CULTIVATION OP ANAEROBIC BACTERIA. 



83 



gelatin, previously cooled upon its walls, which contains the bacteria 

 under investigation. When the anaerobic colonies have developed 

 the test tube must be broken to get at them, or the cylinder of gela- 

 tin may be removed by first warming the walls of the tube. 



Another method, recommended by Liborius, consists in distri- 

 buting the bacteria in test tubes nearly filled with nutrient gelatin or 

 agar which has been recently boiled to expel air. Colonies of anaero- 

 bic bacteria will develop near the bottom of such a tube, while the 

 aerobic species will only grow near the surface. The cylinder of 

 jelly is removed by heating the walls of the tube, and sections are 



} a 



FIG. 56. 



made with a sterilized knife for the purpose of "obtaining material 

 from individual colonies for further cultures, etc. 



Koch and his pupils are in the habit of testing the aerobic char- 

 acter of bacteria in plate cultures by covering the recently made 

 plates with a thin sheet of mica which has been sterilized by heat. 

 The strictly aerobic species do not grow under such a plate ; but, 

 according to Liborius, the exclusion of oxygen is not sufficiently 

 complete for the growth of strict anaerobics. 



Buchner's Method consists in the removal of oxygen by means 

 of pyrogallic acid. The anaerobic species under investigation is 

 planted in recently boiled agar jelly in a small test tube. This is 

 placed in a larger tube having a tightly fitting rubber stopper, as 

 shown in Fig. 55. The small tube is supported by a bent-wire 



