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444                  PATHOGENIC BACTERIA.

most beautifully by Gram's method, by which it can be
best demonstrated in tissues.

Upon gelatin plates small white colonies are produced
in from twenty-four to forty-eight hours. Under the
microscope they are found to be spherical or elongate
(lemon-shaped), finely granular, and lobulated like a
raspberry or a mulberry. When superficial they form
white, elevated, rather thick masses 1-2 mm. in diameter
(Fig. 124). ^

In   gelatin   punctures a large white surface-growth

FIG. 124.—Micrococcus tetragenus: colony twenty-four hours old upon the sur-
face of an agar-agar plate; x 100 (Heim).

takes place, but very scant development occurs in the
puncture, where the small spherical colonies generally
remain isolated.

Upon the surface of agar-agar spherical white colonies
are produced. They may remain isolated or may become

Upon potato a luxuriant thick, white growth occurs.

The growth upon blood-serum is also abundant, espe-
cially at the temperature of the incubator. It has no
distinctive peculiarities.

The introduction of tuberculous sputum or of a most
minute quantity of a pure culture of this coccus into
white mice generally causes a fatal septicemia.