268 TEXT-BOOK OF BACTERIOLOGY. 



every instance, and the significance of the vibrios in causing 

 cholera is no longer in doubt. The verj' intimate relations existing 

 between the bacteria and the disease could only be those of cause 

 and effect. Only adversaries not open to conviction could dispute 

 this; they clung to the fact that successful transmissions from arti- 

 ficial cultures to animals have not been obtained. But they over- 

 looked the fact that, according to experience, cholera is a disease 

 peculiar to man which never occurs in animals under ordinary cir- 

 cumstances, but rather spares them without exception in the most 

 virulent epidemics. 



Koch had pointed out as early as 1876 that there might be some 

 difficulty in the future in differentiating the germs of cholera and 

 typhus abdominalis, since animals were insusceptible to both 

 these affections. 



It is, therefore, not to be wondered at that the experiments with 

 animals failed; this in no way proved or disproved the relation of 

 the bacilli to the disease. We must not demand more than is pos- 

 sible of the experiment under the circumstances, and we may, as 

 far as our knowledge goes and in analogy with other facts, con- 

 sider the specific character of a micro-organism established if it 

 is found in all cases of a disease and in it alone. 



Koch has endeavored, nevertheless, to utilize the experiment with 

 animals to prove his assertions; he has, in fact, succeeded in over- 

 coming some of the resistance and in demonstrating that the cholera 

 bacteria can at least develop pathogenic qualities in the animal 

 body, exert a poisonous influence, and produce symptoms analogous 

 to those observed in human cholera. 



No results followed the mere feeding of the cultures to animals 

 in various ways. Only by placing the bacilli directly into the 

 blood-vessels of a rabbit could the animal be successfully infected 

 and the rods afterward found in the organs; but this procedure 

 was so unlike the manner of ordinary infection that it could not 

 properly be regarded as conclusive. 



Nicati and Rietsch were able to produce a fatal disease like 

 cholera in Guinea-pigs by putting the comma bacilli directly into 

 the intestinal canal, especially the duodenum, after having ligated 

 the biliary duct. 



This fact showed that the cholera bacilli must be placed at once 

 into the intestine, where the reaction is alkaline. The acid gastric . 

 juice destroys and renders harmless the most sensitive comma 

 bacilli (similarly to the anthrax bacilli). This was the one obstacle 

 that frustrated all attempts at transmission. 



But a second factor had to be considered. The prevention of a 



