Page 268 - My FlipBook

266 DENTAL MEDICINE.
the anaesthesia, when the breathing suddenly ceases, instead of
using cold water externally and slapping the patient with wet
towels, Dr. H. A. Hare recommends pouring a quantity of ether
upon the belly, the shock caused by the cold produced by its
evaporation bringing on a very deep inspiration, followed often
by the normal respiratory movements.
Local Anaesthesia.—The fatality attending the use of general
anaesthetics led to the introduction of what are termed " local
anaesthetics," some of which depend upon the therapeutic prop-
erty of cold, which is properly an anaesthetic only when it freezes
the part to which it is applied. The use of cold for such a pur-
pose must necessarily be limited to small parts of the body, and
its utility depends upon the ease and rapidity with which a de-
sired spot of living flesh can be frozen, in other words, tempo-
rarily deprived of its vitality, without inflicting mechanical injury
on the delicate structure of the part.
According to Dr. Richardson, the proposer of the method, the
principle consists in directing on the part of the body a volatile
liquid, having a boiling point at or below blood heat, in a state
of fine subdivision or spray, such subdivision being produced by
the action of air or other gaseous substance on the volatile oil to
be dispersed. When it falls on a part of the body, it comes
with force into the most minute contact with the surface upon
which it strikes.
As a result, there is rapid evaporation of the volatile fluid, and
so great an evolution of heat force from the surface of the part
to which the spray is applied, that the blood cannot supply the
equivalent loss. The part consequently dies for the moment, and
is insensible ; but as the power of the body is unaffected, the
blood, as soon as the external reducing agency is withdrawn,
quickly makes its way again through the dead parts, and restora-
tion rapidly occurs.
• The fluids used are ether, of a specific gravity not exceeding
0.723, highly rectified, and as free as possible from either alcohol
or water—what is known as " absolute ether"—and rhigolene, a
product of petroleum, and the lightest liquid known, ethyl or
methyl chloride, and pental.