THE CULTIVATION OF MICRO-ORGANISMS 123 



when the regulator is not to be heated above 35" C, alcohol when 

 it is not to be heated above 75° C, and toluol for temperatures 

 between 75° and 100° C. 



A very satisfactory regulator is that of Roux. It is con- 

 structed entirely of metal, and its operation is due to the unequal 



expansion and contraction of two 

 metals which are riveted together. 

 Fig. 51 shows this regulator. The 

 gas passes in at e and passes out 

 at d. The amount of gas passing 

 through is regulated by a piston 

 on the end of the set screw inside 

 the tube from which the outlet 

 tube branches off. This piston 



Pig. SI- — Roux bimetallic gas- 

 regulator, a. Set screw; ft, Screw 

 collar; c. Clamp; d. Outlet for 

 gas; e. Inlet for gas. 



Fig. 



-Koch auto^patic gas- 

 burner. 



moves in or out according to the changes of temperature of the 

 water jacket of. the incubator into which the stem (/") of the regu- 

 lator is inserted. This stem is fenestrated and has the riveted 

 metallic strips running down in it. These strips are pivoted at 

 the collar, g. 



The gas coming from the gas-regulator passes to a Bunsen 

 burner, which stands underneath the incubator. This burner 

 should have some kind of automatic device for cutting off the flow 

 of gas in case it becomes accidentally extinguished by a sudden 



