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PATHOGENIC BACTERIA OF THE HUMAN MOUTH. 271

show a strong acid reaction and develop considerable quantities
of gas. Subcutaneous inoculations of mice were followed bv
abscess and necrosis of the skin, occasionally resulting in the
death of the animal. Injections in the abdominal cavity inva-
riably produced the death of the animal in twelve to twenty-four
hours, the autopsi' revealing immense numbers of bacteria in the
abdominal cavity, a considerable quantity of a serous exudation,
peritonitis, etc. Onlv a verv limited number of larg^er animals
—two rabbits and two guinea-pigs—were inoculated. The ani-
mals appeared sick for a time, sitting quietly in the corner of
the cage and refusing to eat. After two or three days, however,
all symptoms disappeared.
Fig. 115.
/i. Bacterium gingivce pyogenes.
This bacterium was found in
the same mouth with the micro-
organism just descril)ed, and also
in a suppurating tooth-pulp of
a second person. It appears in
form of thick, short bacteria with
rounded ends, one and a half to
four times as long as thick. (See
Fig. 115, a.) In plate-cultures
it grows very rapidly, even at
Bacterium gixgiv.e ptogexes.
room temperature, the colonies
Culture in gelatine, 8 days old. «, single
being clearly visible to the naked
cells under 1100 : 1.
eye in twentj^-four hours. Under
the microscope they appear as beautiful, perfectly round, yellow-
ish colonies, with a sharp, dark border. The gelatine becomes
rapidly liquefied, so that in forty-eight hours the first dilution
is completely melted.
Line-cultures on gelatine appear in fifteen hours as a trough
of melted gelatine 1|- mm. broad, the side of the trough being
cloudy and the bottom marked by a line of white sediment.
Line-cultures in agar-agar present a thick, moist, slightly gray-
ish growth l)y transmitted light, having a slight greenish-yellow
tinge under the microscope, colorless at the margin, yellowish
brown toward the middle, and presenting a fibrillated structure.