PATHOLOGY IN ITS RELATIONSTO 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 formalopening of this Biological Laboratory and tobe able to extend to this University, and tothis City, congratulations for the possession ofa laboratory so admirably constructed andequipped and inaugurated with the assuranceof an activity so fruitful and well directed. Theexistence in this place of such a laboratory isnot a matter of local pride alone. It maysa ely be predicted that its influence will befelt throughout this country, and indeed where-ever interest in the biological sciences is found.

With such opportunities as here exist, wemay feel assured that this country will increaseand expand the honorable reputation alreadygained by its contributions to biological know-ledge.

Biology in its widest significance is the studyof life in all its forms and activities, bothnormal and abnormal. No branch of humanknowledge can exceed this in interest andimportance; none has made greater advancesduring this century of scientific progress; none

has achieved greater triumph for humanwelfare ; none has influenced more profoundlymodern philosophical thought.

I am here to say a few words concerning onedepartment of biology, namely, pathology,particularly in its relations to general biology.

Pathology is the study of life in its abnormalforms and activities. The relations of pathologyto practical medicine are necessarily so essentialand intimate, that the broader conception ofthis science as a part of biology is in danger ofbeing 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 thatpathology embraces the investigat’on of thecauses of disease, of the anatomical changesproduced by disease in the organs and tissuesof the body, and of the alterations in functionresulting from disease, it is plain that pathologymust constitute the scientific basis of practicalmedicine. This is not the less true becausethe prevention and cure of disease have notkept pace with the advances in our knowledgeof the nature and causes of disease, and ofnecessity can not do so. Preventive and cura-

tive medicine, however, is constantly makingbeneficent application of pathological dis-coveries, and the most intelligent and efficientmanagement of disease is becoming more andmore that which is founded upon the mostaccurate knowledge of its nature and causes.

Inasmuch as the general public naturallyinterests itself but little in any side of medicineother than the treatment of disease, there is notsufficient general appreciation of the immenseprogress in the science and art of medicine ofto-day as contrasted with that of a half centuryago. The history of medicine is in large partthe history of schools of doctrine. Statelysuperstructures of sweeping generalizations andattempted explanations were erected only to beoverthrown because it was impossible to buildupon a firm foundation of facts. To-day it is

our conviction that these fundamental facts canbe discovered in no other way than by obser-vation and experiment. The adoption of this,the only scientific method of investigation, haswith the aid of modern instruments and devicesnot only greatly enriched medical science, butit has overthrown the era in which, amongscientific physicians, exclusive schools ofdoctrine can prevail. The scientific physician,no more than the scientific chemist, can yield

Pathology in its Relations to General Biology.4

the practical benefits resulting from pathologi-cal discoveries, but it is not my intention onthis occasion to dwell upon the applications ofpathology to practical medicine. I have saidenough 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 hisscience must ever hold a foremost place in anyproper scheme of medical education.

This occasion is an appropriate one to

emphasize especially those scientific aspects ofpathology which give it an important positionamong the biological sciences.

In the first place, I claim that pathology as ascience, quite independently of any practical or

useful applications whatever, is as legitimateand worthy an object of pursuit as any of thenatural sciences. In and for itself alone itdeserves to be studied. Its methods are thoseof observation and experiment, as in otherbiological sciences. Its subject matter is anyliving thing which deviates from the normalcondition. 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 thisknowledge may aid in the prevention and reliefof suffering, added dignity and interest are im-parted to the study.

As there comes a line where th*e distinctionbetween the normal and the abnormal isshadowy 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. Mutualaid is to be derived from a closer union betweennormal and pathological biology. The patholo-gist should not be content with methods ofresearch less perfect than those employed innormal biology. He should not rest satisfiedwith results which stop at the mere descriptionand classification of morbid processes. To beable to give a name to some pathological lesion,and to make it fit into some accepted schemeof classification, should not be the sole aim ofpathological study. Pathological processesshould be studied with the aim of elucidatingtheir real nature, development and causes, theirmutual relations and their dependence uponunderlying laws. The purely descriptive phase

adherence to any exclusive dogma. To theone as to the other no way which leads to truihis debarred.

