PATHOGENIC BACTERIA. 323 



tions (see page 85) should be made and kept at a tempera- 

 ture of 20° to 22° C. At the end of twenty -four hours or 

 less the colonies of the spirillum of cholera should have been 

 developed and should present the picture characteristic for 

 these colonies in gelatin plates (Fig. 97), which enables them 

 to be differentiated from colonies of other bacteria. From 

 one of these colonies, preparations may be made for micro- 

 scopic examination, and a set of tubes may be inoculated. 

 The most characteristic growth will be from stick-cultures in 

 gelatin. The growth in Dunham's peptone solution may be 

 tested for the development of indol and nitrites. 



At the time that the first smear preparations and gelatin 

 plates are prepared, tubes of peptone solution should be inocu- 

 lated directly from the intestinal contents, and kept in the 

 incubator (Schottelius). After development has occurred, the 

 production of indol may be tested by the addition of sul- 

 phuric acid. These tubes are especially valuable when un- 

 favorable material or when material containing small numbers 

 of the spirilla is used. In the incubator the spirilla may be 

 expected to multiply in the peptone solution rapidly, and to. 

 appear upon the surface of the Uquid in large numbers, even 

 forming a visible film in six hours. Smears may be made from 

 the surface part of these tubes, stained, and examined with a 

 microscope. From the same material gelatin plates should 

 be prepared, and examined as soon as the colonies develop. 



When cultures are obtained, their effects may be tested upon 

 guinea-pigs by injecting them into the peritoneum. 



The production of Pfeiffer's phenomenon is an additional 

 means of diagnosis between the cholera spirillum and related 

 forms. This consists in testing the suspected organism with 

 serum from an animal immunized with cultures of cholera 

 bacilli, as ahready explained above. 



In examining suspected water for the spirillum of cholera 

 one or more Uters of water is taken, and to it is added enough 



