1902 Encyclopedia > Rhubarb


RHUBARB. This name is applied both to a drug and to a vegetable.

1. The drug has been used in medicine from very early times, being described in the Chinese herbal Pen-king, which is believed to date from 2700 B.C. The name seems to be a corruption of Rlieum barbarum or lieu barbarum, a designation applied to the drug as early as the middle of the 6 th century, and apparently identical with the prjov or pâ of Dioscorides, described by him as a root brought from beyond the Bosphorus. Bha is said by Ammianus Mar-cellinus to take its name from the river Rha (Volga), on the banks of which a species of Rheum (R. Rhaponticum) grows. It is not, however, known whether the root of this species was the article used under the name of Rha ponticum or Rha barbarum, or whether these names were applied to the drug brought overland from China by way of the Caspian Sea. It is, however, certain that in the early part of the 11th century Chinese rhubarb was dis-tinguished as superior to the Rha barbarum. In the 14th century rhubarb appears to have found its way to Europe by way of the Indus and Persian Gulf to the Red Sea and Alexandria, and was therefore described as " East Indian " rhubarb. Some also came by way of Persia and the Caspian to Syria and Asia Minor, and reached Europe from the ports of Aleppo and Smyrna, and became known as "Turkey" rhubarb. Subsequently to the year 1653, when China first permitted Russia to trade on her fron-tiers, Chinese rhubarb reached Europe chiefly by way of Moscow ; and in 1704 the rhubarb trade became a mono-poly of the Russian Government, in consequence of which the term " Russian " or " crown " rhubarb came to be applied to it. Urga was the great depot for the rhubarb trade in 1719, but in 1728 the depot was transferred to Kiachta. All rhubarb brought to the depot passed through the hands of the Government inspector, acting under the instructions of the Russian minister of war, and all pieces except those of good quality were rejected. Hence Russian rhubarb was invariably good and obtained a remarkably high price. This severe supervision naturally led, as soon as the northern Chinese ports were thrown open to European trade, to a new outlet being sought ; and the increased demand for the drug at these ports resulted in less care being exercised by the Chinese in the collection and curing of the root, so that the rhubarb of good quality offered at Kiachta rapidly dwindled in quantity, and after 1860 Russian rhubarb ceased to appear in European commerce. The drug from that date became known as Chinese rhubarb, although the older names still con-tinue in domestic use in England. Owing to the expense of carrying the drug across the whole breadth of Asia and the difficulty of preserving it from the attacks of insects, rhubarb was formerly one of the most costly of drugs. In 1542 it was sold in France for ten times the price of cin-namon and four times that of saffron, and in an English price list bearing date of 1657 it is quoted at 16s. per lb., opium being at that time only 6s. and scammony 12s. per lb.

Rhubarb is used in medicine as a mild purgative and cholagogue, promoting digestion and improving the appe-tite when given in small doses, probably by stimulating the intestinal secretions. It has a subsequent astringent effect due to the rheotannic acid it contains but this can be. counteracted by giving it with alkaline preparations. It is especially valuable in the treatment of duodenal catarrh or catarrh of the biliary ducts with jaundice ; and in certain skin diseases it has proved to be a valuable medicine, the results obtained being probably due to the chrysophan contained in it.

The botanical source of Chinese rhubarb cannot be said to have been as yet definitely cleared up by actual identification of plants observed to be used for the purpose. Rheum palmatum, R. officinale, R. palmatum (var. tanguticum), R. colinianum, and R. Franzenbachii have been variously stated to be the source of it, but the roots produced by these species under cultivation in Europe do not present the characteristic network of white veins exhibited by the best specimens of the Chinese drug (see Goebel and Kunze, pt. ii., pi. i. figs. lb, 3b).

Chemistry.—The chief chemical constituents of Chinese rhubarb are chrysophan (C15H10O4), rheotannic acid (Cs0H2BO]4), emodin (C13H10Os), a neutral colourless crystalline substance having the formula C10H12O4, a white and a dark brown crystalline resin; it also contains mucilage in the proportion of 11 to 17 per cent., and a considerable quantity of oxalate of lime. An albuminoid principle containing nitrogen and sulphur is also found in the root, which, in the presence of water, as recently shown by Kubli, decomposes the chrysophan into chrysophanic acid and glucose, and apparently exerts a similar action on rheotannic acid, giving rise to the formation of rheumic acid (C20H16O9) and a fermentable sugar. Rheumic acid is a reddish-brown powder, sparingly soluble in cold water. The albuminoid principle is in-soluble in rectified spirit of wine ; consequently a preparation of the root made with that menstruum contains the active principles of the drug in the natural state, whilst an aqueous extract contains them in an altered condition.

