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60 CARIES OF THE TEETH.

There are acids taken with the food that act di-
rectly upon the teeth; as acetic acid, or vinegar.
Professor Westcot says: " Acetic and citric acids so
corroded the enamel in forty-eight hours, that much
of it was easily removed with the finger-nail." And
"Malic acid, or the acid of apples, in its concentrated

state, also acts promptly upon the teeth." Now, these
acids, in the use of many kinds of food, are brought
into frequent contact with the teeth. In the manufac-
ture of vinegar, sulphuric acid is often employed; so
that in this article of food we have that acid either
alone or combined with the acetic, the former acting
with greater energy upon the teeth than the latter.
Acetic acid also facilitates the fermentation of food

retained in the mouth, and thus reproduces itself in
abundance.
After eating apples that contain a great amount of
malic acid, the teeth will be found corroded over all
their surfaces. This acid, as well as the others, affects
the enamel somewhat, and when the latter is very thin,
though it may not be all removed from any particular
point, yet its integrity will be destroyed, so as to be
readily fractured, thus admitting injurious agents to
contact with the dentine, which is much more suscepti-
ble of injury from acids than the enamel: points
imperfectly protected by this are violently attacked

by acetic, malic, and sulphuric acids. In decayed