CHAPTER IX. 



The incubator used in bacteriological work — Gas-pressure regu- 

 lator — Thermo-regulator — The form of 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 ordinary 

 saprophytic forms almost any temperature between 18° 

 to 20° C. and that of the body is favorable. It there- 

 fore 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. 16) 

 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 

 chambers may be inspected without actually opening it. 



