500 BACTERIOLOGY. 



the test for the presence or absence of indol in these 

 cultures should be made. 



In all doubtful cases, in which only a few curved 

 bacilli are present, or in which irregularities in either 

 the rate or mode of their development occur, pure cult- 

 ures should be obtained as soon as possible by the agar- 

 agar plate method and by the method of cultivation in 

 peptone solution, and their virulence tested upon ani- 

 mals. For this purpose cultures upon agar-agar from 

 single colonies must be made. From the surface of 

 one of such cultures a large wire-loopful should be 

 scraped and broken up in about one cubic centimetre 

 of bouillon, and the suspension thus made injected 

 by means of a hypodermic syringe directly into the 

 peritoneal cavity of a guinea-pig^ of about 350 to 

 400 grammes weight. For larger animals more mate- 

 rial is used. If the material injected is from a 

 fresh culture of the cholera organism, toxic symp- 

 toms at once appear; these have their most pro- 

 nounced expression in depression of temperature, and 

 if one follows this decline in temperature from time to 

 time with the thermometer it will be seen to be gradual 

 and continuous from the time of injection to the death 

 of the animal (Pfeiffer 1 ), which occurs in from eighteen 

 to twenty-four hours after the operation. 



In general, this is the procedure employed in the In- 

 stitute for Infectious Diseases at Berlin, under Koch's 

 direction. 



1 Loc. cit. 



