysates from cancer
originating in a different organ. Likewise, the serum of cancerous patients
reacted with such immune sera, and in this case also there was an indica-
tion of an organ specificity. No reactions were found, as a rule, with the
sera of non-cancerous persons. It seems, then, that in carcinoma a protein
antigen is present, which possesses a certain degree of organ specificity
combined with species specificity.

9. It is possible to produce specific immune sera also against spermatozoa,
or, rather, against spermatic fluid, as well as against testicle and epididymis.
According to Ohki, the immune sera against the latter organs owe their origin
to spermatozoa, or to precursors of spermatozoa, which are found in the
tubules of the testicle and epididymis. He finds that the anti-spermatozoa
sera produced in rabbits react most strongly with spermatozoa from the same
species which served as donor, but that a weaker reaction may take place
also with the sperm-antigens from heterogenous species. Even between
spermatozoa of birds and mammals and their immune sera an interaction
may occur. Both precipitin and complement fixation reactions were used in
these tests. They are, on the whole, specific for the spermatozoa present in
testicle and epididymis, although the immune sera against these cells may
also react with the blood serum of the donor species ; but the latter kind of
antibodies can be removed by means of selective absorption, following which
the antisperm antibodies alone remain in the immune serum. It is also
possible to remove by means of specific absorption, through previous addition
of spermatic fluid, the antisperm fraction of the immune serum ; but while,
in this case, according to Hektoen and Schulhof, the antibodies against blood
serum are also removed, according to Strube the precipitins for blood serum
remain intact in the immune serum. It may then be stated that distinct
antibodies may be produced against a spermatic fluid and against a serum
fraction present in the antigen. On the other hand, according to Ohki, it is
possible to obtain immune sera against spermatozoa which do not react with
the serum of the donor. If we accept the conclusion that it is really the
spermatozoa, as such, against which the immune sera are produced, we
should have to assume that the spermatozoa contain both organ and
organismal differentials, or rather their precursor substances. They would
contain organismal differentials or their precursors, because the immune sera
react most strongly with spermatozoa of the donor species ; they are organ-
specific because an immune serum against mammalian spermatozoa reacts
also with avian spermatic fluid. While also in this instance the organ dif-
ferentials seem to be more prominent than the organismal differentials, they
are less so than the differentials of the lens of the eye. It is, furthermore, of
interest that according to Ohki not only heterogenous spermatozoa may
serve as antigens, but also those of homoiogenous, or even of autogenous,
origin.

544 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Similar are the conditions in fishes, as Kodama has shown. Immune sera
against fish spermatozoa are organ-specific ; they react with spermatozoa of
their own as well as of related species, but not with the extract of fish muscle.
However, they are directed also against organismal differentials or their
precursors, as is shown by the fact that they may respond in a quantitatively
graded manner to the spermatozoa of different species of fishes, in accordance
with the phylogenetic relationship of the latter.

The investigations on antisperm immune sera present an interesting prob-
lem, inasmuch as in this case we may have to deal with antigens which are
constituents not of somatic cells and tissues, but of germ cells from which
the somatic tissues develop, after sperm and egg have united during the
process of fertilization. These germ cells must, then, possess substances,
which behave like species differentials, as well as the precursors of substances,
which distinguish different individuals. They must, in addition, contain
substances which are specific for this type of cells and which correspond
therefore to organ differentials. But these differentials would not be identical
with the fully developed substances present in the adult somatic tissues; in
general, the specific substances present in the germ cells would represent,
rather, the precursor differentials, from which the substances in the adult
organism develop. This follows from what is known of the mechanism of
embryonal development and from investigations on the lens of the eye and
the brain, which indicate that also the antigenic function of the organ
differentials arises only in the course of embryonal life. However, the
possibility exists that, after all, the immune sera against spermatozoa do not
develop in response to antigens contained in the spermatozoa proper, but to
a constituent of the spermatic fluid ; still even then these antigenic constituents
would presumably not be derived entirely from ordinary somatic tissues, but
also from constituent parts of the spermatozoa or of the cells from which
the latter develop. This is suggested by the fact that also autogenous sub-
stances may in this instance have antigenic power.

10. It is possible to immunize rabbits against the yolk of the chicken egg.
The antiserum thus produced forms specific precipitates with the egg yolk
of fowl, but not with their blood serum or with chicken embryo extract. We
have to deal, here, with organ-specific substances. The reaction is strongest
with the egg yolk from fowl, while a weaker reaction takes place with the
yolk from other birds, but not with the yolk of fish or reptile eggs (Seng).
There exists in^ this case, therefore, a certain quantitative gradation which
corresponds to the systematic relationship of the organisms involved; but this
correspondence is not complete, inasmuch as the intensity of the reactions
among different species of birds does not seem parallel to their relationship;
and, furthermore, the reactions do not agree with the serum precipitin
reactions. There is, then, present in the yolks of eggs a system of substances
which differ among themselves in their structure in a manner which cor-
responds, to some extent, to the differences in systematic relationship ; yet
these relationship differentials in the egg yolk appear to be independent of
the organismal differentials of the serum proteins. This is perhaps due to

ORGAN (TISSUE) DIFFERENTIALS 545

the fact that in the egg yolk reserve substances are involved, in which species
differences have developed apparently independently of the general organismal
differentials. A similar reservation should, perhaps, be made also in regard
to the other instances cited by us, in which organismal differentials seemed
to be associated with the organ differentials. The possibility cannot be
excluded that there are present in various organs, species-specific substances
which, to a certain extent, are graded according to relationship, but which
need not be identical with the ordinary organismal differentials. Just as the
structures of organs show certain gradations which agree with relationships,
so there may perhaps be present in these organs substances and also structures
of a particular kind corresponding to this specificity. They would represent
secondary or accessory organismal differentials; while the organismal dif-
ferentials, which can be recognized by transplantation and especially by the
cellular reactions against the transplants, would be the basic, primary
organismal differentials. Inasmuch as it is not possible in many cases to
apply transplantation tests for the differentiation of these types of organismal
differentials, it must be stated again that the term "organismal differentials"
is used here, and also in some other chapters, in a more general sense, as
representing substances which are gradegl in accordance with the phylogenetic
relationship of the organisms from which they are derived, and that there
are among these organismal differentials, in the wider sense, the primary
organismal differentials, which are characterized by their presence in all the
tissues and organs of an organism ; the most characteristic constituent of the
latter type of organismal differentials is the individuality differential, which
occurs in all or almost all of the tissues and organs of an individual, and
which differentiates the individual from all the other individuals of the same
species.

In the case of the proteins of the egg white, Hektoen and Cole have shown
that of the five proteins of the white of hen's egg, four are quite distinct from
the proteins of chicken plasma and only the conalbumin of the egg seems to
be identical with serum albumin. A common immune reaction between egg
white and blood plasma of chicken depends therefore upon the admixture of
a protein which is identical in both. On the other hand, there exists a
pronounced species-specificity of the egg-albumins of various species, and
the crystallized egg-albumins of such nearly related species as chicken and
duck are immunologically not identical (Dakin and Dale). Of course, in the
egg yolk and egg white we have to deal not with substances representing the
embryonal precursors of the organismal differentials, but with auxiliary
substances surrounding the embryo or serving as food for it. It might there-
fore be expected that they are chemically and immunologically distinct from
the essential constituents of the developing or adult organisms ; they repre-
sent paraplastic substances which are formed in the adult animal.

We see then, that as a rule substances or cells which contain organ
differentials also contain organismal differentials, but that the proportion in
which these two differentials are present in the same substance or cell differs
in different cases. It seems furthermore that in certain instances organ and

546 THE BIOLOGICAL BASIS OF INDIVIDUALITY

organismal differentials can give rise to distinct antibodies, which may be
separated by means of specific absorption. This relationship between organ
and organismal differentials is further confirmed by a study of the origin
of the organ differentials during embryonal development. Von Szily has
shown that human fetal lens does not yet possess the marked organ-specificity
which is displayed by the adult lens, and that, correspondingly, the anti-
human fetal lens serum reacts also with human serum-albumin. Hektoen
and Schulhof confirmed this finding, although they did not observe it as
regularly as von Szily. In addition, the immune serum against fetal lens
shows a greater affinity for lens material from the same species than for that
from a more distant species; both of these reactions, indicating the presence
of organismal differentials in the fetal lens, may be lost in the course of
further differentiation of the lens tissue. We may then conclude that in the
fetal lens, which differs also structurally from the adult lens, organismal
differentials are more and organ differentials less pronounced than in the
case of the adult lens, and that as the result of complete structural differentia-
tion the significance of the organismal differentials diminishes, while that of
the organ differentials increases. Similarly, Witebsky finds that the organ-
specific lipid constituent of the brain appears only when a certain stage of
embryonal development has been reached, and that it is not yet present in
the brain of very young embroys.

During embryonal development, it may be assumed, we have at first to
deal with substances in which the organismal differentials are prominent,
but in the course of further embryonal development changes tending toward
greater differentiation of the parenchyma and toward the formation of
paraplastic substances take place, which are specific for a particular organ,
and concomitantly with the increase in organ specificity the organismal
specificity decreases or may be lost almost entirely, at least as far as serological
tests indicate. The substances endowed with a marked organ specificity are
formed therefore from substances which possess a greater organismal
specificity. With the increasing complexity of an organism, not only the
organismal differentials become more refined — as is indicated by the trans-
plantation method — but also the organ specificity becomes more pronounced.
An analogous process takes place continuously in certain tissues during adult
life. Certain cells in which the organismal differentials are in all probability
as yet preponderating, become transformed into material in which these
differentials decrease in importance or are lost altogether, and in which
correspondingly the organ differentials begin to predominate. Such a process
seems to occur during the transformation of epidermal cells into keratin,
and presumably also during other tissue differentiations, and this change in
the differentials is apparently a characteristic feature of tissue differentiation
in general.

Organ differentials occur then, ordinarily, in combination with organismal
differentials. In order to immunize against an organ differential of a non-
protein nature it is usually necessary to employ protein substances which
possess different species differentials and which act as carriers for the organ

ORGAN (TISSUE) DIFFERENTIALS 547

differential. Thus homoiogenous lens material does not commonly produce
antibodies against lens, but Hektoen and Schulhof found that it may do so
if the rabbit which is to be immunized by means of homoiogenous lens, has
on a previous occasion been sensitized against heterogenous lens. Otherwise,
if homoiogenous lens does elicit formation of immune substances, these are
very weak; this seems to be true also of spleen. Similarly, it is as a rule
necessary to use heterogenous brain in order to produce organ-specific anti-
bodies against this tissue ; a heterogenous carrier must be combined with
alcohol extracts of lens or brain to produce immunization. On the other hand,
according to Kato, rabbit fibrinogen may elicit in rabbits which are injected
with it, the formation of antibodies against this antigen, although it possesses
the same organismal differential.

Likewise in the case of organ globulins, including thyreoglobulin, homoiog-
enous immunization seems to succeed, perhaps because these globulins do not
occur normally in a free state in the various organs but are bound to other
substances, and if they are freed from the latter, they are strange to the
organism which is not adapted to their effects. In the case of spermatozoa, it
seems that even autogenous cells may serve as antigen, and the same has been
claimed for the lens of the eye and for the skin by some authors, but this has
been contradicted by the findings of others. It is conceivable that organ
differentials may perhaps act as autogenous antigens under certain conditions,
although the organismal differentials cannot act as such. The organism and
all its parts are adapted to the autogenous organismal differential because it
is present in all, or almost all, the organs of the body, whereas each organ
differential is limited to a certain restricted area and is therefore strange to
other areas. There may be also some other variations in the reactions of
different organ differentials. Thus if once the antiserum has been produced,
it may react in vitro even with antigens of a homoiogenous nature, at least
in the case of lens and brain ; but as far as antiserum against fibrinogen is
concerned, a reaction seems to take place more intensely with heterogenous
than with homoiogenous substances.

In regard to the chemical character of the organ differentials, it appears
that different types of substances may be involved. We have seen that
thyreoglobulin as well as globulins from other organs may serve as organ-
specific antigens. Similarly, fibrinogen, serum-globulin and hemoglobin possess
a substance (or organ) specificity in addition to species specificity. In the
lens Hektoen and Schulhof have shown that the two crystallins, which are
of protein character, as well as the whole lens can serve as organ-specific
antigens. In brain and epiphysis organ differentials, which also are pre-
sumably proteins, have been demonstrated. We may then conclude on the
basis of these immunological findings that organ differentials may be of a
protein nature. But there are some other data which indicate that also sub-
stances of a different kind may thus function. In lens, brain, carcinomatous
tissue, and also in leucocytes, substances which seem to represent organ
differentials can be obtained by means of alcohol extraction. Such alcohol
soluble extracts may react in a specific manner directly with the antibodies,

548 THE BIOLOGICAL BASIS OF INDIVIDUALITY

as, for instance, those directed against leucocytes, brain or carcinoma; on
the other hand, they serve as organ-specific antigens in combination with
heterogenous sera functioning as carriers, as has been shown in the case of
lens and brain.

As far as the immune serum against leucocytes is concerned, the reaction
with the organ-specific component of these cells seems to be intensified if the
alcohol soluble fraction is used as antigen, but the species-specific constituent
is also present in this alcohol soluble fraction. Still more pronounced organ-
specific effects can be obtained, according to Witebsky, if boiled suspensions of
leucocytes serve as antigens. In such immune sera the organ-specific com-
ponent predominates decidedly over the organismal-specific component, which
latter may be lacking altogether. Likewise, through heating of thyreoglobulins
the species-specific differential can be destroyed, while the substance- and
organ-specific component remains preserved. In some instances the alcohol
soluble organ differentials were found to be the more specific ones.

We may then conclude that organ or substance specificity may be associated
with an active protein, or with a different substance which in combination
with a protein serves as antigen. In the case of thyreoglobulin or other organ
globulins, the organ specificity is presumably due to a sidechain attached to
a protein. This sidechain may act similarly to the radicles introduced into
complex proteins, or, in general, into complex colloidal substances in the
experiments of Obermayer and Pick, and of Landsteiner and his collabora-
tors. Graded reactions between different organs may perhaps depend upon a
multiplicity of differential substances, some of which may be common to
them while others are distinctive for certain of these organs. On the other
hand, the organismal differentials are native proteins and they are therefore
destroyed by heating, in contrast with the organ differentials, which are not
destroyed by this procedure. There is however, some evidence that in some
organismal differentials an alcohol soluble component may be present; in this
case we may have to deal with the secondary or accessory type of organismal
differentials.

Absorption experiments have shown that after immunization with appar-
ently single substances, such as fibrinogen and thyreoglobulin, antibodies
develop not only against the fibrinogen and thyreoglobulin of the species
which served as antigen — these represent the principal antibodies — but also
against the corresponding substances of related species; these would be
associated antibodies. Now it is possible, as especially Hektoen and his col-
laborators have shown, to remove all the antibodies against certain substances,
the principal as well as the associated ones, by absorption with the antigen
from the original species, while only the associated, but not the principal,
antibodies are removed by absorption with the differential substance derived
from related species. Similar observations have been made by various investi-
gators also in the case of other antigens and antibodies. Here apparently
are involved single substances calling forth the production of antibodies, and
we must therefore assume that in the molecules of these substances graded
differences exist in different species, which correspond to the relationship of

ORGAN (TISSUE) DIFFERENTIALS 549

these species. They may call forth the production of a number of different
immune substances, which differ from one another by the possession of
different species differentials, and the antibodies corresponding to the species
differential of the antigen used for immunization predominate over the asso-
ciated antibodies in their combining power with the antigen.

The experiments with egg yolk suggest that certain substances which serve
as reserve material, or are of a paraplastic nature, may undergo in the course
of evolution chemical changes which more or less correspond to the systematic
relationship of the species in which these substances are found, but that these
chemical transformations may be independent of and may follow a some-
what different course from those which concern the primary, typical organis-
mal differentials.

Chapter J

Idiosyncrasy and Anaphylaxis and Their
Relation to Organismal Differentials

The term "idiosyncrasy" implies a peculiar state of hypersensitiveness
to a certain substance, which may characterize an individual and
distinguish him from others. In an analysis of individuality a discus-
sion of such a condition should therefore be of interest. While usually only a
small minority of persons are affected by an idiosyncrasy towards a substance,
after all, the frequency with which various substances are responsible for
such a condition differs greatly. There exists, for instance, a potential
idiosyncrasy to the injection of foreign serum, especially horse serum, causing
serum disease among a considerable number of individuals; likewise, the
tendency to become hypersensitive to extracts of ascaris is almost universal
among those infested with this parasitic worm. On the other hand, a hyper-
sensitiveness to chicken egg is not frequent, while to less complex chemical
substances, such as antipyrin, it is quite rare.

However, idiosyncrasy has an additional meaning. It signifies an individual
state, which is not explained solely by the specific character of the substance
eliciting it, but which, to a large extent, is due to the characteristics of the
individual affected. Certain of the principal mechanisms involved are now
understood, at least in their general outline, but others are as yet unexplained.

As a rule, hypersensitiveness to most of the substances with which we
have to deal in indiosyncrasy is localized in definite tissues, without otherwise
affecting seriously vital functions of the organism ; but in certain cases central
mechanisms, on the integrity of which all other functions depend, may be
involved and then an idiosyncrasy may cause rapid death. Such an effect may
be observed, for instance, in the so-called serum disease, where in some indi-
viduals even a first injection of a heterogenous serum, usually horse serum,
may call forth very acute general reactions not unlike those of anaphylactic
shock. The organs most commonly affected in idiosyncrasy are the respiratory
system, especially the nasal mucosa in hay fever and the bronchi in asthma,
the gastro-intestinal tract in food hypersensitiveness, the skin in many condi-
tions in which certain substances act primarily on this organ ; and the skin
may show reactions also in cases in which primarily other organ-systems are
involved.

While thus one idiosyncratic individual may differ from another one as
to the factor which causes the hypersensitiveness and elicits the abnormal
reactions, the modes of reaction and the organ-systems which are hyper-
sensitive are remarkably similar in different individuals. In general, it seems
that the tissue on which a given injurious substance acts primarily, is the one
which becomes primarily hypersensitive to that substance, although subse-

550

IDIOSYNCRASY AND ANAPHYLAXIS 551

quently the hypersensitiveness may extend to other tissues. As stated above,
under some circumstances these localized reactions may appear negligible as
compared with the general reactions which take place ; this occurs, for
instance, when a large quantity of the offending substance, such as a foreign
serum, enters into the circulation.

The condition with which we have to deal in idiosyncrasy is evidently very
similar to that observed in experimental anaphylaxis produced in animals by
repeated injections of substances of a protein character. Opie has made it
very probable that local anaphylactic reactions, as those characteristic of the
Arthus phenomenon, are due to a local interaction between the antigenic
protein and the precipitin which developed in response to the antigenic pro-
tein. The presence and significance of precipitins in this reaction has recently
been confirmed by Cannon, who used more accurate quantitative methods for
the determination of circulating precipitin and thus demonstrated the
parallelism between the amount of precipitin formed and the strength of the
allergic reaction. However, at present the possibility cannot as yet be entirely
excluded that also other types of antibodies may be involved in anaphylactic
phenomena. Anaphylactic shock corresponds to the general reactions noted
in some cases of serum disease ; the local status of anaphylaxis, either in the
skin as seen in the Arthus phenomenon, or in the intestines (Schultz), uterus
(Dale), or blood vessels (Friedberger), corresponds to the types of local
hypersensitiveness as they become manifest in various cases of idiosyncrasy.
However, the anaphylactic shock of the guinea pig, which is the animal most
commonly used in the study of this condition, depends mainly upon a
localized hypersensitiveness of the bronchial musculature; but there may also
be associated changes in the nervous and circulatory systems. If we except
some minor variations, there are two main differences which have led to a
separation of the state of idiosyncrasy from that of anaphylaxis : ( 1 ) While
in anaphylaxis the abnormal reaction indicating hypersensitiveness can be
traced to a previous sensitization by the same substance which subsequently
elicits the reaction, in idiosyncrasy the reaction may be induced by a substance
with which the body has apparently not previously been in contact; (2)
while in anaphylaxis we have to deal with a hypersensitiveness to protein
substances, in the case of idiosyncrasy the active substance may be of a
much simpler character. But in some instances of idiosyncrasy the chemical
character of the active substance is unknown, and it is possible that we may
have also, in idiosyncrasy, sometimes to deal with protein substances. (3) In
general, anaphylaxis is a well defined condition of hypersensitiveness which
may be experimentally produced in animals, idiosyncrasy is a condition of
hypersensitiveness which apparently occurs spontaneously in man. In regard
to the first of the differences between these two states mentioned, there is
much evidence of a clinical as well as of an experimental character, which
suggests that also in idiosyncrasy in man a previous but unsuspected sensitiza-
tion may often have taken place. In some of these instances the sensitization
may even have occurred during intrauterine life by way of the placenta, in
others it may become manifest only a considerable time after contact of the

552 THE BIOLOGICAL BASIS OF INDIVIDUALITY

individual with a certain substance had taken place; in still other cases it
appears to develop only gradually during the continued action of an agent
which has been introduced into the bodyfluids. However, in every instance
among a number of individuals treated apparently in the same manner, only
certain ones manifest such signs of hypersensitiveness ; and the persons thus
affected may be few or many under varying conditions.

It has been shown especially by Cooke and Van der Veer that the tendency
to become sensitized against a given agent is often a hereditary characteristic,
in which apparently Mendelian ratios can be demonstrated. The stronger the
hereditary tendency is in children, the earlier the hypersensitiveness to foreign
protein appears. Thus, if both parents transmit to the child the tendency to
hypersensitiveness, the idiosyncrasy tends to appear, on the average, earlier
than when the transmission is unilateral. In the case of Primula extract and
nickel salts, Bloch has shown that while some persons can be more readily
sensitized than others, all persons can, in the end, be made experimentally
hypersensitive to these substances. But to other substances, such as iodoform,
salvarsan and mercury, it is much more difficult to obtain a hypersensitiveness.
The conclusion may then be drawn that there may exist a hereditary pre-
disposition which determines the readiness with which an individual can be
sensitized against a certain substance.

There enter, thus, two separate factors in this set of phenomena: (1) A
hereditary tendency to become more or less readily sensitized by contact with
a certain substance; this is a factor which seems to act in a quantitatively
graded manner; (2) a sensitization which takes place as the result of contact
with a certain substance. The greater the predisposition is, the more readily
is the sensitization accomplished. We have here evidently to deal with condi-
tions similar to those which have been noted in a number of other pathological
conditions and especially also in cancer. In the latter condition we expressed
the relation between the inducing factors and the disease by the formula
H (Heredity) X S (Stimulation) = C (Cancer). Similarly in idiosyncrasy,
the relation apparently exists: H (Hereditary predisposition) X S (Sen-
sitization) = I (Idiosyncrasy). In malignant tumors we find all degrees of
hereditary predisposition to cancer, and in some cases cancer may develop
apparently spontaneously without long stimulation of tissues, as, especially,
when certin embryonal abnormalities end in cancer formation. Perhaps also
in cases of idiosyncrasy in which the quantity of predisposition exceeds a
certain limit, the quantity of external factors needed for the establishment
of this condition becomes so slight that these may escape recognition. There-
fore, in some instances the idiosyncrasy may become manifest apparently on
a first contact with a given substance. It is possible that we have to deal here
with a condition similar to that noticed in those diseases caused by micro-
organisms or viruses, where, in some individuals, there seem to occur spon-
taneously formed antibodies against the causative factor. In this latter in-
stance, also, the question arose as to whether or not these antibodies owed
their origin to the action of an antigen, which might perhaps not be identical
with the agent causing the disease. However, there is some evidence which

IDIOSYNCRASY AND ANAPHYLAXIS 553

indicates that immune bodies may develop under conditions in which the
action of definite antigens can be excluded.

It has been observed that an individual who has manifested signs of hyper-
sensitiveness in one organ or tissue is apt to become hypersensitive also in
another organ, and perhaps to another agent. As already stated, it is largely
the place where a substance acts on the body which determines the tissue
that will become hypersensitive to a given substance in an individual, and
which furthermore determines the character of the symptoms which will
develop; the recipient tissue is the one which, as a rule, tends to become
hypersensitive. There is, in addition, a specific tendency in some individuals
to become sensitive to certain substances, as for instance, poison ivy. Further-
more, we cannot exclude the possibility that in certain individuals there may
be a greater tendency of a special organ or tissue to be affected, while other
tissues are exempt, and lastly, while, as stated, the set of symptoms in a
particular tissue or organ-system is usually very similar in different individuals
exhibiting idiosyncrasy, irrespective of the agent which has caused the hyper-
sensitiveness, nevertheless, minor differences seem to exist; for example,
some agents more than others tend to lead to the production of eczema of the
skin.

In discussing the similarities and differences which exist between the experi-
mental state of anaphylaxis in animals and idiosyncrasy in man, we have
referred to the fact that simple chemical substances, which cannot themselves
elicit experimental immunity or anaphylaxis in animals and thus cannot
serve as antigens, may induce idiosyncrasy, or, to use a term introduced by
Coca, may act as atopens, against which an idiosyncrasy may develop. How-
ever, this difference between anaphylaxis and idiosyncrasy has lost much in
significance since Landsteiner has shown that relatively simple chemical sub-
stances (haptens) may serve as antigens if they are combined with foreign
sera serving as carriers. But there still remains a definite quantitative differ-
ence between the substances which serve as atopens ("idiosyncratogens")
and the substances used by Landsteiner. The latter were organic substances,
which were rendered more complex by the introduction of certain groups,
as, for instance, the azo group, or they were organic dyes in combination
with tyrosin and resorcin, while the former may be very simple inorganic
substances. However, as first shown by Obermayer and Pick, also relatively
simple inorganic groups like iodine may determine a new specificity if intro-
duced into serum protein. There exists a further similarity between certain
experimental findings of Landsteiner and observations which have been made
in idiosyncrasy. Landsteiner has shown that different stereoisomers may give
rise to specific states of anaphylaxis and also that the ortho, para, and meta
positions, respectively, of certain groups in the molecule may determine
specificities. Correspondingly, Nathan and Stern observed in a person an
idiosyncrasy for meta-dihydroxybenzene, although there was no reaction to
ortho- or para-dihydroxybenzene.

It is possible to accomplish a passive transfer of the state of anaphylaxis
from one animal to another by injecting blood serum of the anaphylactic

554 THE BIOLOGICAL BASIS OF INDIVIDUALITY

animal into a normal one. While there is reason for assuming that it is the
"sessile" antibodies, those localized in certain cells and tissues, which are re-
sponsible for the anaphylactic reaction taking place in contact with the anti-
gen, at the same time these antibodies may also be circulating in the blood and
can then be transferred to another individual ; in the latter these specific
antibodies again may attach themselves to certain cells and tissues and render
them hypersensitive to the action of the specific antigens. Similarly, in
idiosyncrasy it is possible to transfer this condition passively in many, al-
though not in all cases, by injecting a small amount of blood serum of an
idiosyncratic person intracutaneously into a normal one. If on the following
day the antigen is re-injected into the same place of the skin, a marked
reaction, indicating hypersensitiveness of the treated tissue, appears. This is
the Prausnitz-Kiistner reaction. This reaction is positive especially in the
transfer to other persons of human blood serum from individuals hyper-
sensitive to plant pollen, egg white, cow's milk, fish, or horse dander. On the
other hand, injection of the serum from cases of drug idiosyncrasy does not
lead to passive transfer of the hypersensitive state. The blood serum of the
hypersensitive donor, in whom the Prausnitz-Kiistner reaction is positive,
contains an antibody, reagin, which can combine with the tissue of a normal
person, into whom it has been introduced, and make this tissue hypersensitive.
Such serum, or rather the antibody which it contains, may also bind comple-
ment when mixed with the specific antigen (allergen), or it may neutralize
the latter. It has been possible to accomplish passive transfer of such anti-
bodies also in the guinea pig. For this purpose it is necessary to inject larger
quantities of the blood serum ; the antibodies again become sessile in certain
instances and induce hypersensitiveness. However, the number of cases of
idiosyncrasy in which this last named procedure has succeeded is much
smaller than that in which a transfer from man to man could be accomplished
by the Prausnitz-Kiistner method. It seems that the passive transfer of idio-
syncrasy succeeds better if the serum containing the antibody is obtained
from animals nearly related to those which are to be passively sensitized.
On the other hand, if the serum which serves as carrier comes from a more
distant species, then it is liable to elicit the production of neutralizing im-
mune substances in the injected animal.

There is an additional method which allows the passive transfer of hyper-
sensitiveness, although in a much more restricted sense. It has been shown by
Naegeli, de Quervain and Stalden, in a case of hypersusceptibility of the skin
to antipyrin, in which the skin was sensitized not throughout the body but
only in certain areas, that following autotransplanatation of a piece of the
hypersensitive skin to a place where the skin was normal, the transplant
retained its hypersensitiveness in the new situation. It may be concluded,
therefore, that the hypersensitiveness actually resides in the tissues, and in
vitro experiments in which the skin was exposed to the influence of anti-
pyrin, it could be shown that it was the epidermal cells in which the specific
changes had taken place ; these responded to contact with this substances
with solution processes. We have, therefore, to deal in instances such as this,

IDIOSYNCRASY AND ANAPHYLAXIS 555

primarily with a hypersusceptibility of epidermal cells rather than of blood
vessels. On the other hand, it is the latter which are essentially affected in
cases in which urticaria develops rapidly following the application of a sub-
stance towards which a person shows an idiosyncrasy.

A number of years ago the writer investigated this question as to whether
a piece of uterus, which has been sensitized to horse serum through a pre-
vious injection of this substance into a guinea pig, would elicit a more rapid
and a more intense lymphocytic infiltration than a non-sensitized piece of
uterus after homoiotransplantation into a non-sensitized guinea pig, when
the latter was injected with horse serum following transplantation of the
piece of tissue. The result was negative ; the response of the host to the trans-
planted piece was not altered. It seems, then, that the chemical change under-
lying hypersensitiveness does not increase the reaction characteristic of
homoiotransplanation. Somewhat similar are the recent observations of
Aronson, who found that if a guinea pig is made hypersensitive to horse
serum, the spleen and bone marrow of this animal have not thereby become
particularly sensitive to the effects of horse serum if the latter is added in
vitro, although the injection of horse serum into the skin of the intact
animal would elicit the Arthus phenomenon. On the other hand, if a guinea
pig has been infected with tubercle bacilli, its tissues are readily injured
through addition of tuberculin, either in vitro (Rich and Lewis; Aronson),
or after homoiotransplantation (Pagel).

So far, we have referred to substances strange to the body as exciting
factors in the production of idiosyncrasy. Is it possible that also autogenous
substances, those originating in the same individual, may cause sensitization?
Observations indicating such an occurrence are on record. Thus Duke found
that in several cases, in which, following pregnancy, milk was retained in
the breast or in which lactation was much prolonged, a state of hypersensitive-
ness to the autogenous milk developed. Injection of the patient's milk into
the skin not only gave rise to local skin reactions, but also to asthmatic
attacks. Furthermore, the hypersensitiveness could be transferred by the
Prausnitz-Kustner method to other normal persons, but it was only human
milk, and not cow's milk, which elicited these reactions, indicating that in
all probability an organismal (species) differential was involved in this
condition. Milk does not, under normal conditions, circulate in the body-
fluids and is, therefore, strange to the central organ-systems of the body;
hence the occurrence of an autogenous sensitization is understandable under
such circumstances. Furthermore, there is reason for assuming that here
an inherited predisposition to such a sensitization may play a certain role. In
this connection we may again refer to the experiments of Guyer, who believes
that in the rabbit precipitating antisera can be formed against lens substance
through injury to the animal's own lens, and to the corresponding experiments
of Henshaw, who found that it is possible in the guinea pig to produce sensitiz-
ing antibodies of an autogenous nature by the application of ultra-violet
radiation to the skin.

As already mentioned, non-protein substances in combination with serum

556 THE BIOLOGICAL BASIS OF INDIVIDUALITY

proteins, may serve as antigens and call forth anaphylactic states. Landsteiner
employed for this purpose heterogenous serum and observed that the same
hapten in combination with a heterogenous serum, different from that which
was used for sensitization, may react with the antibody ; under certain condi-
tions even the hapten, as such, may be able to give rise to this reaction. Accord-
ing to Klopstock and Selters, it is possible to sensitize guinea pigs against
diazotized atoxyl by intravenous injection of a combination of this atoxyl
preparation and guinea pig serum. However, in order to accomplish a sensitiza-
tion by means of subcutaneous application of the antigen it is sufficient to
inject diazotized atoxyl alone, without the combination with guinea pig serum.
A reaction indicating hypersensitiveness is elicited in the sensitized guinea
pig by the intravenous injection of diazotized atoxyl and guinea pig serum;
but again, a reaction can also be obtained by subcutaneous injection of the
atoxyl preparation alone, without the combination with guinea pig serum. In
the latter case the reaction consists in a localized necrosis, a condition closely
resembling the Arthus phenomenon. The authors assume that after sub-
cutaneous injection of the atoxyl preparation, the sensitized animal's own
serum combines with the atoxyl and acts as carrier. In the case of sensitiza-
tion with simple chemical substances, such as certain drugs and the extract
of primula, it is likewise possible that a combination of the hapten with autog-
enous serum takes place during the process of sensitization, and also pre-
ceding the idiosyncratic reaction. But as far as we are aware, a direct proof
that autogenous serum may serve as carrier in the process of sensitization to
such antigens has not yet been given.

Experiments of Landsteiner and Chase showed especially clearly the es-
sential similarity between the conditions of hypersensitivity and anaphylaxis ;
these conditions differ in regard to the site of the body which reacts in these
states and in the greater difficulty with which the reactions of idiosyncrasy
become manifest. Both are antibody reactions. Thus, intraperitoneal injections
of stromata of guinea pig erythrocytes, conjugated with picric acrid or with
dinitrofluorobenzene preceded by injections of dead tubercle bacilli called forth
both states. Subsequent applications of picric acid and blood serum mixtures
induced general anaphylactic reactions, as well as local skin responses. Instead
of sensitizing with picric acid-erythrocyte stromata it was possible also to
cause sensitization by injections of picric acid-guinea pig serum; however,
picric acid and horse serum combinations produced only a state of anaphylactic
sensitization but not one of skin hypersensitivity ; to produce the latter, it was
necessary to use homoiogenous serum. These experiments make it very
probable that antibodies are involved in both anaphylaxis and skin hypersensi-
tiveness. In such processes of sensitization, hereditary factors determining
degrees of response of the individuals may enter (Chase) ; this would be in
accordance with the findings of Lewis, Lurie and Webster, which have estab-
lished hereditary differences between the susceptibility to various bacterial
and virus infections of different strains of animals within the same species.

Though all the facts known so far point to the conclusion that idiosyncrasy
and anaphylaxis are closely related or identical phenomena, certain minor

IDIOSYNCRASY AND ANAPHYLAXIS 557

differences may perhaps exist between them. Thus, while the typical immune
bodies are supposed to be serum globulins and are therefore not diffusible
through collodion membranes, it has been maintained that the antibodies,
which make possible the Prausnitz-Kiistner reaction in serum disease and
other kinds of idiosyncrasy, are dialysable.

As to the relationship between anaphylaxis, immunization and organismal
differentials, states of immunization as well as of anaphylaxis may be elicited
by substances carrying organismal differentials, organ differentials, and,
besides, by substances which have no relation to either. These various sub-
stances may also induce a reaction in the sensitized animal. Phenomena of
immunity can, moreover, be elicited against individuality differentials, but it
is not yet certain that anaphylaxis to organismal differentials, which are so
nearly related to those of the host, has been observed.

As far as idiosyncrasy or so-called allergy is concerned, in many instances
this condition seems to be directed against a species differential. Thus, in
idiosyncrasy against hair of a foreign species the state of hypersensitiveness
is a specific one, affecting the hair of a certain species, although overlapping
reactions do occur (W. Storm van Leeuwen). The experiments of Longcope,
O'Brien and Perlzweig, and those of Forster, make it probable that, on the
whole, the reactions against horse dander are specific and distinct from those
against horse serum, although according to Forster cross-reactions take
place to a limited extent. There may, therefore, be a common species differ-
ential involved also in these reactions. We have already referred to the observa-
tions of Duke, in which hypersensitiveness to human milk was not associated
with hypersensitiveness to cow's milk. In a case of experimentally produced
hypersensitiveness of human skin to various kinds of serum by means of
intracutaneous injection, Frei, Biberstein and Frohlich found a similar over-
lapping of the reactions to that observed in the precipitin reactions. The
relationship of the species used determined the specificity or lack of specificity
of the reactions. However, here we have to deal with anaphylaxis rather than
with idiosyncrasy in the strict meaning of this term. In anaphylaxis, precipitins
may be the antibodies involved, according to Opie.

While, therefore, organismal differentials may be concerned in idiosyncrasy
as the exciting agents, they do not, on the whole, play a very prominent part ;
on the contrary, it seems to be characteristic of idiosyncrasy that relatively
simple substances, quite distinct from the complex substances possessing
organismal differentials, are the principal agents ; it is assumed especially in
the case of drug idiosyncrasies that the person's own serum plays the role of
a carrier, to which the hapten attaches itself. But this is by no means certain ;
it is possible that these substances may act directly on the cell protoplasm of
the sensitive tissues and here call forth specific reactions.

Also, other investigations indicate the relative independence of conditions
of hypersensitiveness from strange organismal differentials. Thus while in
general, in immunization against organ differentials it was advisable to
select as antigens sera of a heterogenous nature, which acted as carriers for
the specific organ-specific haptens, in order to produce skin hypersensitiveness

558 THE BIOLOGICAL BASIS OF INDIVIDUALITY

homoiogenous sera seemed to be preferable as carriers ; at least this was found
to be the case in some experiments. It may be assumed that under these
conditions the conjugation with the hapten made the serum so strange to the
receptor tissue as to prevent a chemical interaction between the receptive cells
and the antigen, notwithstanding the identity of the species differentials in
both donor and host. We have perhaps, to deal with quantitative gradations
in such cases, in the sense that if a substance does not usually enter into
combination with a certain type of cells, it has a better chance to act as an
efficient antigen, and only slight alterations in the chemical constitution of
such a substance are required for its antigenic function, whereas substances
similar to those which commonly come in contact with the cells cannot
readily act as antigens. Frequent contacts of this nature may be assumed to
occur between constituents of homoiogenous blood plasma and cells of spleen
or bone marrow, in contrast to skin cells, where such an intimate contact does
not usually take place.

We have referred to the significance of an inherited predisposition in
idiosyncrasy. While a genetic basis may be conceded, the predisposition to
idiosyncrasy seems not to be of a limited nature, directed against a specific
agent, but rather of a more general character. According to Cooke and Van
der Veer, it is determined by a single dominant factor ; but until quantitative
gradations in the degree of predisposition have been taken into consideration,
the mode of inheritance in idiosyncrasy must be left undecided.

The anaphylactic phenomena, on the other hand, which have been studied
mainly in animals, manifest pronounced species differences as to the readiness
with which anaphylactic reactions can be elicited and as to the organs and
tissues involved. Thus the facility with which the Arthus phenomenon can
be produced varies very much, and, likewise, the relative importance of blood
vessels and bronchi in anaphylactic conditions differs greatly in different
species. In the rabbit, the local reactions of anaphylaxis are very marked in
the skin, while the stomach responds very weakly, and the intestines not at
all; in the dog the order of sensitiveness is just the reverse. In such cases,
again, differentials are involved, which form a part of the Mendelian mosaic
in an organism. In the predisposition to idiosyncrasy, we have presumably
to deal with a character which forms a part of the mosaic constituting an
individual, and, as we have seen, this is to be distinguished from the individu-
ality differential which characterizes an individual as a whole.

The idiosyncrasies, as far as they are known to us, concern human beings
and represent one of their individual characteristics. They are therefore
comparable to various mosaic characteristics which may serve to distinguish
individuals, such as skin patterns, scents, tissue malformations and electric
brain potentials. It is an interesting phenomenon that contact with relatively
simple constituents of our environments can alter the reactions of tissues
with which they come in contact in such a specific and individualized manner.

Chapter 8
Toxins and Organismal Differentials

The organismal differentials are recognized by means of certain
definite reactions which are called forth when a strange differential
is introduced into an organism. The reaction may be a primary one,
or it may be a secondary immune reaction. These effects may follow trans-
plantation of pieces of tissues, as well as injections of bodyfluids or of ex-
tracts of tissues from other organisms, and they cause a disequilibrium of
the host to a degree which varies with the relative strangeness of the
organismal differentials of donor and host; the intensity of the reaction of
the host tissues against a strange graft or material injected is to a large extent
a measure of this disequilibrium and of the degree of strangeness between
host and transplant, although some accessory factors may modify the
intensity of this reaction within certain limits. We have found throughout
that the farther distant the relationship between transplant and host, the
greater the incompatability which results from transplantation. This applies
to transplantation in higher, more differentiated organisms as well as in
embryos of amphibia; but as a rule, it is only the transplant which suffers,
the host being in such a favorable position that no serious injury is inflicted
upon it in the large majority of cases. However, we have referred to some
instances in which the transplant exerted a toxic effect on the host, as, for
instance, in the transplantation experiments of Diirken and Kusche, and in
the transplantation of amphibian eggs in the experiments of Weber and others.
There were indications that in some of these transplantations we had to deal
with the injurious effects of special substances rather than with the specific
action of distant organismal differentials.

If these special substances orginate in an organism and normally come
in contact with its various tissues acting as endorgans, and especially if they are
present under ordinary circumstances in the circulating bodyfluids, they are
as a rule not toxic for this organism. There is a mutual adaptation between
the cells and organs and these autogenous substances. But under abnormal
conditions such constituents of the body may be carried to tissues with which
normally they do not come in contact, and then they may act as poisons ; thus
bile in contact with the pancreas or other tissues of the peritoneal cavity may
be toxic, or if complex substances constituting the body, such as certain pro-
teins, are split in an abnormal manner and these split products come in
contact with organs and tissues of the organism, they may have injurious
effects. Also, if hormones which are not toxins in the ordinary meaning of
this term, are formed in excess, as may occur following an increase in the
amount of tissue producing the hormones or following a more intensive stimu-
lation of this tissue, or if the hormones are deficient in quantity, due to a lack
of the necessary tissue in which they originate or to a lowering of its metabo-

559

560 THE BIOLOGICAL BASIS OF INDIVIDUALITY

lism, injurious effects may become noticeable and abnormal changes may take
place within the economy of the organism.

But if these special substances are introduced into a strange individual they
may here call forth toxic effects. In the preceding chapters we have discussed
already the agglutinating and hemolytic properties of heterogenous blood
sera, which seem to be conditioned by factors other than organismal differ-
entials. We have also discussed states of hypersusceptibility in which otherwise
innocuous substances become strongly toxic.

In a wider sense we may include also the strange organismal differentials
among the toxins. But in a restricted sense we understand by toxins, special
substances produced by certain micro-organisms or by more complex higher
organisms, which are injurious for various species apparently without regard
to relationship. Such toxins are substances which may be formed in special
organs and they may therefore be regarded as belonging to the class of
organ- or tissue-specific substances, without however representing the real
organ or tissue differentials; they represent mosaic characters which have
developed in addition to the typical organ differentials.

In the case of injurious substances derived from bacteria, we have to
distinguish from real toxins, non-specific so-called ptomaines, which pre-
sumably are mainly split products of the medium on which the bacteria grow ;
the latter furnish essentially the proteolytic or lipid-splitting enzymes. The
ptomaines do not therefore contain the organismal differentials. As to the
exotoxins, against which antitoxins can be obtained, these are substances which
are specific for certain types of bacteria ; thus the tetanus toxin differs in its
character and effects from the diphtheria toxin. These exotoxins apparently
do not possess organismal differentials; a gradation in the character of the
exotoxins produced by various bacteria, corresponding to the relationship of
these microorganisms, has not so far been demonstrated. The so-called
endotoxins seem to represent diverse kinds of substances, among which are
nucleoproteins which may be distinctive of different species, as for instance,
those obtained from pneumococci and streptococci. However, nucleoproteins
obtained from various streptococci are less specific than certain other anti-
genic substances present in these microorganisms, and moreover, some
endotoxins appear to be non-proteins and are, perhaps, glyco-lipids.

Among animal toxins it is especially the poisons found in amphibia and
in reptiles which have been studied more intensively. In various species of
urodeles, as well as of anuran amphibia, poisons are produced in the glands of
the skin and also in the parotid gland. The distribution of these substances does
not show a complete parallelism to the relationship of the various species and
their pharmacological effects differ. Some apparently are identical in their
action with digitalis, a plant glucoside. Thus in the European toad, Bufo
vulgaris, several specific substances have been obtained from the skin and
parotid gland; although in different species of Bufo such substances show
some differences, essentially they are of a related nature, acting similarly to
digitalis. Twitty and Johnson recently observed in embryos of Triturus
torosus a substance paralyzing larvae of Amblystoma tigrinum ; this substance
is apparently different from the toxic substances present in the glands of the

TOXINS AND ORGANISMAL DIFFERENTIALS 561

skin of Triturus. Embryos of related species of Triturus also produce this
paralyzing toxin, but either in smaller quantities than Triturus torosus or in
a weaker form. Furthermore, other types of Amblystoma are also susceptible
to its action, though not to the same extent as Amblystoma tigrinum. The
Triturus toxin is not poisonous for various species of Triturus. In some
respects there is noticeable a relation between the amphibian organismal
differentials, on the one hand, and these toxins and also the structure and
metabolism of the poison-producing glands of the skin and parotid, on the
other. However, in other respects these organ-specificities do not parallel the
organismal differentials. Also, Bytinski-Salz has described, in the embryos
of certain anuran amphibia, toxic substances somewhat similar to those which
are produced in the adult cutaneous glands, but the order of toxicity in the
embryonal material and in the adult skin in different species is not the same.
The adult Bufo produces very toxic substances in the skin, while it is
especially the embryos of Pelobates which contain poisonous material.

If we omit from consideration these specific poisons, which do not respect
phylogenetic relationship as far as their orgin and their action on different
organisms is concerned, there still remain substances, formed in the embryo,
having toxic effects, which on the whole run parallel to the distance in relation-
ship between the species producing the toxins and the species serving as a
test object. We have, therefore, to distinguish between two kinds of toxic
substances in these amphibian larvae : (1) Those which are due to peculiarities
of certain organs and which apparently act more or less independently of
their respective organismal differentials, and (2) those more closely related
to organismal differentials, which become more severe in their effects with in-
creasing distance in relationship of the donor and host species. But the
distinction between these types is apparently not very sharp, being one more
or less of degree.

In the case of snakes we find only to a limited extent, that the phylogenetic
position of the respective animals bears a relationship to the character of their
poison glands, the mechanism by means of which the poisons are ejected,
the nature and effects of the venoms, or even to the behavior of these animals.
Important distinctions which can be made between various types of snakes,
as, for instance, those between poisonous and non-poisonous snakes, depend
at least partly on quantitative differences in the size of the poison glands, in
the amount of venom produced, and in the length of the teeth along which
the venom is ejected. The Elapinae show certain characteristic features which
differentiate them from the Crotalus type; thus the Cobra venoms are prin-
cipally neurotoxic, while the venoms of the Viperidae exert a very strong
local action. Different types of Ancistrodon show much similarity in their
effects. While, however, certain characteristics are thus common to related
groups of these animals, there is no definite gradation in the morphological,
chemical and physiological factors which are concerned in the production and
effects of the various snake venoms, corresponding to the phylogenetic
relationship, and the poisons of very distant classes of animals may show
marked similarities in their action. For example, the mode of action of Cobra
venom is more nearly related to that of the venom of Heloderma, which

562 THE BIOLOGICAL BASIS OF INDIVIDUALITY

does not belong to the snakes, than to that of the venom of snakes of the
Crotalus family, although the Cobra is phylogenetically far removed from
Heloderma. The same lack of parallelism between the effects of the venoms
and phylogenetic relationship holds good, also, as far as the susceptibility of
different species of animals to these poisons is concerned. Thus in the study
of the venom of Heloderma it was found that the rat and toad are relatively
little susceptible to this venom ; in this case we meet again with peculiarities
which stand outside the system of phylogenetic relationship. Evidently we
have to deal with characteristics of production and mode of action which
in snake venoms and the venom of Heloderma are intimately connected with
the development of certain organs. In amphibia it is the cutaneous glands and
also the parotid or sublabial glands, in snakes it is presumably the parotid
gland and in Heloderma the sublabial gland which undergo specific changes ;
within certain groups of animals the same kinds of organs may show mor-
phologically, chemically and functionally more or less related changes.

It may then be concluded that the various animal venoms are not, in a
strict sense, representatives of substances carrying the organismal differen-
tials, but that they may have an indirect relationship to the latter in the same
way as have the structure of organs and the organ differentials. Furthermore,
as already stated, with certain restrictions the various substances poduced in
an organism do not exert a toxic action on those cells and organs of its own
body with which they normally come in contact, nor do they interact in an
injurious manner with other substances normally produced in the same
organism; in particular, also, they do not give origin to the formation of
antibodies.

These facts apply to the animal toxins or venoms in general. The organisms
in which the venoms or toxins originate are, to a large extent, although not
necessarily completely, resistant to the poisonous effects they produce. Thus
toads are resistant to the digitalis-like action of the bufagins and bufotoxins,
but not to the bufotenins and to substances acting like epinephrin. As to the
mechanism which underlies this resistance of toads, it is restricted to that
organ which, in susceptible animals, is principally affected by these constit-
uents of the venom, namely, the heart; such resistance extends also to the
digitalis group of substances derived from plants. These effects must be
considered as due to primary mechanisms of adaptation and not to secondary
effects of auto-immunization.

Also, in reptiles the animals which are carriers of the poison glands are,
to a large extent, immune against their own poisons ; they possess an autog-
enous as well as a homoiogenous immunity. Heloderma is not susceptible
to poisoning by its own venom, but it is susceptible to the effects of rattlesnake
venom; likewise, certain non-poisonous snakes seem to be susceptible to
the effects of Heloderma venom. However, inasmuch as the Heloderma
venom is in some essential respects similar in its action to Cobra venom, it
might be expected that a mutual relative immunity exists in Heloderma and
Cobra for both types of venom. Such tests have not yet been made. But
we have found that Calmette's Cobra antivenin exerts a certain antitoxic
effect upon Heloderma venom. A species immunity to a toxin produced by

TOXINS AND ORGANISMAL DIFFERENTIALS 563

a certain species has been observed also in plants. Blakeslee noted that
colchicine, an alkaloid which has specific effects on mitotic cell division, and
which may induce polyploidy in plant and animal tissues treated with this
substance, does not affect the mitotic divisions in Colchicum, the plant from
which this alkaloid is derived; this is the only higher plan examined so far
which has been found immune to it. However, Cornman has recently shown
that if very large doses of colchicine are used mitoses may show the specific
effect of this substance also in Colchicum ; it is very probable that the relative
immunity of Colchicum is due to the partial inactivation of the alkaloid
produced by this plant and not to a lessened sensitiveness of the mitotic
process to colchicine.

As to the mechanism on which depends the immunity of the various species
against their own poisons, certain data are of interest. According to Phisalix,
snakes which in general are immune to their own venom if it is administered
in the usual way, are found susceptible if the venom is injected into the
brain substance, thus showing that the tissue immunity does not extend to
all the tissues of the animal. In this case the natural immunity of a species
against its own venom is therefore not dependent upon a real lack of suscep-
tibility to the poison on the part of those qells upon which the toxic substance
principally acts. But some mechanisms presumably exist which prevent the
poison from reaching the sensitive cells. In this connection it may be men-
tioned that Fleisher and the writer found that the liver and kidney of Helo-
derma, and of species related to the latter, such as the turtle, have the ability
to absorb Heloderma venom more effectively than the organs of species not
as nearly related to Heloderma. This suggests that these organs of Heloderma
may perhaps be concerned in the natural immunity of this animal against its
own venom, and that possibly proteins bearing organismal differentials may
play a role in the process of absorption.

We have to distinguish from the condition of relative immunity of an
organism against autogenous and homoiogenous poisons, a nonspecific in-
crease or lessening of resistance of some species to certain poisons, irrespec-
tive of the phylogenetic relation between the species tested and the species
which produces the poison. Various types of mechanisms may come into play
in such species differences and they differ in different cases.

The differences in the effects which the poisons of amphibia and reptiles
exert in various classes and species of animals are similar to those noted in
various species of parasites and symbionts in general, and in particular,
bacteria and protozoa. In neither instance are the effects determined primarily
by the genetic relations between the organismal differentials of the host and
of the bearer of the injurious agent, whether the latter is an animal or
bacterial toxin ; if the organismal differentials play a part at all under such
conditions, it is only an indirect one, in the same sense in which also the
effectiveness of an organ differential may be affected by its connection with
an organismal differential. Thus it is evident that the virulence of certain
bacteria for one vertebrate species and their lack of virulence for another
does not run parallel to the relationships of the respective microorganisms
and hosts.

564 THE BIOLOGICAL BASIS OF INDIVIDUALITY

It is well known that some bacteria are quite harmless parasites for certain
mammalian species, while others are very injurious, apparently without
regard to the phylogenetic relationship between microorganisms and hosts.
Special mechanisms apply here which are contingent, in part at least, on the
relations of these microorganisms and their toxins to specific organs. More-
over, mechanisms which differ in the case of different toxins may make a
certain substance toxic for a given organ in one species and innocuous for
the corresponding organ in another species. Hence it seems that the injurious
effect of tetanus toxin for some species depends upon the power of the brain
substance in this species to bind this toxin. In a more resistant species the
brain may have a diminished affinity for this toxin. Furthermore, the degree
of injuriousness of certain microorganisms, and of the substances given off
by them, depends upon primarily, preformed mechanisms as well as upon
secondary, acquired immune mechanisms, which latter may become effective
as the result of a primary interaction between host and parasite, leading to
injury in the host. The effects may also vary in very young and in adult or
old host organisms.

The importance of both species and organ in determining the activity
of microorganisms is especially clear in the case of certain fungi or bacteria,
which function as symbionts in some species of insects. There is, here, an
adaptation not only to a particular species of insects, but also to a particular
receptive organ, a mycetoma, which has been formed from the fat tissue
surrounding the digestive tract in this species and which is especially suitable
for the life of the symbionts. These symbionts are found only in this organ
and in one other location in the hosts. The mycetoma is not produced in
response to the presence of the symbionts, as might have been assumed, but
it develops even when they are lacking. If now the mycetoma is transplanted
from the larvae of a species, such as Periplaneta or Psylla, to which these
microorganisms are adapted, to the larvae of another species, for example,
Tenebrio, to which they are not adapted, the transplant may remain alive
throughout the life of these larvae; but such transplanted symbionts manifest
no activity in their new hosts, in contrast to the activity in the old host to
which they had become adapted.

The relations of microorganisms and their toxins to hosts are, then, in a
general way comparable to those of poisonous reptiles, amphibia and other
poisonous animals and their toxins to various species. These relations do not
depend directly upon the organismal differentials of host and symbiont,
parasite or toxic substance, although in certain instances phylogenetic rela-
tionships may play a limited role. The factors which determine the interaction
between hosts and symbionts, parasites and toxins, are in some respects
comparable to the Forssman differentials, which occur without regard for
phylogenetic relationship. The relations between toxins and organism are
essentially of an organ-specific character ; but there may perhaps to a limited
extent also organismal differentials be involved; the toxins show specific
adaptations to the species in which they are produced, and there is a notable
correspondence in the relations of toxins and of parasites or symbionts in gen-
eral to various species acting as receptors for the toxins, or as hosts for the
parasites or symbionts.

Chapter p

The Chemical Nature of Organismal

Differentials

In the preceding chapters we have analyzed by means of tissue reactions
the individuality and species differentials, as well as organismal differ-
entials in general. Immune reactions made it possible to analyze still
further the species differentials and the differentials of genera, orders and
classes of animals, and even of plants; but, individuality differentials were
accessible to serological tests only in a very restricted way. Immune reactions
can be used in the study of all those differentials which are able to function
as antigens. This includes in addition to the organismal differentials, organ
differentials, the heterogenetic differentials of various kinds, and the blood-
group differentials, as well as specific antigens present in certain micro-
organisms and metazoic cells.

In the majority of these cases we have to deal with substances which have
not yet been isolated chemically, but which can be recognized and differentiated
from one another by the tissue and serological reactions which they induce. As
to the chemical nature of these substances, our knowledge is therefore very
limited. However, there can be little doubt that the organismal differentials are
proteins ; this is indicated by their great sensitiveness to heat and to the
action of substances which are known to denature proteins. As to the organ,
heterogenetic and blood-group differentials, proteins may also enter into their
constitution, but they may still retain to a certain degree at least their
characteristics as antigens under conditions in which proteins are denatured.
Therefore other groups than proteins form part of these antigens. They
may be conjugated proteins, combinations of proteins, acting as carriers, and
of complex carbohydrates, lipids, or simpler organic substances acting as
haptens. The combinations with simpler substances are of significance es-
pecially in the state of hypersensitiveness. But even simple inorganic and
organic substances as such, seem to be able to induce idiosyncrasy in certain
individuals predisposed to this condition, although there is the possibility that
even in this case they become effective only in combination with proteins. In
all these instances it has been shown that as a rule the antigenic function
proper, that is, the production of immune substances or antibodies, requires
the combination of these non-protein substances with proteins; but if the
antibodies have once been formed, they may interact in a specific manner
also with the non-protein material functioning as haptens. However, it has
been proven more recently by Heidelberger that in pneumococci, type-specific
and species-specific complex carbohydrates are present, which may act as
antigens and call forth the production of antibodies without having previously
entered into combination with proteins. Specific carbohydrates have been iso-

565

566 THE BIOLOGICAL BASIS OF INDIVIDUALITY

lated also from various other microorganisms, especially from streptococci.

Recent studies of proteins make it very probable that in the organism the
simpler peptid chains are present, not as such, but in association with one
another, and it has been suggested that their molecular weights are multiples
of a unit possessing a molecular weight of 34,500 (Svedberg). Reversible
associations and dissociations may take place. According to Bergmann, such
a unit is built up of 288 amino-acid residues and a protein may consist of
multiples of such units. Within these units certain amino acids recur at
regular intervals, which are characteristic of different proteins. X-ray studies
make it probable, moreover, that such protein chains may be folded and that
parallel fibers may be linked together by means of their active sidechains in defi-
nite patterns, the distance of these chains being ascertainable by the X-ray pat-
tern (Meyer and Mark, Astbury). According to Mirsky and Pauling, these
sidechains are united by hydrogen bonds between the peptid nitrogen and the
oxygen of the carboxyl group.

Denaturation by heat, application of alkali, acid or various other means,
is supposed primarily to bring about breaks in these sidechain bonds and to
unfold the main chains. Denaturation also alters or reduces the specificity of
the proteins ; it may diminish or destroy the specificity of the antigens and it
destroys the individuality differentials. Conversely, in accordance with this
theory of protein structure, we may assume that the specificity, and in par-
ticular, also the specific character of the individuality and species differentials,
depend upon the character and distribution of these patterns and linkages as
well as on the chemical constitution of the amino-acids ; and it may further-
more be suggested that some of these factors are specific for cell and blood
proteins in different individuals; also, that all the cell proteins in the same
individual must have a certain characteristic in common, which differentiates
these proteins from the proteins of all other individuals. At present it seems
impossible to do more than to make this general statement concerning the
possible connections between the nature of the individuality differentials and
theories of protein structure, of which several have been proposed.

There is a second series of investigations which may throw some light on
the structure of various differentials, although they have more significance
for the organ, heterogenetic and blood-group differentials than for the
organismal differentials. These investigations, to which we have already re-
ferred, deal with the experimental modification of antigens and the corre-
sponding changes in the immune substances which are elicited by the injection
of the modified antigens. This method of research was inaugurated by
Obermayer and Pick, who thus laid the foundation for the subsequent
fargoing analysis of the chemical nature of antigens. It is of interest, in this
connection, that the discovery of Jacques Loeb of the possibility of inducing
heterogenous fertilization by addition of alkali to the medium in which the
germ cells are suspended, and thus of modifying the specificity of the fertiliza-
tion process, suggested to Obermayer and Pick the thought that also the
antigen specificity might be accessible to changes by chemical means. They

THE CHEMICAL NATURE OF DIFFERENTIALS 567

therefore began to study the chemical factors underlying the species specificity
of the precipitinogens. Their principal finding was as follows: The species
specificity of cattle serum was not greatly altered by heat, nor by such
substances as alkali, toluol and chloroform, but it was fundamentally changed
by introducing the iodine of Lugol's solution into the protein molecules, by
diazotizing the protein, or by producing xanthoproteins by means of nitric
acid. The species specificity was destroyed by the latter processes and new
specificities were created instead. The antibodies which originated through
immunization with these new antigens, reacted specifically also with other
proteins into which similar chemical radicles had been introduced, but no
longer or very little with the unaltered proteins of the original serum. Fur-
thermore, they made it probable that it was an aromatic constituent of the
protein, tyrosin, to which the new group was anchored. They concluded,
therefore, that the aromatic constituents of proteins were mainly responsible
for the antigen specificity.

