RHUBARB,. The drug well known by this name is the root of some species of Rheum, an important genus of the natural order Polygonacece, Juss., and referred to Enneandria Trigynia in the Linnsean classification. The roots of all the species are thick and fleshy, generally a good! deal branched, and striking deep into the earth. The leaves and stems are annual. The leaves, which are radical and petiolate, rise in spring, coming up in a thick head folded together, and gradually expanding. The footstalks of the leaves are thick, fleshy, and juicy, varying in length in the different species from a few inches to two feet. The leaves themselves are spreading, and very large, being sometimes two feet in diameter. The flowering stems begin to rise at the end of spring, come into flower in June, and ripen their seeds in August and September. The flowers are in a large terminal panicle or compound raceme. They consist of a coloured six parted perianth. The seeds are three cornered, winged, and have the withered perianth adhering to their base. The rhubarbs are extensively cultivated in this country for the sake of the footstalks, and likewise for the medicinal roots.

When grown for the sake of the latter, they should be sown [7:19:227]in the place where they are intended to remain, that the growth of the roots may not be interfered with; but when meant to be used for culinary purposes, or as ornamental plants, the seedlings may be transplanted in autumn. The most important use of the plants of this genus is to furnish the medicinal substance rhubarb.

It is not a little singular, that though this valuable medicine has been in use for centuries, we are still ignorant as to the precise species which yields it. Many endeavours have been made to ascertain this point, both by investigation of the countries from which the commercial rhubarb is brought, and by cultivating the known species and comparing their roots with the rhubarb of the shops, but none of these attempts hitherto has proved successful. Previous to 1732, rhubarb was believed to be yielded by the Rheum rhaponticum, Linn. This species is distinguished by its leaves being roundish ovate, obtuse, pale green, with a few hairs beneath on the nerves and margins. The footstalks are pale green, striated, channelled above, with rounded edges. The roots are large and thick, much divided, and, like those of most of the other species, reddish brown without, yellow within. It is not found, however, that in cultivated specimens the roots yield a product at all resembling true rhubarb; and as this species is a native of the wild land to the north of the Caspian Sea, between the Volga and Ural rivers, and not, so far as is known, of the country from which rhubarb is believed to come, the opinion that it is the true rhubarb plant has long been abandoned. It is chiefly this species, or hybrids of it, which is so commonly cultivated in gardens for the sake of the leafstalks, which are used extensively in the spring for making tarts and preserves. They have an agreeable acidity, owing to their containing, like some other plants of the same natural order, a considerable proportion of oxalic acid.

In 1732, some seeds sent to Paris and Chelsea as those of the true rhubarb plant were grown, and found to be Rheum undulatum. This species is distinguished by its leaves being oval, obtuse, extremely wavy, of a dark-green colour, and by the footstalks being downy, blood-red, with the upper edges elevated. It is a native of China and Siberia, and was long cultivated by the Russians in the latter country as true rhubarb. The culture, however, is now abandoned, and it is well known that the roots which it yields are widely different from those of the genuine drug.

In 1750, Kaaw Boerhaave obtained some seeds which were said to be those of the true rhubarb; and on being grown, they produced both Rh. undulatum and Rh. palmatum. The latter species is distinguished from all the others by its leaves being palmated, with acuminate segments; and its roots on cultivation have been found by M. Guibour to bear the nearest resemblance, in colour, taste, and smell, to the true rhubarb. It appears, however, from the inquiries of Pallas, that the Bucharian rhubarb merchants knew nothing of such a leaf as that of Rh. palmatam, and described the true rhubarb plant as having round leaves with waved edges. This has been supposed to come near to another species, Rh. compactum, which is also occasionally cultivated in our gardens, but its roots are found to differ from true rhubarb in many particulars. Notwithstanding the doubts raised by Pallas, however, the idea that Rh. palmatum is the true rhubarb plant is still extensively entertained, and it has been stated as such in the new edition of the London Pharmacopoeia. It is very doubtful, however, if a decided opinion upon this point is admissible in the present state of our knowledge regarding this subject.

