CULTIVATION OF ANAEROBIC BACTERIA. 85 
gelatin, previously cooled upon its walls, which contains the bacteria 
under investigation. When the anaérobic 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 anaéro- 
bic bacteria will develop near the bottom of such a tube, while the 
aérobic species will only grow near the surface. The cylinder of 
jelly is removed by heating the walls of the tube, and sections are 
made with a sterilized knife for.the purpose of ‘obtaining material 
from individual colonies for further cultures, ete. 
Koch and his pupils are in the habit of testing the aérobic 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 aérobic 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 anaérobics. 
Buchner's Method consists in the removal of oxygen by means 
of pyrogallic acid. The anaérobic 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 
