PATHOLOGY IN ITS RELATIONS 
TO GENERAL BIOLOGY 
—by— 
WILLIAM H. WELCH, M.D., 
Professor of Pathology, Johns Hopkins University, Baltimore. 
An Address delivered at the opening of the New Building of the Biological Department, University of loronto, 
December 19th, 1889. 
TORONTO: 
THE J. E. BRYANT COMPANY (Omxid/) 
logo. REPRINTED FROM 
“THE CANADIAN PRACTITIONER,” 
January i6th, 1890. PATHOLOGY IN ITS RELATIONS TO 
. . GENERAL BIOLOGY . . 
I esteem it a privilege to assist at the formal 
opening of this Biological Laboratory and to 
be able to extend to this University, and to 
this City, congratulations for the possession of 
a laboratory so admirably constructed and 
equipped and inaugurated with the assurance 
of an activity so fruitful and well directed. The 
existence in this place of such a laboratory is 
not a matter of local pride alone. It may 
sa ely be predicted that its influence will be 
felt throughout this country, and indeed where- 
ever interest in the biological sciences is found. 
With such opportunities as here exist, we 
may feel assured that this country will increase 
and expand the honorable reputation already 
gained by its contributions to biological know- 
ledge. 
Biology in its widest significance is the study 
of life in all its forms and activities, both 
normal and abnormal. No branch of human 
knowledge can exceed this in interest and 
importance; none has made greater advances 
during this century of scientific progress; none 
has achieved greater triumph for human 
welfare ; none has influenced more profoundly 
modern philosophical thought. 
I am here to say a few words concerning one 
department of biology, namely, pathology, 
particularly in its relations to general biology. 
Pathology is the study of life in its abnormal 
forms and activities. The relations of pathology 
to practical medicine are necessarily so essential 
and intimate, that the broader conception of 
this science as a part of biology is in danger of 
being lost from view. I deem it, however, im- 
portant for the scientific status and advance- 
ment of pathology to keep in mind and to 
emphasize its relations to general biology, not 
less than those to practical medicine. 
In so doing, it is not intended to detract in 
any degree from the practical value of pathology 
and its applications to the diagnosis and treat- 
ment of disease. When we consider that 
pathology embraces the investigat’on of the 
causes of disease, of the anatomical changes 
produced by disease in the organs and tissues 
of the body, and of the alterations in function 
resulting from disease, it is plain that pathology 
must constitute the scientific basis of practical 
medicine. This is not the less true because 
the prevention and cure of disease have not 
kept pace with the advances in our knowledge 
of the nature and causes of disease, and of 
necessity can not do so. Preventive and cura- 
tive medicine, however, is constantly making 
beneficent application of pathological dis- 
coveries, and the most intelligent and efficient 
management of disease is becoming more and 
more that which is founded upon the most 
accurate knowledge of its nature and causes. 
Inasmuch as the general public naturally 
interests itself but little in any side of medicine 
other than the treatment of disease, there is not 
sufficient general appreciation of the immense 
progress in the science and art of medicine of 
to-day as contrasted with that of a half century 
ago. The history of medicine is in large part 
the history of schools of doctrine. Stately 
superstructures of sweeping generalizations and 
attempted explanations were erected only to be 
overthrown because it was impossible to build 
upon a firm foundation of facts. To-day it is 
our conviction that these fundamental facts can 
be discovered in no other way than by obser- 
vation and experiment. The adoption of this, 
the only scientific method of investigation, has 
with the aid of modern instruments and devices 
not only greatly enriched medical science, but 
it has overthrown the era in which, among 
scientific physicians, exclusive schools of 
doctrine can prevail. The scientific physician, 
no more than the scientific chemist, can yield Pathology in its Relations to General Biology. 
4 
adherence to any exclusive dogma. To the 
one as to the other no way which leads to truih 
is debarred. 
