146

PATHOGENIC BACTERIA.

it is seen to touch the colony and take part of its con-
tents away. In this maneiivre the wire must not toitch
the objective^ the glass^ or anything except the colony.
Having secured the adhesion of a few bacteria to the
sterile wire, the pure culture is made by introducing
them into a sterile culture-medium.

If the pure culture is to be made in bouillon, the tube
is held obliquely, so that when the cotton plug is can-
tiously removed no germs can fall in from the air. The
plug is removed by a twisting movement. The wire, with-
out being allowed to touch the mouth or sides of the
tube, is plunged'into its
contents and stirred about
until the bacteria are de-
tached, and is then re-

FIGS. 31, 32.—The various appearances of colonies of bacteria under the
microscope : a, colony of Bacillus muscoides (Liborius) ; b, colony of Bacillus
anthracis (Fliigge).

moved and the plug replaced. The wire should be im-
mediately sterilized by heating to incandescence, lest the
bacteria be pathogenic and capable of doing subsequent
harm.

If the culture is to be made in gelatin, a different
method is employed. The tube is either held horizon-
tally, or, as is perhaps better, inverted ; the cotton plug-