320 PATHOGENIC BACTERIA. 



cholera excrement; and how many other interesting in- 

 fections are made possible. The literature upon these 

 subjects is so vast that in a sketch of this kind it is 

 scarcely possible to mention even the most instructive 

 examples. One physician is reported to have been in- 

 fected with cholera while experimenting with the spirilla 

 in Koch's laboratory. 



The evidence of the specificity of the cholera spirillum 

 when collected shows that it is present in the choleraic 

 dejections with great regularity, and that it is as con- 

 stantly absent from the dejecta of healthy individuals 

 and those suffering from other diseases ; but these facts 

 do not admit of satisfactory proof by experimentation 

 upon animals. Animals are never affected by any dis- 

 ease similar to cholera during the epidemics, nor do foods 

 mixed with cholera discharges or with pure cultures of 

 the cholera spirillum affect them. This being true, we 

 are prepared to receive the further information that sub- 

 cutaneous injections of the spirilla are often without 

 serious consequences, though cultures differ very much 

 in this respect, some always causing a fatal septicemia in 

 guinea-pigs, others being as constantly harmless. 



Intraperitoneal injection of the virulent cultures pro- 

 duces a fatal peritonitis in guinea-pigs. 



One reason that animals and certain men are immune 

 to the disease seems to be found in the distinct acidity 

 of the normal gastric juice, and the destruction of the spi- 

 rilla by it. Supposing that this might be the case, Nicati 

 and Rietsch, Von Ermengen and Koch, have suggested 

 methods by which the micro-organisms can be introduced 

 directly into the intestine. The first-named investigators 

 ligated the common bile-duct of guinea-pigs, and then in- 

 jected the spirilla into the duodenum with a hypodermic 

 needle. The result was that the animals usually died, some- 

 tiiiR-s with choleraic symptoms ; but the excessively grave 

 nature of the operation upon such a small and delicately 

 constituted animal as a guinea-pig greatly lessens the value 

 of the experiment. Koch's method is much more satisfac- 



