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No.

INTERNATIONAL CONGRESS
OF ARTS AND SCIENCE

PERSEPOLIS

Photogravure from a Painting by Briton Rivi&re

A picturesque display of most remarkable ruins is all that now remains
of Persepolis, the capital of ancient Persia, with which, according to ancient
writers, no other city could be compared either in beauty or in wealth, and
which was generally designated as the " Glory of the East." Alexander the
Great, in his march of conquest, destroyed some of the chief palaces, and the
rest gradually fell into decay. The most important of these ruins is the
Chehel Minar (Forty Pillars). Massive double flights of steps lead to a
platform strewn with ruins, from which still tower some forty colossal marble
columns. These steps together with the artificial terraces are a principal
feature of the ancient palaces of Persepolis.

INTERNATIONAL CONGRESS

OF

ARTS AND SCIENCE

EDITED BY

HOWARD J. ROGERS, A.M., LL.D.

DIRECTOR OF CONGRESSES

VOLUME IX

BIOLOGY

COMPRISING

Lectures on Bacteriology, Embryology, Plant Morphology,

Animal Morphology, Ecology, Plant Physiology,

Plant Pathology, Human Anatomy,

Comparative Anatomy, and

General Biology

UNIVERSITY ALLIANCE

LONDON

NEW YORK

COPYRIGHT 1906 BY HOOGHTON, MIFFLIN & Co.

ALL RIGHTS RKSKRVED
COPYRIGHT 1908 BY UNIVERSITY ALLIANCE

ILLUSTRATIONS

VOLUME IX

FACING
PAGE

PERSEPOLIS Frontispiece

Photogravure from a painting by BRITON RIVIERE

PORTRAIT GROUP OF INTERNATIONAL LECTURERS .

Photogravure from a photograph

A TRAGEDY IN THE HAREM * 284

Photogravure from the painting by PIERRE Louis BOUCHARD

DEATH OF CAESAR 356

Photogravure from the painting by JEAN LEON GERUME

TABLE OF CONTENTS

VOLUME IX

BIOLOGY

Development of Morphological Conceptions ....
BY PROF. JOHN MERLE COULTER, PH.D.

The Recent Development of Biology .....
BY PROP. JACQUES LOEB

PHYLOGENY.

A Comparison between Artificial and Natural Selection
BY PROF. HUGO DE VRIES, Sc.D., LL.D.

The Problem of the Origin of Species .....
BY PROF. CHARLES OTIS WHITMAN, PH.D., LL.D.

PLANT MORPHOLOGY.

Plant Morphology .......... 61

BY PROF. FREDERICK ORPEN BOWER, Sc.D.

The Fundamental Problems of Present-Day Plant Morphology . . 81
BY PROF. KARL F. GOEBEL, Sc.D.

PLANT PHYSIOLOGY.

The Development of Plant Physiology under the Influence of the Other

Sciences ........... 103

BY PROF. JULIUS WIESNER, PH.D., J.U.D.

Plant Physiology — Present Problems ...... 125

BY PROF. BENJAMIN MINGE DUGGAR, B.S., PH.D.

PLANT PATHOLOGY.

The History and Scope of Plant Pathology ..... 149
BY PROF. JOSEPH CHARLES ARTHUR, Sc.D.

Vegetable Pathology an Economic Science ..... 165
BY MERTON BENWAY WAITE, B.S.

ECOLOGY.

The Position of Ecology in Modern Science ..... 17?
BY PROF. OSCAR DRUDE, PH.D.

The Problems of Ecology ........ 191

BY PROF. BENJAMIN LINCOLN KOBINSON, PH.D.

TABLE OF CONTENTS

BACTERIOLOGY.

Relations of Bacteriology to Other Sciences ..... 207
BY PROF. EDWIN OAKES JORDAN, B.S., PH.D.

Some Problems in the Life-History of Pathogenic Micro-Organisms . 219
BY PROF. THEOBALD SMITH, M.D., Pn.B.

ANIMAL MORPHOLOGY.

Animal Morphology in its Relation to Other Sciences .... 244
BY PROF. CHARLES BENEDICT DAVENPORT, B.S., PH.D.

. The Present Tendencies of Morphology and its Relations to the Other

Sciences .......... 258

BY PROF. ALFRED MATHIEU GIARD, NAT. Sc.D.

EMBRYOLOGY.

Advances and Problems in the Study of Generation and Inheritance . 288
BY PROF. OSKAR HERTWIG, PH.D.

Individual Development and Ancestral Development . . . 308

BY PROF. WILLIAM KEITH BROOKS, PH.D., LL.D.

COMPARATIVE ANATOMY.

The Place of Comparative Anatomy in General Biology . . . 323
BY PROF. WILLIAM EMERSON BITTER, B.S., PH.D.

Comparative Anatomy and the Foundations of Morphology . . 336
BY PROF. YVES DELAGE, M.D.

HUMAN ANATOMY.

The Relations of Anatomy to Other Sciences ..... 361
BY PROF. WILHELM WALDEYER, M.D., PH.D., LL.D.

The Problems in Human Anatomy ....... 378

BY PROF. HENRY HERBERT DONALDSON, PH.D.

PHYSIOLOGY.

The Domain of Physiology and its Relation to Medicine . . . 395
BY PROF. S. J. METZER, M.D.

The Relation of Physiology to Other Sciences ..... 403
BY PROF. MAX VERWORN, PH.D., M.D.

Problems of Physiology of the Present Time ..... 416
BY PROF. WILLIAM HENRY HOWELL, M.D., PH.D., LL.D.

Special Works of Reference to accompany Lecture on Ecology . . 435

Works of Reference on Bacteriology, Animal Morphology, Embryology,

Comparative Anatomy, Human Anatomy, and Physiology . . 437

Special Works of Reference on Bacteriology ..... 443
Special Works of Reference on Embryology ..... 444
Special Works of Reference on Comparative Anatomy . . . 445

GROUP OF INTERNATIONAL LECTURERS

The group reproduced here presents many famous lecturers of the Interna-
tional Congress of Arts and Science. In the front row (from left to right)
are Dr. George M. Duncan, Professor of Philosophy, Yale University; Dr.
William A. Hammond, Professor of Philosophy and Aesthetics, Cornell Uni-
versity ; Dr. Ludwig Boltzmann, Professor of Physics. University of Vienna ;
D'r. James McKeen Cattell, Professor of Psychology, Columbia University;
Dr. \Vilhelm Ostwald, Professor of Physical Chemistry, University of Leipzig;
Dr. James E. Creighton, Professor of Philosophy, Cornell University; Dr.
Ifarald Hoeffrling, Professor of Philosophy. University of Copenhagen; Dr.
Benno Erdmann, Professor of Philosophy, University of Bonn ; Dr. Jacques
I.oeb. Professor of Physiology, University of California; and Dr. Svante A.
Arrhenius. Professor of Phvsics, University of Stockholm.

DEPARTMENT XIII — BIOLOGY

DEPARTMENT XIII — BIOLOGY

(Hall 2, September 20, 11.15 a. w.)

CHAIRMAN: PROFESSOR WILLIAM G. FARLOW, Harvard University.
SPEAKERS: PROFESSOR JOHN M. COULTER, University of Chicago.
PROFESSOR JACQUES LOEB, University of California.

DEVELOPMENT OF MORPHOLOGICAL CONCEPTIONS

BY JOHN MERLE COULTER

[John Merle Coulter, Head of the Department of Botany, University of Chicago,
Chicago, Illinois, b. November 20, 1851, Ningpo, China. A.B. Hanover Col-
lege, 1870; A.M. ibid. 1873; Ph.D. Indiana University, 1890. Botanist, Hayden
Survey, 1872-74; Professor of Natural Science, Hanover College (Ind.) 1874-
89; Professor at Wabash College (Ind.) 1889-91; President of Indiana Uni-
versity, 1891-93; President, Lake Forest University (111.) 1893-96; Head of
the Department of Botany, University of Chicago, 1896. Member, Fellow,
American Association for the Advancement of Science; Botanical Society of
America; Associate Fellow, American Academy of Arts and Science; Academic
Internationale de G6ographie Botanique. Author of Synopsis of the Flora of
Colorado; Manual of the Botany of the Rocky Mountain Region; Handbook of
Plant Dissection; Revision of North American Umbelliferce; Manual of the Bot-
any of the Northern United States; Botany of Western Texas; A Synopsis of
Mexican and Central American Umbelliferce ; Morphology of Gymnosperms ;
Morphology of Angiosperms; Plant Relations; Plant Structures; Plant Studies.]

ANY outline of the progress of biology during the century com-
memorated by this Exposition that is compressed within a single
address must be either inadequate or must restrict itself to some
single point of view. The latter alternative must be the one chosen,
not only on account of the vastness of the material, but chiefly that
personal experience may give some value to the presentation. In
the present address, therefore, certain limitations become necessary,
and in this case they are very natural.

In the first place, it would be presumptuous in me to include zo-
ology in any review of progress, for botanists, as a rule, are strictly
limited by their material, and have never confounded botany with
biology. It is true that such subjects as morphology and physiology
are not to be limited by any barrier that may be set up between
plants and animals, but it is also true that the material and literature
with which one is familiar do not often cross this barrier. At the same
time, I think it must be recognized that botany and zoology have
been mutually stimulating, every real advance in the one having
given an impetus to the other, and that, as a consequence, their
progress has been largely along parallel lines. Hence a review of any

4 BIOLOGY

phase of the progress of the one may serve as an indication of the
progress of the other.

In the second place, to outline the progress of biology even from
the standpoint of botany is too large a subject to be included in the
grasp of any one man in such a way that he can recognize the move-
ments in his own experience. The general botanist no longer exists
except in name, and any general survey of botanical activity would
have to be a compilation rather than a contribution. With these lim-
itations, it becomes necessary for me to restrict myself largely to such
an outlook as is given by plant morphology, and even then to speak
only of those conclusions that come naturally to one in contact with
the morphology of vascular plants. And yet I believe that a history of
the development of the fundamental conceptions of plant morphology
may be taken as a fair illustration of what has been going on, not only
in botany in general, but also in biology.

In the third place, the period included in this survey of plant mor-
phology need not extend beyond the middle of the last century, for at
least three reasons: (1) The earlier progress of the science has been
outlined by Sachs in his admirable History of Botany ; (2) modern
morphology finds its beginnings in a very real sense in the work of
Hofmeister; and (3) Darwin's theory of natural selection gave the
strong evolutionary impulse that it has felt ever since.

My principal theme, therefore, is the development of morphological
conceptions as illustrated by plant morphology.

It would be confusing to introduce the mass of details and the
names of investigators suggested by this subject. Nor would there be
any advantage in recording the changes of conceptions in reference to
the great variety of structures developed by the plant body and in re-
ference to their relation to one another. My purpose is to illustrate the
general change of attitude, the shifting of the point of view, in refer-
ence to plant organs, as knowledge has increased. No definite names
or dates can be cited, for the movement has been general and gradual,
developed out of common experience and proceeding from the back-
ground of accumulated knowledge. Disregarding the numerous pos-
sible subdivisions, the attitude of mind towards a plant organ during
the last half-century has presented three distinct phases.

I. The Phase of the Mature Organ

At the beginning of the period under consideration, the morpho-
logist concerned himself chiefly with completed organs, and an over-
shadowing rigid taxonomy compelled the idea of their classification.
A few theoretical types of organs had been selected, and all organs
were forced by the doctrine of metamorphosis to lie upon this Pro-
crustean bed. All parts of vascular plants, for example, were re-

DEVELOPMENT OF MORPHOLOGICAL CONCEPTIONS 5

garded as roots, stems, or leaves under various disguises. It does not
seem unreasonable to characterize this conception as the arbitrary
selection of an ideal type, the natural offspring of the conception of
ideal types that prevailed in taxonomy. In other words, morphology
was dominated by taxonomy, and morphologists were first and
chiefly taxonomists. It is this phase of morphology that must con-
tinue to be exploited chiefly by taxonomists, and which still remains
in those conservative schools in which instruction lags far behind
research. This doctrine of types resulted in the cataloguing of organs
just as species were being catalogued, and, although capable of re-
cording material, it was incapable of advancing knowledge.

An accompaniment of this mental attitude was the explanation of
metamorphoses. It is almost impossible for one age to conceive of the
mental condition that was satisfied with the explanations of a previous
age. In this case it must be remembered that the earlier botanists
were either ecclesiastically trained or not trained at all, and to them
it was entirely satisfying to explain all metamorphoses upon teleo-
logical grounds. It is a matter of great surprise, however, to note how
this point of view is still maintained by some investigators who have
abandoned the doctrine of types, and in every other respect are inhal-
ing a modern atmosphere.

One serious result of belief in the doctrine of types was the use of
the most complex structures to explain the simpler ones; the reading
of complexity into simplicity. For example, the type flower selected
was one that had become completely differentiated; in short, a highly
organized flower. This was read into all simpler flowers, and was even
carried over the boundary of angiosperms and applied among gymno-
sperms, to the utter confusion of terminology and understanding.
Fortunately for the students of cryptogams, a great gulf was thought
to be fixed between plants with seeds and those without, and this the
flower did not cross.

It is safe to say that this phase of morphology, with its types and
teleology, and its use of complex structures to interpret simple ones,
is now in its decline.

II. The Phase of the Structure of the Developing Organ

This type of morphology has chiefly characterized the period under
consideration. Its fundamental conception is evolution; its purpose is
to discover phylogeny ; and its method is based upon the belief that
ontogeny recapitulates phylogeny. As a consequence, there was de-
veloped for the first time what may be called a philosophy of the plant
kingdom, organizing the details of morphology into one coherent whole
about such central facts as alternation of generations and heterospory.
Study of the metamorphoses of plant organs was replaced by a study

6 BIOLOGY

of their development and of "life-histories," and the earliest stages of
gametophyte and sporophyte and reproductive organs were scrutin-
ized and recorded in the greatest detail in the search for relationships.
Shifting its centre of gravity from the mature organ to the nascent
organ, morphology departed very far from special taxonomy, while at
the same time it was laying the solid foundation for general taxonomy.
The reversal of old ideas was conspicuous, and much of the old ter-
minology was found to be false in suggestion and almost impossible to
shake off. For example, it has been a constant surprise to me to see
the persistent use of a sex terminology in connection with flowers by
those who must know better, and who must know also that they are
helping to perpetuate a radical misconception.

A still more important result of this change of front in the mor-
phological attack was the necessary reversal of the method of inter-
pretation. No longer was the flower of highly organized angiosperms
read down into the structures of the lower groups; but from the sim-
plest beginnings structures were traced through increasing complex-
ity and seen to end in the flower, explaining what it is. This meant
that evolution had replaced the old idea of types and metamorphosis,
and was building facts into a structure rather than cataloguing them.
This spirit of modern morphology has not as yet dominated instruc-
tion. Its facts are developed in all their detail, abundantly and skill-
fully, but very seldom do the facts seem to be coordinated. The old
spirit of accumulating unrelated material still dominates teaching, and
crams the memory without developing permanent tissue.

The detailed developmental study of plants and their organs gave
rise to what has been called morphological cytology, but it is an un-
fortunate differentiation, for cytology merely pushes the search for
structure to the limits of technique. It is becoming more and more
clear that every morphologist must also be a cytologist; and certainly
every cytologist should be a morphologist; and there is no more reason
for differentiation on this basis than on the basis of objectives used.

While fully recognizing the magnificent development of morpho-
logical knowledge that has resulted from this point of view, it is inter-
esting to note running all through it much of the rigidity of the older
morphology, leavened to a certain extent by the demands of evolution.
Certain definite morphological conceptions were established, and
organs were as rigidly outlined and defined as under the old regime.
For example, there were no more definite morphological conceptions
than sporangium, antheridium, and archegonium. Unconsciously,
perhaps, a type of each was selected, this time from their display in the
lower plant groups; and this type was read into the structure of higher
groups. The distinctly outlined antheridia and archegonia of bryo-
phytes were compelled to remain just as distinct of definition when
they become confused among surrounding tissues in the pterido-

DEVELOPMENT OF MORPHOLOGICAL CONCEPTIONS 7

phytes; and the beautifully distinct sporangium of the leptosporan-
giates compelled the idea of an imbedded sporangium among the
eusporangiates. In other words, the concept included non-essential
with essential structures, a distinct wall about a sporangium being
just as much a part of the definition as the sporogenous tissue, and its
presence compelled even in the absence of any occasion for it. It can
hardly be doubted that this was a heritage of habit from the older
morphology, for .it is in a sense a continuation of the conception of
types. The recent morphologist who traces a sporangium wall into an
anther is the same in spirit as the older morphologist who saw in the
stamen a transformed leaf.

Associated with this rigidity of conception as to structure was the
idea of predestination, and search was made for the cell or cell-group
that was foreordained to produce a given structure. There was no
idea that the fate of these cells might be changed or that other cells
might share it. The repeated attempts to discover an exact definition
of the term archesporium will serve as an illustration; and the re-
peated failures should have warned sooner than they did. Indif-
ference of primordia was not thought of, and each living cell was
conceived of as having only a single possibility.

The idea of unvarying sequence and predestination not only en-
tered into the conception of developing organs, but also directed an
immense amount of work in connection with the early embryonic
stages of both gametophyte and sporophyte. So far as my own experi-
ence is concerned, it was in this connection that the conception of
rigidity broke down. The multiplication of observations caused defi-
nite sequence and predestination to vanish in a maze of variations.
This type of morphology was necessarily its own corrective, for rigid-
ity could not stand before the accumulation of facts. In a sense, rigid-
ity of conception is easier to grasp, and certainly simpler to present,
than flexibility of conception, for the human mind seems to demand
its knowledge in labeled pigeon-holes. This same spirit permeated
the attitude of the morphologist of this period towards his ultimate
purpose, for phylogeny to him was rather a simple conception. Sim-
ilarity of structure meant community of descent. Such a condition as
heterospory, such a structure as the seed, or such an organization as
the sporophyte, was attained once for all, and the successful plant or
group became the fortunate ancestor of all heterosporous plants, or
spermatophytes, or sporophytes. This was phylogeny made easy.
Multiplied observations showed that similarity of structure often does
not indicate community of descent, and we are staggered before the
possibilities of phylogeny.

The division of morphology that we have been pleased to call cyto-
logy has had the same experience. It was hoped that the more funda-
mental structures would show some reasonable constancy of phe-

8 BIOLOGY

nomenar some rigidity in detail; but we have been confronted here
again by endless variation, and hence most diverse interpretation of
results.

Clearly, belief in a rigid sequence or in predestination could not be
maintained; and in a real sense morphologists have been cataloguing
material for study, and their real problems lie behind these endlessly
variable details.

The phase of morphology just described has certainly been domi-
nant during the last half-century, with phylogeny as its chief
stimulus, and a rigidity of conception that only a multitude of facts
could break down. It is a type that must always exist, as taxonomy
must always exist, and it must be considered fundamental in
familiarizing with material; but, perhaps, it may be said now to be
at its culmination as the dominant phase.

III. The Phase of the Influence of Changing Conditions upon the
Developing Organ

This means experimental morphology, and so far as organs are
concerned its purpose is to discover the conditions that determine
their structure and nature. All idea of rigidity has disappeared in
the fundamental conception of the capacity of living cells to respond
to varying conditions. What may be the possibilities of variations
and what may be the exact conditions responsible for variations,
are questions to be answered by experiment. If the oldest morpho-
logy is in its decline, and the current morphology at its culmination,
experimental morphology may be said to be in its inception. It is
easier to judge of a movement at its decline or culmination than at
its inception, and experimental morphology as yet is fuller of pro-
mise than of performance. In any event, it was an inevitable phase
when multiplied variation had broken down the conception of rigid-
ity. The fundamental question of the possibilities of living cells is im-
mediately confronting us; and the range of these possibilities may
be considered under three heads.

(1) The Varying Structure of an Organ. Perhaps leaf variation,
which enters so largely into taxonomy, may be used as an illustra-
tion. When, under experimentation, leaves can be made to vary
from narrow to orbicular, from dissected to entire, and the exact
physical condition determined that induces the result, any idea of
rigidity in the form or structure of an organ must disappear. An
observed narrow range of variation in nature may be regarded as an
indication of the narrow range of conditions rather than of the nar-
row range of possible response on the part of the organ. From this
point of view an organ is represented by its essentials, without refer-
ence to its non-essentials, and so we are now thinking of sporangia in

DEVELOPMENT OF MORPHOLOGICAL CONCEPTIONS 9

terms of sporogenous tissue, without reference to the presence or
absence of a morphologically constant wall; of archegonia as axial
rows of potential eggs, without concern for an exact morphological
definition of the sterile jacket. The main question is, what deter-
mines the formation of sporogenous tissue rather than of sporangia;
what determines the formation of eggs or sperms, rather than of
archegonia and of antheridia?

(2) The Possibilities of Primordia. This has to do with what I
have called the doctrine of predestination. It is more than a ques-
tion as to the variable form or structure of an organ; it is a question
as to the variable nature of an organ that may arise from a given
primordium. When primordia that usually develop microsporangiate
organs produce megasporangiate ones, or vice versa; when the same
plant body produces sporangia or gametangia in response to con-
ditions imposed by the experimenter; it becomes evident that pri-
mordia may be indifferent not only as to form, but also as to nature.

This meant a general unsettling of morphological conceptions.
To find, for example, that a given cell is not set apart from its first
appearance to function as an archesporial cell, but that there are as
many potential archesporial cells as there are cells in an extensive
tissue; and further to find that the archesporial cell when discov-
ered by its functioning does not necessarily produce all the sporoge-
nous tissue, is to abandon the idea of predestination and of defining
structures on a rigid morphological basis.

(3) The Origin of Species. Probably the greatest triumph of
experimental morphology thus far is that it has put the problem of
the origin of species upon an experimental basis. The ability to vary
and to vary promptly and widely, when considered in connection
with structures used by taxonomists, means new species under cer-
tain conditions. To analyze these conditions is a problem of enormous
complexity, but to have the problem clearly before us is but the
prelude to its solution. There is still a tendency to call things inher-
ent that are not apparent, but this is a habit not easily outgrown,
and such a problem as the origin of species will long have its con-
venient category of "inherent tendencies."

Certain conclusions are inevitable as one considers the perspective
opened by experimental morphology.

In the first place, it would seem that what we have called "bio-
logical laws" are also the laws of physics and chemistry, and the
experimenter must be prepared to use all the refinements of method
developed by physicists and chemists. Much of the work done in
the name of experimental morphology is as yet crude in the extreme,
and we are often left with a confusing plexus of conditions rather
than with a satisfactory analysis. To grow plants, to observe certain
results, and to draw conclusions, too frequently means the arbitrary

10 BIOLOGY

or ignorant choice of one factor out of a possible score to be found in
the uncontrolled conditions.

In the second place, that phase of ecology which deals with what
are called "adaptations to environment" simply catalogues the
materials of experimental morphology and must be merged with
it. To retain it as a distinct field of work is to doom it to sterility,
for it can only bear fruit as it becomes an experimental subject, and
then it is experimental morphology.

In the third place, experimental morphology, with its background
of physics and chemistry, is more closely related to physiology than
it is to the older phases of morphology; which leads to the conclu-
sion that the fundamental problems of morphology are physiological.
We may look at the situation from either standpoint, and say that
the most recent phase of morphology intrenches upon physiology,
or that the boundaries of physiology must be extended enough to
include morphology. To-day the two subjects are handicapped;
for morphologists are not physiologists enough to know how to
handle and interpret their material, and physiologists are not mor-
phologists enough to know the extent and significance of their
material. The training of the future must not differentiate these
two subjects still further, but must combine them for effective re-
sults.

This modern tendency to cross old-established boundaries be-
tween subjects is evident everywhere. Physiology and chemistry
have long possessed common territory; plant morphology and phy-
siology have now found no barrier between them. This simply means
that so long as we deal with the most external phenomena our sub-
jects seem as distinct from one another as do the branches of a tree;
but when we approach the fundamentals we find ourselves coming
together, as the branches merge into the trunk. The history of botany,
beginning with taxonomy, has been a history that began with the
tips of the branches and has proceeded in converging lines towards
the common trunk. The fundamental unity of the whole science,
in fact, of biological science, however numerous the branches may
be, is becoming more and more conspicuous. Already the old lines
of classification have become confused, and one looking through
any recent list of papers finds it impossible to classify them in terms
of the old divisions. Investigators are now to be distinguished by
particular groups of problems in connection with particular material,
and all problems lead back to the same fundamental conceptions.
In other words, the point of view is to be common to all investigators,
and until it is common their results will not reach their largest sig-
nificance.

A fourth consideration is the result of all this upon taxonomy. It
seems clear to one who was originally trained in taxonomy, and

DEVELOPMENT OF MORPHOLOGICAL CONCEPTIONS 11

who has passed through all the phases of morphology described
above, that the conception of species has become so radically changed
that a reconstructed taxonomy is inevitable. When the doctrine of
types disappeared, and when experimental morphology showed the
immense possibilities of fluctuation in taxonomic characters, the
taxonomy of the past was swept from its moorings. Taxonomy
must continue its work as a cataloguer of material, but to catalogue
rigid concepts is very different from cataloguing fluctuating varia-
tions. To do the latter on the old basis is being attempted in
certain quarters, but it soon passes the limit of usefulness and sets
strongly towards the mere recording of individuals. Some new
basis must be devised, and it must be a natural and useful expres-
sion of the relationships of forms as suggested by experimental
morphology.

That this history of the progress of morphology, just outlined, is
a fair indication of general tendencies may be illustrated from plant
anatomy. This subject, not well differentiated from plant mor-
phology among the lower groups, has developed a very distinct
field of its own among vascular plants. Its early phase was that of
classification, in which types of tissues were rigidly defined. This
definite catalogue of tissues continued to be used after evolution-
ary morphology was well under way, and morphologists gradually
abandoned any serious consideration of it, just as they had cut
loose from the old taxonomy. In text-books the juxtaposition of
morphology upon an evolutionary basis and a little anatomy upon
a strictly taxonomic and artificial basis became very familiar.

Recently a second phase of anatomy has begun to appear, and
we find it upon an evolutionary basis. Investigation has passed from
the study of mature tissues to the study of developing tissues, and
the seedling is more important to the anatomist than the adult
body. As in the corresponding phase of morphology, the funda-
mental conception of this new phase is the theory of recapitulation,
and its ultimate purpose is phylogeny. It views tissues as mor-
phology views organs, and is attacking the same general problems.
In so doing it becomes a special field of morphology, no more to be
separated from it than are morphologists who study the sporophyte
to be separated from those who study the gametophyte. It is simply
the development of another line of attack upon morphological prob-
lems. This anatomical morphology, as it may be called, has yet to
accumulate its share of results, and there is no region of morphology
more in present need of investigators. From the small beginnings
it has made it is evident that it must check the conclusions of the
older morphology at every point. Even now no statement as to
phylogeny can afford to neglect the testimony of anatomy.

This second phase of anatomy promises to be accompanied by a

12 BIOLOGY

third, which finds its parallel and probably its suggestion in experi-
mental morphology. In its incipient stage it is known as ecological
anatomy, just as another phase of ecology preceded and then became
merged in experimental morphology. Ecological anatomy can
make no progress until it becomes an experimental subject, and
then it is experimental anatomy, which holds the same relation to
experimental morphology that evolutionary anatomy holds to evo-
lutionary morphology. In other words, it is the same subject, with
the same methods and purpose, and differing only in the struc-
tures investigated. And thus anatomy reaches the physiological
basis, and as a part of morphology fills out the structures to be
investigated from this standpoint.

There remains a region of ecology so vast and vague that it must
be considered by itself for a time. It deals with such complex re-
lationships as exist between soil, topography, climate, etc., on the
one hand, and masses of vegetation, on the other. Just because it
is vast and vague ought it to be attacked. The little incursions that
have been made indicate the possibilities. It evidently includes
some of the great ultimate problems. As yet it cannot define itself,
for it seems to have no boundaries. Its materials were evident but
entirely meaningless in the earlier history of botany, for it needed
all of our progress before it could begin to ask intelligent questions.
By virtue of its late birth it promises to develop more rapidly than
any other phase of botany. And yet, beyond the inevitable prelim-
inary classification of material, its real progress is measured by its
experimental work conducted upon a definite physiological basis.
Tentative generalizations are numerous and necessary, but they are
merely suggestions for experiment. When one understands the close
analysis necessary in the simplest physiological experiment, the pro-
blems suggested by this phase of plant ecology are appalling; but I
see in the whole subject nothing but the largest application of physi-
ology to the plant kingdom.

And now that the various phases of botany all seem to rest upon
physiology, it must be apparent that the most fundamental pro-
blems are physiological. It is only recently that the development of
plant physiology has justified this relationship. Its own history has
been one of progress from the superficial towards the fundamental,
from the behavior of a plant organ to the behavior of protoplasm.
And here it becomes identified with physics and chemistry; and in a
very real sense botany has become the application of physics and
chemistry to plants.

THE RECENT DEVELOPMENT OF BIOLOGY

BY JACQUES LOEB

[Jacques Loeb, Professor of Physiology, University of California, since 1902. b.
Germany, April 7, 1859. Graduate of the Ascanisches Gymnasium, Berlin.
Studied medicine, Berlin, Munich; M.D. Strassburg. Assistant in Physiology,
University of Wiirzburg, 1886-88 ; ibid., University of Strassburg, 1888-90 ;
Biological Station, Naples, 1889-91 ; Associate in Biology, Bryn Mawr, 1891-92;
Assistant Professor of Physiology and Experimental Biology, University of
Chicago, 1892-95; Associate Professor, ibid., 1895-1900;' Professor, ibid.,
1900-02. Author of The Heliotropism of Animals and its Identity with the
Heliotropism of Plants; Physiological Morphology; Comparative Physiology of the
Brain and Comparative Psychology; Studies in General Physiology; The Dynamics
of Living Matter.}

THE task allotted to me on this occasion is a review of the develop-
ment of biology during the last century. The limited time at our
disposal will necessitate many omissions and will force me to confine
myself to the discussion of a few of the departures in biology which
have led or promise to lead to fertile discoveries.

The problem of a scientific investigator can always be reduced to
two tasks; the first, to determine the independent variables of the
phenomena which he has under investigation, and secondly, to find
the formula which allows him to calculate the value of the function
for every value of the variable. In physics and chemistry the inde-
pendent variables are in many cases so evident that the investiga-
tion may begin directly with the quantitative determination of the
relation between the change of the essential variable and the func-
tion. In biology, however, the variables, as a rule, cannot be recog-
nized so easily, and a great part of the mental energy of the investi-
gators must be spent in the search for these variables. To give an
example, we know that in many eggs the development only begins
after the entrance of a spermatozoon into the egg. The spermatozoon
must produce some kind of a change in the egg, which is responsible
for the development. But we do not know which variable in the
egg is changed by the spermatozoon, whether the latter produces a
chemical or an osmotic change, or whether it brings about a change
of phase or some other effect. It goes without saying that a theory
of sexual fertilization is impossible until the independent variable
in the process of sexual fertilization is known.

The investigations of the biologist differ from those of the
chemist and physicist in that the biologist deals with the analysis
of the mechanism of a special class of machines. Living organisms

14 BIOLOGY

are chemical machines, made of essentially colloidal material, which
possess the peculiarity of developing, preserving, and reproducing
themselves automatically. The machines which have thus far been
produced artificially lack the peculiarity of developing, growing,
preserving, and reproducing themselves, though no one can say
with certainty that such machines might not one day be constructed
artificially.

The specific and main work of the biologist will, therefore, be
directed toward the analysis of the automatic mechanisms of develop-
ment of self-preservation and reproduction.

II. The Dynamics of the Chemical Processes in Living Organisms

The progress made by chemistry, especially physical chemistry,
has definitely put an end to the idea that the chemistry of living
matter is different from the chemistry of inanimate matter. The
presence of catalyzers in all living tissues makes it intelligible that
in spite of the comparatively low temperature at which life phenom-
ena occur the reaction velocities for the essential processes in living
organisms are comparatively high. It has been shown, moreover, that
the action of the catalyzers found in living organisms can be imitated
by certain metals or other inorganic catalyzers. We may, therefore,
say that it is now proved beyond all doubt that the variables in the
chemical processes in living organisms are identical with those with
which the chemist has to deal in the laboratory. As a consequence of
this result chemical biology has during the last years entered into
the series of those sciences which are capable of predicting their
results quantitatively. The application of the theory of chemical
equilibrium to life phenomena has led biological chemists to look
for reversible chemical processes in living organisms, and the result
is the discovery of the reversible enzyme actions, which we owe to
A. C. Hill. I think it marks the beginning of a new epoch of the
physiology of metabolism that we now know that the same enzymes
not only accelerate the hydrolysis, but also in some cases, if not
generally, the synthesis of the products of cleavage. It is not im-
possible that the results thus obtained in the field of biology will
ultimately in return benefit chemistry, inasmuch as they may en-
able chemistry to accomplish syntheses with the help of enzymes
found in living organisms which could otherwise not be so easily
obtained.

A very beautiful example of the conquest of biological chemistry
through chemical dynamics is offered by the work of Arrhenius and
Madsen. These authors have successfully applied the laws of chem-
ical equilibrium to toxins and antitoxins so that it is possible to
calculate the degree of saturation between toxins and antitoxins for

RECENT DEVELOPMENT OF BIOLOGY 15

any concentration with the same ease and certainty as for any other
chemical reaction.

We know as yet but little concerning the method by which enzymes
produce their accelerating effects. It seems that the facts recently
gathered speak in favor of the idea of intermediary reactions. Ac-
cording to this idea the catalyzers participate in the reaction, but
form combinations that are again rapidly decomposed. This makes
it intelligible that at the end of the reaction the enzmes and cataly-
zers are generally in the same condition as at the beginning of the
reaction, and that a comparatively small quantity of the catalyzer
is sufficient for the transformation of large quantities of the reacting
substances.

This chapter should not be concluded without mentioning the
discovery of zymase by Buchner. It had long been argued that only
certain of the fermentative actions of yeast depended on the presence
of enzymes which could be separated from the living cells, but that
the alcoholic fermentation of sugar by yeast was inseparably linked
together with the life of the cell. Buchner showed that the enzyme
which accelerates the alcoholic fermentation of sugar can also be
separated from the living cell, with this purely technical difference
only, that it requires a much higher pressure to extract zymase
than any other enzymes from the yeast cell.

III. Physical Structure of Living Matter

We have stated that living organisms are chemical machines
whose framework is formed by colloidal material consisting of
proteins, fatty compounds, and carbohydrates. These colloids
possess physical qualities which are believed to play a great role in
life phenomena. Among these qualities are the slow rate of diffusion,
the existence of a double layer of electricity at the surface of the
dissolved or suspended colloidal particles, and the production of
definite structures when they are precipitated. We may consider it
as probable that the cytological and histological structures of living
matter will be reduced to the physical qualities of the colloids. But,
inasmuch as the physics of the colloids is still in its beginning, we
must not be surprised that the biological application of its results
is still in the stage of mere suggestions. The most important result
which has thus far been accomplished through the application of
the physics of colloids to biology is Traube's invention of the semi-
permeable membranes. To Traube we owe the discovery that every
living cell behaves as if it were surrounded with a surface film which
does not possess equal permeability for wTater and the substances
dissolved in it. Salts which are dissolved in water, as a rule, migrate
much more slowly into the living cells than water. This discovery

16 BIOLOGY

of the semi-permeability of the surface films of living protoplasm
made it possible to recognize the variable which determines the ex-
change of liquids between protoplasm and the liquid medium by
which it is surrounded, namely, the osmotic pressure. Inasmuch
as the osmotic pressure is measurable, this field of biology has en-
tered upon a stage where every hypothesis can be tested exactly,
and biology is no longer compelled to carry a ballast of shallow
phrases. We are now able to analyze quantitatively such functions
as lymph formation and the secretion of glands.

Recent investigations have thrown some light on the nature of
the conditions which seem to determine the semi-permeability of
living matter. Quincke had already mentioned that a film of oil
acts like a semi-permeable membrane. From certain considerations
of surface tension and surface energy it follows that every particle
of protoplasm which is surrounded by a watery liquid must form
an extremely thin film of oil at its surface. Overton has recently
shown that of all dissolved substances those which possess a high
solubility in fat, e. g., alcohol, ether, chloroform, diffuse most easily
into living cells. Overton concludes that lipoid substances, such as
lecithin and cholesterin, which are found in every cell, determine the
phenomenon of the semi-permeability of living matter.

IV. Development and Heredity

We now come to the discussion of those phenomena which con-
stitute the specific difference between living machines and the ma-
chines which we have thus far been able to make artificially. Living
organisms show the phenomena of development. During the last
century it was ascertained that the development of an animal egg,
in general, does not occur until a spermatozoon has entered it, but,
as already stated, we do not know which variable in the egg is changed
by the spermatozoon. An attempt has been made to fill the gap by
causing unfertilized eggs to develop with the aid of physicochemical
means. The decisive variable by which such an artificial partheno-
genesis can be best produced is the osmotic pressure. It has been
possible to cause the unfertilized eggs of echinoderms, annelids,
and mollusks to develop into swimming larvas by increasing transi-
torily the osmotic pressure of the surrounding solution. Even in
vertebrates (the frog and petromyzon), Bataillon has succeeded in
calling forth the first processes of development in this way. In
other forms specific chemical influences cause the development,
e. g., in the eggs of starfish diluted acids, and, best of all, as De-
lage has shown, carbon dioxide. In the eggs of Chcetopterus potas-
sium salts produce this result, and in the case of Arnphitrite, calcium
salts.

RECENT DEVELOPMENT OF BIOLOGY 17

From a sexual cell only a definite organism can arise, whose pro-
perties can be predicted if we know from which organism the sexual
cell originates. The foundations of the theory of heredity were
laid by Gregory Mendel in his treatise on the Hybrids of Plants,
one of the most prominent papers ever published in biology. Mendel
showed in his experiments that certain simple characteristics, as,
for example, the round or angular shape of the seeds of peas or the
color of their endosperm, is already determined in the germ by definite
determinants. He showed, moreover, that in the case of the hy-
bridization of certain forms one half of the sexual cells of each child
contains the determinants of the one parent, the other half contains
the determinants of the other parent. In thus showing that the
results of hybridization can be predicted numerically, not only for
one, but for a series of generations, according to the laws of the
calculus of probability, he gave not a hypothesis, but an exact theory
of heredity. Mendel's experiments remained unnoticed until Hugo
de Vries discovered the same facts anew, and at the same time
became aware of Mendel's treatise.

The theory of heredity of Mendel and de Vries is in full harmony
with the idea of evolution. The modern idea of evolution originated,
as is well known, with Lamarck, and it is the great merit of Darwin
to have revived this idea. It is, however, remarkable that none of
the Darwinian authors seemed to consider it necessary that the
transformation of species should be the object of direct observation.
It is generally understood in the natural sciences either that direct
observation should form the foundation of our conclusions or mathe-
matical laws which are derived from direct observations. This
rule was evidently considered superfluous by those writing on the
hypothesis of evolution. Their scientific conscience was quieted by
the assumption that processes like that of evolution could not be
directly observed, as they occurred too slowly, and that for this
reason indirect observations must suffice. I believe that this lack of
direct observation explains the polemical character of this litera-
ture, for wherever we can base our conclusions upon direct obser-
vations polemics become superfluous. It was, therefore, a decided
progress when de Vries was able to show that the hereditary changes
of forms, so-called "mutations," can be directly observed, at least in
certain groups of organisms, and secondly, that these changes take
place in harmony with the idea that for definite hereditary char-
acteristics definite determinants, possibly in the form of chemical
compounds, must be present in the sexual cells. It seems to me that
the work of Mendel and de Vries and their successors marks the
beginning of a real theory of heredity and evolution. If it is at all
possible to produce new species artificially, I think that the dis-
coveries of Mendel and de Vries must be the starting point.

18 BIOLOGY

It is at present entirely unknown how it happens that in living
organisms, as a rule, larger quantities of sexual cells begin to form
at a definite period in their existence. Miescher attempted to solve
this problem in his researches on the salmon. But it seems that
Miescher laid too much emphasis upon a mere secondary feature of
this phenomenon, namely, that the sexual cells in the salmon ap-
parently develop at the expense of the muscular substance of the
animal. According to our present knowledge of the chemical dynamics
of the animal body it seems rather immaterial whether the proteins
and other constituents of the sexual cell come from the body of the
animal or from the food taken up. The causes which determine the
formation of large masses of sexual cells in an organism at a certain
period of its existence are entirely unknown.

A little more progress has been made in regard to another prob-
lem which belongs to this group of phenomena, namely, how it hap-
pens that in many species one individual forms sperm, the other
eggs. It has been known for more than a century that it is possible
to produce at desire either females exclusively, or both sexes, in
plant lice. In bees and related forms, as a rule at least, only males
originate from the unfertilized eggs; from the fertilized eggs only
females. It is, moreover, known that in higher vertebrates those
twins which originate from one egg have the same sex, while the sex
of twins originating from different eggs may be different. All facts
which are thus far known in regard to the determination of sex
seem to indicate that the sex of the embryo is already determined
in the unfertilized egg, or at least immediately after fertilization.
I consider it possible that in regard to the determination of sex,
just as in the case of artificial parthenogenesis, a general variable
will be found by which we can determine whether an egg cell will
assume male or female character.

V. Instinct and Consciousness

The difference between our artificial machines and the living organ-
isms appears, perhaps, most striking when we compare the many au-
tomatic devices by which the preservation of individuals and species
is guaranteed. Where separate sexes exist we find automatic arrange-
ments by which the sexual cells of the two sexes are brought together.
Wherever the development of the eggs and larvse occurs outside of the
body of the mother or the nest we often find automatic mechanisms
whereby the eggs are deposited in such places as contain food on
which the young larva can exist and grow. We have to raise the ques-
tion how far has the analysis of these automatic mechanisms been
pushed. Metaphysics has supplied us with the terms " instinct " and
" will " for these phenomena. We speak of instinct wherever an animal

RECENT DEVELOPMENT OF BIOLOGY 19

performs, without foresight of the ends, those acts by which the
preservation of the individual or the species is secured. The term
" will "is reserved for those cases where these processes form constitu-
ents of consciousness. The words " instinct " and " will " do, however,
not give us the variables by which we can analyze or control the
mechanism of these actions. Scientific analysis has shown that the
motions of animals which are directed towards a definite aim depend
upon a mechanism which is essentially a function of the symmetrical
structure and the symmetrical distribution of irritability. Symmetri-
cal points of the surface of an animal, as a rule, have the same irrita-
bility, which means that, when stimulated equally, they produce the
same quantity of motion. The points at the oral pole as a rule pos-
sess a qualitatively different or greater irritability than those at the
aboral pole. If rays of light or current curves, or lines of diffusion or
gravitation, start from one point and strike an organism, which is
sensitive for the form of energy involved, on one side only, the tension
of the symmetrical muscles or contractile elements does not remain the
same on both sides of the body, and a tendency for rotation will result.
This will continue until the symmetrical points of the animal are
struck equally. As soon as this occurs there is no more reason why the
animal should deviate to the right or left from the direction of its
plane or axis of symmetry. These phenomena of automatic orienta-
tion of animals in a field of energy have been designated as tropisms.
It has been possible to dissolve a series of mysterious instincts into
cases of simple tropisms. The investigation of the various cases of
tropism has shown their great variety, and there can be no doubt that
further researches will increase the variety of tropisms and tropism-
like phenomena. I am inclined to believe that we possess in the
tropisms and tropism-like mechanisms the independent variable of
such functions as the instinctive selection of food and similar regu-
latory phenomena.

As far as the mechanism of consciousness is concerned, no scientific
fact has thus far been found that promises an unraveling of this me-
chanism in the near future. It may be said, however, that at least the
nature of the biological problem here involved can be stated. From a
scientific point of view we may say that what we call consciousness
is the function of a definite machine which we will call the machine
of associative memory. Whatever the nature of this machine in living
beings may be, it has an essential feature in common with the phono-
graph, namely, that it is capable of reproducing impressions in the
same chronological order in*which they come to us. Even simultane-
ous impressions of a different physical character, such as, for instance,
optical and acoustical, easily fuse in memory and form an inseparable
complex. The mechanism upon which associative memory depends
seems to be located, in higher vertebrates at least, in the cerebral

20 BIOLOGY

hemispheres, as the experiments of Goltz have shown. The same
author has shown, moreover, that one of the two hemispheres suffices
for the efficiency of this mechanism and for the full action of con-
sciousness. As far, however, as the physical or chemical character of
the mechanism of memory is concerned, we possess only a few starting
points. We know that the nerve cells are especially rich in fatty con-
stituents, and Hans Meyer and Overton have shown that substances
which are easily soluble in fat also act as very powerful anaesthetics,
for instance, chloroform, ether, and alcohol, and so on. It may be
possible that the mechanism of associative memory depends in some
way upon the constitution or action of the fatty compounds in our
nerve cells. Another fact which may prove of importance is the obser-
vation made by Speck that if the partial pressure of oxygen in the air
falls below one third of its normal value, mental activity very soon be-
comes impaired and consciousness is lost. Undoubtedly the unravel-
ing of the mechanism of associated memory is one of the greatest dis-
coveries which biology has still in store.

VI. Elementary Physiological Processes

It is, perhaps, possible that an advance in the analysis of the me-
chanism of memory will be made when we shall know more about
the processes that occur in nerve cells in general. The most elemen-
tary mechanisms of self-preservation in higher animals are the respira-
tory motions and the action of the heart. The impulse for the respira-
tory action starts from the nerve cells. As far as the impulses for the
activity of the heart are concerned, we can say that in one form at
least they start from nerve cells, and in all cases from those regions
where nerve cells are situated. But as far as the nature of these im-
pulses is concerned we know as little about the cause of the rhythmi-
cal phenomena of respiration and heart-beat as we know concerning
the mechanism of associative memory. It is rather surprising, but
nevertheless a fact, that physiology has not progressed beyond the
stage of mere suggestions and hypotheses in the analysis of such
elementary phenomena as nerve action, muscular contractility, and
cell division. Among the suggestions concerning the nature of con-
tractility those seem most promising which take into consideration
the phenomena of surface tension. The same lack of definite know-
ledge is found in regard to the changes in the sense organs which give
rise to sensations. It is obvious that the most striking gaps in bio-
logy are found in that field of biology* which has been cultivated
by the physiologists. The reason for this is, in part, that the analysis
of the elementary protoplasmic processes is especially difficult, but
I believe that there are other reasons. Medical physiologists have
confined themselves to the study of a few organisms, and this has

RECENT DEVELOPMENT OF BIOLOGY 21

had the effect that for the last fifty years the same work has been
repeated with slight modifications over and over again.

VII. Technical Biology

I think the creation of technical biology must be considered the
most significant turn biology has taken during the last century.
This turn is connected with a number of names, among which Liebig
and Pasteur are the most prominent. Agriculture may be con-
sidered as an industry for the transformation of radiating into chem-
ical energy. It was known for a long time that the green plants were
able to build up, with the help of the light, the carbohydrates from
the carbon dioxide of the air. Liebig showed that for the growth of
the plant definite salts are necessary, that these salts are withdrawn
from the soil by the plants, and that in order to produce crops these
salts must be given back to the soil. One important point had not
been cleared up by the work of Liebig, namely, the source of nitrates
in the soil which the plants need for the manufacture of their pro-
teins. This gap was filled by Hellriegel, who found that the tubercles
of the leguminosse, or rather the bacteria contained in these tubercles,
are capable of transforming the inert nitrogen of the air into a form in
which the plant can utilize it for the synthesis of its proteins. Wino-
gradski subsequently discovered that not only the tubercle bacteria
of leguminosse are capable of fixing the nitrogen of the air in the
soil in a form in which it can be utilized by the plant, but that the
same can be done by certain other bacteria, for instance, Chlostri-
dium pasteurianum. These facts have a bearing which goes beyond
the interests of agriculture. The question of obtaining nitrates from
the nitrogen of the air is of importance also for chemical industry,
and it is not impossible that chemists may one day utilize the ex-
perience obtained in nitrifying bacteria.

With the discovery of the culture of nitrifying bacteria we have
already entered the field of Pasteur's work. Yeast had been used for
the purposes of fermentation before Pasteur, but Pasteur freed this
field of biology just as much from the influence of chance as Liebig
did in the case of agriculture. The chemist Pasteur taught biologists
how to discriminate between the useful and harmful forms of yeast
and bacteria, and thus rendered it possible to put the industry of
fermentation upon a safe basis.

In recent times the fact has often been mentioned that the coal
fields will be exhausted sooner or later. If this is true, every source
of available energy which is neglected to-day may one day become
of importance. Professor Hensen has recognized the importance of
the surface of the ocean for the production of crops. The surface
of the ocean is inhabited by endless masses of microscopic organisms

22 BIOLOGY

which contain chlorophyl, and which are capable of transforming
the radiating energy of the sun into chemical energy.

Not only through the industry of fermentation and agriculture
has technical biology asserted its place side by side with physical
and chemical technology, but also in the conquest of new regions
for civilization. As long as tropical countries are continually threat-
ened by epidemics, no steady industrial development is possible.
Biology has begun to remove this danger. It is due to Koch if epi-
demics of cholera can be suppressed to-day, and to Yersin if the
spreading of plague can now be prevented. Theobald Smith dis-
covered that the organisms of Texas fever are carried by a certain
insect, and this discovery has had the effect of reducing, and possibly
in the near future destroying, two dreaded diseases, namely, malaria
and yellow fever.

It is natural that the rapid development of technical biology has
reacted beneficially upon the development of theoretical biology.
Just as physics and chemistry are receiving steadily new impulses
from technology, the same is true for biology. The working out of the
problems of immunity has created new fields for theoretical biology.
Ehrlich has shown that in the case of immunity toxins are rendered
harmless by their being bound by certain bodies, the so-called
antitoxins. The investigation of the nature and the origin of toxins
in the case of acquired immunity is a new problem which technical
biology has given to theoretical biology. The same may be said in
regard to the experiments of Pfeifer and Bordet on bacteriolysis
and hemolysis. Bordet's work has led to the development of methods
which have been utilized for the determination of the blood relation-
ship of animals.

VIII. Ethical and Economic Effects of Modern Biology

The representatives of the mental sciences often reproach the
natural sciences that the latter only develop the material, but not
the mental or moral interests of humanity. It seems to me, however,
that this statement is wrong. The struggle against superstition
is entirely carried on by the natural sciences, and especially by the
applied sciences. The nature of superstition consists in a gross mis-
understanding of the causes of natural phenomena. I have not
gained the impression that the mental sciences have been able to
reduce the amount of superstition. Lourdes and Mecca are in no
danger from the side of the representatives of the mental sciences,
but only from the side of scientific medicine. Superstition disappears
so slowly for the reason that the masses as a rule are not taught
any sciences. If the day comes when the chief laws of physics,
chemistry, and experimental biology are generally and adequately

RECENT DEVELOPMENT OF BIOLOGY 23

taught, we may hope to see superstition and all its consequences
disappear, but not before this.

As far as the influence of the applied sciences on ethics is con-
cerned, I think we may hope that through the natural sciences the
ethics of our political and economical life will be altered. In our
political as well as our economical life we are still under the influ-
ence of the ancients, especially the Romans, who knew only one
means of acquiring wealth, namely, by dispossessing others of it.
The natural sciences have shown that there is another and more
effective way of acquiring wealth, namely, by creating it. The
way of doing this consists in the invention of means by which the
store of energy present in nature can be more fully utilized. The
wealth of modern nations, of Germany and France, is not due to
their statesmen or to their wars, but to the accomplishments of the
scientists. It has been calculated that the inventions of Pasteur
alone added a billion francs a year to the wealth of France. In the
light of such facts it seems preposterous that statesmen should con-
tinue to instigate war simply for the conquest of territories. Through
modern science the wealth of a nation can be increased much more
quickly than through any territorial conquest. We cannot expect
any change in the political and economical ethics of nations until
it is recognized that the lawmakers and statesmen must have a
scientific training. If our lawmakers possessed such a training, they
would certainly not have allowed one general source of energy
after another, such as oil-fields, coal-fields, water-power, etc., to be
appropriated by individuals. All these stores of energy belong just
as well to the community as the oxygen of the air or the radiating
energy of the sun. Our present economical and political ethics is
still on the whole that of the classical period or the Renaissance,
because the knowledge of science among the masses and statesmen
is still on that level, but the natural sciences will ultimately bring
about as thorough a revolution in ethics as they have brought
about in our material life.

IX. Experimental Biology as an Independent Science

If we compare the development of biology writh the simultaneous
development of physics and chemistry during the last twenty years,
we must be impressed by the fact that during that time the great dis-
coveries in physics and chemistry have followed each other surpris-
ingly fast. The discovery of the law of osmotic pressure, the theory
of electrical dissociation, the theory of galvanic batteries, the sys-
tematic formulation of physical chemistry, the discovery of electrical
waves, the discovery of the X-rays, the discovery of the new elements
in the air, the discovery of radioactivity, the transformation of ra-

24 BIOLOGY

dium into helium, the theory of radiation pressure, — what have we
in biology that could be compared with such a series of discoveries?
But I believe that biology has important discoveries in store, and that
there is no intrinsic reason why it should be less fertile than physics
and chemistry. I think the difference in the fertility of biology and
the physical sciences is at least partly due to the present organization
of the biological sciences.

General or experimental biology should be represented in our
universities by special chairs and laboratories. It should be the task
of this science to analyze and control those phenomena which are
specifically characteristic of living organisms, namely, development,
self-preservation, and reproduction. The methods of general biology
must be those of chemistry, and especially those of physical chemistry.
To-day general or experimental biology is represented in our univer-
sities neither by chairs nor by laboratories. We have laboratories
for physiology, but to show how little interest physiologists take in
general biology I may mention the fact that the editor of a physio-
logical annual review excludes papers on development and fertili-
zation from his report, as, in his opinion, this belongs to anatomy.
On the other hand, anatomists and zoologists must give their full
energy to their morphological investigations, and have, as a rule,
neither the time for experimental work, nor very often the training
necessary for that kind of work. Only the botanists have kept up
their interest in general biology, but they of course pay no attention
to animal biology. In working out this short review of the develop-
ment of biology during the last century, I have been impressed with
the necessity of our making better provisions for that side of biology
where, in my opinion, the chances for the great discoveries seem to
lie, namely, general or experimental biology.

SECTION A — PHYLOGENY

SECTION A — PHYLOGENY

(Hall 2, September 21, 3 p. m.)

CHAIRMAN : PROFESSOR THOMAS HUNT MORGAN, Columbia University.
SPEAKERS : PROFESSOR HUGO DE VRIES, University of Amsterdam.

PROFESSOR CHARLES O. WHITMAN, University of Chicago.

THE Chairman of the Section of Phylogeny was Professor Thomas
Hunt Morgan, of Columbia University, who began the proceedings
of the Department with the following remarks:

"This Section of the Congress might have been given the title of
evolution rather than of phylogeny; for, while phylogeny deals with
an historical process, the term evolution has come to-day — largely
through the work of De Vries — to include not only a study of the
evolution of the past, but of evolution as it is taking place around us
at the present time. This is not a formal distinction, but one that
stands for a fundamental difference of method that has the most far-
reaching consequences. The study of evolution as an historical ques-
tion must have always been unsatisfactory, for all the doubts that
darken the historical method would have left its conclusions dubious
and unconvincing. Historical evolution could never have attained to
the dignity of an exact science. The disrepute into which phylogene-
tic speculation has fallen in our own times furnishes an example of
what we may expect from the method.

" When, on the other hand, the process of evolution was studied by
the method of experiment, a new era opened. Darwin himself used
extensively the experimental method, and his finest results have been
reached in this way. Much of the general information of the breeders
on which he relied, alas too often, are also the outcome of experiment,
but of experiments by men incapable, in many cases, of employing
the method with scientific precision.

" After Darwin, little was done in this direction, although a few
names stand out as oases in a waste of speculation. Now once again,
as Bateson has remarked, 'After a weary halt of forty years we have
at last begun to march.' It is a pleasure as well as a great oppor-
tunity that we are to listen to-day to the addresses of two biologists
who before all others have undertaken the study of evolution on
a large scale by means of the experimental method. Professor
De Vries has studied in Europe the evolutionary process in the
American plant (Enothera Lamarckiana; while Professor Whitman
has studied in America the evolution of the European pigeons.
Political boundaries disappear before the advances of the sciences."

A COMPARISON BETWEEN ARTIFICIAL AND NATURAL

SELECTION

Br HUGO DE VRIES

[Hugo de Vries, Professor of Botany, University of Amsterdam since 1878. b.
Haarlem, Holland, 1848. Phil. Nat. Doct. University of Leyden, 1870; Sc.D.
Columbia University; LL.D. University of Chicago, Jacksonville College;
Postgraduate, Heidelberg, 1870-71; Wiirzburg, 1871-72; Privat-docent, Halle,
1877; Lecturer in Mutation Theory, University of California, 1904; Member of
the Academy of Sciences, Amsterdam; National Academy of Sciences, Wash-
ington; American Philosophical Society, Philadelphia; Royal Society, London;
Honorary Member of the Academies of Sciences of New York and of California,
San Francisco; Corresponding Member of the Academies of Copenhagen, Brus-
sels, Rome, Regensburg, Upsala, Miinchen, Philadelphia, Christiania; Honorary
Member of the Deutsche Botanische Gesellschaft, Berlin, etc. Author of Intra-
cellulare Pangenesis; Die Mutations-Theorie; Species and Varieties, Their Ori-
gin by Mutation.]

NATURAL selection, as pointed out by Darwin, is one of the great
principles which rule the evolution of organisms. It is the sifting out
of all those of minor worth, through the struggle for life. It is only
a sieve, and no force of nature, no direct cause of improvement, as
has so often been asserted. Its only function is to decide what is to
live and what is to die. Evolutionary lines, however, are of long
extent, and everywhere many side-paths are occurring. It is the
sieve that keeps evolution on the main lines, killing all or nearly all
that try to go in other directions. By this means natural selection is
the one great cause of the broad lines of evolution.

With the single steps of that evolution, of course, it has nothing
to do. Only after the step has been taken, the sieve decides, throw-
ing out the bad, and thereby enabling the good to produce a richer
progeny. The problem how the individual steps are brought about,
is quite another side of the question.

On this point Darwin has recognized two possibilities. One means
of change lies in the sudden and spontaneous production of new
forms from the old stock. The other method is the gradual accumu-
lation of the always present and ever-fluctuating variations. The
first changes are what we now call mutations, the second are desig-
nated individual variations, or, since this term is often used in
another sense, as fluctuations. Darwin recognized both lines of
evolution, but his followers have propounded the exclusive part of
the latter processes.

To my conviction the current scientific belief is wrong on this
point. Horticultural experience and systematic inquiry seem to
point in exactly the opposite direction. The evidence collected of late
by Korshinsky from horticultural practice, may be regarded as inade-
quate for a full proof, most of the single cases being surrounded by

ARTIFICIAL AND NATURAL SELECTION 29

doubt, and resting on incomplete observations. The main conclu-
sions, however, seem to be quite clear, since they are always the same.
Sudden sports cannot be denied to be the chief, and probably the sole,
method of the origination of new horticultural forms.

There is, however, another, more weighty objection. The facts
collected by Korshinsky pertain to varieties, and not to true species.
Most of the varieties, and especially of the horticultural varieties, owe
their origin to retrograde changes, to the apparent loss of some previ-
ously acquired character. Besides these, no doubt, there are other
types, but these may be considered as of a degressive nature. Ancient
characters, once lost, may reappear, and produce the impression of
something quite new, whilst in reality they are only the reviving
of some old latent quality. From a critical point of view the facts
collected by Korshinsky may prove the sudden origin of new varieties
by the loss of characters or by the revival of apparently lost ones;
but they do not afford any cases of really progressive steps.

Systematic evidence has to guide us on this most important point.
The subdivisions of the species afford the material for a closer study
of progressive evolution. In some cases they comply with the type of
horticultural variability, one form constituting a primary t}>-pe, from
which the remaining have obviously been derived. Such derivations
are usually of a retrograde nature, consisting in the loss of color, of
hairs, of spines, of wax on the surface, or of other distinct marks.
Sometimes, however, they are degressive, indicating the reappear-
ance of some latent peculiarity, and thereby seeming to repeat the
characters displayed by some allied but distinct species.

In most of the cases, however, the relation between the lesser units,
constituting a systematic species, is of another nature. They are
all of equal importance. From one another they are distinguished by
more than one mark, often by slight differences in nearly all their
organs and qualities. Such forms have come to be designated as
elementary species. Varieties they are only in the broad and vague
significance of the word.

In some cases these different forms of the same systematic
species are found in distant localities. The representatives of the same
type from different countries or regions do not exactly agree, when
compared with one another. Many species of ferns afford instances
of this rule, and Lindley and other great systematists have often
been puzzled by the wide degree of difference between the members
of one single group.

In other instances the subspecies are observed to grow nearer to
each other, sometimes in neighboring provinces, sometimes in the
same locality, growing and flowering in mixtures of two or three,
or even more, elementary species. The violets exhibit some wide-
spread ancient types from which the numerous local species may be

30 PHYLOGENY

assumed to have arisen. The whitlow-grasses, or Draba verna, have
no probable common ancestors amongst the now living forms,
but they are crowded together in numerous types in the southern
part of central Europe and more thinly spread all around, even as
far as western Asia. There can be little doubt that their common
origin is to be sought in the centre of their dominion and dispersion.

Numerous other instances could be given, proving the occurrence
of smaller types within the systematic species. These subspecies
are of equal importance, and obviously not derived from one another
in a retrograde or a digressive way. They must be considered as
having sprung from a common ancestor by progressive steps in di-
verging directions. Granting this conclusion, they constitute the
real prototypes of progressive evolution, the actual steps by which
progression is slowly going on.

Manifestly, this experience with wild plants must hold good for
cultivated species, too. Once these must have been wild, and in this
state they must have complied with the general rule. Hence we may
conclude that, when first remarked and appreciated by man, they
must already have existed of sundry elementary subspecies. And
we may confidently assert that some must have been rich, and others
poor, in such types.

This assumption at once explains the high degree of variability of
so many cultivated species. This quality is not a result of cultivation,
but, quite on the contrary, is to be considered as originally present,
and one of the decisive causes, which have brought a species up to a
high rank in cultivation. Apples afford an instance; they are notori-
ous for their wide variability, but this term here only means poly-
morphy, indicating the existence of a large number of varieties.
These are found in the wild state all over Europe, differentiated by
various flavors and odors, but lacking the fleshiness which must be
added to each of the differentiating marks by an appropriate culture
and selection.

Alphonse de Candolle, who has made a profound study of the origin
of cultivated plants, comes to the conclusion that the apple shrub
must have had this wide dispersion already in prehistoric times,
and that its cultivation must have commenced in ancient times
nearly everywhere. From this most important statement of so high
an authority we may conclude that the apples have not been taken
into cultivation by man in one single type, but probably in numerous
distinct elementary forms, transmitting thereby the wild variability
in a most simple and direct way to their cultivated descendants.

It would take me too long to describe other examples. It is easily
seen that it is at least as probable that the notorious high variabil-
ity of so many of the most important cultivated plants is older than
their culture, as that it is to be regarded as caused by this culture.

ARTIFICIAL AND NATURAL SELECTION 31

Directing now our attention to the selection of cultivated plants,
it is manifest that this process has to start from distinct forms.
Obviously the choice of the starting-point is as important as the
improvement itself. Or rather, the results depend in a far higher
degree on the adequate choice of the first representatives of the
new race than on the methodical and careful treatment of its off-
spring. Unchangeable qualities determine the value of the new
strain, if they were present in the chosen individual; if not, no
selection can produce them.

This assertion, however, has not always been appreciated as it
deserves, nor is it at present universally acknowledged as a first
principle. The method of selecting plants was discovered by Louis de
Vilmorin, about the middle of the last century. Before him selec-
tion was applied to domestic animals, and even on a large scale.
Vilmorin applied it to his beets, in order to increase the amount of
sugar in their roots. Evidently, he must have made some choice
amongst the numerous sorts of beets of his time, or otherwise chance
must have thrown into his hands exactly one of the most appro-
priate forms. But on this point, no historical evidence is at hand.

Since the time of Vilmorin, selection of agricultural plants has
enormously gained in importance. Only of late, however, Rimpau and
von Ruemker in Germany, and Willet M. Hays in this country, have
begun to apply critical methods to the various parts of the process,
in order to get a better insight. All of them have insisted upon the
necessity of distinguishing between the first choice for a race and the
subsequent improvement by continued selection. The choice of
the most adequate varieties has to become the principle for the
foundation of all experiments in improving races.

Hays clearly states the far-reaching importance of this practical
rule by asserting that half the battle is won by choosing the variety
which has to serve as a foundation stock, whilst the other half de-
pends upon the selection of mother plants within the chosen variety.
The choice of the variety is the first care of the breeder in each single
case, whilst the so-called artificial selection takes only the second
place. Half a century ago the famous Scotch breeder Patrick Shirreff
taught that it is quite useless to search for starting-plants for im-
proved races among varieties of minor value. Only the very best
cultivated types yield the material for further successful improve-
ment.

In practice, as in systematic science, it is usual to call all minor
units within the acknowledged species by the same name of varie-
ties, without regard to their real systematic relations. Complying
with this custom, the principle of the choice of starting-points is
called by Hays "variety-testing." This testing and comparing of
varieties is one of the prominent lines of the work of the Agricul-

32 PHYLOGENY

tural Experiment Stations. Each state and each region, in some
instances even each larger farm, wants its own variety of corn, or
wheat, or other crops. These have to be sought out from amongst
the hundreds of forms generally cultivated within each single
botanical species. Once found, the type may be ameliorated ac-
cording to the local conditions and wants, but this is a question of
subsequent and subordinate improvement.

Summing up the main points of these arguments, we may state
that artificial selection consists of two main principles, called variety-
testing and racial improvement. Quite the same distinction has to
be made in the case of natural selection, and the same double selec-
tion has to be acknowledged, whilst only the names have to be
changed. Instead of variety-testing comes the choice between ele-
mentary species, instead of racial improvement the adaptation to the
local conditions of the environment. Before going into a more de-
tailed discussion of this first principle of comparison, it may be as
well to consider that intermediate step between natural and artificial
selection, which is called acclimatization.

Here the aim is given by man, but the selection is left to nature.
Man, however, does not only point out the object, but has also to
give the starting-points. The choice of the variety is directly per-
formed by the climate. This is manifestly shown by the slow and
gradual dispersion of corn in this country. The larger types are
limited to tropical and subtropical regions, whilst the varieties
capable of cultivation in the northern states are so, according to
their smaller size and stature. They are short-lived, requiring a
lesser number of days to reach their full development from seed to
seed. These qualities are not the result of the cultivation or of the
influence of the climate, since the smaller sorts are historically
known to have grown in tropical America at the time of Columbus
along with the taller types. This is especially on record in the case
of the forty-days or quarantine maize. Cultivation has worked in
this case as a sieve, or rather as a series of sieves with a diminishing
width of meshes, the climate allowing only the shorter-lived forms
to pass the meshes and to expand towards the north. Similar
facts are known for wheat and many other crops, and the famous
trials of Schuebeler in Norway have thrown a clear light upon
the factors of this complicated process.

Artificial selection is a fact needing scientific and critical analysis,
but natural selection is a fact which we may see at work in each
field and in each meadow, but concerning which our real know-
ledge is still very incomplete. In the realm of natural selection, it has,
however, become customary to indulge in hypothetical considera-
tions. And since these have largely been applied to the side cor-
responding with the artificial improvement of races, I may perhaps

ARTIFICIAL AND NATURAL SELECTION 33

be allowed to apply them here to that process, too, which corre-
sponds to the variety-testing of the breeders.

As the easiest and most notorious examples we choose the whitlow-
grasses, or Draba verna, and the wild pansies, or Viola tricolor. Na-
ture has constituted them as groups of highly different constant
forms, quite in the same way as wheat and corn. Assuming that
this has happened long ago somewhere in central Europe, it is, of
course, probable that the same differences in respect to the influence
of climatic conditions will have prevailed as with grains. Subsequent
to the period which has produced the numerous elementary species
of the whitlow-grass, came a period of geographical dispersion. This
process must have been wholly comparable with that of acclimatiza-
tion. Some forms must have been more suited to northern climates,
others to the soils of western or eastern regions, and so on. These
qualities must have decided the broad lines of the dispersion, and
the species must have been segregated according to their respect-
ive climatic peculiarities and their claims on soil and weather. A
struggle for life and a natural selection must have accompanied and
guided the dispersion, but there is no reason to assume that the sun-
dry forms should have been changed by this process, and that we
see them now endowed with other qualities than were theirs at the
outset.

If this sketch strikes you favorably, natural selection must have
played the same part in a large number of other cases, too. Indeed,
it may be surmised that this has been its chief and prominent func-
tion. Taking up again our image of the sieve, we may assert that in
such cases climate and soil are the sifting agents, and in this way
the meaning of the image at once becomes a more definite one. Of
course, next to climate and soil come the biological conditions, the
vegetable and animal enemies of the plants, and other influences of
the same nature.

Thus, everywhere in nature there must be a struggle for life in
which closely related elementary species are competing with one
another, fighting the same enemies. Some succeed, whilst others fail.
Nature in this way performs her primary selection, and hence this
process can be called selection between elementary species, or inter-
specific selection.

The alternate principle could then be called the selection wdthin
the elementary species, or the intraspecific selection. It has now
more closely to be considered. First of all comes the question
whether it plays a prominent or only a subordinate part in nature.

This question may be reduced to another form, in which it is more
accessible to direct investigation. Species, as we see them in nature,
are in the main constant forms, fluctuating within distinct limits,
which are not seen to be transgressed. Now the question arises,

84 PHYLOGENY

whether by artificial intraspecific selection it is possible to trans-
gress those limits. If this were possible, we could pass from one
species into another, and, by slow and gradual changes, convert
a constant type into another equally constant form.

This question of the constancy is the chief side of the problem.
One point is the production of a new character, the other the loss of
the old one, which is assumed to have been changed into the new.
Such losses, however, are exceedingly difficult to obtain. One of the
most instructive examples is that of the lifetime of the sugar-beets.
These races consist of biennial plants, and the whole process of their
culture relies upon the heaping-up of sugar in the roots of the first
year, leaving the production of the stems to the second summer.
Now, this quality is far from being complete. Each year some annuals
are seen in the fields. And not as rare exceptions, as accidental
cases of atavism. Quite on the contrary, one per cent, or even more,
is the rule, and often they go up to ten or more per cent. Selection,
of course, is on this point always as absolute as may be; it has lasted
half a century for the sugar-beets, and many centuries for the forage-
crops. It has not been adequate to root the annuals out, and to
render the biennial character pure.

So it is also with striped flowers and striped radishes, which
yearly produce some unicolored samples, notwithstanding continu-
ous and most severe selection. So it is ever in numerous other
cases; everywhere the intraspecific selection is capable of pro-
ducing ameliorated races, but incapable of making them as constant
as wild species use to be.

Steady and regular advance of cultivated races no doubt occurs,
although it is not at all so general as is often assumed. But when-
ever it occurs, the advance is due to a corresponding continuous
improvement of the selecting methods, and not simply to repeated
selection after the same method.

The truth of this assertion is most clearly seen in the case of the
beets. They are usually adduced as the best proofs of what can be
obtained by continuous selection. But the methods of judging the
beets are steadily being improved, and they have been so, even
since the time of Vilmorin.

Vilmorin's own method was a very simple one. Polarization had
then not yet been discovered. He determined the specific weight of
his beets, either by weighing them as a whole, or by using a piece
cut from the base of the roots and deprived of its bark. Solutions
of salts were made in which the beets swam, and diluted until they
began to sink. In this way the heaviest beets could be selected,
and it was assumed that they were the richest in sugar, too. This
method has afterwards been improved in two ways. The first was
to make large quantities of the salt-solution, choosing a medium

ARTIFICIAL AND NATURAL SELECTION 35

specific weight, and selecting from among thousands of beets those
which sank. The second was the determination of the specific weight
of the sap expressed from the tissues. It prepared the way for the
polarization. This principle was introduced about the year 1874
in Germany. It allowed the amount of sugar to be measured directly
and with very slight trouble. Thousands of beets could yearly be
tested, and the best chosen for the production of seed. The technical
side of these determinations has since been steadily and rapidly
improved. In some factories the exact determination of three hun-
dred thousand polarization-values is effected within a few weeks.

It would take me too long to go into further details, or to describe
the simultaneous changes that have been applied to the culture of
the elite. The detailed features suffice to show that the chief care
of the breeder in this case is a continuous amelioration of the
method of selecting. To these great technical improvements it is
manifest that the progress of the race is in the main due, and
not solely to the repetition of the selection.

Similar facts may be seen on all the great lines of industrial selec-
tion. And whenever the method has reached its height, the race is
soon surpassed by another, started from another varietal choice, or
selected according to a better principle.

Applying this experience to the processes which are assumed to
occur in nature, we may obviously assert that only in cases of a con-
tinuous change of the life-conditions in one and the same direction
any real improvement of races may be expected. All other cases will
only be capable of yielding local races, and such, no doubt, are very
numerous. Selection keeps up the qualities some degrees above the
standard of the species, and it must do so for one strain in one
sense and for others in diverging directions. These local races, how-
ever, will always remain dependent upon their specific life-conditions,
and never become constant in this sense of the word, that the assumed
qualities should become independent specific marks. Even continued
environmental changes do not seem to be adequate to produce
lasting improvements.

Until now we have simply contrasted the mutations and the
fluctuations. I have tried to show that both of them are subjected
to selection, as well artificial as natural. In nature, and in the long
run in practice too, the selection of the products of mutations plays
by far the largest part. Selection of the products of fluctuating vari-
ability gives rise to inconstant, and therefore only temporary races.
In practice the process is called improvement, in nature it produces
the local adaptations and local races. It is not known to yield any
permanent and independent results, the real results remaining
always dependent on the permanency of the agency of the selective
process itself. Thus interspecific selection is the broad base of pro-

36 PHYLOGENY

gress at large, as well in practice as in nature, whilst intraspecific
selection is the base of highly valuable but local and transient im-
provement.

This principal difference between mutative and fluctuative selec-
tion can be supported by a critical examination of the processes of
fluctuation themselves. Fluctuations are the responses of the indi-
vidual plants to the outward influences to which they are subjected.
Of old, all these factors were thrown together under the name of
nourishment, and already a century ago, Knight has pointed out how
largely the variability depends on this factor. Since then, the term
nourishment has been replaced by that of life-conditions, which is,
of course, more appropriate on closer analysis.

Light and space, soil and water, temperature, and numerous minor
factors, determine the growth of the plant and of all its parts. Quite
obviously the development must depend upon them, and at least a
large part of the observed fluctuating variability finds its cause and
its explanation in these influences. It is readily granted that in
observations of plants and animals, taken from their native localities,
these influences are liable to escape the observer. In the experiment
garden, however, exactly the same fluctuations occur, and statistical
studies find a material, which is in no way inferior to that which is
afforded by nature. Here the climatic conditions are daily seen at
work. The differences in soil and manure, in space and exposure, are
in large part dependent on the conscious will of the experimenter.
Partly, of course, they escape his direction, but even then they are
followed and controlled with utmost care, not to say with great
anxiety. In the same bed one individual is affected by them in this
way, and another in a diverging direction, but these relations, though
often unavoidable, are commonly obvious, at least in their main
features. Thence it comes that the experimenter is strongly impressed
by the dependency of fluctuations on outer conditions, whilst the
observer takes the variability as a fact of dubious and hypothetical
explanation.

In our gardens we observe our plants during the whole period of
their development. At each moment they undergo the influences of
the prevailing conditions. But it is evident that each part of the plant
must respond to them in its own way. One branch may be exposed
to the sun, whilst others are more or less shaded. The first will
enjoy all the effects of full light and vigorous assimilation, whilst the
latter have only a scant supply of organic food. On richer branches
the flowers will be more numerous and larger, and their variable
parts produced in greater abundance. On the poor sides reduction
must be the rule.

It seems quite superfluous to work out this discussion any further.
It leads directly to the conclusion that fluctuating variability is, at

ARTIFICIAL AND NATURAL SELECTION 37

least in large part, a process in which the various organs of a plant
act more or less independently. This form of variability is there-
fore to be distinguished by the term of "partial fluctuation."

Opposed to it stands the individual variation, which affects the
whole individual in the same manner, but which influences different
individuals in different degrees and ways. If this individual fluctua-
tion is a response to outer influences too, the question arises, when
do they work, and at which period of its development does the
organism respond to them.

Here for our discussion plants afford great advantages over ani-
mals. For it is clear that, as soon as buds are produced, partial fluctu-
ation must prevail and individual variation become reduced. There-
fore only the embryonic stage pertains to the latter, whilst the
whole subsequent life is ruled by partial responses. The embryo
itself leads its life within the seed, and thus we are induced to
consider the period of the ripening of the seed as one of prominent
significance for the whole group of phenomena collected under the
name of fluctuations.

The life of the germ commences with the copulation of the male
and female sexual cells. Obviously even these must vary, since they
have been previously subjected to varying conditions. The individual
characters of a given organism must, therefore, largely depend upon
the degree of development of latent qualities, already present in the
sexual cells before their copulation. And it is equally manifest that
at that important moment there is as yet no room for partial fluctua-
tion.

As soon, however, as tissues are developed, the chances for the
latter arise and rapidly increase, whilst in the same degree the part
of the individual variability must decrease. Leaving aside the buds
in the axils of the cotyles, and equally discarding the primary root,
we may limit our interest to the terminal vegetative cone of the
young plant, and consider all variations therein provoked as of.
individual nature.

But as soon as this cone begins to differentiate itself, individuality
comes to an end, at least in respect to the responses to varying
agents, and partiality takes its place. In the same measure the
embryonic life is replaced by that of the developing plant. Thus we
might call the individual fluctuation by the name of embryonic
fluctuation, if it is only rightly understood that the variations of the
paternal and maternal cells before their copulation are to be included.

In horticultural practice individual and partial fluctuation play
a very large part. Excluding the embryonic stage from the process
of multiplication, the embryonic variability may be excluded, too.
Hence the almost universal use of vegetative multiplication in all
cases where it is practically applicable. Perennial plants and shrubs

38 PHYLOGENY

and numerous fruit trees owe their large number of varieties,
and the high degree of constancy of all the samples, even, to this
exclusion of one of the two main parts of the common variability.
The term variety is often taken as indicating only one single indi-
vidual with its peculiar characters acquired in the embryonic stage,
which remain unchanged in the thousands and in the millions of its
grafts and cuttings.

Nature, of course, makes some use of vegetative multiplication, too.
But since this process does not play any prominent part in the cur-
rent theories concerning the larger features of progressive develop-
ment, it has no further interest for our present discussion.

One main point, however, has to be considered. It is seen by
looking at the question from the opposite side. In order to take a
definite example, we may ask to what extent an observed character
is due to embryonic variability, and which part falls to the partial
variability. In all cases of branched plants there is no difficulty, and
every one will grant that only the average of all the leaves or all the
fruits or all the flowers can be the result of embryonic changes.

But in the case of main stems and main roots there is no possibility
to determine this average. An annual plant has one main stem,
whilst a perennial species has many of them. The one stem is
obviously to be considered as equivalent to only one of the many in
the latter case. It may be of average height, but it may as well be a
more or less extreme variant.

Exactly so it is in practice. The amount of sugar in an individual
sugar-beet is partly due to embryonic variability and partly to the
subsequent influence of treatment and weather. Now it is manifest
that both are of value for the direct industrial purposes, but it is
equally manifest that both cannot have the same signification for
the value of the seeds which this individual plant may afterwards
produce. Or, in other words, the sugar-amount of a beet is in no way
a full and reliable indication of its value as a seed-bearer. If a high
amount of sugar is due to embryonic variability, it is indicative of
high excellence, and will probably be followed by the production of
seed of primary quality. If, on the other hand, the percentage figure
is reached by exceedingly favorable weather, or by an accidentally
good position of a plant on the field, as to light, space, and the escape
from all its enemies, it is no indication at all of embryonic variability,
and it is very dubious whether it is to have a lasting influence on the
seed, in fact, such a relation is strongly denied by "Rimpau, von
Ruemker, and other German authorities, whilst it was believed in by
the famous English wheat-breeder Hallett.

Granting the exactness of the first view, the sugar-percentage
figures are seen to be reliable only when subsequent or partial
variability is sufficiently excluded. A hundred of selected beets may

ARTIFICIAL AND NATURAL SELECTION 39

be relied upon, if used for the continuance of a single strain, but
each single beet of high percentage should be regarded with doubt.
Direct experiments of Laurent, of Kuhn at Naarden, and others have
proved the validity of this conclusion, showing that the progeny of
extreme variants does not necessarily give always high averages for
the amount of sugar.

Regression has as yet chiefly been studied by means of statistical
methods. It seems probable that it is largely due to the combination
of embryonic and partial variability . If the latter has no influence, or
only a very small influence, upon the embryonic latent qualities of
the new seeds, there must be regression, even if embryonic variability
itself should not be liable to it.

Turning now to the processes in nature, we may assert that the
result of the struggle for life depends on the qualities of the indi-
viduals, but not on the causes of this quality. Any advance gained
by partial variability will be of equal value as the same advance
gained by embryonic fluctuation. Taking the latter as heritable, and
the first as not, or nearly not, it is easily seen that the relation between
the struggle for life and the hereditary qualities is by far not so inti-
mate as has hitherto been assumed.

It may readily be granted that the fittest survive. But it may
also be granted that, in broad figures, half of the fittest have the
power to transmit their fitness to their offspring, whilst the other
half have not. And if, perchance, the same proportion should hold
good for the unfit, it would be of no avail for the next generation,
whether it springs from the fitter or from the less fit parents.

Probably no breeder and no physiologist would take such an ex-
treme view. Some effect of the struggle for life in nature must as
well be granted as for artificial selection. My discussion had only
the aim of convincing you that there is much exaggeration in the
current conceptions concerning the effects of natural selection through
the struggle for life between individuals of the same species. My
chief object was to show that a clear distinction between embryonic
and partial variability points to a prominent part of the latter and
to a lesser chance of fluctuation at large playing a notable role in
the evolution of the whole animal and vegetable kingdom.

If the visible characters of an extreme variant are no reliable
base for the judgment of its hereditary excellence, the question of
course arises, what marks have to be put in its place.

Obviously this is a most vital question. It is equally important
from a practical point of view as with a view to the whole problem
of the part of fluctuating variability in organic evolution.

It has been answered in one and the same way by practical breeders
and by purely scientific experiments. Hays in this country and von
Lochow in Germany have propounded the idea that the fact of

40 PHYLOGENY

heredity itself is the only fully reliable proof of heredity. Or, in
other words, the average constitution of the offspring is the mark
which gives us the information wanted. No visible quality can be
a trustworthy substitute for it, and such are only to be regarded as
surrogates.

This average constitution must be expressed by the hereditary
percentage of true inheritance of the mark under consideration.
If it is determined by the culture of one hundred children of each
mother plant, it constitutes the centgener power of that mother,
as it is called by Hays. Selection has to rely on this percentage-
figure, and the results, already attained, give proof that here a new
method is given which is able to yield large and rapid improvements.
It is the same principle which since the earliest times is, in the
main, ruling the selection of our domestic animals.

If this principle should prevail and come to exclude the selection
on the ground of the visible qualities of the individuals, the com-
parison between artificial and natural selection will largely change
its aspect. For it is evident that the latent hereditary possibilities
of an individual have no influence at all on its chance of surviving
in the struggle for life. Only by very remote considerations would it
be possible to uphold the significance of this, but in all ordinary
cases, this significance for the improvement of the race would be
reduced to nothing.

Thus we see that a close analysis of the factors which provoke
the fluctuating variability goes to prove how uncertain the basis is,
which it affords for an explanation of organic evolution at large.
On many points, artificial and natural intraspecific selection have
been compared, but nowhere is this comparison favorable to the
current theoretical views. On the other hand, the artificial pro-
cesses of variety-testing and the theoretical and presumable selec-
tion between elementary species in nature seem to be perfectly
comparable. The large practical significance of the first points
clearly to an equally large theoretical importance of the latter.
Hence we conclude that interspecific selection through the strug-
gle for life is the always-acting sieve which keeps evolution on the
main lines, and which in this way is the one great Darwinian cause
of all organic progress.

THE PROBLEM OF THE ORIGIN OF SPECIES

BY CHARLES OTIS WHITMAN

[Charles Otis Whitman, Head Professor of Zoology, University of Chicago, since
1892; Director of Marine Biological Laboratory, Wood's Holl, Massachusetts,
since 1888. Graduate of Bowdoin College, 1868; A.M. 1871; Ph.D. Leipzig,
1878; LL.D. University of Nebraska, 1894; Sc.D. Bowdoin, 1894; Fellow,
Johns Hopkins University, 1879. Professor of Zoology, Imperial University of
Japan, 1880-81 : Naples Zoological Station, 1882; Assistant in Zoology, Harvard,
1883-85; Director of Allis Lake Laboratory, 1886-89; Professor of Zoology,
Clark University, 1889-92. Member of National Academy of Sciences; Ameri-
can Academy of Arts and Sciences; The Linnean Society; and various other
scientific and learned societies. Editor of Journal of Morphology; Biological
Bulletin; and Biological Lectures.}

THE problem of problems in biology to-day — the problem which
promises to sweep through the present century as it has the past
one, with cumulative interest and correspondingly important re-
sults — is the one which became the life-work of Charles Darwin,
and which cannot be better or more simply expressed than in the
title of his epoch-making book, — The Origin of Species.

Darwin certainly made this problem one of universal interest, and
no one will deny that the work which he did has revolutionized
both the morphological and the physiological branches of biology.
Indeed, no field of thought has escaped the leavening influence of
his conclusions.

The prevailing belief up to Darwin's time that species were im-
mutable forms, each separately designed and fashioned by the
Creator, and each endowed with all its instincts and equipped
with a structural organization perfectly adapted to its prescribed
sphere of life, — this old belief was certainly effectually exploded,
and is now passing into oblivion.

With one mighty stroke Darwin released biology from the thrall-
dom of supernaturalism. In the place of special creations and cata-
clysmal revolutions, he set up progressive evolution through the
operation of simple natural laws. To unveil that sacred mystery
of mysteries, and reduce it to the level of natural laws, was a shock
to all Christendom. The idea of a self-regulating, progressive evolu-
tion of species appeared, even to many eminent men of science, to
be a "heresy." This was the case with Sir John Herschel, and even
Sir Charles Lyell was at first of the same opinion, although he soon
became convinced that natural laws were just as efficient and
uniform in operation in the organic as in the inorganic world.

The outcome is familiar history. The sciences all the way up
to psychology have experienced a wonderful renascence, and the

42 PHYLOGENY

world at large has moved forward in sympathetic accord to the close
of a truly "Wonderful Century."

Few, however, would now claim that Darwin's solution was
entirely conclusive and complete. From the nature of the case,
Darwin could not exhaust the problem, and no one has made this
clearer than Darwin himself, who examined his own theory with
such critical acumen and breadth of knowledge that he anticipated
nearly every important objection that has since been urged by others.
A problem that is at once the focal point of each and every one of the
biological sciences is not to be exhausted by one man, however long
and successful his work. The problem has grown larger rather than
smaller with every new contribution to its solution. The expansion
of its horizon, however, has not, and, as I believe, is not likely to dis-
close the "death-bed of Darwinism." We have heard the predictions,
but have witnessed no fulfillment.

Among the rival theories of natural selection two are especially
noteworthy. One of these is now generally known as orthogenesis.1
Theodore Eimer was one of the early champions of this theory,
basing his arguments primarily upon his researches on the variation
of the wall-lizard (187-1-81). Eimer boldly announced his later
works on The Origin of Species (1888), and the Orthogenesis of the
Butterflies (1897), as furnishing complete proof of definitely directed
variation, as the result of the inheritance of acquired characters, and
as showing the utter "impotence of natural selection." Eimer's intem-
perate ferocity toward the views of Darwin and Weismann, coupled
with an almost fanatical advocacy of the notion that organic evo-
lution depends upon the inheritance of acquired characters, was
enough to prejudice the whole case of orthogenesis. Moreover, the
controversial setting given to the idea of definitely directed varia-
tion, without the aid of utility and natural selection, made it difficult
to escape the conclusion that orthogenesis was only a new form of
the old teleology, from the paralyzing domination of which Darwin
and Lyell and their followers had rescued science. Thus handicapped,
the theory of orthogenesis has found little favor outside the circle
of Eimer's pupils.

The second of the two theories alluded to is the mutation theory
of Hugo de Vries. The distinguished author of this theory, whose
presence honors this International Congress, and lends special eclat
to the Section of Phylogeny, maintains, on the basis of long-con-
tinued experimental research, that species originate, not by slow,
gradual variation, as held by Darwin and Wallace, but by sudden
saltations, or sport-like mutations. According to this theory, two
fundamentally distinct phenomena have hitherto been confounded
under the term variation. In other words, variation, as used by

1 A name introduced by Wilhelm Haacke (Gestaltung und Vererbung, p. 31).

PROBLEM OF ORIGIN OF SPECIES 43

Darwin and others, covers two classes of phenomena, totally distinct
in nature, action, and effect. Variation proper is defined as the
ordinary, fluctuating, or individual variation, and this is held to be
absolutely impotent to form new species.

It is claimed that no amount of either natural or artificial selection
can by any possibility lead this variation up to the birth of a new
species. The utmost that could be attained would be an improved
race that would inevitably revert to the original state as soon as left
to itself.

Mutation, on the other hand, never advances by slow and minute
modifications, which are continuous and cumulative, but by single,
sudden jumps. In the words of De Vries: "Species have not arisen
through gradual selection, continued for hundreds or thousands
of years, but by jumps (stufenweise) through sudden, though small,
transformations. In contrast with variations which are changes
advancing in a linear direction, the transformations to be called
mutations diverge in new directions. They take place, then, so far
as experience goes, without definite direction." (Vol. i, p. 150.)

The new species arises from the old, but without any visible pre-
paratory steps, and without intermediate connecting stages. Like
the old, it is subject to variation, but as a type, it is essentially
immutable.

De Vries does not deny that variation produces what may appear
to be transitional forms, but he maintains that these forms in reality
have no such meaning. They are to be regarded as phenomena of
" transgressive variability," which may obscure, but not obliterate
the specific limits.

"For," says De Vries, "the transitions do not appear before the
new species, at most only simultaneously with this, and generally
only after this is already in existence. The transitions are therefore
no intermediates or preparations for the appearance of the new
forms. The origin takes place, not through them, but wholly inde-
pendently of them." (Vol. i, p. 362.)

Granting that the position with respect to the mutants obtained
from the evening primrose ((Enoihera Lamarckiana) is unassailable,
does it follow that all new species have arisen by mutation, and
that continuous variation has never had, and never can have, any-
thing to do with the origin of species?

Plausible as is the argument and impressive as is the array of evi-
dence presented, I can but feel that there are reasons which compel
us to suspend judgment for a while on this pivotal point of the muta-
tion theory. America is the original home of the evening primroses,
and it is here that the natural history of the group remains to be
worked out in the light of the experimental results obtained in
Holland.

44 PHYLOGENY

What does it mean that a few mutants keep on reappearing year
after year, and that even the mutants themselves mutate, not in new
lines, but in the same old ones? Persuaded as deeply as I am that
we can never draw from a species anything for which no ancestral
foundations preexist, I anticipate that our wild evening primroses
have revelations to make.

Whatever revelations may await future investigation in this field,
the work done in the Primrose Garden of Amsterdam will stand as
a classical contribution to the new biology, and as one of the very
best models in method of research that we have yet seen.

Natural selection, orthogenesis, and mutation appear to present
fundamental contradictions; but I believe that each stands for truth,
and that reconciliation is not distant.

The so-called mutations of Mnotlnera are indubitable facts; but
two leading questions remain to be answered. First, are these muta-
tions, now appearing, as is claimed, independently of variation, never-
theless the products of variations that took place at an earlier period
in the history of these plants? Secondly, if species can spring into
existence at a single leap, without the assistance of cumulative varia-
tions, may they not also originate with such assistance? That varia-
tion does issue in new species, and that natural selection is a factor,
though not the only factor, in determining results, is, in my opinion,
as certain as that grass grows, although we cannot see it grow.

Furthermore, I believe I have found indubitable evidence of
species-forming variation advancing in a definite direction (ortho-
genesis), and likewise of variations in various directions (amphi-
genesis). If I am not mistaken in this, the reconciliation for natural
selection and orthogenesis is at hand.

I am aware that orthogenesis is held by many to be utterly incom-
patible with both natural selection and mutation. "The Darwinian
principle demands," says De Vries, "that species-forming variability
and mutability be indeterminate in direction. Deviation in all senses
must arise, without favor to any particular direction, and especially
without partiality for the direction proceeding from the theory to
be explained. Every hypothesis which departs from this principle
must be rejected as teleological, and therefore unscientific." (Vol. i,
p. 140.)

Again (p. 180) the same point is amplified: "Again and again, and
by authors of different aims, it has been insisted upon that species-
forming variability must be orderless. The assumption of a definite
variation-tendency which would condition, or even favor, the appear-
ance of adaptive modifications, lies outside the pale of the natural
science of to-day. In fact, the great advantage of Darwin's doctrine
of selection lies in this, that it strives to explain the whole evolution
of the animal and plont kingdoms without the aid of supernatural

PROBLEM OF ORIGIN OF SPECIES 45

presuppositions. According to this doctrine, species-forming varia-
bility goes on without regard to the qualification of the new species
for maintaining themselves in life. It simply supplies the struggle
for existence with the material for natural selection. Whether this
selection takes place between individuals, as Darwin and Wallace
supposed, or decides between whole species, as the mutation-theory
demands, ultimately it is, in either case, simply the ability for exist-
ence under given external conditions that decides upon the perman-
ence of the new form " (p. 180).

I take exception here only to the implication that a definite
variation-tendency must be considered to be teleological because it
is not "orderless." I venture to assert that variation is sometimes
orderly, and at other times rather disorderly, and that the one is
just as free from teleology as the other. In our aversion to the old
teleology, so effectually banished from science by Darwin, we should
not forget that the world is full of order, the organic no less than the
inorganic. Indeed, what is the whole development of an organism
if not strictly and marvelously orderly? Is not every stage, from
the primordial germ onward, and the whole sequence of stages, rigidly
orthogenetic? If variations are deviations in the directions of the
developmental processes, what wonder is there if in some directions
there is less resistance to variation than in others? What wonder if
the organism is so balanced as to permit of both unifarious and
multifarious variations? If a developmental process may run on
throughout life (e. g., the lifelong multiplication of the surface-pores
of the lateral-line system in Amia), what wonder if we find a whole
species gravitating slowly in one or a few directions? And if we find
large groups of species all affected by a like variation, moving in the
same general direction, are we compelled to regard such "a definite
variation-tendency" as teleological, and hence out of the pale of
science? If a designer sets limits to variation in order to reach a
definite end, the direction of events is teleological; but if organization
and the laws of development exclude some lines of variation and
favor others, there is certainly nothing supernatural in this, and
nothing which is incompatible with natural selection. Natural selec-
tion may enter at any stage of orthogenetic variation, preserve and
modify in various directions the results over which it may have had
no previous control.

It has always appeared to be one of the greatest difficulties for
natural selection to account for the incipient stages of useful organs.
Orthogenesis, as I hope to make clear, removes this difficulty from a
large portion of the field.

It should be noted in this connection that the difficulty of incipient
stages is not what it is so generally presumed to be. The advocates
of natural selection habitually assume that the evolution of an organ

46 PHYLOGENY

or character begins with an "infinitesimal rudiment/' which has no
way of emerging from its functionless state except through minute
chance variations in various directions. In this assumption the
problem is misconceived. The characters we meet with to-day have
rarely, if ever, arisen by direct evolution from useless rudiments.
When we know enough about a character to undertake to trace its
genesis, the "rudiment" imagined to lie so near recedes, and we
are led on, not to a "beginning," but to an antecedent; and if we
are fortunate enough to be able to advance farther, we come to
another antecedent, and so on. The series of antecedents stretches
ever as far as we can see. As we repeat this experience with different
characters, looking always for the primordial rudiment, our childish
faith in such "beginnings" gives way to the conviction that the chase
is led by a phantom.

No one of our sense-organs, for example, can be traced to a rudi-
ment, except in the embryological sense. The eye of the vertebrate
may appear as a rudiment in the embryo, but no one can doubt that
it has had a phylogenetic history, the first term of which — if first
there be — must have been very different from its present embryonic
rudiment. To assume that the eye began in some indifferent variation
that fluctuated or mutated, chance-wise, into a state of incipient
utility, and was then developed in a direct line to its present stage of
complex adaptations, either gradually or per saltus, would be hardly
more satisfactory than appealing to a miraculous succession of
miracles. It is impossible to believe that such a system of har-
monious coadaptations could ever arise by mutation; 1 and selec-
tion, although playing a very important part in such achievements,
is probably never equal to the whole task. Without the assistance of
some factor having more continuous directive efficiency, selection
would fail to bring out of the chaos of chance variation, or kaleido-
scopic mutation, such progressive evolution as the organic world
reveals.

In order to show that such a factor is essential, and that it is
actually present, supplying the indispensable initial stages, and
holding the master hand in the general direction of evolution, demon-
strative evidence is, of course, required. Such evidence lies in the
history of specific characters. But how shall we approach such a task,
if no near-by rudiment is to be found as a starting-point? Rudiments
and premutations are alike illusory in this regard, for their beginning
is always and necessarily assumed to lie in the realm of the invisible
and unknowable. If we are to keep always on ground that is open to

1 Darwin frequently emphasized the same objection. In a letter to Asa Gray,
referring to the orchids, he remarks: " It is impossible to imagine so many coadap-
tations being formed, all by a chance blow."

Weismann has shown in a masterly manner how inadequate is the mutation
theory to account for such phenomena.

PROBLEM OF ORIGIN OF SPECIES 47

investigation, we must find our starting-points in known stages. As
the laws of nature are constant, it is not essential to trace entire his-
tories. If some chapters are sufficiently open to observation and
experiment to permit of close study, we may hope, in some of the
more favorable cases, to read the phenomena in their natural order,
and to learn from what goes on in one part of the history the factors
that govern in all parts.

The study of the problem of the origin of species resolves itself,
therefore, ever more clearly into exhaustive studies of single favor-
able characters, in the more accessible portions of their history.

For decisive evidence we must have characters of a comparatively
simple nature, the evolutional records of which, in every case, are to
be read in a considerable number of different species of known com-
mon origin.

It is a great mistake to resort exclusively to domestic races, for
here the ancestry contains so many unknown elements that it is
often impossible to refer phenomena to their proper sources. Even
the so-called "pure breeds " are decidedly impure as compared with
pure wild species. The ideal situation, as regards material, is to have
pure wild species in abundance as the chief reliance, and allied
domestic races for subsidiary purposes.

The pigeon amply fulfills all these prerequisites. A simple and con-
venient character, presenting divergent courses of evolution in some
species and parallel courses in others, is to be found in the wing-bars
and their homologues.

It is to some chapters in the history of this character that we may
now turn for evidence that natural selection waits for opportunities,
to be supplied, not by multifarious variation or orderless mutation,
but by continuous evolutional processes advancing in definite direc-
tions.

The rock pigeons (Columba livia) present two very distinct color-
patterns; one of which consists of black checkers uniformly dis-
tributed to the feathers of the wing and the back, the other of two
black wing-bars on a slate-gray ground. These two patterns may be
seen in almost any flock of domestic pigeons.

The inquiry as to the origin of these patterns involves the main
problem of the origin of species, for the general principles that account
for one character must hold for others, and so for the species as a
whole. Darwin raised the same question, but did not pursue it beyond
the point of trying to determine which pattern was to be considered
original and how the derivation of the other wras to be understood.
Darwin's explanation was so simple and captivating that naturalists
generally accepted it as final. It is but fair to state that Darwin's
conclusions did not rest on a comparative study of the color-patterns
displayed in the many wild species of pigeons. Accepting the view

48 PHYLOGENY

generally held by naturalists, that the rock pigeons must be regarded
as the ancestors of domestic races, the question was limited to the
point just stated.

It was known that the two types interbreed freely, under domesti-
cation, and it had been reported that checkered pigeons sometimes
appeared as the offspring of two-barred pigeons. Moreover, Darwin
discovered that the checkers were homologous with the spots com-
posing the bars. As the main purpose was to show that variation
was present to any extent required for the origin of new species,
rather than to trace its course in any specific case, and as variation
was supposed to be multifarious, and progress to be guided by na-
tural selection of the "fittest," it is not strange that Darwin failed
to get the direction of variation, or to realize that in direction is given
the key to one of the fundamental laws of evolution.

As the two color-patterns are alike in having a common element,
and differ chiefly in the number of elements, it was natural enough
to take the smaller number as the point of departure, and to view
tha larger number as "an extension of these marks to other parts of
the plumage." (Animals and Plants, vol. i, p. 225.) With the ances-
tral type thus determined, and a simple mode of variation pointed
out, Darwin could dismiss the problem with these words: "No import-
ance can be attached to this natural variation in the plumage."

Whence and how the two bars arose was not explained. The mode
of departure assumed to account for the checkered variety would,
however, suggest that the bars themselves originated in the same
manner; that is, from one or two spots arising de novo, as chance-
variations, and the gradual extension of like spots in two rows of
feathers. The one or more original spots, according to the general
theory, would first appear as minute rudiments, and then be grad-
ually enlarged and intensified by the aid of natural selection, guided
by their utility as recognition marks.

Such a mode of origin would presuppose a plain, uniform gray
ancestor, without any spots or bars in the wings, and would raise
many puzzling questions that would be beyond the reach of inves-
tigation. For example: Why two bars? Why at the posterior end
of the wing? Why do the spots taper backwards to a more or less
sharp point in the checkered variety, while presenting a nearly
square form in typical bars? Why should they have first extended
upward, or downward, and in two rather than any other number of
rows of feathers? If two rows of feathers were favored long enough
to establish the bars for ornamental or other purposes, what freak of
natural selection could have then interposed to turn a long- favored,
definitely directed extension into a diffuse general extension, and
thus to neutralize completely the very effects it was invoked to ex-
plain?

PROBLEM OF ORIGIN OF SPECIES 49

Natural selection could not be supposed to originate or to guide
the first indifferent stages of new characters. Mutation would be
equally helpless, and each step would leave a gulf of discontinuity, — a
miracle that nature seems to abhor.

Turning from theoretical impasses to the facts, let us compare the
two patterns.

In the checkered pattern all the feathers are marked alike — no
regional differentiation. In the other type we have a conspicuous
local differentiation, suggesting at once a higher stage of evolution.
Checkered wings are to be found which vary all the way between a
uniform marking and the barred type. If we arrange a number of
unequally checkered wings in a series, running from the most to the
least checkered, we shall see that the pattern approaches more and
more nearly to that of two bars, as the checkers diminish in size and
number. We shall notice that the pigment is reduced more rapidly
in the anterior than in the posterior part of the wing.

As checkers are reduced, they gradually lose their sharp ends, and
approximate the square or rounded form seen in the elements of the
typical bars. The series shows a flowing gradation, that may be read
forward or backward with equal facility. Darwin's view takes the
bars as the starting-point and reads forward. Taking the checkered
condition as the point of departure, the variation runs just as
smoothly in the opposite direction. We here meet an ambiguity
that is everywhere present in color-pattern problems — an ambigu-
ity that is frequently overlooked with disastrous consequences.
The only way to eliminate the difficulty is to take our evidence from
several different sources, and when agreement is found for one direc-
tion, and disagreement for the other, the way is clear.

As an experiment, we may take one or more pairs of pure-bred,
typically barred pigeons, and keep them isolated from checkered
birds for several years, in order to see if the young ever advance
toward the checkered type.

Another experiment should be tried for the purpose of seeing what
can be done by working in just the opposite direction. In this case
we take checkered birds, selecting in each generation birds with
the fewer and smaller checkers, and rejecting the others, in order to
see if the process of reduction can be carried to the condition of three,
two, and one bar, and finally, to complete obliteration of both
checkers and bars, leaving the wing a tabula rasa of uniform gray
color.

If these experiments are continued sufficiently far, it will be found
from the second experiment that a gradual reduction of pigment
to the extreme conditions named can be comparatively easily
effected, and that the direction of reduction will always be the same,
from before backward; while, from the first experiment, it will be

50 PHYLOGENY

seen that it is hopeless to try to advance in the opposite direction,
from the bars forward to the checkered condition. No variations
will appear in that direction, but such as do appear will take the
opposite direction, tending to diminish the width of the bars and to
weaken their color. It is in this way that we must account for the
existence of some fancy breeds in which the bars have been wholly
obliterated. The direction of evolution can never be reversed.

I have tried both experiments for eight years, and as both tell the
same story as to the direction of variation, I am satisfied that further
experiments will not essentially modify the results.

With reduction traveling from before backward, in the manner
described, we get the bars in their typical number, form, and position,
as one of the necessary stages of the process, and without appealing to
de novo origin, incipient rudiments, etc.

But if bars originated in such simple fashion, — the direction of
evolution being precisely the same as that of embryological development, —
if the theory of rudiments must be abandoned in this case, do we not
meet the same theory again in any attempt to account for the
checkers?

What kind of rudiments could be imagined? We might assume
that minute flecks of pigment first appeared, one in each feather;
and then, further, imagine that these purely chance originations
happened to have some slight utility, and that natural selection did
the rest. But it is just as difficult to account for a small as a large
origin de novo, and the smaller it is, the more unfortunate it is for
the theory of natural selection.

If we seek refuge in the doctrine of mutation, are we better off?
Mutation hides itself in the undiscoverable premutation, and so we
have all the difficulty of an incipient stage, and no means of advanc-
ing by ordinary variation.

Fortunately we are not driven to either alternative, for the
checkers arise neither as mutations nor as rudiments, but by direct
and gradual modification of an earlier ancestral mark, which came
with the birth of the pigeon phylum, as a heritage from still more
distant avian ancestors.

This ancestral mark is a dark spot filling the whole central part
of the feather, leaving only a narrow distal edge of a lighter color.
This mark is still well preserved in some of the old-world turtle-
doves — best in the Oriental turtle-dove of China and Japan. The
checker of C. lima differs from the dark centre of T. orientalis
only in form and in having a lateral position. Typically this spot
appears in pairs, one on each side of the feather. The two spots
represent the two halves of the old central spot, which becomes
more or less deeply divided by the disappearance of pigment along
the shaft of the feather. This change begins at the tip of the feather

PROBLEM OF ORIGIN OF SPECIES 51

and advances inward, but usually more rapidly along the shaft
than at the sides, thus resulting in two checkers with more or less
pointed tips.

The direction of change again coincides with that of embryonic
development, the tip of the feather, where it begins, being first in
order of development.

In many checkered rock pigeons we may find in the dorsal (inner)
'feathers of the bars undivided central spots, which pass gradually
into the typical checkers as we pass towards the lower (outer) ends
of the bars. Transitional stages of various degrees thus connect the
derived with the ancestral type in one and the same individual, and
so demonstrate that the two specific marks are not separated by im-
passable mutation gaps.

While it is not necessary to go beyond the wild rock pigeons and
the multitude of domestic races descended from them to learn that
nature has here pursued one chief direction of color variation, always
leaving an open door, however, to minor modifications and improve-
ments through natural and artificial selection, it is, nevertheless, highly
instructive to make a comparative study of the whole group of wild
pigeons, in both adult and Juvenal stages. It is in this field that we
find the same lessons amplified and repeated in multitudinous ways,
confirmation confirmed, convergence of testimony complete.

It will be sufficient here to cite a few examples.

In the little ground doves (Chamcepelia passerina) of Florida,
Arizona, California, Central and South America, and the West Indies,
we find the turtle-dove pattern preserved in the whole breast region
and in the anterior, smaller coverts of the wings, while in the posterior
portion of the wings we meet with lateral spots or checkers, of higher
finish than in the rock pigeons. In many coverts of the wing, we find
the dark centres more or less reduced, with the distal ends of their
remnants in various stages of conversion into lateral spots. Here
again we find most striking proof of gradual change from one specific
type to another.

In the brilliant bronze-winged pigeon (Phaps chalcoptera) of Aus-
tralia, we have still another combination type, in which iridescent
checkers coexist with the original dark centres. Here the checker
seems to arise by direct differentiation of a lateral portion of the
dark centre, the latter still occupying the original field and forming
the ground within which the checker appears as a more highly
colored spot. While the dark centre does not suffer any reduction
in its field, it does lose considerably in intensity of color. The metallic
spots are therefore probably built up by concentration of pigment
at the expense of the dark centres. As these birds make great display
of their colors in the breeding season, this departure from the ortho-
genetic trend of development may be attributed to natural selection.

52 PHYLOGENY

The wild passenger pigeon (Ectopistes) bears checkers closely re-
sembling those^of the checkered rock pigeon, in form, color, and dis-
tribution. In this species the sexes are distinctly differentiated in
color; and we have for comparison three stages in an ascending
series; namely, the Juvenal, the adult female, and the adult male. As
in so many other birds, the male makes the widest departure from
original conditions; the female occupies a lower plane; the young
are nearly alike in both sexes, and may be said to recapitulate
ancestral conditions with less modification than is seen in the adult
of either sex.

In birds taken at random, I count in the left wing and scapulars
90 checkers in a Juvenal, 51 in an adult female, and 25 in an adult
male. This is pretty conclusive evidence that checkers are, or have
been, disappearing in the species. Not only the number, but also the
size of the checkers has been reduced. In the female the checkers
are for the most part two or more times as large as in the male. The
reduction in both respects has been greater in the anterior than in
the posterior half of the wing, and greater along the lower edge than
in the middle and back regions.

In this species we may recognize at first sight the homologues of
the rock pigeon bars. On the secondaries of the female we find the
homologue of the posterior bar, and on the first row of long coverts
the homologue of the anterior bar. The latter is scarcely recognizable
as a bar; for we see only five or six checkers in the upper half of the
row, the lower half being without checkers. Nevertheless, this row
represents, so far as it goes, the elements of a bar, which is already
too far gone to have even a chance to attain the finish of a perfect bar.1

On the secondaries the checkers fall into juxtaposition, forming a
continuous bar, with an irregular posterior outline, which indicates
that the checkers have been unevenly reduced from behind. It is a
rudely finished bar, which has sunk below the horizon of utility, if it
was ever above it, and is now facing ultimate effacement. The re-
duction has advanced further in the male, with no improvement
towards regularity of outline. Here it becomes quite certain that
effacement advances from all sides, leaving but a small remnant of a
bar confined to two or three feathers.

Glancing at the wing as a whole, in both young and old, it is plain
that the process of obliteration is in progress over the entire checkered
area. The elongated, sharp-pointed marks of the earlier pattern
have rounded tips in the adult; the posterior bar is roughly emargi-
nated; the number of checkers is reduced by a half or more; and some
of the remaining ones are but little more than mere dots. It is also

1 In the young, the checkers of this row are more numerous and much more
sharply pointed at the ends. In both respects the Juvenal pattern approaches
more nearly a condition of general uniformity.

PROBLEM OF ORIGIN OF SPECIES 53

equally manifest that the process of reduction is making more
rapid progress in the fore part of the wing and along its lower edge
than elsewhere. There can be no mistake here as to the direction
in which the phenomena are to be read. The direction is as certain
as that the adult male stands in advance of the adult female, and
still more in advance of the young bird. The significance of the case
lies mainly in the fact that it is not an isolated or exceptional one.
Many other species tell more or less perfectly the same story.

A parallel case, only carried still farther in the same direction, is
found in the mourning dove (Zenaidura). The adult male and fe-
male differ but slightly, each having only about a dozen checkers
visible on each side. These are confined to the scapulars, and to a
few feathers at the posterior upper edge of the wing. In the young,
they are more numerous, but less so than in the young passenger
pigeon. The middle and fore parts of the wing in the adult have no
visible checkers, but a few concealed ones which may be seen on
lifting the overlying feathers. These concealed checkers, and other
differences between old and young, show that the species had its
origin in a checkered stock, and that its history has been analogous
to that of the passenger pigeon.

The white-winged pigeon (Melopelia leucoptera) is a most instruct-
ive form. Although a much more highly accomplished bird in the
arts of display of form, feathers, and voice, than the mourning dove,
it has suffered a complete effacement of the checkers it once pos-
sessed in common with other members of the family. Indubitable
proof of this is to be seen in the Juvenal feathers, which, in some
cases, exhibit a few pale vestigial spots in the last two rows of long
coverts, at points where the checkers are usually best developed in
checkered species. Another striking proof is to be found in the
coverts and scapulars of the adult bird, where we find, on lifting
the feathers, distinctly outlined areas, corresponding in shape and
position with reduced checkers, but from which the black pigment
has disappeared. These vestigial outlines, structurally defined,
were first noticed in a female bird of a dark shade.1 The outlines
were more perfect than in lighter birds obtained from Arizona and
California.

