Page 246 - My FlipBook

242 PATHOLOGICAL CONDITIONS.
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result is a whitish mark, caused hj a union of the salt
with the albumen of the cuticle ; but this soon turns
black, by the reduction of the salt and the liberation of
the oxide of silver ; when, for each atom of this set
free, there is liberated an equivalent of nitric acid.
There is here, then, an agent that acts promptly on the
gelatinous portion of the tooth, destroying its vitality
to the extent of the combination which takes place, and

that, by the decomposition of part of the salt, and the
consequent liberation of part of the acid, also acts
with energy on the calcareous portion. The compound
formed by the nitrate with the organic constituents
of the tooth, is insoluble except with a few substances,
and therefore protects the subjacent parts ; and the
precipitation of the reduced oxide on the surface, it is
claimed, affords some additional protection. The in-
solubility of the compound above mentioned, prevents

an absorption of the nitrate by the dentine, and ren-
ders its action necessarily superficial. When the
nitrate is neutralized by a union with it of an equiva-
lent of the constituents of the dentine, no further
chemical action is possible. The compound formed by
this union is soluble in a dilution of the nitrate ; and
if this be applied in too great a quantity, there may
be a larger loss of substance than is desirable or at all
necessary; for, as long as free nitrate remains in
solution in the- cavity, the insoluble compound is not