In the state of uncertainty to which these conflicting opinions gave rise as to the origin of rhubarb, the Empress Catherine U. of Russia, in 1790, sent an apothecary of the name of Sievers into Siberia, to endeavour to penetrate into the rhubarb country and ascertain the true plant; but after four years’ attempts he was ultimately foiled, and returned with no further information than that nothing certain appeared to be known upon the subject

More recently the Rh. Emodi of Dr Wallich (flΛ. Australe, Don), and Rh. Webbianum, both natives of the Hima-layah Mountains, have been found to be valuable as purgatives, and the former was supposed to be the true source of Chinese rhubarb; but Mr Pereira has found that the Hi-malayah rhubarb was quite different from the rhubarb of the shops.

It thus appears that the source of true rhubarb is still unascertained; nor is it at all certain that it is not yielded by more than one species. Professor Royle of King’s College is of opinion, and apparently correctly, that it is obtained in the heart of Thibet, in about 95° east longitude, and 35° north latitude, a country into which as yet no scientific botanist has ever penetrated. It is worthy of remark, that this agrees with the statements of Pallas and other travellers, that the Russian rhubarb is gathered on the mountains surrounding Lake Kokonor, and that this is part of what has been assigned by Murray as the native country of Rh. palmatum.

Here, therefore, an excellent subject for investigation is still open; and it is to be hoped that this desideratum in our knowledge of the botanical materia medica may soon be supplied. Several circumstances however combine to render the attainment of this object difficult. The labour of penetrating into the wild country where the true rhubarb probably grows is not to be overlooked; and jealousy on the part of the dealers in this profitable article of commerce will likewise lead to much inconvenience. It is said that the trade in Russian rhubarb is monopolized by one Buc-hαrian family, who farm it from the Chinese government; and it is not improbable that, in order to prevent the establishment of a rival trade elsewhere, they may already have embarrassed the subject, by purposely furnishing as the seeds of true rhubarb, those of different and inferior species. In attempting to ascertain the true officinal species by cultivation, we are likewise met by this difficulty, that the different species hybridise so readily that their distinctive characters are very readily lost. This is very apparent in the rhubarbs cultivated in our gardens, which, though commonly referred to Rh. rhapontieum, are in great measure made up of hybrids between that species, Rh. compactum, and Rh. hybridum.

Though the true rhubarb plant has not been seen by any scientific botanist, we have some interesting information from other travellers respecting its growth and production. The best accounts appear to be those given by Mr Bell in his journey from St Petersburg to Pekin. Sievers, in his attempts to discover the true rhubarb plant, likewise obtained some information respecting it, and the statements of these travellers differ only in some unimportant particulars. It appears that the plant is not made the subject of special culture, but that enough grows spontaneously to keep up the supply of this valuable drug. The marmots, which breed extensively in this country, contribute in a great measure to the propagation of the plant; for it seems that the seeds germinate almost exclusively on the loose earth turned up by these animals in making their burrows. The natives gather the roots in spring and autumn, and, after removing the cortical part, cut them in small pieces to facilitate the drying. They cut a hole through each piece, and then string them upon a small cord, by which they hang them up to dry on poles or trees, or more commonly about their tents, and occasionally, it seems, upon the horns of their sheep. By this last practice a considerable amount of loss is sustained, as, from the prolonged exposure to moisture, much of the root becomes decayed and useless. According to Sievers, the roots are dried under sheds, out of the rays of the sun, and they sometimes take a whole year to dry.
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Several varieties of rhubarb occur in commerce. The first and most esteemed is Turkey or Russia rhubarb, which was formerly brought to Europe chiefly through the Turkish provinces of Asia Minor, but is now imported through Russia. It is brought from the native country to the frontier town of Kiachta in Siberia, where it is examined by a Russian government officer. All the pieces which are of bad quality are rejected and burned, and those which are good are transmitted to Moscow and St Petersburg, where they are again inspected, and any inferior pieces picked out. From this careful examination Russian rhubarb is always of good quality, and bears a higher price than any other kind.