Similar vestiges are present in the mourning dove, and here their
identification as marks formerly filled out with black pigment is
freed from every shadow of doubt by checkers in all stages of oblitera-
tion.

The large wood pigeon (C. palumbus) of Europe has departed

still more widely from the turtle-dove type, having lost all its black

spots except a few in the neck patches, which have retreated so far

from the tips of the feathers as to be concealed. The gray plumage

1 Captured in Jamaica by Dr. Humphreys.

54 PHYLOGENY

and the white streak along the edge of the wing mark a plane in
the evolution of this bird very nearly identical with that of the
white-winged pigeon. A little higher plane has been reached by our
band-tailed pigeon of the Pacific coast, which is also a species of
turtle-dove derivation, as shown in the neck-marking and in the
voice and behavior.1

These illustrations, which could be extended into the hundreds,
may be concluded with two cases, representing wide extremes, yet
governed by the same law of progressive orthogenetic variation.

The crested pigeon of Australia (Ocyphaps lophotes) stands at
one extreme, at the uppermost limit in the number of bands and in
the perfection of finish. There are eleven, or at most twelve, parallel
bands crossing the wing and scapulars transversely, each band
marking a single row of feathers, with the regularity of zebra stripes.
The width of these bands increases from before backward, begin-
ning with a width of about \ mm. and reaching 4 to 5 mm. on the tenth
band. The eleventh band, located on the long coverts, is especially
interesting, as it begins above with narrow elements, like the pre-
ceding, but is continued, from the third or fourth feather onward,
by elongated checker-like spots. -

This band, or bar, is the homologue of the anterior bar iii the rock
pigeon, and furnishes a standing picture of transitional continuity
from one character to another, and at the same time settles beyond
dispute the direction variation has pursued. So clear and decisive
is the case, that one might safely predict that this entire bar is
destined to be reduced to the narrow band-type seen in the fore part
of the wing. We have only to turn to a closely allied species, the
white-breasted crested pigeon (Lophophaps leucogaster) 2 to find that
it has already realized the prediction to the full, having every checker
in this row converted into a typical band-element.

Moreover, the transformation has already begun in the first
feather of the next and last row, so that the same prediction could
be extended to this bar, which is the homologue of the posterior
bar in the rock pigeon.

Glancing again at Ocyphaps, and looking at the wing as a whole,
the course of transformation, its mode, direction, and future term-
ination are all very clearly defined. The wing-pattern, as shown
especially in the light edges of the Juvenal plumage, takes us clear
back to the turtle-dove type. Next came the checkered pattern
similar to that of the primitive rock pigeon. Reduction of pigment,
proceeding from before backward, fashioned the bilateral checkers
from the uni-central spots. The reduction kept on in the same

1 Minute blotches of black were found in the longer scapulars of a few individuals.
These are probably atavistic reminiscences of lost spots.

2 This bird is comparatively rare, and I have seen but a single pair that recently
came to hand through the kindness of Frank M. Chapman.

PROBLEM OF ORIGIN OF SPECIES 55

direction, shortening the checkers and transforming the rows suc-
cessively into narrow bands, eventually reaching the eleventh row,
where we find only one or two complete steps, followed by a graded
series of 4 to 6 steps, less and less decided, until we lose every trace
of them. So finely graded are these steps in some females that it is
difficult to locate the vanishing-point.

Unless the process of transformation is arrested by the extinction
of the species, or through the intervention of some more potent
modifying influences than have thus far appeared, the fate of both
posterior bars is irrevocably sealed. Granting that natural selection
may be credited with strengthening the iridescent splendor of these
bars, I believe that the orthogenetic influences are bound to prevail
here as in the white-breasted species.

But is there any direct proof that the transformation is actually
making progress to-day? May not these transitional steps go on ap-
pearing generation after generation, without ever making any per-
manent progress?

We have to concede that we cannot follow the processes that
reveal themselves in steps. We can at most only see what is done —
not the doing. We are entirely in the dark as to the time required
to carry the change through a single row of feathers. But we know
that this has been done in three other species of the same family.
We see that after it is done, not before, the transitional steps appear in
the next and last row. Moreover, — and this is as close as we can
hope to get to actual seeing, — we find that progress of just the kind
we are looking for is certainly made in passing from the Juvenal to the
adult plumage. This is an ontogenetic change of a few weeks, which
we can easily demonstrate by experiment to be progressive and con-
tinuous. The corresponding phylogenetic advance has left no other
record, and hence we only know that it took time — that it was not
a momentary salt. In the adult plumage, one or two full steps are taken
beyond the Juvenal stage, and taken precisely at the points premarked
by transitional steps. The number of transitional steps is increased
at the same time.1

As the next and last illustration, I take a case in which the bars
are verging to complete obliteration. The well-known wrild stock
dove (C. anas) of Europe may serve as a convenient and instruct-

1 One point here should not escape attention; namely, that the transitional
steps in Ocyphaps form a linear series; but there is nothing artificial or arbitrary
about it. It is a small-number series, each element of which stands in an appointed
place, and marks the height to which the transformation process rose at that point
in its course. Such a series cannot be open to the objections which De Vries has
very justly made against large-number series, the elements of which are collected
at random and then arranged arbitrarily to display transitional continuity.

In the Ocyphaps series there is some fluctuation, the series varying in length,
but always advancing in one predetermined direction, like a tidal flow guided
along a prepared channel, and flowing to varying distances, according to the
initial momentum.

56 PHYLOGENY

ive example. In this pigeon we find that reduction of the checkers
has swept over the whole wing, leaving nothing except a few obso-
lete spots, which we recognize as vanishing elements of bars formerly
more highly developed, and homologous with those of the rock
pigeon.

Here we find what at first glance looks like extraordinary variabil-
ity, suggesting mutations, incipient stages, bars in statu nascendi, etc.
The selectionist and the mutationist could each find what he looks
for. The first thing to decide is the direction in which the phenomena
are to be read. Is it a positive, progressive upbuilding of new charac-
ters, or a negative, retrogressive weakening of old characters? I
have already anticipated the answer, and will now briefly show how
the direction of variation is decisively settled.

(1) These spots have every outward appearance of being reduced
remnants, such as we get in passing from the checkered to the
barred condition in rock pigeons. They are rounded or squarish
in form, frequently irregular and thin at the edges, dull in color as
if fading, etc.

(2) The smallest stages are not found on the exposed surface of
the feathers, but lie concealed beneath the overlapping feathers
next above or in front. Concealed spots admit of but one interpre-
tation. This pigeon is a not distant relative of the rock pigeon, has
a similar gray ground, and is therefore probably moving in a parallel
direction, only more advanced.

(3) The spots are found at the posterior end of the wing, near the
upper edge, on one to three tertials and on a few long coverts. In some
cases they occur also on a few of the second row of long coverts, but
here they are always very small and completely concealed. They are
thus in the position occupied by vanishing spots generally.

(4) The adult plumage makes no advance in the number of spots,
and some spots (second row of long coverts) visible in the young,
are completely concealed in the adult. This indicates degeneration
unmistakably.

(5) The stock dove, although sometimes having a concealed third
bar of few spots, never appears in checkered dress. It seems to have
moved so far in the opposite direction that no reversal of course is
now open to it.

Taking the checkered pattern as the earlier one, the various con-
ditions of checkers and bars in rock pigeons, domestic races, and,
indeed, in all the wild pigeons, become almost self-explanatory.
We could not explain satisfactorily how just two bars could arise
dc novo in one species, three in another, twelve in another, and so on.
The repetition of dc novo origins would become ever more incredible.
Making phylogeny our guide as to the starting-point, we find it
comparatively easy to thread our way through the maze of patterns

PROBLEM OF ORIGIN OF SPECIES 57

existing among five hundred or more species of pigeons, and even to
trace affinities farther back in the bird world.

The orthogenetic process is the primary and fundamental one.
In its course we find unlimited opportunities for the play of natural
selection, escape the great difficulty of incipient stages, and readily
understand why we find so many conditions arising and persisting
without any direct help of selection.

Charles Darwin.

"As natural selection acts solely by accumulating slight, successive, favor-
able variations, it can produce no great or sudden modification." Origin of
Species, ch. xiv, p. 421.

" Slight individual differences, however, suffice for the work, and are probably
the sole differences which are effective in the production of new species."
Animals and Plants, vol. n, ch. xx, p. 233.

" As modern geology has almost banished such views as the excavation of a
great valley by a single diluvial wave, so will natural selection, if it be a true
principle, banish the belief of the continued creation of new organic beings, or of
any great and sudden modification in their structure." Origin of Species, ch. iv,
p. 98.

August Weismann.

"The simultaneous modification of numerous cofunctioning parts, in essen-
tially different ways, yet in harmonious functional relations, points conclu-
sively to the fact that something is still wanting to the selection of Darwin and
Wallace." Germinal Selection, p. 22.

"We know of only one natural principle of explanation for adaptation, that
of selection." Ibid., p. 61.

"The three principal stages of selection; that of personal selection, as held
by Darwin and Wallace; that of histonal selection, as upheld by Wilhelm Roux
in the form of a 'Struggle of the Parts;' and finally, that of germinal selection,
the existence of which I have endeavored to establish — these are the factors
that cooperate to maintain the forms of life constantly capable of life." Ibid.,
p. 60.

"The harmony of the direction of variation with the requirements of the
conditions of life is the riddle to be solved. The degree of the adaptation which
a part possesses itself determines the direction of variation of that part." Ibid.,
p. 54.

" When a determinant has assumed a certain variation-direction it will follow it
up of itself, and selection can do nothing more than secure it a free course by setting
aside variations in other directions by means of the elimination of those that exhibit
them." Evolution Theory, vol. n, p. 123.

Carl von Nageli.

" Between the theory of selection and that of direct causation, there is, appar-
ently, only a little difference, since, according to the latter, the present condi-
tion of the organic world would likewise result from individual variation and
elimination. But these two processes [selection and direct causation] differ fun-
damentally in their causal import. According to Darwin, variation is the germi-
nating factor, selection the directing and regulating factor; according to my
view, variation is at once both the germinating and the directing factor. Accord-
ing to Darwin, selection is indispensable; without it there could be no progres-
sion, and organisms would remain in the same condition as at the beginning.

58 PHYLOGENY

In my opinion, competition simply removes what is less capable of existence,
but it is wholly without influence in bringing to pass anything more perfect or
better adapted." Theorie der Abstammungslehre, p. 285.

" The fortuitous or directionless variation of individuals would be conceivable,
if it were conditioned by external influences (food, temperature, light, elec-
tricity, gravitation); for, as these causes obviously cannot be brought into any
definite relation to the more or less complex organization, they must effect
sometimes a positive, sometimes a negative, step. If, however, the causes of
variation are internal, in the constitution of the substance, then the matter
stands otherwise. In this case the determinate organization of the substance
must exercise a restricting influence upon its own variation ; and this influence,
as development begins at the lowest point, can only take effect in an upward
direction." Abstammungslehre, p. 12.

" Individuals transmit to their offspring the tendency to be like themselves,
but the offspring are not perfectly like the parents. The tendency to variation
must therefore also be transmitted. A primordium, if all conditions are favorable,
must be able to develop ever farther in a series of generations, as a capital
enlarges to which interest is added annually; for each generation inherits from
the preceding not only the possibility to realize the capital, but also the possi-
bility to add the interest." Individuality in Nature, 1856.

Hugo de Vries.

"According to the theory of mutation, species have not arisen through
gradual selection continued for hundreds or thousands of years, but by steps,
through sudden though small transmutations. In contrast with variations,
which are changes advancing in a linear direction, the transformations to be
called mutations diverge in new directions. They take place, then, so far as
experience goes, without definite direction, i. e., in various directions." Die
Mutationstheorie, vol. I, p. 150.

SECTION B — PLANT MORPHOLOGY

SECTION B — PLANT MORPHOLOGY

(Hall 2, September 22, 10 a. TO.)

CHAIRMAN: PROFESSOR WILLIAM TRELEASE, Washington University, St. Louis.
SPEAKERS: PROFESSOR FREDERICK O. BOWER, University of Glasgow.

PROFESSOR KARL F. GOEBEL, University of Munich.
SECRETARY: PROFESSOR F. E. LLOYD, Columbia University.

BY FREDERICK ORPEN BOWER

[Frederick Orpen Bower, Regius Professor of Botany, University of Glasgow,
Scotland, b. November 4, 1855, Ripon, Yorkshire. Sc.D. Cambridge, England.
Assistant to Professor of Botany, University College, London, 1879-82; Lec-
turer on Botany, Royal College of Science, South Kensington, 1882-85; Fellow,
Royal Society of London; Fellow, Royal Society of Edinburgh; Fellow, Lin-
nean Society of London; Corresponding Member of Deutsche Botanische
Gesellschaft.]

THOSE who organized these congresses left to the guests whom
they honored with their invitation a high degree of freedom in the
handling of their subject. In the exercise of that freedom, which
I gratefully acknowledge, I have decided not to attempt any general
dissertation on the present position of plant morphology as a whole,
but to discuss certain topics only in the morphology of plants, which
at present take a prominent place in that branch of the science of
botany. These centre round the question of the relation of the axis
to the leaf in vascular plants.

The progress of plant morphology has shown certain well-marked
phases in its history, and we stand at the moment on the threshold
of a new one. First came the mere description and delineation of
the mature form, with special reference to the higher flowering
plants. This period included the work of the herbalists, and early
systematists, and led to classification as its chief end: but it was
enlivened by occasional generalizations, such as that of Wolff, who
regarded all appendages of the axis as leaves. It was deeply in-
fluenced later by the poetic gloss cast over it by Goethe, in his ideal-
istic doctrine of metamorphosis. But this, and the development
of the spiral theory, led the stream of botanical thought temporarily
away from fact into a region of surmisings.

From these it was strongly recalled by the initiation of the second
phase, about the middle of the last century, the basis of which was
the dictum, formulated by Schleiden, that "the history of develop-

62 PLANT MORPHOLOGY

ment is the foundation for all special botanical morphology." The
study of development thus introduced for the individual part was
soon extended to the whole life-cycle, and especially among the
lower forms, which had been so long neglected. The year 1848 should
be marked with a white stone in the chronology of every morpholo-
gist, for in that year the essential outline of the life-history of a fern
was completed by Suminsky. Hofmeister followed in quick succession
with the enunciation of the fundamental homologies in fern and
moss; and thus was laid, though upon a purely comparative basis, the
foundation of a scientific morphology for vascular plants. But the
comparisons were still formal, and might have been applied equally
well to dead as to living things. The inspiration of the breath of
life came with the theory of evolution: the facts then first "lived,
and stood upon their feet." It is, however, remarkable how slowly
the change of view brought by the theory of evolution permeated
morphology. Sound though Hofmeister's conclusions were on the
comparison of either generation as a whole, the same could not be
said of the comparison of the parts. It took almost a generation
after the publication of the Origin of Species for botanists to achieve
any practical appreciation of evolution as a factor in the morphology
of the appendages. The position up to 1874 is well reflected in the
text-book of Sachs. Though he himself points out the limitations
necessary to such a method, Sachs proceeds in the morphological
section of his book on the footing that in vascular cryptogams
and phanerogams "every organ is either a stem, or a leaf, or a root,
or hair." Sporangia are held to be the results of metamorphosis of
vegetative parts. The conception of homology which underlies
such a grouping is dictated rather by convenience of definition and
of classification than by any deeply lying aspiration after his-
torical truth. An important step towards placing the morphology
of the appendages upon a sounder footing was taken by Goebel in
1881, when he asserted the independence of the sporangium, as an
organ sui generis, and not a result of metamorphosis of any vegeta-
tive part. This was upheld by Sachs in the following year, in his
Vorlesungen.

Another feature, and perhaps the most important, of the Vor-
lesungen, was that in them Sachs for the first time gave due weight
to the physiological aspect of morphology, and thus harmonized
those two branches of study which had too long been kept asunder.
The increasing attention thus given to physiology, and to the effects
of external influences, has naturally led to the initiation of a third
phase in the history of morphology: I mean the phase of experiment,
with a view to ascertaining the effect of external agencies in deter-
mining form: that phase is still nascent, and carries with it high
possibilities. But it is well in the enthusiasm of the moment to keep

PLANT MORPHOLOGY 63

in view the limitations which hedge it round: it is to be remembered
that the effect of external conditions upon form is always subject
to hereditary control, and that thus the whole field of past history
is still left open to speculation. This seems to have been forgotten
by a recent writer, who remarks that "the future lies with experi-
mental morphology, not with speculative morphology, which is
already more than full-blown." Though this assertion contains an
important truth, inasmuch as it accords prominence to experiment,
the case is in my opinion overstated. All who follow the development
of morphological science will value the results already obtained
from the application of experiment to the problems of plant-form.
But it is necessary at the same time to recognize that the two phases
of study, the experimental and the speculative, are not antithetic
to one another, but mutually dependent: the one can never super-
sede the other. The full problem of morphology is not merely to see
how plants behave to external circumstances now, — and this is all
that experimental morphology can ever tell us, — but to explain,
in the light of their behavior now, how in the past they came to be
such as we now see them. To this end the experimental morphology
of to-day will serve as a guide, and as a check to the speculative
branch, limiting its exuberances within the lines of physiological
probability: but experiment can never replace speculation, for
experiment cannot reconstruct history. It is impossible to rearrange
for purposes of experiment all the conditions, such as light, moisture,
temperature, and seasonal change, on the exact footing of an earlier
evolutionary period: and even if this were done, are we sure that
the subjects of experiment themselves are really the same? There
remain the factors of hereditary character, and of competition,
which cannot possibly be put back to the exact position in which they
once were. There must always remain a margin of uncertainty
whether a reaction observed under experiment to-day would be the
exact reaction of a past age. So far, then, from experiment competing
with or superseding speculation in morphology, it can only act as a
potent stimulus to fresh speculation, wherever the attempt is made
to elucidate the problem of descent. It will only be those who
minimize the conservative influence of heredity, or, it may be,
relegate questions of descent to the background of their minds,
who will be satisfied by the exercise of an experimental method of
morphological inquiry, apart from speculation.

It has already been remarked that, notwithstanding the sound-
ness of Hofmeister's comparison for the alternating generations as a
whole, the homologies of the parts remained unsatisfactory: the chief
reason for this was that the grouping was not derived from com-
parison of nearly allied species; nor does it seem to have been held as
important to consider critically whether such parts as were grouped

64 PLANT MORPHOLOGY

together were or were not comparable as regards their descent. For
long years after the publication of the Origin of Species homology had
no evolutionary significance in the practice of plant morphology.
But in the sister science of zoology this matter was taken up by Ray
Lankesterin 1870, in his paper "On the Use of the Term Homology
in Modern Zoology, and the Distinction between Homogenetic and
Homoplastic Agreements." Many botanists at the present day
would be the better for a careful study of that essay. He pointed
out that the term homology as then used by zoologists belonged to
the Platonic school, and involved reference to an ideal type. This
meaning lay at the back of Goethe's theory of metamorphosis in
plants, and it seems to have been somewhat in the same sense that
homologies were traced by Hofmeister. Lankester showed that the
zoologists' use of the term "homologous" included various things:
he suggested the introduction of a new word to define strict homology
by descent: structures which are genetically related in so far as
they have a single representative in a common ancestor, he styled
"homogenous;" those which correspond in form, but are not genet-
ically related, he termed "homoplastic."

It is important at once to recognize that the strict "homogeny"
defined by Lankester as that of "structures which are genetically
related in so far as they have a single representative in a common
ancestor" can only be traced in the simpler cases of plant-form: it
implies the repetition of individual parts, so strictly comparable in
number and position as to stamp the individual identity of those
parts in the successive generations. The right hand of a child repeats
in position and qualities the right hand of the mother, and of the race
at large: here is a strict homogeny. In the plant-body such in-
dividual identity of parts of successive generations is not common.
It may be traced, for instance, in the cotyledons, and the first plumu-
lar leaves of seedlings of nearly related species, or in their first roots.
But as a consequence of that continued embryology, which is so
constant a feature in the plant-body, the number of the appendages
of any individual is liable to be indefinitely increased, while often
the absence of strict rule in their relative positions makes their
identical comparison in different individuals impossible. This is
especially clear in the case of roots of the second, and higher orders,
for they do not correspond in exact number or position in seedlings.
What we recognize in such cases is, then, not the individual identity:
but their similarity in other respects: and when we group them
under the same head we recognize, not their strict homogeny accord-
ing to the definition of Lankester, but their essential correspondence,
as based upon the similarity of their structure, and of their mode of
origin upon and attachment to the part which bears them. This is
also the case with the antheridia and archegonia of the pteridophytes.

PLANT MORPHOLOGY 65

which are as a rule definite neither in number nor in arrangement,
and are subject to variation in both respects, according to the con-
ditions which may be imposed upon them by experiment : neverthe-
less, they accurately maintain their structural characters, and their
essential correspondence is thus established, but not their individ-
ual identity. It is clear that this is a comparison of a more lax order
than the recognition of their individual homogeny would be.

But if room for doubt of the strictest homogeny be found in simple
cases such as these, what are we to expect from the comparisons of
less strictly similar parts of the plant, such as cotyledons, scale-
leaves, foliage-leaves, bracts, sepals, petals, stamens, carpels? How
far are these to be held to be homogenous, or in some less strict
sense homologous? Or, going still further, how are we to regard those
comparisons which deal with parts of different individuals, species,
genera, orders, or classes? What degree of homology is to be ac-
corded to them? In proportion as the systematic remoteness of
the plants compared increases, and the continuity of the connecting-
forms is less complete, so the comparisons become more and more
doubtful, and the use of the term "homology'' as applied to them
more and more lax, until wre are finally landed in the region where
comparison is little better than surmise. It becomes ultimately a
question how far the term "homology" is to be held as covering
these more lax comparisons, which are certainly not examples of
"homogeny" in Lankester'« sense, and are only doubtfully correlated
together on a basis of comparison of more or less allied forms.

The progress of our science should be leading towards a refinement
of the use of the term "homology:" an approach must be made,
however distant it may yet be, to a classification of parts on a basis
of descent. But though this may be readily accepted in theory, it
is still far from being adopted in the general practice of plant
morphology. None the less, comparison is inevitably leading to the
disintegration, on a basis of descent, of the old-accepted categories
of parts: of these the most prominent, and at the same time the most
debatable, is the category of leaves, and they will lend themselves
best to the illustration of the matter in hand.

To those who, like myself, hold the view that the two alternating
generations of the Archegoniatce have had a distinct phylogenetic
history, it will be clear that their parts cannot be truly comparable
by descent. The leaf of the vascular plant, accordingly, will not be
the correlative of the leaf of a moss. Even those who regard the
sporophyte as an unsexed gametophyte will still have to show7, on a
basis of comparison and development, that the leaves of the two
generations are of common descent. I am not aware that this has
yet been done by them.

But the phylogenetic distinctness of the leaves in the sporophyte

66 PLANT MORPHOLOGY

and gametophyte is not the only example of parallel foliar develop-
ment; Goebel has shown with much cogency that the foliar append-
ages of the bryophytes are not all comparable as regards their
origin: he remarks, "It is characteristic that the leaf -formation in
the Liverworts has arisen independently in quite a number of series "
(Organographie, p. 261), and has shown that they must have been
produced in different ways. Here, then, is polyphyleticism in high
degree, seen in the origin of those parts of the gametophyte which
on grounds of descent we have already separated from the foliar
appendages of the sporophyte.

Such results as these for the gametophyte lead us to inquire into
the views current as to the origin of foliar differentiation in vas-
cular plants. In discussing such questions it is to be remembered
that in different stocks the foliar condition of the sporophyte as we
see it may have been achieved in different ways, just as investigators
have found reason to believe that it was in the gametophyte. We
have no right to assume that the leaf was formed once for all in the
descent of the sporophyte. But at the moment we are unprovided
with any definite proof how it occurred. All the evidence on the
point is necessarily indirect, since no intermediate types are known
between foliar and non-foliar sporophytes. Physiological experi-
ment has as yet nothing to say on the subject. The fossil history
of the origin of the foliar state in the neutral generation is lost, for
the foliar character antedated the earliest known fossil-sporophytes.
There remain the facts of development of the individual, and com-
parison, while anatomical detail may have some bearing also on
the question: but all of these, as indirect lines of evidence, fall short
of demonstration, and accordingly it is impossible to come at pre-
sent to any decision on the point. For the purposes of this discussion,
however, we shall proceed on the supposition that all leaves of the
sporophyte generation originated in essentially the same way,
though not necessarily along the same phyletic line.

There are at least three alternatives possible for the origin of the
foliar differentiation of the shoot, in any progressive line of evolu-
tion of vascular sporophytes: (1) that the prototype of the leaf
was of prior existence, the axis being a part which gradually
asserted itself as a basis for the insertion of these appendages: the
leaf in such a case would be from the first the predominant part in the
construction of the shoot; (2) that the axis and leaf are the result
of differentiation of an indifferent branch-system, of which the
limbs were originally all alike; in this case neither leaf nor axis
would predominate from the first; (3) that the axis preexisted, and
the foliar appendages arose as outgrowths upon it: in this case the
axis would be from the first the predominant part.

The first of the above alternatives, viz., that the prototype of the

PLANT MORPHOLOGY 67

leaf existed from the first, and was in fact the predominant part in
the initial composition of the shoot, has been held by certain, writers
as the basis of origin of the leafy shoot in vascular plants.1 On this
view not only is the whole shoot regarded as being mainly composed
of leaves, but some even contend that the axis has no real existence
as a part distinct from the leaf-bases.2 The way in which this is
pictured as having come about is by branching of a sporogonium of a
bryophyte: the sporogonial head of one limb of such a branching
became vegetative as the first leaf, while the other continued its
growth, and branched again: thus the apex of the first lateral
appendage was of the nature of a sporogonial head: this condition
has been compared with that seen in the embryo of a fern, or of
some monocotyledons.3

This view in its general form represented the plant as constructed
on a plan somewhat similar to that of a complex zoophyte. It has
more recently culminated in the writings of Celakovsky and Delpino.
The former in his theory of shoot-segments (Sprossgliedlehre) starts
from the position that the plant is composed of morphological
individuals: the cell, the shoot, and the plant-stock are recognized
as such. The stock is composed of shoots, and the shoot of cells. Braun
recognized the shoot as the individual par excellence: between the cell
and the shoot is a great gulf, which has not yet been filled : " between
the cell and the bud (shoot) there must be intermediate steps, the
limitation of which no one has succeeded in defining:" the long-
sought-for individual middle step is the shoot-segment (Spross-
glied), which is neither leaf only, nor stem-segment only, but the
leaf together with its stem-segment. Now this appears to me to be
purely Platonic morphology: the intermediate step must occur;
we will therefore discover and define it. The definition of it con-
sists fcin the drawing of certain transverse and longitudinal lines
partitioning the shoot, lines which in the sporophyte have no existence
in nature: the assumed necessity of partitioning the shoot into
parts of an intermediate category between the whole shoot and the
cell brings these assumed limits into existence.

In support of his theory of shoot-segmentation, Celakovsky (loc cit.
p. 101) adduced evidence from the development of the embryos
of certain monocotyledons; from certain inflorescences; from the
origin of the leafy moss stem on the protonema; and from the
actual existence of the leaf-forming segments in mosses and pterido-

1 Goethe, Die Metamorphose der Pflanzen. Gaudichaud, Memoire de I' Academic
de Science, 1841. Kienitz Gerloff, Botanische Zeitung, 1875, p. 55. Celakovsky,
Unters. uber die Homologien, Pringsh. Jahrbuch, xiv, p. 321, 1884. Botanische
Zeitung, 1901, Heft v, vi.

2 Delpino, Teoria generate della Filotassi. For reference see Bot. Jahresbr., vin
(1880), p. 118, also vol. xi (1883), p. 550.

3 Celakovsky, loc. cit. Kienitz Gerloff, loc. cit., compared the first leaf with half
of the sporogonial head, in the case primarily of fern embryos.

68 PLANT MORPHOLOGY

phytes. But objection may be taken to all these lines of evidence.
We should hardly look to either the embryos of seed-plants nor to
their inflorescences for safe guidance as to the origin of the funda-
mental characters of shoot-construction, for both are probably
highly specialized forms of shoot. Particularly would this seem to be
the case in the embryo, which is nursed with a supply of endosperm
within the seed, a condition far removed from what can possibly
be conceived as that of a primitive leafy shoot. Moreover, the fact
that certain monocotyledon embryos conform externally to such a
theoretical description as is given is not sufficiently cogent in the
absence of internal limits of demarkation of the constituent shoot-
segments.

The details of comparison of the moss-plant and protonema are
quite beside our question, which relates to vascular plants: how-
ever interesting the analogies may be between the alternating gen-
erations, they cannot rank as evidence in such a question as this:
for it is quite conceivable that a perfect system of shoot-segmenta-
tion might rule in the one generation, while the leafy development
in the other, having originated by a distinct evolutionary sequence,
might show a quite distinct relation of leaf to axis.

The last line of evidence is from segmentation at the apex of the
shoot in pteridophytes: if one cell-segment regularly produced one
leaf-bearing shoot-segment, this might be held to be valid evidence
of Celakovsky 's view. But this argument does not apply consistently,
as indeed Celakovsky himself admits. It is true that a leaf may be
produced from each apical segment in some ferns: but in dorsi-
ventral ferns, and hydropterids, leaves are not produced from the
ventral rows (Klein, Bot. Zeit., 1884). In Azolla and Salvinia leafless
internodes intervene between successive nodes: thus there is no
constant relation in ferns between apical segmentation and 'leaf-
production. Treub's investigations resulted in his statement that
" there cannot be any constant relation between the leaves and the
segments of the apical cells in Selaginella Martensii." Lastly, in
Equisetum, notwithstanding the regular segmentation of the tetra-
hedral apical cell, the leaves show no regular relation to the segments
in number or position, varying in number from three to about forty.
Thus the argument from apical segmentation even in pteridophytes
does not give consistent support to a theory of shoot-segmentation,
while such evidence is entirely wanting in the vast majority of
phanerogamic plants. Notwithstanding the ingenuity of the theory
as put forward by Celakovsky, in the absence of any structural indi-
cation of the limits of the shoot-segments in the vast majority of
cases, the theory does not appear to me to be sufficiently upheld by
the facts.

An extreme, and indeed, a paradoxical position has been taken

PLANT MORPHOLOGY 69

•

upon this phytonic question by Delpino. As a consequence of his
studies on phyllotaxis he concluded that the axis is simply composed
of the fusion of the leaf-bases : that the leaves are not appendicular
organs, but central organs: that an axis or stem-system does not
exist, and accordingly that the higher plants are not cormophytes
at all, but phyllophytes. There will, I think, be few who will adopt
this fantastic view of the shoot.

The second view, that the axis and leaf are the result of differentia-
tion of an indifferent branch-system, of which the limbs were origi-
nally all alike, has lately been brought into prominence by Potonie".1
Taking his initiative from the branching of the leaves in early fossil
ferns, he recognizes the frequent occurrence of overtopping (Ueber-
gipfelung), that is, the gradual process of assertion of certain limbs
of a branch-system over others: in the branching of fucoids he
finds an analogy for his observations on fern-leaves, and draws the
following conclusion: that "the leaves of the higher plants have
been derived in the course of generations from parts of an Algal
thallus like that of Fucus, or at least from Alga-like plants, by means
of the overtopping of dichotomous branches, and the development
as leaves of the branches, which thus became lateral." Dr. Hallier,
who adopts Potoni6's position, prefers to draw the comparison with
liverworts, which show a similar sympodial development of a dicho-
tomous branch-system.2

It seems not improbable that the condition of many branched
fern-leaves may have been derived through a process of "over-
topping" in an indifferent branch-system of the leaf itself. But it
lies with Potonie to show, on a basis of comparison of forms more
nearly related to them than the fucoids, that the relation of axis
to leaf in the ferns was so derived : and further, that such an origin
is in any way applicable to other foliar developments in vascular
plants, especially pteridophytes, such as the lycopods, equiseta, and
sphenophylls. I am not aware that this has yet been done. But.
granting that this can be done, the question still remains whether
similarity of method of branching is any criterion of comparison as
to descent? And especially whether such comparison is valid be-
tween widely distinct groups, or between the different generations
of an antithetic alternation? It is true that Potonie prefers to regard
such generations as homologous, as is indeed essential for his view:
but that does not prevent others from differing from him, or even
considering the fact that the parts compared belong to different
generations as fatal to his theory. For my own part I am not prepared
to give up the broad conclusions as to antithetic alternation on so

1 Lehrbuch der Pflanzenpalceontologie, pp. 156-159. Also Ein Blick in die Ge-
schichte der Bot. Morph. und der Pericaulomtheorie, 1903, p. 33, etc.

2 Beitrage zur Morphogenie der Sporophylle und des Trophophylls. Morph. d.
Sporophylle u. d. Trophophylls, Hamburg, 1902.

70 PLANT MORPHOLOGY

slender a ground as similarity of method of branching represented in
them both.

For sympodial development of a dichotomous system (and this is all
that such "overtopping" actually is) has occurred in cases where it
cannot be held to have resulted in a branching which is foliar: and
of this instances can be found without going so far afield as the
Fucacece. It has been shown by Bruchmann 1 that the first branch-
ing of Sdaginella spinulosa is dichotomous, and that this is probably
so for all species of the genus. This mode of branching may be re-
peated, but the later branches may lead by most gradual transitions
to the monopodial type. Yet no one would hold that the shoots thus
laterally placed are consequently foliar in their nature. Again,
in Lycopodium the branches of successive dichotomies often develop
unequally: a conspicuous example is seen in L. unilaterale, R. Br.,
where one limb develops as a strobilus, and is pushed to one side
by its stronger vegetative brother. A similar unequal development of
dichotomous branches probably leads to such dendroid forms as
L. cernuum. Progressions from the dichotomous to the monopodial
branching are also to be seen in the case of the roots of Selaginella.
Such examples show that in pteridophytes progressions are found
from the regular dichotomous branching to its sympodial, or even
its monopodial development, in cases where it is impossible to rank
as leaves those parts which are forced to assume the lateral position.
This shows that such progressions are a widespread phenomenon,
occurring in parts of various category. If this be so, then little value
need be attached to the comparison of such branchings in plants
not nearly allied to one another; these may be held to be quite
distinct examples of a general phenomenon, without the one being
in any sense the prototype of the other. Such reflections as these
indicate that the comparison in mode of branching bet ween the leaves
of ferns and the thallus of fucoids, which forms the groundwork of
the view of Potonie" (or between ferns and the thalloid liverworts, as
may be preferred by others), are not to be held as more than distant
analogies; consequently they are no demonstration of the origin of
the leaf by a process of "overtopping."

There remains the third view, which, however, is no new one: for
there have not been wanting those who have assigned a more prom-
inent place to the axis in the initial differentiation of the shoot.
Perhaps the most explicit statement on this point is that by Alex-
ander Braun, who remarks in his Rejuvenescence in Nature (Eng.
ed. p. 107), referring to phytonic theories, that "all these attempts
to compose the plant of leaves are wrecked upon the fact of the
existence of the stem as an original, independent, and connected
structure, the more or less distinct articulation of which certainly
1 Untcrs. u. Selaginella spinulosa, Gotha, 1897, p. 18, etc.

PLANT MORPHOLOGY 71

depends upon the leaf-formation, but the first formation of which
precedes that of the leaves." Unger also in his botanical letters to
a friend (no. viii), described how "The first endeavor is directed
towards the building up with cell-elements of an axis;" " those
variously formed supplementary organs which are termed leaves"
originate laterally upon it; and he concludes that "we may therefore
say with perfect justice that the plant ... is, as regards form, essen-
tially a system of axes." Naegeli contemplated a somewhat similar
origin of the leafy shoot, as an alternative possibility; in fact, that
the apex of a sporogonium-like body elongated directly into that of
the leafy stem: in which case the axis would be the persistent and
prominent part, and the leaves be from the first subsidiary and
lateral appendages. In my theory of the strobilus in archegoniate
plants the central idea was similar to this ; it may be briefly stated
thus: There seems good reason to hold that a body of radial con-
struction, having distinction of apex and base and localized apical
growth as its leading characters, existed prior to the development
of lateral appendages in the sporophyte: for such a body is seen in
certain bryophyte sporogonia, while the prior existence of the axis,
and lateral origin of the appendages upon it, is general for normal
leafy shoots. The view thus put forward is indeed the mere reading
of the story of the evolution of leaves in terms of their normal indi-
vidual development. I have recently shown that all pteridophyte
shoots may be regarded as derivatives from the radial strobiloid
type, with relatively small leaves, which would thus have come into
existence.

It is natural to look to the pteridophytes for guidance as to the
origin of foliar development in the sporophyte, for they are the
most primitive plants with leafy sporophytes. They may be dis-
posed according to the prevalent size of their leaves in a series, lead-
ing from microphyllous to megaphyllous types. I have lately shown
that such a seriation is not according to one feature only, but that
certain other characters which have been summarized as "filicineous"
tend to follow with the increasing prominence of the leaf: this
indicates that such seriation is a natural arrangement. Now it is
possible to hold either that the large-leaved, fern-like plants were
the more primitive, and the smaller-leaved derivatives from them
by reduction; or conversely, that the smaller-leaved were the more
primitive, and the larger-leaved derivatives from them by leaf-
enlargement: other alternative opinions are also possible, such as
that the leaf-origin has been divergent from some middle type, or
that the leaves of vascular plants may have been of polyphyletic
origin.1 For the moment we shall leave these latter alternatives aside.

1 The view recently advanced by Professor Lignier (Equisetales, et Sphenophyl-
lales, Leur origine filicinienne commune, Bull. Soc. Linn, de Normandie, Serie 5, vol.

72 PLANT MORPHOLOGY

Much of the difference of view as to foliar origin centres round
the question whether originally the leaf was relatively large, or small.
Those who hold that the larger-leaved forms were the more primitive
will be naturally disposed towards the view of the original preponder-
ance of the leaf over the axis, and will favor some phy tonic theory;
those who hold the smaller-leaved forms to be the more primitive
will probably adopt a strobiloid theory of origin of the leafy sporo-
phyte. I propose to offer some remarks on the relative probability
of these alternative views.

If large-leaved prototypes be assumed generally for vascular plants,
this naturally involves a widespread reduction, since small-leaved
forms are numerous now, and have been from the earliest times of
which we have any record. Reduction is a ready weapon in the
hands of the speculative morphologist, and it has often been used
with more freedom than discretion. But reduction should never be
assumed in order to meet the demands of convenience of comparison,
nor as a cover for doubt. The justification of a view involving re-
duction must be found in its physiological probability in the case
in question, and this should be backed by comparisons of form, and
of anatomical structure: the conclusion should also be in accordance
with the paleontological record. All suggested cases of reduction
where such justification is absent should be looked upon as doubtful.

Convincing evidence of reduction of leaf-complexity in an evolution-
ary sequence, supported on all these grounds, has been adduced in
the progression from ferns, through cycado-filicinean forms, to the
cycads, and it applies with special force in the case of their sporo-
phylls. Ferns, which are essentially shade-loving and typically zoidi-
ogamic, or amphibious, may be understood to have given rise to
the cycado-filices and cycads, which are more xerophytic, and show
that essential character of land-plants, — the seed-habit. Not only
is such a progression physiologically probable, but it is supported
by paleontological evidence, as well as by detailed facts of anatomy,
and of reproductive morphology. The case for reduction of leaf-
complexity seems to be here fully made out: and somewhat similar
arguments will also apply for other types of gymnosperms.

7, Caen. 1903) is analogous to that of Potonie", though differing from it in detail.
It involves the ranking of the lycopod leaf as a " phylloid," the leaf of the fern as a
true leaf, or "phyllome," differentiated from an indifferent system of "cauloids,"
on which the "phylloid" appendages had become abortive. It regards the leaves
of equiseta and sphenophylls as phyllomes, reduced from the larger-leaved fern-
type. The argument is chiefly based on comparisons as to branching and anatom-
ical structure. I do not think that these grounds suffice to override the probability
that the leaves of lycopods are essentially of the same nature as those of the sphe-
nophylls, or equiseta. (Compare my Studies, no. v.) Professor Lignier's view
further involves the acceptance of homologous alternation, while he makes no
mention of the chromosome-differences of the two generations. Such difficulties
do not arise if the leaves of the sphenophylls and equiseta are regarded as being
in the upward rather than the downward scale of development, a view of them
which would equally harmonize with the anatomical comparisons of Prof. Lignier.

PLANT MORPHOLOGY 73

The facts relating to the vascular system of the shoot have also
their bearing on the question of the relative size of primitive leaves.
The origin of the leaf-trace from the axial stele in conifers, and also
in angiosperms, has been shown by Dr. Jeffrey to be of the type
styled by him phyllosiphonic. This is specially characteristic of those
plants where the leaf is essentially the dominating influence in the
shoot. In this I see a probability, which their physiological position
as land-growing plants would justify, that the seed-bearing plants
at large were descended from a large-leaved ancestry, and had under-
gone reduction of leaf-complexity in their descent. But while we thus
recognize a probability of widespread reduction producing relatively
smaller-leaved forms, it does not follow that all small-leaved vas-
cular plants originated thus: on this point the anatomical evidence
is of importance, as bearing on the origin of the small-leaved stro-
biloid pteridophytes. Of these (putting aside the hydropterids as
being a special reduction-problem in themselves), there remain the
lycopodiales, the equisetales, and the sphenophyllales, which are all
cladosiphonic in the terminology of Dr. Jeffrey: the question will
largely turn upon the meaning of this anatomical feature. I take it
to be as follows: The cladosiphonic character is the anatomical
expression of the dominance of the axis in the shoot: here the leaf-
trace is merely an external appendage on the stele, which is hardly
disturbed by its insertion: this type is seen in certain small-leaved
pteridophytes. The phyllosiphonic character, on the other hand, is
the anatomical expression of the dominance of the leaf over the axis
in the shoot; here the insertion of the vascular supply of the leaf
profoundly disturbs the vascular arrangement in the axis; it is
characteristic of certain large-leaved pteridophytes, and is seen also
generally in seed-plants.

It is a fact of importance that, in the individual life, the one or
the other type is usually constant; but in certain ferns the pro-
gression may be traced from the cladosiphonic in the young plant
to the phyllosiphonic in the mature, thus suggesting a similar pro-
gression in descent, viz., that the large-leaved phyllosiphonic ferns
were derived from a smaller-leaved cladosiphonic stock. Of the con-
verse, viz., the progression from the phyllosiphonic to the cladosi-
phonic state in the individual life, I know of no example among the
pteridophytes, though it is true that there is some approach to it in
the Marsileacece. Thus the anatomical evidence indicates a probabil-
ity that, even in large-leaved ferns, the cladosiphonic was the prim-
itive type, but that the phyllosiphonic, once initiated, is as a rule
maintained; this is shown by its persistence in the seed-plants, even
where the leaf has been reduced in size.

Having thus gained a valuable side-light from anatomy, we may
now return to our central question of the initial relation of leaf to

74 PLANT MORPHOLOGY

axis. Of the three theories already noted, the theory of overtopping,
as applied to the origin of the leaf, may in my opinion be dismissed,
as it is not based upon comparison of nearly related forms, while
the sympodial development of a dichotomous system, on which it is
founded, is a general phenomenon of branching, neither restricted
to leaves, nor to the sporophyte generation. As to the other two, the
facts, whether of external form or of internal structure, seem to me to
indicate this conclusion, that the strobiloid condition was primitive
for certain types, such as the equisetales, lycopodiales, and spheno-
phyllales, that in them the leaf was from the first a minor appendage
upon the dominating axis, and anatomically they have never broken
away from the cladosiphonic structure, which is the internal expres-
sion of their microphyllous, strobiloid state. That the filicales and
also the ophioglossales were probably derived from a microphyllous
strobiloid ancestry, and achieved the phyllosiphonic structure as a
consequence of leaf-enlargement, this being the derivative rather
than the primitive condition; its derivation is even illustrated in the
individual life of some ferns. From the filicales the phyllosiphonic
structure was probably handed on to the seed-plants, and by them
retained, notwithstanding the subsequent leaf-reduction which
followed on their adaptation to an exposed land-habitat. Thus a
strobiloid origin may be attributed to all the main types of vascular
plants; it seems to me to harmonize more readily with the facts
than any phytonic theory does.

A prototype, which was probably a prevalent, though perhaps not
a general one for the pteridophytes, may then be sketched as an
upright, radial, strobiloid structure, consisting of a predominant
axis, bearing relatively small and simple appendages. On our theory
the origin of those appendages in descent would be the same as it
is to-day in the individual development: viz., by the outgrowth of
regions of the superficial tissue of the axis to form them: the axis
would preexist in descent, as it actually does in the normal, develop-
ing shoot. The origin of these appendages may have occurred inde-
pendently along divers lines of descent, and the appendages would
in that case be not homogenous in the strict sense. Thus there would
be no common prototype of the leaf, no morphological abstraction,
or archetypic form of that part. More than one category of append-
ages might even be produced on the same individual shoot, differing
in their function on their first appearance: such has perhaps been
the ease in the calamarian strobilus, where the leaf-tooth cannot
be readily homologized with the sporangiophore. These suggestions
will suffice to indicate how elastic a strobiloid theory is, and how
its application will cover various types of construction, and even
such as are shown by the most complex cones of pteridophytes.

From the comparison of living species there is good reason for

PLANT MORPHOLOGY 75

thinking that all the primitive leaves in certain types, such as the
lycopods, were sporophylls, and that a subsequent differentiation
took place, by abortion of the sporangia: thus a sterile vegetative
region became defined from a fertile upper region. It may be a
question whether this origin by sterilization of sporophylls is appli-
cable to foliage leaves at large: nevertheless analogy, not only with
other vascular plants, but also with the bryophytes, suggests that
a similar differentiation of a sterile from a fertile region has been a
general phenomenon in the neutral generation. At first in the simpler
pteridophytes these regions were essentially similar to one another
in form, as is still seen to be the case in some lycopods. Later,
however, the sterile and fertile regions took divergent lines of de-
velopment in accordance with their difference of function. The
differentiation reaches its climax in the higher flowering plants.
The inflorescence, or flower, on this view, though produced later than
the vegetative region in the individual life, embodies the more
primitive parts, viz., those which bear the sporangia and spores;
the vegetative region is in its origin mostly, if not wholly, secondary.
The physiological reasonableness of this view is too obvious to need
insistence. As the self-nutritive powers of the gametophyte fell off
in the adaptation to the land-habit, the nutritive function was taken
up by the new vegetative system thus intercalated between sexual
fusion and spore-production.

This is in brief outline the strobiloid theory of the shoot in vas-
cular plants, as arising out of the facts of antithetic alternation.
It will be seen that it is essentially in harmony with the view of
Braun, upheld also by Sachs, that the shoot is the real morphological
unit, of which leaf and axis are correlative parts. Those who adopt
it will find their position simplified in regard to another question
which has recently taken afresh a prominent place in morphological
discussions, viz., the theory of cortication (Berindungstheorie). It
is held by Potonie", and a similar view was also maintained by
Celakovsky, that the stem has centrally an axial nature, peripherally
a leaf-nature. The primitive axis (Urcaulom) acquires in the course
of generations, by coalescence with the basal parts of its primitive
leafy appendages (Urbldtter), a mantle, — a "Pericaulom." This is
what we commonly designate the cortex, which is thus regarded
as not being axile in origin, but foliar. In accordance, however,
with our strobiloid theory, we may presume that, as is seen in some
of the bryophytes, the simple sporophyte consisted originally of a
central region, — a primitive stele, — and a peripheral region, a
primitive cortex. From the latter sprang the appendages, as super-
ficial outgrowths, just as at the present day the leaves originate
upon the cortex of the axis. The cortex in such cases would be, from
the first, part of the primitive axis, and the outgrowths processes

76 PLANT MORPHOLOGY

from it. The primitive cortex from which the appendages sprang
may remain a continuous, undifferentiated band, as it actually
does appear in the vast majority of leafy sporophytes; or it may
in certain cases be more or less clearly marked off into regions sur-
rounding the insertion of the individual leaves. But in the fact that
these special cases exist I see no sufficient foundation for the view
that each leaf is, in shoots at large, connected with a definite area of
extended leaf-base: and still less for the theory that in vascular
plants the cortex originated from such coalescent leaf-bases. Our
theory of the strobilus would indeed presuppose that close relation
of cortex and appendage, and absence of limit between them, which
is so common a feature in vascular plants: and furthermore, it will
readily cover the facts where the cortex is delimited into definite
areas round the leaf-bases: but it does not recognize any necessity
for generalizing from such cases of special delimitation, that the
cortex is foliar in its origin, in shoots of vascular plants at large.
It would be more ready to suggest the converse, viz., that the leaves
were cortical in their origin, as indeed they are in the ontogeny.

Discussions such as these on phytonic theory, or theory of corti-
cation, are liable to develop into mere scholastic contests. They
originated in the present case in the use of terms in an unprecise
sense, and the subsequent attempt to attain precision. Both these
theories have proceeded from the assumption that the "leaf" is
an abstract entity, distinct from the stem. Difficulties arise when
the attempt is made to carry out that distinction sharply in practice,
for this is nothing less than the attempt to define precisely things
which in point of fact appear neither uniform nor precise in nature.
The strict definition of terms used in morphological science is doubt-
less in itself a desirable thing; but it must be so conducted as to
harmonize with the facts of individual development, while at the
same time it must not violate evolutionary probability. As a matter
of fact, neither in the mature state, nor in the ontogenetic or phy-
logenetic development of the leaf, does the structure suggest its
sharp delimitation from the axis as a general feature in the shoots
of ordinary vascular plants.

My present position with regard to the phytonic theories and
the theory of cortication is frankly destructive: for, in the first
place, if the evidence from the gametophyte generation be discounted,
the facts of segmentation in the sporophyte are of the slenderest:
further, I do not think that morphological insight will be advanced
by attempts to define precisely the limits of the parts of the vascu-
lar shoot; it seems more in accordance with nature to accept for
vascular plants the view of Braun and of Sachs, that the shoot is
the original unit. What is first urgently required, in order to decide
such questions, is the correct recognition of the phyletic lines which

PLANT MORPHOLOGY 77

eventuated in the various appendages as we see them. Then may
follow definitions of the parts, which may or may not succeed in
assigning their strict limits. When this is accomplished, a termin-
ology may follow, which shall segregate parts which have had a
separate phyletic origin. Thus an evolutionary morphology of the
shoot would be built up. But it is useless to accept the thesis merely
in the abstract, that the basis of morphology must be in phylogeny:
the principle must also be put in practice, and be ultimately re-
flected in our methods, and in the definitions of our terms.

A step in this direction will be the recognition that at present
the word "leaf" is loosely applied: it is, indeed, a temporary make-
shift borrowed from colloquial language, and used in a descriptive
rather than in a strictly scientific sense. It designates collectively
objects which have, it is true, formal and functional, and even
topographical features in common, but have not had the same
phyletic history. There is every probability that the word "leaf"
will continue to be used in this merely popular sense.

This position, with its conservative use of terms fitting awkwardly
upon advancing phyletic ideas, can only be properly understood by
glancing back at the history which has produced it. So long as
species were regarded as the individual results of creative power,
the complexity and variety of their form was relegated to the arcana
of the Divine Mind, and organic nature presented the aspect of a
series of isolated pictures; any similarity which these might show
was to be regarded as indicative of the underlying divine plan. Now
that species have been threaded together by evolutionary theory
into developmental sequences, they, like the ribbon of a cynemeto-
graph, present phyletic history to the mind with all the vividness of a
living drama. While monophyletic views held the field, this seemed
comparatively simple: .but the conclusions thus arrived at in plant
morphology were often palpably improbable. Such difficulties,
together with the substantiation of examples of parallel develop-
ment on a sound comparative basis, led to the modification of mono-
phyletic views, and opened the way for less cramped conceptions.
It is now customary to contemplate the plural origin of such leading
features as sexual differentiation, foliar development, heterospory,
the seed-habit, as well as a host of minor characters. On such ex-
amples we base a general belief that similar structures may be ar-
rived at by divers evolutionary routes. It is this conception of
polyphyleticism that we must make clear in our descriptions, if not
even in our terminology.

It will be objected that to carry through a method of designating
by the same term only such parts as are shown to be of common
descent would produce unwieldy results. Doubtless this is true.
But in the terminology of a science it is not so much convenience as

78 PLANT MORPHOLOGY

truth and clearness which should be the aim. The choice is open
to us either to make the terminology strictly phyletic throughout,
which would certainly be cumbrous, though it would reflect the
true position; or, putting phyletic distinctions in the background,
to use terms in a more or less comprehensive sense, even grouping
together things which we know to have been distinct in phyletic
origin. Such a comprehensive sense is conveyed by the expression
"homology of organization," which, as Goebel points out, "has
only to do with phylogeny in so far as it recognizes a common ca-
pacity for development derivable from undifferentiated ancestors"
(Organographie, Eng. ed., p. 19). This is indeed a collective
term for the results of parallel development; it suffers from the
danger of suggesting some ideal type or pattern towards which
evolution has tended.

For my own part I think it matters little what our terminology
be, or what the separation of categories of parts, provided we attach
clear meanings to the words we use, and select those words as natu-
rally conveying those meanings. For instance, if we fully realize
that the word "leaf" is used in a sense which is not phylogenetic,
but merely descriptive of those lateral appendages on the shoot
which are produced exogenously, and in acropetal order, then let
it remain, ranking as an expression of "homology of organization."
But the appendages thus included may for clearness be conveniently
divided into "phyllomes" on the sporophyte, and "phylloids" on
the gametophyte, as, indeed, I suggested some years ago. Never-
theless, these again are not phyletic unities: they include parts
with distinct histories, which have already been recognized in the
gametophyte, while for the sporophyte a more advanced state of
the science will probably provide definitions. Meanwhile we consent
to a compromise in grouping these together: but the only condition
upon which this can be safely done is the clear knowledge that this
is a compromise by which we secure a certain convenience of de-
scription. Moreover, the acceptance of this compromise must not
be understood to grant free license to argue from one to another of
the forms included, as though they were equivalents: what has re-
sulted in one line of descent can at best only throw a side-light on
what has happened in another distinct line: and in proportion as the
lines involved in a comparison are more remote from one another,
their comparison assumes more and more the character of a mere
analogy. The danger which our compromise brings with it is that
this will not be clearly kept in mind. At all hazards the strict phy-
letic view should underlie all present morphological discussion,
notwithstanding that, for mere convenience, that view may not be
clearly reflected in the classification of the parts. This makes me
hope that the compromise is only a temporary concession, and that

PLANT MORPHOLOGY 79

it will give way ultimately to the demands which a more detailed
knowledge of descent is sure to bring.

It is well, however, in connection with discussions such as these,
to impress upon the lay public that all evolutionary theories are, like
other scientific theories, hypotheses incapable of complete proof.
No one will appreciate this more fully than biological investigators
themselves, for they are in the best position to know how insufficient
the evidence actually is, and how liberal a use has to be made of the
imagination in bridging over the wide gaps in the series of known
forms. The details of a story thus constructed depend so largely on
comparative opinion, and in so slight a degree on positive demon-
stration, that the history as told by competent experts in compara-
tive morphology may vary in material features. A little more weight
allowed for certain observed details, or a little less for others, will be
sufficient to disturb the balance of the evidence derived from a wide
area of fact, and consequently to distort the historical picture. There
is in truth no finality in discussions on the genesis and progress of
organic life, or in the kaleidoscopic changes of opinion, since any new
fact of importance will in some degree affect the weight accorded to
others, and may vary the general result. It will be objected that
conclusions which are so plastic are little better than expressions
of personal taste, that the study of comparative morphology is there-
fore calculated to dishearten its votaries, while the non-specialist
public, which is compelled to take its information at second hand,
will be bewildered, and will conclude that it is useless to pursue a
subject which shows so little stability. But on the other hand, those
who follow the progress of morphology with sympathetic care will
take heart when they compare its present position with that of a
generation ago; it is encouraging to think that it is little more than
half a century since the history of the life-cycle of a fern was first
completed. In some sixty years a vast array of kindred facts have
been acquired, and a theoretic structure is being raised upon them,
which, though still protean, is gradually acquiring some settled form.
Never has the advance of morphological thought been more rapid
than at present. The support of the facts of alternation from the
unexpected quarter of minute cytology has been one of the most
striking features in the recent history of our science. The discovery
of spermatozoids in the cycads and Ginkgoacece has filled in a gap
in the story of evolution, which all followers of Hofmeister must
have felt. But in no field of morphological research has investigation
been more amply rewarded than in palseophytology. The luminous
facts derived from fossils are shedding fresh light on obscure prob-
lems, such as the origin of the seed-habit, and helping us to locate
such difficult groups as the Psilotacece and Equisetacece. When we
regard these rapid advances, and truly estimate the influence they

80 PLANT MORPHOLOGY

bring to bear upon morphological theory, we must surely congratu-
late ourselves on being devotees to a science which is very actively
alive.

But at the same time the detached cynic may find in the methods
of plant-morphologists, or still more sometimes in their want of
method, food for much critical remark. And if he put his finger upon
one mental process which more than another has introduced discord,
it would, I think, be "assumption." It may be that our science is
not worse than others in this respect, but I am very sure that argu-
ments based upon ill-founded assumption have put back the progress
of morphology more than anything else in our discussions. Any one
can find examples for himself in the literature : some of us in our own
writings. It remains for us who tread the difficult path of morpho-
logical theory to beware lest we neglect those warnings with which
its course is so plentifully strewn, for it is just as much the duty of a
scientific man to avoid blurring the issues for others by faulty argu-
ment, as it is to attempt to make clear to them what he himself be-
lieves to have been obscure.

THE FUNDAMENTAL PROBLEMS OF PRESENT-DAY PLANT

MORPHOLOGY 1

BY KARL F. GOEBEL
(Translated from the German by Professor Francis E. Lloyd, Columbia University)

[Karl F. Goebel, Professor of Botany, University of Munich, since 1891; Con-
servator of Botanical Gardens and of the Institute of Vegetable Physiology.
b. Belligheim, May 8, 1855. D.S. Strassburg, 1877; Assistant to Julius Sachs,
1878-81; Privat-docent, Wiirzburg and Leipzig, 1880-81; Special Professor,
Strassburg and Rostock, 1881-82; Regular Professor, Rostock and Munich,
1883-87. Member of the Royal Academy of Science, Munich; Royal Associa-
tion of Sciences, Gottingen; Linnean Society, London; Edinburgh Botanical
Society; and numerous other scientific and learned societies. Author of Char-
acteristic Features of Systematic and Special Plant Morphology; Comparative
Study of the Laws of Development of Plant Organs; Descriptions of Plant Biology;
Organography of Plants.]

A FEW months ago I was in Jena in order to attend the unveiling
of the statue there erected to M. Schleiden. Now there is hardly
any other place which has been of so much significance in the develop-
ment of plant morphology as this small university town. It was there
that Goethe, the originator of the term " morphology," busied him-
self with morphological studies, and founded the idealistic system
which has influenced our thought — often unsuspectedly — till the
present day. There Schleiden, in outspoken opposition to the con-
ceptions of the idealistic morphology, gave new life to the theory of
development founded by Caspar Frederick Wolff in the neighboring
town of Halle in the middle of the eighteenth century, and so paved
the way for the brilliant discoveries of William Hofmeister. And
who does not know what meaning Jena has won as the citadel of
phylogenetic morphology, first through the work of Haeckel in
zoology and later through that of Strasburger in botany? In such a
morphological atmosphere the question forces itself upon us, in what
relation do the morphological questions of the present stand to those
of the past? Are they still unchanged in spite of the immense increase
of empirical material, and have the methods of their solution only
changed? Or have the problems themselves become different?

To reply to this question is not easy, and the answer must vary
with the point of view of the one who makes it. For morphology is
yet far from being an exact science, the results of which force them-
selves upon us with the compulsion of necessity. This is due to the
difficulty of the materials, a difficulty which compels us to seek for
hypotheses and other subjective means of explanation. It thus comes

1 The views set forth in this lecture are presented at length in the author's
Organography of Plants, Jena, 1898-1901, English translation, Oxford, i, 1900;
n, 1905. Concerning the historical significance of Goethe, Schleiden, Hofmeister,
compare Sachs' History of Botany, translation, Oxford, 1890.

82 PLANT MORPHOLOGY

about that views not only concerning the goal of morphology, but
also as to the way in which this goal is to be reached, are widely
diverse, and my own views concerning the fundamental problems of
morphology are certainly far from being approved by all morpholo-
gists.

We may, indeed, say that, apart from minor differences, there are
in morphology two main trends of thought which, apparently, at
least, are opposed to each other, one of which we may denominate
formal, and the other causal. Causal morphology is that the aim of
which is to determine the causes, in the widest sense, of form-rela-
tions; this kind of morphology is the youngest, and is far less widely
diffused than the formal. To us of a later period it may seem like a
remarkable pleonasm to speak of a "formal morphology." Mor-
phology is, of course, the doctrine of form, and therefore any mor-
phology appears to be, in the nature of the case, a formal one, and,
as a matter of fact, has been, in its historical development. But in
spite of this fact, this definition is historically justified, for it desig-
nates the tendency of morphology which regards form as something
which stands alone for itself, and takes cognizance neither of the
functions of organs nor of how they have arisen. This formal morpho-
logy arose at first out of the necessities of taxonomy.1 There had first
to be contrived a terminology for the distinction and description of
single plant forms. From this function morphology soon, however,
became distinct, thus constituting an independent discipline which,
on its part, had done taxonomy a more important service than one
might have at first expected. For while taxonomy, in order to find
its way amid the maze of plant forms, had to keep in view the differ-
ential characters and the separation of single forms from each other,
morphology found itself under the necessity of determining what was
common to the most various forms, and was accordingly directed
toward more general questions; morphology taught, as Goethe ex-
pressed it, " Die Glieder der Pflanzen im Zusammenhange zu betrach-
ten, und so das Ganze in der Anschauung gewdssermassen zu be-
herrschen." It resulted in the knowledge that, when we regard plants
singly, manifold as their parts appear, they may yet be referred to
a few elementary forms, and further, morphological research showed
that the parallelism between different plant forms could be under-
stood most easily under the assumption which we designate the
theory of descent. The establishment of the theory of descent was
the result of the morphological research. This we must here especially
emphasize, for it shows what significance morphology has gained
in respect to our general conception of organisms. But the theory

1 How far the trends of morphology and taxonomy have of recent years drawn
apart is shown, e. g., in Engler's Syllabus of the Families of Plants, the most recent
review of the plant kingdom as a whole. For the most part, the results of develop-
mental researcli remain entirely disregarded in this work.

PROBLEMS OF PLANT MORPHOLOGY 83

of descent has also reacted upon morphological research, to such an
extent, indeed, that it has been held that phylogenetic research is
to be regarded as the sole business of morphology. Thus, for ex-
ample, Scott has said:

"The object of modern morphological botany is the accurate
comparison of plants, both living and extinct, with the object of tra-
cing their real relationships with one another, and thus of ultimately
constructing a genealogical tree of the vegetable kingdom. The prob-
lem is thus a purely historical one, and is perfectly distinct from any
of the questions with which physiology has to do. " *

This position is certainly justified from the standpoint of the pale-
ontologist. For him, for whom nothing but dead material is at hand,
there remains nothing else to do than to make known, through careful
comparative study, the structure and relationships of those organ-
isms whose remains are available. This is a very important business.
The beautiful results of phytopaleontological research, such as have
been attained during the last decade in England and France, have
very materially furthered our knowledge of plant forms, and have
made to live again before our e}7es, in a most surprising manner, and
in the finest details of their structure, types long since vanished from
the surface of the earth.

But does this limitation of morphology to the comparative phylo-
genetic method which is imposed upon the paleontologist exist also
for the morphological study of living plants?

There are many of the opinion of Scott; and, indeed, a special
" phylogenetic method," which is said to be a characteristic of modern
morphology, has even been talked of.2

Were this the case, then the only difference between the morpho-
logy of the present and the earlier, idealistic morphology would consist
in this, that in the place of the general ideas with which this operates,
as, e. g., " type " " plan of organization," etc., there would be found
phylogenetic conceptions. Such general abstractions are, however,

1 Address to the botanical section, British Association for the Advancement of
Science, Liverpool, 1896.

2 Cf. Haeckel, Generate Morphologic, I, p. 50; Strasburger, Ueber die Bedeutung
phylogenetischer Methoden fur die Erforschung lebender Wesen, Jena, 1874; also
the criticism, pertinent according to my opinion, which Al. Braun made concerning
the setting forth of the phylogenetic method, in his treatise, Die Frage nach der
Gymnospermie der Cycadeen (Monatsber. der Berliner Akad., 1875). Al. Braun
rightly maintained that the theory of descent did not offer a new method, but was
really the result of earlier methods, and that the results of paleontology are far
too fragmentary for the construction of a phylogenetic tree of the organic king-
dom. This is yet true, thirty years' later, after we have attained a much more
exact knowledge of the organization of fossil plants through the important work
of Williamson, Scott, Oliver, Renault, and others. We have found, e. g. that the
group of cycadofilices possessed seeds. It has, however, not become possible to
derive a group of living plants from the cycadofilices directly. It has become
highly probable that these have sprung from fern-like ancestors; but from what
form it remains at this time entirely unknown. Concerning fossil plants see the
work of Scott, Studies in Fossil Botany.

84 PLANT MORPHOLOGY

even now difficult to escape, since we can set forth real descent-series
only in the fewest instances, and, accordingly, we cannot actually
point out the stem-forms. Yet Darwin himself said:

" We have seen that the members of the same class, independently
of their habits of life, resemble each other in the general plan of their
organization. This resemblance is often expressed by the term ' unity
of type; ' or by saying that the several parts and organs in the differ-
ent species of the class are homologous. The whole subject is included
under the general term of Morphology. This is one of the most inter-
esting departments of natural history, and may almost be said to be
its very soul." 1

The significance of formal morphology cannot be more forcibly
expressed than it was by Darwin. And yet we see that, in Germany
at least, interest in morphological problems has greatly decreased.
Morphological treatises have become relatively less numerous;
morphological books, even such excellent ones as, e. g., Eichler's
Bluthen-diagramme, do not pass through a second edition, while
anatomical and physiological works appear repeatedly in new edi-
tions; evidently meeting the demands of the botanical public more
fully than morphological works.2 This may be referred to reasons
which lie partly without and partly within morphology itself; .both
turn out to be true. Histology, cytology, and experimental physiology
have developed remarkably; new methods in this field promise new
results; particular lines of work, however, such as descriptive
anatomy, are especially favored because the perfection of the methods
of research have quite materially lightened the task of working
through a vast array of materials, especially for those to whom the
other fields of botanical study are more or less unfamiliar.

But the reasons for the phenomena which lie within the field of
morphology are also clear. Some parts of morphology are well worked
out, as, e. r/.,the doctrine of the more obvious f orm-relations of plants;
and the homologies, at least in the large, are determined, although
in the matter of detail much remains vague, and offers a wide field
for exhaustive studies in development. More and more, however,
these studies bear the stamp of repetition and complement, from
which the stimulus of newness is wanting, or they are carried on
upon materials which are very difficult to obtain. The constructions
of the idealistic morphology, however, often proved to be untenable.

But the first experiments towards a causal morphology brought
disillusion. For only a short time lived the hope of being able to

1 Origin of Species, ir, 142.

2 As Eichler wrote me shortly before his death, he would have boon glad to pub-
lish a second edition of his work in order to bring to light the numerous thitherto
unpublished observations of Al. Braun. The publishers demurred, however, on the
ground that there still remained unsold a large number of copies of the first edi-
tion. Since then the book has, it seems, gone out of print. Nor to my knowledge
has any other morphological work passed through a second edition.

PROBLEMS OF PLANT MORPHOLOGY 85

answer, e. g., the question as to the arrangement of leaves through
the effect of mechanical factors, or to refer the form-relations of a
plant to the direct influences of gravity and light on the plant. It
soon became evident, however, that such involved problems are not
to be unraveled by such simple means, and this may well have re-
sulted in the suppression of interest in morphology.

At this point phylogenetic morphology appeared to take on a new
lease of life. This, however, in natural science is connected, on the one
hand, with the appearance of a new, creative idea, and, on the other
hand, with the discovery of new methods. Now the theory of descent
has powerfully stimulated morphological research. But has it
brought to it, as, e. g., Strasburger has held, a new method, the phy-
logenetic? Alexander Braun has already properly answered this
question in the negative.

Scott, also, has maintained that historical morphology (as regards
both living and fossil plants) is dependent upon comparative study,
that is, makes use of the same method as was in evidence before the
appearance of the theory of descent; indeed, the most important
homologies in the plant kingdom became known through Hofmeister
at a time when the idea of descent was far from that general accepta-
tion which it at first gained through the life-work of Darwin.

The method has then from first to last remained the same: the
most comprehensive comparison not only of mature forms, but
also their development. A special " phylogenetic method" there is
not, but only a phylogenetic conception of morphological problems.
These are, however, just as at first was the case with idealistic
morphology, purely formal. Modern morphology in my sense, how-
ever, differs from the older in this, that it goes beyond the method
of mere comparison. It allows the setting up of genetic trees to
rest for the while, since, with our present knowledge, this meets
with insuperable difficulties, and has brought almost as much disap-
pointment as the idealistic morphology. For just this reason, namely,
because we are persuaded that no other forces have been at work
during the phylogenetic history than those which now control the
development of each particular organism, do we wish, first of all,
more exactly to learn what these are. We are concerned not alone
with the determination of the single successive stages of devel-
opment. These must, of course, be followed, but in addition we
should follow all phenomena which may be got at by our means of
observation, whether directly, by the microscope, or by chemical
anatysis. We may, therefore, say: The basal problem of the pre-
sent-day morphology is not phylogenetic development, but devel-
opment in general. We must, therefore, take our departure from
the investigation of individual development (of ontogeny), for only
this lies before us complete and without any break, and further,

86 PLANT MORPHOLOGY

because the study of ontogeny only may proceed from the experi-
mental point of view. An understanding of development is possible
only when the conclusions to which the observation of the phe-
nomena of development has led us, rest upon experimental proof;
in other words, when we ask questions of nature, and obtain our
answers to them.

Every little step — and with such only are we now concerned -
beyond the mere descriptive consideration of development is here
of significance, and brings the possibility of further progress. And
small indeed, I may add, appears to be such advance to those who
from the beginnings of phylogenetic morphology have, like Sisy-
phus, sustained their courage to roll again and again up the moun-
tain the rock of phylogeny as often as it has rolled down.

It may now be attempted to examine somewhat more closely
in certain particular examples the relation between phylogenetic
and causal morphology. One of the changes which phylogenetic
morphology has brought with it is that it seeks to ascertain which
form is "primitive" and which derived.1 Idealistic morphology
has borne in upon us no conviction on this question, since it derives
all forms from a type which is present only as a conception. But
phylogenetic morphology must, on the one hand, always reckon
with the possibility of polyphyletic development, and, on the other
hand, it can operate not only with reversionary structures, as did the
idealistic morphology, but must be far more concerned in deter-
mining which forms within the series which it proposes stand near-

1 I do not. of course, deny that there are forms which we may designate primi-
tive. What, however, is insisted upon in the above text is as follows:

(1) The different meanings of the word "primitive." It can mean either

(a) A form which stands nearer to the stem form than any other. In this
sense we may designate the Gymnospermcc, e. g., as more primitive
than the Angiospermce, because it may be admitted that all seed-plants
are derived from heterosporous Archegoniatce, while it is the Gymno-
spermcB which maintain this character most evidently.

(fe) "Primitive" is also used often in the sense of "phylogenetically older."
At this point, however, we come into the field of hypothesis, for the
paleontological facts are far too few to afford us a picture of chronologi-
cal series of plant groups. It is known that there are several parallel
developmental series (e. g., the appearance of heterospory in different
groups of Pteridophyta) . Forms which appear primitive may, then, in
reality constitute the end of a very long series, younger perhaps than
one which does not appear to be primitive and is derived from other
stem-forms, with which then it is not genetically related. It is, e. g., very
easily conceivable, though at present incapable of proof, that hetero-
spory, in so far as it is older than isospory, arose at first from spores of
sexual cells (male and female swarm spores), and that from this point
on the development of the spores took on a more or less marked vegeta-
tive character. Were this the case, then the isosporous Pteridophyta
would be phylogenetically younger than the heterosporous, and the Bry-
ophyta would be a parallel development to the Pteridophi/ta. This is, ito
be sure, only a possibility which one may at first regard as fantastic,
which, however, is no more so than many other conceptions which have
been put forth at one time or another.

(2) The difficulty of distinguishing with certainty between primitive and re-

duced forms.

PROBLEMS OF PLANT MORPHOLOGY 87

est the common point of derivation. It seeks, then, with diligence
after "primitive" forms. But in this search we meet with great
difficulties. In the first place, we are inclined to regard those
forms as primitive which have simple form-relations, and unmarked
division of labor. But such forms may also have arisen by reversion,
and if one looks over botanical literature, he sees, at least so far as
the relationships between the larger groups are concerned, there ex-
ists no agreement as to which forms are to be regarded as primi-
tive and which derived; opinion on this point often changes with
the fashion. Thus the thallose liverworts have up till now been
regarded as more primitive than the foliose, because the vegeta-
tive body of the former is much more simple in construction than
that of the latter, and between them there are found gentle grada-
tions. Recently, however, the attempt has been made to derive
the thallose from the foliose forms.1 This is not the place to exam-
ine the evidence for or against such derivation. How vacillating is
the point of view from which it is judged what form is primitive is
shown by the various positions which have from time to time been
given to the apetalous dicotyledons.

The old morphology regarded these as reduced forms because their
flowers are less fully differentiated than those of most of the other
dicotyledons. Eichler has, however, already shown that there is no
ground for maintaining that the corolla in the luliflorce and
Centrospermce has suffered reduction; and on this point we can
only agree with him. But must they, because the perianth shows
simply form-relations and also because the number-relations within
the flower are not always constant, be therefore primitive? Even if
we admit that these groups have a great geological age, it is not
proved that they stand as regards their total organization on a
lower plane of development; old and primitive forms are the same
only when it can be shown that the former stand nearer to the
stem forms of the angiosperms than other forms. If this is not
capable of proof, then the old forms may just as well be the end
terms of long developmental series as others, only that the differentia-
tion of organs has not taken place to the same degree as in the others.
Now, we do not know the stem forms of the angiosperms, and they
may never, perhaps, be known. But even if we content ourselves
by reconstructing them on the basis of comparative study, I can
find no reason, e. g., to regard the Cupuliferce as primitive forms,
while I can find many reasons for not doing so. Here may be cited

1 Wettstein, Handbuch der Systematischen Botanik, n, p. 26, 42. It is certainly
suggestive to regard the development of organs from various points of view. I can-
not, however, regard the attempt of Wettstein as wholly well-founded. It is quite
true that among the liverworts, a thallus may arise at times from a leafy stem. I
have shown this for Pteropsiella (Cephalozia) frondiformis Spr. (Goebel, Rudimen-
tare Lebcrmoose, Flora, 1893, p. 84). But the grounds for regarding this true in
general for the thallose liverworts appear to me not to be at hand.

88 PLANT MORPHOLOGY

chalazogamy, which elsewhere occurs in forms which may be re-
garded as degenerate; the facts that only a few of the ovules develop
further; that at the time of anthesis they are in many forms not
yet present; and finally the dicliny of the flowers. There has been
much contention over the question whether the androgynous flowers
of these forms are to be admitted to be the original form or not.
Let us look at, e. g., the Cupuliferce. Most of the forms have dicli-
nous flowers. In Castanea vesca, however, androgynous flowers
occur regularly: in the male flowers rudiments of the ovary, while
in the female flowers staminodia, are often evident. But we know
that for reduced organs all gradations occur from nearly complete
development to almost entire disappearance. From the formal
standpoint, then, the androgynous flowers may, with at least as
much justice, be regarded as primitive as the diclinous ones, which
more recently have been thus branded.1 Just this question is,
however, fitted to clear up the difference between pure phylogenetic
and causal morphology. The latter says: By the mere comparison
of forms morphological questions may not at all be decided. We
must first of all become more closely acquainted with the forms to
be compared, by seeking to determine the conditions under which,
in living plants, the configuration of parts is produced. Concerning
the flowers of the Cupuliferce the question then arises: is the occur-
rence of male and female flowers dependent upon different conditions,
and are these other than those under which androgynous flowers arise?
As a matter of fact, it may be determined that, e. g., in the oak, the
female flowers always occur in those parts of the twig which are
stronger, that is, better nourished, than those in which the male
flowers occur. This offers us, however, only a point of departure for
a more exhaustive research. When we know better the relation
between the formation of flowers and the total activity of the plant,
when we have the ability at will to cause it to produce male, female,
or androgynous flowers, when we further know how it is determined
that the oak usually brings to development only one out of six
ovules, and why the pollen tube follows a different path than the
usual, then may we further discuss the question whether the Cupu-
liferce are primitive or not — for then shall we have better grounds
for phylogenetic conclusions than we have at present, and we shall
then recognize with great probability the changes which have taken
place in these organs as phenomena resulting from changes in the
total organization of these plants.

1 It was chiefly the fact that among the Gymnospermce the flowers are typically
diclinous that led to the view that this condition is the primitive one for the lower
AngioKperma '. In making such comparisons, however, we should always start
from the group in question, and not from some other one. In a very great number
of cases dioliny is certainly not primitive in angiospermous flowers, so that it ap-
pears entirely probable that also in the remaining cases dicliny is to be derived from
raonocliny.

PROBLEMS OF PLANT MORPHOLOGY 89

So, as the matter now stands, we cannot deceive ourselves on this
point, that the constructions of the old morphology, although con-
fined almost entirely to vestigial series, nevertheless stood on firmer
ground than the modern speculations on the question of primitive
forms. Starting with a completely endowed form, we can follow
the reduction of form through intergradations, and, by reference
to vestigial organs, often with convincing certainty. But by what
means shall we judge a rudimentary organ? Is it more than a gratui-
tous assumption, when, as recently was the case, a certain botanist
declares the lodicules of grasses to be not a perigone, but a rudiment
of a perigone? * Whereby may one recognize a rudiment, i. e., the
attempt to form something new, an attempt which, however, has
remained nothing more? In what way may we distinguish such a
rudiment from a vestigial organ? And, finally, after one has broken
faith with the old vestigial series, is it not still more of the stamp of
formal morphology if he contents himself in arranging forms in series
and then comes to a standstill when he tries to decide at which end
stand the primitive and at which end the derived forms? At any
rate, such a limitation brings out the better the true condition of our
knowledge, for such an arrangement of forms in a series is about
the best service that formal morphology can do. This service is, to
be sure, no small one, for it enhances broad critical comparison,
and is, therefore, the result of hard work. But the desire to give
this arrangement in series a genetic bearing has oftentimes led us
to untenable propositions and explanations. Just as we have little
ground for assigning the Cupuliferce to a primitive position, so have
we as little evidence for regarding the Casuarince also in the same
light. The latter have been placed by a recent systematist at the
apex of his system, because there has been an inclination to find in
them a sort of "missing link" between angiosperms and gymno-
sperms.2 I may, perhaps, mention that I had regarded such a view

1 Engler, Die systematische Anordnung der monocotyledonen Angiospermen. (Ab-
handl. der K. Preuss. Akad. d. Wissensch. zu Berlin, p. 22.) The reasons advanced
by Engler for the view that the primitive flower of the Graminece was naked are
quite beside the mark, as, e. g., when he expresses the opinion that wind pollination
indicates that the types of the Graminece and Cyperacece are very old. Is, then,
the Plantago type very old, or Thalictrum "older" than the other Ranunculece?
We know that wind pollination has appeared in widely different groups of plants,
evidently in part as a reduction of flowers which were not wind-pollinated. A cor-
relation between the flowers and the glumae, or palese, puts Engler on the defense.
We see, however, very plainly in many grasses that leaf-organs which have become
superfluous as a result of their position, have become reduced. A similar process
may have taken place in the perigonal leaves, and the behavior of Streptochceta
strongly indicates this. (Cf. on this point Goebel, Ein Beitrag zur Morphologic der
Graser, Flora, 81. Bd. Erganzungsbd. z. Jahrg. 1895.) The seed and fruit characters
of the grasses also are anything but primitive.

2 Engler (Syllabus, Fourth Edition, 1904) has recently yet again placed the
Casuarince at the point of divergence of the Dicotyledonce, although the conten-
tion that in their macrospore before fertilization " a rudimentary prothallium,
consisting of twenty or more nuclei, arises" cannot be maintained by the earlier
researches of Treub, as I have pointed out (Organographie, p. 894). Frye (The

90 PLANT MORPHOLOGY

as incorrect, even before the evidence was adduced by an American
botanist (Frye) that Casuarina has evidently nothing which marks
it off from other angiosperms. Many of my fellow botanists have
been inclined to point out as a further example of the fruitlessness
of the search for primitive forms those bryophytes which have been
regarded by me as primitive; and I readily ' admit that here also
we cannot point out any conclusive evidence for their primitive posi-
tion, but only for a greater or less subjective probability. Numerous
other examples (as, e. g., the supposed primitive monocotyledons)
may be pointed out, which show that the phylogenetic morphology
has overrated the prospects of results in search for primitive forms,
stimulating as this has been.

This may be seen also if we notice the attitude of phylogenetic
morphology to the problem which the old morphology dubbed
with the not very fortunately chosen name of metamorphosis, and
which historically is that of homologies. Here, also, it may be
shown that the problems have remained the same, while only the
attempts to reach a solution have changed.

The idealistic morphology believes that all organs of the higher
plants may be traced back to caulome, phyllome, and trie home;
it conceived this process not as a real one, but was content with a
conceptual arrangement of different plant organs in these categories,
which were really nothing but abstractions.

That thereby the reproductive organs were left entirely out of
consideration — these were referred to modifications of vegetative
organs — is explained in part by the fact that they occur in the higher
plants less frequently as peculiar parts, and often completely dis-
appear in teratological growths, which are with predilection turned
to account in theoretical considerations; and in part because of the
view that for morphology the function of an organ is a matter of
indifference, and that accordingly in morphological considerations
it can have no significance whether an organ has developed as a
glandular hair, chaffy scale, or as an archegonium, so long as it has
developed out of the outer cell-layer of the plant body! This stand-
point, which is an obviously sterile one, needs no further special dis-
cussion. Let us, on the other hand, see how phylogenetic morphology
has come to terms with the problem of metamorphosis. As an ex-
ample, I select a passage from a prominent American work, in which
Coulter and Chamberlain express themselves concerning the leaf
structures of flowers as follows:

" While sepals and petals may be regarded as often leaves more or
less modified to serve as floral envelopes, and are not so different

Embri/o-sac of Casuarina stricta, Bot. Gaz. xxxvi, p. 104) shows that the embryo-
sac of Casuarina stricta behaves just as in the other Dicoti/lcdonoe. Of this paper,
however, Engler has taken no notice. The whole of Engler's presentation shows
how far the desire to find primitive forms may lead to untenable views.

PROBLEMS OF PLANT MORPHOLOGY 91

from leaves in structure and function as to deserve a separate mor-
phological category, the same claim cannot be made for stamens
and carpels. They are very ancient structures of uncertain origin,
for it is quite as likely that leaves are transformed sporophylls as
that sporophylls are transformed leaves. ... To call a stamen a
modified leaf is no more sound morphology than to call a sporangium
derived from a single superficial cell a modified trichome. The cases
of ' reversion ' cited are easily regarded as cases of replacement. Lat-
eral members frequently replace one another, but this does not mean
that one is a transformation of the other." 1

We see that in this verdict the emphasis is laid on the historical
development, but at the same time this is pointed out to be unknown
to us. With this latter conclusion I am in complete harmony, but
the accentuation of the historical-phylogenetic factor has, on the
other hand, led to a conception of the ontogenetic problem, in which
I can perceive no advance upon the old morphology; there is rather
avoidance of the problem than an attempt to solve it. This, however,
is connected with the purely formal conception, as the phylogenetic
morphology employs it. Let us examine the matter in question.
For a long time we have known that often in the room of the sta-
mens — to confine ourselves to these — flower leaves, or foliage
leaves, or occasionally even carpels, arise. The idealistic morphology
says that this proves that the stamens are "leaves," for these can
be modified the one into the other. Coulter and Chamberlain, how-
ever, deny that a stamen fundament may be transformed into a
flower leaf; they find only a "replacement" of one "lateral member"
by another. It should be remarked that "leaves" exist in nature
as little as "lateral members." Both notions are mere mental ab-
stractions, not the expression of the facts of observation. We speak
of the replacement of one organ by another if these have nothing
more in common than the place of origin. Thus we see that in the
foliose liverworts a branch often arises in the position of a leaf-lobe.2
No one has observed any intermediate form between these; the
lateral shoot in reality takes only the position of a leaf-lobe. The
relation between the stamens and the organs which "replace"
them is, however, quite different. We speak of a transformation
of an organ A into an organ B when B not only stands in the position
of A , but also corresponds with A in the earlier stages of its develop-
ment, and later strikes out on its own line of development. If this is
the case, we should expect to find between A and B intermediate
forms which are different according to the developmental stage at
which A is caused to develop further as B. To use an analogy:

1 Coulter and Chamberlain, Morphology of the Angiosperms, p. 22.

2 Goebel, Rudimentare Lebermoose, Flora, 1893, p. 84. Ueber die einfachste
Form der Moose, ibid. 76, 1892, p. 92.

92 PLANT MORPHOLOGY

Replacement and transformation behave as two fluids which are,
and two fluids which are not, miscible; in the first case the inner
structure is different, and in the second there is a correspondence.
The comparison is a limping one, but still gives us a fair illustra-
tion.

As a matter of fact, we do find every intermediate step between
stamens and flower leaves, and we cannot doubt that these have
come into existence because a stamen, or, in other words, a stamen
fundament, has at different stages of its development received a
stimulus which has caused it to develop into a flower leaf. We find
correspondingly, that the earlier developmental stages of a stamen
and a flower leaf are parallel throughout, while in the above-cited
example of the branch and a leaf-lobe of a Jungermanniaceous
liverwort their developmental histories are throughout different, as is
shown by the arrangement of cells. In the case of stamens, therefore,
there occurs not a replacement, but a transformation. And, indeed,
a limited one. Not any "lateral members" you please may arise
instead of stamens, but only and always those which we subsume
under the concept leaf, because they evidently have peculiarities in
common. Besides, there are also normal flowers which exhibit all
intergradations between flower leaves and stamens. The former
Coulter and Chamberlain would regard as leaves, the latter not;
where, however, is the line of separation between them?

From the limited power of transformation possessed by organs
it results that in causal morphology the problem is, then, not a phy-
logenetic, but an ontogenetic one. Whether sporophylls or foliage
leaves are the older phylogenetically may be disregarded. For it
appears more important first to determine why the power of trans-
formation is limited, why a shoot-thorn or a shoot-tendril may be
transformed only into a shoot, a stamen or a carpel only into a
"leaf;" and second, what conditions are determinative thereto.

The first step toward the solution of the problem is that we learn
to call out experimentally and at will such transformations as we
have heretofore occasionally observed as "abnormalities."

This has been successful in experimental morphology in a great
number of cases, and in the future will be still more so. To be sure,
we are still unable to induce the transformation of stamens into
flower leaves at will, — we only deceive ourselves when we believe
that the art of the plant-breeder has succeeded in doing this, for in
reality all he has done is to isolate such races which have occurred
in nature with more or less doubled flowers, — and in this regard we
stand in contrast to the fungi and insects, the activities of which,
as Peyritsch and others have shown, often — unconsciously of
course — call forth such transformations.1 Yet it has been possible
1 The literature is presented in Goebel, Organographie , part i, p. 165.

PROBLEMS OF PLANT MORPHOLOGY 93

to change scale leaves (cataphylls) and sporophylls into foliage
leaves, inflorescences into vegetative shoots, and, vice versa, plagio-
tropous into orthotropous shoots, hypogseous into epigaeous, not
to mention the interesting results which have been obtained by
Klebs l in his studies of the lower plants.

Let us take, for example, the just mentioned transformations
of scale leaves into foliage leaves and of sporophylls into sterile leaves.
Here developmental study and experiment immediately encroach
on each other. Development has shown that, e. g., the bud-
scales of many trees which in their definitive condition are very
different from the foliage leaves, yet parallel them developmentally
in an extraordinary degree; and that many bud-scales possess the
fundament of a leaf-blade wrhich has failed to develop and has thus
become vestigial.2 Similarly, the fundaments of the foliage leaf and
the sporophyll in Onoclea 3 are the same up to a quite late stage of
development, beyond which each follows its own course. These
facts gave occasion to the question whether or not it were possible
to influence the development at will, and so to cause a scale leaf or a
sporophyll to grow from a fundament which otherwise would develop
into a foliage leaf. It has been shown that such transformations may
be occasioned in a simple way, and the developmental correspondence
makes such a limited transformation without further difficulty cap-
able of being understood. And since seedlings produce, apart from
the cotyledons and certain adaptations in hypogseous germination,
only foliage leaves, which are arranged for the work of photosynthesis;
since further it is seen that all foliage leaves of one and the same
plant, different as they appear externally, yet in reality follow one
and the same course of development, which, as we have seen, is
remarked also in scale leaves and sporophylls, — 1 accordingly come
to the view that other leaf-organs are derived from foliage leaf funda-
ments through a change in the course of development occurring at
an earlier or later period of growth. This conception has found
many opponents, some of them for the reason that they have not
been able to free themselves from the purely historical conception
of the problem.

But the historical question cannot help us over the ontogenetic
problem, any more than the solution of the latter alone can answer
the historical question. Even if it were proved in all cases that sporo-
phylls, flower leaves, sepals, etc., are transformed foliage leaves,
it would remain undecided that these are phylogenetically older

1 Klebs, Die Bedingungen der Fortpflanzung bei niederen Algen und Pilzen, Jena,
1896. Further, Ueber willkiirliche Entwickelungsanderungen bei Pflanzen, Jena,
1903.

2 Goebel, Beitrage zur Morphologic und Physiologic des Blattes. Botan. Zeitung,
1880.

3 Goebel, Ueber kiinstliche Vergrunung der Sporophylle von Onoclea Struthiopte-
ris, Ber. der Deutschen Botan. Gesellschaft, v, 1887, p. Ixix.

94 PLANT MORPHOLOGY

than the former. This phylogenetic problem, however, is with our
present means and knowledge not subject to solution with certainty,
while the ontogenetic problem, on the contrary, is. Problems,
however, which may not be solved appear to me less important
than those which may.

To be sure, the solution of the ontogenetic problem is hedged
about with great difficulties. For the results which have already
accrued, valuable as they may be, take their importance from the
fact that they lay the foundation for the future work: what changes
take place during transformation, and upon what outer and inner
conditions are they dependent? We may not comfort ourselves
nowadays as at one time Goethe could with the view that flowers
differ from the vegetative shoot in a refinement of the sap; rather
would we know what change of the materials, and what other
changes, are connected with the order of successive developmental
stages of the flower. This, to us as good as unacquired knowledge,
should give us a more penetrating glance into the nature of develop-
ment than we have as yet had. To just this purpose plants are
especially well adapted, for experience has shown us that the de-
velopment of a plant is not produced as is the melody in a music
box, in a definite order, so long as the outer source of power is present
to start it; for the experiments of the last few years indicate rather
"that the form-relations of chlorophyll-bearing plants are not pre-
determined in the germ cell, but in the course of development." 1 As
a result we can not only arrest development at any particular stage,
but we can also cause fundaments to unfold which were previously
"latent." Historical morphology has contented itself as regards
the unfolding of latent fundaments also with an historical explana-
tion of the facts. The observation, e. g., that instead of the seed
scale of the Abictineaz under certain circumstances an axillary
shoot appears, has been used by prominent botanists to support the
conclusion that the seed scale has arisen phylogenetically from a
shoot. Such an hypothesis would get beyond the rank of pure sup-
position if a living or fossil form certainly related to the Abietinece
could be pointed out, the cones of which bear in the axils of the cover
scales shoots possessed of macrosporophylls. As long as such proof
is not forthcoming, we stand opposed to a phylogenetic explanation
of this observation, " kilhl bis ans Herz hinan." We seek rather to
establish the conditions under which the fundaments, which other-
wise become seed scales, develop into shoots, and hold before us
therewith the possibility that the forbears of the Abietinece could have
borne their ovules upon an axillary outgrowth of the cover scales,
which, indeed, possessed the ability under certain circumstances
which disturbed the normal development to form shoots, but which
1 Goebel, Flora, 1895, p. 115.

PROBLEMS OF PLANT MORPHOLOGY 95

phylogenetically does not need to have been at any time an axillary
shoot.

The question of the significance of metamorphosis leads us into
another field of morphology. The above-cited examples show that
the transformation of organs always goes on hand in hand with a
change of function. This gives us the occasion to take up a further
problem of modern morphology: the relation between form and
function. The old morphology believed that it should keep away
from this question, because it held that the function of an organ had
nothing to do with its "morphological meaning." Just recently we
have heard that morphology has to do with "members" and not
with the "organs" of a plant. The fact that "members" and "or-
gans" mean one and the same thing, and that for the organism their
members are organs, or tools, shows that here again is a purely arti-
ficial and therefore untenable abstraction. Morphology stiffens to a
dead schematism when it does not take the plant for what it really
is, — a living body the functions of which are carried on in intimate
relation to the outside world. It was the powerful influence of Dar-
winism that turned more attention again to the function of single
plant organs, for, according to one view, which has many adherents,
all form-relations arise through adaptation. D. H. Scott has given
clear expression to this view in the sentence, "All the characters
which the morphologist has to compare are, or have been, adaptive."

This is a widely disseminated conception, but is by no means
as widely accepted. Above all, it must be pointed out that it is not
the result of observation, but is a theory, which enjoys by no means
general acquiescence. True, the conclusion drawn depends upon
the meaning given to the word "adaptive." But, take it as you will,
in the Lamarckian or in the Darwinian sense, in reviewing the
phenomena of adaptation we come face to face with the problem:
are the form-characters fixed adaptational characters solely, or have
we to distinguish between organization and adaptational characters?
There are several grounds which have led to the belief that organi-
zation and adaptational characters coincide. Chiefly the brilliant
results which investigation concerning the functional significance
of structures as well in the flower as in the vegetation organs has
had in the last decade. It was evident that structures to which
were earlier ascribed no sort of function yet have such. And if none
was found, there yet remained the possibility that the structures
concerned had earlier been useful as adaptations. It is, however,
clear that we are hereby near to the danger of accepting something
as proved which needs rather to be proved. In reality, it seems to
me that morphological comparison as well as experiment shows
that the distinction between organization and adaptational charac-
ters is justified, and that the opinion to which Scott has given ex-

96 PLANT MORPHOLOGY

pression has arisen from the admission that specific characters have
arisen through the accumulation of useful fluctuating variations
effected by the survival of the fittest. But we see that in many
cases specific characters are not adaptive. If we follow out, e. <j.,
the systematic arrangement of the Liliiflorce, we see that the par-
ticular groups differ from each other as to whether the ovary is in-
ferior or superior, and whether it later becomes a capsule or a berry,
and, if it is a capsule, whether it is loculicidal or septicirlal. Con-
cerning these characters one may well ask whether one can bring
the berry or the capsule into relation with the question of adapta-
tion; whether it can be shown that the berry-bearing Liliiflone
occur or have arisen chiefly in those regions where also occur many
birds which devour the berries and thus disseminate the seeds. Such
a relation cannot at present be shown to exist. And who would
regard the question whether a capsule opens septicidally, as in the
Colchicacece, or loculicidally, as in the Liliacece, as one which stands
in relation to adaptation? The method of opening is conditioned
by the structure of the fruit in the Colchicaceie and Liliacece, but for
the scattering of the seed it is evidently quite a matter of indifference.
Shall we conclude that in the past it was otherwise?

Here again we are shown that we get along the best when we start
out with the observation of the plants which surround us, and not
with theoretical assumptions and far-reaching phylogenetic hypo-
theses. The theory of mutations formulated by De Vries with such
brilliant results is the result of this kind of patient and step-by-step
observation of the now living plant world. The observations of De
Vries show us that specific characters arise not through the accumu-
lation of useful variations, but by leaps, and have nothing at all to do
with direct adaptation. Such as are disadvantageous in the struggle
for existence are weeded out. But selection cannot effect the origin
of specific or organization characters as such, and this makes it clear
to us why — from the human standpoint — one and the same prob-
lem may be solved in such different fashions.

The mutation theory of De Vries limits itself to that alone which
the observation of the present moment can come at, to the origin of
the so-called " minor species." But how the division of the plant
kingdom into the larger groups has come about, how it has happened
that the " archetypes" have reached such marked development and
others have died out or remained in abeyance, are further prob-
lems, the solution of which may not so soon be looked for. For this,
however, the more intimate knowledge of the factors which regu-
late the development of the individual from the egg-cell to the
ripening of the fruit forms a fundamental starting-point. For this
purpose plants are especially suitable, since, on the one hand, be-
cause of the possession of a punctum vegetationis, they are in later

PROBLEMS OF PLANT MORPHOLOGY 97

life also provided with embryonal tissue, and, on the other hand,
because in their form they are more exposed to the influence of the
outside world than the majority of animals.

An especially important means in order to the causal study of
development has the research into those phenomena proved it-
self, which we designate the regeneration of new formations as the
result of wounding. The questions, what really takes place when
an embryonic cell becomes a permanent cell; the reciprocal influ-
ences of separate plant organs, which we call correlation; further,
the problem of polarity, stand out with great clearness in the phe-
nomena of regeneration. I can, however, at this moment only indi-
cate the problems, and cannot point out the steps which have been
taken toward their solution. A wide vista spreads out before us.
The more must we wonder that of the countless botanical papers
which appear each year not more than perhaps a dozen are con-
cerned with the problem of development.

Summing up this brief presentation, it should have been shown
that morphology, which originally formed a part of taxonomy, later
grew apart from it as an independent discipline. Only when it gives
up this separate position will morphology take on new life, for such
a position is warranted only historically and not in the facts.

The earlier morphologists would have said that morphology has
as little to do with the physiology as with the anatomy of plants,
which latter, at the time when systematic botany was in the ascend-
ant, they reckoned also as physiology. For physiology was then
everything which was not taxonomy. Nowadays it would be car-
rying coals to Newcastle to point out the significance of the cell
doctrine for morphology. For the understanding of alternation of
generations, of inheritance, and other phenomena fundamentally im-
portant to morphology, the doctrine of the cell has become of basic
significance. The same is true in a higher degree for the relation
between morphology and physiology, for all other tasks of the de-
scriptive natural sciences are, after all, only preliminary attempts
at orientation, which at length lead to experimental questioning,
to physiology. Indeed, one may say that morphology is that which
is not yet understood physiologically. The separation of the differ-
ent tasks of botany is not in the nature of things proper, but is only
a preliminary means at first to orientate ourselves with reference
to the maze of phenomena. The barriers between these tasks must,
then, in the nature of the case, fall with further progress. I do not
wish to deny the value of phylogenetic investigation, but the results
which it has brought forth often resemble more the product of
creative poetic imagination than that of exact study, i. e., study
capable of proof. If the knowledge of the historical development
of plant forms hovers before us as an ideal, we shall approach it

98 PLANT MORPHOLOGY

only when we attack the old problems of morphology, not simply
with the old method, that of comparison, but experimentally, and
when we regard as the basal problem of morphology not phyloge-
netic development, but the essence of development in a large sense.
Even if we had the story of development spread out clearly before
us, we could not content ourselves with the simple determination
of the same; for then we should be constrained to ask ourselves
how it has been brought about. But this question brings us straight
back to the present, to the problem of individual development.
For there is for natural science hardly a more significant word than
this of Goethe's: " Was nicht mehr entsteht, konnen wir uns als
entstehend nicht denken. . Das Entstandene begreifen wir nicht."
It is, then, the task of modern morphology to learn more exactly the
factors upon which at this time the origin of structures depends.
To this task, for which there was at that time but little preparatory
work, consisting of a few important attempts by the gifted Thomas
Knight, Wilhelm Hofmeister, who is known to most of us only as a'
comparative morphologist, did a too little recognized service. For
he pointed out, even before this trend of study became apparent in
zoology, that the ill-designated Entwickelungsmechanik pursues
essentially the same goal as the causal morphology of botany.

We may regard as a motto this sentence from Hofmeister's Allge-
meine Morphologic: "Es ist ein Bediirfnis des menschlichen Geistes,
eine Vorstellung sich zu bilden iiber die Bedingungen der Form-
gestaltung wachsender Organismen im allgemeinen." This is even
now the problem of present-day morphology. Comparative consider-
ation, including, of course, the especially important history of devel-
opment, offers us valuable preparation for the intellectual grasp of
the problem, but, above all, for the pursuit of the experimental
method.

That the zoologists also have felt this necessity to strike out into
new ways besides that of comparative morphological observation,
shows anew that for all organisms the problems are really the same.
Let us, then, take for our watchword development, not only as a
problem, but also for the methods with which we seek to bring our-
selves nearer its solution.

SHORT PAPER

DOCTOR J. ARTHUR HARRIS, of the Missouri Botanical Garden, St. Louis,
Missouri, presented a short paper on the subject of " The importance of Investiga-
tion of Seedling Stages," in which the speaker epitomized the recent attempts to
solve the problem of the phylogeny of monocotyledons by reference to the anat-
omy of seedlings.

SECTION C — PLANT PHYSIOLOGY

SECTION C — PLANT PHYSIOLOGY

(Hall 4, September 22, 3 p. m.)

CHAIRMAN: PROFESSOR CHARLES R. BARNES, University of Chicago.
SPEAKERS: PROFESSOR JULIUS WIESNER, University of Vienna.

PROFESSOR BENJAMIN M. DUGGAR, University of Missouri.
SECRETARY: PROFESSOR F. C. NEWCOMB, University of Michigan.

THE Chairman of the Section of Plant Physiology was Professor
Charles R. Barnes, of the University of Chicago, who introduced the
speakers as follows:

"It is perhaps somewhat unfortunate that the study of living things
must be divided so minutely in these modern times. It is a matter of
convenience, in certain respects, to separate plant physiology from
other divisions of botany and from the study of animal physiology.
It is unfortunate, however, in some respects, for the physiology of
plants is fundamentally like the physiology of animals. Indeed, the
solution of some of the most important problems of physiology must
be sought in a study of the simpler phenomena of plants rather than
in the much more obscure, because more complicated, processes in
animals. Naturally, therefore, papers on animal physiology are likely
to be of great interest to the plant physiologist, and papers on plant
physiology should be of equal interest to the animal physiologist.
Even were physiologists one, however, they would still have to
lament their separation from the chemist, on the one hand, and the
physicist on the other, since their study is in reality chiefly applied
physics and chemistry. While, therefore, in late years there has been
a steady specialization and a tendency to express this specialization
by the formation of separate sections and societies, students are
coming to realize more than ever before the fundamental unity of
scientific study and the close relations that exist between what seem
to be quite independent branches.

" The modern history of plant physiology begins shortly after the
great impulse given to the study of nature by several contemporary
events about the year 1860, the most notable of these being the pub-
lication of Darwin's Origin of Species. Ever prominent .in the
renascence of plant physiology will be the name of Julius von Sachs,
and high upon the list of those who have advanced the boundaries
of knowledge in this field will always be the name of the distinguished

102 PLANT PHYSIOLOGY

investigator who honors us with his presence this day. In 1873 Julius
Wiesner founded at the University of Vienna an institute for the
study of plant physiology, one of the earliest, as it has been one of
the most active, of institutes devoted to this subject."

THE DEVELOPMENT OF PLANT PHYSIOLOGY UNDER
THE INFLUENCE OF THE OTHER SCIENCES

BY PROFESSOR JULIUS WIESNER
(Translated from the German by Professor F. E. Lloyd, Columbia University)

[Julius Wiesner, Regular Professor of Vegetable Physiology, University of Vienna,
and Director of the Institute of Vegetable Physiology, since 1873. b. Tschechen
in Mahren, Austria, January 20, 1838. Studied in Technical High Schools,
Brunn and Vienna; University of Vienna, 1856-60; Ph.D. 1860; J.U.D.
(honoris causa) Glasgow, Scotland, 1898; Privat-docent, University of Vienna,
1861-68. Regular Professor, Technic High School, Vienna, 1868-71; ibid.
Forest Academy, Vienna, 1871-73; Rector Magnificus, University of Vienna,
1898-99. Member of the Academies of Sciences, Vienna, Berlin, Munich,
Rome, and Turin, and numerous other scientific and learned societies. Author
of Introduction into Technical Microscopy; The Elementary Structure and
Growth of Living Substance; Anatomy and Physiology of Plants; Biology of
Plants; The Raw Materials of the Vegetable Kingdom.]

I HAVE received the honor of an invitation to speak before this
great International Congress of Arts and Science on the relation of
plant physiology to the other sciences. I gratefully accede to the
request. When I accepted the invitation I did so. however, with
real pleasure, for, I said to myself, I shall see with my own eyes the
great progress which the sciences, especially the natural sciences,
have made in America, and I shall have the opportunity to speak on
a subject with which I have long been busied, and which has, so to
speak, become a part of my life.

It happened that six years ago I spoke in public upon this sub-
ject on the occasion of my induction into the office of Rector of the
University of Vienna. The content of my address at that time has, I
believe, not remained unknown to a wider audience, arid I may pre-
sume that it has become known to my American colleagues through
a translation, with which I was honored, and which was published
in the Yearbook of the Smithsonian Institution for 1898. They will
then understand that I do not desire merely to repeat myself to-day,
and will bear with me, if I give my present address a somewhat differ-
ent turn and content, without losing sight of the main issue, which
is to throw light upon the interaction of the sciences and the com-
plete unification of all human knowledge.

The insufficiency of human understanding compels us to move
the lever of research within a small area, and for all time the prin-
ciple of division of labor will hold good, and, by the same token, the
parceling off of the field of labor will advance.

But, necessary as this division of labor is, it has its drawbacks as
well as its advantages, for it narrows -the horizon of the individual
worker, and leads not seldom to a cramped idea of the goal of the

104 PLANT PHYSIOLOGY

sciences. It is often to be blamed for a classification of the sciences
in the sense that we imagine that we see an assured advantage in a
complete separation of fields of work which we sought to arrive at
by means of definition.

But, quite on the contrary, the greatest advances in the sciences
are to be made through the union of the results gained by individual
research. Not alone through the union of our experiences in special
lines, but more especially through the incidence of one science upon
the rest, is the richest harvest for all concerned to be gained. This
interrelation of the realms of study brings it about that the sciences
do not separate from one another, as the classifiers would have it, but,
as living streams, change their boundaries, and often unite with each
other to form larger units. The final goal, which, to be sure, may
never be fully reached, becomes ever clearer: all human knowledge,
especially all our knowledge of nature, wyill become bound together
into a great unity. This is the leading thought of my address.

In order to brevity, I will not attempt to trace out the early paths
of plant physiology. I take up the thread of its development at that
point where its advance appeared assured, that is, at the time of the
revival of art and science.

The discovery of the New World, and the almost synchronous
announcement of the heliocentric world-system, powerfully stimu-
lated research; and the invention of printing, which had been given to
the world a short time before, made possible the spread of knowledge
in a theretofore unthought-of way, so that the conditions preparatory
to the advance of science were supplied in a manner as never before.

Then the spirit was awakened, and bestirred itself in every branch
of science. We can quite understand that, as a result of the wide
choice of materials for study, a certain irregularity of development
in knowledge should appear. But, in spite of such go-as-you-please
methods, there grew up a " spirit of the times," more or less unnoticed,
which directed the stream of research into more regular channels
than the unconstrained impulses to research might lead one to expect.
How the genius of single greatness and how the apparently unsus-
pected ferments and stimuli of the thought of the times acted upon
one another in the struggle up new steeps of knowledge, may not
at this time be further discussed.

At the beginning of the period which I have in mind, the physicist
was the first to enrich our knowledge of nature. Mechanics — in-
cluding the mechanics of the system of worlds — formed the point
of departure for the studies. Soon followed the discoveries in physics
and chemistry, which were not then separated as they became at
and after the time of Lavoisier. By the physicists were made the
first discoveries in plant physiology, by Mariotte in the seventeenth,
and Priestley in the eighteenth century. Priestlev, who was from our

DEVELOPMENT OF PLANT PHYSIOLOGY 105

present point of view a chemist, not only discovered oxygen, but was
the first to show that this substance is excreted by plants.

These physicists were the forerunners of Hales and Ingen-Housz,
the true founders of plant physiology. Hales, by his studies of sap
movement, laid the foundation for physical plant physiology; on
the other hand, Ingen-Housz, by his discovery that atmospheric
carbon dioxid is dissociated by light in green plants, did the same
for the chemical aspect of this study.

Thus it was that the foundations for plant physiology were laid
by the physicists. The next advance, the firm establishment of the
discovery of Ingen-Housz, came through Th. de Saussure, who was,
in the language of his colleagues, as well as in our own, a chemist.
At the beginning of the eighteenth century there was no relation
between plant physiology and botany. The botanists, who were
of the stamp of the Linnaean School, were completely engrossed
in description, and were quite indifferent to the knowledge of the
life of the plant, alread}' well advanced.

The French were the first to show the relation between plant physi-
ology and botany. The great botanist, Augustine Pyrame de Can-
dolle, came under the influence of his elder colleague and countryman,
Th. de Saussure. The great significance of plant physiology, which
was at that time too closely identified with physics and chemistry,
could not have escaped his far-seeing eye, and he hoped to bring the
young science into new life by pressing into service the knowledge
of the botanist. In addition to his fundamental studies in systematic
botany, he was active as an experimenter in the field of physiology;
and by means of his Physiologie vegetale furthered greatly the know-
ledge of the life processes in plants by his regard for morphological
relations, by the assembling of rich materials for observation, and,
in general, by the bringing together of botanical (as then understood)
and experimental evidence.

To the French belongs the credit of having preserved intact the
continuity of plant physiology, which was effected, in addition to
De Candolle, by the important physiological research of his colleague,
Dutrochet, and by others, until Boussingault, whose activity extends
into the period of the general dissemination of plant physiology.

More slowly was the union of this study with botany accomplished
upon German soil. The bridge which led from the one to the other
was plant anatomy, which, however, shared the fate of plant physi-
ology, in being regarded as something strange within the bounds of
the older botany. This is explained, of course, by the fact that plant
anatomy did not originate with the botanist.

Plant anatomy was first made possible by the invention of the
microscope; in fact, it was this invention which gave the spur to this
study. The earliest anatomical observations of plants were made by

106 PLANT PHYSIOLOGY

Robert Hooke. This eminent colleague of Newton, as is well known,
brought the compound microscope to a considerable degree of per-
fection. Moreover, to test the performance of his instrument, he
studied cork and other plant tissues. These incidental observations
led this keen-minded man to the discovery of the plant-cell. Malpighi
and Grew, however, went much deeper into the subject than Hooke,
and, as Hales and Ingen-Housz are to be regarded as the true found-
ers of plant physiology, so, too, Malpighi and Grew, on account of
their studies of the inner structure of plants, stand in the same
relation to plant anatomy. None of these four, however, were
botanists in the sense of the times in which they lived. Malpighi and
Grew were rather physicians, and their endeavors to learn the inner
structure of plants and animals led them into the then almost com-
pletely unexplored field of plant anatomy. The study of life was
of much more meaning lo these two anatomists than the business
which the botanists set for themselves, and so we see that they
associated their morphological studies writh the problem of life, and
this gave many stimuli in the direction of physiology.

This was the situation at the close of the seventeenth century.
What Malpighi and Grew did, went, a hundred years later, to the
credit of the growing plant anatomy, while plant physiology got no
use from it; we have seen, then, that the founders of plant physiology
went to work as physicists arid chemists; their aim was a pure
physics and chemistry of plants; the anatomical knowledge of
Malpighi and Grew had not been made use of.

Much later was the bond between plant physiology and anatomy
welded. This was accomplished chiefly by the so-called German plant
physiologists in the first third of the previous century. These were
plant physiologists, as a matter of fact, only in name. Unpracticed
in experiment, they stood aloof from the achievements of their
above-mentioned greater forerunners, wrhich were quite foreign and
incomprehensible to them. The works which they wrote on plant
physiology did not show what had been done in this field decades
before. And yet the authors of these works have done a great ser-
vice, in that they furthered the knowledge of anatomy, and out of
this sought, in a one-sided way to be sure, to explain the life of
plants.

In two ways, however, the advance of plant physiology was helped.
First, in that these men established in Germany the relation to botany
of plant physiology, and, in the second place, in that they introduced,
besides the chemical and physical point of view already had, a
morphological one.

