126 



BACTERIOLOGY. 



depend in the main upon the temperatures to which it 

 is to be applied. For low temperatures, regulators con- 

 taining such fluids as ether, alcohol, and calcium chloride 

 solution, which expand and contract rapidly and regu- 

 larly under slight variations in temperature, are com- 

 monly employed ; whereas for temperatures approaching 

 the boiling-point of water mercury is most frequently 

 used. 



The temperature of the incubator is to be regulated, 

 then, by the use of some such form of apparatus as that 

 just described. It should be of sufficient delicacy to 

 prevent a fluctuation of more than 0.2 C. in the tem- 

 perature of the air within the chamber of the apparatus. 



FIG. 30. 



Moitessier's gas-pressure regulator. 



GAS-PRESSURE REGULATORS. A gas-pressure regu- 

 lator is not rarely intervened between the gas supply 



