Reduction of Oxygen 



211 



through tube d, both tubes are withdrawn. It is well to 

 place one Petri dish containing alkaline pyrogallic acid in 

 the rack to absorb any oxygen not successfully displaced. 



3. The Absorption of the Atmospheric Oxygen. This 

 method was first suggested by Buchner, whose idea was to 

 absorb the atmospheric oxygen by alkaline pyrogallic acid 

 and permit the bacteria to develop in the indifferent nitro- 

 gen. Various methods have been suggested for achieving 

 this end, Buchner's own method consisting in the use of two 

 tubes, a small one to contain the culture (Fig. 55) and a larger 

 one to contain the absorbing fluid. A fresh solution of pyro- 

 gallic acid and sodium hy- 

 droxid were poured into 

 the large tube, the smaller 

 tube placed within it, upon 

 some appropriate sup- 

 port, and the whole tightly 

 corked. 



Wright has given the 

 most simple modification 

 by suggesting that the cot- 

 ton stopper of the ordinary 

 culture-tube have its pro- 

 jecting part cut off and the 

 plug itself pushed down the 

 tube for a short distance. 

 Some alkaline pyrogallic 

 acid solution is poured 

 upon the cotton, to satu- 

 rate it, and the tube tightly 

 corked. 



Fig. 54. Botkin's apparatus for 

 making anaerobic cultures. 



4. Reduction of Oxygen. Pasteur and, later, Roux 

 have recommended the cultivation of anaerobic bacteria in 

 association with aerobic bacteria by which the oxygen was 

 to be absorbed. This method is too crude to be employed 

 at the present time, as it destroys the essential character- 

 istics of the cultures by mixing the products of the bacteria. 



Chemic reduction of the oxygen has been attempted by 

 the addition of 2 per cent, of glucose, as suggested by Libo- 

 rius, 0.3-0.5 per cent, of sodium formate, as suggested by 

 Kitasato and Weil, o.i per cent, of sodium sulphate, sug- 

 gested by the same authors, and various other chemicals. 

 None of these additions has been sufficiently successful to 



