CHAPTER VIII. 



The inculmting 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 all grow more luxuri- 

 antly at the temperature of the human body (37.5° C.) 

 than at lower temperatures ; whereas, with the ordi- 

 nary saprophytic forms almost any temperature between 

 18° C. and that of the body is favorable. It therefore 

 becomes necessary to provide some place in which a 

 constant temperature suitable to the growth of the 

 pathogenic organisms can be maintained. For this 

 purpose there have been devised a number of different 

 forms of apparatus. Fundamentally they are all based 

 upon the same principles, however, and a general de- 

 scription of the essential points involved in their con- 

 struction will be all that is needed here. 



This apparatus has the names thermostat, incubator, 

 and brooding oven. It is a copper chamber (Fig. 26) 

 with double walls, the space between which is filled 

 with water. The incubating chamber may be opened 

 or closed by a closely fitting double door, inside of 

 which is usually a false door of glass through which the 

 contents of the chamber may be inspected without 

 actually opening it. The whole apparatus is encased 



