TWO main physicochemical theories of inert gas narcosis have been put forward. The Meyer-Overton1 theory postulates that the intensity of narcotic action varies as the concentration of narcotic in the lipids. More recently, Pauling2 and Miller3 have suggested that the aqueous phases play a dominant part and relate narcotic activity to the tendency to form hydrates or more generally to induce structure ('icebergs') in water.