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0» THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

visible to the naked eye; under weak power without distinct
outlines or wholly transparent at the margin, becoming denser
toward the center, which has a grayish color. Under 320 diam-
eters the sector of a colony has the appearance represented in
Fig. 50. I have named this bacterium Micrococcus ncxifer on ac-
count of the loops formed by the chains of cocci in pure culture.
4. A bacterium somewhat less frequent, which appears under
the microscope as scattered, unequally large, irregular colonies,
composed of a few cells. These colonies are without distinct
form, dark gray : micrococci.
5. The bacterium which I mention as the fifth is conspicuous
to the naked eye for the size of its colonies. It appears in almost
all cultures, but in comparatively small numbers. To the naked
eye the colonies appear milky-white ; under the microscope they
show a gray margin and a yellowish to dark-brown center wholly
opaque. The margin of the colony is occasionally indented and
strongly refractive. Morphology: beautiful round cocci in dense
masses.
Fig. 49.
V •*
• w %»

mmf
Micrococcus
NEXIFER.
W
1100 : 1.
Sector op a Colony of Micro-
coccus NEXIFER 3 D.iYS OLD.
320 : 1.

6. A micro-organism which is remarkable for its very charac-
teristic growth may often be found on culture-plates, whether
inoculated from the secretions of the oral cavity or from decayed
dentine. It forms colorless, transparent, prominent colonies,
which obtain a heio;bt of 1.5 millimeter and a breadth of from
2.5 to 4 millimeters, having the consistency of paste. Under the
microscope the separate cells in form of chains of cocci are dis-
tinctly visible, lying scattered in this paste.