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CARIES OF THE TEETH. 43

tained maturity, are exempt from its ravages. It is
a disease which the vital forces, owing to the nature
of the tissue, can but feebly withstand, at least with
far less efficiency than in more highly organized
structures ; and the restorative process is wholly in-
operative here. Some maintain that softened dentine
does in many cases regain its normal density ; but
this cannot be, unless it retains its vitality. But
any agent possessed of sufficient energy to decompose

the dentine, will destroy its vitality. What is that
decomposition ? Either a lack of vital power to
maintain the integrity of the organic structure, or
the action of some agent having an affinity for a cer-
tain part of the dentine more potent than that vital
power. In either case, the vitality is destroyed. In

an organized structure, removal of one of its essential
constituents occasions a loss of vitality.
Caries usually makes its first attack upon the den-
tine, and progresses most rapidly in the direction of
the tubuli. There are variations from this course;
as, for example, in the large superficial caries on the
labial surfaces of the superior incisors. In many
cases, too, it advances immediately beneath the en-
amel. Portions of the dentine imperfectly protected
by the enamel, on account either of an injured con-

dition or of an imperfect formation of the latter, are
liable to be attacked by this disease ; and points that.