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 necessary 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 saprophytic forms almost any temperature be- 

 tween 18 and 37 C. is suitable. It therefore becomes 

 necessary to provide a place in which a constant tempera- 

 ture favorable to the growth of the pathogenic organisms 

 can be maintained. For this purpose a number 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 of heat and consequent fluctuations in teinpera- 



(157) 



