ASIATIC CHOLERA. 195 



now exhibit, in consequence, numerous characteristic colo- 

 nies. 



From the gelatin-plates, finally, pure cultures are made, 

 with which the cholera-red, and Gruber's and Pfeiffer's 

 reactions are obtained, and experiments on animals are 

 undertaken. When all these yield positive results, then 

 the diagnosis of cholera-bacilli is final and certain. 



Instead of gelatin-plates, agar-plates frequently are made. 

 These have the advantage that they can be kept in the 

 thermostat at a temperature of 37 C. (98.6 F.), and can 

 be examined after from eight to ten hours. It has already 

 been pointed out that only the superficial colonies on agar 

 present an approximately characteristic, light grayish- 

 brown appearance. It is, therefore, useful, in order to ob- 

 tain only such superficial colonies, to have in readiness 

 agar-agar poured in Petri dishes, upon the surface of 

 which the inoculating material (the fertilized peptone-cul- 

 ture) is smeared by means of a platinum loop. As, how- 

 ever, the agar-agar always expresses a certain amount of 

 water of condensation, which renders impossible the growth 

 of isolated colonies, it is necessary to place dishes into 

 which this culture-medium is poured in the thermostat be- 

 fore they are used, until the fluid has evaporated, or they 

 are preserved in an inverted position. It is not sufficient 

 in making a diagnosis to find light grayish-brown, trans- 

 parent colonies, but by means of preparations it must be 

 decided whether the bacteria constituting the colonies cor- 

 respond also morphologically with cholera-vibrios. 



Examination of Water for Cholera-bacilli. The con- 

 ditions are somewhat different if water is to be examined 

 for cholera-bacilli. Formerly it was the custom to dilute 

 freely the usually much polluted water, and to make plates 

 with a portion of a drop. Under these circumstances it was 

 largely a matter of chance whether cholera-germs were 

 obtained or not. It would be necessary for them to be 

 present in the infected water in considerable number, in 

 order to be demonstrated in this way. These difficulties 

 may be avoided by taking large amounts of water for 

 examination. To this end from 100 to 1000 cu. cm. 

 of the suspected water are placed in sterilized flasks, 

 and to each specimen one per cent, of alkaline peptone 

 (preferably the peptone of Witte) and ^ of one per 

 cent, of sodium chlorid are added. The peptone and 