These observations led Obermayer and Pick to distinguish between the
constitutional and the original structure of a protein ; by the latter was meant
its species characteristics. A first type of substances, such as acid, alkali,
toluol, as well as application of heat, leave the latter intact but change the
former, while introduction of a second group of radicles, such at N-N, N02,
or J, Br, changes the species specificity. However, the distinction between
these two types of specificity no longer seems to be as sharp as Obermayer
and Pick assumed. A part of the species-specificity of the serum may still
be left even after introduction of a new group of the second type of substances,
especially after diazotation; on the other hand, specificities may be modified
also by alkali and by heating. Furthermore, even the introduction of the
methyl and acetyl group, or of other groups which do not combine with the
aromatic constituent of the protein molecule, may likewise modify the species-
specificity. Thus, as Landsteiner has shown, esterification with acid alcohol,
acetylation and methylation may cause loss of specificity of a protein, although
these groups do not directly affect the aromatic nucleus of the protein. But
essentially, Obermayer and Pick have established some of the basic facts
concerning the constitution of antigens and their species-specificity. These
investigators also made the important observation that a number of partial
precipitins may develop through immunization with a protein, the constitu-
tion of which has been altered experimentally; and some evidence has been
found by subsequent investigators which confirms the conclusion that the aro-
matic protein group is of great importance for the specificity of the antigen.
Thus, Wells pointed out that gelatin, which lacks the aromatic group, also
lacks antigenic powers, and still later it was shown that the introduction of
the metanilic acid radicle into gelatin changes the latter into a potential
antigen, which reacts also with an antiserum against the combination of
another protein with metanilic acid. Furthermore, Wormall found that iodine,
in altering the specificity of the protein, combines with the tyrosin radicle.
However, while all these data point to the conclusion that the character of

568 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the aromatic group in the protein molecule is of great importance in fixing
the species-specific nature of the latter, still it is apparently not the only
determining factor.

On the foundation laid by Obermayer and Pick, Landsteiner and his asso-
ciates built further and they established, among others, the following im-
portant facts:

(1) Xanthoprotein and diazotized protein show a close serological rela-
tionship ; similarly, there is a strong cross-reaction between iodo- and bromo-
protein ; but there is a sharp serological distinction between the nitrated and
diazotized protein on the one hand, and the halogenated protein on the other.
These differences may depend not only on the nature and the number of the
substituting groups, but also on the place of substitution, and there is an
indication of gradations in these reactions. While in this way a new specificity
can be produced, a remnant of the old organismal specificity may still be
left, and although chemically altered horse serum calls forth the production
of antibodies, which react also with other protein compounds which have
been coupled with similar radicles, still the reaction may remain most
intense with the substituted compounds of horse serum. Antiserum against
diazobenzene serum protein from cattle, precipitates diazobenzene protein
from cattle serum, but not that from human, horse or rabbit serum; nor is
there a reaction with the native, unchanged serum from cattle. Thus it
becomes conceivable that diseased or functionally changed tissues may give
off proteins, which may act as antigens in other individuals of the same
species. We have here to deal with the combination of a species and a struc-
tural specificity of certain substances, which recalls the complex specificity
due to the combination of organ and organismal specificities previously dis-
cussed. However, the chemical alteration of a protein must be fargoing if
the immune serum is to react with antigens derived from a different, non-
related species into which the same group has been introduced.

(2) Introduction of complex organic groups, together with the diazo and
certain other radicles, increases the specificity of the reaction to the new
substance. Of special importance in determining the specificity of the azo-
protein are acid groups which are introduced into the benzene ring, while
the introduction of methyl, methoxyl, halogen and nitro groups is less effec-
tive in changing the specific character of the antigenic substance.

(3) Likewise, the position of certain groups introduced into the protein
molecule helps to determine the specificity of the latter. Hence the same
group, if introduced into the ortho, meta or para position, calls forth in each
case the production of specific antibodies, although weaker cross-reactions
may occur also with other than the homologous antibodies. The specificity of
these substances is therefore not absolute, but relative and graded, and
there are, moreover, certain preparations which elicit reactions that do not
conform to the expected specificity. In addition to the ortho, meta and para
positions, also differences in the stereoisomeric constitution of certain sub-
stances may yield specific antibodies.

(4) Perhaps the most important finding of Landsteiner, however, con-

THE CHEMICAL NATURE OF DIFFERENTIALS 569

cerns the possibility of synthesizing antigens by combining a substance, which
alone is unable to produce antibody formation, with a foreign, heterogenous
protein or serum and thus to obtain a complete antigenic substance. The
serum in this case acts as "carrier" for the specific substance, the hapten,
which latter does not need to be a protein. Landsteiner first synthesized in
this way a hapten and a protein carrier in the case of the Forssman antigen
by combining the alcohol extract from heterogenetic organs with hog serum.
As in Obermayer's and Pick's observations, the protein in the original
antigen and in the substance with which the antibody is tested do not need
to be identical, and if they are very different, then the specificity may be
limited to the hapten. The hapten alone may be able to react with the anti-
body, provided it possesses a sufficiently large molecule, and especially if
this molecule has colloidal properties. Landsteiner succeeded by these means
in separating the ability of an antigenic substance to elicit the production
of an immune substance from its ability to react with such an immune
substance, and he furthermore recognized as a distinct property of an antigen,
or of a part of an antigen, the power to inhibit in a specific manner the
reaction between antigen and immune substance. While as stated, the first of
these functions requires as a rule a combination of a hapten, which may be a
non-protein substance, and a carrier of a protein nature, the latter two func-
tions may be exerted by the hapten alone.

In studying antibodies against azoproteins, Landsteiner found that the
action of an antibody, which developed against a well defined chemical
substance, was not confined to the antigenic substance, but it included sub-
stances chemically similar to the homologous antigen. Landsteiner concluded
that the serological cross-reactions of the proteins of related animals are due
to similarities in the chemical structure of these substances. This constitutes
at least one of the possibilities of such cross-reactions.

As to the inhibiting effect of haptens, Landsteiner extended an early
observation of Halban and thus found that even in cases in which the hapten
does not undergo a visible reaction with the antibody, its presence may be
recognized by its specific inhibiting effect on precipitation, complement fixa-
tion, and hemolysis, which would otherwise occur if the full antigen were
brought into contact with the antibody. It could furthermore be shown that
the reaction between hapten and antibody was the more specific the more
complex the structure of the hapten. If more simple substances served as
haptens, the reaction did not need to be specific. Again, it was especially the
aromatic groups which tended to determine the specificities in the antigen-
antibody reaction. By means of this reaction Wormall showed that if iodine
enters in combination with the tyrosin group of the protein, it calls forth a
new specificity, and that 3.5 iodotyrosin can specifically inhibit the reaction
between iodoprotein and its antiserum.

We have mentioned already that the carrier protein, as a rule, should be
of a heterogenous nature, but in certain cases a homoiogenous, and, perhaps,
even an autogenous serum may exert a similar effect. Thus, as mentioned,
Klopstock and Selters believe that in the guinea pig a combination of

570 THE BIOLOGICAL BASIS OF INDIVIDUALITY

diazotized atoxyl with the animal's own serum may serve as antigen. We
have discussed this problem in a preceding chapter. However, while foreign
sera seem to fulfill the function of carriers of the haptens efficiently,
Armangue, Gonzales and Morata have shown that the Forssman differential,
which by itself is not at all or only very slightly antigenic, can be converted
into an active antigen also by mixing it with kaolin or other absorbent
substances instead of with serum. Zogaya has found that a complex bacterial
polysaccharide may serve as a satisfactory antigen if it is first absorbed by
collodion or carbon particles. Landsteiner and Jacobs confirmed these obser-
vations, but they also noted that purified bacterial polysaccharides or other
complex carbohydrates, when freed as much as possible from N-containing
substances, can no longer be activated by these non-specific, absorbent colloids,
and the same applies to the purified Forssman differential. It seems, then,
that certain impurities which are mixed with the differentials may somehow
enhance their antigenic power, and this process can be still further accen-
tuated by combination with absorbent colloids.

It has been noted by Goebel and Avery that also some glucosides in com-
bination with heterogenous proteins may act as haptens; in this case,
stereoisomeric differences may help to determine specificity and, therefore,
the substitution of a galactose for the glucose radicle in the glucoside may
lead to a new specificity. The stereoisomeric differences in the galactose and
glucose group resulted in the formation of specific antibodies. It is of interest
in this connection that while in the composite antigen the glucoside and
protein are combined into one substance, two separate antibodies seem to
develop in response to the injection of this antigen, and these are apparently
distinct from each other; moreover, it was found possible to remove the
one by specific absorption without at the same time removing the other. The
glucoside as such, acting as hapten, inhibited only the interaction of the
anti-carbohydrate antibody and not that of the anti-protein antibody with the
antigen. In general, it may be stated that, in accordance with the findings of
Landsteiner, a simple antigen, in which the chemical constitution of the hapten
is well known, may cause the production of several distinct antibodies, which
are directed against different groups in these antigens and which can be
removed by specific absorption. Or the antibody may represent, perhaps, a
very complex composite structure, in which different groups combine with
different component parts of the antigens chemically, with different degrees
of firmness ; and conversely, there may be different degrees of dissociation
between the constituents in the antigen and antibody combination. In this way
Heidelberger interpreted the occurrence of various kinds of cross-reactions
between antisera and antigens.

Goebel in more recent investigations analyzed still further the conditions
which cause the specificity of antigens by the use of artificial antigens against
various types of pneumococci. One of these antigens contained the azobenzol
glucoside of glucuronic acid, the other, that of galacturonic acid. The differ-
ence in stereoisomeric constitution of these two glucosides has a marked
influence on the serological specificity of these two antigens. The immune

THE CHEMICAL NATURE OF DIFFERENTIALS 571

bodies produced in rabbits by injection with the glucuronic acid antigen
protects mice against infection with Type II pneumococci ; the antiserum
with the galacturonic acid antigen is ineffective. Furthermore, the immune
serum of rabbits injected with p-aminobenzyl (1 cellobiuronide confers passive
immunity in Types III and VIII pneumococcal infection, whereas the serum
of rabbits immunized with p-aminobenzyl (S gentiobiuronide is inactive. But
both immune sera against cellobiuronic acid and gentiobiuronic acid provide
passive immunity against Type II pneumococcus infection. If the glucuronic
acids are removed from the antigens, no protection is obtained against Type
II pneumococcus. It may therefore be concluded that in the latter case the
two glucuronic acids are the active constituents of the antigen. On the other
hand, immunity against Types III and VIII pneumococcal infection depends
upon the particular union between the two constituents of the two disac-
charides, cellobiuronide and gentiobiuronide, one kind of union being effective
while the other is ineffective.

Not only have relatively simple organic substances, joined to protein by
means of diazotization, served as haptens, but also alcohol extracts of various
cells and organs which, in combination with protein, function as antigens and
call forth the production of antibodies. In this way, Forssman heterogenetic
antigens, blood-group antigens, especially the antigen for blood group A, and
organ-specific antigens have been used. The latter have been prepared also
from boiled organs. In general, these alcohol soluble haptens are heat stable.
They function as complete antigens and call forth the production of anti-
bodies in combination with protein, especially the protein of a heterogenous
blood serum. At first it was assumed that the haptens in these alcohol extracts
were lipids, but subsequent investigations made their lipid nature doubtful
in many instances. In accordance with the work of Landsteiner and Levene,
it is now assumed that the Forssman hapten is a combination of a carbo-
hydrate and a lipid, and it is furthermore assumed that a carbohydrate may
be present also in the blood-group antigen. As to the organ antigens, they
may be proteins, in which, however, other groups are active than those which
represent the organismal and especially the individuality differentials. The
active organ differential groups are heat stable. Some organ and "substance"
antigens are conjugated proteins or combinations between haptens and
proteins.

In regard to the organismal differentials, especially the individuality and
species differentials, these depend essentially on certain characteristic proper-
ties of proteins, which the various parts of an individual, or the individuals
composing a species, have in common. In the beginning of this chapter we
have already discussed some of the properties of cell and tissue proteins and
have mentioned the fact that the individuality differential is lost whenever
the proteins are denatured. We have furthermore stated that the process of
denaturation may depend primarily on a breaking of linkages between certain
sidegroups in parallel peptid chains or in the same peptid chain coiled upon
itself, and such a breaking of linkages must therefore destroy the individ-
uality differential ; or it may depend upon a process of uncoiling. This does

572 THE BIOLOGICAL BASIS OF INDIVIDUALITY

not indicate, however, wherein the individuality differentials of different indi-
viduals differ from each other. In a similar manner we have seen that the
introduction of new sidechains or haptens into a protein may change or
destroy the species differentials ; but it would not necessarily follow that
actually the various species differentials represent combinations of proteins
with different sidechains or haptens; on the contrary, it seems certain that
as far as haptens are concerned pure proteins may be representative of species
differentials. Still, our knowledge as to the chemical properties of proteins,
on which these species differentials depend, is extremely fragmentary. It is
the tissue and serological reactions which have given us our first basic and,
so far, the only definite data regarding the organismal differentials. How-
ever, some of the chemical-physical differences which have been established
between the proteins of different species may be suggestive in this connection ;
no positive data of this kind exist regarding individuality differentials. As
mentioned, in the beginning of this chapter, more recent investigations, espe-
cially those of Svedberg, indicate that the native cell and tissue proteins are
more complex and represent longer peptid chains than had been assumed.
In particular, concerning the hemocyanins, Svedberg has shown that the
molecular weights of these substances, as they are present in the blood of
certain species, are always simple multiples of the well defined component with
the lowest molecular weight. These components are interconnected by reversible
dissociation-association reactions, which are influenced by the pH. The range
of pH in which these complex hemocyanin molecules are stable is characteristic
of the hemocyanins of different species. But marked differences in the pH
stability diagram occur only for species belonging to different orders. All the
species of the same order have similar diagrams. In addition to this pH range,
the isoelectric point of the hemocyanins of different species is to some extent
characteristic of the species.

In regard to the hemoglobins, the extensive investigations of Reichert and
Brown to which we have already referred, have shown that their crystal form
differs in different species ; likewise, the readiness with which they crystallize
differs. But there is the possibility that in these determinations other proteins
from cells may have been admixed to the hemoglobin crystals and may have
contributed to the differences between the crystals of different species. As to
the chemical constitution of hemoglobins, it seems that the hemoglobins of
horse, sheep, cattle and dog contain the same amount of the basic amino-acids,
arginin, histidin and lysin, but differ in their cystin content and in the amount
of total sulfur (Block and Vickery). Horse and donkey hemoglobin differ
also in their solubility, although they cannot be distinguished by the precipitin
test (Landsteiner and Heidelberger). Bailey has found that in myosin the
amid nitrogen, expressed in percentage of total nitrogen, is about the same
in mammals, birds, fish and lobster; and the same applies as far as the
percentage composition of cystin, methionin, tyrosin and tryptophan is con-
cerned. On the other hand, the differences between the amino-acids which
occur in myogen and myosin within the same species are very considerable,

THE CHEMICAL NATURE OF DIFFERENTIALS 573

and much greater than the differences between the myosins of quite un-
related species.

It is probable that not only the nature of the bonds between sidechains in
the same protein, but also the nature of the sidechains as such, may differ
in different proteins. Likewise, according to Bergmann, the various natural
proteins differ from each other in that their individual amino-acid constituents
are represented by different frequencies within the complex protein molecule.
This view implies that the physical-chemical and biological properties of a
particular protein depend in the last analysis on the frequencies with whix:h
the constituent amino-acid residues recur within its peptid chain. However,
no sharp distinction is made here between species-specific and organ- or
"substance"-specific proteins. Of great interest is the suggestion of Bergmann
that it is the cell enzymes, the proteinases (papainases) which not only split
the proteins, but also synthesize them from the constituent amino-acids of
the foodstuffs, and which, because they have a specific constitution, specifically
determine the specificity of the cell proteins which they build up ; therefore,
the cell enzymes and cell proteins must in each instance have the same
specific structural characteristics ; the process of constructing these proteins
would thus be autokatalytic. However, 'according to such a conception this
autokatalytic process should primarily lead to the new formation of specific
enzymes rather than of specific cell substratum. But it may be assumed that
secondarily these specific proteinases would also build up the cell proteins
in such a way that they possess the same characteristic species differentials
as the enzymes. This conception was applied to the species differentials of
cell proteins; but if it should be extended to the individuality differentials,
then it would be necessary to assume that also in the different tissues of the
same individual the proteinases not only possess the same species differential,
but also the same individuality differential, and these enzymes should then
differ in the reactions they call forth in different individuals in accordance
with the differences in their individuality differentials. However, such dis-
tinctions between the enzymes of different individuals have not yet been noted.

By means of electrophoresis, Landsteiner could distinguish the egg
albumins of chicken, guinea hen and turkey from those of duck and goose,
but he could not establish definite differences within these two groups. It was
therefore possible to distinguish between the proteins of species belonging to
different orders, but not possible to distinguish between those belonging to
the same order, such as chicken, guinea hen, and turkey, or duck and goose,
though these could be distinguished by means of the precipitin reaction. This
lack of differences in the electrophoretic mobility of some of the egg
albumins obtained from different species of birds is in contrast to the dis-
covery, by Tiselius, of three different fractions differing in their electro-
phoretic behavior in the apparently homogeneous globulin of rabbit serum.
It is possible that in the protein molecules the organismal differential,
which may function also as antigen, is determined not by a small group, but
by larger groups ; this is suggested by the multiplicity of cross-reactions

574 THE BIOLOGICAL BASIS OF INDIVIDUALITY

between the organismal differential (antigen) of a certain species and the
various antibodies present in the immune serum; the pattern of the protein
corresponding to the order in which certain amino-acid radicles recur in the
molecule may perhaps be a factor which helps to determine the character of
the antibody. This view agrees also with the views recently expressed by
Landsteiner and with the observations of the latter that the specificity of
immune sera for polypeptides may depend upon a pentapeptide in its entirety.
Therefore, large groups and their specific pattern of amino acids may deter-
mine phylogenetic relationship. On the other hand, in contrast to the organis-
mal differentials, the specificity of other antigens such as the various ag-
glutinogens which determine the specific blood-group reactions and which
seem to be complex nitrogen-containing carbohydrates, may be quite distinct
from each other and not show multiple intermediate substances. Here the
differences between the various antigens can be conceived as of a more abrupt
nature and perhaps due to single groups sharply differentiated from those
of other analogous antigens.

While there can be no doubt that it is the proteins which primarily
determine the specificity of the organismal differentials, there are some
serological experiments which indicate that in certain cases also some other
hapten-like substances may perhaps be concerned in similar reactions. Thus,
it has been observed that while whole erythrocytes are required in order to
produce species-specific antisera for the red corpuscles of certain species,
alcohol extracts of the same kind of red corpuscles may react specifically
with such immune sera ; it appears therefore that in this case the antigen
contains an alcohol soluble hapten, and as Landsteiner has shown, the
hemolytic action of such species-spectific hemolysins may be inhibited by
addition of ether extracts of such red corpuscles to the antibody. These
observations would agree with the finding made in the course of our trans-
plantations of tissues and previously discussed, that the species differentials
differ from the individuality differentials in that the former are somewhat
less heat sensitive than the latter. These complex species differentials present
in erythrocytes could resemble the organ differentials which withstand boiling
in contrast to the typical species differentials which are destroyed by boiling;
the organ, tissue or substance specificity may perhaps reside in the hapten,
while the typical species specificity resides presumably in the protein with
which the hapten is associated. In these particular substances the species-
specific component of the antigen may then perhaps consist of a hapten of a
non-protein nature. An important point to be considered in this connection
is the fact that the presence of a chemical factor, graded as to phylogenetic
relationship of the animal group and characteristic of the typical organismal
differentials, has apparently not been demonstrated in these antigens or in
parts of the antigens contained in the alcohol extracts.

It might therefore perhaps be necessary to distinguish between the primary
species differentials of protein nature, and secondary complex differentials
which represent combinations of organ or "substance" differentials and the
species differentials, an interpretation which we have mentioned in previous

THE CHEMICAL NATURE OF DIFFERENTIALS 575

discussions. We have already referred to the polysaccharides which are
found in cell constituents in many kinds of bacteria and which are character-
istic of certain types and species of bacteria, especially of pneumococci. They
were first discovered in pneumococci by Heidelberger. Each type of pneumo-
coccus has its own kind of polysaccharide. These complex carbohydrates
function, as a rule, as haptens, which in combination with foreign proteins
may act as full antigens ; but the polysaccharides of Types II and III pneumo-
cocci may, as such, act as antigens. As Heidelberger has shown, the polysaccha-
ride of Type III pneumococcus consists of numerous units of cellobiuronic
acid, while a single unit is antigenically ineffective, a combination of several
units may unite as antigen with the specific antibody in anti-pneumococcus
type III horseserum. It is possible that within the bacterial cells these
polysaccharides are combined with proteins. In the case of the pneumo-
cocci it can be shown that they are not diffusely distributed within the cell,
but form a constituent of the bacterial capsule. As far as a comparison is
possible between simple unicellular and higher, very complex organisms,
these carbohydrates may be compared to organ differentials of higher
organisms rather than to organismal differentials; they are localized in
certain parts of the cells and as a rule act as antigens only in combination
with other substances ; but at the same time they are specific for group and
also for species of these unicellular organisms in the same way as organ
differentials may carry a species differential. It appears probable that also in
bacteria protein substances situated within the cell body are the carriers of
the typical species and class differentials, and quite recently Heidelberger
and Kendall have begun to separate such substances by methods which pre-
vent or diminish much their hydrolysis during the process of preparation;
some of them may be fully antigenic.

Within cells there arise also the enzymes, endoenzymes and exoenzymes,
as they might be called, which likewise show various kinds of specificities.
From a functional point of view, their most marked specificity relates to the
substratum on which they act and which they convert into different substances,
either by splitting or by synthesizing processes. Enzymes are characterized by
this specific effect, by the conditions under which they act, and by their place
of origin. In accordance with their intimate connection with cells, they consist
of proteins which in some instances may function in combination with
prosthetic groups, especially also with certain vitamins. These proteins have
been obtained in crystalline form (Sumner, Northrop, Kunitz and others).
It has been shown that some enzymes develop from precursor substances
which also have been obtained in crystalline form (Northrop, Kunitz) ; thus
pepsin, trypsin and chymotrypsin are derived from pepsinogen, trypsinogen
and chymotrypsinogen. In addition, there has been distinguished among the
pancreatic proteolytic enzymes, heterotrypsin and beta and gamma chymo-
trypsin. The substratum specificity of these enzymes goes farther than has
been assumed, and Bergmann has shown that simple peptides can be found
on which the various proteolytic enzymes of the pancreas exert a specific
splitting effect. It is the enzyme itself which may convert the precursor sub-

576 THE BIOLOGICAL BASIS OF INDIVIDUALITY

stance into active enzyme by an autokatalytic reaction. But this latter type of
reaction shows only a very imperfect specificity. Pepsin transforms pepsinogen
into pepsin, and trypsin causes the activation of trypsinogen, but trypsin
exerts the same function also towards chymotrypsinogen. While thus the
activating enzyme possesses only a limited specificity, the substratum on
which the enzyme acts — in this case the precursor substance — undergoes spe-
cific changes ; thus chymotrypsinogen can only be converted into chymotrypsin,
whatever the nature of the activator may be.

In those enzymes which consist of a combination of a protein and a
prosthetic group, specificities in the character and action of the enzymes may
depend not only upon the nature of the protein but also upon differences in
the prosthetic group, or in the manner in which the prosthetic group and the
protein are linked. Specific differences in the production of such enzymes in
different cells may, according to Robbins, depend upon the different ability
of different cells to produce a vitamin which forms a constituent part of the
enzyme. As to the relations between enzymes and organismal differentials,
nothing is known in regard to individuality differentials in enzymes. How-
ever, there is reason for assuming that the corresponding enzymes of dif-
ferent species are distinct, although such differences cannot always be dem-
onstrated by means of immune reactions. Thus Kirk and Sumner could not
definitely distinguish between the urease of soy bean and of jack bean by
means of the precipitin reaction or by using the protective action of immune
sera as a test. But that species differences exist has been shown through a
study of the solubilities of various enzymes ; for example, the solubilities of
cattle and swine pepsin differ from each other. In certain instances a species-
specificity has been demonstrated also by the production of immune substances,
especially of precipitins, and of localized anaphylaxis in the guinea pig. Ten
Broeck used the uterus of the guinea pig as test organ and was able to dis-
tinguish between trypsin from cattle and swine and also between chymotrypsin
and chymotrypsinogen. Seastone and Herriot, by means of the precipitin re-
action, could distinguish swine, cattle and guinea pig pepsin from rabbit and
chicken pepsin; but pepsin from swine, cattle and guinea pig could not be
differentiated from one another by these means. On the other hand, pepsin
and pepsinogen could be distinguished by the use of the precipitin reaction.
Moreover, precipitins for enzymes did not react with serum proteins of the
corresponding species. It may therefore be concluded that the proteolytic
enzymes of the pancreas and stomach, and their precursors, possess substance
and organ specificity; furthermore, that the corresponding enzymes and
their precursors from different species differ in their constitution; but no
proof has been given so far that this difference corresponds to the graded
relationship of the various species, or that these enzymes have a chemical
characteristic in common with proteins in other organs of individuals be-
longing to the same species ; nor has it been shown that they possess indi-
viduality differentials.

We have mentioned already that in the process of transformation of the
precursor substance into the active enzyme, the specificity resides in the

THE CHEMICAL NATURE OF DIFFERENTIALS 577

precursor rather than in the enzyme which induces this reaction. This applies
also as far as the species specificity of the enzymes and their precursors is
concerned. As Herriot, Bartz and Northrop have shown, swine pepsinogen
can be converted only into swine pepsin and chicken pepsinogen into chicken
pepsin, irrespective of the species character of the enzyme which serves as
catalyst of this reaction.

A very marked organ and perhaps also organismal specificity of enzymes
has been found in Limulus (Loeb and Bodansky). In this species, urease
occurs in the bodyfluid, muscle, and even in the eggs. Moreover, a urease is
present in the amoebocyte tissue prepared from the amoebocytes of the body-
fluids. This enzyme has been found so far only in Limulus and not in any
of the arthropods which have been examined for its presence. But in
Limulus the urease obtained from amoebocytes differs from that found in the
other organs or tissues in that the amoebocyte-tissue enzyme combines with
various kations, and the degree of its activity depends upon the kind of
kation with which it is combined ; but heavy metal combinations of the
enzyme are inactive, probably because they induce denaturation. This urease
represents therefore, in all probability, a metal protein combination. If the
enzyme obtained from various organs of^ Limulus is injected into the body-
fluids of this animal in sufficient quantity, urea is transformed into ammonium
carbonate, a substance which is toxic and lethal.

Similar in certain respects to the action of enzymes is that of some viruses,
such as the virus of tobacco mosaic disease, which has been found to be a
crystalline nucleoprotein (Stanley), and bacteriophage, which is also a
nucleoprotein, according to Northrop. With this interpretation accord the
experiments of Bronfenbrenner and Kalmanson which have made it very
probable that bacteriophages do not multiply as bacteria do, but are con-
tinually newly formed by the type of bacteria in which they originated. On
the other hand there should be considered also the strong indication that
bacteriophage occurs in association with larger particles of various sizes by
which the phage has been adsorbed, and that the active agent represents a
smaller molecule (Bronfenbrenner). Both the viruses and the phages are
specific in their action as far as the character of the substratum is concerned.
Thus, bacteriophages act primarily only on the bacteria in which they origi-
nated, or on nearly related microorganisms. The phages derived from dif-
ferent bacteria can also be distinguished by immunological methods. To a
certain extent, an adaptation of bacteriophages to new hosts may take place.
Likewise, bacteria and yeasts may produce new enzymes in response to
altered substratum (Euler, Dubos) on which they are cultivated.

In passing from cell protoplasm to enzymes and viruses, we compare the
most complex substances with other substances which are less complex and
less specific. A further step leads to the hormones, some of which are still
proteins, while others represent relatively simple organic substances. In
different species the production and distribution of various hormones may
be different, and some of the complex hormones seem to possess a certain
degree of organismal-specificity (insulin, pituitary hormones), but the large

578 THE BIOLOGICAL BASIS OF INDIVIDUALITY

majority of hormones do not possess a species-specific structure and the
species-specificity of their action depends on the species-specificity of the
substratum on which they act. Vitamins are not of a protein nature, but they
may combine with proteins to form enzymes. While, therefore, neither
vitamins nor the majority of hormones possess organismal differentials, still
there may be differences in the production of these substances in different
species, and these differences are analogous to differences in the structure of
organs and tissues and in the constitution of certain substances which occur
in these organs and which are characteristic also of these species, without a
relation to the phylogenetic position of the species being manifest.

To return to the starting point of this discussion : if an immune serum is
produced against a conjugated protein, the immune substance in the serum
may combine either with the hapten or with protein acting as carrier. In order
to obtain a specific interaction of the antibody with the hapten alone, or
with the hapten or substituent groups when conjugated with a carrier
differing from the one which originally was a part of the antigen giving
rise to the antibody, it is necessary for the antigen to contain a certain
number of the substituent groups. If this number remains below the threshold
of effectiveness, it is solely the carrier which induces the antibody production ;
we have therefore to deal here with quantitative relations (Haurowitz,
Sarafran and Scherwin). In order to produce agglutinins for erythrocytes
to which certain sidegroups or haptens had been attached, it is necessary
for parts of the surface of these to be free of these attachments. Then the
antibody will be directed also against the erythrocytes as such and not only
against the hapten (Pressman, Campbell and Pauling). This condition seems
to be one of the factors which determines whether antibodies other than those
directed against the hapten will be able to cause the agglutination of the
erythrocytes. But also the hapten, as such, may bring about an agglutination
of the erythrocytes if each one of the molecules of this substance had a
chance to attach to itself two erythrocytes during the process of centrifuga-
tion. As to the manner in which a hapten can induce the production of a
specific antibody, the experiments of Pauling and Campbell give some indica-
tion; these investigators succeeded in transforming in vitro bovine gamma-
globulin into antibody by moderate heating, or by adding an amount of alkali
to the medium sufficient to start the process of denaturation; they hold that
the denaturing causes the globulin chain to uncoil. This gives the hapten — a
dye or pneumococcus polysaccharide of type III — a chance to act on the pro-
tein, which thus assumes a configuration most stable under these conditions,
one complementary to the configuration of the hapten. A subsequent lowering
of the temperature of the solution or a restoration of the neutral state effects
a renaturation process in the protein, which then represents a specific antibody.
On the other hand according to Erickson and Neurath regeneration of de-
natured antibody protein may take place even without the presence of the
specific antigen and they suggest that the difference between normal globulin
and antibody globulin may be due to differences in the aminoacid composition
of these proteins.

THE CHEMICAL NATURE OF DIFFERENTIALS 579

However, important and suggestive as the experiments and conclusions
discussed in this chapter are, they do not solve the problem as to the nature
of the organismal differentials. After all, it is most probable that the protein
molecule as a whole, perhaps with the addition of smaller conjugated groups,
represents these differentials, while the larger haptens are characteristic of
organ and certain other differentials. Also, in regard to the part of the cell
where the organismal differential proteins are situated, no certainty exists.
Bensley distinguishes the mobile protein, which is found mainly in the interior
of the cell, from plasmosin, a viscous material extracted with 10% NaCl
solution and rich in nucleoprotein, and from particulate components of the
protoplasm, which are submicroscopic, contain nucleoprotein and phospho-
lipids and are identical with or associated with certain enzymes and viruses.
They are in certain respects similar in constitution to the mitochondria, but
not the same as the latter. There remain some more solid constituents in the
form of membranes and threads. It is very likely that the exoplasm of the
cell, which presumably is rich in plasmosin, plays a prominent role in the
reactions against strange organismal differentials, and this substance may
also contain, or constitute organismal differential proteins ; but the possibility
cannot be excluded that other cell constituents as well may bear these differen-
tials. The following recent observations of Claude suggest that also the par-
ticulate components of the protoplasm may be self-perpetuating and this in
turn suggests that they, too, possess individuality differentials.

Claude distinguishes small cell particles (cytoplasmic granules or micro-
somes) which are suspended in the homogeneous cytoplasmic ground sub-
stance and which correspond to the particulate components of Bensley, from
mitochondria, Golgibodies and especially from the zymogen or secretory
granules. The latter contain more nitrogen and sulphur, but less phosphorus
than the microsomes, but both are composed of phospholipids and ribonucleo-
proteins; there is moreover some indication that the secretory granules con-
tain a material similar to the microsomes and both of these cell constituents
may have therefore a common origin. In contrast to these cytoplasmic cell
components in the chromosomes, which are the most important constituents
of the nuclei, thymonucleic acid is a significant part, but Claude suggests
that both these types of nucleoprotein, the cytoplasmic as well as the nuclear,
may have the ability to reproduce their constituents by autocatalysis.

The prominence of the nucleoproteins in various components of the cell
becomes of special interest if we consider the probability that some viruses,
including agents which are involved in the production of tumors, are of a
nucleoprotein nature.

Chapter 10

Is It Possible by Experimental Means to Change

Organismal Differentials?

Individuality in the sense in which this term is used in our daily life
is considered essentially as a fixed condition, and the criteria of individ-
uality most commonly used are certain structural and functional peculiari-
ties of those parts of an organism which are readily perceived through the
sense organs. Yet, this mosaic individuality is not as constant as it might
appear ; to some extent, the parts constituting it may be under environmental
control and therefore modifiable. However, we have recognized that there is
hidden beneath these criteria something representative of individuality which
under ordinary circumstances is constant, namely, the organismal differen-
tials, and the individuality differentials in particular. But we have also, on
various occasions, referred to experimental findings which might suggest a
certain modifiability of the organismal differentials, and which are, there-
fore, apparently opposed to the fixity which is characteristic of this type of
individuality. Yet an analysis of these data showed that there was no reason
for assuming that an actual change in the organismal differentials had taken
place; on the other hand modifications in the reactions against organismal
differentials were noted in many instances.

This interpretation accords with the genetic origin of the organismal dif-
ferentials; they are determined by the genes of the fertilized ovum acting in
association with the cytoplasm of the growing and of the adult tissues. While
the type of the organismal differentials produced by or inherent in the
tissues of a certain individual or species is constant, except if germinal
mutations should alter the genetic constitution, the amount of these differ-
entials produced might vary under different conditions. Furthermore, the
sensitiveness of a tissue against homoio- or heterotoxins and against strange
host cells might undergo some modifications under various conditions.
Changes in the growth momentum of tissues, or specific adaptations of a
tissue to strange substances may occur and changes in the intensity of
reactions against strange organismal differentials may be observed under
certain conditions. After we have now considered all the principal data
concerning the interaction of blood and tissues and their various constituents,
those belonging to the same individual, as well as homoiogenous and heterog-
enous ones, it might be of interest, to consider connectedly the main observa-
tions which may have a bearing on the problem of the modifiability of organis-
mal differentials.

1. We have observed that after homoiogenous transplantation of cartilage
of guinea pig or rat, the lymphocytic reaction, which may be quite pronounced
in the first three weeks following transplantation, instead of becoming

580

CAN ORGANISMAL DIFFERENTIALS BE CHANGED? 581

stronger if the transplant is allowed to remain in the host for several
months, as a rule actually becomes weaker, and also the reaction of the
connective tissue decreases considerably in intensity in the course of time.
We may assume that this decrease is due either to changes taking place in
the host, which becomes accommodated to the strange individuality differ-
ential of the transplant and therefore reacts less strongly to it, or to similar
changes in the transplant, which ceases to produce the differential with full
strength. These changes would therefore be of an adaptive character, or
they might be due to an injury to the transplant, resulting from the long-
continued action of a strange environment ; however, we would not, under
these conditions, have to deal with actual alterations of the organismal
differentials, but merely with certain modifications of their manifestations.

2. A much further-reaching change in the nature of the organismal
differentials has been assumed by Rhoda Erdmann and Gassul to occur if
amphibian skin, in a first period, is cultivated for some time in vitro and then
transplanted ; they believe that under these conditions it is possible to alter
the individuality as well as the species differentials of the transplant and to
make it more similar to that of the host and thus to improve the chances of
successful transplantation. For this purpose these investigators cultivated
skin for a considerable length of time, first in plasma and tissue extract of
its own species, then, step by step, they changed the type of plasma and
extract, until it approached more nearly in constitution that of the host
organism ; they believed that by this procedure they had succeeded in increas-
ing the compatibility between transplant and host, and moreover, it was
found that the greater the distance in relationship between host and trans-
plant, the longer the time required to effect the transformation of organismal
differentials through preliminary growth in vitro ; this interval could there-
fore serve as a measure of the nearness or distance of relationship between
host and transplant.

In the first experiment of this kind Rhoda Erdmann cultivated embryonal
skin of birds in vitro for from ten to twelve days in homoiogenous plasma,
and after transplantation of this tissue into defects in the skin of living
homoiogenous adult hosts it was observed that the transplant remained alive
longer than corresponding tissue that had not been explanted previously.
Moreover, the graft no longer called forth as strong a lymphocytic and
fibroblastic reaction as does ordinary homoiotransplanted avian embryonal
skin. Rhoda Edmann concluded that the individuality differential of the
embryonal skin had been changed through cultivation in vitro. Mammalian
tissue, on the other hand, which had also been explanted in a first period,
was soon absorbed after homoiotransplantation. Gassul, in continuing these
experiments, noted that if skin of an adult frog, which in tissue culture can
remain alive for as long as six weeks, is kept for several weeks in vitro in
frog plasma, it continues to live after subsequent homoiotransplantation into
the skin of another frog for longer than thirty days, and during this period
behaves like an autotransplant, no reaction developing around it. Conversely,
if a piece of frog skin has been kept for some time in vitro in foreign serum

582 THE BIOLOGICAL BASIS OF INDIVIDUALITY

or plasma and is then homoiotransplanted into a living host, it is cast off
after two to five days. Gassul assumed that cultivation in a heterogenous
medium altered the tissue in such a way that it assumed a heterogenous
character. As far as homoiotransplantation is concerned, he concluded that
the preceding explantation in a homoiogenous medium caused an enhance-
ment of the individuality of the transplanted tissue. However, the success
of the homoiotransplantation under these conditions might rather be inter-
preted as signifying that the individuality differential of the transplant, or,
rather, the intensity of its production, has been weakened, and it elicited
therefore a weaker reaction on the part of the host. Furthermore, Gassul's
conclusions are based on a very small number of experiments in which
tissues were homoioiransplanted and only some of these successfully. As to
the action of heterogenous plasma, especially that of warm-blooded animals,
on tissues kept in vitro, this procedure seems to diminish the success of a
subsequent homoiotransplantation by causing injury of the tissues.

Subsequently, Rhoda Erdmann undertook heterotransplantation of anuran
skin after a preceding cultivation in vitro, in an extensive series of experi-
ments. While, according to the author, normal adult skin of urodeles can be
readily transplanted to other urodele species, it is very difficult to accomplish
such a result in anuran species. The first of these experiments concerned the
transplantation of skin of Rana esculenta to Rana temporaria, and vice versa.
Later, pieces of skin from farther distant species were used for grafting,
following a previous cultivation in vitro. By means of this procedure an
exchange of skin between different families was made to succeed to some
extent ; thus, skin of Buf o and Bombinator could be transplanted to Rana
esculenta, which proved to be the most suitable heterogenous host. Bufo skin
was first cultivated in a mixture of Bufo plasma and Bufo spleen extract,
then in a combination of Bufo plasma and frog extract, and at last in a
mixture of frog plasma and frog extract. Skin thus prepared and afterwards
transplanted into adult Rana esculenta was found living and united with the
skin of the host even as late as fifty days, and not only the transplanted
epidermis but also the skin glands of Bufo survived under these conditions.
In the case of the skin of Pelobates, cultivation in vitro for a period of
twenty-four days was required before it could be successfully transplanted
into Rana esculenta. It is of interest that in some experiments of hetero-
transplantation into farther distant hosts, hemorrhage killed the host, owing
apparently to toxic effects exerted by the transplant.

In interpreting these results we have to consider several possibilities:
(a) In vitro, skin undergoes regenerative growth. It is conceivable that
transplantation of regenerating skin gives better results than transplantation
of ordinary resting skin although in our earlier experiments we did not
observe that homoiotransplantation of regenerating skin in the guinea pig
differed essentially from homoiotransplantation of normal skin, (b) If skin
is cultivated in vitro, it is only the epidermis that is active and grows, while
the underlying connective tissue remains inactive and may become detached
from the overlying epithelium. Thus after transplantation of this tissue, the

CAN ORGANISMAL DIFFERENTIALS BE CHANGED? 583

strange epidermis is in more direct contact with the host tissues and is better
supplied with blood by the underlying capillaries ; this might possibly improve
the chances of survival, (c) There is another possibility which has been
suggested by Bytinski-Salz. Various kinds of amphibian skin contain glands
which secrete poisonous substances. By cultivating the skin in vitro, the
poisons may have been extracted to a large extent previous to transplantation,
or perhaps a depression in the gland activity and a corresponding diminution
in the production of the toxic substances following transplantation may have
been brought about. Still, there remains the possibility that cultivation in
vitro may have induced a change in metabolism of the skin, which enhanced
its transplantability. This change may have been either of a non-specific or
of a specific character, dependent upon the kind of plasma in which the skin
had previously been cultivated. Similar successful experiments with human
skin have more recently been reported by Stone and others ; other surgeons,
however, did not notice an improvement in the results of homoiotransplanta-
tion through a preceding cultivation of the tissue jn vitro.

3. More recently, experiments have been made by Lumsden, in which the
temporary growth of a mouse tumor in a rat, or of a rat tumor in a mouse,
changed the tolerance of tumor tissues in vitro to the corresponding heterog-
enous sera, in which they were subsequently immersed, in such a way as to
suggest that by the growth in the heterogenous species they had apparently
lost their own organismal differentials and assumed the characteristics of the
foreign species. Thus a mouse tumor, after growing in a rat, had become
resistant to serum from a rat which had been immunized against mouse
tumor, but at the same time it had become susceptible to the serum of a
mouse immunized against rat tissue. However, after transplantation of such
tumor cells into rat and mouse, they grew only in the latter ; they still be-
haved therefore as mouse cells and had not really changed their organismal dif-
ferential. It must then be assumed that changes of a secondary nature in some
unknown manner had reversed the reactions towards immune sera. Of a
somewhat similar nature are the experiments of Kimura, in which also
growth in vitro seemed to induce a change in tissues, but in this instance
the change became manifest even in the living organism. However, the
experiments of Albert Fischer indicate that no real change in organismal
differentials occurs in tissues growing in strange media in tissue culture.

4. The growth energy of tumors undergoes various adaptations in the
course of serial transplantations. As a rule, it increases gradually following
the first few transplantations, until finally a tumor may grow successfully
in hosts in which at first negative results had been obtained, sometimes even
in heterogenous hosts. It has been made very probable that the antigenic
properties of cells from spontaneous tumors (Dmochowski) and of leukemic
cells from spontaneous cases (MacDowell) may change within certain limits
in the course of serial transplantations, and that they may thus differ in
their reactions, in certain respects, from analogous cells which had not been
subjected to such treatment.

If we consider all these experiments together, there is no necessity for

584 THE BIOLOGICAL BASIS OF INDIVIDUALITY

assuming that, following these various procedures, a transformation took
place in the specific structure of the organismal differentials, but there is
evidence for the conclusion that the transplantations altered the cells to such
an extent that (1) phenotypic changes occurred, perhaps of a cytoplasmic
nature, which insured a greater resistance to the injurious effects of certain
hosts, or (2) the growth energy of the cells was increased, or (3) the pro-
duction and the diffusion of the organismal differentials of the grafts were
quantitatively diminished, or (4) the transplants were modified in such a
way that their reaction towards other individuals or species were altered by
means of secondary mechanisms without any actual change taking place in
the character of their organismal differentials.

5. If we include in our analysis not only the tissues of higher organisms,
but also primitive, unicellular organisms, we find further analogies to the
above mentioned phenomena. It is known that in protozoa, changes in the
resistance to injurious chemicals as well as to high temperatures can be
produced, and that these may be transmitted to successive generations ; like-
wise, apparently spontaneous variations occur in these organisms and extreme
types of this kind can be selectively propagated. Especially striking are the
experiments in which parasitic protozoa, such as trypanosomes, were made
resistant to immune sera, to drugs, in particular, also to certain dyes, acting
specifically on these organisms. These adaptive changes can be observed in
vivo as well as in vitro. Likewise, in free-living protozoa, for instance in
paramaecia, new biotypes can be produced, which may differ structurally as
well as physiologically from the original type. Effects of this kind are
associated with chemical changes such as the antigenic constitution in
trypanosomes, as indicated by the acquired power of the organism to trans-
form a poisonous form of a chemical into a less poisonous one. These effects
may be transmitted by heredity to many asexual generations; but they seem
to be lost ultimately, especially under conditions of sudden changes in the
genetic constitution, such as those taking place at the time of conjugation or
endomixis. Whether these persistent modifications (Dauermodifikationen of
Jollos) are due to true gene mutations and therefore comparable to real
changes in organismal differentials, or whether they are due to cytoplasmic
alterations from which a return to the old equilibrium would take place
in the course of time is not certain.

There is, therefore, in all these changes the question involved as to their
permanence and also as to the respective role of cytoplasm and genes in
their causation. However that may be we are directly concerned with such
induced modifications or mutations only in so far as they affect the relations
of different races and species to one another.

6. In this connection we must also again refer to the experiments of
Reynolds, who succeeded in modifying the reactions of various protozoan
organisms towards each other by adding to the culture media in which they
were kept, fluids from culture media in which other organisms of the same
type had previously multiplied. In this way he could change the behavior
of pseudopodia belonging to different individuals and thus alter a reaction

CAN ORGANISM AL DIFFERENTIALS BE CHANGED? 585

which apparently depended upon the individuality or species differentials of
two organisms.

7. Somewhat comparable changes to those observed in protozoa have been
induced experimentally in various kinds of bacteria, and especially in
pneumococci. Through serial passages through animals belonging to a
susceptible species the virulence of bacteria can be raised. Similar changes
have been noticed in the case of viruses. Thus the effects of the virus of
poliomyelitis on mice and rats can be greatly increased by serial transfers to
mice ; but at the same time the virulence has become greater thereby also for
guinea pig and Rhesus monkey (Jungeblut and Sanders). In bacteria many
kinds of socalled "dissociation" have been observed and produced experi-
mentally; from apparently fixed bacterial forms, bacteria with different
characteristics have developed and these new types have remained constant.
Modifications of bacteria have also been produced under the influence of
bacteriophage or related substances. Increase in virulence for one host
species and decrease for another species may follow serial passage of
microorganisms or viruses through a certain species of animals. In the case
of viruses, this has followed cultivation on the chorio-allantois of chick
embryos. However, these modifications in the effects or reactions cannot
strictly be attributed to changes in the organismal differentials of bacteria
or viruses.

Dawson observed, in 1919, that when bacterium coli was cultivated
through many generations in culture media, which differed from the usual ones
in their fat and protein content, definite peculiarities developed, which dis-
tinguished the strains thus produced from the original ones ; especially notice-
able was a specific change in the character of the antigens, which after injection
in rabbits called forth the production of immune agglutinins ; accordingly, the
character of the latter was also changed. More specific were the changes
which Burnet produced in a strain of B. melitensis. In this case, it was the
association with a heat-agglutinable paramelitensis strain which transmitted
to the melitensis strain characteristics similar to those of the paramelitensis
and modified the antigenic character of the B. melitensis.

But the most striking results have been obtained with pneumococci.
Pneumococci were formerly classified into four types, which differed, above
all, in the character of the complex carbohydrates contained in their capsules.
More recently, Group IV has further been split into twenty-nine additional
types. In addition, it is possible to distinguish within at least some of the
different types between smooth (S) and rough (R) colonies. The bacteria
from smooth colonies possess their typical capsules and behave therefore in
a characteristic type-specific way. The pneumococci from rough colonies, on
the other hand, have lost their capsules, and with them their type specificity.
Furthermore, there exist within the cell-body proper of the pneumococci
proteins of a specific character. It can be shown that type specific S pneumo-
cocci can be transformed into R pneumococci by cultivating them in
homologous type-specific immune sera. According to Griffith, this transforma-
tion from the virulent S forms into the avirulent R forms may take place

586 THE BIOLOGICAL BASIS OF INDIVIDUALITY

gradually, so that intermediate forms develop, which are able to produce a
trace of soluble specific toxin and cause immunity in the mouse. Subsequently,
it was found by Avery and Dawson that these R pneumococci may regain
their specific properties and again become typical S forms if they are grown
in anti-R serum, that is, in serum of a rabbit that has received repeated
injections of the heated R organisms and has developed immune bodies
against the latter; even normal hog serum may act similarly to anti-R
rabbit serum. The S pneumococci which were recovered under these cir-
cumstances were always of the same type as those from which the R forms
were originally derived. This indicates that the R forms with which one had
to deal in these experiments had retained their type specificity, although they
had lost their capsules, and with the latter, the type-specific carbohydrates.
Thus, a type I pneumococcus which had been converted into the non-virulent
R pneumococcus again became a fully developed type I pneumococcus after
reversion to the original S form. In this case, therefore, the R forms still
possessed, potentially, their type specificity, which under these conditions was
presumably localized in the central bacterial body.

However, the, experiments of Griffith and Dawson seem to indicate that a
still furthergoing change, one of type, is possible. They observed that if a few
living R pneumococci are injected subcutaneously into mice, together with
very large numbers of killed virulent S pneumococci of a type other than
that from which the R forms were originally derived, there may be cultivated
in many instances from the injected mice after death, pneumococci of the
type to which the killed S organisms belonged, which had been used for
injection.

A similar change can be produced even in vitro. Thus when very small
particles of R pneumococci cultures were added to suitable culture media
containing killed S pneumococci, of a type other than that to which the R
cells belonged, S forms developed, which were of the same type as that of the
killed S pneumococci. This result is obtained with special readiness if a
little anti-R serum is added to the culture media. According to Alloway, the
same effect can be noted when instead of adding killed S bacteria, as such,
a heated cell-free extract of the S bacteria is used. We have here, apparently,
results analogous to those which Reynolds obtained in protozoa. The nature
of the substance in the extract, which stimulates the R forms to synthesize the
particular polysaccharides involved, has not yet been determined. However,
it cannot be the soluble type-specific carbohydrate itself, because the addition
of this substance in a purified state does not produce such a transformation.

Of a related character are the experiments of Veblen, who grew micro-
organisms such as streptococcus viridans and bacillus typhosus for several
generations in dilute horse serum and then was able to demonstrate agglutina-
tion of these bacteria by an anti-horse precipitating rabbit serum in high
dilution, the microorganisms losing at the same time their ability to agglu-
tinate on addition of their own specific agglutinating sera. In this case, a
radical change in the organismal differentials of the bacteria, which their
agglutination of the latter by horse serum suggests, can be excluded ; but we

CAN ORGANISMAL DIFFERENTIALS BE CHANGED? 587

may have, perhaps, to deal here with a coating of the outer ectoplasmic layer
of the bacteria with the serum, which would confer on this layer the character-
istics of the foreign serum.

Also, observations of Thomsen, Friedenreich and Hallauer, may have some
bearing on this problem. Thomsen (1927) showed that it is possible to
change human erythrocytes, irrespective of the group to which they belong,
in such a way that they can be agglutinated by human serum, even if the
latter does not have a definite relation to the blood group of the red corpuscles
used. This change can be affected by exposing the erythrocytes to contact
with certain bacterial cultures or their filtrates. Thomsen and Friedenreich
explained this effect by assuming that under these experimental conditions a
new specific receptor "T" is produced in the erythrocytes. In the normal sera
of certain dogs, sheep, hogs, rabbits, guinea pigs, and also of certain mice,
there may be found a T agglutinin acting specifically on the experimentally
produced agglutinable substance. The T agglutinin is distinct from the normal
group-specific agglutinins, anti-A and anti-B. Hallauer, with the aid of
immune agglutinins specific for this agglutinable substance, was able to prove
that a T receptor had actually been newly formed in red corpuscles of man,
as well as of certain other animal species, which had been exposed to such
bacterial filtrates. The corresponding immune agglutinins could be absorbed
by such erythrocytes, and there is, moreover, some indication that the species
differential of these corpuscles is also concerned in the production of these
immune bodies, the antigen, presumably representing a combination of a
special agglutinable factor and an organismal differential, acting as carrier.
As usual, the carrier must be of a heterogenous nature, in respect to the species
which is being immunized. In this case, therefore, there would have been experi-
mentally effected a change of a character which, while determined by nuclear
genes, affects a cell no longer possessing a nucleus. This result cannot depend
upon a somatic mutation of a gene, but it must be due to the alteration of a
factor localized in the cytoplasm. Inasmuch as red blood corpuscles do not
multiply, the acquired characteristic in this instance is not transmitted to
successive generations of cells ; however, it is quite conceivable that a cyto-
plasmic change, acquired by cells which have the power to propagate, might
be transmitted to many successive cell generations.

The mechanisms, to which may be attributed these experimental changes
produced in single cells and in tumor tissue, are not yet understood, and the
findings here reported do not contradict the concept that organismal differ-
entials in higher organisms depend on the genetic constitution of the individ-
ual and find expression by means of reactions which presumably take place
in cytoplasmic structures. Alterations in these manifestations are therefore
not necessarily caused by changes in genetic factors as such, but by modifica-
tions which environmental conditions produce in cells and tissues.

On the other hand, it cannot be excluded at present that certain persistent
modifications produced in parasitic or also in free-living protozoa may be due
to genetic changes caused by adaptative alterations which were induced by
environmental conditions. The fact that they are liable to be lost particularly

588 THE BIOLOGICAL BASIS OF INDIVIDUALITY

at the time when the gene sets undergo marked changes, suggest the pos-
sibility that gene mutations may be involved in these processes. However, the
strictly adaptive natures of such modifications, as well as the fact that after
all they are, as a rule, not permanent, makes it more probable that they are not
due to genetic changes ; they would not therefore represent changes in the or-
ganismal differentials.

From all these observations it may be concluded that there is no evidence
that in higher organisms an actual change in the constitution of the organismal
differentials occurs ; but changes may take place in the quantity of differentials
which are produced and in the character of the reaction against these differ-
entials. On the other hand, in certain unicellular organisms, in which the
criteria used for the definition of organismal differentials in higher organisms
cannot be applied, changes have been observed, which in certain respects may
perhaps correspond to modifications of the organismal differentials.

P^rf "VI Organismal Differentials, Organ Differentials

and Evolution

The students of evolution, paleontologists, systematists, biochemists,
and also geneticists, have used the various tissues and organs, their
structure, chemical constitution, their functions, as well as certain
peculiarities of the whole individual as subject matter for their investigations.
They also studied the mutual structural, functional and chemical adaptation of
the organs and tissues within an individaul or species, as well as their adapta-
tion to the milieu in which this individual or species lived. They analyzed,
therefore, the history of the mosaic characteristics of organisms in tracing
the evolution of species. In a general way, it may be stated that evolution
has led to a gradual increase in differentiation and specialization of tissues and
organs and to a more and more intricate interaction of the organ and tissue
constituents of the organism. On the other hand, the study of transplantation
of tissues, together with serological investigations, has led to the concept of
organismal differentials, which concerns the differences between individual,
species, orders and classes as such, and indicates their relationships. Organis-
mal differentials also have undergone an evolution, which likewise has resulted
in their increasing differentiation and specialization. At first only the coarser
differentials, those of classes and orders, can be recognized ; the mutual
compatibility between different organisms and their parts is therefore rela-
tively greater in primitive organisms. Gradually, a refinement took place in
these organismal differentials; they became more individualized, until in the
end the stage was reached in which the individuality differentials determine
and regulate the interaction of the tissues of which the organism is consti-
tuted, and in which each organism represents an autogenous system ; in this
condition an equilibrium between the constituent tissues and organs of an
individual exists only if they all possess the same individuality differential,
which is autogenous within each individual. Both transplantation of tissues
and serology have led to this conclusion. However, as we have pointed out in
the preceding chapters, at present it is not possible to deal with the organismal
differentials as chemically isolated substances ; we merely study the reactions
which reveal their presence, and into these reactions variables may enter,
which may make it difficult to determine whether certain constellations are
due to the lack of certain organismal differentials or to other variable factors
which prevent these differentials from becoming manifest. Still, the evidence
on hand renders at least very probable the conclusion that the lack of the finer
reactions in the case of the primitive organisms is actually due to the lack of
the finer organismal differentials, and that it is due largely to this factor that
the range of transplantability is wider in the phylogenetically more primitive

589

590 THE BIOLOGICAL BASIS OF INDIVIDUALITY

classes of animals than in the higher ones. There are indications that an
evolution in the organismal differentials has occurred independently of each
other in plants as well as in animals.

However, while in higher animals there has developed concomitantly with
the refinement of the organismal differentials a very pronounced integration
of the various organ systems into one connected, finely balanced mechanism,
in plants so marked a degree of integration has not taken place. The individual
parts of a higher plant remain much more independent of one another than
the parts of a highly differentiated animal. Inasmuch as in the case of animals
a certain parallelism exists between the differentiation of organs and tissues
and their integration into a whole organism, on the one hand, and the differ-
entiation and specialization of the organismal differentials, on the other, the
question may be raised whether, correspondingly, the organismal differentials
are less finely developed in plants and whether the latter possess individu-
ality differentials. The readiness with which grafting between two organisms
can be carried out in plants seems to indicate that individuality differentials
do not play a significant role. If they do exist, then a greater resistance of the
grafts to strange organismal differentials or a less strong reaction of the
host against the transplant covers up these finer differentials. But, there is
reason for assuming that in the course of evolution not only the mechanisms,
which make possible the manifestations of the finer differentials, undergo a
gradual development, but also that the substances, which serve as differentials,
undergo a corresponding evolution. Thus, Steinecke found that antigens
obtained from more primitive plants, when injected into rabbits for the pro-
duction of precipitins, are less differentiated than are those obtained from
higher plants. Accordingly, large group reactions predominate in algae; like-
wise, in cryptogamous plants the differences in the constitution of the proteins
between larger groups of plants are, as yet, slight. In phanerogamous plants
on the other hand, the specificity in the character of the proteins, as manifested
in the precipitin reactions, is greater. It may therefore be concluded that in
lower organisms in plants, we have to deal not merely with less finely
developed reactions against antigens or organismal differentials in general,
but also with less well developed and differentiated organismal differentials
and antigens. We may assume that the same conclusion applies to animals
and that here, also, there is a parallelism not only between phylogenetic
evolution and the fineness of reactions against organisms, but also between
phylogenetic evolution and the development of organismal differentials and
the corresponding antigens.

