CUL TIVA TION OF BA CTERIA. 133

the culture. The serum thus prepared may be white, or
have a reddish-gray color if many corpuscles are pres-
ent, and is opaque. It cannot be melted, but once solid
remains so.

Koch devised a very good apparatus (Fig. 22) for coag-
ulating blood-serum. The bottom should be covered
with cotton, a single layer of tubes placed upon it, and
the temperature elevated until coagulation occurs. The
repeated sterilizations may be conducted in this apparatus,
or may be done equally well in the steam apparatus, the
cover of which is not completely closed, for if the tem-
perature of the serum is raised too high it is certain to
bubble.

Loffler's blood-serum mixture, which seems rather
better for the cultivation of some species than the blood-
serum itself, consists of i part of a beef-infusion bouillon
containing i per cent, of glucose and 3 parts of liquid
blood-serum. After being well mixed this is distributed
in tubes, and sterilized and coagulated like the blood-
serum itself. Most organisms grow more luxuriantly
upon it than upon either plain blood-serum or other
culture-media. Its special usefulness is for the Bacillus
diphtheriae, which grows upon it with rapidity and with
quite a characteristic appearance.

Alkaline Blood-serum.—According to Lorrain Smith,
a very useful culture-medium can be prepared as follows:
To each 100 c,cm. of blood-serum add 1-1.5 c.cm. of a *o
per cent, solution of sodium hydrate and shake it gently.
Put sufficient of the mixture into each of a series of test-
tubes, and, laying them upon their sides, sterilize like
blood-serum, taking care that their contents are not
heated too quickly, as then bubbles are apt to form.
The result should be a clear, solid medium consisting
chiefly of alkali-albumins. It is especially useful for
the bacillus diphtheriae.

Deycke's Alkali-albuminate.—1000 grams of meat are
macerated twenty-four hours with 1200 c.cm. of a 3 per
cent, solution of potassium hydrate. The clear brown fluid