80 Manual of Veterinary Microbiology. 



on the contrary, the organism of tlie ape attenuates 

 the virus of rabies. 



The virulence, modified by one species, may be 

 changed in the same or opposite direction for other 

 species : rouget which has become more virulent in 

 the rabbit is less virulent for the pig; whilst the pass- 

 age of the same germ through the pigeon augments 

 its pathogenic power not only for the pigeon but also 

 for the pig. 



We could multiply examples of the influence of 

 the natural organic media upon pathogenic germs. 

 The virus of rabies attenuated in the ape is also at- 

 tenuated for the dog, guinea pig, and rabbit. Inocu- 

 lated in series to one of these species, it regains the 

 virulence which it naturally possesses in the dog; in 

 the guinea pig and rabbit it may even surpass this, 

 and in the latter attain a maximum of activity be 

 yond which further passages no more modify it. 



III. Evolution of the bacterial disease. 



After what we have seen of the reciprocal action 

 of the organism and pathogenic microbes, little re- 

 mains to be said of the disease itself. 



The determining cause of microbic affections re- 

 sides always in the implantation of the specific germ 

 in a susceptible individual ; but such common causes 

 as cold, mental emotions, overwork, etc., may take 

 an important part in their etiology, by diminishing 

 or suspending the normal phagocytic action, as we 

 have already seen. 



The germs once introduced and having resisted the 

 combined influence of phagocytosis and the bacteri- 

 cidal property, their effects do not immediately become 



