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NITROUS OXIDE. • 477

be due in a measure to the non-oxygenation of the blood during
the presence of this gas in the blood, yet it causes anaesthesia
aside from such influence by a direct action on the cerebral
cortex. The after-effects are rarely disagreeable, and generally a
slight dizziness which soon passes off. Nitrous oxide gas has
the advantages of safety ; also rapid anaesthesia, which is gener-
ally induced in from thirty seconds to a minute and a half, insen-
sibility often occurring before complete unconsciousness ; also
the pleasant odor and taste, thereby preventing repugnance and
nausea; and the complete recovery from its influence without
unpleasant after-effects. It generally requires six gallons or less
to produce anaesthesia with nitrous oxide gas ; hence the rubber
bag from which it is inhaled should have a capacity of about eight
gallons. Nitrous oxide gas is a very useful anaesthetic in all
minor operations, such as the extraction of teeth, opening an ab-
scess, boil or felon, or even amputating fingers, etc. The dis-
advantages it possesses are its brevity of action, and the difficulty
of carrying it from place to place ; but its advantage is its almost
absolute safety, as few deaths have been caused by it directly.
Mode of Administration.—The most improved apparatus con-
sists of an iron cylinder containing 100 gallons or more of the
condensed or liquefied nitrous oxide, to which is attached a rub-
ber gas bag and inhaling tube with a double valve and mouth-
piece. The patient, for dental operations, is seated in a suitable
chair which will admit of the back being lowered to such a de-
gree as will bring the patient to an almost horizontal posture, and
the head well supported. A piece of India-rubber or a firm cork
to which a thin, strong cord is attached, to prevent its slipping
down the throat, is placed between the teeth, so as to prevent
the closure of the jaws, for, unlike chloroform and ether, the
muscles become rigidly contracted under the influence of this
gas ; such a prop also prevents injury to the front teeth by the
patient biting too hard on the mouth-piece of the inhaling tube.
The patient is then directed to breathe deeply and regularly, the
nose being held, to prevent the admixture of atmospheric air, and
the same precautions observed as are necessary when administer-
ing ether or chloroform. (See Ether.) The anaesthetic state, or