thed Erlenmeyer flask (500 c.c. capacity).

Sterile metal funnel with short wide bore delivery tube to
just fit mouth of flask.

Solid rubber stopper to fit the flask (sterilised by
boiling).

Pair of scales.

Counterpoise (Fig. 107).

Sterile metal (nickel) spoon or spatula.

Fractional steriliser (Fig. 140).

METHOD.--

1. Arrange four sterile capsules numbered I, II, III, and IV; pipette 9
c.c. sterile bouillon into the first capsule, and 9.9 c.c. into each of
the remaining three.

2. Pipette 100 c.c. sterile bouillon into the Erlenmeyer flask.

3. Remove the cotton-wool plug from the flask and replace it by the
sterile funnel.

4. Place flask and funnel on one pan of the scales, and counterpoise
accurately.

5. Empty the sample of soil into the mortar and triturate thoroughly.

6. By means of the sterile spatula add 10 grammes of the earth sample to
the bouillon in the flask.

The final results will be more reliable if steps 2, 3, 4, and 5 are
performed under a hood--to protect from falling dust, etc.

7. Remove the funnel from the mouth of the flask; replace it by the
rubber stopper and shake vigourously; then allow the solid particles to
settle for about thirty minutes. One cubic centimetre of the turbid
broth contains the washings from 0.1 gramme of soil.

8. Pipette off 1 c.c. of the supernatant bouillon, termed the "soil
water," and add it to the contents of capsule I; mix thoroughly.

9. Remove 0.1 c.c. of the infected bouillon from capsule I and add it to
capsule II, and mix.

10. In like manner add 0.1 c.c. of the contents of capsule II to capsule
III, and then 0.1 c.c. of the contents of capsule III to capsule IV.

Then 1 c.c. fluid from capsule I contains soil water
from .01 gm. earth.
Then 1 c.c. fluid from capsule II contains soil water
from .0001 gm. earth.
Then 1 c.c. fluid from capsule III contains soil water
from .000001 gm. earth.
Then 1 c.c. fluid from capsule IV contains soil water
from .00000001 gm. earth.

(A) _Aerobes (Vegetative Forms and Spores)._--

11. Pour a set of gelatine plates from the contents of each capsule--two
plates in a set, and containing respectively 0.1 c.c. and 0.4 c.c. of
the diluted soil water. Label and incubate.

12. Pour similar sets of wort gelatine plates from the contents of
capsules II and III, label, and incubate at 20 deg. C.

13. Pour similar sets of agar plates from