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BIOLOGICAL STUDIES ON THE BACTERIA OF THE MOUTH. 83

display a violet color, and if the latter are immediately trans-
ferred to a new plate a pure culture of the given bacterium may
be easily obtained. The brief period of action of the iodine
solution does not destroy these organisms, at least not all of them,
and consequently its application aftbrds an excellent means of
determining and isolating them. They also flourish on ordinary
nutrient agar-agar, but not on gelatine at room temperature.
The reaction is best observed in media containing sugar, less
plainly in amylaceous media. When cultivated on the latter, the
colonies often show concentric variously-colored rings, thereby
giving rise to very delicate and pretty patterns.
In form and in reaction this micrococcus exactly coincides
with one which is found in carious dentine, and which produces
the violet color characteristic of decayed dentine on addition of
the iodine solution. The same has hitherto, without any defi-
nite reason, been considered as " elements of Leptothrix buccalis."
The cells of the Jodococcus magnus are on the average larger
than those of the coccus occurring in dentine ; yet the difl:erence
is not so great that it may not be explained by the great dissimi-
larity in the conditions of growth.
h. A small micrococcus, of which I have succeeded in obtain-
ing a pure culture recently, which, however, I have not more
closely examined. It also gives a blue to violet color with iodine.
c. A micrococcus which gives a beautiful pink color under the
action of iodine. I have observed a slight development of this
bacterium on nutrient agar-agar, but have not been able to per-
petuate it in pure culture.
Other bacteria, whieh are colored slightly blue or violet by
iodine, also occur in the mouth. Their reaction is, however, too
slight to justify a farther examination in this connection.
I have furthermore obtained in pure cultures two yeast-fungi
from the mouth, which show characteristic reactions with iodine.

Cultivable Mouth-Bacteria, partly Xon-Pathogenic, partly
OF Unknown Pathogenesis.
The great number of difterent kinds of bacteria which have
been obtained in pure culture from the mouth has hitherto made
their classification impossible. We are also unable, with few