THE STERILITY OF THE IDEAS UPON CONTAGION 231 



Without doubt it must be admitted that certain skin 

 diseases like favus, herpes tonsurans, thrush, and itch 

 could be produced by animals or vegetables. But of 

 what importance were these maladies when placed by 

 the side of the infectious diseases in which one found 

 nothing comparable? Now cellular pathology explained 

 the latter by the famous principles of heterotopy and 

 heterochronia. Every pathological modification was for 

 it only a physiological transformation displaced in time 

 or place, developing itself in an organ which could not 

 endure it, or at a time when it was abnormal. The 

 secret of the disease was, therefore, in the anatomy of 

 the tissues, which, under this powerful impulse, multi- 

 plied its discoveries and took in all, from tumors to 

 viruses, from exostoses to exanthemata, and to the pus- 

 tules of smallpox or of vaccine. 



The idea that there could be in the tissues organisms 

 come from the exterior which, by penetrating and de- 

 veloping there, impressed upon them specific modifi- 

 cations, was in disagreement with the general current 

 of anatomical ideas; and yet more with physiological 

 views. At this moment in fact, a pleiad of illustrious 

 scientific men, Helmholtz, Du Bois Reymond, Ludwig 

 and Briicke, began to oppose the ancient conception of 

 the vital force, and to explain all physiological phenom- 

 ena of the living being by forces of the physico-chem- 

 ical order. It was the same idea that Liebig followed, 

 as we have seen, in the study of fermentations. Into 

 a coterie shining with such names, it is plain with what 

 welcome the idea would be received of the interven- 

 tion under the form of living and parasitic organisms 

 of this proscribed and everywhere driven out vital force. 



And this is precisely why Pasteur who had overthrown 

 the ideas of Liebig respecting fermentations, found it 

 necessary in continuing his work to meet and overthrow 



