1/12 inch
oil-immersion lens.

11. Proceed with the examination of the deposit as in the case of milk
deposit (see pages 450 _et seq._).

EXAMINATION OF UNSOUND MEATS.

(INCLUDING TINNED OR POTTED MEATS, FISH, ETC.)

The bacterioscopic examination of unsound food is chiefly directed to
the detection of those members of the Coli-typhoid group--B. enteritidis
of Gaertner and its allies--which are usually associated with epidemic
outbreaks of food poisoning, and such anaerobic bacteria as initiate
putrefactive changes in the food which result in the formation of
poisonous ptomaines, consequently the quantitative examination pure and
simple is frequently omitted.

A. Cultural Examination.

Quantitative.--

_Apparatus Required_:

Sterilised tin opener, (if necessary.)

Erlenmeyer flask (500 c.c. capacity) containing 200 c.c.
sterile bouillon and fitted with solid rubber stopper.

Counterpoise.

Scissors and forceps.

Scales and weights.

Water steriliser.

Hypodermic syringe.

Syringe with intragastric tube.

Rat forceps.

Case of sterile capsules.

Filtering apparatus as for water analysis.

Case of sterile plates.

Case of sterile graduated pipettes, 10 c.c. (in tenths of a
cubic centimetre).

Case of sterile graduated pipettes, 1 c.c. (in tenths of a
cubic centimetre).

Plate-levelling stand.

Tubes of nutrient gelatine.

Tubes of nutrient agar.

Water-bath regulated at 42 deg. C.

Bulloch's apparatus.

METHOD.--

1. Place the flask containing 200 c.c. sterile broth on one pan of the
scales and counterpoise accurately.

2. Mince a portion of the sample by the aid of sterile scissors and
forceps, and add the minced sample to the bouillon in the flask to the
extent of 20 grammes.

3. Make an extract by standing the flask in the incubator running at 42
deg. C. (or in a water-bath regulated to that temperature) for half an
hour, shaking its contents from time to time. Better results are obtained
if an electrical shaker is fitted inside the incubator and the flask kept
in motion throughout the entire thirty minutes.

Now every centimetre contains the bacteria washed out from 0.1 gramme of
the original food.

4. Inoculate tubes of liquefied gelatine as follows:

To tube No. 1 add 1.0 c.c. of the extract.
2 add 0.5 c.c. of the extract.