Again, in nitrous oxide the elements nitrogen and oxygen are in chemical combination with each other, while in atmospheric air there is no apparent chemical union whatever.

Medical Properties And Physiological Action

Concerning the therapeutic application of nitrous oxide, Dr. L. Turnbull says: "Neuralgia, uncomplicated, will sometimes be relieved by a few inhalations of nitrous oxide gas. Nervous aphonia, this peculiar form of loss of power over the voice, usually the result of hysteria, will be much improved by the patient inhaling sufficient nitrous oxide gas to produce a partial loss of sensation and muscular relaxation. Local paralysis has been benefited, where there was no brain lesion, by the gentle stimulation by the first stages of the gas, or the tingling and stimulating effect on the muscles. Asthma, when of a spasmodic character is often much improved by causing the patient to pass into the stage of relaxation, employing it every other day for a week or two. It also tends to expand the lungs." Dr. George J. Ziegler found the solution or the gas, in water, of much utility in diseases of the lungs, kidneys, and other affections of this class. Dr. M. Price claims to have employed nitrous oxide gas in many cases of phthisis with advantage, and a number of dentists have been told by consumptive patients that they have been benefited by the inhalation of nitrous oxide gas.

Nitrous oxide gas is not only the most pleasant, but is, combined with oxygen, the safest general anaesthetic in use, and the greatest objection to its administration is the very short anaesthetic stage which it induces, unless the inhalation of the gas be continued, which is impossible in operations upon the mouth. When inhaled, the first effect is dizziness, with ringing noises in the ears, a tingling sensation, extending to the extremities, an uplifting of the whole system, followed by fulness or expansion of the chest, and a loss of sensation throughout the entire body.

According to the temperament, the stage of excitement is transient or prolonged; in some cases there are strange illusions, with a form of intoxication, which may be manifested by declamation, singing, laughing or crying, or melancholy, with a disposition at times to assault all near. Such effects, if the administration is not interrupted, soon pass off. For surgical operations, the gas is given with less admixture of air, and the inhalation persisted in until the stage of excitement is overcome and insensibility produced, when the face becomes exceedingly pale, the respirations, at first shallow, become deep and stertorous, the jaw fixed, the eyes protruding, and a bluish and purplish color about the lips and face, the patient presenting a very alarming and death-like appearance, a condition of which Bartholow says: " So far as the exterior phenomena can afford any indication of the nature of the action, is an asphyxiated state. The blood ceases to be oxygenated, carbonic acid accumulates, and the centres of conscious impressions are rendered inactive in consequence of the deficient supply of oxygen and the excess of carbonic acid. The rational indications of the nature of the narcosis produced by nitrous oxide are confirmed by physiological experiment. It has been found that the exhalation of carbonic acid is decidedly diminished by the inhalation of nitrous oxide, and that animals live no longer in an atmosphere of this gas than in an atmosphere of hydrogen." The same author speaks of the fatal cases that have occurred, as being with propriety attributable to the lethal action of this gas, and refers to various cases under his own observation in which nervousness, vague mental symptoms and headache have been experienced after the inhalations; at the same time he pronounces nitrous oxide to be almost free from danger. Prof. H. C. Wood believes that nitrous oxide acts as an anaesthetic by shutting off oxygen. There is no doubt but that the prompt action of nitrous oxide gas, and the rapid subsidence of the narcosis, have much to do with its safety, and account for the impunity with which it is used. According to recent investigations, nitrous oxide gas has no direct effect upon the heart and vasomotor system, but indirectly causes a rise of arterial pressure by the slight asphyxia it produces. Although the anaesthesia may 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 generally induced in from thirty seconds to a minute and a half, insensibility 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 abscess, boil or felon, or even amputating fingers, etc. The disadvantages 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 consists of an iron cylinder containing 100 gallons or more of the condensed or liquefied nitrous oxide, to which is attached a rubber gas bag and inhaling tube with a double valve and mouthpiece. The patient, for dental operations, is seated in a suitable chair which will admit of the back being lowered to such a degree 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 administering ether or chloroform. (See Ether.) The anaesthetic state, or