THE CULTIVATION OF BACTERIA. lOI 



colony consists of bacteria which have the property of liquefying 

 gelatin, a little funnel-shaped pit or depression forms at the site 

 of the colony. The appearance of colonies may be of great as- 

 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 Culture. — 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 the 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 alike. In that case a 

 pure culture will not be obtained, and the process of plating 

 may have to be repeated. 



