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CAEIES OF THE TEETH. 65
organisms and the determination of their physiological charac-
ters in the production of fermentations or putrefactions.
Dr. W. D. Miller was at work with Dr. Koch in his bacteri-
ological laboratory when the means of cultivating microorgan-
isms on semi-solid media was first established and was at once
able to separate the microorganisms found in the mouth or in
carious dentin into species, and determine the character of each
in the production of acid fermentation or other forms of decom-
position. The finding in the dentinal tubules of microorganisms
which, when growing in artificial culture in the presence of any
form of sugar or starch, uniformly produced lactic acid, which
in time dissolved the calcium salts of the tooth tissue, completed
the full explanation of the local changes taking place in caries
of dentin, but the cause and the nature of caries of enamel was
not so clearly made out.
This history, briefly as it is written here, shows the principal
steps of the unfolding of a knowledge of this disease process
extending through many years of labor done by many individ-
uals, each building upon the discoveries which were made by
his predecessors. The outcome of this work has finally given
complete and exact knowledge of the steps in caries of dentin.
It will also be seen that the work of Dr. Miller was really the
finding of the exact method of the formation of the acids which
the older anonymous German writer (1530), Eobertson (1835),
Eegnard (1838), and others, described as being formed by
decomposition. This brief summary mentions the work of but
a few of the men who seem to have been most fortunate in the
finding and giving expression to facts that have advanced our
knowledge of the processes taking place in caries of the teeth.
As a matter of fact, many men have taken part in this work.
General, Statement.
Caries in its simplest expression consists in a chemical dis-
solution of the calcium salts of the tooth by lactic acid, followed
by the decomposition of the organic matrix, or gelatinous body,
which, in the dentin, is left after the solution of the calcium salts.
In caries of the enamel, the whole substance of the tissue is
removed by dissolving out the calcium salts, there being so little
organic matrix in the enamel that it will not hang together;
consequently a cavity is formed by the simple solution of the
calcium salts of which it is composed. This solution always
begins upon the surface, never in the interior. Decay of the
teeth is therefore caused by an agent acting from without the