The fruit (berries) of Rhamnus cathartica, Linné (Cervispina cathartica, Moench).
ILLUSTRATION: Bentley and Trimen, Med. Plants, 64.
Botanical Source.—Buckthorn is a shrub from 6 to 15 feet in height. Its branches are alternate or nearly opposite, spreading, straight, round, smooth, hard, and rigid, each terminating in a strong spine, after the first year. The leaves are 1 to 2 inches long, about two-thirds as wide, deciduous, bright-green, smooth, simple, and ribbed; the young ones downy; the earlier ones in tufts from the flowering buds; the rest opposite, on the young branches. Petioles downy. Stipules linear. Flowers yellowish-green, on the last year's branches, and numerous; the fertile ones with narrow petals, rudiments of stamens, and a deeply 4-cleft style; the barren ones with an abortive ovary and broader petals. The berries are globular, bluish-black, nauseous, with 4 cells, and as many elliptical, plano-convex seeds (L.).
History and Description.—Buckthorn is indigenous to Europe, and has been observed in this country as an introduced plant. It flowers from April to July, and matures its fruit about the middle of autumn. The parts used are the berries; they are globular, 3 or 4 lines in diameter, slightly compressed at the apex, black, glossy, and inclose a green pulp in which the seeds are imbedded. The juice becomes gradually red, owing to the development of acetic acid, and may be preserved long unchanged in the form of a syrup. It is soluble in water. When evaporated to dryness with alum, or lime and gum Arabic, it forms the color called sap-green. Carbonate of sodium and caustic potash change the solution of sap-green to yellow. Sulphuric, nitric, and hydrochloric acids turn it red. Hence, paper tinged with sap-green might be used as an indicator in place of litmus.
Chemical Composition.—The cathartic principle of this shrub is rhamno-cathartin, a bitter, amorphous substance, isolated from the juice of the berries by Binswanger (1849), and previously by Hubert and Winckler. Mr. George W. Kennedy (Amer. Jour. Pharm., 1885, p. 497) observed the same substance as a brownish deposit from a fluid extract of the bark. It was amorphous, soluble in caustic alkali with deep-purplish-red color, reprecipitated by acids, soluble in diluted and strong alcohol, insoluble in chloroform and ether, nearly so in water, and possessing strongly laxative properties in 3-grain doses. The resin, held in solution by the fluid extract, differed from that mentioned, by being soluble in ether and chloroform. Rhamnotannic acid was also isolated from the berries by Binswanger. The coloring matters of the berries were frequently investigated, and consist of the crystallizable glucosid rhamnin (Stein, 1868 and 1869; rhamnegin of Lefort and Schützenberger), and especially its decomposition product, rhamnetin (rhamnin of Fleury and Lefort), which is also crystallizable. This substance is likewise a constituent of the unripe berries of Rhamnus infectoria (see Related Species). Rhamnin crystallizes in pale-yellow, or golden-yellow, tasteless needles, readily soluble in water, diluted alcohol, and boiling alcohol, nearly insoluble in ether, chloroform, benzol, and carbon disulphide. Soluble, with yellow color, in caustic alkalies. Rhamnetin (methyl quercetin, J. Herzig, 1891) crystallizes in small, golden-yellow plates, nearly tasteless; hardly soluble in water, soluble in boiling alcohol (58.5 parts), and in ether (76 parts). It is soluble, with yellow color, in alkalies, and reduces Fehling's solution and silver nitrate solution in the cold. (For details regarding the earlier chemistry of the constituents of rhamnus, see Husemann and Hilger, Pflanzenstoffe, Vol. II, 1884, pp. 889-89.6.)
Action, Medical Uses, and Dosage.—Buckthorn berries (Rhamni baccae) are powerfully cathartic; 20 of the recent berries cause brisk, watery purging, with nausea, dryness of the throat, thirst, and tormina. These effects are partly removed by giving the juice (Rhamni succus) in the form of syrup, and which formerly enjoyed much reputation as a hydragogue in gout, rheumatism, and dropsy; at present it is seldom employed in practice, but is occasionally employed as an adjunct to other cathartic and diuretic mixtures. Prof. Scudder suggests a trial of small doses of a tincture (berries, ℥viii, to alcohol, 76 per cent, Oj) as a stimulant to the vegetative processes, for its influence on the digestive tract, and in diseases of the nose, throat, and lungs. Dose of the syrup, from 1/2 to 1 fluid ounce. Dose of the tincture, 2 to 30 drops, well diluted with water. A tincture of the bark, made in the same proportions as that of the berries, may be given in doses of from 6 to 30 drops.
Related Species.—Rhamnus infectoria, Linné. Berries resemble in appearance buckthorn berries, except that their color is green-brown or brown. They are known as French berries, and yield several yellow coloring matters. According to Liebermann and Hörmann (Jahresb. der Pharm., 1878, p. 433; and 1879, p. 195) the berries of R. infectoria and R. tinctoria contain about 12 per cent of glucosidal coloring matters. One of these glucosids is Kane's xanthorhamnin (rhamnin of Stein; see R. cathartica). Diluted acids split it into rhamnetin (C12H10O5) and isodulcit (C6H14O10). The decomposition is also brought about by ferments existing in the berries, hence rhamnetin is a prominent constituent of the latter. More recently, J. Herzig (Chem. Centralblatt, Vol. II, 1891, p. 306) established rhamnetin to be the methyl ether of quercetin, and to have the formula C16H12O7, or C15H9O6(OCH3).
PERSIAN BERRIES, the fruit of several species of Rhamnus (R. amygdalina, Desfontaines; R. saxatalis, Linné, etc.) skirting the Mediterranean, also yield these color pigments.