As to the chemical substratum in which the changes take place, which paral-
lel the structural and functional evolution, there is justification for believing
that proteins, either as such or in combination with other groups, play the most
prominent role ; and it may furthermore be held that the phylogenetic evolution
of the organismal differentials was associated with an increasing complexity
of protein substances. However, our knowledge as to such evolutionary changes
in the proteins is as yet very slight. Kossel has shown that in fishes the nuclei
from which the sperm chromosomes are produced consist of combinations of

DIFFERENTIALS AND EVOLUTION 591

protamines or histone-like substances with nucleic acid, and that the prota-
mines and histones of the sperm differ in different species of fishes as regards
the nature and grouping of their amino-acids. But there is apparently no direct
parallelism between the chemical relationship of these substances in different
species and the phylogenetic relationship of the latter, and two different species
of Salmonidae may contain identical protamines. Furthermore, according to
A. E. Taylor, Gay and Robertson, and Wells, it is not possible to produce
species-specific immune bodies against protamines and histones. But, these
simple proteins develop perhaps from more complex nuclear proteins which
may be present in the cells from which the spermatozoa are derived, or else these
may be admixed to the suspension of spermatozoic substances which are anti-
genic and bear organismal differentials. Accordingly, through injection of fish
sperm into rabbits, Kodama could obtain specific immune sera, which reacted
with the spermatozoa of their own as well as of related species, but not with
the extract of fish muscle, and which were therefore organ- or tissue-specific ;
yet these immune sera possessed also organismal differentials as shown by
the fact that they reacted in a graded way with the spermatozoa of different
species of fishes, in accordance with the phylogenetic relationship of these
species. We must then assume that substances other than protamines act
as antigens in this case. In the sperm of mammals we find instead of the simple
protamines or histone-nucleic acid combinations in fishes, more complex
nucleo-proteins. These substances may serve as antigens, which call forth
immune reactions against the organ as well as against the organismal differ-
entials or their precursors contained in the sperm. Also, other animal proteins
may have a species-specific character.

Other instances are known in which differences in species are associated
with differences in the structure of proteins, although these data do not con-
tribute to an understanding of the evolutionary changes which have taken
place in the proteins. Thus, the constitution of globin in the hemoglobin
molecule differs in different species in regard to the relative amounts of amino-
acid nitrogen present and the proportion between lysin and histidin, on the
one hand, and arginin, on the other hand. Osborne and Gortner observed a
certain parallelism between the chemical relationship of the seed proteins in the
wheat and barley groups and the phylogenetic relationship of the species in
which they occurred, and these differences in chemical relationship cor-
respond to immunological reactions (Wells).

As to the chemical constitution of individuality differentials, it is almost
certain that here, too, proteins are involved. The individuality differentials
cannot as a rule be detected by chemical or immunological analysis of blood
sera, but under certain conditions they have been detected in erythrocytes by
means of immunological methods. The great difficulty in the chemical analysis
of the individuality differentials lies in the fact that the preparation of proteins
of cells and tissues for study in many cases causes their denaturation and this
change injures the individuality differentials, which evidently possess very
delicate chemical characteristics.

Not only does the phylogenetic evolution tend in the direction from coarser

592 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to finer differentials and towards individualization, but a parallel evolution
takes place also during the ontogenetic development. Here, also, the organs and
tissues evolve from a relatively simple substratum and this process is accom-
plished through the interaction of chromosomes and their genes with preformed
cytoplasmic structures with the aid of evocators and organizers.

Likewise during embryonal development, the organismal differentials under-
go a transition from less individualized precursors to more individualized
differentials. The processes which lead to this ontogenetic differentiation
exhibit certain remarkable similarities to those noted in the phylogenetic
evolution, or expressed differently, the embryonal development of phylo-
genetically farther advanced organisms resembles and repeats the embryonal
development of phylogenetically earlier stages, as though the number of
mechanisms which living matter can use in attaining the advanced stages of
development is limited and determined by the actual stages through which
the phylogenetic development has passed.

In the same way in which organs and tissues and their differentials, as well
as organismal differentials, develop during embryonal processes, so also during
regeneration of some of the more primitive organisms certain aspects of the
phylogenetic evolution may be repeated, although to a still more restricted
degree than during ontogeny. Regenerating tissues of adult urodele amphibians
behave in some respects like embryonal tissues. Parallel to the increase in the
extent of organ and tissue differentiation, with advancing regeneration there
is a decrease in transplantability. The earlier, less differentiated embryonal
and regenerating tissues are still more plastic and adaptable to environmental
factors than the farther advanced stages, in which the organ and tissue
differentials are more fixed and in which there is a greater tendency on the
part of organs and tissues to develop by means of self -differentiation. In
higher organisms the ability to produce new organs during regeneration is
lost. There is again, therefore, noticeable here a relation between the differ-
entiation and fixity of organs and tissue differentials and the increasing refine-
ment of organismal differentials, both of these processes leading to a greater
immutability and fixity of the organism as a whole.

However, notwithstanding these similarities there is one very significant
difference between phylogenetic and ontogenetic evolution. The former starts
with a primitive substratum, in which the specialized organs and tissues and
the finer organismal differentials of the higher organisms are not yet pre-
formed. Chromosomes and genes, as well as cytoplasm of the primitive organ-
isms, differ greatly from those of the higher ones and this is true of the germ
cells as well as of the cells of the adult tissues. On the contrary, in the fertilized
ovum of a higher organism, all the chromosomes and genes and the precursors
of organ (tissue) differentials and of organismal differentials are present,
and these precursors of organismal differentials differ from those of other
individuals and species. The organs and tissues, and also the organismal
differentials, merely mature in the course of ontogenetic development, whereas
they are newly created in the course of phylogenetic evolution.

Various types of specificities in chemical and morphological structure and

DIFFERENTIALS AND EVOLUTION 593

in the function of organisms and their constituent parts may be distinguished.
There is the specificity of the organismal differentials, and in particular of
the individuality differentials, on which depends the autogenous equilibrium
of a higher organism; the latter determines the controlled interaction between
adjoining cells and tissues and makes possible the integrity of the organism,
guarding it against invasion by strange organisms or their parts. The mutual
adaptation of tissues and also the specific adaptation between the bodyfluids
and the cells and tissues of an individual depend upon this specificity of the
individuality differentials. Upon such a specificity depend also primarily the
reactions to strange organismal differentials, which serve as antigens and cause
the production of the various kinds of antibodies as a means of defense against
the intrusion of foreign elements into the individual organization. This specific-
ity of the organismal, and especially of the individuality differentials, is the
basis of the "essential individuality."

There is, secondly, the specificity of organs and tissues that interact within
the individual and this specificity depends upon the differences in the chemical
and structural constitution of the parts of which the organism is composed.
Various organs with interlocking functions form primary organ system, in
which the correlation between the functions of individual organs may be
controlled by nervous mechanisms or hormones, or both. These primary organ
systems are then combined into larger systems, until in the end the whole
organism acts as a unit. The interaction of the various organs within the same
individual is so perfect that it seems to express the underlying "wisdom of the
body," as Cannon has so aptly called it. The totality of these organs and organ
systems, together with other structural and functional peculiarities of the
organism, represent the "mosaic individuality."

The organ specificities and various structural and functional characteristics
of an individual or species have developed in the course of evolution and they
exhibit a gradation corresponding in a general way to the phylogenetic rela-
tionships of individuals and species. It is possible to reconstruct, to a certain
extent, phylogenetic systems by means of these organ and other structural
characteristics. Certain constituents of organs or tissues may therefore exhibit,
in this respect, characteristics similar to those shown in the typical manner
by the organismal differentials, from which they differ, however, in their
chemical structure and in the fact that they are restricted to a single organ or
part of the body and are not inherent in all the constituent parts of an
organism, as are the typical organismal differentials. They may be designated
as secondary or accessory organismal differentials. It seems that various organ
differential substances may detach themselves from the stem of the organ-
ismal differentials at different stages during phylogenetic as well as during
ontogenetic development, and that these substances may undergo an evolution
more or less corresponding to the systematic relationships ; but still this differ-
entiation in other respects may develop independently of phylogenetic rela-
tionships. Indications of such a process may be noted in certain food reserves,
for instance those of the yolk of the egg and of the seeds of plants; here
there is a development of substances which more or less corresponds with the

594 THE BIOLOGICAL BASIS OF INDIVIDUALITY

phylogenetic relationship of the species, but which, as in the egg yolk, does
not take a course quite parallel to the evolution for instance of the serum
proteins. In many cases it is not possible to distinguish between these accessory
and the primary organismal differentials, because of the impossibility of
carrying out the necessary experimental tests. Also, certain products of organs,
such as enzymes and hormones, so far as the latter are proteins, may possess
organismal differentials; but whether these differentials are of the first or
second type is unknown.

There are present in various species other systems of differential substances
in which a much more limited parallelism exists between the chemical nature
of these substances and the phylogenetic relationship of the species. This is
the case, for instance, in some groups of higher organisms in which the
primary blood-group differentials bear specific relations to certain constituents
of the blood sera. Blood groups of the same kind are found in man and in
certain anthropoid apes, but these close similarities are lacking if man and
less nearly related species are compared. A still more limited parallelism is
shown between phylogenetic relationship and the distribution of the Forssman
heterophile differentials. Such partial parallelisms may be observed also be-
tween the evolution of organ differentials and of the interactions between
certain organs on the one hand, and phylogenetic relationship of the species
on the other. We have referred already to the observation of Sherwin, that
phenylacetic acid is detoxified in more primitive organisms, including monkeys,
by conjugation with glycine, leading to the formation of phenaceturic acid.
In human beings, it combines with glutamine and is eliminated in the urine
as phenylacetyl glutamine ; and according to Power a chimpanzee behaved like
man. Another example of a parallelism between the nature of metabolic
processes and phylogenetic relationship is the following : creatinine phosphoric
acid plays an important role in muscular contraction, but it is almost ex-
clusively found in vertebrate muscle ; in invertebrate muscle its place is taken
by arginine phosphoric acid. However, there are two important exceptions to
this rule. Creatinine phosphoric acid is also found in the muscles of some
echinoderms and of Balanoglossus. The latter is believed to represent a form
transitional between invertebrates and vertebrates.

The distribution of urea and uric acid conforms only partly to phylogenetic
relationship; but there is a definite connection between the production of urea
or uric acid in certain classes or species of animals and the distribution of the
enzymes arginase, xanthine oxidase, urease, allantoinase and allantoicase.
Such a partial relationship applies also as far as the distribution of hemoglobin
is concerned. It occurs in the erythrocytes of all the vertebrates and in the
plasma of annelids and molluscs. In the corpuscles of annelids there occurs
the pigment hemerythrin, and in the plasma of gastropods and cephalopod
molluscs, as well as in the plasma of crustaceans and other arthropods, there
occurs hemocyanin. From such systems all kinds of transitions may be found
to an entirely random distribution of substances, without regard to phylo-
genetic relationship, as for instance, that found in the case of the heterophile

DIFFERENTIALS AND EVOLUTION 595

antigens, with the exceptions already mentioned, as well as in the case of the
melanin pigments.

There are, then, morphological and metabolic characteristics of tissues and
organs which, to a high degree, seem to be correlated with the gradation and
relationship of the organismal differentials; but these characteristics are
limited to certain organs and tissues and they are not common to all the
tissues, organs and organ functions of an organism. There are other structural
and metabolic characteristics of tissues and organs which are only partly
correlated with the organismal differentials and with the phylogenetic develop-
ment, and still others are only slightly or not at all correlated. But, it is only
in the larger groups, such as classes, orders, genera, that the morphological
and biochemical evolution of certain organ and tissue systems can be correlated
with the course of the phylogenetic evolution and with the evolution of
organismal differentials. If we study individual organisms, the distribution of
organ and tissue characteristics is independent of the individuality differen-
tials. In brothers and sisters there are structural, biochemical differences in cer-
tain organs and tissues, as well as psychical differences, which do not parallel the
relations of their individuality differentials ; this is true also of the distribution
of the original blood groups. There is reason for the conclusion that the organ-
ismal differentials have a closer and much more direct correspondence to
phylogenetic relationship than the organ and tissue differentials.

There are, in addition, certain specific functional or structural relationships
between some cells and tissues, which very closely correspond to the relation-
ships between the organisms from which these cells and tissues are derived,
but which are not identical with the primary, typical organismal differentials.
Thus in some instances there exist between germ cells, spermatozoa and ova,
or between germ cells and certain somatic tissues, specific relations which
make possible the distinction between autogenous and homoiogenous relation-
ship. Likewise among infusoria there are mechanisms which enable these
organisms to distinguish the autogenous, homoiogenous or heterogenous
nature of parts of these organisms. We have in this, as well as in other similar
cases, to deal with processes which have developed not in the direct line of
phylogenetic evolution but in side branches and which are peculiar to them ;
in particular, in unicellular organisms, it is not certain what role is played
by genetic factors and what by cytoplasmic modifications in such mechanisms.
In all probability many other mechanisms of a similar nature exist, which
make the interactions between different organisms or between parts of them
specific for species, varieties or individuals. In different cases the mode of
manifestation of these specificities may vary, and likewise the mechanism by
means of which the mutual adaption of cells and tissues is produced may vary.

An organism consists, then, ultimately of systems of graded substances,
some of which possess a very great organismal-specificity while others are
almost exclusively organ-specific, and still others show combinations of organ-
ismal and organ differentials, varying quantitatively in different instances. In
addition, there occur substances which are specific for a certain species or

596 THE BIOLOGICAL BASIS OF INDIVIDUALITY

individual, but show no direct connection with organismal differentials, nor
can they be strictly considered as organ differentials, an instance being the
four original blood groups. These substance-specificities are paralleled by
structural specificities. The full, complex interaction of such specificities
including the marked organismal-specificity in the relationships between
the various parts of an organism and between different organisms represents
perhaps the most characteristic feature of organisms: these specificities all
increase with increasing evolution. To such specificities of substances and
structures there corresponds a specificity of the reactions which take place be-
tween the different constituent parts of an organism, and between different
organisms or parts of them. These specific reactions include the normal cor-
relations and functional reactions between different tissues and organs within
the individual organism ; they include furthermore, the reactions of immunity
and anaphylaxis. On such specific reactions depend also, ultimately, certain
functional correlations between the organism and his environment, by means
of which the environment is distinguished from the individual's own organism
and, within certain limits, is reshaped by the latter, and some constituents
of the environment are transformed into organismal and organ-specific consti-
tuents of the organism. On these specific reactions are contingent, as well,
those functions which make possible the transmisson of specificities to new
generations. The problem of evolution consists largely in the analysis of the
mode of development of these specific systems, on which the specific reactions
depend.

It is due to the combined effects of the individuality differentials and the
various systems of organ differentials and to the resulting organ functions,
that the fullest development of individuality in the highest organisms takes
place. But the individuality differentials, and the organismal differentials in
general, as well as the chemical and morphological structure of organs and
their functions, are themselves determined primarily by genetic factors. As
to the nature of these genetic factors, these differ in the case of individuality
and organ differentials. The various characteristics of an organ, as a rule,
are determined each by one or by a restricted number of genetic factors which
are transmitted in accordance with the laws of Mendelian heredity, although
various complications may arise in this process. This predominating effect of
a single gene or of a few genes, or of certain changes in chromosomes on the
ontogenetic development and on the functions of organs and tissues holds
good, although during the various stages of embryonal life and also during
adult life the cells of the most diverse tissues and organs contain, as far as
it is known at present, complete and identical gene sets. It must be due to the
interaction of the gene sets with a variety of cytoplasmic structures that the
differentiation of tissues and organs within the same organism can take place.
On the other hand, there is reason for assuming that the individuality dif-
ferentials depend upon a very large number of genes or, perhaps, on the
entire gene sets. This conclusion rests on several observations, but especially
on the fact that while, with progressive close inbreeding by means of con-
secutive brother-and-sister matings, the similarity of these differentials in

DIFFERENTIALS AND EVOLUTION 597

two individuals belonging to the same inbred family or strain can be gradu-
ally increased, it is very difficult to achieve complete identity as it exists be-
tween different parts of the same organism. This identity of the individuality
differentials of different tissues and organs in the same organism can be
demonstrated, notwithstanding the existence of great differences between
different tissues and organs.

It is primarily the difference in individuality differentials of the individuals
belonging to the same species which causes the reactions of the host against
the transplant, the local as well as the distant reactions, and which also may
cause immune reactions in an animal after introduction of tissue or its con-
stituent substances or of bodyfluid belonging to a not closely related in-
dividual ; parts of the same individual do not elicit either a contact or a distance
reaction after transplantation ; nor do autogenous substances elicit an immune
reaction, except perhaps parts of the body which, in certain respects, are
separated from and strange to the other parts of the organism, and in par-
ticular products of degeneration, which may differ in constitution from the
living parts. Organ differentials and artificial partial antigens, as a rule,
function as full antigens only in combination with strange individuality or
preferably with strange species and order differentials. It is especially the
strange organismal differentials which interfere with the integrated function
of the host organism into which they are introduced and which make it possible
for the host to react also against specific structures other than organismal
differentials.

As to the progressive evolution in structure, chemical constitution and
function of tissues and organs, and in the constitution of the whole organism,
it is assumed by geneticists, and also by some other students of evolution, that
this is caused by mutations, alterations in chromosomes and genes, in associa-
tion with processes of segregation and selection. If the conclusion is accepted
that mutations are the primary means through which organisms change in
the course of evolution, then it would be further necessary to assume that
changes in organs, caused by mutations, will affect also the organismal differ-
entials in the course of time. As far as the individuality differentials are con-
cerned, there is reason for believing that these depend, as already stated,
upon very many genes and it may therefore be assumed that a change in a
single gene, which might be sufficient to induce a modification in the struc-
ture and function of a certain organ or tissue, would not alter the individuality
differential noticeably, or only to a very slight degree ; but repeated mutations
might produce a more marked effect on the individuality differential. Such
modifications in the genetic constitution would in many instances affect only
superficial mechanisms, which do not control vital processes in the adult, and
they would affect, first, the late stages in embryonal development. Secondarily,
however, such changes might influence also other mechanisms in the organism
and thus alter a variety of characters. As to mutations which result in slightly
further-going changes, such as those which have led to the transformation of
gray Norway rats to "Mutant Albino" or to "Curly Coat," which were ob-
served by H. D. King, even these do not seem to change the organismal dif-

598 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ferentials to any great extent, as is indicated by the exchange of tissues
between these races. But it may be held that certain gradations exist in the
relations between the organismal differentials and these organ mutations,
which are superimposed upon numerous genetic differences which already
exist between different individuals, families and strains. However, in addition
the possibility would have to be considered that changes in organismal differ-
entials depend on specific mutations, which do not affect one single organ or
tissue but certain characteristics common to all organs and tissues.

The analysis of organismal differentials from the viewpoint of evolution
is bound up with the analysis of the genetic differences between races
(strains), subspecies, species and genera, and of the mode of origin of these
genetic differences and of speciation. As a rule, multiple genetic and chromo-
somal differences distinguish races, subspecies, species and genera. These
differences are caused by an accumulation of mutations, which consist either
in changes taking place in chromosomes or in genes. They occur in a popu-
lation which is spread out over a certain geographic area. Subsequent proc-
esses of selection, which vary in character in different environments, seem
to lead to the formation of geographic races and species and may explain the
adaptation which exists between these groups and the environment in which
they live; at least quite commonly certain environmental characteristics are
associated with certain structural and functional characteristics of the or-
ganisms inhabiting certain areas (F. B. Sumner), and these associations
between environment and constitution of organisms seem to develop independ-
ently in various places and in different races or species belonging to the same
wider unit. Such differences between races, species and genera are greatly
aided by lack of interbreeding between adjoining populations and these ob-
stacles to the interbreeding may be produced by a variety of factors. In case
they are due to structural and functional differences in sex organs, such dif-
ferences are of no greater importance in the distinction between species than
differences in other organs and organ systems ; but the consequences of dif-
ferences in sex organs leading to sterility between adjoining populations are
much more important as far as speciation is concerned. There remains still
the problem as to whether the adaptations noted between environmental con-
ditions and structural and functional peculiarities of organisms are caused by
random mutations followed by selective processes, or whether, in unknown
ways, certain ecologic conditions exert a certain influence on the character of
mutations which take place in these environments.

While the number and nature of structural differences, and in particular,
also the interferences with interbreeding between races (strains), species and
genera may be taken as indicators of the degree of difference between the
organismal differentials of these groups, the real relationship between these
organismal differentials can be determined only by the direct tests for or-
ganismal differentials and the structure of the latter is the real criterion of
the nearness or distance in relationship between individuals and species. As to
the character and number of genes which differentiate various species and
whole groups of species, we may refer to the investigations of Landsteiner and

DIFFERENTIALS AND EVOLUTION 599

Miller, who compared the occurrence of the ordinary human agglutinogens and
of M and N agglutinogens in man, the anthropoid apes, as well as in Old World
monkeys and New World monkeys. They could trace in this way the develop-
ment of certain genes corresponding to these agglutinogens within a limited
range of the evolutionary process. Man and anthropoid apes are most closely
related; accordingly, they have agglutinogens A or B, or both A and B, in
common. The distribution of A and B differs in different species, but it also
differs in different human individuals. Factors A and B have not been found
among Old and New World monkeys ; but among certain New World monkey
species and among Lemuridae a factor may occur, which is related to but
not identical with human B. M and N agglutinogens occur as alleles in man,
but in chimpanzee a combination (MN) has been found, which has not been
observed in man. Again there occurs in Gibbons and New World monkeys a
factor similar to but not identical with the human M. It has been assumed
that progenitors for A and B are present in common ancestors of these
species and that B is perhaps the older factor.

Irwin tested by means of a series of immune sera, the number of genes
which were common to various species of pigeons. In comparing two of these
species he concluded that each of these has a number of genes which the other
species do not possess, and in addition there is a set of genes which both
species have in common. Accordingly among the Old World species of pigeons
there are sets of genes which are characteristic of each species, and other
genes are shared by these species. The same applies to the New World species
of pigeons, and a third set of genes is shared by Old and New World
pigeons. These conclusions would imply that the gene constitution of each
class, family, genera, species, strain, and still more, of each individual, is
extremely complex, consisting of numerous sets of genes which two different
groups share and of others which distinguish them. The nearer these species
or groups of species are to one another, the greater is the number of genes
they have in common, and the further distant they are, the smaller is the
number of genes which are identical. These conclusions are based on the as-
sumption that each agglutinogen is associated with or determined by a par-
ticular gene ; however, there is the possibility that each agglutinogen is deter-
mined by more than one gene. Furthermore, it is only one type of phenotypic
characters and one type of genes which have been considered in these in-
vestigations, namely, those which determine the agglutination of erythrocytes
by specific immune sera. But there are innumerable other characters which
are independent of the agglutinogens of erythrocytes and if the gene-deter-
miners of these characters were also included, the complexity in the genie
constitution of tissues would become still much greater.

It seems plausible that mutations causing very fargoing changes in organs
and acting on earlier embryonal processes may modify some of the more
basic organismal differentials, which developed first in the course of evolu-
tion, while mutations affecting the constitution of organs, which were more
recently acquired and which are of a less fundamental nature, may modify
the individuality differentials. In general, it seems that the more similar two

600 THE BIOLOGICAL BASIS OF INDIVIDUALITY

organisms are to each other in their structure and chemical constitution, the
more similar as a rule are also their individuality differentials, and that to
more fundamental differences in chemical constitution and structure corre-
spond furthergoing genetic differences in the organismal differentials. In
the course of phylogenetic evolution the finer organismal differentials devel-
oped gradually; at least they became manifest only in the course of advancing
evolution. Likewise, as evolution progressed, an increasing differentiation
and specialization of tissues and organs took place. Comparable processes occur
during embryonal development ; but here the organismal differentials develop
from precursor substances, the complexity of which increases parallel to the
increasing complexity of the organs and tissues and organismal differentials
in the higher organisms.

However, during ontogenetic development endstages are reached in which
again a decline sets in in the manifestation of the more specific organismal
differentials. The more the cellular substance proper of organs and tissues
diminishes and the more the paraplastic and intercellular substances predomi-
nate, the more specific is the organ and tissue differentiation and the less
prominent become the finer organismal differentials, the species and individu-
ality differentials. The character of the lens of the eye, and presumably also
that of keratin and of other specialized structures which no longer possess the
typical cellular constitution of the tissues from which they originated exem-
plify this change. But this is found only if certain serological reactions are
used as tests for the presence of organismal and organ differentials ; by
means of contact and distant effects of transplanted tissues it is still possible
to demonstrate the presence of individuality differentials in such tissues,
at least in the case of the eye lens. It is therefore probable that in these
paraplastic tissues the individuality differentials have not been entirely lost,
but that their existence cannot be demonstrated by the less sensitive serological
methods ; this may be due to the fact that they have relatively diminished in
quantity perhaps on account of the increasing preponderance of the organ
differentials.

Evolution is essentially the history of the adaptations between organisms
and their environment and between constituent parts within the organism,
the non-adapted organisms being eliminated. But there has been an evolution
not only in the development of the organisms, their tissues, organs, and their
organismal differentials ; there has been an evolution also in those processes
which lead to the decline of these organisms, such as ageing, tendency to dis-
ease, and death, all of which are manifestations of the lack of perfect adapta-
tion. Primitive organisms possess great plasticity in organ formation and
they possess the ability to restitute the whole organism under the influence
of internal and external environmental factors. This plasticity is associated
with a lack of the manifestation of finer organismal differentials and there-
fore with a lack of individuality. The higher organisms constitute much more
rigid, fixed wholes, which exhibit very fine individuality differentials. In the
higher organisms the organ systems have become more complex in structure
and function, and in their interaction with other organ systems. The primitive

DIFFERENTIALS AND EVOLUTION 601

organisms, because of their great plasticity and ability to produce organs and
to restitute whole organisms, are potentially immortal, in the restricted sense
which applies to beings living on a planet and in a universe over which they
have no control. The higher organisms, because of their rigid organization
and lack of plasticity, because of their greater individualization, have lost
the power to restitute the whole organism and to be potentially immortal ; at
best, only small constituent parts still possess such power, and this can be
realized only under artificial experimental conditions. Higher organisms are
more readily discoordinated and disorganized. The delicate mechanisms of
adjustment to one another which their organs and tissues have developed,
no longer enable them to repair more extensive injuries experienced under
the influence of inner and outer environmental factors, to undergo compensa-
tory regulations and to propagate asexually. They have acquired senescence
and associated diseases in the attainment of individuality and one of the
prices they paid for individuality was the potentiality to immortal life.

But while there is a parallelism between the ascending evolution of organis-
mal differentials, the specialization of organs and tissues, the increasing
rigidity of the organism, and the apparent inevitableness of senescence and
death, it is, in the first place, the increasing complexity in the structure, con-
stitution, and metabolic and functional interaction of tissues and organs rather
than the increasing specialization of the organismal differentials which is
responsible for these pathological consequences of ascending evolution. As a
result of the greater differentiation of the organs and their increasingly intri-
cate interaction the organs became more delicate and, in the course of time,
they were no longer quite adequate to the performance of their functions,
and this change becomes more and more cumulative with the advancing years
of the individual. The relative proportion of reversible cyclic and irreversible
non-cyclic processes is more and more altered to the advantage of the non-
cyclic with increasing age of the individual.

Many processes in nature are cyclic, but other processes, as all those sub-
ject to the second law of thermodynamics, are nonreversible, proceeding only
in one direction. The disintegration of radio-active substances is non-
reversible, although under altered conditions also a creation of the latter
may occur. In organisms the essential functions must be cyclic; this is the
case with circulatory, respiratory, alimentary functions, with sleep and
hibernation, with the proliferation of certain tissues. The sexual processes are
also at least partly cyclic, but they sustain the life of the species rather than
the life of the individual. However, these cyclic processes are grafted on
an irreversible process of a non-cyclic character, on one continuous process,
starting with birth and leading to growth, maturity, old age and death. This
process, irreversible as far as the individual is concerned, is the basis of
cyclicity in the species. But, also, the species may be subject to non-cyclic
changes and will be destroyed in the end, when external conditions cause at
an early age a decline in the organisms and make propagation impossible.

We may then regard disease and death as manifestations of insufficient
adaptation between the different constituents of an organism and between or-

602 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ganism and environment. The process of gene mutation itself, which pre-
sumably plays so important a role in evolution, is frequently the source of
maladjustments and therefore many mutations are lethal; in other instances
they may lead to malformations and abnormalities in metabolism and func-
tion, or they provide the basis on which certain environmental conditions can
act in an injurious way. Pathological mechanisms, or mechanisms arising in
response to injurious conditions and tending to counteract them, have their
phylogenetic history as well as normal mechanisms. We should therefore
be able to trace the origin and evolution of disease processes phylogenetically
in the same way as the evolution of normal structures and functions ; but only
the beginnings have been made in this direction.

Thus, we have attempted to trace the development of thrombosis, a partial
or complete occlusion of blood vessels, which in mammals depends upon
changes in the vessels, in the character of the blood flow, and in the com-
position of the blood. From the primitive process of agglutination of amoebo-
cytes in Limulus and the subsequent combination of this with processes
of coagulation of blood in higher invertebrates, this condition ascends through
the lower vertebrates to its full complexity in mammals. But thrombosis,
which represents a disease and has destructive consequences for so many
higher organisms, is closely associated with processes which, instead of being
injurious, have an adaptive value, such as the prevention of bleeding follow-
ing injury. Furthermore, it is of interest in this connection that the mechanism
leading to the primitive thrombus formation as found in Limulus has much
in common with that underlying tissue formation, as we pointed out in a
preceding chapter. In a different field of pathology, Metchnikoff has shown
that it is possible to trace phylogenetically the activity of phagocytes, which
play so important a role in inflammation and in immunity, from simple proc-
esses of digestion in primitive organisms to the most complex reactions against
injurious material in mammals.

In a provisional way we may distinguish four types of inadequacies or dis-
eases which are however not sharply separated from one another but overlap to
a certain extent. 1) The ultimate inadequacy, which becomes manifest in the
course of life in the differentiated and the rigid organisms belonging to the
higher classes of animals, is also the cause of the imperfect utilization of certain
important food factors, as is also the lack of tolerance by certain organs for
food factors which are necessary for other kinds of tissues or organs ; thus,
disharmonies in the organism set in. 2) Likewise, inadequacies in the relations
between the individual and his natural or social environment may lead to such
disharmonies and these, too, have had their evolution. 3) A third type of dis-
harmony causes a disease which may also be traced phylogenetically; it con-
sists in changes in certain tissues, which make them assume a cancerous growth
and thus invade and destroy the organism in which they originated. Cancerous
growth has, so far, been observed only in the relatively rigid organ and tissue
systems of the vertebrates; in those organisms, in which restitutive growth
processes lead to the formation of organs, to multiplication of the individual
animals, or to colony formation, excessive growth stimulation should not cause

DIFFERENTIALS AND EVOLUTION 603

the development of cancer. The latter represents, then, apparently a disturbance
of the organ and tissue equilibrium, which has ensued from the increasing
differentiation and specialization of tissues and organs and from the increasing
rigidity in the constitution of the whole organism, which took place in the
course of evolution.

4) A fourth type of disease is due to the struggle between complex higher
organisms and various types of parasites, especially bacteria, protozoa and
various viruses. In this case the reaction of the host against the invader is due
in part to the effect of specific toxic substances, which injure certain tissues
and organs of the host; also, the direct destructive effect of parts of the host
by parasites may play a role in this disease process. But there are viruses
which, instead of causing a primary destruction, may induce cancerous growth
processes in certain hosts and in certain tissues of these hosts. Moreover,
parasites possess organismal differentials which differ greatly from those of
the host, and these differences may disequilibrate the latter and thus lead to
disease. However, the organism which, as the result of inadequacies in its
own constitution and in its interaction with the living and non-living environ-
ment, receives injuries and becomes diseased, is not merely a passive agent;
it also responds actively to the injurious factors, and these reactions may be
the cause of new diseases superimposed upon the primary ones. Local re-
actions of the host, in the form of so-called inflammatory processes, may cause
a sclerosis (cirrhosis) of certain organs, with serious consequences for the
economy of the organism as a whole. But also thrombosis, and even cancer
in certain respects, may be considered as reactions of the organism against
abnormal conditions ; furthermore, immune processes directed against strange
substances are, in many cases, beneficial, causing the death of the invading
parasite, or helping to destroy strange organismal differentials or to convert
the latter into the differentials of the host. However, in other cases they
may be destructive for the host. This occurs if reactions of a similar nature
to the immune processes lead to states of anaphylaxis or various kinds of
allergy. In these conditions, organismal differentials may also play a part and
there is reason for assuming that the sensitiveness to strange organismal dif-
ferentials becomes greater with furthergoing differentiation and specializa-
tion of the organismal differentials; likewise, the destruction of organs
becomes increasingly serious with the increasing differentiation of organs and
their increasing inability to restitute the lost parts with advancing evolu-
tion. Thus, with progressing evolution disease processes may preponderate
over restitutive processes, although both go hand in hand.

The relations between the host and the various organisms which live on
or in the host may be that of symbiosis or parasitism. As to the role which
organismal and organ differentials play in these relationships, in some in-
stances host and symbiont or parasite may belong to the same species, and
this occurs in plants as well as in animals ; but as a rule they belong to very
distant classes and usually the host is phylogenetically a much higher or-
ganism than the parasite or symbiont. Also, the degree of specificity in these
relationships varies greatly in different cases. There may be an adaptation

604 THE BIOLOGICAL BASIS OF INDIVIDUALITY

of parasite or symbiont to one particular kind of host, or an adaptation to
a number of phylogenetically related hosts or to very diverse hosts, or the
two latter adaptations may exist at the same time. Parasites of animal or
plant origin as wellas viruses may live and propagate in or on very distant
organisms ; there does not need to exist an exact relationship between the
organismal differentials of host and parasite corresponding to phylogenetic
evolution.

However, under certain conditions organismal differentials may play a
certain role in determining the invasion of the hosts by the strange organisms.
The relationship between the organismal differentials of host and parasite
or symbiont may resemble that of certain organ and tissue differentials, or
the distribution of blood-group or Forssman differentials in various species.
But whatever the significance of organismal differentials in these relation-
ships may be, parasites and symbionts are usually adapted to definite host
species and often also to definite organs or tissues within a certain species.
There exists therefore a marked specificity in the relations between host and
invader. This specificity may be so great that it is possible to distinguish
between different strains of hosts by determining the kind of parasites or
symbionts which live on or in them, and conversely, to distinguish between
nearly related parasites or symbionts by determining the host on which they
are found. The mutual relationship between the organismal differentials of
host and parasite may be one of the factors which determine the interaction
between these two organisms; this interaction does not depend however on
the organismal differentials of either host or parasite alone. In this respect
the relationship between host and parasite resembles that between host and
transplant, which depends on the organismal differentials of both host and
graft.

There are indications that the specific adaptation between host and parasite
or symbiont may be due partly, at least in some cases, to the presence of certain
substances in these two organisms which are specifically adapted to each
other. Furthermore, related parasites may contain related antigens, which
may call forth the production of antibodies showing cross-reactions with the
antigens of these parasites. A very instructive observation pointing to the
presence of specifically adapted substances in host and parasite, which make
possible this condition of parasitism, has been made by Welsh, who found
that various species of mites which live between the gills of Anodonta and
other mussels are positively heliotropic when they are removed from their
normal habitat. Addition of extract of the gills or of fluid from the mantle
cavity of the species on which they live makes this heliotropic reaction nega-
tive, and it is only extract or fluid from the species to which they are adapted
which has this effect and not substances obtained from other species of
mussels.

As mentioned, there is noticeable in many cases also a distinct organ- or
tissue-specific adaptation between host and parasite or symbiont. However,
in this respect also, great differences exist in different parasites; some are
adapted to a single organ or tissue, others can live and multiply in several or in

DIFFERENTIALS AND EVOLUTION 605

the large majority of the tissues. This organ-specificity suggests the possi-
bility that a definite species distribution of the parasites may not be due to
the specificity of the organismal differentials of the hosts, as for instance in
certain cases in which the parasites live and propagate only in a single species
or in a very few species, but is due rather to peculiarities which organs in
different species possess. The term organismal differentials would therefore
be used here in a wider sense.

While there exists in the relations between host and transplant frequently
an organismal- as well as an organ-specificity, in some instances the organ-
specificity, in others the organismal-specificity may predominate. But these
specificities are not always rigidly fixed; they may be modifiable through
serial passages of the parasite in a host species other than the one to which
it has been originally adapted. Gradually a change may take place in the
relative virulence of the parasite for various host species; this change in
species-specificity can be obtained also by means of many passages through
the chick chorio-allantoic membrane or the chick embryo, and not only the
species-specificity may be diminished or altered by this procedure, but also
the organ-specificity may be markedly decreased. These effects can be studied
very well in various viruses. There is therefore noticeable, here, a great
similarity between the behavior of certain viruses and of tumor transplants ;
the latter can become adapted to new hosts through many consecutive passages
in different hosts. Moreover, in heterogenous tumor transplants, a good
growth has been observed in the chorio-allantoic membrane of the chick; the
same is true of the growth of heterogenous normal tissues. In both viruses
and tumors an adaptation to a new host occurs in the course of long-continued
transplantations and the chick embryo and chorio-allantoic membrane seem
to lack the power to injure viruses or tissues and tumors possessing heterog-
enous organismal differentials. It remains still to be determined how far these
similarities in the behavior of microorganisms and viruses, on the one hand,
and mammalian as well as avian tissues and tumors, on the other, depend on
similar mechanisms.

The evolution of the organ systems and that of the organismal differentials
has led to the formation of very complex, rigidly integrated organisms, in
which the various organs and tissues are highly specialized. These processes
have also resulted in an increased differentiation between organisms belonging
to the same species and therefore in an increased individualization. In this
individualization, different organ systems have had an unequal part. The
generative system is less important for the individual than for the continuation
of the species, and the so-called vegetative organ systems are essential for
the life and function of the individual, but are not individualized to the
highest degree. It is the nervous system in its interaction with the other organ
systems, and especially with the endocrine organs, whose development in the
course of evolution has made possible the greatest individualization. Increasing
differentiations in the nervous system, in its cooperation with the hormone
system, have made possible the coordination and correlation of the functions
of the various organs and tissues belonging to the same organ system and

606 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the functions of various organ systems with one another; in this sense the
nervous and endocrine systems have made possible the integrated, very com-
plex organisms which have gradually developed in the course of evolution.
But in addition, the nervous system has developed in still another direction ;
it has become the organ system which, above all others, controls our relations
with the environment. The meaning of the environment, its variety and its
richness, depends for each species and for each individual to a large extent
on the constitution and function of the nervous system. While the vegetative
organ systems make possible the life and functioning of the organism in a
rather simple physico-chemical environment, the nervous system has become
the organ which by way of the sense organs, transmits to us a picture of the
environment and which represents the environment within us. Furthermore,
the development of the nervous system in the course of evolution has made
possible the creation of the most individualized type of environment, the
psychical environment, consisting in memories and, in the end, in the pro-
duction of the environment in thoughts and thought-emotion complexes. This
psychical environment has increased in richness and significance with advanc-
ing phylogenetic evolution, but it has reached a high development only in man.
In accordance with the advance in differentiation and individualization of
the human organism, his relations to the environment have also become more
differentiated and individualized and thus many new points of contact have
been created between him and his non-living as well as living environment.
These contacts have affected the natural struggle for health and life with
the non-living environment and with other less highly differentiated organ-
isms ; they have affected also the social competitive struggle with other human
beings for material and psychical goods. In the natural struggle, evolution
has led to the building-up of the physical-chemical sciences, of technique
and industry ; and in the social struggle, notwithstanding many retrogressive
movements, there has been, on the whole, a development in the direction
towards a greater freedom and understanding in the spheres of political,
economical and social relations and towards an increasing valuation of the
dignity of the individual, as well as a beginning development of the psychical-
social sciences.

While man has thus lost the potentiality to immortal life, he has obtained
a greater and richer individuality; he has also gained a life of abstract thought
that may help to shape or, if he so desires, to replace the real life and the
universe, and he has won a certain degree of consistency and continuity in
existence through the persistence of thought and through its transmission
to successive generations.

' Evolution has laid the basis for and has actually led to changes in the
significance and working of the natural struggle and natural selection. A
certain point has been reached in evolution where it has become possible to
replace the crude and brutal struggle, which at least partly controls and
dominates the fate of the more primitive organisms, by a civilization which
in the end tends to become universal ; thus development has taken place by
way of intermediate cultural stages, in which particularistic interests and

DIFFERENTIALS AND EVOLUTION 607

aims functioned instead of the later, more universal ones. Ultimately there
tends to be created a humanistic mode of life, which can develop only at a level
of evolution reached by man. At this level, the physical as well as the psychical
factors of life attain a balance in which the wellbeing, bodily and mental, of
the individual will best be guarded.

Thus the contradiction between our concept of our personality and what
has been considered as the ultimate master of the fate of species and individ-
uals, namely, the natural and social struggle, will be diminished as far as the
latter are in conflict with the physiological needs and desires of the individual,
and only such safeguards will be established in this process as will make possi-
ble the avoidance of retrogression and degeneration, bodily as well as mental,
in human society, without abandoning the principles and ideals of civilization
and their practical application to civilized life. In man, the thought-life pre-
dominates and the realization of ideas may give the deepest meaning to his
existence ; if the ideas represent true abstractions and generalizations, if they
are in harmony with science, they are no longer concerned solely with narrow
circles of individuals, but with all humanity, and finally they may comprise the
universe; they may then become the possession of mankind. Thus the con-
flict between the wishes of the individual and his fate in the natural and
social struggle will, in the end, be mitigated and the struggle for the survival
of the fittest will be replaced by the knowledge and understanding of a
civilized society, in which a conscious direction of further evolution may take
place.

In the course of evolution there have then developed organisms in which
individuality and its constancy depend upon three factors: 1) the structure,
function and interrelations of organs and tissues; 2) the function in particular
of the nervous system especially that on which memory is based and which gives
distinctiveness and continuity to the highest organism, man; and 3) the
action of organismal and individuality differentials.

As to the first factor, organs and tissues are in a constant flux from early
embryonal life through early extrauterine, to adult life and old age ; there is
a greater difference between the structure and function of an embryonal tissue
and organ and the corresponding tissue and organ in the same individual
during old age than between the organ or tissue characteristics of two different
individuals at comparable ages; it is only the potentiality of organs and
tissues to undergo a certain development in the same individual which is
characteristic of the individual and constant. Regarding the significance of
memory in the maintenance of individuality in the psychical sense, the effect
of the latter is imperfect and limited in time ; it cannot fully function as the
expression of individuality. There remains the third factor, the action of
organismal and individuality differentials, which is completely characteristic
of the individual and which maintains its identity in the same organism ; this
factor then represents the essential individuality, whereas the first two factors
merely support this essential individuality; each of these factors has passed
through a definite evolution which we have correlated with the evolution of
the other factors.

Pjirt \^TTT ^e Psyc^ca^Social Individuality

Chapter I

The Physiological Basis of the Psychical-
Social Individuality

IT is preeminently the phylogenetic development of a certain organ
complex, the nervous system, that made possible the phylogenetic de-
velopment of individuality in the psychical-social sense. An individuality
similar to that of the higher mammals, and in particular of man, does not yet
exist in the more primitive organisms. In some of the earliest forms of animal
life there may be found instead of single individuals, groups of individuals,
colonies, which later may separate into single organisms. Gradually within
single organisms a differentiation of the component parts occurs and these
differentiated parts become more and more integrated and coordinated in
such a way that a complex whole results. The process of coordination takes
place largely through the nervous system in conjunction with the hormones, but
it seems that the nervous system itself may exert at least many of its functions
by means of specific hormone-like substances, which it transmits along the
nerve paths. As a rule, however, the hormones are carried to distant areas
by way of the lymph and blood channels and help to influence and correlate
the various parts of the organism. In this process of coordination there are
involved reflexes in which nerve fibers, ganglia cells and hormones, which
circulate in the bodyfluids, may cooperate. In a wider sense, we may include
among the hormones also certain contact substances, which are given off by
one tissue and which act on an adjoining tissue.

Corresponding to the increasing integration of the individual, the nervous
system becomes more complex. This system is lacking in protozoa and in
sponges; however, in certain ciliate protozoans fibers exist, to which the
function of conduction of stimuli and coordination of movements have been
attributed. Sponges may be cut into many small particles and when these are
joined together at random they form a whole new organism. The definite
beginnings of a nervous apparatus consist in a system of nerves without a
central set of ganglia. The primitive nervous system of the simplest inverte-
brates is not yet polarized. The simplest type of a central nervous system is
found in the echinoderms ; in the starfish, for instance, there is a circumoral
nerve ring consisting of nerve fibers with attached scattered ganglia cells, but
as yet without real ganglia. This nerve ring functions as an organ which co-

609

610 THE BIOLOGICAL BASIS OF INDIVIDUALITY

ordinates the movements of the various rays of the starfish (Romanes, A. R.
Moore). Next there arises a segmented nervous system, in which, in addition,
there forms a central system of ganglia, and in which each segment of the
body contains collections of ganglia cells joined by nerve fibers running
lengthwise through successive segments. This is a step towards increasing
integration. The segmented plan, on which the nervous system is built, per-
sists even in the highest organisms. At first the developing central ganglia are
of relatively little importance, because the different parts of which the or-
ganism is composed are still largely independent of one another.

Under favorable conditions certain cells and tissues retain the power to
live independently, even in the highest organisms, but the ability of parts of
the organism to lead their own existence and to restitute the whole organism
when separated from the rest, diminishes step by step ; likewise, the power to
regenerate organs or other portions of the animal lessens or may become
entirely lost. Concurrently with this development and with the increasing
complexity of tissues and organs and their greater tendency to coordination,
the central nervous system gains in importance and becomes more intricate.
However, it is not until the latter has reached a certain stage, after a differen-
tiation of the cortex has taken place in the forebrain, that thoughts may form
on the basis of sense impressions and that the ability to abstract and syn-
thesize becomes possible, and that there thus develops the psychical-social
individuality in its most complete form. The cortex arises first in reptiles.

The phylogenetic development of the social-psychical individuality is thus
paralleled by the evolution of the nervous system with its increasing com-
plications, such as an increase in differentiation and segregation of parts of
nerve cells and fibers in localized areas, the formation of certain projection
systems connecting the peripheral sensory receptor organs with subcortical
ganglia and the connections of the latter with the peripheral effector organs
and later with the cerebral cortex. It is also paralleled by the development
of systems of association fibers within the cortex of the brain, the forma-
tion of distinct ganglia within the more or less diffuse neuropil, and by the
stratification and individualization of the cortex. At the same time there
seems to remain everywhere a less well defined neuropil, consisting of
shorter neurons and collateral nerves; it infiltrates the other, more localized
parts diffusely and to this tissue has been attributed, by Herrick, the integra-
tive activities of a lower type, as for instance, the maintenance of the tonus
in more primitive organisms, as well as those of a higher type. According to
this view, these latter processes would not essentially be localized, as are
certain sensory projection nerve fiber systems, the motor nerve fiber systems
with which they connect, and, although less obviously, the association fiber
systems. Hand in hand thus with the differentiation and individualization of
certain separate mechanisms, new connecting, centralizing systems develop.
In accordance with the increasing complexity of the organization in general,
the number of the primary simple reflexes increases, the complexity of their
interaction likewise increases, and they then extend and become converted
into complex, associated, conditioned reflex systems. The effect eventuating

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 611

from the sensory stimuli received from the environment depends, therefore,
not only on the character of the sense organs, but also on the central nervous
system.

In correspondence with this evolution of the nervous system there seems
to take place also an increasing complexity in the production and action of
hormones. The number of hormones which have so far been demonstrated in
invertebrates is relatively small and their presence has been noted principally
in the higher types, particularly in the arthropods. To mention some of the
hormones and their actions which have been studied best : The experiments
of Roller and Perkins, and others, have shown the existence of a hormone
which is involved in the movement of pigment in the chromatophores of
crustaceans; it is produced in the eyestalk in the sinus gland. Analogous
hormones may affect also the chromatophores of various classes of verte-
brates (G. H. Parker, F. B. Sumner). Kopec and others found that in
Lepidoptera the supraesophageal ganglion controls pupation. In addition in
Hemiptera and Orthoptera molting and pupation are induced by hormones
originating in nervous ganglia. According to Wigglesworth a hormone given
off by the corpus allatum inhibits metamorphosis. In Drosophila a hormone
responsible for pupation is given off by the larval ring gland which is
situated between the two hemispheres of the larval brain (Hadorn), and
Bodenstein has moreover made it probable that this gland induces also the
differentiation of organs into the imaginal state. The last mentioned effect may
however be an indirect one and as in the case of other hormones already
discussed, the changes induced by the ringgland do not depend solely on
the nature of the hormone, but on a balance between hormone and the state
of the recipient tissue. Various other hormones probably exist in inverte-
brates ; there are in particular indications in crustaceans and also in other
invertebrates that hormones may affect the development of secondary sex
characteristics ; furthermore the socalled gene hormones might be mentioned
in this connection. As in the case of vertebrates so also in invertebrates no
strict species specificity of hormones seems to exist and there are even
indications that invertebrate hormones may perhaps affect vertebrate organs
and conversely certain vertebrate hormones may affect invertebrate tissues.

The relative scarcity of the hormones so far discovered in invertebrates as-
well as their distribution in different classes suggests that an evolution com-
parable to the evolution in the central nervous system may have taken place
also in the case of hormones; this would be in accordance with the simpler
structure, the less developed differentiation, integration and coordination, the
more limited organ functions in these more rudimentary animals as compared
with the conditions found in vertebrates. However, there are no exact data
available which would make possible at the present time a definite com-
parison of the number of hormones present in a tissue unit in vertebrates
and invertebrates, and it will be a task for future research to trace the
phylogenetic evolution of hormonal regulations.

In addition to these central mechanisms there are the peripheral receptors,
the sense organs, which in response to physico-chemical factors emanating

612 THE BIOLOGICAL BASIS OF INDIVIDUALITY

from the environment, whether living or non-living, determine the action of
animals. As a rule, these sense organs also undergo an increasing differen-
tiation with phylogenetic evolution, although some of them may be developed
to a higher degree in more primitive organisms than in man. In general, the
mechanistic basis of primitive animal behavior is clearly discernible, but with
further phylogenetic advancement and- with increasing structural and func-
tional complexities new and more complex processes arise, which may render
difficult the analysis of the behavior of the organism as a whole.

The mechanistic character of the behavior of animals was recognized by
Jacques Loeb, and it was with particular clearness discernible in the tropistic
reactions of animals as highly developed as certain insects. Especially sug-
gestive was the observation of this investigator that slight physico-chemical
changes in the environment were able to cause a reversion in the direction of
the tropistic reaction.

Simple non-conditioned reflexes represent the functional elements which
seem to underlie animal reactions. However, it appears that ganglia of the
central nervous system give off, also automatically, stimuli which are trans-
mitted to the peripheral nerves and to the recipient end-organs. This would
mean that a specific stimulation by afferent nerves of the reflex arc or by
hormones is not required for the function of these ganglia, but that they
may discharge stimuli under the influence of non-specific substances or
mechanisms which reach them. Yet, it is probable that the important func-
tions of the central nervous system, which determine the behavior of higher
organisms, are essentially of a reflex nature. The most important complica-
tion which next arose in animal behavior consists in the conditioned reflexes
discovered by Pavlov. Even at a very early phylogenetic stage, former actions
of the environment may modify the subsequent behavior by means of condi-
tioned reflexes. Thus, learning is made possible. But the importance of these
processes is, on the whole, limited in invertebrates, although they seem to be
widely distributed. Thus, conditioned reflexes have been shown to exist in
polyclad flatworms. It has been maintained that they can be demonstrated
also in protozoa ; however, A. R. Moore has pointed out that in the latter
one may have to deal with a condition analogous to the hysteresis of metals
and colloids, in which a longer lasting after-effect of certain treatments can
be shown to exist, comparable to certain fatigue phenomena rather than to
true conditioned reflexes. The latter exist, however, in larvae of lower
vertebrates, as, for instance, in Ambly stoma (A. R. Moore). Even in verte-
brates they bear a definite relation to the inherited structural and reflex
constitution of the various animals and, as stated, represent an addition to
these latter. The more varied the simple reflex activities of the organisms have
become, the more varied may be the conditioned reflexes which are added to
them.

Therefore, behavior at first is rigid and fixed, corresponding to the origi-
nally relatively simple structure of the organisms and especially to their
nervous system and sense organs. There are no indications that individual
differences are very significant in the behavior in the more primitive animals.

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 613

But in vertebrates distinctions between individuals may be recognized. It is
especially the development of conditioned reflexes which leads to the differen-
tiation between individuals of the same species, because individual distinctions
of a finer type depend upon individual experiences of a special kind, and
conditioned reflexes seem to play only a very small part in primitive organisms
under natural conditions, where we have essentially to deal with "forced
movements" based on non-conditioned reflexes.

Even in the apparently most highly developed invertebrates, the social
insects, bees for example, rigid reflexes and complex reflex systems, instincts,
determine the very complex modes of their behavior. While environmental
changes may have a slightly modifying influence, in general these animals are
guided in a reflex manner by scents, colors, and certain spatial characteristics ;
also time factors, such as the position of the sun, may perhaps affect their
activities. While this interaction of some environmental factors with a com-
plex organization may lead to very complicated modes of behavior, still, the
latter remain essentially rigid and forced and are largely non-modifiable.
However, memories seem to play a certain part in the behavior of these
organisms, and further complications, in addition to those caused by condi-
tioned reflexes, are introduced by the changes taking place at some periods in
the life of the individuals, which may lead to changes in the reaction modes.
Although to a very limited extent the reactions of these animals have become
modifiable, in the main they are rigid and fixed. It is the complexity of these
reactions and their social nature, which are the distinctive features in the
behavior of the social insects and which raise their behavior co an apparently
very high level, making it comparable in certain respects to the social life
of higher vertebrates.

While, as we have seen, there are no indications of marked individualiza-
tion in the strict meaning of this term, sharply defined group differences
exist in accordance with structural and functional differentiations within cer-
tain species of insects. The various species of ants differ and show grada-
tions in regard to their psychical-social behavior in a way analogous to the
differences and gradations in the structure and function of various organs, and
in the structure of the body as a whole. In general, the behavior patterns,
which are essentially based on inherited instincts, are similar in nearly related
insects and differ in further distant species ; but in some cases nearly related
species may present very different types of behavior, and relatively distant
species may show similar types of behavior; for example, certain bees are
non-social in their behavior pattern, while insects as distant as bees and ants
may have in common very complex social reaction systems.

Fishes, representing the most primitive class of vertebrates, recognize to a
limited degree individuals and species. There are species differences in be-
havior ; on the whole, behavior patterns are similar in related, and quite different
in more distant species. Individuals belonging to the same species school to-
gether, joining their own species in preference to a strange one ; and conversely,
a certain school receives members of its own species and repels members of a
strange species. In the social dominance system, in which there are individuals

614 THE BIOLOGICAL BASIS OF INDIVIDUALITY

with attributes of graded superiority or inferiority, these gradations serve
to distinguish individuals. Females learn to recognize their former mates;
they attack strange males of the same species, but do not react against their
old mates. Parent fish learn to recognize their young. There are very distinct
and fixed behavior patterns relating to the sexual life, preceding the mating
act; also, the spawning and brooding functions are rigid, inherited species
characteristics. Movements which have the effect of suggestions and lead
to imitations of movements play a part in these actions. In the selection of
territories and nest sites, color distinctions are involved ; but here, also, previ-
ous experiences of having lived in an environment with certain colors may
influence the choice of the nesting place.

The signs which serve as symbols determining recognition, schooling, sexual
acceptance or attack in the social life of fishes, are partly visual, such as recog-
nition of movements and fine distinctions in color designs; but also olfactory
stimuli, extracts of skin, wounds, substances extracted from dead fish of the
same species call forth avoidance reactions in Phoxinus. The essential be-
havior patterns are genetically determined species characters ; but learning
leads to certain modifications in the behavior patterns. If a certain individual
is differentiated from other individuals belonging to the same species, this
does not necessarily mean that the individual recognition in fishes has the
same significance as in man ; although the same term is used in both instances,
we have probably to deal with processes of a different nature. In fishes the
recognition of an individual signifies the sorting out of a fish as representing
a child, a former mate, or a certain degree in the dominance series, one fish
being differentiated from others probably by means of a single sign, such as
a color pattern of the head, a particular movement, or perhaps a certain
olfactory stimulus given off by this fish. In man, on the other hand, an
individual represents a composite of many different bodily signs and psychical
expressions, which have acted on another individual by certain movements,
have given rise to certain experiences and have aroused hopes or fears.
However, the most primitive and the highest vertebrates — fishes and man
— give evidence, in common, that the distinction of individuals and species
depends directly on characteristics of organs and their functions, on move-
ments and expressions, and not on the organismal differentials. These organs
differ in structure and function in different species and individuals, and the
behavior patterns differ accordingly ; but both the structure and functions of
organs and behavior patterns are connected and correlated with the organismal
differentials.

In addition to the reaction modes which we have mentioned, there are some
further indications of the ability of the fish to modify the rigid behavior
patterns as the result of experience. Frustration or perhaps painful sensations
result in an avoidance of certain motor activities, which would have been
carried out under normal favorable conditions. But there is no suggestion
that reproductions of sensations or events are the essential factors in these
learning processes or are the necessary cause of modifications in the way
of reaction, although such reproductions may perhaps also participate. If a

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 615

female fish does not react against a former mate, but reacts against a new
mate, this may merely be due to the loss of a stimulus, owing to former
experiences.

The mechanisms underlying the very complex, strictly determined migrations
of eel and salmon over very long distances at definite periods of life, are
unknown, but there is no indication that higher psychical processes are in-
volved other than those functioning also under other conditions of life. On
the whole, the reactions of fishes under given circumstances can be predicted
by the student of fish behavior, except in instances in which conditioned
reflexes have formed and processes of learning have taken place; in such
cases it would be necessary to know certain phases of the history of a fish
in order to make the predictability complete. There is no need to assume the
existence of free will in the psychical life of fishes. It seems that the greater
part of their behavior is determined by rigid simple reflexes and reflex sys-
tems, but joined to these are modifiable types of behavior based perhaps on
memories of sense impressions and of isolated events, and these may be
associated with simple feelings.

The reactions of birds represent also essentially fixed reflex systems, and,
on the whole, they are very similar to those observed in fishes, although the
signs used by birds are more complicated, insofar as in addition to various
visual stimuli, such as movements, postures, colors, designs, and to olfactory
stimuli, finely differentiated auditory stimuli enter into their psychical life.
Sounds given off by individuals begin already to play a role among amphibia,
but they become much more varied among birds ; there are specific sounds
given off by mates and also by parents and children. Among the birds, too,
are found species distinctions, sex distinctions, and well developed sex
symbolisms used in the sex life of males and females. There is also a seeking
for and claiming of territory in which to live and to breed, and the individual
which is the first to claim a given territory has the advantage over those that
enter later ; the former tends to be the dominant individual. There occur group
reactions as well as individual distinctions, and a definite order exists regulat-
ing dominance in a group. Furthermore, there are migrations to great dis-
tances by birds as well as by fishes, and the flight reflex plays a role in the
life of both, as well as in that of animals.

Again, both fixed inherited mechanisms and a certain degree of modifi-
ability of behavior are involved in determining the tendency to complex sea-
sonal migrations, which many species of birds exhibit. In some species this
process is due merely to definite organ functions and is independent of ex-
perience. However, in other birds only some component parts of the reaction
system, which leads to seasonal migrations, depend upon fixed reflex systems,
while other parts of it appear to be learned from older birds. In the latter
case we have to deal with mechanisms which induce a bird to follow other
birds in their movements ; in this way conditioned reflexes are set up and
the animals learn how to move ; thus a mechanism of tradition may develop.
Furthermore, we may find individual differences in the intensity of the
tendency to migration, the impulse to migrate being much stronger in some

616 THE BIOLOGICAL BASIS OF INDIVIDUALITY

individuals within a certain species than in others. Age and sex functions may
also modify the strength of the reaction, which, in certain species, is appar-
ently much more developed in younger than in older birds. It seems that in
migratory birds environmental changes, arising from seasonal conditions, set
in motion a reaction system which expresses itself in restlessness, but the
mechanisms underlying these migratory tendencies are as yet only imperfectly
known.

The instincts, as well as the kind and range of modifiability of behavior,
are inherited characteristics, and, on the whole, they are very similar in
closely related species and more dissimilar the more distant the species are;
these reactions resemble, in this respect, the organ systems and outer con-
figurations, for instance, in various species of birds which, on the whole, are
similar in nearly related species and differ in more distant species. However,
there may be differences here too between nearly related species ; as, for
instance, in behavior connected with courtship and parental care of the
young. There exists among birds, also, a well developed group life, the groups
consisting of individuals belonging to the same species, and members of one's
own group are distinguished from those belonging to strange groups. The
stimuli which hold certain groups together may be genetically determined in
one species and acquired by experience in another species. Voice, posture and
movements may regulate the activities in a certain group. There are indications
that even conditions comparable to what may be called suggestion in the
human species play a part in the group life, inasmuch as movements of one
individual are quickly transmitted to other members of the flock and elicit
in them a similar behavior. The movements and attitudes of a male may
initiate corresponding actions in the female ; in this case sense organs trans-
mit the mode of reaction and induce imitative behavior in another individual.
Similar effects of suggestions have been noted also in fishes.

