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 



