CULTIVATION OF ANAEROBIC BACTERIA. 155

tubes are connected with a hydrogen generator, and the
gas is allowed to pass through until all the oxyo-en is
forced out and replaced by the hydrogen, after which the
ends of the tubes are sealed in the flame (Fig. 36).

Iviborius has designed a special tube for accomplish-
ing the same thing.

Kitasato and Weil found the addition of 0.3-0.5 per
cent, of sodium formate to be of use in aiding the rapid-
ity of the development of anaerobic cultures. Liborius
found that 2 per cent, of glucose added%to the culture-
medium also increased the rapidity of the process.

The methods now generally employed by bacteri-
ologists for the anaerobic cultivations embrace all the
essentials of the foregoing methods. One of the best
arrangements for the purpose is that devised by Dr.
Ravenel. His inoculations are deeply made in culture-
media as free from air as possible. The tubes are
loosely plugged, and are placed in an air-tight cham-
ber the bottom of which contains pyrogallic acid—py-
rogallic acid i, solution of caustic potash i, water 10.
The apparatus is connected by two tubes with an ex-
haust-pump on one side, and with a hydrogen appara-
tus on the other, by which means the atmosphere is ex-
hausted, and replaced by hydrogen until only pure hydro-
gen remains, after which the chamber is permanently
sealed and the germs allowed to grow. Such a chamber
can be constructed to hold a number of tubes or Petri
dishes, yet not be too large to be stood in an incubator.
Whatever oxygen may have escaped the exhaustion or
have entered by the process of leakage is at once absorbed
by the pyrogallic acid in the lower chamber of the ap-
paratus.

Apparatus for plating out strictly anaerobic bacteria
that have met with great favor are those invented by
Bbtkin (Pig. 38) and Novy (Fig. 39). The first mentioned
combines the replacement of the air by hydrogen and the
absorption of the oxygen possibly remaining by alkaline
pyrogallic acid; the other simply replaces the oxygen by