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134                PATHOGENIC BACTERIA.

is filtered off and pure hydrochloric acid carefully added
while a precipitate forms. The precipitated albuminate
is collected upon a cloth filter, mixed with a small quan-
tity of liquid, and made distinctly alkaline. To make
solutions of it of definite strength it can be dried, pul-
verized, and redissolved.

The most useful formula used by Deycke was a 21/> per
cent, solution of the alkali-albuininate with i per cent, of
peptone, i per cent, of NaCl, and gelatin or agar-agar
enough to make it solid.

Potatoes.—Without taking time to review the old
method of boiling potatoes, opening them with sterile
knives, and protecting them in the moist chamber, or
the much more easily conducted method of Esmarch in
which the slices of potato are sterilized in the small
dishes in which they are afterward kept and used, we
will at once pass to what seems the most simple and
satisfactory method of using this valuable medium—that
of Bolton and Globig i1

With the aid of a cork-borer a little smaller in diam-
eter than the test-tube ordinarily used a number of cyl-
inders are cut from potatoes. Rather large potatoes
should be used, the cylinders being cut transversely, so
that a number, each about an inch and a half in length,
can be cut from one potato. The skin is removed from
the cylinders by cutting off the ends, after which each
cylinder is cut in two by an oblique incision, so as to
leave a broad, flat surface. The half-cylinders are placed
each in a test-tube previously sterilized, and then are
exposed three times, for half an hour each, to the pass-
ing steam of the sterilizer. This steaming cooks the
potato and also sterilizes it. Such cultures are apt to
deteriorate rapidly, first by turning very dark; second,
by drying so as to be useless. Abbott has shown that
if the cut cylinders be allowed to stand for twelve hours
in running water before being dispensed in the tubes,
they do not turn dark. Drying may be prevented by

1 The Medical News, vol. 1., 1887, p. 138.