The pieces of Russian rhubarb are generally from one and a half to two inches broad, sometimes of a flat shape, but more commonly two or three inches long, and somewhat conical. The external surface is always irregular and angular, the bark apparently having been removed in slices. They are always perforated by one large hole, through which the cord has been passed in drying them; occasionally some smaller holes are observed, not passing completely through, which have been made in Russia, for the purpose of examining the interior of the specimens. The colour externally is of a bright golden-yellow, owing to the pieces being covered by powder, formed by their friction upon each other. When broken across they present an irregular and rough surface, having a mottled appearance, owing to the interlacing of yellow and brownish-red veins, which are more distinctly seen when the surface is cut smooth. The smell of the rhubarb is strong and peculiar, and the taste is bitter, astringent, and slightly aromatic. Under the teeth good Russia rhubarb feels gritty, owing to the presence of small crystals of oxalate of lime, which are dispersed in tufts through the root, and which may be seen under the microscope, in a piece which has been boiled in water.

The second variety of rhubarb, though commercially distinct from the Russian, is perhaps originally derived from the same source. It is called East India or Chinese rhubarb, being imported chiefly from Canton or Singapore. It is distinguished from Russian rhubarb by the pieces being larger and heavier, and by their surface being not angular, but rounded, the bark having apparently been removed by scraping, and not by slicing. The holes by which it is perforated are generally smaller than those of the Russian rhubarb, and the portions of the root surrounding the perforation are frequently decayed. The fracture is uneven, and has a mottled appearance, but is usually of a darker colour than the Russian kind. The smell and taste of the Chinese is inferior to that of the Russian, but not in a very marked degree; and it is generally equally gritty under the teeth. The powder of Chinese rhubarb has rather a darker tint than that of the Russian; but the latter is seldom found in the shops pure, and the difference generally is not very apparent. As the Chinese rhubarb is not subjected to the same rigid examination and selection as that brought through Russia, it is of inferior quality, and brings a much lower price in the market. Thus, whilst Russia rhubarb in bond is quoted in the official returns of the prices current, at eight shillings and threepence per pound, the East India is stated to bring only from two shillings and sixpence to four shillings. It does not appear, however, that the Chinese rhubarb is in any essential respect inferior as a medicine to the Russian.

Another variety of rhubarb has been described under the name of Dutch trimmed, or Batavian, which, like the Chinese, is brought from Canton or Singapore, and is always quoted in the prices current as a distinct commercial kind. It is said to resemble the Russia rhubarb in external characters, but is not superior in value to the common Chinese sort, as it appears from the official returns that it brings the same price in the market.

The third commercial variety of rhubarb is the English, or, as it might more appropriately be called, European; for what is called in France French rhubarb is merely an equivalent sort grown in that country. The English rhubarb appears to be chiefly the roots of Rh. palmatum; it is cultivated to a large extent, especially at Banbury in Oxfordshire, where it was first extensively grown about the year 1780, by a Mr Hayward. Towards the end of last century many attempts were made to cultivate the rhubarb in England for medicinal use, accounts of which have been preserved in the Transactions of the Society for the Encouragement of Arts, Manufactures, and Commerce. The expectations which were then formed, and the opinions entertained, of the qualities of the English rhubarb were very sanguine; but though it is still cultivated to a considerable extent for this purpose, it is well known to be very inferior to the foreign kinds. In France a great many varieties of rhubarb are cultivated at a place called Rheumpole, in the department of Morbihan: they are chiefly Rh. undulatum, RA. rhaponticum, and Rh. compactum. The cultivation of Rh. palmatam there has been abandoned, but for what reason is not very apparent. The produce of this cultivation is what is sold in France as French rhubarb.

