An'æsthet'ic, the name applied to any agency which causes either partial or complete insensibility to pain. There are two kinds of anæsthetics: those called local anæsthetics, which affect only a limited area; and those called general anæsthetics, which cause temporary insensibility of the whole body. Anæsthetics of various kinds were used by the ancient Greeks and by the Chinese as early as the third century A. D. When men began to study chemistry systematically, toward the close of the eighteenth century, various anæsthetics were discovered, but it was some time before they came into common use. In 1844 Dr. Horace Wells of Hartford, Conn., used nitrous oxide gas to render the extraction of teeth painless. In 1846 Dr. Morton of Boston employed the vapor of sulphuric ether for the same purpose, and afterwards applied it in cases requiring surgery. In 1847 Sir James J. Simpson of Edinborough announced the discovery of chloroform, and suggested its use instead of ether. These three anæsthetics are taken into the system by inhalation. Local anæsthesia is produced by chilling with ice or by the evaporation of some volatile substance like ether or rhigoline. Cocaine is also used extensively for this purpose.