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BIOLOGICAL STUDIES OiY THE BACTERIA OF THE MOUTH. 93

I found one of these in the contents of an alveohir abscess ; it
grew with tolerable rapidity, liqnelying the gelatine. If culti-
vated without the presence of oxygen, no color is developed, but
if the culture is shaken with air, it will in a few seconds assume
a beautiful green color. I found the second in a cavity of decay,
and the other three in my search for the supposed bacterium of
pyorrhoea alveolaris ; they are colorless, but impart a beautifiil
opalescent color to the gelatine, one of them ha\'ing at the
beginning a decidedly bluish tinge. A pure culture of one of
these is seen in Fig. 3 of the plate. It is, however, impossible
in the lithograph to reproduce the beautiful opalescent color of
this growth. The cultures of one bacterium obtained fi-om the
mouth have a red color on the surface, but are colorless beneath
the surface (Fig. 1, plate) ; the protoplasm of the living cells con-
tains the coloring-matter, and no color is imparted to the gela-
tine. Another has a reddish color, also confined to the bacteria
themselves. Cultures of still another have a decided brownish
color (Fig. 4, plate) ; it liquefies the gelatine, and sinks to the
bottom as a brownish irregular mass.
I have recently isolated a bacterium from the mouth occurring
in form of long large rods and jointed threads, which, cultivated
on the surface of nutritive agar-agar, imparts to the medium, in
the course of a few weeks, a vellowish-brown color which errad-
ually darkens and extends deeper into the substratum as the age
of the culture increases. To this bacterium, whose character-
istics I have not yet sufficiently investigated, I have assigned the
name, Bacillus fuscans.
I shall not enter into a discussion of the biologs' of these bac-
teria. At present we are interested in the question as to what
part they may take, if any, in the production of the various colors
or shades of color in carious dentine.
Of all the chromogenic bacteria above referred to, only the
ones represented in Fig. 4 of the plate and the one described as
Bacillus ftiscans could be looked upon as taking any direct part
in the pigmentation of carious dentine. These, however, as tin-
as we knoAv at present, do not occur with sufficient constancy in
the mouth to admit of assigning an important role to them.
The green-producing bacteria, which I liave named Baderia