42 METHODS OF STUDYING MICROORGANISMS 



organism smeared upon a plate only one kind of colony 

 of organisms will develop. It is the custom to put 

 all material to be examined upon plates of nutrient 

 medium to start with, by which process the worker 

 at once has before him evidence to show how many 

 kinds of bacteria are present and the means of isolating 



FIG. 12. Platinum needle and loop. (Park.) 



pure cultures after the first inoculation. These tubes 

 and plates are placed at body temperature (98 F. 

 or 37.5 C.) in the incubator. An incubator is a doubly 

 insulated metal box, heated by gas or electricity and 

 controlled by an automatic device by which the tem- 

 perature is kept constantly where desired. Practically 



