CHAPTEE 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 luxuriantly 

 at the temperature of the human body (37.5° C.) than at 

 lower temperatures; whereas, with the ordinary sapro- 

 phytic 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 purpose there 

 have been devised a number of different forms of appa- 

 ratus. Fundamentally they are all based upon the same 

 principles, however, and a general description of the 

 essential points involved in their construction will be all 

 that is needed here. 



This apparatus has the names thermostat, incubator, 

 and brooding-oven. It is a copper chamber (Fig. 30) 

 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 



