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PRECAUTIONS TO PREVENT DENTINAL DISCOLORATION 425

the degree of caution which is the accompaniment of an intelligent use
of a force of signal service when carefully applied, but which recklessly
pushed may do injury.^

The Pressure Method of Obtunding the Pulp.
A method of applying cocain to the pulp under pressure has recently
come into use. It consists of laying over the exposed surface, after
the pulp is carefully and broadly uncovered, a small piece of amadou
(punk) filled with a saturated solution of cocain in absolute alcohol or
chloroform. The cavity is then filled with a piece of unvulcanized
caoutchouc. Pressure is effected directly upon the rubber Avith a broad
rounded instrument, so adapted in size that it will not meet with
impediment and yet not small enough to exert force directly upon the
point of exposure. The degree of pressure should at first be slight, and
be gradually increased as the cocain exerts its effect upon the pulp.
The force is exerted by successive steps, terminating when pain follows,
but maintained until the sensation ceases. At length when no pain is
produced by excessive pressure the rubber and punk are removed, when
the pulp is immediately removed by the usual means. This operation
is done quickly, to avoid the return of sensitivity.
Those who pursue this plan state that it produces nearly uniform
results and enables the canal and pulp chamber to be filled immediately.
The indications are that the cocain overcomes the sensitivity of the
surface of the pulp, and that pressure paralyzes the tissue by the com-
pression to which it is subjected. Were the cocain conveyed to the
apex, as when it is instillated, pain would not so soon return.

Precautions required to Prevent Discoloration of the
Dentin.
It sometimes occurs where arsenous acid produces much irritation
of the pulp that the violent congestion occasions disorganization of the
blood corpuscles, resulting in the distribution of the hcmatin throughout
the dentin. This most unfortunate result is liable to follow the applica-
tion to an already congested pulp when the application is made without
first subduing this condition. It is also more liable to happen when
under these circumstances the pulp has not been completely denuded of
the carious matter.
The removal of the ultimate layers of carious matter is important to
permit the pulp to bleed and thus to deplete the engorged vessels. It
is also necessary to avoid making an arsenical application until the
' The student will find much instruction in Price's "Foundation Principles of Den-
tal Cataphoresis," Items of Interest, vol. xx. p. 345 et seq.