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
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
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.