4 
ANNALES DE L’INSTITUT PASTEUR 
of Levaditi, Yamanouchi and M’Intosh that they rapidly become 
avirulent, even when cultivated in a collodion sac within the 
peritoneal cavily of suitable animais. On the other hand, it 
is ratlier astonishing to learn that the saprophytic species, such 
as the microdentium and mucosum , also undergo profound 
alterations in their biological characteristics. Probably the 
cultural conditions accorded them, which undoubledly approxi- 
mate a state of parasitism more than those of the natural 
habitus of these organisms, were responsible for the graduai 
loss of their putrefactive property, and this may constitule an 
example of functional loss through the disuse of certain 
faculties brought about by the new environments. 