Also in other respects the species characteristics of behavior are to a
large extent genetically fixed, although there is a certain range of modifi-
ability in accordance with experience. Fixed species reactions are, for instance,
those of cowbirds, which return to their own species even if they have been
reared by foster parents belonging to different species. The flocking together
of birds of the same species, another fixed mechanism, depends on the in-
herited functions of organs and only in an indirect manner on the identity of
the organismal differentials of the individual birds, although in different
species of birds the degree of specificity in the tendency to gregariousness
seems to vary. The European and African stork, for instance, flocks each
with its own type and the two types do not mingle with each other; but in
certain other species such a strict segregation does not take place, members
of different species undertaking common flights.

The superiority-inferiority relations may begin very early in the life of birds
among nestlings. These reactions depend upon inherited reflex systems, but
they may be influenced by experience gained in testing other individuals. As
stated above, a stranger in a certain territory tends to be inferior in authority
to the first-comer. In herons the male must have established superiority over

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 617

the female before copulation can take place. Here, the parents peck only the
foreign young, while they recognize and respond to the calls of their own ;
but in certain other species parents may take care of strange young as well as
of their own. The aggressiveness differs greatly among different species of
birds and the aggressive behavior may be a complex called forth by definite
stimuli. Thus the aggressive behavior of the falcon is not due to a general
tendency to attack other birds; but these reactions take place only when a
specific stimulus acts on a falcon and releases a chain of reflexes. Perhaps
the movement of another bird sets in motion this mechanism, which seems to
represent an inherited, fixed character.

There is among birds individual recognition in the same sense as among
fishes ; yet, in both it is restricted in significance. Individuals are recognized
as mates, as inferiors or superiors in the order of dominance, as parent or
young, as members of a flock, but not as individuals in the strict sense of the
term. Again, it is a single and relatively simple character, such as color, design
of certain feathers, or sounds, or perhaps combinations of a few of such
signs, which determines recognition. The two partners composing a pair of
immature herons may recognize each other after a separation lasting as long
as twenty days ; voice and feathering serve as signs in this process. Artificial
feathering of the head interferes with recognition. Refeathering the head and
neck of both members of a pair of young herons does not prevent the recogni-
tion of a partner after the lapse of a few hours ; if, hower, the refeathered
birds have been separated for six or more days, they no longer recognize their
partners (Noble, Warm, and Schmitt). Recognition of individuals, as well as
of members of the same group and species, depends therefore in birds, as in
fishes, on mosaic characteristics, and the processes involved, as such, are
fixed by inheritance, as is also the range in which they are modifiable by
experience.

In mammals essentially the same reflex systems and instincts are active,
which determine the behavior in fishes and birds ; these make possible the
distinction between their own and strange species, groups and individuals ;
they play a role in the intake of food, in the sexual life, in the relations
between parents and offspring, in the superiority-inferiority relations within
groups, and in the fight and flight reactions. The additions to the behavior
reactions of fishes and birds which are noted in mammals consist in a greater
modifiability of such reactions. Furthermore, the range of sense organs,
through which the environment acts, is enlarged; by way of olfactory, visual
and auditory stimuli the changes which affect mammals become, on the
whole, more varied and often much more delicate than those perceived by the
more primitive invertebrates. Memories of things and events help to influence
the behavior of mammals, especially of those belonging to the more differ-
entiated species, to a much higher degree than is observed in lower classes
of animals and the actions of mammals. may be purposeful, in the sense that
situations are sought which experience has shown to promise satisfaction of
certain instinctive needs. Among these desired activities is the act of playing,
a modified reproduction of instinctive activities ; but playing is indulged in

618 THE BIOLOGICAL BASIS OF INDIVIDUALITY

without the existence of situations which would give it a functional sig-
nificance in the natural or social struggle. This type of behavior is sought
for its own sake, for the satisfaction which the instinctive action provides,
dissociated from the results to which it would lead if used in the struggle of
life. Also, the modifiable modes of behavior, those based on memories or
representing conditioned reflexes, are built on the foundation of simple
reflexes and instincts ; they are an elaboration of these processes. As a
result of this extension in the range of behavior, the environment, as far as
space, time and the relations to other organisms are concerned, has become
larger ; the differentiation between individuals has become finer.

However, the reflex and instinctive basis of behavior remains and the
response to sense impressions on this primary basis takes place with less
delay than when there is an interference by the restraining effects of thought ;
however, memories of frustrations and pain may inhibit reflex and instinc-
tive actions also in less differentiated mammals. Complex processes, such as
the building of a nest for the young, which in more primitive animals are
purely instinctive, not directed by modifiable thinking, are largely reflex
actions also in mammals. Many years ago the writer followed with interest
the nest-making activities of mother rats, which seemingly indicated the
presence of intelligence and thought. When this nest-making instinct is
active, the mother may be seen running around in the cage carrying every
little article that can be used for nest-making to the place where the nest
is to be. But if the observer thgn transfers the rat from the netwire cage to the
outside of the cage and allows her to run around it, the instinct to gather
material for the nest continues to be active and she now pulls things away
from the nest as soon as she reaches it from the outside of the cage, just as
readily as she formerly had carried things towards the nest. Returned to the
cage, she now again carries back to the nest the things she had taken away
from it. No reasoning can be detected in these actions.

While thus, on the whole, the life of higher mammals is still rigid and
fixed, nevertheless the plasticity of individual and social activities has become
greater than it was in the more primitive organisms. Similarly, the activities
of dogs are not essentially creative, in the sense that the constituents of a
composite experience would first be taken apart and then synthesized in a
new fashion. For instance, a dog looking for a ball which has been thrown
into a basket, attempts, in accordance with inherited reflexes, to recover it
by scratching the basket with his feet and pushing it along with his nose,
without succeeding in obtaining the ball by these means ; he does not discover
the simple expedient of turning the basket over, and if the basket is turned
over by accident, the dog does not readily make use of this experience. A
higher stage has been reached in anthropoid apes. The chimpanzee is able to
invent new modes of action, to compare new combinations by shifting of
mental elements, and thus to accomplish a certain end by means which are
not directly of an instinctive character. In this manner the unpredictability of
behavior, or what appears as freedom of action, is increased ; this increase how-
ever, is very limited, and is closely related to the unconditioned reflexes and

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 619

instincts which are active in these animals. There is no indication that
analytic thought processes occur even in anthropoid apes, and higher types
of creative work are apparently outside the range of their mental capabilities.
On the whole, the actions of mammals are fixed even from a quantitative
point of view. Thus it seems that the distance which must separate a circus
trainer and a wild animal in order to avoid reactions of flight in the latter is
quite definite. A student of animal behavior, who knows the history of an
individual animal, should therefore be able to a large extent to predict its
attitudes and behavior in a certain constellation.

Proceeding now from the other higher mammals to man, very pronounced
complications in the modes of reactions are observed. Not only does the
environment, which acts on us through our sense organs, induce changes
which have a much more varied and also more lasting effect on our behavior
than in other mammals, but abstraction and synthesis, in which the elements
in the environment are separated and then re-arranged in new combinations,
become very prominent. Thoughts develop, in which the constituents of the
environment may appear in combinations different from those in which they
occur under natural conditions; through shifting of these constituents new
concepts are formed.

In man we have to deal largely with secondary mental mechanisms, condi-
tioned thought reflexes, which are much more complex than the simple
reflexes. Pictures and thoughts enter into these reflex chains which ulti-
mately end in tensions, in motor activity or in inhibitions. Just as a sound,
light, color or odor, so a thought, a sentence, or other symbols for more
complex experiences in general, can elicit conditioned reflexes. A further
complication arises when a thought calls forth other thoughts, thus leading
to an extension of thought reflexes. As we remember experiences, so, too,
we remember thoughts. Moreover, abstractions and syntheses may have
their first origin in sense impressions, but the material with which they deal
may have its origin also in our own thoughts or in the thoughts of others ;
once we have made the latter our own, no distinction exists between the
effects of the thoughts of others and those of our own thoughts. Thus
thoughts become the objects of abstraction and synthesis. These various
trains of thought make connection with the simpler non-conditioned, as well
as with the conditioned reflexes, which latter are established much more
readily and in much greater variety in man than in other mammals, and the
resulting various combinations form very finely balanced systems. Our atti-
tudes and actions are determined by these systems of conditioned and
unconditioned reflexes in combination with thoughts, representing primarily
true or false sense impressions and, based on these, reproductions of a real
or imaginary reality. Or thoughts may function as suggestions, and then they
are transferred into actions and attitudes and the content of the thoughts is
converted into vivid pictures of reality which rigidly fix actions and attitudes.

Thoughts are especially effective in their function as suggestions if trans-
mitted to us in the form of a direct or implied command ; but in some respects,
in every thought there is included such a command. On the other hand,

620 THE BIOLOGICAL BASIS OF INDIVIDUALITY

abstraction and synthesis, resulting from our dealings with the environment
as well as with thought processes, may determine our actions and attitudes
without regard or even in opposition to their suggestive effect. In this case
our thoughts act as true or imaginary representatives of reality. On the basis
of our experiences gained in dealing with the outer environmental world or
with our thoughts, we make furthergoing abstractions concerning the char-
acter of abstractions and synthesis in general and their relation to the
environment. Thus logic is built up. The purely logical, rational use of
thoughts as determiners of our actions freed from the elements of suggestion
and detached from their function as instruments in the natural and social
struggle, represents the highest type of human activity and the closest
adaptation to reality. But when thoughts are not concerned with the purely
intellectual reproduction and interpretation of elements of the universe on a
rational, logical basis, they deal with and are instruments in the natural
struggle and in the social struggle, or in a combination of both. In this case
our thoughts function largely as suggestions rather than as representations
of reality and the resulting actions tend the more to be accompanied by
strong emotions, the more they are parts of the social or natural struggle.
The tendency to emotional response decreases in inverse ratio to the increas-
ing importance of thoughts functioning as symbols of reality.

As a result partly of rational thought, but largely also because of the
friction, antagonism and pain developing in the soccial and natural struggle,
the concept of the "I," as contrasted with the concept of others and of the
surrounding world, develops. The "I" is the individuality in the psychical-
social sense. This concept has a very intricate structure, consisting of com-
binations of thoughts and emotions, memories, hopes and fears. Like all
thoughts, it has a complex origin, its sources being within us as well as in
the surrounding world. Hence our "I," our psychical individuality, does not
admit of a sharp separation between us and others, between ourselves and
our environment, although originally the concept developed in contact with
and in antagonism to the environment.

Related to the "I" concept is the state of consciousness in our actions or
attitudes. Conscious psychical processes are those which form easily re-
membered combinations with such other pictures, thoughts, emotions and
experiences as are close to them in time or space, or have certain elements in
common with them. The term "consciousness" is used also in another sense,
in order to express the distinction between psychical and bodily processes ;
our images, thoughts, feelings and emotions are separated by us as conscious
processes from the chemical-physical processes underlying them and associated
with them. In general, most abstract thinking tends to be conscious because
it depends upon large combinations of experiences and remembered analogies;
it requires mental exertion, in contradistinction to the relative absence of
mental effort connected with thoughts when they function as suggestions or
otherwise exist in a relatively dissociated form. When a suggestion or com-
mand, direct or implied, enters into our mental processes, it tends to become
conscious only if it functions as a disturbing element. It is largely this

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 621

conscious thinking and feeling, centering around the "I," which activate in
us the thought and feeling that we possess a distinct individuality. But
frequent repetition of an experience or of certain reactions, and the conse-
quent habit formation result in a loss of the intensity of thinking, of the
ready and extensive association of the momentary thought with other
thoughts, and in particular with the "I" concept, as well as of the accompany-
ing emotions, and thus our mental processes change from the conscious to
the unconscious state. Any impediment, however, arising in our habitual
actions, making them more difficult of performance, again tend to restitute
conscious processes. There is a further factor which intensifies our feeling
that we are distinct individualities in the psychical-social sense ; this is the
idea that we have free will, that our actions are in the last instance determined
by ourselves, without inner mechanisms or outer environmental factors
rigidly controlling our choice. The feeling of freedom of the will is conditioned
by the great complexity of the factors and their intricate connections acting
on us and directing our reactions.

We find, phylogenetically, a progressively increasing complexity in the
activities of organisms and increasing differences between members of the
same species, an increasing individualization which reaches its highest de-
velopment in man. Conditioned reflexes are acquired more readily and in a
greater variety, the more highly developed the species ; but even in apes the
highest degree of apparent freedom of action depends upon a very limited range
of adaptation between the aims sought and the means used to accomplish
them. Moreover, the reactions in organisms concern the satisfaction of
relatively simple needs, both needs and reactions being constituent parts of
instincts. These processes remain, to a great extent, mentally dissociated,
while consciousness depends upon the ready association of a thought with
a large series of other thoughts and with pictures related to it in time, space
and content. We forget, therefore, much more readily what we do as a
simple conditioned thought reflex than what we do consciously ; in the latter
case we are better oriented, but also more subject to inhibition.

While in man thought reflexes also have their root in the needs of the
organism, the variety of his conditioned reflexes increases greatly in all
directions with the increasing number of constellations and suggestions
acting on him. This increasing complexity is made possible through the action
of the cortex of the brain, which mediates between the environment and the
more individualized reactions of the organism. There develop, thus, a multi-
tude of thought-emotion mechanisms and a play of interacting thoughts based
on memory, abstraction and synthesis, the result being that our behavior
appears unpredictable to others ; and it is often inexplicable to ourselves, in
that we commonly err in our judgment or deceive ourselves as to the origin
of our actions, the causal connection between environmental factors and
thoughts, emotions and actions being difficult to establish. The greater the
complexity of the factors acting on and in the individual, the greater the
probability that non-recurring patterns will occur. These original, unique,
unforeseen and apparently unpredictable configurations in the life of the

622 THE BIOLOGICAL BASIS OF INDIVIDUALITY

psychical-social organism, together with his reactions to them, are the ex-
pression of the individuality in the sense in which this term is actually
applied to higher organisms. Hence individuality is associated with the appear-
ance of freedom in his reactions and with the increasing difficulty in estab-
lishing causal relations between the environment of the individual and his
actions. This is the condition we have in mind when we speak of freedom
of the will. The greater the complexity of the constellations into which the
individual and his environment enter, the greater become the individual
variations in actions. Thus, individuality in the psychical-social sense, the
difference between the reactions of different members of the same species,
the complexity of the factors determining the behavior and the non-
predictability of individual responses resulting from these complexities,
increase with increasing complications in structure of the organism as a
whole, and especially of the nervous system.

We may summarize the essential features in which individuality in the
more primitive vertebrates differs from that in the higher vertebrates as
follows : ( 1 ) The stimuli which call forth a reaction are more simple and
stereotyped, (2) the reactions which take place are more limited in number
and are likewise more stereotyped, and (3) the degree of modifiability of
the reaction as a result of previous experiences is of a lower order in these
more primitive forms, and it increases with increasing complexity of struc-
tures. With ascending evolution and the more ready formation of condi-
tioned reflexes, learning takes place more easily. Structurally, this increase
in complexity and modifiability of those conditions of the behavior by which
we judge individuality in the psychical-social sense, is paralleled by the de-
velopment and increasing differentiation of the cortex in mammals and by
the transfer of the control of the most complex reactions from the corpus
striatum to the cortex. As Whitman has already pointed out, the develop-
ment of instincts, which are so significant in the psychical-social life,
especially of the more primitive vertebrates, corresponds to the structural
development of various organ systems; both gain in complexity and in this
respect take a parallel course during evolution, and it is possible to use for
taxonomic purposes instincts as well as organ structures. Instincts and
behavior generally are contingent on certain organ functions and they are
the direct expression of organ differentials and not of organismal differen-
tials, on which they depend only indirectly. Simple changes in texture, color
of the skin or of appendages of the skin, and movements may determine
species and individual reactions, and special movements and composite series
of movements (ceremonies) may function as stimuli in sexual life. Identity
of stimuli in several related species may cause identity of reactions of these
species towards one another, at least temporarily ; if later other stimuli begin
to function, which differ in certain of the species, they may then call forth a
differentiation in the reaction of these species towards members of their own
and towards members of the strange though related species.

The complexity of the reactions and the significance of learning, of
modifiability of behavior through previous experiences, seem to be in general

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 623

greater in birds than in fishes, although the principal reaction types are the
same in both these classes, and may be recognized even in mammals. Thus
certain birds which were hatched or were reared by foster mothers belonging
to a different species, may flock with the strange species; they may even
mate with members of the latter provided the association has occurred at a
sufficiently early period of life. In this case, as in the induction of mutations,
definite sensitive periods do exist in developing organisms, which greatly
antedate the time when the reaction takes place. In this way, through learning,
even the species instinct may to some extent be overcome.

A further indication of the complexity of behavior in certain birds comes
out also in reactions which lead to the hiding of food particles. In one species
these reactions may take place quite openly, in the presence of other birds,
and may thus be ineffective, while in another species they take place when
other birds are absent, and thus will be effective. Birds, through experience,
may learn to recognize dangerous instruments, such as guns during the
shooting season; individuals of the same species may behave differently in
city parks, where their experience has shown that they are safe, and in
other zones where they are exposed to attack. It appears, then, that modi-
fiability and individualization in behavior, in general, are greater in birds
than in fishes, greater in mammals than in birds, and greater among the
higher than among the more primitive mammals ; in animals, it reaches its
highest development in the anthropoid apes, which are, however, still much
inferior to man. Thus evolution of individuality signifies an increasing variety
and variability in individual reactions, a greater adaptabilty to and a greater
significance of the environment ; not only do the possible reactions of the
individual become more numerous, but also space and time become more
differentiated and they assume greater meaning in connection with the
reactions of the animal ; space and time become subdivided to a greater
extent; they also become more individualized.

But, increasing complexity of behavior does not mean the actual loss of
instincts. Essentially the same instincts are present throughout the whole
vertebrate series ; they are, however, associated with and, in the highest
organisms, covered up by reactions in which the behavior is modified first
by memories of sense impressions and by the action of suggestions ; still
later, by thoughts and memories of thoughts, and by the increasing sig-
nificance of abstractions and new syntheses. Concomitantly, there is a de-
crease in the predictability of actions and attitudes of individuals. In order
to make predictions it becomes necessary not only to know and to analyze
the stimuli which act on or in an individual at a given moment, but also to know
his past history, the stimuli which have acted in previous times and the situations
which he has experienced. With the growing importance of thoughts and of
the manipulation of thoughts, with the greater power to make abstractions,
and syntheses, and the increasing significance of the imaginative, creative
mind, the predictability diminishes, not only in regard to the actions of others,
but also to the actions of ourselves. However, there is reason for assuming
that not only actions appear unpredictable, but also the formation of thoughts,

624 THE BIOLOGICAL BASIS OF INDIVIDUALITY

which are contingent on a variety of experiences and on conditions within
the organism. Because instinctive reactions, memories and sense impressions,
previous thoughts and emotions enter as constituents into the type of our
behavior and the texture of our thoughts, both behavior and thoughts have
become so intricate that for practical purposes they are no longer determined
and predictable. Instead of predictability, there arises the appearance of free
will.

In philosophical discussions there are, in its original meaning, two char-
acteristic features associated with the concept "individuality." One assumes
distinctiveness of the whole, and the second the impossibility of division with-
out loss of the individual character. In the latter sense, a primitive animal,
consisting of segments which can be separated from each other, without
destroying the life and main characteristics of the organism, is less indi-
vidualized than a more complex organism in which the parts are more closely
knit together and in which a separation of the significant parts is not possible
without destroying its individuality and even its life. The individualization
of organisms has advanced the further the more integrated the parts are,
so that they form one connected whole.

The bodily mechanism of the more complex organisms is unified into
individual wholes especially by the individuality differentials, the nervous
system, and the hormones carried by the circulating fluids. The psychical-
social individuality is co-ordinated essentially by certain predominant instinc-
tive mechanisms and by those conscious processes which center around the
"I" thought complex ; but this process of integration at best is imperfect
and in various essential respects the psychical organism remains dissociated.
But biologists and philosophers have attempted by other concepts to integrate
the bodily and the psychical parts of an organism into one whole. There is
the concept that a separate agent, not further accessible to analysis, dominates
the parts and unifies them into a living organism ; this agent is assumed to
exist only in living beings and to differentiate the living from the non-living.
Others attribute to the whole, new characteristic features which "emerge" in
a manner not to be foreseen, if one considers merely the parts of which the
organism is composed or the forms from which the organism has evolved.
It is held that the new whole, in a way which is not accessible to further
analysis, determines and directs the functions of the various parts and co-
ordinates these functions. If a part regenerates the complete organism, it is
assumed that the structural plan of the whole determines the regenerative
processes. Similarly, according to this view, the end accomplished by the
functioning of a system of reflexes determines the formation and mode of
action of the reflexes of the functioning whole. Tacitly, thus, an agent endowed
with purposeful action is introduced into the organism ; it not only co-
ordinates the parts but has helped to create the organism.

Another hypothesis assumes the existence of a "mneme" as the agent
unifying the parts of the organisms. The memory of a preceding change
alters the future state and behavior of an organism in a specific manner,
which is conditioned by the character of the first change or experience acting

BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 625

on a specific substratum. The regeneration of lost portions in a primitive
organism is attributed to the initiating action of a psychical process cor-
responding to memory and thought in higher organisms. Adaptive features
characteristic of a species are due to the action of a memory-like agent, and
instincts are remembrances of formerly purposeful actions.

Similarly, a mneme-like agent would direct the return of certain animals at
definite periods of their life to the place where they had been at a preceding
phase, and the sentimental attachment of human beings to their place of
birth and to their nation would be an analogous process. In like manner, the
habits of social insects are compared to human social modes of living and
institutions. But in the origin of the latter there enter thoughts, suggestions,
and many other factors so loosely connected with each other that they
appear as accidental. Human social life is modifiable. Men may even dispense
with social life almost altogether and live as more or less isolated beings.
Human institutions are plastic, although ultimately they also may have their
roots in reflex systems, while insect organization depends almost exclusively
upon the action of reflex systems which are non-plastic, fixed in character.
Thus complex social phenomena, in which modifiable suggestions of various
kinds and experiences in the social struggle due to variable cultural con-
stellations play a prominent part, are considered as closely related to the
reflex actions of more primitive organisms, and the hypothesis is introduced
that the complex factors which are potent in human beings are likewise
potent in much more primitive organisms. Instead of explaining the simple
by the complex, it seems more promising as a method of investigative pro-
cedure to attempt to discover the more simple components in the complex
processes and to reduce, therefore, the latter to the former. On these alter-
native modes of procedure seem to hinge the chief differences between
mechanism and vitalism in the interpretation of living organisms.

A further assumption holds that there is a non-causal, irrational com-
ponent, inaccessible to scientific analysis, in human behavior. A part which
is not yet analyzed and still unknown is identified with the unknowable, and
the unknowable is considered as not subject to the regularities existing
elsewhere in nature and therefore as irrational from the human point of view.
Support for this belief is sought in the lack of determinism which char-
acterizes subatomic phenomena, where it is possible to determine either
position or velocity of the constituents of an atom, but not both at the same
time, and related to it is the assumption that because fictitious statements
play a temporary role in science and because the symbols we use are only
imperfect representations of reality — behaving in certain respects like
metaphors with an "as if" character — all our conclusions are equally fictitious.
The entelechy of Driesch would also constitute a metaphysical factor direct-
ing organisms in general as well as human personality, and even some
experimental biologists, who analyze life processes in accordance with
mechanistic principles postulate in addition the action of specific vital forces
which are inaccessible to experimental methods.

The existence of agents other than those physical-chemical factors known

626 THE BIOLOGICAL BASIS OF INDIVIDUALITY

to be active in both the inorganic world and in organisms, might serve not
only to unify the living individual into one indivisible whole, but might also
imbue him with a distinctiveness which is one of the implied characteristics
especially of human individuality. It would therefore satisfy a deeply felt
desire of man to be "himself" only, to be unique and endowed with self
determination and free will. Yet the investigator must proceed in the study
of individuality according to the rules which alone have proven successful so
far in all the other fields of science.

Chapter 2
Individuality and World

In the preceding chapter we have followed in the animal series the
evolution of individuality in the psychical-social sense and we have seen
that it reaches its full expression only in man. This highest type of
individuality we shall now analyze still further. The term "individuality"
implies a distinction between the organism with its psychical attributes and
activities, the inner world, and the surrounding, non-living, as well as the
living and human social world, the outer world. It also suggests the concept
of the uniqueness of the individual and of his self-determination in his
relations with the environment, in contradistinction to the organism as a
mechanism or an automaton; self-determination carries with it, as a corollary,
responsibility for one's actions and attitudes. These concepts of individuality
have arisen in the course of the activities of daily life, in response to the
problems man has to face and the manifold difficulties he has to overcome.
For a fuller understanding of the development of the feeling of individuality
it will therefore be necessary to analyze the distinction between inner and
outer world.

On the basis of our sense impressions and by means of abstraction and
synthesis, we have created a thought structure of the surrounding non-living
physical and chemical world, as well as of the surrounding living world of
organisms, and in both worlds the same constituents occur. The environ-
mental factors act on our senses as stimuli and may appear to us partly as
variable and partly as constant factors, while we assume that our sense
organs are constant, although they also in reality may be variable. After we
have dissociated from ourselves the outer non-living and living world which,
by means of critical analysis, we have transformed or attempted to transform
into constant and variable physical-chemical units, we consider further the
interactions of the outer world with our sense organs, nervous system and
other constituent parts of our body. In this analysis we may tentatively
regard the elements of which the outer world is composed as more or less
constant and our body and its constituents as variable. Through the study of
the variability of our organism in its interaction with the environment, we
create the science of physiology. As a result of this interaction between the
outer world and our own organism, there develop on the basis of our sense
impressions thoughts and emotions, which on their part may then interact
with our nervous mechanisms, with our muscles and our bodily functions.
There is thus a circuit from the outer world by way of sense impressions
and our organ systems to thoughts and emotions, and from these, in the
reverse way, to the outer world. This circuit we study by means of abstrac-
tions that are shifted and re-synthesized in such a manner. that the essential
constants are separated from variable, accidental factors; such an analysis,

627

628 THE BIOLOGICAL BASIS OF INDIVIDUALITY

as far as sense impressions, the origin of thoughts and emotions and their
effects are involved, represent the subject matter of psychology. As a further
step we recognize in our outer world other human organisms, consisting of
physiological and psychological factors similar to our own, while other living
organisms — animals and plants — show graded differences from ourselves.
The physical-chemical, non-living environment, as well as the world of living
organisms, except ourselves, represents then our outer world, while we,
with our sense impressions, feelings, thoughts, emotions, wills and desires
represent our inner world.

Thus our inner and outer worlds both consist to a large extent of the same
psychical elements, our sensations; also, both worlds are composed of the
same physical-chemical elements and this is true of all organs and tissues of
the body, including those on whose functions our psychical activities depend.
In the physical and psychical realms, the outer world and "we" are consti-
tuted of the same elements. Sense impressions stand on the borderline between
inner and outer world, and they, with our thoughts, represent a combination
of environmental and inner organismal factors. It is by means of sense
impressions that we construct both worlds and connect the two. With their
aid we build an outer world, to which we attribute an existence independent
of our own organism as a separate external reality, which we take for proven
because of the fact that our interpretation of things and our prediction of
future events, made on the basis of our thought-constructions, may prove
correct, and also because of the fact that this reality is experienced in the
same way by all human beings who have adequate knowledge and under-
standing.

We believe that we are aware of our inner world directly, without the
intervention of our sense organs, while we realize that we recognize the
outer world by means of these sense organs. The inner world constitutes for
us our real individuality, and especially those parts of our inner world
centering around the concept "I," which latter again is gained by means of
abstractions and synthesis, like other thoughts. As far as our psychical
elements undergo within us variations which we do not fully understand,
and which are different at different times and which may differ in different
individuals under apparently the same conditions, they are considered as
subjective. The outer world is considered as objective, independent of
changes within us, and to a higher degree constant. This is one of the reasons
why we make such distinctions as outer and inner world.

Through the interaction between the outer world and our sense organs we
become aware of events, which are singled out and differentiated from
others and compared with similar preceding ones. Events then become pre-
dictable; the sense organs appear, thus, to be constant, identical at different
times in the same person in the same environment, and also identical in
different persons; they seem largely independent of other parts of our
variable organism. Those sense experiences which are common to all humans,
which are reproducible and which represent, therefore, a mechanism, we
tend to refer to the outer world. On the other hand, thoughts and emotions

INDIVIDUALITY AND WORLD 629

of our inner world are variable ; they cannot apparently be referred to
environmental constants with the same fixity and definiteness as can the sense
impressions; thoughts and emotions seem individual and indeterminate, dif-
fering in different persons at the same time and place. Hence, thoughts and
emotions appear not to be predictable.

Thoughts represent abstractions and syntheses into which memories of
individually varying experiences enter. The emotional reactions also vary
widely in different persons and have much of the character of a mystery,
because in the individual affected they are largely unanalyzed. In this sense
our bodily organismal constitution as a whole, and especially the brain
activities, in which our thoughts and emotions originate, seem more particu-
larly our own than the operations of the sense organs, which reproduce for
us our environment. What is unique and unexplainable, and therefore appar-
ently free and not a directly determined function of the environment, we
refer thus to the inner world, to our psychical individuality.

But if we analyze our inner world still further, we find, as stated above,
that it as well as our outer world consists largely of sense impressions ;
these enter as essential constituents into our pictures, thoughts and wills,
which are derived primarily from the outside. There may also participate in
the construction of our inner world, those sensations which originate in cer-
tain parts of our own body. When we speak our thoughts or see our own
body, we perceive them through the ear and eye as we perceive those of
another individual. Certain psychologists go so far as to maintain that all
our thoughts are perceived as the result of the activities of our speech
muscles, even if we do not actually speak. It is especially the memory and
anticipation of the feelings associated with muscle contractions in response
to certain thoughts and pictures which make us aware of our will. Further-
more, there is added to the central, psychical constituent of our individuality,
a picture of our bodily configuration. We acquire this picture of our body
gradually as we acquire that of another individual. Our body, as well as our
mind, is to a large extent strange to us. If we see our own image in an
unusual set of mirrors, we are astonished that this is a reflection of our-
selves. The physicist and philosopher, Ernst Mach, when entering a bus and
seeing his image in a mirror exclaimed, "Who is the school teacher that
enters this car !" We have to become acquainted with our own body as with
the body of another person ; also with our own mind as with the minds of
others. The "self" or "I" is an abstraction ; it does not really exist in the
sense in which we believe it exists. We hardly know our own self any better
than we know other individuals or the world around us.

However, when we analyze more in detail our individuality in the
psychical sense, we find that the interactions between what we consider as
outer and as inner world are still more complex than the preceding con-
siderations have indicated. This is due to the fact that the thought reflex
works in two directions. A thought as a representation of the outer world
may set in motion in our organism corresponding functions of various organ
systems, and in particular, motor reactions ; thus the picture of a good meal

630 THE BIOLOGICAL BASIS OF INDIVIDUALITY

stimulates gastric secretion and certain pictures with sexual content may
set in motion, by way of reflex, certain sexual activities. These pictures may
be supplied by social institutions created by us, as for instance, by eating
places, by theatres. The outer world thus interacts with our organismal
functions by means of pictures, thoughts. But, conversely, gastric contrac-
tions during hunger may stimulate certain picture-thoughts of a good meal,
with the accompanying emotions. Or certain reflex processes occurring in
the sexual organs may secondarily call forth the corresponding thought-
emotion complexes, and the memories of the latter may subsequently again
set in motion sexual functions. In this manner a very intricate play between
outer world and inner world, between our thoughts and our organism,
constantly takes place. The outer world acts on our inner world by means
of sensations, pictures and thoughts, which also function as suggestions,
and through them the outer world influences our actions and our attitudes.
Thus, thoughts having their source in sense impressions, exercise their effects
essentially through the things and events which they represent, and there
exist only quantitative differences in vividness and effectiveness between the
direct experience and the effect of thoughts ; both are complicated, but to a
varying degree, by a relationship to other thoughts.

Furthermore, those of our motor reactions which follow thought-emotion
complexes and are often induced by the latter, may lead to thoughts which
are conscious and which make connection with the "I" concept, while the
simple reflexes connecting our senses with our muscles by way of ganglia,
are usually unaccompanied by conscious thoughts. There are, besides, many
sense impressions acting on an organism, together with memories of past
experiences, which do not find direct release in motor actions but merely in
thoughts and emotions ; these again tend to lead to an extension of conscious
thought and emotion processes; they may ultimately find expression in
scientific, philosophic, or artistic productions. In order to be able to under-
stand and predict the phenomena of our varied reactions, there would be
required in all these cases, a much more intricate and searching analysis of
the common factors underlying these processes, than can, as a rule, be made
at the present time.

Processes and things involving common unit factors and differing from
others in experimentally reproducible constellations of these unit factors and
their mutual relations are mechanisms. In general, constant relations between
events, which show definite sequences in time, are what we consider causes
and effects, the former preceding the latter constellations; to establish these
relationships is to explain ; what can be explained in this way is in a wider
sense a mechanism ; it is opposed to what is indeterminable and non-rational.
However, in many instances we are satisfied with attaching a word or a
label to a thing or process, and having thus attained the possibility of
handling in our mind this thing or process for the purposes of mental opera-
tions, especially in accordance with the requirements of the natural and
social struggle, we are satisfied. In contrast to the term "mechanism" "indi-
viduality" implies, by definition, something unique and therefore not repro-

INDIVIDUALITY AND WORLD 631

ducible, not explainable ; hence individuality is assumed to be essentially non-
rational. But in reality, the nature of individuality represents a problem to
be analyzed and explained. The non-rational of today may be the mechanism
of tomorrow. The manifoldness of human individuality depends upon varia-
tions in the organization of the individual and in the reactions of the indi-
vidual to different environments. These are accessible to analysis and there
are at least indications that such variations are the manifestations of con-
nected mechanisms.

Our will is assumed by us to depend on our thoughts and inasmuch as
thoughts appear as isolated phenomena, detached from the reflex circuit of
which they are really a part, and inasmuch as we have forgotten the experi-
ences which gave origin to them, our will appears to us as a free, indeter-
mined phenomenon. It is not predictable, it cannot be duplicated in others,
it is considered by us to be our own, the expression of our individuality,
which is therefore characterized by free will.

Yet the more we study the actions and attitudes of human beings, the
greater the degree of our experience, the less becomes the range of indeter-
mined actions. We learn to know of the reflexes active in us and of the
establishment of conditioned reflexes ; we analyze our sense impressions, our
thoughts, which depend upon sense impressions and complex experiences ; we
observe the accompaniment by emotions of thoughts and motor activity, and
in particular of inhibited activities ; and furthermore, we note the stimu-
lating and inhibiting effects of suggestions, those given from the outside by
the spoken words and actions of others and those resulting from our own
thoughts and actions, which we remember as we do those of others and
which function in like manner. Especially susceptible to analysis are experi-
mental posthypnotic suggestions and their consequences, which subjectively
may appear as expressions of free will. Furthermore as others issue com-
mands to us, so we issue commands to ourselves. We know what, under
certain conditions, will happen to our person, as we know what will happen
to things and living beings around us. Remembering the consequences of
former experiences and the thoughts and actions following our choices and
decisions, new, complex conditioned reflexes, pleasant in some cases, in-
hibiting, painful in others, develop and complicate our attitudes. The choices
and decisions made in the past, act therefore as suggestions tending to
influence our future course. But in addition, we know of the effect of
chemical and physical factors and of changes in our bodily structures and
functions on our thoughts and actions. All our experiences and the subse-
quent analysis of the interaction between our thoughts and our organism
affect and regulate our bodily reactions. This very complex, and therefore
incompletely known and only partly predictable balancing of factors which
determines our actions, is what is felt as freedom of will in the circuit of
outer world — > sense impression — » thought -» reaction. Usually we develop
conscious thoughts only of the central and efferent, but not of the afferent com-
ponents of these thought reflexes, a condition which tends further to foster in us
the feeling of inner freedom. These relations of "ourselves" to "ourselves,"

632 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the effect of our own thoughts and suggestions on our behavior and attitudes,
and especially the fact that the addition or lack of a thought may turn the
balance in our responses in one or the other direction, all these factors
constitute largely the substratum which, in its complexity, gives us the feeling
of freedom ; and it is just this apparently free and non-determined, or rather
self -determining, part of our actions and expressions which we feel as the
most characteristic feature of our individuality.

The most conscious thoughts associating readily with other thought-
emotion complexes, and especially also with the "I" complex, the directing
thought-emotion processes in us are felt as the constants in our individuality,
which operate and connect the states of our changing organism and our
actions in successive periods and apparently make it one homogeneous con-
sistent whole representing our real self. It is this part of us which seems
to us to be independent of the outer world, in contrast with our bodily func-
tions and simpler nervous automatisms, which evidently depend upon the
interaction with the outer world and which do not therefore represent solely
ourselves.

The central governing thought-emotion processes, affect in a direct manner
our own organism, and in particular our muscles, but secondarily they can
also affect and change our environment, of which, to some extent, we thus
become the master. In a measure however, we can, besides, control ourselves.
Our conscious thoughts can automatically, by their mere functioning, suppress
injurious emotional reactions and direct our responses in a rational way.
Thinking, as such, about our actions may thus function in an automatic way
as a moderator, and it is especially through such a mechanism that we feel
our will is free.

But this mechanism needs further analysis. The conditioned reflexes active
in us are often associated with thoughts and pictures which we may describe
and analyze and thus reproduce. These thoughts and pictures may develop
in us also in a more complex roundabout way by means of chains of thoughts
which, however, usually have likewise been set in motion through outside
stimuli. They are of the same kind as those which are transmitted to us by
others, or by reading. Thoughts may thus come to us in various ways. How-
ever, if, as usual, the source of these thoughts is not clear to us, then they
appear to us to originate spontaneously in ourselves and to be the expression
of our free will, of our individuality. The pictures and thoughts, associated
with what we do and entering as a factor into our conditioned reflex
mechanisms, may intensify the reflex action automatically; on the other
hand, also, a process inhibiting these pictures and thoughts and at the
same time making the thoughts conscious may develop, and this latter process
may interfere not only with these pictures and thoughts, but also with the
primary conditioned reflexes which set these processes of thinking in motion.
In this manner rationally connected thoughts may interfere with our primary,
more simple reactions ; they may control and make rational our actions, and
they exert these effects by means of mechanisms which may not become
conscious to us. Complex sense impressions, their memories, as well as

INDIVIDUALITY AND WORLD 633

thoughts, are sources of our pleasure and pain, and we treat thoughts as we
do complex sensations ; we divide them into parts, eliminate some of these
and synthesize others, and again the process of creating these abstractions
gives us the impression of free will ; it appears to us as individual, as an
action carried out in accordance with "our" wishes, in contrast with the
rigidity of a direct sense impression -» motor reaction chain — where the reflex
mechanism is much more evident. Our ability to combine series of thoughts
into into one associated texture, with which process is joined the memory of
thoughts and their subsequent realization in actions and the connection of
these thought textures and actions with the "I" are functions which represent
the highest degree of consciousness.

What we experience, then, above all, as our freedom and as the expression
of our individuality, is this ready formation of picture and thought textures
of a coordinated and of a superordinated kind, the latter representing a
more comprehensive abstraction and synthesis of thoughts.

But observation and analysis reveal to us that there are many limitations
to our apparent freedom. There are, above all, suggestions which limit the
free association of our thoughts, limit thereby our freedom, the expression
of our individuality; however, this lack of freedom is not always conscious,
it is recognized by means of superordinated thoughts only under certain
conditions, more especially if the suggestion takes the form of a command
imposed upon us and thus conflicts with the spontaneous trend of our
thoughts. Also, fashion, ritual, tradition, which are systematized suggestions
often functioning as habits, and the suggestions given us in childhood may
limit the freedom of our actions, the expression of our rational activity ; but
these inhibitions and limitations even more commonly may not become
conscious in us, because as habits they do not usually lead to inner friction
and conflict, but rather give us mild and pleasant emotions, and function as
normal constituents of our psychical life. It is only those suggestions which
strongly disturb our systems of thoughts and wills, which become conscious in
us as outside interferences, against which we react. Other suggestions, on
the contrary, may give us emotions of a very satisfactory kind; they may
sustain and justify our thoughts and wills and support us under adverse
conditions. We justify and uphold then such suggestions and we react
emotionally against thoughts or conditions which tend to oppose them and
to prevent their realization.

However, even suggestions which are accepted as a part of our own
thought-system and which act unconsciously may restrict the freedom of our
thoughts and actions and have far-reaching effects, inasmuch as they may
limit our contact and our relations with the social and non-social environ-
ment, the growth of our individuality, and our ability to discover things and
to exert rational self-control. They may interfere with the processes from
which result recognition of new elements in our environment and a more
adequate adaptation to the environment. They may thus tend to diminish the
horizon and content of our world. In particular, they may restrict the
deeper understanding of the social struggle and the corresponding develop-

634 THE BIOLOGICAL BASIS OF INDIVIDUALITY

merit of sympathy and pity. Thus, rigid ritualized group-action may replace
our initiative and coordination of thoughts and actions as the highest
expression of our individuality. On the other hand, these types of organized
suggestion may also be helpful ; they are economic, inasmuch as they save us
the expense of energy in the process of analytic thinking and of creating;
and moreover, they provide the feeling of security and remove from us the
weight of responsibility. One of the most distinguishing features between
different individuals is the relative power of suggestion, on the one hand,
and of freely associating and directing thoughts, on the other. Furthermore,
the tendency of these thoughts and their resulting actions to make conscious
connections with the "I" and the extent and comprehensiveness of the "I"
differ very much in different individuals, the different "IV varying greatly
as to their content of environmental constituents, especially those of a social
character. The "I" concept is already present in the young child ; it may be
active also in our sleep, where we refer to and connect with "ourselves"
memories usually of recent events, of thoughts we have had or about which
we have read.

The more readily we remember our thoughts and consequent actions, and
the more we are capable of relating them in a consistent and logical manner
to the whole texture of our thoughts, and especially to the "I" concept, the
more our thoughts and actions are modifiable. On the contrary, in so far as
thoughts function as suggestions in us, they are rigid and our actions and
attitudes are not readily modifiable. As stated, individuals manifest marked
differences as to the relative preponderance of modifiable and less modifiable
thoughts, as to their sensitiveness towards thoughts and impressions coming
from the social as well as the non-social environment, and as to the readiness
with which thoughts and impressions act as suggestions. The easily remem-
bered conscious thoughts are relatively labile, while the unremembered
thoughts, suggestions, or the processes underlying or accompanying them,
influence our actions and attitudes in a rigid manner because they are
separate and not readily brought into connection with other thoughts.

The relations between inner and outer world have changed in our con-
sciousness in the course of human history. Man created pictures of an outer
world and of an inner world; in so doing he created not only an anthropo-
centric world, but also an egocentric world. He saw himself, or beings like
himself, everywhere in the outer world. He felt the fate of the others as his
own fate and their experiences called forth emotions of sympathy and pity.
Or he reacted to them as to competitors or enemies with emotions of dislike
and antagonism. He obeyed or struggled against other human beings who
gave him commands. The effects of suggestion predominated very much
over the purely logical-intellectual analysis; the emotions of fear and hope
were correspondingly very active. His world centered around himself. In
this egocentric world things have values as material goods or as psychical
goods. Men fight for these, for the maintenance and elevation of their indi-
viduality and for a certain picture concept which they have of their own

INDIVIDUALITY AND WORLD 635

personality. This is the world of the social struggle and the struggle with
nature.

Poetry and art have been, and continue to be, largely expressions of our
egocentric attitude towards the world ; they represent us and our experiences,
our feelings and emotions. They attach meaning to our world, or they intensify
and extend the meaning and significance of our world and of our life and
they may picture a world and life from which fear and disharmony are more
and more eliminated. They tend to convert an inanimate, cold, non-feeling
world into an animate world, in which feeling and human meaning is
extended and intensified, so that we can find ourselves and beings like us
everywhere. But gradually the character of this egocentric world has under-
gone changes. The surrounding world, the universe, begins to center around
us in a different sense. In the interactions between the outer world and our-
selves we find identities and differences ; we abstract from the differences and
combine new similarities. In this way there is gradually created a second
world, that of simple and complex sensations and a logical world of things
and interactions in which we and beings like ourselves live. It no longer
centers around ourselves and in it we are merely a small part of a strange
universe ; but more and more it becomes to us the real world ; it is the world
revealed by scientific analysis and synthesis. We adapt ourselves also to this
world ; we make it our own by understanding it and we attempt to make it
respond to our needs, wishes, hopes and fears. There still radiate from
ourselves thoughts and emotions out to the universe; the universe is still
bound up with us and we with it in one thought structure.

In the course of time there begins to be added to this analysis of the
outer world, an analysis of our inner world, of the world of myth which
we have created, of social and natural struggles and the emotions they elicit.
We form concepts not only of the environment and of other human beings,
but also or our own organism or parts of it and its relations with the outer
world, and we realize the vast differences between the egocentric and the
non-egocentric conceptions of the universe. These two developments, that of
the egocentric world, eventuating in the formation of pictures of ourselves
around which everything else centers, and that of the objective world, of
which we are merely a very small and relatively unimportant part, have
proceeded side by side throughout human history. It is the varying relative
importance of these two world conceptions which have determined largely
the nature of our civilization, and the life we live is a compromise between
these two antagonistic attitudes.

Yet physiologically each of us remains bound up with his organism, and
the needs and functions of the latter continue to make ourselves the center
of our own small universe; we therefore still make use of poetry and art to,
change the concept of the world around us and of human beings and human
relations in accordance with our needs and wishes. It is the analytic,
scientific world which restricts such egocentric thinking and influences and
changes the values we attach to things and the laws we make. Science creates

636 THE BIOLOGICAL BASIS OF INDIVIDUALITY

new symbols for the manipulation of things and events and for the under-
standing of reality. The new thought constellations, including those concerned
with our own person, are more and more removed from the world in which
we directly live and feel pain and satisfaction, the world of the natural and
social struggle. But the latter also forms a part of our analysis ; our experi-
ences are split by us into parts and these parts are shifted and similar parts
synthesized into new concepts, which, as abstractions, become more and
more removed from the original direct experiences. This thought world is
therefore different from the directly experienced world ; it is a re-organized,
a differently and a better ordered world, which allows us to a certain extent
to understand and to master the world of direct experience. The concepts
thus created are devices allowing us to orient ourselves under new condi-
tions, without undergoing again all the manifold experiencs for which the
concepts stand. Science functions in an objective thought world, which is
less emotion-tinged, less and less actively involved in the various phases of
the social struggle and in the particular desires of our individuality. It is the
world in which also the dominating factors of the egocentric world are studied
as to their origin and nature ; psychical goods and material goods become
here objects of analysis and synthesis. Imagination and its creations in
poetry and art are likewise objects of examination and our particular
individuality recedes in importance, except that it continues to function as
the analyzing and synthesizing, and thus as the scientifically creative agent.
Yet, we can use the symbols thus created in modifying the frictions of the
egocentric world in an effective way; the cruelties of the natural and social
struggle may become more and more mitigated and the individuality sec-
ondarily gains in value on a more realistic foundation. Thus, by means of
science we may, within a certain range, learn to dominate our organism as
well as our environment.

The scientist enjoys his creative work, plays with his thought symbols,
just as the poet, artist and musician play with imaginative thoughts, colors,
shapes and sounds ; they all abstract from the whole reality as it is directly
experienced and select only certain parts of the latter. The poet, artist and
musician create things that are meant to supply and maintain or elevate
directly or indirectly the value of psychical goods in the natural and social
struggle, and thus to sustain and elevate the struggling and suffering indi-
vidual. But the scientist, playing likewise, creates a thing that becomes his
master, is independent of the direct, primitive experience of the individual
and of his struggles. It dominates the investigator, who finds himself more
and more limited by his own creation, the thought structure, which is science.
His erection of these thought structures represents a vital process, in which
imagination is an important instrument, yet which, as far as the influence
of the created concepts reaches, restricts his imagination ; it limits him in
shaping his life, his picture of reality in accordance with his wishes and in
accordance with his imagination. However, even into the building up of
science egocentric tendencies penetrate. The analysis of those elements of
which the outer world is constituted makes possible a mastery of this world ;

INDIVIDUALITY AND WORLD 637

but the knowledge thus gained is used in the social and natural struggle,
not only for helpful but also for destructive purposes. Similarly, biological
concepts are employed not only for the alleviation of the cruelties of the
social and natural struggle, but also as weapons in the social struggle, which
serve to aggravate the latter and to introduce into it added cruelties and to
intensify the unbalance of the mind as well as of the body. Thus the science of
genetics in its applied form as eugenics has been, in certain instances, used by
scientists themselves, as well as by others, in the interest of nationalistic tenden-
cies in a struggle for distinctive psychical class goods and for economic ad-
vantages.

The same tendency reveals itself in still other ways. There are certain
concepts which play a great role in the social struggle and in the adaptation
to the painful realities of the natural struggle. Man constructed in early
times the thought of something which is not subject to the sorrows and
destruction that we experience in actual life, a spirit within us whose ex-
pression is free will. Since free will involves intention on the part not only
of ourselves but also of the other individual, the exercise of it may affect
most keenly the social struggle ; whether we consider an act as hostile or not
depends in many cases not so much on the act itself, as upon the intention
which inspired it. The idea of intention, 'furthermore, is intimately connected
with that of responsibility, hence we mete out gifts to one who is helpful
and virtuous, and punishment to an offender. These thought-constructions
represent an adjustment, by means of which we uphold our individuality in
its more primitive needs, but at the same time they may lead to cruel re-
pressions or to undue elevation, effects which often aggravate the social
struggle. Into such a mental environment of the egocentric world the scientist
is born, as are other human beings, and he, too, often upholds these concepts
which are active in him as suggestions. On the other hand, the application of
the concepts of science, based on an increasing understanding of the springs
of human behavior, tends to substitute understanding, prevention and cure
for punishment and suppression, and thus to mitigate the harshness of the
social struggle.

Human life, then, may be considered essentially as a struggle with nature
and as a struggle with other human beings — a natural and a social struggle.
The natural struggle is a struggle for the maintenance of our organism,
which is so constructed that it gradually deteriorates, ceases ultimately to
function and dies. It concerns itself with the satisfaction of material needs
in an environment to which we are only incompletely adapted and which only
by degrees we learn to know. In certain respects there is an antagonism be-
tween us and nature, which ends with our destruction. At the same time,
we interact with other human beings and in this interaction a complex social
structure has been built up; to this also we are insufficiently adapted. Thus
the struggle for our preservation, which under more primitive conditions was
largely a struggle with nature, becomes, over a wide range of life, a competi-
tive social struggle for material goods, and there is added to this, more and
more, a struggle for psychical goods. This struggle for psychical goods,

638 THE BIOLOGICAL BASIS OF INDIVIDUALITY

however, is closely associated with the struggle for material goods ; it also
affects our organism in its most vital functions and is, therefore, as is the
struggle for material goods, ultimately a contest for the upholding of our
individuality in both its bodily and psychical aspects.

Our individuality requires consideration and respect ; it needs appreciation,
friendliness, friendship and love. These are primary needs, which provide
a favorable mental medium in which we can function and develop without
fears and inhibitions, and in which certain fundamental requirements in
social intercourse are satisfied. We may call the means by which this is accom-
plished simple psychical goods. On the whole, there is the possibility of taking
care of such general and basic needs of all, and the satisfaction of the re-
quirements of one should not exclude the others from receiving their share.
We can be friendly, courteous and understanding to everyone. However, some
distinction sets in even here. We cannot give friendship and love to everyone
to an equal extent. Certain individual distinctions are made ; but if they are
associated with the giving of the more common simple psychical goods to all,
with understanding and appreciation of all others, and if the latter also can
be supplied by those nearest to them with the needed individual psychical
goods in the form of friendship and love — which in a measure partake of the
character of what might be called individual distinctive psychical goods — no
injury should result. Still, even then the psychical balance may be imperfect
and the giving or withholding of such individual distinctive psychical goods
may, in many cases, lead to the bitterest struggles, even within the same family ;
intense mother-love may become so exclusive that it leads to bitter jealousy
and to severe antagonism towards those with whom she has to share the love
of her children.

Of still greater significance perhaps as the source of severe social struggle
are the distinctive psychical class goods ; the latter usually appear as social
caste spirit, family and race pride, and nationalism. These lead to destructive
struggles of a political, economic and social character. They may end in war
and revolution. It is of interest that the struggle for these distinctive psychical
class goods is usually associated with a struggle for material goods ; these two
types are intimately connected, material goods being, to a certain degree,
valued for the sake of the distinctive psychical goods they provide, while the
possession of psychical goods often gives ready access to the acquisition of
material goods. Among the distinctive psychical class goods, those have an
especially devastating effect which make the possibility of acquiring these
goods a constitutional, inherited condition in certain classes of human society.
Under these circumstances no hope of improvement is conceivable. More-
over, the gain in distinctive psychical goods in some is predicated on the lack
of them in others, since if all possessed them they would lose their signifi-
cance as distinctive psychical goods. The effects on these others of social
humiliation, which is the consequence of the social recognition of distinctive
psychical class goods, are very injurious. They cause directly a serious inter-
ference with muscular coordination, with expression, initiative, controlled
imagination and action, and indirectly, an interference also with the functions

INDIVIDUALITY AND WORLD 639

of other organ systems. In the end, the stunting of personalities thus initiated
reacts also unfavorably on those who have been responsible for these effects.
Certain nationalistic, racial and social caste-distinctive psychical class goods
are the most prominent types of these injurious agents, in the production of
which there cooperate human inventiveness, the accidents of history and the
desire for psychical self-maintenance, for elevation of the personality picture,
for mental security and for compensation for injuries received in the social
struggle. Humanity stumbled on these social instruments, as it did on some
of the basic stimulants and narcotics; those who had the power made use of
them, found them to their taste, and their use became general.

These functions and consequences, which apply clearly to distinctive
psychical class goods, apply more or less to all distinctive psychical goods,
although their injurious effect is probably greatest in the case of distinctive
psychical class goods. There are other types of distinctive psychical goods
that are more individual and less injurious, such as recognition, fame and
glorification of a person who excels in ability and creative work. Warriors,
statesmen, philosophers, scientists and artists wish to have the benefit of this
type of distinctive psychical goods, which in addition to other advantages
provides a certain type of immortality and thus promises compensation for
the inevitable defeat in the natural struggle.

Ultimately all psychical goods — simple and distinctive — which we re-
ceive from the outside become converted into and contribute to the creation
of inner psychical goods, of thoughts and emotion complexes, which we
cultivate and which sustain us in the social and natural struggle. Art, philoso-
phy, religion, science, principles in general, serve as the objective material
of these inner psychical goods and, consciously or unconsciously, they center
in us around the "I" concept. From the latter there develops more or less
clearly in every person a personality picture of himself, which is perhaps his
most precious possession. If this is on a high level and unchallenged, the
whole organism functions relatively well; if it is questioned, attacked and
lowered, serious consequences for the wellbeing, mental and physical, of the
individual may follow. Thus the preservation and elevation of inner psychical
goods, more or less centering around a personality picture, become the main
objective and the principal agent in the social struggle of individuals with
one another, and one of the most common weapons used in this struggle is a
suggestion, often attached to a word, thrown into the system of inner
psychical goods of an individual, which acts as an incompatible agent and
which tends to distort and lower his personality. In different individuals the
character of the inner psychical goods varies, in the same sense as do their
convictions, the prominence and potency of their principles, the simple and
distinctive psychical goods which they have received, and their inherent
ability to face the difficulties of the social and natural struggle. Suggestions
which have been given to human beings, often in the early years of their life,
determine largely the character of their inner psychical goods and their person-
ality picture. Inner psychical goods have ultimately the function of steadying
the individual in his social and natural struggle ; and in accordance with the de-

640 THE BIOLOGICAL BASIS OF INDIVIDUALITY

mands arising in the contingencies of these struggles he may alter and shape his
inner psychical goods, add to them or subtract from them, and modify his per-
sonality picture. The opportunist or politician readily sells certain inner psychi-
cal goods, his convictions, principles, for the advantages of material and dis-
tinctive psychical goods. If the personality picture, and in particular the "I"
around which it centers, becomes unduly prominent in all social manifestations,
an individual is judged to be vain. Very often this is a reaction of a compen-
satory character in one in whom social injuries make the personality picture
very conscious and prominent. Related to these processes is the self-conscious-
ness frequently associated with painful discoordination, also the result of social
injuries experienced by sensitive individuals.

While, thus, simple psychical goods are needed for the maintenance of the
bodily and psychical organism in a healthy state, it is especially the individual
distinctive psychical goods received from and given to others, and above all,
the inner psychical goods that differentiate one individual from another, which
individualize human beings in the highest degree ; on the other hand, distinc-
tive psychical class goods, even when they serve as a source of self-elevation
and of security and strength for one's own individuality, as a rule tend to
submerge the individual, making of him a mere representative of a certain
group.

Such are the main factors underlying the social struggle; and they also
are its objectives. Which of these objectives occupies a pivotal position in
a certain constellation or phase in the life of a person depends to a consider-
able extent, although not entirely, on accidents, on suggestions received.
This is the foundation on which our choices and decisions are made. Material
goods are so important a factor in this social struggle, as far as it concerns
the attitudes and actions of wider groups, largely because they satisfy the
most urgent needs and also because they are the least individualized and can,
therefore, most readily unite people of the most divergent kind. Psychical
goods are much more individualized and therefore can less readily lead to
mass movements ; but they have done so in the religious wars of the past and
they often do so even now, as, for instance, in the nationalistic struggles, and
when originators and leaders of political mass movements are spurred on by
certain constellations of inner psychical goods or by psychical injuries re-
ceived, or by an overwhelming desire for power and distinction rather than
by a desire for material goods.

The objectives of the natural and social struggle affect the daily life of
every individual and in a twofold way ; in all his efforts his desire for material
and psychical goods, and in particular also for distinctive psychical goods,
enters as an important motive. Thus, in general, human beings carry on two
kinds of activities, one objective, the other subjective. Their objective
activity tends to increase the available amount of material goods and to con-
tribute new values to the psychical reservoir from which humans obtain what
is best in their inner psychical goods ; this is an activity which tends to in-
crease the health of body and soul in the life of an individual and of the group.
In this manner the values of science and ethics are created. There is added to

INDIVIDUALITY AND WORLD 641

this objective struggle, in which important work of value to humanity is
done, the subjective struggle, which aims at material goods, not for the
whole human society but for the individual and his family, and at distinctive
psychical goods. This second struggle is largely, although not altogether, a
competitive one for a position, for profits in the realm of material goods, and
for distinctive psychical goods yielding recognition, distinction, honor for the
individual and those he represents. From a certain aspect, the struggle for
distinctive psychical goods might be considered as a competitive struggle for
profit in the sphere of psychical goods ; but it is not designated as such, because
while the profit motive is approved by public morality in the sphere of material
goods, it is regarded objectionable in the sphere of psychical goods ; here, the
aims should solely be objective. But if we analyze human activities, we find
present in all of them the objective and the subjective motives. This is true
of the life of individuals pursuing commerce and industry, as well as of those
pursuing pure and applied science and art. However, these two motives are
present in varying proportions in different occupations and in different indi-
viduals.

It is, above all, the manner in which this subjective struggle is conducted
which characterizes individuals. All the psychical characteristics and the
corresponding modes of reaction which distinguish one human being from
another may be called his personality, and it is especially in the subjective
social struggle that the personality becomes manifest. There is still another
motive which may participate in this subjective aspect of human endeavor;
this involves the desire to be distinct from others, to be an individual in the true
sense of the word, particularly in the psychical field, in thinking and feeling,
and in creating; it is accompanied by the wish not to imitate others, but
to express one's own individuality, to receive recognition for this distinc-
tiveness, and to be accepted as an individual in one's own right. The degree
of self-control and self-maintenance and determination which an individual
exhibits in the social struggle is a measure of his "morale." It represents
his ability to resist the results of injurious suggestions which tend to disor-
ganize his personality, depress his self respect, the feeling of his strength
and his ability to maintain himself and to be respected by others and by him-
self.

