[Gk. an, in- ; aisthesis, sensibility.] A chemical substance capable of producing insensibility, much used to prevent pain in surgical operations. Nitrous oxide was first used in tooth drawing in 1844. Ether was used for the same purpose in 1846, and chloroform and other substances later. Now no important surgical operation is performed without an anaesthetic. Local anaesthesia can be produced by cocaine, by freezing the surface with a spray of ether or chloride of ethel, and in other ways.