English rhubarb is found in the shops under two forms; either in pieces cut so as to resemble some of the Asiatic kinds, in which case it is called dressed or trimmed; or in cylindrical pieces four or five inches long, and about one inch thick, which are obviously the smaller portions of the root dried entire or longitudinally split. This last kind is termed stick rhubarb. The first of these is the only one which can be mistaken for foreign rhubarb, but it may at once be distinguished by its being very much lighter than any of the Asiatic kinds, and by its being, especially towards the centre, of a much softer texture. Its fracture, like that of the Russian and Chinese rhubarb, is marked by the reticulated veins, but it has generally rather a pinkish tint. It is sometimes, though not commonly, gritty under the teeth; it has much less astringency and bitterness to the taste than the Asiatic rhubarb, being generally somewhat mucilaginous; and its smell, though often equally strong, is much less aromatic and agreeable. The external appearance of European rhubarb is often very deceptive, for it is a common practice to rub the pieces over with the powder of the Turkey rhubarb, to make it pass for the more valuable drug; but its pinkish colour is easily observed on Brushing the specimen, and its light weight and softer texture at once proclaim the difference.

In selecting rhubarb, the pieces should be found to have a good colour and smell, and to be of a considerable specific gravity. Those which are worm-eaten, or are of a dirty-brown or blackish colour, should be rejected; and, to ascertain these points, brushing the surface should never be neglected, as inferior kinds are very frequently disguised by unprincipled dealers, by covering the surface with powder of good rhubarb; and worm holes are sometimes concealed by stopping them with a paste made of the powder of genuine rhubarb and water.

The chemical analysis of rhubarb is still very imperfect A yellowish crystallizable principle has been obtained from it, to which the names of Rheine, Rhaponticine, and Rhabarbarine have been given; but these various terms have obviously been applied by different chemists to the same substance. This appears to be merely the colouring matter of rhubarb, and not its active principle, which may still be regarded as unknown. Whatever be the nature of the active part of rhubarb, as it exists in the plant it is soluble both in water and alcohol. Water takes up more of the purgative and less of the astringent principles of rhubarb than alcohol; hence infusion is a good liquid form for administering this medicine as a laxative. The watery preparations of rhubarb, however, should always be made [7:19:229]by infusion, and not by decoction, as a high temperature impairs its purgative property. It is for this reason that the common extract of rhubarb of the shops is of no use as a laxative. Rhubarb, from its astringency, has been supposed to contain tannine, but this has not been satisfactorily demonstrated by chemical experiment. The r∞ts contain a certain proportion of starch. This is most abundant in the English sort, which accounts for its generally having a somewhat mucilaginous taste.

The medicinal action of rhubarb varies according to the dose in which it is administered. In small quantities, as three or four grains, it is a gentle stomachic and astringent, and as such is employed in many cases of indigestion, and a relaxed state of the bowels. In cases of diarrhoea in children, which are generally attended with superabundant acidity of the primae viae, there is no safer or more effectual remedy than three or four grains of rhubarb, with twice that quantity of prepared chalk, which may be taken two or three times in the day.

In larger doses, as in quantities from fifteen to thirty grains, rhubarb is a mild and easy laxative, and, from its possessing no irritating qualities, is valuable in all cases where the bowels might be injured by more active substances. It is consequently well adapted to the more irritable constitutions of children and females. Where there is derangement of the stomach or bowels from indigestible matter, or from acidity, rhubarb is a very valuable laxative; and in such cases its action is very much improved by its being combined with magnesia. The well-known Gregorfs powder, introduced by the late professor of physic at Edinburgh, consists of two parts of rhubarb, three of calcined magnesia, and one of ginger, and is one of the best remedies which can be employed in such cases. The usual dose of this for an adult is a tea-spoonful, which may be taken in water, combined with some aromatic tincture, or with a little of the tincture of rhubarb itself.

The colouring matter of rhubarb, and probably its purgative principle, are absorbed into the circulation during its action on the system. That the colouring matter is absorbed, is demonstrated by its presence in the urine, to which it communicates a reddish-brown colour; a circumstance always to be borne in mind in forming an opinion of any case in which rhubarb may have previously been taken. The absorption of the purgative principle is inferred from the fact, that the milk of nurses who are using this medicine sometimes exerts a laxative influence on children at the breast.

In the year 1835, the quantity of rhubarb imported into Great Britain amounted to 81,100 lbs., and in 1836 to 122,142 lbs., of which in the former year 44,522 lbs., and in the latter 44,468 lbs., were retained for home consumption; the duty being one shilling per lb., yielded a net revenue of L.2220 in the one year, and L.2236 in the other. (b. m.)