CHAPTER VIII. 



The incubating oven Gas-pressure regulator Thermo-regulator The 

 safety burner employed in heating the incubator. 



THE INCUBATOR. When the plates have been made 

 it must be borne in mind that for the development of 

 certain forms of bacteria a higher temperature is neces- 

 sary than for the growth of others. The pathogenic 

 or disease-producing organisms all grow more luxuri- 

 antly at the temperature of the human body (37.5 C.) 

 than at lower temperatures ; whereas, with the ordinary 

 saphrophytic forms almost any temperature between 

 18 C. and that of the body is suitable. It therefore 

 becomes necessary to provide some place in which a 

 constant temperature favorable to the growth of the 

 pathogenic organisms can be maintained. For this pur- 

 pose there have been devised a number of different 

 forms of apparatus. Fundamentally they are all based 

 upon the same principles, however, and a general de- 

 scription of the essential points involved in their con- 

 struction will be all that is needed here. 



This apparatus has the names thermostat, incubator, 

 and brooding oven. It is a copper chamber (Fig. 27) 

 with double walls, the space between which is filled 

 with water. The incubating chamber may be opened 

 or closed by a closely fitting double door, inside of which 

 is usually a false door of glass through which the con- 

 tents of the chamber may be inspected without actually 

 opening it. The whole apparatus is encased in either 