By way of illustration of the achievements of 
modern pathology, permit me to contrast for a 
moment with the imperfect, meagre, and con- 
fusing information of former times, the fulness 
of our present knowledge concerning that dis- 
ease, which of all diseases is the greatest 
scourge of the human race. Tuberculosis 
causes the death of not less than one-seventh, 
and, in some form or other and at some period, 
affects probably one-third of mankind. But 
a few years ago, not only was the specific cause 
of tuberculosis unknown, but there was no 
general appreciation of the fundamental fact 
that this is one of the infectious diseases. The 
knowledge of the frequency and wide distri- 
bution of tuberculous disease in other parts of 
the body than in the lungs is an acquisition of 
modern pathology. The pathological anatomy 
of tuberculosis, which not long ago was one of 
the most confusing chapters in pathology, has 
been made clear. The unity of all the pro- 
cesses now known to be tuberculous can be 
established on an anatomical as well as on an 
etiological basis. 'The greatest addition to our 
knowledge of tuberculosis, and in fact one of 
the greatest achievements of modern science, is 
the discovery of the specific living germ 
which causes tuberculosis. We are now en- 
abled to study both within and without the 
body, the form and the properties of this germ, 
the conditions which are favorable and those 
whi h are hostile to its preservation and de- 
velopment. Who can doubt that all this in- 
creased knowledge of the most devastating of 
maladies is destined to help in prevention and 
treatment ? Sanitarians convinced of the pre- 
ventability of tuberculosis have already begun 
the warfare against its spread. 
If one seeks an illustration of immediate 
practical results of the modern investigations of 
the living germs which cause disease, let him 
turn his attent on to the revolution thereby 
wrought in surgical procedures. The possibility 
which is now in the hands of the surgeon jf 
keeping wounds free from all external in- 
fection, is a boon to humanity not less than the 
introduction of vaccination. 
It would be pleasant to follow still further 
the practical benefits resulting from pathologi- 
cal discoveries, but it is not my intention on 
this occasion to dwell upon the applications of 
pathology to practical medicine. I have said 
enough to remove any misapprehension as to 
my belief that pathology should be made to 
serve the ultimate aim of medical education, 
the prevention and cure of disease. 1 his 
science must ever hold a foremost place in any 
proper scheme of medical education. 
This occasion is an appropriate one to 
emphasize especially those scientific aspects of 
pathology which give it an important position 
among the biological sciences. 
In the first place, I claim that pathology as a 
science, quite independently of any practical or 
useful applications whatever, is as legitimate 
and worthy an object of pursuit as any of the 
natural sciences. In and for itself alone it 
deserves to be studied. Its methods are those 
of observation and experiment, as in other 
biological sciences. Its subject matter is any 
living thing which deviates from the normal 
condition. It is not less interesting and im- 
portant to learn the nature and causes of ab- 
normalities in form and function than it is to 
become familiar with the normal, and when this 
knowledge may aid in the prevention and relief 
of suffering, added dignity and interest are im- 
parted to the study. 
As there comes a line where th*e distinction 
between the normal and the abnormal is 
shadowy and uncertain, so the separation be- 
tween normal and pathological biology is not 
sharp. The province of the one encroaches at 
many points upon that of the other. Mutual 
aid is to be derived from a closer union between 
normal and pathological biology. The patholo- 
gist should not be content with methods of 
research less perfect than those employed in 
normal biology. He should not rest satisfied 
with results which stop at the mere description 
and classification of morbid processes. To be 
able to give a name to some pathological lesion, 
and to make it fit into some accepted scheme 
of classification, should not be the sole aim of 
pathological study. Pathological processes 
should be studied with the aim of elucidating 
their real nature, development and causes, their 
mutual relations and their dependence upon 
underlying laws. The purely descriptive phase Pathology in its Relations to General Biology. 
5 
of development of any natural science can be 
only temporary and unsatisfactory. The more 
a pathologist is imbued with the spirit of 
modern biology, the less content will he be to 
stop at this descriptive phase. 
In the next place, it can be justly claimed 
that the study of pathology as a science without 
immediate reference to practical results is, in 
reality, the method which is most likely to yield 
these results as well as to bear fruit in other 
directions. Experience has shown that the most 
important discoveries in science come, not from 
those who make utility their guiding principle, 
but from the investigators of truth for its own 
sake, wherever and however they can attain it. 
