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416 ANESTHETICS.

nitrous oxide will sustain respiration for an indefinite
time.
To a patient in an anaesthetic state, it is not so
readily administered as chloroform or ether ; but the
patient under its influence, is quite as manageable as
with any other agent, and the anaesthesia as perfect,
but not as prolonged without continued administration.
It is scarcely justifiable in ordinary dental practice

to use a more heroic general anaesthetic than the one
here referred to.

LOCAL ANESTHESIA.

Because of the frequently prejudicial and sometimes
fatal consequences to which systemic anaesthesia is
liable, local anaesthesia has been brought into requi-
sition ; the first method of accomplishing this was by
Congelation.—This was effected by the applica-
tion of two parts of pulverized ice and one of salt,
•applied by means of an instrument of the following
description : a vulcanized India-rubber tube, about
five inches long and one inch in diameter, closed at

its superior extremity by a screw-cap, and open at its
inferior, which latter is slightly enlarged and cut out,
so as to leave two lips to reach down on the sides of
the tooth ; within the tube, a follower and a spiral
spring, the latter forcing the former down to the open