The union of plant physiology to botany by means of anatomy
is easy to understand, if we note that the anatomists were first of
all concerned with the determination of morphological relations,

DEVELOPMENT OF PLANT PHYSIOLOGY 107

which were at that time, as they still are, of great significance to
the systematist. Thus anatomy gained entrance into botany in the
beginning of the previous century, while the botanists of that time
yet saw something strange in the physical and chemical conception
of plants. Men such as Hedwig, Treviranus, Link, Meyen, and others,
who belonged to the ascendant school of botanists, went into plant
anatomy. The anatomical point of view must have led them to the
question of the functional significance of cells, vessels, and tissues,
and thus was developed, from the morphological side, the idea of
physiological study of the plant body, just as earlier the physiological
and the chemical methods had led to the same goal.

It was the plant anatomist, then, who made physiology at home
among the botanists, especially in the German countries. The
works on plant anatomy of Treviranus, Meyen, and others, which
appeared during thirty years of the last century, give us evidences
of the spirit of the teachings of that time on the life of plants. The
independent observations and conceptions which are to be found in
these works bore a one-sided morphological stamp; and all that
dealt with the changes of force and materials in the plant had, on
the other hand, the character of compilation, in which the unma-
tured ideas of agriculturists were accorded a larger place than the
researches of the above-mentioned physiologists, who had already
departed the field of action.

The whole of the botany of that time, as it was carried on in Ger-
many, had a one-sided morphological character. Under such cir-
cumstances, plant physiology could not flourish. This one-sided-
ness gave to botany, especially in Germany, its specific stamp, and
even such men as H. von Mohl could not escape the influence of their
time, although his clear intellect made better use of the literary
inheritance of plant physiology than did his colleagues. His mind,
better adapted for the study of nature, led him to question into the
field of experiment, in which he started some fundamental lines of
work, as, e. g., the study of twining, and of the tendrils of plants.
But his strength always lay in anatomy. In even this, where
questioning led straight to experiment, he clung as a rule to mor-
phology. An instructive and pertinent example is his relation to
the question of leaf-fall. The history of plant physiology and the
influence of other studies upon it are reflected so clearly in this
problem that I may be permitted a few moments to follow its devel-
opment.

The physiologists of the earlier epoch had a purely mechanical
conception of this phenomenon. They held that leaves dried up
at their death, and that their stiffened forms were broken from the
twigs by the autumn winds. It was later held that the buds which
developed in the axils of leaves enter between them and the stem like

108 PLANT PHYSIOLOGY

a wedge, and force them off. H. von Mohl showed that this and
other such naive conceptions were untenable, and he tried to point
out the true state of things. His discovery of the scission layer was a
great advance.

Now, for the first time, it was recognized that the loosening of
leaves is brought about by an organic process. But von Mohl con-
ceived the question in a one-sided, almost purely morphological way.
Ten years later, when plant physiology started its larger develop-
ment upon German soil, did they for the first time begin to search
experimentally for the causes of leaf-fall, and since that time the
question has not been allowed to rest, because we have sought to
come at a complete solution by means of combined anatomical,
physiological, and biological researches.1

How much and how long plant physiology suffered in Germany
under the dominion of one-sided anatomical study we are taught
by the Anatomie und Physiologic of Schacht, which was much valued
at this time (1856-59). This work is based almost entirely upon
morphology; experimental study was relegated quite to the back-
grdund; the specifically physiological element is not in evidence.

Yet another remarkable point in the development of German
plant physiology demands explanation, because it shows that, as a
result of meaningless, one-sided handling, disciplines mutually neces-
sary, instead of helping, have hindered each other. I refer to the
conflict of Liebig with the German plant physiologists.

The humus theory, upheld at the end of the eighteenth century
by Hassenfratz, was completely overthrown by Ingen-Housz. Yet it
was revived again among the German agriculturists and accepted
by the German plant physiologists. Their one-sided morphological
conception of the life of the plant and their neglect of the study of
their great forerunners explains this peculiar fact. As is well known,
Liebig laid the new humus theory to rest, as Ingen-Housz had the old.
He did it on the basis of the exact methods of chemistry with yet
greater certainty than Ingen-Housz, and also with better results.
This was the cause which led to a conflict between Liebig and the
German plant physiologists, lasting forty years, which was of no
use to science, and only showed that Liebig did not understand
morphology and that the plant physiologists did not conceive
aright the chemistry of the plant. In one thing both parties were
wrong. They did not understand how much each was necessary to
the other, if they would really further physiology.

The first botanist who studied and mastered equally anatomy and
physiology, and attained that balance between them which is neces-

1 Wiesner, Untcrsuchungcn tiber die herbstliche Entlaubung der Holzgewuchse,
Sitzungsberichtc der Wiener Akademie der Wissenschaftcn, bd. 64 (1871). Ueber
die neuesten biologischen den Laubfall betreffenden Studien, s. Berirhteder Deulschen
Botanischcn Gcscilsch. 1904. Ueber den Sommer-Laub fall, Ueber Treiblaubfall.

DEVELOPMENT OF PLANT PHYSIOLOGY 109

sary for the full fruition of plant physiology, was Franz linger.
It was thus that he did his epoch-making work. There came into play,
however, a personal factor, also, which leads us to understand his
fundamental importance in the development of plant physiology.
He was called in 1849 as Ordinary Professor with Endlicher. He
made an arrangement with that great systematist to teach anatomy
and physiology, and leave taxonomy to his colleague. The compact
was never broken. And thus for the first time in history a real pro-
fessorship of plant physiology became a fact. A new banner was
unfurled in a great university. Thousands of students were intro-
duced by Unger to plant physiology. In Vienna, botany, as an object
of learning, took on a new character: it was seen that there was
something else besides that science of botany which was known to
the privileged few, the knowledge of the inner structure and of the
life of the plant. What furtherance is experienced by a science,
especially in a great university, when a special chair is devoted to
it, every subject to which a similar lot has fallen, has, I suppose,
undergone.

Through Unger's work, plant physiology, in the best sense of the
word, for the first time became so popular in Austria that the estab-
lishment of a special ordinary professorship of this study must have
appeared to be justified. After Unger's resignation such was pro-
vided, and then followed in its train the Institute for plant physi-
ology. When Sachs (1875) urged special chairs and laboratories for
plant physiology as an undeniable help to science,1 they were already
in existence in Vienna and Prag, and the Institute for plant physi-
ology founded in Vienna after the establishment of the special pro-
fessorship of anatomy and physiology of plants was the first work-
shop of the kind laid out on a grand scale, which furnished the stimulus
for the founding of other institutions of the same kind. To-day there
exist in Europe and America well-nigh countless such laboratories,
and from their origin dates the great advance of plant physiology in
the last thirty years.

These arrangements have, however, been fruitful for the develop-
ment of our science in a way which demands our special attention.
Brought into being in great universities, the laboratories for plant
physiology were placed in a centre in which they came into intimate
touch with other domiciles of research, so that the stimulating influ-
ence of the other sciences could hardly have been escaped. Advance-
ment under this permanent contact became ever more marked. This
process has gone on before every one of us, and all who understand
will admit that the present condition of our science could not have
been realized, and the hope for the future could not have been so
promising, if, earlier, plant physiology had remained dependent on
1 Sachs, Geschichte der Botanik, Munchen, 1875, p. 572.

110 PLANT PHYSIOLOGY

itself alone, and had been deprived of that great share which has
to-day been afforded it by science and practice.

Science and practice! How often is their advantageous reciprocity
misjudged! But it is just in the realm of plant physiology that their
reciprocal advancement becomes clear to the unprejudiced, in spite
of the errors which have proved a hindrance to their union for so
long. Starting from a purely theoretical point of view, Liebig entered
the sphere of practical agriculture, and, after an activity full of
vicissitudes in the practical and theoretical trends of thought, led by
practical ideas, worked especially at his experimental farm at Bechel-
bronn in Alsace, and Boussingault worked in the field of plant nutri-
tion, advancing, with the most refined means of research, toward
the solution of plant physiology. What these two accomplished
for agriculture through their researches, especially in regard to
the nitrogenous and mineral foodstuffs of crops, must remain as
difficult to estimate as the great advance which plant physiology
owes to these two men who established the most intimate bond
between chemistry and physiology through the founding of agri-
cultural chemistry.

At the end of the sixties the condition of things \vas thus. Plant
physiology had not only come into relation with botany, but had
become, indeed, an integral part of it. Further, plant anatomy, physics,
chemistry, and practical agricultural chemistry had come to her
assistance. Even animal physiology, now and then at least, came
into a relation to physiology mutually beneficial to both, since the
interrelation of animal and plant life had been clarified by Ingen-
Housz and Saussure. I shall take occasion to return to this question
later.

In spite of the efforts of Unger and others, who sought to portray
plant physiology in comprehensive works, this knowledge, which
had been derived from so many sources, was not yet welded into a
real unit. There appeared in 1865 the Experimental Physiologie der
Pflanzen of J. Sachs, in which was drawn up a critical summary of
the sum total of the knowledge gained up to this time. This work
gave a great impulse to new research. It was a most seasonable under-
taking, which, not only by its rich contents, but also by its incom-
parably clear and illuminating presentation, did not fail to exert
a great effect in the further development of plant physiology.
Unger's researches and his scholarly activity and Sachs' Experimental
Physiologie contributed the most to the fruition of plant physi-
ology in Germany in the second half of the last century.

Thus, although Hales laid down the first guiding principles of
plant physiology, we have seen that its further development took
place in France and Germany. If we except the discovery made first
by Priestley, that oxygen is excreted by plants, — a conclusion

DEVELOPMENT OF PLANT PHYSIOLOGY 111

clarified and strengthened by Ingen-Housz, — England took no
further part in the building up of plant physiology as the product of
chemical, physical, and anatomical study. Another great impulse,
however, emanated from England, the introduction of the principle
of development into botany. This, excepting that of a few fore-
runners, was the work of Robert Brown.

Although this eminent student dealt with development only as a
morphological principle and turned it to account especially in tax-
onomy, yet his method of viewing the vegetable organism from the
standpoint of development at once quickened the study of anatomy,
which up to this time had taken into consideration only the mature
plant, and must be credited, of course, to physiology. Robert Brown
taught the doctrine of ontogenetic development. This, however,
paved the way for phylogenetic development, which similarly
emanated from England, and had its chief champion in Darwin.

The principle of phylogenetic development was of importance
first in morphology. By the appropriation of physiological methods
and by the application of this principle to purely physiological mat-
ters, this historical conception entered with happy results into our
sphere. We ask, nowadays, not only how this form, species, genus,
etc., has arisen, but we also set before ourselves the question, writh
reference to the process of differentiation and life processes, how
far these are referable to direct influence and how far to peculiarities
which have become fixed by inheritance in the course of generations.

Darwin's great influence on the development of our science is not
confined to the historical conceptions of physiological phenomena,
and in general to that which is connected with the origin and per-
petuation of characters beyond the limits of the individual life, with
adaptation and inheritance. His conception of organic life has in
manifold other ways furthered the development of our science,
especially in that he widened our horizon by a unified conception
of the whole organic world.

That to-day there may no limit be drawn between plant and animal
physiology, and that we may, with advantage to the botanists and
zoologists, and in general to the study of nature, approach a general
physiology, is chiefly referable to Darwin's influence, even though
in this particular this great student also had his forerunners.

Fechner, with true insight, had already pointed out the irritability
of plants. But he preached to deaf ears : the contemporary physi-
ologists were in the bonds of a purely mechanical conception of plant
life. A rich harvest came to Darwin through the Power of Movement
in Plants, in which he showed that plants, without having nerves,
yet are able to receive stimuli, to transmit them, and to react in
places which are removed from the point of stimulus.

Thus was indicated the way to make use in plant physiology of

112 PLANT PHYSIOLOGY

the experience of animal physiologists. This late intimate contact
of so nearly related disciplines, which earlier had been led up to,
and again and again failed of, has shown itself in the highest degree
fruitful ; and the physiology of irritability, which earlier was pushed
forward by Sachs, and later by Pfeffer and his school, and is at the
present time in the forefront of interest, is referable to the beneficial
influence upon plant by animal physiology. I beg to be allowed to
emphasize this influence still more, and to indicate the interaction
of these two sister sciences.

In spite of Fechner's earlier suggestion on the point, there is no-
thing to be found in Sachs' Experimental Physiologic on the mat-
ter of irritability. The most important and most frequently adduced
phenomena, as heliotropism and geotropism, were referred to tissue
tensions and similar purely mechanical effects. Almost all plant
physiologists followed the path which was pointed out by the gifted
morphologist, Hofmeister. Only a few of the most striking move-
ments of plant organs, as, e. g., those of the leaves of Mimosa pudica,
were spoken of by Sachs as "the so-called phenomena of irritability."
He stood in this under the influence of the great animal physiologist,
Bruecke, who, in order to get a more comprehensive idea of the life
of organisms, took up plant physiology and studied closely the
sensitiveness of Mimosa pudica.

In his Pflanzenphysiologie, still following Hofmeister, Sachs ex-
plains positive geotropism as a bending under weight, — that the
root-tip as a result of its weight when the root is placed in a hori-
zontal position, bends downward in the subapical part, which is
composed of soft, plastic, and tender cells. Sachs says expressly
that, just as the end of a piece of sealing-wax bends downwards
when the part behind is softened by heat, the heavy and stiff end
of the root bends out of the inclined, or horizontal, into the vertical
position.

In his later writings this account, which was out of all harmony
with the facts of anatomy, was not held to, for the conception of the
phenomenon of irritability underwent a total change, doubtless
under the undoubted influence of animal upon plant physiology.
The way we to-day regard irritability in plants is a reflection of the
matter from the animal point of view. Pfeffer took this position in
the first edition of his celebrated Plant Physiology, and yet more
clearly and decidedly in the second edition, recently completed.
Nowadays the phenomena of heliotropism and geotropism — not to
pass beyond the examples cited — are regarded as those of irritabil-
ity in the sense of the animal physiologists. The causes of stimulation
(gravitation, light, etc.) have been determined, the point of recep-
tion shown, transmission of stimuli proved, and the whole course
determined in detail. The value which accrued to plant physiology

DEVELOPMENT OF PLANT PHYSIOLOGY 113

through its union with animal physiology forms a debt which the
former is trying to pay to the latter, and which in part has been paid.
It was the recognition of heliotropic and geotropic phenomena in
plants which guided us to discovery of analogous phenomena in
animal organisms. And thus we see that the long-separated and
independently parallel disciplines have become united into a more
symmetrically developing general physiology.

It seemed as if the doctrine of the cell, so important for physio-
logy, would have had a happier fate than all the other branches of
natural science. Its founders, Schleideri and Schwann, had worked
into each other's hands. Schleiden regarded this as a fortunate
circumstance, which, as he expressed it, "protected the doctrine of
cell-life entirely from the one-sidedness of a simply botanical or
zoological point of view."1 But it has turned out otherwise. The
iron law of division of labor holds good here, also, and only after long-
drawn-out special researches in both fields has the conviction grown
upon us that experience in one field has something to teach us in the
other also. About half a century after the founding of the cell theory
the large results of animal histology worked a change. The happy
discovery of kar}-okinesis in the animal cell taught the botanists,
who saw their enlightenment near at hand in the study of plant cells,
in wrhich traces of karyokinesis had been seen, by means of the tried
methods of the animal histologist. From day to day the union of
plant and animal histology advanced, and our knowledge of the
organic elements gradually became more unified, the condition
which Schleiden held as an ideal, and, in company with Schwann,
had prepared for.

In the field of botany, morphology and physiology sprang up
slowly side by side from the several above-mentioned foundations.
That we see at this time interrelations between them indicates a far
advanced condition. But this significant union is taking place by
no means without contention. There yet sticks in the heads of many
morphologists that these two parts of botany will thrive the better
the more completely they are separated from each other. Advan-
tageous as the division of labor has been, and as much as the study
of details has led to this, it must yet be clear to the far-sighted that
the solution of the great questions of plant life is possible only by
a morphological-physiological treatment. To express it roughly,
we may understand a machine when we take note not only of the
structure and form of its component parts, but also of their func-
tion and work; so may we get an intellectual grasp of the living
plant when we study its morphology in relation to its functions. To
make use of all demonstrable morphological facts in the explana-
tion of life processes is one of the most obvious phases of modern

1 Schleiden, Grundzugederwiss. Bot., Vierte Aufl., Leipzig, 1861. Vorrede, p. xi.

114 PLANT PHYSIOLOGY

plant physiology, and is to be seen in the development of our science
clearly enough. One needs only to compare the older works of Sachs
with his last book, Lectures on Plant Physiology. In the latter work
for the first time morphology comes into living relations with physi-
ology, and this is more clearly evidenced by his presentation of
anisotropy, in which he makes the attempt to explain the relation
between the formation and the direction of plant organs under the
influence of constant outside directive forces. Similar attempts to
explain the form-relations of plant organs from analogous points of
view were made soon after. Everywhere the most intimate rela-
tion between form and structure, and function, was sought after.
This research was directed not only at causal but also at teleologi-
cal explanations, for which experimental evidence was, as far as
possible, advanced. Schwendener and his school were active in both
directions, furthering the union of morphology and physiology, and
thus laying the foundations for a physiological plant anatomy.

The increasing invigoration of physiology by morphology has in
more recent times been of the same importance for the further de-
velopment of our science as the influence of Darwin's basic idea of
phylogeny was to numerous problems concerning plant life. The
question which now stands to the front is, how have forms arisen,
and what functions are bound up with morphological relations, and
also how we are to distinguish between ontogenetic and phylogenetic.
E. g., Has a particular form or a particular tendency of an organ
originated with the individual, or is it referable to inherited pecu-
liarities, or is it the product of ontogenetic and at the same time
of phylogenetic development?

The study of ontogeny is the peculiar domain of physiology in the
narrower sense — that is, the mechanics, chemistry, and physics of
the living organism — so far as the development which takes place
before our eyes is approachable by direct observation and experi-
ment. That which may be determined inductively concerning the
life, the origin and fate of plants and the plant world may be got at
only by following the individual development.

The riddle of ontogeny, and the question of phylogeny (which
is well-nigh unanswerable by direct methods) open the door of specu-
lation, and the scope of the problems of the origin and development
of the organic kingdom are thus discovered. These have stimulated
many students outside of the circle of the observational and experi-
mental sciences to seek help, or at least suggestion, in philosophy.

Indeed, at the present time the philosophical element in natural
science has come strongly to the front. The reawakening of research
in the theory of descent is indeed the chief cause of this modern phe-
nomenon, which, I believe, commenced in the organic natural sciences,
and then passed over into the inorganic.

DEVELOPMENT OF PLANT PHYSIOLOGY 115

Whatever we may think on the cause of this phenomenon, philoso-
phy has stepped so far to the foreground within the natural sciences
that, in discussing the relations of the sciences to the plant physi-
ology of that time, I cannot avoid examining how far philosophy is
in debt to our science.

The question what philosophy is has been very variously an-
swered. If we regard it in the widest sense as the science of all being
and happening, and especially of the underlying principles, it is then
evident that it, or at least part of it, must form a proper constitu-
ent of the natural sciences.

The desire to penetrate the ultimate causes of phenomena is
deeply rooted in mankind. This desire, as Whewell at one time so
truly remarked, is a curiosity to reach beyond the goal, to step be-
yond the bounds, which shut in the human spirit. Within these
bounds rule the experiences of knowledge. Human knowledge shuns
everything which is not made sure by experience. Thus the limit
is drawn within which philosophy may and can make itself of ser-
vice in the natural sciences.

He who follows the development of the natural sciences with a
comprehensive view must come to the result that a sound philosophy,
based upon experience, has always existed in natural science. The
problems which many scientific workers have set themselves are indeed
of a simple kind, so that a philosophical penetration into the objects
dealt with may not have been sought for by them. But the masters,
the leaders, have ever been philosophers, so far as they controlled
their observations with logical power, bound together scattered obser-
vations with an intellectual insight held in check by criticism, and
tested by experience the theories which they formulated. Herein,
however, is indicated the limit up to which speculation is permissible
in natural science. Hypothesis may be used as a means, but is justi-
fied only so long as it stands in harmony with experience.

Such philosophy has obtained since the rejuvenescence of the
natural sciences, wherefore this period has properly been called the
inductive; such philosophy will and must always obtain, because
this kind of philosophy is the living element of natural science.

I do not have in mind that philosophy used by students of the
natural sciences, but seldom called so by them, when I speak of the
help which they have sought for in philosophy, but rather of that
of the specific philosophers, or, as I may say, of the speculative
philosophy, or, in brief, of "philosophy."

Highly instructive for the relation of philosophy to the study of
natural science is the relation of Newton to the previous philosophers.
This has been shown by Brewster.1 The vortex theory of Descartes

1 Brewster, Sir Isaak Newtons Leben, Deutsche Uebersetzung, Leipzig, 1833,
p. 276 ff.

116 PLANT PHYSIOLOGY

was a real hindrance to the acceptance of Newton's theory of the
motions of the heavenly bodies. And concerning the assertion that
Newton depended upon Bacon, Brewster has shown conclusively
that Newton searched out the truth by observation and b}' experi-
ment in part worked out by himself and partly borrowed from
Copernicus and Galileo.

But, in order to speak of the influences of philosophy on botany,
must we not point out Schleiden, who, it may be presumed, placed
this science upon a new basis? The methodological basis proposed by
him, which may be referred back to Kant, had the value of quite
setting aside the harmful academic philosophy of Schelling, which
caused not a little confusion among the mediocre botanists of that
time, and of adhering to exact observation and to the logical pre-
sentation of the facts. But the advance of our science by no means
took its origin from his philosophical teachings; this was effected
by students such as Hugo von Mohl and others. Schleiden's schemati-
zation of the cell was a fruitful idea, and his activity, in the sense of
Robert Brown in the field of ontogenetic development, brought a rich
return. But all this had nothing to do with the Fries-Appelt philoso-
phy, often cited by him, and with his continual reference to Bacon.
His criticism, however, often overshot the mark in matters of plant
physiology, and has hindered rather than helped on the develop-
ment of our science. The greater part of Saussure's experiments he
cast aside as "completely useless;" the fact that green plants in an
inclosed space can, in spite of gas exchange, keep the surrounding
air in a condition in which it remains apparently unchanged qualita-
tively and quantitatively, was regarded as an impossibility, and in
spite of Ingen-Housz and Saussure, it was boldly asserted that Bous-
singault first proved that green plants absorb carbon dioxid in
sunlight. Fechner's views in regard to the irritability of plants,
with \vhich all physiologists to-day agree, were not only opposed by
Schleiden from the philosophical standpoint, but he even scouted
them with derision.

The whole literature shows how little use "philosophy" has been
to plant physiology. I will touch upon this with only one example,
which, however, will show also that students of science themselves
enter into abstract thought so far as it is advantageous to them in
the solution of their problems. Schopenhauer, in his work, Zur Phi-
losophic und Wissenschaft der Natur (1851), broke a lance for the
doctrine of vital force. His arguments against the purely mechanical
conception of life are completely justified; but it was these same
arguments which were advanced ten years ago by Johannes Miiller.
So far as Schopenhauer and Miiller are in accord with one an-
other on this point, the student of science can follow the philo-
sopher. But when he encroaches on the field of metaphysics, and

DEVELOPMENT OF PLANT PHYSIOLOGY 117

identifies vital force with the will, he can offer nothing further to
the scientist.

As often as philosophy has disturbed natural science, as did the
so-called nature philosophy in the period of Schelling, has the sound
thought of the scientist always repaired the damage which has
been done to our science by the misuse of the human mental power.

The marked philosophical movement of to-day in the natural sci-
ences revolves chiefly about the questions of the origin of life, about
the vital force, about the alternative mechanism or vitalism, and
about the propriety of a teleological conception of nature.

The further our knowledge of facts extends, the greater becomes
the gulf between the lifeless and the dead. Schleiden would have it
that the }^easts arise spontaneously from the nutritive fluids; even
after the epoch-making researches of Pasteur the attempt was made
to show that bacteria arise spontaneously. But this is all past, and
there is no fact to support the idea that the living can arise from
the non-living. A new support for the correctness of this view is
to be found in the conception, supported by an immense amount of
evidence, that in the organism, also, the organized or living elements
can arise only from the living.1

The specific philosophers have offered us nothing on the question
of origins. For when Kant, with a far-seeing eye, expressed the view
that the living may not arise from the non-living, it was the scientist
in him that spoke. When, on the other hand, Naegeli supported
the idea of generatio spontanea, arid, indeed, represented the view
that this continues without interruption (while the monists are
usually content with the once-for-all origin), this eminent man
denied the scientist in him, and descended to doctrinaire specula-
tion. So various is the human disposition that the great philosopher
Kant expressed himself on the question of primal origin for a whole
century, just as the scientist must at the present moment, while so
eminently a modern scientist as Naegeli took the position in this
matter not simply of a philosopher of the monist type, but rather
of a metaphysician. The arguments of E. von Hartmann that there
is now no generatio aequivoca, because, in view of the stability of both
organic kingdoms, this is no longer necessary, had obviously no effect
upon scientists.

But the recent attempts of a prominent scientist to bring back the
problem into the field of physics and chemistry by making an analogy
between crystal formation in metastabile solutions with spontaneous
generation was only an intellectual idea without further consequence
in leading to a solution of the question.2

1 Wiesner, Die Elementarstruktur und das Wachstum der lebenden Substanz, Wien,
1892, p. 82 ff.

2 Ostwald, Vorlesungen uber Natur philosophic, Leipzig, 1902, p. 345 ff.

118 PLANT PHYSIOLOGY

Thus to-day we are resigned as regards the question of the origin
of life, just as the physicist is as to the origin of matter; and as he
pursues his studies on the assumption of the existence of matter, so
also we do best when we take for granted the living stuff, and study
observationally its nature without speculation upon its first origin.

The kernel of the doctrine of vitalism, which we have recently
regarded as dead and buried, was forced again into recognition by
the great Johannes Miiller, after the attempt to reach a purely
mechanical conception of life had been wrecked. Truly, we may no
longer hold that in the living individual a force reigns which controls
everything within. We really see at work within the organism the
chemical and physical forces which are active in the inorganic world.
But that which within the organism directs the mechanical forces
toward a definite goal and unifies harmoniously all that happens
within a living individual and leads to a particular purpose (Enhar-
mony of the Organism) J cannot be understood from our experience
with lifeless nature.

It has often been attempted to refer the whole life of plants and
animals to psychological manifestations. This is, however, an ex-
treme view, which fails of profit; while the primitive psychical mani-
festations in the life of plants, particularly with reference to the
consideration of Fechner, may be allowed some consideration.

It will be admitted by every far-sighted observer that the purely
mechanical conception of life has been set aside, but that, however,
there is no reason to take an extreme vitalistic point of view. In
order to accentuate the rejection of extreme mechanism in the con-
trol of the organism b}>- means of a certainly unprejudiced judgment,
I cite the opinion of an eminent physicist and astronomer, which
was published at the time when the mechanical view of nature was
in vogue, but which has not been properly appreciated. In August,
1868, Frederick A. B. Barnard, in his address at the opening of the
Chicago meeting of the American Association for the Advancement
of Science, spoke the following words. "The vital principle differs
from every form of force known to us, and from every other known
property or quality, in that it confers upon the body which it ani-
mates a special character of individuality, and in that it is incapable
of being insulated or of being transferred from body to body. We
know it only through the peculiar organizing power which belongs
to it, and which is manifested not merely in the chemical changes
which it determines, but in the external forms which the resulting
compounds assume."

The manifestation of mechanical forces in addition to that of

1 Wiesner, Biologic, Zweite Auflage, Wien, 1902.

2 Presidential Address, seventeenth meeting of the American Association for
the Advancement of Science. Translated into the German by Kloden, Berlin,
Weidemann'sche Buchhandlung, 1869.

DEVELOPMENT OF PLANT PHYSIOLOGY 119

a specific " principle " in the life of organisms could not be better ex-
pressed; and the reference to " individuality " is a pregnant thought
with regard to the enharmony evident in every living form.

It seemed as if the last traces of teleology would have been effaced
from biology by Darwin's theory of selection. No one has expressed
this more clearly than Schleiden, who, always a tireless opponent of
every teleological conception, speaking concerning Darwin's doctrine,
cried out in triumph at the close of his activity as a student: "Tele-
ology belongs no more to science, but has its place now only in mere
talk." 1 His opposition to teleology started from a one-sided, pedantic
philosophy, but his disputatious arguments gained great weight with
the majority of the botanists of his time, and his influence in this
direction has remained, sporadically to be sure, up till our time. Most
of the botanists of his time were so overawed by him that scarcely
one of them dared to speak of the purposes of organs or of purpose-
ful arrangements in organisms and so on. And this, as a result,
worked a desolation in morphology, and made more difficult its union
with physiology.

In this also, however, Schleiden by his hypercriticism overshot the
mark. For it was just this great scientific movement, which Darwin
set up through the rehabilitation of the doctrine of descent, that of
necessity placed teleology in its right place. And this teleology, en-
riched by an immense number of facts, contributed materially to the
advance of the biological sciences. It has also brought it about that
eminent and scientifically educated philosophers, such as Wundt,
enforced again the recognition of teleology together with causal-
ity. In this the reaction of natural science upon philosophy is only
slightly indicated. It extended, however, much further, for the
rehabilitation of the theory of knowledge is the result of the advance-
ment of natural science; and the cooperation of eminent scientists,
such as Boltzmann, Mach, Ostwald, Reinke, and other also scienti-
fically trained philosophers, shows, in the building up of the theory
of perception, how science entered this field to its advancement.

That which in the teleological conception concerns transcend-
entalism we leave to the specialists in the theory of knowledge.
We stand on the ground of experience, and permit of metaphysics,
as we have said above, only as a source of helpful ideas, which, how-
ever, may be permitted only when they do not negate experience, and
only so long as they prove themselves useful in opening up to us
new directions for inductive research. If through this kind of scien-
tific operation the clear area within which we move appears to be
limited within narrow confines, yet our advance within them is the
more certain.

1 Schleiden, Grundzuge der wissenschaftlichen Botanik, Vierte Auflage, Leipzig,
1861. Vorrede, p. viii.

120 PLANT PHYSIOLOGY

The wanderings of the academic philosophers on the extreme
limits of human knowledge, and even beyond them, lead only to
transitory results, which in turn may be called into question, while
science advances steadily in its development. A celebrated physicist
and thinker has said that sound human understanding is a lasting
product of nature, while philosophy is a meaningless, ephemeral, arti-
ficial product.1

Only that philosophy will profit us which has arisen from the true
spirit of science, even though it advances in the causal and teleo-
logical only by way of description. In the spirit of our descriptive
methods let us not, when opportunity offers, withhold from speaking
of the purposefulness of organization, or of purposes and goals in the
realm of life, as in the adequate observation of a machine. In doing
so, we renounce the explanation and exposition of final causes of
things and events; this lies beyond the limits of the knowledge of
nature and beyond the power of man.

From mathematics we have greater hope for the furtherance of
our science. Small beginnings are already visible, which at first
attain only to a primitive expression in arithmetical representa-
tion of quantitative experiments. A further advance is to be noticed
in representing mathematically simple physical relations, e. g., to
express the entrance and exit of gases into and out of the plant as
phenomena of effusion or gas transpiration, or the graphic repre-
sentation by means of a system of coordinates of the relation of a
phenomenon (e. g., heliotropism) to a variable factor (e. g., inten-
sity of light). When a simplification of the conception of a morpho-
logical relation (e. g., leaf arrangement) or of a state (e. g., rigidity or
elasticity of the plant body or the use of light to plants) is possible,
we use mathematical expressions to advantage, and similarly for
precise illustration of certain principles (e. g., by means of the bio-
chronic equation of H. de Vries), etc.

Yet these are, as we have said, only small beginnings. Mathe-
matical calculation plays yet a very minor role in plant physiology
because, in the lack of deeper knowledge of the facts, everything
seems as if so hidden in a cloud that the congeries of active factors
may not yet be brought to a corresponding mathematical form;
that the setting up of a mathematical formula or equation of any
kind from which, upon the basis of adequate observations, future
conditions may be inferred, appears not yet possible. Animal physi-
ology has already taken the lead, in that in some questions it uses
the differential equation, and so it may be expected that mathe-
matical calculation, after the example of physics, will become an
important means of advance in our science.

Almost every problem in plant physiology gives us in the pro-

1 E. Mach, Die Analyse der Empfindungcn, Dritte Auflage, Jena, 1902, p. 29.

DEVELOPMENT OF PLANT PHYSIOLOGY 121

cess of its solution a reflection of the history of our science, ever
showing how changeable its limits are and from what various di-
rections, often unexpectedly, its help comes. A pertinent example
has been already advanced by me, — that of leaf-fall. Allow me to
give as briefly as possible two other examples of great illustrative
power.

The problem of leaf position has been till recently purely descrip-
tive, although treated in part with great mathematical and geo-
metrical precision. Later, by Schwendener, it was brought, as a
mechanical problem, out of the field of morphology into that of
physiology. Quite recently it has been shown that, with reference
to illumination, the simplest positions for lateral and for vertical
axes, the approximation of leaf positions to the irrational limits of
value are the most purposeful. Thus the problem of leaf position
was at first morphological, then physiological, and finally biological,1
or, as we may more precisely say, ecological, whereby it is, however,
not said that it cannot be further advanced from the side of morpho-
logy and physiology.

In the second place, our great problem of photosynthesis (carbon
assimilation). Priestley discovered the excretion of oxygen by the
plant, Scheele that of carbon dioxid. But neither was able to say
under what conditions these took place. Ingen-Housz first showed
that the photosynthesis correlated with oxygen secretion takes
place only in the green organs of plants under the influence of light.
The explanations of the chemistry involved which obtained from
the time of Th. de Saussure to Boussingault are well known. Ana-
tomy now took a hand, and showed us, in the living body of the
chlorophyll grain, the place where photosynthesis takes place. The
knowledge of the spectrum of chlorophyll, contributed by the physi-
cist, led to the attempt to study the absorption of light by chloro-
phyll from the physiological point of view. First it was shown how
the pigment chlorophyll by light absorption influences the process
of transpiration2 and then the same in regard to photosynthesis.3
The reference of fermentation to an enzymatic process has raised
the question whether photosynthesis may not be a process of this
kind. As you know, we are in the midst of a strife of opinions as to
whether or not photosynthesis is a matter bound up with the living
condition or has to do merely with an enzymatic process. And now
the chlorophyll question wanders into the realm of cosmic physics,
in that on the one hand the view is set forth that the correlations
between photosynthesis and the life of plants and animals presents
itself not as a struggle for the elements or for energy, but as a struggle

1 Zur Biologie der Blattstellung , Biol. Centralblatt, 1903, p. 209 ff.

2 Wiesner, Untersuchungen uber den Einfluss des Lichtes auf die Transpiration.
Sitzungsbericht der Wiener. Akad. d. Wissensch., 1876.

3 The well-known works of Engelmann, Reinke, and TimirjazefT.

122 PLANT PHYSIOLOGY

for entropy,1 and on the other side, the attempt has been made
to show, on the grounds of observation, what proportion of the
energy of the sun which is used on the earth by green plants is
rendered available for the life of organisms. I here come to the
calculation of Pfaundler and to the beautiful and important re-
searches carried on by Brown and Escombe to determine the
"economic coefficient," which have shown approximately how much
of the sun's energy is fixed by the transpiration of green plants in
the light, and by photosynthesis. It wras found that in sunlight far
more energy is employed for the purpose of transpiration than for
that of photosynthesis, and that, in diffuse light, relatively more
energy, in comparison with transpiration, is consumed in photo-
synthesis than in sunlight. Since we in recent times recognize only
green plants as autotrophic, the opinion — entirely problematical, to
be sure — may well arise that life upon the earth must have begun
with green organisms. Now, however, as you know, it has been
shown by Hueppe and Winogradski that certain bacteria also fix
carbon dioxid, and are in every way to be regarded as autotrophic.
Chlorophyll is, then, not absolutely necessary to photosynthesis;
but rather has this become to us, according to our present under-
standing, in the course of the development of the plant world, a
wonderful, purposeful means of building up organic substance
under the influence of light.

And yet many more details may thus be advanced, to show that
even one and the same problem may be brought to its solution by
the most different branches of science.

I have, to be sure, only in the most cursory manner tried to show
how plant physiology has arisen under the influence of the other
branches of natural science, and, finally becoming a part of botany,
was advanced by morphology.

How physiology has come into relation with the other branches of
science, especially the mental sciences, and has affected practical
life, has already been dwelt upon by me.

In order to complete the picture of the interaction of the special
sciences, I would, at the close, draw attention to the fact that, young
as plant physiology is, it has been of help to pure science far beyond
the bounds of botany.

I may mention the advance which plant geography, at first espe-
cially a statistical account of the plant world, has made since it was
organized upon physiological and ecological bases by Schimper,
Warming, and others. It is no paradox when I say that plant physi-
ology has reacted advantageously upon the further development of

1 Boltzmann. Drr zu-eite Hauptsatz dcr mechanischcn Warmrthrnrie. Vortrag
Wiener. Akad. d. Wissrnfich., Almanack, 1886, p. 246. See also L. Pfaundler, Die
Wcltwirtschaft iin Lichtc der Physik, Deutsche Revue, 1902.

DEVELOPMENT OF PLANT PHYSIOLOGY 123

chemistry, physics, meteorology, and climatology, and upon other
studies far distantly removed, according to earlier conceptions; and
that it will do this with still more advantage in the future. Plant
physiology is often in need of things, e. g., on the part of physics and
meteorology, which these sciences do not have to give her, so that
the plant physiologists are compelled to work independently in these
apparently strange fields. I may recall Pfeffer's important discoveries
in osmosis, which, as is well known, have been of great importance
in the theory of osmotic action.

In order to learn the actual, but apparently highly overestimated
mechanical effect of rain upon plants, a close student of this question
had need of data which were not to be found in the meteorological lit-
erature, and himself determined the weight of the heaviest raindrop,
its rate of fall, and its kinetic energy.1 From this study both plant
physiology and meteorology profited. The same plant physiologist,
incidentally to his studies of the use of light by plants, contributed
to the science of climatology by his thorough observations of photo-
chemical climate.2

These are random examples merely, but nevertheless indicate
that plant physiology is in condition to render service to the so-
called exact sciences.

If I should speak a word for the later advantage to physics through
plant physiology, this might seem to be an oratio pro domo. For this
reason I refer to the remarks of a celebrated physicist. Ernst Mach
says in one of his best known works, "Not only may physics help
and clarify biology (in the widest sense as the doctrine of life), but
biology may stand in this relation to physics. . . . Physics will
accomplish yet more for biology, after it has grown by means of the
latter." 3

I hasten to a close. I have not intended to present new facts,
but rather to use well-known ones in order to support my leading
thought to which I gave voice at the outset.

I have tried to present to you a picture in which the development
of plant physiology under the influences of the other sciences is por-
trayed; but in reviewing it I feel that it is very incomplete.

The disproportion between the extent of my duty and the time
at my disposal will explain in part the failure to realize my aim.
Still more, however, is this due to the difficulty of my subject, for
one must master all the sciences which stand in relation to plant
physiology in order to give an effective account of its development.
On account of the specialization to which we are all committed,

1 Wiesner, Beitrage zur Kenntnis des tropischcn Regens, Sitzungsber. d. Wiener.
Akad. d. Wissensch., 1895.

2 Wiesner, Beitriige zur Kenntnis des photochemischen Klimas, Denkschriften d.
Wiener. Akad. d. Wissenschaftcn, 1896 u. 1898.

3 E. Mach, Analyse der Empfindungcn, Jena, 1902, p. 74.

124 PLANT PHYSIOLOGY

hardly any one is properly fitted to carry out this task. I readily
admit that there are many others who could have done this better
than I. Yet I believe that I have drawn for you some of the more
important outlines of the development of our science.

As a chief result of my analysis I have shown the evidence of con-
tinual change, of separation and union, of scientific work. Not only
are the results gained in divided labor united within small special
fields to the advantage of science. Perhaps of still greater advantage
is the contact and union of studies which are apparently Jieteroge-
neous. Fruitful ideas and methods come often enough not from the
narrowly circumscribed field of study, but to a certain extent from
outer and apparently foreign realms. And just in the results thus
obtained, the facts teach us that all human wisdom, all which to-day
furthers the struggle after knowledge, forms only one great unity,
which to the individual comes with more reality the deeper he has
gone into science.

Yet one thing I would not leave unmentioned at the close. Out of
the depths of the past, science has emerged, at first a mixture of truth
and fiction, of the results of study which are often intertwined with
strange embellishments, inventions, and dark hints. In the older
writings, and further on in the literature up till the present time, -
in lessening amount, to be sure, — religious conceptions, or wonder
at creation, appear side by side with the results of research. But
throughout the conviction rings that these reflections, much as the}7
may be in themselves justified and partake of the noblest aspirations
of the human mind, must be separated from science, and belong
to another sphere.

And yet another form of vague inner impulse still rules, even
though it has already been much suppressed, in the realm of science. —
the metaphysical element. A trace of the metaphysical, as salt to
the bread, will perhaps always remain, because, as already shown,
thoughts which help the weakness of the human understanding are
as crutches to the lame. We may be allowed to compromise with
these small remnants of a once rampant metaphysics, if we enter-
tain such ideas only so long as they do not come into clash with
our experience, and really help us in the sure way of observation.
There are indeed optimistic theorists who expect that natural science
will reach complete fruition only after the last trace of metaphysics
has been eradicated.1

1 E. Mach, loc. tit., p. 7.

PLANT PHYSIOLOGY — PRESENT PROBLEMS

BY BENJAMIN MINGE DUGGAR

[Benjamin Minge Duggar, Professor of Botany, University of Missouri, b.
Gallion, Alabama. B.S. Mississippi Agricultural and Mechanical College, 1891;
A.B. Harvard University, 1894; M.S. Alabama Polytechnic Institute, 1892;
A.M. Harvard, 1895; Ph.D. Cornell, 1898; Postgraduate, Alabama Polytech-
nic Institute, 1891-92; Harvard, 1893-95; Cornell, 1896-98; Leipzig and
Halle, 1899-1900. Assistant Professor of Botany, Cornell University, 1900-01;
Plant Physiologist, Bureau of Plant Industry, U. S. Department of Agriculture,
Washington, 1901-02. Member of the Society for Plant Morphology and
Physiology, Botanical Society of America, Deutsche botanische Gesellschaft,
American Association for the Advancement of Science. Author of articles for
botanical magazines, Experiment Station bulletins.]

To the very year one century has elapsed since Theodore de Saus-
sure published his remarkable investigations relating to the nutrition
of plants and to the influences upon plants of certain well-known
physical forces. Although preceded by the publications of Duhamel,
Hales, Ingen-Housz, and Senebier, as well as by those in a somewhat
different line, by Konrad Sprengel and others, we may look upon
the work of de Saussure as a wonderful production for his time and
as strikingly indicative of the status of plant physiological problems
a century ago. His paper may be regarded in a sense as the original
charter or constitution of plant physiology. Fortunately, it is as-
signed to an eminent and experienced botanical historian to recite
the amendments which mark the wonderful growth of this historic
instrument. There remains, therefore, the task of suggesting some
directions of future growth.

No distinction need here be made between those problems which
are readily seen to involve the closest work in such other sciences as
physics and chemistry and those which do not show a relationship
so close. There is certainly much in physiology which must be based
upon physics and chemistry, but when dealing with the causes of
the activities of living organisms, it is in relatively few cases that
explanations may ever be offered in terms of physics and chemistry
alone. Nor is it possible to offer such explanations without the
assistance of these sciences. The progress of the work in physiology
is indissolubly bound up in the development of other sciences. The
benefits are, however, mutual, and as physiology acknowledges the
fundamental importance jaf these related sciences, they in turn must
acknowledge the important contributions, often of fundamental
nature, which have resulted through physiological investigation.

In such a paper it would be impossible to do more than outline
briefly some of the relationships of special problems which, for one

126 PLANT PHYSIOLOGY

reason or another, merit emphasis. In general, the problems in plant
physiology have been well brought out and systematized through
the monumental work recently completed by Professor Pfeffer. To
him the science owes a debt of gratitude which may be acknowledged
as well by one who attempts to suggest future work as by the his-
torian. Again, due recognition should be made of those who have
in recent years based upon this or any similar topic valedictory
addresses before various botanical organizations, — notably, those
of Professors Vines, Ward, Barnes, Reynolds Green, and others.

The fact that every cell or organ requires its food materials, or at
least its nutrients, in liquid form, readily emphasizes the funda-
mental importance of those problems suggested by the relation of
the plant to solutions. The mechanisms for absorption and the general
and special diosmotic properties of the living cell, all of which have
been studied with the most consummate skill, have yielded matchless
results, yet the rewards for future research show at present no dis-
tinct limitations. It has not been possible to determine the nature
of the plasmatic membrane which directly or indirectly possesses
such marked powers of selection and accumulation. The conditions
under which the activities of this membrane may be modified are
but poorly understood; and it is, perhaps, quite beyond the present
possibilities to determine the mechanism of this modification, for
in that must be involved one of the most important vital activities
of protoplasm. Perhaps when many more data have been accumu-
lated by a study of plants of diverse habitat, the conditions of this
modification may be more clearly distinguished. It is known that
continued endosmosis of a particular solute depends largely upon
the use or transformation of this solute within, yet it is not always
possible to demonstrate any change in the substance absorbed. In
any event, it is necessary to ask further light upon the exosmotic
resistance of the plasmatic membrane to the accumulation of turgor-
producing substances, or, in other words, to a further explanation
of what may' be termed one-way penetration. To these phenomena
the processes of excretion and secretion are closely allied, whether
they are ultimately, periodically, or continuously the function of cer-
tain protoplasts.

Further chemical knowledge is needed dealing with the meaning
of high pressures and of the accommodation of very high pressures
in the fungi. As a rule, those protoplasts seem to be resistant to
such high pressures which are also resistant to cold, desiccation, and
other stimulation. Mayerburg, working* under the instruction of
Professor Pfeffer, has recently applied himself to a study of the
method by means of which the organism may regulate its turgor.
It is evident that one of two propositions must be assumed, and that
increased turgor may be produced either (1) by the penetration

PLANT PHYSIOLOGY — PRESENT PROBLEMS 127

of substances from without, or (2) by substances of strong osmotic
action produced within the cell through the stimulative action of
external agents. It was determined in this case that in general no
absorption of the substances bathing the plant occurs; therefore,
osmotic substances are produced within the cell and largely by in-
creased concentration of the normal organic cell products. The
extent and method of this capability for turgor regulation are highly
important, as is also the general question of the relation of turgor
to growth. In recent times some of the important problems in this
connection have been well suggested by the work of Ryssleberghe,
Puriewitsch, Overton, Copeland, and Livingston.

The absorptive systems of plants seem to be admirably adapted
for their needs from a diosmotic point of view. Diffusion may, there-
fore, be sufficiently rapid to supply all demands of the absorbing
cells or organs. Nevertheless, the assumption that ordinarily diffusion
through the cell and plasmatic membrane is sufficiently rapid prop-
erly to provide for the translocation of metabolic products from cell
to cell is certainly open to further inquiry. Present knowledge of the
translocatory processes is insufficient. Plasmatic connections between
cells are now known to be of common occurrence, and this fact has
given further interest to the above inquiry. Brown and Escombe
are of the opinion that the plasmatic connections are eminently
adapted for all of those phenomena which they have found to belong
as subsequently mentioned, to multiperforate septa. They claim,
further, that with slight differences of osmotic pressure the necessary
concentration of gradient for increased translocation would be very
simply effected.

Thus far it has been difficult to throw any light upon cell-absorp-
tion and selection in many complex natural relationships by calling
in the assistance of the dissociation theory and the ionic relationships
of the salts in the soil. The external relationships of nutrient salts,
or the relative abundance of these in substrata supporting vegetation,
constitutes a problem with which the physiologist must be concerned.
It is only necessary to glance at the results of work done by various
experiment stations in this country to be convinced of the great
physiological importance which may be attached to such studies.

Recent results tend to emphasize the importance of considering
to a greater degree the physical conditions of the soil. Some have
even gone so far as to claim that practically all soils contain a suffi-
cient quantity of plant food, and that the all-important question
is the regulation of the water-supply in accordance with the quality
of the particular soil. This latter, however, is an error into which
few physiologists have fallen. Nevertheless, precise studies upon
the relation of plants to the physical characters of soils afford pro-
blems which should receive the best attention. Many of the pro-

128 PLANT PHYSIOLOGY

blems are not new, and in a qualitative way, at least, the problem
of the relationship of the conservation of moisture and the tilth of the
soil to productiveness has been duly appreciated by the best agro-
nomists. We must notice with regret, therefore, that botanists have
not always appreciated the importance of such work. Either directly
or indirectly the water factor is a chief one in regulating the activities
of the living plant and must be considered from every possible point
of view.

It may, perhaps, be less a problem than a routine matter to de-
termine the relation of the rate of absorption of salts in the soil
solutions to water under the varying conditions of growth and
transpiration. Nevertheless, information of this nature is important.

In spite of all the recent work, the physical explanation of the
ascent of water in. trees is a problem which must be mentioned.
The renewed investigations which have been made along this line
from an objective point of view will undoubtedly contribute to its
eventual solution.

It is a matter of interest that in their studies of the physics of
transpiration, Brown and Escombe have found evidence to regard
this process also as a matter of diffusion through multiperforate
septa, rather than a matter of mass action. It is calculated that by
diffusion water may pass out of the stomates to an extent as much
as six times the actual amount of transpiration which has been
observed in special cases.

The great number of cytological investigations which have been
completed within the past ten years indicate notable advancements
in a most important field; and this is particularly true with rela-
tion to the study of nuclear phenomena. Through this work light
has been thrown upon many problems of cell physiology and of
development: and as a result of the latter new theories of heredity
have been advanced. Nevertheless, the field for investigation has
been constantly broadened and many new lines of research made
possible. In spite of the excellent results accomplished, there is yet
great uncertainty as to the interpretations which have frequently
been made. In no field of work, perhaps, is it possible for the per-
sonal factor to enter into the results more largely than in this.
Again, it is unfortunately true that fixed material has been studied
almost to the exclusion of all other and that even general observa-
tions relating to the conditions of growth have been omitted in
many instances. Much attention has been bestowed upon the min-
utest details which seem to be of morphological significance in the
nucleus; but 'often the purely physiological side has been insuffi-
ciently emphasized. It is quite possible that in different plants
the exact method of chromosome division, or the manner of nucleo-
lar disappearance, may not be similar; and it is certainly well

PLANT PHYSIOLOGY — PRESENT PROBLEMS 129

known that external conditions may considerably modify the de-
tails of spindle formation, and perhaps other details in nuclear and
cell-division. The important point in every case is to determine if
the same physiological purpose may be accomplished.

It is extremely important, however, to the subject of physio-
logy that the methods which have made possible these cytological
advances shall be extended and utilized in developing a knowledge
of all of the various activities of the cell. In this way, a clearer
insight may be given of many abstruse metabolic processes; and
certainly further light may be thrown upon the matter of protoplas-
mic decompositions and secretions, the production of enzymes and
alkaloids, tannins and other products. Going hand in hand with
observations upon fresh material, the limitations of micro-chem-
istry alone should determine the possibilities in this direction of the
work.

In such cytological investigations, Fischer's work on the artifi-
cial production of effects resembling those seen in fixed protoplasm
should be borne well in mind. This work is timely, and may assist
in checking irrational developments b}^ forcing a proper regard for
a comparison of the effects observed in fixed tissues with those
shown by the living material.

There are, moreover, but few directions in which the study of
metabolism and metabolic products may not profit from cytologi-
cal research. A notable instance of what there is to be done is well
indicated by the work of the late Dr. Timberlake on the division
of plastids and the development of the starch grain.

Photosynthesis is a topic which has received a full share of
physiological investigation throughout the past century; yet the
problems demanding attention are too numerous for complete enu-
meration. The mechanism of gaseous exchange in leaves has repeat-
edly been experimentally proved to be the function of the stomates.
After critical physical experimentation, Brown and Escombe have
recently reported that the results of their studies of diffusivity
through multiperforate septa are closely applicable to the herb-
aceous leaf with its stomates and substomatic chambers. Assuming
their calculations to be correct, and granting that all of the incom-
ing carbon dioxide is removed, it is estimated that with the stomates
open the maximum observed rate of fixation of C02 in Helianthus
(which is .134 c.c. per square centimeter per hour) would be only
5.2 to 6.3 per cent, of the theoretical capacity of the diffusion appa-
ratus of the plant. In other words, with a gradient between the
outer and inner air of only 5 to 6.5 per cent, pressure, the maximum
observed fixation is well accounted for.

Important problems in the general study of photosjmthesis may
well begin with that of a better knowledge of the structure of the

130 PLANT PHYSIOLOGY

chloroplasts and the constitution of chlorophyll. Neither of these,
however, is absolutely essential to further physiological observa-
tions of a fruitful kind. One of the questions long ago raised is still
pertinent: what is the connection between chlorophyll and the
plastid in which it is imbedded? An answer to this question may
perhaps afford in time an answer to the general inquiry as to the
location of the true photosynthetic property. If chlorophyll is al-
ways the same chemically, it is perhaps probable that the first pro-
duct of photosynthesis may always be the same, although this is
not necessarily true. In any case, the chief problems hinge upon the
method of decomposition of carbon dioxide and water and the syn-
thesis of the first organic product. Neither the hypothesis of Bayer,
Erlenmeyer, Crato, Bach, Putz, nor any other, has, to any consid-
erable degree, been made capable of experimental proof, although
that of Bayer has been most generally accepted. Each of these
assumptions offers some suggestions for future work. Perhaps it
may as well be said that they, to a certain extent, bias future re-
search. Nevertheless, even when the chemical reactions in this
synthesis become known it may yet remain problematical how the
energy of sunlight, that is, of those rays most absorbed, with wave
lengths of 660 to 680 ^a, is made available, or whether it is this energy
directly or indirectly which is concerned in the decomposition. It
has been well assumed that the light-waves may not be immediately
serviceable, but only after the transformation into other forms of
energy. Further, it is not known to what extent this energy is oper-
ative in subsequent transformations. The conditions under which
photosynthesis occurs have been worked out with a fair degree of
accuracy, the status of these problems having been well set forth
by Ewart and others. It is known that when deleterious agents act
at a given concentration merely to inhibit the assimilatory function
(the cell not being permanently injured) there is no evident change
in the chlorophyll, from which it has been inferred that the assim-
ilatory arrest has its origin in the plasmatic stroma. In all cases
photosynthesis cannot long proceed except under conditions of
health of the protoplasts. Nevertheless, the effects of deleterious
agents have not always been studied by very delicate tests, and
further attention might be bestowed upon this matter by the use of
the photobacterial method, or other delicate methods, recently sug-
gested, for it is of considerable interest to determine the relation
of the photosynthetic activity to such agents as compared with
other activities.

Recently the effects of temperature on photosynthesis have been
carefully worked out by Miss Matthaei. She states that the curve
of synthetic activity rises with the increased temperature, that it
is in general convex to the temperature abscissae and somewhat

PLANT PHYSIOLOGY — PRESENT PROBLEMS 131

similar to the curve of relation between temperature and respira-
tion. There is a certain maximum for each temperature. It has also
been ascertained that there is a certain economic light intensity
beyond which there is no increased photosynthetic activity, and
doubtless only injury. This is of special interest in connection with
some recent work by Weis. Recognizing the facts that plants are of
very different types with relation to their light requirements, he has
sought to get an expression of their assimilatory energy. He finds
that (Enothera biennis, a well-marked sun plant, fixes under favor-
able conditions of temperature, and in direct sunlight, about three
times as much CO2 as in diffuse light (light of one sixtieth to one
ninetieth this intensity). On the other hand, Poly podium vulgar e
assimilates in diffuse light somewhat more energetically than in
direct, while Marchantia polymorpha occupies a position intermedi-
ate. This will be welcomed by physiologists as a field for whole-
some ecological study, for an extension of such investigations to an
analysis of plant associations with relation to the light factor may
yield profitable results.

In 1901, Freidel made the surprising report of success in securing
outside of the living plant a gas exchange similar to the photosyn-
thetic action of chlorophyll. He was later unable to confirm his
previous conclusions, nor were the subsequent results of Macchiata
and Herzog concordant. Recently, Molisch has employed upon this
problem the photobacterial method of Beijernick. He finds that
the expressed sap of certain plants may for a time maintain photo-
synthetic activity, but since usually the sap loses this power when
filtered through a Chamberlain filter, it is believed to be due to the
presence of living plasmatic particles. Nevertheless, it is claimed
that an exchange of gases characteristic of photosynthesis may pro-
ceed in a solution of the leaves of Lamium album dried crisp at 35°
C. and then "rubbed up" in water and filtered. The observation
demands much further study, for it must be remembered that the
test is by means of the liberation of oxygen, and Ewart has shown
that some bacterial pigments may have the power, of evolving
oxygen. In the last-named case the gas evolved appears to be, as
he states, " occluded oxygen absorbed from the air by the pigment
substance excreted by the bacteria."

It cannot be stated at the present time, however, as was assumed
from FreidePs first work, that there is any enzyme concerned in the
photosynthetic activity.

To a large extent the problems involved in a study of the assimi-
lation of nitrogen are limited by the very imperfect chemical know-
ledge of nitrogenous products, and may not, therefore, be very
clearly defined. Practically, the whole question of the formation
of amides, proteids, or other nitrogenous compounds in plants

132 PLANT PHYSIOLOGY

remains in obscurity. It is known that these are formed in both
non-chlorophyllous and chlorophyllous plants, and that while in the
former it may proceed in darkness, in the latter, light is apparently
required for the most vigorous synthesis. In the latter case it may
seem to suggest that there is need of the active cooperation of the
chlorophyll apparatus; but here again the influence may be only
indirect, since the roots, as well as the aerial parts of chlorophyll-
bearing plants, are said to possess, to a certain extent, this synthetic
power. Interesting suggestions have been recently made by God-
lewski. The part played in photosynthesis by nucleus and cytoplasm,
respectively, is unknown and may be important.

Some careful studies have been made dealing with the sources
of organic nitrogen in certain of the molds, but owing to the very
great variety of fungous habitats, further studies may indicate
unusual specialization, — perhaps even to such extent as is now
known to be true with the bacteria.

Saida has confirmed and extended the early work of Puriewitsch
and others, clearly demonstrating that under certain conditions
some of the fungi are able to utilize to a variable degree the atmo-
spheric nitrogen. It would be interesting in this connection to give
further attention to various groups of saprophytic fungi. In a pub-
lic lecture Moore has recently made known the results of remark-
ably definite experiments showing that the organism (or organisms)
of leguminous tubercles assimilates free nitrogen apart from its
hosts, and that, therefore, the symbiotic association gives the para-
site no nitrogen-assimilating advantages. Moreover, this nitrogen-
assimilating capacity increases under conditions of artificial culture,
and this increased power is heritable to a considerable extent at
least. This is an important fact and deserves further attention.

Recently Reinke, Benecke, and others have focused our atten-
tion upon the nitrogen supply in sea-water. They find that the
organisms Clostridium Pasteur ianum and Azotobakler chroococcum
are found in the ooze of sea-bottoms; and the suggestion is made
that the external but nevertheless close association of these micro-
organisms with certain marine alga? may explain the power of these
algse to grow so vigorously in situations in which they are found.
The nitrogen supply is probably one of the most important prob-
lems relating to the marine algae. It is to be borne in mind, however,
that the question of fundamental interest is always that of how
these micro-organisms are able to utilize the nitrogen which is ab-
sorbed in gaseous state. No such power is known among phanero-
gams. It has not yet been demonstrated to be possible with the
lower alg;e, and certainly none of the interesting results so far ob-
tained indicate that it is a very fundamental character of fungi
and bacteria. In this connection, perhaps, it may also be stated

PLANT PHYSIOLOGY — PRESENT PROBLEMS 133

that nothing whatever is known concerning the method by which
carbon dioxide is chemo-synthetically utilized by the nitrite and
nitrate bacteria.

There are many interesting problems afforded by the general
phenomena of metabolism, with relation both to those products
which may be immediately utilized and to those which may be stored
up for future use. It is well known that during active growth special
foods may be taken out of circulation and stored up. The stimulus
to such storage is not easily determined. In many instances it is
apparently the protoplasm which is decomposed in order that these
storage products may be formed; therefore, so far as possible a
study of all protoplasmic decomposition phenomena is especially
necessary. The deposition of the cell-plate and the storage of reserve
cellulose are especially interesting. It will be extremely difficult to
follow the succession of changes involved, yet some information will
undoubted!}7 be gained.

The migration of compounds, particularly of those containing
nitrogen, magnesium, and potash, to growing vegetative parts and
to the developing seed is most remarkable. The production, whether
regulatory or otherwise, of the numerous by-products in the cell,
such as tannin, pigments, organic acids, etc., is also of peculiar inter-
est. The functions of some of these compounds must be most im-
portant, and should receive further attention. Tannin, particularly,
is doubtless of much economic importance in the regulation of turgor
and in augmenting the resistance to injurious external agents. Astruc
has recently shown that acids are found in the younger parts of non-
succulents and mostly in the region of maximum turgescence; and
that there is a progressive decrease of such compounds in the older
organs. In succulents, moreover, very slight changes in the external
conditions materially affect the acid content.

It cannot be expected that all of the information desirable with
relation to the composition and action of hydrolyzing and oxidizing
enzymes will be obtainable until more is known of the proteids, to
which group the ferments seem to belong, or with which they are
at least closely related. Whether these enzymes are concerned with
the metamorphoses involved in rendering soluble or transforming
pectin, proteids, glucosides, starches, cellulose, fats, or sugars, their
physiological activities are in the highest degree remarkable, and
worthy of the closest study. The problems which relate to their
occurrence, composition, production, and action require, however,
the combined attention of physiologists and organic and physical
chemists. In recent times, through the work of Brown and Morris,
Fischer, Green, Prescott, Vines, Loew, Beijerinck, Newcombe,
Woods, and many others, these compounds have received renewed
attention. It may be that at present too many obscure phenomena

134 PLANT PHYSIOLOGY

are passed over with the superficial explanation that they are the
result of enzyme action, and, therefore, require no further considera-
tion. It is known that the ferments are largely concerned with the
regulatory production or modification of numerous metabolic pro-
ducts. The activity of each enzyme is circumscribed, yet the power
to do work borders upon the miraculous. It is asserted that invertin
may invert 100,000 times its volume of cane-sugar, and pepsin may
transform 800,000 times its volume of proteids. The chemist is
especially concerned with the composition and occurrence of these,
but the physiologist is interested not alone in the occurrence and
specific action of the enzymes, but also with the effects upon the
general metabolism of the individual plant, with the methods and
conditions regulating the secretion of these products, and with their
vitalities or limiting external conditions. Ferments may be concerned
with external cellular digestion, that is, with the solution and absorp-
tion of foodstuffs from without, thus necessitating exosmosis, or
with intracellular modifications, preparatory to the direct use of the
substances modified in metabolism or in translocation. Again, the
ferments may be present only at a certain definite period in the life
of a cell, produced, undoubtedly, by special requirements and special
stimulation.

When isolated, or at least when outside of the cell, many enzymes
are most active at temperatures far above those which may be main-
tained within the living cell. An explanation of this fact is difficult.
Comparative studies of their reactions to light, heat, toxic agents,
and other stimuli should be made. In the penetration of parasites,
cellulose-dissolving ferments are important, but further information
is needed before it can be said that the presence or absence of such
enzymes to any great extent affects the resistance of certain varieties
and species to fungous attacks. It has been stated that the resistance
of plants to fungous attacks is due largely to the presence of certain
enzymes or toxalbumens present in the cells of the host; and by
others it has been suggested that susceptibility is frequently a special
property due to the presence of certain oxidases, which are regulated
by external conditions.

It has been shown that the mosaic disease of tobacco and other
similar diseases are accompanied by certain oxidase ferments which
appear to prevent the digestion of reserve food. The ferment is de-
veloped in the growing parts of the plant, it may be transferred
from plant to plant, and on the decay of the diseased organism, it is
supposed to be set free in the soil. It is believed that it is then capable
of diosmosis and infection of the young seedling. While it cannot
be shown at present that the enzyme is beyond all question the
direct cause of the disease, this field of work is certainly one which
might yield most interesting results. In this connection it may be

PLANT PHYSIOLOGY — PRESENT PROBLEMS 135

stated that peach "yellows" and several other important contagious
diseases are believed to be of somewhat similar nature. It is also
claimed that the keeping qualities of fruits may bear a certain relation
to the amount of enzymes present at the time of storage; and, there-
fore, a knowledge of the time and conditions of the production of
such enzymes would have great economic value.

In general, Czapek found no enzymes to occur in the excretions
from the roots of higher plants, and it is now generally believed that
the roots of one plant may develop no excretions injurious to neigh-
boring plants, and, therefore, there may be no biological relation
between the roots of non-parasitic plants associated in the given
plant society. It must be said, however, that the information at
hand may not be taken as final. There are yet some peculiar facts
with relation to the rotation of crops which may not be readily
explained on the grounds of the exhaustion of plant nutrients or of
the physical condition of the soil.

The fermentation of tobacco and tea, or hay and manure, involves
enzyme actions which in recent times have received some attention,
although the problems which are of most physiological importance
require solution. The general belief is that in all cases of enzyme
action these compounds do not form a part of the substance upon
which their action is exerted, but they act as a key in each particular
case, unlocking, or rendering labile, a certain organic compound,
which is then subject to rearrangement and transformation. This
is all, however, too speculative for profitable consideration, although
such speculation may have no evil influence if it is not permitted
to encourage the reference of all unusual phenomena to an unusually
obscure and difficult process.

The early perfection of water-culture methods permitted a careful
study of the mineral nutrient requirements in the higher plants.
Pure culture methods have afforded a more accurate means of study-
ing the needs of fungi and certain algae. As usually installed, water
cultures of the higher plants contain bacteria, so that they afford
only a practical test of the requirements. The problem demands
some confirmatory tests, at least, under pure culture conditions,
particularly when organic compounds are employed. It is possible
to grow, in a limited way, higher plants under pure culture conditions.

With the fungi, exact studies may be made upon the influence
of the different nutrients on the general form and upon the produc-
tion of conidia, etc. It has been found, for instance, that, in the
absence of potassium, Sterigmatocytis niger may produce no conidia
or very curious modifications of the conidiophores. By far the most
interesting problems with relation to the mineral nutrients are those
which have to do with the roles of these elements in metabolism.
The effect of the lack of one or another element is made manifest by

136 PLANT PHYSIOLOGY

some general macroscopic change, and sooner or later, by disturbing
pathological changes and subsequent death. It is reported, for ex-
ample, that the absence of iron prevents the development of a healthy
green color, and a scarcity of potassium is made evident, especially
in reduced photosynthesis.

We are yet merely at the threshold of these problems. A cytological
and microchemical study of numerous plants in various conditions
of culture is needed. Loew has instituted some good work in this
direction. He attempted a careful microscopic study of Spirogyra
under the conditions indicated. Although well rewarded, he has not
followed up the result. The problem is, nevertheless, again under
serious investigation, and when much time and thought shall have
been devoted to it, with the utilization of the best cytological methods
available, important results may be anticipated. The possibilities
of the future are particularly dependent upon this, that investigation
must be made of all macroscopic changes as well as of all demon-
strable microscopic changes.

The interrelations of parasites and hosts, or of symbionts, are of
such great physiological interest that some of the most significant
problems may not justly be omitted in this connection. It has long
been assumed that the conditions of nutrition of a host plant deter-
mine to a considerable extent its immunity to parasitic attack. Ward
was unable to detect in the bromes any modification of resistance
due to either high cultivation or to lack of sufficient mineral nutrients.

The results which have been attained with the Uredinacese have
established the fact of the existence of " biologic forms." This opened
a new problem in the study of the Uredinaceae and it was later ascer-
tained that similar host-restricted forms are present in other groups
of the fungi, especially in the powdery mildew Erysiphe graminis.
Salmon has found bridging host species by means of which the para-
site may pass from one species or host to another; for example, the
form of E. graminis on Bromus racemosus is incapable of affecting
B. commutatus , but does not fail to affect B. hordeaceus; and the spores
produced on the latter will then affect the previously immune B. com-
mutatus. From infection studies it is further found that there are
biologic forms among the grass hosts as well. Salmon reports that this
restriction of the parasite to certain hosts may be broken down if
the vitality of the leaf has been lowered by traumatic means. In
this case penetration would result either in the injured area or cer-
tainly within the sphere of the traumatic influence. Spores produced
by such infections proved capable of infecting uninjured leaves. The
application of these results is certainly far-reaching; yet they must
be extended and confirmed before a conservative explanation may
be advanced. It is undoubtedly more or less in line with the well-
known capacity of such fungi as Botrytis, Nectria, and certain Basidio-

PLANT PHYSIOLOGY — PRESENT PROBLEMS 137

mycetes to become parasitic under special conditions. Two leading
inquiries may be suggested: (1) What constitutes immunity or
resistance in the host? (2) What constitutes virulence or attenuation
in the parasite?

As the result of practical experiments in cross-inoculation, on the
one hand, and of close morphological study, on the other, some in-
vestigators have long claimed that there are racial or specific differ-
ences between the organisms producing the tubercles on the roots of
certain leguminous plants. From the results obtained by Moore
(in the U. S. Department of Agriculture) which have been reported
but not yet published, I am permitted to recite a further interesting
fact of accommodation. When an organism isolated from one host
species is grown for a time artificially, under special conditions of
nutrition, its host limitations are in great measure broken down,
and it may produce tubercles on a variety of leguminous plants.
It is likewise conceivable that in the case of certain yeasts the tem-
peratures at which spores are formed, and the specific fermentative
activities, may be changed by special conditions of cultivation.

In view, therefore, of the work already accomplished it is certainly
evident that the propriety of basing what are termed species upon
certain physiological characters has distinct limitations. I do not
intend to bring into this paper a discussion of the inadequacy of the
present nomenclature system from a physiological point of view.
It may be said, however, that it is scarcely possible for the system-
atist to consider all physiological characteristics or to appreciate
the confused ideals of the physiologist.

Stimulated by the marked advancement which has been made in
physical chemistry, especially in the knowledge of electrolytic dis-
sociation, the past few years have added much to our fund of inform-
ation with relation to the toxic action upon plants of solutions of
both acids and salts, as well also as of certain non-electrolytes. The
work of Kahlenberg and True, Heald, Krdnig and Paul, Clark, and
others has contributed enough data for an appreciation of the lim-
itations of toxic action. Nevertheless, no broad generalizations are
as yet possible. Indeed, it is not generalizations which are wanted,
but further experimental data bearing upon the relation to the toxic-
ity of the ions and molecules and their respective interactions.

Studies may well be made dealing with the relation of nutrition
to toxic agents, the effects of temperature and other conditions
upon such action, and the accommodation of organisms to increas-
ing strengths of deleterious agents. Naegeli's work on the oligo-
dynamic action of copper is beginning to be appreciated, and in one
way or another the results have in recent times been repeatedly
confirmed. In most cases, however, no allowance has been made
for the action of the nutrient salts which may be present in the

138 PLANT PHYSIOLOGY

culture fluid and which may affect in a very dissimilar way two
different electrolytes. In this connection it is only necessary to call
attention to the toxic action of certain compounds of mercury, in
which increased toxicity, due to the presence of small amounts of
some other* salt of the same acid as the mercury salt used, is indeed
quite remarkable. Within the past few months an unusually inter-
esting paper has appeared in which Kanda reports the action of
certain toxic agents upon plants grown in pots as compared with
those plants grown in water cultures. His important conclusions
are as follows: (1) A strongly dilute copper sulphate solution, even
0.000,000,249 per cent, is injurious to seedlings of the common garden
pea in water cultures; and neither a solution ten times nor one a
hundred times more dilute produced any stimulative effect. (2) In
pot experiments with soil, the same seedlings are uninjured when
watered twice a week during a period of from five to eight weeks
with a solution of .249 per cent; in other words, even after from
five to seven grams of copper sulphate were present in each pot.
No explanation is offered of this remarkable diversity of action,
but within the past few months another paper has appeared which
may throw light upon the results given. True has ascertained that
finely divided paraffin, quartz-sand, filter-paper, or other insoluble
substances are all found to reduce the toxic action of the deleterious
salt. It is explained on the assumption of an absorption of the toxic
molecules by the surface of the insoluble particles. Increasing the
number of grains of sand, for instance, in any toxic solution pro-
duced the same effect as increasing the dilution. From the results
of these two papers it would seem, therefore, that we have two
entirely different sets of conditions to deal with when any test of
such action is made in water cultures, on the one hand, and in soils,
on the other. If Kanda's results are confirmed, an extensive series
of tests with both fungi and higher plants should be made in order
to determine some relation which may give a working basis for
further comparisons. In fact, much of the work thus far done will
have to be reexamined in the light of these results, for if any pre-
cipitate or other solid particles have been present in the solutions,
an error will enter into the calculations. The question will also arise
if the surface extent of the vessel used in the culture is of any con-
sequence. The practical bearing of these results in the treatment of
soils is a matter which may prove of unusual economic interest.

Loew observed that marked injury results when such a plant as
Spirogyra is placed in a solution of a magnesium salt, or in a solution
in which magnesium is in excess. From all of the results obtained
Loe\v has inferred that there is present in all plants requiring cal-
cium an essential calcium protein compound. When magnesium
must, owing to the predominance of this element, be substituted

PLANT PHYSIOLOGY — PRESENT PROBLEMS 139

for calcium in this proteid compound, there results a lessening of the
capacity for imbibition, attended by unfavorable consequences.
It has been further ascertained by the work of May, Kearney and
Cameron, Kusano, Aso, and others, that there is for each plant a
certain more or less definite relation between calcium and magnesium.
Nevertheless, further experimental proof is needed before this
brilliant hypothesis may be acceptable in its entirety. It may here
be noted that in a paper read by the writer before the Society for
Plant Morphology and Physiology it is indicated that magnesium
compounds exert upon the marine algae the least injurious action of
all nutrient bases. On the other hand, it has not been demonstrated
that the marine algae require calcium.

The general phenomenon of chemotaxy, or chemotropism, de-
mands searching investigation in view of the recent work of Jen-
nings on flagellates, that of Newcombe on root responses, and other
studies on the fungi. There is much to be done in determining the
effects of heat and cold upon special processes, in a study of the
relations of temperatures to other conditions of the environment,
and in showing the limitations of accommodation phenomena.
In the latter study, moreover, the effects of accommodation upon
the general constitution of the organism should be followed. Stimu-
lation at high or low temperatures merely expresses an intensified
or modified irritability. It may be observed in this place that death
at the supramaximal or subminimal may be due to changes of a
very definite nature; but, as Vines has indicated, this means very
little. To say that death at the supramaximal is due to the coagu-
lation of an albuminoid as suggested by Kuehne is insufficient.
For the immediate effect upon the protoplasm of this high tem-
perature must also be of consequence. The external conditions of
temperature of the effects of a modification of conditions are more
or less readily determinable; but it has not been possible to follow
the internal changes which result. It may be noted that the freezing-
point of a plant is lower than that of the expressed sap; yet of
course the freezing-point is not necessarily a valuable indicator of
injury. The effects of temperature upon reproduction will be treated
of later.

The symbiotic relationship of fungus and root to Mycorhiza offers
a fine opportunity for careful investigation. The studies which have
already been made serve only to put the reader in a state of hopeless
confusion.

The universal phenomenon of irritability as manifested by trophic
phenomena has been a fruitful field of investigation. The general
methods of irritable response have been determined; and the best
work of such investigators as Haberlandt, Noll, Czapek, Newcombe,
MacDougal, and others has more recently been directed to the deeper

140 PLANT PHYSIOLOGY

problems relating to the internal mechanism of response and to the
exact methods of transmission of the stimulus, as well as to the
immediate changes in the cells affected.

A word may be said concerning the regeneration phenomena,
which are strikingly characteristic of the lower groups of plants,
but which in the higher plants do not seem to be well emphasized,
and are certainly less understood. The regeneration of the root-tip has
been best studied. In none of the higher plants has it been possible
from a single isolated active non-sexual cell, or a small group of
cells, to regenerate the plant.

Although a study of the physiology of reproduction may be said
to have had its origin in the early observations of Camerarius, all
early studies represented largely only the ecological aspect of the
subject. It is only in very recent years that rapid strides have been
made in the general physiology of reproduction. The effect of con-
ditions upon the production of antheridial or archegonial thalli,
or of pistillate or staminate flowers among dioecious and polygamous
plants, has received very slight attention. During the present year
Laurent has published the results of experimentation during a period
of seven years with the effects of fertilizers, or plant nutrients,
upon spinach, hemp, and Mercurialias annua. It will be seen that
according to his results an excess of nitrogen or calcium has a tend-
ency to produce staminate flowers in the spinach, while potassium
or phosphorus tends to increase the production of pistillate flowers.
The seed produced on the pistillate flowers of these plants gave a
preponderance of female plants; but from these plants, in turn,
the seed yielded a larger number of staminate plants. So far as I
have been able to learn, it has never been determined if in a case of
dicecious perennial plants it is possible by a change of conditions to
induce a temporary or permanent change from pistillate to stamin-
ate flowers, or vice versa. In the same way, the influence of graft-
ing or budding a scion of one upon the other has not been made out,
although it is assumed that the flower will be characteristic of the
scion.

It is with reference to the effects of external conditions upon the
production of sexual and asexual fruiting organs that unusual
progress has been made. In this direction a field of great magnitude
has been opened by the work of Klebs, and it is evidently being
pursued along all possible lines. As yet this work has been extended
only to a few green algae (as, for example, Hydrodictyon and Vau-
cheria); several fungi (Sporodinia grandis and Saprolegnia mixta
especially) ; certain yeasts and bacteria, and finally, to several spe-
cies of phanerogams. While with the algae the light relation is of pre-
vailing importance, with the fungi it is more particularly a matter
of nutrition or transpiration. As a rule, with the latter Klebs finds

PLANT PHYSIOLOGY — PRESENT PROBLEMS 141

the stimulus to reproduction in the failure of the food-supply in the
immediate vicinity of growth. That is, beginning with a well-nour-
ished mycelium, a diminution of food-supply, other conditions being
constant, usually compels reproduction. A change in the specific
chemical content may be effective, and in other cases there are other
concurrent stimuli. In the study of phanerogams it would seem
that the problem is one which is, as a rule, far more complex. It has,
however, been found possible with a few species to produce at will
continuous vegetative growth or continuous flowering, to induce
fruiting in a well-nourished vegetative shoot, and to incite vegetative
growth in a flowering axis. It is probable that all shades of differ-
ence will be found in the capability of plants to have these processes
distinguished by releasing stimuli; and it remains for the future to
determine to what extent this is possible.

The general law which seems to be warranted is, that conditions
most favorable for growth do not favor reproduction. The problem,
then, is to determine for every organism what are these conditions
under which, on the one side, growth, and on the other, reproduction,
m&y occur. Whether, under any circumstances, the complete cycle
of development may be run without any change in conditions ap-
parently awaits proof.

In grafting it would seem that seldom, if ever, do any characters
of the stock pass into those of the scion except such characters as
may be due to the presence of diffusible metabolic products, or pro-
ducts capable of self-propagation upon requisite stimulation. In
this manner it has been shown that albinism may be transmitted
from stock to scion. Again, Strasburger has indicated that atropin
is accumulated in the potato when on a potato stock there is grafted
a scion of Datura stramonium. It has been found that hardiness
in the stock may affect the scion to a marked degree, but here the
real problem is to determine what constitutes hardiness.

Fusion possibilities in vegetative cells are more or less common
in all groups of plants. In basidiomycetes parallel filaments fuse
under many conditions of development, and a pseudoparenchy-
matous tissue may result. In grafting, the layers which fuse may
represent different species or even different genera. Little is known
concerning the factors influencing such fusions. Allusion may also
be made to the fact that plasmodia of the same species of myxomy-
cetes (at least, when produced in nearly similar conditions) fuse
with one another. It should be accurately determined if this is an
inherent property of the same race or species only, and if this fusion
tendency may be weakened or dissipated by diversity of conditions
under which the plants may be grown. The solution of such pro-
blems with simple and rapidly culturable organisms may even throw
some light upon the more complex problems of self-sterility and

142 PLANT PHYSIOLOGY

prepotence (in the sense in which these terms are used horticulturally)
in higher plants — phenomena which may not be explained with
present information. It has been found that tomato and tobacco
fruits are sometimes formed without pollination; and the same is
true of other plants. In certain cucurbits the act of pollination
seems to afford a stimulus for the development of the fruit, even
the dead pollen serving to call forth this response. Under such cir-
cumstances it may well be that other chemical stimuli may produce
the same effect. On the whole, there are no more interesting pro-
blems in physiology than those relating to pollination, the penetra-
tion of the pollen tube, and conditions of fertilization. Many phases
of these problems have thus far been studied by gardeners and
horticulturists alone.

In this connection may be mentioned another fusion phenomenon
of physiological interest, — that of double fertilization in the angio-
sperms. This fusion of the second sperm nucleus with the endo-
sperm nucleus (itself a compound of two nuclei of the gametic
groups) or with one of the polar nuclei, may have a special signifi-
cance, or it may be merely the expression of the fusion tendency
which has not been lost, although the function of the endosperm
nucleus may have undergone specialization. In the case of the
pine, it will be remembered that the second sperm nucleus fre-
quently undergoes division in the cytoplasm of the egg. What is
meant by the fusion of the gametes? This is always a fundamental
problem. It may be strictly a matter of the fusion of characters, or
it may further be a stimulus to embryonic growth. It is a remark-
able fact, however, that this stimulus to embryonic growth does not
merely involve the embryo itself. The limitations of the correlations
which seem to exist between the mere process of fertilization and
incitation to growth in the extra-carpellary structures are extremely
complex. On the other hand, the process of fusion is often imme-
diately followed by the resting period.

It would be extremely well if further attention could be directed
to the matter of parthenogenesis in the higher plants. Except in
the case of Nathanson's studies upon Marsilia, little has been done
to indicate the conditions which may induce or which may tend
to induce this process. In recent years, artificial fertilization, or
stimulus to a certain growth of the egg in the lower animals, has
been effected by chemical agents, by changes in the density of the
solution, and by other means. This work has demanded world- wide
attention from animal physiologists. It has been too much neglected
from a botanical point of view, although the difficulties involved
in similar studies with plants would be, for the most part, immeas-
urably greater. Yet it is certainly possible to prosecute such studies
along the lines indicated.

PLANT PHYSIOLOGY — PRESENT PROBLEMS 143

Except in the case of Sporodinia grandis, and perhaps one or two
other species of Mucoracece, mycologists have experienced great
difficulty in securing the zygosporic stage of these fungi. The recent
paper by Blakeslee, announcing the conditions governing zygo-
sporic formation in this family, seems to open a field for investiga-
tion wholly novel and suggestive. The substance of his results is
that this family may be divided into two principal categories, desig-
nated, respectively, as homothallic and heterothallic, these terms
corresponding to monoecious and dioecious forms among higher
plants. Sporodinia grandis belongs to the homothallic type, both
gametes in every union developing from the same thallus. Rhizopus
nigricans belongs to the second and larger class, the heterothallic
type, in which the two gametes are invariably the product of two
mycelia, which mycelia are sometimes of diverse vigor. When, in
.culture, the two strains, as they are termed, grow together, zygo-
spores are abundantly produced along the lines of contact. These
are the striking results of this important paper; but other related
physiological facts have been observed, and only further investigation
can tell whether this is a special case of gametic union in the fungi,
or whether similar phenomena may be found to be characteristic
of other groups where there is gametic union.

The discovery of Mendel's hybridization studies and the inde-
pendent confirmatory evidence furnished by De Vries, Correns,
and others, all indicate the necessity of differentiating unit charac-
ters and of following separately the inheritance of each unit char-
acter. The idea which it involves of the purity of the gametes with
respect to unit characters, the segregation of unit characters in
the formation of the gametes, is one of fundamental importance.
Such work has given a marvelous impetus to studies in inheritance.
Numerous investigators have followed up this work, but it will be
many years, perhaps, before a test of the Mendelian laws can be
carefully made with any great number of plants and animals. The
exceptional instances already reported of the appearance of mosaic
characters and the dissimilarity in the product of reciprocal crosses
themselves indicate further fields for experimental research. Only
a word need be said bearing upon the phylogenetic side of physi-
ological work, since phylogeny, as well as pathology or ecology,
constitutes a separate section of biological science. The admirable
work accomplished by De Vries, serving beyond all question to de-
monstrate experimentally the origin of species by leaps or mutations,
necessitates laying further stress upon discontinuous variation as
a factor in the origination of existing species of plants. It is to be
doubted, however, that most botanists will at present concur in
such an opinion as that the evidence advanced is sufficient to disregard
or disparage the part which is played by continuous variation in the

144 PLANT PHYSIOLOGY

origination of species. Continuous variation must be manifest by
relatively slight variations; and it would be unfair to expect at
this time the experimental proof of its efficiency. It may even be
assumed that there is a complete series between continuous varia-
tions and discontinuous variations, as well, perhaps, as between
the possibilities of inheriting immediately or ultimately such varia-
tions. Many of the problems in plant physiology are distinctly
practical problems. The task of the physiologist is primarily to
study the activities of plants irrespective of practical bearing. To
have the greatest possible breadth and force, however, the culti-
vated plant may not be neglected in any of its artificial environmental
conditions. It is unfortunate that as yet physiological botany has
not been made fundamental to agronomy, horticulture, forestry,
and other sciences, arts, or commercial pursuits. Physiology can-
not be limited by any practical problems, nor can any sacrifices
be made, but a sympathy with commercial endeavor will invigorate
the work, will afford equipment, and will contribute towards the
common good.

In conclusion, it may be said that present-day physiology, even
more than any other section of biological science, is fundamental.
Many phases of pathology, ecology, phylogeny, and experimental
morphology, especially, may not be clearly differentiated as sections.
Broadly conceived, plant physiology concerns itself:

(1) With the relationships of existing organisms, ontogenetically
and phylogenetically. Phylogeny would necessarily claim much of
this general field, as would also morphology, ecology, and other sub-
divisions.

(2) With the functions or activities of organs, tissues, and cells,
and the interactions and interrelations of these one \vith another
and with external forces. It is here that morphology touches physi-
ology most closely, and here experimental morphology must have
its basis.

(3) With the incorporation and excretion of matter, metabolism,
and growth, the sources and uses of energy, irritability, and the
minute constitution of living matter. In this last are included many
of the most fundamental problems, not necessarily problems in-
volving the question "What is life?" but problems concerned with
the resolution of those factors and an intimate knowledge of those
materials which make life possible.

SECTION D — PLANT PATHOLOGY

SECTION D — PLANT PATHOLOGY

(Hall 1, September 23, 10 a. TO.)

CHAIRMAN: PROFESSOR CHARLES E. BESSEY, University of Nebraska.
SPEAKERS: PROFESSOR JOSEPH C. ARTHUR, Purdue University.

MERTON B. WAITE, U. S. Department of Agriculture.
SECRETARY: DR. C. S. SHEAR, U. S. Department of Agriculture.

THE Chairman of the Section of Plant Pathology was Professor
Charles E. Bessey, of the University of Nebraska, who opened the
Section with the following remarks:

" It gives me great pleasure to preside over this Section of the Con-
gress of Arts and Science, since I have been interested in watching
the development of the subject with which it deals from its beginnings
in this country. The subject is still so new in American botany that
many of us in this room remember when it had no existence. Some
of us remember the efforts, about twenty years ago, of a few botanists
who felt that the United States Department of Agriculture should
undertake a systematic and scientific study of plant diseases and
their causes. We recall the formal and informal letters we wrote,
and the protesting articles which we published in scientific journals.
We remember our gratification, not unmixed with some bewilderment,
when the Commissioner of Agriculture acceded to our urgent sugges-
tion by appointing a specialist in agrostology to the position of plant
pathologist. Although scientifically illogical, this proved to be a
fortunate appointment, and good work was at once undertaken, and
rapid progress made in the study of certain plant diseases, accom-
panied by experiments in regard to the best methods of eradicating
them.

" From this time of small beginnings so much progress has been
made that to-day this country stands foremost in this department
of botany. In the United States Department of Agriculture the
Division of Plant Pathology now commands the services of many
trained specialists, and. in addition, more than half of the experiment-
station botanists are plant pathologists.

" Gentlemen, I congratulate you upon the fact that, while you
represent one of the most recent developments of botanical science,
it is one which you have pushed with such vigor that in the short
period of a score of years it has grown from nothing to its present

148 PLANT PATHOLOGY

proportions, and I congratulate you further in that you are engaged
in work which is at once scientific and immediately useful to the
community. I trust that your deliberations to-day may result in
giving still further encouragement and impetus to this department
of pure and applied science."

THE HISTORY AND SCOPE OF PLANT PATHOLOGY

BY JOSEPH CHARLES ARTHUR

[Joseph Charles Arthur, Professor of Vegetable Physiology and Pathology, Purdue
University, b. Lowville, New York. 1850. B.S. Iowa State College, 1872;
M.S. ibid., 1877; D.Sc. Cornell, 1886; Post-graduate, Johns Hopkins, Harvard,
1879, University of Bonn, 1896. Botanist, New York Experiment Station,
1884-87; Professor of Botany, Purdue University, 1887. Member of the
Botanical Society of America; American Association for the Advancement of
Science; Indiana Academy of Science; Society for the Promotion of Agricul-
tural Science ; Association Internationale des Botanistes ; Torrey Botanical
Club; etc. Author of Plant Dissection ; Living Plants and their Properties, etc.]

PLANT pathology, in so far as it has become a science, is an eminently
practical one, and credit must be given for the initiative of its devel-
opment largely to the stimulating demands of economic interests.
The more intelligent and intensive methods employed in agriculture,
horticulture, and floriculture during recent years have emphasized
the profitableness of making due provision for maintaining the health
of a crop and for evading and combating diseases in their multi-
form disguises and modes of attack. It is the reciprocal stimulus
of the cry from the commercial world to the man of science that has
led to the present highly creditable and valuable understanding of
the causes of many forms of diseases in plants, and of their thera-
peutic treatment. Although far from being a well-rounded and
clearly established science, yet its high standing in the long roll of
departments of classified knowledge is widely recognized, and its
rapidly increasing growth is as sure to be maintained as the arts of
productive commercialism continue to outstrip and dominate those
of war.

Pathology of plants, as an independent subject, having its own
lines of growth and its own terminology, is of very recent standing.
Essentially all the part that rises much above empiricism and natural
deduction from cursory observation has come to light within a quarter
of a century. Very little that cannot be quite as properly relegated
to mycology, morphology, and physiology antedates 1880.

The beginnings of the science as displayed in the earliest works
giving an independent treatment of the subject are but little more
than a century old. These writings are interesting in showing how
carefully and effectively the paucity of facts was displayed upon a
nomenclatural scaffolding built in imitation of the ancient edifice
of human medicine and surgery. A glance at them will prove not
only entertaining, but indicate the early lines through which our
knowledge has been derived and the primitive influences moulding

150 PLANT PATHOLOGY

its form. A representative work of the early school of pathologists
is by von Zallinger of the Austrian Tyrol, whose treatise De mor-
bis plantarum appeared in 1773. It is a scholarly and compre-
hensive work. Here are some of the topics considered: In what
does the life and death of plants consist? Plants have diseases;
wherein lies the health of plants? What may be called a disease
of plants ? Unfavorable appearances are indications of disease ; how
many general symptoms of diseases may be found? How many
groups of diseases are there? If I should continue, it would soon
appear that the work culminates in a classification of diseases based
upon symptoms. The fundamental idea of the work is that when
symptoms are correctly understood, knowledge of the disease fol-
lows with certainty, and treatment may be prescribed accordingly.
The classification of diseases, as stated by the author, follows that
of contemporary medicine, modified by the methods introduced
by Tournefort and Linnaeus. There are five general classes, divided
into nineteen orders and eighty-four genera. Thus the second class is
called Paralyses, and is divided into four orders: Anorexice, Adynamia
excretionum, Anaphrodisice, and Commata. The last order, Commata,
embraces three genera, Apoplexia, Lethargus, and Lethargus gcmmarum.
It is easy to see from the vantage-ground of present knowledge that
this is more a classification of ideas than of facts. In truth, although
the author recognizes the value of a knowledge of causes, the wrork
does not touch upon the true etiology of any disease, and furthermore
does not suggest a single prophylactic or therapeutic measure of even
meager worth.

A similar work to the preceding is the second part of J. J. Plencks'
Physiologia et Pathologia Plantarum, published at Vienna in 1794.
But a more progressive work, in that it exhibits a better acquaintance
with conditions in nature, is that of the Freiherr von Werneck, head
forester, who lived in the Rhine provinces, and in 1807 published
a Versuch einer Pflanzen-Pathologie und Therapic. Von Werneck
philosophized thus: The simpler composition a body has, the fewer
driving-wheels contribute to its action, but also the briefer, more
obscure, and more involved is the chain of causes that lie at the basis
of the movement. In order to be able to recognize each simple driving-
wheel, or, what is the same thing, each simple cause, we must know
the full connection of each simple condition and the value of the
contribution of each simple ingredient to the whole. But the incom-
pleteness of our knowledge of the plant body makes this determina-
tion of simple causes impossible.1 The author goes on to distinguish

1 Je einfnchor zusammengesetzt ein KSrper ist, je weniger Triebrader zu seiner
Bewegung beitragen, je kiirzer aber auch, je dunkler und verwickelter ist die Kette
von Ursachen, welche den Grand der Bewegung enthalten. Um jedes einzelne
Triebrad, oder — welches einerlei ist — jede einzelne Ursache bestimmen zu
konnen, miissten wir den ganzen Zusammenhang jedes einzelnen Verhaltnisses und

HISTORY AND SCOPE OF PLANT PATHOLOGY 151

between immediate and remote causes, and to write learnedly upon
many pertinent topics. But the amount of real knowledge of facts
is small and inconsequential. Seven substances are listed as all
that the author had found serviceable in the treatment of diseased
plants during eighteen years of experience. They are: Lime, acids,
alkalies, balsams, honey, corrosive sublimate, and mineral water.
From perusal of his account one is forced to conclude that not much
good was accomplished by the application of these remedies.

One more work should be brought forward in this connection. In
1795 J. M. Ritter von Ehrenfels, living not far from Vienna, pub-
lished a work on the diseases of fruit-trees, which he addressed to
the horticulturists among the middle classes. It was written with
enthusiasm and inspired by patriotism and love of nature. Scholastic
terms are largely discarded and a familiar but dignified style adopted.
A work on the same lines at the present time would find place in
the "Rural Science Series" or the "Nature Library." However, as
in the other works mentioned, it is very evident that the science of
pathology and therapeutics was in its helpless infancy.

There is no need to pursue the examination of the works of the begin-
ners further. Enough has been displayed to show that, for the most
part, in trying to systematize what little was known regarding the
subject, they made a brave showing writh borrowed finery of words.
Nevertheless, an efficient terminology is not only attractive at any
stage of a science, but in its later development nearly indispensable,
in order to express exactly and concisely what has been definitely
established. Its need is much felt even at the present time. At the
Madison Botanical Congress in 1893, the matter was discussed in
detail, and it was agreed that "it is desirable for vegetable patho-
logists to unite upon an international and purely scientific classifica-
tion of plant diseases," which should be provided, for the most part,
with a nomenclature based upon Greek and Latin roots, and that
the common names, used by people in general, should be codified,
and so far as feasible restricted in application to definite phenomena.
The remarks of Professor Bessey at that time are still pertinent, and
still deserve to be put into action. "We have two problems before
us," he said. "One is the scientific classification of diseases or patho-
logical phenomena; the other the determination of what are the
corresponding vernacular terms used by the people. The first of these,
the scientific classification, should be international; the work of
deciding upon the ordinary vernacular terms need not be interna-
tional." Nothing was done at the Madison meeting but outline the
subject, and the committee * appointed at the time to continue the

den Werth des Beitrags jedes einzelnen Bestandtheils zum Ganzen kennen. Aber
die Unvollkommenheit unserer Kenntnisse vom Pflanzen-Korper macht auch diese
Bestimmung der einzelnen Ursachen unmoglich (p. 11).

1 This " Committee on the Nomenclature of Plant Diseases" was composed of

152 PLANT PATHOLOGY

work has made no subsequent report. In returning to the historical
survey, we find that the borrowed nomenclature of the early patho-
logists rapidly fell into disuse, as the subject developed, because
unsuited to its needs. Yet at the present time there is no question
but that a vast accumulation of observation and deduction could
be made more available by a purification of names, due consideration
being shown to philology and to that curious, indefinable force to
which we all submit, usage. We need not adopt the scholastic terms,
but in some cases they might prove suggestive.

Plant pathology is debtor to many sciences for suggestions and
foundation material, but the debt to human and animal medicine
and surgery is not large, and consists chiefly in the transfer of names,
with superficial reasons underlying the application.

The next influence that swayed pathology came from a wholly
different quarter, and proved of more than temporary strength. In
the publication of the treatises on plant physiology and structure
by A. P. de Candolle in France, Schleiden and Sprengel'in Germany,
and the translations from German texts into English and other
languages, observations upon deviation from the normal in plant
life found considerable substantial basis upon which to rest. Back
of these were the discoveries and doctrines of Malpighi, DuHamel,
Hales, and Knight, of the earlier physiologists, and Treviranus, Molden-
hawer, and especially von Mohl, of the later physiologists of this
period, to give direction and strength to the course of ideas, although
their influence upon pathology was only indirect. I am now speaking
especially of the period from about 1800 to 1850.

Another influence upon the development of the subject during
this time, destined to become greater than all others, was the grow-
ing interest in mycology. The fungi that are largely instrumental
in producing diseases are the very small or microscopic forms. In
the study of the classification of these during the first half of the
nineteenth century, Persoon, Nees von Essenbeck, Link, and Le-
veille especially deserve mention, while Sowerby, Corda, and the
brothers Tulasne furthermore contributed much by way of splendid
folio illustrations of a large number of species. The systematic
diagnoses of the species were chiefly the work of De Candolle, Che-
vallier, and Castagne in France, S. F. Gray and Greville in Great
Britain, Sommerfelt and Fries in Scandinavia, Link, Wallroth, and
Rabenhorst in Germany, and Schweinitz in America. Of these the
greatest influence was exerted upon systematic mycology by De
Candolle, Fries, and Link. Treatises on pathology became more

Professor Byron D. Hulsted, of Rutgers College New Brunswick, N. J., as chair-
man, and Messrs. W. F. Swingle, L. R. Jones, Chas. E. Bessey, W. A. Kellerman,
Geo. F. Atkinson, and B. F. Galloway. It was to report to the botanical section
of the American Association for the Advancement of Science. The time of service
was not limited. See the Proceedings of the Madison Botanical Congress, 1893.

HISTORY AND SCOPE OF PLANT PATHOLOGY 153

abundant at the last of this period, but were chiefly by German
and Austrian botanists. The best of these were by linger in 1833,
Wiegmann in 1839, Meyen in 1841, and Nees von Essenbeck in 1842.
In these and other works an enumeration and consideration of the
parasitic fungi occupied half or more of the space. It must not be
inferred, however, that any clear notion had yet developed regard-
ing the relation which parasitic fungi hold to the host and to the
accompanying disease. Throughout this period it was generally
maintained that their existence was conditioned by the host. At
first it was thought that parasitic fungi could not be reproduced by
their spores, but were generated by the fermenting sap of the plant,
or by a transformation of the perverted tissues. When it became
clear that the spores did reproduce the fungus, it was still asserted
that the fungus was a product of the disease and that its form was
dependent upon the kind of host, or upon the state of the host at
the time it was attacked by the disease. Endophytic species were
frequently called pseudo-organisms, and the opinion was general
that they might be transformed from one kind into another, accord-
ing to the state of the weather, degree of moisture, amount of nu-
trition supplied by the host, or other uncertain factors.

It is not a part of the speaker's purpose to sketch the history of
plant pathology, but in a perspective outline to trace the dominant
influences that at successive stages of the science bore strongly
upon the course and rapidity of its development. We have seen
that prior to the beginning of the nineteenth century the science
had so little knowledge at command that it might be said to be in its
helpless infancy. During the first half of the nineteenth century
it made rapid growth, nourished by the pabulum derived from the
studies of plant structure and function, and from the systematic
study of fungi, although harboring many erroneous beliefs. This
period may be looked upon as a lusty childhood, full of activity and
promise, but guided by unstable and imperfect theories. The next
period extended from about 1850 to 1880, during which there was
accumulated much positive knowledge of the fundamental features
of the science that gave substantial basis for coming usefulness.
It was a period of youth, to be followed by the period of established
maturity.

The greatest single service rendered to pathology during this
interim of thirty years was performed by De Bary in establishing
the fact that healthy plants may be attacked and penetrated by
fungi, which may there flourish and propagate, thus disproving
the long-held theory that parasitic fungi were emanations of the
higher plants. This did not lead at once to a full understanding of
parasitism, but it cleared the way for an intimate study of the
endophytic fungi. In this line of research De Bary was unmistakably

154 PLANT PATHOLOGY

the leader. In 1853 he published his investigations on the rust fungi
and the diseases caused by them, with special reference to the
cereals and other useful plants; and in 1865 he gave to the world
the first demonstration of hetercecism among the Uredinales.

Nothing could better show the unprejudiced attitude and clear
judgment, together with facility for turning unintentional sugges-
tions to account, which De Bary displayed in his studies, than this
demonstration of hetercecism. For nearly a century English and
Dutch farmers had been convinced from observation that the cup-
fungus on barberry bushes in some manner promoted, or possibly
gave rise to, the very unlike wheat-rust. These two forms of fungi
are so dissimilar in appearance and structure that professional
botanists would not entertain the notion that they were but two
forms of the same species. Nearly at the beginning of the century,
and more than fifty years before De Bary began his experiments,
Sir Humphry Davy, the greatest chemist of his times, and well
versed in the natural sciences, said: "The popular notion among
farmers, that a barberry tree in the neighborhood of a field of wheat
often produces the mildew [English term for rust], deserves exam-
ination. This tree is frequently covered with a fungus, which, if it
should be shown to be capable of degenerating into the wheat
fungus, would offer an easy explanation of the effect."1 Others
before and after Davy recorded similar opinions. After De Bary
had shown by sowing spores of wheat-rust on barberry leaves, and
raising the cup-fungus, that the views of the English farmer were
well grounded, Continental botanists made many additional studies
of hetero?cious rusts, and in 1880 Professor Farlow started the work
in America. But in Great Britain, where the annual field demon-
stration was so plain as to attract the attention of the unlettered,
De Bary's results were discredited for more than a quarter of a
century, and almost the only work in heteroecism so far done,
unless we include the recent brilliant work of Marshall Ward and
his pupils on the transference of the uredo-stage to allied hosts, was
accomplished in the decade following 1883, by Plowright of King's
Lynn, a physician quite isolated from direct scholastic influences.

In the study of life-histories of rust-fungi, and in the introduction
of a culture method of observation now employed among all classes
of plants, as well as in many other ways, De Bary contributed greatly
to the advancement of mycology. The economic problem of the
cereal rusts, for which De Bary supplied an interpretation of the
most fundamental unknown quantity, transcends that of all others
in plant pathology, if measured by the annual money loss to the
cultivator in America, Australia, and possibly other countries. It
is yet an unsolved problem. De Bary's services culminated in his

1 Davy, Elements of Agricultural Chemistry, 2d ed., p. 2G6, London, 1814.

HISTORY AND SCOPE OF PLANT PATHOLOGY 155

classical work on the morphology and biology of the fungi, pub-
lished in 1884 at Leipzig, and three years later issued in the English
language.

Beside great progress made in mycology during the thirty-year
period now under consideration, another subject was started and
well advanced, which was to become one of the most important sci-
ences affecting pathology, whether of plants or animals, and destined
to exert the greatest influence, furthermore, upon human well-being.
Pasteur had prepared the way by his epoch-making researches on
wine and beer, and the diseases of silkworms, for many excursions
into the new world of the "infinitely little," the mighty pigmy
kingdom of the bacteria, discovered by Leeuwenhock a century
before, but almost unrecognized until now. It had been shown
that bacteria were plants, although their power of rapid movement
kept many students from fully accepting the fact, when, at the
beginning of this period, Cohn, the distinguished botanist of Bres-
lau, first systematized the flora of this new realm, and established
the infant science of bacteriology. Already Koch, then a young
physician practicing in the vicinity of Breslau, had placed the
question of the bacterial origin of certain contagious diseases of
animals beyond doubt by his studies of anthrax, but it was not
until the last of the period that any plant disease was definitely
shown to have a similar origin. In 1880 Dr. Burrill, of the Uni-
versity of Illinois, published his studies on pear-blight, which he
called the anthrax of trees, demonstrating that it was always
accompanied by an enormous production of minute, colorless bac-
teria, and that the disease could be set up in perfectly healthy trees
by inoculating a few of these bacteria into the young shoots. As
in the case of every important discovery, it required subsequent
studies fully to establish the claims of the discoverer, and to pro-
cure popular acceptance of the truth. Even to-day, after the lapse of
a quarter of a century, there appears to be a lurking suspicion in the
minds of most European botanists that, after all, the bacteria ac-
companying pear-blight are not, strictly speaking, the cause of this
destructive disease of pomaceous trees. This is doubtless in part
due to the fact that the disease does not occur in Europe and other
countries outside of North America, for which our trans-Atlantic
fruit-growers have reason to be profoundly grateful, although prob-
ably unaware of their good fortune. If our distinguished botanical
visitors from across the waters to this Congress will observe the
great injury which the disease has produced this year in American
orchards, in many places killing outright a majority of the pear-
trees, and doing immense harm to apple- and quince-trees, and will
let it be known upon their return that the statements regarding
this disease are not boastful tales to be classed as characteristic

156 -PLANT PATHOLOGY

of this endlessly expansible country, but sober facts, they will do a
distinct service, not only to their eminent colleagues, but to the
whole science of plant pathology. For when important truths
are not accepted by the students of a science, the progress of the
science suffers. That this first claimant among contagious diseases
of plants is truly of bacterial origin is a statement as worthy of
acceptance as that two and two make four, without need of mental
reservation.

After this digression let us glance at the general treatises on the
subject of pathology which went into the hands of the public dur-
ing the thirty years preceding 1880, for one of the indications of
cumulative activity and interest in scientific matters is the produc-
tion of handbooks. They serve as maps to show the extent of ex-
ploration, the direction of advancement, and especially as a record
of accepted knowledge, all in addition to their usefulness as prac-
tical reference-books for the cultivator.

It may be stated first that essentially all treatises of this period
were by German authors, or reflections from German writings.
The one work that exerted the greatest influence was by Kiihti
of Lower Silesia, afterward at the University of Halle, not only
because it gave the latest information regarding parasitic fungi, to
which the work was chiefly devoted, but because the author poured
a hot fire of criticism into the camp of hero-worshipers, who ex-
tolled Schleiden and Schacht, both extensive writers upon physi-
ological and economic botany, and Liebig, the agricultural chemist,
and who, in admiration of the great and brilliant service these men
rendered to science and to economics, were blind to their errors
and to the drag upon progress which these errors imposed. He
decried the medieval tendency to lean upon authority, and ad-
vocated closer study of natural phenomena. "It is the problem
of the times," he says, "it is the problem, especially of the younger
husbandmen, to progress energetically, to unite science with prac-
tice, and to apply the results of the former to the improvement
of the latter, for personal profit as well as for the benefit of our fellow
men. But it is not words or phrases that will lead us to this, — re-
sults, economically important results, must we be able to show; but
in order to do this, we must understand that to examine methodically,
see clearly, observe sharply, and interpret correctly the natural
laws underlying the association of phenomena, is the true fruit of
scientific study." l The admonition was timely and effective. The

1 Es ist die Aufgabe der Zeit, es ist die Aufgabe, insbesondere der jtingeren
Landwirthe, riistig fortzuschreiten, die Wissenschaft mit dem Leben zu ver-
kniipfen und die Ergebnisse der ersteren auszubeuten zur Vervollkommnung
des letzteren, zum eigenen Vortheil wie zum Nutzen unserer Mitmenschen. Aber
nicht Worte und Phrascn sind es, die uns dazu fiihren, — Resultate, practisch be-
deutsamc Resultate, miissen wir aufzeigen konnen, und um dies zu vermogen,
miissen wir einsehen lernen, dass methodisch untersuchen, klar sehen, scharf

HISTORY AND SCOPE OF PLANT PATHOLOGY 157

German investigator and the German cultivator became the fore-
most promoters of the science and practice of plant pathology, and
maintained the supremacy almost, if not quite, to the present time.

Beside Kiihn's admirable work issued in 1858, and also a dozen
or so small handbooks showing the popular interest, two especially
notable works, covering the whole range of the subject as then
understood, appeared during this trental period. They were by
Sorauer, director of the experiment station at Proskan in Silesia,
issued in 1874 and enlarged and improved in 1886, and by Frank,
of the University of Leipzig, issued in 1880, both authors after-
ward continuing their labors in Berlin. The two works are essentially
alike in the division of the topics, except that Frank devotes over
a hundred pages to harmful insects, while Sorauer, like most plant
pathologist s of the present time, leaves the consideration of insects
almost wholly to the entomologist. Disregarding the chapter on
insects, both authors devote approximately one half of their space
to parasitic fungi, one third to external influences, such as unfavor-
able conditions of soil, moisture, air, and food-supply, and the
remaining one sixth to wounds and galls. There is no need to go
into detail regarding these works; their essential features have been
preserved in all general treatises up to the present time, and are
familiar to every one having some acquaintance with the subject.

At the beginning of the ninth decade of the nineteenth century
plant pathology was a subject for scholars and for those who wished
to know the reason for things, but it had no great economic im-
portance. It taught many useful matters, but only in a small way.
The part pertaining to parasitic growths was an adjunct of my-
cology, that arising from non-parasitic causes was an adjunct of
plant physiology, and that having to do with wounds and galls
was an adjunct of plant anatomy. But as a unified and independent
science it had little standing. To-day shows a great change. There is
such a vigorous growth in so many directions that as a science
it seems unsettled and ill-balanced, but its merit as an important
and vital part of useful knowledge has been recognized. It has
become a utilitarian science of vast possibilities. Like the subject
of electricity, which not long since was a department of physics of
only moderate prominence, it has felt the energizing effect of a
demand to help in forwarding the great economic enterprises of the
times, which are the foundations of commerce. In the early days
plant pathology was developed by botanists who had special love
for the subject, working at such odd times as their regular duties
permitted. To-day it has its organized and independent workers,

beobachten und den naturgesetzlichen Zusammenhang der Erscheinungen richtig
auffassen lernen, die wahre Frucht naturwissenschaftlicher Studien ist. — Klihn,
Die Krankheiten der Kulturgewachse , Berlin, 1858.

158 PLANT PATHOLOGY

and the results are far more numerous and valuable; just as the
mineral output of the world has been vastly increased where large
corporations have supplanted the individual miners who worked
for personal gain and love of wild life.

To start the science into this augmented development required an
unusual combination of circumstances. So long as the farmer was
content to lose from ten to fifty per cent of his crop of grain from
smut, rust, or other fungous diseases, and ascribe it to the vague and
uncontrollable action of the weather or the season, no concentration
of effort was made to understand the nature of the disease, as a dis-
ease, and to invent methods of eliminating it from the fields. It
required an epidemic severe enough to bring discomforts and threaten
poverty in order to start an outcry that would be heeded, and
divert the forces of science into a new channel. Such an occasion was
the epidemic of potato disease of 1844 and 1845 in northern Europe,
and notably in Ireland, where a famine resulted. But the region
did not possess scientific men prepared to cope with the situation.
Another such occasion was the introduction of the grape mildew
into the wine districts of France. The downy mildew of the grape,
common in America, but never epidemic, was first noticed in south-
western France in 1878. By 1882 it had .become so destructive
that in many vineyards about Bordeaux, where proximity to the
ocean kept the atmosphere moist and favorable to fungal growth,
the leaves dropped from the vines and the harvest of fruit was almost
worthless. Here was a critical situation, and the man to cope with
it was not wanting. That man was M. Millardet, professor in the
Academy of Science at Bordeaux. A fortunate observation at this
time was put to the test during the season of 1883, and through per-
sistent study and experimentation carried on by Millardet, and by
others under his direction, and by still others working independently,
the most important fungicide yet known was soon in general use,
and a great industry saved to France. The substance employed has
been called from the first the Bordeaux Mixture, and consisted of
lime and sulphate of copper in solution, which was sprayed upon
the foliage.

It was the introduction of spraying in the early eighties that
gave new life and new direction to the study of pathology. It also
shifted the geographic centre of activity in the study of plant dis-
eases from Silesia, where it had remained from the earliest times,
westward into France. Nevertheless France was not destined to
hold this advantage long.

