Exclusion of Atmospheric Oxygen 



219 



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 characteristics of the cultures by mixing the products 

 of the bacteria. 



Chemic reduction of the oxygen has been attempted by the addi- 

 tion of 2 per cent, of glucose, as suggested by Liborius, 0.3-0.5 per 

 cent, of sodium formate, as suggested by Kitasato and Weil, o.i 

 per cent, of sodium sulphate, suggested by the same authors, and 

 various other chemicals. None of these additions has been suffi- 

 ciently successful to merit continued favor, and at the present time 

 this method is not employed. 



5. Exclusion of Atmospheric Oxygen by Means of Various 

 Physical Principles and Mechanical Devices. This has appealed 

 to the ingenuity of many experimenters, and many means of accom- 

 plishing it have been tried with success. 



Fig. 67. Buchner's method of mak- 

 ing anaerobic cultures. 



Fig. 68. Hesse's method of making 

 anaerobic cultures. 



The most simple plan is that of Hesse, who made a deep puncture 

 in recently boiled and rapidly cooled gelatin or agar-agar, then cov- 

 ered the surface of the medium with sterile oil. The so-called 

 " shake culture" is another very simple method, suggested by 

 Liborius and Hesse. The medium to be inoculated, contained in a 

 well-filled tube or flask, is boiled to displace the contained air, cooled 

 so as no longer to endanger the introduced bacteria, then inoculated, 

 the inoculated bacteria being distributed by gently shaking. On 

 cooling, the medium "sets," the organisms below the surface remain- 

 ing under anaerobic conditions. 



Kitasato first used paraffin as a covering for the inoculated medium, 