By way of illustration of the achievements ofmodern pathology, permit me to contrast for amoment with the imperfect, meagre, and con-

fusing information of former times, the fulnessof our present knowledge concerning that dis-ease, which of all diseases is the greatestscourge of the human race. Tuberculosiscauses the death of not less than one-seventh,and, in some form or other and at some period,affects probably one-third of mankind. Buta few years ago, not only was the specific causeof tuberculosis unknown, but there was no

general appreciation of the fundamental factthat this is one of the infectious diseases. Theknowledge of the frequency and wide distri-bution of tuberculous disease in other parts ofthe body than in the lungs is an acquisition ofmodern pathology. The pathological anatomyof tuberculosis, which not long ago was one ofthe most confusing chapters in pathology, hasbeen made clear. The unity of all the pro-cesses now known to be tuberculous can beestablished on an anatomical as well as on an

etiological basis. 'The greatest addition to ourknowledge of tuberculosis, and in fact one ofthe greatest achievements of modern science, isthe discovery of the specific living germwhich causes tuberculosis. We are now en-abled to study both within and without thebody, the form and the properties of this germ,the conditions which are favorable and thosewhi h are hostile to its preservation and de-velopment. Who can doubt that all this in-creased knowledge of the most devastating ofmaladies is destined to help in prevention andtreatment ? Sanitarians convinced of the pre-ventability of tuberculosis have already begunthe warfare against its spread.

If one seeks an illustration of immediatepractical results of the modern investigations ofthe living germs which cause disease, let himturn his attent on to the revolution therebywrought in surgical procedures. The possibilitywhich 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 theintroduction of vaccination.

It would be pleasant to follow still further

Pathology in its Relations to General Biology. 5

As has already been mentioned, pathologyhas to do with abnormalities, not in man alone,but in all living things, both animal and vege-table. The points of contact between animaland vegetable pathology are more numerousthan might at first glance appear. The studentof animal pathology can draw many instructivelessons from such subjects as the behavior ofwounds and the parasitic affections in plants.We are most of us probably inclined to thinktoo much of the separation between the patho-logy of man and that of the lower animals.While there is a wide distinction in the dignityof the object of study, yet from a scientificpoint of view this separation is of little account.Pathological investigations of diseases ofanimals constitute no less genuine and valuablecontributions to pathology in general, than dosimilar investigations of human diseases. 1 headvancement of recent years in the educationand aims of those who devote themselves to

animal pathology, will serve to bring into closerrelations the students of human and those ofcomparative medicine.

It may be useful for us to consider brieflysome of the relations and points of contactbetween human and comparative pathology.

In the first place there are many diseaseswhich are common to man and to animals.These can often be studied to greater advantageupon animals in which many conditions can becontrolled, which are beyond our control inman. In animals every stage of developmentof the disease can be studied, and in general,fresher material can be obtained. We canmodify in various ways external and internalconditions 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 singlespecies affords most incomplete knowledge.For instance, the pathologist whose sole know-ledge of such a disease as tuberculosis is derived from the study of the disease as it occursin man, has a far less complete understandingof this affection, than one who is also familiarwith the striking peculiarities of this affectionin cattle, swine, fowls, and other animals.

Especial importance attaches, of course, to

the study of such diseases as are communicable

of development of any natural science can beonly temporary and unsatisfactory. The morea pathologist is imbued with the spirit ofmodern biology, the less content will he be tostop at this descriptive phase.

In the next place, it can be justly claimedthat the study of pathology as a science withoutimmediate reference to practical results is, inreality, the method which is most likely to yieldthese results as well as to bear fruit in otherdirections. Experience has shown that the mostimportant discoveries in science come, not fromthose who make utility their guiding principle,but from the investigators of truth for its ownsake, wherever and however they can attain it.It is short sighted to fail to see that the surestway to advance pathology, even in its relationsto practical medicine, is to cultivate it as ascience from all points of view. It is impossibleto foresee what may be the practical applicationto-morrow of any pathological fact discoveredin the laboratory, no matter how remote frompractical bearing it may seem to-day.

