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LOCAL ANESTHESIA. 417

end. When this instrument is to be used, tie a piece
of oiled silk or membrane loosely over its inferior
end, fill it expeditiously two-thirds full with the ice
and salt, prepared as above, adjust the follower and
spring in place, screw on the cap, and apply at once.
The sac of the instrument is to be pressed and worked

gradually down till it invests a portion of the gum on
each side of the tooth to be extracted. As the ice
melts in the sac, the follower forces the unmelted
portion down next to the tooth and gum. The appli-
cation should be continued from one to three minutes,
or till the margin of the gum is congealed—as will
be indicated by its hardness and whitened appear-
ance—and then the tooth should be extracted as
expeditiously as possible, though with all the ordinary

skill and care.
If the contiguous teeth are sound, and not to be

extracted, they must be protected as far as possible
from the influence of the application—as they may
be, by having their crowns enveloped in thin sheets
of wax, oiled silk, or any other substance that is a
non-conductor, and is not too bulky. Where some

such protection is not afforded, great injury is liable
to ensue.

If the tooth to be extracted is sensitive, the tem-
perature should be reduced by holding in the mouth
cold w ater, and finally a piece of ice; and immediately
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