To harmonize the various conflicts of individuals and groups in the social
struggle certain codes have been established. Ethics and law have significance
as means of such an adjustment. They represent balances that compare and
weigh two or more contrary claims or needs, but these decisions, although
generalized, are as yet very imperfect, because they cannot very well include
in their comparisons and weighings the different individualities around which
the needs and claims center. Ethics, with its concepts of justice and of the
dignity of the individual, includes in its consideration also the sphere of
psychical goods, while law, with its more formal concept of justice, pre-
ponderantly limits itself to the sphere of material goods and bodily injuries,
where comparisons and weighings can be made more readily in an objective
manner than in the sphere of the more individualized psychical goods. In

642 THE BIOLOGICAL BASIS OF INDIVIDUALITY

particular, such terms as egoism, altruism, have a meaning only in the con-
text of the social and natural struggle ; they signify certain attitudes, balanc-
ings between our needs and those of others in these struggles. It is largely
in such a world of varying conflicts that the individual lives and his activi-
ties take their course.

This world of the social and natural struggle is essentially the egocentric
world, from which, step by step, the objective world of science has detached
itself in the past and will continue to detach itself in the future. It is only
if we consider the different psychical states active in the sphere of the social
and natural struggle as this struggle has developed in the course of human
history that we understand some of the characteristic desires and needs of our
individuality, as manifested by our wish to attain an absolute significance
and an independence of time and space. To accomplish these aims the in-
dividual longs (1) to be free and self-determining; (2) to be unique and
constant, essentially unchangeable, a self-conscious continuity; (3) to be
eternal, and (4) to obtain appreciation and self-justification in the face of
attacks and criticism, to prove worthy of existence and to be in harmony
with the laws of man and of the universe. Let us examine such needs and
desires and state to what degree they may rest on constants in the human
constitution finding expression in the present social constellations and how
far they may be founded on illusions.

1. Free will and self-determination. The concept of psychical individuality
implies, as we have seen, the feeling of freedom, the existence and manifesta-
tion of a self-determining entity, which according to the belief of many
assumes the character of a spirit or soul, which is an eternal factor ; this
"self" is distinct in each person and sharply differentiated from the processes
underlying our machine-like automatisms, and it presupposes the action of a
directing principle coming from the inside, rather than a mechanism dependent
upon the interaction between organism and environment by way of definite
reflexes acting in preformed channels.

That there are fixed factors determining our actions we have already dis-
cussed ; in certain cases the automatisms active in thinking and in the mani-
festation of emotions become so evident that, under these conditions, we are
ready to abandon the concept of individuality. Thus the lack of freedom is
especially clear in the hypnotized person, or in the person who, after having
been hypnotized and then awakened, carries out the commands given to him
during hypnosis ; others around him recognize his lack of freedom, although
he is not aware of it himself. A lack of freedom is shown also by a sleeping
person, or by one who is under the influence of certain drugs, which change
his thoughts, emotions and behavior ; also by the insane. The thoughts of in-
dividuals suffering from the same type of mental disease may be very similar
in character and only slightly or hardly at all individualized. A further evi-
dence of automatism is furnished by cases of a split or double personality,
where normally connecting memories are conspicuously disconnected at a
certain point, although in reality every individual has a multiple personality
dependent on the existence within him of mutually incompatible suggestions,

•INDIVIDUALITY AND WORLD 643

tendencies, principles; between such incompatibilities he is constantly balanc-
ing, at one time one, and at another time another of these factors predominat-
ing. Our feeling of freedom and self-determination depends upon this finely
balanced system of thoughts with which we adjust ourselves to conditions in
an ever-changing environment. It depends, too, upon a certain continuity in
thought; the thoughts of one moment must be remembered in the following
period and must manifest a certain degree of consistency. We may lose the
feeling of freedom in the case of ourselves and of others as soon as this finely
balanced, connected system of thoughts and emotions is interfered with,
owing to abnormalities in the functioning of the organism.

Thus, although the lack of freedom and the automatic character of human
behavior may be evident to us under certain conditions, for the most part, we
largely ignore the factors determining our reactions, and they are indeed
mostly unknown to us. We live, think and act in accordance with the require-
ments of the situations which we meet. The interactions between the situations
and our organism and our responses remain largely unanalyzed. Even if we
should be aware of them, as a rule we abstract from this knowledge in the
process of living. Here we feel we are free.

2. Continuity and consistency in individuality. We need not only the feel-
ing of inner freedom and self-determination, we also need a feeling of
continuity and self-consistency. These needs are intimately connected with
each other and they both depend upon the interlocking of thoughts, the un-
interruptedness of memory which joins the experience of one time-unit with
those of the following, which creates a connected texture cf remembered
sensations, feelings, thoughts and wills.

In our changing environment, amidst the varying conditions under which
we live, we have principles which as such remain fixed, in contrast with the
shifting manifestations and expressions of these principles. We have conscious
thoughts which direct us in our aims and we have memories of ourselves.
When we become aware of abnormal, irrational reactions within us, we try
to make them accord with our directing thoughts and principles. These latter
attempt to co-ordinate all our thoughts into one consistent whole, which
centers around the "I." Our individuality is conceived of as being more than
merely a peculiarly constituted mosaic of factors, all of which may exist also
in others, although in different arrangements and with different degrees of
intensity; the picture of ourselves as a coordinated, rational personality be-
comes fixed in our mind, notwithstanding the changes which take place in
our body and in our thoughts continually. Thus we live in a world of illusion,
since in reality we are subject to a continuous change. Furthermore our dis-
tinctions as to what is our own and derived from the inside and what is derived
from our environment are quite generally erroneous. We attribute to things
within us, to our individuality, what is really of external origin, such as the
suggestions which have acted on us and influenced our behavior. Quite com-
monly we believe that reflex actions, having their beginning outside of us,
originate within us if the afferent parts of the reflex arc remain hidden from
us. Thus we may hold ourselves responsible for actions of an automatic char-

644 THE BIOLOGICAL BASIS OF INDIVIDUALITY

acter. On the other hand, we often attribute to the outside and we blame others
for what is essentially determined by our own inherited and acquired consti-
tutions.

Our mental processes, and in particular the thoughts concerned with our-
selves, function in a definite mental milieu, in a medium of nerve and
endocrine gland activity, to which we are accommodated. We have adapted
ourselves to a certain intensity of feeling, energy or lassitude, to a certain
kind of emotional reaction, to a certain mode of thinking and rhythm of
reactions taking place within ourselves and within others. In this milieu we
feel at home; it is here that we are accustomed to direct our thoughts, our
movements, to talk and to respond to other persons. If these processes take
place smoothly, we do not especially become aware of ourselves, of the control
we exert over ourselves and we take the continuity of our personality for
granted. We do not usually notice very gradual and connected changes. But
if our milieu is abruptly, acutely changed, our reactions are changed in a
sudden way. also; thus, under unfavorable environmental conditions, under
the influence of drugs, in sickness, we may become tense, irritable, involved in
conflict with others and with ourselves. Our usually self-controlling thoughts
cannot at once accommodate themselves to the altered organism on which
they have to act ; they find different effects, different responses ; there is an
interference with our personality, a disturbance in our continuity, a rift
within us.

Similarly we are accustomed to the set of suggestions in which we live.
Often insidious in their action, these function in a mild way because we are
adapted to them, because they have been with us for a long time. They are
not considered as strange to us, as an outside product forced on us, but as
something adopted by us, or as having originated in our own thought system ;
they arouse no sensation of discontinuity in our self-directing personality.
But if we receive a sudden command, then we react to it as an interference
and as opposed to us. This changed situation is no longer compatible with
our feeling of freedom, continuity and self-consistency. The same result
follows if forced thoughts, new to us, incompatible with the rest of our
personality, develop in us. Then the idea of continuity in our individuality
is interrupted ; we experience an interference with our individuality, especially
if under the changed circumstances our responses become different and un-
controlled. However, should other disturbing factors interfere also with
our ability to reason, to analyze, then the consciousness of cleavage and of
discontinuity in our personality may be lacking.

But under normal conditions we have the feeling that we are constant in
a changing world. We have an intimate acquaintance with our environment,
we have the knowledge of what to expect in it ; there is a certain permanence
from day to day in our bodily organism and it is distinct from other organ-
isms. Thus we are satisfied that our individuality is continuous, forming one
definite entity, that there is identity of the self in one moment with the self
of the past and of the future.

And furthermore, the individual himself, as well as those around him,

INDIVIDUALITY AND WORLD 645

attribute to his psychical individuality the character of uniqueness to a much
higher degree than it actually possesses. As we have stated, also the psychical
individuality (personality) is a mosaic in which the constituents were acquired
from various sources, partly as inheritance of peculiarities in the structure
and function of certain organs from the ancestors of the individual, partly
through suggestions and thoughts taken over from other individuals with
whom he has been in contact. Very little, as a rule, has he himself contributed
to this mosaic. What distinguishes an individual is the way in which these
various constituents are combined and accentuated. The uniqueness of the
psychical individuality is furthermore due to the uniqueness of individual
experiences. And here again, the individual experiences are not really unique,
but the series as a whole, the order in which they are joined together and
the relative significance of each one of these experiences for the individual may
be unique. The psychical individuality represents, thus, a biological-historical
system, in which environmental factors play a very important role. It is the
selection and chronological order as well as the intensity of the influences and
experiences which have acted on the individual, especially in the course of
his most formative, impressionable period of life — but also later — which help
to determine his psychical character and his uniqueness. But even these
historical factors are not usually entirely unique. Other individuals have
experiences, if not identical, at least somewhat similar, and the scientific
analysis of the effects of these series of experiences on the nature of the
psychical individuality seems feasible. In contrast to the psychical individual-
ity which thus represents a biological-historical system, the other two types
of individualities, one of them based on the character of the various tissues
and organs and of their combinations, of which in certain respects the psy-
chical individuality really represents merely a part, and the other based on the
character of the individuality differential, are purely biological, and much
more independent of more or less accidental environmental factors and more
fixed and determined in their nature. This genetic fixity and relative inde-
pendence of accidental conditions characterizes especially the individuality
differentials, but almost equally as much the tissue and organ differentials.

3. The permanence of our individuality. Wre are involved in a struggle with
nature, which we learn to dominate only within a very limited range. Our
organism ages, becomes sick and dies. This natural struggle invariably ends
in defeat. But the directing, apparently self-determining agent in our individu-
ality, that which seems really characteristic of us, we conceive as imperishable,
eternal. We have built thought structures expressing and justifying this
interpretation. But even if we do not accept these views, still we live essen-
tially in the world of our thoughts, emotions and wishes, which are "we,"
and these thoughts we feel are free, not limited by the realities of life and
nature. And in this thought-world we apparently continue to act quite inde-
pendently of the changes which actually take place in us, of our real fate.
Thus we see ourselves as continuing to live after our death in the world
of our thoughts. We want to transmit to the world our thoughts and attitudes
and change the world into one more suited to our needs, into a better world,

646 THE BIOLOGICAL BASIS OF INDIVIDUALITY

the idea of which means something to us although we are no longer here to
experience it, to benefit by it. Our children shall live in our spirit and con-
tinue in our ways and lead our efforts to fruition. But even in the face of
death men also keep up their petty ambitions and competitive self assertion.
The individual has lived and may still continue to live in a thought-world,
which does not take heed of his waning powers nor of the mortal disease which
may affect him ; these changes often do not tend to enter as real constituents
into the construction of his mind. His thought-world may remain fixed and
he does not foresee an end to it.

4. Self-justification of our individuality. The individual lives in a struggle
with nature and with his social world ; in this struggle he receives injuries and
inflicts injuries. In others, he sees himself and the injury of others he feels
as his own injury. There exist laws which are disregarded by him and he
acts contrary to them ; he suffers from the pangs of conscience and fears
the consequences of what he does. In such a conflict he needs approval of
his actions and his individuality, he needs justification for his existence,
absolution for his failures and for his infringements of those laws which are
believed to be absolute. And yet, in determining his responsibility, he often
attributes to himself what originated in others, and to his environment he
attributes what was his own ; even here he is unable to discern the real from
the unreal and, insofar, he again lives in a world of illusions.

However, all these psychical reactions in human beings which have here been
discussed and which tend to express and safeguard their individuality, are not
elementary psychical phenomena, but are conditioned by the social setting in
which they occur, by the social traditions, customs, and ethical standards which
direct and control the life of the social groups, large or small, to which the
individuals belong. The psychical individuality as we have just described it,
exists therefore only in an advanced stage of human social development, where
the sets of active suggestions are wider, more numerous and more varied than
in the more primitive societies, but where they are also less firmly fixed, more
accessible to influences which may change them, where the manifestations
of the social struggle are more complex and may affect also the thought-life
and emotions of the individual to a higher degree, and above all, where a
social reservoir of scientific and philosophical thought is available, which
may serve as a source of inner psychical goods to which the individual has
access. There has thus taken place an evolution also of the psychical-social
individuality; but it is the task of the history of civilization to trace this
evolution.

Individuals are the units which constitute groups. Groups of various kinds
are aggregations of individuals in which the distinctive characters of com-
ponent parts are disregarded and characteristics common to all are used to
distinguish one group from all the other groups. In a certain sense, the group
concepts are thus opposed to and destructive of the features which constitute
the individual. The group concepts as far as they concern man are abstractions.
This applies to all groups, whether nations, races, economic classes, social
castes, or societies of various kinds ; also, whether they are based on moral

INDIVIDUALITY AND WORLD 647

attributes, beliefs and principles, occupations and professions, family asso-
ciations, or other personal relationships such as friendships and feuds. It is
essentially as members of such groups that we enter into communication with
individuals ; we possess the group-suggestions and we may be subject to
acutely acting ones, such as those manifest, for instance, in the mob spirit,
and individuals are largely, to us, therefore, representatives of groups, sym-
bols of various activities, tendencies, principles or associations of human
beings. Yet within these groups individuals are distinguished by the possession
of special group characteristics. Each individual is a composite as a member of
many groups and these groupings are not the same in different individuals. But
in addition, we recognize various distinctive signs of individuals, such as
structural characteristics, movements, ways of speaking, expressions of
various thoughts and emotions and special attitudes which distinguish one
individual from another and which are partly independent of groups.

However it is, after all, only a small part of the individuality of others
and of himself which each person learns to know. The meaning of individual-
ity, therefore, is based largely on the subjective experiences of the individual
himself, and the knowledge thus derived is imperfect and faulty. The recogni-
tion of the distinctive features of the individual and of the meaning of in-
dividuality are problems with which the1 study of the body and mind is
concerned. Science provides instruments for the analysis of the physical
and psychical mosaic of which the individual is composed and makes possible
the investigation of genetic and environmental factors entering into his con-
stitution. But science in carrying out this analysis splits individuality into
many constituent parts, which then are joined together again into new groups
or types more significant than the conventional ones which a more superficial
observation furnishes. Science thus shows that what is most significant in
individuals as separate entities is not the elements of which the individual
consists, but the mode and the quantitative manner in which these elements
are joined together, and in this sense it deprives to some extent individuality
of its distinctiveness and uniqueness and it diminishes in man what has been
considered as the most characteristic feature of his individuality.

As we have pointed out earlier in this chapter there is a far going differ-
ence between the psychical-social and the physical-physiological individuality.
In contrast to the physiological and physical individuality which is distinct
and sharply separated from the surrounding world, the psychical individuality
forms in certain respects one connected whole with its environment. The
evidence given in our preceding discussion has shown that in the psychical
sphere the individual is not sharply separated from the non living things
and other organisms. The psychical individuality is composed of elements
which are interwoven in such an intricate way with the world surrounding
the individual that it is difficult to make a sharp distinction between those
elements which belong to the one and to the other. Moreover the intricacy of
these connections increases the difficulty of establishing in the actions of the
individual the relations of cause and effect. If we consider the fact that the
psychical-social individuality depends largely on the nervous system for its

648 THE BIOLOGICAL BASIS OF INDIVIDUALITY

development and expression and that the nervous system acts as the agent and
representative of the outer world within us it can be readily understood that
there is an intimate connection between the psychical individuality and the
outer world.

It is these relations between the individuality and the surrounding world as
well as the relations which exist between individuality in the physical and
physiological sense (body) and in the psychical sense (soul) which have been
the main problems with which philosophy has dealt throughout its history.
Therefore essentially the problems of philosophy have been largely concerned
with the meaning of individuality.

Chapter J
The Evolution of Individuality

In a preceding part we have followed the evolution of organisms from
their primitive beginnings to man. At first, the organisms are relatively
simple as far as the differentiation of their organs and the character of
their organismal differentials are concerned. They are still very plastic, re-
sponding readily with a modification of organ and tissue formation to certain
changes in the environment. They also reproduce with ease lost parts of their
body, even relatively small pieces having the power to do so. Presumably
this relatively great plasticity of the organs and the relative simplicity of the
organismal differentials are connected with each other. *

With advancing evolution, the plasticity of the organism, its readiness to
respond to the environment, decreases ; more and more the organism becomes
a fixed, closed system, in which structural complexity and integration in-
crease; at the same time, the organs become more specialized and the or-
ganismal differentials more differentiated and individualized. The increasing
independence of the environment applies not only to the adult organism, but
also to the embryo, whose development, in the higher organisms, takes place
within the body of the adult mother ; in this way the influence of environmental
factors on development is more completely excluded. Within the mother's
body the greater specialization of the organ and organismal differentials takes
place, the finer structural differentiation and the fuller integration occur and
a more individualized organism is formed. It is born in a state in which the
animal is more or less fully developed as far as its structural characteristics
are concerned.

Concurrently and intimately connected with this increase in the specializa-
tion of organ and organismal differentials and in the individualization of the
organism, a greater refinement in the immune mechanisms is established. This
latter change adds still further to the individualization of the organism and
tends to transfer a greater part of its reaction to certain environmental
alterations from the external world into the interior of the ariimal. We can
consider the gradual refinement of the organismal differentials and of the
processes on which their manifestation depends, as well as the increasing
delicacy and significance of the immunity reactions, which are largely based
on corresponding changes in the various differentials, as mechanisms of
defense on the part of the organism as a whole against interference from the
outside, and therefore as mechanisms guaranteeing the integrity of the or-
ganism and its increased independence of the environment. As a result of
these alterations, there is a change in the circuit of relationship between or-
ganism and environment, in that the influence of the environment on the or-
ganism becomes less and the effect of the organism on the environment be-
comes greater in the course of evolution. With this increasing refinement of

649

650 THE BIOLOGICAL BASIS OF INDIVIDUALITY

individualization there decreases the potentiality of small somatic parts to
reproduce the whole organism in an apparently unending series, and corre-
spondingly, there decreases the potentiality ito immortal life of these parts. In-
stead, this potentiality to immortality becomes dependent entirely on the
special mechanism of sexual reproduction, which in the higher organism is
of such a kind that at no time are the sex cells exposed to the direct action
of the environment. However, certain somatic ceLls and tissues of these dif-
ferentiated organisms still retain their potential immortality, as exemplified
in the propagation of tumor tissues in succeeding generations of hosts and
of embryonal tissues kept in tissue culture ; but in these cases the tissues are
able to manifest a potential immortality only if they are supplied with an
environment in which the complex substances specifically needed for their
growth, as well as other needs, are experimentally provided. They cannot
be propagated in the natural inorganic environment, which would be adequate
for the propagation of parts of lower organisms.

In this first circuit of the relationship between organism and environment,
the evolution of individuality consisted in the development of an organism
which became more and more autonomous, more and more independent of the
environment, except that it needed the environment as the source of its food
and energy. However, there arose on the basis of and closely connected with
this circuit, a second one, in which the evolution went in the opposite direction.
Here, the increasing complexity and differentiation of the organism led, on
the contrary, to a more intimate interaction between the organism and the
environment. This environment became increasingly important and it deter-
mined to a large extent the fate of the individual, his ability to maintain
himself and to find satisfaction in his world. In this second circuit, organism
and environment were connected by way of sense organs, nervous system and
muscular system, by means of which the organism acted again on the environ-
ment. The evolution of this circuit depended on the refinement of these
specific organs and their organ differentials. Thus the organism came into
contact with a much more extensive part of its environment and the contacts
became more specialized and variegated. An early stage of this development
was reached with the production of conditioned reflexes in the interaction
between environment and organism. Alterations occurring in the nervous
system as the result of repeated stimulation, made it possible that simple
environmental factors more or less loosely or accidently connected with the
direct stimulus, were able effectively to replace the latter. Furthermore, pic-
tures and thoughts, representing environmental factors and systems of such
factors, eventually could substitute for the environmental factors and systems
themselves and thus determine the mode of reaction of the organism. Thus,
conditioned thought reflexes developed. Concomitantly, a great refinement
took place in the manner in which the nervous system was affected by these
outer and inner factors, and the intracerebral reactions became longer-lasting
and more significant. These various changes left important after-effects in
the form of memory and thoughts ; analysis and synthesis thus became possi-
ble.

THE EVOLUTION OF INDIVIDUALITY 651

Thoughts reproduced environment, and in the environment thus reproduced
the social environment became more and more prominent ; this type of inter-
action between organism and environment did not, therefore, take place in the
same rigid way as in primitive organisms, such as insects, but with the crea-
tion of thought so many possibilities of response arose that the actions of the
individual became very varied. At the same time the environment affected
the organism in a new way through the development of imagination and
suggestion.

As a result of these modifications, the apparent freedom and the greater
individualization in the psychical-social sense of the higher organism have
evolved. In this second circuit the environment influences and in a delicate
manner changes the living substratum on which it acts ; it gains in importance
in comparison with the inheritable rigidity of the basic functions of the first
circuit. While thus in the more primitive organism genetic conditions deter-
mine more directly the behavior, and while also in the highest, most complex
organism, man, the basic functions are essentially fixed in a rigid way by
genetic factors, there develops in man a special mechanism which makes
possible a very sensitive interaction between organism and environment ; in
this sphere, the environment becomes a factor of great importance in directing
the behavior of the individual. In the more primitive organisms, individuality
is largely fixed; in man the psychical individuality is to a great extent
modifiable, environmental in character. The content of our mind is given
us by the daily experiences in life; in particular, by the suggestions of the
persons we meet, in whom all these influences have also entered ; but it is also
given us by poets, artists, philosophers and scientists. In this psychical-social
aspect our individuality has become the more modifiable, the greater the re-
finement of the nervous system has become.

The factors entering into human behavior have reached such a degree of
complexity that the actions of individuals are often unpredictable, and the
illusion of indeterminateness in Willing and doing arises. Furthermore, the
contacts between individual and environment have become not only much
more varied and extensive — the individual being in contact with an ever en-
larging part of the universe — but they are also intensified. Suffering and pain
of the mind and elations have evolved, which had previously not existed. With
the increase in the importance of the central nervous mechanism there in-
creased the anticipations, the dread of disease and suffering and of annihila-
tion, as well as the fear of the intentions and actions of other human beings ;
but there developed also new satisfactions of wider visions, of deeper under-
standing. The human organism is not only shaped by the environment, but
more and more it reacts against it and learns to understand and modify it.
There develops the pleasure of creative, playful interaction with the environ-
ment ; but not only does man interact with the environment, he interacts and
learns to experiment with and, to a certain extent, to shape his own psychical-
social organism and those of others. While thus, in certain respects, the in-
dividuality becomes increasingly pronounced, in other respects, in conse-
quence of the more and more intricate interaction between environment and

652 THE BIOLOGICAL BASIS OF INDIVIDUALITY

psychical-social individuality, a separation between individuality and environ-
ment, especially the social environment, becomes impossible. Hence the
second circuit has been refined into a modified, a third circuit, which leads
from the social as well as the natural environment to the nervous system, to
thoughts and suggestions, and back again to the social and natural environ-
ment.

In this third circuit thoughts and suggestions have been profoundly modi-
fied, not only by the natural but also by the social environment, and, more-
over, they have become the more important and powerful, because they did not
live an isolated, separate existence, but were connected with systems of tradi-
tions, myths, philosophy and science. All of these latter formed one whole, a
system acting as a huge social thought-reservoir, which became more and
more independent of the individual. However, the individual not only received
from this thought-reservoir, thoughts and suggestions determining his actions
and orientation to world and life, but conversely, he contributed to it his own
thoughts, suggestions and emotional reactions, as manifested in the various
forms of art, in science and philosophy and the conventions of social life. In-
tensified satisfactions were felt in the creation of concepts concerning the
universe and in victories won in the social and natural struggle, and these
concepts entered into the social thought-reservoir and thus became the posses-
sion of all, freed from the index of the individuality which had contributed
to their creation and which was able to create because it had previously
received important constituents from this common source.

At the same time this social thought-reservoir has become the source of
much suffering because of its mode of origin, reflecting as it does our imper-
fect manner of thinking. Reality, the totality of our environment in its inter-
action with our body and thoughts, is too vast and too complex for us ; it is
more than we can manipulate. We can concentrate at one time only on certain
features of it ; necessarily we abstract and, subsequently, parts which diverse
abstractions have in common are synthesized by us into a new concept. Thus
generalization follows abstraction. Some of these procedures are carried out
in a relatively satisfactory manner, such as the abstractions and generaliza-
tions in mathematics and science ; and also the more simple abstractions used
in ordinary life, sensations such as hot, cold, red, blue; or comparisons of
quantities of weighable substances : "much," "little," these all are fairly satis-
factory abstractions, serviceable and more or less in harmony with reality.
But there are many inadequate or false and arbitrary abstractions and gen-
eralizations. They occur especially in all those realms of life where our emo-
tions are affected, and where the social struggle enters. This is true especially
of many moral, political and social concepts, such as those expressing ap-
proval or condemnation, those of fashions and rituals ; the fact that they are
often purely arbitrary, and not representative of real and significant things
and processes is not usually recognized. And some of these concepts not only
represent inadequate abstractions and generalizations, but also injurious ones ;
this applies in particular to many social concepts which serve as instruments
in the social struggle for material and distinctive psychical goods. All these
ideas enter the psychical-social reservoir ; here they remain, as it were, frozen

THE EVOLUTION OF INDIVIDUALITY 653

in the form of words and are transmitted from generation to generation.
They are used as suggestions and give origin to conditioned thought reflexes,
which are associated with a certain environment. This system of thought
reflexes, with the accompanying emotions and the psychical-social environ-
ment, forms then, one whole; it carries injuries and pain. From this reservoir
in general, we receive our instruments in the social struggle ; we may leave
unchanged what we have taken and give it back again with all its inherent
imperfections ; or we may add new imperfections by using concepts faultily
in the social struggle. Only gradually and very slowly is a modification of
the thought-reservoir accomplished through the psychical reactions of in-
dividuals who suffer, and these may find expression in the work of poets,
philosophers and scientists; also through the play of mind which leads to
the creation of new ideas.

However, the social thought-reservoir acquires an additional significance
for us. In seeking for something to take the place of the absolute, yet some-
thing to which we may fix our aims and motives and which provides more than
a satisfaction of our passing needs, something which is lasting and independ-
ent of the changing and ephemeral in us and in things around us, we turn
to this thought-reservoir in our search for a constant in the universe and in
man; we attempt to convert it into a trustworthy source of our valuations
and principles and, therefore, also of our inner psychical goods. To build
it up, make it consistent, to extend it, so that it becomes more and more
universal in the course of time, we conceive as our highest task. In these
efforts there begins to develop, step by step, a common, general reservoir for
all humanity, instead of the many particularistic group reservoirs which had
originally existed.

Our psychical-social individuality, representing combinations of thoughts,
wishes and wills, accompanied by emotions and functioning within the frame-
work of the body — the elementary organ systems — with the aid of the
nervous system and of the system of hormones, represents thus something
intermediate between our bodily organism and the social thought-reservoir.
It takes its origin in the body and reaches out into this reservoir, which is
common to all but with which we each have our individualized contacts.
Within this reservoir is that which is relatively constant, but constant only
as compared with the fleeting existence of the individual. The individual
varies and disintegrates, but our social thought-reservoir appears lasting, the
depository of fixed values. Here is what remains of the individual, what he
took from it and what he added to it. The psychical-social individual to a
large extent consists of things borrowed from this reservoir, and to it, in the
pain of the natural and social struggle, he joins his fortunes. Here he deposits
his discoveries, thoughts and principles, to which, if possible, he adds his
individual name, so that in the reservoir he may live when his physical self
has died ; at the same time in so doing he eliminates his individuality as much
as he can from the social struggle and disappears in the impersonal, the
unselfish, in the realm of lasting principles where all individual pain and
individual desires end.

Thus a fourth and shorter circuit has developed as the latest phase in the

654 THE BIOLOGICAL BASIS OF INDIVIDUALITY

evolution of individuality ; it connects the individual with the social thought-
reservoir and from there leads back to the individual. These relations of the
individual to the thought-reservoir were used by man in an attempt to regain
the potential immortality which, in the sphere of the first circuit, had been
lost with advancing evolution, and thus to obtain compensation for the injuries
and destruction experienced in the social and natural struggle. But this effort
is in vain. The thought-reservoir reflects the world, the social environment,
life as a whole, and in making connections with it a part of the psychical
individuality is sacrificed. This last circuit represents the highest point, the
last phase in the evolution of individuality, the latter entering into that which
is common to all and thus in part giving up its separate existence.

Yet, while the individual lives and struggles, the social thought-reservoir
exerts a real function in his activities. It has a steadying, stabilizing effect on
him and it may restrict the excesses in which his personality may express
itself. Thus he is limited, is made less free, but at the same time it renders
the individual, in his sensory-nervous-muscular circuit, less dependent on the
environment. It brings continuity into his reactions, which are then deter-
mined not solely by momentary impressions and responses, but by thoughts
and traditions acting as relative constants, as principles in an ever changing
world and life. In this manner a development is achieved in the psychical-
social sphere, not unlike that acquired in the first, the primary circuit, which
latter results in the building up of a very differentiated system, more and
more detached from and independent of the environment, a process charac-
terized by such conditions as homoiothermia, homoiohydria, homoiotonia, and,
in general, by what has been called by Cannon, homoiostasis. Corresponding
to this latter development, there has resulted from the evolution of the
thought-reservoir and from its interaction with the individual a kind of
psychical homoiostasis, in which the psychical individuality is weighted
down, anchored and fixed to something that holds it firm in the movements
and struggles of existence.

There has thus taken place an evolution of two types of individuality. The
first is connected with the differentiation of the organ differentials and with
the evolution of the individuality differential and its manifestations, from a
very primitive character to the state of great refinement reached in mammals.
The second is connected with the evolution of the psychical-social factors,
leading to the gradual creation and refinement of the indivdual in the psychi-
cal-social sense. This second evolutionary process is related only indirectly
to the development of the individuality differentials ; it depends directly upon
the increasing complexity and refinement of certain organ differentials, espe-
cially of the nervous system. There is, therefore, no perfect parallelism between
these two evolutionary processes. While in the first process a gradual, step-by-
step development of the individuality differential occurs, in the second process
the most important, far-reaching change has taken place suddenly in the tran-
sition from anthropoid apes to man.

Corresponding in certain respects to the types of circuits which connect
the individual and his environment four stages may be distinguished in the

THE EVOLUTION OF INDIVIDUALITY 655

evolution of the psychical individuality: (1) The most primitive stage is
represented by that of the simple reflex mechanisms, to which the simple
conditioned reflex is added as an important extension. The action of hormones
may further complicate this mechanism. (2) Superimposed upon this stage is
the one in which there are active more or less isolated, disconnected pictures
of things and events, developing in response to the needs of the moment;
they may become memories and may direct actions. (3) In a third stage,
thoughts which represent simple abstractions are produced. These may exert
their effects as suggestions, extending from others to ourselves ; or as auto-
suggestions originating within us. It is partly, or perhaps largely, by means
of auto-suggestions that our thought determine our present and our intended,
our future, actions and attitudes. (4) The highest stage is reached with the
functioning of extended, conscious and rational thoughts which then may
affect our actions and attitudes. The further development of the psychical
individuality coincides with the history of civilization. In the evolution from
the first to subsequent stages the directness of the relationship between the
organism and the environment decreases ; more and more there are placed
between the two, psychical factors ; and, concomitantly, the contact with and
the understanding of the environment enlarges and deepens. Thus, in the
interaction between our psychical individuality and the outer world, con-
stituents of the latter play a greatly predominating role, so that the relative
importance of external factors and of inner factors in the functioning of
the organism becomes entirely different. The essential content of what we
call "mind" is composed of things given us from the outside, from the non-
living environment, and, above all, from the living, social, human environment.
While the simple reflex action is largely of the same kind in all individuals
of the same species, with increasing psychical development and especially
with the development of analytic thought, the differentiation between individ-
ual organism is greatly increased and real psychical individualities are created.

But while the dependence of our personality on the environment, and
especially on the social environment, becomes greater, at the same time con-
sistency of thought and the building up of a social thought-reservoir, with
which we enter into increasingly intimate connection, cause our individuality
to become more fixed, steady, independent of the environment, which, on the
contrary, we now begin to modify and to shape more and more in accordance
with our desires ; and this environment, on which we are able to act and which
we can alter, includes in certain respects our own organism, in the bodily
as well as in the psychical-social sense.

These various circuits, which develop as steps in the evolution of individ-
uality, remain connected with one another in a more or less intimate manner.
The later circuits are superimposed upon and depend for their existence and
function upon the primary circuit, which is the basic one. While the latter
gives thus to the more complex, higher circuits the possibility of maintenance,
development and of further evolution, while changes occurring in the primary
circuit affect all the higher circuits, and while, in particular, its derangement
causes serious interference with the function of the higher circuits, there

656 THE BIOLOGICAL BASIS OF INDIVIDUALITY

takes place also the reverse interaction, inasmuch as the character and func-
tioning of the higher circuits in which thoughts more and more predominate,
affects very potently the character and normal function of the primary
circuit.

As a result of this evolution of individuality, suffering, injuries, pains and
satisfactions are multiplied, intensified and individualized; and all these ex-
periences in the psychical-social sphere affect also the primary individuality
as manifested in the first circuit, the effects of psychical experience becoming
very far-reaching and important for the organism as a whole. More and
more, psychical experiences come to depend on intricate social organizations,
on social structures, in which the social struggle, the creation, acquisition and
distribution not only of material but also of simple and distinctive psychical
goods and the state of inner psychical goods play an important part. Thus,
with the increasing differentiation and refinement of the sense organs and
of the central nervous system and with the corresponding development of a
complex psychical and social life, our interactions with the environment are
extended, our experiences multiplied and our living intensified. The psychical
individuality which has now been created, attempts to maintain and to
elevate itself and in these efforts it collides with similar efforts of other in-
dividuals and this is one of the principal causes of the social struggle which
greatly affects the psychical life and may lead to injuries. Under these condi-
tions there develop the need and desire for an adequate environment, suitable
for bodily and psychical requirements ; the individual is spurred on to modify
the natural and social environment and the social thought-reservoir, and by
these means to effect changes also in the character of the material as well as
of the various types of psychical goods, and so to gain rest and security
for himself in the natural and social struggle.

It is primarily by facing directly the difficulties and dangers in the social
and natural struggle, by analysing and learning to understand these difficulties,
that he may hope to overcome them and be victorious in these struggles as
far as this is possible. Thus he may in the end achieve for himself calmness
and strength and he will give to others understanding. The product of
analytic and generalized thinking has thus entered the social thought reser-
voir; it lias become an instrument which man uses and which may be of
advantage to him in the material and social struggle. This advantage is now
accessible to all and is no longer individual, but it is enduring only, if the
underlying thinking process was sound.

Others may renounce the life of the social and natural struggle, as far as
their thought is concerned; they know the impossibility of actually overcom-
ing the struggle in life and they retire into a type of thinking in which
thought is freed more and more from the disturbing elements inherent in
the sphere of the social struggle. Thought reproduces events, life and world
instead of serving as an instrument in the social struggle and it also enters
the social thought reservoir. Man by means of his thoughts divests himself in
part of his psychical individuality and identifies himself with the whole.

But, as indicated already, thinking, especially when it is concerned with

THE EVOLUTION OF INDIVIDUALITY 657

the furthergoing analysis of man and his life, while it may provide satisfac-
tion and in the end give strength and calmness, may also under certain condi-
tions, interfere with the normal reflex and instinctive processes ; especially if
it tends to reproduce events in the painful social struggle, these pictures may
have disturbing effects and be injurious to the thinking individual. Thinking
in general causes fatigue, especially consistent thinking that subordinates itself
to reality which it wishes to express, and it is a difficult process. It is due to
this fact that in general man avoids analytic, objective thinking as much as
possible and devotes himself rather to the processes of willing and doing, and
to emotional experiences, and the events in the social struggle are allowed
to take their course and the serious consequences of this struggle may become
aggravated.

Evolution has thus led to a gradual loss of the plasticity and to an increas-
ing differentiation, integration, rigidity and fixity of the body, and asso-
ciated with this process there has developed an increasing individualization
by variious means. This development has taken place, (1) by a refinement of
the organismal differentials and the creation of the individuality differentials
or by making the latter manifest; (2) by an increasing differentiation and
integration of the organ and tissue systems, and (3) by the creation and
intensification of the psychical individuality with the aid of certain organ
systems. Associated with this increase in individualization and close integra-
tion, deficiencies have developed in the organization of the body which become
more apparent with advancing age and in the end lead to the death of the
individual.

Not only the bodily organization but also the psychical individuality which
has developed in the course of evolution is imperfect and deficient. This is
composed largely of suggestions which exist as separate, mutually dis-
harmonious constituents of the mind, whereas the integrating true thought
processes, which would be able to unify these disconnected parts into one
consistent whole and to effect greater harmony between the individual and
human society, do not function adequately.

Parallel to the evolution of the individual, the social life as well has under-
gone a progressive evolution. It began with the rigidity of the social organiza-
tion of animal groups, as represented by the relations between certain
unicellular organisms, by primitive colonies, by the essentially fixed and
determined character of insect societies and by the less firmly knit social
organizations among vertebrates. Within the vertebrates a further evolution
in the same direction has taken place ; it made its greatest advance in the
change from the social life of monkeys and apes to that of human beings.
In the latter, free imagination and thought even in the restricted way in
which they are active have almost completely overcome the limitations of
animal societies. Human society is thus no longer fixed, but it has become a
modifiable state determined by varied suggestions as well as by rational
thought and directed by the needs and desires for material and psychical
goods. While the simple and distinctive psychical goods used and valued by
human beings also may have roots in the psychical life of animal groups, they

658 THE BIOLOGICAL BASIS OF INDIVIDUALITY

have undergone a much farther and individualized development in man, in
whom the inner psychical goods have been entirely newly created. This evolu-
tion has led to the abolishment of those rigid modes of organization, which
characterize the different types of animal societies, and has replaced these
by the modifiable constitution of human society which is accessible to direction
by rational thought.

To recapitulate, the evolution of individuality has taken place in two op-
posite directions. The body developed from a state of relative variability,
which depended upon and was to a large extent directed by the environment,
to a state of relative fixity, autonomy and unyieldingness, much less subject
to environmental conditions. From the point of view of the bodily organism,
the inner constitutional factors have overbalanced therefore the environmen-
tal factors to a larger extent in the further advanced organism than in the
more primitive ones. There then took place, parallel to the evolution of the
body, the evolution of the sense organs, of the central nervous system and
of the psychical-social mechanism, in which the environment again has be-
come of increasing significance. Associated with these two tendencies in
evolution there occurred the development of the social struggle as a manifesta-
tion of the greater importance of psychical activity and psychical needs, in
contrast to the natural struggle, which was primarily concerned with the
satisfaction of the requirements of the body.

Thus, in matters which relate to man as a psychical-social organism, it is
the environment which has become a preponderating influence and which
largely determines his fate. To adapt the psychical-social environment to the
needs of man, so that he can function in the most adequate manner, is,
therefore, the most important task which humanity has now to face.

Bibliography*

I. Books and General Reviews

Allee, W. C. : The Social Life of Animals, New York, 1938.

Frank, Philipp: Between Physics and Philosophy, Cambridge, 1941.

Goldschmidt, R. : Mechanismus u. Physiologie d. Geschlechtsbestimmung, Berlin,
1920; Einfiihrung in d. Vererbungswissenschaft, Leipzig, 1923.

Jennings, H. S. : The Biological Basis of Human Nature, New York, 1930.

Korschelt, E. : Regeneration and Transplantation, Vol. II; Transplantation,
Berlin, 1931.

Landsteiner, Karl: The Specificity of Serological Reactions, Springfield, 1936.

Lexer, Erich: D. Freien Transplantationen, Stuttgart, 1919-1924.

Loeb, Jacques: Comparative Physiology of the Brain and Comparative Psychol-
ogy, New York and London, 1900; The Mechanistic Conception of Life,
Chicago, 1912; The Organism as a Whole, New York and London, 1916.

Loeb, Leo: Transplantation and Individuality, Biol. Bull. 40: 143, 1921; Physiol.
Reviews 10: 547, 1930; The Biological Basis of Individuality, Science, 86:
1, 1937.

Loeb, Leo: Causes and Nature of Cancer, Am. J. Med. Sc, 159: 781, 1920. Acta,
Union Internat. Contre Cancer 2: 148, 1937; Journal National Cancer In-
stitute, 1 : 169, 1940.

Loeb, Leo, and collaborators : The Venom of Heloderma, Carnegie Institution of
Washington, 1913.

Marchand, F. : Der Process der Wundheilung mit Einschluss der Transplanta-
tion, Stuttgart, 1901.

May, R. M. : La Transplantation Animale, Paris, 1932.

Morgan, T. H., A. H. Sturtevant, A. J. Muller, and C. B. Brii>ges : The
Mechanism of Mendelian Heredity, New York, 1922.

Morgan, T. H. : The Theory of the Gene, Yale Univ. Press, New Haven, 1926.

Muller- Freienfels, Richard: Philosophic der Individualist, Leipzig, 1923.

Nuttall, G. H. F. : Demonstration of Blood Relationship among Animals by
Means of the Precipitin Test, Cambridge University Press, 1904.

Przibram, Hans: Tierpfropfung, Braunschweig, 1926.

Rensch, Bernhard: D. Prinzip Geographischer Rassenkreise u. d. Problem d.
Artbildung, Berlin, 1929.

Scharrer, Berta: Endocrines in Invertebrates, Physiol. Reviews 21: 383, 1941.

Schoene, Georg: Die heteroplastische und homooplastische Transplantation,
Berlin 1912.

Snell, G. D., Editor: Biology of the Laboratory Mouse, Philadelphia, 1941.

Stockard, C. R. : The Physical Basis of Personality, New York, 1931.

Sturtevant, A. H. and G. W. Beadle, An Introduction to Genetics, Philadelphia,
1939.

Sumner, F. B. : Genetic, Distributional and Evolutionary Studies of the Sub-
species of Deer Mice (Peromyscus), Bibliographia Genetica IX, The Hague,
1932.

Thorndike, E. L. : Human Nature and the Social Order, New York, 1940.

Vochting, Hermann: Uber Transplantation am Pflanzen Korper, Tubingen,
1892.

* The following bibliography is very incomplete. In view of the considerable number
of subject matters discussed, reference to papers had to be limited to those articles on
which the conclusions presented in this book are mainly based and especially the articles
by the author and his collaborators and a number of representative articles by other
investigators are listed; but equally important papers had to be omitted. However refer-
ences to the latter can be found in the books, reviews or papers cited.

659

660 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Wells, H. G. : The Chemical Aspects of Immunity, New York, 1929.

Wilson, E. B. : The Cell in Development and Heredity, III edition, New York,
1928.

Woglom, W. H. : The Study of Exper. Cancer, George Crocker Special Research
Fund, New York, 1913.

Wright, Sewall: The Physiology of the Gene, Physiol. Reviews 21: 487, 1941.

Zinsser, Hans, J. F. Enders and L. D. Fothergill: Immunity, Principles and Ap-
plication in Medicine and Public Health, New York, 1939.

II. Papers

Auderhalden, E. : Individual Biochemical Differences, "Lehrbuch d. physiol-
Chemie" III edition, vol. 1 page 376, 1914.

Adams, A. E., E. M. Deforest and B. Granger : Class Specificity of Hormones,
Proc. Soc. Exp. Biol. & Med. 42: 354, 1939.

Addison, W. H. F. and L. Loeb : Relations betwe.en Structure and Growth of Epi-
dermis of Pigeon and Guinea Pig. Arch. f. Entwicklgsmech. 37: 635, 1913.

Adelmann, H. B. : Transplantation of Neural Plate and Eye Formation in Uro-
deles, J. Exp. Zool. 54: 291, 1929.

Adelmann, H. B. : Effect of Substratum on Heterotopic Development of Neural
Plate of Amblystoma, J. Exp. Zool. 57: 183 and 223, 1930.

Allen, B. M. : Effect of Grafted Anterior Hypophysis on Metamorphosis in Tad-
poles, Anat. Record 44: 207, 208, 1930. Transplantation of Thyroid Anlage
into Anuran Tadpoles, Anat. Record, 44 : 207, 1930.

Alloway, I. L. : Transformation in Vitro of R Pneumococci into S Pneumococci
of a Different Type, J. Exp. Med. 55 : 91, 1932.

Ambrose, A. M., F. W. Power, and C. P. Sherwin : Phenylacetic Acid and Its
Mode of Elimination, J. Biol. Chem. 101 : 699, 1933.

Anderson, R. L. : Skin Grafts as Indicators of Interspecific Relationship in Tri-
turus, Anat. Record (Supplement), 54: 60, 1932.

Anderson, Katherine: Adaptive Changes in Herpes virus, Science, 90: 497, 1939.

Andervont, H. B.: Immunity Induced by Mouse Sarcoma 180, Publ. Health
Reports, 47: 1859, 1932.

Andervont, H. B.: Influence of Trypan Blue upon Resistance of Mice to Trans-
plantable and Induced Tumors, Publ. Health Reports 51: 591, 1936.

Andrewes, C. H. : Immunological Relationships of Fowl Tumors, J. Path. & Bact.
34: 91, 1931. Transmission of Fowl Tumors to Pheasants, J. Path. & Bact. 35:
407, 1932. Immune Sera Against Fowl Tumors, J. Path. & Bact. 35: 243,
1932.

Anson, M. L., J. Barcroft, A. E. Mirsky and S. Oinuma: Correlation between
Spectra of Hemoglobins and their Affinities for Oxygen and Carbon Mon-
oxide, Proc. Roy. Soc. Ser. B. 97: 61, 1925.

Appel, Fred W. : Testes Grafts in Ovariectomized Fowls, J. Exp. Zool. 53: 77,
1929.

Appel, Max, O. Saphir, M. Janota and A. A. Strauss: Complement-fixing Anti-
bodies in Blood Serum and in Aqueous Fluid of Anterior Chamber of Eye,
Cancer Research 2: 576, 1942.

Aschner, M. : Symbiosis between Insects and Bacteria; Mycetoma Formation,
Naturwissenschaften 20: 501, 1932.

Avery, O. T. : Chemo-immunological Study of Pneumococci Infection and Im-
munity, Naturwissenschaften, 21 : 777, 1933.

Axhausen, G. : Transplantation of Bone, Arch. f. Klin. Chir. 88: 23, 1909; Trans-
plantation of Epiphyseal and Joint Cartilage, Arch. Klin. Chir. Ill: 832,
1919.

BIBLIOGRAPHY 661

B

Baldwin, H. A.: Skin Grafting and Blood Groups, Med. Rec. 98: 686, 1920.
Balinsky, B. J. : Xenoplastic Transplantation of Ear Vesicles, Arch. f. Ent-

wicklgsmech. 110: 63 and 71, 1927.
Ball, H. A. : Effect of Intravenous Glycogen Administration on the Growth of

Transplanted Cancers, Cancer Research 2: 823, 1942.
Baltzer, T. : Chromatin and Development of Hybrids of Echinoderms, Arch. f.

Zellforschg. 5: 497, 1910.
Barker, L. E. : Effect of Proteolytic Digestion Products on Monocytes in Tissue

Culture, J. Exp. Med. 57: 689, 1933.
Barnett, E. J. : Species Specificity in the Production of Toxin by Woodticks,

J. Am. Med. Assn. 109: 846, 1937.
Barrett, M. K. : Anaphylaxis and Hemorrhage in Transplanted Tumors, J. Nat.

Cancer Inst. 2: 625, 1942.
Bashford, E. F., J. A. Murray and W. Cramer : Natural and Induced Resistance

of Mice to Growth of Cancer, Proc. Roy. Soc. B. 79: 164, 1907.
Bauer, K. H. : Homoiotransplantation of Epidermis in Identical Twins, Beitr. z.

Klin. Chir. 141 : 442, 1927.
Baskirzew, N. J. and N. N. Petrow: Transplantation of Bone, D. Zeitsch. f.

Chir. 113: 490, 1912.
Baumgartner, Leona: Age and Antibody Production, J. Immunol. 27: 407, 1934.
Bautzmann, H. : Organizer Action of Chordo-mesoderm in Triton, Arch. f. Ent-

wicklgsmech. 114: 177, 1928.
Bautzmann, H. : Transplantation of Pieces of Organizer Tissue in Amphibian

Embryos, Naturwissenschaften 17: 818, 1929.
Bautzmann, H., J. Holtfreter, H. Spemann and O. Mangold: Induction of

Embryonal Development, Naturwissenschaften 20: 971, 1932.
Bayer, Gustav, and Th. Wense: Intraocular Transplantation of Testicle in

Rabbit, Arch. f. Entwicklgsmech. 137: 372, 1937-38.
Bayliss, W. M. : Principles of General Physiology. London 1915. (Coalescence of

protoplasms, p. 21.)
Beadle, G. W. and B. Ephrussi: Transplantation of Organs in Drosophila (Gene

hormones) C. R. Acad. Sci. 201 : 620, 1935.
Becher, H. : Blood in Parabiotic Rats, Verh. d. Anat. Gesselsch. 37: 227, 1928.
Belogolowy, G. : Transplantation of Eggs into Peritoneal Cavity in Pelobates and

Rana, Arch. f. Entwicklgsmech., 43 : 556, 1917/18.
Bensley, R. R. : Chemical Structure of Cytoplasm, Science, 96: 389, 1942.
Bergel, A. : Homoiotransplantation of Tailblastema in Rana Fusca, Arch. f.

Entwicklgsmech. 113: 172, 1928.
Bergmann, Max, S. J. Fruton and H. Pollock: Substance Specificities in En-
zyme Action (Pancreatic Trypsins), Science, 85: 410, 1937.
Bergmann, Max and Carl Niemann : Newer Biological Aspects of Protein

Chemistry, Science, 86: 187, 1937.
Bernstein, Felix: Inheritance of Blood Structures in Man, Zeitsch. f. induktive

Abstammgs und Vererbungslehre 37: 237, 1925.
Bert, Paul: Transplantation of Animal Tissues, These, Faculte de medecine de

Paris, No. 118, 1863; Transplantation of Tail in Rats; Effect of Various

Modes of Treatment of Tissue Preceding Grafting, J. de TAnat et d. la

Physiol. 3: 417, 1866.
Bert, Paul: Recherches experimentales pour servir a l'histoire de la vitalite

propre des tissus animaux, Paris 1866.
Birkelbach, W. : Nephrectomy in Parabiotic Rats, Zeitsch. f. exp. Pathol. &

Therap., 8: 465, 1911.
Bittner, J. J. : Genetic Studies of Transplantation of Tumors, Am. J. Cancer,

15: 2202, 1931; 16: 322, 1932; 17: 699, 1933; 17: 709, 1933; 17: 717, 1933;

17: 724, 1933; 36: 44, 1939; J. Genetics, 29: 17, 1934; 31: 471, 1935.

662 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Bittner, J. J. : Transplantation of Splenic Tissue in Mice, Public Health Rep. 51 :

244, 1936.
Blakeslee, A. F. : Susceptibility of Colchicum to Colchicine, Am. J. Bot, 26: 163,

1939; Science 89: 10, 1939.
Bloch, Bruno: Allergy, Anaphylaxis and Idiosyncrasy, Klin. Wochschr., 7:

1067 and 1113, 1928.
Blumel, P. and Heinrich Poll: Skin Pattern and Mental Characteristics, Med.

Klinik, 24: 1924, 1928.
Blumenthal, H. T. : Organismal Differentials and Leucocytes in Circulating

Blood, Arch. Path., 27: 510, 1939; Arch. Path., 31: 295, 1941.
Blumenthal, H. T. : Effect of Spontaneous and Transplanted Rat and Mouse

Tumors on Red and White Cells of Blood and Bone Marrow; Cancer Re-
search, 1: 196, 1941.
Blumenthal, H. T. : Transplantation of Spontaneous Tumors, Cancer Research,

2: 56, 1942.
Bodenstein, Dietrich : Pupation Hormone, Biol. Bullet., 84: 14 and 34, 1943.
Bohn, G. W. and C. M. Tucker: Immunity to Fusarium Wilt in the Tomato,

Science, 89: 603, 1939.
Bonnevie, Kristine : Skin Patterns and Race and Family Characteristics, Zeitsch.

f. ind. Abstammungs u. Vererbungslehre, 50: 219, 1929.
Bordet, J.: Hemolysins and Hemagglutinins, Ann. de lTnstit. Pasteur, 12: 688,

1898.
Borghi, B. : Effects of Injections of Homoiogenous and Heterogenous Leuco-
cytes, Krankheitsforsch., 8: 308, 1930.
Born, G. : Union of Amphibian Larvae, Arch. f. Entwicklgsmech., 4: 349 and

517, 1897.
Bornstein, A., Fr. Wohlwill u. K. Schorlitz: Transfusion with Heterogenous

Defibrinated Blood, Arch. Exp. Path. & Pharmac, 127: 253, 1928.
Borst, Max : Grafting of Normal Tissues, Brit. Med. J., p. 383, II, 1913.
Borst, Max : Transplantation, Vol. I in L. Aschoff's Textbook of Pathological

Anatomy, 7th edition, p. 656, Jena, 1928.
Borst, M. : Lack of Success in Homoio and Heterotransplantation. Report, XII

Internat. Med. Congress, London, Oxford Univ. Press, 1913.
Boyd, William C. : Cross Reactivity of Hemocyanins, Biol. Bullet., 73: 181,

1937.
Boyden, A. A.: Precipitin Reaction and Animal Relationship, Biol. Bullet., 50:

73, 1926; Proc. Soc. Exp. Biol. & Med., 29: 955, 1932.
Boyden, Alan: Serology and Biological Problems, Sigma Xi Quarterly, 24: 152,

1936.
Boyden, A. and J. G. Baier, Jr. : Precipitin Technique, J. Immunol. 17: 29, 1929.
Brahn, B. and F. Schiff: Complex Nature of Blood Group Substance, A. Klin.

Wochenschr., 5: 1455, 1926.
Braus, H. : Biochemical Reactions of Amphibian Larvae, Arch. f. Entwicklgs-
mech., 22: 564, 1906.
Breedis, E., T. Robertson, R. S. Osenkop and J. Furth : Sarcoma Formation

in Transplanted Lung Tumors in Mice, Cancer Research, 2: 116, 1942.
Breuhaus, H. C. and F. A. McJunkin: Effect of Macerated Kidney on Mitot.

Rate of Kidney Epithelium, Proc. Soc. Exp. Biol. & Med., 29: 894, 1932.
Browman, L. G. : Testicular Heterotransplantations in Rats and Mice, J. Exp.

Zool., 95 : 283, 1937.
Brown, J. B : Homoiotransplantation of Skin in Identical Twins, Surgery, 1 :

558, 1937; (with V. P. Blair) Transplantation of Skin to Defects Caused by

Burns, Surg. Gynec. & Obst., 60: 379, 1935.
Brown, F. A., Jr., and H. E. Ederstrom : Dual Control of Certain Black Chroma-

tophores of Crago, J. Exp, Zool., 85 ; 43, 1940.

BIBLIOGRAPHY 663

Brown, F. A., Jr., and Allison Meglitsch : Comparison of Chromatophorio-

trophic Activity of Insect Corpora Cardiaca with That of Crustacean Sinus

Gland, Biol. Bullet., 79: 409, 1940.
Bruck, Carl: Racial Differences in Human Blood, Berl. Klin. Wochschr., 44:

793, 1905.
Bruda, B. E. and H. Pfeiffer : Significance of Spleen and Reticuloendothelial

System for Immunity Against Transplanted Tumors in Parabiotic Rats.

Zeitschr. f. ges. exp. Medic, 68: 116, 554, 1929.
Bruda, B. E. : Significance of Reticuloendothelial System in Transplantation of

Tumors, Centralbl. allg. Pathol., 45: 409, 1929.
Buchbinder, L. : Blood Grouping of Macacus Rhesus, J. Immunol., 25 : 33, 1933.
Bullock, F. D. and G. L. Rohdenburg: Heterologous Tumor Grafts, J. Cancer

Research, 3: 31, 1918.
Bungeler, W. : Tumor Transplantation in Animals Which Are Under the In-
fluence of Colloidal Substances, Frankf. Zeitschr. f. Pathol., 35 : 67, 1927.
Burgess, A. N. : Reactions of Tissues of Susceptible and Non-Susceptible Mice

to an Inoculable Tumor, J. Med. Research, 16: 575, 1909.
Burns, E. L., F. H. Scharles and L. F. Aitken: Specific Adaptation in Inter-
action of Blood Serum and Tissue Extract, Am. J. Physiol., 97: 233, 1931.
Burns, R. K., Jr. : Parabiosis of Amphibian Larvae. Anat. Record, 31 : 30, 1923 ;

Transplantation of Larval Gonads in Urodele Amphibians, Anat. Record,

39: 177, 1928.
Burns, R. K., Jr., and L. M. Burns : Growth of Whole Organism and of Limbs

in Two Species of Amblystoma United in Parabiosis, J. Exp. Zool., 53 : 455,

1925.
Burr, H. S. and F. S. C. Northrop: Electrodynamic Fields of Living Organisms

(Individual specificity). Proc. Nat. Acad. Sc, 25: 284, 1939.
Bytinski-Salz, H. : Action of Xenoplastic Implants and Embryonal Extracts on

Amphibian Embryos, Arch. f. Entwicklgsmech., 114: 665, 1929.
Bytinski-Salz, H. : The Presumptive Gastrula Ectoderm in Hetero and Zeno-

transplantations in Amphibia, Arch. f. Entwicklgsmech., 114: 593, 1929.
Bytinski-Salz, H. : The Ability of the Posterior Areas of Medullary Plate to

Function as Organizer, Arch. f. Entwickglsmech., 123: 518, 1931.

Campbell: Psychiatry and General Practice, J. A.M. A., 112: 2577, 1939.

Cannon, P. R., R. B. Baer, F. L. Sullivan and I. E. Webster: Reticulo-
endothelial System and Formation of Antibodies. J. Immunol., 17: 441, 1929.

Cannon, P. R. : Antibodies and Protein Reserves, J. Immunol., 44: 107, 1942.

Carnot, P. et C. Deflandres: Transplantation of Pigmented Skin in Guinea
Pigs, C. R. Soc. Biol., 48: 178, 430, 1896.

Carrel, Alexis and C. C. Guthrie: Anastomoses of Blood Vessels and Trans-
plantation of Kidney, J.A.M.A., 47: 16 and 48, 1906. Amputation of Thigh
with Retransplantation, Am. J. Med. Sc, 81 : 297, 1906.

Carrel, Alexis : Double Nephrectomy and Reimplantation of a Kidney. Arch. f.
Klin. Chir., 88: 379, 1909.

Carrel, Alexis : Transplantation of Blood Vessels, Organs and Limbs, J.A.M.A.,
51: 1662, 1908; Remote Results of Retransplantation of Kidney and Spleen.
J. Exp. Med., 12: 146, 1910.

Casey, A. E. : Enhancement of Malignancy in Brown-Pearce Rabbit Tumor, Proc.
Soc Exp. Biol. & Med., 29: 816, 1932; A Species Limitation of an Enhanc-
ing Material Derived from a Mammalian Tumor, Proc. Soc Exp. Biol. &
Med., 30: 674, 1025, 1933.

Celakowsky, L. W. : Phagocytosis of Substances by Plasmodia of Myxomycetae.
Flora 76: 182, 1892 (Erganzgsband).

664 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Celler, H. L. and F. Hamburger: Specific Antibody Formation after Feeding
Protein, Wien. Klin. Wochschr., 18: 271, 1905.