The experiments upon animals and otherinvestigations which have led to the pre entaccuracy in the localized diagnosis of lesions ofthe central nervous system, and have renderedpossible the surgical treatment of many of theselesions we owe in large part to physiologistsand pathologists who had little thought of thepractical applications of the results of theirresearches. The instrument and methods whichhave enabled ophthalmology to attain suchperfection in diagnosis and treatment rest uponresearches in physiological optics belonging tothe domain of pure science. It could not havebeen anticipated by those who began the studyof the microscopic organisms which cause fer-mentations and infectious diseases, that theirstudy would lead to a revolution in surgicaltreatment, and would open prospects which itwould now be hazardous to specify as to theprevention and cure of infectious diseases.Did time permit, and were it necessary, muchmore evidence of similar character could bebrought forward to show that those who workin laboratories, it may be without a thought asto the practical utility of their investigations,are no less genuine contributors to the scienceand art of medicine, than those who studydiseases by the bedside.

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 diseaseswhich have received the most attention fromthe students of human pathology.

One of the most important departments ofcomparative pathology is experimental path-ology, die value of which to human pathologyhas long been recognized. To make of experi-mental pathology a distinct specialty, and toendow it with a separate professorship as isdone in some foreign universities, does notseem to me to be in the direction of the mostfruitful and healthy development. 'The experi-mental method is the handmaid of pathology inall its branches, and is the only means of solv-ing many important problems. The experi-mental production of diseases in the loweranimals affords an insight to be gained in noother way as to the causes, development, lesionsand functional manifestations of many diseases.Experience, however, has shown that graveerrors are likely to be committed by experi-mental pathologists who have no knowledge ofthe natural diseases and conditions of theanimals used for experimentation. How often,for example, have those studying the questionof experimental tuberculosis mistaken forgenuine tubercles nodules produced by parasiticentozoa, jand to what misleading conclusionshave such incorrect observations led.

There are as many general pathologicalprocesses which can be studied to better ad-vantage in animals than in man. Such subjectsas inflammation, oedema, thrombosis, embolism,and infection have been elucidated in large partby observations made on animals. Due cautionis of course to be exercised in applying suchobservations directly to human beings.

Inasmuch as it is rarely possible for us toproduce artificially all of the conditions whichcause natural diseases, and as our very methodof experimentation is in itself often a perturbat-ing factor, it is no less important to studyanimal diseases resulting from natural causes,than it is to study the same diseases experi-mentally produced. Of course there are manydiseases which have not yet been opened tothe experimental method of investigation.

Questions of etiology and of pathogenesisare among those which have received and are

destined still further to receive the greatestillumination from studies of comparativepathology. At present, probably no subjectengages the attention of pathologists to agreater degree than the microscopic organismswhich cause infection. If we had been con-fined to human beings in the study of infectiousdiseases, our knowledge in this direction wouldhave been only a small fraction of what it isat present. In no single instance could thecomplete chain of proof required to demonstratethe 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 ofpathological study, at present only partly culti-vated, is found in the infectious diseases ofanimals and of plants, not only on account ofthe great economic interests often involved, butalso as a means of widening and deepening ourconceptions as to the causes, development,prevention and treatment of infectious diseasesin general. Any pathologist who is at allfamiliar with the remarkable and peculiar con-ditions under which the so-called Texas CattleFever of the United States develops andspreads, will realize that the complete elucida-tion of all the etiological factors of this diseasenot only would contribute to the solution of agreat economic question, but also would openfresh points of view in our conceptionsof infectious agents and their properties. Whenwe consider the many conditions which it is inour power to control in studying animaldiseases, and above all the possibility of sub-mitting to an experimental crucial test ourconclusions, it is clear that the study of naturaland artificial infections, as well as of many otherdiseases in animals, is calculated to advance inthe highest degree the science of pathology.It is not a small thing that questions whichwere onceconsidered to be wholly transcendental,as for instance the doctrine of immunity againstinfectious diseases,have been brought within theworking domain of experimental pathology.

Nor is it in the causation ofinfectious diseasesalone that the comparative study of humanand of animal diseases is destined to advanceetiology. It is reasonable to expect that thiscomparative study will help to clear up many

Pathology in its Relations to General Biology. 7

factors, at present obscure, in the causation ofhuman diseases, including the influence ofsocial conditions.

But let us take a broader view of comparativepathology than that which considers abnor-malities only in man and in animals related toman in structure and function. I believe thatmany problems and facts in human pathologyawait for their complete elucidation the sameapplication of the comparative method of studywhich has made of normal anatomy virtually anew science. What a barren mass of ap-parently unrelated facts is human anatomywhen studied without reference to comparativeanatomy and embryology ! If knowledge is theunderstanding of the real nature of a thing, andhow it came to be as it is, then there is noknowledge of human anatomy without the aidof comparative anatomy and embryology. Howdifficult and unmeaning is the old method ofstudying the anatomy of the human brain andhow fascinating does the anatomy of this organappear in the light of development!

