1911 Encyclopædia Britannica/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 Rheum barbarum or Reu barbarum, a designation applied to the drug as early as the middle of the 6th century, and apparently identical with the ρῆον or ρᾶ of Dioscorides, described by him as a root brought from beyond the Bosporus. 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 frontiers, Chinese rhubarb reached Europe chiefly by way of Moscow; and in 1704 the rhubarb trade became a monopoly 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; 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. 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 cinnamon and four times that of saffron, and in an English price list bearing date of 1657 it is quoted at 16s. per ℔, opium being at that time only 6s. and scammony 12s. per ℔.
The dose of rhubarb is anything from ½ up to 30 grains, according to the action which is desired. The British Pharmacopeia contains seven preparations, only one of which is of any special value. This is the Pulvis Rhei Compositus, or Gregory's powder, which is composed of 2 parts of rhubarb, 6 of heavy or light magnesia and 1 of ginger. The dose is 20 to 60 gr.
Rhubarb is used in small doses—½ to 2 gr.—as an astringent tonic, since it stimulates all the functions of the upper part of the alimentary canal. In many cases of torpid dyspepsia it is very efficient when combined with the sub nitrate of bismuth and the bicarbonate of sodium. The more characteristic action of rhubarb, however, is purgation, which it causes in doses of 15 gr. and upwards. The action occurs within seven or eight hours, a soft, pulpy motion of a yellow colour being produced. The colour is due to the chrysarobin, which is also the purgative constituent of the drug. Rhubarb is also a secretory cholagogue, increasing the amount of bile formed by the liver. The drug is apt to cause colic, and should therefore never be given alone. The ginger in Gregory's powder averts this unpleasant consequence of the aperient properties of rhubarb. The drug is peculiar in that the purgation is succeeded by definite constipation, said to be due to the rheotannic acid. This explanation is hardly satisfactory, however, since it is difficult to see how the rheotannic acid can be retained in the bowel during the process of purgation. Rhubarb has, therefore, definite indications and contra-indications. It is obviously worse than, useless in the treatment of chronic constipation, which it only aggravates. On the other hand, it is very valuable in children and others, when diarrhoea has been caused by an unsuitable dietary. The drug removes the indigestible residue of the food and then gives the bowel rest. Rhubarb is also useful in the weaning of infants, since it, is partly excreted in the maternal milk, and gives it a bitter taste which the baby dislikes.
Some chrysarobin is absorbed and is excreted in the urine, which it slightly increases and colours a reddish brown. The colour is discharged by the addition of a little dilute hydrochloric acid to the urine.
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. tangulicum, 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.
Chemistry.—The most important constituent of this drug, giving it its purgative properties and its yellow colour, is chrysarobin, C30H26O7, formerly known as rhein or chrysophan. The rhubarb of commerce also contains chrysophanic acid, a dioxymethyl anthraquinone, C14H5(CH3)O2(OH)2, of which chrysarobin is a reduction product. Nearly 40% of the drug consists of calcium oxalate, which gives it the characteristic grittiness. There is also present rheotannic acid, which is ofisome practical importance. There are numerous other constituents, such as emodin, C15H10O5, mucilage, resins, rheumic acid, C20H15O9, aporrhetin, &c.
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. Two of the most important centres of the trade are Sining-fuin the province of Kan-suh, and Kwanhien 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 sulgected to a preliminary drying on stone slabs heated by fire un erneath. 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.
European Rhubarb.—As early as 1608 Prosper Alpinus of Padua cultivated as the true rhubarb a plant which is now known as Rheum rhaponticum, a native of southern Siberia and the basin of the Volga. This plant was introduced into England through 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 considerable 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. More recently 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%, English rhubarb 21% and R. officinale 17%. In France the cultivation of rhubarb was commenced in the latter half of the 18th century-R. compactum, R. palmatum, R. rhaponticum and R. undulatum 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 compactum was begun in Moravia in the beginning of the present century by Prikyl, an apothecary in Austerlitz, and until about fifty 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. 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 R. rhaponticum and its varieties, and R. undulatum. It is known in America as pie-plant. Plants are readily raised from seed, but strong plants can be obtained in a much shorter time by dividing the roots. Divisions or seedlings are planted about 3 ft. apart in ground which has been deeply trenched and manured, the crowns being kept slightly above the surface. Rhubarb grows freely under fruit-trees, but succeeds best in an open situation in rich, rather light soil. The stalks should not be pulled during the first season. If a top-dressing of manure be given each winter a plantation will last good for several years. Forced rhubarb is much esteemed in winter and early spring, and forms a remunerative crop. Forcing under glass or in a mushroom house is most satisfactory, but open-ground forcing may be effected by placing pots or boxes in a good depth of stable litter over the roots and burying and leaves. Several other species, such as R. palmatum, R. officinale, R. nobile and others, are cultivated for their fine foliage and handsome inflorescence, especially in wild gardens, margins of shrubberies and similar places. They succeed in most soils, but prefer a rich soil of good depth. They are propagated by seeds or by division.
- According to Mr F. Newcombe, Med. Press and Circ., August 2, 1882, the Chinese esteem the Shen-se rhubarb as the best, that coming from Kanchow being the most prized of all; Sze-chuen rhubarb has a rougher surface and little flavour, and brings only about half the price; Chung-chi rhubarb also is greatly valued, while the Chi-chuang, Tai-huang and Shan-huang varieties are considered worthless.