CHAPTER XX. 

 STUDY OF THE PHYSIOLOGY OF BACTERIA. 



Of the environmental conditions influencing the growth 

 of bacteria the following are the chief ones ordinarily deter- 

 mined : 



A. Temperature.— The optimum temperature for growth 

 is usually about the temperature of the natural environment 

 and ordinarily one determines merely whether the organism 

 grows at body temperature (37°) and at room temperature 

 (20°) or not. For exact work the maximum, minimum and 

 optimum temperature must be ascertained by growing in 

 "incubators" with varying temperatures-. 



A bacteriological incubator is an apparatus for growing 

 bacteria at a constant temperature. This may be any tem- 

 perature within the limits for bacterial growth. If tempera- 

 tures above that of an ordinary room are desired, some 

 source of artificial heat is needed. Electricity, gas or oil 

 may be used. A necessary'' adjunct is some device for main- 

 taining the temperature constant, a " thermoregulator" or 

 "thermostat." For lower temperatures a cooling arrange- 

 ment must be installed. For the great part of bacteriologi- 

 cal work only two temperatures are used, 20° so-called " room 

 temperature" (this applies to European "rooms" not to 

 American) and 37° or body temperature. Incubators for 

 37° of almost any size and style desired may be secured from 

 supply houses and need not be further described. Figs. 138 

 and 139 illustrate some of the types. 



For use with large classes "incubator rooms" are to be 

 preferred. The author has one such room for 37° work with 

 200 compartments for student use which did not cost over 

 $60 to install. 



The styles of incubators for lower temperatures, 20° and 

 below, are not so numerous nor so satisfactory^ The author 

 (210) 



