Rheum. U. S. (Br.) Rhubarb.
"The rhizomes and roots of Rheum officinale Baillon, Rheum palmatum Linné, and the var. tanguticum Maximowicz (Fam. Polygonaceae), and probably other species of Rheum grown in China and Thibet, deprived of most of the bark tissues and carefully dried. Preserve Rhubarb in tightly-closed containers, adding a few drops of chloroform or carbon tetrachloride, from time to time, to prevent attack by insects." U. S. "Rhubarb is the rhizome of Rheum officinale, Baill., and other species of Rheum, collected in China and Thibet, deprived of most of the cortex, and dried." Br.
Rhei Rhizoma, Br.; Rhubarb Root; Rhubarbe de Chine, Fr. Cod.; Rhubarbe, Fr.; Rhabarber, G.; Rabarbaro, It.; Ruibarbo, Sp.; Hainoung, Chin.; Schara-modo, Thibet.
Notwithstanding the length of time that rhubarb has been in use, it has not yet been determined from what precise plant the Asiatic drug is derived, the remoteness of the region where it is collected, and the jealous care with which the monopoly of the trade is guarded, having prevented accurate information.
The terms rha and rheon, from the former of which were derived the names rhabarbarum and rhubarb, and from the latter the botanical title Rheum, were applied by the ancients to a root which came from beyond the Bosphorus, and which is supposed, though upon somewhat uncertain grounds, to have been the product of Rheum rhaponticum L., growing on the banks of the Caspian Sea and the Volga, This species was also at one time believed to be the source of the medicine now in use; but the true rhubarb has long been known to be wholly distinct from the Rhapontic, and derived from a different source. It was not until the year 1732 that any probable information was obtained as to its real origin. At that time plants were received from Russia by Jussieu in France, and Rand in England, which were said to be of the species affording the genuine rhubarb, and were named by Linnaeus, under this impression, Rheum Rhabarbarum, a title which has since given way to Rheum undulatum. Subsequently, Kaau-Boerhaave obtained from a merchant, who dealt in the rhubarb of Tartary, some seeds which he said were those of the plant producing the root sold by him. These, having been planted, yielded two species of Rheum. R. undulatum, and another which Linnaeus named R. palmatum. Seeds transmitted by Mounsey from St. Petersburg to Hope, and planted in the botanic garden at Edinburgh, produced the latter species, and the same was also raised at Upsala from a root received by Linnaeus from De Gorter, and was described in 1767 by the younger Linnaeus, two years after the appearance of Hope's paper in the Philosophical Transactions. Thus far the evidence appears equally in favor of R. palmatum and R. undulatum. Colonel Przewalski concluded from personal observation that R. palmatum produces rhubarb; but the specimens of the root which he brought to St. Petersburg were stated by Dragondorff to be essentially different from true rhubarb. Claims have also been made from time to time for various other species of Rheum as sources of the drug. Pallas, upon exhibiting the leaves of R. palmatum to some Bucharian merchants, was told that the leaves of the rhubarb plant were entirely different in shape, and the description he received of them corresponded more closely with those of R. compactum than any other known species. Seeds of this plant were, moreover, sent to Miller from St. Petersburg as those of the true Tartarian rhubarb. Wallich, superintendent of the botanical garden at Calcutta, received seeds that were said to be those of the plant which yielded the Chinese rhubarb, growing on the Himalaya Mountains and the highlands of Tartary. These produced a species not previously described, which Wallich named R. Emodi, from the native title of the plant. It is the R. australe of Don and of Colebrooke, and has been ascertained to afford a root which, though purgative, is very unlike the official rhubarb. In 1867, French missionaries in Southeastern Thibet forwarded to Soubeiran of Paris, live specimens of a plant which they asserted to yield the true rhubarb, and Baillon subsequently described the flowering plant under the name of R. officinale. Its root resembles the true rhubarb, but the most careful cultivation has failed to obtain an identical product, and it cannot yet be considered as settled how far the commercial drug is obtained from it, Senier found that, as raised in England, the root of R. officinale yielded less than half the percentage of extract obtained from the East Indian drug. In ten grain doses the extract was decidedly cathartic.
Tschirch in discussing the origin of Chinese Rhubarb has come to the conclusion that that obtained from Szetschwan, "southern" rhubarb, is derived from Rheum officinale, while that obtained from Kukunoor, "northern" rhubarb, is the product of Rheum palmatum tanguticum (A. Pharm., 1907, p. 680; and S. W. P., 1910, xlviii, 292).
Hosseus (P. J., 1911, 87, p. 429) as a result of study of material furnished by Tafel, a Tibetan explorer, concludes that the best medicinal rhubarb is derived from R. palmatum. He believes that the belief that some of it comes from the R. officinale or other species is due to the fact that Tibetans dig up the root of these other species of rhubarb for the purpose of deceiving Europeans.