It is short sighted to fail to see that the surest 
way to advance pathology, even in its relations 
to practical medicine, is to cultivate it as a 
science from all points of view. It is impossible 
to foresee what may be the practical application 
to-morrow of any pathological fact discovered 
in the laboratory, no matter how remote from 
practical bearing it may seem to-day. 
The experiments upon animals and other 
investigations which have led to the pre ent 
accuracy in the localized diagnosis of lesions of 
the central nervous system, and have rendered 
possible the surgical treatment of many of these 
lesions we owe in large part to physiologists 
and pathologists who had little thought of the 
practical applications of the results of their 
researches. The instrument and methods which 
have enabled ophthalmology to attain such 
perfection in diagnosis and treatment rest upon 
researches in physiological optics belonging to 
the domain of pure science. It could not have 
been anticipated by those who began the study 
of the microscopic organisms which cause fer- 
mentations and infectious diseases, that their 
study would lead to a revolution in surgical 
treatment, and would open prospects which it 
would now be hazardous to specify as to the 
prevention and cure of infectious diseases. 
Did time permit, and were it necessary, much 
more evidence of similar character could be 
brought forward to show that those who work 
in laboratories, it may be without a thought as 
to the practical utility of their investigations, 
are no less genuine contributors to the science 
and art of medicine, than those who study 
diseases by the bedside. 
As has already been mentioned, pathology 
has to do with abnormalities, not in man alone, 
but in all living things, both animal and vege- 
table. The points of contact between animal 
and vegetable pathology are more numerous 
than might at first glance appear. The student 
of animal pathology can draw many instructive 
lessons from such subjects as the behavior of 
wounds and the parasitic affections in plants. 
We are most of us probably inclined to think 
too much of the separation between the patho- 
logy of man and that of the lower animals. 
While there is a wide distinction in the dignity 
of the object of study, yet from a scientific 
point of view this separation is of little account. 
Pathological investigations of diseases of 
animals constitute no less genuine and valuable 
contributions to pathology in general, than do 
similar investigations of human diseases. 1 he 
advancement of recent years in the education 
and aims of those who devote themselves to 
animal pathology, will serve to bring into closer 
relations the students of human and those of 
comparative medicine. 
It may be useful for us to consider briefly 
some of the relations and points of contact 
between human and comparative pathology. 
In the first place there are many diseases 
which are common to man and to animals. 
These can often be studied to greater advantage 
upon animals in which many conditions can be 
controlled, which are beyond our control in 
man. In animals every stage of development 
of the disease can be studied, and in general, 
fresher material can be obtained. We can 
modify in various ways external and internal 
conditions so as to reach a clearer comprehen- 
sion of the morbid processes. Moreover, the 
same disease may present interesting patholo- 
gical peculiarities in different species of animals, 
so that the study of its occurrence in a single 
species affords most incomplete knowledge. 
For instance, the pathologist whose sole know- 
ledge of such a disease as tuberculosis is de 
rived from the study of the disease as it occurs 
in man, has a far less complete understanding 
of this affection, than one who is also familiar 
with the striking peculiarities of this affection 
in cattle, swine, fowls, and other animals. 
Especial importance attaches, of course, to 
the study of such diseases as are communicable 6 
Pathology in its Relations to General Biology. 
from animals to man, as for instance, anthrax, 
glanders, tuberculosis, many entozoic affections, 
etc., and in general these are the animal diseases 
which have received the most attention from 
the students of human pathology. 
One of the most important departments of 
comparative pathology is experimental path- 
ology, die value of which to human pathology 
has long been recognized. To make of experi- 
mental pathology a distinct specialty, and to 
endow it with a separate professorship as is 
done in some foreign universities, does not 
seem to me to be in the direction of the most 
fruitful and healthy development. 'The experi- 
mental method is the handmaid of pathology in 
all its branches, and is the only means of solv- 
ing many important problems. The experi- 
mental production of diseases in the lower 
animals affords an insight to be gained in no 
other way as to the causes, development, lesions 
and functional manifestations of many diseases. 
