distilled water into a large flask (or glass
beaker, or enamelled iron pot) and add 1000 grammes (roughly, 2-1/2
pounds) of fresh lean meat--e. g., bullock's heart--finely minced in a
mincing machine.

2. Heat the mixture gently in a water-bath, taking care that the
temperature of the contents of the flask does not exceed 40 deg. C. for
the first twenty minutes. (This dissolves out the soluble proteids,
extractives, salts, etc.)

3. Now raise the temperature of the mixture to the boiling-point, and
maintain at this temperature for ten minutes. (This precipitates some
of the albumins, the haemoglobin, etc., from the solution.)

4. Strain the mixture through sterile butter muslin or a perforated
porcelain funnel, then filter the liquid through Swedish filter paper
into a sterile "normal" litre flask, and when cold make up to 1000 c.c.
by the addition of distilled water--to replace the loss from
evaporation.

5. If not needed at once, sterilise the meat extract in bulk in the
steam steriliser for twenty minutes on each of three consecutive days.

Calf, sheep, or chicken flesh is occasionally substituted for the beef;
or the meat extract may be prepared from animal viscera, such as brain,
spleen, liver, or kidneys.

NOTE.--As an alternative method, 5 c.c. of Brand's meat
juice or 3 grammes of Wyeth's beef juice, or 10 grammes
Liebig's extract of meat (Lemco) may be dissolved in 1000
c.c. distilled water, and heated and filtered as above to
form ordinary or single strength meat extract.

Media, prepared from such meat extracts are, however,
eminently unsatisfactory when used for the cultivation of
the more highly parasitic bacteria; although when working in
tropical and subtropical regions their use is well-nigh
compulsory.

~Reaction of Meat Extract.~--Meat extract thus prepared is acid in its
reaction, owing to the presence of acid phosphates of potassium and
sodium, weak acids of the glycolic series, and organic compounds in
which the acid character predominates. Owing to the nature of the
substances from which it derives its reaction, the total acidity of meat
extract can only be estimated accurately when the solution is at the
boiling-point.

Moreover, it has been observed that prolonged boiling (such as is
involved in the preparation of nutrient media) causes it to undergo
hydrolytic changes which increase its acidity, and ~the meat extract only
becomes st