All the plants of this genus are perennial and herbaceous, with large branching roots, which send forth vigorous stems from four to eight feet or more in height, surrounded at their base with numerous very large petiolate leaves, and terminating in lengthened branching panicles, composed of small and very numerous flowers, resembling those of the Rumex or dock. There is some difficulty in arranging the species, in consequence of the tendency of the cultivated plants to form hybrids, and it is frequently impossible to ascertain to which of the wild type's the several garden varieties are to be referred. Lindley, Flora Medica, states that R. rhaponticum, R. hybridum, and R. compactum, and their hybrids, are the common garden rhubarbs.
R. officinale Baillon is described in the Pharmacographia "as a perennial, noble plant, resembling the common garden rhubarb, but of larger size. It differs from the latter in several particulars: the leaves spring from a distinct crown rising some niches above the surface of the ground; they have a subcylindrical petiole, which, as well as the veins of the under side of the lamina, is covered with a pubescence of short erect hairs. The lamina, the outline of which is orbicular, cordate at base, is shortly 5- to 7-lobed, with the lobes coarsely and irregularly dentate; it attains 4 to 4 1/2 feet in length, and rather more in breadth. The first leaves in spring display before expanding the peculiar metallic red hue of copper."
Besides the species already mentioned, R. leucorrhizum, growing in the Kirgheeze desert in Tartary, R. capsicum, from the Altai Mountains, R. webbianum, R. speciforme, and R. moorcraftianum, natives of the Himalaya Mountains and R. crassinervium and R. hybridum, cultivated in Europe, but of unknown origin, yield roots which have either been employed as purgatives or possess properties more or less analogous to those of official rhubarb, though they have not entered into general commerce. In Java, the root of an indigenous species is used as a purgative. According to the analysis of J. H. Schmidt, it contains more chrysophan and emodin, and less chrysophanic and rheotannic acids, than does the official drug.
According to Aitchison (Nature, July 9, 1885), a rhubarb plant has been found in Northern Afghanistan in which there are usually only three enormous root leaves four feet long and five feet broad, lying flat upon the ground. The fruit is large and of a brilliant scarlet. The root is said to possess purgative properties, but the fruit is preferred, and is given in the form of a decoction.
Rhubarb is produced abundantly in the elevated lands of Tartary, about the lake Koko Nor, and is said to be cultivated in the neighboring Chinese province of Shensee, and in that of Sechuen. From these sources it is generally supposed that our supplies of Russian and Chinese rhubarb were exclusively derived; but the root is also collected in Bootan and Thibet, on the north of the Himalaya Mountains, and it is probable that the plant pervades the whole of Chinese Tartary. It flourishes best in a light sandy soil. It is stated by Bell, who, on a. journey from St. Petersburg to Pekin had an opportunity of observing it in a growing state, that it is not cultivated by the Tartars, but springs up spontaneously, in tufts, wherever the seeds have fallen upon the heaps of loose earth thrown up by the marmots. In other places the thickness of the grass prevents their access to the soil. The root is not considered sufficiently mature for collection until it has attained the age of six years. It is dug up twice a year in Tartary, in the spring and autumn; in China not till the winter. After removal from the ground, it is cleaned, deprived of its cortical portion and the smaller branches, and then divided into pieces of a convenient size. In China these are bored with holes, and strung upon cords to dry—according to Bell, about the tents and on the horns of sheep; according to Sievers, under sheds, by which the rays of the sun are excluded, while the air has free access. The Chinese are said first to place the pieces on a stone slab heated by fire beneath, and afterwards to complete the drying process by exposing them to the sun and air. In Bootan the roots are hung up in a. kind of drying room, in which a moderate and regular heat is maintained. Much time and attention are devoted to the preparation of the root, and Sievers states that a year sometimes elapses from the period of its collection before it is ready for exportation. A large proportion of its weight is lost in drying, according to some accounts four-fifths, according to others not less than seven-eighths. It is probably in order to favor the drying that the periderm is removed. Rhubarb which has been dried by artificial heat is known commercially as high dried and often can be recognized by its more or less blackened surface, and its heavy, scarcely fragrant odor. The trade in rhubarb is said to have formerly centered in the Chinese town of Sinin, where a Bucharian company or family was established which possessed a monopoly of this trade in consideration of a tribute paid to the government. At present rhubarb is chiefly purchased for the European trade at the town of Hankow, on the upper Yangtse, the yearly export reaching over 5000 peculs (pecul = 133.33 lbs.). There were formerly two varieties of Asiatic rhubarb, the Russian and the Chinese, but at present little or no rhubarb finds it way overland to Europe. As long back as 1687, the Russian government subjected the export of rhubarb from China into Russia to official surveillance, and finally monopolized the trade entirely. At Kiakhta a very rigorous inspection of the drug was enforced, the selected pieces being finally sewed into linen sacks pitched and coated with hide. All the pieces which did not pass examination were committed to the flames, and the remainder was sent to St. Petersburg. This variety was sometimes called Turkey rhubarb, from the circumstance that it was formerly derived from the Turkish ports, whither it is said to have been brought from Tartary by caravans through Persia and Anatolia. Inferior parcels of the root, which could not pass the inspection of the Russian authorities, were said to enter Russia by Tashkend, and to be known to the druggists of that country by the name of Tashkend rhubarb. Russian rhubarb no longer occurs in commerce. The description of it is given in the U. S. D., 19th edition, page 1061.
