Anaesthetics (Gr. av, privative, and I feel), substances which can produce a general or partial suspension of nervous sensibility. In the common acceptation of the term should be included all drugs which have the faculty of so acting upon the brain that this effect can be caused; for instance, all the forms of narcotics and diffusible stimulants.

But by general consent this title is now confined to the most volatile forms of chemical agents which can produce the effect when inhaled or applied externally, and the effects of which are transitory; the terms narcotization and coma being applied where a long-continued effect is caused by other agents. The general action of all anaesthetic agents is through the medium of the blood, into which they are taken either from the lungs, the stomach, or by the skin, and carried by the circulation to the brain, where they produce a profound but transient state of intoxication. Anaesthesia is said to be either general Or local: general, when all power of sensibility is suspended; local, when only a particular part of the body is affected, the brain and the rest of the system remaining as ordinarily. Loss of sensation in restricted portions of the body has been attempted in various ways, as by long pressure upon the nervous trunks leading to the part, first put in operation by Ambroise Pare, afterward adopted by Dr. Moore, about 1784; the application of carbonic acid gas, recommended by Dr. Hickman in 1823, a procedure which was revived by the late Dr. Simpson; the application of the various ethers, especially chloroform; and by a true freezing of the part, as recommended by Dr. James Arnott of London, who employed for the purpose a mixture of pounded ice and common salt enclosed in a muslin bag.

The most useful method has been found to be the employment of ether spray, directed in a continuous stream upon the part by means of an atomizing apparatus. Various anaesthetic agents have been employed at different times - the several kinds of ethers, nitric, acetic, sulphuric, etc, protoxide of nitrogen ("laughing gas "), aldehyde, olefiant gas, naphtha, car-buretted hydrogen, Dutch liquid, benzoin, chloroform, and amylene, a substance introduced by Dr. Snow of London; but none of them have proved so successful, or are now so generally used, as sulphuric ether and chloroform. This latter substance was discovered in 1831, but its chemical composition was not accurately known till 1834. (See Chloroform.) Its use for the same purpose as sulphuric ether was first proposed by Dr. J. Y. Simpson of Edinburgh, in 1847. The advantages claimed for it over ether are the smallness of the dose required, a more perfect action, less depression when the heart or lungs are diseased, a more rapid effect, less disgust to the patient during inhalation, absence of persistent odor, and lastly, that it is cheaper.

Hut as unfortunately it has happened that several deaths have occurred from its use, it cannot be looked upon as so safe an agent as ether, from the use of which, no matter in how large quantities or how carelessly, not one death has yet been reported. The benumbing of the nerves of sensation by the administration of narcotic drugs has been practised for many years, and, as records show, was known to the ancients; but with the exception of certain traditions as regards the use in the East of the mandrake (atro-pa mandragora) and hashish (cannabis Indica) in the form of vapor for this purpose, we have no proofs that anaesthetic inhalation was ever employed. Richard Pearson recommended the inhalation of sulphuric ether for asthma, etc, in 1795; and in 1816 Nysten described an instrument for its use. In Sir Humphry Davy's " Researches concerning Nitrous Oxide," published in 1800, is this remark: "As nitrous oxide in its extensive operation seems capable of destroying physical pain, it will probably be used with advantage during surgical operations in which no great effusion of blood takes place." Dr. J. C. Warren of Boston prescribed ethereal inhalation for the relief of pulmonary inflammation in 1805, and Mr. Wesley Smead of Cincinnati published an article on this treatment in 1822. The power of the ethers to produce insensibility was mentioned by Godman in 1822, Mitch-ill in 1832, Prof. Samuel Jackson in 1833, and Wood and Bache in 1833. But its application as an agent for the relief of pain during surgical operations was first publicly made at the Massachusetts general hospital in Boston, Oct. 16, 1846, by Dr. W. T. G. Morton of that city, who subsequently secured a patent for the use of the article under the name of "letheon." On Jan. 2 of the next year a new claimant for the discovery came before the public, in the person of Dr. Charles T. Jackson of the same city; and still later the same claim was advanced in behalf of Dr. Horace Wells of Hartford. (See Jackson, Morton, and Wells.) - The objects gained by the administration of anaesthetics are various, according as we have to do with surgery, midwifery, or medicine.

In surgery: 1. A protracted and careful examination, and consequently more accurate diagnosis, can be made in many cases of disease and injury, where the intense pain caused by the examination prevents the manipulation of the surgeon, as in fractures, dislocations, and stone. 2. From the total relaxation which the muscles receive under a full dose, the reduction of many forms of dislocation, hernias, etc, is facilitated. 3. In military service, under its influ-ence, men can be removed to a distance where the operation can be conveniently performed, instead of as formerly being obliged to operate upon the field of battle or in places otherwise unfavorable. 4. The general use of many forms of remedial operation is extended, which otherwise are attended with such exquisite agony that they were rarely resorted to unless from most extreme necessity, as for instance the application of the actual cautery and moxas. 5. Many operations can now be performed for the relief of long-continued disease, or after injury, which before would have been hazardous, owing to the depressed or feeble state of the patient. 6. Many delicate operations can now be easily performed where perfect quiet is demanded of the patient, and which can hardly be afforded by any amount of exercise of the will, as in operations upon the eye, dissection of nerves, or the taking up of arteries. 7. Patients will now apply earlier than heretofore for relief in surgical diseases, the dread of the surgeon's knife often having induced them to postpone it until the case became almost hopeless. 8. The mortality from operations has materially decreased, for it is well known that pain has a serious tendency to depress the nervous system and produce death from exhaustion. - In midwifery: 1. In addition to preserving the mother from the pain always incident to parturition, we have the power of preserving her strength unimpaired when the labor is long continued or especially severe. 2. In all cases of instrumental labor or those requiring manual assistance, the aid can be afforded with greater ease to the accoucheur and more safety and less accompanying suffering to the mother. 3. Many cases in doubt in diagnosis can be more correctly solved. 4. From the relaxation of the muscular fibres, the exit of the child through the uterine neck or the vaginal passage, when they are rigid, is facilitated. 5. Anaesthetics have the power of keeping in abeyance and reducing the violence of one of the worst complications of labor, puerperal convulsions. 6. The recovery of the patient after labor is assisted, and the chances of subsequent dangers lessened. - In medicine: 1. As a relief from severe or exhausting pain in disease, as from toothache, passage of calculi, or neuralgia. 2. As a narcotic in mania, delirium tremens, excitement, or wakefulness from any cause. 3. As an antispasmodic for cholera, hysteria, asthma, convulsions, etc.