THE CULTIVATION OF BACTERIA. 91 



sistance in determining the character of doubtful species. The 

 appearance in gelatin plates of the colonies of the spirillum of 

 Asiatic cholera, for instance, is one of the most characteristic 

 manifestations of this organism. 



Pure Cultures. — From these colonies pure cultures may 

 be obtained by what is called "fishing." Select a colony from 

 which cultures are to be made; touch it lightly with the tip of a 

 sterilized platinum wire, taking great care not to touch the 

 medium at any other point. Introduce the wire into a tube of 

 gelatin. Sterilize the wire and plug the tube. In a similar 

 manner, and from the same colony, inoculate tubes of agar, 

 bouillon, milk, potato and blood-serum. At the same time it 

 is well to make a smear preparation from the colony and to stain 

 with one of the aniline dyes so as to determine the morphology 

 of the bacteria. The growths which take place in the tubes 

 should contain one and the same kind of bacteria. As seen 

 under the microscope their bacteria should have the same general 

 form and appearance as those seen in the colony from which 

 they were derived. This will be the case, provided the colony 

 has resulted from the development of a single bacterium or from 

 several bacteria of the same kind. Occasionally, however, a 

 colony will develop from several bacteria which may not all be 

 ahke. In that case a pure culture will not be obtained, and the 

 process of plating may have to be repeated. 



