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214: THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

much trouble. The alkaline products of the putrefjiug- pulp
and of the inflamed suppurating or disintegrating gums neu-
tralize the acids formed in the dental cavity by fermentation.
The process of decalcification ceases, partially at least, whereas
the dissolution of the already softened dentine proceeds. The
decalcified layer of dentine must gradually l)ecome thinner under
such circumstances. If a just extracted carious tooth be kept
in a putrefying albuminous solution for some length of time, the
softening of the dentine completely ceases, while the dentine
which has already been softened gradually disappears.

THE MICRO-ORGANISMS OF DENTAL DECAY.
Our knowledge of the micro-organisms most directly con-
cerned in the destruction of the substance of the tooth is as yet
very deficient. We have l>een able to establish the tact that all
micro-organisms of the human mouth which possess the power
of exciting an acid fermentation of foods may and do take part
in producing the first stage of caries ; also, that all possessing a
peptonizing or digestive action upon albuminous substances may
take part in the second stage ; and, finally, that those possessing
both properties at the same time may take part in the produc-
tion of both stages. But whether there is any one bacterium
which may always be found in decayed dentine, and which
might therefore be entitled to the name of /Ae bacterium of tooth-
decay, or whether there are various kinds which occur with
considerable constancy, we are not able to say.
During my experiments upon the bacteria of decay in the
year 1883, I isolated four ditferent kinds of bacteria from decay-
ing dentine. These I described in the Independent Practitioner
for July, 1884.
I have frequently met with them in more recent investiga-
tions, and they have also been observed by others. I do not
consider the experiments I then made sufiieiently extensive or
conclusive to be incorporated here, and experiments now in
progress, with new methods and larger material, are not yet
concluded, it being necessary to examine at least fifty to one
hundred different teeth in order to arrive at satisfactory results.
The researches recently made by Vignal and Galippe,'^ and

^^