Experience, however, has shown that grave 
errors are likely to be committed by experi- 
mental pathologists who have no knowledge of 
the natural diseases and conditions of the 
animals used for experimentation. How often, 
for example, have those studying the question 
of experimental tuberculosis mistaken for 
genuine tubercles nodules produced by parasitic 
entozoa, jand to what misleading conclusions 
have such incorrect observations led. 
There are as many general pathological 
processes which can be studied to better ad- 
vantage in animals than in man. Such subjects 
as inflammation, oedema, thrombosis, embolism, 
and infection have been elucidated in large part 
by observations made on animals. Due caution 
is of course to be exercised in applying such 
observations directly to human beings. 
Inasmuch as it is rarely possible for us to 
produce artificially all of the conditions which 
cause natural diseases, and as our very method 
of experimentation is in itself often a perturbat- 
ing factor, it is no less important to study 
animal diseases resulting from natural causes, 
than it is to study the same diseases experi- 
mentally produced. Of course there are many 
diseases which have not yet been opened to 
the experimental method of investigation. 
Questions of etiology and of pathogenesis 
are among those which have received and are 
destined still further to receive the greatest 
illumination from studies of comparative 
pathology. At present, probably no subject 
engages the attention of pathologists to a 
greater degree than the microscopic organisms 
which cause infection. If we had been con- 
fined to human beings in the study of infectious 
diseases, our knowledge in this direction would 
have been only a small fraction of what it is 
at present. In no single instance could the 
complete chain of proof required to demonstrate 
the causation of an infectious disease by a 
specific micro-organism have been furnished. 
The far-reaching principle of preventive vac- 
cination or inoculation would not be k! own. 
A most important and promising field of 
pathological study, at present only partly culti- 
vated, is found in the infectious diseases of 
animals and of plants, not only on account of 
the great economic interests often involved, but 
also as a means of widening and deepening our 
conceptions as to the causes, development, 
prevention and treatment of infectious diseases 
in general. Any pathologist who is at all 
familiar with the remarkable and peculiar con- 
ditions under which the so-called Texas Cattle 
Fever of the United States develops and 
spreads, will realize that the complete elucida- 
tion of all the etiological factors of this disease 
not only would contribute to the solution of a 
great economic question, but also would open 
fresh points of view in our conceptions 
of infectious agents and their properties. When 
we consider the many conditions which it is in 
our power to control in studying animal 
diseases, and above all the possibility of sub- 
mitting to an experimental crucial test our 
conclusions, it is clear that the study of natural 
and artificial infections, as well as of many other 
diseases in animals, is calculated to advance in 
the highest degree the science of pathology. 
It is not a small thing that questions which 
were onceconsidered to be wholly transcendental, 
as for instance the doctrine of immunity against 
infectious diseases,have been brought within the 
working domain of experimental pathology. 
Nor is it in the causation ofinfectious diseases 
alone that the comparative study of human 
and of animal diseases is destined to advance 
etiology. It is reasonable to expect that this 
comparative study will help to clear up many Pathology in its Relations to General Biology. 
7 
factors, at present obscure, in the causation of 
human diseases, including the influence of 
social conditions. 
But let us take a broader view of comparative 
pathology than that which considers abnor- 
malities only in man and in animals related to 
man in structure and function. I believe that 
many problems and facts in human pathology 
await for their complete elucidation the same 
application of the comparative method of study 
which has made of normal anatomy virtually a 
new science. What a barren mass of ap- 
parently unrelated facts is human anatomy 
when studied without reference to comparative 
anatomy and embryology ! If knowledge is the 
understanding of the real nature of a thing, and 
how it came to be as it is, then there is no 
knowledge of human anatomy without the aid 
of comparative anatomy and embryology. How 
difficult and unmeaning is the old method of 
studying the anatomy of the human brain and 
how fascinating does the anatomy of this organ 
appear in the light of development! 
A light similiar in kind, if not equal in inten- 
sity, will be shed upon human pathology by 
a fuller insight into comparative pathology. 
