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PATHOGENIC BACTERIA OF THE HUMAN MOUTH. Ibl

pathogenic micro-organisms entering the mouth from time to
time some may obtain at least a temporary foothold, or may
propagate themselves for a certain length of time, as long as the
conditions remain favorable, or finally may establish themselves
permanently.
The observations of many bacteriologists have led to the
unanimous conclusion that there is a large number of well-char-
acterized mouth-microbes which will not grow on any of the
artificial nutrient media now in use. The thought therefore
suggests itself that there may be other bacteria in the mouth,
which, possessing no striking morphological features and not
growing on artificial media, have thus far escaped detection, and
which, nevertheless, may possess pathogenic properties which
they may unfold under propitious circumstances.
For the present, therefore, we distinguish two groups of
pathogenic mouth-microbes, the non-cultival)le and the culti-
vable.
1. ]SrON-CULTIVABLE PATHOGENIC MoUTH-BaCTERIA.

As has been stated above, there is a considerable number of spe-
cies of bacteria in the mouth which do not appear to grow on any
of the media at present in use among others, Leptothrix innomi-
;
nata, Bacillus buccalis maximus, Jodococcusvaginatus, Spirillum
sputigenum, and Spirochsete dentium. These occur in every
mouth, the last-mentioned sometimes even in almost pure culture.
Nevertheless, all attempts at cultivation, and thousands of them
have been made, proved futile. For some years I myself made
hundreds of experiments with diverse solid and liquid nutrient
media, in order to obtain a pure culture of Spirillum sputigenum
and Spirochete dentium, but in vain. Up to the present, no
one, as far as I know, has been more successful than I.
Since these well-known microbes will not grow outside of the
mouth, we may suspect that there are other organisms in the
mouth, less known or wholly unknown, pathogenic as well as
non-pathogenic, which are not cultivable. This, of course,
renders it difficult, if not impossible, to acquire a knowledge of
their properties.
An important contribution to the study of this group of mouth-
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