

232 



BACTERIOLOGY. 



water-jacket, to lessen or increase the space between 

 the surface of the mercury, B, and the inner tube, D, 

 thus allowing of the passage of a greater or less quan- 

 tity of gas to the burner through the tube D (Fig. 33). 



FIG. 33. 



FIG. 32. 



Small incubator. 



Thermo-regulator. 



Other forms depend upon the contraction or expansion 

 of metal, or the use of the electric current to control 

 the flow of the 2;as. 



O 



The temperature in the air chamber is kept above 

 that of the surrounding air by means of a gas flame 

 regulated as above described, or, when that cannot be 

 obtained, a lamp. 



The temperature is reduced by passing a stream of 

 cool water through the water chamber, which is itself 

 regulated. When very accurate investigations are to be 



