PATHOGENIC BACTERIA. 



319 



ing, and, provided the drying be complete, is usually killed 

 within twenty-four hours. It is killed in five minutes at a 

 temperature of 65° C. and in one hour at 55° C. It may retain 

 its vitaHty in water for a long time; observations vary widely 

 in respect to determining 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 



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^i .'C^Bb^'j'.' 



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a. b. c. 



Fig. 97. — Spirillum or Cholera, Colonies on Gelatin Plates. (X 100 



TO 150.) — {Frdnkel and Pfeiffer.) 

 a. Twenty-four hours old. b. Thirty hours old. o. Forty-eight hours old. 



favorable conditions 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 ani- 

 mal is known which suffers from spontaneous cholera except- 

 ing man, though a disease resembling cholera can be reproduced 