A light similiar in kind, if not equal in inten-sity, will be shed upon human pathology bya fuller insight into comparative pathology.We possess at present scarcely the rudiments ofa comparative general pathology, but how use-ful and significant is even our fragmentaryknowledge of this subject. The charm andimpressiveness with which Metschnikoff hasdeveloped and presented the phagocyticdoctrine is due largely to illustrations drawnfrom comparative pathology. It is impressiveto see pictured in living forms, from the lowestup to the highest, the combat with invadingmicro-organisms of infection. While the phago-cytic doctrine can not be accepted in itsentirety, it is interesting to observe that itreceived its origin and its chief support fromobservations made upon the lower forms oflife, rather than from those on man and thehigher animals.

The interesting and important discoveriesconcerning the curious parasitic organismsassociated with malaria may seem to the studentof human pathology anomalous and withoutanalogy, but in Prof. Wright’s admirable ad-dress to-day upon the sporozoa, we have hadpresented to us not only the life history of theclass of organisms to which the malarial

parasites probably belong, but also many ex-amples of similiar parasitic affections of loweranimals. We may expect still further infor-mation concerning this interesting group ofinfectious micro-organisms from researches incomparative pathology.

Take, for instance, one of the most disputedand still unsettled problems in pathology, theconditions which cause multiplication of thefixed cells of the body, a question which isintimately associated with the still broader oneof the response of cells to the action of externalstimuli. Can it be doubted that if we wereacquainted with the behavior of cells in alltypes of living things, from the unicellularorganism upward, under the influence of suchstimuli as cause inflammation in human beings,under the influence of losses of substance andunder various other conditions, we should havea much clearer comprehension of one of thefundamental and most common pathologicalprocesses in man ?

The interesting studies of heredity by Weiss-man and others pertain in part to pathology,and also illustrate brilliantly the value of thecomparative method of research.

The application of embryology to the ex-planation of congenital malformations is familiarand has long been an acquisition of humanpathology. More recent is the endeavor torefer the origin of the genuine tumors toanomalies in foetal development. It is probablethat experimental and comparative pathologyalso will shed much light upon the still obscurequestion as to the origin of tumors.

A large mass of observed pathological factswe must now accept without adequate explana-tion. It is often the fundamental and commonmorbid processes which are most obscure.For many of these we may hope to find satis-factory explanation in the results which thecomparative study of pathology will afford.At present nothing is to be gained by attempt-ing to generalize from scanty and incompleteobservations in comparative pathology. Wemust first accumulate a store-house of facts.We need investigators who shall study patho-logical conditions, not in man alone, or in thehigher animals alone, but also in the simplerforms of plant and animal life. Something hasbeen done in this direction, more indeed than

Pathology in its Relations to General Biology.

is generally utilized in human pathology, butmuch more remains to be done. Conditionsand processes which are difficult to comprehendin animals ofcomplex organization often becomeclear in organisms of simple structure. Ourpathological concepts are now derived almostwholly from observations made upon highlycomplex forms of life. I believe it to be no

illusion to anticipate in thought a time whenall forms and kinds of living matter will be in-cluded in the domain of pathology, and whenpathological laws will be derived from results ofinvestigations which begin with unicellularorganisms and which end with man. By theadoption of this comparative method of study,pathology will in reality acquire greater sim-plicity and deeper significance than it nowpossesses.

As the student of normal biology does notattempt to cultivate equally the whole fieldbelonging to his subject, so the pathologist can-

not be expected to cover in his investigationsthe whole domain of pathology as thus broadlyoutlined. There will be special workers invarious departments. As in normal biology, soin pathological biology from the combinedlabors of all there will be constructed a sciencebroader, richer and fuller of meaning than thatwhich we now possess. The ideas which Ihave 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 thisbiological laboratory. Permit me, in conclusion,to say that it is in a medical school in intimateand organic connection with a university wheresuch laboratories exist that the highest cultivation of pathology as a science is to beexpected. Here is the favorable atmosphere,here the stimulus of allied sciences, and herethe most enlightened appreciation and en-couragement.