THE STUDY OF THE GROWTH OF BACTERIA 121 



media by simply inoculating the media with some pus or blood 

 containing them, by means of a sterile pipette or platinum needle. 

 But such cultures are made up of colonies of different sorts of 

 bacteria some pathogenic, some non-pathogenic, etc. To sepa- 

 rate the various bacteria so that they will grow in isolated groups, 

 is a comparatively easy matter, and is accomplished in several 

 ways. The simplest is to employ several tubes of agar or blood 



FIG. 28. Colonies in gelatine plate showing how they may be separated and 

 the organisms isolated. (Williams.,) 



serum. Over the surface of each of these, a platinum loop con- 

 taining pus, or other matter, is rubbed successively. These tubes 

 are then incubated. After a few hours, the first one exhibits a 

 copious growth of many different kinds of bacteria growing con- 

 fluently together, from which it is impossible to isolate any pure 

 cultures. The second tube is less covered with bacteria while, 

 the third, instead of containing a mass of bacteria, exhibits tiny 

 little dots, or colonies (pure cultures) growing discretely isolated. 

 By means of a sterilized platinum needle these little colonies 



