ATMOSPHERE 297 



2. Seal the cultures forming set B in Buchner's 

 tubes (vide page 239). 



3 . Seal the cultures forming set C in Bulloch's appara- 

 tus; exhaust the air by means of a vacuum pump, and 

 provide for the absorption of any residual oxygen by the 

 introduction of pyrogallic acid and caustic soda in solu- 

 tion (vide page 245). Treat set D in the same way. 



4. Observe the cultivations macroscopically and 

 microscopically at intervals of twenty-four hours until 

 the completion, if necessary, of seven days' incubation. 



5. Control these results. 

 Gases Other than Oxygen. 



Apparatus Required: 



Bulloch's apparatus. 



Sterile gas filter (vide page 40). 



Gasometer containing the gas it is desired to test (SO 2 , N 2 O, 

 NO, CO 2 , etc.) or gas generator for its production. 



METHOD. 



1. Prepare at least seven tube cultivations upon 

 solid media and deposit them in Bulloch's apparatus. 



2. Connect up the inlet tube of the Bulloch's jar with 

 the sterile gas filter, and this again with the delivery 

 tube of the gasometer or gas generator. 



3. Open both stop-cocks of the Bulloch's apparatus 

 and pass the gas through until it has completely re- 

 placed the air in the bell jar as shown by the result of 

 analyses of samples collected from the exit tube. 



4. Incubate under optimum conditions as to tem- 

 perature. 



5. Examine the cultivations at intervals of twenty- 

 four hours, until the completion of seven days. 



6. Remove one tube from the interior of the appara- 

 tus each day. If no growth is visible, incubate the 

 tube under optimum conditions as to temperature and 

 atmosphere, and in this way determine the length of 

 exposure to the action of the gas necessary to kill the 

 organisms under observation. 



7. Control these results. 



