BACTERIA IN THE SOIL 



141 



u 



oxygen can obtain entrance through the sealed entrance 

 tube, or through the exit tube immersed in mercury. Yet 

 through this latter channel any gases produced by the cult- 

 ure could escape if able to produce sufficient pressure. 



3. The Absorption Method. Instead of adding hydrogen 

 to the tube or flask containing the anaerobic culture, it is 



feasible to add to the medium 

 some substances, like glucose 

 or pyrogallic acid, which will 

 absorb the oxygen which is 

 present, and thus enable the 

 anaerobic requirement to be 

 fulfilled. To various media 

 gelatine, agar, or broth (the 

 latter used for obtaining the 

 toxins of anaerobes) 2 per 

 cent, of glucose may be added. 

 Pyrogallic acid, or pyrogallic 

 acid one part and 20 per cent, 

 caustic potash one part, is also 

 readily used for absorptive pur- 

 poses. A large glass tube of 

 25 cc. height, named a Buch- 

 ner's cylinder, having a con- 

 striction near the bottom, is taken; and about 

 two drachms of the pyrogallic solution are placed 

 in the bottom of it. A test-tube containing the 

 culture is now lodged in the upper part above the 

 constriction. The apparatus is now placed in 

 the incubator at the desired temperature, and the 

 contained culture grows under anaerobic condi- 

 tions. As the pyrogallic solution absorbs the 

 oxygen it assumes a darker tint. 



4. Mechanical Methods. These include various 

 ingenious tricks for preventing an admittance of oxygen to 



FRANKEL'S TUBE 



For Cultivation of 

 Anaerobes 



BUCHNER'S 

 TUBE 



For Cultivation 

 of Anaerobes 



