vii.] PRODUCTION OF CHOLERA. 121 



canal the infectious matter of cholera, and in just as effective 

 a form as human beings, but no case of an animal having an 

 attack of cholera has ever been observed there. Hence I 

 think that all the animals on which we can make experi- 

 ments, and all those, too, which come into contact with 

 human beings, are not liable to cholera, and that a real 

 cholera process cannot be artificially produced in them." 



I have quoted thus at length from Koch, to show how care- 

 fully he had investigated from all points of view the question 

 of the communicability of cholera to animals, and how 

 precise and definite is his conclusion arrived at in this matter. 

 This is the more important since his advocates and imitators 

 leave this entirely out of sight. After Koch had thus 

 declared himself (at the Cholera Conference in Berlin, 

 July 1884), von Pettenkofer acknowledged to be a high 

 authority on cholera refused on epidemiological grounds, 

 to be described below, to accept Koch's comma-bacillus as 

 the active cause of cholera ; in fact he was so convinced of 

 the contrary that he offered with other medical men, under 

 any conditions to be determined in committee, to swallow 

 any amount of pure cultivation of Koch's comma-bacilli. 

 Fortunately, about that time Nicati and Rietsch had published 

 certain experiments by which they thought they had suc- 

 ceeded in artificially producing cholera in dogs and guinea- 

 pigs. These gentlemen, struck by the fact that in cholera 

 cases with rice-water dejecta the intestinal contents are free 

 from bile, thought the exclusion of bile from the intestine 

 probably formed a conditio sine qua non for the success of 

 the experiment. Any one who has had any experience of a 

 choleraepidemic must be struck with the extravagance of such 

 an idea. Is it not known that many and many a light case of 

 cholera occurs, in which the intestinal contents during the 

 onset of the disease is still mingled with bile, and that as 



