Source, Etc

Arnica rhizome, or arnica root as the drug is commonly termed, consists of the rhizome and roots of Arnica montana, Linne (N.O. Compositoe), a small plant with a creeping perennial rhizome, indigenous to central Europe and common in the meadows on the lower mountain spurs. It should be collected in the autumn, after the aerial parts have died down, and dried.

Description

The rhizome, which is horizontal or oblique, is slender, nearly cylindrical in shape, and usually curved. It averages about 5 cm. in length and about 5 mm. in thickness, and varies in colour from yellowish brown to nearly black. From the flanks and under surface numerous dark, brittle, wiry curved and twisted roots about 8 cm. in length are given off, and the scars that are left, when these break off or perish, together with the encircling scars of cataphyllary leaves, render the surface of the rhizome, which is in addition longitudinally shrivelled, distinctly rough. Usually it is simple and often terminated by the hairy remains of leaves; sometimes, after the plant has flowered, the growth of the rhizome, which has thus been terminated, is continued in the same direction by the development of a bud on its under surface; the rhizome thus formed will in due course itself flower, and the further growth will again be ensured by the development of one of the lower buds. Thus the rhizome occasionally assumes a jointed appearance.

The rhizome breaks with a short fracture, and is often discoloured in the interior. The transverse section of a favourable specimen shows a comparatively thick whitish or yellowish bark, in which near the wood is a circle of darker oleo-resin ducts. The wood consists of yellow wedge-shaped wood-bundles and broad medullary rays enclosing a large whitish pith which in longitudinal sections is seen to be continuous. The root also shows a thick white bark with a ring of oleo-resin ducts and a yellowish wood. The drug has a faint but rather agreeable apple-like odour and a bitter acrid taste.

Fig. 174.   Arnica rhizome. Natural size. (Holmes.)

Fig. 174. - Arnica rhizome. Natural size. (Holmes).

Fig. 175.   Arnica rhizome. Transverse section of rhizome, v, bast; o, primary cortex; y, wood bundles; r, medullary rays; c, pith; p, oleo resin ducts. Magnified 10 diam. (Berg.)

Fig. 175. - Arnica rhizome. Transverse section of rhizome, v, bast; o, primary cortex; y, wood-bundles; r, medullary rays; c, pith; p, oleo-resin ducts. Magnified 10 diam. (Berg).

The student should observe

(a) The curved rhizome with wiry roots,

(b) The characters of the transverse section,

(c) The scars of cataphyllary leaves.

Constituents

Arnica rhizome contains about 0 5 per cent. of volatile oil, and a bitter and acrid principle, arnicin, which has been obtained in the form of a minutely crystalline yellow powder. It also contains tannin, but no starch, the reserve material being inulin, the latter character being useful in distinguishing it from any starch-forming rhizome. The drug yields about 8 per cent. of ash.

Uses

The tincture diluted with water is a popular application for bruises, preventing swelling and hastening the absorption of effused blood. It appears to increase the activity of the circulation in the skin, but should be used with caution, as it is liable to produce extensive dermatitis.

Arnica is not often given internally; it has a depressing or, in over doses, irritant action, causing vomiting, pain, and purging.

Substitutes, Etc

Foreign roots and rhizomes are occasionally present in the drug as imported, and have to be separated by hand-picking. Amongst these may be mentioned the erect rhizome of the common avens (Geum urbanum, Linne), which has an odour recalling cloves, and the rhizomes of species of Hieraciutn, which have no oleo-resin ducts.