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METHODS OF BACTERIOLOGICAL EWESTIGATIOX. 65

4. By subcutaneoii.s inoculations. The hair is shaved or cut olt"
and the skin cleansed at some point which cannot be licked or
scratched by the animal, a fold of skin pulled up with the pincette,
and a slight incision made with a pair of sterilized scissors. The
skin is then loosened from the subcutaneous tissue so as to form
a small pocket, into which the material is brought on the point
of an instrument or platinum wire.
5. By intravenous inoculations, best made in rabbits by inject-
ing the large vein at the base of the ear.
6. By injecting the material directly into the pleural or the
abdominal cavity.
Less freciuentl}', more dithcult operations are unlertakL-n for
injecting or applying the material to various internal parts of the
body,—for example, into the duodenum, to avoid the action of
the gastric juice.

Examination of Micro-organisms under the Microscope.
Bacteria are frequently examined in a fresh (living) condition,
in order to determine whether they are motile or not, but more
particularly to study their mode of development. A small
quantity of the material to be examined is brought upon a glass
slide in a drop of pure water, and covered with a cover-glass,
when it is ready for examination under the microscope. For a
more careful study the method of hanging-drops is used. A
drop of bouillon on a cover-glass is inoculated with a very
minute quantity of the material ([lure culture), and the cover-
glass placed with the dro[t on the under side upon the concavity
of a hollow object-glass (Fig. 18 «), the sides of the cover being

then fixed to the slide (object-glas^) by means of wax, fat, or
paraffine, to prevent evaporation. The development of the bac-
teria may be observed for hours in succession. If it is desired
to maintain a constant temperature above that of the room, the
beatable object-table may be used.