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200 DENTAL MEDICINE.

The quantity of arsenious acid to be employed for devitali-
zation will depend upon the structure and class of the tooth,
varying from the jU-, z^-, A to the ^V o( a grain ; also the length
of time the arsenical preparation should remain in the tooth, as
the condition of the pulp and tooth, the age of the patient, the
quality of the tooth structure and the susceptibility of the patient
should all be considered. While in most cases pulps are readily
devitalized by the application of a moderate quantity of the
agent, in other cases it appears to be impossible to accomplish
this object without extra measures are resorted to. In teeth of a
soft, frail structure, owing to an excess of organic matter, the
arsenic is rapidly absorbed ; but if, on the other hand, the tooth
is of a dense structure, the retention of the arsenical preparation
for a much longer time may not be attended with any injurious
effects, such as peridental inflammation. From twelve to twenty-
four hours are generally required to enable the arsenious acid to
properly devitalize the pulp of a tooth ; the difference in time
depending upon the quantity of the acid employed, as well as
upon other circumstances already enumerated. To produce a
speedy effect, the pulp should be freely exposed by the careful
application of the excavator, and the devitalizing agent applied
directly to the exposed surface of the organ. Accuracy as to
the quantity of the arsenious acid to be employed may be arrived
at by having a grain, in the form of the dry powder, divided into
forty, sixty, or one hundred parts. A pellet of cotton, on the end
of an excavator, may then be saturated with creasote or carbolic
acid or, what may be more painless, oil of cloves, and the desired
quantity of the powder, being taken up on the pellet, can be
placed directly in contact with the exposed surface of the pulp,
and secured in the carious cavity by means of a second pellet of
cotton, saturated with either sandarach or shellac varnish, a solu-
tion of gutta percha and chloroform, wax, or softened gutta
percha. To properly secure the arsenical preparation in the
cavity of a tooth, a concave disk of thin platinum may be placed
over it, and a temporary filling of soft gutta percha, or oxy-
phosphate of zinc, introduced into the carious cavity. Many
condemn the use of sandarach or other varnish to seal the arsenic