In September, 1SS4, the American Association for the Advance-
ment of Science appointed a committee l on the "Encouragement

1 The members of this committee were J. C. Arthur, C. E. Bessey, W. G. Farlow,
T. J. Burrill, J. T. Rothrock, W. J. Deal, and C. H. Peck. The following year the

HISTORY AND SCOPE OF PLANT PATHOLOGY 159

of Researches on the Health and Diseases of Plants/' three of its
most active members being now members of this Congress. In
April, 1885, the committee addressed a memorial to the United
States Commissioner of Agriculture, calling attention to the desira-
bility of instituting investigations into the diseases of plants under
government auspices. The communication was well received, as
were subsequent ones, and in July, 1885, Professor F. L. Scribner
of Girard College, Philadelphia, was appointed to begin the work.
The first report by Professor Scribner appeared in the Yearbook of
the Department for 1886, and amply justified the wisdom of the
movement.

Professor Scribner with wise foresight directed his greatest efforts
toward a study of the diseases of the grape, enlisted the interest
of many able vineyardists, and became familiar with the great
activity then manifested in France. In 1887 the French Govern-
ment commissioned Professor Viala, of the National School of
Agriculture at Montpellier, to visit the United States and make
an extended study of grape diseases throughout our territory, and
in this enterprise Professor Scribner cooperated, the field work
extending from June to December.

Thus it came about that the activity in the practical application
of all that science had to offer in preventive, palliative, or curative
treatment of the diseases of crops, especially of the grape, an activity
that had recently attained notable proportions in France and Italy,
was transplanted to America at a favorable moment, when the
Government began to recognize the important interests to be sub-
served by thus protecting and increasing the output of the culti-
vator. This movement received another great impetus in 1888, when
the state experiment stations were established by act of Congress,
many of them including a botanist on the staff of investigators,
whose principal duty lay in the direction of the study and dissemin-
ation of information regarding plant diseases. It was at this time
and during the next few years that many American botanists went
to the German universities for longer or shorter periods, and brought
back enthusiasm for deep, critical study of difficult subjects. Still
another factor which seems to the speaker of immense importance
in this connection is the education of the cultivator in the recogni-
tion of diseases and in the comprehension of their causes and the
extent of the losses that accrue. This has been effected by the bul-
letins and other publications issued by the Government and by the
state experiment stations, by the return of graduates from the
agricultural colleges into the active management of farms, orchards,

committee was reduced to five members bv substituting the name of C. V. Riley
for the last three; and at the next meeting, in 1886, the committee was discharged,
having accomplished the particular object had in view when appointed.

160 PLANT PATHOLOGY

and gardens, by the teachings of farmers' institutes, horticultural
societies, and similar organizations, and to a less degree by other
agencies. The result attained in twenty years is marvelous. At
first only few cultivators could understand the nature of the efforts
made in their behalf, and great indifference was shown toward
suggestions for warding off or controlling fungous diseases, even
when emphasized by abundance of proof and demonstration. But
with increase of knowledge has developed widespread interest. The
prophylactic and precautionary suggestions emanating from the
laboratories are rapidly incorporated into daily practice. Great
as is the increase in personal and national wealth, which this change
has wrought, even greater is its importance in the reaction which
has been exerted upon the growth of the science. It may be true,
as many times asserted of late, that America now leads in the de-
velopment of plant pathology, both as a science and in its appli-
cation as a useful art, and if so, this laudable situation has been
secured by increasing the opportunities for scholarly research and
by the cooperation of an educated constituency.

I have said that the introduction of spraying gave new life and
new direction to the study of pathology. So successful have been the
results that it has furnished a sufficient reason for the expenditure
of large sums of money, in both government and state institutions,
for equipment and men to carry on the wTork. The division of plant
pathology in the United States Department of Agriculture, founded
by Professor Scribner, developed by Dr. Galloway, and now admin-
istered by Dr. Woods, has within twenty years grown to commanding
proportions, with many laboratory workers and field observers,
using during the present year an appropriation of 3130,000. entirely
apart from what is expended in other departments of the Bureau of
Plant Industry. It is safe to affirm that if it had not been possible
to show that the efforts of the pathologists were resulting in the
saving of many millions of dollars to the country annually, this
material growth could not have been secured, and a large part of
the fundamental knowledge developed in connection with the work
would not have become available, while the general stimulus em-
anating from conspicuously successful enterprise must have been
wanting.

A few words regarding some salient features in the history of spray-
ing will give more concrete form to these statements. I have said
that Bordeaux Mixture was the first efficient prophylactic substance
employed. Although it had been known for a hundred years that
copper sulphate, the active ingredient of Bordeaux Mixture, could
be used to free seed-wheat of the germs of hard smut, yet attempts
to employ it in other ways in controlling fungous enemies usually
resulted in disaster, until the fortunate addition of lime reduced the

HISTORY AND SCOPE OF PLANT PATHOLOGY 161

danger of injury to foliage, and made it the most important agent
known to-day for the direct treatment of plant diseases. Many
experiments have been tried with a wide range of substances, but
none has been found to supplant it, although other preparations of
copper, like the ammoniacal solution, are used for special cases
when the staining of the foliage due to Bordeaux Mixture is objection-
able. The methods of application have been refined and extended,
early replacing the coarse whisk-broom first employed, until now
a great variety of machinery is in the market, and choice may be
had of many kinds of nozzles, and of knapsack, barrel, or power
pumps of varied designs.

The general introduction of spraying was hastened by the advent
of the Colorado potato beetle, which marched in armies across the
country from the western plains to the Atlantic coast in a period
of about ten years, leaving the potato-fields a waste of withering
stalks. Something had to be done to hold in check these voracious
insects, that threatened to do for America what the potato fungus
had done for Ireland in 1845. As a result of these strenuous condi-
tions, the arsenite insecticides were brought into use. At first they
were applied in powder, but when the Bordeaux Mixture proved
serviceable for fungi, it was found that both insecticide and fungi-
cide could often be applied in one operation, and since then the
practical work of the entomologist has to a considerable extent
run parallel with that of the pathologist.

Success in spraying naturally stimulated inquiry into remedial
and protective agents for fungous diseases not amenable to spraying
methods. Attention was first directed to a method of protecting
wheat, oats, and similar grains from smut, which would be more
efficient and less hazardous than the very old one of steeping the
seed in a solution of blue stone. In 1887 J. L. Jenson of Denmark
brought out a method of applying hot water to the seed, that proved
very effective, and was widely adopted. Ten years later H. L. Bolley
of North Dakota introduced formalin for the same purpose, which
is now extensively employed. It has also been found effective and
is easily applied in the prevention of potato-scab, and has recently
been used for flax where the presence of a fungus threatened to put
an end to the industry.

In this connection a very ingenious method of ascertaining what
kinds of fungous spores and how many are attached to the surface
of seeds was devised not long ago by Professor Bolley. The seeds
to be examined are washed with pure water, which is then revolved
at high speed in a centrifuge. The resulting drop of sediment is
placed under the microscope, and all the germs, large and small,
that were present on the seeds are now clearly visible, providing
unmistakable evidence of the fungous parasites infesting the field

162 PLANT PATHOLOGY

during the last season, and indicating what should be done to pre-
vent a recurrence of these fungi in the next crop.

But great as has been the service to agriculture and horticulture
by this development of spraying and its related operations as well
as the reciprocal service to the science itself, yet it is the outgrowth
of but one division of the science, and that not necessarily the largest
one.

Much work has been done, and still more is contemplated and
under way, in the breeding of resistant varieties of various kinds of
crops, with the double purpose in view of securing larger products
and at the same time evading the destructive attacks of certain fungi,
insects, and other small enemies. This work is likely to yield excellent
results, especially where parasitic forms show adaptations within
narrow limits. It must be borne in mind, however, that our know-
ledge regarding the range of adaptability of parasites is not large.
Even the whole meaning of parasitism is not yet available to guide
the plant-breeder. Much progress has recently been made toward a
knowledge of parasitic adaptations and variations by the researches
of Klebahn, Eriksson, Marshall Ward, and others, on the grain- and
grass-rusts. Especially significant in this connection are the results
obtained by Ernest S. Salmon at Cambridge University, who found
that by mutilating or otherwise partially killing the tissues in the
vicinity of the spot on which the spores of the grain mildew, Erysiphe
graminis, were sown, a "biologic" form of barley mildew could be
grown on wheat, which under normal conditions would be entirely
immune to it. Moreover, when a form was once established by thus
lowering the vitality of an immune host, as we may assume was
the main effect of the mutilation, spores from the growth thus
produced would infect uninjured individuals. Thus through the
presence of a wound a parasitic fungus was enabled to gain a foot-
hold and maintain itself on a crop, wheat in the instance cited, which
had before been completely immune to it. This is surely a highly
interesting situation. What assurance have we that after years of
work in establishing an immune variety of grain or vegetable some
mishap, like an untimely frost, a hail-storm, or an army of locusts,
may not lower the vitality or cause injuries that will give just the
right opportunity for the fungus, which we have taken so much
pains to circumvent, to gain a foothold in our supposed immune
crop, and profiting by the greater vigor of the new host, become
after a short period of adaptation a greater pest than it was to the
old varieties. Thus at the end of our effort comes worse disaster
than preceded it. The moral of this fable is clear. Pathologists
should turn more attention than at present to a study of the con-
ditions underlying parasitism, of the degree of adaptation, and of
the range of variation, among fungi which cause the diseases most

F HISTORY AND SCOPE OF PLANT PATHOLOGY 163

dreaded among cultivators. There are some abstruse and what
to many are theoretical questions which need to receive careful
answers in order to supply proper guidance for those working upon
avowedly practical problems.

But I am in danger of infringing upon the ground of the speaker
who is to follow me. It does not, in fact, come into the province
of this discourse to speak of work under way at this time, or to
point out the unsolved problems, except to indicate the branches
of knowledge whose methods or facts are being turned to account.

I may at this point barely touch upon the aid that cytology is
rendering to pathology by the illumination which it brings into the
matter of the intricate life-histories of many parasitic fungi. Just
at present we are awaiting with much interest the cytological results
of investigations into the nuclear history of rust-fungi, in order to
determine which sets of spores have merely conidial or vegetative
powers, and which have sexual and consequently more intense
powers of reproduction. Such knowledge will enable us to direct
our attacks upon their activity with greater clearness and accur-
acy.

Taking a general survey of the field, the advance since 1880 is
most largely along the study of parasitic diseases, and especially
of the organisms which produce these diseases. It is natural that
the life-histories of the fungi should first receive attention, especially
the numerous small forms on field crops, and that the work should
extend gradually to the large but frequently obscure forms on forest
trees, and then to the minute and more obscure micro-organisms,
the bacteria, yeasts, and possibly amoeboid forms. Up to the present
time the energy of investigators has been largety absorbed in study-
ing the inciters of disease; the means by which the assaulting
organism overcomes the resistance of the host has received small
elucidation, and the nature of the physiological perturbations in-
duced by the parasitic organisms, or by any other cause, is almost
an unexplored field.

If I have said little about bacterial diseases, which have been
studied with such brilliant success and with such clear and discrim-
inating judgment by Erwin F. Smith of Washington, or of diseases
caused by enzymes, to which we were introduced by the researches
of Loew, or of the well-marked diseases of unknown origin, such as
yellows and rosette of peach-trees, it is that I do not doubt but you
will hear them more ably and entertainingly presented by my suc-
cessor upon the programme. Neither is it desirable that I should
discuss the advance likely to be brought about by the new theories
and methods in the study of the action of poisons, as these are
applied to the explanation of diseases, as well as to the devising of
remedies.

164 PLANT PATHOLOGY

In the long list of indebtedness held against plant pathology by
various sciences, physiology stands foremost with the largest ac-
count, a condition fully recognized as early as the days of A. P.
de Candolle, and especially emphasized at the present time. But
in close succession follow mycology, anatomy, bacteriology, chem-
istry, cytology, physics, toxicology, phylogeny, and other subjects
in diminishing degree. That the science is largely in an uncrystal-
lized condition, when looked at from our new points of view, is prob-
ably the reason why no handbook written from the modern stand-
point and covering the whole subject has appeared since 1880,
with the exception of the small, introductory, but highly luminous
work by Marshall Ward, issued in 1891.

I trust that in this cursory presentation of the history and scope
of the science of plant pathology I have made clear some of the
lights and shadows that give interest to a subject of great economic
and scientific importance.

VEGETABLE PATHOLOGY AN ECONOMIC SCIENCE

BY MERTON BENWAY WAITE

[Merton Ben way Waite, Vegetable Pathologist, United States Department of
Agriculture, since 1887. b. Oregon, Illinois, January 23, 1865. B.S. University
of Illinois, 1887. Author of Pollination of Pear Flowers; Pear Blight and its
Remedy; and other botanical papers.]

VEGETABLE pathology is a practical, economic science and is an
important aid to horticulture and agriculture. The science of botany
began, in its early days, as an economic study of medicinal herbs,
but the development of the subject has been mainly along the lines
of pure science. There are no higher motives for study than the pure
love of knowledge. To discover the laws and facts of plant life, for
the satisfaction of knowing, has doubtless been the object of most
of the researches of the botanists. Botany is rapidly becoming a
practical science, but no one despises more than myself the attitude
which assumes that knowledge for its own sake is not worth while
attaining. The enthusiasm of the botanist is proverbial. The study
was so fascinating that men pursued it for its own sake. In this way
the various departments of botanical science have been built up.

Vegetable pathology utilizes all botanical knowledge and turns
it to practical account. Doubtless the diseases of plants have been
studied to a certain extent as pure science, but the enormous pro-
gress of the last twenty years in the study of plant diseases under
the support of governments, experiment stations, and other public
institutions, has been due to the practical utility of the knowledge
obtained. Vegetable pathology calls to its aid all departments of
botany as well as entomology, chemistry, physics, geology, and
allied natural sciences. How different were the methods of the
systematic botanist half a century ago from the investigating
pathologist of to-day. The one working in some attic or small room,
with his bundles of dried flowers and ferns and his collections in
pigeon-holes; the other, with his expensive laboratory facilities,
chemical and physical apparatus, greenhouses, gardens, and other
equipment. And yet the systematic botanist laid the foundation
for pathological wrork. The early mycologists, even if some of their
descriptions were only three lines long, have left us very deeply
indebted for the names and classification of the fungi. The work-
ing pathologist must know systematic mycology as well as the classi-
fication and names of flowering plants. He must be an all-around
botanist. A copy of Saccardo's Sylloge Fungorum is an essential
in every well-equipped pathological laboratory.

166 PLANT PATHOLOGY

Mycology is so intimately connected with vegetable pathology
that some have thought the terms synonymous. The parasitic fungus
is frequently spoken of as the disease. The fundamental concep-
tions are distinct, however, even if in practice the work is inter-
woven. The mycologist studies fungi for themselves; the patho-
logist for the diseases they produce — in other words, from the
standpoint of the host plant. If we acknowledge indebtedness to
the early systematic mycologists, what must we say of the life-
history of the fungi? To the studies in the biology of the fungi, as
worked out by De Bary and his pupils, we trace the direct start-
ing-point of modern investigation work in pathology. By no means
are all plant diseases caused by parasitic fungi; yet the fungus
diseases are so numerous and important that with their knowledge
well under way, we are prepared to understand and distinguish
from them the injuries produced by insects and mites, poisons and
unfavorable environment, as well as the physiological and other
non-parasitic troubles.

Plant physiology is another of the great aids to pathology. Phys-
iology not only enables us to understand the disturbances in growth
and nutrition of plants produced by parasitic fungi and other para-
sites, but it enables us more fully to understand the non-parasitic
diseases. Through the researches of Dr. A. F. Woods an entirely
new type of physiological disease is known to be produced by the
action of enzyms. The study of enzymic diseases is in its infancy,
but promises to enable us to unravel some of the most mysterious
plant troubles. In this type of disease we have the curious anomaly
of non-parasitic diseases which are contagious or at least commun-
icable.

The closely allied subject of anatomical botany is also of great
importance to pathologists. Not only is the knowledge of normal
plant anatomy necessary in the study of abnormal structures, but
the methods which have been developed in the study of anatomy
are in every-day use by the pathologist in his researches. Especially
useful are the histological and microscopical methods. Processes of
imbedding, sectioning, and staining are absolutely necessary to the
study of pathology.

Cytology is another very useful branch of botany to the patho-
logist. The finer studies in parasitism are possible only through a
knowledge of normal cytology and through the use of cytological
methods of research. Very little in fact has yet been done in cyto-
logical pathology, but this is surely one of the most promising lines
for the future.

Plant ecology also lends aid to the pathologist. Disease in plant
life may be defined as a condition of the plant by which it is par-
tially or wholly incapable of responding to its environment. How-

VEGETABLE PATHOLOGY AN ECONOMIC SCIENCE 167

ever, plants may be sickened by poisonous substances in the soil,
may be injured by extremes of heat and cold, or injuriously affected
by other environmental conditions so that disease results. After
these unfavorable conditions have passed away, the plants are not
prepared to respond to normal conditions. The ecologist under-
stands the effect of environment on plants, their adaptations and
struggles in competition with other plants and with unfavorable
environment. When the plant succumbs wholly or partially in this
struggle it becomes a pathological subject. Here ecology blends
into pathology.

Bacteriology, although somewhat allied to mycology, deserves
special mention as an aid in the study of plant diseases. A con-
siderable number of plant diseases — no one knows how many as
yet — are caused directly by parasitic bacteria. The study of these
bacterial diseases forms in itself a very important department of
vegetable pathology, and has enabled us to understand with consider-
able clearness a very large group of plant diseases. The usefulness
of bacteriology is, however, still wider than this. The special methods
developed in bacteriological research have quite revolutionized the
life-history studies of fungi. I refer especially to the use of artifi-
cial culture media and the methods of isolating, cultivating, and
inoculating parasitic germs. By these processes results which were
only possible by the most laborious and uncertain methods thirty
years ago can now be accomplished with the greatest facility by
a student of only a few months' training.

Zoology, the sister science of botany, has contributed along many
lines to botany, and therefore to pathology. Animal physiology,
anatomy, and cytology have been extremely helpful. Many of the
methods of sectioning and staining, especially the finer cytological
and embryological methods, have been first worked out on animal
tissues.

Entomology is connected with plant pathology in many ways.
While the study of insects is itself quite distinct from the study
of fungi, yet not infrequently the plant diseases produced by these
diverse agents are difficult to distinguish till properly studied. The
pathologist must know a good deal about insect injuries and diseases
to distinguish them readily from fungus troubles. Furthermore,
insects are largely concerned in the distribution of bacteria and the
spores of fungi, and are thus important agents of infection. In
the treatment by spraying in many cases an insect pest and fungus
disease are killed at the same application. For example, the lime
sulphur salt spray on dormant peach-trees kills the curl-leaf fungus
and the San Jos£ scale. Bordeaux Mixture with Paris green or
arsenate of lead kills the apple-scab and the coddling moth.

The utilization of physiological botany, the methods of staining,

168 PLANT PATHOLOGY

botanical microchemistry, as well as the studies of fungicides,
bring the science of chemistry into continual use in pathological
work. In fact, the limitations of the working bacteriologist and
pathologist of to-day are largely in knowledge of chemistry. Most
pathologists acknowledge that they have too little training in chem-
istry for the best results. The knowledge of theoretical chemistry,
especially organic chemistry, is imperatively demanded in the further
advancement of plant disease investigation. Perhaps no branch
of natural science is of more use to pathologists at the present stage
than physiological chemistry. It is opening the doors to entirely
new fields of investigation in plant diseases. The general methods
of research and laboratory equipment of the chemist are in frequent
use by the pathologist.

A knowledge of physics is also of the utmost use to the working
pathologist. While he can scarcely be expected to make investiga-
tions in the physical composition of soils, yet he must be prepared
to utilize and understand the results obtained by workers in that
line. We now know with more certainty than ever that many of
the physiological processes in plant life are directly attributable to
physical laws.

The plant pathologist should also have a general knowledge of
horticulture and agriculture, or at least agronomy. He should
understand the cultivation of plants, and should be prepared to
master quickly and thoroughly the culture of any specific plant
when occasion demands.

I have attempted to show that, while vegetable pathology is a
somewhat narrow specialty, it requires very broad training on the
part of the investigator. An ideal pathologist should have a thorough
knowledge of systematic botany, including mycology, of physiolog-
ical and anatomical botany, of cytology, ecology, and bacteriology,
as well as a knowledge of zoology, entomology, chemistry, and
physics, and allied sciences. I need scarcely mention that he should
also have a good preparation in the languages, especially German,
French, Italian, and Latin, and in such incidentals as drawing,
photography, photomycrography, etc. A knowledge of horticulture
and agronomy becomes absolutely essential when he starts in field
work. Such a pathologist, of course, scarcely exists. Such com-
plete equipment is hardly to be expected in one individual. No
one realizes their deficiency more than the pathological workers
themselves.

The Treatment of Plant Diseases

The object of an investigation of a plant disease is to find out
the cause and remedy. If it is a parasitic disease the nature and life-
history of the parasite must be determined. Its complete life-his-

VEGETABLE PATHOLOGY AN ECONOMIC SCIENCE 169

tory is frequently necessary for full knowledge of the disease. The
different stages of the organism must be worked out, where it spends
the winter, how it reinfects the host plant, the climatic and other
conditions which favor or retard its development or its parasitism.
The stage at which it is most vulnerable, as well as the means of
reaching and killing it, must be found out. If it is a non-parasitic
disease, the causes or conditions which produce it are often still
more difficult to ascertain, and the method of removing them or
circumventing them is to be discovered.

The treatment for plant diseases is yet in its infancy, but suc-
cessful results have been reached in many specific instances and
along several lines more or less distinct. These may be classified as
follows: (1) spraying with fungicides; (2) disinfection by means
of germicides and fungicides; (3) eradication methods; (4) breed-
ing resistant or immune varieties of the host plant; (5) cultural
methods.

Spraying. The discovery of Bordeaux Mixture by Millardet about
1885 proved the starting of an important and successful era in the
treatment of plant diseases. Spraying has probably accomplished
more good up to the present time than any other method, or per-
haps than all other methods together. The success of Bordeaux
Mixture led to extensive studies of the other compounds of copper,
some of which promised for a time to supersede the original prepara-
tion. While for certain uses copper acetate, and especially the am-
moniacal solution of copper carbonate, have proved to be the best
form of copper, yet the Bordeaux Mixture remains by far the most
important fungicide. The sulphur compounds, whose use antedates
that of copper, have also retained their place in the list of fungicides.
The lime sulphur salt or the lime and sulphur mixture, on account
of its usefulness in killing at one application certain fungi as well as
scale and other insects, has become the greatest spray for dormant
trees. During the last year or two dust-spraying, or, more properly
speaking, dusting of plants, has come into prominence. The object
here is to avoid the carrying and applying of large quantities ' of
water, and instead to prepare the fungicide in a dust form, so that
it can be thrown on the plant more economically. Rain or dew is
expected to supply the necessary water to dissolve and more thor-
oughly distribute the fungicide over the plant. It has proved more
satisfactory in the prevention of the coddling moth and leaf-eating
insects, in the application of insecticides, than it has in the pre-
vention of the fungus diseases. These are more difficult to prevent,
and in many cases even too difficult to prevent by the finest sprays,
so that the results in dusting are not thoroughly satisfactory.

Bordeaux Mixture has achieved notable triumphs in the prevention
of the black rot and the Peronospora of the grape, apple-scab and

170 PLANT PATHOLOGY

pear-scab, pear leaf-blight on the pear and quince, leaf-blight of the
plum and cherry, and the mildew and leaf-blight of the potato.
Many other diseases are capable of prevention by spraying with this
valuable fungicide. Curl-leaf of the peach is preventable by spraying
with Bordeaux Mixture or the simple solution of copper sulphate
shortly before the buds swell in early spring. The lime sulphur mix-
ture is about equally successful applied at the same time. There are
still some troublesome problems in the application of Bordeaux
Mixture and other fungicides to growing plants. For some unex-
plainable cause, under certain climatic conditions, apples and pears
are russeted or even deformed by the absorption of the poisonous
copper through the cuticle. How to prevent this and to make
Bordeaux Mixture that will be uniformly safe in spraying these
fruits is an unsolved problem. Peaches and Japanese plums when
sprayed in foliage, with Bordeaux Mixture or any other fungicide
which has been tried, will, under most conditions, suffer severely. In
most cases the fungicide kills round spots, which drop out of the
leaves, producing a shot-hole effect, and at various intervals, from
a few days to a month or two, all leaves touched by the fungicide
fall to the ground. This defoliation results, of course, injuriously
to the growth of the tree and the fruit. How to find a fungicide
that will prevent the brown rot of the peach and plum and not in-
jure the foliage is one of our most serious problems.

Disinfection methods. Certain diseases of plants are carried over
mainly by means of spores or mycelium of the fungus which cling to
seeds, tubers, and cuttings, etc. Where these can be disinfected and
all the parasites destroyed, successful crops can frequently be grown
in infested localities. One of the first treatments of this type was
the dipping of wheat infested with smut in a solution of copper
sulphate. Jensen found that hot water could be used for the loose
smut of oats and other smuts successfully. The germination of the
seed was even benefited by the treatment. Recently formalin has
come into use for the same purpose, at first by the expensive method
of dipping, and later by simply sprinkling it over the grain. Potato-
scab was found by Arthur and Bolley to be preventable by dipping
in a weak solution of mercuric chloride. Later they substituted
formalin as a preferable disinfectant. The black rot of the sweet
potato is preventable to a large extent by keeping the houses and
hotbeds annually disinfected with copper solutions or formalin, and
by selecting for planting only the sound tubers free from disease.

Eradication. No more puzzling disease as to its cause exists than
the so-called "yellows" of the peach. There are two other serious
diseases of the peach and plum of a somewhat similar nature, namely,
the peach rosette of the Southern States, and the "little peach" of
New York and Michigan. We are thus justified from their similarity

VEGETABLE PATHOLOGY AN ECONOMIC SCIENCE 171

in calling this type of disease the "Yellows Group." Peach yellows
has been demonstrated repeatedly to be readily controllable by
promptly digging up the diseased trees and burning them as soon
as they appear in the orchards. Thus, while the yellows is one of
the most obscure diseases as to its cause, it is one of the cheapest
diseases to control. A careful inspection of the orchard two or three
times during the season, especially at the ripening of the fruit, and
the digging out of an occasional tree for the benefit of the rest of
the orchard, is vastly cheaper than the thorough and repeated spray-
ings necessary to prevent the average fungus disease. Rosette is
pretty certainly preventable by the same means. The writer is
now engaged, with his assistants, in testing the feasibility of this
treatment for the "little peach," with every prospect of success.

Pear-blight, the bacterial disease which attacks the blossoms,
young shoots, and the bark of pomaceous fruit-trees, can be remedied,
or rather prevented, only by the eradication method. It is more
quickly contagious than the "Yellows Group" diseases, and the erad-
ication is more laborious and difficult and not quite so successful.
Black knot of the plum may be mentioned as another fungus disease
which can be controlled by the eradication method. Simply cutting
out the infected limbs in the fall or winter has been demonstrated
to control the disease. Even some of the leaf-spot diseases, such
as the leaf-spot of the violet, can be controlled by picking all the
infected leaves as soon as they appear.

Breeding resistant varieties. Until recently our object has been to
discover some method of spraying or disinfecting the diseased plants,
or by destroying and thus losing them in the fight against disease.
At best all these methods are somewhat extravagant and wasteful.
By breeding varieties of plants which are immune to disease, or
which are resistant to a greater or less degree, we may even avoid the
necessity of treating the disease. No more desirable method can
be imagined of getting around a troublesome plant disease. In
fact, in cases of some root diseases, there may be no possibility of
using the other methods. For an example, Orton, in his work on the
root-rot of the cotton and cowpea, found resistant varieties which
would not take the disease, and grew a fine crop on infested soil
where common varieties were entirely destroyed. Swingle and Web-
ber found that by the use of the sour orange as a stock on which
to bud oranges, they were able to grow trees resistant to the root-
rot of the orange. Webber found that the Drake Star orange was
resistant to the Phytoptus rust on the orange. Bolley is breeding
varieties of flax resistant to the flax Fusarium disease. In case of
tobacco the mosaic disease appears to 'be susceptible of circum-
vention by selecting the plants free from the trouble. Mr. A. D.
Shamel has achieved a notable triumph in selecting tobacco in the

172 PLANT PATHOLOGY

root-rot districts of Connecticut and Florida. Carleton, by breeding
and selection, and by the introduction of resistant varieties of wheat
from Russia and other parts of the world, has made excellent pro-
gress in growing wheat free from the rust. In this case, it would not
pay to spray the wheat-fields, even if it were possible; so about the
only way to avoid the losses from this disease is by growing resistant
wheat. Of course resistance to a disease of parasitic nature is only
one phase of plant breeding and selection. General vigor, ability
to. withstand unfavorable climatic conditions, productiveness, and
special adaptability to certain soils and climates, or else wide range
of adaptability are parts of the object of the plant-breeder.

This brings us to the fifth and last method of controlling disease.

Cultural methods. Every grower of plants finds that with most
diseases, if he can grow strong, vigorous plants, they will be either
immune to the disease or they will suffer so slightly from it as to
grow successfully in spite of the trouble. By selecting proper soil and
other environmental conditions for exacting plants, by the intelli-
gent use of fertilizers and manures, the cultivator is able frequently
to grow his crops with but little loss from disease.

In the arid regions of the United States the irrigated orchards and
vineyards are almost entirely free from the fungus diseases of humid
sections, such as black-rot and mildew of the grape, apple- and pear-
scab, bitter-rot of the apple, and the ordinary leaf-spots. In Virginia
the Newtown Pippin, when grown on the black, mountain loam soils.
on the higher slopes and coves of the Blue Ridge Mountains, is nearly
free from apple-scab and the fly-speck and smut fungus. It is also
partly immune to the bitter-rot fungus. In low situations, or on
the red clay hills at the foot of the Blue Ridge, it is extremely sus-
ceptible to all these troubles, so much so as to be commercially a
failure there.

The selection of proper soils and localities for the peach, apple,
and pear is a matter of the utmost importance in the commercial
production of these fruits. This is true, of course, also of most of our
garden vegetables and other crops. By the use of fertilizers we can
frequently push plants into greater growth so as to enable them to
resist partly or wholly certain types of diseases. Peach-trees infested
by the root-rot, if heavily fertilized, will live and bear profitably
without any indication of the presence of the disease. This is espe-
cially true in the Lake region, where the root-rot is apparently slower
in its action than in the Southern States. The effect of fertilizers and
stable manures is even more prominent in case of certain insect
troubles than with the fungus diseases. A young peach-tree may
be so sick from the attacks. of the black peach aphis on the roots as
to have every leaf rolled up and yellowed by the disease, and yet a
bushel of stable manure placed around the tree in the winter and

VEGETABLE PATHOLOGY AN ECONOMIC SCIENCE 173

incorporated with the soil in the spring may push it into a vigorous
growth the following summer, so that no trace of the symptoms can
be noticed.

The study of root parasites gives us an additional reason for the
rotation of crops. In fact, judicious rotation of crops is one of the
best methods of shaking off and avoiding certain diseases. Nursery
stock of the peach, when grown in an old peach location where
a nursery or orchard has previously been located, will usually be seri-
ously affected with root troubles, such as crown-gall, root-rot, and
other fungus root parasites, eel worms or Heterodera, not to mention
root aphis and other insect troubles. This can be nearly all avoided
by growing the trees on a clean piece of land which has never been
in peaches.

The application of lime to the soil has proved very beneficial in
preventing the club-root of the cabbage and allied plants.

It should be noticed in this connection that not all diseases are
preventable by high culture. Certain diseases on fruit-trees, such as
pear-blight and apple-scab, more readily attack vigorous, well-fed trees
than thxey do those growing moderately. Brown rot of the peach
attacks trees with large heavy foliage on rich soil , or where an excess
of nitrogenous fertilizer has been used, more seriously than it does
less thrifty trees. It is necessary, therefore, for the cultivator to
understand his particular plant as to its requirements and as to its
diseases. No one has to know plants so intimately as the pathologist.

The early successes in the treatment of plant diseases have led to
vigorous prosecution of this work by the Government. The section
of Vegetable Pathology, of the Department of Agriculture, was or-
ganized in 1886, by one investigator. In 1888 there were four work-
ing pathologists. In 1893 there were nine. During the present season
there are about one hundred investigators employed in the Vegetable
Pathological and Physiological Investigations of the Department,
the majority of whom are now in the field studying the diseases of
plants. Considerable progress has been made by other governments,
notably France and Germany. Nearly every prominent experiment
station in the world has a plant pathologist on its staff. Our own
state experiment stations have at work in nearly every state in the
Union from one to five investigators. In Australia, in the Philippines,
in Java, in Japan, and, in fact, in nearly every country where scientific
botany is being pursued, contributions to the knowledge of plant
diseases are being made.

SECTION E — ECOLOGY

SECTION E — ECOLOGY

(Hall 7, September 23, 3 p. TO.)

SPEAKERS: PROFESSOR OSCAR DRUDE, Kon. Technische Hochschule.

PROFESSOR BENJAMIN ROBINSON, Harvard University.
SECRETARY: PROFESSOR F. E. CLEMENTS, University of Nebraska.

THE POSITION OF ECOLOGY IN MODERN SCIENCE

BY OSCAR DRUDE
(Translated from the German by Miss Jane Patten, Boston, Mass.)

[Oscar Crude, Professor of Botany, Konigl. sachs. Technische Hochschule, since
1879, and Director of the Botanical Gardens and Experiment Station of Dres-
den since 1890. b. Braunschweig, June 5, 1852. Graduate Student of Techuische
Hochschule, Braunschweig, 1870; Gpttingen, 1871-74; Ph.D. Gottingen, 1874.
Privy Councilor, Saxony; Assistant in Herbarium, Gottingen, 1874—79; Privat-
docent of Botany, Gottingen, 1876-79. Member of the Leopold-Caroline Ger-
man Academy of Natural Historians; German Botanical Association; French
Botanical Association; Zoological-Botanical Association of Vienna: and numer-
ous other scientific and learned societies. Author of Atlas der Pflanzenverbreit-
ung ; Handbuch der Pflanzengeographie ; and many other works and memoirs in
botany.]

IF, at a Congress fifteen years ago, ecology had been spoken of as
a branch of natural science, the equal in importance of plant mor-
phology and physiology, no one would have understood the term.
That to-day in St. Louis it is given this rank is due to the zeal with
which new lines of scientific research, inspired by discoveries in the
most widely separated fields, have been followed during the last ten
years; and no country has been in advance of America in placing
in their true light the versatility, lofty aims, and scientific depth
of ecology. In this country the floras of Minnesota, Illinois, Penn-
sylvania, and Missouri, also those including the region from the
Appalachian Mountains and the Western territories to New Bruns-
wick and Nova Scotia, have attempted to show how their contents
are to be regarded by the light of ecology.

This new tendency has not arisen from any chance discovery;
just as in the case of the study of bacteria, instruments had to be
perfected before it could be placed upon a firm foundation.

In reality, this branch of science dates from the earliest period
of botanical investigation, for in addition to the formal descrip-
tions of those early times are found traces of a refreshing, vitalizing

178 ECOLOGY

insight which connect mere description of the living form with the
vital phenomena of the animate world.

Individuality and independence, however, had first to be woven
from the weakest as well as the strongest threads which unite the
" sciences of the earth," essentially geographical in substance, with
the vital phenomena of the plant and animal kingdoms.

Physiology had taught how, with the aid of physics and chem-
istry, experiments could be made in the laboratory; it was obvious
that these experiments could be repeated out of doors, where the
changing play of nature's forces could be observed and fresh data
obtained, which later could serve as a basis for further experiments
in the laboratory.

At the same time this new tendency took strict account of the
morphological development of those organs which, independently,
according to their adaptation to the environment, determine to what
biological form a plant or animal belongs. The ability of a plant
to perpetuate its existence as a tree with deciduous or evergreen
leaves, as a perennial whose powers of rejuvenation have endured
for centuries, as a weed dying after the quick ripening of its seed,
or else as a freely swimming or submerged wrater-plant, or a plant
exposed to the stress of storms and winds, is just as important
from the ecological standpoint as are the various means of loco-
motion developed by animals for the purpose of securing nourish-
ment, such as springing, running, creeping, fluttering, and flying
through the air, or wriggling through the dark earth, swimming
freely on the surface of the water, diving in its shallows, — or else
banished for life to the depths of the ocean.

We find the greatest variation in vital conditions in passing from
pole to pole, from the ocean to the ice and snow of the mountain
peaks, from the sun-scorched desert to woody and shady valleys,
or to the cool caves hidden in the cliffs where is seen the greenish
glimmer of the Schistostega. For each change in the vital condi-
tions we find specially adapted forms of animal and plant life, and
in the fundamental principles of animal and plant geography we
find the earnest endeavor to contrast the more physiographical
details of distribution with the dependence of the adapted form
upon the environment; this latter, with its great biological im-
portance, being more especially the province of the zoologist and
botanist.

In this manner has the study of ecology come into being, and,
since it has been most clearly and easily followed in botany, the
word in its modern meaning has come to denote more especially
the ecology of plants. Therefore the honor to address this Congress
upon the subject of ecology has been given to a botanist, who is
a plant geographer as well.

POSITION OF ECOLOGY IN MODERN SCIENCE 179

By the word "ecology" we understand the vital phenomena
exhibited by plants and animals in the struggle for space, under
conditions enforced by the climate and the physiography of a
country. "Struggle for space" is Ratzel's appropriate version of
Darwin's proverbial phrase, "struggle for existence," whose pur-
port, however, remains unchanged. In the struggle for space each
organism requires a place in which he can fulfill his career ; that is,
secure nourishment, and leave behind him descendants capable of
occupying a similar location. Each organism is closely associated
with its environment; each plant, each animal, lives, like mankind,
in a special world of its own.

These considerations show us that ecology is the borderland to
which the sciences of biology and geography can both lay claim.
Thus the ecologist, persuaded of the importance of the various vital
problems which here cover common ground, must have a com-
plicated equipment for his varied work; he must be as familiar
with the use of the balance, photometric and thermometric instru-
ments, as with the absolute dominion of lifeless nature. In order
not to be betrayed into forming hasty conclusions, he must work in
the herbarium as a florist, with the microscope as a physiological
anatomist, and also bear constantly in mind the geological develop-
ment of present conditions.

Yet until now botany and zoology have held aloof from one an-
other in this new scientific departure, although it is just here that
victories common to both have been achieved, — as, for instance,
in the biology of the flower whose form shows adaptation to the
needs of the insect world ; or in cases where there is mutual de-
pendence between plant and animal, the one affording domicile,
the other protection, as in the case of the Imbauba trees of Brazil,
wrhich furnish food and lodging to armies of ants, who in turn protect
the trees from the devastating hordes of leaf-cutting ants. In this
connection, too, has been brought to light the usefulness of the
modest earth-worm and the versatility shown by plants in the
methods used for protection from the voracious assaults of snails
and caterpillars. The dire need of animals struggling to obtain
their scanty nourishment is often revealed at the same time as
the silent efficacy of the protective forces of the plant kingdom.

We can readily understand how through all ages the effect of large
troops of Herbivora has been harmful to the plant world, while the
effect of their enemies, the Carnivora, has been beneficial, and how
these two influences must have produced various changes in the
formations.

In determining the dependence of organic life upon the physio-
graphic character of a country, the science of botany is naturally
of the utmost importance, since the individual plant is found actually

180 ECOLOGY

connected with the outer world. Animals that live alone, or are
banded together in flocks, swarms, or herds of the same species,
are naturally incapable of building formations dependent upon the
climate and inseparable from the soil. Their power of locomotion
is a hindrance to the close connection with Mother Earth that is
maintained by the flora.

Ecology is new in name only, and while stress has lately been
laid upon the versatility of its special methods, we find the sources
from which they have been derived far back in the past century,
and the connection between ecology and geography, as evidenced
by the restriction of the animate world to stations with special
physiographic features, is expressed in the excellent floras of earlier
days. Linnaeus, in his Flora lapponica, a work which until recently
has hardly received due recognition, has given us an example of how
a flora may not only give a diagnosis of the different species, but
also a description of their mode of life. A flora containing a descrip-
tion of the methods employed by the most widely distributed plants
in perpetuating their existence, unfolding their blossoms, and ripen-
ing their seeds, is of the utmost importance for the true comprehen-
sion of the part played by every species in covering the soil with
verdure. The worthy florists of that early period undoubtedly recog-
nized the fact that the appearance of similar associations followed
definite laws which they endeavored to express in the terminology
used in their diagnosis of the situation; thus they actually were the
founders of the modern doctrine of "plant formations."

But in order that ecology should advance to the rank of an inde-
pendent branch of science capable of further development, the
creative genius of an investigator was needed, who, unsatisfied by
the older methods of description, could work from a more general
basis. During his long journeys through distant lands, Alex, von
Humboldt had recognized the special scientific value of the mutual
relations existing between the annual change of season and the form
of vegetation assumed by predominating plants. Accordingly, he
chose a few representative orders of the plant kingdom, fifteen in
number, such as palms, conifers, cacti, tree-ferns, mosses, and lichens,
which by their mode of growth and perennation give a certain de-
finite physiognomy to the district in which they predominate, since
each one of these groups gives rise to landscapes totally differing
in character. Von Humboldt was undoubtedly guided by the
ecological spirit, as we should say to-day, in the elaboration of his
excellent system, whose defects lay in the then existing confusion
of vegetative form with systematic character.

Alphonsc de Canclolle enumerated these defects, when, in his
Geographic botanique raisonnee, he laid the foundation upon which

POSITION OF ECOLOGY IN MODERN SCIENCE 181

could be based the study of a flora from the evolutionary point of
view, and confined climatological considerations within their proper
limits. But A. Grisebach in his earlier works had already begun to
develop the doctrine that the victories of the all-conquering clima-
tological factors find their outward expression in "formations"
composed of special forms of the vegetation with which our earth
is decked. The cactus alone does not determine the arid character
of the desert, nor the Mauritia palm the tropical character of the
Amazon region, nor the Lodoicea that of the Seychelles Islands.
Mosses and lichens are not the only plant growth on the Siberian
and Canadian tundras; and among the conifers the northern
larches bear witness to quite different ecological conditions from
those designated by the cedars of Lebanon, or the Araucarias
which grow in eastern Australia and on the southern shores of the
American tropics. With these plants, however, grow other species
having the same requirements in regard to light, heat, and moist-
ure, and all these together make up a typical formation in their
common station.

Since Grisebach elaborated these fundamental ideas and gave
them general expression in his Vegetation der Erde (1872), he may be
regarded as the founder of the third period in the development of
ecology, just as I regard von Humboldt, with his Essai sur la geo-
graphie des plantes, to be the founder of the second and Linnaeus that
of the first, which began with the appearance of his Flora lapponica.

As yet, however, the ability to penetrate the intimate relations
existing between climate and plant life was lacking. The discovery
of mere outward facts of contiguity furnished only the barest out-
line, which still needed the accumulation of important data for its
true comprehension.

Knowledge of the evolution of the earth and of organic species
became the aim of scientific research. Darwin's great intellectual
achievements bore universal fruit. Such men as Moritz Wagner
attempted to extend questions of theoretical evolution so as to in-
clude the problem of the distribution of species, until then regarded
as something fixed and unalterable, and thus the idea of evolution
became involved in the explanation of present conditions. In a sim-
ilar attempt, especially in botany, to give formal diagnosis a more
natural bent, the mere description of organs was transformed to bio-
logical morphology, while anatomy was changed to physiological
anatomy. For floristic purposes the attempt was made, by means
of the clear and simple methods used originally in experimental
physiology, to correlate organs with the physiological factors of the
environment.

While these new tendencies, developed from morphology and
physiology, which to-day form the closest connection between the

182 ECOLOGY

organic and the inorganic worlds, were advancing and the vast
amount of material already collected was being worked over, a special
branch of science had arisen, namely, the biology of the flower, which,
instigated by Darwin's work upon the mutual relations existing
between different organisms, set aside the ancient opinion that
zoology and botany could proceed side by side with absolute dis-
regard of their dependence upon one another.

The pivot upon which investigations concerning the pollination
of flowering plants turned was the "law of avoidance of self-fertil-
ization." Facts which to-day are universally taught in the schools
still remained to be proved by such men as Darwin, Hildebrandt,
Hermann Miiller, and others. It was discovered with astonishment
that Koelreuter toward the middle of the eighteenth century, and K.
Sprengel in 1793, had already disclosed "the secret of Nature in the
structure and fertilization of flowers." Until then, however, no one
had applied the biological relation between flowers, wind, and the
insect world, as shown in the phenomena of pollination, important
enough to be included in the science of botany, nor had any one
made clear the mutual dependence of the animal and plant king-
doms in their household economy. These factors in the struggle
for existence were now given their full value, and the different appear-
ance of various associations was explained by the absence of this or
that insect, while in tracing the boundaries which limit the area of dis-
tribution of certain plants and animals, as, for instance, Aconitium and
Bombus, the organisms were found by Kronfeld to be interdependent.

Thus in the fourth period of the development of ecology, widely
separated branches of science are brought together in order to explain
the life-history of a certain region. These, however, must be united
in the realm of geography to form a new entity, and, by their correla-
tion of numerous data, prove the propriety of their use. The evolu-
tionary tendency, which extends far back into the geological past,
and is based upon knowledge of the areas of distribution of hosts
of related genera and species, has been considered, especially in
botanical geography, as a subject quite separate from that which
treats of the vegetative forms and the formations as physiological
entities, dependent upon external factors.

The division of entire continents into zones, as seen in the atlases
of physical geography, gave expression to this feeling. It was also
necessary to extend the ecological method to the field covered by the
publication of special floras, and with renewed interest and zeal to
begin the revision of the enormous mass of material collected
therein. This work had already been begun in the floras of central
Europe, which were soon followed by the excellent departmental
work of the North American Surveys. Occasional brilliant descrip-
tions of tropical floras, such as the descriptions of the vegetation

POSITION OF ECOLOGY IN MODERN SCIENCE 183

of Lagoa Santa, in Brazil, also that of Juan Fernandez and the
division of Mt. Kinabalu, in Borneo, into regions, quickly bore
the methods of the doctrine of formations to distant lands, whose
floras until then had only been known to us through the systematic
enumeration of their orders. Thus the way was prepared for the
recognition of ecology as a new and special centre, and scarcely ten
years have elapsed since this centre, which would unite biology to
the natural sciences, was demanded.

Whoever wished to pursue the study of the physiology and devel-
opment of organs, in order to understand the weapons used in the
struggle for space on land or in water; whoever wished to study the
mutual relations of species, rather than their inherited character-
istics, or to consider the flora and fauna not only as they determine
the characteristic appearance of the country they inhabit, but also as
being the external, vital result of the effect of geographical factors,
which is capable in its turn of influencing the aspect of nature, had
to be called an ecologist, whether he wished to be so designated or
not. Even the name of this new branch of science was still in dispute
and no one was satisfied. To-day, however, we need not concern
ourselves with the name. From the beginning, the mutual relations
existing between the various branches of science exerted upon
ecology the powerful influence which usually only accompanies the
gradual change from the purely scientific to the utilitarian point of
view.

In this historical sketch we have now reached the fifth period,
which begins with the publication of MacMillan's well-known study
of the Lake of the Woods (1897) and Warming's Lehrbuch der okolo-
gischen Pftanzengeographie. These works emphasize the special pro-
vince of ecology and give preference to the methods employed in
the organic natural sciences rather than to those used in the geo-
graphical. It soon appeared as if this daughter of bio-geography
would destroy the reputation of her mother and usurp her place,
but the opportune appearance of Schimper's work, based upon the
same foundation and fulfilling Grisebach's unattainable dream,
completely restored the connection between the highly specialized
ecological and the broader geographical points of view. The most
distinguishing characteristic of this last period, however, is the
closer bond of union established between ecology and phylogeny.

Evolutionary thought, which is the keynote of modern natural
science, may proceed along two lines: according to the variation
of species in regard to their spatial requirements, or according to
the variation of an association under the influence of successive gen-
erations, each of which has undergone modifications. In this way
the study of phylogeny is extended to the field of floristic geo-
graphy. The connection between these two lines of thought will be

184 ECOLOGY

readily seen, if we consider certain recently evolved, feeble endemic
species in connection with their nearest relatives, and also study the
history of their modification under the influences of time and ex-
ternal circumstances. As such species we may mention the glacier
willows of Nova Zembla and the twenty-three species of the genus
Hieracium, restricted to the Faroe Islands and described by Dahl-
stedt. The presence of such species gives a decided geographical
character to the region in which they occur.

Under the title Geographic botanique exptrimentale, Bonnier en-
deavors to prove the direct effect of change of climate upon the
variability of specific forms, and G6neau de Lamarliere uses the
phrase physiologie specifique to express the idea of the degree of
adaptation accomplished. R. von Wettstein draws his conclusions
from different premises, since he considers that the species which
have been developed have been derived from related species and
from those closely restricted to the same location. Having made this
assumption, he then proceeds to search for the causes which have
been influential in the accomplishing this end.

The ecological point of view includes those things concerning the
question of continuance in a given location, the power of obtaining
nourishment, and the certainty of establishing the succession, which
are not general and uniform, but which differ according to the vary-
ing factors of the environment. Ecology is the study of epharmony
in the organic world, and the possibility of variation possessed by
species, as well as the mere fact of their life together, is an ever-
present, dynamical factor in the determination of the external
appearance of our earth. But it is not enough simply to discover
and describe these various specific relations; we must press forward
and from the mass of accumulated data obtain an intimate compre-
hension of the organic form in its dependence upon Mother Earth!

During the course of our historical sketch of the development of
the ecological idea, three special points of view have been made
manifest, namely:

(1) The relation of the organization of ecological forms to the
morphology of plants and animals (morphological relation).

(2) The relation of the ecological formation to the physiography
of the country (physiographical relation).

(3) The relation of ecological epharmony to the phylogeny of
systematic groups in both animal and plant kingdoms (phylo-
genetic relation).

If we wish ecology to rank as a special branch of biology, we must
undoubtedly consider these three points of view as inseparable, and
we may give our attention to either one or the other, just as, until
recently, most North American studies have been devoted to inves-

POSITION OF ECOLOGY IN MODERN SCIENCE 185

tigation of the ecological station and the analysis of the smallest
associations. The union of the morphological, geographical, and
phylogenetic points of view upon the physiological basis of adapta-
tion and dependence, alone gives us the essence of ecology. There-
fore we will devote the following remarks to an elucidation of these
three fundamental ideas, and try to show how intimately their
connecting threads are interwoven.

(1) Considering the many internal and external differences in the
adaptation of various organs to the environment shown by aquatic,
rock-living, forest, and swamp plants, or springing, flying, creeping,
and swimming animals, it has been thought expedient to elaborate
this point of view separately, which serves as a basis for physiolog-
ical anatomy. The works of Schwendener, Vesque, and Haberlandt,
which turned the methods of systematic, anatomical description into
physiological channels, gave botany its freedom. Yet it is difficult
to develop a special ecological system of instruction from morphology
and anatomy alone, since an inextricable network is formed by the
relations existing between inherited systematic structure, climatic
factors, regional peculiarities, and the influence of coexisting plants
and animals, whether friends or foes.

Each one of these relations is capable of forming a basis for com-,
parative analysis and classification. The dissatisfaction felt with
earlier as well as with more recent divisions, such as those given in
Reiter's Consolidation der Physiognomik (1885), is explained by
the inconsistencies which necessarily attend the incessant change
from morphological to physiological or physiographical character-
istics, and it is doubtful whether we shall ever be able entirely to
avoid them. The difficulties are most apparent when we attempt
to change the accustomed systematic arrangement of our museums
to one which shall represent the ecological features of a given forma-
tion. It is, however, necessary to work out this new point of view,
using ecological types as a basis.

There are quite a number of individual morphological forms
having no definite ecological meaning; undershrubs, shrubs, and bulbs
are found distributed in the most dissimilar stations in every clime,
while their requirements in regard to season, warmth, and light
differ totally. Undoubtedly the most important forms of vegetation
are those which depend directly upon the climate and whose appear-
ance typifies to the geographer, unversed in ecological methods, a
certain definite landscape. Von Humbolclt tried to do justice to
the importance of these forms when he made the first attempt at
classification.

The principles of ecology have been of especial value in the intro-
duction of ecological names, which refer to annual periodicity, such
as "evergreen leather-leaf plants," "trees bearing a tufted, ever-

186 ECOLOGY

green crown," and "leafless, perennial succulents," in place of the
systematic names of orders whose predominance characterizes a given
landscape, such as conifers, palms, and cacti. The leaves have come
to be more and more regarded as a distinguishing characteristic,
and to them is dedicated Hansgirg's Phyllobiologie, in which they
are classified according to their pubescence, their flexible or rigid
character, or according to their structure for protection from light,
wind, or rain, or the method they adopt for shedding water, either
by means of "spouts," or of an impervious wax covering. It
is their structure which bears the imprint of the climatic seal and
determines the fundamental form of tree, shrub, bulb, and mat,
just as their period of activity determines the length of the season.
Thus in groups formed according to leaf and vegetative period, we
naturally find the most diversified sub-groups, among which may be
reckoned those classified according to the mode of displaying the
flower, the manner in which it is fertilized, the protection of the pollen
from rain, or the characteristics of parasitic or insectivorous plants,
while there may still be others arranged according to the station,
either in light or shade, on dry or moist soil, or humus or on rock.
As yet, science has not succeeded in obtaining a satisfactory
enumeration of the separate ecological forms, for this, the science in
its anatomical and physiological aspect is still too young, but it is
a pleasure to see the increase in investigation along these lines and
the severe criticism to which the results are subjected. For the
future, we can predict a classification of living forms, which, based
upon observation of external appearance, will appeal to a far larger
circle than do the intricacies of phylogenetic research, whose
embodiment in a system offers just as great difficulties to the more
formal methods of classification.

(2) Ecology is the doctrine of reciprocal biological relations and
of the adaptations acquired in the struggle for space and necessi-
tated by the existing conditions of soil and climate; we may there-
fore consider that these terms show us the links by which ecology
is indissolubly bound to the geographical sciences. Still, it would
not be right to consider botanical geography as only the same
matter as botanical ecology, since, taken by itself, and without due
regard to the ecological interpretation of phenomena, there exists
also an abstract, geographical method of considering the organic
world.

If, however, we survey the organic world from the geographical
point of view, it seems to us of the utmost importance to divide it
into organic districts which will represent the essential characteristics
of continents, islands, mid-ocean, and seacoast. From the biological
point of view it seems of the utmost importance to discover the

POSITION OF ECOLOGY IN MODERN SCIENCE 187

causes determining the different areas of distribution, by an investi-
gation of the life-history of our present environment, or, when this
fails to give the required explanation, find out, by patient research
among the geological records of the past, the locations where ana-
logous conditions must have prevailed.

The essence of geography is the endeavor to acquire knowledge
of the distinctive features of the earth, and for this purpose all the
data of related sciences must be collected. Since the organic sciences
are constructed from separate bits of knowledge, they must take each
fundamental element into account, that is, consider each individual
species according to its inherent qualities and external form. The
tendency of ecology to accumulate minor details obstructs the broad
view 'towards which it has painfully toiled, until the introduction
of the freer methods of geography aid it in uniting the results of
divided effort. We have here before us an excellent example of the
intimate connection between two branches of science, the one being
the complement of the other and acting as a stimulus to further
investigation.

The attempt has been made to introduce into ecology various
phrases which shall have a definite, geographical application, but
in order to do this, due justice has not been done to existing facts.
The phrase recently used, "Climate creates a flora, soil determines
the formation/' seems to me to be unfavorable for the advancement
of future research along those lines where climate and soil furnish
a causal explanation.

Climatology especially must be restricted within its proper limits,
where, however, it must be given all its privileges, as, for instance, in
the classification of continental zones. It seems to me entirely wrong
to allow the undue influence of a certain factor to establish unnatural
scientific divisions in a subject whose inherent worth lies in the cor-
relation of the most heterogeneous data. The defects which arise from
the use of a single morphological characteristic have been recognized
in systematic classification, so that here, where the investigator must
deal especially with the complexity shown by determining factors,
the giving prominence to one factor alone will enable him to illumine
only a small portion of the field and will give him but imperfect
means of taking his bearings.

In the determination of both large and small divisions the natural-
ist is ever haunted by the same questions : for which forms of vegeta-
tion, as well as for their union into formations, is each district best
adapted, and by what vital conditions does it differ from neighboring
districts?

It is strange that until now the ecological branch of animal geo-
graphy has almost neglected this, to me, most interesting side of the
question. Yet the periodic phenomena of animal life, so often con-

188 ECOLOGY

temporaneous with those of plant life, should invite the investigation
of the naturalist. Recently, in the subtle work of Kobelt, animals
have been divided into great groups according to their behavior
toward the northern winter, as well as according to the cause and
forms of their migrations. This immediately brings up questions
as to the climatic limits of their distribution, the southern boundary
of hibernation, and also of the parallel which separates the winter
and summer quarters of the northern eider-duck from those of the
Antarctic penguin which cannot fly. With these we may compare
the shorter migrations of reindeer and bison.

The time may not be far distant when the geographical maps of
the animal kingdom will emphasize this point of view more strongly
than the fact of mere territorial distribution. For its part, botanical
geography is occupied in making clear in separate, experimental
works, the connection between landscape and formation, and, by
imitating geology in the publication of special maps, a long-felt need
is being satisfied. Such actual accomplishment counts much in a
field where our wish to make clear the cause so far outstrips our
ability to do so, for we must not forget that in all other special scien-
tific branches the final aim lies before us much more clearly than in
ecology, which must be regarded as a place of public assemblage,
and it would fare but poorly if it spoke of a final aim before suffi-
cient work had been accomplished in the investigation of all vital
phenomena.

The difficulty of stating clearly the reasons for the changing garb
of this or that formation is shown by the circumspection used
in MacMillan's work upon the Lake of the Woods, where, for the first
time in America, this attempt has been made. We find another ex-
pression of this difficulty in the rows of figures enumerated in Jac-
card's comparison of analogous association in the mats of the Swiss
Alps. The vital question here is: Why, when fruits and seeds are so
widely disseminated, do the stations of the different species remain
so clearly defined within the areas of distribution? Even if we
could empirically determine the vital needs of a single species by
a consideration of its climatic requirements, area of distribution,
and nature of the station, we should still be unable to explain the
inherent differences caused by a greater or less degree of acclimat-
ization, or the changing association of species and their different
bearing in widely separated districts.

(3) Thus we are led to a consideration of the essence of species,
in whose powers of adaptation and variation we find the key to the
important problems which weigh upon us when we regard the abund-
ant forms of life which take part in the world's work and live in peace
and harmony under the favorable and unfavorable influences to

POSITION OF ECOLOGY IN MODERN SCIENCE 189

which they are subjected. This last point of view is that of ecological
phylogeny, or the study of the variability of species during the
struggle for space under the direct influence of newly acquired
qualities.

The accumulated data concerning isolated, endemic species and
the nearly related forms of a large specific group distributed over an
extensive area, are only seen in their true light when we observe the
ecological requirements in connection with distinguishing systematic
characteristics and also take into consideration the results of recent
research concerning the variability of species. Thus we may study
from an ecological standpoint the problem suggested by Jaccard as to
the cause of the reduction in number of species inhabiting a limited
area, the number of genera being correspondingly large. This fact has
long been noticed on islands in mid-ocean, and comparison has shown
it to be equally true for separate mountain ranges. It appears as if a
natural genus, rich in species, were permeated by certain fundamental
ecological qualities, which enable it to appear in many places as
victor in the struggle for space, yet each species of this same genus
can only appear in a few places, so that an association may consist of
many different genera, but each genus will be represented by only a
few species. This appears to be the solution of the problem concern-
ing the development of representative species in widely separated
districts whose floral elements appear to have had the same ancestry.
This is shown by a comparison of the European, North American,
and East Asiatic floras, where we so often find nearly related species
filling a similar ecological role. The larch belonging to all three
continents, many moorland shrubs, the beech and the birch, all
having a wide distribution, can be cited as affording excellent exam-
ples of this fact. Sorbus Americana in the mountain regions of New
England and New York holds a position similar to that of Sorbus
aucuparia of central Europe. Few species have remained exactly
the same; the greater number have been broken up into representa-
tive forms, showing on the one hand species with decidedly similar
ecological adaptation, while on the other hand many species have
developed into dissimilar forms possessing dissimilar modes of life.

The persistence of certain ecological habits in a species, genus, or
family, is made the basis of paleontological conclusions. We judge
of the climate of central Europe during the Miocene epoch by the
conditions existing to-day in places where we find Taxodium, Sequoia,
Sassafras, Magnolia, and Platanus. The beeches and firs of that time,
we consider, were relegated to the mountainous districts. It seems to
us hardly probable that a plant like Taxodium, which in the warm
Miocene reached as far north as Spitzbergen and Greenland, and has
remained unchanged inform for one hundred thousand years, should
alter its climatic requirements; we feel rather that it persists to-day

190 ECOLOGY

only in those places where the hypothetical Tertiary climate still
predominates.

If we need still further illustration, we might mention the fact
that agriculture, developed through centuries of human experience,
is a branch of ecology which long preceded methodical science. In
agriculture man took the household economy of plants into his own
hands in order to provide them with the necessary light, the most
propitious time for germination and ripening of the seed, and the
most suitable soil, paying due regard, however, to the succession of
seasons peculiar to the country and to the meteorological conditions.

A botanical garden to-day, richly equipped with natural planta-
tions of every kind, greenhouses, moist and dry, hot or warm, bright,
or illumined by cool, green light, shows how many plants, native to
all climates and having the most varied requirements, may actually
be brought together in a small space by means of the careful imita-
tion of those conditions which we observe in the immense extent of
territory stretching from equator to pole. Progress in horticulture
denotes a minute observance of the vital phenomena of all the plants
we wish to assemble about us, and physiological investigation of the
effect of temperature and season give us the knowledge necessary
to change winter to spring in our drawing-rooms and conserva-
tories.

Humanity gladly claims its share of the achievements which
beautif}^ existence. Universal cultivation of the intellect cannot
remain unaffected by results, which, together with those of other
branches of natural science, escape from their special field to become
so widely disseminated as to fill the thoughts of man and counter-
balance the effect of the strictly logical, mathematical point of view.

Ecology has arisen from the need to unite originally separate
branches of science in a new and natural doctrine; it is characterized
by the breadth of its aims, and its peculiar power and strength lie
in its ability to unite knowledge of organic life with knowledge of
its home, our earth. It assumes the solution of that most difficult
as well as most fascinating problem which occupies the minds of
philosophers and theologians alike, namely, the life-history of the
plant and animal worlds under the influences of space and time.

THE PROBLEMS OF ECOLOGY

BY BENJAMIN LINCOLN ROBINSON

[Benjamin Lincoln Robinson, Asa Gray Professor of Systematic Botany, Curator
of Gray Herbarium, Harvard University, b. November 8, 1864, Bloomington,
Illinois. A.B. Harvard University, 1887; Ph.D. Strassburg University, 1889.
Fellow of the American Academy of Arts and Sciences; Fellow of the American
Association for the Advancement of Science; Member of the Botanical Society
of America; Corresponding member of the Botanical Society of Brandenburg.
Author of A Flora of the Galapagos Islands; and numerous papers on sys-
tematic botany. Editor of Synoptical Flora of North America; Rhodora, Journal
of the New England Botanical Club.]

ONE hundred years ago our country more than doubled its ex-
tent. At the anniversary of this great event, one of the most mo-
mentous in our national history, it is fitting that its widespread
effects should be considered not merely in relation to the growth and
material prosperity of our country, but to all phases of the intel-
lectual and scientific development of the nation. Our subject this
afternoon is certain problems regarding plant life, problems which
have become practical, important, and even vital to the interests of
the American people, largely through the very territorial accession
which we are now commemorating. While the Louisiana Purchase
doubled the area of the United States, it increased in a far higher
degree the physical and climatic diversity of the country. The
newly acquired territory contained wider prairies, higher moun-
tains, greater forests, deeper gorges, and more arid plains than any
east of the Mississippi. It was a region of extremes of altitude, tem-
perature, and precipitation. Its successful exploration, settlement,
and agricultural development presented to our government and
national energy problems as intricate in their solution as they were
vast in magnitude.

Furthermore, the subsequent annexation of Texas and Cali-
fornia was a logical sequence of the Louisiana Purchase, for it would
scarcely have occurred had Louisiana remained in foreign posses-
sion. When the great Southwestern and Pacific States, with their
still more varied climate and floras, are thus brought also into con-
sideration, it will be seen that the Louisiana Purchase has directly
or indirectly increased by many times the extent and importance
of the botanical problems of our nation.

It is a matter of common experience that one of the best indica-
tions of the value of wild land is furnished by its native vegetation;
and it is of interest to notice how early in the exploration of the
Louisiana Purchase this fact was realized. The management of this
great and beautiful exposition has named this very day in honor of

192 ECOLOGY

Lewis and Clark, the first effective explorers of the original Louis-
iana. Every botanist may recall on this occasion with pleasure the
fact that Captains Lewis and Clark gave much attention to the
strange and varied vegetation of the regions traversed during their
intrepid journey into the pathless wilderness, which will always form
one of the most thrilling and dramatic incidents of our national
history. What is more remarkable, they brought back with them
a considerable number of plants. It is pathetic to think under what
difficulties and with what devotion to science these plants were
collected, prepared as scientific specimens, labeled, securely packed,
and transported thousands of miles overland under circumstances
which made each pound of baggage a source of untold labor and
peril. It was through these specimens, so heroically obtained, that
the floras of the vast and varied valleys of the Missouri and Upper
Columbia first became known to science.

At the time of Lewis and Clark the study of plants had but two
important branches. These were classification and economic botany.
A plant was investigated solely with the objects, first of determining
its place in a rather arbitrary system, and second of discovering its
uses. At the beginning of the twentieth century, on the other hand,
botany, now become one of the richest sciences in carefully observed
and accurately recorded facts, is divided into many highly special-
ized fields of research. While the extent to which this subdivision
has now been carried is often a surprise to the non-botanical, such
terms as plant classification, plant anatomy, vegetable histology,
physiology of plants, vegetable pathology, paleo-botany, and the
like, are readily comprehensible to the intelligent layman. He may
derive from them a considerable idea of the nature and import-
ance of the subjects they designate, even though he may be igno-
rant of their extent and details. The word ecology, however, is too
recent and technical in its application to be familiar to many who
have not been professionally engaged in some phase of botanical
work. The term, although equally applicable to plants and animals,
has been used far more freely by botanists than zoologists, and it is
solely in its botanical sense that it is here employed. Of the various
definitions of ecology I believe none surpasses in terseness and
excellence that suggested by Professor Barnes. "Ecology is that
portion of botanical science which treats of the relations of the
plant to the forces and beings of the world about it."

The scope, significance, and probable future of ecology can only
be understood after some examination of its origin and history.
The subject, although older than its name, is still a relatively new
one, and it is worth while to examine its position with regard to the
older branches of botany. The relation of ecology to plant geo-
graphy is especially complicated and difficult to state. Discussions

THE PROBLEMS OF ECOLOGY 193

on this subject are apt to leave the reader a little in doubt whether
ecology is to be regarded as a phase or subdivision of plant geo-
graphy, or whether plant geography is only a generalized form of
ecology, or finally whether the two are capable of separation even
by a rather vague boundary. So much, however, may be said with
definiteness. These branches of botany have arisen independently
and differed greatly in their history and point of view. They have
both dealt with adaptation of plants to conditions of soil, climate,
and communal life, but have approached the subject from opposite
sides. Plant geography, much the older of the two subjects, was
at first closely allied to systematic botany. It was pursued chiefly
by systematists, and consisted largely of a series of generalizations
upon the distribution of genera and species and their rough group-
ing into floras. More and more has the plant geographer studied the
adaptive traits of plants, and observed their biological rather than
their systematic relationships, until he now bases most of his con-
clusions upon ecological data. On the other hand, the ecologist,
beginning with the individual plant and examining the relation of
its structure to its activities and the activities to the environment,
has been gradually and naturally led to wider and wider general-
ization regarding the influence of structure upon distribution and
of environment upon structure, until in his plant societies and
plant formations, he has speedily arrived by another path at just
the point more slowly reached by the plant geographer.

The material of these two branches of botany is nearly or quite
coextensive. It is difficult to find any ecological modification of
a plant which is not at least in some slight way connected with its
distribution, and conversely the present distribution of plant life,
which forms the subject-matter of plant geography, has undoubtedly
resulted immediately or remotely from ecological causes. It has been
well said that plant geography is the study of the present conse-
quences of past ecological conditions.

By its nature plant geography has been descriptive and classi-
ficatory. With all due regard to their natural affinities, adaptation,
and gradual association, it has grouped plants primarily according
to the soil and climatic conditions in which they grow. Ecology deals
with the dynamics of plant life, with such phenomena as competition
among plants, crowding and tension of floras, migration of plants,
parasitism, symbiosis, and the complex relations of benefit and
injury which exist between plants and animals. It is of all depart-
ments of botany the most recent in development, rapid in growth,
and fascinating in subject-matter. The details of classification, ana-
tomy, and physiology are dry and cold compared with such ecological
discoveries as the varied modes in which plants are protected against
the attacks of animals, the complicated ways in which they scatter

194 ECOLOGY

their seeds, or the highly complex adaptations of their flowers to se-
cure cross-pollination. What facts of systematic botany, for instance,
can be compared in popular interest with the adaptations of the ant-
plants or the marvelous biological relations of the Yucca flower and
Pronuba moth so critically studied by a distinguished botanist of
this city? Ecology presents plants in their most human aspect. It
deals with their struggles for room, light, and food.

It would be natural to suppose that a subject so varied and fascin-
ating would have been among the earliest phases of plant study to
receive attention, but it is only within the last two decades that
ecology has asserted itself as a department of botany. Of course,
the observations and records upon which ecology rests have been
accumulating for centuries. The task which has been accomplished
in recent years is the arrangement of these observations in new se-
quences and their interpretation from a new point of view. It is
scarcely necessary to say that the new standpoint was furnished by
the theory of evolution.

This being true, however, it would be natural to ask why the effect
was not more immediate, and why a quarter of a century elapsed
between the clear enunciation of the Darwinian hypothesis arid the
first organized study of ecology. This was due chiefly to two causes.
In the first place the Darwinian theory itself was, in its varied aspects,
a matter so important, and so violently discussed in its early years, as
to leave among speculative biologists little attention for other mat-
ters. On the other hand, mechanical improvements in the micro-
scope, microtome, and other such apparatus had just then opened
great vistas of technical research along the lines of plant anatomy and
physiology, which consequently formed in the sixties, seventies, and
eighties the most popular fields of botanical study. Here the spirit of
investigation was by no means speculative. Anatomical structures
were studied in great detail, but there was an almost morbid reluct-
ance to theorize upon their physiological significance. In like manner
the physiologist was measuring and weighing, timing and recording
the vital processes of the plant, but his work was chiefly in the labor-
atory, and he was not given to speculating upon adaptations to en-
vironment or the complex influences which determine plant distribu-
tion. The plant physiology of the seventies wras as far removed from
ecology as human physiology is from sociology.

In the late eighties and early nineties a feeling arose almost simul-
taneously in several quarters that anatomy to be of real value should
be physiologically interpreted, and that physiology should go forth
from its laboratory to observe and name a host of processes and
forces of nature, which are no less important because in many in-
stances they can neither be measured nor weighed. The new science,
thus called into existence, was first spoken of as biology of plants,

THE PROBLEMS OF ECOLOGY 195

but it was quickly found that the term biology, already overloaded
with meanings, would prove but poorly distinctive in this applica-
tion, and the name ecology was substituted.

It is easy to understand the rapid growth of the subject. The most
attractive phenomena of nature were awaiting its reclassification.
The speculative biologist had done much to clarify ideas upon the
evolutionary history of the vegetable kingdom. The unspeculative
histologist and physiologist had been accumulating a great wealth
of facts, which were ready at hand to be correlated by broad and
interesting generalizations. Systematic botany added its well-nigh
boundless literature regarding the affinities and diagnostic features
of plants. Conditions were all favorable.

One of the greatest difficulties of the ecologist has been to find a
simple basis of classification for the phenomena covered by his sub-
ject. Their great diversity has made it hard to group them in a logical
system. Their common element is too slight to suggest a consistent
arrangement. It is true, ecology can in a very broad way be divided
into the relations of plants to their inorganic environment, to other
plants, and to animals; but this does not go far toward a satisfactory
classification. The clearest and by all means the best basis for the
grouping of ecological facts is their geographic aspect. As has been
already mentioned, there are few if any ecological modifications of
plants which cannot be in some way correlated with their habitat.
It is in this way that ecology has now become inextricably merged
into phytogeography, and that phytogeography enriched by ecolog-
ical methods has become one of the most attractive and promising
fields of botanical research.

Having thus endeavored to make clear the general nature and
origin of ecology, together with its historical relation to phytogeo-
graphy, I may proceed to their joint problems, treating henceforth
the two subjects as coextensive and forming but a single discipline.

The examination of plant life from a new point of view necessitated
to a great extent a new nomenclature. All ecological phenomena, and
especially every phase of plant distribution, had to be reexamined
in a detail which could not be technically expressed by existing
words. Old terms were redefined and new ones invented in bewilder-
ing succession. This nomenclature is still inchoate, for the growth
of interest in ecology has been so sudden that there has been no time
for its language to become fixed by usage or for any survival of the
fittest to determine which of its many synonymous terms will prevail.
There are at present two general practices or tendencies apparent.
Many of the most critical and effective writers on plant relations have
contented themselves with a small number of new terms. In express-
ing a novel idea for which no technical term was at hand, they have
avoided coining one, and have used instead some descriptive phrase.

196 ECOLOGY

On the other hand, it has seemed desirable to some of the more strenu-
ous, especially in America, to make up an extensive and highly elab-
orated vocabulary.

Neither of these practices should be hastily condemned. The for-
mer method of expression, even if seemingly less precise and erudite,
has the great advantage of immediate clearness. It is businesslike,
practical, and free from any suggestion of affectation or pedantry.
But on the other hand, in favor of such an elaborate terminology as
that suggested by Professor Clements, it may be forcibly urged that
a well-chosen technical term, even for an obscure conception, not
only makes for brevity, but does much to fix and clarify the idea. It
gives a convenient handle to a thought which may be otherwise diffi-
cult to grasp and awkward to employ. It may be further argued that
most branches of science are considerably incumbered by a faulty
and often misleading nomenclature of casual and unsymmetrical
growth, by no means ideal, yet too firmly fixed to permit of reform.
Is it not, therefore, desirable that ecology, a new branch of science,
should be supplied at once with an adequate and consistent termin-
ology, and thereby be spared many wordy wranglings and abortive
nomenclature reforms which must inevitably result from a laissez
faire policy in this matter? It cannot be denied that this reasoning
has weight. Surely there is no systematist who does not regret the
lack of convention in this regard among early writers upon his own
subject.

The first great problem of ecologists is, therefore, to establish an
adequate, expressive, and logical language of their subject, — to es-
tablish, I repeat, not merely to invent such a terminology. If effective
uniformity in methods of expression can be accomplished, it will well
repay prolonged effort and do much to give precision as well as dig-
nity to the subject. In just this matter of nomenclature it may be
thought that the systematist is in a poor position to offer advice, but
surely he may be permitted on the score of long and trying experi-
ence to voice some cautions.

It has been suggested that ecological terms should be chosen by
priority. This idea recalls the advice which a great art critic is said
to have given when asked what step should next be taken in develop-
ing one of our municipal art galleries. His unexpected counsel was to
burn it up. The principle of priority might not so completely destroy
the fine arts of ecology, but it would inevitably singe and blacken
them. Priority is only barely tolerable in taxonomy. No system-
atist determines his names by it absolutely, and the most annoying
disagreements have arisen from varying efforts to restrain its ill
effects. Were the principle of priority of expression to be adopted
in ecology, many well-selected and now current terms of relatively
recent origin would have to give place to the vaguer, poorly defined

THE PROBLEMS OF ECOLOGY 197

terms of the earlier plant geography, or else some recent initial date
would have to be fixed, and this would give great and perhaps unfair
prominence to the works which happen to have been published at or
shortly after that date. It has been found difficult enough for sys-
tematists to arrive at an agreement regarding this matter of an initial
date, even in regard to authors of the rather remote past. It would
be much harder for ecologists to make such a decision concerning
a literature which is still chiefly of living authors. But, even if this
matter of an original date could be harmoniously settled, the prin-
ciple of priority would be a bad one. It would mean, not that the
most fit, maturely considered, carefully discussed, and well defined
term should be adopted, but that chance expression which happened
to be used when the idea was first glimpsed. Furthermore, the matter
of doubtful and partial synonymy of terms would present great diffi-
culties in any such plan. Even aided by their far more formal
descriptions and carefully preserved type-specimens, systematists
often find synonymy almost impossible to unravel. Let this be a
warning to ecologists.

Although this problem of terminology is so difficult that it should
be taken very seriously, it need not be disheartening to the ecologist.
The compilation and precise definition of a few hundred appropriate
Latin terms with their vernacular equivalents in the more important
European languages should not present a task of insurmountable
difficulty for a well-chosen international commission, and would do
wonders towards a solution of the trouble. The task is in no way
comparable to that imposed by the two or three hundred thousand
names with which systematic botany is weighted down.

During the brief course of its existence the progress of ecology both
in the organization of earlier observations and in the discovery of
a host of new facts has been flatteringly rapid. Of late, however, there
has been a little cooling of enthusiasm, a barely perceptible tendency
toward reaction, a slight question whether the subject of ecology will
fulfill the promise of its hitherto conspicuous development. This
feeling has been, if I rightly understand it, that the striking general-
izations have now been made and the most accessible facts observed;
that for its further progress ecology must now pass to details, and
that these details will be found to have been already discovered and
recorded to a considerable extent by the anatomist, physiologist, and
systematist.

With this view7 1 have no great sympathy. It is quite true that the
ecologist has now reached a period of detail work in which results
will come more slowly and be less spectacular, but still the point of
view of ecology is admirably distinct, and the problems of the subject
are endless.

In the first place, let us consider the division of vegetation into

198 ECOLOGY

life-zones, plant formations, plant societies, etc. Who will say that
this highly interesting work of the ecologist is approaching completion?
His scheme as yet is but an outline map, filled out only in a few isolated
areas. Great reaches of territory have been wholly unexamined. Ad-
mirable work has been done locally. Even considerable tracts, espe-
cially in Europe, have been examined in detail, and the results brought
together in Engler and Drude's noble work, Die Vegetation der Erde.
Warming, Schimper, Goebel, and others have extended ecological
work to portions of the tropics of both hemispheres. In our own
region there are many examples of critical work on restricted areas,
as, for instance, Mr. Kearney's study of the Dismal Swamp and its
environment, Professor Ganong's observations on the vegetation
about the Bay of Fundy, our chairman's studies in Minnesota,
Pound and Clement's organized presentation of the phytogeography
of Nebraska, and Professor Cowles's interesting examination of the
southern borders of Lake Michigan. Yet let any one who doubts
ecological opportunity take a map of the world and note what an
exceedingly small fraction of its surf ace has been seen by the eye of the
ecologist, and what vast fields are still awaiting examination. There
is not one of our states, even the smaller and more thoroughly exam-
ined Eastern ones, which does not offer to the plant geographer mater-
ials for monographic study and a volume as full of new information
and valuable records as the phytogeography of Nebraska already
mentioned. Just beyond the limits of our country is the great expanse
of British America, readily accessible, healthful in climate, with a
rich flora, taxonomically well explored and recorded by an indefat-
igable government naturalist, but offering for the most part virgin
soil to the ecologist. Mexico, of which now even the remoter parts
can be reached by rail, is a country of boundless floral wealth. With
enormous mountains, wide plateaus, low tropical jungles, and exten-
sive deserts, it offers in relatively close proximity an astonishing
diversity of climate from arctic to torrid and from the parching dry-
ness of arid sands to the most dense and oppressive moisture of the
tropics. It possesses a vegetation far more varied in character and
probably more rich in number of species than all the rest of the North
American continent. Each mountain and valley seems to have its
individual flora. To date, perhaps half a dozen trained ecologists
have made hasty trips through small portions of Mexico. In their
hurried records they have accomplished only the slightest beginning
upon the varied and seemingly endless problems which the country
offers. Although more difficult of access, Central and South America
offer no less of ecological diversity and interest. Surely the unex-
plored territory on our own continent alone offers the ecologist the
work of a century.

But it is by no means the case that these hitherto unexamined

THE PROBLEMS OF ECOLOGY 199

'Tegloiis 'present to the ecologist his only opportunity. His observa-
tions can be indefinitely extended, not merely in breadth, but in
depth. To the taxonomist there seems to be a serious defect in many
ecological publications, a lack of accuracy arising from the author's
imperfect knowledge of systematic botany. Too often the ecologist,
in characterizing his plant formations and plant societies, is contented
with mentioning a few of the more obvious, showy-flowered, and
easily determined spermatophytes. It is rarely, indeed, that he states
fully and correctly the numerous species of goldenrods, willows,
rushes, sedges, and grasses, to say nothing of cryptogams, which
form such a large and important part of the flora he is studying.
These groups are for him inconveniently technical, and he is all too
apt to sum them up in a sort of generic way by such vague expres-
sions as " Solidago species," "several undetermined Junci," "many
sedges," etc. When the taxonomist protests against this superficial
treatment of important groups, the ecologist replies in a superior
manner that he cares little for such nearly related species, that they
intergrade,and are from his more philosophic point of view relatively
insignificant; that, in fact, he believes the systematist to have split
up species in these more difficult groups far beyond what is natural
or practical. Several prolific ecologists have intimated that they care
but little about the details of post-Grayan classification. They men-
tion as single species such perfectly demonstrated and undeniable
complexes as Antennaria plantaginifolia, Viola cucullata, Potentilla
canadensis, and Taraxacum ofjicinale.

What makes this matter the more unfortunate is that the ecologist
is rarely a collector in the taxonomic sense. His lists are often made
in the field, and are subject to no check or control by means of ade-
quate and carefully preserved specimens. This course seems all the
more venturesome at a time when the systematist is becoming daily
more reluctant to make field determinations, being fully aware how
untrustworthy and valueless such identifications are, and how im-
possible it is for any memory to retain the details of recent specific
segregation. Under these circumstances, how can the ecologist hope
to make accurate field-lists, or how, without specimens preserved as
vouchers, can he expect that his catalogues will be intelligible, not
to say convincing, to other botanists?

In making these strictures on certain all too common ecological
methods I do so by no means in the spirit of adverse criticism, but
merely with the hope of showing more clearly the great problems
still ahead of the ecologist. For a writer on plant relations who con-
tents himself with mentioning Antennaria plantaginifolia as though
it were a single species closes his eyes to a whole vista of most inter-
esting observations along his own line. The taxonomist has proved
that, instead of being a single species, this is a highly polymorphous

200 ECOLOGY

group of nearly related, although rarely, if ever, intergrading species.
He knows that they have different ranges and habitats, and further-
more that by their parthenogenetic tendencies and the rarity of the
staminate plant they offer to the biologist problems of exceptional
interest. This is but one of many cases where from an indifference to
the refinements of modern classification the ecologist has as yet failed
to perceive lines of fascinating investigation appropriate to his own
subject. Why should the ecologist by his own confession and pre-
ference be fifteen or twenty years behind the times in his taxonomic
equipment?

While this is undoubtedly the rule, I am glad to say there are
notable exceptions. The care with which Mr. Kearney has based his
ecological study of the Dismal Swamp upon a large series of numbered
specimens, critically identified and preserved at a great centre of
taxonomic work, merits high praise. Other equally notable instances
of conscientiousness in these matters might be cited.

In general, however, life-zones, plant formations, and plant soci-
eties have been indicated merely by the more conspicuous plants,
identified largely in the field and with but little attention to herb-
arium records. Were ecologists from this time on for many years
to explore no new territory, but merely extend their observations to
the less conspicuous plants and more technical genera, were they
to take full advantage of the most modern and detailed taxonomy,
were they to place correctly in its ecological class each sedge and rush,
each aster, lupine Antennaria, stemless violet, and Sisyrhinchium,
not to speak of cryptogams, they would find no lack of profitable
occupation or interesting results.

In the definition of plant associations there is almost always
vagueness. To some extent this is inherent in the subject. Floras pass
into each other gradually, and sharp definition is as impossible as it
would be unnatural. Yet there can be no doubt that further study
could make the classification more definite. At present plant form-
ations and societies are characterized, as we have seen, usually by
a few typical and conspicuous plants, other plants often being men-
tioned as of more general distribution, occurring promiscuously in
differing ecological conditions. In examining ecological lists it is
noticeable that just these less readily classified plants are in many
instances those which the systematist is inclined to segregate into
two or more species. It is impossible to escape the conviction that
the ecologist by studying these segregations could often place their
components with greater definiteness than he does at present the
aggregates, thereby attaining an added completeness and precision
in phytogeographic groups.

From these facts it seems clear that ecology may obtain new depth
by the aid of modern taxonomy. The converse is equally true. In

THE PROBLEMS OF ECOLOGY 201

several matters the systematist must look to the ecologist for help in
solving the most difficult problems of his field. In our present classi-
fication of plants there is still much that is artificial. On account
of the overwhelming number of species to be examined and placed
in the system, it has been as yet absolutely necessary to interpret
each chiefly by the historic type. Every thoughtful systematist
knows how arbitrary this is, and how seriously it hampers a natural
characterization of individual species. The majority of plants have
been first described from a very few specimens, or in many cases from
a single individual, which ever thereafter remains the type of the
species. That this historic type really represents the most typical
form of the species can only be a matter of accident. In many cases
it certainly does not. Yet, up to this time, it has often been impossible
to solve by purely taxonomic investigations the difficult question
which of several intergrading forms or varieties should be considered
typical, central, or original, and which are secondary, peripheral, or
derived.

A complicated problem is here involved. It is true that it has
been somewhat obscured, although by no means hidden, by some sys-
tematists, who have thought to minimize the difficulty by the minute
subdivision of their species. This, however, is obviously only a matter
of words. To call a variety by a specific name does not stop its free
intergradation, nor solve the problem of its origin and variability.
It is certain that there are many variable species and that the varia-
tions have proceeded from a recent common type. It is further to
be inferred that this typical form is in many instances still extant,
but sure guides to its recognition are still a great desideratum in
systematic botany. The question is one of development influenced
by ecological conditions. It can be solved only by the closest scrutiny
of distribution and habitat, past and present, with relation to the
varying forms. Thus problems without number, of the greatest deli-
cacy, requiring the closest observation and soundest judgment, are
here opened to the ecologist who will turn his attention to questions
of geographic variation in polymorphous species.

To turn now to a very different opportunity for successful work, I
would call attention to the rarity of what may be called experimental
ecology. It is not to be denied that some very interesting work has
been or is still being carried on along this line, as, for instance, Pro-
fessor Gaston Bonnier 's studies of the influence of altitude upon alpine
plants cultivated at different levels, but on the \vhole the field has
been little worked. Of course, it may be said that much of what is
classed as agriculture, horticulture, and forestry is a sort of experi-
mental ecology. But in these practical branches the scientific aspect
is apt to be obscured by the more conspicuous economic and aesthetic

202 ECOLOGY

interests, and the results to ecology are not great. The field here
opened is boundless.

It is one of the chief difficulties of the ecologist measuring the effects
of the different forces of nature upon plant life, that they are all acting
at once. Each plant when in a state of nature is simultaneously
affected by the physical and chemical nature of the soil, amount of
light, degree of moisture, exposure to wind, density and purity of the
air, crowding of other plants, and attacks of animals. Its develop-
ment is the mathematical resultant of the composition of these forces.
To understand their relative influence upon the plant it is necessary
to isolate them. To do this it is only needful to vary one influence
while maintaining the stability of the others. Such experiments
require no great ingenuity, and may even be applied to plant com-
munities of some size; thus the addition of a single chemical substance
to the soil, changing the amount or character of the light-, adding or
withdrawing competing plants, modifying the degree of moisture
in air or soil, or controlling in some single regard the animal environ-
ment, are nearly always possible, and often very easy experiments.

It may be said that these things have all been done repeatedly by
the plant physiologist. This is very true, but it is to be remembered
that his point of view has been different. He has tried these experi-
ments to learn the specific reaction upon the particular plant. To the
ecologist, however, their interest would be in the comparative effect
upon the different components of a flora, for it would be thus that he
would gain new insight into the fundamental factors in distribution.

Professor Warming, a great leader in ecological investigation, said
some years ago, "There is scarcely a more attractive biological field
than to determine what the weapons are with which plants force one
another from their positions." Professor Ganong, in recently com-
menting upon this idea, says, "To-day we know no more of that sub-
ject than when Warming wrote those words." May not this problem
be simplified by reversing it? Would it not be better to begin not
with the weapons, .but with the vulnerability of plants? Is it not
safe to assume that when certain plants give way in competition it
is because they are to a greater extent subject to some one or more
adverse influences? The nature of these and the degree to which each
species of a community is affected by them can to a great extent be
determined by experiments such as have been suggested. When the
relative vulnerability of the different plants has been found, it may
be logically assumed that the weapons of the more resistant are
nothing other than their superior faculties of withstanding these
untoward influences, forces which by artificial control may be ascer-
tained with definiteness and measured with precision.

To this point I have spoken chiefly of the development of ecology
as a pure science. Although we live in an age when the pursuit of

THE PROBLEMS OF ECOLOGY 203

knowledge for its own sake needs neither excuse nor apology, never-
theless, it is in its practical application that every science excites the
keenest interest. An investigation void of immediate or indirect
effect upon human welfare is relatively unattractive. An expert
mathematician recently told me that there were great fields in his
subject, hitherto unexplored, because they are too remote from any
known application to physics, astronomy, mechanics, or any other
branch of applied mathematics. The same is true, although perhaps
to a lesser extent, in certain phases of biological work. They seem
too far from probable usefulness to stimulate the investigator to
their enthusiastic pursuit. This can, however, in no wise be said of
ecology. Dealing as it does with the vital relations of plants to their
surroundings, it yields information of the highest importance to
the farmer, nurseryman, and landscape gardener. Indeed, it bridges
just that all too wide gap between theoretical and applied botany,
connecting the abstruse fields of plant anatomy, plant physiology,
and classification with the concrete applications of botany in agri-
culture, horticulture, and forestry. The ecologist will never lack
that wonderful stimulus which comes to the investigator who is
conscious that his work is important to the welfare of his fellow
beings, and intimately bound up with human progress.

SECTION F — BACTERIOLOGY

SECTION F — BACTERIOLOGY

(Hall 15, September 24, 10 a. m.)

CHAIRMAN: PROFESSOR HAROLD C. ERNST, Harvard University.
SPEAKERS: PROFESSOR EDWIN O. JORDAN, University of Chicago.

PROFESSOR THEOBALD SMITH, Harvard University.
SECRETARY: Dr. P. H. Hiss, JR., Columbia University.

RELATIONS OF BACTERIOLOGY TO OTHER SCIENCES

BY EDWIN OAKES JORDAN

[Edwin Oakes Jordan, Associate Professor of Bacteriology, University of Chicago,
Chief of Serum Division, Memorial Institute for Infectious Diseases, b. July 28,
1866, Thomaston, Maine. S.B. Massachusetts Institute of Technology, 1888;
Ph.D. Clark University, 1892; Post-graduate, Clark University, 1890-92; Pas-
teur Institute, Paris, 1896. Lecturer on Biology, Massachusetts Institute of
Technology, 1889-90; Associate in Anatomy, University of Chicago, 1892-93;
Instructor, ibid. 1893-95. Member of the American Public Health Associa-
tion; The Society for Experimental Biology and Medicine; Association of
American Pathologists and Bacteriologists; Society of American Bacteriologists;
Fellow of American Association for the Advancement of Science. Translated
Huepe's Bacteriology; Editor of The Journal of Infectious Diseases.]

IT is possibly a contemporary delusion that we are living in a pe-
riod of unexampled mental activity. The life of the intrepid modern
scholar affords opportunity for self-deception. If one becomes a
member of a sufficient number of learned and quasi-learned societies,
and attends committee meetings for an adequate variety of purposes,
the impression of profitable intellectual endeavor may be prematurely
acquired. There is much, however, to account for the prevailing
sensation of breathless advance. The physiologic and psychologic
accompaniments of a breakneck pace are not altogether lacking
in the modern world, and there are bacteriologists, in particular,
who will lend a credent ear to affirmations of the rapidity of scien-
tific progress. However this may be, few can question that the
development of the science of bacteriology has been marked by an
unusual tempo. To those who have followed this development
closely, discovery has trod upon the heels of discovery in bewil-
dering succession. The scant thirty years of its history have been
crowded with feverish activities, which have found their best justi-
fication in the results accomplished. At present the science touches
nearly many human interests, and sustains manifold and far-reaching
relations to the whole body of natural knowledge. It is no matter
for surprise that such should be the case with a science that owes

208 BACTERIOLOGY

its birth to a chemist, that concerns itself with microscopic organisms
belonging both to the plant and animal kingdoms, and that extends
its ramifying branches into the regions of medicine, hygiene, and the
industrial arts.

In several respects the history of bacteriology might be held to
epitomize that of the other natural sciences, or of the living organism
itself. Advance in complexity of structure entails greater complex-
ity of relations and adjustment; maturity has more extensive
connotations than youth. Bacteriology is a relatively youthful
branch of the stream of knowledge, but in late years it has per-
ceptibly widened its banks. It has even encroached upon certain
neighboring sciences. Modern physiography uses the term piracy
to designate the capture by one stream of that portion of a water-
shed legitimately belonging to another stream. In the same way,
one natural science, owing to peculiarities in its subject-matter, in
its evolutionary history, or in the tools with which it works, may
enter upon a piratic career, and appropriate territory which for va-
rious reasons has remained unexploited by the science to which
topographically it may seem to belong. This annexation of neigh-
boring fields has been not uncommon among the natural sciences,
and bacteriology has not shown itself free from the general tend-
ency. A notorious instance of piratic conduct on the part of bac-
teriology is the virtual appropriation of the whole field of micro-
biology. Perhaps most familiar in this connection are the discoveries
concerning the life-histories of various microscopic animal para-
sites. The tracing-out of the relations between parasites and hosts
in Texas fever, malaria, and dysentery has by no means been ex-
clusively or even largely the work of zoologists. On the contrary,
it is well known that much of the most important work in this
direction has been carried out by bacteriologists, and that the lit-
erature on these topics is chiefly to be found in the technical bac-
teriologic journals. A recent instance of this tendency is the renewed
study of the remarkable protozoa called trypanosomes, which has
in large part been undertaken by bacteriologists and by bacterio-
logic methods. Perhaps the most notable triumph yet accomplished
in this field is the successful cultivation of these pathogenic protozoa
outside of the animal body, a feat which has been achieved by one
of the foremost American bacteriologists. The exploitation of zoo-
logic territory by bacteriologic workers is one of the many instances
of successful borderland invasion, and, like the Louisiana Purchase,
illustrates the impotence of territorial lines to prevent natural ex-
pansion. Many reciprocal piratic inroads among the sciences are
due to the acquisition by one science of new tools which, when
workers become generally acquainted with their use, are found to
be applicable to other problems in other fields. Bacteriologic

THE RELATIONS OF BACTERIOLOGY 209

technique is one of these efficient tools the possession of which con-
duces to piracy; it can, however, never be forgotten that bacterio-
logy itself owes its powerful equipment to a study of spontaneous
generation which was undertaken primarily for the interest felt in
its philosophic bearings.

Bacteriology stands in close relation to at least four other more
or less defined fields of natural knowledge: to medicine, to hygiene,
to various agricultural and industrial operations and pursuits, and
to biology proper. Bacteriology, as has been often said, is the
youngest of the biologic sciences, and for this reason has as yet con-
tributed relatively little to the enrichment of the parent science.
Morphologically the bacterial cell is so small and so simple as to
offer many problems of surpassing interest, but of great difficulty.
The question as to whether a bacterium is a cell without a nucleus,
or a free nucleus without any cytoplasm, or a cell constituted in the
main like those of the higher forms of life, has, to be sure, been
practically settled in favor of the latter view. But there are other
debated and debatable morphologic questions to which up to the
present no satisfactory answer has been given, and to which our
current microchemic methods are perhaps unlikely to afford any
solution. On the physiologic side, the achievements of bacteriology
in behalf of general biology have as yet been far from commensurate
with its potentiality. This may be partly because of its temporary
engrossment in other seductive lines of research, partly because of
the lack of workers adequately trained in bacteriologic methods and
at the same time possessed of an appreciation of purely biologic
data. It may be justly urged that a rich harvest of fundamental
physiologic facts waits here for the competent investigator.

There is no need to dwell in detail upon the manifold practical
applications of bacteriology to the arts and industries. Particularly
in agriculture and kindred occupations have the advances in bac-
teriology been immediately and intelligently utilized to bring forth
in turn new facts and unveil new problems. The processes of cream-
ripening and vinegar-making, the phenomena of nitrification, of
denitrification and nitrogen fixation, the modes of causation of
certain diseases of domestic plants and animals, have all been
elucidated in large measure by bacteriologic workers. A new di-
vision of technologic science, dealing with the bacteriology of the
soil, of the dairy, and of the barnyard, of the tan-pit and the canning-
factory, has already assumed economic and scientific importance.

It is often a temptation to distinguish radically between pure
science and applied science and to look upon the latter as unworthy
the attention of the philosophically minded. True science can admit
of no such distinction. Nothing in nature is alien to her. She can
never forget that some of the most fruitful of scientific theories have

210 BACTERIOLOGY

been the outcome of the search for the utilitarian. Man's know-
ledge of the universe may be furthered in various ways. It is well
known that the work of Pasteur was particularly characterized by
applications to the problems of pure science of knowledge acquired
in the study of the practical. One thing plays into the hands of
another in wholly unexpected fashion. An attempt to improve the
quality of beer gives birth to the germ theory of fermentation, and
this in turn to the germ theory of disease; the chemistry of carbon
compounds leads to the discovery of the anilin dyes, and these same
anilin dyes have made possible the development of microchemic
technique and thrown open spacious avenues for experiment and
speculation; the attempt to obtain a standard for diphtheria anti-
toxin has resulted not only in the achievement of the immediate
practical end, but in the discovery of unexpected theoretic consid-
erations which have dominated the progress of an important branch
of scientific medicine during the last five years. It will not be a hope-
ful sign for the advancement of science when the worker in pure
science ceases to concern himself with the problems or avail himself
of the facilities afforded by the more eminently utilitarian aspects of
natural knowledge.

In the quarter-century of its history, bacteriology has sustained
close and mutually advantageous relations with the science of
medicine. This has been the scene at once of its greatest endeavors
and of its greatest triumphs. To recount these would be superfluous.
There is hardly an hypothesis in scientific medicine that has not
been freshened and modified, hardly a procedure in practice that
has not been influenced by bacteriologic conceptions. The experi-
mental method in particular has been given new support and re-
ceived brilliant justification. Experimental pathology and experi-
mental pharmacology practically owe their existence to the methods
and example of bacteriology. The security afforded by aseptic
surgery has made possible physiologic exploits that could not other-
wise have been dreamed of, a pregnant illustration of the way in
which applied science may directly further the advance of pure
science. Conspicuous as these achievements of bacteriology have
been, it cannot be truly said that the field is exhausted. There is
hardly an infectious disease of known or unknown origin that does
not still harbor many obscurities. Some of the most difficult pro-
blems that medicine has to face are connected with the variation and
adaptation of pathogenic bacteria. The phenomena of immunity,
certainly among the most complicated and important that human
ingenuity has ever set itself to unravel, still await their full de-
scription and interpretation. The study of the ultramicroscopic,
or perhaps more correctly the filterable viruses, is being prosecuted
with great energy and in a sanguine spirit. The extension of bac-

THE RELATIONS OF BACTERIOLOGY 211

teriologic method into the field of protozoon pathology has been
already referred to, and constitutes one of the latest and most hopeful
developments in the study of the infectious diseases. Medicine,
perhaps more than any other department of human knowledge, is
most indebted to and maintains the most intimate relations with
the science of bacteriology.

At the present time the relations of bacteriology to public hygiene
and preventive medicine seem to me of particular importance, and
it is upon this theme that I wish chiefly to dwell. Personal hygiene
is not necessarily pertinent to this topic, but falls rather into the
same province with the healing art. Matters of diet, of clothing, of
exercise, of mental attitude, affect the individual, and contribute
more or less Largely to his welfare. But except in so far as the indi-
vidual is always of moment to the community, they do not affect
the larger problems of public hygiene. The pathologic changes that
take place in the tissues of the diseased organism and the methods
that must be employed to combat the inroads of disease in the
body of the individual patient must for a long time to come remain
questions of supreme importance to the human race. But over and
above the treatment and cure of the diseased individual, and the
investigation of the processes that interfere with the proper physi-
ologic activities of the individual organism, rises the larger and
more far-reaching question of the prevention of disease.

Racial and community hygiene are but just beginning to be
recognized as fields for definite endeavor. The project may seem
vast, but the end in view is undoubtedly the promised land. More
and more will the problems of curing an individual patient of a spe-
cific malady become subordinated to the problem of protection.
More and more will scientific medicine occupy itself with measures
directed to the avoidance of disease rather than to its eradication.

Whatever else may be said of it, this is certainly the age of delib-
erate scrutiny of origins and destiny. Man no longer closes his
eyes to the possibilities of future evolution or to those of racial
amelioration. If we are to remain to a large extent under the sway
of our environment, we can at least alter that environment advan-
tageously at many points. We are no longer content to let things
as we see them remain as they are. On the surface the wider rela-
tions of disease have often seemed of little significance, as, before
Darwin, the so-called fortuitous variations in plants and animals
were considered as simple annoyances to the classifier; the causes
of this variation were deemed hardly worth investigation. The rise
and fall of plagues and pestilences have been readily attributed to
the caprices of the genius epidemicus, and it has sometimes been
thought idle to ascribe recurrent waves of infection to anything
but "the natural order." Another phase, entered upon later, and

212 BACTERIOLOGY

from which we have not yet entirely emerged, possesses its own
peculiar perils. In meditating on the cosmos, the agile mind is
always tempted to fill in the gaps of knowledge with closely knit
reasonings or fantastic imagery. The imaginative man of science
still frequently finds himself beset with the temptation to erect
an unverifiable hypothesis into a dogma and defend it against all
comers. It is now fortunately a truism that a more humdrum and
plodding course has proved of greater efficacy in advancing natural
knowledge. Theories that stimulate to renewed observation and
experiment have been of the greatest service, but unverifiable specu-
lations have often been a barrier to further advancement. Meta-
physics tempered with polemic is not science, whatever be its
allurements.

If the attainment of a rational position in public hygiene, com-
munity hygiene, or preventive medicine must, then, be regarded as
the main objective* point in the campaign against disease, it follows
that the part played by bacteriology in this advance will be an
important one. The relations of bacteriology to public hygiene are
fundamental. The etiology of many of the most widespread and
common diseases that afflict mankind is intelligible only through
the medium of bacteriologic data. The modes of ingress of the
invading micro-organisms, the manner of persistence of the micro-
organism in nature, the original source of the infectious material,
and all the varied possibilities of transmission and infection can be
apprehended only through the prosecution of detailed bacterio-
logic studies. It is only by this means that the weak point in the
chain of causation can be detected and the integrity of the vicious
circle attacked. Success will inevitably depend upon a thorough
understanding of the circumstances governing and accompanying
the initiation and consummation of the disease process. Yellow
fever cannot be suppressed by burning sulphur or by enforcing a
shot-gun quarantine; the bubonic plague is not to be combated by
denying its existence.

In the warfare against the infectious diseases a rational public
hygiene is ready to avoid the mistake of beating the air. A prelim-
inary survey of the possibilities reveals several distinct types of dis-
ease; those that are practically extinct or far on the road to extinc-
tion in civilized communities, those that remain stationary, or decline
but slightly, and those that show a more or less consistent increase.
The economy of energy would suggest that it is not a far-sighted
policy for public hygiene to focus its endeavors exclusively upon those
diseases that are yielding naturally before the march of civilization.
The conditions under which civilized peoples live to-day are in them-
selves sufficient to render the foothold of many infectious dis-
eases most precarious. What nation now fears that typhus fever

THE RELATIONS OF BACTERIOLOGY 213

will become a national scourge, or who looks to see the citizens of
London driven into the fields by the Black Death? It is of course
true that the continuance of this immunity can be secured only by
unremitting watchfulness, although so long as existing conditions of
civilized life are maintained, the recurrence of great epidemics may
be relatively remote. The pestilences that once stalked boldly through
the land slaying their ten thousands are now become as midnight
prowlers seeking to slip in at some unguarded door within which lie
the young and the ignorant. Already some once-dreaded maladies
have become so rare as to rank as medical curiosities, and their ulti-
mate annihilation seems assured.

There are other diseases, however, that civilized life, or at least
modern life, appears to leave substantially unchecked, and some that
it even fosters. These may be considered as shining marks for the
modern hygienist. The scale between hygienic gain and loss is always
in unstable equilibrium. There is no such thing as consistent improve-
ment all along the line. As Amiel wrote in his journal, "In 1000
things we advance, in 999 we fall behind; this is progress." It is al-
most a biologic axiom that progress in one particular entails loss in
others. To maintain the efficiency of all parts of the complex of civili-
zation calls for eternal vigilance. It may be that while we are waxing
complacent over the fact that the opportunities for infection with cer-
tain parasites are diminishing, and that other parasites are gradually
losing what we vaguely denominate as their virulence, unforeseen and
greater evils are raising their heads. The increasing exemption from
certain diseases will itself lead to an increased prevalence of others as
diversely vulnerable age groups are formed. In general, it will occur
that the diseases peculiar to the advanced age groups will increase
as the diseases of childhood and youth succumb to hygienic measures.
A different age distribution of the population will bring in its train
new problems of preventive medicine, which must be successfully
solved if the issue is to be fairly met.

There are not lacking instances of a dawning consciousness on the
part of mankind that the proper development of public hygiene
involves a far more comprehensive view of its relations than has
hitherto been taken. The study of tuberculosis is being approached
by methods of unexampled broadness. We are just beginning to re-
cognize the way in which the roots of this destructive malady are
well-nigh inextricably interwoven with the whole social fabric. Bac-
teriologic, architectural, and economic data are all levied upon for
contribution to our knowledge of what is universally recognized as
one of the most important of all human diseases. Here, as elsewhere,
the care and cure of the infected individual still looms large, but
beyond and above this is beginning to be placed the prevention of
infection, the drying-up of the stream at its source. That for this

214 BACTERIOLOGY

heavy task public hygiene will require the aid of many workers in
many different fields is abundantly evident. For all of them, however,
bacteriology must furnish the only definite point of view. In the
full consideration of the "exciting causes," the tubercle bacillus
can never be allowed to drop into the background. Given foul air,
insufficient food, inhalation of dust, excessive and exhaustive labor,
and the other deplorable accompaniments of modern industrialism,
and it still must be constantly kept in mind that without the tubercle
bacillus these predisposing causes would never result in a single
case of tuberculosis. On the other hand, without these contributing
factors the tubercle bacillus would almost sink to the level of the
negligible "non-pathogenic organism." Witness the impotence of
the bacillus to produce infection, or even maintain itself, in the tissues
of those individuals able to live an outdoor life.

It is evident that in the case of tuberculosis the forces of civilization
are on the whole working for its extinction rather than for its perpetu-
ation. The available statistics demonstrate that before the modern
movement for the suppression of the disease began, and, in fact, even
before the discovery of the tubercle bacillus, pulmonary tuberculosis
was already on the decline in widely separated parts of the world, —
in London, in Boston, and in Chicago.1 It is, perhaps, significant that
pulmonary tuberculosis is now one of the tenement-house problems,
and that as such it occupies a strictly delimited field. As yet the
campaign against tuberculosis has been a desultory one, waged by
a few enthusiasts without adequate material or moral support on the
part of the community at large, but signs are multiplying that this
condition will be a transient phase. The comparative absence of
intelligent, systematic endeavor for the suppression of disease is cer-
tainly a curious phenomenon in an age of otherwise extensive coor-
dination and organized action. The executive talents and restless
energy lavished on commercial, industrial, and engineering projects
may some day be turned to devising and carrying out hygienic
measures. If it were necessary to find an argument in the economic
value of human life, it would be readily forthcoming. The recent
movements for the study and suppression of tuberculosis mark one
of the first attempts to apply bacteriologic knowledge in a determined
and radical way to a problem of public hygiene. As regards the ulti-
mate extinction of tuberculosis, there may be more or less groping
after ways and means, but there need be no misconception as to the
scope of the problem.

There are other fields in which a similar mode of procedure based
on ascertained bacteriologic facts and principles has been indicated

1 Biggs, N. M., The Administrative Control of Tuberculosis. Medical News, 84,
p. 337, 1904.

Vital Statistics of the City of Chicago for the years 1899-1903 inclusive, Chicago,
1904.

THE RELATIONS OF BACTERIOLOGY 215

and is being at least in part carried out. In typhoid fever the evidence
from epidemiology has long pointed unmistakably to drinking-water
as being the chief vehicle of infection, and the first step toward sup-
pression of this disease has been already taken in most civilized
countries. The last half of the nineteenth century witnessed an im-
provement in the sanitary quality of public water-supplies which has
diminished perceptibly the death-rate from typhoid fever .This
change has been in part effected by the introduction of water from
unpolluted sources, in part by the installation of sand filters. To cite
a few well-known cases: For five years before the introduction of a
filtered water, the annual typhoid fever death-rate in Zurich, Switzer-
land, averaged 76; in the five years following the change it averaged
10. In Hamburg, Germany, for a corresponding period before filtra-
tion, the typhoid death-rate was 47; after the change it fell to 7.
In Lawrence, Massachusetts, under similar conditions the typhoid
rate was reduced from 121 to 26, and in Albany, New York, from 104
to 38. A similar effect has been noticed where an impure water has
been replaced by water from unpolluted sources. In Vienna, Austria,
the abandonment of the River Danube as a source of supply in favor
of a ground water diminished the typhoid fever death-rate from over
100 to about 6. In the United States the city of Lowell not long ago
exchanged the polluted water of the Merrimac River for a ground
water-supply, with the result that the typhoid fever death-rate was
reduced from 97 to 21. In spite of these remarkable facts, there has
been a lethargic slowness in profiting by the lessons that they teach.
Many communities have remained to this day unobservant and
negligent, and especially in the United States, the condition of the
average public water-supply demands radical reform. A method that
has not only reduced the deaths from typhoid fever by about 75 per
cent., but has also reduced the number of cases proportionately, is
worthy of universal adoption. If the fatality in all cases of typhoid
fever was diminished, say from 12 per 100 cases to 3, by the use of
a new drug or an antitoxin, the world would ring with the discovery.
The introduction of a pure water-supply has achieved an analogous
reduction in the death-rate, and confers further the enormous benefit,
of preventing the occurrence of a similar proportion of cases.1 In
the city of Albany, New York, the annual number of deaths from
typhoid fever prior to the installation of a filter-plant averaged 89
during a ten-year period; in 1902 there were but 18 deaths from this
cause, representing a diminution not only of 71 deaths, but of over
700 cases.

Important as is the function of a pure water-supply in preventing
typhoid fever, it is now clear that public hygiene cannot stop here.

1 Jordan, E. O., The Purification of Water Supplies by Slow Sand Filtration,
Journal of the American Medical Association, 1903, p. 850.

216 BACTERIOLOGY

In some countries, as in Germany, for example, where the larger
cities and towns are supplied in the main with water of a highly
satisfactory character, there still remains a notable residue of cases
of typhoid fever. These, we know, are due to contact infection, to con-
tamination of raw foods, such as milk, oysters, and the like, to the
conveyance of the specific germ on the bodies of flies, and to similar
modes of dissemination.1 It is a fact full of significance that the ex-
istence of these various modes of spread is recognized, that they are
held to be matters of public concern, and that preventive measures
are being instituted under expert bacteriologic control for suppressing
the existing sources of infection. One of the most difficult problems
in this campaign lies in the prompt recognition and rigorous super-
vision of the mild and obscure cases. It may be comparatively simple
to isolate and disinfect with thoroughness in the franker types of the
disease, but it is not clear that the danger is most critical on this side.
The application of searching and delicate bacteriologic tests is often
necessary to determine the suitable mode of action. The dependence
of public hygiene upon bacteriologic data and methods has rarely
been better exemplified.

