THE RELATIONS OF PATHOLOGY 117 



manifestations of certain diseases are so much alike that differen- 

 tiation finally was accomplished as the result largely of the study 

 of the more or less characteristic structural changes in the tissues of 

 the body. In some cases differentiation could be made only after 

 the discovery of the specific causative organism. This was the case 

 with diphtheria. The clinical manifestations and the local anatom- 

 ical changes in the throat caused by the bacillus of diphtheria may 

 be reproduced in streptococcal and other infections. Now it is self- 

 evident that real penetration into the nature of a disease demands 

 its complete separation from other, in certian respects more or less 

 similar, diseases. In the case of diphtheria, for instance, complete 

 etiologic differentiation was essential in order that the real value of 

 diphtheria antitoxin might be learned. It may be mentioned, too, 

 that it required the discovery by Koch of the same bacillus in 

 practically all forms of human tuberculosis before the doctrine of 

 the dual nature of this disease, at one time advocated by Virchow 

 on anatomic grounds, received its final overthrow. 



In various local inflammatory diseases such as pleuritis, peri- 

 carditis, peritonitis, meningitis, and in many so-called septic con- 

 ditions, i. e., local infections with general intoxication but with or 

 without bacteremia, the same clinical manifestations and anatom- 

 ical changes may be produced by different organisms. The diseases 

 being different etiologically are consequently also in all likelihood 

 different chemically in spite of their clinical and anatomical sim- 

 ilarities, and for these reasons deeper penetration into their nature 

 as well as progress in direct treatment will depend largely on study 

 of the organisms concerned and of the products of their activities. 

 Clearly an essential step in this direction is the differentiation of the 

 diseases on etiologic grounds. Other examples of analogous nature 

 could easily be cited. 



Now, practically every disease the nature of which we in some 

 degree understand may be cited in illustration of the close synthesis 

 of clinical observation (clinical pathological physiology), patho- 

 logical morphology, etiology, and microbiology, experimental and 

 comparative methods, and especially more recently of chemistry 

 in the development of our knowledge of disease. To the fullest ex- 

 tent this is true of certain infectious diseases. Starting with normal 

 physiology and anatomy, these have become the principal methods 

 by which material is accumulated for that pathological physiology 

 which Virchow put as the chief end of medical investigation. And 

 it is along this road too that the medical student passes to reach 

 membership in the medical profession; for here also "ontogeny 

 repeats phylogeny." Finally these are also the very methods of 

 procedure employed by the true physician in solving the problems 

 r >f diagnosis and so of treatment presented by the individual patient 



