METHODS FOR THE MICROSCOPIC STUDY OF BACTERIA 211 



water are also run in, to wash the rubber tube free from caustic alkali. 

 The apparatus is working properly when the rubber tube between the 

 pinch-cock and the bottle is collapsed, indicating a partial vacuum 

 within the bottle itself. Residual oxygen is rapidly absorbed within 

 the pyrogallate solution, leaving an inert atmosphere of nitrogen. 



The bottle is incubated, medium uppermost, for the required time. 

 Inspection of the surface of the medium will show the colonies. After 

 incubation the pinch-cock is carefully opened, admitting air very gently 

 to avoid spattering the medium, and the stopper is removed. The 

 pyrogallate solution is poured out and residual traces removed with 

 clean water. The bottle is drained standing upon end, mouth down, 

 and then the colonies are ready for fishing. The colonies which develop 

 are all surface growths : the isolation of gas-forming anaerobic bacteria 

 is as readily accomplished as the isolation of non-aerogenic types. 



FIG. 26. Novy jar for anaerobic cultures. (Park.) 



Pure cultures of anaerobic bacteria may be obtained in an atmos- 

 phere of hydrogen; plates prepared in the usual manner are placed 

 on a rack in a Novy jar or other similar vessel provided with a tightly 

 fitting stop-cock, through which hydrogen can be admitted in sufficient 

 volume to displace the air. The stop-cock must be hydrogen-tight. 

 The procedure is to place inoculated plates without covers on a rack 

 within the jar in an inverted position, one above the other. A few 

 grams of pyrogallic acid are placed on the bottom of the jar with a 

 small piece of solid sodium hydroxide. At the last moment, when 

 everything is in readiness, 20 to 30 c.c. of water are gently poured 

 down the side of the jar to prevent spattering, and the cover quickly 

 clamped down. A current of hydrogen gas, either from a cylinder or 

 from a Kipp generator, is passed through the jar at a fairly rapid rate. 



