The medicinal use of the berries was familiar to all the writers on botany and materia medica of the 16th century. Syrup of buckthorn first appeared in the London Pharmacopœia of 1650; it was aromatized by means of aniseed, cinnamon, mastich and nutmeg.
Description—The fruits, which are only used in the fresh state, are small, juicy, spherical drupes the size of a pea, black and shining, bearing on the summit the remnants of the style, and supported below by a slender stalk expanded into a disc-like receptacle. Before ripening the fruit is green and distinctly 4-lobed, afterwards smooth and plump. It contains 4 one-seeded nuts[644] meeting at right angles in the middle. The seed is erect with a broad furrow on the back: in transverse section the albumen and cotyledons are seen to be curved into a horseshoe form with the ends directed outwards.
The fresh juice is green, has an acid reaction and a sweetish, afterwards disagreeably bitter taste, and repulsive odour. It is coloured dingy green by ferric chloride, yellow by alkalis, red by acids. According to Umney[645] it should have a sp. gr. of 1·070 to 1·075, but is seldom sold pure. By keeping the juice gradually turns red.
Microscopic Structure—The epidermis consists of small tabular cells, followed by a row of large cubic cells and then by several layers of tangentially-extended cells rich in chlorophyll. This thick epicarp passes into the loose thin-walled and large-celled sarocarp. Besides chlorophyll it exhibits numerous cells each containing a kind of sac, which may be squeezed out of the cell. These sacs are violet, turning blue with alkalis. Similar, yet much more conspicuous bodies occur also in the pulp of the Locust Bean (Ceratonia Siliqua L.).
Chemical Composition—The berries of buckthorn and other species of Rhamnus contain interesting colouring matters, which have been the subject of much chemical research and controversy. Winckler in 1849 extracted from the juice Rhamnocathartin, a yellowish uncrystallizable bitter substance, soluble in water but not in ether. Alkalis colour it golden yellow; perchloride of iron, dark greenish brown.
In 1840 Fleury, a pharmacien of Pontoise, discovered in buckthorn juice a yellow substance forming cauliflower-like crystals to which he gave the name of Rhamnine. This body has been recently studied by Lefort,[646] who identified it with the Rhamnetine of Galletly (1858) and the Chrysorhamnine of Schützenberger and Bertèche (1865). Though obtainable from the berries of all kinds of Rhamnus used in dyeing (including the common buckthorn), it is got most easily and abundantly from Persian Berries. When pure, and crystallized from absolute alcohol, it is described as forming minute yellow translucent tables. It is scarcely soluble in cold water, though colouring it pale yellow; is soluble in hot alcohol, insoluble in ether or bisulphide of carbon. It is very soluble in caustic alkalis, forming uncrystallizable reddish-yellow solutions. From alkaline solutions it is precipitated by a mineral acid in the form of a glutinous magma resembling hydrated silica. Lefort assigns to it the formula C₁₂H₁₂O₅ + 2H₂O.
This chemist has likewise found in the berries of Rhamnus, though not with certainty in those of R. cathartica, a neutral substance isomeric with rhamnine, to which he has given the name of Rhamnegine. Unlike rhamnine it is very soluble in cold water, but in all other respects it agrees with that body in chemical and physical properties. The two substances have the same taste, almost the same tint, the same crystalline form, and lastly they give rise to the same reactions with chemical agents.
The conclusions of Lefort have been contested by Stein (1868) and by Schützenberger (1868), the latter of whom succeeded in decomposing rhamnegine and proving it a glucoside having the formula C₂₄H₃₂O₁₄. Its decomposition gives rise to a body named Rhamnetin, C₁₂H₁₀O₅, and a crystallizable sugar isomeric with mannite. Schützenberger admits that the berries contain an isomeric modification of rhamnegine; but in addition another colouring matter insoluble in water, which appears to be the Rhamnine of Lefort, but to which he assigns a different formula, namely, C₁₈H₂₂O₁₀. This is also a glucoside capable of being split into rhamnetin and a sugar. There are thus, according to Schützenberger, two forms of rhamnegine which may be distinguished as α and β, and there is the substance insoluble in water, named by Lefort Rhamnine.
The question of the purgative principles of buckthorn, it will be observed, has not been touched by all these researches.
Uses—From the juice of the berries is prepared a syrup having strongly purgative properties, much more used as a medicine for animals than for man. The pigment Sap Green is also made from the juice.