126 PATHOLOGY 



branches of pathology * is not sufficiently known among the laity, 

 and attempts through governmental interference to lay difficulties 

 in the way of experimental investigation (vivisection as it is called 

 by the laity, scientific animal torture according to its opponents), 

 are constantly being made, not seeing that misuse of it, even 

 if it should occur, is considerably outweighed by its undeniable 

 value. Pathologic anatomy, bacteriology, pathologic chemistry, 

 and above all, pathologic physiology, cannot fulfill their scientific 

 value without animal experiment. A large part of the progress 

 in pathology is bound up with experimental research. Every ad- 

 vance in pathology has sooner or later been of use to man. Could 

 our progress in the pathology of the infectious diseases, and our 

 progress in the prevention and treatment of them, have been made 

 without experimental pathology? The explanation of the origin 

 of tumors must also finally arrive by experimental investigations, 

 and just there it will be of especial value to be able to carry on the 

 experiments on the same kind of animal in which the tumor natur- 

 ally occurs. If we should succeed in finding a specific, probably 

 parasitic cause, the possibility of demonstrating the pathogenicity 

 of this disease-producer on animals of the same sort is incalculable. 

 But such experiments presuppose exact knowledge of the pathology 

 of the animals experimented upon, that is, comparative pathology, 

 and many discussions of the present day have turned on the point 

 whether changes which were found after the experiment were 

 results of the experiment or chance pathologic findings to which 

 the experiment had no genetic relation. If one does not know 

 what kind of tumors occur in the organs of the animal which he is 

 using for experimental purposes, he will easily fall into the danger 

 of considering new formations as the result of the microorganisms 

 injected by him and will report having produced a tumor when 

 merely a spontaneous new growth existed. 



So far I have considered animals only as passive objects of ex- 

 perimental pathology. I have spoken of animals and plants merely 

 as the most important subjects for comparative pathology. There 

 are, however, much closer relations between pathology and botany 

 and zoology. Both these sciences have had increasing importance 

 for pathology, as surer proof was brought that the most important 

 causes of disease belong to the plant and animal kingdoms. 



Investigation of the causes of disease, of the different conditions 

 which form the basis of deviations from normal types, belongs as 

 much in the realm of pathology as the study of these deviations 

 and their development itself. The etiology and pathogenesis are 

 a part of pathology, and it is especially through them that patho- 



1 R. Virchow, Ueber den Werth des pathologischen Experiments, Internat. Med. 

 Congress, London, 1887, Berlin, 1899. 



