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70 THE MICRO-OROANISMS OF THE HUMAN MOUTH.

neutral media. Finally, I adapted my experiments to the boy's
food, and made up a mixture whose composition showed the
greatest possible similarity to the contents of the cavity. I fur-
thermore tried dentine glue instead of gelatine, which I pro-
cured by boiling decalcified teeth. Nevertheless, all these
attempts remained fruitless. Only line cultures atlbrded a very
limited growth, but the colonies never developed more than
fifteen to twenty cells, and a transference to a second plate
proved futile, no further growth taking place. Vignal's experi-
ments in reference to this question will be mentioned later.
It is very easy, as has been done by a writer in the October
number of the Oest. Ungar. VuTiefjahrsschnft filr ZoJmheilkuude,
1889, who signs himself tz, to account for the tailure to culti-
vate these micro-organisms on the assumption that they are
strictly parasitic (ride page 17), and consequenth^ cannot, under
any condition, grow when separated from their host. I find it,
however, more reasonable to explain the failure on the simple
ground that these bacteria are very sensible to slight changes in
the culture media, and that no one has yet succeeded in construct-
ing an artificial medium sutficiently similar to that found in cer-
tain mouths to admit of their cultivation. I have by no means
given up the hope of yet obtaining cultures of these most inter-
esting forms.
We must guard against the very common error of considering
every thread-forming organism which occurs in the oral cavity,
or is obtained in pure culture from the juices of the mouth, as
" Leptothrix buccalis," inasmuch as threads are formed by various
micro-organisms.

Leptothrix luiccalis.

Leptothrix buccalis is a name chosen by Robin "^ for those
organisms in the human mouth which were formerly described
as animalcula, tooth-animalcules, Blihlmann's fibers, denticolte,
Almost every living organism occurring in the mouth was
etc.
designated by this common name.
Hallier,^^ and many of his successors up to the present time,
adopted this view. The motile bacteria of the mouth were