26 INFECTION AND IMMUNITY. 



A large number of animal diseases have their 

 specific microbes, as do certain other human dis- 

 eases which hardly concern us as to the subject in 

 hand. 



In addition to the diseases mentioned, there are 

 losy several, of unknown etiology, which from analogy 

 we must recognize as entities because of their con- 

 stant clinical and anatomical manifestations. Scar- 

 let fever, measles, German measles, chickenpox, 

 smallpox, yellow fever, typhus fever and hydro- 

 phobia, are undoubtedly due to micro-organisms. 

 Mallory recently found in the skin of four scar- 

 let fever patients a protozoon-like body which he 

 believes to be the cause of the disease, although 

 he admits that much desired proof has not been ob- 

 tained. 



It is possible that smallpox and vaccinia will be 

 eliminated from the diseases of unknown causa- 

 tion, owing to the evidence of protozoon etiology 

 that Councilman and his colaborers have obtained ; 

 however, for the present, the question is sub judice 

 in view of the fact that the forms described bear a 

 close resemblance to certain well-known types of 

 cell degeneration. 



The following animal diseases, of unknown 

 etiology, may also be mentioned in this connec- 

 tion: Foot and mouth disease, peripneumonia, 

 bovine pest, sheep-pox (clavelee), chicken-typhus 

 or chicken-pest and epithelioma contagiosum of 

 fowls. 



to The following appear to be the chief reasons for 

 Dis iicrobes! the failure to discover the organisms of these dis- 

 eases: 1. Inability to cultivate the microbe. 2. 

 Mixed, or symbiotic infections. For a long time it 

 was supposed that the so-called hog-cholera bacillus 



