CULTIVATION OF ANAEROBIC BACTERIA.    157
but when the stopper is turned a little the jar is hermet-
ically sealed. Alkaline pyrogallic acid in a test-tube, or
in the bottom of the jar, will serve to absorb any remain-
ing oxygen. The larger jar (Fig. 39, a) is intended for
Petri dishes, the smaller one (6) for test-tube cultures.
Roux has suggested the simplest method of cultivating
anaerobic bacteria. The germs are distributed through
freshly boiled, still liquid, gelatin or agar-agar, as in
making the dilutions for plate-cultures, then drawn into
a long, slender sterile piece of glass tubing of small
calibre. When the tube is full the ends, which should
have been narrowed, are closed in a flame, and the cul-
ture is hermetically sealed in an air-tight chamber. The
chief difficulty is in transplanting the growing colony.
To do this the tube must be opened with a file or-a dia-
mond at the point where the colony desired is observed.