CHINESE RHUBARB (India Rhubarb, Rheum Sinense vel Indicum) is in cylindrical or roundish pieces, sometimes flattened on one or both sides, of a dirty brownish-yellow color externally, appearing as if the cortical portion of the root had been removed by scraping, and the surface rendered smooth and somewhat powdery by attrition. The best pieces have a rather close and compact texture, and, when broken, present a ragged uneven surface, variegated with intermingled shades of dull red, yellowish, and white, which are sometimes diversified or interrupted by darker colors, and especially marked with dark lines so arranged as to form an internal ring of star-like spots. The pieces are generally perforated with small holes, intended for convenience of suspension during the drying process, and portions of the suspending cord are not unfrequently found remaining in the holes. According to Elborne (P. J., xv, 497), Chinese rhubarb is the product of R. palmatum and R. officinale, the first variety has a red-grained fracture with white latticework veins, while the second variety has a longitudinal ramification of white veins with a black-grained fracture. Chinese rhubarb has a peculiar somewhat aromatic odor, and a bitter, astringent taste, is gritty when chewed, imparts a yellow color to the saliva, and affords a yellowish powder with a reddish-brown tinge. With the pieces of good quality others often come mingled, defective from decay or improper preparation. These are usually lighter, and of a dark or russet color. Like all the other varieties of rhubarb, this is liable to be attacked by insects, and in almost every large parcel pieces may be found which have suffered from this cause. The Shensi variety is preferred, that of Sechuen and Kansuh are less valuable.
Chinese rhubarb is the only kind recognized by the U. S. P., and is officially described as "sub-cylindrical, barrel-shaped, or conical pieces known in commerce as 'rounds,' or in plano-convex pieces known in commerce as 'flats' or in irregularly formed pieces, frequently with perforations. It is hard and moderately heavy; attaining a length of 17 cm. and a diameter of 10 cm., often cut in pieces of variable form and size; outer surfaces yellowish-brown, mottled, with alternating, longitudinal striae of grayish-white parenchyma and reddish or brownish medullary rays; small stellate groups of fibro-vascular tissue and occasionally reddish-brown cork patches, smooth and sometimes covered with a bright, brownish-yellow powder; fracture uneven and granular, presenting a characteristic mottled appearance; odor aromatic, characteristic; taste characteristic, slightly bitter and astringent, gritty when chewed and tingeing the saliva yellow. Under the microscope, sections of Rhubarb show numerous thin-walled parenchymatous cells containing either a large number of starch grains or a. single large rosette aggregate of calcium oxalate; scattered among the parenchyma are stellate groups of compound fibro-vascular bundles, the latter composed of narrow medullary rays separating the wedges, having large tracheae in the outer part and separated by a prominent cambium from an internal phloem or sieve; among the grayish-white parenchyma of the inner bark occur narrow, yellowish-brown, irregular medullary rays. Not more than 15 per cent. of the drug should show a hollow or dark central area. The powder is bright orange-yellow to yellowish-brown; becoming red with alkalies; when examined under the microscope it exhibits calcium oxalate in rosette aggregates, mostly from 0.05 to 0.1 mm. in diameter, occasionally attaining a diameter of 0.15 mm.; starch grains numerous, somewhat spherical, single or 2- to 4-compound, each with a single cleft, from 0.002 to 0.02 mm. in diameter; tracheal fragments few, mostly reticulate, occasionally spiral. Boil 0.1 Gm. of powdered Rhubarb with 10 mils of an aqueous solution" of potassium hydroxide (1 in 100); allow it to cool, filter, acidulate the filtrate with hydrochloric acid and shake it with 10 mils of ether; on standing the ethereal layer is colored yellow. Shake this ethereal solution with 5 mils of ammonia water; the latter is colored cherry-red (presence of emodin) and the ethereal layer remains yellow (presence of chrysophanic acid). Rhubarb, when exhausted with diluted alcohol, yields not less than 30 per cent. of dry extract. Rhubarb yields not more than 13 per cent. of ash." U. S.
