n6 



BACTERIOLOGY 



holes into the interior of the air-chamber, and often another into 

 the water standing in the water-jacket. A gas-regulator passes 

 through another hole, and is immersed in the water standing in 

 the water-jacket. There are various forms of gas-regulators 



FIG. 46. Incubator. 



more or less complicated. The simplest and least expensive 

 thermo-regulators for gas are made of glass and filled with mercury 

 or with mercury and some lighter liquid, the heavy mercury 

 serving to close the chief source of gas supply when the desired 



