34 



APPLIED BACTERIOLOGY FOR NURSES 



the colonies are not too closely crowded, and then, by 

 means of a sterile straight platinum wire, carefully 

 transferring some of the bacteria from a single colony to 

 a tube of sterile medium. This process is spoken of as 

 *'fishing" a plate. It is obvious that, even though the 

 original material contained many different kinds of 

 bacteria, the cultures obtained by ^'fishing" will each 

 contain but a single kind in pure culture. 



Fig. 17. — Smith's fermentation-tiibe (McFarland). 



The cultivation of bacteria on different media con- 

 stitutes an important means of studying and identify- 

 ing the various species. For example, certain bacteria 

 when grown in gelatin cause the gelatin to become 

 fluid, while others do not. Certain bacteria cause milk 

 to turn sour and coagulate, some cause it to become 

 putrid, while others apparently leave it unchanged. 



