History—The plum-tree (P. domestica L.) from which it is supposed the numerous cultivated varieties have descended, is believed to occur in a truly wild state in Greece, the south-eastern shores of the Black Sea (Lazistan), the Caucasus, and the Elburz range in Northern Persia, from some of which countries it was introduced into Europe long before the Christian era. In the days of Pliny, numerous species of plum were already in cultivation, one of which afforded a fruit having laxative properties.
Dried prunes, especially those taking their name from Damascus (Pruna Damascena), are frequently mentioned in the writings of the Greek physicians, by whom as well as at a later period by the practitioners of the Schola Salernitana, they were much employed.
In the older London pharmacopœias, many sorts of plum are enumerated, but in the reformed editions of 1746, 1788, and 1809, the French Prune (Prunum Gallicum) is specially ordered, its chief use being as an ingredient of the well-known Lenitive Electuary; and this fruit is still held by the grocers to be the legitimate prune. The same variety is regarded in France as the prune of medicine.
Description—The prune in its fresh state is an ovoid drupe of a deep purple hue, not depressed at the insertion of the stalk, and with a scarcely visible suture, and no furrow. The pulp is greenish and rather austere, unless the fruit is very ripe; it does not adhere to the stone. The stone is short (⁷/₁₀ to ⁸/₁₀ of an inch long, ⁵/₁₀ to ⁶/₁₀ broad), broadly rounded at the upper end and slightly mucronulate, narrowed somewhat stalk-like at the lower, and truncate; the ventral suture is broader and thicker than the dorsal.
The fruit is dried partly by solar and partly by fire-heat, that is to say, it is exposed alternately to the heat of an oven and to the open air. Thus prepared, it is about 1¼ inches long, black and shrivelled, but recovers its original size and form by digestion in warm water. The dried pulp or sarcocarp is brown and tough, with an acidulous, saccharine, fruity taste.
Microscopic Structure—The skin of the prune is formed of small, densely packed cells, loaded with a dark solid substance; the pulp consists of larger shrunken cells, containing a brownish amorphous mass which is probably rich in sugar. This latter tissue is traversed by a few thin fibro-vascular bundles, and exhibits here and there crystals of oxalate of calcium. By perchloride of iron, the cell-walls, as well as the contents of the cells, acquire a dingy greenish hue.
Chemical Composition—We are not aware of any analysis having been made of the particular sort of plum under notice, nor that any attempt has been made to discover the source of the medicinal property it is reputed to possess. Some nearly allied varieties have been submitted to analysis in the laboratory of Fresenius, and shown to contain saccharine matters to the extent of 17 to 35 per cent., besides malic acid, and albuminoid and pectic substances.[963]
Uses—The only pharmaceutical preparation of which the pulp of prunes is an ingredient, is Confectio Sennæ, the Electuarium lenitivum of the old pharmacopœias. The fruit stewed and sweetened is often used as a domestic laxative.
Substitute—When French prunes are scarce, a very similar fruit, known in Germany as Zwetschen or Quetschen, is imported as a substitute.[964] It is the produce of a tree which most botanists regard as a form of Prunus domestica L., termed by De Candolle var. Pruneauliana. K. Koch,[965] however, is decidedly of opinion that it is a distinct species, and as such he has revived for it Borkhausen’s name of Prunus œconomica. The tree is widely cultivated in Germany for the sake of its fruit, which is used in the dried state as an article of food, but is not grown in England.
The dried fruit differs slightly from the ordinary prune in being rather larger and more elongated, and having a thicker skin; also in the stone being flatter, narrower, pointed at either end, with the ventral suture much more strongly curved than the dorsal. The fruits seem rather more prone to become covered with a saccharine efflorescence.