Nitrous oxide has all the physiological properties which entitle a medicine to rank among the cerebral stimulants. In whatever mode introduced into the system, it especially stimulates the cerebral functions. But it has another important property, wholly independent of its powers over the nervous centres; that, namely, of directly oxygenizing the blood, which renders it highly useful in several morbid affections. Its exhilarating effect on the spirits, and the species of intoxication or delirium induced by it when inhaled, have been rendered familiar to every one through the public exhibition of its extraordinary powers in this respect. The most remarkable circumstance connected with its influence on the brain, is the exemption of those who have experienced its excitant effects from the subsequent depression, which, as an almost universal rule, follows stimulation. I know no other explanation which can be offered of this peculiarity, than that, in consequence of its chemical nature, the exhaustion of the cerebral cells through the over-excitement it produces, is immediately repaired by the nutritive material, oxygen and nitrogen, which it offers to them; the carbonaceous and hydrogenous matter being always ready in the blood. Besides its general stimulating effects, nitrous oxide is said to have decided aphrodisiac properties, similar to those sometimes exhibited under the influence of ether.

Besides the exhilarating powers of nitrous oxide, Davy also discovered its anaesthetic property, and even advanced so far as to suggest that advantage might be taken of this property in obviating the pain of surgical operations. But no practical advantage was taken of this sugges-tion until the year 1844, when Dr. Horace Wells, of Connecticut, who had been thinking of the means of rendering surgical operations painless, and especially the extraction of the teeth, having become acquainted with the anaesthetic property of nitrous oxide, immediately turned his knowledge to account by trying au experiment on himself. Having occasion for the extraction of a tooth in his own person, he put himself under the influence of nitrous oxide, while the operation for extraction was performed, and was happy to find that the operation was entirely painless. Soon afterward, as the result of his experiment, two important surgical operations were performed, one by Dr. Marcy, and the other by Dr. Ellsworth, of Waterford, Connecticut, both of which confirmed the expectations of Dr. Wells. (Med. and Surg. Reporter, Feb. 10, 1866, p. 111.) For sixteen or eighteen years after this, the subject of nitrous oxide inhalation seems to have been forgotten by the profession, probably under the excitement of the ether and chloroform discoveries, until revived by Mr. G. L. Colton, of New York, in its application to dentistry, and by Dr. J: M. Carnochan, of the same place, in its application to higher surgery. In the former respect, it has now come into extensive use; and thousands, if not tens of thousands, every year experience its benefits. In surgery, too, it is slowly making its way, but is as yet far from having superseded ether and chloroform. There are some objections to it as an anaesthetic in the more serious surgical operations which are not applicable to dentistry. Though very speedily induced, its anaesthetic effect is as quickly over; so that, to maintain the insensibility long enough for most of the serious operations, it is necessary frequently to renew the inhalation; and as, in the case of nitrous oxide, this requires the co-operation of the patient, it can readily be perceived that there must generally be considerable difficulty, and sometimes an impossibility of sustaining the anaesthetic action of the medicine a sufficient length of time. One great advantage, however, which the nitrous oxide has over all the other known anaesthetics is, that it is itself a supporter of respiration, so that a temporary exclusion of the atmospheric air from the lungs would not endanger asphyxia, while its place was supplied by the nitrous oxide. The period at which the anaesthetic effect takes place after the administration of nitrous oxide, varies exceedingly. It may take place in a minute or two, or not till a great deal longer; much depending upon the depth of the inhalation. One writer states that he has known anaesthesia to come on after only three deep and slow inhalations; while the process is often prolonged to twenty inhalations, in cases of superficial breathing from compressed or diseased lungs. (Bod. Med. and Surg. Journ , Sept. 7, 1865, p. 118.) The duration of the insensibility is short, generally, perhaps, not much exceeding the time required for inducing it.

The use of nitrous oxide as an anaesthetic in surgery is gradually spreading. It has been employed in Philadelphia in several of the higher surgical operations; but the general conclusion thus far obtained is, I believe, that it is more especially adapted to dentistry, and to surgical operations which require little time; but that for the more protracted cases ether is preferable. The insensibility to pain is quite as complete, while it lasts, as that caused by the other anaesthetics: and the only objection, therefore, is its brevity. When some method shall be contrived for continuing the effect, without the instrumentality of the patient, there is no reason, so far as is now known, why the nitrous oxide should not supersede all others; being in its administration much less unpleasant than ether, in its effects vastly less dangerous than chloroform, and in its after-effects less disagreeable than either of the others, both of which are not unfrequently followed by nausea and depression.

The danger from inhalation of nitrous oxide, when managed with due caution, may be considered as absolutely nothing. Of course if used in cases not adapted to it. harm may result as from any other remedy. If, for example, it were to be applied in cases of active congestion of the brain, acute inflammation, and general plethora, it would be likely to prove injurious, like alcoholic remedies under the same circumstances. But with ordinary caution in this respect, and care to use only a perfectly pure article, there is really no danger, unless from the existence of some latent predisposition, which might be called into action by this as by any other medicine. In a single dental establishment, out of 4,000 cases in which it was used, not the least injury resulted in a single case. (Boston Med. and Surg. Journ., Sept, 29, 1864).

Nor is it simply as an anaesthetic that nitrous oxide is likely to be employed. Its conjoined powers of general stimulation especially directed to the cerebral centres, and of directly oxidizing the blood, render it applicable to a great number of diseases, in which life is endangered by general prostration, loss of brain power, and insufficiently oxidized blood. The collapsed condition of cholera; the vast prostration of the pernicious chill; the cold stage of all other fevers in which reaction is feeble or insufficient, as in malignant cases of typhus, yellow fever, diphtheria, scarlet fever, erysipelas, etc.; the debilitated states of these same fevers, and of others, as enteric for example, in their course, or towards their close; cases of positive or threatened asphyxia, from strangulation, drowning, cold, and narcotic poisons; all these afford decided indications for this remedy, to which the only objection, in such cases, is the inconvenience of its administration. Hitherto the remedy has made little headway in this direction; but in an interesting report of Dr. Geo. G. Shumard, Medical Director in the U. S. Army, an account is given of eight cases of disease, of the character above mentioned, which were considered hopeless under any ordinary treatment, in which the inhalation of this gas. even under circumstances not the most favourable for its effective exhibition, was followed in all by decided signs of improvement, and in three was believed to have saved life. (Boston Med. and Surg. Journ., Jan. 18,1863, p. 446 )