The vigorous warfare that is being waged against malaria in many
tropical countries affords a further and striking illustration of the
utilization of existing resources for the avoidance of specific infection.2
It is hardly necessary to reiterate the obvious truth that malaria con-
stitutes the chief and, perhaps, the only serious obstacle to the colon-
ization of the tropics by the white races. Political and economic
questions of the gravest import to mankind are bound up with the
fortunes of a protozoon and a mosquito. The complex life-cycle of
the malarial parasite offers an unusual number of points of attack.
As is well known, several distinct views are current as to the best way
of interrupting the continuity of transfer between man and the mos-
quito. It is conceivable that by the destruction of the malarial para-
site within the body of man, the supply of parasites for the mosquito
may be cut off and the circle broken at this point. If the mosquitoes
are prevented from becoming infected, man is safe. It is claimed by
the adherents of one school that this method has proved very effect-
ive in certain localities where it has been systematically employed.
The extermination of the parasite in the blood of man by the admin-
istration of quinin certainly constitutes an important weapon in the

1 Schuder, Zur Aetiologie des Typhus, Zeit. f. Hyg., 38, p. 343, 1901.
Hutchinson, R. EL, and Wheeler, A. W., An Epidemic of Typhoid Fever due to

Impure Ice. American Journal of Medical Science, 126, p. 680, 1903.

Ficker, M., Typhus und Fliegen, Archiv. f. Hyg., 46, p. 274, 1903.

Hamilton, A., The Fly as a Carrier of Typhoid, Journal of the American Medical
Association, n. 577, 1903.

Newman, G., Channehof Typhoid Infectionin London, Practitioner, 72, p. 55, 1904.

2 Die Bekampfung dcx Malaria (Koch, R., und Ollmig), Die Malariabekamp-
fung in Brioni (Frosch, P.), in Puntacroce (Bludau), in der Maremma Toscana
(Gosio, B.), etc., Zeit. f. Hyg., 43, 1903, Heft 1.

THE RELATIONS OF BACTERIOLOGY 217

armory of public hygiene, whether or not it prove to be the most
efficient one or the most economic in execution. In this same cate-
gory are to be put the attempts to prevent the infection of the
mosquito by guarding malarial patients against the bite of Anopheles.
It is obvious that this plan may often be difficult of execution, be-
cause of the impossibility of exercising efficient control over the
movements of individuals suffering from latent or recurrent infection.
A second possibility consists in the general protection against
mosquito bite of all persons dwelling in infected regions. The pestifer-
ous insect may beat its wings in vain against the windows of a mos-
quito-proof dwelling; if it cannot come near enough to the human
being to inject the contents of its poisoned sahVary gland, no single
case of malaria will result. In parts of Italy, it is said, this mode of
prevention has been practiced with brilliant success in protecting
railway employees, forced by the exigencies of their calling to reside
in highly malarious localities.1

A third point of attack is presented in the possibility of destroying
or at least arresting the propagation of the insect host of the malarial
parasite. The extermination of a number of species belonging to a
widely distributed and abundant insect genus may seem in itself a
gigantic task to undertake. Remembering the ambiguous success
that has attended the efforts of the human race to combat the ravages
of certain insects injurious to agriculture, it is not easy to be sanguine
concerning the speedy extinction of Anopheles. It is noteworthy that
the most considerable triumphs attained along economic lines have
been effected by the utilization of the natural enemies of the noxious
forms. Efficient foes of Anopheles have so far not been discovered.
There is no question, however, that in definite localities the numbers
of individual mosquitoes belonging to malaria-bearing species may be
enormously diminished by the destruction of the breeding-pools. The
labors, in this direction, of English health officials in various parts of
the \vorld, have been rewarded by a decisive decrease in the preval-
ence of malaria.2

It will not escape remark that the effect of any one or of all of these
protective measures is cumulative. A diminution in the number of
mosquitoes, or in the number of persons harboring the malarial pro-
tozoon in their blood, or in the number of infected or non-infected
individuals bitten by mosquitoes, wrill inevitably produce a lessening
in the amount of malaria in a given region. This will in turn diminish
the opportunities for mosquitoes to become infected, and will at least

1 Celli, A., La Malaria in Italia durante il 1902, Annali d' Igiene sperimentali,
13, p. 307, 1903.

La Socic'te pour les etudes de la Malaria, Archives italiennes deBiologie (1898-1903)
39, p. 427, 1903.

2 Ross, R., Report on Malaria at Ismailia and Suez. Liverpool School of Trop-
ical Medicine, Mem. 9, 1903.

218 BACTERIOLOGY

put a check upon indefinite extension of the disease. It is significant
that a high degree of success apparently attends the enthusiastic and
persistent application of any one of the measures instanced.

While malaria, typhoid fever, and tuberculosis are to-day fairly in
the field of view of public hygiene, such is not the case with a host of
other maladies. A beginning is made here and there, but the vast
majority of the diseases that affect mankind still lack an intelligent
and organized opposition. This is partly because of insufficient know-
ledge. At the present time the apparent increase in pneumonia pre-
sents an imperative field for research. It seems unlikely that the
available modes of attacking this disease are to be exhausted with
attempts to improve individual prophylaxis. A clear understanding
of the tangled web of statistical, climatic, racial, bacteriologic , and
hygienic questions that environ this urgent problem of public hygiene
is likely to come only through renewed investigation of the phe-
nomena. If it is true, as some conjecture on what seems insufficient
evidence, that the virulence of the pneumococcus is increasing, what
is the bacteriologic strategy suited to the emergency? Or if it turn
out that an increase in the number of victims to pneumonia is
largely made up of those who have escaped an early death from
tuberculosis, what procedure is indicated?

We cannot always take refuge from the consequences of inaction
under the plea of ignorance. There are few, if any, instances in which
public hygiene is utilizing to the full the knowledge that it might pos-
sess. Some responsibility rests upon those who are prosecuting bac-
teriologic studies to see that the bearings of their investigations are
not overlooked or neglected by those who are constituted the guard-
ians of the public health. There is here no question of the sordid
self-interest or commercial exploitation sometimes miscalled "prac-
tical application." In the long run the saving of life may play into
the hands of the idealist. If John Keats had not died of pulmonary
tuberculosis at the age of twenty-five, the modern world would be
a different place for many persons. It is not possible to estimate the
loss to literature, science, and art since the dawn of intellectual life
which must be laid at the door of the infectious diseases. The relations
of bacteriology to public hygiene, if properly appreciated and culti-
vated, will lead to an improvement in the conditions of life which will
enhance both the ideal and material welfare of the race, and will give
greater assurance that each man shall complete his span of life and
be able to do the work that is in him.

SOME PROBLEMS IN THE LIFE-HISTORY OF
PATHOGENIC MICRO-ORGANISMS

BY THEOBALD SMITH

[Theobald Smith, Professor of Comparative Pathology, Harvard Medical School,
since 1896; Director of the Pathological Laboratory, Massachusetts State Board
of Health, b. Albany, New York, July 31, 1859. Ph.B. Cornell University, 1881 ;
M.D. Albany Medical College, 1883; A.M. (Hon.) Harvard. Assistant and Di-
rector of Pathological Laboratory, Bureau of Animal Industry, U. S. Depart-
ment of Agriculture, 1884-95; Lecturer and Professor of Bacteriology, Medical
Department, Columbian University, 1886-95; Member of the Board of Directors,
Rockefeller Institute for Medical Research, 1901-. Member of the American
Academy of Arts and Science; Association of American Physicians; Ameri-
can Public Health Association; Association of Pathologists and Bacteriologists.
Author of many papers and reports on infectious diseases of animals ; also papers
on bacteriology and general pathology.]

OUR knowledge of the profound influence which the microscopic
organisms, known as the bacteria, exercise in the life of the globe, may
be considered an acquisition of the last quarter-century. The surmises
and hypotheses of the half-century preceding were then made over
into well-attested facts.

The activities of micro-organisms manifest themselves in many
different ways. The functions carried on by the bacteria of the soil
are known to be of fundamental importance to higher plant life. The
work of the bacteria producing fermentation, putrefaction, and decay
is of similar importance in preparing the way for the soil bacteria and
ministering to the wants of higher organisms. Out of this latter class
there has arisen a group which has given these micro-organisms all the
notoriety they possess. It is a small group, but formidable in that it
is in partial opposition to the higher forms of vegetable and animal
life. It is these parasitic forms to which I shall devote my address, as
it is they which have preoccupied my attention for some years. In
thus passing over large groups of bacteria I simply register my inabil-
ity to properly present their claims, and I trust that others here
present will fully supplement my paper by dealing with them in
deserving fashion.

While bacteriology, strictly speaking, deals only with a fairly well-
defined group of unicellular plant-like forms standing near the limit
of microscopic vision, medical bacteriology has been gradually widen-
ing its scope to a study of all unicellular and even higher parasitic
forms, which multiply more or less indefinitely and continuously for
a time in the invaded body. In addition to the bacteria proper, the
protozoa, and those highly important ultra-microscopic organisms
which seem to have certain characters not possessed by either of the
other two groups, are now frequently gathered into medical bacteri-

220 BACTERIOLOGY

ology, because of certain underlying principles of action which govern
them in common as parasites.

Bacteriology differs from the older sections of biology in several
important particulars. In the first place, it has been developed under
the stress of practical demands. The enormous economic and sanitary
significance of bacterial life has pushed forward this study very
rapidly, and the problems undertaken have been suggested almost
wholly by considerations arising in agriculture and medical practice.

In the second place, bacteriology, at least so far as the parasitic forms
are concerned, is essentially a study of two realms, that of the par-
asite and that of the host, of two organizations, widely different, acting
upon one another and entering into complex, reciprocal relations. The
older departments of biology do not present such a complicated aspect.
Thus anatomy or morphology has, at least until very recently, dealt
with structure and development without considering the relation of
the individual to its environment. That was relegated to physiology
and pathology. With the bacteria the morphologic aspect dropped
nearly out of sight because of the difficulty encountered in analyzing
structures so minute and relatively simple. Even the classification
gradually evolved, as more and more forms were examined, is at
present very largely a physiologic one, the characters being based
on the action which the bacteria exert upon the medium in which
they multiply.

Then again, there was no ulterior interest in the study of bacteria
as such, which is a strong impulse in many other departments of
biologic science. It is what bacteria do, rather than what they are, that
commanded attention, since our interest centres in the host rather
than in the parasite. This tendency manifested itself in a peculiar way.
As soon as bacteria could be handled in pure culture, the study prose-
cuted most actively was how most quickly to destroy them. Disin-
fection, sterilization, and all agents which act destructively upon bac-
teria were diligently sought for. The first impulse of the youthful
branch of bacteriology was thus to destroy, rather than to study and
analyze. When, some years later, the anti-bodies were discovered,
the rush toward the bactericidal serums was equally manifest.

Bacteriology in its scientific form was thus ushered into existence
largely by medical men who had definite practical ends in view. It
presented from its beginnings a dual aspect for study, and its chief
aim from the first was the destruction of one of the elements, the
parasite. Slowly, however, the more impartial study of host and par-
asite in their mutual relation began to take root, and to-day there is
scarcely a department of physical, chemic, and biologic science which
does not have some share in the unfolding of this complex relation
existing between plant and animal life, on the one hand, and the
micro-organisms acting as parasites, on the other, As a result of this

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 221

rather unique state of affairs, bacteriology is not a self-contained,
well-defined field of work, but one greatly subdivided by aims and
methods of study. A realm as large as that of micro-organisms may wel 1
claim attention in many workshops of science.

The short time at my disposal does not permit a wide survey of the
field of bacteriology, and I have deemed it best to discuss in a general
way the parasitism of bacteria and to outline the probable results of
any attempts of medical and sanitary science to modify this parasit-
ism. In undertaking this task 1 have adopted the somewhat discred-
ited method of presenting actual hypotheses, partly new, partly old,
in a new dress. These furnish a definite point of attack, and are better
suited for discussion than any presentation which boxed the compass
with the views already well known.

Infectious diseases have frequently been portrayed as a battle
between two organisms, the host on the one hand, the parasite on
the other. There are few diseases, even among those not strictly in-
fectious in character, in which this battle does not go on at some stage,
and in which the activity of bacteria may be ignored. For some years
the analysis of this warfare has been the chief problem of bacteriology
and pathology. What are the weapons of offense and defense on
either side? Are the weapons simple or complex? Are they changed
as the struggle progresses to suit the immediate state of the battle?
Do the combatants themselves change during long or short periods
of time, and does the character of the disease change as a consequence?
Is the behavior of parasites, when posing for us in the culture-tube,
different from that in the animal body? These and other queries
may easily be read into the special literature of the last decade.

To realize the great complexity of this struggle we need but to review
the gross facts of disease which express themselves in epidemics, on the
one hand, in individual disease, on the other. We meet all gradations
of severity, from rapid death to a mild transient disturbance, from a
disease lasting hours to one lasting fifteen or twenty years, or even
longer. Even the simplest generalizations concerning such a varied
phenomenon must necessarily be subject to many exceptions, and
perhaps gross inaccuracies. This is evident from the heated discus-
sions which have been waged over the humoral and cellular phe-
nomena, the antitoxic and bactericidal forces of the blood, and the
phagocytic activities of certain cells, each party to the discussion
claiming, at least for a time, that the opponent had no case. Though
the brilliant researches of Metchnikoff and Ehrlich, and the funda-
mental discovery of Behring and Kitasato, have to a certain degree
exposed the mechanism of warfare, the exposure is only fragmentary,
and the hypothetic reconstructions based on it are leading as usual
to further controversy. We do know that no two species of micro-
organisms carry on the warfare just alike, and that the same parasite

222 BACTERIOLOGY

finds a somewhat different situation in every host attacked. The
problem of the immediate future is to determine where the brilliant
discoveries of Metchnikoff, Nuttall, Behring, Bordet, Ehrlich, and
others belong in the life of each microbe, and to construct for each
disease the exact nature of the contest.

in the following pages I do not intend to enter into any discussion
concerning the intimate life of bacteria, but simply to point out cer-
tain biologic problems which seem to lie on the surface, as it were,
and which illustrate the close relation existing between bacteriology
and general biology. They have suggested themselves to me from the
comparative standpoint, one up to the present but poorly cultivated
in medical science.

The researches of Roux, Kitasato,and Behring, Van Ermengen and
others, have shown that certain species of bacteria secrete toxins
during their vegetative period. These toxins are soluble in the me-
diums in which these species multiply. Besides these physiologically
well-defined poisons, there are others which are closely linked to the
body substance of the bacteria, and which have become familiar to
us in such well-known substances as tuberculin and mallein. According
to the theory of R. Pfeiffer, this second class of poisons is liberated
only by the disintegration of the bacteria, and the intoxication of
the host, due to its destructive action on the bacilli, is a kind of post-
mortem effect of the parasites. Other bodies, the so-called lysins, which
act destructively upon red and white corpuscles, have also been de-
monstrated by Van de Velde and by Ehrlich and his pupils, but their
significance in disease is not yet clear.

In the host, on the other hand, during the multiplication of micro-
organisms, there appear bodies known as anti-bodies, which have
aroused the greatest interest. They neutralize the soluble toxins,
agglutinate the invading bacteria and disintegrate them. They also
precipitate or coagulate albuminous bodies. Their action is specific,
being directed toward the invaders. These are the main weapons
which thus far have been found. Are there other offensive and de-
fensive bodies? What course do the bacteria pursue in the presence
of the gradually accumulating anti-bodies of the host? Do they forge
new weapons or not?

Professor W. H. Welch in his Huxley lecture presented the theory
that the mechanism of the production of anti-bodies on the part of the
invaded host was set in operation by the micro-organisms as well, and
that various tissue poisons might have their origin in overproduced
bacterial receptors thrown off under special stimulation by host
substances. This theory implies that bacteria may not unfold all their
activities in the culture-tube, and that the latter give us no reliable
clue as to their behavior in the living body.

On this point we may perhaps get some light by a consideration of

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 223

the plasticity of micro-organisms. It has long been known that the
pathogenic power of bacteria is reduced gradually in artificial cultures.
It is also well known that by a series of inoculations, or passages
through animals, the virulence may be restored, and even raised above
the natural level. Bacteria have been gradually accustomed to
originally destructive doses of poisons in culture-fluids. Very recently
it has been shown that they may be gradually trained to multiply in
strongly bactericidal serums and to refuse to be clumped in strongly
agglutinating serums.

These adaptations persist for a certain time, and are transmitted
for a limited period, even in culture. In other words, the modifica-
tions are more or less gradually acquired and gradually lost. The same
is true of the anti-bodies of the host. The antitoxin circulates in
the blood of the horse long after the stimulation by toxins has ceased.
In the immunized animal the agglutinating properties do not disap-
pear at once. I am, therefore, inclined to believe that the bacterium
freshly removed from its usual environment will, at least for a time,
exercise all its functions, provided the special nutritive substances
which may be needed to carry on those functions are present.

The theory of Professor Welch would then resolve itself into a ques-
tion of nutrition. In the body of the host there are certain substances
which give rise to special toxins when acted upon by special bac-
teria. If we could offer these special substances to freshly isolated
bacteria, there is no reason why the assumed toxin should not be
formed. We must, therefore, take into account two possibilities, the
adaptation of microbes to originally destructive agencies, and the pro-
duction of poisons from specific substances elaborated by the host.

I have entered into this much of detail concerning the mutual
relation of micro-organisms and host, in order to make clear the
hypothesis, which, it seems to me, accounts very well for the general
phenomenon of infection. It is that the tendency of all invading
micro-organisms in their evolution toward a more highly parasitic
state is to act solely on the defensive while securing opportunity for
multiplication and escape to another host. By tendency 1 mean a
general slow movement through long periods of time. The following
data are in its favor :

(1) The production of diffusible toxins survives parasitism inde-
finitely, and is readily brought about in cultures.

(2) Where toxin-producing bacteria have become adapted to a de-
finite species, as in diphtheria, the toxin itself acts upon a number of
different species. In other words, the parasitic relation is far more
specialized than the chief pathogenic product.

(3) No strictly invasive bacteria have yet been found producing
diffusible toxins which appear to be of any real significance in the
disease process.

224 BACTERIOLOGY

(4) Those which produce such toxins are not strictly invasive bac-
teria.

(5) The injury due to invasive bacteria is known to be due to the
disintegration of bacteria and the setting free of poisons locked up
in the bodies of the microbes.

(6) Pathogenic bacteria manifest less biochemic activity than the
related saprophytic forms.

(7) The hemolytic and leukocidic toxins of bacterial filtrates may
be due to autolysis of the bacteria. Jordan has shown that hemolysis
is, at least in part, due to a change in the reaction of the culture-fluid.

According to this hypothesis, micro-organisms, in slowly adapting
themselves to the parasitic habit, would gradually eliminate active
toxin production and other aggressive weapons as of little use, and
strengthen whatever defensive mechanisms they may accidentally
possess the rudiments of. If these are capable of marked develop-
ment, we may expect such types of disease as tuberculosis, leprosy,
glanders, and syphilis, in which the parasitic habit is carried to a high
state of perfection. If their mechanisms of defense are not capable
of much development, they will soon be destroyed, or else become
adapted to live upon the skin, and especially the mucous membrane,
as opportunists and occasional disease producers,

In this adaptation the possession of somatic poisons set free dur-
ing disintegration may play an important part. They may give
rise to just sufficient toxin to produce a local protecting nidus of
necrotic tissue, until the time for escape to some other host arrives.
This assumption is supported by the fact that diseases of some
duration are usually focal in character. The micro-organisms mul-
tiply only in certain foci, which sooner or later become evident as
the visible seat of disease.

It may be claimed that defensive and offensive methods are
practically the same, and that it is simply a play upon words to
make any distinction between them. But reflection will convince
us that offensive methods mean direct injury, whereas defensive
methods simply mean a neutralization of the offensive weapons or
else a condition which is invulnerable to them, such as an envelope
made of a special substance.

According to Ehrlich and his pupils, the anti-bodies which appear
in the course of disease are not new bodies, but overproductions
of bodies present in minute quantities normally. The parasitic
microbe is thus at the very beginning of the invasion confronted
with these bodies. At the termination of the disease there are no
new bodies present, but the anti -bodies are on hand in relative
abundance. The situation which the invader has to face is thus
qualitatively the same at the beginning and at the end of the attack.
How does he meet it by defensive methods?

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 225

Three possible fates await the invaders: (1) They are largely
destroyed within the body; (2) they are excreted, or discharged
through various channels; (3) they remain indefinitely in the
body after the disease is over, to be eventually destroyed or elimin-
ated.

That the micro-organisms are largely destroyed within the body
in the course of the disease is not open to dispute; this class is of
no special significance to us. Of most importance are those that
escape to continue their life-cycle in another subject. The mechan-
ism of elimination is of vital importance to the parasite. It assumes
many forms, and is admirably adapted in the various specific diseases
to perpetuate the existence of the species.

The survival of the microbes after the disease is over may be
explained partly on the ground that in nearly all diseases some of
the microbes pass their final stage near the surface of the skin, or
mucous membrane, or in organs in direct or in indirect contact with
the outer air, so that escape outward is readily effected through
destruction of tissue, and hence protection from the bactericidal
forces of living tissue. The small number which in some types of
disease remain alive for some time after the disease process has
subsided may also be inclosed in small foci of necrotic tissue, and
thus escape destruction temporarily.

I am inclined to belie ve, however, that among the problems of
the future will be the elucidation of still another mechanism for the
protection and escape of the micro-organism. It is highly probable
that in a certain number of species of bacteria, after the active
vegetative stage a latent stage follows, during which the parasite
which has escaped destruction provides itself with some protective
envelope which also aids it in its passage to a new host. This envelope,
which may be some specific substance not recognizable with the
microscope, or which may be represented by the capsules in some
groups, may be a defensive body of the parasite stimulated to over-
production by the anti-bodies of the host. This body also interferes
with the metabolism of the microbe, and thus acts in the double
capacity of stopping the disease and protecting the microbe at the
same time. This hypothesis suggested itself to me while endeavoring
to account for the peculiar behavior of tubercle bacilli under culti-
vation.

It is well known that tubercle bacilli from the diseased tissues
of cattle grow very slowly, and then only upon certain culture-
mediums, such as blood-serum. After several years of continuous
cultivation they multiply vigorously in glycerin bouillon, and can
hardly be distinguished in appearance from those human varieties
of the bacillus which grow richly from the first or second transfer.
There seemed to be no justification to assume that the bacillus had

226 BACTERIOLOGY

completely changed its metabolism under artificial cultivation. The
more rational hypothesis seemed to be the one which assumed the
existence of some protective substance only slightly acted upon
by the serum, not at all. in glycerin bouillon, and therefore a hin-
drance to multiplication. After repeated transfers, this protective
substance was slowly lost, either through a selection of bacilli, or
absence of stimulation on the part of the host, or both causes com-
bined, and the growth became as luxuriant as with the more sapro-
phytic human varieties. It is obvious that each group or species
of bacteria would have its own special protective device, depending
upon original capacities of the species, which would be gradually
developed in power and efficiency with the perfection of parasitic
relations.

The formation of protective or defensive coverings, the strength-
ening or modification of the cell-wall, or the secretion of defensive
fluids, would account for certain phenomena which are familiar to
bacteriologists much better than the current theory which bases
parasitism exclusively upon toxin production, active or passive.

In cultures we should expect a loss of power to form protective
substances because the anti-bodies are absent. Hence the uni-
versal tendency toward the reduction and final loss of virulence,
with apparently the metabolic and vegetative activities unchanged,
and the frequently observed regaining of virulence by passages
through series of animals.

In the evolution of parasitic bacteria I assume, then, that though
the function of toxin production may have been the entering wedge
toward a parasitic existence, there is a progressive loss of this func-
tion as of little use to the parasite after it has once acquired a foot-
hold, for the action of toxins at a distance from the focus of mul-
tiplication does not aid the parasite, while it may destroy the host.
In other words, with the invasion of the tissues of the latter it
became necessary for the invader to concentrate its powers in its
immediate vicinity, and for this purpose those poisons set free by
the disintegration of the parasite may be of use in protecting the
focus where the younger forms are, by necrosis of tissue, plugging
of vessels, etc., and thereby keeping away the bactericidal forces
until the bacteria have accumulated sufficient protective power
to subsist in a latent condition, and are read}^ to be discharged
outward. With the loss of active toxin production according to
this hypothesis, and the loss of other, now useless, metabolic activ-
ities, there goes hand in hand a strengthening of the defensive
functions. This strengthening I interpret as the gradual develop-
ment of certain substances which the non-immune host is unable to
act upon, or at most only in a slight degree. This substance, which,
as it were, shoves itself between the parasite and the common

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 227

bactericidal forces of the body, bears the specific pathogenic char-
acter of the microbe. It is the substance which, according to the
nomenclature of Ehrlich, calls forth the amboceptor from the re-
sources of the host to combine with it, and thus open the way for
the usual bactericidal forces or complements according to Ehrlich.
The existence of this specific protective body will account for the
varied resistance of animals to the same micro-organism and the
relative difficulty to induce immunity. The more difficulty the
body has in producing the amboceptor, the greater the difficulty
in acquiring immunit}\

In the departments of preventive arid therapeutic medicine, the
isolation of this protective substance apart from the body toxins
would be of prime importance in combating disease by inducing
individual resistance. In fact, the theory that the so-called immun-
izing and disease-producing substances are separate is not new,
but has been presented under various forms. The tendency to
give up the toxic extracts of bacteria, and use the latter in their
entirety in immunization, pays tribute to these unknown bodies.
The most prominent example of this change was the abandonment
by Koch of the old tuberculin, a boiled extract, and the utilization
of the entire tubercle bacilli, ground and uninjured by heat, in the
production of immunity in tuberculosis.

The foregoing hypothesis, that the tendency of microbes in per-
fecting the parasitic habit, is to act solely on the defensive, is to
a certain degree supported by a phenomenon of considerable bio-
logic importance, which I wish to discuss very briefly.

If we examine the statistics of the various infectious diseases we
are struck with the relatively low mortality of most of them. There
are few highly fatal plagues now known. To be sure, the mortality
of many infectious diseases is regarded as formidable by sanita-
rians, but if we disengage ourselves from the humane view for the
moment, and take the biologic standpoint, we will agree that the
relatively high mortality of 25 per cent to 50 per cent indicates a
very decided preponderance of the resisting powers of the human
race. The odds are always against the invading microbe. This state
of affairs appears for the moment to contradict the results of ex-
perimental bacteriology, which teach us that the virulence of mi-
crobes may be more or less rapidly raised by repeated passages
through susceptible animals, or even through those which possess
considerable resistance. The accustoming of bacteria to antiseptics,
bactericidal and agglutinative serums, has already been mentioned.
With this capacity for adapting themselves to the defensive mech-
anisms of the host, why should not the infectious diseases become
more, rather than less, virulent? What is it that keeps their viru-
lence on a low level? This problem has occupied my attention for

228 BACTERIOLOGY

a number of years, but only recently did a fairly satisfactory ex-
planation present itself. Before entering upon it I have still one
other phase of the problem to consider.

Of a given number of races of the same species of bacteria, the
one which becomes parasitic on a given host species is not neces-
sarily the most virulent for that species. This phenomenon im-
pressed itself upon me during the study of a number of races of
the bacillus of Septicemia hemorrhagica, or, more familiarly, rabbit
septicemia. Races of this species have been found very widely dis
tributed among mammals and birds. Epizootics due to it have
been described as occurring among cattle, carabao, game, swine,
rabbits, guinea-pigs, fowls, geese, etc. It lives in the upper air-
passages of many domestic animals in health.

The rabbit may be successfully inoculated with any of these races.
Some are very virulent, for the merest scratch of the skin inocu-
lated with them will result in death within twenty-four hours. But
the rabbit is not attacked spontaneously by them, although they
are ubiquitous. The race which has fastened itself upon the rabbit
is one of a very low degree of virulence for that animal. Similarly
the highly virulent tubercle bacillus of cattle is encountered only
occasionally in man, although the opportunities for a transfer from
cattle to man are very good.

On first thought, it would seem to us that the most virulent race
would be the one to crowd out any less virulent races and finally to
predominate. But comparative pathology shows us that the con-
trary may be true.

The explanation for these apparently discordant facts readily
flows from a consideration of the life-history of parasitic micro-
organisms. This briefly consists of three phases, the entry into the
host, the temporary multiplication therein, and lastly, the escape
to another host. Each step in this life-cycle must be carefully and
deliberately worked out in the evolution of parasitic organisms,
and each demands a special mechanism adapted to the purpose.
One step is as important as the other. The parasite must find an
unguarded entry, or one which yields readily to its efforts. It must
have a means of defense within the body, and it must finally reach
the exterior to enter a fresh subject.

As a result of these needs, each micro-organism producing disease
has one or several avenues of entry and escape. In some of the
protozoa there is but one avenue, and this is highly specialized and
is through the body of some insect. Among the bacteria the chan-
nels of escape are less highly developed, and there may be several.
As a rule, the microbe adapts itself eventually to a locus more or
less in direct contact with the exterior, and in some instances the
loci of entry, multiplication, and exit have coincided. If we think

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 229

over the various infectious diseases of man and animals, of which
we have any definite information, we shall be surprised to find in
how many the points of attack are in organs or tissues in direct
communication with the exterior. In the most common type of
tuberculosis, pulmonary consumption, the process is almost wholly
limited to the respiratory organs. In typhoid fever the process is
to a large degree carried on in the intestinal wall. In dysentery and
cholera it is wholly so. Even in the very protracted disease of
leprosy, the skin is the chief seat of the disease, while the discharge
of bacilli from the ulcers of the nose is the rule in the tuberculous
type. In that exquisitely parasitic, highly specialized group of
micro-organisms producing the eruptive diseases, the final process
is carried on in the skin. In these diseases the mechanism of escape
is the most perfect.

On the other hand, among the spore-bearing pathogenic bacteria
the means of escape is uncertain. Thus the anthrax bacillus betrays
its saprophytic nature, as pointed out by Koch many years ago,
in its inability to produce spores within the body. Were it not for
the accidental discharges of blood from the mucous surfaces and
the operations of man, the bacillus might not escape at all to sporu-
late. Similar conditions obtain for the bacillus of tetanus and of
Rauschbrand. Both produce disease probably in an accidental
manner, and not as progressive parasites. Their continued exist-
ence is assured by vegetation and spore formation outside of the
body, and it is highly probable that the species would continue to
exist if they did not attack animal life, and that their incursions
into the bod}'- are of no use to them. On the other hand, all attempts
to demonstrate the production of spores in bacteria whose exist-
ence depends largely or wholly upon parasitism have thus far
failed. The spore is evidently poorly fitted to parasitism, and is
replaced by other devices of more adaptability.

The mechanisms of invasion and escape bear a distinct relation to
the pathogenic power or virulence. It is safe to assume that those
varieties or species no matter how virulent, will be eventually de-
stroyed if these mechanisms are imperfect. In fact, the more virulent
the microbe, the more rapid the death as a result of invasion, the
less the opportunity for escape. Hence there will be a selection in
favor of those varieties which vegetate whence they can escape.
The surviving varieties would gradually lose their highly virulent
invasive qualities and adapt themselves more particularly to the
conditions surrounding invasion and escape. That some such pro-
cess of selection has been going on in the past seems the simplest
explanation of the relatively low mortality of infectious diseases.
These individuals or races of microbes which invaded the host too
rapidly and caused death would be destroyed in favor of those

230 BACTERIOLOGY

which vegetated more slowly and in tissues permitting escape of
the microbe after a certain time.

We may now return to the rabbit septicemia bacillus. The reason
why the most virulent type of this group does not pass to rabbits is
due to the fact that there is no satisfactory mechanism of entry and
escape. This presupposes a lesion, a wound as a place of entry, and
the excretion and transfer into a wound in another animal. In the
rabbit this difficulty is worked out in the way usual with this bacillus.
The microbe adapts itself to vegetate upon the mucous membrane
of the upper air-passages. Under certain conditions it invades the
lungs, pleural and pericardial, more rarely the peritoneal cavity,
producing pneumonia and extensive exudates on the serous mem-
branes, and causing death. The disease of the thoracic organs evi-
dently follows some predisposing cause, which enables the bacillus
to make a temporary invasion from the mucous membrane. This
incursion into the body is not essential to the life of the race. In fact,
a little reflection will show that the bacteria which invaded are not
likely to be transmitted, whereas those on the mucosa are readily
handed down from old to young. The virulence of the bacillus is thus
kept on a low level, so low that subcutaneous inoculation of pure
cultures produces merely a local lesion. This type of disease is quite
different from that produced by inoculation with highly virulent
races. These multiply rapidly in the blood throughout the body.

We can now appreciate Pasteur's failure to exterminate the rabbits
of Australia. He believed that with races of this bacillus on "hand
which destroy life very quickly, all that is necessary is to start the
disease among rabbits, and it will tend to spread. The stricken rabbit
with its blood full of germs does not offer the means for inoculating
a second, and so the virulent race perishes.

We can understand, furthermore, why the bacteria associated with
definite diseases in animals produce a diseased condition with diffi-
culty after inoculation. The virulence of the specifically adapted
microbe is of a relatively low order, and in the production of epizootics
various conditions must be realized which assist the micro-organism.
The careful analysis of these conditions will form one of the great
problems of pathology in the immediate future.

The phenomenon of the elimination of the most virulent races and
the establishment of parasitic races of less invasive power I have por-
trayed in the simplest terms. But it is probably much more complex.
The parasite, to be successful, must also stand in a definite relation
to the tissue through which it enters. It is quite probable that the
race of rabbit septicemia bacilli of high virulence would not be able to
maintain itself in the mucus of the upper air-passages. This ability
to multiply in certain places is evidently an acquisition which gives
the particular race its specific character. Without doubt the bovine

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 231

tubercle bacillus, though of great virulence, does not possess the
specific power of entering the human body, or, it may be, of main-
taining itself after entry in certain tissues, such as the lymph-nodes,
except under certain accidental, favoring conditions not yet under-
stood. Perhaps the process of cultivating vaccine virus in the skin has
deprived it of the capacity for entering through the respiratory tract,
and has converted it into a purely inoculable virus.

In the study of pathogenic bacteria the relative ease with which
pure cultures may be obtained from the blood and other organs only
accessible by way of the blood has made this a favorite way of
obtaining such cultures. But it may be asked whether we are not in
this way obtaining bacteria of maximum virulence. May not the
non-agglutinability of some typhoid bacilli immediately after isola-
tion be accounted for in this way? In general, the bacteria thus
obtained can differ but little from the type, as they are all recently
descended from a single bacillus, or a very few which caused the infec-
tion. It is different in the so-called passages through series of animals
in which the usual portals of entry and exit are circumvented and
the bacteria injected into the body and withdrawn therefrom directly.
As a result of such passages many species of bacteria have been made
more virulent, and Pasteur was able to modify greatly the unknown
virus of rabies.

Besides the maintenance of virulence, and its occasional augmenta-
tion, a slow decline to complete loss of virulence may be looked for
under conditions abnormal for the microbe. This probably goes on
where the bacteria multiply, partly or wholly protected from bac-
tericidal influences. The bacilli of tuberculosis, which multiply in
cavities of the lungs or in muco-pus of the air-tubes in chronic cases,
must be regarded as degenerating in virulence. And we actually en-
counter races varying considerably in pathogenic power. In the
throats of well persons, or those who had diphtheria months ago,
bacilli without any power of toxin production, but with all the other
characters of genuine diphtheria bacilli, are occasionally encountered.

During the elimination of the more virulent races of micro-organ-
isms, there goes on as well a gradual weeding-out of the most suscept-
ible hosts. In a state of nature in which medical science plays no part,
there must occur a slight rise in the resistance of individuals, due to
selection, and perhaps acquired immunity, which meets the decline
of virulence on the part of microbes until a certain norm or equilibrium
between the two has been established. This equilibrium is different
for every different species of micro-organism, and is disturbed by any
changes affecting the condition of the host or the means of trans-
mission of the parasite. One result of the operation of this law is the
low mortality of endemic as compared with epidemic diseases. Cer-
tain animal diseases, while confined to the enzootic territory, cause

232 BACTERIOLOGY

only occasional, sporadic disease, but as soon as they are carried
beyond this territory, epizootics of high mortality may result. Cli-
mate in some cases enters as an important factor, but the most import-
ant, perhaps, is the slight elevation in virulence brought about by
a more highly resistant host. The most susceptible animals are weeded
out, and the rest strengthened by non-fatal attacks. The virulence
of the microbe rises slightly to maintain the equilibrium. In passing
into a hitherto unmolested territory, the disease rises to the level of
an epizootic until an equilibrium has been established.

The same is true of human diseases, among which smallpox is a
conspicuous example. The great pandemics of influenza, which seem
to travel from east to west every one or two decades, soon give way
to sporadic cases, and the careful work of many bacteriologists would
indicate that the influenza bacilli found at present have fallen to the
level of secondary invaders, and are parasites of the respiratory tract
in many affections.

As pathogenic micro-organisms differ not only in the degree of par-
asitism attained, but also in their essential nature, a great variety of
diseases is the result. In a crude way they may be arranged into three
classes:

(1) Micro-organisms which live upon the skin and the mucous
membranes, and invade the body only when lesions exist in these
structures, or where the general resistance is impaired.

(2) Micro-organisms which appear only occasionally from some
unknown but permanent focus. They produce epidemics often highly
fatal, but they are successfully pushed back, because the strain cannot
readily adapt itself to the new conditions.

(3) Micro-organisms which are most highly adapted for a parasitic
existence, and which produce diseases of a relatively fixed type.

As regards the first class, the conditions under which they produce
disease rise more and more into prominence. The factor microbe
becomes almost secondary to other factors. Many of our most com-
mon diseases obey certain meteorologic laws. Thus diphtheria and
pneumonia are chiefly winter diseases, because the conditions of
throat and lungs which favor them are largely due to cold weather,
or, we might say, the cold weather acting upon an indoor sedentary
population, or one subjected to untoward influences, injures the re-
spiratory tract. Some microbes of this class depend upon the prepara-
tion made for them by others. Thus the exanthematous diseases,
such as scarlatina and smallpox, are frequently associated with or
followed by the invasion of streptococci, and the majority of deaths
are due to such secondary invasion. The streptococci live upon the
mucous membranes, and whenever the proper opportunity comes
they invade more vital territory. This group of bacteria is the fre-
quent cause of death in chronic diseases. Some years ago Professor

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 233

Flexner pointed this out, and denominated the invasion as a terminal
infection. I think that they may also be appropriately styled the
parasites of the diseased state.

Among the second group we may place such diseases as Asiatic
cholera and the bubonic plague. The origin of the first is unknown.
The definite host of the second is probably the rat.

Among the third class we have such groups of. diseases as tubercu-
losis, leprosy, syphilis, and glanders, on the one hand, and the erup-
tive diseases, on the other. The former are very chronic, protracted,
the latter acute, rapid in their course. In the eruptive diseases the
infection seems to depend solely upon the specific susceptibility of
the individual, and immunity is easily brought about by protective
inoculation.

In tuberculosis and leprosy the mode of infection is evidently very
different from that of the group just mentioned. Prolonged exposure,
as in family life, seems necessary to successful infection, and even then
many exposed individuals escape. In tuberculosis, heredity plays
a very prominent part in the eyes of the physician, because the dis-
ease appears to propagate itself in families. This is probably due
to the necessity for more intimate association and repeated exposure
in order that the disease might appear. Here the disease is long
drawn out, the parasite may become in a sense individualized, and the
attack upon a new host may have to be made repeatedly. With these
highly parasitic forms the necessity for a frequent transfer to another
host is slight. In leprosy, the disease may last fifteen years to twenty
years, and then death ensues, usually as a result of the attack of the
secondary invaders.

From the biologic standpoint which I have endeavored to present,
we may conceive of all highly pathogenic bacteria as incompletely
adapted parasites, or parasites which have escaped from their cus-
tomary environment into another in which they are struggling to
adapt themselves, and to establish some equilibrium between them-
selves and their host. The less complete the adaptation, the more
virulent the disease produced. The final outcome is a harmless par-
asitism, or some well-established disease of little or no fatality, unless
other parasites complicate the invasion. The logical inference to be
drawn from the theory of a slowly progressive parasitism would
be that in the long run mortality from infectious diseases would be
greatly reduced through the operation of natural causes. But morbid-
ity would not be diminished, possibly greatly increased, by the wider
and wider diffusion of these parasites, or potential disease producers.
The few still highly mortal plagues would eventually settle down
to sporadic infections, or else disappear wholly because of adverse
conditions to which they cannot adapt themselves.

In this mutual adaptation of micro-organism to host there is, how-

234 BACTERIOLOGY

ever, nothing to hinder a rise in virulence in place of the gradual de-
cline, if proper conditions exist. In fact, it is not very difficult to fur-
nish adequate explanations for the recrudescence and activities of
many diseases to-day, though the natural tendencies are toward a
decline in virulence. In the more or less rapid changes in our environ-
ment due to industrial and social movements the natural equilibrium
between host and parasite established for a given climate, locality,
and race or nationality is often seriously disturbed and epidemics of
hitherto sporadic diseases result. Typhoid fever will serve as one illus-
tration of my thesis. It is ordinarily a sporadic infection, passing
from the sick to the well by direct contact. Our knowledge that the
infection of this and other diseases is contained in the discharges of
the sick, and a growing sense of cleanliness, led years ago to the large
systems of sewerage, which have made a crowded city life possible.
But the removal of sewage from our immediate surroundings was the
beginning of new trouble. The sewage was led into water-courses
from which drinking-water came. Hence the great epidemics in place
of sporadic disease. The direct transmission of the parasite on a small
scale was largely checked, but the indirect transmission greatly
favored. The dweller in cities with unprotected water-supply is still
further endangered by the fact that the typhoid bacilli returned in
the water may represent more virulent varieties than those handed
down by his ancestors in rural communities. The motley population
brought together by migrations from all parts of the globe bring the
various races of bacilli with them to be redistributed on a large scale.

Conditions may even create diseases artificially. Thus in child-
birth, the physician through want of cleanliness may in his examina-
tion actually inoculate a wounded surface with streptococci or other
septic bacteria. In a hospital badly managed, such germs may be
made to pass artificially through a series of individuals, and their vir-
ulence raised. In nature this could not take place, because there would
be no physician. Hence the transfer would not take place. The his-
tory of maternity hospitals before the period of asepsis in surgery
is a sufficient proof for the theory advanced. Hospital erysipelas and
hospital gangrene were diseases artificially bred. With the introduc-
tion of the principle of asepsis in medicine and surgery, the artificially
created diseases were destroyed, because the transportation facilities
of the bacteria were cut off.

These illustrations indicate that so-called natural law does not
stand in the way of our having highly virulent types of disease if we
are ignorant enough to cultivate them. The micro-organism is suffi-
ciently plastic to shape itself for an upward as well as a downward
movement. Among the most formidable of the obstacles toward a
steady decline of mortality is the continual movement of individuals
and masses from one part of the world to another, whereby the partly

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 235

adapted parasites become planted as it were into new soil and the
original equilibrium destroyed. These various races of disease germs
become widely disseminated by so-called germ-carriers, and epi-
demics here and there light up their unseen paths. Fortunately for
us, the conditions under which these micro-organisms may establish
themselves are in many cases so complex that they cannot be real-
ized. It is highly probable that the bubonic plague cannot get a foot-
hold or maintain itself among us, while Asiatic cholera might have a
better chance, through our still greatly unsatisfactory water-supplies.
Many tropical diseases would fail to take root in our climate. The
mysterious rise and disappearance of leprosy in the Middle Ages has
astonished many students of epidemiology. Possibly some slight
bias of the micro-organism may have accomplished what seems almost
a miracle. Perhaps the right race or variety, once introduced, may
repeat the history of the Middle Ages in our day or in that of the
coming generation.

Another obstacle to the amelioration of infectious diseases is the
rapid change going on in the habits of individuals and the ferment
in our conceptions of health and well-being, which are continually
upsetting any established equilibrium and making us more resistant
to some diseases, more susceptible to others. Of great interest is the
effect upon the human race of the assiduous care of those afflicted
with certain chronic diseases which is just now expressing itself in
the establishment of sanatoriums for the cure of the tuberculous.
If this movement should gain great headway, there may be a race of
immunes gradually developed who may be able to stand the untoward
conditions of indoor city life much better than the naturally robust
and physically superior who have no so-called hereditary taint.

Of still greater interest is the vast vaccination experiment to whose
beneficent influence the century just past bears ample testimony.
The vaccinated individual is either wholly immune, or else the dis-
ease contracted after exposure is abortive, and the eruptive stage
does not come to full development or maturity. The excretion of the
infecting organism is thereby greatly interfered with, and it is not im-
probable that in the mildest cases it may not reach that maturity
necessary for the successful infection of others. In view of the adapt-
ability of micro-organisms in general, it is not beyond the range of
possibility that a variety of the smallpox organism may through a
chain of accidents arise as a result of successive passages through
partly protected individuals. To-day it seems fairly well established
that a single vaccination in infancy is not an adequate protection
during life, and at least one nation — a nation which not only culti-
vates but consistently utilizes science — prescribes two vaccinations
as necessary to complete protection. Whether in the days of Jenner
repeated vaccinations were deemed necessary I have not been able to

236 BACTERIOLOGY

verify; but we may assume without immediate fear of experimental
contradiction that a century of incomplete protection may have
worked some changes in the smallpox organism. In any case, it is
obvious that our thesis implies, in addition to the natural decline of
virulence, also a gradual rise in virulence whenever the resistance
of susceptible individuals is raised on a very large scale. Either the
micro-organism, if a true parasite, will perish, or else it will aug-
ment its invasive powers to meet those of its host.

Another problem has been created for the diphtheria bacillus by the
extensive use of diphtheria antitoxin. Will the thorough protection
of one group of human beings lead to the decline or to the increase in
virulence of the diphtheria bacillus circulating among the individuals
of this group? What effect will the transfer of such bacilli to unpro-
tected groups have? These and similar queries may be answered not
many years hence, for a generation of microbes represents a very
short space of time.

It may not be out of place to call attention here to the bearing of my
thesis upon the recent attempts to utilize parasitism in ridding us
of undesirable or noxious animals. In bacteriology there have been
attempts to destroy field-mice and rats with certain species of bacteria.
In entomology, parasitism is such a familiar phenomenon that it has
been seized upon on a number of occasions to destroy otherwise un-
assailable insect pests.

Leaving out of consideration the presumptive dangers of introduc-
ing new species into a locality or country, which must always be taken
into consideration, although they may be of no significance, we have
to consider the chances of success as compared with the cost of intro-
ducing and maintaining the parasites. In any event, we need not
expect a destruction of the noxious species, for that is not the end of
parasitism. A reduction in numbers is all that need be looked for.
The new parasite will probably fail to become acclimated at first,
and it may be necessary to reintroduce it for a number of years. During
this period some few may become adapted to their environment, and
continue as parasites. Whether the equilibrium finally established
will be of economic value, must be observed rather than predicted.
In bacteriologic experiments of this kind the continued vigorous activ-
ity of the bacteria from year to year need hardly be expected. The
disease will either die out or continue on a low level of mortality,
in accordance with the general laws I have detailed, unless bacteria
whose destructive powers are maintained and carefully gauged in
the laboratory are distributed at definite intervals.

In conclusion, I will simply call attention to another problem affect-
ing the future well-being of mankind, the possibility of new infectious
diseases arising in the flux and change incidental to human progress.
We have assumed that the capacity for a parasitic existence probably

PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 237

depends on some original offensive power of the microbe which it
accidentally possessed, such as toxin production, or the presence of
intracellular toxins combined with defensive powers. These, pos-
sessed independently of the host, were probably the entering wedges
to be further developed or dropped, according to necessity. It is more
than probable that all species of bacteria which possess these rudi-
mentary invasive powers have already availed themselves of the
opportunity to become parasites of animal life on the one hand, of
vegetable life on the other, and that no startlingly new diseases will
arise from saprophytic forms.

Subsidiary problems there are, however, concerning the modifica-
tions and readaptations of the parasitic forms already in existence.
These may be grouped under two heads:

(1) The transfer and adaptation of parasites from one host species
to another.

(2) The increase of invasive properties of parasites of the same
host.

Are there any new diseases likely to appear as a result of the suc-
cessful adaptation of parasites of higher animals to the human sub-
ject? This is a legitimate question, though difficult to discuss, for
want of material at present. Among the more important possibilities
I will simply mention the bovine tubercle bacillus and the hog-cholera
group of bacteria. The larger number of parasites on animals are so
specialized, however, their receptor apparatus, according to Ehrlich,
may have been so curtailed, that parasitism on a relatively distant
species may be impossible.

As regards the second problem, that microbes may gain in invasive
power on the same host, the principle I have endeavored to establish
would stand in the way of any rise in virulence, because the most
invasive forms of a varying species would have the least chance for
transmission. Whatever increase in disease-producing power may
be acquired must be gained under special conditions, one of which is
association with other microbes. Thus, if we could conceive of the
same streptococcus, originally an inhabitant of the normal throat, as
passing on account of some series of accidents through the bodies of
a number of scarlatina patients, this streptococcus might thereby rise
temporarily to the level of a serious menace to the throats and perhaps
other organs of relatively healthy people.

Again, certain microbes, like B. coli, the pneumococcus and men-
ingococcus, may, by living upon catarrhal mucous membranes, and
passed from case to case, acquire enough temporary pathogenic power
to cause localized epidemics under favorable conditions. Any advan-
tage thus gained would soon be sacrificed, and the microbe return to
the normal condition, unless a satisfactory mechanism of transmission
could be established.

238 BACTERIOLOGY

It will be seen that there are many problems before the bacteriologist,
problems which have something akin to those of the student of races,
varieties, and species among higher forms of life. These problems
must be attacked with the same patience and pertinacity that were
exercised by Mendel, Darwin, De Vries, and many others in the effort
to trace the rise of new species.

In dealing with the great problems of pathogenesis and parasitism
as applied to the micro-organisms in such a summary and hasty man-
ner, and in endeavoring to trace the law of a declining virulence (and
hence mortality) and an advancing parasitism, I may have left some
doubts in the reader's mind concerning the ultimate value of medi-
cine, preventive and curative, in controlling these diseases, since it
might be assumed, according to the hypotheses presented, that they
would take care of themselves. This impression will, I think, be dis-
pelled by a little further development of the ideas presented.

The social and industrial development of the human race is con-
tinually leading to disturbances of equilibrium in nature, one of whose
direct or indirect manifestations is augmentation of disease. In order
to avoid this calamity, or reduce its force as much as possible, we must
make special compensations or sacrifices to restore or maintain the
normal balance. The more clearly the kind of compensatory action
required is foreseen, the more promptly it is put into effect, the less
disease there will be. It is the true function of medical science to dis-
cover and put into effect those compensatory movements which will
counterbalance the temporary ill effects of what, for want of a more
illuminating term, we call human progress.

It is largely through the phenomenon of parasitism that nature
attempts to restore the equilibrium, and in this micro-organisms play
the most important part. As soon as the individual falls below a cer-
tain level he may become the prey of a microscopic, or even an ultra-
microscopic world. Hence the importance of bacteriology in medical
science. Much has already been done in determining ways and means
for the counterbalancing of the ravages of this microscopic world, but
science cannot rise above natural law. It must work through it.
The optimism of the world frequently places science above natural
law and believes it capable of correcting any and all excesses of in-
dividuals and races. We may be certain that it will never be able to
eliminate the factor of parasitism. Its most important work will con-
tinue to be to analyze this factor into its minutest details and to devise
means by which this analysis may be made useful in turning aside or
at least in deadening the shock of disease.

SHORT PAPER

PROFESSOR FREDERICK P. GORHAM, of Brown University, presented a paper to
this Section on " The Production of Light by Bacteria," in which were set forth
both the importance of the study of photogenic bacteria and the various species
which have thus far been discovered.

SECTION G — ANIMAL MORPHOLOGY

SECTION G — ANIMAL MORPHOLOGY

(Hall 2, September 21, 10 a. m.)

CHAIRMAN: DR. LELAND O. HOWARD, Department of Agriculture, Washington,

D. C.
SPEAKERS : PROFESSOR CHARLES B. DAVENPORT, University of Chicago.

PROFESSOR ALFRED GIARD, The Sprbonne, Pans.
SECRETARY: PROFESSOR C. H. HERRICK, Dennison University.

THE Chairman of the Section of Animal Morphology, Dr. Leland
O. Howard, of the United States Department of Agriculture, in
calling the Section to order, briefly spoke of the enormous pro-
gress in research in animal morphology during the past decade, and
congratulated the Section upon its good fortune in having as its
principal speakers such representative workers in this branch of
science from Europe and from America. He spoke of the wide range
of the investigations which have been conducted for many years
by Professor Alfred Giard, and mentioned especially the fact that
among European zoologists Professor Giard is probably the best
informed concerning the investigations of American workers. His
interest in American investigations, and his reviews and comments
upon American publications, have endeared him to American
biologists, while his own brilliant investigations have commanded
our respect.

The work of Professor C. B. Davenport, the Chairman stated, was
too well known to the Section to need any comment from him.
His admirable work, and his acknowledged leadership of a new and
important school of investigators, are generally acknowledged, and
his recent appointment as Director of the Carnegie Institution
Station for Experimental Evolution, at Cold Spring Harbor, is
the latest recognition of this fact.

ANIMAL MORPHOLOGY IN ITS RELATION TO OTHER

SCIENCES

BY CHARLES BENEDICT DAVENPORT

[Charles Benedict Davenport, Director of the Station for Experimental Evolution,
Carnegie Institution of Washington, b. June 1, 1866, Stamford, Connecticut.
S.B. Polytechnic Institute of Brooklyn, 1886; A.B. Harvard University, 1889;
Ph.D. ibid. 1892. Assistant in Zo6logy, Harvard University, 1887-91; In-
structor in Zoology, ibid. 1891-99; Assistant Professor of Zoology, University
of Chicago, 1899-1901; Associate Professor of Zoology, ibid. 1901-1904;
Director of the Biological Laboratory of the Brooklyn Institute of Arts and
Sciences, since 1898. Member of the American Academy of Arts and Sciences;
American Association for the Advancement of Science; Socie'te' Zoologique de
France; Allgemeine Entomologische Gesellschaft, etc. Author of Experimental
Morphology; Statistical Methods; and other works and monographs on zoology.]

IN the system of classification adopted by the organizers of this
Congress the science of animal morphology is apparently to be
defined so as to exclude comparative anatomy. I take it, conse-
quently, that it is intended to include only the broader problems
connected with the form of animals, — such as the phylogenetic
evolution of form, the embryological development of form, and the
restoration of the mutilated form, — in general, the form-producing
and form-maintaining factors.

Expressed in this way the relations of animal morphology become
more evident; and clearly the first and most intimate of these
relations is with the morphology of plants. The separation of animal
morphology from plant morphology in the department of biology,
while according with a division of the subject found to-day in
our universities, is, I think, not an ideal condition. For the form-
producing and the form-maintaining factors are, at bottom, the
same in all organisms. The problem of what factors have worked
to determine whether a fish or a man shall have such and such a
form is identical with that of the determination of the form of a fern
or an oak. Little by little the morphologists that deal with the
broader aspects of their science are being forced to face the absurd-
ity of its division on the basis of the material studied. In cytology
it is found that the maturation of the germ-cells, the fertilization of
the egg- and cell-divisions, are identical processes in the two "king-
doms."1 To admit a plant cytology and an animal cytology is only
less absurd than to admit a mammalian cytology, an avian cytology,
and a reptilian cytology.

What is true of cytology is true of the other branches of morpho-

1 The most recent and best general work on cytology is that of E. B. Wilson,
The Cell in Development and Inheritance, 2d edition, New York, 1901.

RELATIONS OF ANIMAL MORPHOLOGY 245

logy, such as embryology in its broadest sense, the phenomena of
regeneration and regulation in organisms,1 and especially the evo-
lutionary history of specific forms. While in taxonomy we must
continue to have botanists and zoologists, as we shall continue to
have ornithologists, entomologists, etc., yet outside of the purely
descriptive subsciences I would the gulf between botanists and zoo-
logists were annihilated, and that we had biologists separated rather
in regard to subjects, and university chairs, journals and societies
devoted to evolution, cytology, ontogenetic processes, and form
regulation, without regard to the systematic position of the material
studied. Then we might hope to advance a subject instead of mull-
ing over endless descriptive details.

We have next to consider the relations of morphology to form
evolution, or phylogeny. Before we can consider how a new form
arises, we must clear the field by seeking some element of form.
The mass of material in the organic, like that in the inorganic
world, early led to an attempt at the classification of these materials
in both biology and chemistry. In chemistry a certain number of
kinds of materials have in course of time been catalogued and are
called substances, each of which has its particular molecular com-
position. In biology, likewise, many thousand kinds of organisms
have been catalogued, and these are called species, each made up
of particular sorts of individuals. Chemistry has gone a step farther
in its analysis of non-living matter, and recognized that the different
molecules are made up of diverse combinations of a relatively
small number of units called atoms. To-day biology has to recog-
nize that its individuals are likewise diverse combinations of units
— relatively very numerous — which, following De Vries,2 we call
unit characters, or we may use the simpler name of "character-
istics." Characteristics are thus to individuals what atoms are to
molecules. As the qualities and behavior of molecules are deter-
mined by their constituent atoms, so the essence of the individ-
uals of any species is determined by its constituent characteristics.
And as we may construct new substances at will by making new
combinations of atoms, so we may produce new species at will by
making new combinations of cluracteristics. The making of new
combinations in molecules or species is a useful work, but it is not
evolution. Evolution in the non-organic or the organic world is first
achieved when we can make new atoms or new characteristics,
as the case may be.

This conception of species, which has arisen during the present

' See T. H. Morgan, Regeneration, New York, 1901.

2 Compare De Vries : Die Mutationstheorie, ' ' Die Eigenschaften der Organismen
aus scharf von einander unterschiedenen Einheiten aufgebaut sind." Bd. I, p. 3,
Leipzig, 1901.

246 ANIMAL MORPHOLOGY

decade, has its germ in the work of Mendel,1 and, in consequence
of the stimulating researches of De Vries,2 Correns,3 Tschermak,4
Bateson,5 and others,6 has developed into a stately doctrine, a
doctrine which bids fair to revolutionize biology as the atomic
theory did chemistry. It adds at once a new dignity and interest
to morphology as well as to the description of species, or taxonomy.
In describing the form of an animal we are enumerating its qualities.
Many of these are directly the unit characters of the species; others
are composite and may be analyzed, by appropriate methods of
breeding, into the elemental characteristics.

I may illustrate this by reference to domesticated poultry,7 to
which I am now paying some attention. It is impossible to enu-
merate all of the characteristics of poultry, but the following are
some of the most striking :

Size: Large and dwarf, which are exemplified in the Asiatic
breeds and the bantams.

Colors: Black; buff or red; white; brown (in the female), the
male being often bronze, green, black, yellow and white; barred

1 Mendel's work was first published in Verhandl. naturf. Verein in Briinn, Ab-
handlungen, iv, 1865. Published 1866. A translation in English is given by W.
Bateson, Mendel's Principles of Heredity, Cambridge [England], 1902.

2 De Vries (Sur la loi de disjunction des hybrides, Comptes rend, d' Academic des
Sciences, Paris, cxxx, 845-847, 1900), and C. Correns (G. Mendel's Regel iiber das
Verhalten der Nachkommenschaft der Rassenbastarde, Ber. Deut. Bot. Ges. xvin,
158-168, 1900) rediscovered Mendel's paper simultaneously.

H. de Vries, Ueber erbungleiche Kreuzungen, Ber. Deut. Bot. Ges. xvnr, 435-443
(1900) ; Sur les unites des charactires specifiques et leur application a I' etude des
hybrides, Rev. gen. de Botanique, xn, 257 (1900); Die Mutationstheorie, Bd. u
(1903).

3 C. G. Correns, Ueber Levkoyen-Bastarde, Zur Kenntniss der Grenzcn der Men-
del'schen Rcgcln, Botan. Centralbl. LXXXIV, p. 97 (1900); Ueber Bastarde zwischen
Rassen von Zea Mays, Ber. Deut. Bot. Ges. xix, 211 (1901); Bastarde zwischen
Maisrassen, Bibliotheca Botanica, Heft 53 (1901); Ueber Bastardirungs-V ersuche
mit Mirabilis-Sippen, Ber. Deut. Bot. Ges. xx, 594-608 (1903).

4 T. E. Tschermak, Ueber kiinstliche Kreuzungbei Pisum sativum, Zeitschr. f. d.
Landwirthsch. Versuchswesen,iu, 465-555 (1900); Weitere Beitrdge iiber Verschied-
enswerthigkert der Merkmale bei Kreuzung von Erbsen und Bohnen, ibid. IT,
641 ff. (1901); Ueber Ziichtung neuer Getreiderassen mittelst kunstlicher Kreuzung,
ibid, iv, 1029. Die Theorie der Kryptomerie und des Kryptohybridismus, Bcihefte z.
Bot. Centralbl. xvi, 25 pp. (1903); Weitere Kreuzung sstudien an Erbsen, Zeitschrift
/. d. Landwirth-Versuchswesen in Oesterr. 106 pp. (1904) .

5 W. Bateson and E. R. Saunders, Experimental Studies in the Physiology of
Heredity, Reports to Evolution Committee of the Royal Society of London, i, 160
pp. (1902).

6 A few important papers may be cited: W. E. Castle and G. M. Allen,
The Heredity of Albinism, Proceedings of the American Academy of Arts and
Sciences, xxxvm, 601-622 (1903); W. E. Castle, Heredity of Coat Characters in
Guinea Pigs and Rabbits. Papers of the Station for Experimental Evolution,
-no. 1 (Carnegie Institution of Washington, 1905); C. C. Hurst, Experiments in the
Heredity of Peas, Journal of the Royal Horticultural Society of London, xxvm,
483-494 (1904); L. Cu£not, L'Ph'rfditc de la pigmentation chez les souris, Arch,
de Zool. expir. x, notes, 27-30(1902), ibid, i, notes, 33-41 (1903); ibid, n, notes,
45-56 (1904).

7 _ Extensive books have been written on the different races of poultry. The fol-
lowing are the most important of those in English: W. B. Tegetmeier, The Poultry
Book, London, Routk-dge, 1867; L. Wright, The New Book of Poultry, London,
Cassell & Co., 1902; The Poultry Book, New York, Doubleday, Page & Co.

RELATIONS OF ANIMAL MORPHOLOGY 247

(as in the Plymouth Rock) and spangled (having centre of feather
of different color from periphery).

Comb: Single, pea, rose (flat, covered with tubercles, like a file),
walnut; replaced by crest.

Legs: Feathered, featherless; black, blue, yellow, horn-color.

Body -shape: Short and chunky; tall and slender.

Now the various varieties of fowl are made up of various com-
binations of these characters. Thus we may have Plymouth Rocks
which, instead of having bars, are pure white, or all buff; or the
single comb may be replaced by a rose comb (when they are called
Wyandottes); the usually clear legs may be feathered; and, finally,
they may be " bantamized."

Any desired characteristic in the whole catalogue of poultry
characteristics might be engrafted upon an original Plymouth
Rock stock. We might put on it the crest of the Polish fowl or the
twisted feathers of the frizzle, or the loose barbs of the silky, or the
taillessness of the rumpless, or the long tail-feathers of the Japanese
long-tailed fowl. All this is, of course, possible because of the cross-
fertility of the races having these different characteristics. By
similar procedure we might make a white, blue-eyed, deaf, long-
haired, tailless, seven-toed cat; engraft the horns of the Dorset
sheep upon the hornless Southdown; add the fecundity of the two-
nippled horned Dorset to the multi-nippled condition of Dr. Alexan-
der Graham Bell's flock.1 We might expect, after some experience,
to do this with the same certjainty that we can get calcium chloride
and carbonic acid out of a mixture of hydrochloric acid and marble.

The bearing of this illustration, I repeat, is to show us that char-
acteristics of species are entities, not a little of whose interest lies
in the question of their origin in each case. When we know how
such characteristics arise, then we may call them forth at will, and
so determine the evolution of organic form. For the present it is
sufficient that by the acquisition of new characteristics new species
have arisen from preceding ones.

This assertion is justified by the examination of any extensive
synopsis of species. Take, for example, De Bormans's synopsis of
Forficulidse in Das Tierreich.2 Take any synoptic key at random.
Apterygida japonica has two large tubercles at the end of the abdo-
men. Apterygida allipes has four small ones. Anisolabis xenia differs
from A. Uttorea by slightly smaller size, and especially by having
two teeth in the forceps in the male, or three in the female, instead
of none at all. I do not mean to assert that species have arisen only

1 Bell has given an account of his flock in Science, ix, 637, May 5, 1899, and
Science, xix, 767-768, May 13, 1904. He has also published privately (1904) a
catalogue of his sheep.

2 De Bprmans, A., and H. Krauss, 1900, -Das Tierreich, 11 Lief. Forficulidce and
Hemimeridce, Berlin, xvi + 142 pp.

24S ANIMAL MORPHOLOGY

by an addition or subtraction of characteristics, but this is a com-
mon method. Very often we find one characteristic being replaced
by another. Thus in Lepidoptera one species may differ from another
in the replacement of red by yellow; or one earthworm will differ
from another by having the sexual openings in different segments.
We have no reason for thinking that these characteristics are
not integral entities as much as those distinguishing domestic
races. The modern morphologist, therefore, with the significance
of characteristics in mind, must appreciate that in enumerating
these characteristics he is enumerating the steps of evolution.

The relations of morphology to embryology are so intimate that
the latter is commonly reckoned a subdivision of the former. Cer-
tainly the interpretation of the adult form depends on a knowledge
of its development. "In terms of the ancient riddle," says Bateson
(Nature, vol. LXX, p. 412), in his recent address as president of the
section of zoology in the British Association, " in terms of the ancient
riddle, we must reply that the owl's egg existed before the owl, and
if we hesitate about the owl we may be sure about the bantam."
The characteristics of the adult form are implicit in the fertilized
egg, and are determined by the Anlagen of the characteristics wrapped
up in that egg. We know now that upon the symmetry of the egg
and of the successive cleavages often, if not typically, the symmetry
of the adult form depends,1 and that to the lack of symmetry of
cleavage in gasteropods their lack of symmetry is probably to be
referred.2 In the successive cleavages definite organ-tracts are
marked off,3 and still later the epidermal organs, such as hair,
feathers, and scales, — the bearers of the more evident heredity
characteristics, — are laid down in regular lines, radiating often from
single points or groups of cells,4 thus simplifying the problem of

1 H. E. Crampton, 1894, Reversal of Cleavage in a Sinistral Gasteropod, Annals
of New York Academy of Science, vni, 167-170.

2 E. G. Conklin, The Embryology of Crepidula, Journal of Morphology, xnr,
1-210, April, 1897.

3 Compare the results of H. E. Crampton, Experimental Studies in Gasteropod
Development, Archiv fur Enturickelungsmechanik, m, 1-19 (1896), in which the
removal of an early cleavage cell led to a corresponding defect in the larva. Even
more striking are the results of E. G. Conklin with ascidians, Organ-Forming Sub-
stances on the Eggs of Ascidians, Biological Bulletin, vin, 205-230, March, 1905,
who finds organ-tracts preformed in the uncleft egg.

4 That metamerically repeated organs are laid down from definite bands of cells,
sometimes originating in "pole-cells," has long been known, through the studies of
Hatschek and of Whitman, Contribution to the History of the Germ-Layers in Clep-
Kine, Journal of Morphology, i, 108-179 (1887). Compare also the following: E. B.
Wilson, The Embryology of the Earthworm Journal of Morphology, in, 388-450
(1899); E. B. Wilson, The Origin of the Mesoblast- Bands in Annelida, Journal of
Morphology, iv, 205-219; W. M. Wheeler, Neuroblasts in the Arthopod Embryo,
Journal of Morphology, iv, 337-344. That multiple organs of other sorts are laid
down in linos appears for feathers from the work of Nitzsch,Pterylography(1867),
translated by P. L. Slater, Ray Society; and for hairs, J. C. H. de Meijere, Ueber
die Haare d(r Saugethiere, inbesonders uber ihre Anordnung, Morphologische Jahr-
buch, xxi, 312-424.

RELATIONS OF ANIMAL MORPHOLOGY 249

inheritance of peculiarities of plumage or coat color by referring
them back to transmission through particular cells or cell-groups. It
has thus been possible to show that all the numerous dorsal append-
ages of the nudibranch mollusk Eolis are derived from material split
off in a regular manner and at regular intervals from a group of cells
lying in the tail-end of the developing animal. * Thus the interpreta-
tion of the mechanism of transmission of qualities is first gained from
a study of embryology.

A second way in which embryology has been regarded as indis-
pensable to morphology is in the light it has thrown on homology.
By homology — the will-o'-the-wisp of morphology — is meant such
a similarity of unlike things in different species as would justify
their receiving the same name. And one of the strongest grounds
of a homology is similarity of origin regardless of function or even
ultimate anatomical connections. The search for homologies has
led to the idealization of the "type," and this, more than anything
else, has blinded morphologists to the facts of variation and evo-
lution. When, however, twenty-two vertebrae in place of twenty-
one can nonplus the seeker after homology, its ethereal nature is
sufficiently indicated.2 Homology may, indeed, exist between
normal types, but the abnormal or pathological is often beyond
homology, and yet just the abnormal is, paradoxical as it may
sound, the important for evolution.

As we study an organism's form, we see that it is not made up
merely of a great number of characteristics, but that these charac-
teristics are, on the whole, such as enable the animal to thrive in
its environment. We are struck by their "adaptive" nature.

I am well aware that twenty years or so ago this side of morpho-
logy — the side, namely, of the accounting for an organism's form
on the ground of use — was little cultivated. Morphology had for
its aim the discovery of the interrelation of parts in the individual
organism and the homology of parts in different individuals or
species, and if it sought to go farther it indulged only in speculative
inferences as to the probable function of the parts. On the whole,
the student's attention was directed towards connections of organs
and his natural inquiry as to use was stifled. Some one said that
function varies while the form persists.3 This phrase became a
dogma, and function was considered a matter too trivial for con-
sideration. Homology was the study for men of science; analogy
was for the dilettanti. Morphologists should have been warned by
cases like the whale, whose teeth cannot be homologized with those

1 C. B. Davenport, Studies in Morphogenesis, i, On the Development of the Cerata
in asolis, Bulletin of the Museum of Comparative Zoology, Harvard College, xxiv,
141-148, 1893.

2 See W. Batesoix, Materials for the Study of Variation, 28-33 (1894) .
1 Sometimes called "Dohrn's Law."

250 ANIMAL MORPHOLOGY

of other mammals, and not have underrated the limitations of
homology nor the importance of the study of adaptations. Only
within the last few years have we come to recognize that every
organ is more than a homologue: it is also a successful experiment
with the environment.

The existence of that relation between form and environment which
we call adaptation has been recognized for centuries, yet its full sig-
nificance is still obscure. The prevailing theory (of Darwin) assumes
that a change in environment precedes any change in form and that
adaptation is, therefore, necessarily achieved by a change in the
mean of the form to meet the changed demands of the new environ-
ment. This theory may, indeed, be said to be the natural outcome of
the morphological doctrine of fundamental fixity of type. The type
could be bent to meet new conditions, but could receive nothing new
nor suffer loss of parts. I find that in the pre-Darwinian epoch Prich-
ard * suggested that the Creator made the various species and placed
them in habitats for which their structure fitted them. We see in this
suggestion translated into modern terms the germ of a very different
theory of adaptation from the prevailing one. I expressed this nearly
two years ago about as follows: 2 "The world contains numberless
kinds of habitats or environmental complexes capable of supporting
organisms. The number of kinds of organisms is very great; each
lives in a habitat consonant with its structure." Each species is
being widely dispersed, while, at the same time, it is varying or
mutating. By chance, some variants of the species get into an environ-
ment worse fitted for them; others into one better fitted. "Those
that get into the worse environment cannot compete with the species
already present; those that get into a habitat that completely accords
with their organization will probably thrive, and may make room for
themselves, even as the English sparrow has made room for itself in
this country. This process may go on until the species is found only
in the environment or environments suited to its organization. As
Darwinism is called the survival of the fittest organisms, so this may
be called the theory of segregation in the fittest environment."

The principle that animals are found in habitats for which their

1 J. C. Prichard, Physical History of Mankind, 3d ed., 1836-37, vol. i, p. 96:
" The various tribes of organized beings were originally placed by the Creator in
certain regions, for which they are by their nature peculiarly adapted." I owe
this reference to F. Darwin's More Letters 0} Charles Darwin, vol. i, p. 45, New
York, Appleton.

2 The A nimal Ecology of the Cold Spring Sand Spit, with remarks on the Theory
of Adaptation, The Decennial Publications of the University of Chicago. Preprint
dated Jan. 1, 1903. This was written in the autumn of 1902. The sentences
quoted are on page 21 . The same idea is worked out in my paper, The Collembola of
Cold Spring Beach, with special reference to the movements of the Poduridie, Cold
Spring Harbor Monographs, n, pp. 24, 25, July, 1903. In T. H. Morgan's book,
Evolution and Adaptation, this view is adopted. This book was published in
November, 1903.

RELATIONS OF ANIMAL MORPHOLOGY 251

structure fits them, and not elsewhere, points to the close relations
existing between morphology and geography. We find the animals
of the seashore, such as sponges, hydro- and anthozoa, and tunicates,
to be largely sessile, and, in consequence, of the radiate type of
structure. This sessile habit makes it possible for them to maintain
their hold on the rocks from which the beating waves tend to tear
them. Those which are not actually permanently attached have
means enabling them to cling closely to the rocks; such are the ech-
inoderms, the mollusks, many annelids and crustaceans. The ani-
mals of the surface of the sea, such as siphonophores, ctenophores,
jelly-fishes and larvae, are without such clinging organs; they include
species whose organization permits them only to float or swim at or
near the surface. The deep sea could have been populated more
readily, so far as proximity goes, from the surface organisms than
from those of the shore-line; but only the latter offered the struc-
tural features consonant with life at the sea-bottom, and so the deep
sea became populated thence. In the swift-flowing rivers we find
powerful swimmers or animals that can hold fast to the bed of the
stream and in ponds, we find those species which have some means of
preserving their continuity in time of drought. In caves * we get not
any forms which happen to be washed into them, but only darkness-,
moisture-, and contact-lovers. In deserts whole groups of animals are
absent, only those occurring with thickest skin, — least apt to lose
water by transpiration, — such as certain snakes, lizards, and hard-
shelled beetles.2 In general, in studying the geographical distribution
of animals in environments presenting extreme conditions we find
that they clearly have been selected from groups presenting the most
favorable characteristics. All of this indicates that, often at least, the
already existing morphological conditions have determined the fitness
of a species to cope with the environment — morphological charac-
teristics have determined geographical and climatic distributions.

Morphology as the science of form is often contrasted with physi-
ology, the science of function. Yet between the two is the closest
possible relation, because an organ implies a function, and every
morphological characteristic has a corresponding physiological char-
acteristic. As physiological characteristics are transmissible in the
same way as morphological, we may think of any individual as being
made up of such functional characteristics, just as a molecule is made

1 Compare C. H. Eigenmann, Cave Animals : Their Character, Origin, and their
Evidence for or against the Transmission of Acquired Characters, Proceedings of
American Association for the Advancement of Science, Forty-eighth Meeting
(1899), p. 255. Also P. C. K. Absolan, Einige Bemerkungen iiber mahrische Hohlen-
fauna, Zoologische Anzeiger, xxm, 1-6 (1900). For a popular account of our
caves and their fauna, see W. S. Blatchley, Gleanings horn Nature, pp. 99-178
(1899).

2 For a delightful and accurate general account of the animals of our native
deserts, see John C. Van Dyke, The Desert, New York, 1901.

252 ANIMAL MORPHOLOGY

up of atoms, and in the transfer from one race or species of a set of
morphological characteristics, we transfer likewise the corresponding
set of physiological characteristics. Thus, to return to poultry, we
find the rate of growth, the age at maturity, the egg-production,
the brooding instinct, and the resistance to disease, to be characteris-
tics of various races, and it is quite possible to combine such charac-
teristics — in so far as they are not incompatible — in various ways.
Thus. we have poultry that mature early, lay many eggs, and are not
broody — of these the white Leghorn is a good example. Or, we may
have poultry that grow large, mature late, lay throughout the winter,
and are very broody — such are the Cochins. This similarity in
capacity for making combinations which we see between physio-
logical and morphological characteristics proves their close kinship
and the unscientific nature of the division which would relegate their
study to distinct sciences.

What is true of domesticated races is true also of wild species. Bio-
logy has suffered from the circumstance that species have been studied
almost exclusively from dead specimens. Attention is focusqd on
proportions in the dimensions of bones, on number of spines, on an-
tennal joints, on shell-markings, and so on, and we seem to have over-
looked entirely the fact that all these characters constitute only one
face of the shield. The structural descriptions of the systematist give
us a no more adequate idea of the characteristics of species than does
the sight of this exposition on a Sunday, when all wheels are stopped
and only the form, beautiful and grand as it is, remains, give us an
adequate idea of it. And so in the study of species we cannot under-
stand the form characteristics without considering also the function
characteristics. I may illustrate this by some studies which Miss Small-
wood 1 has been making at Cold Spring Harbor. She started with
a species of Amphipoda — Talorchestia longicornis — that lives on the
beach where it is rarely covered by the tide. After studying its form
and behavior for several months she investigated a second species
of the same family of Orchestidce, Orchestia palustris, that lives on the
salt marsh to the limit of the highest tides. After studying this for
some weeks with respect to behavior correlated with structure, she
has begun on still a third species of the same family, Alorchestes,
which is a typical aquatic organism. The instructive thing that comes
out of her studies is that in just the same way as these species differ
in structural characteristics they differ in functional characteristics,
and the two kinds of differences go hand in hand, and they have to
be studied together to be fully intelligible.

In still another way are the dynamical and static characteristics

1 Mabel E. Smallwood, The Beach Flea, Talorchestia longicornis, Cold Spring
Harbor Monographs, i, May, 1903. Compare also her paper, The Salt Marsh A mphi-
pod, Orchestra palustris, Cold Spring Harbor Monographs, 3, March, 1905.

RELATIONS OF ANIMAL MORPHOLOGY 253

bound together, for every form or part has not merely a form or
function, but a development, and development is a dynamical pro-
cess. A decade or two ago embryological development was regarded
as a purely morphological subject, as a series of stages, and little
attention was paid to the causes that produce the stages and the suc-
cession of organs. During the last decade, however, partly under the
stimulus of physiologists who have entered the field of embryology,
its dynamical problems have been studied also by morphologists.
As a result of the researches of Loeb, Driesch, Herbst, E. B. Wilson,
Morgan, and many others, we have come to recognize that the egg is
organized, — cytoplasm as well as nucleus, — and that it exhibits
varying degrees of organization in different cases. Sometimes it seems
as though every part of the egg was totipotent, as in the medusse; in
other cases, the different parts of the cytoplasm seem told off to de-
velop into particular and definite organs, as in some mollusks. We
have learned, further, that at every stage new organs are called forth
and their development directed by stimuli proceeding from already
existing organs.1

Moreover, it has been found that even adult structures are depend-
ent upon external conditions for their form. It appears that peculiar
functioning may alter the form of internal organs, as has been de-
monstrated in the case of a ship's trimmer and of a cobbler by Lane,2
and as a vast number of pathological cases testify, such as the altera-
tion of the arrangement of plates in the spongy tissue in the head of
the femur,3 and the functional hypertrophy of the other kidney after
the loss of one. Morphologists have been forced to realize that form
and structure cannot be dealt with aside from function and behavior.
Every part of the living body is a sensitive, responding part whose
sensitiveness determines structure. This is seen particularly well when
the body is mutilated or a part removed; then begins the wonderful
process of regeneration or regulation by which, under control (in the
higher animals) of the nervous system, the lost parts are in many
cases restored. In truth, the work of the morphologist has extended
into the realm of the form-developing and form-maintaining factors,
and this is a physiological realm.

From these experiences I conclude that the morphologist who studies
form characteristics only is too narrow. Characteristics in their two-

1 The literature on this subject is extensive; recent resume's are given in E. B.
Wilson's The Cell in Development and Inheritance, 2d ed., 1903 ; also, T. H. Morgan's
Regeneration, New York, 1902. Read also E. B. Wilson, The Problem of Develop-
ment, Science, xxi, 281-294, Feb. 24, 1905.

2 Lane's papers were published in the English Journal of Anatomy and Physi-
ology, fifteen or twenty years ago.

3 On the architecture of the spongy tissue of the head of the femur, see H. Meyer,
Archiv fur Anatomie u. Physiologic, 1869; J. Wolff, Virchow's Archiv fur pathol.
Anat. L (1870) and LXI (1874); also Roux, Gesammelte Abhandlungen, and Roux,
Der Kampf der Theile im Organismus, Leipzig, p. 27, 1881.

254 ANIMAL MORPHOLOGY

fold aspect of form and function should be the object of his investiga-
tions— their difference in allied species, their integrity, their behavior
in breeding, their phylogenetic origin, their embryological develop-
ment, and their maintenance in the adult.

Morphology has relations with sciences quite outside of biology. I
have already insisted that the problems of form and structure are also
physiological problems, but in last analysis they are, I think, pro-
blems of physics and chemistry. For myself, I have no doubt that we
shall some day be able to prove that each characteristic of an organ-
ism depends upon a specific substance in the germ-cell, and we may
hope by altering this substance experimentally to change the corre-
sponding characteristic. Such a change is mutation, and mutation in
last analysis, as De Vries maintains, depends upon external condi-
tions.

Apart from this it is certain that the physiological processes in-
volved in the individual's characteristics are modifiable, and, indeed,
controlled by physical agents in the environment.1 Thus it has been
possible to show that certain salts play special roles in the develop-
ment of particular organs or characteristics (Herbst). Loeb, indeed,
has shown that regeneration of hydroids does not occur in the absence
of potassium. We know, likewise, that iron is necessary to the forma-
tion of the chromatin of the nucleus.

The physical conditions have likewise an influence in morphogene-
sis. The rate of development is controlled within limits by tempera-
ture; the number and position of stomata and of leaves by light and
moisture; the number and form of plant hairs by moisture; the
position of branches and leaves on a stem by gravity ; the formation
of a hydranth in a hydroid stock by light. So evident is this depend-
ence of morphogenesis upon physical agents that two individuals
of the same family develop alike only under the same conditions of
environment.

There remain to be considered the relations of morphology to the
queen of the sciences, — to mathematics. Until recent years little
relation has been recognized, and this I attribute to the fact that few
naturalists have a type of mind that attracts them to mathematics.
They have usually been led to their science through a love of nature,
— a passion that belongs rather to the poetic type of mind than to
the severely precise mathematical. And so I find that, even to-day,
when the bearing of mathematics on morphological problems cannot
be overlooked, few morphologists take an interest in the subject of
biometry by which the two sciences are connected.2

1 References to the literature on this general subject up to five or seven years
ago will be found in my Experimental Morphology, New York, vol. i, 1897; vol. n,
1899.

2 For references on biometric subjects I may be permitted to refer to my Statis-
tical Methods, 2d ed., New York, 1904, which includes also a summary of results.

RELATIONS OF ANIMAL MORPHOLOGY 255

The fact that few morphologists have a taste for mathematics
cannot stay the inevitable trend of the science toward greater pre-
cision of expression and toward mathematical analysis. Until recent
years characteristics have been described only in the crude language
of adjectives and adverbs — where greater precision is necessary,
quantitative expression is inevitable. So we have seen during the
past ten years the rise of biometry and its application to many mor-
phological problems. Biometry had its beginning in the suggestive
investigation of Galton; its great development in the last ten years
has been due, above all, to the tremendous activity of Karl Pearson
and the workers he has gathered about him. By the aid of efficient
methods of analysis we are able to state quantitatively not only the
mean value of any measurable characteristic, but also the degree
of its variability and the closeness of associated variability of two
interdependent organs. Moreover, it is possible to study the nature
of the variability exhibited by any characteristic in any homogeneous
lot of individuals and to draw an inference from the nature of this
variability — as exhibited in the variation polygon — concerning the
condition of the characteristic in question in the given race. A person
of experience can tell from a glance at the variation polygon whether
the race is in a condition of equilibrium so far as this characteristic
goes, or whether it is breaking up into several forms, or is, perhaps,
evolving into some other condition. The quantitative expression
gives a means of measuring change of the mode from epoch to epoch
which Weldon used in studying the crabs at Plymouth, and which
enabled him to demonstrate a progressive change in form. It gives
also a means of measuring the alteration of an organ in different en-
vironments, and so of estimating the effects of changed external con-
ditions. Thus it has been shown that the modal number of ray flowers
in the ox-eye daisy depends upon the conditions of nutrition in the
soil; the chela of the male crab, Eupagurus, is relatively smaller in
deep Avater; the mud-snails, Nassa, of brackish water are depauperate.

Again, mathematical methods have given us a measure of the corre-
lation between organs, so that, the exact relation between human
stature and the length of a long bone being known, the stature of ex-
tinct races may be calculated from a collection of disinterred femurs.
Pearson has been able to show that there is no correlation between
shape or size of the head and intelligence, and to demonstrate the
efficiency of vaccination and the non-inheritableness of cancer. The
opinion that various bodily characteristics are bound together has
been substantiated by studies in the correlation of all sorts of organs
in plants and animals and the degree of this correlation measured. This

There is also one journal devoted exclusively to biometry, Biometrika, published
in London and edited by Pearson, Weldon, and Davenport, with the advice of
Francis Galton.

256 ANIMAL MORPHOLOGY

index of correlation measures the degree of morphological kinship or
of physiological interdependence. Symmetry gains a quantitative
expression, and it is interesting to find that originally non-symmetrical
organs which have secondarily gained antimeric relations — as in
animals that habitually lie on one side — gain a very high index of
correlation. Thus 1 find in the scallops (Pect en) , which are lamelli-
branchs that have come to lie on the right side, the index of correla-
tion between the dorso-ventral and antero-posterior diameters is
97 per cent, whereas the correlation between the breadths of the
right and left valves is only 86 per cent. As heredity is only one
phase of correlation, the inheritance of characteristics can, by the
new methods, be exactly measured. It is demonstrated that there is
such a thing as prepotency of one parent, and that heredity is weak-
ened by change of sex. It is shown that mental and physiological
characteristics are inherited exactly like morphological characteristics :
and that the relationship between the leaves of a branch or the zooids
of a colony is like that between brothers of a family. We learn that
all inheritance is not all of one kind; that certain characteristics,
like stature and skin color, blend in the offspring; while others, like
the coat color in mice, refuse to blend, and may be inherited according
to Mendel's law.

By mathematical analysis the selection of particular characteristics,
or those of a particular degree of development, has been demonstrated,
and the exact effect of the selection process upon the frequency poly-
gon has been made clear. Extreme variants are often annihilated,
although in other cases the position of the mode is shifted. Finally,
through quantitative studies the existence of local races has been
clearly proved — the degree of their differentiation and its depend-
ence on environmental conditions has been measured. It has been
shown that a characteristic does not remain the same in all localities
and under all conditions, but may become slightly altered. This fact
speaks strongly for the contention that new species may in some
cases have arisen by the summation of infinitesimal differences —
that not all evolution is by mutation.

In concluding this address I am impressed by the fact that to-day
any science ramifies in all directions toward every other. There can
be no doubt that the most fruitful work in any science is to be done
in the border-line between it and some other science. There is another
corollary to this close interweaving of the sciences, and that is that
the existing classifications have become antiquated. Our university
departments, our societies, and our journals still, for the most part,
draw the old lines. Yet the true work of science has, I apprehend,
overleaped the barriers of these classifications, and the best workers
will in the immediate future be no longer botanists, or zoologists, or
chemists, or mathematicians, but will be interested in particular sub-

RELATIONS OF ANIMAL MORPHOLOGY 257

jects, — in following some favorable lead into the unknown. The
embryologist who is interested in processes, the cytologist who is
interested in the fertilization of the egg, will feel free to work on any
material, whether plants or animals or crystals or colloidal mixtures
— and by any methods that seem likely to be of aid to him. And I
hope to live to see the day when our now overgrown zoological and
botanical societies shall languish while groups of men devoted to a
common subject and investigating it with the most diverse material
will meet together to discuss results of common interest. When a
subject no longer demands vigorous investigation, and the centre of
activity is shifted elsewhere, I should like to see the old associations
abandoned and new ones formed to advance the newly risen problems.
Our large societies are a hindrance, I sometimes think, rather than
a means of advancement to science. We want smaller meetings with
more acute interest. And, finally, I cannot but remark on the vast-
ness of the preliminary training which the present ramifications of
every science make necessary. Research in the fields between the
old sciences has rewards for the investigator, but he who would reap
those rewards must prepare himself through years devoted to gaining
the mastery of many sciences.

THE PRESENT TENDENCIES OF MORPHOLOGY AND ITS
RELATIONS TO THE OTHER SCIENCES

BY ALFRED MATHIEU GIARD

(Translated from the French by Robert M. Yerkes, Harvard University)

[Alfred Mathieu Giard, Professor of Zoology (Evolution), at The Sorbonne, Univer-
sity of Paris; Member of the French Institute, b. Valenciennes, France, August
8, 1846. B.L. 1864; B.S. 1869; Student at Superior Normal School, 1867-70;
Licenciate in Mathematical Sciences, 1869; Licenciate in Physical Sciences, 1867;
Licenciate in Natural Sciences, 1869; Doctor of Natural Sciences of the Faculty
of Sciences, Paris, 1872. Professor of Zoology of the Faculty of Sciences at Lille,
1873-87; Professor of Natural History of the Faculty of Medicine at Lille,
1876-87; Master of Conferences of Zoology at the Superior Normal School,
1887-89; Professor of Zoology of the Faculty of Sciences, Paris, 1890. Member
of Academy of Sciences; President of the Society of Biology; President of
the French Association for the Advancement of Science, 1905; Former Presi-
dent of the Entomologic Society of France; Member of Academies of Brussels,
St. Petersburg, Prague; Academy of Natural Science of Philadelphia; Linnean
Society of London, etc., etc. Author and Editor of Scientific Bulletin of France
and Belgium; Studies from the Maritime Zoologic Station at Wimereux; Re-
searches on the Synascidice; Controversies upon Transformism, etc., etc.]

ALMOST forty years ago, on the occasion of a great international
manifestation of human thought such as this in which we are con-
vened at the present moment, in his report concerning the progress
of physiology 1 presented to the Universal Exposition of Paris in
1867, the illustrious Claude Bernard tried to show that the sciences
should be separated into two classes: one, including astronomy
and the natural sciences, sciences of contemplation and observation,
which should tend only toward the prevision of facts; the other,
in which he placed physics, chemistry, and physiology, which alone,
he said, are the explanatory, active, and nature-conquering sciences.

This kind of contrast established between the sciences of nature,
to the laws of which we submit passively, and those in which the
activity of man intervenes is the reiterated but considerably improved
expression of the opinion of the philosophers of the seventeenth
century, especially of Thomas Hobbes, who in his book, the Leviathan,
expressed it in these terms: "The Register of Knowledge of Fact
is called History. Whereof there be two sorts; one called Naturall
History ; which is the History of such Facts, or Effects of Nature,
as have no Dependance on Mans Will; Such as are the Histories
of Mctalls, Plants, Animals, Regions, and the like. The other is Civill
History ; which is the History of the Voluntary Actions of men in
Common-wealths."

1 Claude Bernard, Rapport sur le progrcs de la Physiologic gtnerale en France
(1867), p. 132, and Revue des cours scientifiques (1869), p. 135 et passim.

PRESENT TENDENCIES OF MORPHOLOGY 259

In conceding to the sciences of nature the power to predict facts,
Claude Bernard gave them, at least in appearance, a very wide
range; for what constitutes the essence of a science, as had been
recognized already by Locke, is prevision of the future, and one
may repeat with W. Ostwald, "The greatest leaders of man have
been those who saw most clearly into the future." 1

But if we seek to understand better the thought of the great
French physiologist, we soon realize that the role of contemplative
observer attributed by him to the morphologist is very modest
in comparison with the far more exalted part which he proposes
to reserve for the sciences called experimental or nature-conquer-
ing.

It is to these the duty comes at the same time to foresee the
events at will and to create them at need: for the observer con-
siders phenomena in the state in which nature offers them to him;
the experimenter causes them to appear under the condition of
which he is master. The naturalist is a describer; the physiologist
is a creator.

Debatable at the time it was advanced, and, in fact, soon debated
by men of great ability, the division of the sciences proposed by
Claude Bernard was not able to resist the progress of ideas, so rapid
at the close of the nineteenth century.

It rested in great part upon a misunderstanding of the conception
of the word experience, to which we saw fit to give, as we shall see
later on, a less restricted significance than that of the school of
Magendie and of certain physiologists to-day.

Furthermore, to those who may desire to see in this discussion
something besides a question of a word and a change of labels, it
will be easy to reply directly by the history of the conquests due
to morphological studies since the middle of the last century.

Especially in the new and so little known domain of cytology
can it not be said that all that we know concerning the fundamental
question of cell-division is the fruit of the efforts of the morpho-
logists, that the methods employed by the histologists to elucidate
the problem of cell-division go far beyond simple observation, and
that they have required as much persevering ingenuity, as much
technical skill and accessory knowledge, as any experiment in pure
physiology involves?

The triumph of the doctrines of Lamarck and Darwin, the splen-
did intellectual movement aroused even as early as 1857 by the
publication of the Origin of Species, the controversies of all sorts
aroused by the theory of modified descent, soon began to overthrow
the views of naturalists and to assign a new significance to mor-

1 Wilhelm Ostwald, The Relation of Biology and the Neighboring Sciences (Uni-
versity of California Publications, Physiology, vol. 1, p. 15, Oct., 1903).

260 ANIMAL MORPHOLOGY

phological researches, as to the work assignable to other branches
of biology.

Natural history was able in its turn to aspire to the title, explana-
tory and nature-conquering science. And if this transformation of
opinion does not occur more promptly and more nearly simultane-
ously in all countries of high scientific culture, the fault is largely
that of the naturalists themselves, for their obstinacy in preserving
ancient dogmas, for their defiance of valuable ideas for which the
authors have been ignored at first in their own country.

So long as biologists obstinately support the view of Cuvier and
of R. Owen that vegetable and animal species are immutable and
that the supreme end of science is classification, it is evident that
the history of living beings can be only the exact description of
their external form and of their internal structure in the adult and
in the larval states, the comparison of these forms and of these
structures, the study of the habits, that is to say, the relations
of the organisms among themselves and to the environment, the
distribution of these organisms over the surface of the earth con-
sidered as the result of caprice or of the intelligence of an omnipo-
tent Creator. Outside of their practical applications (the utilization
by man of animal or vegetable products), natural history yet can
give enjoyments similar to those that we experience at the sight
of an object of art, of a kind, however, of which the technique
escapes us, and of which the results remain for us an inexplicable
enigma.

But the point of view changes entirely, if in the place of con-
sidering creation in a static state as a whole, thenceforth immut-
able, we consider it from the dynamic point of view; if we no longer
study the natura naturata, but the natura naturans, in seeking to
discover the relationships of living beings, and to unravel the com-
plicated processes by which forms and organisms are determined
and related to one another; if we cease to admire devotedly the
harmonies of animals and vegetables either among themselves or
with the surroundings which environ them, and to hold to the
childish finality of which Bernardin de St. Pierre has given us the
most perfect expression; if, in a word, we abandon the anthropo-
centric method in order to seek to explain how these harmonies
gradually became established or modified as the conditions of the
environment in which they were realized were being established
or modified.

Even as early, as 1877 at the congress of German physicians and
naturalists which met that year at Munich, one of the first and most
ardent protagonists of the Darwinian doctrine, Ernest Haeckel, could
proclaim with entire justice: "By the theory of descent, biology
in general, and especially zoology and systematic botany, are truly

PRESENT TENDENCIES OF MORPHOLOGY 261

raised to the rank of natural history, a title of honor which they
have borne for a long time, but which they merit only in our day.
If these same sciences still are often designated, and that even
officially as descriptive natural sciences in contrast with the ex-
planatory sciences, this proves that a false idea exists even at
present of their true significance. Since the natural system of
organisms is regarded as the expression of their genealogical tree,
taxonomy, so dry in its descriptions, makes a most vital place in
the history of the genealogy of classes and of species." l

A still more important consequence resulted from these new
conceptions. The theory of descent introduced into the biological
sciences a unity of view, a community of end, which established
among them the closest relations of mutual dependence and sup-
pressed all futile questions of supremacy or of precedence. Indeed,
whatever were the methods employed, deduction or induction, ob-
servation or experiment, anatomy, physiology, ethnology, geonomy,
taxonomy, paleontology, all these parts of a whole thenceforth
indivisible should tend to the realization of the same programme:
to retrace in a manner as exact and as complete as possible the
history of the manifestations of life upon our planet, while leaving
to the metaphysicians and to the poets the business of seeking the
earliest origins or of celebrating the finalities.

A hasty glance will permit us to appreciate what results have
already been obtained by this concourse of converging efforts and
what hopes we may conceive for the future, when, extending its
frontiers, biology shall benefit by the progress of science, with
which thus far it has had only too distant relations. Thus, while
the old branches of morphology rejuvenated and vivified will cover
themselves with a new foliation, we shall see develop about her
new branches swollen with an abundant and vigorous sap: cytology,
promorphology, tectology, experimental morphology (or the crea-
tion of forms by the action of primary factors), genesiology, bio-
metry, etc.

But the very fact of the direct dependence of these different parts
of the science, their mutual interferences, the complex of causes
which have presided at their birth and over their evolution, fre-
quently render this exposition difficult and at times perhaps ob-
scure.

I may be permitted to excuse myself in advance and to claim
all the indulgence of my audience if I have not always succeeded
in finding the lucidus ordo that the Latin poet claims. You will
kindly excuse me also for often having given a dogmatic and aphor-

1 E. Haeckol, The Theory of Evolution in its Relations with Natural Philosophy,
Congress of German Naturalists in Munich (Revue Scientifique, December 8,
1877, p. 531).

262 ANIMAL MORPHOLOGY

istic form to the propositions for all of which the evidence is perhaps
not sufficient. A more complete demonstration would have required
the lengthiness that I have insisted on avoiding. My conviction,
too decisively and perhaps too strongly expressed, is based in every
case upon mature reflection and upon the experience of long years
of study.

Certainly the change of orientation introduced into the natural
sciences by the transformation theory does not detract from the
positive value of the results previously acquired by the purely
descriptive method, and we cannot overlook the materials slowly
accumulated by our predecessors. We can continue to proclaim
accord in this matter with Cuvier: "La determination precise des
especes et de leurs caracteres distinctifs fait la premiere base sur
laquelle toutes les recherches de 1'histoire naturelle doivent etre
fondles; les observations les plus curieuses, les vues les plus nou-
velles perdent presque tout leur me"rite quand elles sont de"pour-
vues de cet appui; et malgre* I'aridit6 de ce genre de travail, c'est
par la que doivent commencer tous ceux qui se proposent d'arriver
a des result ats solides."

A great number of naturalists devoted to the systematic study
of morphology received the idea of the variability of species with
mistrust, thinking that this idea undermines the principles upon
which their science of predilection rests. Events have not been slow
in proving that these fears were chimerical. In order to demon-
strate scientifically the reality of variations often very slight at
first, it was necessary to be more precise than formerly, and some-
times even to give minute descriptions of the forms under discus-
sion. The preservation of types in collections and museums, their
graphic representation and their careful comparison with related
species became more and more prominent, and certainly the ad-
vances of systematic natural history have been strongly stimulated
by the disputes of the partisans and the adversaries of the theory of
descent.

The study of new forms, the search for intermediate types, abnor-
malities, mutations, local varieties, no longer have as their sole
purpose the satisfaction of a vague feeling of curiosity. The know-
ledge of slight modifications of structure, of slight steps in normal
morphology, have become precious elements for the construction
of phylogenetic trees.

Natural classification, instead of being a subjective entity, variable
with the conceptions peculiar to each systematist. is now presented
to the mind as an objective reality: the genealogical history of
living beings of which we can already conceive a general plan, very
imperfect undoubtedly, but for the establishment of which all later
discoveries should cooperate.

PRESENT TENDENCIES OF MORPHOLOGY 263

The works of specification have a higher end, a r61e not only of
description but also of prediction and origination; they rise a step
in the scale of human knowledge. Their interest then becomes much
more important.

And this interest is not limited to the science of beings actually
living, it extends to the study of extinct forms hidden, in a petrified
state, in the depths of the earth.

Paleontology opens before us as a gigantic collection of archives,
and despite the regrettable gaps which the future undoubtedly
will more and more fill up, it furnishes us the most precious docu-
ments for the retracing of the ancestral lines of plants, of animals,
and of man himself. Veritable medailles de la creation, the fossils
enable us to reconstruct upon firm foundations the natural history
of living beings in the exact sense of the word by methods analogous
to those that brought into use history, properly so-called, as the
sociologists and philosophers understand it.

From this moment paleontology forms with zoology an indis-
soluble whole and these two divisions of morphology reciprocally
furnish cooperation. But zoology is incomplete. Despite the efforts
of generations which preceded us we are still far from knowing all
the living beings which actually exist on the surface of the earth.
Paleontology has given us only very rare indications, if we consider
the great number of organisms which have disappeared without
leaving permanent traces (protoplasmic beings which lack a skele-
ton or which have a slightly resistant skeleton, etc.), especially if
we think of the difficult and rarely realized conditions which were
necessary to assure the fossilization and the preservation of animals
through all the vicissitudes of the earth's surface. Many of these
gaps in the morphological series are in course of disappearing or will
disappear little by little, thanks to the more effective methods of
investigation which we possess, thanks also to the progress of phys-
ical geography and to the more intensive study of the countries
thus far unexplored.

Geonomy, or the study of geographical distribution, also, is
greatly illuminated and simplified by the doctrines of transforma-
tion. The actual distribution of animals and plants should no longer
be considered as the result of chance or of a directive principle which
replaces the old creations by new ones just as one sees the scene
change in the theatre each time the curtain rises.

A causal connection exists between the past and the present.
Paleontology indicates to us those portions of the earth in which
we should seek forms with archaic characters, and geonomy in turn
enables us to divine the changes of the earth's surface and reveals
to us the distant causes for the suppression of animals which have
already disappeared.

264 ANIMAL MORPHOLOGY

But still more than geonomy, a new science or rather an ex-
ceedingly rapid development of a too much neglected branch of
the science of morphology, should soon remedy the inevitable in-
sufficiency of the actual zoological principles and of our paleonto-
logical knowledge.

So long as the naturalists were content to catalogue and to com-
pare among themselves, after the fashion of a collector of arms or
of objects of art, some of the many forms whose astonishing variety
they admire as the fruit of the inexhaustible imagination of an
infinitely ingenious Creator, it was to the adult states especially,
considered as perfect, that they directed their attention. It was of
little importance to them to know how the objects of their favorite
passion were formed. With the exception of some rare precursors
(Aristotle in antiquity, Malpighi, Swammerdam, Harvey, C. F. Wolff
in a more recent period) the majority of biologists were not interested
in the study of development.

Even to-day, moreover, we find among the systematists a sort
of vestige of this state of mind. Among a thousand entomologists
how many are there who have the least interest in the collecting
of caterpillars or the larvae of insects? Of a hundred ornithologists
how many deign to admit the nests or the young of birds into their
collections ?

It is not the least service that the theory of evolution has ren-
dered to biology that it has shown the importance and the necessity
of embryological studies.

It is only fair to recognize that the ground was prepared by the
simultaneous development of other collateral branches of science,
and especially by the progress of micrography and the advent of
the cellular theory.

However, we have the right to maintain that it is especially to
a desire to verify in a new way the ideas of Lamarck and of Darwin
that we must attribute the abundance and the perfection of em-
bryological investigations pursued after J. Miiller and von Baer, by
Gegenbaur, Haeckel, Leuckart, Huxley, Loeven, Van Beneden,
Agassiz, and others.

By its continuity, by the dependence of its successive phases,
by the causal nexus which determines them and the relations among
themselves, the development of larva? and of embryos, or in modern
language, the ontogenetic series of embryological stages is marvel-
ously fitted to illustrate the theory of modified descent by exam-
ples which afford convincing evidence.

Undoubtedly even before the publication of the works of Darwin
and the beautiful group of embryological monographs, of which
we are about to speak, Serres had foreseen, by a kind of divina-
tion of genius, the fruitful idea of the transitory repetition in indi-

PRESENT TENDENCIES OF MORPHOLOGY 265

vidual development of the forms which are permanently realized
in the actual zoological series. But this idea could not be fully
understood and bear all its fruits until it was completed and solidly
demonstrated by Fritz Miiller in his admirable little book Fur
Darwin,

From that time the triple parallelism existing between the zoo-
logical series, the ontogenetic series and the paleontological series,
appeared as a necessary consequence of the phylogenetic kinship
of animals, and as the evident interpretation of their genealogical
relations. Furthermore, as should happen in the application of all
serious theories, the apparent exceptions due to abbreviations or
to falsifications of ontogenetic evolution may be foreseen and ex-
plained partly by the principles of the Darwinian doctrine: natural
selection and the struggle for existence.

It is then with good reason that the principle of Serres and of
Fritz Miiller has been called by Haeckel the fundamental bio-
genetic law, if we give to this word law the meaning that we ordin-
arily give it in experimental sciences, that of a general formula
susceptible of sufficient verification and permitting us indefinitely
to predict new facts. Rich in the works of Daubenton, of Haller,
of Camper, of Pallas, of Vicq d'Azyr, comparative anatomy seemed
to have received from the genius of Cuvier forever indestructible
foundations.

It could not escape, however, from the renovating action of evo-
lutionary ideas. The problems that it always had in view, the ques-
tions that it apparently had answered, soon reappeared in improved
forms; Huxley, Gegenbaur, Leuckart were not slow to show us in
what direction definite solution was to be sought.

The pretended law of the correlation of forms (Cuvier), the prin-
ciple of connections (Et. Geoffrey Saint-Hilaire), that of the balanc-
ing of organs, the idea of the degeneration of types (de Blainville),
the notion of rudimentary organs, etc., instead of being simple
empirical formulas, became the synthetic expression of real and
necessary relations between organisms related by consanguinity, and
if they had not already been firmly established inductively, these
conceptions could have been deduced as the necessary corollaries
of the genealogical kinship of living beings.

If we turn to the memoirs of the period and to the famous dis-
cussion between Cuvier and Et. Geoffroy Saint-Hilaire concerning
the unity of organic structure, a discussion in which Goethe followed
the Peripatetics with so much passion that he concentrated the
strength of his mind upon it to the neglect of the political revolution
which occupied every one in 1830, we recognize with astonishment
that neither the one nor the other of the illustrious adversaries
appreciated the much greater significance the debate would have

266 ANIMAL MORPHOLOGY

acquired if it had taken account of the ideas that Lamarck had
already supported for twenty years in the midst of the most general
indifference of naturalists and philosophers.

It appears, indeed, from numerous passages of the Philosophic
anatomique, that Et. Geoffrey Saint-Hilaire himself saw in the unity
of the plan of organization merely the expression of an ideal kinship
and that he attempted to explain it, as has often been done more
recently, by a comparison with the successive products of human
architecture destined for similar uses.1

From the philosophic point of view, then, there was not an abyss
between Cuvier and Geoffrey. Both were creationists, but while
Cuvier admitted the plurality of types (realized at least to the
number of four by the Creator), Et. Geoffrey Saint-Hilaire con-
sidered the entire animal kingdom as the manifestation of a new
unique thought developed according to an invariable plan in its
chief lines, modifiable only in details.

We appreciate, without the necessity of insistence on the advan-
tage, what light is cast upon this question of the plan of organization
by the theory of modified descent and the study of progressive
adaptations of living beings to conditions which vary according to
time and place.

We appreciate also the precise and profound meaning which
attaches to the previously vague notions of analogy and homology,
the more recent ones of homomorphy and homophyly, etc.

The convergence of forms under the influence of ethological
factors (pelagic life, parasitic life, etc.) ceased to hide the true
affinities and little by little caused the factitious groups introduced
by what we might call the idola ethologica to disappear from the
purified classification.

The idola tectologica were more difficult to eliminate. The idea

1 Here are a few very significant lines on the subject by Geoffrey : " Des rapports
que j'apergois entre des mate"riaux, lesquels reviennent les memes pour composer
les animaux, de ces donne'es qui produisent une certaine ressemblance chez tous
les etres, tant a 1'interieur qu'& I'exteYieur, j 'arrive a une deduction, a une id6e
g6ne"rale qui comprend toutes ces coincidences; et si je les embrasse et les exprime
sous la forme et le nom d'unite" d'organisation, je ne me propose par la que de tra-
duire ma pense"e en un langage simple et precis; mais d'ailleurs je me garde bien
de dire ce que j'ignore, qu'une chose serait faite avec intention a cause d'une autre?
En definitive, je me crois, dans ces conclusions, aussi fondds en raison que si, voyant
d'ensemble les nombreux Edifices d'une grande ville et me restreignant aux points
communs que leur imposent les conditions de leurs existences, j'en venais a re"-
fle"chir sur les principes de 1'art architectural, sur I'uniformit6 de structure et d'em-
ploi d'un autre grand nombre d'e"difices. Une maison n'est point faite en vue d'une
autre; mais toutes peuvent etre ramene'es intellectuellement £ 1'unite" de composi-
tion, chacune e"tant le produit de mate"riaux identiques, fer, bois, platre . ., . de
meme qu'& I'unit6 des fonctions, puisque 1'objet des toutes est e'galement de servir
d'habitation aux hommes ..."

Et plus loin: "Toute composition organique est la re'pe'tition d'une autre, sans
etre de fait produite par le de>eloppement et les transformations successives d'un
meme noyau. Ainsi il n'arrive a personne de croire qu'un palais ait d'abord e'te'
une humble cabane.qu'on aurait e"tendue pour en faire une maison, puis un hotel,
puis un Edifice royal. (Et. Geoffroy Saint-Hilaire, Philosophic anatomique.)

PRESENT TENDENCIES OF MORPHOLOGY 267

of organic type, so important as we have come to see, has been
obscured for a long time by the imperfection of our knowledge con-
cerning individuality or rather concerning individualities of differ-
ent orders. Among the composite animals especially, such as the
sponges, the hydroids, the bryozoa, the synascidians, we have for
a long time attributed an exaggerated taxonomic value to the
cormogenesis, that is, to the mode of grouping of the individuals,
while neglecting the real relations of kinship that the anatomy of
these individuals reveals. It is not the least service rendered by
E. Haeckel to biological science that he first attempted to fix the
rules of this branch of morphology, which is like the architectonics
of living beings and which has been called tectology. Especially
among the metazoa, the tectological idea of the person, that is to
say, of the original diblastic being (gastrula) which constitutes the
most common mode of individuality, is an acquisition of inestim-
able value.

Foreseen by de Blainville and by Huxley, who deduced it from
purely anatomical considerations, this idea was clearly established by
Haeckel as early as 1872, thanks especially to the admirable embryo-
logical investigations of Alexander Kowalevsky, investigations which
proved the existence of the gastrula larva in all the groups of multi-
cellular animals in which the development is explicit.

Despite the recent attacks to which it has been subjected, the
theory of the gastrula, properly understood, is established as surely
as that of the homology of the blastodermal layers which is the
immediate consequence of it.

The rational application of the principle of Fritz Miiller is suf-
ficient to account for the difficulties offered by certain condensed or
coenogenetic developments and the objections presented by some
authors who often hold to that which they have studied in only a very
small number of types (sometimes one unique type) , chosen by reason
of practical convenience and without regard to the disturbances of
ethological factors to which these types were subjected.

The idea of an original form common to species but often pro-
foundly modified by the influence of environment renders evident the
folly of basing comparisons upon promorphology solely — that kind
of crystallography or geometry of living beings.

Such groups as those of the Radiaria or Radiata, the Bilateralia,
etc., are purely artificial and inspired solely by the idola promorpho-
logica.

The truth remains, however, that it would be very desirable to
pursue further than has been done at the present time the promor-
phological studies of which Haeckel has furnished the basis in his
admirable general morphology. In this respect, as in many others,
morphology is directly dependent on geometry and mechanics. There

268 ANIMAL MORPHOLOGY

is material for numerous problems of very vital interest for those
who do not wish to content themselves with the easy but childish
solution of final causes.

"Voir venir les choses," Savigny has said, "est la meilleure fagon
de les observer. " Morphology, in brilliantly illuminating comparative
anatomy, makes possible the rectification of numerous errors of tax-
onomy and the better appreciation of the value of different taxonomic
groupings. But at the same time that they aided in the advancement
of normal morphology, embryological studies, extended to abnormal
forms of development, demonstrated the great influence of the science
of monstrosities or teratology. Soon, thanks to the patient investiga-
tions of Dareste and to the abilities of Chabry and W. Roux in the
artificial production of animals, teratology became an experimental
science, and it was from that time easy to understand how in inter-
vening in a more or less constant manner at different periods of onto-
geny the cosmical or biological factors have gradually been able to
modify the larval forms and indirectly the adult forms of living beings.

As a result of the science of the habits and relations of living beings
either among themselves or with the cosmical environment, ethology
or bionomy, somewhat neglected since the time when Reaumur, De
Geer, etc., cultivated it with so much success, gains a new interest and
offers to every biologist a collection of experiments prepared by nature
and of which it is necessary only to interpret the results.