Chambers, H., G. M. Scott and S. Russ: Action of X-rays upon Transplanta-
tion of Spontaneous Carcinoma of Rat, J. Path. & Bact, 23: 384, 1919-20.

Chambers, H. and G. M. Scott: Immunity to Jensen Rat Sarcoma J. Path. &
Bact, 35 : 283, 1932.

Chase, M. W. : Inheritance of Susceptibility to Skin Sensitization, J. Exp. Med.,
73: 7U, 1941.

Cheever, F. S. and H. R. Morgan: Intraocular Inoculation of Brown-Pearce
Carcinoma and Tumor Immunity, Cancer Research, 2: 675, 1942.

Child, C. M. : Senescence and Rejuvenescence, Univ. of Chicago Press, Chicago,
1915.

Christiani, R. : Thyroid Grafts, Arch, de Physiol., 7: 65, 1895. Grafts of Excess
Thyroid Tissue, C. R. Soc. Biol., 52: 1136, 1900; 58: 361, 1905; J. de Physiol,
et de Pathol, generale, 3: 200, 1901; Vitality of Tissues Separated from the
Body, C. R. Soc. Biol., 55: 828, 1903; Compensatory Hypertrophy of Thy-
roid Grafts, C. R. Soc. Biol., 55: 782, 1903; Thyroid Grafts in Birds, C. R.
Soc. Biol., 56: 192, 1904; Thyroid Grafts in Fishes and Amphibia, C. R. Soc.
Biol., 56: 227, 1904; Heterotransplantation of Thyroid, J. de Physiol, et de
Pathol, generale, 6 : 476, 1904.

Christiani, H. and A. Christiani : Effect of Age on Transplantation of Thy-
roid: C. R. Soc. Biol., 58: 531, 1905; Persistence of Homoiotransplants of
Parathyroid, C. R. Soc. Biol., 92: 1278, 1925.

Claude, Albert: Constitution of Protoplasm, Science, 94: 451, 1943.

Clemmensen, John: Transplantation of Tumor Cells to Normal and Preirradi-
ated Heterologous Organisms, Am. J. Cancer, 29: 313, 1937.

Cloudman, A. M. : Genetic Analysis of Carcinomata Developing in the Same
Gland of an Individual Mouse, Genetics, 17: 468, 1932.

Cloudman, A. M. : Effect of Parabiosis on Transplantation of a Hepatoma in
Inbred Strains of Mice, Cancer Research, 3: 27, 1943.

Cloudman, A. M. : Parabiosis and Transplantation of Tumors, Cancer Research,
3: 47, 1943.

Coca, A. F. : Atopy, p. 1004 in The Newer Knowledge of Bacteriology and Im-
munity by E. O. Jordan and I. S. Falk, Univ. of Chicago Press, 1928.

Cohen-Kysper, A. : Significance of Genes for Determination and Development,
Naturwissensch., 21: 229, 1933.

Cole, Leo J.: Each After His Kind, Science, 93: 289, 316, 1941.

Cole, W. H. : Transplantation of Skin in Frog Tadpoles, J. Exp. Zool., 35 : 353,
1922.

Collins, H. H. and E. F. Adolph : Skin Pattern in Urodele Amphibia, J. Morphol.,
42: 473, 1926.

Coman, D. R. : Human Neoplasms in Tissue Culture, Cancer Research, 2: 618,
1942.

Copher, G. H. and J. A. Key: Transplantation of Bladder and Bone Formation,
Arch. Surg., 29: 64, 1934.

Coonfield, B. R. and A. Golden: Physiological gradient in Mnemiopsis during
regeneration (Organ differentials), Biol. Bullet., 73: 197, 1937.

Cori, C. F. : Action of Hormones as Cause of Cancer, J. Exp. Med., 45 : 983,
1927.

Cornman, Ivor: Susceptibility of Colchicum to Colchicine, Bot. Gazette, 50:
104, 1942.

Correns, C. : Self Sterility and Individual Substances, Biol. Centralblatt, 33: 389,
1913.

Correns, C. : Individuality and Individual Substances, Naturwissenschaften, 4:
183, 193 and 210, 1916.

BIBLIOGRAPHY 665

Correns, C. : Non-Mendelian Heredity, Verhandl. d. V. Internat. Congress f.

Vererbungswissensch. Berlin, 1927, vol. I. Leipzig, 1928.
Corson-White, E. P. and Leo Loeb: Effect of Physical Injuries on Growth of

Tumor Cells, Centralbl. Bakt. 56: 325, 1910. Transplantation of Stationary

and Retrogressing Tumors, Centralbl. f. Bakt., 56: 488, 1910.
Cosak, G. : Defense Powers against Infections in Young Nurslings, Jahrbuch f.

Kinderheilkunde, 149: 53, 1937.
Crampton, H. E. : Transplantation of Portions of Pupae of Lepidoptera, Arch. f.

Entwicklgsmech., 9: 293, 1900.
Crossen, R. J. : Homoiotoxins and Lymphocytes in Guinea Pig, Arch. Pathol.,

6: 396, 1928.

D

Dakin, H. D. and H. H. Dale: Crystalline Egg Albumens of Hen and Duck,
Bioch. J., 13: 248, 1919.

Dale, H. H. and P. Hartley : Anaphylaxis to Proteins of Horse Serum, Biochem.
J., 10: 408, 1916.

Danchakoff, Vera and V. E. Danchakoff: The Age Factor in Grafts; Trans-
plantation of Embryonic and Adult Spleen of Amphibia into Tail of Tadpoles.
Contributions to Embryology, Carnegie Instit. of Washington, 21 : 127, 1930.

Danchakoff, V. and S. M. Leiden: Digestive Activity of Mesenchyme, Biol.
Bullet., 43 : 97, 1922.

Danchakoff, Vera : Mesenchymal Activity, a Factor in Resistance Against Mouse
Sarcoma in Chick, Proc. Soc. Exp. Biol. & Med., 16: 67, 1919.

Danchakoff, Vera: Grafts of Adult Spleen on Allantois, Am. J. Anat, 24: 127,
1918.

Danforth, C. H. and F. Foster: Endocrine and Genetic Factors in Skin Trans-
plantation in Fowl, Proc. Soc. Exp. Biol. & Med., 25: 75, 1927: J. Exp. Zool.,
52: 443, 1929.

Dannheiser, F. : Parabiosis (blood and urine), Beitr. z. Klin. Chir., 145: 304,
1928-29.

Davis, J. S. : Skin Transplantation, Johns Hopkins Hospital Reports, 15: 307,
1910.

Davis, J. S. : Skin Grafts and Blood Groups, Annals of Surgery, 66: 89, 1917.

Davis, Hallowell: Electric Phenomena of Brain and Spinal Cord, Annual Rev.
Physiol., 1 : 345, 1939.

Dawson, A. B. : Transplantation of Skin in Necturus, J. Morphol., 34: 487, 1920.

Dawson, A. B. : Degree of Differentiation of Mature Erythrocytes of Vertebrates
(Species specificity), Collecting Net, 7: 117, 1932.

Dawson, A. J. : Bacterial Variations Induced by Changes in Composition of Cul-
ture Media, J. Bacteriol., 4: 132, 1919.

Dederer, C. : Homoiotransplantation of Kidney and Ovary (by blood vessel
anastomosis), Surg., Gynec. & Obst., 31: 45, 1920.

Defalco, R. I. : Serological Tests for Avian Organismal Differentials, Biol.
Bullet., 83: 205, 1942.

Demoll, R. : Injuriousness of Inbreeding, its Nature and Treatment, Zool. Jahr-
bucher, Abt. f. Physiol, u. Zoolog., 39: 443, 1923.

Dervieux, M. : Individual and Species Specific Precipitin Reactions against Hu-
man Sperm. C. R. Acad. d. Sci., 172: 1384, 1921.

Detwiler, S. R. : Transplantation of Limbs in Amblystoma, Formation of Nerve
Plexuses, J. Exp. Zool., 31: 117, 1920; 35: 115, 1922; 57: 183, 1930.

Deucher, W. G. and A. E. W. Ochsner: Skin Grafting and Blood Groups, Arch,
f. Klin. Chir., 132: 470, 1924.

Van Deventer, I. K. and T. Reich : Antihuman Fibrinolytic Streptococci, Proc.
Soc. Exp. Biol. & Med., 31 : 821, 1934.

666 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Van Deventer, I. K. : Fibrinolysin of Streptococci and Specific Adaptation, Proc.

Soc. Exp. Biol. & Med., 32: 50, 366, 1934; 32: 1117, 1935.
Dmochowski, L. : Serological Specificity of Experimental Tumors, Am. J. Can-
cer, 37: 252: 1939.
Dobrzaniecki, W. : Homoiotransplantation and Blood Groups, Ann. Surg., 90 :

926, 1929.
Dobzhansky, Theodosius : Biological Adaptations Scientific Monthly, p. 391,

November 1942.
Doerr, R. and W. Berger: Immunological Analysis of Serum Protein, Zeitschr.

f. Hygiene, 96: 191, 1932.
Domm, L. V.: Testes Grafts in Ovariectomized Fowl, Anat. Record, 44: 204,

1930.
Driesch, H. : Fusion of two blastulae of Echinus, Arch. f. Entwicklgsmech., 10:

411, 1900.
Durken, B. : Introduction in Experimental Zoology, Transplantation, p. 227, Ber-
lin, 1919.
Durken, B. : Interplantation of Embryonal Cells, Arch. f. Entwicklgsmech., 107:

727, 1926.
Dyke, S. C. : Skin Grafts and Blood Groups, Lancet, p. 579, 1922.
Dltschl, L. and B. Niekau: Blood Vessel Communication in Parabiotic Rats,

D. Zeitsch. f. Chir., 186: 76, 1924.

E

Eden, Rudolf: Skin Grafting and Blood Groups, D. Med. Wochschr., p. 85, 1922.
Edwards, J. E., H. B. Andervont and A. J. Dalton : Transplantation of Malig-
nant Hemangioendothelioma of Liver in Mouse, J. Nat. Cancer Inst., 2:

479, 1942.
Ehrenpreis, Alfred: Transplantation of Spleen in Urodeles, Arch. f. Mikr.

Anat., 102: 573, 1924.
Ehrhart, Albert: Immune Reactions and Phylogenesis in Zoology, Zeitschr. f.

Imm. forsch., 60: 156, 1929.
Ehrich, W. E. and Harris, T. N. : Seat of Production of Immune Substances,

J. Exp. Med., 76: 335, 1942.
Ehrlich, P. and J. Morgenroth : Isohemolysins in Goats, Berl. Klin. Woch., 37:

453, 1900.
Ehrlich, P. : Immunization against Transplants of Cancerous Tissues by Inocu-
lation of Normal Tissues, Zeitschr. f. arztl. Fortbild., 3: 211, 1906; Arb.

a. d. Inst. f. Exper. Therap. z. Frankfurt, 1 : 77, 1906.
von Eiselberg, A.: Transplantation of Skin, Wien. Klin. Woch., 666, 1889.
Eisen, M. J. : Constancy of Transplanted Mammary Carcinoma in Inbred Rats,

Cancer Research, 2: 488, 1942.
Eisler, M. : Antigen Common to Human Cells and to Shiga Bacillus, Zeitschr.

f. Imm. forsch., 65 : 38, 1930.
Ekman, G. : Transplantation of Ectoderm of Gills in Anuran Amphibians,

Morphol. Jahrbuch, 47: 419 and 576, 1913.
Elson, J. : Auto and Homoiotransplantation of Cross Striated Muscle Tissue in

the Rat, Am. J. Pathol., 5 : 425, 1929.
Enderlen, u. M. Borst: Blood Vessel and Organ Transplantation, Verh. d.

deutsch. Path. Gesellsch. 13, 1909; Munch. Med. Wochenschr., 57: 1865,

1910.
Ephrussi, B. and G. W. Beadle: Transplantation of Organs in Drosophila (gene

hormones), C.R. Acad. Sci., 98: 1935.
Erdmann, Rhoda: Explantation and Relationship, Zeitschr. f. indukt. Abstam-

mungs und Vererbungslehre, 30: 301, 1923.

BIBLIOGRAPHY 667

Erdmann, Rhoda : Relationship of Anuran Families Tested by Means of Im-
plantation Experiments of Skin Grown in Tissue Culture, Arch. f. Ent-
wicklgsmech., 112: 739, 1927.

Ericks-Aensel, I. B. and The Svedberg: Molecular Weights and P. H. Sta-
bility Regions of Hemocyanins, Biol. Bullet., 71 : 498, 1936.

Ermatinger, L., F. B. Queen and R. F. Parker: Fate of Skin Bacteria after
Autogenous and Heterogenous Transplantation of Skin, Proc. Soc. Exp.
Biol. & Med., 26: 113, 1928.

Ernst, Max: Hormonal Growth of Mammary Gland in Parabiotic Rats, D.
Zeitschr. f. Chir., 202: 231, 1927.

Eysh, W. H.: Selfsterility in Plants, Science, 94: 144, 1941.

Famulener, L. W. : Transmission of Immunity (serum hemolysins) from Mother

to Offspring in Goats, J. Inf. Diseases, 10: 332, 1912.
Faure-Fremiet, M. E. : Experimental Involution and Tissue Structure of

Sponges, Arch, d'anat. microscop., 27: 421, 1931; 28: 121, 1932.
Fels, Erich : Effect of Parabiosis on Internal Secretion, Med. Klin., 25 : 557,

1929.
Ferguson, L. C, Clyde Stormont and M. R. Irwin : Antigens in Erythrocytes

of Cattle, J. Immunol., 44: 147, 1942.
Fichera, M. G. : Immunization by Means of Embryonal and Fetal Grafts, Arch.

d. Medec. Exp. et d'anat. pathol., 21 : 617, 1909.
Fick, R. : tiber d. Vererbungssubstanz, Arch. f. Anat. u. Physiol. (Anat. Abt.)

p. 101, 1907.
Filatow, D. : Lens Formation in Rana Esculenta from Transplanted Epithelium

of Bufo., Arch. f. Entwicklgsmech., 106: 475, 1925. Transplantation of Epi-
thelium and Mesenchyme of Extremity Bud in Embryos of Axolotl., Arch. f.

Entwicklgsmech., 113: 240, 1928.
Finkler, W. : Transplantation of Head in Insects, Arch. f. mikr. Anat. u.

Entwicklgsmech., 99: 104, 119, 126, 1923.
Fischer, A.: Interaction of Two Fragments of Pulsating Heart Tissue, J. Exp.

Med., 39: 577, 1924.
Fischer, H. : Regeneration and Transplantation of Pancreas in Amphibia, Arch.

mikr. Anat., 77: 1, 1911.
Fischer, Heinrich : Attempts to Influence Homoiotransplantation in Animals,

Arch. f. Klin. Chir., 156: 224, 1929.
Fischer, O. : Paroxysmal Hemoglobinuria, Klin. Wochschr., 7: 2061, 1928.
Fitzgerald, J. G. : Racial Differences in Human Blood, J. Med. Res., 21 : 41, 1909.
Flanders, S. E. : The Role of Arrhenotoky in the Adaptation of Insects, Science,

90: 82, 1939.
Fleisher, M. S. and Leo Loeb: Transplantation of Tumors in Animals with

Spontaneous Tumors, Surg., Gynec. & Obst., 17: 203, 1913; J. Med. Res.,

34: 1, 1916; J. Cancer Research 1: 331, 1916.
Fleisher, M. S., Miguel Vera and Leo Loeb: Immunization against Actions

of Substances Inhibiting Tumor Growth, J. Exp. Med., 20: 522, 1914.
Fleisher, M. S. and Leo Loeb: Heredity Transmission of Differences in Sus-
ceptibility to Growth of Transplanted Tumors in Various Strains of Mice,

J. Cancer Res., 1: 331, 1916.
Fleisher, M. S. : Variations in Percentage of Takes and Growth Energy of

Transplanted Tumors, Zeitschr. f. Krebsforsch., 14: 8, 1914.
Fleisher, M. S. : Relationship of Various Antiorganic Sera, J. Immunol., 7: 51,

1922.

668 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Fleisher, M. S. and N. Arnstein : Specificity of Antiorganic Sera, J. Immu-
nology: 6: 222, 1921.

Fleisher, M. S.: Reaction about Heterogenous Transplants, J. Med. Res., 37:
483, 1918. Influence of Immune Serum upon Reaction about Transplanted
Tissues, J. Med. Res., 39: 1, 1918. Leucocytic and Fibroblastic Reactions
about Transplanted Tissues, J. Med. Res., 42: 163, 1921. Heterotransplanta-
tion of Lens and Cornea, J. Med. Res. 42: 491, 1921. Autotransplantation
and Homoiotransplantation of Cornea, Iris, and Lens, J. Med. Res., 42: 173,
1921. Immunity in Relation to Transplanted Tissue, J. Med. Res., 43: 145,
1922.

Fleisher, M. S., E. P. Corson-White and Leo Loeb: Quantitative Investigations
on Immunity against Tumors in Mice, Centralbl. f. Bakt., 63 : 450, 1912.

Forssman, J. : Problems of Immunity and Heterogenetic Antigens, Wiener Klin.
Wochenschr., 42: 669, 1929.

Frank, J. A.: Sperm Extracts and Fertilization, Biol. Bullet., 76: 190, 1939.

Freeman, W., and I. W. Watts: Functions of Frontal Lobe, Yale. J. Biol. &
Med., 11: 527, 1939.

Freeman, N. E. and A. E. Schechter: Specific Adaptation of Dog Serum,
Science, 96: 29, 1942.

Frei, W., H. Biberstein, and H. Frohlich : Sensitization of Skin and Rela-
tionship in Animals, Klin. Woch., 6: 71, 1928.

Freund, E. and G. Kaminer : Biochemische Grundlagen der Krebsdisposition.
Wien, 1928.

Freund, Jules: Age and Antibody Formation, J. Immunol., 18: 315, 1931. Age
and Skin Reactions against Pneumococci, J. Exp. Med., 54: 171, 1931.

Friedenreich, V. : Heredity of Human Blood Group Factors, Hospitals tidende.,
81 : 293, 1938, Abst. in. J. A.M. A., Ill : 760, 1938.

Friedenthal, H. : Production of Specific Precipitins with Blood of Mammoth,
D. Med. Woch., 30: 901, 1904.

von Frisch, R. : Psychology of Fish Clusters, Naturwissenschaft., 26: 601, 1938.

Fruton, J. S. and Max Bergmann: The Specificity of Pepsin Action, Science,
87: 557, 1938.

Fuchs, H. I. and collaborators : Tumor Specific Antigens and Antibodies in the
Blood of Cancer Patients, Z. f. Imm. forsch., 80: 420, 1933; 78: 272, 1933;
80: 233, 1933. Diagnostic Methods for Cancer, Munch. Med. Woch. No. 43,
p. 1711, 1932.

Galtsoff, P. S. : Amoeboid Movement, Regeneration and Agglutination of Dis-
sociated Sponge Cells, Biol. Bullet, 45: 153, 1923; J. Exp. Zool., 42: 183,
1925; Biol. Bullet, 57: 250, 1929 (with V. Pertzoff) ; J. Gen. Physiol., 10:
239, 1926-27.

Gargano, C. : Transplantation of Selachian Embryos, Arch. Ital. de Biologic,
63: 398, 1915.

Gassul, R. : Homoiotransplantation of Explanted Adult Frog Skin, D. Med.
Woch. 35: 1163, 1922; Arch. f. Entwicklgsmech. 52: 400, 1923.

Gates, Ruggles, R. : Process of Organic Evolution, Science 93: 335, 1941.

Gebhardt, H. : Regeneration and Transplantation in Planarians, Arch. f. Ent-
wicklgsmech. 107: 684, 1926.

Geinitz, B. : Embryonal Transplantation between Urodeles and Anurans, Arch,
f. Entwicklgsmech. 106: 357, 1925.

Gerard, R. W. : Higher Levels of Integration, Science 95: 309, 1942.

Gey, G. O. : Tissue Cultures of Endocrine Organs and their Transplantation,
Anat Record, 70: 1937-38 (Supplement).

BIBLIOGRAPHY 669

Giard, Alfred: Antagonism between Transplantation and Regeneration, C. R.
Soc. Biol. 3: 180, 1896.

Gier, H. T. : Morphology and Behavior of Intracellular Bacteriods of Roaches,
Biol. Bullet. 71 : 433, 1936.

Gilman, L. C: Mating Types in Paramecium, Biol. Bullet. 80: 384, 1941.

Glaser, Otto: Fertilization and Egg Secretions, Biol. Bullet. 41: 63, 1921.

Glaser, R. W. : Fungi as Intracellular Symbionts in Insects (Mycetocytes and
Mycetomas) ; the Relation of these Symbionts to Rickettsia, Arch. Path.
9: 71 and 557, 1930.

Godlewski, E. : Stimulation and Inhibition of Regeneration in Axolotl, Arch. f.
Entwicklgsmech. 64: 108, 1928.

Goebel, W. F. : Hydrolytic Products of Specific Carbohydrate from Friedlander
Bacillus, J. Biol. Chem. 74: 619, 1927.

Goebel, W. F. and O. T. Avery: Chemo-immunol. Studies in Conjugated Carbo-
hydrate-Protein, J. Exp. Med. 50: 521, and 533, 1929.

Goebel, W. F. : Saccharide Containing Antigen in Immunity Against Pneumo-
cocci, Science, 91: 20, 1940.

Goetsch, W. : Regeneration and Transplantation in Planarians, Arch. f. Ent-
wicklgsmech. 49: 359, 1921.

Goetsch, W. : Animal Chimaerae and Artificial Individualities, Naturwissen-
schaften 11: 327, 1923.

Goetsch, W. : Chimaerae in Coelenterates, Zool. Anzeig. 56 : 289, 1923.

Goetsch, W. : Reproduction in Animal Chimaerae, Zeitsch. f. ind. Abstammgs.
u. Vererbgslehre 33: 294, 1924.

Gohrbandt, E. : Transplantation of Homoiogenous Skin in Parabiotic Animals,
Arch. f. Klin. Chir. 139: 471, 1926.

Golanitzky, I.: Transplantation in Animals in Which Dyes had been Injected,
Centralbl. f. allg. Pathologie 24: 809, 1913.

Goldfarb, A. J. : Experimentally Fused Larvae of Echinoderms, Arch. f. Ent-
wicklgsmech. 41 : 579, 1915.

Goldner, Jacques et I. Frasin : Intraocular Transplantation and Retransplanta-
tion of Thyroid in Rabbits, C. R. Soc. Biol. 125 : 210, 1937.

Goldschmidt, R. : Some Aspects of Evolution, Science 78: 539, 1933.

Gonzalez, P., M. Armanque and F. Morato : Use of Absorbents in Immuniza-
tion with Lipoids, C. R. Soc. Biol. 110: 216, 1932.

Goodman, Leroy: Transplantation of Ovaries into Anterior Chamber of Eye
of Adult Male Rats, Anat, Record 59 : 223, 1934.

Goodpasture, E. W. : Virus Infections of Tissues Transplanted on Chorioallantois
of Chick Embryo, Science 95 : 391, 1942.

Gorer, P. A. : Genetic and Antigenic Basis of Tumor Transplantation, J. Path. &
Bact. 44: 691, 1937; 47: 231, 1938.

Gortner, R. A. : Biochemistry and the Problem of Organic Evolution, Scientific
Monthly 30: 416, 1930. '

Goto, N. : Internal Secretion of Ovary in Parabiosis, Arch. Exp. Path. &
Pharmac. 94: 124, 1922.

Gottschaldt, K. : Urnwelterscheinungen im Erbpsychologischen Bild. Natur-
wissenschaften. 25: 431, 1937.

Graefenberg, E. and I. Thies: Effect of Fetal Guinea Pig Serum on Normal
and Pregnant Guinea Pigs; Difference in Toxicity Between Serum of New-
born and Older Individuals, Zeitschr. f. Imm. forsch. 9: 749, 1911.

Graefenberg: Toxic Effects of Transplantation of Testicle in Rabbits, D. Med.
Woch. No. 7: 331, 1911.

Grauer, R. C. and G. H. Robinson : Lactation in Benign mam. Adenoma in
Rats, Am. J. Cancer 16: 191, 1932.

Grave, Caswell: Metamorphosis in Ascidians, Collecting Net 12: No. 8, 1937.

670 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Graves, W. W. : Organ Specificity of Scapula; its Age Incidence, Am. J.
Psychiatry 93: 1109, 1937.

Green, C. V.: Size Inheritance and Growth in Cross of Mouse (Heterosis),
J. Exp. Zool. 59: 213, 247, 1931.

Green, R. G. : Nature of Virus Adaptation, Science 95: 602, 1942.

Greene, H. S. N. : Heterologous Transplantation of Human and Other Tumors
in Anterior Chamber of Eye of Guinea Pigs, Science 88: 357, 1938; Cancer
Research 2: 649, 1942.

Greene, H. S. N. : Immunity Against Tumors Transplanted into Anterior Cham-
ber of Eye and into Testicle, Cancer Research 2: 669, 1942.

Gregoire, Ch. : Lymphocytic-epithelial Symbiosis in Thymus, Extrait des Ar-
chives d. Biol. 46: 717, 1935.

Gregory, P. W. and W. E. Castle: Size Inheritance in Rabbit, J. Exp. Zool. 59:
199, 1931.

Griffith, Fred: Types of Pneumococci, J. of Hyg. 27: 113, 1928.

Gross, Ludwik : Specific Immunity to Transplantable Neoplasm, Am. J. Cancer
31 : 609, 1937. Spontaneous Recovery from Transplanted Sarcoma in Sexually
Immature Mice, Cancer Research 2: 571, 1942. Intradermal Immunization of
C3H Mice Against a Sarcoma that Originated in an Animal of the Same
Line, Cancer Research 3: 326, 1943.

Gruneberg, H. : Inheritance of Human Skin Patterns, Zeitsch. f. ind. Abstammgs
und Vererbgslehre 46: 285, 1928.

Guerriero, C. : Action of Hormones on Transplanted Uterus: C. R. Soc. Biol.
103 : 719, 1930.

Guyer, M. F. : Testes of Hybrids from Guinea Hen and Common Fowl, J. Morphol.
23 : 45, 1912.

Gyorgy, P. and E. Witebsky: Transfusion of Blood from Identical Blood Group
and Anaphylaxis, Munch. Med. Wochschr. 76: 195, 1929.

H

de Haan, J. A. Bierens: Homoiogenous and Heterogenous Union of Eggs and

Early Embryonic Stages in Echinids, Arch. f. Entwicklgsmech. 36: 473, 1913;

37:420,1913.
von Haberer: Transplantation of Adrenal Gland, Arch. f. Klin. Chir. 86: 399,

1908; 94: 606, 1911.
Haddow, Alexander: Erythrocyte Individuality and Transplantation of Fowl

Sarcoma, J. Path. & Bact. 39: 345, 1934.
Hadley, C. E. : Compatibility of Skin of Rana Pipiens and Rana Clamitans as

Tested by Transplantation, J. Exp. Zool. 54: 127, 1929.
Hadorn, E. : Ring Gland in Drosophila, Proc. Nat. Acad. Sci. 23: 478, 1937.
Hadorn, E. and James Neel: Effects of Hormone of Ring Gland on Pupation in

Drosophila, Proc. Nat. Acad. Sci. 23: 478, 1937; Arch. f. Entwicklgsmech.

138:281, 1938.
Haeckel, E. : Allgem. Entwicklgsgeschichte der Organismen, 1866.
Haecker, V. : Individual Biochemical Differences, in "Allgemeine Vererbungs-

lehre," 1911,p.23ff.
Halsted, W. S. : Auto and Homoiotransplantation of Parathyroid in Dogs, J. Exp.

Med. 11: 175, 1909.
Hamburger, Fr. Arteigenheit und Assimilation, Leipzig u. Wien 1903.
Hamburger, Fr. : Assimilation of and Immunization against Proteins, Wiener

Klin. Woch. 14: 1202, 1901; 15: 1188, 1902; (with B. Speck) 17: 641, 1904;

Species Differences, Digestive Changes and Assimilation of Proteins, Wien.

Klin. Woch. 26: 1948, 1913.
Hammond, J. Uterine Grafts, Brit. J. Exp. Biol. 4: 349, 1926-27.

BIBLIOGRAPHY 671

von Hansemann, D. : Relations between Hybridization and Transplantation,
Arch. f. Entwicklgsmech. 42: 126, 1916.

Harde, E. : Intracerebral Transplants of Tumors, Annales de l'Instit. Pasteur,
42: 1259, 1928.

Harms, W. : Transplantation of Ovaries in Lumbricidae, Arch. f. Entwicklgs-
mech. 34: 90, 1912; in Tritons, Arch. f. Entwicklgsmech. 35: 748, 1913.

Harms, W. : Transplantation of Thumb Pad in Rana, Zool. Anzeiger, 39: 145,
1912.

Harms, W. : Transplantation of Ovaries into Different Species in Triton, Zool.
Anzeiger 37: 225, 1911; Arch. f. Entwicklgsmech. 35: 748, 1912-13.

Harrison, R. G. : Embryonic Transplantation and Development of Nervous Sys-
tem, Anat. Rec. 2: 385, 1908.

Harrison, R. G. : Growth and Regeneration of Tail of Frog Larvae, Arch. f.
Entwicklgsmech. 7: 430, 1898.

Harrison, R. G. : Transplantation of Limbs and the Development of Nerves, J.
Exp. Zool. 4: 239, 1907; Proc. Nat. Acad. Sci. 1: 539, 1915.

Harrison, R. G. : Heteroplastic Transplantation of Limbs, Proc. Nat. Acad. Sci.
10: 69, 1924. Heterotransplantation of Eye in Amblystoma, Anat. Record.
31 : 299, 1925.

Harrison, R. G. : Relations of Symmetry in Transplanted Limbs, J. Exp. Zool.
32: 1, 1921.

Harrison, R. G. : Development and Growth of Eye Studied by Means of Hetero-
plastic Transplantation, Arch. f. Entwicklgsmech. 120: 1, 1929.

Harrison, R. G. : Development of Balancer in Amblystoma J. Exp. Zool. 41 : 349,
1925.

Harrison, R. G. : Organizer Action, Science 85 : 373, 1937.

Harrison, R. G. : Symmetry in the Developing Embryo, Collecting Net, 11: 217,
1936.

Harvey, E. B. : Parthenogenetic Merogony, Biol. Bullet., 71 : 101, 1936.

Harvey, E. B. : Crossfertilization in Echinoderms, Collecting Net, p. 118, 1932;
Science, 94:90, 1941.

Harvey, E. N. : Specificity of Luciferin and Luciferase, J. Gen. Physiol. 4: 285,
1922.

Haterius, H. O., M. M. Schweizer and H. H. Charipper: Persistence of Hypo-
physeal Transplants in the Eye, Endocrinol. 19: 673, 1935.

Haurowitz, F., K. Sarafran and Paula Schwerin : Antigenic Properties of Sub-
stituted Serum Globulins, J. Immunology 40: 391, 1941.

Hazen, E. L. : Incitants of Human Botulism; Specificity of Toxins and Species
Differentials, Science 87: 413, 1938.

Hedin, S. G. : Specific Inhibition of Action of Rennet, Zeitschr. f. Physiol.
Chemie 63: 143, 1909; 74: 242, 1911; Immunization against Rennet of Calf,
Zeitschr. f. physiol. Chem. 77: 229, 1912.

Hediger, H. : Psychological Investigations in Circus, Naturwissenschaften 26:
242, 1938.

Hediger, H. : The Significance of Flight in the Life of Animals, Naturwissen-
schaften 25 : 185, 1937.

Heidelberger, M. and F. E. Kendall : Protein Fractions in Streptococcus Hemo-
lyticus, J. Exp. Med. 54: 515, 1931. Polysaccharides of Pneumococci, J. Exp.
Med. 53:625, 1931.

Heidelberger, M. and K. Landsteiner: Antigenic Properties of Hemoglobin,
j. Exp. Med. 38:561,1923.

Heidelberger, M., W. F. Goebel and O. T. Avery: Polysaccharides in Fried-
lander Bacilli, J. Exp. Med. 42: 701 and 709, 1925.

Heidelberger, M. and W. F. Goebel: Hydrolytic Products of Specific Poly-
saccharides of Pneumococci, J. Biol. Chem. 74: 613, 1927.

672 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Heidelberger, Michael: Structure of Natural and Synthetic Antigens, Science

84:498, 1936.
Hektoen, L. and W. H. Welker: Precipitin Reactions of Serum Proteins, J.

Inf. Dis. 35 : 295, 1924.
Hektoen, L., H. Fox and K. Schulhof: Precipitin Reaction of Thyroglobulin,

J. Inf. Dis. 40: 641, 1927.
Hektoen, L : Precipitin Test for Human Serum, J. A.M. A. 78: 704, 1922.
Hektoen, L., and A. G. Cole: Precipitin Reaction of Egg Albumin and Fowl

Blood Protein, J. Inf. Dis. 40: 647, 1927; Protein of Egg White, J. Inf. Dis.

42:1,1928.
Hektoen, L. and W. H. Welker: Precipitin Reaction of Fibrinogen, J. Inf.

Dis. 40: 706, 1927; J.A.M.A. 85: 434, 1925.
Hektoen, L. and K. Schulhof: Lens Precipitins (alpha and beta crystallins),

J. Inf. Dis. 35 : 433, 1924.
Hektoen, L. : Precipitin Reaction of Lens, J. Inf. Dis. 31 : 72 1922.
Hektoen, L. and K. Schulhof: Erythroprecipitins, J. Inf. Dis. 33: 224, 1923.
Hektoen, L. and W. H. Welker: Precipitin Reaction of Bence-Jones Protein,

J. Inf. Dis. 34: 440, 1924.
Hektoen, L., F. S. Robscheit-Robbins and G. H. Whipple: Precipitin Reaction

of Muscle Hemoglobin, J. Inf. Dis. 42: 31, 1928.
Heller: Transplantation of Parts of Joints, Arch. f. Klin. Chir. 104: 845, 1914.
Henle, Werner: Specificity of Mammal. Spermatozoa, J. Immunol. 34: 325, 1938.
Henle, W., Gertrude Henle, and L. A. Chambers: Head and Tail Specific

Fractions of Spermatozoa, J. Exp. Med. 68: 335, 1938.
Henle, Werner and Leslie A. Chambers: Serological Specificity of Heavy

Particles from Normal Organs, Science 92: 313, 1940.
Henshaw, P. S.: Autogenous Antigens Produced in Skin Exposed to Radiation,

Physiol. Zool. 2: 168,1929.
Hermannsdorfer, A.: Toxic Effects in Parabiotic Rats, D. Zeitschr. f. Chir. 178:

289, 1923.
Herrick, C. J.: Evolution of Cerebral Localization Pattern, Science 78: 439,

1933.
Herrick, E. H. : Skin Grafts and Cell Movements in Frog Tadpoles, Biol. Bullet.

63:271,1932.
Hertwig, O. : Vegetative Affinity and Species Specificity of Cells and Tissues,

in "D. Zellen and Gewebe," Jena, 1898 and Hertwig, O. und G. Allgemeine

Biologie, Jena, 1923.
Heston, W. E. : Parasites, in "Biology of Laboratory Mouse," Philadelphia, 1941.
Hesselberg, Cora: Auto and Homoiotransplantation of Thyroid in Guinea Pig,

J. Exp. Med. 21 : 164, 1915.
Hesselberg, Cora, William Kerwin and Leo Loeb: Auto and Homoiotrans-
plantation of Uterus in Guinea Pig, J. Med. Research 38: 11, 1918.
Hesselberg, Cora and Leo Loeb : Successive Transplantations of Thyroid Tissue,

J. Med. Res. 38 : 33, 1918.
Hicks, R. A. and C. C. Little: Blood Relationships of Four Strains of Mice,

Genetics, 16:397, 1931.
Hinschberger, G. : Reaction of Homoiotransplants of Thyroid Gland in Guinea

Pigs to anterior Pituitary Gland, C.R. Soc. Biol. 106: 234, 1931.
Hirschler, Jan : Serological Differences between Larval and Adult Tissues in

Amphibia, Biol. Zentralblatt, 42: 303, 1922.
Hirszfeld, Ludwig: Inheritance of Blood Groups, Klin. Woch. 10: 1910, 1931.
Hirszfeld, L. and W. Halber : Differences and Relationships of Blood Groups in

Man and Animals, C. R. Soc. Biol. 99: 1166, 1928.
Hirszfeld, L. and W. Halber: Relations between Group Specific Structures in

Man and Animals, Zeitschr. f. Imm. forsch. 59: 17, 1928.

BIBLIOGRAPHY 673

Hirszfeld, L., W. Halber and J. Rosenblatt: Reactions of Human Embryonal
Extracts with Anticancer Immune Serum, Serum of Carcinoma Patients,
and Serum of Pregnant Women, Zeitschr. f. Imm. forsch. 74: 209, 1932.

Hirszfeld, L. and W. Halber: Complement Fixing Antibodies against Extracts
of Cancer Tissue with Serum of Cancer Patients and Pregnant Women,
Zeitschr. f. Imm. forsch. 67: 286, 1930.

Hirszfeld, L. : Immunity and Serological Maturation of Cells, Klin. Woch. schr.
10: 1931.

Hirszfeld, L., W. Halber and J. Laskowski: Serological Specificity of Cancer
Cells, Klin. Woch. 8: 1563, 1929.

Hitchcock, H. B. : Amphibian Skin after Transplantation into Lymphsac (tissue
culture in vivo) and in Tissue Culture (in vitro), J. Exp. Zool. 81 : 299, 1939.

Hoffmeistek, W. : Homoiogenous and Heterogenous Transplantation of Organs,
D. Zeitschr. f. Chirurg. 207: 1, 1928.

Hofmann, K. and Max Bergmann: Enzyme Specificity (Heterotrypsin), Sci-
ence, 89: 86, 1939.

Holman, Emile: Skin Grafting and Protein Sensitization, Surgery, Gynec. and
Obstetrics, 38: 100, 1924.

Holtfreter, J;: Character of Inductor Substances, Naturwissenschaften, 20: 973,
1932; 21: 766, 1033.

Holtfreter, J. : Organizer Action of Combination of Entomesoderm and Ecto-
derm, Biol. Zentralbl. 53 : 404, 1933.

Holtfreter, J. : Induction by Dead Embryonic Material and Specificity of In-
duction, Arch. f. Entwicklgsmech. 128: 584, 1933; 132: 225 and 307, 1934.

Hooker, S. B. and W. E. Boyd: Tyrosin and Histidin-diazo-arsanilic Acids as
Haptens, J. Immunol. 25 : 61, 1933.

Hopfner, E. : Transplantation of Blood Vessels and Replantation of Amputated
Extremities, Arch. f. Klin. Chirurg. 70: 417, 1903.

Horowitz, N. H. : Tissue Reaction to Transplantation of Muscle in Triturus
viridescens, J. Exp. Zool. 76: 105, 1939.

Horstadius, Sven : Determination in Development of Echinoderm Egg, Acta
Zoologica9: 1, 1928.

Huggins, C. B. : Transplantation of Bladder and Bone Formation, Proc. Soc.
Exp. Biol. & Med. 27: 349, 1930; J. Exp. Med. 58: 393, 1933; 60: 199, 1934.

Humphrey, R. R. and R. K. Burns, Jr. : Toxic Effects in Heteroplastic Parabiosis
or Grafting in Amblystoma, J. Exp. Zool. 81 : 1, 1939.

Ingebrigtsen, R. : Transplantation of Arteries and Isoagglutinines, Miinch. Med.

Wochschr. 59: 1475, 1912.
Ingle, D. T. and R. W. Cragy: Effect of Hormone on Autotransplants of Thyroid

Tissue, Endocrinology 24: 550, 1939.
Ingle, D. T. and E. C. Kendall : Effect of Adrenal and Pituitary Cortical

Hormone on Atrophy of Adrenal, Science, 86 : 245, 1937.
Irving, Laurence: Adaptive Processes and Species Differences in Respiration

of Mammals, Am. J. Physiol. 124: 729, 1938; Physiol. Reviews, 19: 112, 1939.
Irwin, M. R. and L. J. Cole: Immunogenetic Studies of Species and of Species

Hybrids in Doves, J. Immunol. 33: 355, 1937.
Irwin, M. R. : Resistance to Disease in Inbred Strains of Rats, J. Immunol. 24:

285, 297, 1933.
Irwin, M. R. and R. T. Hill: Parabiotic Twins in Doves; Agglutination of

Erythrocytes by Blood Serum, Proc. Soc. Exp. Biol. & Med. 33 : 566, 1936.
Irwin, M. R. : A Genetic Analysis of Species Differences in Columbidae, Genetics,

24:709, 1939.

674 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Irwin, M. R. and R. W. Cumley: Speciation from the Point of View of Genetics,
Biolog. Symposia 2: 31, 1941.

Irwin, M. R. : Dissimilarities between Antigenic Properties of Red Blood Cells
of Dove Hybrids and Parental Genera, Proc. Soc. Exp. Biol. & Med. 29:
850, 1932.

Ishii, O. and Leo Loeb: Transplantation of Mouse Carcinoma with an Experi-
mentally Decreased Virulence, J. Med. Res. 31 : 223, 1914.

Issajew, W. : Inheritance in Animal Chimaerae, Biol. Centralbl. 43: 115, 1923-
24; J. Genetics 14: 278, 1924.

J

Jacobs, M. H. and A. K. Parpart: Species Differences in Permeability of

Erythrocytes, Biol. Bullet. 73 : 380, 1937.
Jacobs, M. H. : Permeability, Annual Rev. Physiol. 1: 1, 1939.
Jacobs, M. H. : Absorption of Chemicals by Red Blood Corpuscles and Relation-
ship, Science 89: 10, 1939.
Jaeger, Gustav: Uber d. Bedeutung d. Geschmacks u. Geruchsstoffes, Zeitschr.

f. Wissensch. Zool. 27: 319, 1876.
Jehn, W. : Nephrectomy in parabiosis, Zeitschr. f. exper. Pathol. & Therapie 6:

16, 1909.
Jennings, H. S. : Fundamental Units in Biology, Science 84: 445, 1936.
Jennings, H. S. : Individual Reactions in Protozoa, Science, 92: 539, 1940; 94:

447, 1941.
Jennings, H. S. : Sex Reaction Types and their Interrelations in Paramecium

Bursaria, Proc. Nat. Acad. Sc. 24: 112, 1938.
Jensen, C. O. : Transplantation of Mammary Gland Carcinoma in Mice,

Centralbl. f. Bakt. 34: 28, 1903.
Jensen, Paul: Individual Physiological Differences Between Cells of the Same

Species, Pfliigers, Arch. 62: 172, 1896.
Jianu, J.: Retransplantation of Thigh in Dog; Retransplantation of Extremities

in Man, Pedicle Transplantations, Arch. Klin. Chir. 102: 57, 1913.
Joest, Ernst: Transplantation in Lumbricidae, Arch. f. Entwicklgsmech. 5: 419,

1897.
Johnson, M. W. and Oscar Riddle: Class Specificity of Hormones, Proc. Soc.

Exp. Biol. & Med. 42: 260, 1939.
Jollos, Victor: Genetik u. Evolutions Problem, Leipzig 1931. Modifications and

Mutations in Drosophila through Action of Heat, Naturwissenschaften, 21 :

831, 1933.
Jones, E. : Breakdown of Hereditary Immunity to Transplantable Tumor by

Introduction of Irritating Agent, J. Cancer Res. 10: 448, 1926.
Jones, P. F. : Selective Fertilization in Pollen Mixtures, Biol. Bullet. 38: 251,

1920; Science 55: 348, 1922.
Jost, L. : Self Sterility in Some Plants, Bot. Zeitschr. 65 : 77, 1907.
Jungeblut, C. W. and E. T. Engle: Neutralization of Virus of Poliomyelitis

by Certain Normal Animal Sera; Effect of Age of Animals, Proc. Soc. Exp.

Biol. & Med. 29:879, 1932.
Jungeblut, C. W. : Blood Groups and Power of Human Serum to Inactivate

Virus of Poliomyelitis, J. Immunol. 24: 157, 1933.
Jungeblut, C. W. and Murray Sanders: Transmission of Murine Strain of

Poliomyelitis to Guinea Pigs and Rhesus Monkeys, J. A. M. A. 116: 2137,

1941.

K

Kallas, Hellmuth : Precocious Puberty in Parabiosis, C. R. Soc. Biol. 100: 979,
1929.

BIBLIOGRAPHY 675

Kalmanson, G. M. and J. J. Bronfenbrenner: Bacteriophage, J. Immunol. 45:

13, 1942.
Karshner, W. M. : Hemagglutination in Chicken, J. Lab. & Clinical Med. 14:

346, 1928/29.
Keeler, Clyde E. : Transplantation of Adult Frog Eyes, J. Exp. Zool. 54: 461,

1929.
Kelley, R. W. and Leo Loeb: Autogenous Transplantation of Pigmented Dorsal

and Ear Skin to Defects in White Skin in the Guinea Pig, Anat. Record 44:

487, 1939.
Keysser, Fr. : Transplantation ; Attempt to Improve Results of Homoiogenous

Transplantation by Immunization with Tissue Extracts, Beitr. z. Klin.

Chir. 110:660, 1918.
King, H. D. : Regeneration and Transplantation in Hydra viridis, Arch. f.

Entwicklgsmech. 13: 135, 1902.
King, H. D. : Regeneration and Transplantation in Asterias, Arch. f. Ent-
wicklgsmech. 7: 351, 1898.
Kirk, J. S. and J. B. Sumner: Immunological Identity of Soy and Jack Bean

Urease, Proc. Soc. Exp. Biol. & Med. 29: 712, 1931-32.
Klopstock, A. and H. Lehmann-Facius: Cytolytic Reactions against Carcinoma

and Embryonal Cells in Immune Sera, Klin. Woch. 67: 1085, 1928.
Klopstock, Felix and Ernst Simon: Specific Antigens in Cancer, Z. f. Krebs-

forsch. 37:127, 1932.
Kodama, H. : Serological Tests for Fish Eggs, Arch. f. Hyg. 78: 247, 1912/13.
Kodama, Sh.: Effect on Liver of Parenteral Injection of Liver Emulsion,

Transaction Jap. Path. Soc. 13: 86, 1923.
Koller, G. : Internal Secretion in Invertebrates, Biol. Reviews 4: 269, 1929.
Koller, Gottfried: Hormone bei Wirbellosen Tieren, Leipzig 1938.
Kolodziejski, Z. : Transplantation and Regeneration of Skin in Axolotl, Extrait

d. Bullet, de FAcad. Polon., Serie B 1928.
Kopec\ St. : Effects of Castration and Transplantation of Sex Glands in Lepidop-

tera, Arch. f. Entwicklgsmech. 33: 1, 1912. Effect of Brain on inception of

Insect Metamorphosis, Biol. Bullet. 142: 323, 1922.
Koppanyi, Th.: Retransplantation of Eyes in Vertebrates, Arch. f. Entwicklgs-
mech. 99 : 15, 42, 60 and 76, 1923.
Koppanyi, T. : Transplantation of Testicles of Urodeles, Arch. f. Entwicklgs-
mech. 102: 707, 1924; Transplantation of Spleen in Rats, J. A. M. A. 83:

1654, 1924.
Kornfeld, Werner: Metamorphosis of Transplanted Gills in Salamanders, Arch.

f. Entwicklgsmech. 40 : 369, 1914.
Korschelt, E. : Regeneration and Transplantation in Lumbricidae, Verh. d.

deutsch. Zoolog. Gesellsch. Vol. 6-8 : 79, 1896-98.
Korschelt, E. : Morphogenetic Induction Following Transplantation, Arch. f.

Entwicklgsmech. 117: 1, 1929.
Kossel, H. : Proteins of Fish Sperm, Zeitsch. f. physiol. Chem. 88: 163, 1913.
Kozelka, A. W. : Genetic and Hormonal Factors in Skin Grafting in Fowl, J.

Exp. Zool. 61 : 431, 1932. Individuality of Red Blood Cells in Fowls, J. Im-
munol. 24: 519, 1933.
Kczelka, A. W. : Serological Studies of Tissue Antagonism, Physiol. Zoology,

6: 159, 1933.
Kozelka, A. W. : Parabiosis of Chicks; Effect on Secondary Sex Characters,

27th annual meeting, Am. Assoc. Zoologists, Anat. Record 44: 209, 1930

(Abstract).
Kraus, R., K. Ishiwara and R. Winternitz: Effect of Normal Serum and of

Serum of Carcinoma Patients on Embryonal Cells, Wien. Klin. Wochenschr.

25 : 583, 1912.

676 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Kreezer, George: Individuality in Electroencephalogram, Report of Committee

on Research, Yearbook, Am. Philosoph. Society, p. 196, 1938.
Kritschewski, J. L. : Antigenic Differences between Embryonal and Adult Tis-
sues, Centralbl. f. Bakt. 72: 81, 1914; J. Inf. Dis. 32: 192, 1923.
Kritschewski, J. L. u. R. E. Messik: Relation of Forssman Antigen to Blood

Group Antigens in Man, Zeitschr. f. Imm. forsch. 65: 405, 1930; 52: 339,

1929.
Kronenberg, M. : Individuality, Naturwissenschaften 11: 325, 1923.
Krusius, F. F. : Antigenic Characteristics of Lens, Zeitschr. f. Imm. forsch. 5 :

699, 1910.
Kubanyi, A.: Skin Grafting and Isoagglutination, Arch. Klin. Chir. 129: 644,

1924.
Kuhn, Alfred: Physiological Effects of Some Genes on Development in Ephestia

(Gene hormones), Naturwissenschaften 20: 974, 1932.
Kuttner, H. : The Problem of Heterotransplantation, Zentralbl. f. Chir. 51: 19,

1934.
Kupelwieser, H. : Stimulation of Echinus Eggs by Sperm of Worms, Arch.

Zell forsch. 8:352, 1912.
Kurz, Oscar: Transplantation of Leg in Triton, Arch. f. Entwicklgsmech. 34:

588, 1912.
Kylin, Eskel: Transplantation of Hypophysis, Acta Med. Scandinavia 91: 428.

1937.

Lake, G. C, T. B. Osborne and H. G. Wells: Immunological Relationship of

Hordein of Barley and Gliadin of Wheat, J. Infect. Dis. 14: 364, 1914.
Lambert, R. A. and F. M. Hanes: Cultivation of Tissue in Plasma from Alien

Species, J. Exp. Med. 14: 129, 1911.
Lambert, R. A. : Comparison of Growth of Normal Cells and Cancer Cells in

Tissue Culture, J. Exp. Med. 17: 499, 1913.
Lambert, R. A.: Influence of Mouse-Rat Parabiosis on Growth in Rats of a

Transplantable Mouse Sarcoma. J. Exp. Med. 13: 257, 1911.
Lancefield, D. S. : Genetics of Crosses of Two Races of Drosophila obscura,

Zeitschr. f. ind. Abstammungs u. Vererbungslehre 52: 287, 1929.
Lancefield, R. C. : Serological Differentiation of Hemolytic Streptococci, J.

Exp. Med. 57: 571, 1933.
Landsteiner, K. : Agglutination Reactions of Normal Human Blood, Wien

Klin. Woch. 14: 132, 1901.
Landsteiner, K. : Hemolysins, Agglutinins and Anti-Ferments, Centralbl. f.

Bakt. 27: 357, 1900.
Landsteiner, Karl and Karl Leiner: Differences in Erythrocytes of Different

Individuals. Centralbl. f. Bakt. 38: 548, 1905.
Landsteiner, Karl and Max Reicher: Differences in Erythrocytes of Indi-
viduals in Various Diseases. Centralbl. f. Bakt. 39: 712, 1905.
Landsteiner, K, J. van der Scheer, and D. H. Witt: Group Specific Floccula-

tions with Human Blood. Proc. Soc. Exp. Biol, and Med. 22: 289, 1925.
Landsteiner, K. and J. van der Scheer: Serological Examination of Species

Hybrids. Proc. Soc. Exp. Biol, and Med. 21: 252, 1924. J. Immun. 9: 213

and 221, 1924.
Landsteiner, K. and C. P. Miller, Jr. : Serological Studies on Blood of Primates.

J. Exp. Med. 42: 841, 853, and 863, 1925.
Landsteiner, Karl: Cell Antigens and Individual Specificity. J. Immunol. 15:

589, 1928; Complex antigens, Klin. Woch. 6: 103, 1927.
Landsteiner, K. and J. van der Scheer: Serological Differentiation of Steric

BIBLIOGRAPHY 677

isomers, J. Exp. Med. 48: 315, 1928. Antigens of Erythrocytes, J. Exp. Med.

42: 121, 1925.
Landsteiner, K. and P. A. Levene: Heterogenetic Haptens, J. Immunol. 14: 81,

1927.
Landsteiner, K. and C. P. Miller, Jr. : Individual differences of blood of

chickens and ducks, Proc. Soc. Exp. Biol, and Med. 22: 100, 1924-25.
Landsteiner, K. and P. Levine: Individual Differences in Human Blood, J. Exp.

Med. 47: 757, 1928. J. Immunol. 17: 1, 1928; Proc. Soc. Exp. Biol, and Med.

28 : 309, 1930.
Landsteiner, K. and P. Levine: Inheritance and Racial Distribution of

Agglutinable Properties of Human Blood, J. Immunol. 18 : 87, 1930.
Landsteiner, K. and P. Levine: Group Specific Substances in Human Spermato-
zoa, J. Immunol. 12: 415, 1926.
Landsteiner, K. : Serological tests with Blood of Cavia Porcellus and Cavia

Rufescens, Proc. Soc. Exp. Biol, and Med. 28: 981, 1931.
Landsteiner, K. and A. S. Wiener: M. Agglutinogens in the Blood of Monkeys,

J. Immunol. 33: 19, 1937; Rh Antigen in Erythrocytes, Proc. Exp. Biol. &

Med. 43: 223, 1940; J. Exper. Med. 74: 309, 194.
Landsteiner, K. and P. Levine: Multiplicity of Isoagglutinin Reactions in

Human Blood. J. Immunol. 17: 1, 1929.
Landsteiner, K., Levine P., and J. van der Scheer: Anaphylactic Reactions

produced by Azo Dyes. Proc. Soc. Exp. Biol. & Med. 27: 811, 1930.
Landsteiner, K. and P. Levine: Differentiation of Human Blood Type by

Means of Normal Animal Serum, J. Immunol. 20: 179, 1931.
Landsteiner, K. and P. Levine: Immunization of Chimpanzees with Human

Blood, J. Immunol. 22: 397, 1932. Individual Differences in Chicken Blood,

Proc. Soc. Exp. Biol. & Med. 30: 209, 1932.
Landsteiner, K. and John Jacobs : Immunization with Haptens, Proc. Soc.

Exp. Biol. & Med., 29: 570, 1932; 30: 1055, 1932-33.
Landsteiner, K. and J. van der Scheer: Anaphylactic Shock by Azo Dyes, J.

Exp. Med. 57:633, 1933.
Landsteiner, K., L. G. Longsworth, and J. van der Scheer: Electrophoresis

of Egg Albumin and Hemoglobins, Science, 88 : 89, 1938.
Landsteiner, K. and J. van der Scheer: Cross Reactions of Egg Albumin sera,

J. Exp. Med. 71 : 445, 1940.
Landsteiner, K. and M. W. Chase : Sensitization with Simple Chemical Com-
pounds, J. Exp. Med. 66: 337, 1937; 73: 431, 1941.
Lane, C. E. and I. E. Markee: Responses of Ovarian Intraocular Transplants

to Gonadotropins, Growth 5 : 61, 1941.
Lathrop, A. E. C. and Leo Loeb: Action of Hormones as Cause of Cancer,

J. Cancer Research 1 : 1, 1916.
Lauer, A.: Skin Patterns, Zeitsch. f. ind. Abstamm. u. Vererbgslehre 50, 74,

1929.
Lauer, A. : Blood Groups in Dog, Zeitschr. f . Imm. forsch. 68 : 434, 1930.
Lazarus-Barlow, W. S. and R. H. Parry: The Brain and Immunity Reactions

to Jensen's Rat Sarcoma, Brit. J. Exp. Path. 4: 80, 1923.
van Leeuwen, W. Storm : Allergens of Animal Hair, Zeitschr. f. Imm. forsch.

68:427, 1930.
Lehmann, W. and H. Tammann: Transplantation and the Action of Dyes,

Beitr. z. Klin. Chirurg. 135 : 259, 1925.
Lehmann, W. and H. Tammann: Immunizing Function of Reticuloendothelial

System, Z. F. Imm. forsch. 45 : 493, 1926.
Lehmann-Facius, H. : Serological Diagnosis of Cancer, Zeitschr. f. Imm. forsch.

67: 377, 1930 (with T. Toda) ; Klin. Woch. 9: 2430, 1930; 75: 217, 1932; 80:

181, 1933.

678 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Lenart, Georg and Julius Konig: Skin Grafting and Isoagglutinins, Klin.
Wochschr. 7:549, 1928.

von Lengerken, H. : Head Transplantation in Coleoptera, Zool. Anzeiger, 59 :
166, 1924.

Levine, Milton and David State: Blood Transfusions, J.A.M.A. 120: 275, 1942.

Levine, Milton and David State: Skin Sensitivity to Human Plasma, Science
96:68, 1942.

Levine, Philip and E. M. Katzin: Isoimmunization in Pregnancy, Proc. Soc.
Exper. Biol. & Med. 45 : 343, 1940.

Levine, Philip, E. M. Katzin and Lyman Burn ham : Isoimmunization in Preg-
nancy, Erythroblastosis Foetalis, J.A.M.A. 116: 825, 1941.

Levine, P., E. M. Katzin, P. Vogel, and Lyman Burnham : Pathogenesis of
Fetal Erythroblastosis, Science 94: 371, 1941.

Levine, P. and K. Landsteiner: Immune Isoagglutinins in Rabbits, J. Immunol.
21:513, 1931.

Levy, S. E. and Alfred Blalock: Transplantation of Adrenal in Dog Leg by
Blood Vessel Anastomosis, Annals of Surgery 109: 84, 1939.

Lewis, J. H. and H. G. Wells: Immunological Properties of Alcohol-soluble
Vegetable Proteins, J. Biol. Chem. 66: 37, 1925.

Lewis, J. H. : Immunological Specificity of Brain Tissue, J. Immunol. 24: 193,
1933. Antigenic Properties of Insulin, J. A. M. A. 108: 1136, 1937.

Lewis, M. R. : Transmissible Monocytoma of Mouse, Am. J. Cancer, 36 : 34, 1939 ;
and E. G. Lichtenstein : Breaking Down of Resistance of Mice to Trans-
plantation of Tumors of Another Strain, Am. J. Cancer 28: 746, 1936.

Lewis, W. H. : Development of the Amphibian Lens under Influence of Optic
Vesicle, Am. J. Anat. 3: 505, 1904. Transplantation of Otic Vesicle in Am-
phibian Embryos, Anat. Record 1 : 141, 1907. Transplantation of Neural
Plate in Amphibian Embryos, Anat. Record 4: 191, 1910.

Leypoldt, H. : Transplantation in Lumbricidae, Arch. f. Entwicklgsmech. 31: 1,
1911.

Lieske, Rudolf: Grafting in Plants, Ber. d. Bot. Gesellsch. 38: 353, 1921.

Lignac, G. O. E. u. G. A. Kreuzwendedich von dem Borne: Heterotransplan-
tation of Tumors in Mice Injected with Trypan Blue, Krankheitsforschung,
6: 265, 1928; 7: 119, 1929.

Des Ligneris, M. : Biological Characters of a Tumor Produced in Vitro ; Speci-
ficity of Neutralizing Substances, C.R. Soc. Biol. 121 : 1579, 1936. Specificity
and Immunity in Tissue Cultures with Liquid Media (Immune and heterog-
enous sera), Arch. f. Exper. Zellforschung 18: 456, 1936.

Lindeman, V. F. : Transplantation and Metamorphosis of Frogskin, Physiol.
Zool. 2:255, 1929.

Lillie, F. R. : Problems of Fertilization, Univ. of Chicago Press 1919.

Lillie, F. R. : Growth Rate and Hormone Threshold, Am. Naturalist, 46: 171,
1932.

Lillie, F. R.: Studies of Fertilization, J. Exp. Zool. 14: 515, 1913; Biol. Bullet.
40:1, 1921.

