Arnicae Rhizoma, B.P., Arnica Rhizome.

Related entry: Arnica Flowers
Synonym.—Arnicae Radix.
Arnica rhizome is obtained from Arnica montana, Linn. (N.O. Compositae), a small plant indigenous to Central Europe. The rhizome and rootlets should be collected in the autumn, after the stem has died down. The horizontal, cylindrical rhizome is dark brown in colour, varying from 2.5 to 5 centimetres in length, and from 4 to 6 millimetres in thickness. It is usually curved, and bears brittle wiry rootlets on its under surface. The surface is rendered rough by the scars left when these break off, together with the encircling scars of cataphyllary leaves. It is often terminated by the hairy remains of the stem and leaves. The transverse section exhibits a rather thick yellowish cortex, near the inner margin of which is a circle of dark oleoresin ducts. Arnica rhizome is not often adulterated, but foreign rhizomes are occasionally present; the genuine drug may readily be distinguished by the characters given. It yields about 8 per cent. of ash.
Constituents.—Arnica rhizome contains from 0.5 to 1.0 per cent. of volatile oil, with a pungent, aromatic taste, and the bitter, yellow, crystalline principle, arnicin. Tannin and inulin are also present, but the drug is free from starch.
Action and Uses.—The action of arnica rhizome is the same as that of the flowers, and a tincture mixed with water (1 in 40) is a popular application for sprains and bruises when the skin is unbroken.
PREPARATIONS.

Extractum Arnicae Liquidum, B.P.C.—LIQUID EXTRACT OF ARNICA. 1 in 1.
Liquid extract of arnica is diluted with 20 parts of warm water for use instead of the tincture, being further diluted with 30 to 40 parts of water as in the case of the tincture for application on lint to bruises and swellings.
Linimentum Arnicae, B.P.C.—LINIMENT OF ARNICA. Syn.—Arnica Opodeldoc.
Tincture of arnica, 5: camphor, 1; hard soap, 4; alcohol, to 20. Liniment of arnica is applied with friction as a mild counter-irritant.
Tinctura Arnicae, B.P.—TINCTURE OF ARNICA.
Arnica rhizome, in No. 40 powder, 5; alcohol (70 per cent.), sufficient to produce 100. Tincture of arnica is rarely given internally. Mixed with 30 to 40 parts of water this tincture is applied to chilblains, bruises, and sprains when the skin is unbroken.