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92 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

(Fig. 1 , Plate III). My present opinion, however, is that the one
I obtained is not the one I have been seeking.
A number of times I have found cavities of decay, usually
dark brown, in which the surface of the dentine was colored
with a bright yellow mass of cheesy consistency. I have not
been able to obtain a pure culture of this bacterium on gelatine,
though I have repeatedly observed a slight growth on potatoes.
Any one who will keep a lookout for the two appearances
just described will certainly see them. A case which was inter-
esting in more than one respect occurred at the polyclinic of the
Dental Institute at Berlin, some time ago. A man presented
himself, having a swelling on the right side of the face, almost
as large as a man's fist, connected with the inferior wisdom-
tooth (impeded eruption). The larger portion of the surface of
the mouth and tongue was covered with a canary-yellow deposit,
which could not be accounted for by anything that the patient
had taken into his mouth.
I found a bacillus in the pus which was evacuated upon the
extraction of the tooth, and also in the yellow layer upon the
surface of the cheeks and gums, which reproduced the same
color in pure cultures, and besides showed considerable patho-
genic action. I had no opportunity to see the patient again,
consequently do not know the result of the infection. A pure
culture of this micro-organism on gelatine is seen in Fig. 2 of the
plate.
I have found in the human mouth and isolated no less than
eight diiierent kinds of bacteria which produce a yellow^ pigment,
not including the well-known yellow sarcina. These bacteria
are themselves yellow, but do not impart any color to the culture-
medium.
I have made a great many attempts to cultivate the sup]»osed
])acterium of greenstain, but so far without success. I have
indeed isolated five ditferent species of bacteria from the mouth
which impart a f/reen color to the culture-r/iedi'i, although themselves
colorless, and all of which grow well on the usual media, l)ut I
do not bring any of them into causal connection with the green-
stain, since, as far as my observation goes, the bacterium of
g-reenstain, if there be such a thing, does not grow on gelatine.