CHAPTER VIII. 



The incubating-oven Gas-pressure regulator Thermo-regulator The 

 safety burner employed in heating the incubator. 



THE INCUBATOE. 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 grow more luxuriantly 

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

 at lower temperatures ; whereas for the ordinary sap- 

 rophytic forms almost any temperature between 18 

 and 37 C. is suitable. It therefore becomes neces- 

 sary to provide a place in which a constant tem- 

 perature favorable to the growth of the pathogenic 

 organisms can be maintained. For this purpose a num- 

 ber of different forms of apparatus have been devised. 

 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. 



The apparatus known as thermostat, incubator, or 

 brooding-oven, is a copper chamber (Fig. 29) with 

 double walls, the space between which is filled with 

 water. The incubating-chamber has a closely fitting 

 double door, inside of which is usually a door of glass 

 through which the contents of the chamber may be in- 

 spected without actually opening it. The whole appa- 

 ratus is encased in either asbestos-boards or thick felt, 



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