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THE DECAY OF THE TEETH, ETC. 169
most commonly externally, in a part where the teeth in their
most sound state receive little or no nourishment, we cannot
refer to that cause.
necks, and in the spaces produced by their formation and relative posi-
tion ; in regard to frequency, that it is in proportion to the depth of
the superficial depressions, and the degree and nature of the lateral
projections and interstices.
" This being the case, and decay never being found to commence upon
the plain and smooth surface of the tooth, it cannot for a moment be
doubted that the predisposition to caries depends upon the external
configuration or conformation of the teeth. It must be equally evident
from the partial nature of the disease, and from the insufficiency of all
general causes, as before pointed out, to explain its origin, that the ex-
citing cause of caries must be one whose operation is partial, and
having a peculiar action upon those parts of the teeth, which are by their
action predisposed to decay. The only cause of the partial operation and
the particular situations of decay, is the corrosive or chemical action of
the solid particles of the food which have been retained and undergone
a process of putrefaction or fermentation in the several parts of the
teeth best adapted lor their lodgment." (1)
Harris entertains similar opinions upon the nature of caries. According
to this writer : " Caries of the teeth is the result of the action of che-
mical agents, and not that of any operation of the animal economy, and
it consists simply in the decomposition of the calcareous molecules of
the organs. The fluids of the mouth, especially the mucous, when in a
vitiated condition, contain an acid, namely, the septic (nitrous), which
has a strong affinity for the earthy ingredients of these organs ; and it is
by the action of the former upon the latter that the affection is pro-
duced."^)
Mr. Tomes, in his Lectures on Dental Surgery (p. 199), has promul-
gated what has been termed the chemico-vital theory of caries. " If,"
he says, "the views I am about to explain are sound, caries may
be defined to be death and subsequent progressive decomposition of a part
or the whole of a tooth.
" I believe that the dentine from abnormal action loses its vitality,
and with the loss of vitality the power of resisting chemical action, and
that consequently the dead part is, under favouring circumstances, de-
(1) A Practical Treatise on the Human Teeth, by William Kobertson,
pp. 36. London, 1846.
(2) See the American edition of Fox's work, with notes by Chapin A.
Harris, M.D., pp. 161. Also Harris's Dental Surgery.