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Full text of "Pathogenic Bacteria"

ANTHRAX.

359

fuchsin, the bacilli decolorized with a very weak acid and
then counter-stained with a watery solution of methyl blue.
. Upon the surface of gelatin plate-cultures the bacillus
forms beautiful and highly characteristic colonies (Fig.
103). To the naked eye they appear first as minute

FIG. 103.—Bacillus antliracis: colony upon a gelatin plate; x 100 (Frankel and

Pfeiffer).

round whitish dots occurring upon the surface, and caus-
ing liquefaction of the gelatin as they increase in size.
Under the microscope they can be seen in the gelatin as
egg-shaped, slightly brownish granular bodies, not attain-
ing their full development except upon the surface, where
they spread out into flat, irregular, transparent growths
bearing a partial resemblance to tufts of curled wool.
From a tangled centre large numbers of curls extend,
each made tip of parallel threads of bacilli. As soon as
the colony attains any considerable size liquefaction be-
gins. These colonies make beautiful adhesive prepara-
tions. If a perfectly clean cover-glass be passed once
through a flame and laid carefully upon the gelatin, the
colonies can generally be picked up entire when the glass is
removed. Such a specimen can be dried, fixed, and stained
in the same manner as an ordinary cover-glass preparation.