CHAPTER VIII. 



The incubating-oven -The safety burner employed in heating the 

 incubator Thermo-regulator Gas-pressure regulator. 



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 the incubator, or brooding- 

 oven, is a copper chamber (Fig. 28) with double walls, 

 the space between which is filled with water. The 

 incubating-chamber has a closely-fitting double door, 

 inside of which is a door of glass through which the 

 contents of the chamber may be inspected without 

 actually opening it. The whole apparatus is encased in 

 either asbestos-boards or thick felt, to prevent radiation 



186 



