Rhizoma Arnicæ, Arnica Root; F. Racine d’Arnica; G. Arnicawurzel.
Botanical Origin—Arnica montana L., a perennial plant growing in meadows throughout the northern and central regions of the northern hemisphere, but not reaching the British Islands. In western and central Europe it is an inhabitant of the mountains, but in colder countries it grows in the plains.
In high latitudes, as in Arctic Asia and America, a peculiar form of the plant distinguished by narrow, almost linear leaves has been named A. angustifolia Vahl; but numerous transitional forms prove its identity with the ordinary A. montana of Europe.
History—The older botanists as Matthiolus, Gesner, Camerarius, Tabernæmontanus, and Clusius were acquainted with Arnica and had some knowledge of its medicinal powers, which appear to have been expressly recommended, towards the end of the 16th century, by Franz Joël, professor of Greifswald, Germany.[1440] All parts of the plant were no doubt popular remedies in Germany at an early period, but Arnica was only introduced into regular medicine on the recommendation of Johann Michael Fehr of Schweinfurt and of several other physicians.[1441] But for enthusiastic laudation of the new remedy, all these writers fall far short of Collin of Vienna, who imagined that in Arnica he had found a European plant possessing all the virtues of Peruvian Bark.[1442] In his hands fevers and agues gave way under its use, and more than 1000 patients in the Pazman Hospital were alleged to have been cured of intermittents by an electuary of the flowers, between 1771 and 1774. Such happy results were not obtained by other physicians.
Arnica (herba, flos, radix) had a place in the London Pharmacopœia of 1788, but it soon fell out of notice, so that Woodville writing in 1790, remarks that he had been unable to procure the plant from any of the London druggists. Of late years it has gained some popular notoriety as an application in the form of tincture, for preventing the blackness of bruises, but in England it is rarely prescribed internally.
Description—The arnic root of pharmacy consists of a slender, contorted, dark brown rootstock, an inch or two long, emitting from its under side an abundance of wiry simple roots, 3, 4 or more inches in length; it usually bears the remains of the rosette of characteristic, ovate, coriaceous leaves, which are 3-to 5-nerved, ciliated at the margin, and slightly pubescent on their upper surface. It has a faintly aromatic, herby smell, and a rather acrid taste.
Microscopic Structure—On a transverse section, the rootstock exhibits a large pith surrounded by a strong woody ring. In the innermost part of the cortical layer, large oil-ducts are found corresponding to the fibro-vascular bundles. Neither starch granules, inulin, or oxalate of calcium are visible in the tissue. The rootlets are of a different structural character, but also contain oil-ducts.
Chemical Composition—Several chemists have occupied themselves in endeavouring to isolate the active principle of arnica. Bastick described (1851) a substance which he obtained in minute quantity from the flowers and named Arnicine. He states it to possess alkaline properties, to be non-volatile, slightly soluble in water, more so in alcohol or ether; when neutralized with hydrochloric acid, it forms a crystalline salt.
The Arnicin extracted by Walz (1861) both from the root and flowers of arnica is a different substance; it is an amorphous yellow mass of acrid taste, slightly soluble in water, freely in alcohol or ether, and dissolving also in alkaline solutions. It is precipitable from its alcoholic solution by tannic acid or by water. Walz assigns to arnicin the formula C₂₀H₃₀O₄; other chemists that of C₃₅H₅₄O₇. Arnicin has not yet been proved a glucoside, although it is decomposed by dilute acids.
Sigel (1873) obtained from dried arnica root about ½ per cent. of essential oil, and 1 per cent. from the fresh; the oil of the latter had a sp. gr. of 0·999 at 18° C. The oil was found to be a mixture of various bodies, the principle being dimethylic ether of thymohydroquinone