Pathogenic Bacteria

SUPPURA TION.

187

as round disks with circumscribed, smooth edges. They
are distinctly granular and dark-brown. When the col-
onies are grown upon agar-agar plates the formation of
the pigment is much more distinct.

In gelatin punctures the growth occurs along the whole
length of the needle-track, and causes an extensive lique-
faction in the form of a long, narrow, blunt-pointed,
inverted cone (Pig. 52) full of clouded liquid, at the apex

FIG. 52.—Staphylococcus pyogenes aureus: puncture-culture three days old
in gelatin (Frankel and Pfeiffer).

of which a collection of golden or orange-yellow precipi-
tate is always present. It is this precipitate in particu-
lar that gives the organism its name, " golden staphylo-
coccus."

The most characteristic growth is upon agar-agar.
Along the whole line of inoculation an orange-yellow,
moist, shining growth occurs. When the growth takes
place rapidly, as in the incubator, it exceeds the rapidity