Lipschutz, A.: Transplantation of Dried Ovaries, Virch. Arch. 272: 245, 1929.
Lipschiitz and H. Kallas, Virch. Arch. 277: 694, 1930.

Little, C. C. : The Genetics of Tumor Transplantation, in "Biology of the Labo-
ratory Mouse," p. 279, 1941.

Little, C. C. and E. E. Tyzzer : Inheritance of Susceptibility to a Transplantable
Tumor, J. Med. Res. 33: 393, 1916.

Little, C. C. : Factors Influencing Growth of a Transplantable Tumor in Mice,
J. Exp. Zool. 31 : 307, 1920.

Little, C. C. and L. C. Strong: Genetic Studies of Transplantation of Two
Adenocarcinomata, J. Exp. Zool. 41 : 93, 1924.

BIBLIOGRAPHY 679

Little, C. C. and B. W. Johnson, Inheritance of Susceptibility to Implants of

Spleen Tissue in Mice, Proc. Soc. Exp. Med. Biol. 19: 163, 1922.
Little, C. C. : The Genetics of Tumor Transplantation in Mammals, J. Cancer

Research 8: 74, 1924.
Little, C. C. : Role of Heredity in Determining Incidence and Growth of Cancer,

Am. J. Cancer 15: 2780, 1931; J. A. M. A. 106: 2234, 1936.
Little, R. B. : Isoagglutinins in the Blood of Cattle, J. Immunol. 17: 377, 1929.
Loeb, Jacques: Nature of Hybrids Between Eggs of Strongylocentrotus and

Sperm of Molluscs, Arch. f. Entwicklgsmech. 26: 476, 1908.
Loeb, Jacques: Is Species Specificity a Mendelian Character? Science 45: 191,

1917.
Loeb, Leo: Syngenesiotransplantation in Guinea Pig, J. Med. Res. 39: 39, 1918;

41: 305, 1920; Am. J. Pathol. 3: 29, 1927.
Loeb, Leo : Auto and Homoiotransplantation in Guinea Pig Kidney, J. Med. Res.

37: 229, 1917; cartilage, Am. J. Pathol. 2: 111, 1926; thyroid, Am. J. Path.

2:99, 1926.
Loeb, Leo, Marian Moskop-Kirtz and H. T. Blumenthal : Transplantations in

Mice, Unpublished Experiments.
Loeb, Leo: Factors in Life and Growth of Transplanted Tissues, J. A. M. A. 59:

726, 1917; Proc. Soc. Exp. Biol. & Med. 17: 153, 1921; Transplantation and

Family Relationship, Am. Naturalist 54: 45, 1920; Mode of Inheritance of

Individuality Differential, Am. Naturalist 54: 55, 1920.
Loeb, Leo : Individuality Differential and Reactions against Transplanted Tissues

and Tumors, J. Cancer Res. 10 : 252, 1926.
Loeb, Leo and Sewall Wright: Individuality Differentials in Inbred Families

of Guinea Pigs, Am. J. Path. 3: 251, 1927.
Loeb, Leo and H. C. McPhee: Individuality Differentials in Inbred Families of

Guinea Pigs, Am. Naturalist, 65: 385, 1931.
Loeb, Leo and H. D. King: Transplantation and Individuality Differentials in

Inbred Strains of Rats, Am. J. Path. 3 : 143, 1927.
Loeb, Leo: The Organization of Blood Clots after Auto, Homoio and Hetero-
transplantation, J. Med. Res. 37: 353, 1918.
Loeb, Leo: Transplantation and Potential Immortality of Mammalian Tissues,

J. General Physiol. (Jacques Loeb, Memorial Vol.) 8: 417, 1926.
Loeb, Leo: Tissue Transplantation and Anaphylaxis, J. Immunol. 2: 557, 1917.
Loeb, Leo: Transplantation of Regenerating Epithelium and Serial Transplan-
tation of Epithelium, Arch. f. Entwicklgsmech. 24: 638, 1907.
Loeb, Leo and W. H. F. Addison : Transplantation of Skin of Guinea Pig into

Animals of Different Species, Arch. f. Entwicklgsmech. 37: 73, 1909.
Loeb, Leo and W. H. F. Addison : Transplantation of Pigeon Skin into Pigeons

and into Other Species, Arch. f. Entwicklgsmech. 32: 44, 1911.
Loeb, Leo and H. D. King: Transplantation and Individuality Differentials in

Inbred Strains of Rats, Am. J. Path. 3: 143, 1927; Arch. Path. 12: 203, 1931;

Loeb, Leo, H. D. King and H. T. Blumenthal, Biol. Bullet. 84: 1, 1943.
Loeb, Leo and H. D. King: Analysis of Organismal Differentials of Gray Nor-
way Rats and of Two Mutant Races, Am. Natur. 69: 5, 1935.
Loeb, Leo and R. M. Simpson: Effects of Age and Hormones on Stroma of

Thyroid and Mammary Gland, Science 88: 433, 1938.
Loeb, Leo : Auto and Homoiotransplantation of Cartilage and Bone in Rat, Am.

J. Path. 2: 315, 1926.
Loeb, Leo: Auto and Homoiotransplantation of Thyroid Gland in Rat, Am. J.

Pathol. 2: 301, 1926.
Loeb, Leo: Behavior of Organs after Transplantation in Rat and Power of

Resistance of Constituents of Various Organs, J. Med. Res. 39: 189, 1918.

680 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Loeb, Leo: Heterotransplantation of Kidney, J. Med. Res. 42: 1317, 1920-21;

Heterotransplantation of Thyroid, J. Exp. Med. 31 : 765, 1920.
Loeb, Leo: Influence of Changes in Chemical Environment on Life and Growth

of Tissue, J.A.M.A. 64: 726, 1915.
Loeb, Leo: Grafting of Tissues into Nearly Related Individuals in Rat and

Mode of Inheritance of Individuality Differentials, J. Med. Res. 39: 393,

1918.
Loeb, Leo: Syngenesiotransplantation in Rat, Am. J. Pathol. 3: 45, 1927.
Loeb, Leo : Multiple Transplantations of Thyroid and the Lymphocytic Reaction,

J. Med. Res. 39: 71, 1918.
Loeb, Leo : Tumor Growth and Tissue Growth, Proc. Am. Phil. Soc. 47 : 3, 1908.
Loeb, Leo: Transplantation of White and of Pigmented Skin in the Ear of the

Guinea Pig, Arch. f. Entwicklgsmech. 6:1, 1897.
Loeb, Leo: Growth of Epithelium, Arch. f. Entwicklgsmech. 13: 487, 1902;

Growth of Epithelium in Agar and Blood Serum, J. Med. Res. 8: 109, 1902.
Loeb, Leo and Cora Hesselberg: Hypertrophy in Autotransplants of Thyroid

Gland, J. Med. Res. 40: 265, 1919; The Effect of Homoiotoxins in Hyper-
trophy of the Thyroid, 41 : 283, 1920.
Loeb, Leo : Effect of Administration of Thyroid, Thymus, Theelin and of a

Meat Diet on Hypertrophy of Thyroid, J. Med. Res. 42: 77, 1920.
Loeb, Leo: Transplantation of Tissues from Mouse to Rat and vice versa, Am.

Naturalist 69: 239, 1935.
Loeb, Leo and W. J. Siebert: Transplantation of Skin and Cartilage in Chicken,

Arch. Path. 20 : 28, 1935.
Loeb, Leo and J. S. Harter : Heterotransplantation of Cartilage and Fat Tissue,

Am. J. Path. 2: 521, 1926.
Loeb, Leo: Thyroid Gland, Iodine and Anterior Hypophysis; Mechanism of

Compensatory Hypertrophy of Thyroid Gland, Klin. Woch. 11: 2121 and

2156, 1932.
Loeb, Leo: Transplantation of Benign Tumors in the Rat, J. Med. Research, 7:

44, 1902; in dog: J. Med. Res. 17: 299, 1907 (with S. Leopold); in rat, J.

Cancer Research 1: 427, 1916 (with M. S. Fleisher).
Loeb, Leo: The Causes of Cancer, Scientific Monthly 47: 51, 1938.
Loeb, Leo, V. Suntzeff and E. L. Burns: Effects of Age and Estrogen on

Stroma of Vagina, Cervix and Uterus, Science 88: 432, 1938.
Loeb, Leo: Action of Hormones as Cause of Cancer, J. Med. Res. 40: 477, 1919;

J. Cancer Research 8: 274, 1924; Internat. Confer, on Cancer, London 1928,

p. 48; Quantitative Relations Between Factors Which Cause Cancer and

the Rapidity and Frequency of the Cancerous Transformation, C.R. Soc.

Biol. 89: 307, 1923; La Presse Medicale 31: 709, 1923.
Loeb, Leo and M. S. Fleisher: Inheritance of the Factors Determining Growth

of Tumors, Centralbl. f. Bakt. 67: 135, 1912.
Loeb, Leo: Transplantation of Tumor in Rats, Virchow's Arch. 167: 175, 1902;

172: 345, 1903; J. Med. Res. 6: 28, 1901; 8: 44, 1902.
Loeb, Leo: Tissue Growth and Tumor Growth, J. Cancer Res. 2: 135, 1917.
Loeb, Leo: General Problems and Tendencies in Cancer Research, Science 43:

293, 1916; Quantitative Relations between Factors Causing Cancer and

Rapidity and Frequency of Cancerous Transformation, J. Cancer Res. 8:

274, 1924.
Loeb, Leo: Inheritance of Cancer in Mice, Am. Naturalist 55: 510, 1921 ; Heredity

and Internal Secretion in Etiology of Cancer, Rep. Internat. Confer, on

Cancer, London, p. 48, 1928.
Loeb, Leo: Inoculability of Tumors and Endemic Occurrence of Cancer Internat.

Clinics 3: 115,1907.
Loeb, Leo: Problems of Experimental Tumor Investigation, Zeitschr. f.

BIBLIOGRAPHY 681

Krebsforsch. 5: 451, 1907; Transplantation of Tumors, Virchow's Arch.
172: 345, 1903; Conditions Determining Variations in Energy of Tumor
Growth, Am. Medicine 10: 265, 1905.

Loeb, Leo: A Contact-combination Tumor in a Mouse, Centralbl. f. allg. Pathol.
u. path. Anat. 22: 993, 1911.

Loeb, Leo : Formation of Sarcoma after Transplantation of Adenocarcinoma in
a Japanese Mouse, Zeitschr. f. Krebsforsch. 7: 2, 1908.

Loeb, Leo: Germ Cells and Somatic Cells, Am. Natural. 49: 287, 1915.

Loeb, Leo : Graded Relation Between Intensity of Hormone Action and the
Character of Recipient Tissue, Endocrinology 12: 161, 1928.

Loeb, Leo: Inherited Organ Specificity and Its Age Incidence (hormones and
the process of ageing), Harvey lectures 36: 228, 1940-41.

Loeb, Leo : Mode of Action of External Stimuli in Formation of Placentomas,
Arch. f. Entwicklgsmech. 32: 67, 1911; Effect of Combination Stimuli on
Growth of Transplanted Uterus of Guinea Pig, Arch. f. Entwicklgsmech.
31: 456, 1911.

Loeb, Leo: Production of Deciduomata, Zentralbl. f. allg. Path. & Path. Anat.
18: 563, 1907; J. A. M. A. 50: 1897, 1908; Arch. f. Entwicklgsmech. 27: 463,
1909; 31: 456, 1910-1911.

Loeb, Leo: Immunity and Adaptation, Biol. Bullet. 9: 141, 1905.

Loeb, Leo: Movements of Amoebocytes and the Experimental Production of
Amoebocyte Tissue, Washington University Studies 8: 5, 1920; Amoeboid
Movement and Agglutination in Amoebocytes of Limulus and the Relation
of These Processes to Tissue Formation and Thrombosis, Protoplasma 2:
512, 1927.

Loeb, Leo and I. T. Genther : Differences in the Reactions of Individual Amoebo-
cytes, Arch. f. Exper. Zellforsch. 9: 214, 1930.

Loeb, Leo and Oscar Bodansky: Ursease of Limulus, J. Biol. Chem. 61: 79,
1926; 72: 415, 1927.

Loeb, Leo and I. Lorberblatt: Urease of Limulus, Proc. Soc. Exp. Biol. &
Med. 25: 323, 1928; T. Biol. Chem. 78: 417, 1928 (with M. E. Field);
Biochem. Zeitschr. 236: 298; 244: 222, 1932.

Loeb, Leo: Specific Adaptation of Tissue Coagulins, Montreal Med. J. 32: 507,
1903; Virchow's Arch. 176: 101, 1904; Biochem. Centralbl. 6: 829 and 889,
1907; with M. S. Fleisher, Biochem. Zeitsch. 28: 169, 1910.

Loeb, Leo: Evolution of Thrombosis, Virchow's Arch. 173: 35, 1903; 176: 10,
1904; 185: 160, 1906; Hofmeister's Beitr. z. Chem. Physiol, u. Pathol. 5:
534, 1904; 6: 260, 1905; 8: 67, 1906; 9: 185, 1907; Protoplasma 2: 512,
1921; 4: 596, 1928.

Loeb, Leo, M. S. Fleisher and L. Tuttle: Interaction Between Blood Serum and
Tissue Extract in Coagulation of Blood, J. Biol. Chem. 2: 461 and 485, 1922.

Loeb, Leo, A. Strickler and Lucius Tuttle: Cause of Death after Injection
of Heterogenous Blood Serum, Virchow's Arch. 201: 5, 1910.

Loeb, Leo: Specific Adaptation Between Body Fluids and Blood Cells in In-
vertebrates, J. Med. Res. 42: 277, 1921 : Amoeboid Movement, Tissue Forma-
tion and Consistency of Protoplasm, Am. J. Physiol. 56: 140, 1921.

Lohner, L. : Theory of Effects of Inbreeding, Zeitschr. f. ind. Abstammungs und
Vererbgslehre, 33: 260, 1924.

Lohner, L. : On Individual Substances and Biochemical Individual Specificity,
Pfiuger's Arch. 198: 490, 1923.

Lohner, L. : On Human Individual and Regional Scents, Pfliiger's Arch. 202:
25, 1924.

Lohner, L. : Inbreeding and Biochemical Individual Specificitv, Rivista di Biol.
3: 3, 1921.

Loeper, M. et R. Turpin : Influence of Artificial Lymphocytosis on Evolution of

682 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Sarcoma in Rat, C. R. Soc Biol. 91: 164, 1924: Lymphocytes and Cancer,

a Critical Review; Annales de Medicine 16: 236, 1924.
Lorenz, Konrad : Formation of Concept of Instinct, Naturwissenschaften 25 : 289,

307 and 324, 1937.
Lucre, B. M. Strumia, S. Mudd, Morton McCutcheon and E. B. H. Mudd:

Specific Adaptation of Serum in Phagocytosis, J. Immunol. 24: 455, 1933.
Lucke, B., M. McCutcheon, M. Strumia and S. Mudd: Specific Adaptation

in Opsonin and Bacteriotropin Action, J. Exp. Med. 49: 797, 1929.
Lumsden, T. : Immunity to Transplanted Tumors, Lancet 213: 1283, 1917; 217:

814, 1920; Am. J. Cancer, 15: 563, 1931.
Lumsden, T. : Method of Demonstrating Effect of Cytotoxins, J. Pathol. & Bact.

44: 515, 1937.
Lumsden, T. : Agglutination Tests in the Study of Tumor Immunity; Am. J.

Cancer 32: 395, 1938. Blood Groups and Agglutination of Human Red Blood

Corpuscles by Rat Sera, Am. J. Cancer, 35: 222, 1939.
Lumsden, T. : Antiserum Against Spontaneous Mouse Carcinoma, J. Path. &

Bact. 35: 441, 1932.
Lumsden, T. (with A. C. Kohn-Speyer) : Cytotoxins for Normal and Tumor

Cells; Protection of Cells Against Homologous Antibodies, J. Path. & Bact.

32: 185, 1929.
Lurie, Max B. : Human and Bovine Tubercle Bacilli in Organs of Rabbits,

J. Exp. Med. 48: 155, 1928.
Lux, L., G. M. Higgins and F. C. Mann: Functional Homoiografts of Rat

Adrenal Gland Grown in Vitro, Anat. Rec. 70: 29, 1937.

M

MacDowell, E. C, J. S. Potter and M. J. Taylor: Influence of Transplanta-
tion upon Immunological Properties of Leukemic Cells, Proc. Nat. Acad. Sc.
25 : 416, 1939.

MacDowell, E. C. : Genetic Aspects of Mouse Leukemia, Am. J. Cancer, 26 : 85,
1936.

McJunkin, F. A. and B. D. Roberts: Effects of Insulin on Pancreatic Islets of
Young Rats (Tissue specificity of hormones), Proc. Soc. Exp. Biol. & Med.
29: 893, 1932.

MacNider, Wm. DeB. : Acquired Resistance to Injury of Regenerating Renal
Epithelium, Science 88 : 447, 1938.

Madison, R. R. : Fibrinolysis by Streptococci of Human and Animal Origin,
Proc. Soc. Exp. Biol. & Med. 31 : 1018, 1933/34; 34: 299, 301, 1936.

Mahr, M. M. : Serological Tests for Organismal Differentials in Monezia, Biol.
Bullet. 83: 88, 1942.

Mangold, O. : Induction by Neurula in Urodeles, Naturwissensch. 21: 761, 1933.

Mangold, O. : Heterogenous Induction in Urodeles, Naturwissensch. 19: 905,
1931.

Mangold, O. : Autonomous and Complementary Induction in Amphibia, Natur-
wissensch. 20: 371, 1932.

Mangold, Otto: Transplantation in Triton and the Specificity of Germ Layers,
Arch, f . Entwicklgsmech. 100 : 198, 1923/24.

Mangold, Otto and F. Seidel: Homoiogenous and Heterogenous Fusion of
Segmenting Triton Eggs, Arch. f. Entwicklgsmech. Ill: 593, 1927.

Manley, O. T. and David Marine: Transplantation of Ductless Glands,
J. A. M. A. 67: 260, 1916. Age and Autotransplantation of Spleen in Rabbits,
Proc. Soc. Exp. Biol. & Med. 14: 123, 1916-17.

Mann, L. S. and W. H. Welker: Antiserum for Carcinoma, Am. J. Cancer,
39: 360, 1940.

BIBLIOGRAPHY 683

Mann, F. C. : Failure of Homoiotransplantation of Mammary Carcinoma in
Dogs, J. Cancer Res. 4: 331, 1919.

Manwaring, W. H. and I. L. Azeverde : Serum Antibodies and Their Precursors
in Tissues, J. A. M. A. 91 : 386, 1928.

Marine, David and O. T. Manley: Homoiogenous and Autogenous transplanta-
tion of Spleen, J. Exp. Med. 32: 113, 1920.

Marker, I. E. : Role of Nerves in Transplants of Uterus, Am. J. Physiol. 100:
374,' 1932.

Markham, F. S. : Submaxillary Gland Virus of Guinea Pig, Am. J. Pathol. 14:

311, 1938.

Marshall, H. T. and Oscar Teague: Racial Differences in Human Blood,
Philipp, J. Science 3: 357, 1908.

Martins, Th.: Exchange of Hormones in Parabiotic Animals, C. R. Soc. Biol.
102, 605 and 614, 1929. Transplantation of Hypophysis into Anterior Cham-
ber of Eye of Rat. Action of Oestrin, C. R. Soc. Biol. 123 : 702, 1936.

Masson, J. C: Skin Grafting, J. A. M. A. 70: 1581, 1918.

Matson, A. A. and E. O. Brady: Serological Determination of Blood Relation-
ship, Especially of the American Indian, J. Immunol. 30: 445, 1936; Matson,
A. A. Proc. Soc. Exp. Biol. & Med. 31 : 964, 1934.

Matsuyama, Rokeno: Parabiosis in Rats, Frankf. Zeitschr. f. Pathol. 25: 97,
1921.

Matthey, Robert: Transplantation of Eye in Triton, Arch. f. Entwicklgsmech.
109: 326, 1927.

May, R. M.: Skin Grafts in Lizards, Br'it. J. Exp. Biol. 1: 539, 1923-24.

May, R. M. : Hormonal Effects of Embryonal Hypophysis after Intraocular
Transplantation in Rats, C. R. Soc. Biol. 124: 920, 1937.

May, R. M. : Subcutaneous Transplantation of Thyroid from Embryos or New
Born Animals in Rats, C. R. Acad. d. Sciences 199: 807, 1934. Intraocular
Transplantation of Thyroid and Parathyroid in Rat, C. R. Acad. d. Sc. 194:
1525, 1932; Arch. d. Biol. 44: 149, 1933.

Mayeda, T. : Transplantation of Skin in Parabiotic Rats, D. Zeitsch. f. Chir.
167: 295, 1921.

Meisenheimer, J. : Transplantation of Ovaries in Butterflies, Zool. Anzeiger 35 :
446, 1909-10.

Meyns, R. : Transplantation of Testicles in Frogs, Arch. f. Physiol. 132: 433,
1910; Arch. f. mikr. Anat. 79: 148, 1912.

Mez, Carl and H. Ziegenspeck: Serological Diagnosis of Species Relationship
of Proteins in Plants, Bot. Arch. 12: 163, 1925.

Mez, Carl: Phylogenesis in Plants and Serum Reactions, Naturwissenschaften,
18: 1125,1930.

Miles, W. R. : Polarity Potential of Human Eye (organ specificity), Science 88:
437, 1938.

Milojevich, B. D. : Transplantation of Regenerates of Extremities in Triton,
Arch. f. Entwicklgsmech. 103 : 80, 1924.

Mirsky, A. E. and Linus Pauling: Structure of Native, Denatured and Coagu-
lated Protein, Proc. Nat. Acad. Sc. 22 : 439, 1936.

Moevus, Franz: Caritonoids Directing Sex Reactions in Algae, Naturwissen-
schaften, 27 : 97, 1939.

Montalenti, G. : Ontogenesis of Hybrids between Bufo Vulgaris and Bufo
Viridis; Mechanism of Injury, Physiol. Zoology 6- 329, 1933.

Moore, A. R. and J. C. Welch : Association Hysteresis in Amblystoma, J. Comp.
Psychol. 29: 283, 1940.

Moore, A. R. : Function in Aganglionic Central Nervous System, J. Comp. Psychol.
28:313, 1939.

Moore, C, V. Suntzeff and Leo Loeb : Specificity in Inhibiting Action of Blood

684 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Serum on Coagulating Effect of Tissue Extract, Am. J. Physiol. 114: 1, 1935.
Moore, R. A., H. B. Rosenblum, S. G. Tolins, and R. Melchionna: Physiol.

Response of Prostatic and Vesicular Tissue Transplanted into Eye, Proc.

N.Y. Path. Soc. 18: 1936-37.
Moran, T. : Lipoid Antibodies after Treatment with Organ Suspensions, Zeitsch.

f. Immunitatsforsch. 67: 115, 1930.
Morgan, T. H.: Auto fertilization, J. Exp. Zool. 78: 271, 319, 1938; 80: 19, 1939;

85 : 1, 1940; Biol. Bullet. 161 : 82 and 172: 82, 1942.
Morgan, T. H.: The Rise of Genetics, Science 76: 261, 285, 1932.
Morgan, T. H.: Self Fertilization in Ciona, Biol. Bullet. 8: 313, 1905.
Morgan, J. E. and S. J. Webster: Malformations, Tumors, and Certain Other

Abnormalities in Identical Twins, J. A. M. A. 110: 1744, 1938.
Morgenroth, J. and R. Bieling: Amboceptors and Receptors; Organ Specificity

and Tissue Specificity, Biochem. Zeitschr. 68: 85, 1915.
Moritz, Otto: Psytoserology, Biol. Zentralbl. 48: 431, 1928; Arch. f. Wiss.

Botanik. Planta, Abt. E. 7: 759, 1929; Beihefte z. Bot. Centralbl. 46: II Abt.

114, 1929.
Morpurgo, B. : Parabiosis in rat, Verhandl. d. deutsch. pathol. Gesellsch. 13: 150,

1909; Klin. Woch. 2: 129, 1923; Frankfurt. Zeitschr. f. Path. 34: 337, 1926.
Morpurgo, B. : Effect of Trypan Blue Accumulations and of Starvation on Homoio

and Hetero Transplanted Skin in Rats, Verh. d. d. path. Gesellsch. p. 330, 1928.
Morville, P.: Development of Blood Characteristics During First Years of Life,

Acta Path. Scandinavia 6: 39, 1929.
Mottram, I. C. : Effect of Radiation on Rous Chicken Tumor, Brit. J. Exp. Pathol.

9:147, 1928.
Mudd, Stuart and Maria Wiener: Antigenic Structure of Hemolytic Strepto-
cocci; Relationships of Nucleoproteins, J. Immunol. 45: 21, 1942.
Murphy, J. B. and E. Sturm : Action of Inhibitor Extracted from Chicken

Tumors on Mouse Tumor, J. Exp. Med. 56: 483, 1932.
Murphy, J. B. : A Source of Defense to Heteroplastic Tissue Grafting, J. A. M. A.

59: 874, 1912; 62: 199, 1914; J. Exp. Med. 17: 482, 1913.
Murphy, J. B. : Heteroplastic Tissue Grafting Effected Through Roentgen Ray

Lymphoid Destruction, J. A. M. A. 62: 1459, 1914.
Murphy, J. B. and J. J. Morton : The Lymphocytes as a Factor in Natural and

Induced Resistance to Transplanted Cancer, Proc. Nat. Acad. Sc. 1 : 435,

1915; J. Exp. Med. 22: 204, 1915.
Murphy, J. B. : The Lymphocyte in Resistance to Tissue Grafting, Malignant

Disease, and Tuberculous infection, Monograph 21, Rockefeller Institute

1926.
Murphy, J. B. : Factors in Resistance to Heteroplastic Tissue Grafting, J. Exp.

Med. 19: 181, 1914; 19: 513, 1914; The Effect of Adult Chicken Organ

Grafted on the Chick Embryo, J. Exp. Med. 24: 1, 1916.
Murphy, J. B. : Transplantability of Tissues to the Embryo of Foreign Species ;

Tumor immunity, Jr. Exp. Med. 17: 482, 1913.
Murphy, J. B. and Ernest Sturm : Conditions Determining Transplantability of

Tissues in the Brain, J. Exp. Med. 28: 183, 1923.
Myer, Max, W. : Auto and Homoiotransplantation of Kidney in Guinea Pig, Arch.

f. Entwicklgsmech. 38: 1, 1913.

N

v. Naegeli, C. : Mechanisch-physiol. Theorie d. Abstammungslehre, Munchen u.

Leipzig 1884.
Naegeli, Oscar F. de Quervain and W. Stalder: Cellular Localization of

Allergy, Klin. Woch. 9: 924, 1930.

BIBLIOGRAPHY 685

Nather, Karl: Attempts at Immunization Against Transplanted Tumors with

Weakened and Killed Carcinoma Cells and Autolysates, Zeitschr. f. Krebs-

forsch. 19: 115, 1922.
Needham, J. : Chemistry and Biology of Organismal Growth, Proc. Roy. Soc.

Med. 29: 1577, 1936.
Neumann, H. O. : Transplantation of Uterine Mucosa. Virch. Arch. 272: 265,

1929.
Neurath, A. : Shape of Protein Molecule, J. Am. Chem. Soc. 61 : 184, 1939.
Newman, H. H. : Production of Monsters by Hybridization, Biol. Bullet. 32: 306,

1917; Inheritance in Teleost Hybrids, J. Exp. Zoology 16: 447, 1914.
Niekau, B. and L. Duschl: Haematol, u. pathol.-anatom. Studies in Parabiotic

Rats, D. Zeitschr. f. Chir. 191 : 221, 1925.
Nilson, H. W. and D. I. Ingle: Auto, Syngenesio and Homoiotransplantation of

Adrenal Cortex in Rats, Science 84: 424, 1936.
Nissen, R. : Lymph Glands and Bone Marrow in Parabiosis, Zeitschr. f. d. ges.

Exper. Med. 35: 251, 1923; D. Zeitschr. f. Chir. 19: 197, 1925.
Northrop, J. H. : Chemistry of Enzymes, Columbia University Press, 1939.
Noble, G. K. : Neural Basis of Social Behavior in Vertebrates, Collecting Net,

14: 121, 1939.
Noble, G. K. : The Experimental Animal from the Naturalist's Point of View,

the Instinctive Basis of Human Actions, Am. Naturalist 73: 113, 1939.
Noble, G. K. and Brian Curtis : Social Behavior of Jewel Fish. Bullet. Am. Mus.

Nat. History 76 : 1, 1939.
Noble, G. K., M. Warm and A. Schmidt: Social Behavior of the Black Crowned

Night Heron, The Auk 55 : 7, 1938.

Oberling, C, M. Guerin and P. Guerin: Transplantation of Mammary Fibro-
adenoma in Rats; Bullet. Assoc, franc, p. l'etude du Cancer, 26: 483, 1937.
Obermayer, F. and E. P. Pick: Precipitin Formation, Wien. Klin. Woch. 16: 659,

1903; 17: 265, 1904; Precipitin Reactions and Species Specificity, 19: 327,

1906.
Ohli, Masato : Organ Specificity of Spermatozoa, Okayama-Igakkai-Zasshi 43 :

2441 and 2641, 1931.
Ollier, L. J. : Transplantation and Regeneration of Bone, C. R. Acad. d. Sciences

126: 1252 and 1316, 1898.
Ollier, L. J. : Traite experiment, de la regeneration des os et de la production

artificielle de tissus osseux, Paris, 1867. Bone Transplants in Man, Arch, de

Physiol, norm, et path. 21 : 166, 1889.
Opie, E. L. : Significance of Allergy in Disease, Medicine 15: 487, 1936.
Orcutt, M. L. and P. E. Howe: Globulins and Agglutinins in Blood of Calves,

J. Exp. Med. 36:291,1922.
Osborne, H. F. : The Creative Principle in the Origin of Species, Science, 79

41, 1934.
Oshikawa, K. : Antibody Formation by Transplants, Z. F. Imm. Forsch. 33

297, 1922.
Oshima, T. : Homoiotransplantation of Skin in Man, Arch. f. Klin. Chir. 103

440, 1914.
Ottensooser, F. and E. Strauss : Immunochemistry of Globin, Biochem. Zeitschr

193 : 426, 1928.

Parker, G. H. : Humoral Agents in Nervous Activity, Cambridge University
Press, 1932.

686 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Parker, R. C. : Stability of Functionally Distinct Races of Fibroblasts, Science,
76: 219 and 446, 1932.

Pauling, Linus and C. Niemann: Structure of Protein, J. Am. Chem. Soc. 61:
I860,' 1939.

Pauling, Linus and D. H. Campbell: Production of Antibodies in Vitro, J.
Exp. Med. 76:211, 1942.

Peebles, Florence: Regeneration and Grafting in Hydrozoa, Arch. f. Entwick-
lgsmech. 10: 435, 1900; 14; 49, 1902.

Perkin, E. B. and B. Kropp: The Crustacean Eye Hormone as a Vertebrate
Melanophore Activator, Biol. Bullet. 63: 108, 1932.

Perthes, Georg: Homoiogenous Transplantation of Skin, Centralbl. f. Chir. 44:
426, 1917.

Pfeiffer, C. A.: Hormones and Transplantation (ovaries) (age and transplanta-
tion), Am. J. Anat. 55: 195, 1936; (testicles) Proc. Soc. Exp. Biol, and
Med. 32:603, 1935.

Pillemer, L. and E. E. Ecker: Specificity of Keratin, Science 88: 16, 1938.

Pirschle, Karl: Grafting Experiments with Petunia, Naturwissenschaften. 26:
629, 1938.

Plant, F. : Antisera Against Brain, Klin. Woch. 8: 1801, 1929.

Poll, H. : Skin Patterns, Hereditary Skin Diseases and Malformations, Dermat.
Woch. 89 : 849, 1927.

Pressman, D., D. H. Campbell and Linus Pauling: Mechanism of Immune
Agglutination, J. Immunol. 44: 101, 1942.

Prowazek, S. : Coalescence of Protoplasm in Algae, Biol. Centralbl. 27 : 737,
1907.

Putnoky, J.: Growth of Mouse Carcinoma in Rats, Am. J. Cancer 32: 35, 1938;
38: 191,1940.

Pybus, F. C. and H. R. Whitehead: Immune Reactions and Cancer, J. Path,
and Bact. 32: 195, 1929.

R

Rabes, Otto: Transplantation in Lumbricidae, Arch. f. Entwicklgsmech. 13:
239, 1902.

Rabl: Homologie und Eigenart, Verh. d. deutsch. pathol. Gesellschaft. II Jahr-
gang, 1899. (Centralbl. f. Allgem. Pathol. 10: 831, 1899.)

Raffel, D. : Gene Mutations in Paramecium Aurelia, J. Exp. Zool., 63: 371, 1932;
Biol. Bullet, 62:244, 1932.

Rand, H. W. : Inhibiting Agencies in Ontogeny and Regeneration, Anat. Record
29:98, 1924-25.

Rand, H. W. and Mildred Ellis : Form Determining Dominance in Transplanta-
tion in Planarians, Proc. Nat. Acad. Sci. 12: 570, 1926.

Rand, H. W. and E. Browne: Inhibition of Regeneration in Planarians by Graft-
ing, Proc. Nat. Acad. Sci. 12: 575, 1926.

Raper, J. R. : Hormones in the Sexual Reactions of Heterothallic Achlyas,
Science, 89:321, 1939.

Reed, Sheldon, C. and J. M. Henderson : Skin Grafting and Pigment Cell Mi-
gration, J. Exp. Zool. 85 : 409, 1940.

Rehn, E. and A. Wakabagashi: Syngenesiotransplantation of Bone and Joint,
Arch. f. Klin. Chir. 97: 1, 1912.

Rehn, E. : Transplantation of Fat Tissue in Rabbits, Arch. Klin. Chir. 97: 35,
1912.

Renner, O. : Inheritance in Species Hybrids, Zeitschr. f. inductive Abstammungs.
u. Vererbgslehre, 32 : 317, 1923.

Reynolds, B. D. : Interaction of Protoplasmic Masses in Arcella Polyposa, Biol.
Bullet. 46 : 106, 1924.

BIBLIOGRAPHY 687

Ribbert, Hugo: Transplantation of Ovaries, Testicles, Mammary Gland, Arch.
f. Entwicklgsmech. 7: 688, 1898.

Ribbert, H. : Transplantation of Fibroma in Dog, Centralbl. f. allg. Pathol, u.
path. Anat. 21 : 625, 1910.

Ribbert, H. : Compensatory Hypertrophy and Regeneration, Arch. f. Entwicklgs-
mech. 1 : 69, 1895.

Rich, A. R. and M. R. Lewis: Nature of Allergy in Tuberculosis as Revealed
by Tissue Culture Studies, Bull. Johns Hopkins Hosp. 50: 115, 1932.

Richter, M. N. and H. L. Jaffe: Transplantation of Thymus into Bone Mar-
row, J. Exp. Med. 47: 981, 1928; Regeneration of Autoplastic Lymphoid
Transplants, J. Exp. Med. 47: 977, 1928.

Richter, M. N. and E. C. MacDowell : Experiments with Mammalian Leukemia,
Physiol. Reviews, 15: 509, 1935.

Ries, Erich : Regeneration, Reduction and Budding in Clavellina, Arch. f.
Entwicklgsmech. 137: 326, 1937-38.

Ries, Erich : Differentiation of Organs and Tissues during Embryonal Develop-
ment, Naturwissenschaften. 25: 241, 1937.

Ries, Erich : Experimental Study of Symbiosis ; Transplantation of Mycetoma,
J. Morphol. u. Okol. d. Tiere 25 : 184, 1932.

Riess, E. Transplantation of Periosteum, Arch. f. Klin. Chir. 129; 750, 1924.

Rife, D. C. : Handedness of Twins, Science 89: 179, 1939.

Ritter, E. : Analysis of Coloration in White Axolotl, Naturwissenschaften. 17:
874, 1929.

Rivers, T. M. : Virus Diseases (Species and tissue specificity of viruses),
J. A.M. A. 107:206,1936.

Robb, C. K. : Growth of Parts in Relation to the Whole, Brit. J. Exp. Biol., 6:
311, 1929.

Robbins, W. : Heterosis, Am. J. Bot. 28 : 216, 1941.

Robbins, W. J.: Thiamin and Plant Growth; Specificity in the Power to Syn-
thesize Thiamin, Science, 89: 303, 1939.

Robinson, G. H. and R. C. Grauer: Transplantable Benign Adenomas in Rat;
Am. J. Cancer 16: 184 and 191, 1932.

Rohde, Carl: Homoiotransplantation, Parabiosis, Blood Groups, Beitr. z. Klin.
Chir. 134: 111, 1925. Transplantation of Bone, Arch. f. Klin. Chir. 129: 435,
1924.

Roessle. R. : Chemical Individuality of Embryonal Cells, Miinch. Med. Woch.
52: 1276, 1905.

Roffo, A. H. : Transformation of a Race of Rats Non-Receptive to Cancer into
a Receptive Race, C.R. Soc. Biol. 83 : 968, 1920.

Rothen, A. and K. Landsteiner: Adsorption of Antibodies by Egg Albumin
Films, Science 90: 65, 1939.

Rous, Peyton and J. B. Murphy: Tumor Implantations in the Developing
Embryo, J. A.M. A. 56: 741, 1911.

Rous, Peyton, and O. S. Robertson: Production of Homoiogenous Antibodies
in Rabbits : Free Antigen and Antibody Circulating Together, J. Exp. Med.
27:509, 1918.

Rous, Peyton: Comparison of Transplanted Tumor and of Embryonal Tissue
Transplants in Mouse, J. Exp. Med. 12: 344, 1910.

Rous, Peyton: Sarcoma of the Fowl Transmissible by an Agent Separated from
the Tumor Cell, J. Exp. Med. 13: 397, 1911.

Rous, Peyton and J. B. Murphy: Histological Signs of Resistance to Transmis-
sible Sarcoma of Fowl, J. Exp. Med. 15: 270, 1912.

Rous, Peyton: A Transmissible Avian Neoplasm, J. Exp. Med. 12: 696, 1910.

Rous, Peyton : Transmission of a Malignant Newgrowth by Means of a Cell-
free Filtrate, J. A. M. A. 56: 198, 1911.

688 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Rous, Peyton: The Virus Tumors and the Tumor Problem, Am. J. Cancer 28:
233, 1936.

Roux, W.: Cytotropism, Arch. f. Entwicklgsmech. 1: 43, 161, 1895; 3: 381, 1896.

Rubens-Duval, H. : Local and General Reactions of the Organism Against Can-
cer, Rapport Congres du Cancer, Strassbourg 1923, Paris.

Russ, S. and G. M. Scott: Cross Immunity with Rat Tumors, J. Path. & Bact.
30 : 564, 1927.

Russ, S., Helen Chambers, and G. M. Scott: Local and Generalized Action
of Radium and X-rays upon Tumor Growth, Proc. Roy. Soc. 92: 125, 1921.

Sabin, A. B. and P. K. Olitzky: Cultivation of Poliomyelitis Virus in Vitro in

Human Embryonic Nervous Tissue (organ specificity of virus), Proc. Soc.

Exp. Biol, and Med. 34: 357, 1936.
Sachs, Hans: Age Differences in Blood, Centralbl. Bakt. 34: 686, 1903.
Sachs, H. : Species and Individuality Differentials as Antigens ; Their Chemical

Constitution, Wiener Klin. Wochenschr. 41 : 431, 1928.
Sale, Llewellyn: Autogenous and Homoiogenous Transplantation of Pigmented

Skin in Guinea Pigs, Arch. f. Entwicklgsmech. 37: 248, 1913.
Saltykow, S. : Transplantation of Tails of Embryos or Adult Rats and Mice;

Effect of Age. Arch, f . Entwicklgsmech. 9 : 329, 1900.
Salzer, H. : Transplantation of Thyroid, Arch. f. klin. Chir. 83: 881, 1909.
Sampson, M. M. : Iso and Heteroagglutination of Spermatozoa by Egg Ex-
tracts, Biol. Bullet. 43 : 267, 1922.
Sandstrom, C. J.: Chorio-allantoic Transplantation, Anat. Rec. (supplement) 54:

59, 1932; Biol. Bullet. 79: 329, 1940.
Santos, F. V.: Transplantation in Planaria, Biol. Bullet. 57: 188, 1929; Physiol.

Zoology, 4: 111,1931.
Sauerbruch, F. and M. Heyde: Parabiosis (Ileus and uremia), Ztschr. f. exp.

Path. u. Ther. 6 : 33, 1909.
Sauerbruch, F. and M. Heyde: Parabiosis (Causes of induction of labor)

Munch. Med. Woch. 57: 2617, 1910.
Sauerbruch, F. : Cellular Defensive Processes in Parabiosis, Munch. Med.

Woch. 70 : 860, 1923.
Saxton, J. A., Jr., M. M. Schmeckebier, and R. W. Kelley: Transplantation

of Autogenous Pigmented and Unpigmented Ear Skin in Guinea Pigs, Biol.

Bullet. 71 : 453, 1936.
Schaxel, J. : Transplantation and Pigmentation of Skin in Axolotls, Verhandl.

d. deutsch. Zool. Gesellschft. 28-31 : 32, 1923-26.
Schaxel, J.: Transplantation of Regenerating Buds in Different Races of

Axolotl, Verh. d. deutsch. Zool. Gesellsch. 28: 55, 1923. Inhibition of Re-
generation in Urodeles, Zool. Anzeiger 56 : 128, 1923.
Schenck, E. G. : Constitution of Globin in Animals and Man, Arch. exp. Path.

u. Pharmak. 150: 160, 1930. Genealogy of Proteins, Naturwissenschaften 18:

824, 1930.
Schermer, S. and O. Hofferber: Blood Group of Horse, Zeitsch. f. Imm.

forsch. 67: 497, 1930.
Schermer, S. and A. Kaempffer: Blood Groups of the Horse, Zeitschr. f. Imm.

forsch. 80: 146,1933.
Schermer, S., W. Kayser, and A. Kaempffer: Isoagglutinins in Blood of Man

and Hog, Zeitschr. f . Imm. forsch. 68 : 437, 1930.
Schiff, F. : Mode of Inheritance of Factors M and N, Klin. Woch. 9: 1956, 1930.
Schiff, F. and O. v. Verschuer: Blood Groups in Twins, Klin. Woch. 10: 723,

1931.

BIBLIOGRAPHY 689

Schmidt, Georg: Parabiosis, D. Zeitschr. f. Chir. 171: 141, 1922.

Schoene, G. : Transplantation of Non-Autogenous Tissues, Verh. d. deutsch.

Gesellsch. f. Chir. 37: 174, 1908. Transplantation of tumors and normal tis-
sues, Beitr. z. klin. Chir. 61 : 1, 1909. Transplantation Immunity, Munch.

Med. Wochenschr. 59: 457, 1912. Hair in Skin Grafts, Zeitschr. f. d. ges.

exp. Med. 1: 444, 1913. Syngenesiotransplantation, Beitr. z. Klin. Chir., 99:

233, 1916.
Schoene, G. : Immunization Against Transplants of Cancerous Tissues by Inocu-
lation of Normal Cells, Verhandl. d. deutsch. Gesellsch. f. Chir. 36: 213,

1907.
Schotte, O. E. and K. P. Hummel: Lens Induction at Expense of Regenerating

Tissues of Amphibians, J. Exp. Zool. 80 : 131, 1939.
Schultz, W. : Transplantation and Hybridization, Arch. f. Entwicklgsmech. 35:

484, 1912; 36: 353, 1913; 37: 285, 1913; 41: 120, 1915; 43: 361, 1917-18.
Schultz, W. : Transplantation of Ovaries to Different Species and Varieties,

Arch. f. Entwicklgsmech., 29: 79, 1910.
Schulze, Werner : Parabiosis, Klin. Woch. 1 : 2007 and 2052, 1922.
Schweitzer, M. D. and J. Furth : Susceptibility to Transmitted Leukemia in

Inbred Mice, Am. J. Cancer 37: 224, 1939.
Schwind, J. L. : Heterotransplantation of Limb and Shoulder Girdle of Am-

blystoma, J. Exp. Zool., 59: 265, 1931.
Secerov, S. : Transplantation of Skin and Change in Coloration in Fish, Arch. f.

Entwicklgsmech., 33: 716, 1912.
Seelig, M. G. : Autogenous and Homoiogenous Transplantation of White Skin

in Guinea Pigs, Arch. f. Entwicklgsmech. 37: 259, 1913.
Seevers, C. H. and D. A. Spencer : Autoplastic Transplantation of Guinea Pig

Skin Between Regions with Different Characters, Am. Naturalist 66: 183,

1932.
Selter, G. E. : Chemical Antigens and Lipoid Antibodies, Zeitschr. f. Imm.

forsch. 68 : 409, 1930.
Shaw-Mackenzie, J. A.: Immunity and Malignant Tumors, Lancet 256, 1926.
Shawan, H. K. : Skin Grafting and Blood Groups, Am. J. Med. Sciences 157:

503, 1919.
Shen, Gertrud: Regulation in Early Gastrula of Triton and origin of Cyclopia,

Arch. f. Entwicklgsmech. 137: 271, 1937-38.
Shimidzu, Takeo: Haemagglutination in Animals, Tohoku J. Exp. Med. 18:

27, 1931-32.
Shiple, G. and C. P. Sherwin: Phenylacetic Acid, its Mode of Elimination,

J. Am. Chem. Soc. 44: 618, 1922.
Shirai, Y. : Transplantation of Rat Sarcoma into Brain, Japan. Med. World,

No. 2, page 14, 1921 (cited from Woglom, Cancer Review 1929).
Shull, G. H. : The Genotypes of Maize, Am. Naturalist, 45: 234, 1911.
Siebert, W. J. : Auto and Homoiotransplantation of Thyroid Gland into Brain

of Guinea Pigs, Proc. Soc. Exp. Biol, and Med. 26: 236, 1928.
Siebert, W. J.: Effects of Graded Degrees of Heat on the Results of Homoio

and Heterotransplantation of Cartilage and Thyroid, Proc. Soc. Exp. Biol.

& Med. 26: 238, 1928; Arch. Path. 12: 590, 1931.
Silberberg, Martin : Causes and Mechanisms of Thrombosis, Physiol. Reviews

18 : 197, 1928.
Silberberg, Martin : Influence of Anterior Pituitary Extract on Autotransplan-

tation and Homoiotransplantation of Thyroid, Arch. Path. 17: 381, 1934.
Simmonet, H. and J. Pretresco: Parabiosis, Bullet, et Memoires de la section

d'endocrinology 21 : 417, 1938.
Simpson, G. G. : The Role of the Individual in Evolution, J. Washington Acad.

Sci. 31 : 1, 1941.

690 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Smirnova, E. : Heterogenous Transplantation of Malignant Tumors into An-
terior Chamber of Eye, Bullet, de Biologic ct de m^decine exper. 4: 6, 1937.

Smith, E. L. : Solution of Chlorophyll-protein Compounds, Science 88, 170, 1938.

Smith, P. E. : Parabiosis Between Hypophysectomized and Normal Tadpoles,
Anat. Record 21 : 83, 1921.

Smith, Theobald and R. B. Little: Protective Effect of Colostrum in New-
born Calf, J. Exp. Med. 36: 181, 1922.

Smith, Theobald and R. B. Little: Cow Serum as Substitute for Colostrum,
J. Exp. Med. 36:453, 1922.

Sonneborn, T. M. : Sexuality and Genetics in Paramaecium Aurelia, Proc. Am.
Philos.Soc. 79:411, 1938.

Sonneborn, T. M. and R. S. Lynch : Racial Differences in Conjugation in
Paramaecium Aurelia, Biol. Bullet. 62: 258, 1932.

Spangler, J. M., J. M. Murray, and C. C. Little: Genetics of Susceptibility to
Transplanted Tumors, J. Nat. Cancer Inst. 3: 123, 1942.

Spek, Josef : Winter buds, Regeneration and Totipotent cells in Clavellina, Arch.
f. Entwicklgsmech. Ill : 119, 1927.

Spemann, H. and O. Schotte: Xenoplastic Transplantation, Naturwissen-
schaften20:463, 1932.

Spemann, H. : Transplantation in Larvae of Triton : Species and Organ Speci-
ficity, Naturwissenschaften 7: 581, 1919.

Spemann, H. : Chimaerae Produced Through Embryonal Heterotransplantation
in Triton, Arch. f. Entwicklgsmech. 48: 533, 1921.

Spemann, H. and H. Mangold: Implantation of Heterogenous Organizers in
Triton, Arch. f. Entwicklgsmech. 100: 599, 1924.

Spemann, H. and B. Geinitz: Heterogenous Transplantation and Organization,
Arch. f. Entwicklgsmech. 109: 129, 1927.

Stakman, E. C. : Plant Disease Fungi Constantly Evolving New Types, Science
88:438, 1938.

Steinach, E. : Feminization of Male Guinea Pigs and Rats Through Transplan-
tation of Ovaries, Arch. f. Physiol. 144: 71, 1912.

Steinecke, Fr. : Serodiagnosis of Plant Proteins and Phylogenetic Development
of Plants, Naturwissenschaften 13: 853, 1925.

Stern, Kurt and R. W. G. Wyckoff: Specificity of Catalase, Science 87: 18,
1938.

Stern, L. : The Functioning of Barrier Between Blood and Brain, Schweiz.
Med. Woch. 59 : 935, 1929.

Stevenson, H. W. : Tumor Immunity in Chick Embryo, J. Cancer Research, 2:
449, 1917; 3: 63, 1918.

Stilling, H. : Transplantation of Adrenal into Testicle, Beitr. z. path. Anatomie,
37:480, 1905.

Stone, L. S. and P. Saphir: Regeneration of Lens of Eye of Anurans, Urodeles
and Fishes, J. Exper. Zoolog. 85 : 71, 1940.

Stout, A. B. and Clyde Chandler: Tetraploidy and Compatibility in Fertiliza-
tion in Plants, Science 94: 118, 1941 ; 96: 257, 1942.

Strong, L. C. : Genetics of Pituitary and Ovarian Grafts, J. Heredity, 27: 219,
1936.

Strong, L. C. : Transplantation of Two Tumors Originating in the Same Mouse ;
Somatic Mutations, J. Cancer Research, 13 : 103, 1929.

Strong, L. C. : Tissue Specificity in Transplantation of Tumors ; its Genetic
Basis, J. Exp. Zool. 36: 67, 1922; J. Exp. Med. 39: 447, 1924.
Proc. Nat. Acad. Sciences, 12: 181, 1926; J. Exp. Zool. 45: 231, 1926.

Strong, L. C. and C. C. Little: Tests for Physiological Differences in Trans-
planted Tumors, Proc. Soc. Exp. Biol, and Med. 18: 45, 1920.

Strong, L. C, R. T. Hill, C. A. Pfeiffer, and W. U. Gardner: Genetic and

BIBLIOGRAPHY 691

Endocrine Studies on a Transplantable Carcinoma of Ovary, Genetics 23:
585, 1938.

Strong, L. C. : Genetic Study of Transplantation and Origin of Tumors, J. Can-
cer Res. 10 : 219, 1926.

Stunkard, W. H. and C. H. Willey: Immunity to Infection with Heterophyid
Trematodes, Biol. Bullet. 81 : 279, 1941.

Summers, F. M. : Normal and Regulative Development in the Colonial Ciliate,
Zoothamnium Alternans, Biol. Bullet. 73: 354, 1937.

Sumner, F. B. : Genetic and Distributional Studies on Peromyscus, J. of Genetics
23 : 275, 1930.

Sumner, J. B. and J. S. Kirk: Antienzymes, Science 74: 102, 1931.

Sumner, J. B. : Isolation and Crystallization of Urease, J. Biol. Chem. 69: 435,
1926.

Sussman, Ph. O. : Individual Differentiation of Protein by Means of Precipi-
tates, Wiirzb. Abhandl. aus d. ges. Gebiet d. Med. 22: 297, 1925.

Takakusu, S. : Internal Secretion in Parabiotic Rabbits, Biochem. Zeitschr.

128: 1, 1922.
Takewaki, K. : Endocrine Factors in Transplantation of Ovaries, J. Faculty

Science, Univ. Tokyo 3: 155, 1933.
Takewaki, K. : Ovary in Parabiosis of Rats, Faculty of Science, Imp. Univ.

Tokyo 3: 153, 1933.
Taliaferro, W. H. and Clay G. Huff: Genetics of Parasitic Protozoa. Am.

Assoc. Advancement of Science, Publ. No. 12, p. 57, 1940.
Taube, E. : Transplantation of Amphibian Skin, Arch. f. Entwicklgsmech. 98:

98, 1920; 49: 270, 1921.
Taylor, Alfred, J. Thacker, and D. Pennington : Growth of Cancer Tissue

in Yolk Sac of Chick Embryo, Science 96 : 342, 1942.
Ten Broeck, C. : Enzymes (trypsins) as Antigens in Anaphylactic Reactions in

Vitro, J. Biol. Chem. 106 : 729, 1934.
Tennent, D. H. : Heterogenous Fertilization and Hybrids in Echinoderms, J.

Exp. Zool. 12: 391, 1912; J. Morphol. 23: 17, 1912; Carnegie Inst. Public

No. 391, p. 105, 1929; Scientific Monthly p. 117, Aug. 1929.
Thiersch: Skin Grafting, Arch. f. Klin. Chir. 17: 318, 1874. Successful Trans-
plantation of White Skin on Negroes and vice versa, Verh. d. deutsch.

Gesellsch.f. Chir. 15:17, 1886.
Thomoff, Z. Individuality Reaction and Serum Therapy, Zeitsch. f. Imm. forsch.

67: 396, 1936.
Thomsen, O. and T. Kemp: Differentiation of Blood Groups in Animals, Zeitsch.

f. Imm. forsch. 67:251,1930.
Thurston, E. W., J. E. Smadel, and Leo Loeb: Inhibiting Action of Serum on

Tissue Extracts in the Coagulation of Blood, Am. J. Physiol. 114: 19, 1935.
Tillett, W. S. and R. L. Garner: Fibrinolysins of Streptococci, J. Exp. Med.

58 : 485, 1933 ; 60 : 239 and 255, 1934.
Tirala, L. G. : Transplantation in Criodilus, Arch. f. Entwicklgsmech. 35 : 523,

1912.
Tiselius, A. and E. A. Kabat: Electrophoresis of Immune Serum Science 87:

416, 1938.
Todd, Ch.: Individuality of Red Corpuscles, Proc. Roy. Soc. B. 106: 20, 1930;

107: 197,1930; 117:358,1935.
Todd, Ch. and R. G. White: Hemolytic Immune Isolysins in Ox, Am. J. Hyg.

10: 185, 1910; Proc. Roy. Soc. Ser. B 82: 416, 1910.
Todd, Ch. : Recognition of the Individual by Hemolytic Methods. J. Genet. 3 :

123, 1913-14.

692 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Travis L. E. and Abraham Gottlober: Individuality of Brain Waves, Science
84! 532, 1936.

Treibman, W. : Immunization of Rabbits Against Human A Factor, Zeitschr. f.
Imm. forsch. 79:274, 1933.

Turck, F. B. : The Action of the Living Cell, New York, 1933.

Tschernischoff, A.: Transplantation of Ovaries, Ziegler's Beitr. z. path. Anat.
59: 162, 1914.

von Tschermak, A. : Allgemeine Physiologie, Berlin 1916.

Tureen, L. L. : Effect of Age of Host on Fate of Thyroid Transplants in Guinea
Pigs. Am. J. Path. 3: 501, 1927.

Turner, C. D. : Intraocular Transplantation of Gonads and Sex Accessories
from Mouse to Rat, Proc. Soc. Exp. Biol, and Med. 36: 314, 1937. Trans-
plantation of Suprarenal Glands of Rat into Anterior Chamber of Eye, Proc.
Soc. Exp. Biol. & Med. 39: 133, 1938. Intraocular Transplantation of Pre-
pubertal Testes in the Rat, Am. J. Anat. 63: 101, 1938. Homoiotransplanta-
tion of Suprarenal Glands from Prepubertal Rats into Eyes of Adult Hosts,
Anat. Record, 73 : 145, 1939.

Turner, C. D., R. Haffen, and L. S. Amant: Persistence of Medullary Tissue
in Homoiotransplanted Adrenals, Proc. Soc. Exp. Biol, and Med. 41 : 474,
1939.

Twitty, V. C. and J. L. Schwind: Growth of Heterotransplanted Eyes and
Limbs in Amblystoma, J. Exp. Zool. 59: 61, 1931.

Twitty, V. C. : Growth Directing Substances and Transplantation in Amphibia,
Cold Spring Harbor Symposia on quantit. Biol. 2: 148, 1934.

Twitty, V. C. and H. H. Johnson: Motor Inhibition in Amblystoma Produced
by Triturus Transplants, Science 80: 78, 1934.

Tyler, Albert: Fertilizin and Specific Adaptation, Proc. Nat. Acad. Sciences
25: 317, 1939; 20: 39, 1942; Biol. Bullet. 81: 190, 1941.

Tyzzer, E. E. : Role of Inflammation in Immunity of Mice to Transplanted
Tumors, J. Cancer Research 1 : 117, 1916.

U

von Ubisch, L. : Germ Layer-chimaerae, Naturwissenschaften 21 : 325, 1933.
von Ubisch, L. : Reciprocal Chimaerae of Echinocyanus and Parechinus, Arch.

f. Entwicklgsmech. 129 : 68, 1933.
Uhlenhuth, Eduard: Metamorphosis of Transplanted Eyes in Salamander,

Arch. f. Entwicklgsmech. 36: 211, 1913; J. Gen. Physiol. 1: 525, 1918-19.
Uhlenhuth and Seiffert: Immunity Against Transplantable Tumors, Med.

Klin. 21 : 576, 1925.
Underwood, H. L. : Anaphylaxis Following Skin Grafting for Burns, J. A. M. A.

63: 775, 1914.
Urbach, E. and H. Schnitzler: Intracutaneous Immunization of Mouse Against

Cancer Tissue, Wien. Kiin. Woch. 41 : 941, 1928.

Veblen, B. B. : Adaptive Changes of Bacteria to Serum Precipitins, Proc. Soc.

Exp. Biol, and Med. 27: 204, 1929.
von Verschuer, O. : Constitution and Heredity, Klin. Woch. 8: 769, 1929.
Verworn, M. : Transplantation of Nuclei, Pfliiger's Arch. 51: 115, 1892.
Villata, G. : Effects of Trypan Blue in Homoiotransplantation of Bone in Rats,

Arch. p. 1. Science med. 54: 401, 1930.
Vogel, H. H., Jr. : Transplantation of Autogenous and Homoiogenous Skin in

Adult Rana Pipiens, J. Exp. Zool. 85 : 437, 1940.

BIBLIOGRAPHY 693

Volker, H. u. K. Erichsen: Transfusion of Surviving Extremities with
Defibrinated Blood, Arch. f. exper. Path. u. Pharmak. 127: 269, 1928.

Voss, H. E. : Endocrine Function of Heterotransplanted Organs, Biologia gener.
3 : 571, 1927.

W

Waddington, C. H., J. Needham, and D. M. Needham, Physico-chemical Nature
of Organizers, Naturwissenschaften 21 : 771, 1933.

Walsh, L. S. N. : Blood Interrelationship of Horses, Asses and Mules, J.
Immunol. 9 : 49, 1924.

Warner, S. G. and M. C. Reinhardt: Effect of X-rays on a Tumor of Known
Genetic Constitution, Proc. Soc. Exp. Biol, and Med. 42: 673, 1939.

Webster, L. T. : Virus of Japanese B. Encephalitis, of St. Louis Encephalitis
and Louping 111 Virus, Science 86: 202, 1937.

Webster, L. T. : Classification of Primary Encephalitides of Man According to
Virus Etiology, J. A. M. A. 116 : 2840, 1941.

Wedd, B. H., A. C. Morson, and S. Russ: Immunity Conferred Upon Mice by
Radium Irradiated Mouse Carcinoma, J. Path. & Bact. 18: 566, 1913-14.

Weichardt, W. : Production of Isocytolysins, Munch. Med. Wochenschr. 48:
2035, 1901. Individual Blood Differences, Hyg. Rundschau. 13: 756, 1903.

Weigl, R. : Transplantation and Metamorphosis of Skin in Amphibia, Arch. f.
Entwicklgsmech. 29: 620, 1910.

