PATHOGENIC BACTERIA. 



393 



mining how long. In the ordinary food-substances it may 

 survive long enough to allow them to act as carriers of the 

 infection if eaten raw. It is an important fact that the cholera 

 spirillum is not a strict parasite, but under favorable con- 

 ditions it may maintain its vitality for some time outside of 

 the human body. 



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 

 spontaneous cholera excepting man, though a 

 disease resembling cholera can be reproduced 

 in animals when certain conditions are com- 

 plied with. The acid of the gastric juice de- 

 stroys the organism, and this makes it im- 

 possible to infect animals by. way of the 

 alimentary tract unless this acidity is overcome 

 with an alkali before the introduction of the 



ril u lirp FIG. 103. Spiril- 



lum of cholera, 



The following plan was adopted by Koch : stab - culture i n 

 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 pure culture of the cholera spirillum 

 was introduced into the stomach. When guinea-pigs are 

 treated in this manner, in most cases a condition closely 

 simulating cholera is produced. The animal dies with 

 symptoms of collapse. The small intestine is more or less 

 filled with a watery, flocculent fluid containing a large number 

 of the spirilla of cholera. The mucous membrane of the 

 intestine is swollen and reddened. 



When guinea-pigs receive an intraperitoneal injection fiom 



gelatin, two days 

 old. (Friinkelcnd 

 Pfeiffer.) 



