THE CULTIVATION OF BACTERIA. 



85 



unequal expansion and contraction of two metals which are 

 riveted together. Fig. 25 shows this regulator. The gas 

 passes in at e and passes out at i. The amount of gas pass- 

 ing 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 moves in or out according 

 to the changes of temperature of the 

 water jacket of the incubator into 

 which the stem (/) of the regulator is 

 inserted. This stem is finestrated and 

 has the riveted metallic strips running 

 down in it. These strips are pivoted 

 at the collar, g. 



The gas coming from the gas-regu- 

 lator 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 acci- 

 dentally extinguished by a sudden 

 draught of air or from any other 

 cause. The automatic burner in- 

 vented by Koch is an ingenious, 

 simple and effective device (^Fig. 26). 

 The coils of metal seen on each side 

 at the top of the burner are so 

 arranged that when they expand 

 they turn the disk below so as to 



support the arm coming from the stop-cock; when they 

 cool they turn the disk in the opposite direction, and 

 allow the arm to fall and cut off the gas. Some incon- 

 venience will arise from irregularities in the flow of gas 

 from the main supply-pipe. Any incubator will vary a little 

 from such causes. In the experience of the writer, natural 



Fig. 25. — Roux Bimetallic 

 Gas Regulator, a, Set screw; 

 6, Screw collar; c, Clamp; 

 d. Outlet for gas; e, Inlet for 

 gas. 



