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ARSENIOUS ACID. I99

Dental Uses.—The devitalizing power of arsenious acid being
far more powerful than its escharotic power, it has been em-
ployed for many years to destroy the vitality of the pulps of
teeth, for which purpose it is generally combined with either the
acetate or sulphate of morphia and sufficient creasote to form a
paste, to prevent, or at least mitigate, the extremely painful action
of the arsenic when topically applied to living tissue. It was for-
merly supposed that creasote was a solvent for the arsenic, but this
is now denied. Carbolic acid may be substituted for the creasote.
As the danger of absorption is great, there is considerable risk
in applying arsenious acid to the teeth of young persons, or those
very susceptible to the influence of this agent ; hence other
escharotics, such as repeated applications of carbolic acid, or
pepsina porci, with dilute hydrochloric acid, or nitric acid,
chromic acid, or chloride of zinc, or the galvanic cautery, or the
surgical method of introducing into the body of the pulp a
barbed wire, are employed in such cases. The arsenious acid,
when employed for the devitalization of dental pulps, has been
combined with pulverized charcoal, under the impression that the
latter prevents the rapid absorption of the arsenic, and thus limits
its action mechanically rather than therapeutically.
The creasote (or carbolic acid), employed in combination with
the arsenious acid as a nerve paste, obtunds sensibility, acting as
a styptic, antiseptic and escharotic ; hence some depend upon
this agent alone to modify the action of the arsenic, and dispense
with the morphine.
Tannic acid and tincture of aconite are sometimes substituted
for the morphine and creasote, or carbolic acid in the preparation
of a nerve paste. Arsenious acid is also employed alone, in the
form of a dry powder, to devitalize pulps of teeth ; but it is not
only more painful, but less prompt in its action than when it is
combined with other agents. Previous to the application of the
arsenical preparation, chloroform, tincture of aconite, sulphate
of atropine, cocaine, etc., may be applied to the exposed portion
of the pulp, and the painful effect of the arsenic be thus modi-
fied. The spray of rhigolene, or absolute ether, has also been
employed for this purpose.