Is it not remarkable indeed to see the bionomy of the adult modify
the development of the embryo so profoundly as sometimes to hide,
in the course of evolution, the affinity which exists among related
forms?

Does not the vegetable or animal diet of a mammal, for example,
follow as a consequence primarily of the state of perfection at birth
and also of the abbreviation of the embryological processes, since the
young are not sufficiently protected by their parents, whose rapid
movements in search of nourishment or for the avoidance of an enemy
they must follow?

The animals which are fixed in the adult state, and especially para-
sites, which early establish themselves upon the host and never leave
it, necessarily have an explicit development, and the motile larva? are
provided with organs of sense which permit them to choose with care
the resting-place where the greater part of their existence will pass.
On the contrary, in pelagic beings, which early in life are exposed to
a thousand dangers, there would be every reason why the progeny
should be protected by direct, rapid and coenogenetic development or
be trusted to a strange nurse, as is the case with the copepods of the
group MonstrillidfE. Even evolutionary phenomena as complicated
as those in the Coleopteran, Meloides, under the name of hyper-
metamorphosis, become easy of explanation if we view them in their

PRESENT TENDENCIES OF MORPHOLOGY 269

relation to bionomic conditions and as a necessary consequence of the
life which their ancestors had to lead.

Not less interesting, it seems to me, are the embryological pecul-
iarities that I have brought together under the name " poecilogonie."
Two beings belonging to the same species as like as possible in the
adult stage, so much alike sometimes that the eye of the best-trained
specialist cannot detect the least difference between them, may pre-
sent in the series of their ontogenetic stages and even in the ovarian
form very marked differences, if their embryonic bionomy is not the
same; if, for example, the environment has not the same chemical
composition or if the season of development is different, or yet again
if the biological conditions vary with the cosmic surroundings in
the different habitats of a widely dispersed species, whence the terms
poecilogonie geographique, poecilogonie saisonniere, etc.

What is more astonishing than these curious experiments of mor-
phology realized by nature, which I have formerly discussed under
the name of parasitic castration? And however mysterious the
modifying action of the indirect gonotome may be to us, is it not very
instructive from the morphodynamic point of view to see this para-
site, by action at a distance upon a host of determined sex, cause
the appearance of the characters of the opposite sex even when these
characters will have no value for the animal which possesses them?
Finally, this notion of a morphological complex constituted by the
host and its parasite acquires primary importance when. we relate
these parasitic complexes to the unstable biological equilibrium of
homophysical or heterophysical complexes in more or less perman-
ent equilibrium, realized either in the galls or in symbiotic forms
such as the lichens, plants with mycorhiza, etc.

At most the notion of complexes of different beings associated in
harmonious symbiosis is only a generalization of what we observe
in all multicellular organisms in the course of their evolution.

As early as the middle of the eighteenth century C. Fred. Wolff had
established upon a firm basis the theory of epigenesis. He showed
that living beings do not develop, as had been thought, at the expense
of a preformed rudiment, growing much as the image of an object
enlarges when examined successively with glasses of gradually in-
creasing powers of magnification.

The different organs of an animal are formations of a relative au-
tonomy which work together in the construction of a whole whose
equilibrium is not preestablished and whose plan may sometimes be
modified during the course of construction.

It is well understood that in respect to reciprocal dependence the
different systems of organs vary considerably. Sometimes this de-
pendence is very close, as when the appropriate functions of the
organs are themselves very closely united, respiration and circu-

270 ANIMAL MORPHOLOGY

lation, for example. It can be much less close when it acts with
reference to parts adapted to very distinct roles, organs of locomo-
tion and the digestive apparatus, or better the tegumentary system
and the skeleton, etc.

But the independence is especially great if we consider on the one
hand the organs which subserve the life of the individual and on
the other those which are destined to insure the perpetuation of the
species.

The soma and the gonads, to employ modern expressions which
designate these twro totalities, are in a certain sense two organisms,
which are juxtaposed or incased the one in the other, whose devel-
opment may proceed very unequally, although any modification
effected in one has in general an influence upon the other.

It is because of their reliance upon this notion fundamentally
exact, but exaggerated and enveloped with a metaphysical atmo-
sphere, that the partisans of the ancient theory of evolution (pre-
existence and germinal localization, preformation of the embryo)
have for a long time struggled against the ideas of C. F. Wolff.

In following the same line of thought more recently, A. Weismann
has sought to construct his well-known theories upon the assump-
tion of the non-transmissibility of acquired characters.

Finally, it is the same consideration which, when extended to the
first phases of embryology, to different cellules of the morula and even
to different regions of the unsegmented egg, has served as the basis of
the mosaic theory of W. Roux, which has since been so ingeniously
modified by E. B. Wilson.

While adhering to the strict observation of facts easiest to verify,
we shall call only that epigenesis which, in revealing to us the pos-
sibility of a vital concurrence between the organs and even between
the plastids which constitute multicellular beings, permits us to
explain easily all the complex facts of evolutionary polymorphism;
progenesis, neotenie, dissogonie, poecilogonie , and in general the curious
peculiarities of development that since Chamisso and Steenstrup we
have grouped under the very improper name of alternate generations
or of geneagenesis (de Quatrefages).

There is thus established a vast array of information which is suffi-
ciently extended to constitute to-day a new branch of morphology
which we may call genesiology.

The object of genesiology is the study, both descriptive and experi-
mental, of different evolutionary modes.

In the preceding pages we have at different times spoken of experi-
ments and of the experimental method in a sense different from that
which is often given to these words by the physiologists of the old
school. This is the place perhaps to indicate the manner in which we
understand the introduction of experimentation into the morpholog-

PRESENT TENDENCIES OF MORPHOLOGY 271

ical sciences and the results which may follow for the later develop-
ment of these sciences.

An experiment always necessitates the preliminary analysis of the
phenomena by which the fact that one wishes to observe and if pos-
sible to measure is conditioned. It assumes a hypothetical solution
of which it will show the reality or the non-existence. Every experi-
ment is then preceded by an induction and followed by one or more
observations. The experimental method is always, as Chevreul called
it, a method a posteriori.

Experiment creates nothing; it has precisely the same value and
the same logical significance as the proof of a mathematical opera-
tion.

For an experiment it is not necessary to demand, as some seem to
believe, a complicated plan, a richly equipped laboratory and costly
apparatus.

It is necessary indeed not to confound the precise measure of a
phenomenon which often is obtained by the aid of very delicate in-
struments writh the pure and simple establishment of a causal relation
between one fact and the other facts which determine it, an establish-
ment which is the basis of the experiment itself. Even if the fact were
accidental, as the fall of the apple before the eyes of Newton, its de-
termination may nevertheless become an experiment. And it is only
the mind of the observer which will give it this character.

Das 1st ja was den Menschen zieret
Und dazu ward ihm der Verstand
Dasz im innern Herzen spiiret
Was er erschafft mit seiner Hand.

Where the unscientific person sees without interpreting and
takes a purely contemplative attitude, the naturalist worthy of the
name supplies the supposition of voluntary acts the action of whose
factors he wishes to study.

An animal receives in the hunt or by some other accident a ball
in the left side of the neck; the right side is paralyzed. If the fact
is well determined and freed from all cause of error its voluntary
reproduction in the laboratory would be only the verification of
an experiment already realized.

Not only does nature at present offer us, as we have said-, nu-
merous experiments, many of which are very difficult to repeat,
but we may also say that paleontology furnishes us experimental
data of incalculable value. The arguments which it furnishes to
transformational morphology are not, as is sometimes pretended,
purely conjectural; the degree of certainty that they possess is not
inferior to that in astronomy or in the other divisions of the phys-
ical sciences whose objects are partly inaccessible to us.

272 ANIMAL MORPHOLOGY

Hilgendorf and Hyatt studied the different layers of the tertiary
lake of Steinheim in Wurtemberg. They recognized that certain
forms of Planorbis differing little among themselves in the deep
layers (the oldest) * are separated little by little from one another,
and finally, in the most recent layers, constitute species as reliable
as any of those described in this genus of mollusks.2 Is this a work
of pure contemplation and description? Is it not manifest that
the authors have reconstructed in their thought a gigantic experi-
ment, and if they have not in their power the complete determination
of this experiment, do they not at least possess sufficient elements
to infer the evolution of the forms without determining the factors
of this evolution other than the time-factor, the action of which is
unexceptionable in this instance?

Clearer and still more evident and in any case more in line with
current ideas is the application of the experiment in the study of
the Lamarckian or primary factors of evolution (cosmical factors,
ethnological, etc.) 3

Indeed it is especially by a return to the ideas of Lamarck that
transformationism should cause morphology to progress more
rapidly in the experimental path.

Certainly the conceptions of Darwin were in many respects justi-
fied by experiment, even in the strictest sense of the word, and
Darwin has proved it himself by his beautiful investigations con-
cerning self- and cross-fertilization and concerning climbing plants
and carnivorous plants, etc. But it is necessary to recognize how
many experimental verifications relative to natural selection, to
heredity, demand conditions rarely realized, a length of time which
renders them easy of accomplishment only by a group of persons
(societies of scholars), or necessitate large resources which most
investigators cannot command.

Apart from some brilliant exceptions concerning whom we shall
have occasion to speak later, the disciples of Darwin who have
followed most closely the tendencies of their master have under-
stood experimentation in the very large sense that we give to this
word as applied to a great number of investigations relative to
secondary factors.

The importance of the study of primary factors in evolution did
not escape Darwin, but, excellent observer though he was, he was

1 The four oldest forms were the uncertain varieties of the same species:
Planorbis laevis.

2 The Genesis of the Tertiary Species of Planorbis at Steinheim, Proceedings of
the Boston Society of Natural History, 1880; and Transformations of Planorbis at
Steinheim, American Naturalist, 1882, p. 441; also Stearns, Proceedings of the
Academy of Natural Sciences, Philadelphia, 1881.

3 To convince us of this, it is only necessary to examine the two beautiful
volumes recently published by C. B. Davenport under the title, Experimental
Morphology (New York, 1897-99), in which we shall find an excellent resume of
what has thus far been attempted in the study of the primary factors.

273

undoubtedly dismayed by the complexity of the role of these factors
and did not attempt to disentangle the mechanisms which give rise
to the numberless variations of living beings.

These variations exist. He indicates them, and, without refer-
ring them to their immediate causes, attempts first of all to show
that they may be so determined as to constitute races, then new
species.

Darwin had read Malthus; he recognized the law of a division
of labor borrowed by H. Milne-Edwards from political economy;
he found that the method of the sociologists was good, and that in
a science which was complicated and still young, as was biology,
one might employ the methods in use equally in meteorology, in
statistics, etc., in resting upon the law of great numbers without
seeking to discover distant causes and to penetrate to the essence
of the phenomena.

Thus he showed the importance of selection for the fixing of
acquired characters when they offered some utility in the life-
struggle and thus assured the survival of their possessor through
a better adaptation.

But he did not seek to establish in each particular case the
exact determination of the appearance of indifferent or advan-
tageous varieties. Perhaps he was deterred from this path by the
failure of his eminent predecessor, Lamarck, in the energetic effort
which he had made to explain in terms of surrounding conditions
(acting directly or indirectly by the creation of new needs) the
gradual modifications of living beings and the transformation of
species.

We must not forget, also, that at the outset of the nineteenth
century, and even at the moment when the Origin of Species ap-
peared, the state of the physical and chemical sciences did not
permit of successful approach to most of the problems of external
physiology, the search for the solution of which had been important :
chemical investigations determining variations of color, the influence
of different kinds of radiations, the morphogenic action of saline
solutions, of osmosis, etc.

However satisfactory they may have been for the mind, and
despite the enormous progress that they had wrought in morpho-
logy, the ideas of Darwin began to appear insufficient; we may
even believe for a moment that the exaggerations of some of the
disciples of the master merely compromised the triumph of the
doctrine and led thought back toward the finalistic explanation of
the ancients, now learnedly resuscitated under the name of neo-
vitalism. The words natural selection, mimicry, convergence,
heredity, and others like them, which in the thought of Darwin had
only a provisional value, became for the philosophers and even for

274 ANIMAL MORPHOLOGY

certain biologists, convenient formulas which served to mask the
ignorance in which we most frequently find ourselves in regard to
the immediate cause of variation.

Nevertheless, when in 1880 he published his very suggestive little
book, Die Existenzbedingungen der Thiere, Carl Semper already
attempted to lead back the naturalists to the study of primary
factors. To the experiments of rare precursors concerning the mor-
phogenic influence of change of alimentary regimen (Hunter, Ed-
mondstone), of the modifications of salinity of the water (Smanke-
vitch), of heat, of light, etc., he added original researches concerning
the best conditions for crossing and for the reproduction of Lim-
naea, and especially he brought together into a volume which,
although limited, was very complete in its content for the period,
an enormous mass of biological observations, many of which have
exactly the same demonstrative value as the best laboratory ex-
periments. Since then, investigations of this sort have been under-
taken with enthusiasm on many sides and especially in America.
The impulse is given and we may rest assured that the movement
will increase in force as the parallel advances of physics and chem-
istry permit of the application of greater precision in these studies
and of access to certain questions which up to the present seemed
inaccessible.

The opening-up of new scientific fields such as physical chemistry
and bio-chemistry will soon furnish us means for taking up success-
fully the work which Lamarck was able to trace only in its general
outline.

The dependence of morphology in its relation to the physical
and chemical sciences is still more manifest in that branch, so new
and so full of promise, which we know under the name of cytology.

Although the cellular theory, already sketched by Malpighi,
had been completely formulated by Raspail (1835) and by Schleiden
(1838) for plants, then by Schwann (1839) for animals; although
Virchow about the middle of the last century had proclaimed his
celebrated aphorism omnis cellula e cellula, it is only during the
last twenty years that cellular morphology and cytology have
attained a wonderful development, thanks to the investigations
of Van Beneden, of Strasburger, and of a brilliant group of young
biologists.

The history of this magnificent structure, its general plan and
its details, have been very exactly retraced in a work already class-
ical, The Cell in Development and Inheritance, published as early
as 1896 by E. B. Wilson, one of the able investigators who with
0. and R. Hertwig, Boveri, Maupas, Guignard, etc., have most
actively contributed to its construction. But how laboriously this
difficult work has been prepared by the numerous improvements

PRESENT TENDENCIES OF MORPHOLOGY 275

of microscopical technique due to Leydig, Ranvier, to Max Schultze,
to Flemming, etc.

And these improvements in their turn have been made possible
of attainment by the advances of chemistry and especially of the
chemistry of dyes (the anilin dyes in particular). Despite the em-
pirical and crude way in which we make use of each new con-
quest of the physical and chemical sciences, despite the existence
of methods, which are still imperfect, such as those of Golgi, of
Cajal, and of Apathy, what morphologist would be blind enough
to deny the importance of the new data which we owe to technical
processes of which the theory is very often unknown to us? But
chemistry has rendered us services not less important in enabling
us to penetrate into the finer structure of the chromatin substance
and of the albuminoids in general. In this fruitful way, which Robin
had already attempted, but which has been opened to us by Schut-
zenberger and by Kossel, cytological morphology will certainly
find the key to many of the enigmas which arrest it at the present
time. And what progress shall we not be able to attain through
the chemistry of colloids of which our present chemistry is, in a
fashion, only a special case.

That cytological morphology should be contributed to equally
and in large measure by physics and especially by optics, is too
evident to be necessary to insist upon. I desire only incidentally
to make a remark which will show what influence scientific studies
which are very dissimilar in appearance may have upon one an-
other.

There is no doubt that the perfecting of micrographic apparatus,
and especially of immersion objectives, has been due in such large
measure to the desire of the constructors to satisfy a clientage
which is special and sufficiently large in certain countries, namely
the collectors of diatomes, that these amateurs, sometimes unjustly
disdained by those who wish to establish air-tight partitions between
scholars of different orders, have indirectly rendered great service
to pure histologists and to those who study the most delicate pro-
blems of cytology and of cytogeny.

The bacteriologists, while aiming at a very different and much
more practical goal, have contributed still more than the diatomists
to the perfecting of our micrographic equipment in extending to a
new class of investigators, the pathologists and clinicians, the daily
use of the microscope.

And in this domain of pathological anatomy we again see pro-
duced these very fruitful interactions with the science which more
especially interests us. The study of tumors, cellular teratology,
at the same time that it is illuminated by the facts of normal cyto-
logy, furnishes us with very suggestive views concerning the signi-

276 ANIMAL MORPHOLOGY

ficance of chromatin reduction and of its unexpected connections
with the new phenomena of the first embryological phases (Borel,
Moore, and Farmer).

The idea of phagocytosis, studied by Haeckel in the biology of
the protozoa, by Rouget in the examination of the leucocytes of the
blood, increased in value and importantly developed by Metchnikoff,
who made many applications of it in the domain of pathology, has
come by a most fortunate turn of events to elucidate certain of the
most obscure of the morphological phenomena of embryology, the
coenogenetic processes of ovogenesis and of metamorphosis.

For a long time the introduction of the mathematical sciences in the
domain of morphology has been regarded with suspicion; it seemed
dangerous indeed to wish to bind by very simple formulae facts so
complex as those studied by zoologists and botanists.

Little by little, however, the necessity of determining by precise
measures the extent of variations due to primary factors and of
seeking to find the laws of these variations has made itself felt. Among
the first Delboeuf attempted not without success the application of
algebra to the problem of the formation of races. But it is especially
to Galton and to his school that the most important of the works of
mathematical biology and biometry are due.

Whatever be the character to which we give our attention, if we
consider a great number of specimens of a given species we recognize
that the individual variations (continuous or fluctuating variations)
of this character, numerically expressed, do not exceed two extreme
limits which are reached by a very small number of the individuals.
Between these two extremes there is a constant mean variation with
the greatest number of observed specimens. It results, that if we
take as abscissa the lines which represent the extent of the fluctua-
tions and as ordinates the distances corresponding to the number
of individuals which present a certain fluctuation, we obtain a curve
which Quetelet called a binomial and which is in reality only a curve
of probable error. We also often give to these curves the name
Galton's curves, because of the very extended use that this eminent
biologist made of them in the study of the question of heredity.

By artificial selection breeders and horticulturists succeed in dis-
placing more or less rapidly the apices of the Galtonian curves and
in directing fluctuation in the way they desire. Natural selection
does not operate otherwise for the modification of the form of species
and it is to this action that Darwin attributed in great part the trans-
formation of species.

Wallace, more especially, considered selection as the sole factor
determining the evolution of living beings.

It was reserved for Hugo de Vries to show through long and delicate
cultural experiments, the exaggeration into which the immoderate

PRESENT TENDENCIES OF MORPHOLOGY 277

disciples of Darwin (Romanes, Weismann) had fallen.1 Guided by
his earlier studies concerning the Galtonian curves and impressed
with the constancy of certain forms, such as the species described
by the botanist Jordan, whose origin was difficult to explain by fluc-
tuations, De Vries supposed that after periods of relative fixity during
which they are subject only to fluctuating variations, living beings
may pass through shorter periods when their forms are abruptly
modified in different directions by discontinuous changes.

Biologists clearly recognized this kind of variation in what they
call sports. De Vries has called them mutations and he has shown the
importance of mutability especially in the study of a biannual plant,
(Enothera Lamarckiana, an American species introduced into Europe,
especially into many localities of the Low Countries. From 1880 to
1899 each year De Vries has planted in the botanical garden at Am-
sterdam from 15,000 to 20,000 seeds of this plant. Besides thou-
sands of normal individuals, his cultures have produced seven new
types, represented each year by a variable number of individuals and
capable of reproducing themselves by seed with great regularity.
Among the 50,000 (Enothera plants that he has observed during ten
years De Vries has counted 800 that might legitimately be called (Eno-
thera Lamarckiana, but which are divided as we have just said into
seven groups, to which it was fitting to give the systematic value
of subspecies, as the botanists would not have failed to do if these
plants had been found in the fields where their origin was not known.

A great number of biologists have believed that they found in the
splendid studies of De Vries unanswerable arguments against the
theory of selection. It is impossible for me to share their opinion. I
should say even that in examining the question closely and in penetrat-
ing to the bottom of the matter, it is impossible for me to find in the
theory of mutations anything except a useful complement of the La-
marckian and Darwinian doctrine of continuous variation.

As the economist Bastiat has said, in all complex phenomena where
multiple causes intervene in different ways, there is that which we
see and there is also that which we do not see.

What we see in a mutation is the abrupt and sudden appearance of
a character which did not previously exist, but this character is only
the sudden manifestation of a state which has been prepared very
slowly in the ancestors of the individuals in which it appeared. In
order to obtain a chemical reaction, in order to cause the color of a
liquid to change, it is often necessary to add the reagent drop by drop,
until an instant when all at once the reaction occurs and the new
color appears. The mutation is the result of a new state of equilibrium
in the varying organism. All the individuals in which this new equi-
librium appears are in a different state internally from that of their
1 H. de Vries, Die Mutationstheorie, Leipzig, 1901-03.

278 ANIMAL MORPHOLOGY

ancestors, they are in internal fluctuation and it is this that we do not
see.1

If modifications should be produced in the veins of an insect's wing,
for example, it is impossible that these modifications should express
themselves otherwise than by a new mechanical disposition constitut-
ing in relation to the preceding a sudden variation in the disposition of
the cells and of the veins. In the same way, the appearance of a new
vertebra or of a new metamere in an animal whose metamerism was
fixed could occur only in discontinuous fashion and not by infinitesi-
mal fractions of a vertebra or of a metamere. The fact that mutations
always appear in limited number (seven in the case of CEnothera
Lamarckiana) shows clearly that a certain number of positions of
equilibrium are in question, among which there are no realizable
morphological transitions, and of which some seem difficult to obtain.
Of the seven species of CEnothera, a single one, CEnothera gigas, has
proved robust. The others are for the most part very weak, and de-
mand much care in order to flower and to mature their seed. Often,
indeed, there are only two possible equilibriums; this is true in the
case of dimorphism or ditaxies of colors, to use the language of Cou-
tagne, so common in plants, in mollusks, in the lepidoptera, etc.

In reality, as I wrote a dozen years ago, while fluctuations may be
compared to gradual oscillations from one side to another of a mean
position, mutations represent so many states of stable equilibrium
among which continuous passage cannot be established. The inter-
mediate forms of these states of equilibrium are not explicitly real-
ized because they do not correspond to sufficiently stable states. The
following trivial comparison will serve to render my thought easier
of apprehension: we cannot rise a half or any fraction of a step of a
stair. In such cases progress is necessarily discontinuous, or, what
amounts to the same, is manifested only in a discontinuous manner.
But we cannot adduce from these facts any argument against the
formation of species by natural selections; there is all the more reason
why it is not necessary to seek the unique and complete solution
of the very complex problems of transformation.2

1 A botanist whose original researches concerning variation in plants have not
attracted sufficient attention, A. T. Carriere, made an ingenious comparison in thi.«
connection :

"Nous pouvons," he says, "afin de nous repre"senter le double effet, 1'effet lent
et 1'effet brusque sous lequel se montre le dimorphisme (ce que nous appelle"rions
aujourd'hui une mutation ditaxique) supposer une horloge a secondes dont on ne
verrait que le cadran. Dans ce cas, 1'effet continu mais lent, nous serait repre-
sente" par le balancier, qui, bien que nous ne le voyions pas, ne s'arrete cependant
jamais, et 1'effet brusque ou intermittent par chaque saut que feraient les ai-
guilles, saut qui est la rdsultante d'une action incessante tellement lente qu'ellc
n'est point appreciable a nos sens et qui ne se manifesto d'une maniere sensible
que lorsqu'il y a une certaine quantite" de force accumule'e." A. Carriere, Produc-
tion et fixation des varictcs dans les vfqctaux, Revue horticole. note 42, p. 71. Paris,
1868.

2 A. Giard, Sur un exemplaire de Pterodela pedicularia L. a nervation doublcmcnt
anormale, Actes de la Socie'te' Scientifique du Chili, iv, p. 21, 1895.

PRESENT TENDENCIES OF MORPHOLOGY 279

Besides, as Darwin has never denied the existence and the import-
ance of mutations, which he called single variations, so from his side
De Vries has never sought to destroy the theory of selection.

Instead of operating slowly upon fluctuating individuals, it acts
upon species in process of formation. The struggle for existence
exists among mutations and among the forms from which they
proceed, as W. Hubrecht has very correctly observed in the clear
analysis that he has recently given of the ideas of his compatriot:
"Far from having undermined Darwin's Darwinism, De Vries has
completed, purified, and simplified it," and only those think otherwise
who combat Darwinism for other than scientific reasons, and at the
bottom of their hearts wish much evil to the demonstrations of De
Vries and to all other possible forms of the theory of evolution.1

Another interesting application of mathematics to the morpho-
logical sciences is presented by the study of hybrid forms. The laws
of Mendel, recently verified by De Vries, Tschermak, Bateson, etc.,
carry the calculus of probability to the furthest limit. It will be
useless to insist longer upon the numerous and important problems
relating to morphological heredity whose solution depends on the
rational study of numerical data which are as numerous as possible.

From all of these considerations we deduce at present a conclu-
sion of remarkable generality; to wit, that the natural laws of evo-
lution seem to enter into the movement toward physical laws which
has manifested itself for some time. They assume more and more
the character of static laws. Thus guided by the conducting line
of the theory of descent, subjected to the precise measure of a per-
fect mathematical exactness, and controlled at each instant by
the experimental method, morphology each day becomes more the
explanatory science par excellence of the world of organized beings.
Morphological phenomena are the translation, the tangible expres-
sion, the perceivable criterion of physiological experiments, and
the latter borrow all their interest from the morphological mani-
festations which they engender.

In connection with breeding and horticulture the morphologist
becomes in truth a creator. He is still more so when, in calling up
and grouping in thought the conditions under which living beings
are successively formed in the course of centuries, he perceives the
causal nexus which connects the new forms with those which have

1 " I have purposely insisted on these points, because here and there a tendency
seems to prevail to look upon Darwin's views upon the origin of species as unsatis-
factory and obsolete and to proclaim the necessity of replacing them by broad
new hypotheses with which the name of De Vries should be coupled. These tend-
encies are in great favor with those that bear a grudge to the so-called Darwin-
ism for other than scientific reasons, and who in their innermost hearts would at,
the same time like to see a similar fate reserved for De Vries's demonstrations, and
even for the whole theory of evolution." A. A. W. Hubrecht, Hugo de Vries's
Theory of Mutations (The Popular Science Monthly, July, 1904, p. 212).

280 ANIMAL MORPHOLOGY

preceded them, and foresees to a certain extent the transformations,
undoubtedly less extended, which the forms, still possessed at
present of a certain plasticity, will undergo in the future.

At all events, in pretending that the morphologist plays the r61e
of creator, we do not intend to affirm that he could, as the adver-
saries of the evolutionary theory have sometimes demanded with
ridiculous unreasonableness, transform hie et nunc one animal species
into another species through a simple modification of food and me-
dium, and, for example, produce the ox from the sheep by placing
the latter for some generations in especially favorable conditions.
Such a result would be the negation of the Darwinian doctrine itself,
which, we know, makes great use of modifications accumulated
by heredity and irrevocably fixed in definitely established organisms.

What the morphologist is able to attempt, and what in fact he
does attempt, is to discover and to analyze the small variations
which are determined by primary factors, and to determine thus
how by a slow summation these variations, at first insignificant,
are united to give origin, either by a continuous or by an apparently
discontinuous process, to the much more evident characters which
separate species.

I do not dare even to believe, with some bold pioneers of modern
science, that the most perfect knowledge of the auto-regulation of
organisms will perhaps permit us to modify these auto-mechanisms
and to obtain thus a rapid variation of animals and plants.1

After a series of innumerable transformations of which it is
sometimes possible to discover some traces in the form of fossil
impressions in the depths of the earth, the majority of living beings
have arrived at a relatively stable state of equilibrium. They have
exhausted the possibilities of what I have called their plastic poten-
tial, they are able to effect only feeble oscillations about a mean
position, and no considerable change in the ethological conditions,
in general, can be compensated for by a new arrangement of regu-
lative reaction.

And even for those which still have a reserve of plasmatic elas-
ticity sufficient to permit of new adaptations, we must not forget
that they can develop only in a certain number of well-defined
directions, and that we must always bear in mind two essential facts
which regulate the transformations which are hereafter possible:

' ' So far as I am aware no one has vet found a method of bringing about a rapid
variation in animals or plants. I am inclined to believe that this failure is at least
partly due to the existence of mechanisms of regularisation. . . . We again meet
with two possibilities: we shall either succeed by a series of continued slight
changes in one and the same form in bringing about a large transformation from
the original form, or we shall obtain the result that in each form the possibility
of evolution is limited, and that at a certain point the constancy of a species is
reached." J. Loeb, The Limitation of Biological Research (University of California
ublications, Physiology, vol. i, no. 5, Oct. 1903).

PRESENT TENDENCIES OF MORPHOLOGY 281

first, the indestructibility of the past; second, the irreversibility of
evolution.

It is there, we may say in passing, that all the difficulty of the
question of spontaneous generation or abiogenesis lies. If by a
miracle we should happen to produce from non-living material as
simple a living being as can be imagined, this new being would
certainly be different from all actually existing species, for the
latter have a past that the other would not have, and they bear in
their organism, which may be as rudimentary as we choose, traces
of all action to which their ancestors have been subjected.

We may even infer that the hypothetical monads whose forma-
tion we might bring about by abiogenesis would differ from those
which have originated at other times by the same process. Besides
the fact that the environmental conditions in which they appeared
would necessarily be different, the complexes of organic materials
which would serve in their formation also would have their history,
and everything leads us to think that the properties of inanimate
bodies, as those of living beings, are to a certain extent functions
of their antecedents.

Thus is explained why even to-day there exist very old living
forms which are not developed because they no longer have available
plastic potential, and which would perish before they would undergo
transformation.

Thus is explained why it is vain to hope through special environ-
mental conditions to raise relatively inferior forms of life to a higher
level, and why it is useless to seek to modify physically or morally
in a desirable sense races which are considered rightly or wrongly
as relatively inferior, but in any case otherwise differentiated. Evo-
lution is not reversible, and we cannot by any process cause a living
being to return toward the point at which it was separated from
its original phylum in order to make it follow a different way from
that which it had at first taken.1

But the limits imposed upon our science by nature should not
hinder us from admiring its grandeur and from noting its prodigious
development.

It is never necessary to doubt progress. It is almost thirty years
since, in the course of a lesson on the first phases of development of
the animal egg, I said, not without regret: "La Morphodynamique

1 The generality of the pcecilogonic process shows the instability of evolution.
For according to Brillouin, irreversibility is introduced into rational mechanics
with instability. Irreversibility, which is the almost universal character of natural
phenomena realized in finite time, is by no means an objection to mechanical ex-
planation (mechanics of the nineteenth century or the more general mechanics
which caused us to discover electromagnetism) of the physical-chemical world.
Wherever we actually introduce it in order to come to an issue in a numerical
theory, of viscosity or of friction, a most profound analysis will cause the recog-
nition and study of the instability of molecular equilibrium. (Marcel Brillouin,
Notices sur ks travaux scientifiques, pp. 19-20, 1904.)

282 ANIMAL MORPHOLOGY

soupc.onne'e par Lamarck, a peine aborde"e par quelques raresbio-
logistes, est un territoire scientifique que la plupart des naturalistes
de nos jours ne verront que comme Moi'se vit la Terre promise
seulement de loin, et sans pouvoir y entrer." 1

My hopes have been greatly surpassed by reality. Under the
name of embryological mechanics (Entwicklungsmechanity , and of
biomechanics, of biometry, etc., the new fields toward which I
directed my course of scientific exploration at the beginning of my
career have been partly recognized and opened up by young and
able investigators. Scientific progress follows a geometrical pro-
gression, of which the ratio increases unceasingly. As a river, with
its impetuous waters increased by the contributions of numerous
tributaries whose synthesis it effects, morphology majestically de-
ploys its course, and the delicious aesthetic experience that the con-
templation of living beings procures us is the least recompense of
of our troubles and of our persevering efforts.

For the realization of a work of art, what anonymous collabor-
ators come to the assistance of a painter or a sculptor! The artisan
who weaves the canvas, the quarryman who furnishes the stone,
have their share of merit in the final result, and we owe them also
a share of the recognition. It is the same in our sciences of nature,
where each day brings an increasing solidarity among all the workers.
The different branches of biology are united among themselves,
as we have seen, by multiple and intertwining bonds, and a special
branch such as morphology depends not only on the progress of
neighboring branches, but also on the development of other sciences,
even those which are apparently most distant.

Specialization, which perforce becomes more and more intense,
also renders the more desirable synthetic efforts and the coordina-
tion of results.

Let us hope, then, that in the near future a collective organ-
ization may replace the anarchical state which exists at present,
and which uselessly absorbs so much activity which might be
better employed in bringing the various sciences into a hierarchy
and directing them toward a common end. Scientific solidarity
should be the preface and the model of social solidarity.

1 A. Giard, Cours de Zoologie (Bull. sc. Fr. et Belg., t. vin, p. 258), 1876.

SHORT PAPERS

PROFESSOR C. JUDSON HERRICK read a paper for DR. C. S. HERRICK of Gran-
ville, Ohio, on the " The Dynamic Character of Morphology."

The speaker said in part: There is a price which any organism must pay for a
high degree of specialization in a single direction. The liver fluke of the sheep de-
pends for the perpetuation of its species upon a series of complicated adjustments
to various environments, the failure of any one of which is fatal. Such cases of
extreme adaptation are usually found only on the terminal twigs of the phyletic
tree, and it has come to be a biological truism that the main line of evolutionary
advance passes through the generalized types.

Perhaps something similar holds true for scientific disciplines. There is certainly
danger that extreme development of any specialty may cut it off from the vital
relations with environing fields upon which its continued existence depends, and
the elaboration of a "pure morphology" is certainly not exempt from such a
danger.

But we have only to be true to our own traditions to enable us to retain our
place in the growing axis of biological progress. Anatomy, out of which morpho-
logy grew up, belongs to the most static group of the descriptive sciences. But
morphology is not the description of form; it is the explanation of form, and
from its inception has been quickened by genetic and functional motives.

Morphology is one of the most dynamic of all the sciences; from the start it
has been morphogenesis, and the key to the problems of structure is behavior. To
draw another illustration from my own specialty, comparative neurology and'
comparative psychology have joined hands in wedlock from which we trust there
is henceforth no divorce, and we trust not without hope of offspring.

So long as morphologists have sufficient breadth of view to assimilate the
relevant data from all other sciences, there is small danger of our science becoming •
specialized to death, however minute may be the subdivision of our problems and
however extreme may be the refinements of our methods. But isolate morphology,
and it will perish.

The present problem of our specialty, therefore (if we may single out one as
preeminent), is, as it always has been, the relation of morphology to other sciences.

PROFESSOR J. G. NEEDHAM, of Lake Forest University, presented a paper on
"The Contribution of Animal Morphology to Education," in which the speaker
said in part:

Two phenomena of great importance accompanied the early development of;
animal morphology:

(1) The general recognition of the principle of evolution.

(2) The general introduction of the laboratory method in zoSlogy.

The first profoundly affected every department of human knowledge: the
second profoundly influenced the development of every branch of biological
science.

These were the necessary — not accidental, nor even incidental — accompani-
ments of the development of animal morphology : for when the theory of natural
selection offered the first satisfactory explanation of a possible method of evolution
zoologists were quick to recognize that the facts of the structure and develop-
ment of animals offered a ready means of testing its validity. The distinguished
comparative anatomists of the first half of the nineteenth century, and the rising
school of embryologists, had prepared the way: and the early tnorphologist found

284 ANIMAL MORPHOLOGY

at hand structural data of great diversity and in great abundance, awaiting a
new interpretation. They took the "natural system" of the old comparative
anatomists, and breathed into it the breath of life. In so far as it was natural its
naturalness lay not in association of like forms, but in kinship. Homology came
to have a new significance, and phylogeny and ontogeny came to the fore; and
enormously productive researches began into the correspondence in development
of race and individuals. It is not too much to claim that the general and prompt
acceptance of the idea of evolution is due primarily to the work of morphologists.
That which belongs to general intellectual culture of the race belongs to the
curricula of the schools. Among the early morphologists were some eminent edu-
cators, who were not slow to recognize the great pedagogic value of the materials
in their hands. They were the first among zoologists to reduce their materials to
satisfactory pedagogic form. While perhaps they did not create the laboratory
method in zoology, they made it general. While other phases of zoology are likely
to receive, and are worthy of more attention than they receive at present, the
materials of morphology will always be of the highest general pedagogic value
because they so well illustrate the commoner phenomena of evolution, division of
labor, specialization, progressive and retrogressive development, redundancy and
reduction of parts, parallelisms and divergent lines of development, etc. To me
it seems doubtful if these phenomena, which belong to evolution in every field of
knowledge, are demonstrable in any other field with such definiteness and economy
of time and satisfaction as in this one. Therein lies the chief pedagogic utility of
the materials of morphology.

A TKAGKDY /A Till: II A Kb M.

I'liotut/ra'ttrr from a Paint'ini; hy /'I'-T/V L'nitx Bouchard.

An uprising in :i harem is not so rare that the polygamous chief can afford to
ignore such a possibility; so, to intimidate the unfortunate inmates he inflicts
the most terrible punishments for violations of fidelity or attempt to escape.
In the painting here shown the artist has pictured a terrible scene, in which an
uprising of the enslaved wives is discovered by the concealed husband, who has
summoned his mutes to seize the women, one of whom has fainted as the drawn
drapery from an alcove reveals the presence of her cruel lord. The picture is
full of action arid Oriental richness, but almost terrifying in its illustration of
customs that flourish in Mohammedan countries. This painting, which is one
of P.ouchurd's masterpieces, lias become famous in France as I,CK M i <!.•>• ill,
S'' mil. ;md was originally exhibited in the Salon of 1S87.

SECTION H — EMBRYOLOGY

SECTION H — EMBRYOLOGY

CHAIRMAN:
SPEAKERS:

SECRETARY:

(Hall 9, September 23, 3 p. TO.)

PROFESSOR SIMON H. GAGE, Cornell University.
PROFESSOR OSKAR HERTWIG, University of Berlin.
PROFESSOR WILLIAM K. BROOKS, Johns Hopkins University.
PROFESSOR T. G. LEE, University of Minnesota.

THE Chairman of the Section of Embryology was Professor Simon
H. Gage, of Cornell University, who opened the Section with the fol-
lowing remarks :

"In this great International Congress of Arts and Science, it is
peculiarly fitting that one of its sections should be devoted to em-
bryology, that branch of biology which has to do with the unfolding
and development of the egg into a complex and independent organ-
ism. We are fortunate in having for our chief speakers men — one
from the old world and one from our own country — who have
taken a leading part in our generation in discovering and expound-
ing the processes and laws of development and the relations of organ-
isms from parent to offspring in an endless chain."

ADVANCES AND PROBLEMS IN THE STUDY OF
GENERATION AND INHERITANCE

BY OSKAR HERTWIG
(Translated from the German by Dr. Thomas Stotesbury Githens, Philadelphia.)

[Oskar Hertwig, Regular Professor of General Anatomy and History of Evolution
since 1888; and Director of the Anatomical-biological Institute since 1888,
University of Berlin, b. Friedburg, Hessen, April 21, 1849. Student of Medicine,
Jena, 1868; Zurich, 1869; Jena, 1870; Bonn, 1871-72; M.D. Bonn, 1872; Ph.D.
Bononiensis, 1888. Privy Councilor of Medicine, 1897; Regular Professor of
Human Anatomy and Director of Anatomical Institute, Jena, 1881-88. Member
of the Physio-Medical Society, Erlangen; Royal Academy of Science, Berlin;
Academy of Sciences, Munich, Stockholm, Copenhagen; and many other scientific
and learned societies. Author of Text-Book of the History of Evolution of Man
and of Vertebrates; The Elements of the Science of Evolution; Timely and Disputed
Questions of Biology; and numerous other works and memoirs on anatomy.]

FROM the time of Greek science until our own day, no other pro-
blem has interested the scientific investigator as much as that of
animal development. Still after many centuries, difficulties remain
that appear insurmountable to human powers. This is especially
true of the secret problem of generation. In earlier centuries, the
old anatomists with their incomplete methods of investigation could
not win true knowledge, which, however, they sought to replace by
hypotheses, which were generally without permanent value, and
sprang from the earth like mushrooms. At the end of the seven-
teenth century more than 300 could be enumerated, and when the
famous physiologist Haller brought together the work of several
centuries, in his great handbook of physiology, he commenced the
chapter on generation with the complaint, which was certainly
justified at that time, " Ingratissimum opus, scribere de iis, quae
multis a natura circumiectis tenebris velata, sensuum luci inaccessa
hominum agitantur opinionibus."

The century of natural sciences, the nineteenth century, was the
first to lay a scientific basis for the study of generation, as well as
for that of so many branches of natural science. Since then such
great advances have been made, that if Haller should, in our day,
begin again to write the chapter on generation, he would certainly
term it, in contrast to the year 1746, an " opus gratissimum. "

For is it not a pleasant task to follow the way in which the torch
of science has constantly more brightly illumined a realm, which for
many centuries was looked upon as one of the most hidden; also
how, on the successfully trodden way, the new discoveries have, with
certainty and regularity, been crystallized around the already deter-
mined truth ? Therefore, I may surely count upon a general interest

GENERATION AND INHERITANCE 289

when I give a comprehensive sketch of the position and problems
of our present development in the realm of generation.

The theme corresponds also to the general programme of the Board
of Managers of this Congress. It is their object to show, in the great
series of addresses which lie before us, a proof of the inseparable
connection of all branches of science. Our theme will show us, step
by step, how botanists and zoologists, students of the Protista,
anatomists and physiologists, work hand in hand when they inves-
tigate the general basic truths of their various sciences in the realm
of generation, as here, every step forward in one of these immediately
assists each of the others. The goal of truth, for which we seek from
various starting-points, is the great science of life, biology, to whose
investigation the separate ways lead. In another connection still,
we shall see how the development of biology is dependent, in more
than one connection, upon the development of other sciences, espe-
cially of physics and chemistry, and thus forms an integral limb in
the regular development of the great tree of knowledge. To give
a convincing example of this natural connection, the most important
discoveries which biology has made in the last hundred years were
made possible, in great part, by the development of physics. Con-
sider the advance in physical optics, and the technic connected there-
with, which through Abbe's labors gave us the compound microscope,
that wonderful instrument already brought to the highest perfection
and destined to overcome, in the rapid course of conquest, the new
world of the smaller micro-organisms. Embryological investigation,
especially, was seen to take a great spring forward the moment
physiologic knowledge showed that animals are built up of smaller
individuals, the cells, and thus are nothing more than communities
of innumerable, socially connected, elementary organisms. Embryo-
logy is indebted to the students of plant anatomy for the impulse
toward this new study which is built upon the knowledge of the
construction and origin of plants, based upon Schleiden's teaching.
For, standing upon Schleiden's shoulders, Schwann has shown the
dominion of the cell theory in the animal body.

At this time the study of generation received its first scientific
basis. The beginning of individual life, the egg itself, is a cell, as
Schwann had already conjectured. The spermatozoa also, which in
the time of Johann Miiller were frequently looked upon as parasitic
organisms in the seminal fluid, comparable to infusoria, wrere soon
explained by Kolliker as elementary parts of the animal, as they too
arise from cells. Thus the organism reproduces new individuals of
its own sort by loosing from their bonds single cells, as sexual pro-
ducts, which may begin an independent life in a new process of
development. While until now the progress came from the botanical
side, animal embryology, on the contrary, now began to have a fruit-

290 EMBRYOLOGY

ful influence on the study of generation in plants. The question
which next pressed itself upon the embryologist was: Why must
the egg, that the young being may develop from it, first experience
the effect of the semen? Why must it, except in the rare cases of
virgin generation, be fertilized? This matter still remained a pro-
blem which actively demanded a solution. Ordinarily the process
was explained by saying that the egg, in order to begin development
and to divide, needed an external stimulus, and that this stimulus
to development was a chemical process arising either from the
seminal fluid or from the spermatozoa.

Some investigators who endeavored to observe fertilization in
suitable objects, believed that they were able to see under the micro-
scope that some of the numerous spermatozoa which surrounded the
ovum forced their way in, dissolved, and mixing with the yolk, acted
as the fertilizing agent. For a time the question as to the penetra-
tion of the spermatozoa in the egg was the burning question of the
day in science. What value was laid upon the observation of a
spermatozoon inside the yolk-sac, may readily be seen from the fact
that Barry, as well as Nelson, Keber, and Meissner, called together
a congress of professors and doctors in order to show them the dis-
covery, and to permit them to see the proof for themselves.

The state of the knowledge of generation up to the year 1875,
Wundt has expressed as follows in his text-book of physiology:
"The important condition for fertilization is, in all probability, the
penetration of the spermatozoa into the egg contents, which may
be shown in the various classes of vertebrates. After the sper-
matozoa have penetrated into the egg they rapidly lose their mobility
and dissolve themselves in the yolk. We do not possess a theory,
or even a plausible hypothesis, concerning the nature of the process,
by which after their penetration into the yolk they provoke in this
the process of development."

With the year 1875, a new stage begins in the study of generation.
At that time I was fortunate enough during a long sojourn for study
at the Bay of Villafranca to determine more accurately the process of
fertilization, in an extraordinarily favorable object, the egg of the
ordinary sea-urchin, Toxopneustes lividus.1 As in the sea-urchin the

1 My investigations on the first stages of development in the egg of the sea-
urchin began Easter, 1875, in Ajaccio, where I studied especially the changes in
the division of the egg. At that time, however, I did not succeed in observing
the process of fertilization, although my attention was directed toward it. I first
succeeded when I went from Corsica to Villafranca, with my brother (who was
making a study of Radiolaria) and there continued my investigations for some
time. When, therefore, Bolsche, in the first volume of his encyclopaedia Men of
Our Time, p. 228, writes: "Oscar Hertwig made in Ajaccio the discovery of the
act of fertilization in the sea-urchin which will form for a long time a turning-point
in the history of our knowledge of the sexual act of generation, thus of one of the
deepest mysteries of all nature," the name of the place Ajaccio should be replaced
by Villafranca.

GENERATION AND INHERITANCE

291

sexes are separate, and as the eggs which almost the whole year
through may be found in the mature condition are small and trans-
parent, it is here an easy task to observe the artificial fertilization
on the object-glass and under the microscope. The complete trans-
parency of the egg permits, even with extreme magnification, the
most minute processes to be observed during life. That which has
already been discovered can be controlled and more accurately deter-
mined in many details in preserved material.

Thus the important points of the process of fertilization could be
explained and later positively determined by me and the numerous
investigators who have since then occupied themselves with the
Echinodermata (Diagram I).

DIAGRAM I. The fertilization process in the ovum of Toxopneustes lividus.

FIG. 1 . The mature egg at the moment of fertilization. Of the numerous sperma-
tozoa one has already penetrated the egg at a point which is determined by the
"reception eminence." In the spermatozoon the head (&), the middle piece (m),
and the terminal filament may be distinguished. The egg-nucleus (eik).

FIG. 2. The egg a few minutes later has excreted the yolk-sac (Membrana vitel-
lind). The head and the middle piece have separated from the terminal filament,
which has disappeared, and have changed into the male pro-nucleus (sfc) and the
centrosome (c). The latter is surrounded by protoplasmic rays. The distance
between the sperm-nucleus and the egg-nucleus has lessened.

FIG. 3. A few minutes later. The egg- and sperm-nuclei have approached one
another in the centre of the ovum. The originally simple centrosome has divided
in two. The protoplasmic rays around the two nuclei have become larger.

FIG. 4. The egg- and sperm-nuclei lie against one another and have become flat-
tened at the place of contact. The centrosomes are arranged on opposite sides
of the nuclei. The protoplasmic rays have spread themselves out over the entire
yolk.

292 EMBRYOLOGY

After the mixing of the sexual products, numerous spermatozoa
approach the egg-cell by a swinging motion of their tails, but only one
penetrates, if the egg is normal and capable of life (Fig. 1, k and rri).
The point of penetration is known to be a small conical process, the
reception eminence (Empfangnis Hugel), which extends from the
egg-surface toward the closest spermatozoon. To others, entrance
is immediately made impossible by the fact that the egg at once
excretes a fine but impenetrable skin, the membrana vitellina, largely
as a protection against this.1

The internal fertilization process immediately follows the external.
Of the three parts which, as is well known, may be distinguished in
the spermatozoon, the head, the middle piece, and the contractile
terminal filament, the last is thrown off and has no more importance
in the process. The head, on the contrary, which was formed from the
nucleus of the spermatozoon-forming cell, and which contains the
chromatin (Fig. 1, k, and Fig. 2, sk), begins to change into a small
round vesicle which I have called the seed or sperm-nucleus, and
which by the absorption of juice from the protoplasm begins slowly to
increase in size (Figs. 3 and 4, sk). The middle piece (Fig. 1, m) con-
tains a tiny cell-organ, the much-studied centrosome (Fig. 2, c), which
in spite of its extreme minuteness plays a striking and important
role in the division of the nucleus. It moves in front of the sperm-
nucleus, and its position in the living cell is easily recognizable, because
in its neighborhood, evidently as a result of a stimulus proceeding
from it, the protoplasm arranges itself in radial bands in a figure
like iron-filings around the pole of a magnet.

Interesting phenomena begin now, in rapid succession, to fix the
eye of the observer. The original nucleus of the egg and the newly intro-
duced sperm-nucleus draw mutually together and move with increas-
ing rapidity through the yolk toward one another (Figs. 2, 3, and 4).
The sperm-nucleus (sk) which is constantly preceded by the radiance
with the centrosome (c) included therein, changes its place more
quickly than the egg-nucleus. Soon the two meet in the middle of the
egg (Fig. 3), where they are inclosed by a common radiance which
has now extended over the entire yolk. They lie against one another,
becoming flattened on the contact surfaces, and then lose their
separation from one another with the formation of a common nuclear
sac. Egg- and sperm-nucleus are thus united to form a common egg-
nucleus in wrhich the chromatin of the male and female sexual cells is
contained. At this point the internal process of fertilization may be
looked upon as concluded.

Two or more nuclei in the egg-cell were already described several

1 The formation of the Empfangnis Hiigel was first observed by Fol, when, in
connection with mv experiments, he made a very thorough study of the fertiliza-
tion process in Erhinodcrmata (liecherches sur la ft'condation et le commencement
de rh('nog<'nie, Genf, 1879).

GENERATION AND INHERITANCE 293

times before 1875 in different objects (mollusks, nematodes) by
Warneck (Ueber die Bildung und Entwickelung des Embryos bei Gas-
tropoden, Bull, de la soc. des. Natur. de Moscou, vol. xxm), Biitschli
(Studien uber die ersten Entwicklungsvor gauge der Eizelle, 1876), and
Auerbach (Organologische Studien, vol. n, 1874), and their coalescence
with one another was observed. It, however, occurred to no one to
see in this coalescence of egg- and sperm-nuclei the process of fertil-
ization. The nuclei were looked upon as new formations (vacuoles)
in the egg whose nucleus had been lost. Biitschli believed that the
germinal vesicle was completely thrown off. Auerbach thought it was
dissolved by karyolysis. Thus it was taught that when seminal bodies
penetrated into the egg-cell, they were destroyed by complete solution.

Born is therefore wrong when he states in an article which ap-
peared in 1898 (Anatom. Anzeiger, vol. 14, no. 9), "Auerbach has
given the modern study of fertilization its lasting basis. It should
never be forgotten that this service belongs to Auerbach alone."

Auerbach was far away from the correct interpretation of the phe-
nomena. He knew only that through the coalescence of two nuclei
which arose as vacuoles in the yolk at opposite ends of the egg,
material differences, individual mistakes in composition, between
the two halves, were adjusted. According to his conception, "The
necessity for the whole complex of phenomena is caused by the
special peculiarity of the fertilized Nematode eggs, namely, by their
elongated shape and by the peculiar condition during the act of.
fertilization by which the eggs forcing themselves through a narrow
canal offer at first only their anterior polar region to the zoosperms."

Otherwise, Auerbach has expressed himself very correctly as to the
relation between his and my investigations in speaking of my work.
(Jenaer Literatur Zeitung, dritter Jahrgang, 1876, no. 101, p. 107).
After a short reference to the contents, he remarks: "These observa-
tions confirm, as the author explains, as regards the conjugation of
two nuclei of independent origin in the egg, those of the writer, but'
vary from these in that the author ascribes to the two nuclei nott
merely, as the present writer, a slight qualitative difference caused by
fertilization, and does not look upon them merely as new formations,
but rather sees in one the morphological remainder of the egg-nucleus,
in the other that of the sperm-cell. It is evident that if, in the
further development of the subject, the results won by the author
should be confirmed, a new light will be thrown upon the fertilization
process, the aim of which would be accordingly a conjugation of the
nuclei of a male and female sexual cell." Hensen was among the first
to value correctly the importance of the theory of fertilization pro-
posed by me. In his article "The Physiology of Generation," in Her-
mann's Handbuch der Physiologic, vol. vi, part 2, p. 126, he remarks:
"This conception of fertilization must be looked upon as a fortunate

294 EMBRYOLOGY

one. It deepens our knowledge of the process of fertilization because
it adds to the previously considered chemical and physical elements
the morphological element which is so important in the phenomena
of life and inheritance by showing that the essential substance has
a definite form. Also the new experiences with regard to the im-
portant role which the nucleus plays in cell-division, as well as for
the study of fertilization, come into play, and at the same time the
formation of the polar bodies as a preparatory stage for the con-
jugation of the nuclei is explained in a far better way than was
previously possible."

On the basis of these observations fertilization may be looked upon
as union between two different cells which arise from a male and a
female individual. The essential in this process is evidently the union
or, to use the expression of Weismann, the amphimixis of the egg and
sperm-nuclei. That this is a general law of biologic nature is now
doubted by none. For fertilization is the same process in all classes of
animals as in the Echinodermata. Many of these, such as Ccelenierata
and Vermes, as Tunicata and Mollusca, as Crustacea and Insecta, have
been investigated by various scientists. The numerous Vertebrata,
in which the process has been followed, Mammalia, Reptilia, and
Amphibia, Cyclostomen and Amphioxus, all show the same process.

The discovery of the fertilization process in animals has immedi-
ately brought about similar discoveries in the plant kingdom. The
fertilization of P keener ogamia, previously studied without result
by many investigators, was now quickly explained by Strasburger.
Our knowledge in this and other points was completed by Guignard,
Nawashin, and others. We now know that the pollen grain, which is
analogous to the spermatozoon of animals, carries into the egg-cell
of the ovary a sperm-nucleus which combines with the egg-nucleus.
The correspondence is even greater in the Cryptogamia, as here ex-
ternally the vegetable spermatozoid is very similar to the animal
spermatozoon, and fertilization proceeds in a similar way. Even
among the lowest organisms, Infusoria, Rhizopoda, Flagellata, Algae,
and Fungi, the process of fertilization is seen to be the same.

By this natural law of sexual generation, which is now so surely
founded and based upon a complete series of observations, the old
discussion which once played so great a role in the history of the sci-
ences and engaged for a long time the naturalists and philosophers,
the strife between the Ovists and the Animalculists, has been decided.

From the sixteenth to the eighteenth century the dogma of pre-
formation ruled : the doctrine that the embryo of a being was built
up of the same organs and parts as the parent, and thus was nothing
less than an extraordinarily minute reproduction of it. Most scien-
tists (S\vammerdam,Harvey, Spallazani, Bonnet, Haller) looked upon
the egg as the preformed embryo, as may be seen from the well-

GENERATION AND INHERITANCE 295

known saying, "omne vivum ex ovo." But when Leeuwenhoek, dur-
ing his microscopic discoveries, found the spermatozoa, the thought
occurred to him that the worm-like bodies in the semen which moved
independently, and thereby showed a certain resemblance to the low-
est organisms, should be more properly considered as the miniature
beings. He, therefore, proposed the hypothesis that the spermatozoa
penetrated into the egg during fertilization in order that the latter
might serve them as a suitable nourishment for their future growth.
No less a person than Leibnitz accepted this hypothesis.

Strangely enough, in both hypotheses, which appear to be ex-
cluded together with the dogma of preformation, a seed of truth
seems to be hidden. For, as is easily seen from our present stand-
point, both egg and sperm take an equal part in the formation of the
new being. Both are cells, one of which represents the properties of
the female, the other the properties of the male progenitors. Both
unite to produce a mixed product, which has inherited the peculiar-
ities of both parents.

Here we see again how the development of scientific views in the
realm of embryology is dependent upon the contemporary develop-
ment of all science. We can appreciate the fact that the old scien-
tists could not understand the process of generation, because at that
time the lack of microscopic assistance hid from them the concep-
tion of the elementary construction of the organisms.

The thought of the union of two organisms into a new unit could
not occur to the adherents of the preformation theory, for if embryos
are already miniature beings composed of many organs, how could it
be possible that they should unite in pairs to form a single individual,
and at the same time their organs and tissues flow together into one?

For us who know that the germs are merely cells separated from
their parents, thus similar to simple elementary organisms, the con-
ception of an amphimixis has no such difficulty, and for us it is now
a determined fact. We can follow under the microscope the union of
a male and a female cell and even the union of their component parts,
especially their nuclei and the substances contained therein. With
the knowledge of amphimixis the phenomenon that children may
resemble both their parents, a fact for which scientists until the
nineteenth century could give no logical explanation, is brought
within our understanding. They resemble both, because they are
formed from a union of the substance of the father and mother; in
other words, from a paternal and a maternal element.

At this point the problem of generation and fertilization passes
over into the most difficult of all problems, the problem of inheritance.
However, before we approach this more closely, it will be well to
make ourselves familiar with the series of phenomena which stand
in the closest relation to the problems of generation and inheritance

296 EMBRYOLOGY

and also belong to the most important discoveries of modern biology.
Here also the discoveries for which we must thank, in the first place,
zoologists and embryologists, have reacted favorably upon the in-
vestigations of botanists.

The older zoologists, Fritz Miiller, Loven, and others, had already
noticed that from the egg-cells of the most distant classes of ani-
mals two minute spheres of protoplasm were thrown off, a short
time before or during fertilization (Diagram in, Figs. 3, 4, 5, pzl,
pz2p). These were called the polar bodies, because at the place of
their extrusion from the ovum the first plane of segmentation began.
Their importance remained an enigma. Many scientists believed
that they constituted an excretion by the extrusion of which the egg
purified itself of useless substances, before the beginning of its
further development. Then Biitschli observed that the nucleus of
the unfertilized egg is concerned in the formation of the polar bodies,
that it projects from the surface of the yolk in the form of a nuclear
spindle, which, as he believed, is then extruded in the form of the
polar bodies. This was a great advance, but combined with an error
with regard to the entire meaning of the process which soon after
was rightly determined by Giard and myself. For more accurate
investigation showed us that the polar bodies were not formed by
extrusion, but by two true divisions which followed immediately
upon one another, and that in the second division half of the spindle
and of the chromosomes remained behind in the egg, and here became
the nucleus of the mature egg. The process only differed from an
ordinary cell-division in that the parts were so unequal in size.
The polar bodies should, therefore, better be denoted polar cells.

For what reason and to what end, we may ask, are these two
insignificant polar cells formed with such great regularity in the
entire animal kingdom? On this also light was soon thrown by the
accurate study of an extremely favorable object for investigation,
the egg of the horse roundworm, Ascaris megalocephala, which has
been as productive of results in the study of the process of fertiliza-
tion as the egg of the Echinodermata. Its invaluable advantage
consists in the fact that it gives us a deeper insight into the relation
of that substance which plays the most important role in the divis-
ion of the nucleus, namely, the chromatin.

Of the chromatin we know by investigations which are among
the most brilliant of the histological advances of the last decennium
(see Diagram u, showing nuclear and cell division) that the chro-
matin at the beginning of the nuclear division is changed into a
long convoluted chromatin thread, and that this in the second phase
(Fig. 2) breaks up by cross-segmentation into a very definite number
of segments or chromosomes (ch) which arrange themselves in the
middle of the nuclear spindle (Fig. 3, sp) to a symmetrical figure,

GENERATION AND INHERITANCE

297

DIAGRAM II. Six stages of cell-division and nuclear division (Karyokinesis).

FIG. 1. The first stage. Cell in the resting spherical form, showing a nucleus and
one centrosome (c). The nucleus shows a network of linine with threads and
granules of chromatin (ch).

FIG. 2. Second stage. During the preparation for division (pro phase) the
chromatin has drawn together into a thread which has immediately broken up
into four pieces (chromosomes). The centrosome (c) of Fig. 1 has divided, and
between the two parts a spindle has arisen.

FIG. 3. Third stage. The spherical nucleus has dissolved. The two centrosomes
of Fig. 2 are more widely separated and the spindle between them has become
much larger. The four chromosomes (ch of Fig. 2) have arranged themselves
symmetrically in the middle of the spindle to form the mother star.

FIG. 4. Fourth stage. The four chromosomes of the spindle have split longitud-
inally each into two daughter chromosomes (ch 1 and ch 2).

FIG. 5. Fifth stage. The daughter chromosomes which arose by longitudinal
splitting have separated further and further from one another toward the opposite
ends of the lengthening spindle (formation of two daughter stars). The cell begins
to segment in the middle.

FIG. 6. Sixth stage. The segmentation has become complete, and the mother cell
is thereby divided in half. In each daughter cell a spherical daughter nucleus,
which contains the chromatic substance of four daughter chromosomes (ch), has
arisen from half of the spindle. By each daughter nucleus (k) lies a centrosome (c).

298 EMBRYOLOGY

the mother star. Each chromosome then begins to split longi-
tudinally into two identical parts, the two daughter chromosomes
(Figs. 3, 4, 5, ch). We are justified in seeing in this the true task of
the complicated nuclear division, as the two halves now move away
from one another toward the opposite ends of the nuclear spindle
(Fig. 5, chl and ch?} and form the two daughter stars, which after
the division of the cell in two parts form in each the basis of a
daughter nucleus. These promptly return to the spherical form.

Extended comparative observations in the most widely separated
classes of animals have demonstrated a definite numerical law in the
chromosomes. It states: In all cells of an animal or plant species
the same number of chromosomes always arise during a division
of the nucleus. In one species four, in another twelve or sixteen or
twenty-four, etc. The number of chromosomes is four only in one
variety of Ascaris. For this reason, and because the few chromo-
somes are at the same time of very considerable size, the eggs of the
horse roundworm are of great advantage for studies in the question
which now concerns us.

These remarks with regard to the phenomena of nuclear division
must first be made, in order to understand the progress which has
been brought about by the study of Ascaris eggs in the remarkable
investigations of van Beneden, which immediately followed the
excellent work of Boveri.

Two fundamental facts were discovered concerning the behavior
of the chromatin in the ^.scan's egg (Diagram in). One of these
facts concerns the process of fertilization. Egg- and sperm-nuclei
(Fig. 5, eik and sk) remain, in the egg of Ascaris, separated from
one another for several days, and prepare themselves separately
for the formation of the first karyokinetic spindle. From the chro-
matin network, chromosomes arise in the way described above,
two in the egg-nucleus (Fig. 5, wch), two in the sperm-nucleus (mch).
We can thus easily follow their fortune in the further stages of di-
vision, and determine that of the four chromosomes of the nuclear
spindle, two arise from the egg-nucleus, two from the sperm-nucleus.
When the chromosomes split longitudinally, in the stage of the
mother star, we see their products, the daughter chromosomes, sepa-
rate from each other, in the way described above (Fig. 7, wch and
mch), to form the daughter stars, and finally enter into the forma-
tion of the daughter nuclei of the two new cells. In this case incon-
trovertible proof has been brought that in the first division of the
fertilized egg an equal amount of chromatin from the egg-nucleus
and the sperm-nucleus is brought to each of the daughter nuclei.

This process apparently repeats itself in every later division,
so that finally the nucleus of every tissue cell is composed of equal
amounts of chromatin of maternal and paternal origin, which has

GENERATION AND INHERITANCE

Fig.l. Fig.Z.

sp

299

DIAGRAM III. The process of fertilization, the formation of polar cells and the first
division of an egg of Ascaris megalocephala bivalens.

FIG. 1. The egg at the moment of fertilization. It shows still a spherical nucleus
(kb) in which the chromatic substance is arranged in two groups of four (tetrads,
ch). The spermatozoon, shaped like a tailed sphere, has pressed halfway into the
egg. Its nucleus (k) is composed of two chromosomes.

FIG. 2. From the spherical nucleus a spindle with two tetrads has arisen (ch).
The spermatozoon (s) has pressed into the middle of the egg.

FIG. 3. At the animal pole of the egg, where the spindle lay in Fig. 2, the first
polar cell (pzl) has been formed by budding. It receives from each tetrad of the
spindle two chromosomes connected in pairs (a dyad), while the other two chro-
mosome pairs (ch) remain behind in the egg with the half spindle (sp). The
spermatozoon (sk) begins to dissolve, except the nucleus, which begins to become
spherical.

FIG. 4. In the same way as the first the second polar cell is formed by budding
(/>22). From each of the pairs of chromosomes (Fig. 3, ch) of the previous stage,
a chromosome comes to live in the second polar cell, while the other remains behind
in the egg and forms the egg-nucleus (eik), which then contains two chromo-
somes, as does the spermatazoon (sk).

FIG. 5. Egg- and sperm-nucleus approach each other until they touch, but do
not unite. In order to distinguish their chromosomes those of the egg-nucleus are
drawn as a white circle (wch), those of the sperm -nucleus as a black circle (inch),
as was done in the previous Figs. 1 to 4.

FIG. 6. Egg- and sperm-nuclei have together formed a spindle of whose four
chromosomes half (wch) arise from the egg-nucleus, the other half (mch) from the
sperm-nucleus. The polar cells, as m Figs. 7 and 8, have been omitted.

300

EMBRYOLOGY

Rq. 7. «<*

FIG. 7. The female aua male chromosomes of Fig. 6 have divided longitudinally
and separated from each other in two groups of daughter chromosomes: (sp)
spindle; (c) centrosome.

FIG. 8. The two halves of the egg contain daughter nuclei, half of whose chromo-
somes arise from the egg-nucleus, half from the sperm-nucleus.

been constantly increasing by growth. Of course the equal division
cannot be determined later by direct observation, as is the case in
the first division, but after what we know of the nature of nuclear
division this view may be considered in the highest degree probable.

Still more important is the second fact determined on the Ascaris
egg. The chromosomes of the egg- and sperm-nuclei are an excep-
tion to the above-mentioned numerical law. Whereas in Ascaris
megalocephala bivalens four chromosomes always arise from the
resting nucleus, only half as many, that is, two, occur in the egg- and
in the sperm-nuclei (Figs. 4, 5, eik and sk). How is this exception
from the numerical law to be explained? How is it brought about?
A very accurate study of the method of origin of the polar cells,
as is possible in Ascaris, gives a satisfactory explanation.

Some time before the origin of the polar cells remarkable changes
occur in the contents of the nucleus which justify the great con-
sideration which they have received, and which have been the
object of extended investigation. In this variety of Ascaris four
long threads arise from the chromatin network and split longitud-
inally into double threads before the height of karyokinesis, the
usual time of splitting. These threads immediately place themselves
across each other, and thus produce, while gradually becoming
shorter, a tetrad of chromosomes, a stage which has been shown
in the development of many species of animals. When now the
nucleus dissolves and the first polar spindle is formed from its
contents, the eight chromosomes arrange themselves in the middle,
in two tetrad groups. Later each tetrad group, of the first polar
spindle, separates into two groups of chromosomes, connected in
pairs (Fig. 3) , or in other words, each tetrad divides in two dyads,
of which one passes into the first polar cell (pzT), the other passes
into the egg.

GENERATION AND INHERITANCE 301

And now there occurs a second striking variation from the usual
process of nuclear and cell-division. While otherwise, after division,
the nuclear substance always passes for a time into the spherical
resting state, here it immediately prepares itself for a second divis-
ion, which leads to the cutting-off of a second polar cell. The half
of the first polar spindle remaining in the egg (Fig. 3, sp) immediately
enlarges itself into a second complete spindle, in whose middle the
two dyads lie. These immediately separate into their individual
dements, of which two are taken up into the second polar cell
(Fig. 4, pz"*), and two remain in the egg, and here form the basis of
the egg-nucleus. Thus of the entire chromatin mass of the egg-
nucleus which was divided into eight chromosomes, the mature egg
only contains the fourth part, that is, from each of the two tetrads
only one single chromosome (Fig. 4, eik, ch). Instead of once, as
in usual cell-division, the chromatin has been divided twice by two
polar divisions; in other words, it has been quartered. Therefore,
the egg-nucleus only contains half as much chromatin as the nucleus
of an ordinary tissue-cell or an embryonal cell. Immediately after
each division, it is, to a certain extent, only half a nucleus, and as
such is an exception to the numerical law of chromosomes. Weis-
mann has called the whole process, by which is effected the reduction
of the nuclear mass and the number of chromosomes to half, a "re-
duction division."

As the sperm-nucleus in Ascaris only possesses half the number
of chromosomes of a normal nucleus, the conclusion may be drawn,
that in it also a reduction must have occurred, as occurs in the
egg by the formation of the polar cells. By such consideration, I was
led to seek for a corresponding process in the formation of sperm,
which premise showed itself as correct.1

As an accurate comparison of the egg- and sperm-formation in
Ascaris shows, there exists in the two a complete parallel, which
may be followed into the smallest detail. The unripe egg with a
spherical nucleus, the egg mother cell or ovocyte (Diagram m,
Fig. 1), corresponds to the sperm mother cell or spermatocyte
(Diagram iv, Fig. 1), as each undergoes a reduction by the forma-
tion of polar cells. Also the chromatin arranges itself in the nucleus
in this extremely characteristic way which is observed nowhere ex-
cept in sexual cells in two groups of four each (Diagram iv, Fig. 1 ch.)

1 Even before my investigation Platner determined by a study of the process of
sperm-formation in Lepidoptera and Pulmonata a reduction process in the sperm-
nuclei, although in a less striking and less comparative way. He drew the conclusion
"the spermatocytes correspond to the ova. In both cases a reduction of the
chromatic substance to a quarter of its original quantity occurs, while a second
division follows immediately on the first without a period of rest between." (Plat-
ner, On the Meaning of the Polar Bodies, Biologisches Centralblatt, vol. vui, p. 193,
1889, and Contributions to the Knowledge of the Cells and their Division, Arch, fur
mikrosk. Anat., vol. xxxin, 1889.)

302 EMBRYOLOGY

Then the sperm mother cell is split up by two divisions, which follow
upon one another without a resting stage being interposed, first
into two daughter cells (Fig. iv), and immediately by a second di-
vision which causes the actual reduction into four granddaughter
cells of equal size. By these processes, each of the two tetrad groups
(Fig. 2, ch, and Fig. 3) divide into two pairs of chromosomes, which
are shared by the two daughter cells (Fig. 4). Then each pair of
chromosomes (Fig. 5, ch) falls again into its individual elements,
which are taken up by the granddaughter cells (Fig. 7). These,
therefore, contain, as does the mature egg and the polar cells, only
a single chromosome from each tetrad group, altogether only two
(Figs. 7, 8). Their nuclei are, therefore, reduced to half-nuclei.

Many will have asked, what aim this noteworthy reduction of
the chromatin, which constitutes the important process of egg- and
sperm-ripening, may have. The explanation is easily seen if we
consider, in connection with the chromatin reduction, the succeed-
ing fertilization, and consider that by this a second nucleus is brought
into the egg, which combines with the egg-nucleus and thus doubles
its chromatin mass. Thus from two half-nuclei a complete nucleus
is again formed, from which then arise all the nuclear generations
of the new being. Thus ripening and fertilization of the egg stand
to one another in a supplemental relation. That fertilization is
needed to replace the chromatin reduction may be proved by a con-
sideration.

As the numerical law of the chromosomes has taught us, chro-
matin is a substance which shows a tendency to be constant in a
given species, not only in relation to its mass, but also in regard to
the number of chromosomes in which it splits during karyokinesis.
Thus it is a substance which after cell-division increases to the
double and is then halved by division, etc. If we now consider that
the process of reduction did not occur, then by fertilization two
complete nuclei would be united, and the result would be a doubling
of the chromatin, in relation to the normal. By every new sexual
generation the same process would be repeated, and thus in the
course of generations a summation of nuclear substance would be
brought about, which in a short time would lead to such a lack of
relation between it and the protoplasm, that the contents of a cell
would no longer have room for it.

Led by similar considerations we may say: By the reduction
which precedes fertilization the summation of the nuclear mass and
the number of chromosomes to the double and multiple which is
normal for the species under consideration, is hindered in the sim-
plest way possible.

Thus, the phenomenon of reduction is a general biologic law of
the greatest value. What has been observed in one species of animal

GENERATION AND INHERITANCE 303

has gradually been confirmed in numberless other cases, in verte-
brates and invertebrates. And time and again that which we have
already seen has been repeated. These discoveries of the embryo-
logists placed new problems before the botanist, which he imme-
diately seized and solved. In the sharper position of the question
which was now possible, phenomena were gradually observed in
the Phcenerogamia and Cryptogamia, which, although no tso easily
explained as in the animal kingdom, showed that, in the develop-
ment of the vegetable sexual products, a reduction process by nu-
clear divisions following close upon one another, also occurred. Even
in Infusoria and different sorts of lower unicellular organisms, cor-
responding processes have been observed.

We have reached in the realm of the study of generation a position
which has been attained to the same degree in the study of very
few of the other complicated phenomena of life. We can unite many
facts in a few general laws which possess value for the entire or-
ganized world and for which we can use the expression "law" with
the same justification and in the same sense as physicists and chem-
ists in their determinations of law-abiding phenomena of lifeless
nature. In a few decennaries discoveries have been made, which,
supplementing each other, have been connected with each other,
and have deepened in an unsuspected way our knowledge of gener-
ation.

And as the middle point of these discoveries there stands a well-
characterized substance, which is contained in a small amount in
the nucleus of every cell, and whose striking changes during cell-
division have drawn upon it the attention of biologists, the chroma-
tin. That this wonderful substance must have a great importance
in the life of the cell is hardly to be doubted after the foregoing
experiences. Let us attempt to penetrate somewhat deeper into
its importance. We are hereby brought back to the important pro-
blem of inheritance upon which I already touched in connection
with the demonstration of fertilization, but had retained for later
mention. If the egg- and sperm-cell conveys to the new being
the properties of the father and mother, how does it come about,
we may ask, that these share in the process to such an unequal
degree, as the egg gives to the new being one hundred or one thou-
sand times more substance than the insignificant spermatozoon?
Naegeli, in his book Concerning the Mechano- Physiologic Theory
of Generation, which is very rich in ideas, has attempted to answer
the question by theoretic discussion, by the view that the sexual
cells consist of different substances, which possess a different value
for the inheritance of parental characteristics. The important sort
he designates idioplasm.

Idioplasm is a purely hypothetic conception, for Naegeli himself

304 EMBRYOLOGY

has not stated what substance in the cell is actually the idioplasm.
A real basis must therefore first be won by empiric investigation.
This occurred contemporaneously and independently by Stras-
burger and myself; Weismann, Kolliker, and others soon followed.1

Proceeding from the facts of karyokinesis, of fertilization and
maturation, I concluded that the substance of the nucleus, and here,
especially the chromatin, corresponded to the idioplasm of Naegeli.
Three important considerations appeared to me to point in this
direction.

First: The chromatin is the only substance known to us which
occurs in exactly equal amount in the sperm- and egg-cells. As a
proof 1 will recall briefly the already mentioned brilliant discovery
of van Beneden, according to which the egg- and sperm-nuclei of
Ascaris megalocephala bivalens contain the same number of chromor
somes, that is, two, which are of equal size.

Second: the fact that the chromatin is the only substance which
passes over in equal quantity from the mother cell to the daughter
cell, after it has doubled its volume by nourishment and growth.
The complicated process of karyokinesis evidently serves only for
this purpose. The arrangement of the chromatin particles in threads,
the division of the chromosomes longitudinally, the distribution
of their split halves toward the poles of the spindle, and the equal
distribution in the daughter cells.

Thus, this substance, in which rests the peculiarity of the organ-
ism, is carried down from one cell generation to the next as a valu-
able inheritance, and thereby is the principle by which every cell
of the organism is "idioplasmatically enabled," as Naegeli expresses
it, to become the germ of a new individual. Here also numerous
phenomena of generation and regeneration find their explanation.
For in many plants and lower animals we see that actually almost
every small cell complex separated from the rest of the organism
is able to reproduce the whole. From the root-cells of a plant, buds
may form, to reproduce the aerial part, and from the stem-root, cells
may develop, as is seen in slips. This is because, in cells, which
during the course of development have adapted themselves for a
certain function, the deposits contained in their inherited mass are
still slumbering, and may be newly awakened and forced into a
definite development.

Thirdly and finally, we may base our opinion upon the chroma-
tin reduction. I might denote this as a proof of the justification of
the theory. Without having known of the finer processes which
occur during the formation of the polar cells, Naegeli had already

1 I have given the different historical and critical opinions, in regard to the
theory of fertilization and inheritance, in my article Comparison of Egg and
Sperm Formation in Nematoda, Arch, fur mikrosk. Anat., vol. xxxvi, pp. 77-127,
1890, and in Zeit. und Streitfragen der Biologie, vol. i, p. 16, 1894.

GENERATION AND INHERITANCE

305

Fig. 9.

DIAGRAM rv. Spermatogenesis, or development of the seminal bodies from the
seminal mother cells (spermatocytes) in Ascaris megalocephala bivalens.

FIG. 1. Seminal mother cell with a nucleus (k) in which two tetrads (di) have
formed. Centrosome (c) with rays.

FIG. 2. Seminal mother cell from the nucleus of which a spindle (sp) with two
tetrads has developed. Centrosome (c).

FIG. 3. Spindle in which each tetrad has divided into paired chromosomes (dy-
ads).

FIG. 4. The seminal mother cell is divided into daughter cells (tz) each of which
incloses a spindle with two pairs of chromosomes (dyads) (ch). The centrosome
(c) has divided into two daughter centrosomes between which a small new spindle
is formed.

FIG. 5. The new spindle (sp) in each daughter cell has enlarged and included
the two pairs of chromosomes (ch1 and chj).

FIG. 6. In each spindle the pairs of chromosomes have separated from one
another and approached the poles of the spindle.

FIG. 7. The two seminal daughter cells have divided into four granddaughter
cells (e2),each of which includes only two chromosomes (one element of the tetrad
of Fig. 1) and one centrosome.

FIG. 8. The two chromosomes of the granddaughter cells (ez) have flattened
against each other eventually to form one small, compact, spherical nucleus (k).

FIG. 9. Each granddaughter cell changes into a seminal body (sp) conical in
shape. Nucleus (k).

306 EMBRYOLOGY

shown the necessity of a reduction process from purely theoretic
considerations. He said: "If, in every propagation by fertilization,
the volume of the idioplasm, however constituted, doubles itself,
the idioplasm body would be so much increased, after several
generations, that it could no longer find room in a spermatozoon.
It is thus absolutely necessary that indigenous propagation the union
of the parental idioplasm bodies occur without causing, by the united
mass, a corresponding increasing growth of this material."

The process suspected by Naegeli was soon after discovered in
the development of the polar cells, which, however, were first ex-
plained in another way by their discoverer himself, Ed. van Beneden,
and were first recognized by Weismann as the process by which a
summation of the parental mass as a result of fertilization was pre-
vented. Weismann agrees with Naegeli that reduction was so cer-
tainly required by theoretic considerations that the process by which
this occurred must be found if it were not contained in already
known facts. I, however, doubt as little as does Weismann that
the reduction of the idioplasm, which is theoretically demanded,
occurs by the formation of polar cells.

When one fact thus agrees with another, which is very rare in
this way in biologic processes, we may certainly say, in spite of the
objections raised by several investigators, that the idioplasm of
Naegeli is found in the chromatin of the cell-nucleus, and that this
hypothesis is adapted in a high degree to serve as a starting-point
and leading star.

How many questions whose solutions in part we are already
beginning to determine, which in part wait upon the future, force
themselves upon the investigator !

Does an actual penetration of the. two idioplasms occur during
the union of the egg- and sperm-nuclei, or do they remain alongside
of one another, temporarily or permanently ? and in corresponding
way, how does the reduction process act? To how many ques-
tions, again, the origin of female and male sex and the generation
of bastards gives rise! May we find a morphological basis by the
study of the sexual production of bastards for the law of Mendel,
which has been confirmed in great part by recent investigations of
Tschermak, Correnz, and De Vries on bastards ?

And what a perspective the following consideration opens! If
the chromatin is the substance by which the peculiarity of each
organism is determined, it must be of somewhat different composi-
tion in each of the numberless organized species. In the insigni-
ficant mass of an egg-nucleus, or a sperm-nucleus in the head of
a spermatozoon, only visible under the microscope, the numberless
peculiarities by which one species is separated from another are
compressed in their elementary forms. Will human intelligence

GENERATION AND INHFJEUTANCE 307

ever succeed in penetrating into this world of the smallest organic
differences, which are now invisible to us? Will, in the future, the
means of investigation of the biologists, perhaps the discovery of
a more powerful microscope and the mastery of the same, increase
the circle of vision of our successors as much as was done by the
discovery and mastery of the compound microscope?

Or, will the chemist succeed in so increasing his knowledge of th'e
nature of proteid bodies that we may expect valuable conclusions
in regard to the nature and difference of idioplasm, that is, the
chromatin substance, from this direction? Who will dare to deter-
mine where, and how far away, a limit may be set to the possibility
of human knowledge ?

Far, far away lies in any case the goal, shimmering before us in
the distance. For its attainment the individual branches of natural
science, from to-day on, must have united themselves, by extension
of their borders, to a great united science of nature, as the leading
spirits are now trying to consummate. For the investigator who will
busy himself with this deepest problem of life must unite in one
person biologist, chemist, and physicist, and must master the depths
of each of these sciences.

In looking so far into the future, with its unlimited possibilities,
we may well repeat the words with which our great teacher, Carl
Ernst von Baer concluded the preface to his Embryology of Ani-
mals: "Until then there will still be a prize for many. The palm,
however, will be carried off by that fortunate one for whom it is
reserved to refer the active power of the animal body to the general
laws of life of the world whole. The tree from which his cradle will
be fashioned is not yet planted.'''

INDIVIDUAL DEVELOPMENT AND ANCESTRAL
DEVELOPMENT

BY WILLIAM KEITH BROOKS

[William Keith Brooks, Henry Walters Professor of Zoology, Johns Hopkins
University, b. Cleveland, Ohio, March 25, 1848. A.B. Williams College; LL.D.
•ibid.; Ph.D. Harvard College; LL.D. Hpbart College. Associate Professor and
Professor, Johns Hopkins University, since 1877. Member of the National
Academy of Sciences; American Academy of Science; American Philosophical
Society. Author of Foundations of ZoSlogy; Scientific Results of the Voyage of
H.M.S. Cliallenger. Editor of Memoirs of Biological Laboratory, Johns Hopkins
University.]

NEAR the end of the last century, zoologists of a speculative turn
were asking whether the changes that make up the history of species
are induced by the external world, or are inherent in germ-cells and
the living beings that arise from them. We had been told by Haeckel
that the inheritance of acquired characters is a necessary axiom of the
monistic creed, and, by Weismann, that acquired characters never
are, and never can be, inherited, because the architecture of germ-
plasm forbids.

So the dispute went on, in the good old a priori way, with no sign
of any end except an armed truce, until wise and prudent zoologists
resolved to stop disputing and get to work.

One of the fruits of this resolution was a wonderful series of obser-
vations and experiments upon the behavior of eggs and embryos
under abnormal conditions, the results of which are so instructive,
and so full of food for reflection, that they mark an epoch in the his-
tory of embryology, making one of its most notable chapters. In so
far, the resolution to cease from arguing, and to get to work, has been
altogether good, although one need read but little in the current
literature of embryology to find that we have not succeeded in laying
aside speculative questions. Many embryologists are now asking
whether the cell-differentiation which takes place during individual
development is inherent in eggs or their chromatin, or induced by the
interaction between the constituents of the egg, and between cell and
cell, and between the developing embryo and the external world.

The dispute that was laid aside as vain and idle was whether the
development of species is inherent or acquired. The new question
is whether individual development is innate or superadded; but the
distinction is only a verbal one because that which is true of individ-
uals is also true of them when considered collectively.

Some embryologists tell us that each cell that enters into the com-
position of a multicellular organism is a complete representative of
the species, having the same constitution and the same significance

INDIVIDUAL AND ANCESTRAL DEVELOPMENT 309

in inheritance as the fertilized egg; that each cell has the constitu-
tion which is characteristic of the species; that it .might, under proper
conditions, have become a germ-cell, or any one of the various cells
of the body, because the substance of inheritance is transmitted
equally to all cells.

According to another view, a germ-cell is the only complete and
independent representative of the species, since the substance of
inheritance is held to be contained, in its completeness, in no cells
except those that are predestined to produce new organisms, while
the ordinary tissue-cells are held to be absolutely and inevitably out
of the line of descent to future generations, because they contain only
so much of the substance of inheritance as is necessary for trans-
mitting the hereditary characteristics of these cells and their pre-
destined descendants.

I believe that a little study of the word inheritance will show us an
easy way out of these paradoxes, and I do not believe I could make
a better use of my hour, or one that would do more to promote re-
search in embryology, than to point out how far the dispute is a
verbal one. So far as the word is used inductively, it means the
resemblance of child to parent, of descendants to ancestors, while
the difference between child and parent is called variation. These
words are also used, metaphorically, to designate the cause or the
explanation of the resemblances and differences between descendants
and ancestors, just as gravitation is used metaphorically to designate
that which makes things gravitate, and geotropism that which makes
roots grow downwards, and selection that which brings about sur-
vival in the struggle for existence. In what I have to say, I shall
restrict myself to the inductive meaning of these words, for I know
that your minds and your words are so free from the bonds of meta-
physics that you know we accomplish nothing by asserting that
heredity makes beings inherit, or that variation makes them vary,
or that selection selects.

Let us, therefore, consider the word inheritance as a term to desig-
nate the resemblance between parent and child. You all know that
while the descendant does, on the average, resemble its ancestors and
collateral relatives more than it resembles anything else in nature,
it is never identical with them. We say, in our careless way, that
organisms exhibit specific identity behind, or in spite of, their in-
dividuality, when we mean that, while they resemble their parents,
they are different from them. This diversity in unity is true of all
natural objects, but it is most notable and impressive in familiar
living beings, in our friends and acquaintances, in our dogs and
horses, and in the plants that we tend with our own hands. We may
think of the casual stranger on the street, or the unknown citizen of
Timbuctoo, or the stalks in the corn-field that we pass in the train,

310 EMBRYOLOGY

as representatives of species, and nothing more, but all the living
beings that we know practically, we know as individual members of
their kind. We may, for our own purposes, and in our minds, consider
their kinship apart from their individuality, but this does not show
that they are separable in fact. Living beings do not exhibit unity
and diversity, but unity in diversity. These are not two facts, but one,
and the separation is in our minds, or our words, and not in nature.
The delight of intimate acquaintance with animals is due to the in-
separableness of their specific unity from their individuality, and our
attempts to separate, in our minds, what is not separable in fact,
lead us to two narrow and partial views of the facts, two crude and
imperfect mental concepts, neither of which corresponds to anything
in nature.

All this is familiar, but I ask you to reflect upon it; to decide for
yourselves whether it does not mean that inheritance, or resemblance
to ancestors, and variation, or difference from ancestors, are only
imperfect mental concepts, crude ideas, and not facts; whether the
fact is not the individuality in kinship of living beings. Each of you
must answer this simple question for himself. I cannot regard them
as facts, since they seem to me to be only imperfect ideas of facts;
mental states which we have reached by fixing our attention upon
a partial and uncritical view of our sensations and perceptions, to the
neglect of that which has not interested us nor seemed to concern us.

If you agree with me that resemblance to ancestors does not exist
in nature apart from individuality or difference from ancestors, that
inheritance is not a fact, but only an imperfect idea of a fact, admitting
of correction and improvement by comparison with nature, and in
no other way, — if you agree to this, what becomes of the notion of
a substance of inheritance? There is, no doubt, a material equivalent
for every idea, but the material equivalent for the notion of a sub-
stance of inheritance is in the brain of the speculative philosopher,
and not in germ-cells. St. Paul says faith is the substance of things
hoped for, the evidence for things not seen, but in science the evi-
dence for things not seen is to be sought by using our eyes, and I can
discover no basis for the notion of a substance of inheritance except
faith, because inheritance seems to me to be a term to designate a
narrow and imperfect view of facts, and not itself a fact.

I hope you will not accuse me of opposing the scientific study of
inheritance and variation, for nothing is farther from my thoughts.
The resemblances and differences between ancestors and descendants
are as worthy of study as arithmetic, which has been of inestimable
value to mankind, although there is, in nature, no quantity without
quality. We cannot make any progress in natural knowledge without
fixing our attention upon some narrow and imperfect view of nature,
to the temporary neglect of that which does not interest us, but things

do not cease to be because we ignore them. The paradoxes into which
the biologists fall, in their efforts to locate the substance of inherit-
ance, remind me of the perplexity of the school-boy, who, having tried
to add together six cows and nine horses and four apples, wonders
whether the result is horses or cows or apples. If he were to attribute
the virtue of arithmetic to a substance of numeration, and to wonder
whether it resides in apples or in cows, he would be still more like
those who speculate about the location of the substance of inheritance.

If you choose to declare that my contention that inheritance is not
a fact is a metaphysical subtilty, I cannot help it. Call me a metaphy-
sician if you will. Hard words cannot hurt me, nor need they scare
me. But may it not be the speculative zoologist, who hunts in germ-
cells and in chromatin for the material support of the imperfection
of his ideas, who is the real metaphysician, and not I, who plead for
nothing but the correction of our judgment, and its reduction to
exactness, by comparison with nature?

Some embryologists tell us that all the cells that enter into the
structure of a multicellular organism are inherently identical with
each other, and with the fertilized egg, in their constitution, and in
the possibilities of their development. Each, we are told, might have
replaced any other if it had been exposed to the same conditions, and
might have become a germ-cell under proper conditions. According
to this view, cell-division is always division into parts that are iden-
tical with each other, and with the cell that gave rise to them, and it
is only because they are exposed to different conditions that cells
become specialized and differentiated during development, and not
because there is any inherent difference between them. According
to this way of looking at individual development, any attempt to
account for it by the imaginary architecture of the germ or of its
chromatin is idle, because the architecture of the organism does not
exist in the germ, since it is the resultant of the reciprocal interaction
between the germ and the developing embryo with the conditions
of their existence. You will permit me to say that, with certain quali-
fications and reservations, this view of the nature of individual
development commends itself to me as a step in the right direction.
The correlation between the normal development of one part of the
body and the development of other parts is a familiar fact. The
changes that take place in the habits and the plumage of certain
birds, as the reproductive organs become functional on the approach
of the breeding-season, are known to all, as is also the arrest of these
changes when the reproductive organs are removed or aborted by
disease. The awakening of the body into full and rounded perfection
which comes with the functional maturity of the reproductive organs
is so notable in our most familiar mammals that it has come to be
regarded as the typical illustration of the correlation between de-

312 EMBRYOLOGY

velopmental changes in one part of the body and similar changes in
other parts, although this is, no doubt, an important factor in all
development. Other well-known facts, such as the development of
a bud into a leaf-shoot under certain conditions, and into a flower-
shoot under others, lend support to the doctrine that there is a cor-
relation between the history of each cell and its interactions with
other cells, but the doctrine that cell-division is always division into
like parts, and that it is the internal environment of each cell that
calls out one of its possibilities and leaves the others latent, is not
in itself an answer to the question why, as the egg develops into
ar> embryo, its cells find themselves in a little world of their own
making, which is so much like that in which their ancestors developed
that the end-product is an individual fitted for the normal life of its
kind.

This seems to me to be the real problem of embryology. The ex-
ternal world of a hen's egg in an incubator is the same as that of the
duck's egg beside it. So far as the duckling and the chick owe their
fitness for the world into which they are to be born to mechanical condi-
tions, they must owe it to conditions which they find within the egg, or
make there for themselves, through their own activity as living beings.
So far as the nutritive and chemical changes that go on in the hen's
egg, the effects of gravity and pressure, of the interaction of cell and
cell, of organ and organ, are more like those under which ancestral
hens developed than they are like those under which ancestral ducks
developed, this must be due to a characteristic difference between
the interactions of a chick and those of a duck. While it is, no doubt,
in the interaction between the living organism and the world around
it that life consists, this does not, in itself, tell us why the internal
environment of the cells of the developing chick is so much like that
of ancestral embryos that the end-product is fitted for the life of
fowls.

The hypothesis we are considering is inadequate in so far as it fails
to consider the truth that the development of the chick, or that of
the human infant, or that of any other organism, is a preparation for
a test that is to come later, in the struggle of life: since the most
significant fact in the reciprocal interaction between the developing
organism and its -environment is that it is a preparation for its inter-
action, at a later period, with an environment of competitors and
enemies. So far as the origin of an individual organism, fitted for the
state of life into which it is to be born, is in question, the orderly
unfolding, by the interaction between a germ and its internal environ-
ment, of all the stages which made up the ancestral environment for
epigenetic development, in due succession and order, seems to be more
like evolution than epigenesis, unless, indeed, there is something in
this interaction which we have not yet considered. Unless we can find

INDIVIDUAL AND ANCESTRAL DEVELOPMENT 313

an epigenetic explanation of the specific constitution with which the
germ begins its development, I do not see how we can account for the
facts of individual development from the standpoint of epigenesis.

The hypothesis we have been considering has much to commend
it, and it is, no doubt, a step in the right direction. Inasmuch as it
emphasizes the familiar truth, so often forgotten by speculative zoo-
logists, that a living being is no metaphysical abstraction, no self-
sustaining, self-sufficient entity, no thing in itself, but a natural body
in a natural world, of which it is a part, and with which it is in continual
reciprocal interaction, — so far as it carries our vagrant minds back
from metaphysics to this great scientific truth, — it seems to me to
be altogether good; for the amount of idle speculation which has
sprung from neglect of this truth is appalling. I ask your attention
to it because I shall have more to say about it. It has been a familiar
thought with me for nearly thirty years, not because of any original-
ity of my own, but because I learned it from the study of the Origin
of Species. I have lost sight of it now and then, amid the paradoxes
and perplexities of speculative biology, but I have found them to
vanish like mist before the wind so soon as I recalled it; so I ask you
to bear in mind, at least for the rest of my hour, that a living being
is no self-sufficient whole, but a natural body which is part of a
natural world, and that this truth is no metaphysical subtilty, but
a fact.

So far as it insists upon, and is based upon, this important truth,
the hypothesis we have been considering seems to me to be sound
and valuable. Inasmuch as it fails to consider the truth that indi-
vidual development is a preparation for the struggle of life, it seems
to me to be only a partial and imperfect account of individual de-
velopment.

It is not the only view that has advocates. You know what a prom-
inent place in literature the doctrine of germ-plasm has held. Accord-
ing to this doctrine, individual development is the unfolding of the
organization that preexists in the germ. With qualifications which
need not detain us, it is the doctrine that the species resides, in its
completeness, in no cells except germ-cells, and that differentiation
is due to the differential distribution of the substance of inheritance,
each cell being held to receive only so much of this substance as bears
its hereditary qualities and those of its predestined descendants. So
far as it deals with individual development, its essential feature is the
definitiveness of cell-division, for it is based upn the opinion that the
ordinary tissue-cells are utterly and completely cut off from posterity
because no cell except a germ-cell contains all the hereditary qualities
of the species.

I shall not discuss this doctrine in detail, because it seems to me to
arise from neglect of the truth that neither a germ-cell nor any other

314 EMBRYOLOGY

cell is a self-sufficient whole, and because I cannot conceive how a
new species can arise if this view is well founded. As is a tissue-cell
to a germ-cell, so is a germ-cell to ancestral germ-cells. If tissue-cells
are out of the line of descent to new generations, and predestined for
their parts in individual history, so must germ-cells be predestined
for their parts in ancestral history, and out of the line of descent to
anything strictly new; but the notion that the conduct of the breeder
of carrier-pigeons and fantails and tumblers was predestined in the
germ-plasm of the rock pigeon carries Calvinism to giddy heights that
I cannot scale.

Other zoologists tell us that, since the germ-cell is formed by a pro-
cess which may be regarded as modified fission, it is fundamentally
symmetrical with the body that produced it, and its axes and poles
coincident with those of the parent, so that it is practically equivalent
to a complete organism from the first, so far as its stereometry or
promorphology is in question. This doctrine may, perhaps, rest on a
basis of fact, but it gives no account of the stereometry of the parent.

Others, who agree that the organism is a unit, a complete whole,
a specific being, from the egg onwards, assert that, while cellular differ-
entiation may enable us to infer organization, it is a serious error to
regard it as the measure, or the means, of organization; that the egg
is young organism, and not a mere germ that is to become an organ-
ism; that there is no qualitative or essential difference between an
unicellular and a multicellular organism, between an unicellular
germ and the being that arises from it; and that, while complexity
increases as development progresses, division into cells is not the
means, but only the indication of its progress. There seems to me to
be a basis of truth for this doctrine also, but when its advocates tell
us that the species is contained in the hen's egg as completely as it
is in the hen, their words seem to me to be meaningless, because I
have learned from Darwin that the species is neither in the egg nor in
the hen, since it is in that reciprocal interaction between the living
being and the world around it which I have learned to call the struggle
for existence.

Thus the current literature of embryology brings us back to the
question we had agreed to lay aside, whether development is inherent
in the egg or induced by the conditions of its life.

It may interest you to know what an old question this is. More than
two hundred and fifty years ago, that great man of science, William
Harvey, declared his intention to "seek the truth regarding the follow-
ing difficult question : Which and what principle is it whence motion
and generation proceed? Whether is that which, in the egg, is cause,
artificer, and principle of generation, innate or superadded? Whether
is that which transfers an egg into a pullet inherent or acquired?
In truth," says he, "there is no proposition more magnificent to

INDIVIDUAL AND ANCESTRAL DEVELOPMENT 315

investigate, or more useful to ascertain, than this: How are all
things formed by an univocal agent? How does the like ever gen-
erate its like? Why may not the thoughts and opinions now preval-
ent many years hence return again, after an intermediate period of
neglect?"

Summing up the results of his investigation of this magnificent
proposition, which occupied him for many years, he says: "It appears
clear from my history that the generation of the chick from the egg
is the result of epigenesis, and that all its parts are not fashioned
simultaneously, but emerge in their due succession and order. For
the part that was at first soft and fleshy, afterwards, without any
change in the matter of nutrition, becomes a nerve, a ligament, a
tendon; what was a simple membrane becomes an investing tunic;
what had been cartilage is afterwards found to be a spinous process of
bone, all variously diversified out of the same similar (homogeneous)
material."

It is more than two hundred and fifty years since this proof was
given that, so far as it is discoverable by our senses, individual de-
velopment is epigenesis, or new formation, and not the unfolding of
the preexistent; yet, dissatisfied with facts, we go on hunting, with
what we call our mind's eye, for an invisible substance of inherit-
ance, holding that development must be evolution in essence, however
epigenetic it may appear to sense.

If I venture, at this late day, to point out that ancestral develop-
ment may be as epigenetic, from beginning to end, as individual de-
velopment, and that the species for which we are seeking is not, and
cannot be, in the germ, I do so because this proof is neither new nor
original with me. It is so old that many "up-to-date" zoologists
tell us it is antiquated, abandoned, no longer worthy the attention of
advanced thinkers.

According to this view, the species is not in chromatin, nor in
germ-cells, nor in differentiated cells, nor in living beings at any stage
of existence, nor in the conditions of existence, because it is in that
reciprocal interaction between the organism and the rest of the natural
world which has been called the struggle for existence. Neither the
stability of species nor the mutability of species is in living beings,
because it is through extermination in the struggle of life that the
type is kept true to its kind, and also through this struggle that it
becomes changed.

You will note that it is as great an error to locate species in the
external world as it is to locate it in germ-plasm. It neither exists
in the organism nor in the external world, because it is in the recip-
rocal* interaction between the two. The biological types, of which
those who call themselves statistical biologists tell us, are neither
external standards to which living beings approach and from which

316 EMBRYOLOGY

they recede by variation, nor are they standards fixed in living
beings by inheritance.

No two objects, alive or dead, ever are exactly alike, and as we
all know that life is a struggle, and admit the diversity of nature,
neither the stability of species nor the mutability of species is any-
thing more than we might expect. Inheritance and variation are
not two things, but two imperfect views of a single process, for
the difference between them is neither in living beings nor in any
external standard of extermination, because it is in the inter-
action between each living being and its competitors and enemies
and sources of food and other necessaries of life. It would be idle
to seek, within the germ, or in the conditions of its existence, for a
principle of inheritance, or for the cause of variation, because species
is in the interaction between the organism and its environment.

The specific stability of a growing embryo is no more separable
from its individuality than the height of a man is separable from
the man. We can think of the height of men without thinking of
the men, and we can tabulate statures and treat them by statistical
methods, but, while we may, for some purpose that we have in
view, withdraw our attention from the men, each height still remains
the height of an individual and particular man. So, too, we may
tabulate the differences between animals without thinking of their
kinship, or we may tabulate their resemblances without thinking
of their individuality, but this is no more reason for thinking
inheritance and variation are two things than for thinking a man
and his stature are two things, or for thinking the head of a man is
anything else than a man's head.

Individual dogs are more like other dogs than they are like any-
thing else in nature, and yet one dog is different from another. Is
there any reason for thinking the case of cells is any different?
Daughter cells may be different, even when they are more like each
other than they are like any other cell. The difference between
homologous twins and ordinary twins, or puppies of the same litter,
shows that germ-cells are not identical, and this is shown, still more
clearly, by experiments like those of Mendel. The fact that cells
are different is no more proof that they are specifically differen-
tiated than the difference between dogs is proof that the races of
dogs were foreordained.

Cell-division may be neither integral nor differential, for the
sameness, or kinship, of cells is not philosophical or abstract identity,
but practical equivalence in the economy of the organism. When
we say two cells are the same in substance, I cannot discover
that we mean anything more than our meaning when we say- the
report of a conversation is the same in substance as the original
conversation.

INDIVIDUAL AND ANCESTRAL DEVELOPMENT 317

Cell-differentiation is neither inherent in germ-cells nor induced
by the conditions of existence, because it is in the reciprocal inter-
action between them. They who seek it in germ-cells or in chro-
matin forget that these are not self-sufficient entities, but parts
of the natural world. They who seek it in the conditions of exist-
ence forget, or fail to perceive, that development is a preparation
for a test that is to come later in the struggle of life.

The reciprocal interactions that are characteristic of normal de-
velopment are of a very peculiar sort. They are not merely actions
and reactions, but responses or answers, and I ask you to consider
what this word means, because experimentalists often content
themselves with a very imperfect concept of its meaning.

If I kick a dog, his actions are not ordinary reactions. They are
preparations for meeting the further violence of which the kick is
a warning. Events do not take place anyhow and at random in
nature. They are so related to each other that each is a sign of
others that may be expected in course of nature, and for which
scientific knowledge helps us to prepare, but it is the preparation,
and not consciousness of it, that is useful. When a chick hears the
warning cry of the hen it runs to her for protection from the threat-
ened danger, although it may not know the source of danger, nor
even what danger is. There is a relation, external to the chick,
between the warning cry and threatened danger, and the effect upon
its bodily machinery of the warning is an act which is suited for
escaping the danger of which the warning is the sign. Since the
danger is not discoverable in the structure of the chick, experiment-
alists are apt to ignore this characteristic of responses, that which
makes them responses and not ordinary reactions; but neither the
warning cry nor the danger is to be found in the chick, yet the
stimulants which bring about vital responses are thought worthy
of study. The ability of the chick to make responses does not re-
strain it from aimless or injurious acts. Its fitness is not abstract
or metaphysical, but practical. It may escape danger by means of
its mother's warning, or it may be drawn into danger by an imita-
tion of it, but the bird that falls into the net of the fowler is blotted
out of history. Natural selection is not an agent who does things,
but a general word for formulating the struggle of each individual
for existence, and the survival of the fittest. There is nothing
general or abstract in this struggle, for it is preeminently private
and particular. We speak of the struggle for existence; but my
struggle has not been like yours, and the struggle for existence is
only a formula. Species have come about according to but not
because of or by means of the principle of the survival of the fittest,
for a formula can do nothing. The fitness of living beings is not
ideal or abstract, but private and particular. We say an animal is

318 EMBRYOLOGY

fitted for its place in nature, although it is clear that the fitness is
not in the organism, but in its interaction with its environment.
It is dependent and relative fitness, for an external change may
make unfit what before was fit.

So far as the development of an embryo is a preparation for the
struggle of life, it is like the preparation of the kicked dog for further
violence. This struggle is in no way incompatible with the genera-
tion of sports and mutations and monsters and abortions and fail-
ures, but it is incompatible with the survival of those that fail in
the battle of life.

What is true of development as a whole is also true of its suc-
cessive stages. So far as the interaction between each cell and
the internal conditions of its existence is a response to or a prepara-
tion for the next step in development, by changes of the same
general character as those that take place in the reproductive
organs of the bird and modify its plumage, and so far as the sum
of these changes fits the embryo for the state of life into which it is
to be born, it may survive and have descendants, but the embryo
that does not follow substantially the same course of development
as its allies is cut off from history.

Since the germ-cells produced by an organism are, on the average,
more like those that produced it than like any other germ-cell, they
tend to follow a course of development which is practically but not
exactly the same. Since the struggle for existence is no philosophical
abstraction, no generalization, but a practical matter of personal
experience it does not depend, in any way, upon the causes or upon
the origin of the differences between the organism that survives
and the one that fails. It is therefore perfectly compatible with
the evidence that the germ-cells and the other cells of the body are
practically alike, and that the differences between them are not
inherent, but relative to and dependent upon the conditions of their
existence; nor is there any incompatibility between it and belief that
all cells and all organisms are practically so much alike that a new
animal kingdom might arise, in course of time, from a germ-cell of
any modern organism.

So far as the germ-cell from which the new being arises, and the
cells that compose the tissues and organs of its parents, and the
germ-cells from which the parents arose, are practically alike, and
so far as the development of the new organism goes on under con-
ditions which are practically the same, on the average, as those
under which parents developed, the resemblance of child to parent,
which theories of heredity attempt to explain, is neither more nor
less than we might expect, and there is no problem, because all
experience teaches that similar bodies act and react in the same
way under similar conditions.

INDIVIDUAL AND ANCESTRAL DEVELOPMENT 319

The doctrine that individual development is due to the reciprocal
interaction between the embryo and its internal environment is
inadequate, but when it is joined to the doctrine that ancestral
development is due to the reciprocal interaction between the living
being and its environment of competitors and enemies, it seems to
me to give an outline of an epigenetic account of both individual
development and ancestral development: an outline which it will
require generations of investigators to expand and perfect. In view
of this, is it not time to have done with the pre- Darwinian meta-
physical notion of species as something that resides in living beings
and is handed down by a substance of inheritance?

SECTION I— COMPARATIVE ANATOMY

SECTION I — COMPARATIVE ANATOMY

(Hall 2, September 24, 3 p. m.)

CHAIRMAN: PROFESSOR JAMES P. McMrrRRicH, University of Michigan.
SPEAKERS: PROFESSOR WILLIAM E. RITTER, University of California.

PROFESSOR YVES DELAGE, The Sorbonne; Member of the Institute

of France.
SECRETARY: PROFESSOR HENRY B. WARD, University of Nebraska.

THE PLACE OF COMPARATIVE ANATOMY IN GENERAL

BIOLOGY

BY WILLIAM EMERSON RITTER

[William Emerson Ritter, Professor of Zoology, University of California; Director
of San Diego Marine Biological Laboratory, b. November 19, 1856, Columbia
County, Wisconsin. B.S. University of California; A.M., Ph.D., Harvard Uni-
versity; Post-graduate, Cooper Medical College, University of California; Har-
vard University; University of Liverpool; Zoological Station, Naples. Success-
ively Instructor, Assistant, and Associate Professor of Biology, University of
California, 1891-1901. Member of California Academy of Sciences; Washington
Academy of Sciences; National Geographical Society; American Association for
the Advancement of Science, etc. Editor of Zoological Publications, University
of California. Author of numerous papers on morphology and general zoology.]

ANY science is far along on its road of progress when it has clearly
defined and correlated its problems, and laid firm hold on the methods
by which these may be most effectively worked at. By its problems,
I do not mean its few largest, most nearly ultimate ones alone, but
as well its numerous lesser ones. And by its methods I have not
in mind its laboratory processes only; but as well its intellectual
methods, its ways of handling data, of applying principles, and
especially its attitudes of mind.

Biology regarded as a science, rather than as composed of numer-
ous more or less closely related but still independent sciences, is
rather far behind the other physical sciences when looked at from
this point of view. Its rearward position is the inevitable conse-
quence of the prodigious complexity of the biological field, and of
the recency with which it has come into possession of its great
unifying generalizations; and I do not advert to its status with
the least suggestion of derogation from the splendor of its achieve-
ments, but to emphasize the wisdom of having an occasional "round-
up," as we Westerners would call it, like the present, from our many
so widely scattered grazing-grounds. The daily work of the cytologist
and the paleontologist, for example, are so wide apart that these

324 COMPARATIVE ANATOMY

co-workers are ever prone to forget that they in reality belong to
the same fold.

Just here I must take exception to the notion, too widely current,
and sanctioned by the place given paleontology in the arrangement
of departments and sections for this Congress, that the science of
extinct animals and plants belongs to geology rather than to bio-
logy. Whatever else paleontology may be, it is first and foremost
a department of biology, and is one of its most distinctive and
important departments. And while I am in the business of crit-
icising the programme, I must mention another matter, less, how-
ever, in the way of fault-finding than for defining or explaining
my own attitude toward the topic to which I am assigned. In the
division of Biology we have sections of Embryology and Com-
parative Anatomy. This is in accord with the best views and the
best practice; but from my standpoint it is impossible to separate
the twro, and I cannot consent to discuss the relation of compara-
tive anatomy to biology, and limit myself to the narrower under-
standing of the term; i. e., to the conception that it has to do with
adult structure alone. I must treat it as extending to the later
stages of development at least.

It may be remarked here that I do not count myself a profes-
sional comparative anatomist, but rather a zoologist. My working
interests are about as follows: comparative anatomy, in the sense
above indicated, as furnishing the tools; and general biology as
furnishing the standpoint and larger motive for my profession as
a zoologist.

As a final preliminary to my task proper, I must preach a little.
This I do with reluctance, because for preaching, except by those
called and ordained to the business, I have little taste. But the need
being urgent, and the occasion opportune, I proceed, with at least a
show of boldness, to preach. The theme of my sermon is a plea for
greater catholicity of spirit among biologists. Would that we might
never again have hurled at us throne utterances, as it were, on the
all-sufficiency of such and such a new method of research; or of
the utter uselessness of such and such an old method; or, again,
on the all-absorbing importance of some newly found problem, and
the unimportance, even insipidity, of other old problems. True, the
biological domain is boundless, and the workers in it are human, and
hence narrowly limited in power of individual accomplishment.
But limitation in strength does not necessarily mean smallness of
spirit.

Let not the guilt be on our heads (and by our I do not mean the
other fellows') of dissuading beginners from going into some particular
line of work, embryology or histology, for example, because "it is
dead," or there is "nothing more in it." And don't let us cocaine

COMPARATIVE ANATOMY AND GENERAL BIOLOGY 325

the ambition of a fellow worker in morphology or taxonomy, for
example, by such questions as "who cares for such matters? "
Attitudes of mind like this do harm, lots of harm. They harm in-
dividuals, and they harm science. They are off the same piece with
pathies in medicine; and "pathies" are bad everywhere. Scientific
work done in the " pathy " spirit is pretty sure to be top-heavy and
lop-sided; and the scientific man who cultivates a piece of scientific
ground in this spirit is quite sure to run off and leave it for some
other new piece before he has really found what it will produce.
It seems as though we American biologists are rather more given
to fashion in our scientific tastes than are those of other nations,
though the frailty is by no means a national trait. Think how the
phylogeny fashion prevailed a decade and a half ago, and note how
strange and alone one looks now who dares be found busying him-
self with questions in this field. One might about as well be seen
at an evening ball in a Norfolk jacket as to venture to touch a ques-
tion of phylogeny in the presence of an up-to-date biological com-
pany. And yet who would soberly contend that problems in this field
are without importance, or are all solved, or are insoluble? And
the so-called morphological method, why had it such vogue some
years ago, and why is it so ignored now? What has become of
cell-lineage? Have all the extremely interesting questions that were
attracting so much good work a few brief years ago been settled?
Why do we hear only an occasional voice from this realm now?
How long will it be before the field of regeneration, now so bustling
with life, shall be as lone as the temples of Psestums? Judging from
history, long before its problems have been solved. How long will
biometry remain in its present high favor? Let us sincerely hope
that it will for many and many a decade; while, however, we must
expect, relying on history as a guide, that it will soon have to take its
place in the garret with the many other out-of-date garments.1 The
burden of my complaining is not at all that we strike out on new
lines of work and new methods, and this with enthusiasm and
vigor; but that we do this with too much narrowness, with too
much contempt for the older problems and methods, and, above
all, that \ve go off and leave them for still newer things before they
have been thoroughly tried out. Not only breadth of training,
but as well breadth of spirit, is an imperative demand in any science.
With benediction on the preached word, we may turn now to com-
parative anatomy.

