PATHOGENIC BACTERIA. 319 



The animals ordinarily used for laboratory experiments 

 are, in their normal condition, not susceptible to infection 

 with the spirillum of cholera through the alimentary canal, 

 and no animal is known which suffers from cholera except- 

 ing man, though a disease resembling cholera can be re- 

 produced in animals when certain conditions 

 are complied with. In particular it is 

 necessary to avoid the influence of the acid 

 gastric juice. 



The following plan was adopted by 

 Koch : The gastric juice was neutralized 

 with a solution of sodium carbonate; 

 the movements of the intestines were quieted 

 by the injection of i c.c. of tincture of 

 opium for each 200 grams of the body- 

 weight; and a portion of a pure culture 

 of the cholera spirillum was introduced into 

 the stomach. When guinea-pigs were 

 treated in this manner, in most cases a 

 condition closely simulating cholera was SpirnTum of 

 produced. The animal died with symptoms cholera, stab-cui- 

 of collapse. The small intestine contained ture in gelatin, two 

 a watery, flocculent fluid in which the spi- d * ys l * <! k - 



* el and Pfeiffer.) 



nlla of cholera were numerous. The mucous 

 membrane of the intestine was swollen and reddened. 



When mice or guinea-pigs receive an intra-peritoneal in- 

 jection from a pure culture, death usually results, appar- 

 ently from the toxic substances contained in the culture. 

 Pfeiffer has shown that by repeated doses, insufficient to 

 kill the animal, of cultures whose vitality has been de- 

 stroyed by heat or otherwise, the animal may be made im- 

 mune. He has also shown that when living comma bacilli 

 are introduced in the peritoneum of an immune animal they 

 are rapidly destroyed and disintegrated (see page 189). He 



