num loop is manufactured, some 2.5 mm. by 0.75 mm., with parallel
sides, and calibrated by careful weighing, to determine approximately
the amount of moist bacterial growth, the loop will hold when filled.

1. The cultivation must be prepared on a solid medium of the optimum
reaction, incubated at the optimum temperature, and injected at the
period of greatest activity and vigour, of the particular organism it is
desired to test.

2. Arrange four sterile capsules in a row and label them I, II, III, and
IV. Into the first deliver 10 c.c. sterile bouillon by means of a
sterile graduated pipette; and into each of the remaining three, 9.9
c.c.

3. Remove one loopful of the bacterial growth from the surface of the
medium in the culture tube, observing the usual precautions against
contamination, and emulsify it evenly with the bouillon in the first
capsule. Each cubic centimetre of the emulsion will now contain
one-tenth of the organisms contained in the original loopful (written
shortly 0.1 loop).

4. Remove 0.1 c.c. of the emulsion in the first capsule by means of a
sterile graduated pipette and transfer it to the second capsule and mix
thoroughly. Drop the infected pipette into a jar of lysol solution. This
makes up the bulk of the fluid in the second capsule to 10 c.c., and
therefore every cubic centimetre of bouillon in capsule II contains
0.001 loop.

5. Similarly, 0.1 c.c. of the mixture is transferred from capsule II to
capsule III (1 c.c. of bouillon in capsule III contains 0.00001 loop),
and then from capsule III to capsule IV (1 c.c. of bouillon in capsule
IV contains 0.0000001 loop).

The dilutions thus prepared may be summarised in a table;

Capsule I = 1 loopful + 10 c.c. water [.'.] 1 c.c.=0.1 loop.
Capsule II = 0.1 c.c. capsule I + 9.9 c.c. water [.'.] 1 c.c.=0.001 loop.
Capsule III = 0.1 c.c. capsule II + 9.9 c.c. water [.'.] 1 c.c.=0.00001 loop.
Capsule IV = 0.1 c.c. capsule III + 9.9 c.c. water
[.'.] 1 c.c. = 0.0000001 loop.

6. With sterile graduated pipettes remove the necessary quantity of
bouillon corresponding to the various divisors of ten of the loop from
the respective capsules, and transfer each "dose" to a separate sterile
capsule and label; and to such doses as are small in bulk, add the
necessary quantity of sterile bouillon to make up to 1 c.c.

7. Multiples of the loop are prepared by emulsifying 1, 2, 5, or 10
loops each with 1 c.c. sterile bouillon in sep