Arnica, a genus of plants of the natural order compositœ. The arnica montana or leopard's bane grows in the mountainous districts of the north and middle of Europe, blossoming in June and July. Its flowers, leaves, and root are employed in medicine, but the flowers are usually preferred. A tincture and extract are prepared from the flowers, and a tincture from the root. An infusion may be used. Arnica contains a volatile oil, bitter extractive, and resin, the first being probably the active constituent. When taken internally arnica produces increased rapidity of the pulse, headache, dizziness, and spasmodic twitchings of the muscles, with occasional vomiting and diarrhoea. Externally it is a slight irritant. It has been used, more in Germany than in this country, in low forms of fever and nervous diseases. It is largely used as a remedy for sprains and bruises.