tap (first
adjusting the tap so that no escape of gas shall take place) and connect
it with the Orsat.

10. Remove, say, 100 c.c. of gas from the receiver, reverse the tap and
force it into the culture flask. Remove 100 c.c. of mixed gases from the
culture flask and replace in the receiver.

Repeat these processes three or four times to ensure thorough admixture
of the contents of flask and receiver.

11. Now withdraw a sample of the mixed gases into the Orsat and analyse.

In calculating the results be careful to allow for the volume of air
contained in the flask at the commencement of the experiment.

For the collection of gases formed under anaerobic conditions a slightly
different procedure is adopted:

1. Fix a culture flask (500 c.c. capacity) with a perforated rubber
stopper carrying an ~L~-shaped piece of manometer tubing, each arm 5 cm.
in length.

2. Prepare a second ~L~-shaped piece of tubing, the short arm 5 cm. and
the long arm 20 cm., and connect its short arm to the horizontal arm of
the tube in the culture flask by means of a length of pressure tubing,
provided with a screw clamp.

3. Fill the culture flask completely with boiling medium and pass the
long piece of tubing through the plug of an Erlenmeyer flask (150 c.c.
capacity) which contains 100 c.c. of the same medium.

4. Sterilise these coupled flasks by the discontinuous method, in the
usual manner.

Immediately the last sterilisation is completed, screw up the clamp on
the pressure tubing which connects them, and allow them to cool.

As the fluid cools and contracts it leaves a vacuum in the neck of the
flask below the rubber stopper.

5. To inoculate the culture flask, withdraw the long arm of the bent
tube from the Erlenmeyer flask and pass it to the bottom of a test-tube
containing a young cultivation (in a fluid medium similar to that
contained in the culture flask) of the organism it is desired to
investigate.

6. Slightly release the clamp on the pressure tubing to allow 4 or 5
c.c. of the culture to enter the flask.

7. Clamp the rubber tube tightly; remove the bent glass tube from the
culture tube and plunge it into a flask containing recently boiled and
quickly cooled distilled water.

8. Release the clamp again and wash in the remains of the cultivation
until the culture flask and tubing are completely filled with water.

9. Clamp the rubber tubing tightly and take away the long-armed glass
tubing.

10. Prepare th