viii.] THE INFECTIVENESS OF CHOLERA. 147 



a causal relation to definite bacteria has been fully estab- 

 lished ; I cannot overlook the fact that our knowledge of 

 the different species existing in the normal intestine and in 

 the cholera-intestine is far too incomplete to warrant our 

 assuming anything of so definite a nature ; I cannot overlook 

 the extremely great difficulties in harmonizing the conditions 

 under which the positive experiments on animals have been 

 carried out with the actual conditions of infection obtaining 

 in nature ; I cannot overlook the great discord that exists 

 between what is known of the comma-bacilli as regards their 

 behaviour in gastric juice, and their extremely limited 

 capability of multiplying in the normal intestine on the one 

 hand, and the fearful susceptibility to cholera infection of 

 healthy and vigorous persons in cholera epidemics on the 

 other. 



But these are not the only difficulties. In all bacterio- 

 logical inquiries referring to infectious diseases the results 

 of such inquiries, if they are to be accepted as well- 

 established, must be in harmony with the well-founded 

 facts discovered by epidemiology ; the bacteriological portion 

 of the inquiry is no doubt a very important one, but unless 

 it well harmonizes with well-established other facts not 

 appertaining to bacteriology, it cannot claim our full 

 confidence. Now, I maintain with von Pettenkofer that 

 some important parts of our knowledge concerning comma- 

 bacilli do not harmonize with well-established epidemio- 

 logical facts. Some of these have been already discussed, 

 others will be discussed now. Some of the facts as to the 

 spread of cholera difficult of explanation are those pointed 

 out by von Pettenkofer in reference to the dependence of 

 epidemics on locality and season. Certain localities appear 

 to enjoy a special immunity against the spread of cholera. 

 Versailles and Lyons, Birmingham and other towns, are 



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