Ether, chloroform, and a number of related compounds, ethyl chloride, methylene chloride, etc., form a group of these alcohol derivatives, in which the property of rapid volatilization causes the formation of vapors which are capable of rapid absorption by the respiratory mucous membrane with the production of general anesthesia. Nitrous oxide causes a similar anesthesia, but its mode of action is very dissimilar.

To Dr. Oliver Wendell Holmes is due the credit of proposing the term "anesthetic." This group occupies a position between the preceding one and the next - Hypnotics.

The use of drugs to abolish pain in surgical operations has probably never been entirely forgotten, but their general and systematic employment only commenced with the use of nitrous oxide by Wells, in 1844, and of ether by his pupil Morton. Shortly afterward a great number of substances were tried by Simpson, with the result that he chose chloroform as being the most convenient and safe. The power of producing anesthesia, as already pointed out, is common to most of the substances of the fatty or alcohol series. But it is greatly modified by a number of circumstances; the position in the fatty or alcoholic group of the radical or alkyl which forms the basis of the substance, and the nature of the element or radical with which the alkyl is combined, being two prominent ones. Thus in the case of the alkyls, their action differs according as they are combined with hydrogen in the hydrides, with hydroxyl, OH, in the alcohols, or with both oxygen and hydroxyl, as in the acids.

Some members are useful as hypnotics, simply inducing sleep as one of the first results of their action; although if the dose be large, the sleep may pass into complete unconsciousness or anesthesia, with loss of reflex action. For the production of prolonged sleep a substance is required whose action will be slight, and at the same time prolonged; but for anesthesia a substance is needed that will act rapidly and powerfully, but will be quickly eliminated and cease to act very shortly after its administration is discontinued. Hypnotics therefore are found among the substances which have a heavy molecule, and are either liquid or solid in form, so that they may be given by the mouth, and being absorbed into the blood continue to act for a length of time. Anesthetics are found among the lower members of the series which have a light molecular weight, and are either gases or volatile liquids. Although heavy liquids like paraldehyde, or solids like chloral hydrate, will act as anesthetics when given in large doses, yet their use as such would be very dangerous, for the line between their anesthetic action and their paralyzing action on the respiratory center is very narrow and might easily be crossed by a very slight excess in dose.

An ideal anesthetic should be a substance capable of rapidly and safely producing profound anesthesia, and susceptible of speedy elimination, so that consciousness may be restored soon after withdrawal of the anesthetic, with no discomfort to the patient. The typical anesthetic should also be convenient and safe - a stable, non-irritating, pleasantly odorous, homogeneous liquid, with a boiling-point neither too high nor too low. Unfortunately there is no substance which fully meets these requirements, ether and chloroform approaching nearest to the ideal agent.

Local anesthetics are used to deaden the sensation or abolish the sensibility of the peripheral nerves of a localized, particular area. The most important are - cocaine, carbolic acid, iodoform, eugenol-acetamide, antipyrine, orthoform, anesthesin, holocaine, etc. Some aromatics are also quite powerful anesthetics. The physiological action of local anesthetics is given under the respective agents.