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112 THE MICRO-OROANISMS OF THE HUMAN MOUTH.

and 1885, have been verilied by ditterent investigators, Vignal®^
investigated the action of seventeen ditterent month-bacteria cul-
tivated on various nutrient substances, particuhirly on such con-
taining carbohydrates. Seven of these micro-organisms dissolve
albumen, five cause it to swell up or make it transparent, ten
dissolve fibrin, four cause it to swell up and become transparent,
nine dissolve glutine, seven coagulate milk, six dissolve caseine,
three transform starch, nine convert lactose into lactic acid,
seven invert crystallized sugar, seven ferment glucose and
partially convert it into alcohol.
Hneppe*^^ also calls attention to the presence of lactic acid in
the oral caA^ty. He isolated two ditterent micro-organisms (one
of which seems to be identical with one described by me), which
formed lactic acid in saccharine solutions.
As already mentioned above, by-products, such as butyric
acid, formic acid, acetic acid, etc., are often produced in lactic
acid fermentation of carbohydrates. But, as far as my observa-
tion goes, these In'-products are produced in comparatively very
small quantities, so that they perform no important role in the
various processes in the human mouth. Moreover, direct state-
ments as to the detection of these acids in the human mouth are
entirely wanting in the literature of this subject. A great deal
has been said about butyric and acetic acids as causes of dental
decay. These statements, however, have no scientific founda-
tion whatever. Any other proof of the presence of these acids
in the human mouth than that which I myself have produced
has not l)een given.

2. The Spontaneous Bntijric Avid Fermentation
does not appear to take place in the human mouth ; at any rate,
the Bacillus butyricus has not been detected in it ; furthermore,
the free access of air is not favorable to the development of this
bacterium. Whether other kinds of the butyric acid forming
bacteria, which are tolerably widespread in nature, occur in the
human mouth and there cause their characteristic fermentation,
is not known ; the possibility is not to be excluded. I only affirm
that as yet the occurrence of butyric acid fermentation in the
human mouth has not been proved.