Weijer, Fr. : Races and Varieties in Mosquitos, Naturwissenschaften 25 : 529,
1937.

Weil, R. and C. Bernheim : Hormone Effects on Autotransplanted Thyroid
Glands in Guinea Pigs, C.R. Soc. Biol. 121 : 449, 1936.

Weiss, Ch. : Bacterium Melaninogenicum, Fibrinolysin and Serological Types,
Proc. Soc. Exp. Biol, and Med. 37:473, 1937.

Weiss, Paul : Transplantation of Extremities in Amphibia, Arch. f. Entwicklgs-
mech. 99 : 168, 1923 ; 104 : 317, 1925.

Wells, H. G. and T. B. Osborne: Anaphylactic Reactions with Proteins of Milk,
J. Inf. Diseases 29: 200, 1921.

Wells, H. G. : Chemical Constitution and Immunological Reactions of Proteins,
J. Immunol. 1 : 467, 1916.

Wells, H. G. and T. B. Osborne: Anaphylactic Reaction with Proteoses of
Seeds, J. Infect. Diseases 17: 259, 1915.

Wells, H. G. and T. B. Osborne: Biological Reaction of Vegetable Proteins,
J. Infect. Diseases 12: 341, 1913; 14: 377, 1914.

Wells, H. G. : Chemistry of Anaphylaxis; Proteins of Hen's Egg, J. Inf. Dis-
eases, 9: 147, 1911.

Welsh, J. H. : Specific Influence of Host on Light Response of Parasitic Water
Mites, Biol. Bullet. 61 : 497, 1931. Laboratory Experiment in Animal Be-
havior, Science, 75: 591, 1932.

von Wettstein, F. : Generic Hybrids in Mosses, Zeitschr. f. Induktive
Abstammungs u. Vererbungslehre 33 : 253, 1924.

von Wettstein, W. : Effect of Hybridization on Resistance to Disease, Natur-
wissenschaften 25 : 434, 1937.

von Wettstein, F. : Inheritance by Means of Cytoplasm, Naturwissenschaften
19:280, 1931.

Wetzel, G. : Transplantation in Hydra, Arch. f. mikr. Anat. 45 : 273, 1895.

White, P. R. : Growth Without and With Differentiation in Plants in the Test
Tube, Science 89: 12, 1939.

Wieman, H. L. and T. C. Nussman: Heterotransplantation of Spinal Cord in
Amblystoma Embryos, J. Exp. Zool. 53 : 45, 1929.

694 THE BIOLOGICAL BASIS OF INDIVIDUALITY

Wiener, A. S. : Rh factor in Erythrocytes and Transfusions, Arch. Path. 32:

227,' 1941.
Wiener, Maria, C. A. Zittle, and Stuart Mudd: Antigenic Structure of Hemo-
lytic Streptococci ; Type Specific M Protein, J. Immunol. 45 : 29, 1942.
Wigglesworth, V. B. : Function of Corpus Allatum in Growth and Reproduc-
tion of Rhodnius, Quart. J. Micros. Science 79: 91, 1936.
Wildegans: Transplantation of Skin, Arch. f. klin. Chir. 120: 415, 1922.
Wilhelmi, R. W. : Serological Reactions and Species Specificity in Helminths,

Biol. Bullet. 79: 64, 1940. Serological Tests for Organismal Differentials,

Biol. Bullet. 79: 64, 1940; 82: 179, 1942.
Willheim, R. and K. Stern: Serodiagnosis of Cancer, Biochem. Zeitschr. 226:

315, 1930.
Williamson, C. S. : Length of Survival of Homobgenous Kidney Transplants

in Dogs, J. Urology 10 : 275, 1923.
Winkler, F.: Transplantation of Pigmented Skin in Amphibia, Arch. f. Ent-

wicklgsmech. 29 : 620, 1910.
Witebsky, Ernest, N. C. Klendshog, and P. Swanson: Agglutinogens, Ag-
glutinins and Blood Transfusions, J.A.M.A. 116: 2654, 1941.
Witebsky, E. and G. Sollazzo: Organspecific Brain Structures in Ontogenesis

Z. f. Imm. forsch. 67:1, 1930.
Witebsky, E. and K. Komiya : Antibodies Against Leucocytes, Zeitschr. f. Imm.

forsch. 67:480, 1930.
Witebsky, Ernst: Serological Analysis of Cells and Tissues, Naturwissen-

schaften 17: 771, 1929. Serological specificity of Carcinoma Tissue, Klin.

Woch. 9:58, 1930.
Witebsky, E. and E. Morelli: Serological Analysis of Sarcoma, Zeitschr. f.

Imm. forsch. 78 : 179, 1933.
Witebsky, E. : Common Antigens in Human Blood Group A Hogblood and in

Forssman Differentials, Zeitschr. f. Imm. forsch. 48: 369, 1926; 49: 1 and

517, 1927; 51: 161, 1927.
Witebsky, E. and K. Okabe: Group Antigens in Human Organ Extracts;

Reactions with Isoagglutinins, Zeitschr. f. Imm. forsch. 52: 359, 1927; 54:

131, 1927.
Witebsky, E. and J. Steinfeld: Organspecificity, Zeitschr. f. Imm. forsch. 58:

271, 1928.
Wodsedalek, J. E. : Sterility in the Mule, Biol. Bullet. 30: 1, 1910.
Woglom, Wm. H. : A critique of Tumor Resistance, J. Cancer Res. 7: 283, 1922;

Rapport Congres du Cancer, Paris p. 118 Strassbourg 1923.
Woglom, Wm. H. : Absorption of Protective Agents from Rats Resistant to

Transplantable Sarcoma, Am. J. Cancer 17: 873, 1933.
Woglom, Wm. H. : Recovery in Locke's Solution of a Retarding Agent from

Immune Rats, Am. J. Cancer 30 : 477, 1937.
Woglom, W. H. : Immunity to Transplantable Tumors, Cancer Review 4: 129,

1929.
Wolfe, H. R. : Application of Precipitin Reaction to Studies of Relationship in

Mammals, Birds and Reptiles, Biol. Bullet. 76: 108, 1939.
Woodward, A. E. : Physiological Significance of Precipitates from Egg Secre-
tion of Arbacia and Asterias, J. Exp. Zool. 26: 459, 1918.
Woods, A. C, E. L. Burky, and M. B. Woodhall: Organ Specific Properties

and Antigenic Power of Alpha Crystalline, Transact. Am. Ophthalm. Soc.

29: 168, 1931.
Wormall, A. : Immunological Specificity of Halogenated and Nitrated Protein,

J. Exp. Med. 51 : 295, 1930.
Wyckoff, R. W. G. : Ultracentrifugal Purification of Macromolecular Proteins,

Science 86: 92, 1937.

BIBLIOGRAPHY 695

Wyman, L. C. and C. Tum Suden : Homoiotransplantation of Adrenal Cortical
Tissue, Science 85 : 589, 1937.

Y

Yamakami, K. : Individuality of Semen; Specific Inhibition of Isohemagglutina-
tion, J. Immunol. 12: 185, 1926.

Z

Zacherl, H. : Ovarian Function in Parabiosis, Krankheitsforschung 6: 174, 1928.
Zangemeister, W. and Eva Krieger: Serological Reactions Between New-born

Children and Parents, Miinch. Med. Woch. 75: 1577, 1928.
Zeller, E. A. : Specificity of Diamino Oxydase, Naturwissenschaften. 26 : 578

1938.
Zozaya, J. and Janet Clark : Immunization with Polysaccharides of Pneumo-

cocci, J. Exp. Med. 57: 21, 1933.
Zuckerman, S. : The Social Life of Monkeys and Apes, New York, 1932.

Author and Subject Index

Abderhalden, 22
Addison, 24, 59, 123
Adelmann, 265
Adelsberger, 481, 491
Adaptation, various types of, 14

— in unicellular organisms and viruses,

584-587, 588

— of bacteria and formation of new en-

zymes, 572

— of symbionts in insects to mycetoma

and to species, 564

— in tissues, 580-584, 588

— to autogenous toxins and to microor-

ganisms, 559, 562-563
Adaptive changes in host against trans-
planted tumors, 397, 398

tissues, tumors and viruses, 605

transplantation of normal tissues,

396, 397

transplantation of tumors, 390-

397, 436-437, 438

Adaptive variations, 364, 376, 377
Adolph, 226

Affinity, vegetative and sexual, 19
Ageing, chemical changes in, 527-528

— and evolution, 601

Algae, specific adaptation in, 293, 294

Allantois, transplantation into, 177-178

Alloway, 586

Alverdes, 246

Amoebocytes and tissue formation, 298-301

Amphibia (adult), transplantation and in-
dividuality in, 226-231

— , autogenous, homoiogenous, and heter-
ogenous transplantation of skin, 226-
227, of other organs, 229

— , urodeles and anurans, differences be-
tween, 231

Anaphylaxis and transplantation, 158, 163-
164

— immunization and organismal differen-

tials, 556-557, 558, 559
Anderson, 229
Andervont, 357, 358, 409
Andrewes, 357, 430
Annelids, transplantation and individuality,

218-223
— , homoiogenous transplantation, 218-219,

221, 222
— , autogenous transplantation, 219
— , tissue and organ equilibria, 219-221, 222-

223
Annelids, heterogenous transplantation,

221-223
Anson, 539

Anterior-chamber of eye, transplantation
into, 179-182

, and hormones, 179-180

, transplantation of tumors in-
to, 181
Antibodies, against autogenous tumors, 402
— , multiple, against single experimental

antigens, 570
— , production of, in vitro, 578-579
Antigens and antibodies in embryonal and
adult tissues, 524-526

— and autogenous substances, 516-518

— in blood of horse, donkey and mule,

519-521

— in cancer and in embryonal tissue, 429-

430
— , carrier and hapten, 568-570, 574-575

— in Cavia hybrids, 521
— , complex, 565

— of erythrocytes, changes in, 586-587
— , experimental ; graded specificity of,

568-569

— in hybrids of Berberis, 523

— in hybrids of doves, 521-523

— and individuality differentials, 23

— , other than organismal differentials in
transplantation of tumors, 402, 427,
431

— and organ specific substances, 23

— (complex), and species differentials, 22,

23

— in tumors, organismal differentials, 377,

378, 380-381

Apolant, 340, 343, 343, 344, 345, 385, 400,
401, 412, 425, 432, 434

Appel, T. W., 138, 181

Appel, Max, 412

Armangue, 570

Aronson, 551

Arthropods, transplantation and individu-
ality in, 223-225

Arthus phenomenon and idiosyncrasy, 551-
556

Ascoli, 407, 511

Askanazy, 254

Astbury, 566

Athrepsia, and immunity against trans-
planted tumors, 159, 169, 401, 403, 432

Atopen, 553

Atwell, 180

Avery, 504, 570, 586

Autogenous equilibrium, 14, 24, 141, 142,
212, 286

and cancerous growth, 142

— substances, 13

— tissue regulators, 71

697

698

THE BIOLOGICAL BASIS OF INDIVIDUALITY

Autogenous transplantation, 139

in birds, 59-63, 138

in mice, 54-55

in guinea pigs and rats, 37-51

of thyroid gland, 37-38, 136-137

of thyroid gland, effect of feeding

thyroid substance, 41

of skin, 136

of cartilage and fat tissue, 41, 42,

45

of ovary, 136

of striated muscle tissue, 45, 46

of uterus, 47-48

of uterus and development of pla-

centoma, 49-50

of arteries, 167-168

of kidney, 50-53

of leg, 167-168

of thymus, 138-139

of tumors, 136

reactions in, 61, 62, 141-142

B

Bacteriophage, specificity of, 577

Baeslack, 388, 408, 419

Bailey, 572

Balinsky, 246, 305

de Baloghi, 349

Baltzer, 309

Bancroft, 539

Barnes, 382

Barth, 450

Bartz, 577

Bashford, 24, 256, 340, 345, 363, 373, 389,
391, 400, 401, 402, 411, 412, 424, 425,
432, 434, 435, 436

Baumgartner, Leona, 527

Bautzmann, 262

Bayer, 145, 147, 179

Beadle, 272

Becht, 181

Beebe, 414

B eh ring, 22

Begg, 355

Belogolowy, 251

Benign tumors, effect of hormones, 359,
360, 361

, organismal and tissue differentials,

359-362

, transplantation of, 359-362

Bensley, 542, 579

Berger, 535

Bergmann, 566, 573

Bernstein, 471, 493, 494

Bert, 166

Besredka, 470

Biberstein, 557

Biochemical differences between individu-
als, 23-24, 150-151, 169

Bittner, 96, 138, 370, 371, 373, 389

Blacher, 446, 447

Black, 499

Blakeslee, 563

Bloch, 552

Block, 572

Blood cell reaction and age of donors
of transplants, 186

induced by protein, 197, 198

induced by heated tissues, 195-

196

induced by tissues treated chemi-
cally, 196-198

Blood, transfusion of, 19

Blood groups, agglutinogen, agglutinins
and organismal differentials, time of
origin, 492-493

, antigen, agglutinins and organismal

differentials, 478, 479-486, 487-488,
495-497

, and constitution, 153, 497

Blood group differentials and Forssman
differential, 491-492

Blood groups and individuality differen-
tials, 22, 150-156

, mode of inheritance, 494-

495

Blood groups, secondary and unusual; in-
dividuality differentials, 485

in different species of animals, 486-

491

and racial differences, 486

Blood vessel anastomosis and transplanta-
tion, 166-167, 167-169

Blumenthal, 12, 13, 28, 61, 63, 65, 119, 122,
151, 162, 164, 186, 196, 197, 344, 362,
422, 423, 424, 439, 493, 524, 540

Bodansky, Oscar, 577

Bodenstein, 449, 611

Bordet, 22

Born, 223, 234, 235, 236, 247, 451

Borrel, 24, 343, 358

Borst, 24, 157, 168, 169

Boyd, W. C, 499

Boyden, 499, 500, 501

Brain, transplantation into, 178-179

— , homoiogenous transplants in, 178-179

Braus, 236, 246, 247, 524

Brian, 305

Bronfenbrenner, 577

Browman, 138

Brown, A. P., 461, 519, 539, 572

Browne, E. N., 204, 205

Bruck, 150, 502

Buchbinder, 479, 487

Buchner, 22

Bullock, 407

Burack, 358

Burgess, 158, 417, 418, 424

Burnet, 585

Burns, R. K., 247, 451

Burt, 204, 205

Bytinski-Salz, 266, 267, 269, 561, 583

INDEX

699

C

Campbell, 578

Camus, 525

Cancer, nature and causes, 333-337

Cannon, P., 528, 551, 581

Cannon, W. B., 463, 593

Caritonoids, as species and strain specific
substances, 293

Carlson, 181

Carnot, 136

Carrel, 167, 168, 185, 190

Caspari, 407, 408, 411, 426, 433, 438

Castle, 320

Celakowsky, 294

Cellular reactions of host against trans-
planted tissues, 6, 8, 24, 27-28

and active immunity,

159-160, 162-163

; their specificity, 130-

141

tumors, 416-427

Chambers, H., 386, 389, 433, 438

Chambers, L. A., 542

Chameleon, transplantation of skin in, 227

Chandler, 318

Charipper, 180

Chase, 556

Cheever, 181, 182, 412

Chemical constitution of organismal dif-
ferential, 196-197, 272-273

and of organ differentials,

465, 565-579

organizers, 272-273

hemocyanins, 572

hemoglobin, 572-573

myosin and myogen, 572-573

Chemical nature of antigens and anti-
bodies, 573-574

carrier, its specificity, 569-570

experimental antigen, 566-571

differentials in idiosyncracy, 565

individuality, species and organ

differentials, 565-566, 571-574, 578

species differentials and precipi-

.. tinogens, 567

and specificity of enzymes, 575-576

and specificity of viruses, 577

Child, 204, 215, 216, 450

Chimaerae in coelenterates, 209-213

Christiani, 136, 144, 145

Cienkowski, 294

Circuits between organisms and environ-
ment, 650-656

Claude, 542, 579

Clemmensen, 357

Cloudman, 370, 371, 383, 398, 416

Clowes, 340, 388, 408, 411, 414

Coca, 553

Coelenterates, heterogenous transplanta-
tion in, 212-213

Coelenterates, colony formation and indi-
viduality in, 213-214

— organismal differentials and tissue equi-

libria, 204-214

— and potential immortality, 214
Cole, A. G., 545

Cole, W. H., 226

Cole, L. J., 522-523

Collins, 226

Colloidal dyes and immunity against
tumors, 357-358

Colony formation and individuality differ-
ential-like substances, 296, 302

Coman, 357

Compensatory hypertrophy of thyroid
gland, endocrine function in, 148-149

Conklin, 19

Concomitant immunity against transplant-
ed tumors, 403-408

in inbred strains, 404

Constitution, 25-26

Constitution and mosaic individuality, 26
Contact substances, 13
Cooke, 552
Cornman, 563
Xorrens, 18, 20, 21, 316, 319, 460
Corson- White, 387, 406
Cox, 526
Cragy, 146
Craig, 387

Cramer, 389, 432, 434, 435, 436
Crampton, 223

Criteria of compatibility between host and
tumor or normal tissue-transplants,
366-367, 377-380
Crossen, 67
Cuenot, 364, 367

Da Fano, 160, 419, 420

Dakin, 504, 505, 545

Dale, 504, 505, 535, 537, 545

Danchakoff, 420

Danforth, 59

Davis, Hallowell, 462

Dawson, A. J., 585, 586

Defalco, 500, 535, 541

Demerec, 321

Demoll, 325

Dervieux, 516

Desflandres, 136

Detwiler, 245, 248, 277, 280

Dick test, 526-527

Dmochowsky, 394, 429, 431, 583

Doerr, 535

Doncaster, 310

Driesch, 237, 240, 625

Dubos, 577

Duhey, 470

Duke, 555, 557

700

THE BIOLOGICAL BASIS OF INDIVIDUALITY

von Dungern, 159, 488, 491, 511, 520
Dunn, 490

Duran-Reynals, 356, 391
Diirken, 229, 250, 251, 559

East, 316, 317, 319, 323, 324, 325

Eaton, 84, 89

Ebeling, A. H., 190

Ebeling, 420

Echinoderms, transplantation and individu-
ality, 225

Egocentric and objective world, 634-637,
642

Ehrenpreis, 228

Eh rich, 426

Ehrlich, 22, 23, 24, 151, 158, 159, 248, 340,
358, 373, 374, 386, 390, 400, 401, 403,
411, 412, 432, 434, 501, 510-511, 514,
515, 517

von Eiselsberg, 339

Eisen, 376, 381, 413

Eisler, 487

Ekman, 245, 246, 280

El son, 45

Embryonal tissues and eggs, homoiogenous
and heterogenous transplantation, 237-
242

amphibian, autogenous, homoioge-
nous and heterogenous transplantation,
234-237

avian, transplantation into adult

birds, 252

mammalian, transplantation into

mammals, 253-256

syngenesiotransplantation, 255

transplantation into allantois of

chick, 253

Embryonal and tumor tissue, comparison,
433

Emge, 358, 360

Enderlen, 24, 168

Engle, 147, 526

Ephrussi, 272

Equilibrium, organismal (autogenous, spe-
cies, class), 331-332, 471, 475-476

— between blastomeres, 282-283
Erdmann, Rhoda, 187, 229, 397, 581-583
Ermatinger, 120

Euler, 577

Evolution of disease and death, 601-604

— and genetic constitution, 597-600

— of individuality, 649-658

and change in relations between

organism and environment, 649

and of nervous system, 605-606,

657-658

and of civilization, 606-607

Eysh, 317

Famulener, 526-527
Faur£-Fremiet, 301, 303
Fere, 252

Ferguson, L. C, 151

Fertilization, autogenous and transplan-
tation, 315-321

— and organismal differentials, 307-314

— and transplantation, 307-308, 311, 312.

313-314
Fibiger, 346
Fichera, 159, 255
Fick, 19, 20, 21
Filatov, 244, 245
Finkler, 224, 225
Firket, 339
Fischer, Heinrich, 159
Fischer, 488

Fischer, A., 187, 205, 353, 397, 583
Fitzgerald, 502
Fleisher, M. S., 161, 343, 344, 364, 366,

368, 370, 389, 395, 400, 403, 406, 407,

408, 534, 540, 542, 563
Foreign bodies, cellular reaction against

198-199
Forssman, 479
Forssman (heterogenetic, heterophilic),

antigen and organismal differential,

478-482, 487
Foster, 59
Forster, 557
Foulds, 407
Freeman, N. E., 471

Free will, intention and responsibility 637
Frei, 557

Freund, Paula, 255
Freund, E., 429
Freund, J., 527
Friedberger, 526, 551
Friedenreich, 490, 587
Friedenthal, 22, 498
Frohlich, 557
Fuchs, 429
Fujinami, 355
Furth, 357, 374, 381, 382, 391, 392, 4^. H§$

Galtsoff, 302, 303
Gardner, W. U., 361
Garner, 470
Gassul, 397, 581-582
Gay, 591

Gaylord, 340, 411, 414
Gebhardt, 215, 217
Gegenbaur, 20

Gene-hormones and organismal differen-
tials, 272
Genetic constitution and antigens, 151-152

INDEX

701

Genetic constitution and individuality, 8,

9, 10, 21, 22, 108, 134, 150-153, 175-176,

292, 293
of normal tissues and tumors, 373-

374, 376, 378-379, 382
and organismal differentials, 24, 74,

596-597
and organ differentials, 464,

596
Genetic factors in fertilization, 315-318, 319,

320-321

in behavior, 616-618

Genther, 187

Gey, 357

Gheorgiu, 391, 392, 421

Giani, 167, 168

Giard, 275, 276

Gley, 525

Godlewski, 278

Goebel, 504, 570

Goetsch, 204, 209, 210, 215, 216, 217, 249

Gohrbandt, 175

Goldfarb, 237, 240

Goldschmidt, 453-454

Goldsmith, 205, 214

Gonzalez, 570

Goodale, 60, 84, 136

Goodman, 180

Gorer, 378, 410

Gortner, 503-504, 536

Goto, 172

Grades of reaction, 34-35

Graefenberg, 528

Graeper, 246, 277, 281

Graves, W. Wm. 459

Grave, C., 473

Grauer, 358

Gray, 310

Greene, H. S. N., 181, 182, 357, 392, 411,

412, 421, 425
Greer, 181
Gross, L., 220, 440
Growth energy, experimental changes in

transplanted tumors, 385-390, 391, 395-

396
, its stimulation in transplanted

tumors, 388-389
Growth momentum and transplantability

of tumors, 375-376
Growth rhythms in tumors, 370
Gruber, 22
Griinbaum, 22, 498
Guerin, 358
Guerriero, 147
Gussio, 353
Guthrie, 167, 484
Guyenot, 449
Guyer, 517, 541, 555
Gye, 355

H
Haaland, 343, 364, 403, 432, 435, 436, 437

de Haan, 237, 238, 240

Haberer, 146

Haddow, 154

Hadley, 226

Hadorn, 449, 611

Haendel, 344, 408

Halban, 569

Halber, 428, 489

Hallauer, 587

Halsted, 136, 146

Hamburger, 22, 23, 510

Hammond, 253

Hanau, 339

Hanes, 187, 353, 414, 415

Hapten and carrier, 504, 568-569

Hapten, inhibiting effect of, 569, 574

Harde, 178, 421

Harmes, 218, 227, 229

Harris, T. N., 426

Harrison, R. G, 236, 237, 246, 247, 277,

278, 279, 280
Hartley, 535, 537
Harvey, G. N., 474
Harvey, E. Browne, 309
Haterius, 180
Haurowitz, 578
Heat, effect on transplants, 69-70, 118-119,

195-196
heterotransplants, 118-119, 195-

196
Heart embryonal, union of parts of and

organismal differentials, 295
Heidelberger, 538, 565, 572, 575
Heiman, 358, 360
Helff, 282
Hektoen, 181, 488, 499, 535, 537, 540, 543,

545, 546, 547, 548
Hellmich, 245, 249, 282, 305
Hemocyanins, 15
Hemoglobins, 15, 18
Hemolysins and hemagglutinins for homoi-

ogenous erythrocytes, 151-152, 510-511
Henle, 542
Henshaw, 517, 555
Herbst, 20, 240
Heredity and transplantation of tumors,

363-383
Hermannsdorfer, 174
Herriot, 576, 577
Hertwig, O., 18, 19, 307, 364
Hesselberg, Cora, 24, 39, 47, 124, 160, 425.
Heteroagglutinin and heterohemolysin,

482-483
Heterogenous transplantation, 7, 8, 116-130
and autogenous transplantation, 208,

209, 210, 211

and bacteria, 117-121

in birds, 59

of blood clots, 121-122

between rat and mouse, 126-127

702

THE BIOLOGICAL BASIS OF INDIVIDUALITY

between Peromyscus and mouse,

127-128

Heterogenous transplantation and blood
cell reaction, 162-163

of arteries, 167-168

of cartilage, 125-126

of kidney tissue, 125

of guinea pig skin, 123-124

of pigeon skin, 124

of thyroid gland, 124-125, 136

of testicle, 138

of tumors, 391-392, 393-394

of cancer, adaptive changes in, 350,

351

of chicken sarcoma, 355-356

of tumors into chorio-allantoic mem-
brane, yolk sac of chick embryo, brain
or anterior chamber of eye, 356, 357

; growth in radiated animals, 357

Heterosis, 323-325

Heterotoxins, 8, 12, 13, 122

— primary and secondary reactions

against, 161-162

— and blood cell reaction, 119-120, 162-163

— and growth processes, 129

— and lymphocytes, 117-120

— and polymorphonuclear leucocytes, 118-

123

Heyde, 166

Hicks, 499-500

Higashi, 538

Higgins, 146, 180

Hiraiwa, 253

Hirszfeld, 427, 428, 429, 486, 488, 489, 491,
511, 520, 526, 527

His, 19

Hitchcock, 187, 188, 230

Hoadley, 253

Hoepfner, 167

Hofferber, 488

Hoffman, 503-504

Holman, 154

Holtfreter, 262

Homoiogenous transplantation, 6, 7

Homoiogenous transplantation, effect of
age, 40, 41, 66, 67, 137

three phases following, 66, 67

mechanism of, 66-70

differences in intensity of reaction

in different hosts, 67-69

reaction against living and dead tis-
sue, 69-70

and immunity, 158, 159, 169

and blood cell reaction, 162, 163

attempts to improve results, 163, 164

and autogenous transplantation, 208,

210-211

in guinea pig and rat, 38-47

in mice, 55-58

in rabbits. 139

in birds, 59-63

of arteries, 167-169

of blood clots, 121-122

Homoiogenous transplantation of cartilage,

bone and fat tissue, 42-45

of leg, 167

of kidney tissue, 50-53

of ovary, 136

of parathyroid, 136

of skin, 136

of striated muscle tissue, 46, 47

of thyroid, 38-41, 136-137

; effect of feeding thyroid

substance, 41

of tumors, 340-347

of uterus, 47-49

; development of placentoma,

49-50
Homoiotoxin, 8, 12, 122, 170

— and lymphocytes, 117-119

— primary and secondary, 160-161
Hormones, specificity of 577-578
Hormones and transplantations, 49-50, 109-

111

in amphibia, 228-229

into anterior chamber of eye,

182, 183
Hooker, 499
Horowitz, 229
Huck, 484
Huggins, 531
Hunt, 270
Huppert, 18
Huxley, Julian, 220
Hybridization, 19

— and transplantation, 24

in inbred guinea pigs, 91-94

in inbred rats, 84-88

in inbred mice, 98-115

Hydra, 204, 205

Hypersensitiveness, and heredity, 553, 555,

556, 558

— , lack of in transplanted uterus and re-
actions against homoiogenous differen-
tials, 555

— , hapten and carrier, 556, 557

Idiosyncrasy, organ and organismal differ-
entials, 557-558
— , and mosaic individuality, 558

— against autogenous substances, 555

— and anaphylaxis, 551, 553-554, 556
— , passive transfer of, 553-554, 555
Immortality, potential of tissues, 190-194,

433

Immunity active, against transplanted em-
bryonal tissues, 255-256

, tumors, 401, 402

INDEX

703

— and organismal differentials in tumor

transplantation, 400-432

— active, against tumors and organismal

differentials, 345-347, 412-413
Immunity against transplanted tumors fol-
lowing regression of a tumor, 408-412

— active, against transplanted tumors pro-

duced by inoculated normal tissues,
412-413 '

— against heterogenous chicken sarcoma,

355-356

— active, against transplanted tumors and

weakening of growth energy, 406-407
Immunization against heterogenous cancer,
348-349, 350-352, 354-355

— active, of tumor cells, 395

Immune substances against transplanted
tumors, 414-415

, homoiogenous against spleen and

lens, 547

Immune reactions and organismal differ-
entials, 5-6, 25

against altered species differentials,

567-569, 570-571

Inbreeding, 321-325

— and individuality differentials, 24, 60-

61, 83-115, 365
— , effects in different strains of mice, 100-

101, 109-111
— , effects of mutation, 88

— and intensity of tissue reactions, 8-9,

60-61

— in rats, 84-88

— in guinea pigs, 89-97

— in mice, 98-115

Inbred strains, tumor transplantations in,

363-371
Inner and outer world, 627-630, 634-635
Individuality, definition, 3
— , history of concept, 17-18
— , mosaic, 4, 5, 14-15, 21, 25

— essential, 14-15, 24-25

— , differentials, 5-7, 10, 140-141, 150-151,
169-170, 175-176

— , and the organism as a harmonious sys-
tem, 15

— , mosaic, its phylogenetic development,
593

— , in the psychical-social sense, 17

— , its symbolic representation, 16

— as a system of specificities, 595-596

— and potential immortality, 600-601

— , psychical-social, its physiological basis,

609-626
— , mechanisms of integration and their

evolution, 609-612

— and lymphocytes, connective tissue and

blood vessels, 6

— and immunity, 15, 23, 24, 139

— and allergy, 15

— or organs and tissues, 457-465

— of tumors and environmental factors,

435-436
Individuality, structural and psychical, their
evolution, 623-624

— and world, 627-648

— , bodily and psychical, its integration,
624-626

— and mechanism, 630-631, 633-634, 642-

643
— , world and science, 647-648

— psychical, its uniqueness, 644-645

— and the social and natural struggle, 641-

642, 646
— , contrast between "I" and the others,
620-621

— and consciousness, 620-621

— and free will, 621, 623-624, 627-634, 637,

642-643

— psychical and environment, 623

— psychical and predictability of actions,

623-624

— and its psychical needs, 642-647

— and psychical goods, 639, 641

— and morale, 641

— , ethics and law, 641-642

— continuity and consistency, 643-645

— and self-justification, 646-647

— , psychical, its permanence, 645-646

— among primitive people and in civilized

society, 646-647

— and groups, 646-647

— and the problems of philosophy, 647-648
Individual differences in behavior of ani-
mals, their evolution, 612-619, 621

as to relative importance of analytic

thought and suggestion, 633-634

in strength of reactions against in-
dividuality differentials, 29, 161

, demonstration by serological meth-
ods, 510-518

and hemagglutinins, 513-514

and blood group differentials, 514-

515

, comparison of transplantation and

serological tests, 514-516

and heterogenous production of pre-
cipitins, 516

, attempts to change their nature, 165

Individuality differentials, local actions,
67-69

, functions of, 15, 593

and serological tests, 518

, actions against, 72-73

Ingbrigtsen, 154

Ingle, 146, 180

Insects, social, 613

Instincts and bodily structures, parallelism
in evolution, 622

— , behavior and organ differentials, 622

704

THE BIOLOGICAL BASIS OF INDIVIDUALITY

Interplantation and organismal differen-
tials, 251
Interracial transplantation, 131-135

in birds, 59-60

Irving, 461

Irwin, 151, 172, 175, 521-523, 599

Ishii, 411, 421

Issayew, 204, 209, 213

Ito, 348

Krebs, 357

Krehbiehl, 358

Kritschewski, 427, 481, 492, 525

Kross, 353

Krusius, 540

Kiihn, 18, 21, 272

Kunitz, 474, 575-576

Kurz, 328

Kusche, 250, 251, 559

Jacobs, M. H., 495

Jacobson, 146

Jaeger, Gustav, 20, 460

Jaffe, H. L., 138

Janda, 251

Janota, 181

Jennings, 291

Jensen, C. O., 24, 339, 340, 363, 385, 400,

401, 404, 432, 435
Jensen, P., 287, 288, 296
Joest, 218
Johannsen, 20

Johannsen's pure lines, 316, 364, 367
Johnson, B. W., 96
Johnson, H. H., 560
Jollos, 377
Jolly, 228
Jones, 323, 325
Jores, 159
Jost, 316

Jungeblut, 526, 585
Just, 473

K

Kaempffer, 488

Kalmanson, 577

Kaminer, 429

Karshner, 490

Kellars, 173

Kelley, 141

Kendall, E. C, 146

Kendall, F. A., 575

Kerwin, 47

Keysser, 170

Kidd, 430

Kimura, 397, 583

King, H. D., 73, 83, 84, 131, 184, 204, 209,

219, 225, 324, 597-598
Kirk, 576
Kirschbaum, 382
Klinckhard, 488
Klopstock, 506, 556, 569-570
Knauer, 23, 136
Kodama, 544, 591
Koller, 611
Kopec, 224, 225, 611
Koppanyi, 228
Kornfeld, 451
Korschelt, 218, 220, 221
Kossel, 527, 590-591
Kozelka, 60, 138, 152, 154, 184
Kraus, 22

Lambert, 172, 187, 353, 414, 415

Lancefield, D. E., 311

Lancefield, R. C, 505

Landsteiner, 22, 23, 150, 152, 478, 481, 483,

485-487, 488, 490, 493, 494, 499, 502, 504,

505, 506, 507, 514, 520-521, 525, 538, 548,

553, 556, 567-571, 572, 573-574, 598-599.
Lattes, 516
Lauer, 170

van Leeuwen, Storm, 557
Lehmann, F. E., 271
Lehmann, W., 159, 164
Lehmann-Facius, H., 427, 428, 429, 506,

541
Lens, of eye and individuality differentials,

12
Leopold, 342, 358
Letterer, 517

Leukemia, transmission of, 361-362
Levene, P. A., 571
Levin, I., 368, 425
Levine, M., 495
Levine, P., 171, 481, 487, 488, 491, 492,

499, 502, 507, 514
Lewin, C, 351, 364, 414, 433, 438
Lewis, J. H., 503, 505, 535
Lewis, M. R, 392, 419, 555
Lewis, P. A., 556
Lewis, W. H., 244, 267
Leypoldt, 218, 222
Lexer, 154, 167, 168, 169, 170
Lieure, 228
Lignac, 357, 395, 426
Des Ligneris, 355
Lillie, F. R., 454, 472-473
Lindemann, 451, 452
Linkage between susceptibility and other

factors in transplantation of tumors,

371
Lipschiitz, 147
Little, C. C, 24, 84, 96, 138, 369, 370, 371,

373, 378, 434, 438, 439, 473, 499-500
Little, R. B, 528
Local reaction and blood cell reaction in

transplantation, comparison of, 65
Lockemann, 528
Loeb, Jacques, 21, 204, 205, 237, 309, 312,

473, 519, 566, 612
Loehner, 324
Long, 365
Loncope, 557

INDEX

705

Lubarsch, 157

Lucke, 470

Ludford, 357

Lumsden, 346, 347, 354, 355, 378, 394, 407,
410, 414, 415, 429, 433, 436, 437, 583

Lurie, 556

Lux, 146

Lymphocytes, destructive action of, 62-63

— , in immunity against transplanted tu-
mors, 401, 416-426

— , and organismal differentials, 24

— , in various types of transplantation, 79-
80

— , specific attraction by different tissues,
114-115

M

Mach, Ernst, 629

McCutcheon, 981

MacDowell, 382, 394, 413, 431, 583

McPhee, 84, 89

Macrea, 354

Maisin, 357, 358

Mangold, 246, 262, 264, 265, 266, 267, 269,

272, 279, 287
Manley, 139

Mann, F. C, 146, 343, 358, 359
Mann, L. S., 429, 542
Marchand, 157
Marine, 139
Mark, 567
Markee, 180
Marks, 345
Marsh, 84

Marshall, 501, 502, 506
Martins, 173, 180
Masse, 357, 358
Mathey, 228
Mat son, 486
Matsuyama, 173
Maus, 387

May, R. M., 60, 180, 227
Mayeda, 175, 176
Mayngord, 358

Mechanistic basis of behavior, its evolu-
tion, 612-619, 620, 625
Meisenheimer, 224
Mendel, 18

Mendelian heredity in tumor transplanta-
tion, 367-373
Mendlovitsch, 492, 525
Mercier, 364, 367
Metchnickoff, 22
Meyer, 566
Meyns, 227, 228
Mez, 500-501
Michaelis, 363, 388
Miller (with Fibiger), 346
Miller (with Rhoads), 413
Miller, C. P., 491, 502, 514, 599
Milojevich, 279, 280, 453
Mirsky, 566

Moenkhaus, 312

Moevus, 291, 292, 293, 294

Montalenti, 312, 313

Moore, A. R., 610, 612

Moore, C. R., 147

Moore, R. A., 180

Morato, 570

Morau, 339, 363

Morelli, 428

Moretti, 215

Morgan, H. R., 181, 182, 412

Morgan, L. V., 204, 216, 220

Morgan, T. H., 204, 237, 240, 277, 320

Morgenroth, 23, 151, 510-511, 514, 515, 517

Moritz, 523

Morpurgo, 171, 172, 173, 364

Morphogenic substances and recipient tis-
sues, organismal differentials and rela-
tive specificity of, 443-456

Mosaic structure of organs and mosaic
individuality, 457-459, 461-463

Mottram, 353, 410, 418, 425, 430

Mudd, 470

Multiple factors in transplantation of
tumors, 356, 357, 388

Murphy, J. B, 24, 160, 163, 177, 178, 346,
391, 412, 414, 418, 419, 420, 422, 425,
434

Murray, P. S. F., 253

Murray, J. A., 340, 363, 389, 391, 400, 432,
434, 435, 436

Murray, J. M., 369

Mutations and transplantability of tumors
439

Mutscheller, 218, 220

Mutz, 204, 210

Myers, 24, 125

Myxomycetae, specific adaptation of, 293-
294

N

Naegeli, C. v. 17, 19

Naegeli, O., 554

Nathan, 553

Natural immunity against transplanted

tumors, 401-403
Needham, 262, 263
Neilson, 254
Neumann, 146
Nicholas, 255
Nilson, 146
Noble, 617

Northrop, J. H., 474, 575-577
Number and nature of susceptibility fac-
tors in transplantation of tumors, 369-
371, 378-379
Nussman, 246
Nuttall 22, 498, 499

Oberling, 358

Obermayer, 23, 540, 548, 553, 566-568, 569

706

THE BIOLOGICAL BASIS OF INDIVIDUALITY

Objective and subjective aims in social
actions, 640-641

O'Brien, 557

von Oettingen, 492

Ohki, 543

Olitzky, 526

Oliver, 430

Oilier, 18, 23, 184

Opie, 551, 557

Orcutt, 528

Organ differentials, 5, 7

as antigens, 13

autogenous, homoiogenous, heterog-
enous as antigens, 546-547

Organ and organismal differentials, chem-
ical nature of, 547-549, 565-579

, evolution of, 273-274, 589-607

Organ blood group-and Forssman differ-
entials and secondary organismal dif-
ferentials, phylogenetic relationship of,
594-596

Organ differentials during embryonal de-
velopment, 545-546

Organ and tissue differentials, their an-
alysis by serological methods, 530-549

Organ differentials, serological criteria,
532-534

Organ- (substance-) and organismal dif-
ferentials (as tested by serological
methods) of adrenal gland (medulla),
541

and organismal differentials of brain,

535, 541-542, 546-547

and organismal differentials of car-
cinoma, 542-543

and organismal differentials of case-
in, 537

and organismal differentials of egg

albumin, 537, 545

and organismal differentials of egg

yolk, 544-545

and organismal differentials of epi-
physis, 541-542

and organismal differentials of fib-
rinogen, 547

— and organismal differentials of globin,
538

— and organismal differentials of hemo-

globin, 537-539

and organismal differentials of kid-
ney, 534, 542

and organismal differentials of lens,

530, 535, 540-541, 546, 547

and organismal differentials of leu-
cocytes, 540

and organismal differentials of liver,

542

and organismal differentials of mi-
tochondria, 542

and organismal differentials of

mouse organs, 542

Organ- (substance-) organismal differen-
tials of proteins of blood serum, 535,
537

and organismal differentials of skin,

547

and organismal differentials of

spermatozoa, 543-544

and organismal differentials of thy-
reoglobulin, 539, 547

Ontogenetic development, organ and tissue
equilibrium and organismal differen-
tials, 242-243

Organ or tissue specificity, 444-446, 447-456

Organizers, 205-207, 215, 239

Organizers, tissue differentiation and or-
ganismal differentials, 256-258, 259-274

Organismal differentials, 5, 10

, primary and secondary, 11, 17, 295-

296, 321, 464-465, 545, 548, 549, 593-
595

and organismal specificity, 443, 446-

447, 447-456

and specific adaptation, 443

Organismal tissue equilibrium, 463-464

Organisms as systems of specificities, 595-
596

Organismal differentials and non-living
substances, reactions against, 64-65,
199, 202

and the reactions against strange

differentials, 589-590

of hybrids between nearly related

species, 519-523

and reaction of blood cells, 12-13,

61, 63-65

and hormones, 13, 143-149, 271, 273-

274

and unicellular organisms, 295-297

and formation of Plasmodia or colo-
nies, 204, 213

in coelenterates, 211-213

in invertebrates, 225

and growth substances in transplan-
tation in amphibian embryos, 247-249

in embryonal tissues, 64

and organizers, 268-274

and plasticity of organs, 231, 286

and tissue differentials, evolution of

286, 589-607

Organismal differentials, evolution in
plants, 590

, during phylogenetic, embryonal de-
velopment and during regeneration,
591-593

, in transplantation of tumors, 15,

361-381

, growth energy and adaptive pro-
cesses in transplantation of tumors,
384-399

, and susceptibility factors in trans-
plantation of tumors, 439

INDEX

707

Organismal differentials, as antigens in im-
munity against transplanted tumors,
402

, and organ differentials as antigens,

13, 477

Osborne, 502-503, 505, 536

Oscillating growth of transplanted tumors,
386-388

Ottenberg, 484

Ottensooser, 538

Pagel, 555

Panimmunity and organismal differentials,

411
Parabiosis, 5, 166-167, 171-176

— and individuality differentials, 171-176

— union of nerves, 171

— , harmonious phases in, 173

— , disharmonious phases in, 173-176

— and blood group antigens, 171
Parasite (symbiont) and host, specificity

of relation, 603-605

Parasitism (symbiosis) as parabiotic
state, 167, 176

Parker, G. H., 611

Parker, R. C, 446, 462

Parker, R. R, 120

Parsons, 348

Pasteur, 22

Pauling, 566, 578

Pavlow, 612

Peebles, 204, 209

Pennington, D., 178, 357

Perkins, 611

Perlzweig, 557

Personality, 1, 2, 641

— , inner psychical goods and health, 639-
640, 641

Perthes, 138

Pertzoff, 303

Petit, 343, 358

Pfeiffer, 137, 147, 179, 184

Pfliiger, 20

Phelps, 354, 410

Phisalix, 563

Picco, 358

Pick, 23, 540, 548, 553, 566-568, 569

Piepho, 440, 450

Pierce, 141

Planarians, transplantation and individual-
ity in, 214-217

— , homoiogenous and heterogenous dif-
ferentials, 217

— , tissue equilibrium in, 214-217

Plasma, individual, 20

Plasmodium formation in myxomycetae,
294-295

Plasticity of behavior, 618-620, 622-623,
625

Phylogenetic evolution of organismal and
tissue differentials, 231-233

Phylogenetic and ontogenetic development
of organismal and organ differentials,
256-257

Poetry and art, their meaning, 634-636

Poll, 327, 364, 459

Polysaccharides as antigens, 574-575

Prausnitz-Kiistner reaction, 554, 555, 557

Precipitins and species relationships, 22

Precursors of individuality (organismal)
differentials, 9, 21, 22

Pregnancy as a parabiotic state, 167, 176

— of host, its effect on transplants, 255

Pressman, 578

Pretresco, 173

Price, 147

Przibram, 225

Protein, specificity of, 19, 22-23

, evolution of, 590-592

Proteinases and protein synthesis, 573

Protozoa, union of free living, 287-291

Protozoan protoplasm and organismal or
tissue differentials, 287-293

Prowazek, 294

Pseudopods, reactions against autogenous,
homoiogenous and heterogenous pro-
toplasm, 287-289

Psychical goods, 638

, simple, 638, 639-640

, individual distinctive, 638-639

, distinctive class, their injurious ef-
fects, 638-639

, inner, 639-640

Purdy, 350, 355

Pure lines, 20

Putnoky, 349, 350, 392, 393-394

Queen, 120

de Quervain, 554

Rabes, 218

Rabinovitch, 507

Rabl, 18, 19

Race differences, 458-460

Rand, 141, 204, 214, 215

Reactions, all or nothing, 138

— , graded, 60

— , variations in strength against strange

individuality differentials in different

strains and individuals, 67-69
— against primary and secondary homoio-

and heterotoxins, 163
Reciprocal fertilization and transplantation,

311-312
Recovery from injuries in transplanted

tumors, 386-387
Reflexes, conditioned, 612-613
Regeneration and organismal differentials,

250, 257-258
Regeneration and transplantation, 275-286
Reichert, 461, 539, 572

708

THE BIOLOGICAL BASIS OF INDIVIDUALITY

Reinhard, 393

Resistance, difference between embryos
and adult organisms, 524-529

— , increase in and physiological matura-
tion, 526-527

Retrogression-immunity against transplant-
ed tumors in relation to organismal
differentials, 411-412

Reverdin, 18

Reynolds, 288, 289, 290, 584, 586

Reynaud, 147

Rhoads, 413

Ribbert, 24, 136, 159, 343, 358, 359

Rich, 555

Richter, M. N., 138

Ries, 224, 303

Ritter, 446-448

Rivers, 532

Robbins, 324, 576

Robertson, O. H., 430, 526

Robertson, T. B., 591

Robinson, G. H., 358

Roessle, 524

Roffo, 364, 391

Rohdenburg, 407

Rollett, 18

Romanes, 610

Roskin, 426

Rous, 24, 159, 177, 253, 254, 255, 256, 353,
355, 358, 365, 388, 391, 412, 414, 415,
418, 425, 430, 433

Roux, 22

Roux, W., 295

Rubinstein, 427

Russ, 386, 389, 410, 418, 425,

Russell, 158, 256, 344, 401, 404, 407, 418,
424, 425, 432, 434

Rutloff, 218

Ruud, 453

Rywosch, 525

Sabin, A. B., 526

Sachs, Julius, 20

Sachs, H., 491, 525

Sale, 136

Salter, 287

Salzer, 146

Sampson, 472

Sanders, 585

Sandstrom, 154, 155, 253

Santos, 204, 215, 216, 217, 219

Saphir, 181, 412

Sarafran, 578

Sauerbruch, 166

Saxton, 141, 181, 357, 421, 448

Scents and individuality, 459-461

Schaxel, 246, 250, 277, 278, 280, 281

Schecter, 471

van der Scheer, 499, 520-521

Schenk, 527

Schermer, 488

Schwerin, 578

Schick test, 526, 527

Schiff, 481, 483, 491, 492, 494, 525

Schmeckebier, 141

Schmitt, 617

Schoene, 23, 24, 74, 157, 158, 159, 176, 184,
218, 326, 330, 345, 403, 412, 434

Schotte, 250, 261, 266, 267, 270, 449

Schrader, 487

Schulhof, 535, 540, 543, 546, 547

Schultz, E., 291

Schultz, W. H, 551

Schultz, W., 19, 24, 59, 229, 307, 326, 327,
328, 329, 330, 453, 519

Schultze, Max, 287

Schwarz, 407, 408

Schwarzmann, 481

Schweizer, 180

Schwentker, 532

Schwind, 247

Sclerosis of thyroid gland of mice and
transplantation, 102-103, 105-106

Scott, 386, 389, 433, 438

Seastone, 576

Seelig, 407

Seidel, 269

Selection in strains of mice as cause of
hereditary changes, 364, 373

Selection of tumor strains in serial trans-
plantation of tumors, 390-391

Self consciousness, 639-640

Self-fertilization in higher plants, 315-320

Ciona, 320-321

Sellers, 556, 569-570

Senescence of tissues, 194

Serological methods for analysis of or-
ganismal differentials, 5, 6, 8, 129,
158-163

Serological differences between reactions
of fetal or newborn and adult organ-
isms against strange differentials, 524-
529

Sherwin, 594

Shimudzu, 490

Shirai, 178, 357, 420

Shope, 357

Sia, 526

Siebert, 60, 118, 119, 178, 195, 196

Silberberg, 145

Simonnet, 173

Sittenfield, 368

Skin patterns and individuality, 457-459

Skipper, 354

Skubisrewski, 252

Smirnova, 181, 357, 421

Smith, Carrol, 144

Smith, P. E., 173

Smith, Theobald, 528

Somatic mutations in transplantation of
normal tissues, 397

Somatic mutations in tumor transplanta-
tion, 372-373, 375-376, 393-394

INDEX

709

Sonneborn, 291, 292, 293
Spangler, 369

Species differences in reactions against in-
dividuality differentials, 28-29
Species differentials of normal tissues,

constancy of, 397-398
in transplantation of tumors, con-
stancy of, 393-395
constancy of, in heterogenous tu-
mors, 350-351, 352-353, 356
, demonstration by serological meth-
ods, 498-509

and anaphylaxis, 502-506

and complement fixation, 502, 504

and electrophoresis, 573

and hemagglutinins, 502

and hemolysins, 501

, inhibition of reaction against them

by haptens, 502, 504

and precipitins, 498-501

and precipitins in plants, 500-501

and preformed serum agglutinins

and hemolysins, 506-508
Specific adaptation, 14, 16, 17, 292, 293,
466-468

in transplantation of normal tissues

and tumors : see parts I and IV

in action of substances in autolyzed

muscle (cytose), 473

in agglutination of spermatozoa by

egg extract, 472-473

in antifertilizing action, 473

in blood group agglutination, 471-

472

in enzyme action, 473-474

in fibrinolysis, 470

in hemolysis, 470-471

between heterogenous sera and cells,

508

in immune reactions, 468-469, 474

in metamorphosis of ascidian larvae,

473

in phagocytosis, 470

in relations between host and para-
site, 475
in solution of egg membrane by ex-
tract of spermatozoa, 472-473

in tissue coagulin effect, 469-470

Specificity of organs, tissues and sub-
stances, three types, 466-468
Spek, 282, 304
Spemann, 261, 262, 267, 269
Splenectomy in homoiotransplantation, 165
Spontaneous and transplanted tumors,

comparison, 437-439
Stages in development of psychical indi-
viduality, 654-655
Stalden, 554
Stanley, 577
State, 495
Steinach, 137

Steffenhagen, 344, 408

Steinecke, 501, 590

Steinfeld, 541

Stern Fr., 553

Stern K., 429

Stern L., 179

Stockard, 182, 227

Stone, H. B., 583

Stormont, 151

Stout, 318

Strain differences in intensity of reactions
against individuality differentials, 29,
363-383

Strain differences in transplantation of tu-
mors in mice, 364, 367, 368

Strain of host in its relation to hetero-
transplantation of tumors, 349-350,
355-356

Strassburger, 18

zur Strassen, 237, 240, 241

Strauss, E., 538

Strauss, A. A., 181

Strieker, 403

Strickler, 507

Stroma reaction in immunity against trans-

, planted tumors, 417, 424-426, 434, 436

Strong, L. C, 84, 369, 370, 371, 372, 373,
382, 437, 438, 439

Strube, 543

Struggle, social and natural, 635, 636-638,
639-642

Strumia, 470

Sturm, 346

Sturtevant, 311

Substance specificity, 535, 536

Summers, 302

Suggestion, 616, 633-634, 637, 640, 644, 657

Sumner, F. B., 598, 611

Sumner, J. B., 474, 575-576

Siissman, 516

Svedberg, 566, 572

Syngenesio-toxin, 8, 12

Syngenesiotransplantation, 6-8, 72-73, 137,
138

— in rats, 73-74

— in guinea pigs, 80-82

— in man, 138

— in birds, 59-63, 136, 138

— of testicles and ovaries, 137, 138

— of skin, 138

— by blood vessel anastomosis, of kidney,

168

— by pedicle, 170
von Szily, 541, 546

Takewaki, 147
Tamman, 159, 164
Taube, 226

Taylor, Alfred, 178, 357
Taylor, A. E., 591

710

THE BIOLOGICAL BASIS OF INDIVIDUALITY

Teague, 502

Ten Broeck, 576

Tennent, 309, 310, 311

Testicle, transplantation into, 182, 227

Thacker, 178, 357

Thiersch, 18, 23

Thies, 528

Thomoff, 514

Thomsen, 483, 525, 587

Thought and extension of personality, 656

— as symbol of reality and as suggestion,
619-620

— , will and emotion, 657

Thought world and experienced world,
635-636

Thought reservoir, its significance for the
individual, 652-656

Thrombus formation and organismal dif-
ferentials, 306

Tiesenhausen, 252

Tillett, 470, 504

Tiselius, 573

Tissue culture and individuality differen-
tials, 187-189

Tissue differentials, 5, 7, 10, 169

and organismal differentials in trans-
plantations in amphibian embryos, 244-
252

Tissue equilibrium, 273-274

, isoregulation and alloregulation,

285-286

, phylogenetic and ontogenetic evo-
lution, 283-286

in planarians, 214-215

Tissue formation and organismal differen-
tials, 298-306

in amoebocytes and organismal dif-
ferentials, 301 (298-302)

in sponges and organismal differen-
tials, 303-304

in Tunicates, 304-305

in embryos and organismal differen-
tials, 305-306

Tissues and organs in invertebrates, fixity
and plasticity, 225-226

, differences in transplantability,

29-30

in the rat, 74-80

, in the guinea pig, 80-

82

Tissues, physiology of, 36, 62, 127

Todd, 23, 24, 151, 152, 512-514, 515, 516,

523
Toxins, organ and organismal differen-
tials, 559-564

— , bacterial, 560, 564

— in Paramecia, 292

— in invertebrate eggs and embryos, 241-

242, 267, 269

— in amphibia, 227, 228, 251-252, 560-561,

562

Toxins, in reptiles, 561-563

— in snakes, 561-562

— in Heloderma, 562-563
Transplantation, methods of, 30-32, 139
— , methods of examination, 137-138

— , as method for analysis of organismal

differentials, 5, 6, 33, 74-75
— , terminology, 35-36

— and athrepsia, 159

— , variable factors, 32-34, 62, 78-79

— and lack of function, 159

— and underfeeding, 145

— and pregnancy, 145

— and immunity, 157-165

— by blood vessel anastomosis, 166-169

— by pedicled flaps, 169-171

— and fertilization, 11, 307-314

— and hybridization, 24, 307-314

— and family, relationship, 13, 24

— multiple, 33-34, 86, 90-91, 103

— successive (serial), 24, 86, 90, 162-163

of thyroid in inbred mice, 104-106

of ovary, 111

in rabbits, 139

and immunity, 160-162

— and blood group antigens, 170-171

— and age, 59, 60, 87-88, 100
in inbred strains of mice, 101-

104
in guinea pigs and rats, 137, 147,

184-186
— , effect of non genetic factors, 52, 60,

61, 62

— serial and potential immortality of tis-

sues, 104-105, 190-194

— reciprocal, 127-128, 130

— interracial, 131-135

— and hormones, 136-137, 139, 143-149

— of adrenal gland in mice, 112-113

— of anterior hypophysis in mice, 111-

112

— of thyroid and parathyroid in mice, 113-

114

— of bone, bone-marrow and cartilage, 78

— of fat tissue, 78

— of Fallopian tube, 76-77

— of kidney, 77

— of liver, 77

— of ovary, 75-76

— in inbred strains of mice, 109-111, 98-

115

— of skin, 75

— of spleen, 77

— ■ of striated muscle, 78

— of testicle, 77-78, 137

— of uterus, 77

— of blood clots and plasma clots, effect

on blood cells, 121-123

— of normal tissues and cancer, 338-340,

433, 439-440

INDEX

711

Transplantation, of tumors, autogenous and
homiogenous, 340-347

, heterogenous, 347-358

— and organismal differentials,

432-441

Transplanted tumors, their growth in hy-
brids, 367, 368-370, 371, 378-379, 380-
382

and organ and tissue differentials, 440

and spontaneous tumors, relations be-
tween, 373, 435

Transplants of tumors and metastases, 435

Transplantability of different tumors, 364

Transplantation of adenoma, 358-362

Treibman, 489

Trophoplasm, 19

Tropisms, 612

Trypan blue in homoiogenous transplan-
tation, 164-165

Tschistowitch, 22

Tsurumi, 407

Tubularia, 204-205

Tumors, nature and causes ; their organ
and organismal differentials, 333-441

Turn Suden, 146, 180

Turner, G. D., 179, 180

Tuttle, 507

Turck, 473

Twitty, 247, 248, 560-561

Tyler, A., 473

Tyzzer, 24, 96, 158, 343, 363, 367, 368, 369,
370, 373, 378, 404, 414, 415, 417, 418,
419, 424, 425, 433, 434, 437, 438

u

von Ubisch, 331

Uhlenhuth, E., 235, 451

Uhlenhuth, 344, 408, 426, 433, 438, 499,

511, 524, 530
Uhlenhuth effect, 344-345
Umehara, 358
Urease of Limulus, specificity of, 577

Walsh, 519

Warm, 617

Warner, 393

Weber, A., 252, 559

Webster, L. T., 556

Weigl, 451

Weiss, P., 263, 276, 277, 279, 448-449

Weichardt, 510

Welker, 429, 535, 537, 542

Wells, G. H., 502-503, 505, 536, 567, 591

Welsh, J. H., 475

Welti, 228

Wense, 145, 147, 179

Wettstein, 18, 21

Wetzel, 204

White, R. G., 512

White, P. R., 189

Whitman, 622

Wieman, 246

Wiener, 152, 171

Wigglesworth, 449, 611

Wilhelmi, 499, 500, 501

Williamson, 168

Willier, 253

Willheim, 429

Wilms, 252

Wilson, H. V., 302

Witebsky, 427, 428, 491-492, 536, 539-540,

541, 542, 546, 548
With, 490
Woglom, 344, 345, 354, 372, 381, 389, 408,

410, 412, 413, 415, 421, 425, 433, 434,

436, 437, 438
Wolfe, H. R., 499, 500
Wolfe, J. M., 358, 360
Wound healing in mammals, autogenous

tissue regulation, 306
Wormall, 567, 569
Wright, A. W., 358, 360
Wright, Sewall, 83, 84, 89
Wulff, 358
Wyman, 146, 180

Veblen, 586

van der Veer, 552, 558

Velich, 339

Verworn, 20, 291, 296

Vickery, 572

Villata, 164

Virus of chicken sarcoma, adaptation to

different species, 356-357
Vitamins, 578
Voechting, 218
Vogel, 142
Vorlaender, 426

w

Waddington, 262, 263

Xenotransplantation, 261-262, 268-269
X-rays, effect on transplantation, 177

Yamagiwa, 414

Yasuda, 317

Yves Delage, 275, 276

Zakrzewski, 173, 383, 416
Zangemeister, 516
Zeinitz, 261, 267
Zinsser, 507-508, 511
Zogaya, 570

THIS BOOK
THE

BIOLOGICAL BASIS

OF

INDIVIDUALITY

By Leo Loeb

was set, printed and bound by The Collegiate Press of
Menaslia, Wisconsin. The type face is Linotype Old
Style N-o. 1 set 10 point on 12 point. The type page is
28 x 48 picas. Tlie text paper is 50-lb Basis White
Stonewall Eggshell. The binding is Bancroft Buckram
M. Tire jacket is Hammermill, Gray, Ripple Finish.

With THOMAS BOOKS careful attention is given to
all details of manufacturing and design. It is the Pub-
lisher's desire to present books that are satisfactory as
to their physical qualities and artistic possibilities and
appropriate for their particular use. THOMAS BOOKS
will be true to those laws of quality that assure a good,
name and good will.