We possess at present scarcely the rudiments of 
a comparative general pathology, but how use- 
ful and significant is even our fragmentary 
knowledge of this subject. The charm and 
impressiveness with which Metschnikoff has 
developed and presented the phagocytic 
doctrine is due largely to illustrations drawn 
from comparative pathology. It is impressive 
to see pictured in living forms, from the lowest 
up to the highest, the combat with invading 
micro-organisms of infection. While the phago- 
cytic doctrine can not be accepted in its 
entirety, it is interesting to observe that it 
received its origin and its chief support from 
observations made upon the lower forms of 
life, rather than from those on man and the 
higher animals. 
The interesting and important discoveries 
concerning the curious parasitic organisms 
associated with malaria may seem to the student 
of human pathology anomalous and without 
analogy, but in Prof. Wright’s admirable ad- 
dress to-day upon the sporozoa, we have had 
presented to us not only the life history of the 
class of organisms to which the malarial 
parasites probably belong, but also many ex- 
amples of similiar parasitic affections of lower 
animals. We may expect still further infor- 
mation concerning this interesting group of 
infectious micro-organisms from researches in 
comparative pathology. 
Take, for instance, one of the most disputed 
and still unsettled problems in pathology, the 
conditions which cause multiplication of the 
fixed cells of the body, a question which is 
intimately associated with the still broader one 
of the response of cells to the action of external 
stimuli. Can it be doubted that if we were 
acquainted with the behavior of cells in all 
types of living things, from the unicellular 
organism upward, under the influence of such 
stimuli as cause inflammation in human beings, 
under the influence of losses of substance and 
under various other conditions, we should have 
a much clearer comprehension of one of the 
fundamental and most common pathological 
processes in man ? 
The interesting studies of heredity by Weiss- 
man and others pertain in part to pathology, 
and also illustrate brilliantly the value of the 
comparative method of research. 
The application of embryology to the ex- 
planation of congenital malformations is familiar 
and has long been an acquisition of human 
pathology. More recent is the endeavor to 
refer the origin of the genuine tumors to 
anomalies in foetal development. It is probable 
that experimental and comparative pathology 
also will shed much light upon the still obscure 
question as to the origin of tumors. 
A large mass of observed pathological facts 
we must now accept without adequate explana- 
tion. It is often the fundamental and common 
morbid processes which are most obscure. 
For many of these we may hope to find satis- 
factory explanation in the results which the 
comparative study of pathology will afford. 
At present nothing is to be gained by attempt- 
ing to generalize from scanty and incomplete 
observations in comparative pathology. We 
must first accumulate a store-house of facts. 
We need investigators who shall study patho- 
logical conditions, not in man alone, or in the 
higher animals alone, but also in the simpler 
forms of plant and animal life. Something has 
been done in this direction, more indeed than Pathology in its Relations to General Biology. 
is generally utilized in human pathology, but 
much more remains to be done. Conditions 
and processes which are difficult to comprehend 
in animals ofcomplex organization often become 
clear in organisms of simple structure. Our 
pathological concepts are now derived almost 
wholly from observations made upon highly 
complex forms of life. I believe it to be no 
illusion to anticipate in thought a time when 
all forms and kinds of living matter will be in- 
cluded in the domain of pathology, and when 
pathological laws will be derived from results of 
investigations which begin with unicellular 
organisms and which end with man. By the 
adoption of this comparative method of study, 
pathology will in reality acquire greater sim- 
plicity and deeper significance than it now 
possesses. 
As the student of normal biology does not 
attempt to cultivate equally the whole field 
belonging to his subject, so the pathologist can- 
not be expected to cover in his investigations 
the whole domain of pathology as thus broadly 
outlined. There will be special workers in 
various departments. As in normal biology, so 
in pathological biology from the combined 
labors of all there will be constructed a science 
broader, richer and fuller of meaning than that 
which we now possess. The ideas which I 
have endeavored to present, although neces- 
sarily in a brief and cursory manner, concern- 
ing pathology in its relations to general biology, 
are naturally suggested by the opening of this 
biological laboratory. Permit me, in conclusion, 
to say that it is in a medical school in intimate 
and organic connection with a university where 
such laboratories exist that the highest culti 
vation of pathology as a science is to be 
expected. Here is the favorable atmosphere, 
here the stimulus of allied sciences, and here 
the most enlightened appreciation and en- 
couragement.