Menthol

Menthol is a camphor obtained from oil of peppermint by cooling. It has been used by the Japanese for 200 years and is known by them as Hakka-no-Hari; indeed, native gentlemen always went about till recently with a medicine-box containing this drug. The chief source is the Mentha arvensis purpurescens, the oil of which yields more menthol than that of peppermint. In many nervous affections, such as neuralgia, toothache, headache, &c., menthol in the form of cones often gives instant relief. When the cone is rubbed on the skin a twofold action results. The menthol rapidly evaporates, giving a sensation of cold; but if evaporation be prevented it acts as a rubefacient, producing a feeling of warmth. Menthol has also antiseptic properties, and is used with success in solution in diphtheria, &c. It has an odour resembling but differing from that of oil of peppermint. It is liable to be adulterated with thymol, eucalyptol, &c., and then is often irritating to the skin.