One can hardly take up seriously such a question as that of the
place comparative anatomy holds now, and in the future is likely

1 Since my arrival in St. Louis, I have been told by an American acquaintance
recently returned from Europe that a well-known leader of a school opened a few
months ago is expressing the view that " biology ought to be fumigated of statist-
ical method."

326 COMPARATIVE ANATOMY

to hold in biology, without turning an eye searchingly to the past.
If this be done, one's general conclusions cannot escape being
largely influenced by what he finds there. When it is found, for
example, how many of the largest, most securely established dis-
coveries and generalizations in biology have been reached through
comparative anatomy primarily, the general notion becomes strong
that the subsidiary science, that in the past has contributed so
largely to progress, will continue to be potent in the future. The
presumption, at least, this way is strong. It is not my office to
review history here, but a few instances will be allowable as giving
cogency to the present point. The discovery of the circulation of
the blood is usually and justly regarded as a physiological one; yet
it is noteworthy that, although Harvey made abundant use of both
the experimental and the quantitative methods of research, he still
almost always speaks of himself as an anatomist; and the great
store he placed on comparative studies is well known. "Had anat-
omists only been as conversant with the dissection of the lower
animals as they are with that of the human body," he says, "the
matters that have hitherto kept them in a perplexity of doubt
would, in my opinion, have freed them from every kind of diffi-
culty." And the thoroughgoing way in which his practice accorded
with his theory, both in his studies on the circulation and on gener-
ation, is \vell known to all familiar with his work.

To Malpighi more than to any earlier biologist belongs the honor
of having recognized some of the fundamentally unifying phe-
nomena and principles of the living world as a whole. This he did,
more than in any other way, through his comparative researches
on plants and animals, particularly on marine animals, during the
years of his incumbency of a chair of medicine in the University
of Messina.

The true interpretation of fossils, begun by the Dane, Nicholas
Stensen, a man remarkable, even in a period so remarkable as that
of the mid-seventeenth century, and carried to such brilliant frui-
tion by Cuvier, was, you will recall, strictly a matter of application
of the data and principles of comparative anatomy. So one might
go on almost indefinitely, instancing epochal advances largely
contributed to by comparative anatomy, in aspects of biology not
themselves usually counted as belonging to anatomy at all.

The first point of significance of comparative anatomy for bio-
logy I am going to notice is that of its value as a discipline, or, more
strictly for my present aim, as furnishing a point of view. Be it
noted that the biological habit of mind, or point of view, whatever
be the phrase that best expresses it, is, as all will agree, essential
to healthy enthusiasm and sound accomplishment in biological re-
search; and that this must come through training in and the cul-

COMPARATIVE ANATOMY AND GENERAL BIOLOGY 327

tivation of the various provinces of biology. Biology is indeed a
science, though only from the point of view of its fundamental
principles and ideas, not from the point of view of the materials
which it furnishes to be actually wrorked upon. One cannot be a
biologist practically, excepting through some of its subdivisions.
Now in my opinion there is no single sub-science of the whole bio-
logical realm that contains in itself so many of the elements fitted
for giving the biological point of view as comparative anatomy.
And it seems to me that particularly now, when so much import-
ance is rightly being placed on the experimental and statistical
methods of research, it needs to be strongly emphasized that as a
method or instrument of research it is the fact of comparison that
has given and ever must give anatomy its great significance. Right
here is one of the points at which my plea for catholicity comes
strongly to the front. Some workers in fields recently become
so full of promise and so enticing are actually assuring us, in the
morning glow of their day of promise, that the comparative method
is impotent, and that the future of biology is committed wholly to
these new methods! It is assuring, however, to note that a dis-
tinguished leader in one at least of the new schools does not hesitate
to condemn this sort of thing in harsher terms than I have felt like
using.

I would especially mention the importance of comparative ana-
tomy in the preliminary training of medical students. If there be
any biologist above all others for whom the biological point of view
is of consequence to the general good, that one is the physician.
But if the physician is to attain this point of view, he must do it
by some other route than his strictly medical studies. It cannot
be reached by the study of any single kind of organism. In the
main, then, the preliminary training of the prospective medical
student must be relied on for gaining the desired end. This is not
the place to discuss the matter, but I have reached the conviction
that in the United States, at least, that part of the preliminary
training of medical students which pertains to the higher verte-
brates is, in a majority of our universities, defective. I believe we
are drilling on the single type, mammal, too exclusively, and to the
sacrifice of what would be practicable and of much greater value
in the comparative anatomy of higher vertebrates, the mammals
particularly.

The place of comparative anatomy in biology that may stand
second in our presentation is that of its significance for systematic
zoology; or, in the restricted way in which I shall be obliged to
treat this head, its significance for determining affinities of the
larger groups of animals. There can be no doubt that some of the
most important, though at the same time most difficult, of biological

328 COMPARATIVE ANATOMY

problems are here. It is probable, too, that fruitless theory has
reached its climax in this field. That paleontology is the court of
final appeal here for every case that can be carried before it there
is no question. Since, however, a class of cases is ever on hand
that can never be taken to this court, I propose to make these
the centre of consideration, with the understanding, though, that
most of the general conclusions set forth have application more
or less strictly to other cases as well. I have in mind the problems
of the relationships between the primary divisions of the animal
kingdom.

It is well to remind those disposed to value lightly efforts to
trace phylogenies through morphology and embryology that if
we are ever to know the interrelationships of the primary sub-
divisions of animals, the knowledge will have to be gained from
these sources. A well-known paleontologist has lately remarked
that "Perhaps the most disappointing element in paleontological
results thus far is the lack of all information concerning the origin of
the great subkingdoms, or phyla, of animals." (Woodward, 1898.)
These results, or rather lack of results, ought not to be counted
against paleontology, for, as we now see, paleontology should never
have been held responsible for this task: That science is, of course,
able to say almost nothing about extinct animals that did not possess
hard, imperishable parts. Now, looked at comprehensively, the
evidence of paleontology, morphology, and of embryology concur in
support of the belief that the phyla of the animal kingdom all had
their origin in ancestors much simpler and smaller than any repre-
sentatives of these at present known to us, in ancestors so small and
simple, in fact, that preservable hard parts had not yet arisen. A
well-established skeleton, even of a simple type, must be regarded
as always marking a comparatively advanced state of evolution.
Thus, even such simple representatives of the ccelenterata as Dycto-
rema or Diplograptus of Hallfrom the Silurian must be supposed to
have but gradually acquired a sufficiently chitinous hydrotheca
to enable them to leave even such remains of them as we have; and
consequently, that they must have had a long line of ancestors
about which paleontology can never expect to get much direct
information. Similarly with the actinozoa, all the evidence we have,
both from comparative anatomy and from embryology, leads to
the unequivocal conclusion that the coral-producing members of
the class acquired the skeleton now so characteristic of them only
after a long evolutionary course. Or consider the mollusca. Which-
ever of the two prevailing theories of the origin of the phylum be
favored, constant and characteristic as is the shell, and early as is
its appearance in ontogeny, there is no possibility of its being a
really primitive structure. In other words, the evolutionary career

of the phylum was a long one before this character was acquired.
If the turbellaria-like ancestry be the theory advocated, then the
evidence from comparative anatomy is positive that the shell is a
comparatively recent acquisition. On the other hand, if the trocho-
phore theory be defended, the interpretation of the shell, so well
stated by Korsheldt and Heider (1900, vol. iv, p. 323), would un-
questionably have to be adopted. "The very early rise of this
organ (the shell gland), which may in a few cases be found even
before the trochophore form fully develops, must be regarded as a
shifting back to an early period of the embryonic development of
this feature, which was only a recent acquisition."

So we might go through nearly the whole list of the fundamental
types of animal organization and show the extreme improbability,
if not the impossibility, that their earliest ancestry will ever be
accessible to the paleontologist.1 This view is of course only the
rigorous application of the " Law of the Unspecialized," apparently
first definitely formulated by Professor E. D. Cope. That this prin-
ciple has not been sufficiently recognized at all times by morpho-
logists there is no doubt. The effort to make out the transformation
of a Limulus-like arthropod into a marsipobranch-like vertebrate
can but be regarded as one of the most extreme cases of disregard
of the principle.

It may be held as practically certain that paleontology will never
be able, by direct discovery, to bridge the gaps between any of the phyla
of animals. All it will be able to do in this direction will have to be
by inference, and when resort is had to this method, paleontology
is worse off than comparative anatomy, since the range of its avail-
able data for any particular problem is less. The paleontologist
must rest his case on the testimony of a single organ system, the
skeletal, while the morphologist has at his command all the systems
of organs. True it is that frequently the testimony of the different
systems is so conflicting that the difficulty of balancing it up and
deciding just what the total signifies is exceedingly great; and in
such cases the morphologist is somewhat prone to feel that he has
too much, or, rather, too many kinds of evidence; that he could
do better could he be rid of some of his facts. But, of course, the
paleontologist's seeming advantage here is of a perilous sort. It is
similar to that of the systematist's, whose species of plants or
animals are beyond question so long as he does not have too many
to fit into his descriptions. Since, then, it is by the morphological

1 I do not forget in this connection the extremely interesting observations made
in recent years on fossil remains of soft tissues, as for example, of medusa? (Walcott)
and of striated muscles (Dean, 1902). It is, however, hardly conceivable that
remains of this sort will ever be found in sufficient abundance and condition of
preservation to make them of real importance in the solution of phylogenic
problems.

330 COMPARATIVE ANATOMY

and ontogenetic routes, or not at all, that we must make the passage
from phylum to phylum, we are bound to do the best we can with
the data we have.

One experienced with some of the problems in this field, and like-
wise acquainted with its literature, must be impressed by the lack
of general guiding principles of procedure; and especially by the
lack of criteria for estimating the value of evidence. Several bio-
logists have felt this, and have made praiseworthy attempts to fill
the needs. Among these should be especially mentioned Gegen-
baur, Cope, Dohrn, E. B. Wilson, Montgomery, and Gaskell. I
desire to devote some attention to this topic. The time being so
limited as to make it impossible to treat it with any measure of
fullness, I merely pick out some of the points that seem to me of
most immediate importance for the present state of progress, and
tendencies without special regard to their logical order or their
coherence.

(a) My first point is one of professional delimitation, and attitude
of mind, rather than of general biological principles. I state it thus:
We must cease to be embryologists as distinguished from anatomists
when it comes to any particular problem of affinities between
groups of animals. Montgomery (1902, p. 225) has recently said:
"As to which of these methods is the more correct has been and
probably will continue to be a question of dispute. The compara-
tive anatomists maintain one side, the embryologists another, and
probably because the former are less conversant with the facts of
embryology, and the latter with the facts of adult structure." I
suppose this statement of the present attitude of embryologists and
anatomists toward one another is true; and I am absolutely sure
that so long as it is, we shall not touch solid ground for our general
conclusions. What I would insist on is that there is no sufficient
reason why it should be so.

True, no one can compass in his personal investigations the whole
range of both embryology and comparative anatomy, but that is
in no wise essential. All that is necessary is to redraw our lines of
specialization. Instead of drawing them around masses of facts
and through problems, as is so frequently done, they must be drawn
around problems, and through, if necessary, masses of data. There
is no reason why a zoologist should come to what he would regard
as a final opinion on the relationship, for example, of the mollusca
and annelida without having himself examined with equal thorough-
ness the facts of both anatomy and embryology bearing upon the
question.

Having reached a position where we might use the facts of devel-
opment and adult structure with equal facility and equal favor,
we should certainly find that in nearly every problem of phylogeny

COMPARATIVE ANATOMY AND GENERAL BIOLOGY 331

development must be relied on for light in certain places, whereas
adult structure will be the safer guide in others. Fifteen years ago
Gegenbaur said, speaking as a comparative anatomist: "Ohne die
Kenntniss des letzeren [i. e., adult structure] wie die Anatomic ihren
darstellt, wiirde die Ontogenie sich auf gleichem Wege befinden,
wie der Wanderer der sein Ziel nicht kennt."

More recently Driesch, and still later E. B. Wilson, O. Hertwig,
and others, coming at the matter from the embryological side, have
insisted upon the importance of what Driesch has aptly styled the
prospective value of parts of even the very early embryo, in ques-
tions of homogeny. With the common truth underlying these two
formulations firmly grasped; and with the principles of develop-
mental mechanics thoroughly applied to embryology and compara-
tive anatomy alike, through both experiment and the study of
nature's own experimenting, one might confidently predict good
progress for the future in deepening insight into the past evolution-
ary career of the animal world.

My remaining points, more than the first, are attempts to state
certain general biological principles that may serve as more or less
reliable guides in handling isolated cases. I earnestly hope, however,
to avoid the misfortune of being understood to suppose that I have
discovered any laws that run on by some mysterious power all their
own, bending the incidents of animal structure to their own ends,
whether or no. All, of course, I am attempting is to formulate the
concordant results of numerous widely separated observations. If
there is anybody in the world who has reason to be skeptical of the
invariableness of laws in the realm of living things, it is the zoologist.

(6) My second point, then, has to do with what was called by
Cope the "Law of the Unspecialized; " and also with the law or
principle of change of function, first brought into prominence by
Dohrn. ' It may be stated thus: The probability that an organ or part
in one group of animals has arisen from another in another group by
change of function, is inversely proportional to the degree of specializ-
ation of the supposed ancestral organ or part.

I cannot but believe that had this generalization been clearly
before the minds of several zoologists who have in recent years
advanced theories as to the origin of various groups of animals,
they would never have become sponsors for views with which they
now stand credited. One may instance Dohrn's attempt to derive
the vertebrate copulatory organs from annelid gills; and any num-
ber of Gaskell's laborious efforts to show that the various organs of
the vertebrate have been derived from organs highly specialized
for wholly different functions, in the supposed arthropod ancestor.
The role of comparative anatomy in applying this principle is obvious.
Grade of specialization can. of course, only be tested by consider-

332 COMPARATIVE ANATOMY

ing adult structure. And while the indispensability of comparative
anatomy is clear, it is well to note again how causal morphology
would join hands with comparative anatomy here. To recur to the
example of the supposed origin of the cbpulatory organs from gills:
Due consideration for the functional demands of these two sorts
of organs would lead to recognition of the extreme unlikelihood of
the transformation of the latter into the former.

(c) My third effort at a guiding generalization takes the follow-
ing form of statement: In attempting to find the origin of a given
type of animal organization foremost attention should be given to the
organs and parts most characteristic of the type, since the discovery of
the origin of these would be most decisive for the origin of the type itself.
Thus, could the view be fully established that mammalian hair
originated from epidermal sense buds like those found in amphibia,
this would be the strongest sort of evidence in favor of the view
that the ancestry of the mammals runs back to the amphibia.
Again, this principle would dictate that search for the origin of the
mollusca should be particularly promising in investigations on the
phylogeny of the mantle, and the shell gland. It would seem as
though this principle is so obvious that it should have elicited the
regard of every student who inquires into the relationships of larger
groups, at least; yet it is surprising to find how largely it has been
neglected. Theories of the origin of the chordata, for example, are,
several of them, almost wholly wanting in any serious attempt to
find how one of the very most characteristic things in the chordate
type of organization, viz., the axial skeleton, arose. Of course a
corollary to this principle would be that organs and parts merely
occasional and incidental within a given group (unless they can be
proven to be rudiments) can have but slight significance for the
affinities of groups as wholes. Thus it is really surprising that an
investigator with the store of learning that Gaskell possesses should
have so nearly set at naught his own theory by a complete disre-
gard of the principle. This author supposes, and goes to great pains
to prove, that the tubular muscles of ammocoetes are derived from
the veno-pericardial muscles of limulus and scorpions. And he tells
us this is "the strongest argument in favor of my theory." In
a word, the strongest argument Gaskell has in support of his view
as to the origin of one of the largest, most distinctly circumscribed
phyla of the animal kingdom, rests on an obscure group of muscles
found only in the larva of one small division of this phylum!

The importance of comparative anatomy for the application of
this principle is likewise obvious enough. It must be the chief
reliance for determining the constancy of a part through a series
of animals.

(d) The fourth and last principle that I here present is one

COMPARATIVE ANATOMY AND GENERAL BIOLOGY 333

which, while it belongs mainly to the province of comparative
anatomy and embryology, laps farther over into the field of devel-
opmental mechanics than any of the others noticed. I may say,
too, that I have found less suggestion of it in the writings of other
zoologists than I have of the preceding ones. I state it as follows:
The reliability of an organ or part as evidence of genetic relation-
ship is directly proportional to the unlikelihood of its having arisen
independently within the limits of the groups of animals being com-
pared; and the test of unlikelihood of di- or polyphyletic origin of
a part is the number of more or less distinct elements that enter into
its composition; or, what amounts to about the same thing, the com-
plexity of the part. To illustrate: Were .paleontology to discover
structures in Silurian strata, one kind of which would be allowed
by all to resemble closely mammalian hair, and another kind as
closely to resemble avian feathers; and should there be an entire
absence of direct evidence as to the creatures these structures
belonged to, the feather-like structures would furnish stronger
presumption of the existence of birds in Silurian times than would
the hair-like structures of the existence of mammals in the same
epoch; and this on the strength of the evidence itself, and without
appealing to any collateral considerations, like, for example, the
fact that the general course of evolution makes it probable that
birds originated earlier than mammals. The stronger probability
attaching to feathers would be due to the much greater complexity
of feathers than of hairs, this making it less likely that feathers
should have arisen more than once. Or, again, the complexity of
the ambulacral system of echinoderms diminishes the probability
that such a system would have been elaborated more than once,
and consequently its presence in any sort of an animal, however
generally unlike any known echinoderm, would still be strong
evidence of kinship with the echinoderms.

Inadequate as has been my treatment of the role of comparative
anatomy in the investigation of problems of affinity, still less
adequately am I able to deal with its significance for other groups
of problems. Its relation to the various aspects of experimental
zoology, for instance, is intimate and vital. The best thing I can
say in this connection is that, were it my office to prescribe the
qualification that should be exacted of all who would go into experi-
mental morphology, for one thing I should insist upon thorough
familiarity with Roux's Problems, Methods, and Scope of Develop-
mental Mechanics, which introduced his Archiv to the biological
world; and further, I would exact unqualified accord to that portion,
at least, of the essay that sets forth the author's views concerning
the relation of developmental mechanics to the several older bio-
logical disciplines.

334 COMPARATIVE ANATOMY

Certain it is that nothing fuller of promise has come into biolog-
ical science for many years than the set of tendencies in ideas and
methods of investigation that have crystallized into the expression
" developmental mechanics." It has sometimes seemed to me,
though, that the alternative term, causal morphology, would have
been more fortunate. The kernel of the thing is, as I understand it,
search after the causes of the form of organisms; or really causes of
morphogenesis.

Now where does anatomy come in here? Why, in the first place,
it is anatomy, is n't it, that shows us what it is we are seeking the
cause of? A rather important preliminary to explaining a thing is
to know what we are going to explain. Anatomy, then, in the first
place, is the source of supply, so to speak, of the very problems
developmental mechanics proposes to solve. But has anatomy
exhausted its usefulness in this direction when it has handed out
the raw material of a lot of problems? By no means. The moment
anatomy becomes seriously comparative, that moment it is on the
threshold of causal morphology; for as soon as parts obviously
homogeneous, but with considerable differences, are recognized in
different groups of animals, a differential in the producing cause of
the common part must almost of necessity be assumed by the
observer; and since this differential will usually be closer at hand,
so to speak, than the cause itself, it is pretty sure to stimulate
inquiry as to what the cause has been. And even this much, general
and vague though the effort may be, is undoubtedly on the high-
road of search after causes of animal form. To illustrate: One's
knowledge of the anatomy of the human limbs, let us say, may be
complete; but the causes that have produced these limbs are so
complicated and obscure, that even were he, as a human anatomist
pure and simple, to raise the question of how they came to take
the form they have, the absence of even a starting-point for an
answer would be apt to prevent an effort in this direction. But now
let this anatomist add to his knowledge an acquaintance with
the structure of the limbs of, say, a spider monkey. He could
hardly escape recognizing that the difference between the limbs
of the two animals is connected causally with the different uses to
which they are put by their respective possessors. In other words,
the cause of the difference in limb structure, being relatively near
by and simple, can hardly escape him. He is forced, almost, by
comparative anatomy, into the way of causal morphology, or
developmental mechanics. But we must recognize that obser-
vation, however extensive and painstaking, and however faithfully
and thoroughly it be coupled with comparison, and with reflection
on the causal efficiency of function, of correlation, of conditions
of development, etc., must always still fall short of direct proof of

COMPARATIVE ANATOMY AND GENERAL BIOLOGY 335

the cause of the form. Conclusions from this method must usually
be presumptive. Hence we must wherever possible call experi-
mentation to our aid, for this is preeminently the method that
yields evidence direct and immediate. But here again we must
recognize limitations. Undoubtedly there is a wide range of form
and structure that lies wholly beyond the reach of direct experi-
mentation. How, for example, can we hope to touch, except per-
haps indirectly and from afar, such a problem as that of the phylo-
geny of mammalian teeth? It is quite possible that experiments
on the developing teeth might be made, as, for example, by depriv-
ing the emb^o of salts necessary to tooth substance; or by arti-
ficially altering the pressure on the incipient teeth in some of the
marsupials whose embryonic life is largely extra-uterine. But with
all the necessary complexities of manipulation, and with the wide
scope of inference that would be necessary to determine the bear-
ings of the results of such experiments, I do not see that this method
can be expected to yield results for the problem as trustworthy as
those that may be looked for from comparative embryology. And
the same thing must, it seems, be true of very many problems
presented by the higher animals especially.

I should like, did time permit, to say something on the part
comparative anatomy must play in the, to me, wonderfully enticing
field of animal ecology. But I must forbear.

I may state the essence of this paper thus: From the point of
view of its problems rather than of its materials and methods of
research, the great biological field is indeed one. Its essential unity
can be realized and preserved, and these problems most effectually
worked at, by drawing the lines of specialization around problems
rather than around masses of facts. By this procedure we should
be led to appraise more justly methods and facts, and should be
compelled to see the necessity of employing any and all of these
that might help us on our way. Comparative anatomy ever has
held, and ever must hold, both for its methods and its substance, a
place of foremost importance in biological research. It, along with
embryology, which indeed it must include so far as concerns later
stages of development, is one of the surest passports of training to
the biological point of view.

It is of primary importance in furnishing and applying criteria
of the value of evidence in problems of affinity, of phylogeny, and
hence of classification.

It is, in both its methods and substance, of great importance to
Developmental Mechanics.

COMPARATIVE ANATOMY AND THE FOUNDATIONS OF

MORPHOLOGY

BY YVES DELAGE
(Translated from the French by Robert M. Yerkes, Harvard University)

[Yves Delage, Member of the French Institute, Professor of Comparative Zoology,
Anatomy, and Physiology, University of Paris (Sorbonne), since 1889; Director
of the Maritime Zoologic Station at Roscoff . b. Avignon, France, May 13, 1854.
M.D. Faculty of Paris, 1880; N.S.D. ibid. 1881; Officer of Academy, 1883;
Officer of Public Instruction, 1889; Chevalier of the Legion of Honor, 1894;
Laureate of the French Institute, Grand Prize in Physical Sciences, 1881;
Laureate of the Anthropological Society of Paris, Broca Prize, 1898. Tutor
at the Lyceum of La Rochelle, 1874; Instructor of Zoology at the Faculty of
Sciences of Paris, 1878; Master of Conferences, ibid. 1882; Professor of the
Faculty of Sciences of Caen, and Director of the Maritime Zoologic Station at
Luc-sur-mer, 1883; Member of Geneva Institute; Imperial Society of Natural-
ists of Moscow; Imperial Academy of Medicine, St. Petersburg; President of the
Zoological Society of France; British Council for the Advancement of Science,
Imperial Academy of Sciences, St. Petersburg; Imperial Society of Naturalists,
St. Petersburg; Royal Society of Microscopy of London. Author of The Struc-
ture of Protoplasm and the Theories on Heredity and the Great Problems of
General Biology; Treatise on Concrete Zoology, with E. Herouard; The Biologic
Year : An Annual Account of the Labors in General Biology (one volume a year
since 1897).]

LIKE those of nearly all branches of knowledge, the first rudi-
ments of comparative anatomy are as old as man himself. Ever
since he has been able to reflect and observe, even before he knew
how to speak, man has carried on the study of the majority of the
sciences or of their applications. He studied astronomy the day
he noticed that the sun rose each morning at a point on the horizon
and that it set each night at an opposite point, and that he could
expect the repetition on following days of the same phenomenon;
he studied arithmetic as soon as he could count the warriors of his
tribe and the sheep of his flock; geometry when he could draw the
boundary of a circle by means of a cord attached to a stake; phy-
sics when he succeeded in lighting a fire by striking two flints or
by rubbing together two pieces of wood; chemistry, and of the
most delicate kind, the first time he raised bread-dough with sour
dough of the preceding day. In the same way he began compara-
tive anatomy when he gave the same name to similar parts of differ-
ent beings, when he called the extremities of the horse as well as
of the dog, "feet." All the general terms of anatomy, such as head,
tail, horns, hair, liver, heart, etc., have for their preliminary con-
dition data of comparative anatomy, defaced and intuitive if you
please, but clear and positive nevertheless.

This kind of rudimentary comparative anatomy, which has for
its basis a collection of resemblances of such a nature, recognizable

off-hand without intellectual effort, has not progressed since ancient
times, and persons who have not made a special study of them are,
in this respect, at about the same stage as our ancestors of old. •

Comparative anatomy could but slowly depart from this intui-
tive phase. In order to become a true science, it was obliged to
wait until another science from which it borrows its materials for
study, zootomy, was established. For the latter is a science which
does not impose itself upon the attention of man. By reason of its
utilitarian character, human anatomy, "anthropotomy," was
studied first, by medical men, and zootomy only by chance, for the
sake of the aid it was able to furnish to anthropotomy by com-
parison of the structure of man with that of animals. On that
account zootomy has wrongly been called comparative anatomy,
and even in our day some people still consider comparative ana-
tomy as being only the anatomy of animals compared with that
of man; they confound it with zootomy, which conception is most
inaccurate.

True comparative anatomy has for its first object the presenta-
tion in another grouping of the facts of zootomy and the. comparison
of them among themselves.

Zootomy describes the arrangement and structure of all the
organs in each animal, and passes in review successively all animals;
it gives a complete and concrete picture of the organization of each
one. Comparative anatomy studies in all animals successively the
position and structure of a given organ, and proceeds thus success-
ively with all the organs; it gives a complete but abstract picture
of the constitution of each one throughout the animal kingdom.
It is, therefore, not creative; it only points out from another point
of view the facts which zootomy has already made known. In that
sense it is not, properly speaking, a science. It is not, however,
less useful, and one is wrong to slight it on the pretext that it has
not an independent personality in the general tableau of the sciences.
It enlarges the views of the anatomists, determines a multitude of
ideas, points out new aspects of things. It is the necessary comple-
ment of zootomy, and no one may be a perfect anatomist, if, after
having studied zootomy, he does not review from the standpoint
of comparative anatomy the ideas acquired in that study in order
to study them anew.

This first object of comparative anatomy is not considered by
anatomists as the most important, or as that to which this science
owes the high dignity with which they invest it. It pursues another
aim more elevated and more difficult to attain, but also more merit-
orious: the discovery of general laws which may be deduced from
the comparative study of the structure of animals. There com-
parative anatomy is creative, for zootomy alone could not pretend

338 COMPARATIVE ANATOMY

to the discovery of these laws; it becomes a true science having
its own object. It remains dependent upon zootomy for the mater-
ials- which it borrows therefrom, but it is no longer content with
retouching, with rearranging its facts; it draws from them new
conclusions.

Here, as everywhere in biology, these so-called laws cannot be
considered as directive principles, as active forces, but only as
general propositions summarizing a large number of the facts of
observation. The following are the most important of these propo-
sitions:

Law of connections. If we compare the characteristics which the
same organ presents in a more or less extended series of animals,
we perceive that these characteristics are more or less variable
according to their nature: color and form are in general very much
so, structure, the relations of contiguity, are fairly so; but there is
one which is almost invariable, and that is connection, or, in other
wrords, the relations of continuity. For example, the pelvic fins of
fishes called jugulars are greatly displaced, since they are carried in
front of the pectoral fins, but the nerves and arteries which they
receive are given off, nevertheless, from a point situated behind
that from which the nerves and arteries of the pectoral fins start;
the lungs of serpents elongate to form cylinders which are placed
one behind the other, the posterior far towards the rear of the body
in a region very different from that which it occupies in other ani-
mals; but their point of insertion in the pharynx, the glottis, re-
mains unchanged; the statocysts of lamellibranchs are situated
in the foot, far from the place wrhich they occupy among the other
mollusks, where they are near the cerebral nervous centres, but
their nerve connects them with that centre, a direct emanation of
which they therefore remain. This principle of connection is equi-
valent to considering organs as attached at a fixed point, which is
their place of origin, by an elastic cord, which allows them to make
all changes of place without losing their connection with the fixed
point. This cord is a thread of Ariadne which permits regaining the
point of departure despite the most distant migrations. In tracing
back these organs among all animals to the place of origin which
their connections indicate, an important share of their differences
is made to disappear, and their comparison is made clear. This is
the principle of Geoffroy Saint-Hilaire.

Principle of the balancing of organs. It is well known that the
relative development of organs in the body is very different among
different animals. Geoffroy Saint-Hilaire remarked that , when one
organ attains an excessive development, one or more of the others
suffers a corresponding atrophy. This principle results from the
fact that the necessities of nutrition do not allow a number of organs

COMPARATIVE ANATOMY AND MORPHOLOGY 339

to function at the same time with an activity greater than the
average. If certain ones have a very great activity, they develop
beyond measure, but, correlatively, others become relatively inert
and atrophy.

Principle of coordination or of correlation. As far down as life is
possible, there is every necessity that organs and their functions
should be bound together among themselves by mutual relations,
in a manner analogous to the wheels of a mechanism. Thus it is that
the elk could not carry the enormous weight of his antlers unless
the muscles of his neck had undergone a considerable develop-
ment. Other correlations, without resulting from physiological
necessities quite as rigorous, appear like the expression of very
general provisions. For instance, mammals which have hoofs are
herbivorous and have a large and flat maxillary condyle, and teeth
with a large crown striated with a crest of enamel, in order to tri-
turate plants as if between millstones; carnivores, on the contrary,
which have large canines, have a transverse condyle and a foot
with five digits provided with nails. It follows that it is possible,
to a certain extent, and sometimes with remarkable precision, to
deduce the formation of certain parts by that of certain others;
seeing the canine tooth of a lion, the hoof of a horse, the antlers of
an elk, we may divine the transverse condyle and the clawed foot
of the first, the flat condyle and molar teeth of the second, the
powerful cervical muscles and the cervical vertebrae with high
apophyses of the third. It is to Cuvier that we owe this principle
and its chief applications, and the same author's principle of the
subordination of characteristics is but another expression of the same
view.

Principle of the division of labor. The general functions which
organisms must fulfill in order to live and reproduce their kind
are the same from one end to the other of the scale of beings. Simple
creatures which occupy the bottom of the scale fulfill their functions
almost without organs. The substance which constitutes their
bodies, protoplasm, possesses the rudiments of all the indispensable
properties; it assimilates and excretes, it feels, it moves, it divides.
As we mount towards organisms more and more perfect, we perceive
that the progressive perfecting has for its foundation the formation
of special organs more and more differentiated, better and better
fitted to accomplish in a more perfect manner a special work, and
less and less capable of performing multiple functions. Thus the
motile and nervous functions are divided between two very different
elements, the muscle-cell, possessing an energetic and rapid con-
tractility, but insensible, and the nerve-cell, incapable of energetic
movement, but well suited to receive impressions and to transform
them into motor impulses.

340 COMPARATIVE ANATOMY

This principle, brought to light and developed with much skill by
H. Milne-Edwards, belongs as much to comparative physiology as to
comparative anatomy. It is very general, and is verified among all
living beings, both animals and plants. Certain facts are in a way
corollaries of it. Thus, organs, even those which are specialized with
reference to a given function, may be numerous among lower beings,
and have a tendency as soon as and in proportion as an organism
perfects itself, to be reduced to a pair, or even to one. Thus the loco-
motor members, so numerous in the annelids and myriopods are
reduced to four pairs in the arachnids, to three among the insects,
to two in the vertebrates, and to one pair in man.

Principle of the change of functions. This principle, due under this
name to A. Dohrn, to whom also we owe the demonstration of numer-
ous applications of it, had been clearly formulated by H. Milne-
Edwards under the name of the principle of physiological borrowing.
He points out that when a new function becomes established, it at
first borrows its organs from parts already existing, which change
their functions to those to which the modifications correlative with
the change have made the organs exactly appropriate. Examples of
this are innumerable. One might cite the pectoral fin of the whale,
which is only its anterior limb transformed; the poison-gland of the
viper, which is a salivary gland; the copulatory appendages of the
crab, which are modified abdominal feet.

It is evident that for the establishment of the majority of these
laws comparative anatomy calls upon comparative physiology, and
it is even noticeable that the most suggestive laws, those of Milne-
Edwards, for example, are more physiological than anatomical.

There is, however, one last principle which comes wholly from
anatomy, and which is proving itself more rich in consequences than
all the others united. It may be remarked, in fact, that the number
of these general principles is very limited, and it seems as if there were
not many more to be discovered. If it were limited, therefore, to the
second object, comparative anatomy in having acquired the dignity
of a science, properly speaking, could not be considered a very fertile
science.

The principle to which I allude is the following:

Principle of the uniform constitution of animals. A glance at the
organization of beings suffices to show that their structure presents
striking resemblances. All mammals have mammary glands and
hair, all birds have feathers and wings, all vertebrates have limbs and
a bony skeleton, the majority of animals have a stomach, an intestine,
a mouth and an anus, muscles for motion, a nervous system to control
these muscles, sense-organs often quite comparable, a circulatory
apparatus, etc.

This principle is an idea the acquisition of which goes back to the

COMPARATIVE ANATOMY AND MORPHOLOGY 341

most remote times. Aristotle formulated it clearly. Nevertheless, it
has been established scientifically, with the necessary details, for the
first time by E. Geoffroy Saint-Hilaire, under the name of the princi-
ple of analogy.

Extending over the whole of the animal kingdom, it is true only
for very general and very vague structures. If we go into details, we
find important divergences, and it is only by forcing and falsifying
comparisons that we can succeed in establishing apparent analogies
between organizations thoroughly unlike. The nervous system of a
mollusk has almost no resemblance to that of a vertebrate; the
organization of a sea-urchin has almost nothing in common with that
of an ascidian; the olfactory organ of a crab does not resemble in
any possible way that of a mammal.

It is not the same, however, if, in place of extending the comparison
to the whole of the animal kingdom, we limit it to a small number of
large groups. It is the merit of Cuvier that he established these
groups by means of comparative anatomy; they are the phyla of the
animal kingdom.

In any one phylum the organization of all the beings which com-
pose it is truly very similar, and if there are differences, real, various,
and profound, they are not incapable of reduction.

This principle furnishes to comparative anatomy a third object; it
points out a third aim more elevated than the first two, and more
difficult to attain. Here not only does comparative anatomy become
an independent science because of this object, but it opens to research
an unlimited field. It is no longer, as in its first aspect, the simple
complement of another science; it is no longer, as in its second aspect,
a science limited to the discovery of some rare general principles; it
acquires a new dignity, and it presents itself as so vast that its study
will never be achieved.

This third aim of comparative anatomy is the comparison of all the
beings belonging to the same type, it is the search for the fundamental
conformity under the divergences of detail.

This fundamental conformity makes it possible to conceive for each
phylum a type of structure from which is derived, as a modifica-
tion of the type, the structure of each of the forms constituting the
phylum.

If all the organisms of the same phylum are derived from a single
type, the organs of each one of them are derived from the organs of
the type. Therefore, whatever may be the differences presented by
corresponding organs of two members of the phylum, these differences
are secondary, accidental, subordinate to a fundamental conformity,
and the organs, representing the same organ of the type, represent
one another and are homologous.

The chief and the highest aim, therefore, of comparative anatomy

342 COMPARATIVE ANATOMY

becomes the search for homologies. The science of homologies, or
morphology, is considered the essential part of comparative anatomy,
at once the noblest and the most fruitful.

In the comparison of organs of different beings, Geoffroy Saint-
Hilaire and his contemporaries took into account all the character-
istics, physiological as well as anatomical. Thus they were not afraid
to compare the lungs of mammals with the gills of fishes. To R.
Owen is due the credit of distinguishing between physiological and
anatomical characteristics; he pointed out that the former furnish
only superficial analogies, while the latter form the true basis of
homology. Thus the wing of an insect and the wing of a bird are
analogous as being organs of flight, but they are by no means homo-
logues, having an essentially different structure, since the wing of a
bird is the homologue of the arm of man, for we find in it, in modi-
fied form but with similar arrangement, the bones of the arm, the
forearm, and the hand, and a goodly number of muscles which serve
to move it.

It is evident, then, that morphology depends entirely upon the idea
of an animal type. The solution, therefore, of morphological problems
depends upon the idea of a uniformity in the structure of beings and
upon the significance of types.

Now these conceptions vary. The Deists, and therefore Aristotle,
explain uniformity of structure by unity of plan. A creative God
created species, and by an act of his will constructed them according
to a uniform plan, varying only in details and in the application of its
fundamental facts.

The aim of comparative anatomy is to discover this plan, either by
the study of animals or by rethinking the thought of God.

Others, in a conception more or less pantheistic, attribute to nature
what the preceding had made proceed directly from God. There is
still a plan, but an unconscious one, or rather a model, a type, an
immaterial entity, unrealized, but which yet controls the realization
of real forms as the laws of nature direct the phenomena which are
subject to them.

This type is understood in two ways. According to one, it is a pro-
totype, the original form, of which real beings are gradual improve-
ments; according to the other, it is an archetype, the perfect form, of
which existing creatuies are the repeated models, infinitely various,
but always degraded, degenerate.

The aim of comparative anatomy is to find this type and to deter-
mine how nearly real forms approach to it.

This conception of types, apparently less childish than that of the
unity of plan, has been in fact more troublesome; for, because of its
greater philosophical attraction, it has seduced more and higher intel-
lects and has directed their efforts towards an end not less chimerical.

COMPARATIVE ANATOMY AND MORPHOLOGY 343

The introduction into biology of the concept of descent has pro-
duced an important change: the ideal prototype has become an
objective reality in the form of the ancestral type. It is certain that
two given forms, if, at least, they are not too different from one an-
other, have common ancestors, of which the latest is that one from
which they differ least. This latest ancestor is the material prototype
from which they have both really been derived. The organs of the
ancestor have truly become the organs of the two derived forms as
far as we may consider as one and the same thing the organs of one
being and the almost identical ones of its immediate descendant.
We, then, have the right to say that from the phylogenetic point of
view the organs of the later forms represent those of the ancestor, and
that those of their organs which represent the same organ of the
ancestor represent those of one another. The idea of representation
gains body and becomes a reality, and morphology, which is the
science of representations, becomes a positive science.

The aim of morphology therefore becomes precise and more pos-
itive. It consists in determining homologies, considering as homo-
logues those organs which in the ancestor were represented by a
common rudiment.

Morphology, then, has phylogeny as its basis. But phylogeny is not
a science of direct observation; it is constructed inductively from
the facts of comparative anatomy, of paleontology, and of compara-
tive embryology.

The theme of morphology is, then, as follows: to compare organs
which we suppose may be homologues and which belong to two differ-
ent species, to determine by comparative observations, anatomical,
paleontological, and embryological, not all of the characteristics of
the ancestor of the twTo species, which is the aim of pure phylogeny,
but the typical constitution of that organ in the common ances-
tor, and to see whether the two organs have surely been derived
from the ancestral type. In that case they are called homologous,
whatever may be their differences; in the contrary case they are
not homologous, whatever may be their resemblances.

This is the matter in its brutal clearness.

Let us take an example: what, in the foot of the ox, is the homo-
logue of the hoof of the horse? The answer is not evident. A philo-
sopher of nature could well conceive an archetype according to which
the whole of the foot of the ox corresponds to the hoof of the horse.
But the anatomist dissects these parts and finds only one digit in
the foot of the horse while he finds two in that of the ox. The em-
bryologist sees the five digits of the unguiculates shown at first in
the horse and the ox; digit number one disappears first, afterwards
numbers two and five; the ox preserves three and four; in the
horse number four disappears in its turn, leaving only the middle

344 COMPARATIVE ANATOMY

digit, number three. He supposes, therefore, that the ancestors have
undergone this progressive reduction. Paleontology when consulted
shows effectively that such has been the case, and finally we con-
clude that the hoof of the horse corresponds to the inner hoof of the
ox because they both correspond to digit number three of a five-toed
ancestor.

In this order of things, the difference in the method of procedure
between those who take observation for their guide and those who,
confining themselves only to the powers of the mind, seek to think
again the thought of God in order to divine the secrets of nature, is
not without analogy to that which is manifested in the science of
etymology. During a certain epoch the attempt was made to divine
etymologies according to phonetic resemblances and the meaning of
roots freely interpreted. What is the etymology of savage? We look
and find soli vagus, one who wanders alone, the savage living more
solitary than civilized man. Any other resemblance equally happy
could furnish a different etymology of the same value. But when we
set ourselves to study the embryology of words, that is to say, the
real history of their successive modifications, we find that savage
comes from sauve ; la sauve, in the ancient tongue, is a forest, and the
name comes from sylva, so that sauvage comes from sylvaticus. This
is perhaps less pretty than soli vagus, but it has the advantage of
being true.

To be just, we must remark that the search for homologies by
means of observation is not the exclusive advantage of the partisans
of descent.

If the transformists more often call to their aid paleontology and
embryology, there is there only a difference in the habitual orienta-
tion of thought, and not at all an inherent necessity for a difference
in the point of view. The deist could equally well seek in paleonto-
logy and embryology indications of the thought of the Creator, and
the philosopher of nature could as well look there for the appli-
cations of the laws of nature by which he hopes to remount to the
archetype. For the former, at least, there are examples. And it is
probable that if the transformist idea had never been born, deists and
natural philosophers would have come nevertheless to look to paleon-
tology and embryology for the facts capable of demonstrating their
opinions.

This extension of the field of comparative anatomy, which borders
on morphology, or the science of homologies between similar organs
of different beings, is not the last.

Anatomists have dreamed of comparing among themselves not
only the organs of different beings, but also the organs of the same
being which present a certain similarity, and to seek among them for
homologies. To these last have been given the name of general

COMPARATIVE ANATOMY AND MORPHOLOGY 345

homologies, in opposition to those which we have examined above
and which are the special homologies.

Thus we have been asked if the occipital bone is homologous to the
vertebrae, the humerus to the femur, the hand to the foot, etc.

For the partisans of the theories of unity of plan, of prototype, or
of archetype, the problem of the general homologies does not differ
essentially from that of the special homologies. Unity of plan may
manifest itself as well in the parts of the same creature as in different
creatures. The prototype or the archetype may be conceived as having
the hand identical with the foot and the occipital formed like a
vertebra. For the partisans of modern ideas, the matter is a little
more difficult, for there is no ancestral type in which respectively the
hand and foot, the leg and the arm, the occipital and the vertebrae,
are represented by single structures, so that the problem for the trans-
formists appears quite as subjective a one as for the philosophers
who preceded them. The transformists have succeeded, moreover, in
giving to the solution of the problem a certain objectivity, reasoning
in the following manner: if the occipital were formed exactly like
a vertebra, the foot like the hand, the femur like the humerus, we
should not hesitate to consider them as homologous, just as we do
not contest the homology of the vertebrae among themselves. If,
then, in descending the scale of beings by means of comparative
anatomy, if in constructing phylogeny by means of paleontology and
embryology, we find beings or stages where those parts which we
are comparing are more and more similar among themselves, even
to the point of being identical, we should have the right to homologize
them; otherwise, not. Thus we have come to recognize that the occi-
pital is not a vertebra, and that the homologue of the tibia is, in the
forearm, the radius, although in a superficial examination it would
appear to be the ulna, as some anatomists, experts in their science,
too, have drawn and described it.

Since we have now shown what comparative anatomy is according
to generally admitted ideas and under its three aspects, namely : the
presentation of zootomical ideas in an arrangement facilitating the
comparison of organs, the search for the lawrs of organization, and the
search for homologies, we must now go more deeply into our subject
and examine the bearing of comparative anatom^, the value of its
results, and the solidity of its conceptions.

As far as the first two aspects of comparative anatomy are con-
cerned, we have little to add to what we have already said.

We must recognize that in so far as comparative anatomy limits
itself to presenting zootomical facts in another order, it is not a true,
independent science, neither in its foundations nor in its results; it
is nevertheless extremely useful, indispensable even in furnishing not
only to the student, but also to the scholar, a larger view of things,

346 COMPARATIVE ANATOMY

a greater variety of points of view, permitting more general con-
ceptions.

When it searches for the laws of organization, comparative ana-
tomy, although remaining tributary to zootomy and a little to physi-
ology for the facts of which it makes use, becomes more independent
because of its aim, but it continues to be a narrow, limited science,
since the number of general principles which it strives to discover
is very limited.

In the search for homologies, comparative anatomy allies itself
with embryology and paleontology; thus it gains all its amplitude
from the importance and the infinite number of problems upon which
it borders. In elevating and enlarging itself, however, does it still
maintain its solidity?

Two organs are homologous, we have said, when they are derived
from the same organ or rudiment in their common ancestor, but
that ancestor is in no case precisely known. When the homology
to be sought is easy, one may often determine by induction the an-
cestral character from which are derived the characters to be com-
pared. Thus, although the common ancestor of the dog and the
cat is not known, we may affirm that it had a tail, and that this tail
has become the tail of the dog along one line of descent and that of
the cat along another; and that, consequently, the tails of the dog
and the cat are homologous. This renders no service, however, for
the organs are so similar that their homology is evident without
any reasoning.

But if one asks what is in man the homologue of the pineal eye
of the lizard, the matter is more delicate. The common ancestor
of man and of the lizard is not known; we cannot infer anything
certain relative to the first appearance of the pineal eye; so the
question remains unanswered.

And this is almost constantly the case. Thus, when phylogeny
furnishes the required response, the question is solved in advance;
again, when the question is difficult, phylogeny remains mute.

We must, then, lower its pretensions, and in place of phylogeny,
whose responses would be certain if we only knew them, but which
we do not know, we must turn to ontogeny.

The latter also gives answers, not without value, but which are
indirect and necessitate an induction into which error may glide.
We admit, in general, that when organs are represented at some
stage of ontogenesis by very similar rudiments, these organs are
homologous, however dissimilar they may be in the adult; and,
inversely, that they are not homologous, however similar they may
be in the adult, if they are represented in ontogenesis by dissimilar
rudiments.

If ontogenesis were a faithful copy of phylogenesis, this reasoning

COMPARATIVE ANATOMY AND MORPHOLOGY 347

would be admissible. But it is not, and the deviations from the
parallelism of ontogenesis and phylogenesis are not recognizable by
sure signs.

The examples in proof of this assertion are not rare. Here is one :
when the larva of the echinoderms metamorphoses into the defini-
tive form, sometimes it retains the mouth, which is merely dis-
placed by passing to the left side; sometimes the mouth closes and
a new mouth breaks through on the left side. From the ontogenetic
point of view the mouths are not homologous in the two cases; the
homologue of the mouth of one of the forms is, in the other, an
imperf orate point of the surface of the body.

Is it necessary, then, to say that in two species of starfish, the
adults of which present the two cases given above, Asterina gibbosa
and Asterias glacialis, for example, animals as like one another as
are the cat and the dog, the two mouths are not homologous, that
the representative of the mouth of Asterias glacialis is such or such
imperf or ate point on the edge of the disk of Asterina? 1

It seems from all the evidence that the common ancestor of Asterias
and of Asterina had the normal mouth of a starfish, and that this
mouth has become the mouth of Asterias, on the one hand, and of
Asterina, on the other, so that phylogenetically the mouths of
Astenas and Asterina are homologous, although ontogenetically
they are not. Nevertheless, some morphologists, ready for anything,
do not fear to reject this common-sense conclusion, and to declare
that the mouth of Asterias and that of Asterina are not homo-
logous.

But on the other hand many morphologists reject that conclu-
sion, and in other cases, otherwise entirely similar, all agree to take
the reverse of that fashion of reasoning.

Among the insects, the embryo shows at the beginning of its
development an imagination which appears exactly like that which
in the majority of other animals (including the other arthropods)
gives rise to the primitive gastric cavity. If it became that cavity,
we would not fail to homologize it with the archenteron, but since
it develops into something entirely different, the mesoderm, we pass
in silence over this homology, thus making an exception to our
established principles.

Why do we make such an exception to our principles? Because,
in spite of our professions of faith, we do not take as a criterion
ontogenesis alone as a copy of phylogenesis. When the ontogenetic
homology is too strongly opposed to a certain intimate sense of
homology which we have within us, we lay it aside, passing it over

1 In the same way we refuse to recognize as similar the general body-cavities
of two animals, in spite of resemblances which render them almost identical, when
one arises as an enterocoel and the other as a schizocoel.

348 COMPARATIVE ANATOMY

in silence in order not to avow to ourselves the contradictions of our
logic. And what is this intimate sense of homology which directs
us thus? It is nothing less than the remains of the old concept of
the archetype which slumbers in us and wakes occasionally.

When, in two allied forms (the instance is found in the mollusks) ,
the blastopore becomes in one the mouth, in the other the anus
(Paludina), we might conclude that the mouth of the one is the
homologue of the anus of the other. We do not, however, and we
are right. But this proves that we do not hold to the criterion which
we have erected in our statement of homologies. We abandon
ontogenesis, and take for our guide connections and structure, that
is, the same characteristics which we declared entirely insufficient
to determine homologies if they were not corroborated by develop-
ment.

After phylogenesis and ontogenesis, it is to connections that we
attach the most importance in determining homologies, and very
often we content ourselves with them as a criterion. This confidence
in connections has its reason for existence in the fact that we know
that organs modify more easily their relations of vicinity than their
relations of continuity. But it is not wholly founded on observation;
it proceeds in part from the conception of an archetype with which
our minds are imbued, and from the fact that we conceive more
easily of the derivation of that archetype by the stretching and
displacement of organs, elastic and pliable after the manner of
gutta-percha, than by the transposition of masses in the way one
treats the first draught of a wax model.

We must not forget, in fact, that in ontogenesis the mesodermal
masses change place thus in toto, without maintaining any relation
with their place of origin, and that even invaginations, infoldings,
detach themselves and become free in order to go and plant them-
selves elsewhere (imaginal disks of insects, enteroccelic vesicles
of the echinoderms, urinary bladder of the vertebrates which be-
comes detached from the intestine and opens with the ureters, etc.)

Thus, the criterion of homology which, in order to be objective,
ought to remain wholly phylogenetic, is almost never so, and it
borrows, according to the case, from ontogenesis and from anatomy.
And according to the case, sometimes we accept the conclusions to
which we are led, although they may seem to clash with the most
reasonable comparisons, sometimes we reject them for the same
reason.

It must be remarked, in fact, that when the criterion ceases to be
directly or indirectly phylogenetic, it ceases to be concrete. That
kind of material continuity between the organs of the ancestors and
similar organs of the descendants which exists in phylogenetic
homologies disappears in anatomical homologies.

COMPARATIVE ANATOMY AND MORPHOLOGY 349

When two organs whose phylogeny is unknown resemble one
another in certain anatomical characteristics and differ in certain
others, if we affirm their homology, that is to say, if we subordinate
their differences to their resemblances, we do so only by comparison
with an entirely subjective type to which we refer them.

In the construction of this subjective type we have no other
guides than certain anatomical characteristics, so that our premises
and our conclusions are one and the same thing; in other words,
we make a vicious circle.

For example, when we homologize the endostyle of the ascidians
with the thyroid gland of Ammocetes and the other vertebrates,
we presuppose a common phylogenetic origin for these organs,
but since we know nothing whatever of this common ancestor,
in reality we conceive of an abstract form in which the endostyle
and the thyroid are replaced by one and the same rudiment from
which we suppose that these organs are derived.

This abstract form is nothing else than the archetype of the
natural philosophers, more refined, more certified, fashioned more
by observation, but not less subjective.

The fact is more striking in what concerns general homologies.

No one disputes the homology of the rudimentary mammary
gland of man with that of woman. Nevertheless that homology
could not in any way be based on phylogenesis. It has been inter-
preted as a mark of a primitive hermaphroditism, but that opinion
is untenable, since the ancestors of man had ceased to be herma-
phrodite millions of generations before they were provided with
these glands. Here, then, the homology is founded solely upon the
unconscious conception of an archetype common to male and female
based upon anatomical resemblances without any possible phylo-
genetic significance.

In the vertebral theory of the cranium we do exactly the reverse.
We conclude from anatomical and embryological observations that
without doubt no ancestor of the vertebrates had a cranium com-
posed of true vertebrae identical with those of the backbone, and
we go on from there to declare that no part of the skull, not even
the occipital, is homologous to a vertebra.

If, however, the occipital, although developing by the localized
ossification of a cartilaginous cranium continued by the addition
of a membrane bone, were found to be identical in form with a
vertebra of the backbone, would we deny that homology? We
should have the right, but we should fall into the same exaggeration
as in the case of Asterias and Asterina.

There is no use in insisting further upon having the right to con-
clude that the criterion of homology is nothing absolute. We
announce our pretension of borrowing that criterion from phylogeny;

350 COMPARATIVE ANATOMY

as a matter of fact, that furnishes us nothing certain, and we turn
to ontogeny and to anatomy, granting more value to one kind of
argument or to the other, according to the case, without any fixed
rule. In fact, we bring together all that we know concerning the
organs whose homology is in dispute, and we proclaim homology
when we find between these organs a sufficient conformity of char-
acteristics. In general, we interpose the condition that this homo-
logy shall not oppose the idea, very vague, very hypothetical, very
individual, which we may have concerning the phylogenetic deriva-
tion of the organs under consideration; but in many. cases we for-
get this, and are guided by the unavowed conception of an abstract
type constructed according to anatomical characteristics of every
order.

The foundations of homology are a mixture in varying propor-
tions of comparative anatomy studied profoundly, of paleontolog-
ical data too often incomplete, and of a hypothetical phylogeny,
together with a dose, not to be overlooked, of that mysticism with
which natural philosophers constructed their archetype.

This formula may appear a little irreverent to the devotees of
morphology; it is just, nevertheless. If we go to the bottom of
things, we must recognize this fact: to homologize is simply to
compare, to establish resemblances and differences in character-
istics, and to proclaim that these are casual, secondary, while those
are fundamental.

Now, there is nothing more delicate than pronouncing upon the
comparative dignity of characteristics. There is a question of the
orientation of ideas, dependent upon time and place, a question of
mode of which it is prudent to be suspicious.

When R. Owen distinguished in the determination of homologies
physiological characteristics from anatomical, and established the
difference between analogies and homologies, he rendered a real
service, for there is always an advantage in not confounding things
which are distinct; but it is less certain that he did a good thing
when he gave the precedence to homology over analogy in the com-
parison of characters, for it has led to an exaggerated disdain of
physiological characteristics.

When we proclaim an homology like that of the lungs of mammals
with the swimming-bladder of fishes, for example, we assume a
grave and sententious tone, as if we were filled with a feeling of
our own merit in announcing a fundamental truth which remains
hidden in a superficial examination. If, on the contrary, we announce
an analogy, we take a tone light, and almost a little contemptuous,
in order to set off well the small value of a wholly superficial re-
semblance in which we must not place too much confidence.

Is this right?

COMPARATIVE ANATOMY AND MORPHOLOGY 351

Is not this subordination of propriety to substance an effect of
the influence which the materialistic conception of the universe
exercises upon our minds? Will our sons continue to think thus if
the energetic conception, quite as reasonable as the other, if not
more so, comes to outweigh it? And we ourselves, should we also
be on the affirmative side if we were the spiritual sons of other
natural philosophers, who had placed in the first rank in their con-
ceptions not organs, but functions, who had conceived of beings as
having to accomplish a series of physiological actions, the nature
of the organs by which they accomplish them being of subordinate
interest?

Perhaps in that case we should be more struck by the fact that
the gill of the fish and the lung of the mammal both serve for respira-
tion than by the difference in their structure and in their material
origin.

Is there not also more interest in seeing two organs, otherwise
very different both in structure and in phylogenetic origin, coming,
under the influence of the necessity to realize functions and by the
action of similar surrounding conditions, to have functional and
structural resemblances at times astonishing, than in establishing
the fact that two organs different in structure have a similar em-
bryonic or phylogenetic origin?

Is the convergence of analogous organs less worthy of respect
than the homogeny of homologous organs?

Here are a fish and an octopus. We admit, rightly, without doubt,
that they have not a common phyletic origin, or, at least, that their
community of origin, if it exists, dates from a stage when their
special organs were not differentiated. They both have an eye
which, in spite of certain differences, presents a conformity of struc-
ture really striking. In spite of their difference of origin and their
absence of relationships, the two protoplasms which constitute the
fertilized egg of the octopus and that of the fish both develop a spe-
cialized organ, an eye, which is remarkably similar in both. In the
two phyletic series of the octopus and the fish, under the influence of
a fundamental conformity of the substances constituting the organ-
ism and of a similar reaction to the analogous surrounding con-
ditions, there are formed these two eyes, which are almost identical,
although they are not related.

Examples of this kind are numerous. Here is another quite as
striking. Many forms belonging to the groups of the mollusks, of
the ccelenterates and the worms have special organs of equilibra-
tion, statocysts, consisting of a heavy mass sustained by sensitive
hairs arising from the epithelial lining of a vesicle. The crustaceans
have on their antennules statocysts notably different in structure.
Only one, Mysis, has statocysts very similar to those of the mol-

352 COMPARATIVE ANATOMY

lusks, not on the antennules, but on the telson. This situation pre-
vents our homologizing them with the antennulary statocysts of
the other crustaceans, and the difference in phyletic origin prevents
homologizing them with those of the mollusks, the worms, or the
ccelenterates. Is not a fundamental conformity so profound, between
organs phylogenetically distinct, quite as remarkable a thing as the
resemblance of origin revealed by embryology between two organs
the structure and functions of which are very different?

Is it right, then, to place the latter in the holy tabernacle of homo-
logies in order to prostrate ourselves before it, while we relegate
the former to the despised chaos of analogies?

But, some one says, comparisons must nevertheless have a sanc-
tion, and homologies must be distinguished from analogies.

That may be, but there is no need to sacrifice the one to the
other.

Let us return to the case of Asterias and Asterina.

When we have proved and noted that the mouth of the one does
not proceed from the same point of the larva as does that of the
other, we have given to embryology all that it has a right to claim,
and it is only just to render to anatomy what it has a right to
demand in declaring that in all other respects the mouth of Asterias
and that of Asterina are identical.

In the presence of these divergences, shall we clash with embryo-
logy in proclaiming an homology wrhich it rejects, or torture anatomy
in denying an homology which the latter claims? The simplest
thing is to clash with or torture nothing by saying nothing.

Where is the necessity of formulating a general proposition which
shall certainly be false on a certain side, when it is possible to sepa-
rate it into two true propositions, in saying that the mouth of
Asterias and that of Asterina are similar in all respects except that
they are not homogenic.

But, some one says, that is what we do when we declare that the
two mouths are not homologues, since by definition homology is
nothing else than phyletic homogeny.

That would be true if we held scrupulously to that definition;
but as a matter of fact, in the search for homologies we turn to all
possible characteristics, even at times to physiological ones, for-
bidden though they are. We must many times reduce homology
to the modest significance of homogeny.

Homology has become and will remain in biological language
the mark of an important, fundamental resemblance, reducing to a
subordinate and superficial significance and to a secondary interest
whatever differences there may be.

There are words which are to ideas what infectious microbes are
to the body. Such, in the science of evolution, are " tendencies of

COMPARATIVE ANATOMY AND MORPHOLOGY 353

nature/' "hereditary propensity/' "latent characteristics; " in com-
parative anatomy such are "organs representing one another."
Like the phrase in physics, "horror of nature for a vacuum," they
correspond to nothing real. Many agree to this, but that does not
prevent us from continuing to bring them to the front as if they
contained a positive explanation. The progress of ideas lessens
their harmfulness, it does not destroy it.

If, instead of proclaiming that two organs are homologues, we
should content ourselves with saying that they have the same embry-
onic rudiment, or similar connections, or a corresponding structure,
and that this authorizes us in a certain measure to think that they
come from the same rudiment in some ancestor more or less distant,
we should say only what we have the right to say, and what would
carry with it nothing difficult. It is not the same when we decree
a decisive epithet implying that there is something important and
fundamental in resemblances, while differences are accidental and
subordinate.

There is, without our taking it into account, in this subordination
of certain characteristics to others, a remnant of the mystical con-
ception of the archetype. After having made the archetype object-
ive in the ancestral type, most of the time wre lose sight of it, and we
give a fanciful reality to an entirely subjective type, a simple schem-
atization of abstract ideas. We create mental images of types of
organs, of types of structure indefinitely varied and divided up
according to the needs of the moment, and we lose sight entirely
of the idea of finding the realization of them in an ancestral form
previously existing. In each instance wTe are ready to answer that we
are taking the phylogenetic point of view, but most of the time it is
not so, and if it should be necessary to sustain that pretension with
good arguments, we should find none at all.

This tendency to schematization is not wholly bad. It aids the
mind in grouping scattered facts in such a manner that one may
consider them as derived one from the other according to simple
rules. There is nothing inconvenient in conceiving of types of ani-
mals, types of organs, types of structure, as numerous, as varied, as
one wishes. But this is so only on condition of never forgetting that
they are creations of our minds, without any objectivity, destined
only to facilitate intellectual operations. The morphological type
must be considered only as an instrument of thought, and not as a
mystic entity, more or less hidden, which we may by observation and
study find again just as it is and not otherwise. We are at liberty to
construct it, the only condition being that it shall be advantageous
for study and that we shall never take it for anything else than it is.

There must always be present in our minds the fact that an homo-
logy is never absolute, that organs represent one another in certain

354 COMPARATIVE ANATOMY

respects, relatively to certain categories of characters, and never
wholly.

To homologize is to compare. Now, things are never so different
that we cannot compare them, nor so similar that the comparison will
not be false in some points. The tail of the dog represents almost
identically that of the jackal, a little less so that of the ox, a little less
that of the bird, a little less that of the serpent or of the fish; it does
not represent that of the scorpion or the crayfish, but it would be an
exaggeration to say that it has nothing in common with the last two.
One comparison is always permissible. When Oken compares the
vault of the skull to that of the heavens, there is this in his favor, that
one, like the other, is a hollow hemisphere having inside it something
which thinks. The mistake is made when we attempt to draw from
such distant resemblances consequences more exact or more ex-
tended. The mistake is the same, in a lesser degree, when, after
having homologized, for example, the radius with the tibia, we
imagine, as some of us have a tendency to do, that there is not in
one of these bones a single tuberosity or furrow which has not in
some more or less hidden form its representative in the other.

What must we conclude from this study?

Comparative anatomy is a science which arranges, classifies, sep-
arates, brings together, groups, and labels information, reunites
scattered facts under general formulas, compares, finds likenesses,
differentiates, subordinates, makes a hierarchy of characters. It is
the science of the study, the library, the museum. It borrows much
from nature through zootomy, paleontology, embryology, but it is
through meditation that it puts its materials to work. It attempts
at times to rise even to the explanation of phenomena, but always
in an indirect way and without hope of verification a posteriori, in
the way in which history explains politics.

It is not a laboratory science.

In that respect it is and it remains a science of the past.

The future, in biology, is for experimental researches, those where
one puts on an apron, where one weighs, dissolves, corks up, heats,
filters, distends, compresses, shakes, sections, cuts, electrolizes, etc.,
where one works with substances or with living beings which one sub-
mits to physical and chemical agencies or to conditions of life which
cause them to vary in a methodical manner in order to produce modi-
fications and thereby to discover, if possible, the causes of forms,
of structures, and of their variations.

Does this mean that we must renounce comparative anatomy,
and that this science, in which the Saint-Hilaires, Cuvier, J. Miiller,
Owen, Gegenbaur, and many others have become famous, has no
further service to render? Certainly not. It continues to be in-
dispensable to all of those who are engaged in biology in order to

COMPARATIVE ANATOMY AND MORPHOLOGY 355

diversify points of view, enlarge conceptions, coordinate information,
in order to reduce to a small number of essential propositions the
multitudes of scattered facts to which it gives a significance and
which it causes to converge toward general principles, in order to
permit unexpected and suggestive groupings, to show the chief bear-
ing of ideas which seem commonplace or of resemblances appar-
ently insignificant.

As a science explanatory of biological phenomena, it furnishes its
share of ideas and facts, but it is not armed properly to solve pro-
blems, and allows itself to be distanced by experimental researches in
cytology upon the sexual elements, in fecundation, parthenogenesis,
ontogenesis, teratogenesis, the action of agents of every kind upon
living beings in the diverse conditions of their biology, in heredity,
variation, the acquisition of specific characters, and in the nervous
functions, from the most elementary sensations up to instinct and to
the highest manifestations of intelligence.

In certain works on paleontology the importance of diverse beings
or groups of beings at different epochs is represented by the varying
width of a band which traverses the successive stages of the geo-
logical epochs. If we should do the same in order to represent the
relative importance of comparative anatomy in the different epochs
of our history, we should have to figure it as a line of extreme thin-
ness traversing the ancient epochs, suddenly becoming very large
at the beginning of the last century, and retaining even to our day
a respectable amplitude, which, however, does not seem destined to
increase indefinitely in the future.

Experimental researches in biology meanwhile would take the
form of a triangular band whose summit would be turned down
towards the past epochs, while the base, growing larger and larger,
will without doubt continue to enlarge during a length of time im-
possible to foresee and perhaps unlimited.

SHORT PAPER

PROFESSOR GEORGE LEFEVRE, of the University of Missouri, read a paper
before this Section on " Artificial Parthenogenesis in Thalassema Mellita," giving
the results of his studies at the Laboratory of the United States Bureau of Fish-
eries at Beaufort, N. C., during the previous summer.

«t.

in- •»>)

iiO C/ J

•>i' ' l»b".i; •];>

DEATH OF CAESAR
Photogravure from the Painting "by Jean Leon Gertime.

This is an artistic reproduction of the famous painting by Geroine depicting
in a most dramatic manner the tragic climax to the conspiracy that was
formed against Caesar under the leadership of Brutus. The painting was
first exhibited at the Paris Exposition of 1867. at which Ge"r6me was awarded
one of the eight grand medals.

SECTION J — HUMAN ANATOMY

SECTION J — HUMAN ANATOMY

(Hall 2, September 22, 3 p. m.}

CHAIRMAN: PROFESSOR GEORGE A. PIERSOL, University of Pennsylvania.
SPEAKERS: PROFESSOR WILHELM WALDEYER, University of Berlin.

PROFESSOR H. H. DONALDSON, University of Chicago.
SECRETARY: DR. R. J. TERRY, Washington University.

THE Chairman of the Section of Human Anatomy was Professor
George A. Piersol, of the University of Pennsylvania, who opened
the meeting by remarking:

" Those of us who have listened to the general addresses delivered
during the earlier sessions of the work must have been impressed
with the breadth and comprehensiveness of the acknowledged pur-
poses of this Congress. These purposes have been not only to bring
into touch the widely diverse divisions of science, but also to afford
opportunities for exchange of thought between those concerned with
problems more or less akin. For, with the ever-increasing mass of
details that each year adds in all branches of knowledge, it becomes
less and less probable that the single mind can master the minutiae
of more than a limited domain.

"In recognition of the inevitable specialization that the develop-
ment of science has brought, have been arranged the hundred and
more sections of which our own — that of Human Anatomy — is one.

" Human anatomy represents one of the oldest biological specialties,
for what more natural than that man's complex organism should have
early attracted searching inquiry? But specialization begets narrow-
ness, and this, coupled with the potent influence of the long prevail-
ing views regarding man's assumed exceptional origin and place in
nature, did much to retard the establishment of human anatomy
upon the broad basis that it to-day enjoys.

The too often well-founded charges formerly made by our bro-
thers, the zoologists and comparative anatomists, that the human
anatomist, ignoring morphological significance, failed to obtain a
true perspective in his exclusive studies of man, are, happily, rap-
idly losing force, as on all sides has arisen a keen appreciation of the
necessity and value of regarding man as a member of the great zoo-
logical family.

" Who shall estimate the stimulating influence of the broad-gauged
men who enjoyed the golden age of opportunity during the last
century and added so much of epoch-making significance? Among

360 HUMAN ANATOMY

the many, we recall the names of Johannes Miiller, Hyrtl, Henle,
and Luschka; of Sappey, Owen, Huxley, and Turner; and of our
own great fellow countryman, Joseph Leidy. Two additional names
of men to whom anatomy owes much must be mentioned: those of
His, the sudden ending of whose productive life science even now
mourns, and of Koelliker, — the Nestor of anatomy, — who, in spite
of his more than fourscore years, still contributes to the science he
has so long and brilliantly served.

" In keepingwith the broad spirit of a great international exhibition
was the happy inspiration to invite distinguished scientists from
across the seas to participate in the sessions of this Congress. And
it is particularly appropriate that this Section is to be addressed by
an acknowledged leader in anatomy; one whose broad interests and
many-sided accomplishments give to his words, written or spoken,
an interest and authority universally recognized. I have the great
pleasure of introducing Professor Waldeyer, of the University of
Berlin."

THE RELATIONS OF ANATOMY TO OTHER SCIENCES

BY WILHELM WALDEYER
(Translated from the German by Dr. Thomas Stotesbury Githens, Philadelphia)

[Heinrich Wilhelm Gottfried Waldeyer.Professor of Anatomy, University of Berlin,
since 1883. b. Hehlen, Brunswick, Germany, October 6, 1836. M.D., Ph.D.,
LL.D. Assistant at the Physiological Laboratories of Konigsberg and Breslau,
and Professor of Pathological Anatomy, University of Breslau, 1865-72; Pro-
fessor of Human Normal Anatomy, University of Strassburg, 1872-83. Per-
manent Secretary of Royal Prussian Academy of Sciences; also member of
fifty-seven academies and learned societies. Author of Ovary and Egg; The Sex
Cells; Topographical Anatomy of the Pelvic Organs; and numerous other noted
works and articles on anatomy.]

WHEN I attempt to treat correctly, according to the general pro-
gramme, that branch of science which concerns itself with the study
of the structure of our own bodies, let me first recall that here we must
create something for life out of death. Even the most long-lived man
passes over the stage of the world like a shadow-picture. He passes
quickly away after a short instant of existence, "a walking shadow
signifying nothing."

But if the life of the individual signifies nothing, the stream of
living individuals which constantly flows over our planet shows in
man the greatest, the most important, the most powerful being which
the world has brought forth, and I place against the words of the great
Briton, those of the great Grecian,

IIoAAa ra Sctva /c'cruSev di/$pu>7roi Seivdrepov TreAei.

Thus we see that man does not hesitate, in his search for true know-
ledge of how life springs from death, to lay the hand of investigation
even on his dead, in order to learn from them what he is. It has,
indeed, cost him centuries of severe struggle, of the building-up of
culture, before he attained this. Man has killed his kind without
scruple in thousands, in millions, in billions; yes, has boasted of it,
and has praised the act in songs and poems, and does still to this
day; but before the blank, senseless corpse, the memento mori, he
felt ashamed. The mutilation of corpses, w7hen it has occurred,
has always been severely judged. Even the fame of Achilles has
not been increased by the fact that he dragged the corpse of Hector
around the holy city. In earlier times the opening of bodies was
looked upon as a desecration. This is why human anatomy, al-
though placed among the most ancient studies, was first raised to
the rank of a science when investigation of human bodies could be
undertaken in increasing number, owing to the powerful efforts of
educated men with a determined aim.

362 HUMAN ANATOMY

I may be permitted, in order to explain more clearly and better,
on the one hand, what branches of human science have been assisted
by anatomy, and on the other hand, which have furthered it, to
give a short sketch of the principal epochs in the course of develop-
ment of human anatomy.

I think we may distinguish three great divisions of this develop-
ment. A first, pre-Galenic, which we may also designate in a certain
sense as prehistoric, a second, the period of Galenic anatomy, and
a third, the period of Vesalic anatomy, which extends until the time
of Theodor Schwann and Johannes Miiller, 1839, or, in round
numbers, 1840. At that time begins the epoch in which we now are.

If I may briefly describe the first period, whose beginning is as
unknown to us as that of the human race, anatomy consisted of a
sum of unconnected facts concerning the inner and outer parts of
the body, such as were obtained from immediate experience and
from the observation of the body in its different motions. It was
also obtained by the observation of wounds, — note the descriptions
in Homer, — and from sacrifices of man and animals. The fact that
the human race undoubtedly first appeared in the tropics and
subtropics, and at first neither required nor used clothing, permitted
observations to be easily made.

That which was so determined and handed down became, with
increased culture, more and more the property of the priests, and
of the physicians, who were generally of the priestly class. But what
we can learn from the Assyrian excavations, from old Egyptian,
old Chinese, old Japanese, old Thibetan, and old Indian literary
and other monuments is not sufficient to display this historically.
Therefore, I use the expression, "prehistoric," because in part their
material is entirely false, and nowhere is a complete system brought
together. It is merely "anatomic fragments " which we get to know.
From them we can form no clear idea of the state of anatomic
science of the time under consideration, or to what extent their
medical therapeutics was influenced by their anatomic knowledge.
There is, indeed, much in the papyri of Egypt and in the voluminous
Indian and Chinese literature, but in the short sketch given here,
I can only mention it in the above way.

In pre-Galenic times the anatomic knowledge of the Greeks
appears to be more accurate. We possess statements that, already
before the time of Hippocrates, dissections of human bodies were
carried out, and we may assume that among the Indians and
Egyptians this was also occasionally the case. We know, however,
nothing more definite, and these dissections were certainly rarely
performed with sufficient care or with the definite intention of ob-
taining clear anatomic knowledge. Otherwise, the writings which
have come down to us would contain more facts.

THE RELATIONS OF ANATOMY 363

The anatomic writings which are ascribed to Hippocrates contain
many more facts, and these are much more correct; but, even from
them it is plain to be seen that a systematic study of the corpse
was not the basis of the facts contained in them. That dissections,
especially for anatomic study, were carried out by the Hippocratic
school, is open to strong doubt.

From this time on, the slowly collected anatomic data are increased
by numerous physicians, philosophers, and naturalists, but even
these advances can hardly be referred to systematic dissection of
the body. It is especially striking that Aristotle, who had so much
at his command, and whom we thank for so much in zoology and
zootomy, knew as little about the anatomy of man as is found in
his writings.

The data obtained by Herophilus and Erasistratus, who lived
between the middle of the fourth and the first third of the third
century before Christ, seem to me to show that they were the first
who made truly anatomic dissections on the human body. That
they opened the body cavities of many corpses is certain, but I
believe we may go further and say that they have dissected carefully.

Unfortunately, hardly anything of their writings is preserved,
and just as little of Marinus, the precursor of Galen, whose twenty-
volume anatomy has only been preserved in Galen's abstract, as
have some facts concerning the advances of Herophilus and Erasi-
stratus. Thus it appears to me to be justified to let this epoch reach
to Galen.

Galen of Pergamos, who lived in the third century of the present
era, was more student and compiler of extraordinary industry than
original investigator, but nevertheless he must be placed at the
apex of the second period of anatomic study, partly because he
brought together everything which had been determined before
his time, exercised critical judgment on it, and added to it his own
investigations, which, however, were only obtained on animal
material, especially apes; principally because the standard of
anatomic science codified by him remained authoritative for all
the cultured races for 1300 years and more. During all this time
his work remained the authority, an almost unique example in the
history of science.

Several causes coincide to explain this striking fact. One of these
is, of course, the giant work which Galen performed. It seemed
built to last for centuries. The principal reason is that man hesi-
tated to lay hands on human bodies, and if in each century a few
physicians rose above such thoughts, where could they find a place
to carry on anatomic studies? Even a simple opening of the body,
"obduction," was not permitted. There were no "Anatomic Insti-
tutes." These were reserved for a later epoch. If, occasionally.

364 HUMAN ANATOMY

the opportunity offered for the performance of an autopsy, the
deviation found in one or a few cases was not sufficient to shake
an authority as well founded as Galen's. For that, a material was
required like that on which Vesalius worked, and a mind like his
own to interpret it.

Andreas Vesalius (1515 to 1564, his period is usually given,
although neither date is certain) and Gabriel Fallopius made a
new departure in anatomy. They replaced uncertain data, mostly
founded on chance observations and on animal dissections, by
systematically arranged observations, based on methodical inves-
tigations of human bodies. I name Fallopius with Vesalius, not
only because he immediately corrected many false ideas of the latter,
but because he was one of the most accurate observers whom we
find in anatomic literature, and therefore, in his short life (1523
to 1562) made so many discoveries in the realm of descriptive
anatomy that he was equaled by no one before or since, and finally
because we have received from him the first orderly attempt toward
a general anatomy. As third among the founders of scientific ana-
tomy, Eustachius of Rome, the contemporary of Vesalius, must be
mentioned.

Even before the time of Vesalius, comparatively systematic autop-
sies on human bodies had been undertaken, especially in Italy, and
even in a scientific way, and with the agreement of the government.
This was the case in Bologna, Venice, Rome, Florence, Padua, and
other places. Padua possessed as early as 1446 an anatomic theatre.
Vesalius himself, born in Brussels, received the greater part of his
anatomic education at Paris and Louvain. Thus we see that the
final complete revolution was to some extent prepared for, as new
periods always have their dawn.

From Johannes Miiller and his pupil Schwann we must date the
last period of the development of our knowledge. Men like Malpighi,
Morgagni, William Harvey, Albrecht von Haller, and K. E. von Baer,
have, indeed, carved lasting marks in the flourishing tree of our
science by their brilliant discoveries and well-founded systematic
compilation of contemporary anatomic studies, as well as by fruitful
comparisons of the same, with allied sciences, but none of these had
the same epoch-making influence as Miiller and Schwann. The found-
ing of the cell-doctrine by Schwann, 1839, which first made possible
a scientific general anatomy and histology, was the most influential.
At the same time, through the action of Miiller's genius, another
spirit was introduced into anatomic descriptions in general anatomy,
as well as in embryology and comparative anatomy, of which the
composition of Henle's text-book of systematic anatomy on the one
hand, and Gegenbaur's work on the other, give proof. At the same
time the text-books of histology and general anatomy, as well as those

THE RELATIONS OF ANATOMY 365

of topographic anatomy, begin to be more -numerous; also the special
treatises on these subjects, and, finally, the searching investigation of
specialists in the anatomy of certain regions begins at this time.

Human anatomy continues to develop itself more and more com-
pletely in all these directions up to our own day. We must recognize
the branch of human anatomy, and limit ourselves to this branch
according to the following scheme:

(1) Descriptive anatomy of the human body.

(2) Topographic anatomy of the human body.

(3) General anatomy.

(4) The anatomy of different ages of man from the first develop-

ment until natural death caused by old age.

(5) The anatomy of the human races in all these relations.

All these must receive scientific enlightenment from the general
history of development, as well as from comparative anatomy of that
branch of animals to which man belongs physically, the vertebrata.

I may be permitted to make here an explanatory observation. We
must distinguish sharply, as is not always done, between general
anatomy, histology, or the study of tissues, and microscopic anatomy.
General anatomy is the most inclusive. Histology is only a small
part of general anatomy, which also includes general morphology,
the study of the form of the animal body, especially in connection
with the vertebrata, as well as the general physical properties of the
component parts of the human and animal body. Chemical considera-
tions, of course, come in also. Microscopic anatomy is, on the con-
trary, an artificially created division which practical necessity has
permitted to remain. It belongs to descriptive as well as to gen-
eral anatomy, and has no sharp limits from descriptive anatomy
as far as this can be determined by observation with the naked eye.
With the same justification one might speak of a maceration anatomy,
of a staining anatomy, of a dissection anatomy of a serial section
anatomy. By the retention of the term microscopic anatomy we only
satisfy a practical need. It must be clear to us that it remains de-
scription, whether the anatomy of the external form and relation-
ships, for instance, of the human liver is depicted, and the form,
color, and limits of the lobes is described, or whether the construction
of these lobes from special liver cells, as the essential part and from
a connective tissue framework with blood and lymph vessels, nerves
and fine bile-ducts, is demonstrated and the details of their relations
described.

This, in my opinion, is the way in which the realm and position
of human anatomy in the plan of science must be considered.

In conformance with the task set before us, we must now deter-
mine to what causes and motives the development of human anatomy
is due, and which sciences have assisted in its development.

366 HUMAN ANATOMY

We may divide the causes and motives into immediate and medi-
ate. As far as we can tell, it was the needs of medicine and of the
treatment of the sick which, in the most ancient times, gave origin
to the investigation of the human body. I do not consider here the
knowledge of the external form, which the simple observation and
examination of the naked body and the necessity of naming the
individual parts must give. Animal sacrifice and divination from
sacrifices, still more human sacrifice and cannibalism, as well as the
examination of large wounds and the natural attempt to bind them
up, in order to stop hemorrhage and to replace dislocated limbs,
as well as the occurrences during delivery and in many other con-
nections, gave man from his first appearance on the earth an oppor-
tunity to attain anatomic knowledge. We find it among the prim-
itive people of to-day, to the extent to which a people without script
can attain. The oldest anatomic and medical writings which have
come down to us show, already, a mass of facts obtained in the above
way, which was perhaps greater than those in any other realm of
biology at that time.

Knowledge developed more rapidly with the awakening of scien-
tific medicine. At first it was naturally the requirements of practice,
particularly those of surgery and obstetrics, which were the cause of
development. The requirements of internal medicine were not felt
until later. Much later, but with so much the greater energy, physi-
ology, zoology, comparative anatomy, and human pathologic ana-
tomy showed their effect. The last, as well as human physiology,
is inconceivable without an accurate knowledge of human anatomy.
Zoology, comparative anatomy, and embryology are not absolutely
necessary to human anatomy, but none of these sciences can fully
reach its goal without a knowledge of the most highly developed
creation, man.

State medicine felt the need of caring for anatomy among the
latest of the branches of medical instruction, but finally furthered
anatomic study. At the same time jurisprudence comes into relation
with anatomy, with animal as well as human.

In all of this connection, excepting that of jurisprudence, the
biologic character which all have in common played a part. But
even the purely mental sciences, especially philosophy, and in this,
above all, psychology and the theory of perception, as well as the
history and beginnings of philosophy, required a study of anatomy
for their further development. The relations of the latter to psych-
ology and the theory of perception, as well as to other branches
of philosophy, first became striking when we began to penetrate
more deeply into the finer anatomy of the brain. Here, in spite of
books so numerous that one might fill libraries with them, we still
stand in the first stage of our knowledge. The anatomy of the brain

THE RELATIONS OF ANATOMY 367

is of little more use to philosophers than was the Galenic anatomy
to the surgeons of that time. Philosophy will thus remain one of the
factors which continually stimulate more detailed anatomic studies.
We shall return to this later.

Manifold are the facts concerning human anatomy which are
found in history and tradition. In the first place, the history of
human anatomy is an important part of general history, especially
of the history of education. To determine the history of anatomy
requires a considerable knowledge of the subject. Illustrations of
anatomic objects occur frequently among prehistoric remains. I will
recall only votive tablets and relics. With an accurate knowledge of
anatomy, many facts in the history can be rightly determined. The
method introduced and developed by Welcker, His, and Kollmann, of
reconstructing the head by placing skin and hair over the skull bone,
can be of importance in the determination of the identity of a person-
ality. Although we are now only at the beginning, I am convinced
that we may expect much of value from this method.

The reconstruction of the head has, also, a relation to one of
the most important non-medical contributors to anatomy, the fine
arts. Since early times its requirements have given an impulse to
the study of anatomy, especially to that of the external form and the
anatomy of bodies in motion. We may, indeed, say that it was
the artists who first developed and furthered the study of this branch
of anatomy. I need only recall Leonardo da Vinci, Michael Angelo,
Raphael Sanzio, and Albrecht Diirer. To this point also we shall
return.

Finally, we may say, according to the proverb, "Homo sum,
humani nihil a me alienum puto," that everything connected with
man and with humanity requires a knowledge of the construction
of the human body. We need not be surprised, therefore, if advances
in the study of anatomy come from unforeseen and unexpected direc-
tions. I shall only mention here the great realm of sociology and
personal hygiene.

Although these are the principal factors which have required a
study of human anatomy, and which in the future will impel a pro-
gressive development and increase in the knowledge of the same,
there is one factor which must not be left out of consideration, which
is and will remain active in the development of all sciences, as well as
of human anatomy. This is the great advance in the general condition
of scientific and public life, as well as in the condition of the masses.
Such advances may require a long preparation, but in a short period
great advances and discoveries will occur, astonishing the people
themselves. Thus, fortunate political conditions, political revolutions,
and social changes, even fortunate wars, whose result is a long time
of peace, may mean the beginning of a new period, as well for the

368 HUMAN ANATOMY

conqueror as for the conquered, accompanied by rapid development
in all branches. All these things act as yeast upon the intellectual
labors of a people. Can it be a mere coincidence that the first improve-
ment of medical knowledge by the Hippocratic school occurred at
the time of Pericles, that the Galenical school followed soon after
the bloody time of the Roman emperors, that previously the develop-
ment of anatomy in a high degree occurred in the short and bloody
period of the Ptolemies, or finally, that the almost phenomenal blos-
soming of anatomy at the time of Vesalius, Eustachius, and Fallopius
followed soon after the beginning of the Renaissance, the invention
of printing, and the discovery of America? A wonderful period this
was at the beginning of the sixteenth century!

Philosophy, the mother and starting-point of all sciences, in
which they all come together, assisted materially in its develop-
ment, not only because it placed new problems before anatomy,
but because its recent conceptions and systems have affected the
progress of anatomy and that of related sciences, to a degree hardly
suspected by those who have accepted its ideas. The philosophy
of Cartesius and the application of the inductive method by Francis
Bacon, Bacon of Verulam, were, of course, not without an influence
upon all natural sciences, as well as on the development of anatomic
teaching.

But we should appear thankless, if we did not mention the valu-
able assistance which influential and sagacious men, be they rulers
and statesmen, be they wealthy burghers, have given to the cause
of anatomy. The Ptolemies, Medicis, many of the popes of the
sixteenth century, the Hohenstaufens, Frederick II, and others
have assisted by laws and regulations in the development of ana-
tomy, at a time which was most difficult and unfavorable for the
same. In this country, in which all sciences are advancing with an
unexampled energy, a steadily increasing number of large-hearted
citizens consider it their greatest honor to use their hard-earned
wealth in the service of science.

Human anatomy has also received valuable aid from the found-
ing of universities and other scientific institutions. If the problems
may be mentioned which anatomy has still to solve, it will be shown
that special grants for the same are among the most worthy objects
for wealthy donations.

Our science, as all others, may hope for considerable advance
from the cooperation of the academies and learned societies of the
whole world, which has been brought about at the end of the century
by the "Association of Academies." The first problem which was
taken up by the Academies this year, the advancement of the study
of the brain, is in large part anatomic. I cannot neglect referring in
this place to the name of William His, who studied this problem

THE RELATIONS OF ANATOMY 369

with all his mighty energy until his death, which occurred May 1 of
this year, — praising him, and at the same time regretting that he
could not survive the taking-up of this task by the Academies.

In addition to the medical sciences, which we have already
mentioned among the mediate influences, other natural sciences
have had an immediate influence upon the development of anatomy.
If medical sciences must be mentioned here again, this is justified
by the fact that surgery, internal medicine, obstetrics, and the
many modern specialties, have had an immediate influence upon
anatomy, by their careful investigations on the living and the com-
parison of healthy with diseased organs. They have discoTered
many new facts and shown others in the proper light, but this
need not be gone into in detail here.

In addition to the medical branches, human anatomy must be
especially indebted to botany and zoology; above all, however,
to embryology and comparative anatomy. Botany helped espe-
cially in the first completion of general anatomy, above all, the
study of the cells and tissues, and has advanced in this direction
considerably farther than human and comparative anatomy. The
cells themselves were first discovered by botanists, but this is
easily understood, because the botanical objects are generally much
easier to prepare, and especially to examine in the fresh state, than
those of zoology and human anatomy.

Besides these, physics in all its branches, chemistry, and mathe-
matics, have given much aid to the anatomists and will continue
to do so.

It is, in the first instance, the estimation of mass, number, and
weight whose improvement and refinement have always exercised
a beneficial influence on anatomy. I shall mention here only the
balances, the pelvimeter, the measuring-scale, the measuring-cylin-
der, the micrometer, the kinds of delicate counting-apparatus, the
manometer and thermometer, and the apparatus for the deter-
mination of capillarity. We may also mention here the principal
mechanical instruments of anatomists, knives, scissors, sounds,
tubes, and syringes.

Especially interesting is the history of the microtome, which was
first made use of by the before-mentioned anatomist of Leipzig,
William His. In this case mechanics received a great furthering
from anatomy, before which the problem of making an uninter-
rupted series of extremely thin sections of the most various objects
was placed.

We could hardly believe, unless we were familiar with the subject,
what difficulties were here to be overcome, and how much genius
was required in the performance of this task, and we are still work-
ing at the problem.

370 HUMAN ANATOMY

When we compare the old anatomical apparatus of Leyser (or
Lyser), which is described in his CuUer Anaiomicus with a com-
plete anatomic armament of the present time, we see at a glance
the great progress which has been made in this elementary part of
technique. The great influence of the above-mentioned sciences is
also shown in the material which we use to-day, improved steel,
nickel-plated instruments, etc.

This influence is even more marked in the realm of optics. If
we require any proof of the fact that one science can be helped
by another, we have only to mention the relations of optics to
human anatomy, and, of course, its relation to the other natural
sciences.

No other agent has done more to illumine the obscure subject
of the human body than has light, from the simplest arrangements
for good illumination, by the correct disposition of windows in the
dissecting-room, to the ultra-microscope and radioscopy or "Rontgo-
graphy." Artificial illumination has made such extraordinary ad-
vances in our time that, especially with electric lighting, we can
concentrate the light upon any given point and limit it as we will.
Then we have the various mirrors, the vaginal speculum, which was
known to the physicians of ancient Greece and Rome, the laryngeal
mirror, whose fifty-year jubilee we celebrate to-day, the rhino-,
pharyngo-, and cesophagoscopes, the otoscope, the cystoscope,
and above all Helmholtz's brilliant discovery, the ophthalmoscope,
whose latest stereoscopic modification by Dr. Thorner may be seen
here in the German "Department of Education." All these dis-
coveries have, in addition to their practical importance, been of
the greatest service in the study of human anatomy, especially that
of the living, and will still continue to be.

The electric light permits, by its endless adaptability, a large
number of additional applications, especially for the illumination
of body cavities and hollow organs. I will recall only the transillu-
mination of the accessory sinuses of the nose.

From lenses and eyeglasses, among which are the dissection eye-
glasses of Briicke, we pass to the simple and later to the compound
microscope, one of the most important inventions which has ever
been made or will ever be. How great the progress is which results
every year in this special realm, is also shown here by the exhibi-
tion of the noted firm of Zeiss in Jena. Every step forward which
is made here is of great benefit to human anatomy.

For anatomic study and the demonstration of new facts, we may
mention the drawing apparatus, the projection apparatus, the
episcope, and epidiascope, and above all, photography, whose
future development we cannot yet foretell. With this discovery,
France, which opened the way and has always led in the investiga-

THE RELATIONS OF ANATOMY 371

tion of light, has made an advance which cannot be too highly
valued.

As, in the starry heavens, the photographic plate shows us worlds
which could have been recognized in no other way, so also the same
plates show us finer details in the structure of the bodily tissues,
which were only incompletely seen before. It fixes our eyes upon
them, makes possible comparative observations, and makes much
certain which otherwise would have remained doubtful.

Radioscopy stands above all others in its great value for descrip-
tive and topographic anatomy. This it is which, in the truest sense
of the word, has illumined the obscurity of the human body, and,
in connection with photography, has been one of the most important
advances, not only in anatomy, but in general medicine. Only a few
years have passed since Rontgen, then living at Wiirzburg, made his
overwhelming discovery, and the World's Fair Exhibit at St. Louis
convinces us to-day of the extraordinary importance which it has
won for medicine.

Physics and chemistry meet in the technique of injections, which
are so important for the advancement of anatomy. The manufacture
of a suitable apparatus, the syringe, in which also the air-pump
plays a role, falls to mechanics, as do the thermometer and manometer,
and, on the other hand, the production of a suitable material is aided
by chemical studies. Since Ruysch of Holland, who was the first
worker in this field, and his famous countryman, Swammerdam,
Lieberkiihn in Berlin, Hyrtl in Vienna, Thiersch, the surgeon of
Leipzig, the optician Schobl in Prague, the anatomist Teichmann
in Krakau, Sappey in Paris, Taguchi in Tokio, Dalla Rosa in Vienna,
and Gerota, who was at that time assistant at the Berlin Anatomic
Institute, and is now professor at the University of Bukarest, have
done great service in this field; those since Teichmann especially
with the difficult injection of the lymph-vessels.

Teichmann prepared an injection-mass which is still the best for
the rougher lymph- and blood-vessel injections. Sappey developed
the mercury injection, which had been used by the older anatomists,
Monro, Mascagni, Cruikshank, and Fohmann. Taguchi and Dalla
Rosa used Japanese and Chinese India-ink, which had previously
been used by von Recklinghausen for the injection of large and small
lymph-vessels. Gerota's injection-mass, devised a few years ago,
and the syringe of his own construction, denote a marked advance
in the technique of the injection of the smaller lymph-vessels, which
has already made possible important advances in human anatomy.

These injections with soft masses were followed recently, in Ber-
lin, by the injection of fluid metal masses, devised by Wood and
Rose, which after hardening permit no more change of shape in the
injected vessels or canals, and thus are of especial service in topo-

372 HUMAN ANATOMY

graphical anatomy. The method is also of value because Rontgen
pictures of the vessels injected with metal can be taken, and thus
we may determine their position without their being distended or
stretched. Recently quicksilver injections, on account of their simpler
technique, have been used a great deal for the taking of radiographs,
but displacement and distortion are not excluded. Further study will
determine what is best in each case.

The injections of the blood-vessels of human bones recently carried
out by Lexer of Berlin, with a special technique, show that important
advances may be daily expected, as these injections have shown
certain points which were hitherto unknown to anatomy. Radio-
graphs of the same may be seen here in the German "Department of
Education."

A procedure which is closely related to injection is corrosion. I
believe that corrosion following injections of metal was first carried
out by Bidloo. Hyrtl was recognized as the master of this method,
but in the hands of F. E. Schulze, Merkel, Schiefferdecker, Zondeck,
and others, striking results have been obtained in the anatomy of the
viscera, especially of the lungs and kidneys.

The various procedures which are proposed to conserve the ma-
terial of human anatomy are more allied to chemistry. Here we may
consider the preparation of bodies for dissection, the conservation
of separate organs, the special methods of preparation, and finally
those for exhibition purposes in museums. Thus we may here dis-
tinguish between a preparatory technique, a special technique, and
a museum technique. We may add that these are different for macro-
scopic and microscopic anatomy. I cannot stop to mention all the
points in which anatomy must be grateful to physics and chemistry
in this connection, but shall only mention those which have been
recently developed. For the conservation of objects for investi-
gation the method of freezing has been used, especially in America.
France, and especially Russia, have made us familiar with the tech-
nique of frozen sections, which was raised to its highest point by
W. Braune.

Recently in America simple hardening in strong formalin solution
has been used instead of freezing. I have seen here, with Professor
Potter of the St. Louis University, especially fine formalin specimens
and sections.

The use of chemical methods has advanced us materially in the
art of macerating and bleaching bones. I will again recall in this
connection the anatomist of Krakau, Ludwig Teichmann, my teacher
in anatomy. The fibrillation procedure of Jacob Stilling of Strassburg,
which promises good results in the preparation of brains, nerves, and
muscles, also rests upon a chemical reaction.

The technique of microscopic anatomy may also be considered as

THE RELATIONS OF ANATOMY 373

related to chemistry. We no longer stand upon the purely empiric
basis which has existed since the introduction of carmine into the
technique of staining by J. Gerlach of Erlangen, when we wish to
determine the use of a new stain. Three procedures must be men-
tioned as especially valuable, the corrosion method of Carl Weigert of
Frankfurt-on-the-Main, whose early death was deplored by all anato-
mists of this land, the staining in vivo of Ehrlich, who is also known all
over America as an investigator of the first rank, and the method of
Dr. Kaiserling, who assisted the German universities in arranging their
exhibition here a few months ago, the method of preserving anatomic
preparations so that they retain their natural colors for a period
of time hitherto not thought possible. The exhibition of the Berlin
Pathologic Institute will give everybody an opportunity of convincing
themselves of the superiority of this method for normal, as well as
pathologic, anatomy.

I can only refer in passing to the procedure of Golgi for the micro-
scopic study of the central nervous system, and its recent improve-
ment by S. Ramon y Cajal of Madrid, the method of Coccius, His,
and von Recklinghausen, of impregnation with silver, that of J.
Cohnheim, of impregnation with gold, and the osmic acid fixation
method of Max Schultze. I may also mention that an encyclopedia
of the technique of micro-anatomic methods has recently appeared
in Berlin under the editorship of Rudolph Krause, which occupies
a large quarto volume, and shows adequately how great an advance
has been brought about in anatomic methods by the study of chem-
istry.

Of the art methods, that of taking casts is especially to be men-
tioned, which has been adapted to scientific purposes by W. His and
by Born's method of modeling with wax plates. These not only serve
for the obtaining of specimens for investigation, but also to clear up
obscure topographical relationships, especially in embryonal ana-
tomy and the form of certain cavities. A glance at the section of this
exhibition where this is displayed will show what a great importance
and high development the technique of taking casts has reached.

It may be mentioned that the relation of the fine arts to human
anatomy was developed, to a high degree, many centuries ago. Illus-
trations for purposes of instruction were prepared by Henri de Mon-
deville (about 1300), and we find some in the book of Berengarius da
Carpi about 1500. The recent advance in anatomic illustrations, in
books, and in atlases, is shown by all the journals, archives, and peri-
odicals connected with the subject. It is also seen in our text-books,
which have been prepared in great number in the United States, of
which I will only mention the excellent topographical anatomy of
Deaver, the classic work of W. Braune and Sappey on the same sub-
ject, and on the anatomy of the lymph-vessels, the recent atlases of

374 HUMAN ANATOMY

Toldt, Spalteholz, Brosike, Sobotta, 0. Schultze, and above all, the
anatomy of the human embryo by W. His. Some of these books,
which are well adapted to show the influence of the recent improve-
ment in the technique of illustrating on anatomic teaching, may be
seen in the German "Department of Education."

Finally, I will merely touch upon the marked influence which the
founding and continuing of special archives and journals and regular
yearly reviews and yearly compilations have had upon anatomy, as
well as upon all other sciences. I may also mention the societies for
the study of anatomy (since 1886) and the International Cyclo-
pcedia of Literature recently prepared by the London Royal Society.
Anatomy must also be grateful to philology, as this has made possible
the systematization of its extremely complicated nomenclature. The
start in this direction was made in Germany at the suggestion of W.
His. We may hope that in the same way an anatomic language which
will be adapted to all people will develop and retain the interest of
succeeding generations in scientific unity. I am of the opinion that
this will only be possible by the historic method.

When we pass to the second part of our subject, the consideration
of the influence and improvement which has been exercised by human
anatomy upon other branches of art and science, we may dispose of
it much more briefly, because the influence is generally reciprocal.
We shall enumerate the branches concerned, as far as may appear
desirable, and give examples here and there. It is not necessary to
insist upon the great importance of anatomy to the other medical
sciences. Following a noted saying, we may state "Anatomia est
fundamentum medicinae." Before Richard Lower had discovered
the course of the vagus nerve to the heart, there could be no thought
of a physiology of the cardiac action, and Marcello Malpighi's dis-
covery of the capillary blood-vessels set the keystone to Harvey's
doctrine of the circulation of the blood. We know how important the
determination of normal anatomic facts is for pathologic anatomy,
and it is not in vain that our pathologic anatomists constantly turn
to the study of normal anatomy. Men like Morgani and Rudolph
Virchow, Cohnheim, Cornil, Marchand, Orth, yon Recklinghausen,
Carl Weigert, and others have clearly understood the importance of
this close connection.

The problem of embryology could only be definitely determined
when Karl Ernst von Baer, in the year 1817, discovered the mam-
malian ovum. The detailed investigations of human anatomy, which
have been performed more carefully than those of any other animal,
are of the greatest importance for comparative anatomy and zo-
ology.

We may also see how more accurate anatomic knowledge has been
of use to practical medicine, in the physical methods of investigation

THE RELATIONS OF ANATOMY t 375

in internal medicine, and in many other ways. How this has helped
the latter may be seen by a reference to lumbar puncture, introduced
by Quincke, which is constantly becoming more important, and
which could only be performed after the detailed anatomic inves-
tigations of Axel Key and Gustav Retzius. This method has also
brought about a long series of anatomic studies. That we may
conclude with a more general example, let us recall what a mighty
and beneficial influence on the development of internal medicine was
exercised by Hermann Boerhaave, whose Institutiones Medicae and
Aphorismi de Cognoscendis et Curandis Morbis rest entirely on an
anatomic basis. We may also recall how great an influence was
exercised by the memorable Anatomic Generate of Francois Xavier
Bichat. Was not the cell-doctrine necessary, before a scientific
bacteriology could develop? How carefully every obstetrician and
gynecologist must study the human pelvis, and every new discovery
which is made in this branch of human anatomy is of use in practice.
The history of the last few years shows that much is yet to be learned.
What can I say of surgery, in which anatomy must constantly watch
over the course of the knife?

The great influence of anatomy on practical medicine is, however,
shown most markedly in special branches, laryngology, rhinology,
otology, neurology, urology, etc. When a physician wishes to devote
himself to any of these branches, he first studies carefully the anatomy
of the particular part. If he has forgotten this, he is forced to review
it carefully unless he wishes to become a charlatan. The anatomists
can instruct him on this point, and it is not necessary for me to speak
more at length about it, in this country in which special branches are
so strongly developed.

We need not prove that human anatomy forms an indispensable
basis for anthropology, ethnology, and sociology. We need only recall
the names of Blumenbach, R. Virchow, and Anders and Gustav
Retzius, father and son.

Further study and advance in the knowledge of anatomy is also
important for philosophy, especially for psychology. This stands
to reason. The investigation of the brain is the task of human anatomy.
The organ of thought must be investigated to its smallest details, and
we may state without fear of contradiction that philosophic sciences
will burst into renewed bloom, when anatomy and physiology have
cleared up the dark and intricate labyrinth of the brain. Much that
can now only be reached with effort, and is then hardly clear, will
become comprehensible.

And now, last, not least, the fine arts. The representation of men,
be it as a true and characteristic imitation, as a portrait, be it in
historic paintings, in ideals, in caricatures, whether with the brush
and pencil or with the knife and chisel, will always be the principal

376 HUMAN ANATOMY

task of the fine arts and demand its greatest powers. To give a picture
exact in the smallest details, I might say a photographic representa-
tion of the human figure, is not the aim of art. It should much more
give what is characteristic in the expression, in a portrait, as the posi-
tion of the limb and the attitude of the body should stand in relation
to the expression in painting, and, I may say, give the point to carica-
ture. In order to illustrate the last point, tell the same joke to two
different persons ; one breaks forth spontaneously into hearty laugh-
ter, while the other laughs only in order not to seem discourteous.

I can give no better example of what photography may do for us,
than the exhibition of persons walking, which are often shown in our
illustrated journals. The photograph has exactly shown the phase
of the step, at the moment of the exposure, and yet this reproduc-
tion is ugly and even ridiculous. The step as a whole is composed
of a coordinated series of little motions, which we may analyze by
instantaneous photography. When we arrange these "phase pic-
tures " close to one another, by a special apparatus, the kinemato-
graph, the natural movement of walking again appears. The artist
must understand this. He must represent motions, in his figures,
at the most characteristic time. Then their effect is natural, and
they attract us. I see, in the fulfillment of this task, the anatomic
side of the fine arts; and here anatomy has been of the greatest
service to art, and with the development of methods will become
still more so. Thus the artist must study human, and in certain
cases animal, anatomy, as this gives a firm basis for the further
study of the living body, in rest and in motion. From the naked
figure we shall then pass to the clothed, and study the changes
which are made in the position of the standing and moving figure
by restricting garments. Thus are made the magnificent draped
figures, in statues and paintings, which so please and surprise us.
The observation and close imitation of nature, combined with ideal-
istic modification of the same, is what we wonder at in master-
pieces. Although the head of the Venus of Milo is treated some-
what conventionally, we cannot deny that the rest of the body lives,
and we expect, every moment, the marble breast to stir with life.
It is this, also, which attracts us to the masterpiece of Velasquez
in Prado, "Las Lancas," and which causes us to gaze with wonder
and sympathy at the motion and expression of the two principal
figures. This is also shown in the portraits of this painter, perhaps
the most noted of all artists, and also in the portraits of Holbein,
Diirer. Raphael, and Rembrandt.

We find the same truth and comprehension of nature in the
small and quiet figures of Meissonier and Millet, and we find it again
in the marble statues of Hildebrand and Schaper, whose statue of
Goethe, in the Berlin Zoological Garden, appears to me to be the

THE RELATIONS OF ANATOMY 377

model of an idealized draped figure in a position of rest. It is not
possible to reach the greatest perfection without careful anatomic
studies, either on the dead or on the living. I am well aware that
there have been good painters who have bothered little about
anatomy; it is not anatomy alone which enables the artist to per-
form great works; but perhaps every one of those masters who has
not been well trained in anatomy would have done better with a
good anatomic knowledge. That which belongs to the artist, as
such, can only be strengthened and refined by a careful study of
anatomy. The before-mentioned great artists of the fifteenth cen-
tury realized this perfectly, as is shown by the numerous anatomic
studies which they have left. Fra Bartolommeo worked in the same
way.

Thus we see that human anatomy receives much from her sister
sciences and from the arts, and gives much to them, and what she
gives is greater and more valuable than what she receives. This is
because she is the basic science of all biology, because she has made
the most highly organized being the subject of her studies. Besides,
she has the advantage that she may be assisted by observation of
one's self, as can no other branch of biology. We shall only compre-
hend the mechanism of the living body when our anatomy of the
human central nervous system is further developed. Here we are
still, as I have already mentioned, only at the beginning of our
knowledge. Let us hope that interest in our investigations and
methods will receive greater diffusion by the example of the found-
ing of the academies of the world. Let us hope that the horror of
the material of anatomists will disappear more and more from all
classes of humanity, especially from the circle of the educated.
We must attempt to reach the point where all assist with the good
work. Sapienti sat.

THE PROBLEMS IN HUMAN ANATOMY

BY HENRY HERBERT DONALDSON

[Henry Herbert Donaldson, Professor and head of the Department of Neuro-
logy, University of Chicago, b. 1857, Yonkers, New York. A.B. Yale Col-
lege, 1879; Ph.D. Johns Hopkins University, 1885; Sheffield Scientific School,
1880; College of Physicians and Surgeons, New York, 1881. Fellow, Johns
Hopkins University, 1881-83; Instructor in Biology, ibid. 1883-84; Associate
in Psychology, ibid. 1887-88; Assistant Professor in Neurology, Clark Univer-
sity, 1889-92; Professor of Neurology, University of Chicago^ 1892-96; Dean
of the Ogden (Graduate) School of Science, ibid. 1892-98. Member of the
American Psychological Association; American Neurological Association;
American Physiological Society; American Statistical Association; American
Society of Naturalists; Association of American Anatomists. Author of Growth
of the Brain.}

FOR the solution of the problems presented to him, the anatomist
is by no means limited in his technique to the scalpel or the micro-
scope, but justly claims the right to use every aid to research which
other departments of science are able to furnish. His position,
therefore, in the scientific field is determined by the standpoint
which he occupies and from which he regards animal structures,
rather than by any special means and methods employed for their
study.

By common consent anatomical material includes not only struc-
tures which may be easily dissected and studied with the unaided
eye, but also those which tax the best powers of the microscope for
their solution. But even within such wide limits the material that
ordinarily comes to hand leaves much to be desired, and in elucidat-
ing this or that feature in the structures under examination, it is
often found necessary to modify the physiological conditions under
which these structures have been working, in the hopes that their
appearance may be altered thereby, and so be more readily under-
stood.

Taken in a broad way, this is the reason why the data of patho-
logy and experimental morphology are so important for the devel-
opment of anatomical thought, helping as they do in the solution
of the problems connected with the finer structure of the animal
body, just as embryology and teratology illuminate the gross mor-
phological relations in the adult.

I am quite aware that in making the foregoing statements I have
suggested more modes of investigation than are at present used in
connection with man. But the anatomy of the human body in
adult life forms in itself so limited a field that no investigator can
possibly confine himself to this portion alone, and there is every
reason for here treating the subject in the larger way. As we see

PROBLEMS IN HUMAN ANATOMY 379

from the history of human anatomy, it was brought into the medical
curriculum in response to the demands both of physiology and sur-
gery, but gradually became most closely associated with the latter.
For a long time its relative significance as a medical discipline was
very great, because it represented the only real laboratory work
which appeared in the training of the medical student. Indeed, a
generation ago the exactness of anatomical methods was so lauded
in comparison with the methods then commonly used in medicine,
that anatomists came to scoff at the vagueness of their colleagues,
while to-day, if we may be persuaded by some of our physiological
friends, they have remained only to prey on the time of students
who might be better employed. Although such a thrust may be
readily parried, it is, nevertheless, necessary to admit that times
are changed, and that as a laboratory exercise human anatomy is
to-day outranked by several of the subjects in which the laboratory
work permits a more precise formulation of problems and their more
rapid and definite solution. However, it still retains, rightly enough,
much of its former eminence.

Among the problems in human anatomy, there is, perhaps, none
more important than the way in which it is to be presented to the
five young gentlemen ranged around a subject in the somewhat
trying atmosphere of the dissecting-room. Just what they may be
expected to learn from such an experience would require some time
to state. Certain it is that these beginning anatomists are almost
all of them intending to become physicians, and some of them to
become surgeons, and to this end they are building up a picture
of the human body which will be useful to them in their profession.
They are doing this by the aid of the best pedagogical means at their
command, namely, the reinforcement of the ocular impressions
by the contact and muscular sensations that come from the actual
performance of the dissection itself. If previously they have had
some experience in the dissection of the lower mammals, they will
note at once the differences shown in the case of man, and if their
embryology is at their command, it will be easy for them on sug-
gestion or on their own initiative to appreciate how some of the
peculiar relations between parts of the human body have been
developed. Beyond this the information obtained is of the same
order as that of the vocabulary of a language. The student gets
a certain number of discrete pictures of the different parts of the
body more or less clearly impressed upon his mind, and when he
has occasion later to deal with these same parts, he has the advan-
tage of finding himself in the presence of familiar structures. How
far in this first experience the special groups of facts which are some-
times set apart under the head of surgical anatomy should be intro-
duced, is a more or less open question. The present weight of opinion

380 HUMAN ANATOMY

demands that they should still be kept by themselves. Nevertheless,
while the anatomical experience of the average medical student
should rest on a broad scientific background, he should at the same
time have a distinct appreciation of the eminently practical value
of the information he is expected to acquire.

The question at once arises how the monotony of long-continued
dissection can be relieved, and the student maintained in a con-
dition of sufficient receptivity to make the work really worth while;
for the acquisition of vocabularies has never been counted as one
of the greater pleasures of life. There are several legitimate devices :
in the first place, if it is possible, for the student to have near at
hand a microscope which may now and then be used for the examin-
ation of the different tissues as they appear in the cadaver. This
cross-reference between the gross and microscopic appearance will
serve to bring into close connection with one another two classes of
facts which are often separated to their disadvantage, and to revive
the histological pictures which should be incorporated in gross
structures, but which in most cases remain forever apart from them.
On the other hand, a search for anomalies or variations serves to
give both a reality and purposefulness to the work and to make a
student feel that in return for the large amount of time necessarily
required for his anatomical training, he is, in some small measure at
least, contributing to the science. It is unavoidable, this expenditure
of time, and absolutely necessary that the student should do these
things with his own hands, in order to obtain the three-dimensional
impression of the structure with which he deals.

