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ETIOLOGY OF CARIES. 737

not always a stranger, or because the delicateness of its tissue was not able
to resist the agents with which teeth are constantly brought in contact, the
ivory becomes the seat of a change which affects at the same time its color
and the force of cohesion w^hich unites its particles. A yellow or brown
spot manifests itself near the enamel, Avhich it invades by degrees until it
extends upon the surface of the crown. This envelope loses in this respect
its transparency, a natural consequence of the separation of the elements
which constitute it. Whilst the interval layer of ivory which unites the
enamel with the subjacent layers is not destroyed, the spot preserves the
color, and even shining aspect, which belongs to the teeth ; but it loses this
brilliancy as soon as the connection is severed which binds the ivory and
enamel together."
He then proceeds with the presentation of the usual arguments in
favor of the old hypothesis, which are fairly represented in the above.
It is easy for us of the present generation to see that these arguments
were based upon erroneous observations, but we must remember that
very many facts that are thoroughly established to-day were then either
unknown or the observations leading to their establishment were
accredited by comparatively few persons. And in this instance the
great majority of dental operators asserted that decay did begin in
the interior of the dentine. This illustrates some of the difficulties in
the way of advance of thought.
It must be remembered that at the time these works were written the
views expressed by Robertson and Regnard were in the most direct
opposition to the theory generally lield—namely, that caries resulted in
some way from inflammation of the dentine ; and, as might be expected,
they were not very readily accepted. These authors denied in toto the
influence of inflammation in the production of caries, and advanced
what has since been known as the chemical theory—that all caries of
the teeth is the result of chemical action or is caused by the operation
of a corrosive agent acting from without. This entirely precluded the
idea that decay ever, in any case, had its beginning in the internal parts
of a tooth, and the accuracy of the observations that led to that belief
was boldly questioned and denied. Further, the origin of the corrosive
agent was accounted for on the hypothesis (for it could not at that time
have been said to be proven) that it was produced at the very spot
where decay began by the lodgment and fermentation of particles of
food. Each of these authors proceeds to examine most attentively the
particular spots at which each of the several teeth are most liable to the
beginnings of decay, and finds that it never occurs on clean and smooth
surfaces, but, on the contrary, the attack is in all instances made at such
points as collect and retain alimentary particles, as in the interstices
between the teeth, in pits and grooves in the enamel, or at such points
as, from any cause whatever, retain particles until fermentation takes
place ; consequently, they claim that decay is caused by an acid produced
by the fermentation of particles of food at the spot where the decay com-
mences. So far as it is here expressed, I believe this view^ of the etiology
of caries to be strictly correct, and that the facts developed during the
succeeding years tend to confirm it.
When we consider the fact that at the time these authors wrote the
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