212 MICROSCOPIC AND CULTURAL STUDY OF BACTERIA 



The hydrogen should enter at the top, and the outlet for the gas should 

 be as near the bottom of the apparatus as possible. A sample of the 

 escaping gas, collected in a test-tube by downward displacement, 

 will ignite without an explosion when all oxygen is displaced. The 

 inlet tubes are closed, and incubation practiced in the usual manner. 

 An atmosphere of nitrogen is to be preferred to an atmosphere of 

 hydrogen whenever it is practicable. 



b c d 



af 



FIG. 27. Koch i&fety 

 burner. (Park.) 



FIG. 28. Dunham thermo- 

 regulator. (Park.) 



FIG. 29. Roux Bimetallic 

 regulator. (Park.) 



2. Anaerobic Cultures in Fluid Media. A simple method of main- 

 taining anerobiosis in fluid media, sufficiently effective for ordinary 

 usage, is to overlay a flask or test tube containing dextrose broth 

 with a layer of albolene about 1 cm. in depth. Immediately before 

 inoculation all residual oxygen in the medium should be removed 

 by an exposure of half an hour in the Arnold sterilizer, or ten minutes 

 in an autoclave. The liquid is cooled rapidly to minimize reabsorp- 

 tion of oxygen. Wright 1 has maintained anaerobic conditions in test- 

 tube cultures with alkaline pyrogallate solution. Test tubes are 

 prepared with absorbent cotton plugs, which are made tighter than 

 ordinary usage demands. After the culture medium (freed from dis- 

 solved oxygen by heating and rapid cooling) is inoculated, the cotton 



1 Mallory and Wright, Pathological Technic, 4th ed., p. 126. 



