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 develjopment 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 tempera- 

 10 (145) 



