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CHAPTER VII.

original investigations on the decay of the teeth.

Introductory Remarks on the Histology and Chemistry of
THE Teeth.

The peculiar structure of the barcl dental tissues, especially of
the dentine, not only determines to a great extent the manner in
which the change designated as decay advances in the tissues,
but also accounts for the microscopic appearances characteristic
of this disease, and also greatly influences the spreading of caries
in the tissues. I shall, therefore, as briefly as possible, call atten-
tion to those structural properties of enamel and dentine, which
are of special significance.
Furthermore, an intimate knowledge of the chemical compo-
sition of the hard dental tissues is requisite to an understanding
of the process of decay.
Dentine forms the chief constituent or fundament of the
human tooth, and retains approximately the original form of the
tooth after the removal of the enamel and cement. For our
piirpose, dentine may be defined as a dense, glue-giving basis-
substance, impregnated with lime-salts and traversed by sheathed
tubules radiating from the pulp-chamber. These, the dentinal
tubules, have a diameter of 1.3-2.5/^; their average diameter is
consequently greater than that of bacteria, with the exception
of Crenothrix, Beggiatoa, and a few other species as yet not met
with in the human mouth. They are straight or slightly undu-
lating, and radiate from the pulp-chamber to the surface of the
dentine. They are not empty, but contain living matter, and,
b}" means of their many ramifications and anastomoses, form a
delicate net-work, particularly on the border of the enamel. The
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