226 The Cultivation of Anaerobic Organisms 



is replaced by hydrogen. The result is a hydrogen-nitrogen jar under approxi- 

 mately atmospheric pressure. The whole process should take about r5 minutes. 

 In order to have an index of the completeness of anaerobiosis, the second stop-cock 

 is connected with a bottle of 20 per cent, sodium hydrate, freshly washed with 

 hydrogen. By means of slight suction throuph the first stop-cock, 25 r.c of 

 the sodium hydrate solution are drawn into the jar. Both stop-cocks art now 

 closed, the ends sealed with cement, and the jar is incubated. If the jar is 

 satisfactory the solution of sodium hydrate and pyrogaUic acid will remain 

 colorless indefinitely. This solution should not be relied upon to absorb any 

 remaining traces of oxygen, but is simply an indicator of the pressure of oxygen 

 and if it becomes discolored shows that there has been a mistake in technic, 

 and the jar is unsatisfactory, therefore the cover should be removed and the 

 process repeated. 