In this connection just a word as to the way in which the beginner
may be aided in the comprehension of his work. The excellent
diagrams and pictures which are now used to illustrate the b st
anatomical text-books carry us as far as that means of assistance
can probably go. Pedagogical experience points strongly, however,
to the superior value of the three-dimensional model, and although
such models are more difficult to collect, harder to care for, and
require more space and caution in their use, they are so far superior
to any other device, except an illustrative dissection itself, that the
collection of them in connection with anatomical work becomes a
moral obligation.

If we turn now to the wider uses which may be made of anatomical
material as it usually appears in the dissecting-room, we find that
a number of directors of laboratories have been utilizing this material
for the accumulation of data in such a form that it may be later
treated by statistical methods. Thus they have weighed and meas-
ured in different ways various parts of the cadaver, and in some
cases determined the correlations between the organs or parts
examined. It cannot be too strongly emphasized that the results

PROBLEMS IN HUMAN ANATOMY 381

thus obtained are to be used only with the full appreciation of the
fact that the material ordinarily available for examination in the
dissecting-room belongs in all countries to a social group which
contains the highest percentage of poorly developed and atypical
individuals. The conclusions, therefore, that can be drawn from
the investigations of this material must always be weighted by its
peculiar nature. To illustrate what is here meant by the peculiar
character of this material, we may take as an instance the bearing
of the results obtained from material of this sort on the problem of
the brain-weight in the community at large. It must be admitted
that the figures which we have at our command for this measure-
ment are, with the exception of one short list, derived from the
study of individuals belonging to the least fortunate class in the
community, and it is not fair, therefore, to carry over these data
and apply them directly to the average citizen who is of the normal
type and moderately successful in the general struggle for exist-
ence. From what has been said, it is plain that much of the work
now being carried on in the dissecting-room comes very close to the
lines which have been followed for years by the physical anthropo-
logists; yet, because these have for the most part concerned them-
selves with the study of the skeleton, have limited their comparisons
to the various races of men, and have developed no interest in
surgery, they have for a long time stood apart, and only recently
joined forces with the professional anatomists. This step has cer-
tainly been to the advantage of anatomy, and as one result of it,
anatomical material not previously utilized will now be treated by
statistical methods. But all the work to which reference has here
been made is on the body after death. So manifest are the dis-
advantages arising from the conditions which are thus imposed
that the necessity is felt on all sides of extending our observation
as far as possible to the living individual. As an example of such
an extension, we have the determination of the cranial capacity
and brain-weight in the living subject which has resulted from the
labor of Karl Pearson and his collaborators.1 The methods which
have been employed for this purpose are capable of giving as accu-
rate results as are ordinarily obtained from post-mortem examina-
tions, and, moreover, have the advantage of being applicable at
any time to any group in the community which it is desired to
investigate.

To redetermine, as far as possible, from studies on the living,
all the relations which have been made out post-mortem, becomes
a very immediate and important line of work.

But even under the general limitations which apply to the dis-
secting-room material, it is desirable to refine our knowledge of

1 Pearson and collaborators, Phil. Transactions of the Royal Society, 1901.

382 HUMAN ANATOMY

the human body by classifying the subjects according to race, and
thereby bringing into relief the slight anatomical differences that
exist between the well-marked races of Europe -and the races of
other parts of the world. The history of anatomical differences
due to sex lacks several chapters, and it is possible also to show
the modifications of structure which come from the lifelong pursuit
of certain handicrafts which call for peculiar positions of the body or
for the unusual exercise of certain muscles; as, for example, the
anatomy of a shoemaker.1

Such results as the one last mentioned have a direct bearing on
the modifications of the human form which may be introduced
by peculiarities of daily life and work, and bring anatomy into
connection with the problems of sociology; while, on the other
hand, both lines of work are contributory to the broader questions
of zoological relationship and susceptibility to modification.

Yet when we have gained all the information which the scalpel
can give, there still remains the whole field of finer anatomy, the
extent of which it is so difficult to appreciate.

While recognizing that the human body may be regarded as a
composite, formed by the fitting together of the series of systems,
and while, in some instances, we have a more or less accurate
notion of the way such a system appears, — as, for instance, in the
case of the skeleton, — yet a much better understanding of the
relation of the soft parts would follow an attempt to extend this
method of presentation, and to construct phantoms of the body
in the terms of its several systems in some way which would show
us the system in question as an opaque structure in a body other-
wise transparent. This is, of course, the final aim of the various
corrosion methods, or those which depend on injection or differ-
ential coloration of structures which may be viewed in three di-
mensions.

When the vascular, lymphatic, nervous, and glandular systems
can be thus exhibited for the entire body, or for the larger divis-
ions of it, it will be possible to see the human form transparently,
and to see it whole; a feat difficult to accomplish, but worthy of
earnest endeavor. The development of such phantoms should
serve to make more impressive the familiar fact that in many or-
gans and systems the total structure is built up by a more or less
simple repetition of unit complexes, as. for example, the liver by
the hepatic lobule, the bones by Haversian systems, and the spinal
cord by the neural segments.

Tf we pass now from the consideration of the systems of tissues
to that of their structural elements, we enter the domain of his-

1 Lane, W. A., Journal of Anatomy and Physiology, vols. xxi and xxn, 1887 and
1888.

PROBLEMS IN HUMAN ANATOMY 383

tology and cytology. Starting with the differentiation of the ti»
sues by means of empirical staining methods, investigators have
gradually come to appreciate the chemical processes which under-
lie the various color reactions, and as we know now, there already
exist methods for determining in the tissues several of the chem-
ical elements, such as iron, phosphorus, etc., to say nothing of the
more or less satisfactory identification of complex organic bodies
by means of definite reactions. This being the case, it is possible
to imagine representations of the body built up on the basis of
these microchemical reactions, representations which would show
it in the terms of iron or in the terms of phosphorus, thus yielding
us an image which might be compared with that obtained by aid of
the spectroscope when the picture of the object is taken by means
of one out of the several wave-lengths of light which come from it.

The contemplation of the multitudinous opportunities for in-
vestigation and comparison which appear within this field lead
us to pause and inquire what is properly the purpose of all this
anatomical work; for without a strong guiding idea we are liable
to repeat the errors of earlier generations, and merely accumulate
observations, the bearing of which is so remote from the actual
course of scientific progress that the investigations are mainly use-
ful as a mental exercise for the individuals who conduct them. Ana-
tomical results begin to have a real meaning only when correlated
with physiology, and when we learn that a tissue with a certain
structure is capable of performing given functions, we feel that we
are really bringing our anatomy into touch with the life-processes.
It is to aid in the accomplishment of this end that men devote their
lives to anatomical work. With the variation that we find every-
where in organic structures, it should be and is possible to discover
by comparison what variations in the structure of a tissue or a
cell are accompanied by the best physiological responses. It is
along this line that we must necessarily work in order to reach
human life, either through medical practice or other avenues of
approach, for in the end the object and purpose of all science is
to ameliorate the unfavorable conditions which surround man,
and in turn to produce a human individual more capable of resist-
ance to disturbing influences, and better suited for the enjoyment
of the world in which he lives.

Considering anatomical work with this thought in mind, the pro-
blems which it presents can be grouped according to their relative
value and importance. The approach may be made from two sides.
On the one hand it is, for example, extremely worth while to direct
years of labor to the determination of the finer structure of living
substance, because the more closely we approximate to a correct
view of that structure, the more readily will our anatomy and physi-

384 HUMAN ANATOMY

ology run together, and the clearer will be the conception of the
sort of structure which it will be most desirable to increase for the
attainment of our final purpose. On the other hand, if we follow
the path from the grosser to the finer anatomy, we are led to in-
quire whether there is any one part or system of the human body
which at the present moment is specially worthy of attention.
When we say that the nervous system is such a part, I think that
even those who are not engaged in the study of it will admit that
there are some grounds for the statement. The peculiar feature
which sets the nervous system apart is the fact that its enlarge-
ment, both in the animal series and during the development of the
individual, is in a very special way accompanied by changes in its
physiological and psychological reactions. To be sure, we think of
it as built up fundamentally by the union of a series of segments,
but the relationship established between these segments becomes ul-
timately so much more important than the constituent units that in
the end we find ourselves working with a single system of enormous
complexity, rather than a series of discrete units; a state of affairs
which is not paralleled in any other tissue. In addition to this, the
nervous system as a whole is par excellence the master system of
the body, and as such, the reactions of the organism are very largely
an expression of its complexity. Indeed, within the different classes
of vertebrates, the various species may be regarded as compound
bodies composed of four fundamental tissues, and a species could
well be defined by the quantitative relations found to exist be-
tween the nervous, muscular, connective, and epithelial constitu-
ents. Working from this standpoint, Dubois,1 the Dutch anato-
mist, stimulated by the work of Snell,2 has brought forward evi-
dence for the view that when, within the same order, several species
of mammals similar in form, but differing in size, are compared
with one another, the weight of the brain is found to be closely
correlated with the extension of the body surface, and by inference
with the development of the afferent system of neurones. This view
would seem to imply that in these cases there is the same density
of innervation of each unit- area of skin; but the correctness of this
inference can only be determined by the careful numerical study of
the afferent system of the animals compared. It will appear, how-
ever, that under the conditions imposed the relative weight of
the brain depends upon the fact that each unit-area of skin, repre-
sented by the nerves which supply it, calls for a correlated addi-
tion of elements to the central system, and thus the increase in
one part is followed by a corresponding increase in the other. When,
however, the large and small individuals within the same species

1 Dubois, Archiv fur Anthropologie, 1898.

2 Snell, Archiv fur Psychiatrie und Nervenkrankheiten, 1892.

PROBLEMS IN HUMAN ANATOMY 385

are compared, it is found that the increase in the brain-weight fol-
lows quite another law, and that in this latter case it is relatively
much less marked than in the former. This result at once suggests
that the mechanism of the increase is dissimilar in the two cases.
For the solution of the problems that are raised by such investi-
gations as those just cited, we need to employ quantitative methods,
and on this topic a word is here in place.

Microscopic anatomy and histology, like all the sciences, have
passed through a series of phases which are as necessarily a part of
their history as birth, growth, and maturity are a part of the life-
history of a mammal. The microscope in its early days enabled
Schwann to propound the fruitful theory that the tissues were
composed of cells. A preliminary survey showed that these cells
were different in their form and arrangement in the different parts
of the body, and a still more careful examination with the aid of
various dyes or solutions altering the tissues in a differential way
gave the basis for yet finer distinctions. This phase in the develop-
ment of the science, however, may be fairly compared with quali-
tative work in chemistry, where the object is to determine how
many different substances are presented in the sample examined.
Naturally, the next step is the introduction of quantitative methods,
and we are, therefore, now using the methods of weighing, measur-
ing, and counting for the purpose of rendering our notions more
precise, and thereby facilitating accurate comparisons. When
emphasizing this point, we do not, however, forget that hand in
hand with this quantitative work the qualitative tests have been
marvelously refined, and that these necessarily form the foundation
for quantitative work, since all such work must deal with the ele-
ments or groups of elements which can be sharply defined, and the
basis for their definition is given through qualitative studies. As
progress is made along these lines, we appreciate more and more
that it is of importance for us to know not only how much brain
and how much spinal cord by weight normally belong to a given
species of animal, but also the quantitative relations of the different
groups and classes of elements which compose these parts. We are
continually asking ourselves how far the range in gross weight of the
central nervous system may be dependent on changes in the number
of elements in the different divisions or localities, and how far
dependent on the mere increase in the bulk of the individual units
without any change either in their absolute number or relative size.
Work along this line rests as we know on the neurone theory, that
epoch-making generalization concerning the structure of the nerv-
ous system which was put forward by our honored colleague
Professor Waldeyer.1 Most of us are aware that, at the moment
1 Waldeyer, Deutsche medidnische Wochenschrift, 1891.

386 HUMAN ANATOMY

this theory is the subject of lively and voluminous discussion, and
that Nissl,1 for example, urges the inadequacy of the conception
on the ground that it does not account for the gray substance in the
strict sense.

No one can fail to appreciate the very great importance of the
satisfactory conclusion of the present dispute, and earnestly desire
that we may obtain conclusive evidence on points involved; but how
ever the question of the gray matter may be settled, the enormous
importance of the neurone conception, and the value of it for the
purposes of the microscopic analysis of the nervous system, will
remain untouched, while our quantitative determinations, applied
to the neurone as we now understand it, will still have a permanent
value.

Returning to the questions which are raised by the previously
mentioned investigations of Dubois, we require in the first instance
to determine the number of neurones connecting the skin with the
central nervous system, and to see how this number varies in the
different species of mammals similar in form but unlike in size.
There is only one animal, the white rat, on which as yet such studies
have been made, so that the whole field lies practically open. Should
we be able to get good numerical evidence in favor of the view that
under the conditions named above the afferent system could be
taken as an index of the size of the brain, it would show us at once
that in the laying-down of the nervous system certain proportions
were rather rigidly observed, and bring us to the next step, namely,
the determination of the influences which control those proportions
and the possibility of effecting an alteration in them. In the mean
time, there is every reason to prepare for the application of these
results to man, and although the programme here is simple enough
to state, it will involve great labor to carry it through.

So far as the numerical relations in man are concerned, we have,
through the work of Dr. Helen Thompson 2 an excellent estimate
of the number of nerve-cell bodies in the human cortex, and through
that of Dr. Ingbert,3 a reliable count of the number of medullated
nerve-fibres in the dorsal and ventral roots of the thirty-one pairs
of spinal nerves of a man at maturity. It is easy to see, however,
that we must get some notion of the amount of individual varia-
tion to which these relations are subject within the limits of one
race and one sex before it is desirable to attempt to learn whether
the difference in race or sex here plays an important role. It is to be
anticipated, however, that the differences dependent upon race and
sex will be comparatively slight, and especially so when contrasted

1 Nissl, Die Neuronenlehre und ihre Anhanger, 1903.

2 Thompson, Journal of Comparative Neurology, 1899.

3 Ingbert, Journal of Comparative Neurology, 1903 and 1904.

387

with the differences which we may anticipate as existing between
the adult and the child at birth. This aspect of the problem illus-
trates, in a concrete form, the sort of question which is raised by
the anatomical study of the body during the period of growth.
The embryologists have worked out the formation and early devel-
opmental history of the various organs and parts of the human
body, but the study of the later fetal stages have been blocked by
the scarcity of material, and the inconvenience of dealing with it.
On the individual at birth, we have again more extensive observa-
tions, but for the period comprised between the first two years of
life and the age of twenty our information is again scanty. The
lower death-rate during this part of the life-cycle, as well as social
influences, combine to keep material between these ages out of the
dissecting-room. Here is an important part in the life-history of
man which needs to be investigated along many lines, and during
which it is most desirable to have a record of the changes in the
nervous system expressed in quantitative terms. In the general
problem which is here under discussion, our next step would be to
enumerate in man at birth the medullated nerve-fibres in the roots
of the spinal nerves. Such an enumeration will probably show us
between birth and maturity a very large addition to the number of
these fibres, but we still have to determine at what portion of the
period, and according to what laws this addition takes place. At
this point our observations on animals will assist us, and we should
certainly look for the occurrence of greatest addition during the
earlier part of the growing period.

Let us assume, then, that we have obtained results which show
us the normal development of this portion of the nervous system
between birth and maturity. These observations could be used as
a standard. Once possessed of such a standard, we are prepared to
determine variations in the nature of excesses or deficiencies, and
in this instance the question of deficiencies is the one most easy to
handle.

The studies of Dr. Hatai 1 on the partial starvation of white rats
during the growing period show that very definite changes can be
brought about in the nervous system when these animals are de-
prived of proteid food for several weeks. As a result of such treat-
ment, the total weight of the nervous system is reduced much
below that of the normal rat. Such a result, however, leaves two
points still undetermined: (1) the general nature of the changes
bringing about a diminution in weight, and (2) the parts of the
system in which changes occur. In testing our animal material by
quantitative methods, we should in the first instance direct attention
to a possible decrease or arrest of growth in the afferent system of
1 Hatai, American Journal of Physiology, 1904.

388 HUMAN ANATOMY

sensory nerves, and seek to determine whether the unfavorable
conditions have not retarded the growth-process in this division of
the nervous system. If the results of such observations are positive,
we may expect to find a corresponding modification in man, when
the human body during the period of growth is subjected to unfa-
vorable conditions of a similar nature. As a matter of fact, such
unfavorable conditions do exist in the crowded quarters of our
larger cities, and it seems highly probable that we have there in
progress examples of partial starvation quite comparable with the
experiments conducted in the laboratory. Under these circum-
stances, it is important to discover in the case of our animals how
far a subsequent return to normal food conditions will modify the
anatomy of a nervous system which has been subjected to proteid
starvation for some weeks. At present there are no observations
which indicate whether or no recovery in the nervous system will
take place, and it will probably require some time to reach a definite
conclusion. The work necessary for a determination of the ana-
tomical changes exhibited by the animals alone constitutes by no
means a light task, since in order to obtain reliable results and to
eliminate the factor of individual variation a series of individuals
must be examined, and it requires a very definitely sustained interest
to carry through the long line of enumerations necessary for such
an investigation. The examination of the growth of the nervous
system in animals subjected to definitely unfavorable conditions
is, however, only one part of the work.

It will be necessary to contrast the changes there found with the
effects of special feeding, care, and exercise in other groups, in order
to see how far above the ordinary form the nervous system can be
anatomically improved by any such treatment; and experiments
in this direction are already being conducted by Dr. Slonaker. Of
course, the results which have been obtained and may be obtained
on the animals studied in this way should not be directly applied
to the case of man, because it seems quite evident that the higher
organization of man is responsible for his ability to resist to a re-
markable degree the disturbing effects of an unfavorable environ-
ment. The impression is abroad that the reverse is the case, and
that it is man who is more responsive to unfavorable surround-
ings. I believe, however, that this current view will prove to be
incorrect, for the lower mammals at least, and that when we place
such animals where the conditions for them are abnormal, their
limited powers of adaptability lead them to be more seriously
affected than are animals which are more complexly organized.
If such is the case, variations of the same amount should not be
expected to appear in man, but there is every reason to assume that
the variations which do appear will be of the same general character,

PROBLEMS IN HUMAN ANATOMY 389

and that we might look for them in the human nervous system
where we find them in that of the rat. When it is possible to see
how the anatomy of the nervous system may be altered during
the post-natal growth-period, we shall be prepared to take up the
problem of how it may be improved during embryonic arid fetal
life, and how the actual number of potential neurones is deter-
mined and their relative distribution controlled, and this should lead
ultimately to the attempt to breed animals with improved nervous
systems in which we shall know the nature of the improvement in
considerable detail.

It may be urged that putting the problems in this way indicates
a greater interest in the application to physiology of the anatom-
ical results than in the results themselves. But I take it that
the interest of a machinist in building a machine is to make the
parts for one that will go, and that no less honor is due him for
his painstaking care in determining the construction of the dif-
ferent parts and their right relations, because at the end of the
operation he has devised something capable of doing work. Simi-
larly it is possible that a man's interest from day to day shall be
absorbed in the technique of anatomical science, and yet, it is
nevertheless distinctly advantageous, if his anatomical observations
bear on the performances of the living animal, and a final result
is obtained which is the synthesis of research in two associated
fields.

In drawing up the preceding outline, no one is more aware than
the writer of the fact that problems connected with the nervous
system have alone been considered. Without doubt those more
interested in the other systems of the human body could duplicate
for these the problems which have been suggested in connection
with the nervous system, so that the account given above may
be taken simply as an illustration of the sort of thing that seems
worth doing. In presenting these illustrations it has been my pur-
pose to indicate a standpoint from which the anatomical problems
can be profitably regarded, and to draw attention to the use of
quantitative methods in the study of anatomy, and especially as
applied to the body during the period of active growth.

Yet perhaps the largest of our problems, and certainly one which
appeals to all of us, is the ways and means for the solid advance-
ment of our science. Alongside of the question of how we shall
hand down to successive generations of students the facts already
established, lies the still more fundamental problem of the best
method of building-up the body of anatomical knowledge.

It is not my purpose to advocate as a means to this end the sharp
separation of teaching from investigation. It is a rare man who
can stand the strain of such a division, whether he chooses one or

390 HUMAN ANATOMY

the other, and there is, moreover, much to be said for such an arrange-
ment as will bring the average student into a laboratory where he
can himself see how research work is conducted. Yet it would be
possible to name institutions in which the relative amount of time
required for teaching as compared with that left free for investiga-
tion might with advantage be readjusted, and almost all of our
educational institutions at the same time admittedly lack the funds
and often the educational purpose, which would justify them in
attempting to meet the various difficulties connected with ana-
tomical investigations on a large scale. Yet no one questions the
importance of striving for a more rapid advance. A response to
this feeling finds its expression in the several research funds which
are now available in this country and abroad for the endowment
of investigation, and in the plan presented to the International
Association of Academies, and, it should be added, largely due to
the initiative of Professor Waldeyer, for the establishment in vari-
ous countries of special institutes for the furtherance of research in
embryology and neurology.

These two subjects were first selected owing to the peculiar dif-
ficulties of obtaining the needed material, and the great labor
necessary to prepare the complete series of sections which are
required in many cases. These conditions make it imperative that,
if we would avoid large loss of labor and much vexation of spirit,
the work in these lines should be coordinated, standards adopted,
and the material of the laboratory, like the books of a library or
the specimens in a museum, be available for the use of other in-
vestigators. Nothing, I believe, is further from the minds of those
engaged in this plan than an attempt to produce anatomical re-
sults on a manufacturing scale. But the questions calling for solu-
tion in the fields here designated are so numerous that such an
arrangement will merely mean a subdivision of labor in which each
institute will take one of the larger problems and direct its main
energies to the study of this, so conducting the work that it shall
be correlated with that in progress elsewhere. The director of such
an institute will be justified in extending his work through assist-
ants just as far as he can carry the details of the different re-
searches in progress, and thus knit them into one piece for the
education of himself and his colleagues. When we pass beyond
this limit, admittedly subject to wide individual variation, there
is little to be gained, but the evils of excessive production, should
they arise, carry within themselves the means of their own correc-
tion.

This step, which is assuredly about to be taken, should enable
us in the future to do things in anatomy not heretofore possible,
and when, some years hence, there is another gathering of scientific

PROBLEMS IN HUMAN ANATOMY 391

men, with an aim and purpose similar to that of the present one,
it is easy to predict that we shall be able to listen to a report on
the important advances in anatomy arising from coordinated and
cooperative work.

SECTION K — PHYSIOLOGY

SECTION K — PHYSIOLOGY

(Hall 4, September 23, 10 a. m.)

CHAIRMAN: DR. S. J. METZER, New York.

SPEAKERS: PROFESSOR MAX VERWORN, University of Gottingen.

PROFESSOR WILLIAM H. HOWELL, Johns Hopkins University.
SECRETARY: DR. REID HUNT, Washington.

THE Chairman of the Section of Physiology was Dr. S. J. Met-
zer, of the Rockefeller Institute, New York City, who took for his
introductory topic :

THE DOMAIN OF PHYSIOLOGY AND ITS RELATION

TO MEDICINE

PHYSIOLOGY is of medical parentage, was reared by medical men,
and is still housed and fed by medical faculties. Yet it is medicine
against which its frequent declaration of independence is directed.
Medicine is a practical science, and is too inexact, and physiology
wishes to be a pure, exact science. It, therefore, tries to keep aloof from
medicine, and manifests a longing for association with, or, still better,
for a reduction to, physics and chemistry. It urges, furthermore,
that the affiliation with medicine binds physiology down to only one
species of animal with intricate, complicated conditions, while it would
be more beneficial to physiology if it would direct its energies toward
a study of monocellular organisms where the conditions are so simple.

Permit me to discuss briefly the domain of physiology and the im-
portance of its relations to medicine as they present themselves to
my mind. There can be no doubt whatsoever that physiology has a
perfectly legitimate object entirely of its own. Perhaps I may elucidate
this statement in the following crude way. All natural phenomena
impress us in two ways , — as matter and as force. The phenomena are
either inanimate or animate. The studies of inanimate matter are to
be found in mineralogy, crystallography in a part of chemistry, etc.
The studies of the forces or energies of inanimate phenomena are
carried on by physics and physical chemistry. In the fields of living
phenomena, matter is studied by gross and minute anatomy and by
descriptive zoology and botany, or, in short, by morphologyy. The
studies of the forces, the energies, or the functions of living matter
are the proper domain of physiology. Now this definition permits
a few deductions. All these four divisions are bound, as sciences, to

396 PHYSIOLOGY

have something in common in their methods of investigation; they
must employ the inductive method, and must strive to reach in their
results that degree of certainty which the nature of each individual
science permits it to attain. But the four divisions differ greatly from
one another; each one has its own subjects and laws and its own
problems, which have to be solved by methods peculiarly adapted
for each division. It is certainly clear to every one that it cannot be
the essential task of animal morphology to reduce itself to mineralogy
because it can be demonstrated that some anatomical objects con-
tain lime and other mineral substances. It seems to me it ought to be
also clear to every one that it cannot be the sole task, and not even
the essential task, of physiology to reduce itself to physics and chem-
istry because some or many of the living phenomena are governed
to some extent by known laws of physics and chemistry. Physiology
has to study the functional side of life, and in the attempts to eluci-
date its complex phenomena it certainly has to employ also the known
facts of physics and chemistry. But if we would confine the domain
of physiology to such parts only which can be interpreted by the laws
of physics and chemistry of to-day, we should have to give up nine
hundred and ninety-nine out of a thousand of the phenomena of life
as still inappropriate for physiological study. The four divisions of
the natural sciences are closely interwoven, and each one can, of course,
profit by the experience of the others. Boyle, Mayow, Priestley,
Lavoisier, and others attempted to unravel the nature of oxygen,
nitrogen, and carbon dioxide gas by the aid of experimental studies of
the physiology of respiration. The physicist or the chemist employs
any method which would help him to shed light upon his subject, but
physics and chemistry have methods peculiar to themselves, and that
is the secret of their great success. And so it should be with physi-
ology. However, when physiology broke away from medicine, it ran
into the arms of physics and chemistry, and is still largely there. The
early successes which have attended the new venture, which, by the
way, is the case with every new venture, led to the conception that
this is the most desirable, the most natural union. An analysis, how-
ever, of the work in animal physiology in the last few decades will
show the fact that the too great gravitation towards physics and
chemistry prevented the development in many directions of a purely
physiological character.

I contend that physiology is an independent science with a clear
outline of its domain, but it ought to direct its declaration of inde-
pendence not only towards medicine, but also towards such exact
sciences as physics and chemistry.

As to the standard of precision and exactness to be required of
physiology, let me say this. Certainly no physiological problem can
be solved with that exactness, with that absolute reliability which is

PHYSIOLOGY AND ITS RELATION TO MEDICINE 397

now the standard for a good many problems in physics and chemistry.
Above all, in the studies of the energies of life we lack the controlling
factor of synthesis. If we can produce synthetically urea or sugars or
other dead constituents of a dead or living body, we cannot yet make
synthetically the smallest living organ of the smallest homunculus.
But what of it? Each science has its own degree of attainable exact-
ness. Physics and chemistry have one standard, and paleontology or
geology is bound to have another standard of exactness. There is no
one standard of exactness for all sciences. The scientific demand upon
work in any science is to strive for that degree of exactness which is
attainable in each specific field of investigation.

I contend, further, that physiology ought not and cannot be pro-
perly developed upon the basis of a morphological unit. We might just
as well attempt to put up the mineral crystals as a basis for the study
of physics.

I may say, further, that in my opinion the knowledge of vital ener-
gies would progress more rapidly if we were guided in our investiga-
tions by the view that the actual processes in the phenomena of life
are of a very complex nature. The desire to reduce the multiplicity of
phenomena to a few simple principles is a philosophical importation of
a psychological origin. Certainly premature attempts to offer simple
interpretations for complex phenomena have often been an obstacle
for a further development of our knowledge of the actual processes.

Physiology, however, may take some useful hints from the other
sciences. It may learn from such exact sciences as physics and chem-
istry that the exactness and dignity of a science do not suffer by com-
ing into intimate contact with the necessities of daily life. On the
contrary, we find that those chapters of physics and chemistry whose
results found practical application are best developed. The contact
of a science with life and its actual necessities works, on the one hand,
as a stimulus to investigation, and, on the other hand, as a corrective
against an indulgence in mere hobbies. The experimental method
as such is no talisman against such scholastic degeneration. A study
of the literature of the last few decades will show that physiology,
too, could well stand such a corrective.

Physiology could also learn from morphology that a special atten-
tion to the human being does not necessarily lead to a neglect of the
uniform study of the entire animal kingdom. The marvelous com-
plete studies of gross and minute human anatomy, which was of such
immense service to pathology and surgery, was in no way an obstacle
to the brilliant development of the broad science of zoology.

There is, however, one difference between the studies of the energies
of inanimate phenomena and the studies of the vital energies, to which
I would like to call special attention. For physics there is only one
kind of energies; they are all normal. If the physicist meets with

398 PHYSIOLOGY

conditions which apparently do not agree with some established law,
he does not transfer these conditions to a pathologist in physics for
further investigation. On the contrary, he is only too glad to have
such an opportunity; it usually leads to an elucidation of the old law,
or, still better, an entirely new law might be discovered. When Kirch-
hoff was surprised by the apparently contradictory fact that by the
addition of the yellow light of sodium to the sunlight the dark D-
lines in the spectrum, instead of becoming lighter, became still darker,
he did not turn away from the problem. On the contrary, he was glad
of this opportunity; in fact, as he stated once, he was longing to meet
such a complete contradiction. The result was the establishment of
the law of the proportion between emission and absorption of light
and the creation of the nearly new science of spectral analysis. Or, to
quote a more recent instance, the exceptions to van 't Hoff's law of
osmosis which were met with in salt solutions and which had been
displayed by some as a proof against the validity of that law, served
Arrhenius as a basis for the establishment of the far-reaching law of
electrolytic dissociation. It is totally different, however, with physi-
ology. Its domain is, as we saw above, the study of the functional
side of living phenomena. Here, however, we find the artificial and
unsound distinction between normal and abnormal functional phe-
nomena. Physiology set up some laws; and if conditions appear
which do not fit in with these laws, physiology declines to deal with
them; it refers you to medicine. Are the laws governing the vital
functions under pathological conditions actually different from those
controlling the functions in health? Certainly not. The laws which
physiology establishes must be capable of covering the functional
phenomena in all conditions of life. The apparent exceptions in dis-
ease should serve in physiology, as in physics, to unravel the real
nature of the laws governing the functions of living phenomena,
whether they occur in health or in sickness. For instance, the pro-
cesses occurring while the body is in a state of fever should give a clue
to the understanding of the mechanism of the constancy of the ele-
vated temperature of warm-blooded animals. Or the conditions pre-
vailing when urine contains albumin should be seized as a means of
studying the remarkable phenomenon in the normal urinary secretion,
namely, that of all the endothelial cells of the body the kidney endo-
thelia alone do not permit normally the passage of albumin. Or the
conditions of the blood and the lung tissues in pneumonia could serve
as an aid in studying the factors concerned in the formation of fibrin.
And so on and so on in many thousand instances of daily occurrence.
Some very important discoveries in physiology were thus recently
brought to light through medical experience and by medical men,
with hardly any aid from physiology. The anatomy of the cases of
myxoeclema and cretinism and the results of the complete removal of

PHYSIOLOGY AND ITS RELATION TO MEDICINE 399

the thyroid gland for goitre revealed the physiological importance of
that ductless gland for which physiologists, with one single exception,
had no interest. This discovery helped at the same time to establish
and to introduce into physiology the far-reaching conception of in-
ternal secretion. Furthermore, the observation of Bouchard, Lancer-
eaux, and other medical men of the occurrence of a degeneration of
the pancreas in cases of diabetes mellitus, led to the discovery, by
two medical men, of the remarkable fact that the complete removal
of the pancreas in dogs leads to diabetes. This discovery demonstrated
at the same time the further principle that even glands with a distinct
external secretion have besides a physiological importance for the
body by virtue of their internal secretion. In the long list of workers
on this subject we hardly find a single physiologist.

I could quote a good many more instances in which medical studies
brought out important physiological facts and how physiology is
slow to avail itself of such golden opportunities.

The physicists are only too glad to meet with exceptions; the
physiologists run away from them. Is there any well-founded justifi-
cation for such a course in physiology? I believe none. I believe it
is simply an erroneous position. It would lead me too far to attempt
here a discussion of the causes which led to this position in physiology.
But I say without hesitation that this position is deplorable, is harmful
to physiology as well as to medicine. Animal experimentation is the
essential method of developing physiology. Now, then, nature makes
daily thousands of experiments upon man and beast, and physiology
refuses to utilize them for its own elucidation. I feel quite sure that a
study of the functional processes in pathology, or at least the system-
atical taking up of physiological problems indicated by pathological
processes, by minds naturally endowed and properly trained for
physiological studies, would greatly elucidate the proper sphere of
physiology itself, and would at the same time be of incalculable
value to pathology and medicine.

And medicine is greatly in need of such a physiology. 1 am afraid
that the actual situation in medicine is not fully grasped, even by a
great many of its enlightened disciples. To state the critical point in a
few words : The actual disturbance in most of the diseases is primarily
of a functional nature, but the essential part of the present know-
ledge in medicine is morphological in its character! This discrepancy
is due to the uneven development of the sciences of -medicine. When
the empirical art of medicine awoke to the necessity of acquiring a
scientific basis, it found ready for its disposal an already well-defined,
precise anatomy, but only a vague, incoherent physiology. It set out
and continued to work in the precise lines of anatomy, in which it
attained a marvelous completeness. By this step, however, mor-
phology became the dominant factor in medicine, and the definition

400 PHYSIOLOGY

of a disease became inseparably coupled with that which was found
in the body after it succumbed to the disease. When, at a later period,
physiology also became a precise science, it broke away at the very
onset of its regeneration from medicine; it wished to be exact, to be
a pure science, and thus gained no influence upon pathology, which
it refused to study. So it came about that medicine is made up
of a complete knowledge of the anatomical conditions after death, of
nearly a complete morphology of the symptoms of the disease during
life, but of only a vague, makeshift mechanical interpretation of the
functional disturbances during the actual course of the disease. The
last decades have seen the birth and marvelous growth of the know-
ledge of the etiology of disease. Animal and vegetable invaders were
recognized as the essential cause of many diseases. But the study of
the functions of the body whose lot it is to grapple with the invaders
received only a secondary attention, and that again essentially from
morphological quarters. At the present time still more knowledge
is being diligently added to the stores of medical wisdom. Chemistry
has taken a powerful hand in the studies of physiology and pathology,
and is attaining brilliant results. But we should not be misled. The
studies are essentially morphological in their nature. It is physiolog-
ical and pathological chemistry, and but very little chemical physio-
logy and pathology. Even if the hopes of the new school of brilliant
chemical investigators will, indeed, be realized, viz., that in a not far-
off future they will know the structure of proteids and all their con-
stituent bodies, it will be the knowledge of the proteids of the dead
bodies, it will be a brilliant post-mortem chemistry. Living animal
matter, however, is something, else than dead proteids, as living
plants are something else than carbohydrates, although the know-
ledge of the latter has already reached the ideal stage where some of
them can be produced synthetically. No, a study of life, normal and
abnormal, is essentially a study of energy, of function; of course, the
knowledge of the underlying morphology, dead or living, is a pre-
requisite for such studies. And let me state right here that there seems
to be a difference in the make-up of the human mind with regard to the
different studies. Some are more apt and better endowed to grapple
with the problems of energy, and others, again, have natural talents
for the science of morphology. Only a few, however, have the good
fortune of becoming educated in the lines of their natural endow-
ments, and still fewer have the genius to work out their natural des-
tinies against all odds, against all education and training. Now the
men who did and who now do the original work in the medical sciences
received their training in the studies of medicine, four fifths of which
is profoundly developed, magnificent morphology. We cannot won-
der, therefore, that most of the original contributions to the medical
sciences are essentially of a morphological character. Even in the very

PHYSIOLOGY AND ITS RELATION TO MEDICINE 401

recent brilliant additional departments of medicine, in bacteriology
and chemistry, the research work is, as already stated above, for the
most part of a morphological stamp. It is true that a few men of
genius in medicine, Cohnheim, for instance, broke their acquired
chains and made an attempt to study pathology from a functional
point of view. Such attempts, however, were not many, and their
permanent influence is not extensive. What is now termed general
pathology or even pathological physiology consists, in the first place,
of a collection of histological, bacteriological, and chemical facts of
a general but essentially of a morphological nature, including at the
same time the applications of a few well-established physiological
facts to pathology and a few results from direct experimentation in
pathology. That is not a study of physiology under pathological con-
ditions, and certainly not a study of general physiological laws which
can be stimulated by and derived from a study of pathological pro-
cesses. And it is just this kind of study which is missing, and which
could be developed only by a purposeful and concerted action of the
men who have a training in the study of the functional side of life,
among whom there are surely many who have a natural endowment
for such studies.

The following review of the present situation in medicine will show
us the place left vacant by physiology, and the disastrous consequences.
The studies of pathological anatomy extend over all divisions of
medicine, are lucid and nearly complete. Diseases which are exclu-
sively due to palpable anatomical changes are "quite well understood.
Their harmful effects are, for the most part, of a mechanical nature.
In proportion as they are understood, these forms of disease become
amenable to an efficient treatment; it is mechanical, it is surgery.

The studies of the etiology of diseases revealed and continue to
reveal many of the foreign originators of disease, the animal and
vegetable invaders of the living organism. This new and lucid know-
ledge led again to some effective measures in the treatment of dis-
eases, it led to clear plans in preventive medicine, it gave means to
the surgeon to enter with impunity into the interior of living organisms,
and in a few instances it discovered actual remedies for non-surgical
diseases.

But most diseases are something more than mechanical disturb-
ances, or exclusively anatomical changes. There is, in the first place,
that large group of so-called functional diseases which has no patho-
logical anatomy, and for which clinicians have very little interest. But
even those numerous diseases in which the post-mortem examination
revealed distinct anatomical changes were only results of the advanced
stage of the disease. The disease during life consisted primarily
surely in disturbances of a functional character, in reactions to foreign
causes, reactions of living energies, the physiology of which we have

402 PHYSIOLOGY

possibly as yet not even an inkling of. The so-called organ physiology,
which appears to the teachers of physiology to be so extensive that
it can hardly be taught to students of medicine in one year's lectures,
is of astonishingly modest assistance to the understanding of the
actual processes of disease. For instance, in the present knowledge
of the entire section of the diseases of the respiratory tract, physiology
has hardly any share. The knowledge of the few physiological prin-
ciples which are applied there can be acquired in one hour's instruc-
tion. The extensive knowledge in this chapter of pathology is essen-
tially of a morphological nature. Do the functions of the involved
organs take no part in these pathological processes? Most certainly
they do; but we know too little of it, and the clinician passes over
the gap with some makeshift mechanical expl anations. The same is true
in neurology; in fact, in nearly every chapter of internal medicine. It
is impossible to dwell here on the particulars of our subject. What is
the result? First-class clinicians employ their brilliant faculties in
continually developing the morphology of diseases and their diagno-
sis. But treatment? There is either a nihilism pure and simple, or
some sort of a symptomatic treatment is carried on with old or new
drugs upon a purely empirical basis. Or there is a great deal of loose
writing upon diet, air, water, psychotherapy, and the like, and a great
deal of semi-popular discussion in international, national, and local
meetings and popular prize essays on the best methods of treatment,
— with a net result of only a very modest actual benefit for the poor
patient, who, in addition to his affliction, has now to feel the tight grip
of the modern health officer. There is no efficient treatment of
internal diseases in any way comparable with the specific surgical
treatment of mechanical diseases, no specific quelling, correcting, or
curbing of primarily functional disorders. And there never will be
such a specific functional therapy before there is a physiology which,
like physics, will be only too glad to meet with many exceptions in
order to understand properly all the rules by which the energies of
all grades of living phenomena are guided.

THE RELATION OF PHYSIOLOGY TO OTHER SCIENCES

BY MAX VERWORN
(Translated from the German by Dr. Thomas Stotesbury Githens, Philadelphia')

[Max Verworn, Professor of Physiology and Director of the Physiological Institute,
University of Gottingen, since 1901. b. Berlin, Germany, November 4, 1863.
Ph.D. Berlin, 1887; M.D. Jena, 1889. Assistant Instructor and Privat-docent
in Physiology, University of Jena, 1891; Professor Extraordinary, ibid. 1895.
Author of Psycho-physiologische Protisten Studien; Allgemeine Physiologic; and
numerous other works and memoirs.]

WHAT is physiology? Ask any educated person, who does not
belong to the narrow circle of naturalists and physicians, concern-
ing physics and chemistry, concerning botany and zoology, con-
cerning anatomy and pathology, even concerning psychology, and
you will receive an intelligent answer. Ask him, however, con-
cerning physiology, and he is generally unable to give any inform-
ation. It is the peculiar fate of physiology that it is the least
known of all the great branches of natural science, even among
the educated classes.

I have often asked myself why this should be. Why do the
educated classes lack a clear conception of physiology? We may
here think of several reasons. To me, however, it appears that
one cause is of especial importance, that is, the one-sided limitation
of physiology to its own special problems.

For a long time the great general questions have been neglected
by physiology, the questions which interest the masses. Hardly
another branch of biology requires specialism as much as physi-
ology, which, in each of its different branches, requires such various
and manifold preparatory education that the individual investi-
gator must generally limit his work to a single branch in order
to make any advance in the short span of his life. This is why
the work of physiologists is not understood among the masses.
Its connection with the great problems is generally not clear to
them.

This one-sided immersion in special problems has even led to
an isolation of physiology among those sciences which originally
stood nearest to it. Physiology was, at one time, closely amalga-
mated with anatomy and pathology, with zoology and botany,
with physics and philosophy. Even since the scientific renaissance
of the sixteenth century, physiology stood in the closest connec-
tion with all these branches until far into the nineteenth. For a
century, however, this connection has become looser and looser,
and toward the end of the preceding century physiology was al-

404 PHYSIOLOGY

ready almost entirely isolated. Indeed the isolating differen-
tiation began its destructive work, even in its own special realm.
This was the time when, in Germany, Hoppe-Seyler's efforts were
directed toward the separation of physiologic chemistry as a sepa-
rate science. If he had succeeded, the individual branches of
physiology itself would have lost sympathy with one another. This
danger now appears to be past, although now and then a voice is
still heard in favor of the separation of physiologic chemistry.
But even without this, the whole development of physiology is
a classic example of the constantly increasing tendency of the pre-
sent day toward differentiation of special branches.

At a time when the expansion of separate branches has reached
as extreme a degree as at present, at a time when the immersion
in certain special questions threatens to result in a complete loss
of relationship, and, in fact, has already partly succeeded, at such
a time the need of compilation makes itself more and more felt.
This has already been recognized in this country, in which the
restricting fetters of tradition and historic development do not
weigh so heavily as in the Old World. Compilation was, therefore,
the word which has brought us together to-day. As concerns my
own branch, I must greet this tendency with especial joy. Per-
haps the spirit of union, which is felt here to-day, will succeed in
reviving the natural relations which unite physiology with so many
other sciences, to the mutual advantage of all branches and to
the furthering of human knowledge.

If I attempt in the following to sketch briefly the manifold
relations of physiology, I will turn my attention above all to those
relationships from which we may expect in the future especial
advantages for the further development of our knowledge.

The natural relationships between physiology and other sciences
follow of necessity from the aim which the former follows. Physi-
ology is the science of life. In this conception there is universal
agreement. We may clothe this naked definition in different gar-
ments, but its germ remains always the same. The general aim of
all physiologic investigation is the analysis of the phenomena of
life. We may ask, however, what principle should physiologic
investigation follow in this analysis; but in regard to this there
has not always been universal agreement. Different periods and
different investigators have given different opinions. We have
varied often between purely mechanical and more mystical prin-
ciples. First one, then the other, has ruled alone. At times the
adherents of the first, at times those of the second have increased.
After a long period, full of valuable results, in which the purely
mechanic consideration of life-phenomena ruled, the pendulum has
swung again, in the last decennium of the past century, toward

THE RELATIONS OF PHYSIOLOGY 405

the side of mysticism. Certain investigators have felt that it was
necessary to consider in scientific questions the tendency of the
times, which in art and literature was toward mysticism. An
attempt has even been made to revive the old doctrine of "life-
power." This movement has ended in speculation and fantasy
in the problem of development, which is not yet ready for experi-
mental investigation. Among physiologists, whose daily expe-
rience brings immediately before their eyes the truthfulness of
the mechanical conception, the mystical views have found no ad-
herents. But especially in semi-scientific circles such words as
"Vitalism" and " Neovitalism " have been considered the most
modern in science and spread abroad with more energy than under-
standing. In opposition, the standpoint of scientific physiology
is, to-day, completely clear.

In reality the matter is quite simple. The subject of investiga-
tion of physiologic experiment is the living organism. As natural-
ists, physiologists can only have the task of analyzing scientifically
the phenomena of the living body. Only that which is percep-
tible is, however, accessible to scientific analysis, and nothing but
perceptible objects can ever be the subject of scientific investiga-
tions. The general principles and laws of phenomena in the per-
ceptible world are studied by physics and chemistry, and both
have carried their knowledge to a high degree. The organism, as
a perceptible object, must be subject to the general laws which
rule the perceptible world, and, therefore, we cannot analyze the
life-phenomena of organisms otherwise than according to the prin-
ciples of physics and chemistry. Physiology is, in other words, the
special physics and chemistry of organisms. As organisms are
composed of the same elements which are found in the inorganic
world, no other factors can apply than those which are seen in the
inorganic world, and the special peculiarities of the organism can
only be based upon the specific combination of physical and chem-
ical phenomena, for physiologic analysis must finally go back to
general principles, as only then is its task fulfilled. For mystic
factors, not of a physical or chemical nature, there is no place in
physiology; as they would not be comprehensible by human know-
ledge if they were not perceptible or with perceptible effects, and
therefore would always remain hypothetical.

This standpoint has always given practical results. Everything
which has ever been fixed by physiologic investigation has arisen
from the practical application of this conception of physiology,
as the physics and chemistry of the organism. "Life-power" has
not made the slightest addition to the explanation of life-phenom-
ena, in the entire development of physiology.

From the conception of physiology as the special physics and

406 PHYSIOLOGY

chemistry of the organism, arises of itself the extremely close connec-
tion with these two general natural sciences. Physics and chem-
istry ascertain the general laws which rule the perceptible world,
and physiology analyzes the action of these laws in the special system
of the organism, as geology studies the activity and force of gen-
eral physical and chemical principles in the special system of the
planets, or mineralogy in the special system of crystals and minerals.

The organism is, therefore, for the physiologist, only a special
case of a system, which he must analyze according to the general
principles of physics and chemistry. Physiology, therefore, receives
from physics and chemistry its general conception of the laws of
phenomena in the physical world. The more deeply physics and
chemistry penetrate into the knowledge of general laws, so much
more deeply can the investigation of the phenomena of life proceed.
Physiology is, in this relation, entirely dependent upon the develop-
ment of physics and chemistry, and must follow their progress
attentively. To-day this is especially important. The rapid devel-
opment of the great mass of facts and theories, which have recently
been united under the name of "physical chemistry," appears to
be destined to unite these previously independent sciences to a
uniform scientific branch. A number of theories of a general nature
have already been proposed which must have a marked influence
on the investigation of the phenomena of life. The effect of this
great progress in the realm of physical chemistry is already begin-
ning to be felt in physiology. The recent conceptions regarding the
nature of solutions, the theory of ions, the conception of osmosis
and diffusion and of electrochemical processes, the knowledge of
the laws of chemical equalization and the effect of mass, and many
other new ideas, are already beginning to have as fruitful an influ-
ence upon the investigation of the phenomena of life as a half-
century ago the discovery of the laws of energy exercised.

But the conception and symbols of physics and chemistry
will be still further developed, and will be materially changed, in
the course of time. We live to-day in a period in which the well-
proved symbols of physics and chemistry, hoary with age, such as
the conception of matter, of atoms, and of force, begin to waver.
New symbols, new allegories, new conceptions will come in their
place. It would, therefore, be illogical to expect that physiology
could solve all the phenomena of life without fail, by the present
knowledge of physics and chemistry. It is still far away from this
goal. Physics and chemistry cannot explain quite all of the simpler
phenomena of the lifeless natural world, with their present symbols.
But however the conceptions of physics and chemistry may change
in the course of time, one fact remains: no other principles can come
into play in the world of organisms than enter into that of lifeless

THE RELATIONS OF PHYSIOLOGY 407

nature. Physiology can never be anything else than physics and
chemistry, that is, the mechanics, of living beings.

It does not appear to be superfluous to warn here against one of
the consequences which may occur from a short-sighted exaggera-
tion of this conception of physiology. The aim of all the so-called
exact sciences is, admittedly, the demonstration of laws in mathe-
matical form. We occasionally meet with the view that, in the
exact natural sciences, nothing shall be the object of investigation
which cannot be measured according to mass and number. This
conception is destined to hinder the development of scientific
knowledge, as the first step toward the explanation of many phe-
nomena can, in most cases, only be made by qualitative and not
quantitative investigations. A weighing and measuring, a numerical
demonstration, is often only possible after a certain number of
qualitative communications have been made, and physics and chem-
istry have seldom arrived at great and accurate results without
this pioneer work. In physiology the relationships are still more
complex, as here we have to do with the most intricate system of
processes which we know of in nature, and in large part the first
work has yet to be done. Here, there is still less often the possibility
of a determination according to mass and number, and, therefore,
if we throw aside in hasty blindness the study of qualitative relation-
ships, we cast away, ourselves, the place on which we must set our
feet firmly before we can climb higher. Physiology must still leave
a large place for qualitative investigation, although the ideal goal is
mathematical demonstration of the processes in the living organism,
from which we are still far removed. It would be extremely ridicu-
lous to attempt to determine a definite method for physiologic
investigation. All schemes will do harm. Every means, every
method, must be welcomed, if we wish to make even a small step
forward. Therefore, physiology is not merely limited to the methods
of physics and chemistry, but will always seek after the peculiar
methods which are required by its special problems, although the
problem of physiological investigation is only the mechanical analy-
sis of life.

Man is for man the most interesting object of study. No wonder
that the analysis of life was begun directly upon man, without con-
sidering that he is the most complicated and most difficult of all
objects. The beginnings of sciences are never systematic, as their
methods, problems, and aims are only seen in the course of their
development. Thus it was seen later that mechanical analysis of the
phenomena of human life could only be reached by investigating
and analyzing analogous phenomena in other living objects, in the
simplest forms. Geniuses did this earlier, of course. Harvey, Leeu-
wenhoek, Swammerdam, Malpighi, Redi, and others, are among the

408 PHYSIOLOGY

first of the comparative physiologists, although Johannes Miiller
and his contemporaries were the first to emphasize the necessity of
comparative anatomy and of comparative methods in physiology.
Physiology of man requires a physiology of animals.

Plant physiology developed itself independently as a necessity
of botany, and this independence has remained almost complete,
until very recent times. Each has made its way without much
consideration of the other, but to-day they have many points of
contact. Immersion in special problems, especially on the side of
animal physiology, has, however, hindered general interest in its
development. Only in recent times has the need of general physi-
ological points of view succeeded in bringing the two branches
closer to one another. The late but strong development of a general
physiology, which, in contrast to special physiology of man, of
animals, or of plants, sees its task in the analysis of the phenomena
of life common to all organisms, is here the uniting band which
previously was completely lacking.

The comparative method in physiology, as it flourished at the time
of Johannes Miiller, should have led sooner to the development of
a general physiology, for it certainly pointed out the way toward it.
But the great discoveries in the special branch of human physiology,
which the second half of the preceding century brought forth,
delivered the comparative method completely into oblivion, and
the efforts in this direction were thus abruptly interrupted. At the
same time were lost the relations of physiology to zoology, which
before had been most intimate. Every one-sided development,
however, experiences a modification, when it has reached a certain
point, by a process which is to some extent automatic. The defect
increases more and more, until finally, of itself, it impels this cor-
rective process. This is what we see to-day. General physiology
has suddenly begun to develop itself rapidly.

A renewed study of morphology supplied the impulse. The great
discoveries of Schleiden and Schwann gave morphology a different
appearance and could not remain without influence upon physiology.
The construction of organisms from structural elements similar
throughout, forced the conclusion that the processes which occur in
the individual structural elements are merely the external life-phe-
nomena of the organism. Thus, every physiologic problem must
finally end in a study of the cell, and the cells, as the general structural
element of living substance, attain an especial interest for physiology.
The cell is the seat of the actual life-processes, which shows us life
in its simplest form and includes in itself all the secrets of living sub-
stance. We must know what occurs in the cell, and study its general
physiology.

But the life-phenomena of the different forms of cell show them-

THE RELATIONS OF PHYSIOLOGY 409

selves not less manifold than those of the great, many-celled or-
ganisms. The general physiologic properties of cells must be re-
cognized and be distinguished from the specific life-phenomena of
separate cell-forms, and this is only possible by use of the compara-
tive method. The different sorts of free living and tissue-building
cell-forms, from the animal and plant kingdoms, became the objects
of physiologic study, and a mass of general physiologic facts resulted
from these investigations. The general physics and chemistry of the
cell led us deeply into the knowledge of the general phenomena of
life.

But we are only at the beginning. The new discoveries of physical
chemistry give, for the analysis of cellular life, new points of view
and new methods. The phenomena of assimilation and dissimila-
tion, the facts of chemical balance, the disturbances of this balance
by external factors, the inner automatic renewing of assimilation,
the general effects of irritants, and many other phenomena of general
physiology, begin more and more to lift their veils. New expe-
riences stream toward general physiology, from the most various
sources, which must crystallize themselves around the different
parts of the system, after a firm nucleus of phenomena and facts
has been determined to connect them. Thus the realm of general
physiology grows larger and larger, and begins to break down the
isolation of physiology among the biologic sciences. Let us guard
the new branch of general physiology from being overtaken by the
old fate of physiology, one-sided development. This is only to be
avoided if we constantly keep before our eyes its great aim, the
mechanical analysis of the general phenomena of life.

Before all, it is to be desired that general physiology may develop
its own special problems as freely as possible, unhindered by atten-
tion to special problems and methods. The analysis of the general
phenomena of life can easily lead to one-sided methods and one-
sided points of view. Even the cellular investigations of general
physiologic problems can degenerate selfishly. Here we must be
sure to take into consideration the most varying cell-forms, and we
must not merely consider individual cells, isolated as such, but also
the general relationships and connections which arise from the
communistic life of cells and the mutual influence of life-processes
in the cell community. The investigation of the dependence of
cell-life upon the surrounding life-conditions and the effect of every
change of life-condition upon the life of the cell itself is of the
greatest importance for the explanation of the immoderately com-
plicated processes in the complex organism.

Also, in regard to methods, there must be no one-sidedness in
general physiology. The great results of physical chemistry threaten
general physiology with the danger of only working by that method.

410 PHYSIOLOGY

That would be a mistake. We must not cast aside the old methods
of chemical analysis and physical investigation. A science must not
base its existence upon only one method, as a science only lives as
a problem, and the problem of physiology requires the most manifold
•methods, according to the position of the question at the time.
General physiology will only flourish as long as it retains the many-
sidedness of its methods and its objects; but as long as it flourishes,
£O long will physiology retain its connection with the other biologic
sciences, and at the same time form the connecting link between
biology and mechanics.

In another direction, also, general physiology seems to be destined
to act effectively in reviving old natural relationships, namely, in
the realm of medicine. Physiology is one of the daughters of
medicine. At first its existence depended on the needs of practical
medicine, until Galen, whom we may call the father of scientific
physiology, recognized clearly that the complete development of
medicine is not possible, if it is not based on the phenomena of nor-
mal life. Physiology since his time has always retained more or less
close relations to medicine, but has gradually developed itself to an
independent science with its own aims. To-day we see the plainest
expression of this historic relationship between physiology and
medicine, in the fact that in most countries physiology in the uni-
versities belongs to the medical faculties.

The relationship between physiology and medicine has become
now closer, now looser. In the last decennium of the past century
it has become somewhat looser, but physiology has always retained
its place in medical instruction. We find, even in old tradition, the
view generally expressed that physiology is one of the bases of
medical learning, but a view is now found among many that physi-
ology is to a certain degree a luxury, a decorative element of med-
ical science. If we examine the average well-educated practicing
physician to determine what in reality is of use to him in his know-
ledge of physiologic phenomena, we find very little. A few indis-
tinct impressions concerning the principal functions of the organs,
and a few superficial chemical data which he has himself adapted
"so as to make them of use in practice." That is all. Of the actual
processes in the organs, tissues, and cells of the body, of the ex-
tremely close -and important correlations of different parts which
lie at the basis of the preservation of the entire mechanism, he
has no idea. In order to reach this result a two or three semes-
ters' study of physiology is not required. Actually physiology,
apart perhaps from the branch of metabolism, has been overtaken
by a certain isolation among the branches of medicine. Why is
this?

Again we see the same cause. For a long time special subjects

THE RELATIONS OF PHYSIOLOGY 411

have stood in the foreground of physiologic interest, which have
little or nothing to do with practical medicine. What an immense
extent the investigation of the production of electricity in muscles
and nerves has reached, in the physiological laboratories and lec-
tures, and what could and can practical medicine do with these
things? What an exaggeration Ludwig's discovery of the graphic
method for the representation of motions has called forth in the
physiologic instruction of the physician? We have even heard the
opinion expressed that only that which could be demonstrated
graphically should be taught in physiology. Yes, many physi-
cians believe that they must go to practice with a Marey's sphyg-
mograph in their pocket. And of what use have all these sphyg-
mograms and respiration curves been in modern practice? They
have disappeared. The graphic pocket apparatus lies among the
old rubbish. Practical medicine has cast aside the false exactness
which was imposed upon it. Instead of these, it has itself created
general physiologic conceptions. Our entire knowledge of the
physiologic protection of the normal body against infection, our
whole experience with regard to artificial and natural immunity,
which plays so dominant a role in modern medicine, did not arise
from physiologists. The enormous development of this whole
branch of medicine shows plainly t»he need of medicine for physi-
ology, and especially for basic and general physiologic concep-
tions.

It appears to me that general physiology may have a very stim-
ulating effect upon the further development of our medical opin-
ions. There is one branch of medicine with which physiology has
the very closest relationship; that is, the teaching of stimuli and
their effects.

It is really a very paradoxical phenomenon, that physiology
has worked for centuries with various methods of stimulation in
their largest as well as in their smallest relationships, without
ever investigating systematically the general laws of the effects of
stimuli, without even attempting a sharp and general definition
of the meaning of stimulus. Only the more recent development
of physiology has brought about a closer approach to this ques-
tion, and has already extended the truth to a certain degree,
although many important points still wait explanation. The study
of the effects of stimuli, in a large number of the most different
independent and tissue-forming cells, has here permitted a fairly
definite determination of laws, and, above all, has permitted the
sharp fixation of the general conception of stimulus. To-day we
can define this, in its most general sense, as a change in the ex-
ternal influences which affect the existing condition of a living
system. Thus, the effects of stimuli find their expression in a quan-

412 PHYSIOLOGY

titative or qualitative change of the existing processes of life. The
latter group of effects is less extended in the normal life of the
adult organism, and until now has been least studied. It appears,
however, as far as we can determine from an extensive analysis,
only as a secondary result of primary stimulation of the first group.
The great mass of stimuli in the course of the life of the normal
organism only cause quantitative changes of phenomena already
existing in the living system, i. e., either an increase of the same
(excitement), or a decrease (paralysis).

The analysis of the effects of stimulation has now gone much
further. I must, however, limit myself to-day to the most gen-
eral indications. I will only be able to show how extraordinarily
important this analysis is for the basic question of medicine, — what
is disease? Disease is nothing else than life under changed ex-
ternal relationships, i. e., life under the influence of stimuli. Thus,
pathology comes finally to be a study of the effect of stimuli, and
it needs no argument to show that the physician cannot pene-
trate too deeply into the knowledge of the effects of stimulation
and the laws governing them. Above all, medical diagnosis, which
by many physicians is considered the most important part of medi-
cine, requires a comprehensive knowledge of the laws of stimuli.
The physician must ask himself at the sick bed, what part of the
organism is primarily affected by a stimulus? Does the effect con-
sist in a quantitative change, an excitement or paralysis, or in a
qualitative change of the normal life-processes? How may this
change of the affected part act upon neighboring or distant parts
of the body, as a result of the correlation of all the elements in
the body, and how will the entire vital mechanism of the organism
be disturbed? Those are the fundamental questions which every
physician must lay before himself in a given case, if he wishes to
have a fitting conception of the disease. Only then can he use his
therapeutic means effectually. But it is not necessary for me to
emphasize that this analysis must proceed as far as the cells them-
selves. A greater than I, almost a century ago, demonstrated so
convincingly this requirement of pathology, that our entire present-
day medicine rests upon the basis of cellular pathology. Since
the epoch-making work of Rudolph Virchow, cellular pathologic
investigation has developed almost exclusively toward the side
of morphology, not toward that of physiology. A picture of a mi-
croscopic preparation of the diseased part, beautifully colored,
with red or blue nuclei, etc., floats before the eyes of the well-edu-
cated physician, at the sick-bed. It does not occur to him, how-
ever, that the cells which he sees in imagination are alive, and
he overlooks completely the chemistry of healthy and diseased
cells. This is the place where general cellular physiology must

THE RELATIONS OF PHYSIOLOGY 413

come in, and here general physiology must come into the closest
relation with medical diagnosis, if further progress and deeper
knowledge are desired.

But therapeutics can, as little, do without an accurate know-
ledge of the effects of stimuli. The fundamental peculiarity of
living substance, automatic regulation, is of the first importance
for therapy, as Ewald Hering first showed clearly. If any stimulus
has disturbed the balance of normal metabolism or kinetics, it
restores itself immediately after the cessation of the stimulus,
unless the latter has exceeded certain limits, in which case death
results. The therapeutic test of the physician consists to a great
degree in preventing the harmful effects of stimuli, for the organ-
ism cures itself. "Medicus curat, natura sanat." Naturally the
use of any therapeutic measure requires the same profound know-
ledge of the phenomena of stimulation, for every therapeutic in-
fluence upon the organism is, essentially, a stimulus. And it is
evident that the physician should only use stimuli whose effects he
knows accurately, if he will effect a definite result of stimulation, for
therapeutic purposes. For this reason pharmacology and toxicology,
as well as therapy, base a large part of their usefulness on the phe-
nomena and experiences of the physiology of stimulation. If they
will proceed in a truly scientific manner, they must answer the
same questions, and proceed in the same way, in the demonstra-
tion of the effects of medicaments and poisons, as that which was
described in connection with diagnosis. Thus, in the whole realm
of medicine, we are more and more forced to the necessity of the
closest union with general physiology.

I might conclude here, but I feel that I should touch at least
superficially a question which is much discussed to-day, that of
the relation between physiology and psychology.

You will say, if physiology is the study of the phenomena of
life, it must include psychic as well as physical phenomena, and
psychology is thus nothing more than a branch of physiology.
But the question is really not so simple; the psychic phenomena
of any other organism are, of course, accessible to our mechanical
analysis, but in the analysis of our own psychic phenomena we must
put aside the principles and methods of physics and chemistry. Also,
it has been shown that the chain of physical occurrences in the
organism cannot undergo an interruption of continuity anywhere, not
even in the brain. A physical process is always, and only, the result
of another physical process, and the starting-point of a third. Thus
there remains in the series of physical processes no place for any
psychic link. We have, however, demonstrated that psychic pro-
cesses only occur when definite physical conditions are fulfilled,
so that the question concerning the relation of physiology to psych-

414 PHYSIOLOGY

ology is in reality nothing more than the ancient problem of the
relation between body and soul.

Since the beginning of human thought, man has striven to solve
this problem, but one attempt after another has been shattered. At
times it was thought that the solution had really been found, but the
old problem was always found smiling scornfully from the other side.
The alchemy of the Middle Ages busied itself with this question, as it
attempted to prepare gold from baser metals. Time and again the
yellow metal shone forth from the crucible, but finally it was always
found to be nothing but golden pigment. Perhaps our efforts are
like those of the alchemists, and all our straining is useless, because
the problem cannot be solved; perhaps the problem is like those of
ancient times, such as the squaring of the circle, or the discovery of
perpetual motion, which are in reality not true problems. Perhaps
what Mephistopheles says is true,

" 0 glaube mir, der manche tausend Jahre
An dieser harten Speise kaut,
Dass von der Wiege bis zur Bahre,
Kein Mensch den alten Sauerteig verdaut."

Whence arises this conception of a dualistic relation of soul and
body? We are accustomed to hearing Descartes mentioned as its
source. I believe this is wrong. It is true that Descartes has most
sharply defined dualism when he contrasted the body, as that
which has dimensions, with the soul, as that which has not dimen-
sions. But the concept is much older. We find it already in the
philosophy of the ancients. It is not true that the dualism of body
and soul is foreign to the thought of primitive man. On the con-
trary, the thought of a contrast between body and soul is very
generally distributed among the primitive peoples of the earth,
from Greenland to Tierra del Fuego; from the negroes of the tropics
to the inhabitants of the South Sea. This shows that we have here
to do with one of the most ancient thoughts of mankind.

The imaginative life of primitive peoples shows us plainly the
origin of this dualistic conception. It is the sharp contrast be-
tween life and death, between waking and sleep, which led to the
thought of a soul present in the body, a soul which may leave the
body and again return to it, a soul which after death leads a shadowy
existence as a spirit. This group of ideas, around which the entire
spiritual life of primitive peoples revolves, has even developed
into the conception of two distinct souls, in many of the Indian
and Eskimo races. One of these, the perceptive spirit, which may
occasionally during lifetime leave the body and enter other bodies,
for instance in sleep and in dreams; the other spirit, which retains
life, which passes away with the last breath, and, floating in the
atmosphere, influences the fortunes of mankind, as a spirit.

415

"Zwei Seelen wohnen, ach, in meiner Brust ;
Die eine will sich von der andern trennen."

But are these reasons, which gave origin to the twofold, or even
threefold division of human nature, still binding for us? I answer
no. The contrast of body and soul exists not at all. It is a decep-
tion. If we prove anything that we know in the entire physical
world, if we analyze any existing substance, we find nothing but
a sum of impressions. Impressions are, however, psychic elements.
Hume actually believed that there was nothing to our bodies,
except merely impressions, and Kant drew his "Ding an sich"
from this conception. This was pure hypothesis, and Kant him-
self understood that the "the thing itself," must always be in-
accessible to our knowledge, and that all knowledge must remain
limited to our impressions. Why, then, should we conceive of such
a mystic unknowable and objectless Something? It is completely
unnecessary. If we analyze the world in a purely empiric manner,
and discard, in a strictly scientific way, every hypothesis, we find
no such dualism in the world. The entire world consists of psychic
impressions, and nothing else is to be found anywhere.

We must accustom ourselves to this incontrovertible fact, which
is becoming to-day more and more widespread. The world, then,
appears completely uniform, and many of the difficulties disappear.
There is not a division into material and psychic, parallel to one an-
other. Here all is unity, a mighty sum of psychic impressions and
their complexes; that is, the Psyche, that is, the world, and all
scientific investigation consists in the analysis of its contents. The
limits between science and psychology also disappear. We pursue
the same method in both sciences; we analyze psychic complexes and
lay down general laws; we do the same in physiology. As a special
science it is thus limited to a special part of the entire corporeal
world, to the complex of impressions, which we as organisms feel.
Thus physiology is a part of psychology, as well as of natural sci-
ence. For in the broadest sense psychology includes all science.

I am at the end. Many wanderers travel far awray, seeking for
truth. They spread themselves toward north and south, toward
east and toward west. They wander through the world on painful,
intricate paths. At the end, however, they all meet at their goal.

Thus it is with knowledge; however far they may be sepa-
rated from one another, however specialized and differentiated
they may be, as they penetrate more deeply, all sciences approach
one another more and more closely. Finally, however, all the paths
of investigation end, as their last goal, in the one great realm of
psychology.

BY WILLIAM HENRY HOWELL

[William Henry Howell, Professor of Physiology, Johns Hopkins University,
and Dean of the Medical Department, b. February 20, 1860, Baltimore, Mary-
land. A.B. Johns Hopkins University, 1881; Ph.D. 1884; M.D. University of
Michigan, 1890; LL.D. Trinity College, 1901; Post-graduate, Johns Hopkins
University, 1881-84. Professor of Physiology and Histology, University of
Michigan, 1889-92; Associate Professor of Physiology, Harvard University,
1892-93. Member of the National Academy of Sciences; the American Philo-
sophical Society; the American Association for the Advancement of Science;
American Physiological Society; American Society of Naturalists; Society for
Experimental Biology and Medicine, etc. Editor of The American Text-Book
of Physiology; American Journal of Physiology, etc.]

MOST of the masters in physiology have attempted in one way or
another to lay before their fellow craftsmen their ideas concerning the
right methods to be used in physiology, its natural boundaries, and
its future development. We read these utterances sometimes with
admiration, sometimes with doubt, but always with interest, and also,
alas, with disappointment. For it has not been given to any of our
saints or prophets to pierce very far into the uncertain future, and
one seeks in vain for a fundamental thought or principle which shall
illuminate the mystery of life. Our greatest men have, in fact, been
wise enough to teach us by example rather than by precept; the
chief lesson that one may learn from their lives and writings is that
we must continue to investigate, to observe, and to experiment, and
that in this way only can sure progress be made toward the goal of
which we all dream. The time seems not yet ripe for the master-mind
to gather the scattered data and mold them into great generalizations
or laws such as have been achieved in other sciences. We must, per-
haps, admit that the philosophical basis of physiology, its general prin-
ciples and quantitative laws, have been borrowed in large part from
other departments, and that the subject has not as yet fully repaid
this indebtedness by contributions derived solely from its own re-
sources. We have no names to which science as a whole owes as much
as it does to Galileo, Lavoisier, Newton, Mayer and Joule, Darwin or
Pasteur,1 and since we may claim that our greatest physiologists
rank with the first intellects of their age, their failure to penetrate
farther into the causation of vital phenomena must be attributed
to the intrinsic difficulties and complexity which the subject offers
to the human mind. None of us can change this condition, and
those who desire to forecast the future must be content, therefore,
to view the subject from the standpoint of past experience and the

1 While two of the names quoted have a right to be classed among physiologists
(Lavoisier and Mayer), the contributions made by them which have been so funda-
mental to all sciences were in the departments of chemistry and physics.

PRESENT PROBLEMS OF PHYSIOLOGY 417

history of other sciences whose field of work has presented appar-
ently less formidable difficulties.

In what may be termed the golden period of physiology, that is, the
latter two thirds of the nineteenth century, the period during which
the subject became established definitively as an experimental science,
the rich and abundant harvest of facts gathered by the first workers
who adopted exclusively experimental methods awoke enthusiasm
and brightest anticipations. The workers in physiology were ani-
mated by a confident belief that their science was on the highroad to
a successful solution of the nature and properties of living matter.
Now, however, at the beginning of the twentieth century, one hears
frequently the voice of dissatisfaction and criticism. Although the
workers are more numerous, and the methods and appliances are more
complete, the harvest of facts is not so rich nor so significant. There-
fore to many it would seem that the methods used are at fault; there
is need at least for a new point of view. It requires but little reflection
to become convinced that some of the implied or expressed criticism
directed toward recent work in physiology is unjust and is founded
upon a misconception of its true nature and development. I refer
particularly to the belief so frequently expressed that much of the
current investigation in physiology is sterile as regards its immediate
applicability to practical medicine, and the further statement that the
subject itself has become isolated in a measure from the other bio-
logical sciences.1 I do not contest the accuracy of these statements,
but both results must be regarded as a necessary outcome of the nor-
mal and healthy development of the science of physiology. The general
history of physiology is known to us all; it is not necessary to enter
into details. It arose out of medicine and developed in intimate rela-
tions with the study of anatomy. But even in its earliest history its
most significant results were obtained by the use of the experimental
method, and in the nineteenth century its separation from the purely
observational sciences was clearly recognized. The establishment of
physiology as an experimental science is usually attributed to Jo-
hannes Miiller and his pupils or their contemporaries who fell under
his influence. But as I read its history, its modern characteristics,
whether for good or for evil, owe their origin as much to the French
as to the German school. Johannes Miiller himself was not preeminent
as an experimenter, — he made use of anatomical rather than physio-
logical methods; but his contemporary Magendie was a typical modern
physiologist, and whatever may have been the extent of his personal
influence during life, there can be no question that his methods of
work and his points of view are the ones that were subsequently

1 Meltzer, Vitalism and Mechanism in Biology and Medicine, Science, vol. xix,
p. 18, 1904. Verworn, Einleitung, Zeitschrift fur Allgemeine Physiologic, i, p. 1,
1902.

418 PHYSIOLOGY

adopted in physiology. I am not concerned at present, however, with
the attempt to estimate justly the relative influence of these great men
and their pupils; the simple point that I wish to insist upon is that
they established physiology as an experimental science, and pointed
out that its most intimate relationship must be with the other ex-
perimental sciences of physics and chemistry. Physiology, said Ber-
nard, is not a natural but an experimental science, and most recent
writers have defined the subject as consisting essentially of the phys-
ics and chemistry of living matter. The two results spoken of above
have followed as an inevitable outcome of this course of develop-
ment. As an independent science, with specific problems of its own,
physiology has naturally loosened its connections with the art of
medicine. Formerly one of the handmaids of the noble art, it has
been freed in a measure from this servitude, and although its results
must always be of the greatest importance to the scientific side of
medicine, it can no longer be expected to devote itself mainly to
the immediate needs of the physician. The practical problems of
medicine that can be studied by physiological methods have been
undertaken less and less frequently by the physiologist proper; they
have fallen to the hands of the pathologist and the clinician. Physi-
ology does its part in this work by giving to such men the needful
technique and training which have been developed by the study of
its own problems, and the results obtained redound no less to the
credit of physiology because the investigator concerned happens to
be classified as a pathologist or clinician. All of the sciences are
characterized by this mutual helpfulness; the methods and stand-
points developed in one frequently give essential aid to the workers
in a related science; and the full outcome of the labors of the nar-
row specialist cannot be justly estimated by the immediate results
in his own department. The physiologist proper, the specialist in
physiology, must devote himself to the peculiar problems of his
own subject. It cannot be otherwise, for who else is to attempt the
solution of these problems ? The practical interests of such work to
medicine may seem to be remote, but it is hardly necessary to repeat
the often-quoted injunction, founded upon past experience, that the
solution of a special problem of a fundamental nature carries with
it in the long run the most important practical results. The state
of affairs in physiology is exactly similar to what has long been
recognized as proper and natural in chemistry and physics. The
chemical problems of practical medicine are not solved by the
chemist, scarcely indeed by the physiological chemist. But those
who undertake these problems avail themselves to the fullest of the
knowledge and methods of chemistry, and without this aid their
work would be impossible. In the same way physiology will continu-
ally aid in the immediate practical work of medicine, although those

PRESENT PROBLEMS OF PHYSIOLOGY 419

who designate themselves as physiologists may less and less frequently
give their own hands to such work. We who are physiologists should
not be lukewarm nor too critical in our attitude toward the work of
the specialist. Those who undertake the solution of the problems of
medicine find a large and sympathetic audience; their work wins
quick recognition, and oftentimes substantial rewards; while those
who attempt the more special and peculiar work of the science of
physiology are not likely to attract the attention or the interest of
physicians; they must look to their colleagues for encouragement
and recognition. What has happened to physiology in this matter
of its relation to medicine will eventually be true of the other medical
sciences. The tendency is already well developed in the subject of
anatomy. The specialist in this subject is no longer interested chiefly
in the surgical or medical bearing of his problems; he has questions
of his own that look toward the understanding of the great laws of
growth and development. Medicine should not wish to keep its child-
ren forever tied to its own apron-strings. In proportion as they
develop normally and healthfully, they must look forward to an inde-
pendent existence, and the great mother doubtless will find most
honor and help from her offspring as they reach their maturity and
contribute to her support otherwise than by immediate hand-service.
It has been inevitable also that the development of physiology as
an experimental science should cause it to grow away from the other
biological sciences. Anatomy and the morphological side of botany
and zoology are observational sciences, and their methods vary widely
from those employed in physiology. It is still true, of course, that
purely anatomical work may furnish important data for physiological
conclusions, for .instance, in the physiology of the nervous system; yet
the tendency of physiology is and has been to depart from such meth-
ods, and there has become apparent an increasing lack of sympathy,
a lessening of mutual understanding of each other's work between the
anatomist and the physiologist. We cannot expect the old relation-
ship to be renewed by a return of physiology to its ancient methods.
On the contrary, if there is to be a restoration of the former close
union, the advance must come from the side of anatomy. Many of the
problems of this latter science will eventually call for the test of
experiment, and even now an increasing number of its workers are
occupying, as it were, a middle ground between the two subjects, —
deriving their problems from the side of anatomy and their methods
from the side of physiology. Through the influence of this band of
workers it is possible that the two sciences may be brought more
closely into touch with each other than has been the case for the last
few decades. But while the bond between physiologist and biologist
has been less cordial than in former years physiology has found a com-
pensation in the ever-increasing intimacy of its relationships with

420 PHYSIOLOGY

physics and chemistry. The physiologist looks more and more to chem-
istry, physics, and physical chemistry for suggestions and methods.
How can it be otherwise, if the current statement be true that physi-
ology in the long run has to explain the physics and chemistry of
living matter? The truth of this point of view will be apparent to any
one who will trace the development of physiology, and it is brought
forcibly to the mind of every teacher of the subject when he attempts
to direct the training of one who looks forward to a career as a special-
ist in physiology. I believe that every physiologist feels that the chief
preparatory training in his subject should consist in a thorough
grounding in physics and in chemistry. If many of the results of recent
physiological investigations have not been as decisive as we would
wish, is it not probable, nay, almost certain, that the fault lies not in
the nature of the problems investigated, nor altogether in the character
of the experimental methods employed, but in the inadequate training
of the workers? If our investigators were better equipped in the
matter of technical training, there would perhaps be less cause for
complaint on the score of results, for in physiology, as in the other
experimental sciences, the number of problems that may be studied by
known methods is very large, one might almost say indefinitely large.
We need in physiology not only the great experimenters like Ludwig
and Bernard, men with an inborn spirit of curiosity and a talent for
experimental inquiry, but also a large number of productive investiga-
tors whose capacity may be of a lower order, but whose training shall
be complete enough to insure the acquisition of exact and positive
results.

If, as I believe, every one will admit the correctness of the facts
stated above regarding the tendency of modern physiology to
imitate closely the methods used in physical and chemical investi-
gations, the only point to be considered in this connection is whether
or not this tendency is premature. Is physiology, in fact, in a suffi-
ciently developed state to employ the methods of the exact sciences?
After all, most of the criticism regarding current physiological
investigation seems to carry with it the implication that in great
part at least the subject as yet is not prepared for the quantitative
methods of the other experimental sciences. In considering this
point much depends necessarily upon the meaning one gives to the
term physical and chemical methods. If we restrict this term to
purely physical or chemical studies of living matter in the cell or
in the organism, the contention of those who are dissatisfied with
the results of recent work is more readily understood, although,
in my opinion, far from being justified. Dealing with a substance
whose composition is very complex and unstable, and whose struc-
ture is not known, it is apparent that rapid progress cannot be
expected and exact results cannot often be obtained even by the

PRESENT PROBLEMS OF PHYSIOLOGY 421

employment of accurate methods of research. Such work demands,
as Ludwig expressed it, that we shall explain each phenomenon as a
function of the conditions producing it, or, to use Mach's phraseology,
as a function of those variables upon which it depends. It is neces-
sary in such experiments that one condition or set of conditions
be kept constant while another is varied in a known way. While
this end is often attained in the study of the properties of dead
matter, it seems entirely obvious that the complex and unstable
living matter should offer much greater difficulty, and that the
results obtained should be much less definite and conclusive. Hence
the numerous investigations in physiology that lead to diverse and
inconstant conclusions. Hence also the error into which falls the
over-sanguine physiologist who imagines that he can borrow his
method from physics or chemistry and apply it forthwith to the
successful study of the properties of living matter. Every one must
grant that this kind of work represents the highest ideal of physio-
logical investigation, an ideal toward which the science should
endeavor to develop; but judging solely by the results obtained
hitherto, one may be forced to admit that the acquisition of positive
knowledge by these methods has been slow and uncertain. Such
relatively simple problems as the elasticity of the living tissues, the
hydrodynamics of the blood-flow, the electrical phenomena of the
functional nerve-fibre, the chemical changes of the foodstuffs during
digestion and absorption, the chemical changes of respiration and
secretion, are still the subjects of apparently endless controversies.
Few of the problems of this character that occupied the attenton of
our predecessors fifty years ago have been solved satisfactorily. In
each generation certain conclusions are accepted and taught, but
we are all aware how constantly our views are undergoing change,
and how few are the facts that we may consider as definitively
demonstrated. The writers of text-books are obliged to prepare
frequent new editions not only for the purpose of adding new ma-
terial, but of correcting the old. In fact, in respect to the exact
methods of research, the state of physiology is not greatly differ-
ent from that of physics or chemistry a century ago. Doubtless much
of the work done by these methods is poorly done, or at least leads
to no positive conclusions, owing to the intrinsic difficulties of the
subject. But granting all this, it seems to me nevertheless that
in this direction lies the path of greatest honor for those whose
capacity and training mark them as leaders in the subject. We
cannot seriously criticise this kind of work without surrendering all
hope of the future of physiology. We can only justly criticise the
lack of judgment in those who undertake it without sufficient pre-
paratory training or knowledge of the subject.

If, on the other hand, by physical and chemical methods we under-

422 PHYSIOLOGY

stand the experimental method, whatever may be the character of
its technique, then the question suggested above becomes relatively
simple. This, I believe, is the standpoint assumed by the founders
of modern physiology, and this is the truth which they wished to
emphasize when they claimed that physiology is essentially an
experimental science which must develop along lines similar to
those worked out in physics and chemistry. When Magendie com-
pleted the demonstration of the division of function between the
anterior and the posterior roots of the spinal nerves, a distinction
that had been assumed by Bell on anatomical grounds, he used the
chemical and physical method; he stimulated each root, and thus
arrived at a positive conclusion which could never have been reached
except by the employment of the experimental method. And those
observers like Langley, who in our own day "are slowly unraveling
the physiological mechanism of the so-called sympathetic or auto-
nomic nervous system and are using experimental stimulation at
every stage of the work, are also in this sense employing the physical
and chemical method. From this point of view there is no room for
criticism regarding the progress, past or future, of the science of
physiology. Most of our advance in knowledge has been due to
direct experimental inquiry, and the opportunities for further satis-
factory work of the same character are lacking only to those who
fail in the zeal or talent requisite to imagine and carry out experi-
mental investigations. A recent writer1 has said, "He who cannot
discover and classify new facts in any branch of natural science
after a few weeks, or at most a few months, of industrious work
must indeed be ignorant or unskilled." As regards experimental
physiology, I cannot agree with this author in the implied sim-
plicity of the task of discovery of new facts. I fancy that the
unpublished history of the subject contains records of many inves-
tigations which were carried out by observers neither ignorant nor
unskilled, but which failed to unearth any new facts. But this
much seems to me to be certain, that in physiology at present there
is abundant opportunity for every grade of investigation. The
subject is not so far advanced that new facts of even the simplest
kind are without value. That purely anatomical studies may have
a profound influence upon physiological theories is illustrated in the
most striking way by the history of the so-called neurone doctrine
and by the modified views upon this subject that are beginning to
be felt in consequence of the anatomical work of Apathy, Nissl,
Bethe, and others. For physiology, however, it is all-important that
the ideas suggested from the anatomical side shall be verified and
expanded by the experimental method. Bethe's experimental

1 Ostwald, The Relations of Biology and the Neighboring Sciences, University
of California Publications, Physiology, i, p. 11, 1903.

PRESENT PROBLEMS OF PHYSIOLOGY 423

researches upon the degeneration and regeneration of peripheral
nerve-fibers have added greatly to the significance of his anatomical
work, and will insure the recognition of the importance of the
newer ideas concerning the physiological mechanisms of the nerv-
ous system. While I agree most heartily with Verworn l that
physiology should claim "vollstandige Freiheit in der Wahl des
Objekts und in der Wahl der Methoden," I find it necessary to supple-
ment this demand by the restriction that the methods, to be physi-
ological, must be experimental. This peculiarity constitutes the
shibboleth that serves to distinguish the physiologist from his
biological comrades. So long as any physiologist answers to this
designation, he should be recognized as a worthy member of our
guild. The tendency sometimes exhibited by our most active and
prominent workers, to magnify the importance of their own, per-
haps newer, methods, by contemptuous or despairing criticism of
the methods employed by other workers, seems to me not only
ungenerous and unjustifiable, but even positively injurious to the
advancement of our science. There is opportunity for important
results from all good methods whether old or new, and he whose
training or opportunities enable him to do his best work along
well-established lines need not be discouraged or diverted in his
labors because newer modes are the sensation of the hour. Our
greatest teachers have been characterized always by a large-minded
sympathy for work of all kinds so long as it is well conceived and
well executed. •

In all the biological sciences there is an opportunity for physio-
logical work. Hypotheses based upon anatomical facts call for the
test of experiment, and the methods that suffice in the beginning
may be relatively simple, so that little or no technical training is
required for the work so far as the experimental side is concerned.
The experimental zoologist has entered upon such a field. For no
good reason he has selected this designation, which seems to suggest
the formation of a new specialty. As a matter of fact, experi-
mental work upon animals is necessarily physiological, and the
experimental zoologist must look for his methods and implements
to the science of physiology. Work of this kind has all the fascina-
tions of pioneer life; it holds out the possibility of rich discovery,
of unexpected finds, and will doubtless attract from physiology
and from anatomy the adventurous spirits with large ideas, together
with many who are simply dissatisfied with conditions as they are.
I cannot, however, sympathize with those who, stirred by the results
already reported, seem to feel that all of the energy and ability of
our subject should be diverted to this kind of work. On the con-
trary, however important and attractive this work may be, it is

1 Loc. tit.

424 PHYSIOLOGY

distinctly not the best field for the trained specialist in physiology.
There is a large domain discovered by the pioneers of other times
which needs development. Crude methods will not suffice for this
work, and it constitutes the special field for the best-trained artisans
in physiology. This most difficult and most fundamental work
must be accomplished through the agency of the exact methods of
physics and chemistry, and if those who have the requisite training
are devoting themselves energetically to this duty, those of us who
may lack the ability or special training for such complex under-
takings should not be too critical of the results. In the nature of
things the work of the pioneer is likely to bring greater glory and
recognition to those who make a success of it, but the regions he
opens must be subsequently explored and developed. Those who do
this latter work are the ones who really determine the importance
of each new discovery; they are the ones who ascertain for us
whether it is a barren country that has been opened up, or one rich
in the possibilities of wealth. This, as I see it, is the kind of work
in which the great body of physiologists is actually engaged at
present, and it is a kind of work in which the technical methods of
physics and chemistry must be of increasing importance.

But whether physiological work is directed along purely physical
or chemical lines, or is, to use a current designation, biological in
character, so long as its experimental side is emphasized, it is pure
physiology, and must, if pursued with energy and ability, contribute
to the advancement of our science. This has been the line of devel-
opment of modern physiology from the time when its founders first
pointed out the inadequacy of observational methods and unsup-
ported speculative reasoning. Those who were responsible for
giving* it this direction of growth felt that its future was thereby
assured. "La physiologic, " said Bernard,1 " de'finitivement engaged
dans la voie expe"rimentale, n'a plus qu'a poursuivre sa marche."
For a long time we have been advancing along this path, and it is
only necessary to look back to realize the great progress that has
been made. When we look forward, however, difficulties present
themselves that have made some physiologists doubt whether after
all the experimental way will lead us to the end that the science
has in mind. The apparently insuperable obstacles continually
obtruding themselves always alarm unduly some of our leaders.
Fifteen years ago a well-known physiologist, who has himself done
much valuable experimental work, exclaimed that our present
methods of investigation had reached their limit.2 "The smallest
cell exhibits all the mysteries of life, and our present methods of

1 Bernard, De la physiologic genfrale, Preface, Paris, 1872.

2 Bunge, Physiological and Pathological Chemistry, Introduction, English trans-
lation, London, 1890.

PRESENT PROBLEMS OF PHYSIOLOGY 425

its investigation have reached their limit." But in the brief period
that has elapsed since that complaint was made, many additions of
striking importance have been made to our knowledge, "with the
help of chemistry, physics, and anatomy alone." Since that time
the discovery of internal secretions has opened a new field of experi-
mental work; the methods of physical chemistry have found a
fruitful application in the problems of secretion and absorption;
physiological chemistry has steadily added to our knowledge of the
composition of the body; our conceptions of the influence and
extent of the action of enzymes has been greatly broadened, and
the whole subject of so-called biological reactions, as illustrated by
the acquisition of immunity toward foreign substances, has been
added to our means of research.

Long ago Borelli and his followers, the iatro-physicists and iatro-
chemists, had rightly conceived the method by means of which the
problems of physiology should be approached, and if in the eight-
eenth century the workers in this subject became discouraged and
forsook the narrow path of physio-chemical methods and explana-
tions for the broad and easy road of "baseless and senseless hypo-
theses," 1 who can doubt that the progress of physiology was
thereby delayed ? Whatever may seem to be the difficulties ahead,
however inadequate our methods may appear, the history of physio-
logy, like that of the other experimental sciences, teaches us in the
clearest possible way that if we follow steadfastly the advice of our
greatest teachers and continue to experiment, to try, new methods
will be developed continually which will prove adequate to the fruit-
ful investigation of the seemingly impossible problems that con-
front us. We have many examples in our own subject of the un-
wisdom of crying ignorabimus. Take the instance of the velocity of
the nerve impulse. The greatest living master of physiology, im-
pressed by the idea that the action of the nerve must depend upon
the movement of an imponderable material propagated with a
velocity comparable to that of light, had declared that it was hope-
less to think of arriving at an experimental determination of this
velocity within the short distance offered by the animal body. Yet
a few years afterward Du Bois Reymond discovered the electrical
phenomena of the stimulated nerve, and reasoning from this fact,
Helmholtz was led to his beautiful and simple experiments, by
means of which the velocity of the nerve impulse was accurately
measured. Miiller's surrender of the problem was due to a false
assumption, and without doubt we or our descendants will find that
many of the questions that seem to us beyond the limit of experi-
mental study will be made accessible to investigation by the dis-
covery of new facts and methods. To judge from the past, the great-
1 Reil, Archiv fur die Physiologie, vol. i, p. 4, 1796.

426 PHYSIOLOGY

est danger and mistake lies always in that hopeless attitude of
mind which assumes that what is impossible now to our methods
and to our limited vision will remain so forever. I cannot myself
see any reason why the physiologist should be despondent of the
future, nor why he should depart in any way from the rule laid
down by Harvey, "to search out and study the secrets of nature
by way of experiment." l Those who criticise existing tendencies
and methods, and speak vaguely of a better way, have nothing
definite to offer, except a return to the barren and disastrous method
of speculation by way of the "inner sense." 2

There are certain large problems in biology which, by defini-
tion at least, belong to physiology, but which as a matter of fact
do not at present form a subject of investigation by physiologists.
Such, for instance, are the great questions of development and
heredity, and the varied and important reactions between the
organism and its environment included under the term ecology,
or bionomics. The course of development in biology has been such
that in recent years these questions have fallen mainly into the
hands of the morphologists. But the methods employed by the
morphologists in their investigations tend to become more and
more experimental, and we may infer that the workers who devote
themselves to these problems will be compelled to have recourse
more and more to the technical methods of physiology. It is there-
fore a fair question as to whether or not it is desirable that the
specialist in physiology should give his attention to work of this
character. Burdon-Sanderson, in an address before the British
Association for the Advancement of Science, 1893,3 took the ground
that the field of physiology proper, as determined by the course
of development, lies altogether in the province of what he calls
the internal relations of the organism, that is, "the action of the
parts or organs in their relations to each other." This definition
is at least an approximately accurate statement of the scope of
physiology as it has existed during the past two or three genera-
tions. I say approximately accurate, because as a matter of fact
some recognized physiological work has concerned itself with the
reactions between the organism and its environment, such work,
for instance, as the effect of external temperature upon heat pro-
duction, or the effects of altitude upon the elements of the blood.
Still the reaction to the environment has been studied by the
physiologist only in so far as the adaptation can be detected at once
or within a relatively short period of time. Those reactions that
are detectible only or mainly in the progeny have been left very

1 Quoted from Pye-Smith, Harveian Oration, Nature, vol. xix, 1893.

- Bnnge, loc. cit.

3 Nature, vol. xix, 1893.

PRESENT PROBLEMS OF PHYSIOLOGY 427

properly to those sciences whose dominant method is that of obser-
vation and comparison. In this regard the history of physiology
offers an analogy to that of physics. Most of the problems of astro-
nomy and geology are in a wide sense physical problems, but in
the division of labor made necessary by the extent of the field to
be cultivated, the specialist in physics has limited himself to the
study of the properties of inanimate matter so far as they can be
approached by the methods of laboratory experiment. The wider
relations of this matter to the cosmical processes throughout the
visible universe, and its transformations during long periods of
time, have formed the subject-matter for independent although
related sciences. The astronomer or geologist makes much use of
physical knowledge and physical methods, but his subject is large
enough to form an independent department of science. A similar
division of labor has been followed in the sciences that deal with
animate nature, and the part that has fallen to the physiologist
is mainly the experimental laboratory study of the properties of
living matter. It seems proper, and indeed necessary, that the broader
ecological problems should form an independent science which
will need specialists of its own. Work of this kind cannot be re-
garded as lying within the province of the specialist in physiology,
although without doubt the development of the physiological
sides of the subject will be made largely through methods and
technique borrowed or adapted from physiology, and on the other
hand the results obtained from ecological work will doubtless
exert a reflex influence upon the methods and especially the the-
ories of physiology.

The matter stands otherwise, however, in regard to the deeply
interesting and important facts of embryological development.
The laws of growth and senescence, the secrets of fertilization and
heredity, must be studied in the long run by the physiologist; they
are intrinsically physiological problems and must yield at last
to the experimental methods of the laboratory. These questions
have been studied heretofore chiefly by anatomical methods; but
this is the natural order of development. The anatomical side is
the simpler; it precedes and serves as a basis for physiological in-
vestigation, as the renaissance of anatomy in the sixteenth cen-
tury formed the logical precursor of a similar awakening in physi-
ology in the seventeenth century. The anatomist has been forced,
so to speak, to take up first the problems of development, but of
necessity the need for experimental work has soon made itself
felt. The results that have been obtained by the use of the simple
but ingenious experiments so far employed have been most sug-
gestive, and indicate clearly that a promising future awaits the
further extension of this method. If for a time longer such work

428 PHYSIOLOGY

shall be done mainly by those whose training has been received
in the observational sciences, it seems inevitable that the specialist
in physiology must also enter the field. Chemical and physical
methods are clearly adapted to the study of these problems, for in
the end we expect to find the scientific explanation of growth and
development in the physical and chemical properties of living
matter. The subject is as truly a part of physiology as the pro-
cesses of secretion and nutrition. In the current literature upon
the subject there is at present a freedom in the formation of hypo-
theses and a reliance upon the virtues of the syllogism which tend
to bring it into sympathetic relations with philosophy rather than
with physiology. But as the store of observed and demonstrable
data is increased, the boundary-line between the probable and the
improbable will be more sharply drawn, and more objective methods
and less ambiguous theories will mark the development of the subject
along experimental lines.

In the strictly physiological literature of the past century, a char-
acteristic feature has been the absence of philosophical speculation.
Although the physiologists have been concerned most directly
with the problems of life, they, of all the biological family, have
been least productive in the philosophical discussions that have
prevailed during this period. Those who were most conspicuous in
laying the foundation of our exact knowledge followed upon an age
of free speculation, and therefore, as it were by protest against
this tendency, devoted themselves to an empirical study of the sub-
ject, following the admonition of Harvey mentioned above; of
Hunter, whose advice was, "Don't think, try;" and of Magendie,
whose guiding principle of work was similarly expressed.

At the present time there are indications that the workers in
physiology are dissatisfied with this cautious attitude. There
seems to be a reaction against the purely empirical procedure, and
a demand for the discussion of the underlying philosophical prin-
ciples. This tendency, in fact, has seemed to affect all of the ex-
perimental sciences. "All sciences," says Ostwald,1 "are tending
to be philosophical;" and he and others see in this fact an indica-
tion of the approach of an era of synthesis in science, a beginning
of the unification of all the widely separated specialties toward a
common end. Others will perhaps view this tendency with alarm,
and imagine that history is repeating itself; that after a century
of objective experimentation the restless mind of man is reverting
to the speculative methods of the eighteenth century and attempt-
ing after the manner of other days to reach by a shorter path the
final goal of an understanding of the mysteries of the universe.
Truly, when one examines the results of this recent tendency, he

1 Loc. cit.

PRESENT PROBLEMS OF PHYSIOLOGY 429

finds in them but little to encourage his hopes of a more rapid
advance in knowledge. While many protest against the inadequacy
of our present methods, the progress that is actually being made
is accomplished, as formerly, by those who adhere to the tried
method of experimenting continually in every direction. So far as
I can see, it is still the duty of the physiologist to insist upon the
necessity and value of empirical work. What we need is not so
much philosophical theories as new experimental methods, and
these will be discovered only by those who, trained in the technique
of the subject, are continually attempting to modify and improve
existing methods. Physiology needs a Pasteur rather than a Des-
cartes. It is possible that the sciences of physics and chemistry,
being so much farther advanced than that of physiology, may
feel acutely the need of reconstructing their philosophical basis
in order that their working hypotheses may better adapt them-
selves to future experimental work, but in physiology the guiding
principles which we have received from these sciences still hold
out richest possibilities of results, and we have not within the
limits of our own subject reached that degree of development which
calls for a fundamental change in methods or theory. While de-
precating, therefore, in the strongest possible way any effort to
minimize the importance of the experimental work as now car-
ried on in physiology, it seems to me, nevertheless, quite evident
that some value must be given also to the character of the general
philosophical idea upon which this work is based. The purely
agnostic point of view is suited, perhaps, to individual minds; and
where our ignorance is so great the empirical attitude is doubtless
the most modest, and theoretically the most justifiable. But hu-
man nature is such that an entirely neutral and judicial stand-
point fails to arouse in it much enthusiasm or strenuous endeavor.
In science we need enthusiasm, for much work is to be done, and
scientists as a body, like their fellow mortals, are not content to
hold themselves aloof from speculations regarding the final object
and significance of their labors. The nature of the underlying phil-
osophical belief has always had an important influence upon the
extent and character of scientific work, and we must take this factor
into our reckoning in any attempt to estimate the conditions that
contribute to the advance or to the retrogression of science.

Toward the middle of the nineteenth century magnificent work
in physiology was being done in Germany and in France. The
methods that were employed by Flourens, Magendie, and Bernard
were as productive and as modern as those used by their contem-
poraries in Germany, but the influence of the latter school was
seemingly more widespread, if we may judge this influence by the
effect upon the entire body of investigators in physiology. Recent

430 PHYSIOLOGY

historians,1 outside of France, trace the modern revival chiefly
to the German school, to the work and the influence of Du Bois
Reymond, Ludwig, Helmholtz, Briicke, et al. It. has seemed to
me that one reason for the seeming neglect of the equally import-
ant work of the French school lies in the fact that the leaders in
the German school were animated by a philosophical principle
whose influence not only guided their own work, as it did, indeed,
that of the French physiologists, but which was so emphasized
and displayed before the eyes of men that it kindled enthusiasm
and attracted recruits from all lands to the army of investigators
in physiology. The flag under which they marched bore the motto
of mechanism, and its followers were animated by the hope that
physico-chemical and anatomical methods applied to the experimental
study of the properties of living matter would soon bring these mys-
teries under the control of science. So rapidly indeed were results ac-
cumulated in the beginning that the over-sanguine believed the end
nearly in sight, and the hope was entertained by not a few that
we should soon understand the structure of living matter, and per-
haps be able to manufacture it with our own hands. We realize
now that this hope was premature. We know much more than
our predecessors at the beginning of the nineteenth century; the
science has marched onward at a rapid' rate; but what seemed to
be the end of the forest is only a small clearing, an open space,
and in front of us still lies an apparently pathless wilderness. Na-
turally, therefore, the question has arisen as to whether or not we
are following the right route; there has been a more or less gen-
eral revival of the old discussions regarding mechanism and vital-
ism. On the basis of the knowledge and experience obtained by
a century of work, there is a disposition to orient the subject anew
regarding these guiding principles of investigation.

Recent writers have recognized various degrees or kinds of
vitalism, the mechanical and psychical, the natural and transcend-
ental, and the neo-vitalist, as distinguished from the vitalist of the
eighteenth century. Leaving aside ultimate views as to idealism
or materialism which can scarcely be supposed to exert any direct
influence on scientific work, it seems to me that the vitalist in
physiology now is what he has always been, one who believes that
there is a something peculiar, a quid proprium, to use Bernard's
expression, inherent in or indissolubly connected with living matter,
a something that is different from matter and energy as understood
in physics and chemistry, a something, therefore, that does not neces-
sarily manifest itself in accordance with so-called physico-chemical
laws. The name that we may give to this something matters but

1 Tigerstedt, Zur Psychologic der naturwissenschaftlichen Forschung, Helsing-
fors, 1902; Burdon-Sanderson, loc. cit.

PRESENT PROBLEMS OF PHYSIOLOGY 431

little; we may call it soul, animal spirits, vital principle or force,
ether, nervous fluid, inner sense, consciousness or psyche, but plus
c'est change, plus c'est la meme chose. We may differ as to whether
this something is connected with living matter in all its forms or
whether its manifestations are limited to the nervous tissues, but
if we admit its existence as a causal factor in any of the phenomena
of life, then it seems to me that we adopt the standpoint of vitalism,
and the nature of our work as well as our theories will be influenced
thereby. The standpoint of the mechanist is simple. He believes
that all the properties of living matter are of a chemico-physical
nature, that is, properties that are dependent upon the structure
and arrangement of the molecules and the eternal characteristics
of their constituent parts. The C, H, 0, N, S, P, etc., that enter into
its composition carry with them their individual properties, and if
nothing else is present in living matter, the phenomena exhibited
by it must be a resultant of these properties, as the phenomena
exhibited by sodium chloride depend upon the combination of the
properties of the constituent sodium and chlorine. From this stand-
point we may assume that if there is in living matter any recog-
nizable form of energy not hitherto classified, it is intrinsically pre-
sent in dead matter also, and we may hope to discover its existence
by purely physico-chemical methods of investigation, with the
probability, indeed, that it will be recognized first by the chemist or
the physicist with his more exact methods and more favorable
conditions for quantitative analysis. If we are unwilling to adopt
this standpoint, then it seems to me that, unless we deem it wiser
to assume an entirely agnostic attitude, we are logically forced to
take one of two positions. With the older physiologists we may
boldly assume the existence in living organisms of a finer stuff inter-
mingled with the so-called matter, a substance that is not matter
as we understand that term in science, but which, in combination
with matter, gives to living things their distinctive characteristics;
or we may assume the existence in the universe of a reality other
than matter, with the belief that it is influenced by and exerts an
influence upon matter only in the living form, in some such way
as the earlier physicists postulated an ether that can be affected by
matter only when in a certain state of vibration. If I read them
correctly, most modern scientific authorities adopt substantially
this latter point of view. The so-called psychical phenomena of life
are differentiated from the physical, but at the same time it is
admitted that the subjective or psychical manifestations are depend-
ent upon physico-chemical changes in the material substratum.
Huxley states the matter with his usual candor and clearness :
"It seems to me pretty plain that there is a third thing in the uni-
verse, to wit, consciousness, which in the hardness of my head or

432 PHYSIOLOGY

heart, I cannot see to be matter or force or any conceivable modifi-
cation of either." It is perhaps a question of terms only as to whether
this point of view is properly designated as vitalism. Inasmuch,
however, as it assumes a something that can be influenced only by
living matter, possibly only by special forms of living matter, and
in turn can only act upon living matter, it draws a line between
the properties of the animate and the inanimate which represents
a real distinction, and those who hold to this point of view or any
modification of it can scarcely escape, for want of a better term, the
designation of vitalist, even though it is recognized that the reaction
between the subjective and the objective world may be governed
by laws that are, strictly speaking, as mechanical as those reactions
of matter that have been generalized under the laws of physics and
chemistry. In this sense I believe that the majority of physiologists
belong to the school of vitalists. The methods that they employ
and the nomenclature they use are, however, mechanical, because
the science recognizes that its ultimate aim is to understand the
mechanics of living matter, and that in this way only, if at all, shall
we be able to arrive at a conception of the relations of this matter
to a reality of a different order. The older physiologists, and some
of recent times, have used the conception of vitalism as a convenient
and easy means of accounting for many processes which further
investigation has shown to be purely mechanical. Experiences of
this kind tend to strengthen our belief that most of the unknowns
confronting us at present will be analyzed eventually in terms of the
conceptions of physics and chemistry; but there is always present
in physiology the tendency to assume that what is not clearly or
conceivably reducible to the laws of matter and energy must there-
fore belong to the "irreducible residuum." The nature of this
residuum, the connotation of the term vitalism, varies somewhat
with each generation.

Bernard, in his lucid and masterly discussion of the phenomena
of life, came to the conclusion that the irreducible residuum, to which
the laws of chemistry and physics are not and cannot be applicable,
is the power of development of the egg. "Car il est clair que cette
proprie'te' Evolutive de Poeuf, qui produira un mammifere, un oiseau,
ou un poisson, n'est ni de la physique ni de la chimie. ... La
force Evolutive de 1'oeuf et des cellules est done le dernier rempart
du vitalisme." * In our own day the study of the mechanics of devel-
opment is actively pursued by many investigators, and I fancy that
few modern physiologists are inclined to take a truly vitalistic
view of the process. However much the facts of development are
beyond the possibility of explanation in terms of our present
chemico-physical knowledge, it is clearly conceivable that the
1 Bernard, Revue des Deux Mondes, ix, p. 326, 1875.

PRESENT PROBLEMS OF PHYSIOLOGY 433

observed processes may all be due solely to the material structure
of the fertilized ovum acting in accordance with physico-chemical
laws, and that, therefore, our present methods of investigation
may eventually bring these phenomena within the limits of a scien-
tific explanation. The irreducible residuum recognized to-day, and
indeed admitted always by many of the physiologists who are
reckoned among the mechanists, is the psychical reaction, the phe-
nomenon of consciousness. However much we may come to know
of the physico-chemical processes that give rise to this reaction, it
has been asserted by most of the scientific authorities of our time
that the psychical side itself is beyond the possible application of
the methods of physics and chemistry, a conclusion that, as it seems
to me, is tantamount to the admission of the existence of a non-
material reality. The study of consciousness has therefore been
eliminated from the subject of physiology on the ground that the
methods of our science are inapplicable. I fully agree, however, with
the timely and courageous statement of Minot * that "Conscious-
ness ought to be regarded as a biological phenomenon, which the
biologist ought to investigate in order to increase the number of
verifiable data concerning it." If for the present this task is con-
fided to the workers in the independent science of psychology, the
only successful methods that they can employ are those of obser-
vation and experiment, and eventually the latter mode of investi-
gation must become the more important, and the subject must be
recognized as destined to come within the province of experimental
physiology. To Minot the most important work at present is to
be accomplished by an extension of the comparative method to the
psychological study of all forms of life, but to the physiologist it
would seem that a no less promising although technically more
difficult field will be found in neuro-pathology, which holds out
hopes that definite variations in the psychical reaction may be con-
nected with distinct alterations in the structure and properties of
the material substratum. One can scarcely doubt that the combined
labors of the psychologist, biologist, physiologist, and pathologist
will eventually accumulate many verifiable data concerning con-
sciousness. We are not able at present, it is true, to form any con-
ception of the nature of the relation between the subjective and the
objective, but new facts may alter wonderfully our insight into this
mystery, and it is the clear duty of physiology to participate in the
work of accumulating all possible data bearing upon this relation.
The introspective method alone is insufficient, and we have no
alternative but to trust hopefully in the less pretentious method of
scientific observation and experiment. We may believe that in this

1 Minot, Presidential Address, American Association for the Advancement of
Science, Pittsburgh Meeting, Science, xvi, p. 1, 1902.

434 PHYSIOLOGY

way a basis will be obtained upon which philosophy may reason,
more surely and more successfully than is possible now, concerning
the psychical life and its relations to the mechanical phenomena of
the universe.

If I may summarize briefly my point of view regarding the
present problems of physiology, what I have wished to emphasize
is this. The experimental method, physical, chemical, biological, or
anatomical is the life and hope of the subject. Its future depends
solely upon the steadfast recognition of the necessity and possibil-
ities of this means of research. Every investigator who is. anxious
to add to the stock of physiological knowledge should experiment
ceaselessly by those methods which he is most capable of using,
while those who are looking forward to the highest work in physi-
ology should fit themselves by a thorough training in physics or
chemistry, since the most difficult and the most fundamental pro-
blems in the subject require the use of the methods and modes
of thought of these sciences. There must be an outlying division of
workers who will keep the subject in touch with practical medicine,
and other divisions through which communications will be estab-
lished with psychology and the morphological sciences; but the
flower of the army, the imperial guard, will consist of those who
have been disciplined in the methods of physics and chemistry, and
who are able to apply this training to the study of the properties
of living matter.

SHORT PAPER

PROFESSOR E. P. LYON, of St. Louis University, read a contribution before
this Section " On the Theory of Rheotropism in Free Swimming Animals," in
which he discussed the orientation of organisms in streams of water, a phe-
nomenon frequently observed, but having received thus far little attention.

SPECIAL WORKS OF REFERENCE TO ACCOMPANY
PAPER ON ECOLOGY

(Prepared by the courtesy of Professor Oscar Drudt)

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436 BIBLIOGRAPHY: DEPARTMENT OF BIOLOGY

American readers will find more extensive bibliographies in:

COVILLE, F. V., and MxcDouoAL, D. T., Desert Bot. Lab. of the Carnegie Insti-
tution, Publication no. 6, Washington, Nov., 1903 (pp. 46-58).

CLEMENTS, FRED. ED., Research Methods in Ecology, Lincoln, Neb., 1905 (pp.
324-334).

WORKS OF REFERENCE ON THE SECTIONS OF BAC-
TERIOLOGY, ANIMAL MORPHOLOGY, EMBRYOLOGY,
COMPARATIVE ANATOMY, HUMAN ANATOMY, AND
PHYSIOLOGY

(Prepared by the courtesy of Prof essor Henry B. Ward of the University of Nebraska)

BACTERIOLOGY

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BESSON, Technique Microbiologique et Se"rotheropique. Paris, 1897.

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Jones. Oxford, 1900.
HORROCKS, W. H., An Introduction to the Bacteriological Examination of Water.

London, 1901.
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438 BIBLIOGRAPHY: DEPARTMENT OF BIOLOGY

RIDBAL, S., Water and its Purification. London, 1902.

SMITH, E. F., Bacteria in Relation to Plant Diseases. Vol. I. Carnegie Institution,

Washington, D. C., 1905.
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ANIMAL MORPHOLOGY

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EMBRYOLOGY

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London, 1878.
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CHITTENDEN, R. H., Physiological Economy in Nutrition. New York, 1904.
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SPECIAL WORKS OF REFERENCE ON THE SECTION OF

BACTERIOLOGY

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EMBRYOLOGY

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SPECIAL WORKS OF REFERENCE ON SECTION OF
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(Prepared by Courtesy of Professor William E. Ritter)

COPE, E. D., The Primary Factors of Organic Evolution. Open Court Pub. Co.,
Chicago, 1896. Most of the evolutionary views, that concerning the " Law of the
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wechsels. Leipzig, Wilhelm Engelmann, 1875.

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seventeenth, and eighteenth centuries. Cambridge Press, 1901.
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HARVEY, WILLIAM, On the Motion of the Heart and Blood in Animals. Willis's
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stance of this classical work is given by Sir Charles Lyell in the historical part
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446 BIBLIOGRAPHY: DEPARTMENT OF BIOLOGY

WILSON, E. B., The Cell in Development and Inheritance. The Macmillan Com-
pany, 1900. By far the best general presentation in the English tongue of
current views on development. A summary of the author's own important
researches and conclusions, contained originally in numerous special papers,
will be found here.

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Cambridge Natural Science Manuals, University Press, 1898.

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