Production and Commerce.—Rhubarb is produced in the four northern provinces of China proper (Chih-li, Shan-se, Shen-se, and Ho-nan), in the north-west provinces of Kan-suh formerly included in Shen-se, but now extending across the desert of Gobi to the frontier of Tibet, in the Mongolian province of Tsing-hai, including the salt lake Koko-nor, and the districts of Tangut, Sifan, and Turfan, and in the mountains of the western provinces of Sze-chuen. According to Richthofen the best rhubarb is collected exclusively from wild plants in the high mountains of western Sze-chuen between the sources of the Hoang-ho and the rivers Ya-lung Keang and Min-keang, and comes into trade under the name of Shen-se rhubarb. Two of the most important centres of the trade are Sining-fu in the province of Kan-suh and Kwan-hien in Sze-chuen. From Shen-se, Kan-suh, and Sze-chuen the rhubarb is forwarded to Hankow, and thence carried to Shanghai, whence it is shipped to Europe. Lesser quantities are shipped from Tien-tsin, and occasionally the drug is exported from Canton, Amoy, Fuh-chow, and Ning-po.

Very little is known concerning the mode of preparing the drug for the market. According to Mr Bell, who on a journey from St Petersburg to Peking had the opportunity of observing the plant in a growing state, the root is not considered to be mature until it is six years old. It is then dug up, usually in the autumn, and deprived of its cortical portion and smaller branches, and the larger pieces are divided in half longitudinally ; these pieces are bored with holes and strung up on cords to dry, in some cases being previously subjected to a preliminary drying on stone slabs heated by fire underneath. In Bhutan the root is said to be hung up in a kind of drying room, in which a moderate heat is regularly maintained. The effect produced by the two drying processes is very different; when dried by artificial heat, the exterior of the pieces becomes hardened before the interior has entirely lost its moisture, and consequently the pieces decay in the centre, although the surface may show no change. These two varieties are technically known as kiln-dried and sun-dried ; and it was on account of this difference in quality that the Russian officer at Kiachta had every piece examined by boring a hole to its centre. The best rhubarb occurs in pieces of a yellowish colour externally, more or less marked with a network of whitish veins, the surface being convex and smooth. Internally it presents no signs of decay, but is compact, marbled with reddish-brown and white, mixed sometimes with iron grey. The smaller cylindrical sections of the root which have not been divided longitudinally are technically known as "rounds," and have usually a hole with a piece of string left in it; the flat pieces are more rarely pierced. Inferior qualities are shrunken and shrivelled on the surface, and externally of av brownish tint, showing traces of the darker bark, and when broken open are frequently decayed in the centre.

European Rhubarb.—As early as 1608 Prosper Alpinus of Padua cultivated as the true rhubarb a plant which is now known as Rheum Rhaponticum, L., a native of southern Siberia and the basin of the Volga. This plant was introduced into England througli Sir Matthew Lister, physician to Charles I., who gave seed obtained by him in Italy to the botanist Parkinson. The culture of this rhubarb for the sake of the root was commenced in 1777 at Banbury in Oxfordshire, by an apothecary named Hayward, the plants being raised from seed sent from Russia in 1762, and with such success that the Society of Arts awarded him a silver medal in 1789 and a gold one in 1794. The cultivation subsequently extended to Somersetshire, Yorkshire, and Middlesex, but is now chiefly carried on at Banbury. English rhubarb root is sold at a. cheaper rate than the Chinese rhubarb, and forms a con-siderable article of export to America, and is said to be used in Britain in the form of powder which is of a finer yellow colour than that of Chinese rhubarb. The Banbury rhubarb appears to be a hybrid between R. Rhaponticum and R. undulatum,—the root, according to E. Colin, not presenting the typical microscopic structure of the former. During the last few years very good rhubarb has been grown at Banbury from Rheum officinale, but these two varieties are not equal in medicinal strength to the Chinese article, yielding less extract,—Chinese rhubarb affording, according to H. Seier, 58 per cent., English rhubarb 21 per cent., and R. officinale 17 per cent. In France the cultivation of rhubarb was commenced in the latter half of the last century,—is!, com-paction, R. palmatum, R. Rhaponticum, and R. undulatum, L., being the species grown. The cultivation has, however, now nearly ceased, small quantities only being prepared at Avignon and a few other localities.

The culture of Rheum eompactwm was begun in Moravia in the beginning of the present century by Prikyl, an apothecary in Austerlitz, and until twenty-five or thirty years ago the root was largely exported to Lyons and Milan, where it was used for dyeing silk. As a medicine 5 parts are stated to be equal to 4 of Chinese rhubarb. Rhubarb root is also grown at Auspitz in Moravia and at Ilmitz, Kremnitz, and Frauenkirchen in Hungary; R. Emodi is said to be cultivated for the same purpose in Silesia.

The cultivation of Rheum palmatum, var. tanguticum, has been begun within the last few years in the United States.

Rhubarb is also prepared for use in medicine from wild species in the Himalayas and Java.

2. The rhubarb used as a vegetable consists of the leaf stalks of several hybrids between the species R. rhaponticum, R. undulatum, R. palmatum. The petioles of R. officinale have also been proved to be edible; but that plant is grown more frequently on account of its ornamental foliage (see HORTICULTURE, vol. xii. p. 287). (E. M. H.)

The above article was written by: E. M. Holmes.

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