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46 CARIES OF THE TEETH.

to the dentine. Decay is found at the terminations
or intersections of these fissures earlier than at any
intermediate points. The indentations, or grooves.

on the sides of the teeth, are usually attacked by ca-
ries at that point next to the neck. Less frequently.
the disorder is exhibited at the neck, just beneath the
border of the enamel, under which it barrows with a
transverse extension.
The order in which the elements are removed, is
governed by the nature of the agent which effects the
decomposition ; and this is usually one having an
affinity for the calcareous elements strong enough to
destroy the texture of the dentine, and remove the

earthy portion. Those acids which have an affinity
for the lime of the dentine, produce its decomposition
in this manner. When the decay is thus caused, the
portion remaining in the cavity is soft, and approximates
the gelatinous condition as the calcareous material is
abstracted. Agents of a different character, too. often
produce decay. Alkalies will act upon the animal
portion of the dentine, and remove it; and in caries
thus produced, the residue is friable and chalk-like.
In other cases the constituents are simultaneously
removed. Nitric acid will cause an entire breaking-
up of both the earthy and the animal constituents.

The dentine outside of the decay may be in an in-
flamed and irritable condition, so that contact with the