LABORATORY TECHNIC 



39 



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 as 

 well as the means of isolating pure cultures after the first 

 inoculation. These tubes and plates are placed at body 



FIG. 11. Showing certain macroscopic characteristics of colonies. 

 Natural size. (Abbott.) 



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 temperature is kept constantly where desired. Practically 

 all pathogenic bacteria develop best at this temperature. 

 The bacteria of the soil and water grow best at about 70 F. 



