in the centrifuge, adjust by the
addition or subtraction of saline solution so that they counterpoise
exactly, and centrifugalise for ten minutes.

NOTE.--Each tube now contains the deposit from 100 c.c. of
the milk sample and the amount can be read off in hundredths
of a centimetre. The multiplication of this figure by 100
will give the amount of "Apparent Filth," in "parts per
million"--the usual method of recording this quality of
milk.

9. Pipette off all the supernatant fluid and invert the tube to drain on
to a pad of sterilised cotton-wool, contained in a beaker. (This wool is
subsequently cremated.)

10. Examine both cream (C^{1}) and deposit (D^{1}) microscopically--

(a) In hanging-drop preparations.

(b) In film preparations stained carbolic methylene-blue, by Gram's
method, by Neisser's method, and by Ziehl-Neelsen's method.

Note the presence or absence of altered and unaltered vegetable fibres;
pus cells, blood discs; cocci in groups or chains, diphtheroid bacilli,
Gram negative bacilli or cocci, spores and acid fast bacteria.

11. Adapt the final stages of the investigation to the special
requirements of each individual sample, thus:

~1. Members of the Coli-typhoid Group.~--

1. Emulsify the deposit from the second centrifugal tube (D^{2}) with 10
c.c. sterile bouillon and inoculate three tubes of bile salt broth as
follows:

To Tube No. 1 add 2.5 c.c. milk deposit emulsion
(=25 c.c. original milk.)
To Tube No. 2 add 1.0 c.c. milk deposit emulsion
(=10 c.c. original milk.)
To Tube No. 3 add 0.5 c.c. milk deposit emulsion
(= 5 c.c. original milk.)

2. Inoculate tube of bile salt broth No. 4 with 1 c.c. of the original
milk.

3. Inoculate further tubes of bile salt broth with previously prepared
dilutions (see page 445) as follows:

To tube No. 5 add 1.0 c.c. from capsule I.
To tube No. 6 add 0.1 c.c. from capsule I.
To tube No. 7 add 1.0 c.c. from capsule II.
To tube No. 8 add 0.1 c.c. from capsule II.
To tube No. 9 add 1.0 c.c. from capsule III.
To tube No. 10 add 0.1 c.c. from capsule III.
To tube No. 11 add 1.0 c.c. from capsule IV.
To tube No. 12 add 0.1 c.c. from capsule IV.

and incubate anaerobically (in Buchner's tubes) at 42 deg. C. for a
maximum period of forty-eight hours.

4. If growth occurs complete the investigation as detailed under the
corresponding section of water exa