"surgical period," as it is termed, is generally manifested by snoring, although this symptom does not invariably occur; when it does, however, it indicates a state of profound anaesthesia, to which it is unnecessary to carry the patient when performing many minor surgical operations.

As more or less excitement follows the inhalation of this gas, when it is largely mixed with atmospheric air, such a condition is either prevented or abbreviated by holding the nose of the patient during the inhalation. The patient should not partake of food for at least two hours before the administration of the gas, but at the same time should not be in a weakened condition for want of it; and the dress, if tight, should be previously loosened, and as soon as the operation is completed the head should be gently moved to one side, to allow the blood to escape from the mouth. Fresh air should then be admitted into the room, and the patient supplied with it by means of a fan. (See Administration of Anaesthetics.)

Therapeutic And Dental Uses

According to the investigations of Dr. Ziegler, nitrous oxide is an efficient restorative when administered either in its gaseous state by the lungs, or in conjunction with liquids by the alimentary canal. He recommends the use of this gas in moderate quantities, so as not to generate too much carbonic acid. Regarding nitrous oxide and oxygen as of primary importance in asphyxia, and the natural antidotes to narcotizing agents and asphyxiated conditions, he advocates their use whenever practicable, either alone or in combination with heat, and claims that they will often save life in apparently hopeless cases.

The rapid action of nitrous oxide and the transient nature of its effects on the system, render it a very useful anaesthetic agent for all minor surgical operations - such as extracting teeth, lancing abscesses, devitalizing nerves of teeth, etc., etc. It has also been successfully employed in the performance of some capital surgical operations, where the anaesthesia has been kept up from fifteen minutes to half an hour.

Nitrous Oxide And Oxygen Or Air, Combined

Oxygen gas may be combined with nitrous oxide gas with great advantage ; also nitrous oxide and atmospheric air, although the good effects of the latter mixture are not so well marked as those of former mixture, yet both mixtures lessen the unpleasant symptoms which may ensue from pure nitrous oxide. It is claimed for these mixtures absence from all blueness of the features, regular, softly-snoring breathing, muscular relaxation, and absence of conjunctival reflex ; also that the jerky muscular movements, especially common to children under nitrous oxide, are completely abrogated ; in fact that the presence of oxygen, or air with nitrous oxide renders the anaesthesia much safer. Dr. Hewitt claims that these mixtures are better than pure nitrous oxide for children, anemic and debilitated patients, for those who have previously exhibited great susceptibility, and are consequently difficult to manage in dental practice for the reason of the short period of available anesthesia, those who under nitrous oxide alone have experienced very disagreeable sensations, patients advanced in years, those with large tonsils, and those suffering from heart or lung diseases. An apparatus is now manufactured, based on the ideas of Dr. Hewitt, but with certain modifications, for combining nitrous oxide and oxygen gases or air, which are very satisfactory in carrying out this "non-asphyxial method," as this mixing together of the two gases, or air, and their administration is called. The anaesthesia is produced by the nitrous oxide alone, the office of the oxygen, or the air, being that of a modifier of the effects of the nitrous oxide, as there is no danger of asphyxia from such combinations. There are two cylinders in this apparatus, one for the nitrous oxide and the other for the oxygen, and a mixing chamber in which the combination occurs, and from which the combined gases flow to the inhaler. If nitrous oxide alone is used with this apparatus, there is always on hand the oxygen, which the opening of a valve will admit at once to overcome any tendency to asphyxiation which may develop.

Dr. Hewitt's conclusions on the administration of definite mixtures of Nitrous Oxide and Air and of Nitrous Oxide and Oxygen, are as follows: "1. When pure nitrous oxide was administered to the human subject in such a manner that no free oxygen gained admission during the administration, certain phenomena arose which might be regarded as being either (1) phenomena of anaesthesia or (2) phenomena of asphyxia. 2. The anaesthetic phenomena of nitrous oxide, although apparently very different from those of ether or chloroform, were in their essential features remarkably similar. 3. The most conspicuous of the asphyxial phenomena of pure nitrous oxide were (1) embarrassed and deeply stertorous breathing; (2) cyanosis; and (3) anoxemic convulsion. All these might be eliminated without interfering with the anaesthetic effects of the gas by administering with it certain proportions of oxygen, either pure, or as atmospheric air. 4. There were other less obvious asphyxial phenomena, such as wide dilatation of the pupils, swelling of the tongue and adjacent structures, and rapid cardiac action, which, like the more important symptoms above referred to, might be prevented or modified by similar means. 5. Under the influence of pure nitrous oxide breathing became deeper and quicker than usual. At the end of from 55 to 66 seconds its rhythm became altered either by (1) obstructive stertor, (2) anoxemic convulsion attacking the respiratory muscles, or (3) both conditions combined. Paralytic cessation of breathing was very rare, and when it occurred was dependent quite as much upon cerebral anemia from defective circulation as upon the presence of un-oxygenated blood in the vessels supplying the respiratory centres. 6. The deep and obstructive stertor of pure nitrous oxide narcosis was not met with when employing mixtures containing moderate percentages of air or oxygen. With such mixtures only soft snoring breathing was produced. When the percentage of air or oxygen was considerable (thirty per cent of air or thirteen per cent. of oxygen) respiration became less and free from all obstruction. 7. The most marked cyanosis was met with when very small percentages of air (from three to six per cent.) or oxygen (under three per cent.) were administered with nitrous oxide. As the percentage of air or oxygen increased cyanosis lessened, till with 30 per cent of air it was very slight, and with 11 per cent of oxygen it disappeared altogether."

Dr. Hewitt goes on to state that the same favorable results occurred with the mixture of air or oxygen in regard to such symptoms as anoxemic convulsion, reflex excitement movements, etc., which were much more pronounced when pure nitrous oxide was administered; also that the duration of the anaesthesia was found to be longest after the administration of mixtures containing from 3 to 11 per cent of oxygen, the maximum duration having been attained with 7 per cent mixtures; and that with nitrous oxide and air mixtures the resulting anaesthesia was distinctly longer than with pure nitrous oxide, but the results were very uncertain in these cases. The shortest anaesthesia was recorded with nitrous oxide alone and with nitrous oxide mixtures containing 30 per cent of air. His best results were obtained with mixtures of nitrous oxide and oxygen, the next best with nitrous oxide and air, and the worst with nitrous oxide free from air or oxygen. He also found that there was no one mixture of nitrous oxide with air or with oxygen which would successfully anaesthetize every patient. also that mixtures containing 5, 6, or 7 per cent. of oxygen were the best for adult males, and mixtures containing 7, 8, or 9 per cent. the best for females and children; that the next best results to those last mentioned were to be obtained by mixtures of nitrous oxide and air, from 14 to 18 per cen. of the latter being advisable for anaesthetizing men, and from 18 to 22 per cent. for anaesthetizing women and children.

At a recent meeting of the Paris Academy of Medicine, a method was suggested to obviate the disagreeable incipient effects of nitrous oxide gas, which are often manifested by bad dreams and the perception of noises aroused in the mind of the patient when still in a state of partial consciousness, by soothing strains of sweet music by a powerful phonograph, the tubes of which are applied to the patient's ears before the gas is administered and during the operation of extracting teeth.