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 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. 30) 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, 

 148 



