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OF THE CAVITY OF THE TEETH. 53
never to undergo any alteration, when completely formed, but
by abrasion; they do not grow softer, like the other bones, as
we find in some cases, where the whole earthy matter of the
bones has been taken into the constitution.
From these experiments it would appear, that the Teeth are
to be considered as extraneous bodies, with respect to a circula-
tion through their substance; but they have most certainly a
living principle, by which means they make part of the body, and
are capable of uniting with any part of a living body ; as will
be explained hereafter : and it is to be observed, that affections
of the whole body have less influence upon the Teeth than any
other part of the body. Thus in children affected with tho
rickets, the teeth grow equally well as in health, though all the
other bones are much affected ; and hence their Teeth being of a
larger size in proportion to the other parts, their mouths are
protuberant. (?',)
OF THE CAVITY OF THE TEETH.
Every Tooth has an internal Cavity, which extends nearly the
whole length of its bony part. It opens, or begins at the point
of the fang, where it is small ; but in its passage becomes larger,
and ends in the body of the Tooth. This end is exactly of the
shape of the body of the Tooth to which it belongs. In general
it may be said, that the whole of the Cavity is nearly of the
shape of the Tooth itself, larger in the body of the Tooth, and
(?/) [The dentinal tubules and their ramifications, the lacunae and
canaliculi of the cement, and even the inter-fibrous spaces of the enamel,
are probably all provisions by which fluid of a nutrient character may
permeate the dental tissues. But there is no proper circulation through
the calcified structures of the human tooth, unless in those exceptional
instances in which the Haversian canals may be traced in the cement or
dentine. Change of material is much slower than in bone, as is proved
by the above experiments of Hunter, which have been confirmed by the
observations of Flourens and others. (1) There can be no doubt, how-
ever, that the formation and development of the teeeth are considerably
influenced by constitutional states. Early caries having its origin in a
faulty condition of the dental tissues is one of the most frequent results
of a weakly, ill-nourished childhood.]

(1) Kulliker, op. cit., p. 309.