"In compact, firm, cylindrical, barrel-shaped, conical or plano-convex pieces, often perforated, the perforation sometimes containing a fragment of cord. Surface rounded or slightly angular, but not shrunken, marked with reddish-brown lines embedded in a whitish ground-substance; usually covered with a bright brownish-yellow powder. Fracture granular and uneven, the pinkish-brown fractured surface exhibiting numerous reddish-brown points and lines on a white ground-substance. For a short distance within the cambium the structure is radiate; within this there' is a more or less distinct ring of closely approximated vascular bundles with central bast and radiating, reddish-brown medullary rays; in the parenchymatous cells abundant starch grains, an amorphous yellow substance and very large cluster-crystals of calcium oxalate. In powdered Rhubarb large cluster-crystals of calcium oxalate, often more than 100 microns in diameter, simple or compound starch grains, the single grains seldom exceeding 20 microns in diameter, fragments of reticulated vessels and of parenchymatous tissue, and small yellowish masses and globules which assume a reddish-pink color with solution of ammoniac it is free from added starch and from sclerenchymatous cells and fibres. Characteristic, somewhat aromatic odor; taste bitter, slightly astringent. Ash not more than 15 per cent." Br.
EUROPEAN RHUBARB.—In various parts of Europe, particularly in England, France, Belgium, and Germany, the rhubarb plants have been cultivated for many years, and considerable quantities of the root were at one time brought into the market. At present it appears not to be imported into the United States.
English Rhubarb.—This formerly came in two forms. In one the root was cut and perforated in imitation of the Russian. The pieces were of various shapes and sizes, sometimes cylindrical, but more commonly flat, or somewhat lenticular, and of considerable dimensions. In the other, the so-called stick rhubarb, the pieces were somewhat cylindrical, five or six inches long by an inch or less in thickness, and more or less irregular upon the surface, as if they had shrunk unequally in drying. English rhubarb (from Rheum rhaponticum) is lighter than the Asiatic, more spongy, and often somewhat pasty under the pestle. It is redder, and when broken exhibits a more compact and regular marbling, the pinkish lines being arranged like rays from the centre towards the circumference. The "star-like spots" are either wanting or very few and scattered. The powder also has a brighter yellow tint. The odor is feeble and less aromatic than that of the Asiatic varieties; the taste is astringent and mucilaginous, with little bitterness, and the root, when chewed, scarcely feels gritty between the teeth, and but slightly colors the saliva. Few crystals of calcium oxalate are discoverable by means of the microscope. Much English rhubarb is obtained from R. officinale, and is put on the market in flat, concave, and convex pieces weighing from three to four ounces each. Externally the convex surface has deep longitudinal furrows and a longitudinal ramification of conspicuous veins, giving rise to an appearance of net-vein markings. In the centre of the concave surface is a small hole similar to that formerly seen in Russian rhubarb. On the inner surface the stellate markings resemble very closely those found in the East Indian rhubarb. The fracture of this form is not red, but shows a whitish parenchymatous tissue with blackish veins. When rapidly grown in rich soil, English rhubarb is lighter, more spongy, and less active than when slowly grown without high cultivation. It is probable that the powder is used to adulterate that of true Asiatic rhubarb, but of this we have no positive evidence.
French Rhubarb. Rhapontic Rhubarb. Crimea Rhubarb.—The rhubarb produced in France is, according to Guibourt, chiefly from R. rhaponticum, R. undulatum, and R. compactum, that of R. palmatum, which most closely resembles the Asiatic, having been found to degenerate so much as not to be a profitable object of culture. Most of the French rhubarb is produced in the neighborhood of L'Orient, in the department of Morbihan, and the spot where it grows has, from this circumstance, received the name of Rheumpole. Two kinds were described by Guibourt, both under the name of Rhapontic root—one proceeding from the R. rhaponticum, growing in the gardens in the environs of Paris; the other, from this and the two other species above mentioned, cultivated at Rheumpole.
Rhapontic rhubarb is still found to some extent in European markets. Tschirch has proposed a ready method for detecting the admixture. It depends on the insolubility in ether of the crystalline principle rhaponticin or ponticin. (A. Pharm., 1905, p. 443; and S. W. P., xliii, p. 253.) Hesse has also made an elaborate study on the chemistry of rhapontic root grown in Austria. (J. f. prakt. Chem., 1908, lxxvii, p. 320.)
The rhapontic root differs in section from true rhubarb by its distinctly radiated structure, unbroken by the peculiar arrangement (star-like spots) of the vascular tissue which occurs in true rhubarb.
Choice of Rhubarb.—In selecting good rhubarb, without reference to the commercial variety, those pieces should be preferred which are moderately heavy and compact, of a bright color, brittle, presenting when broken a fresh appearance, with reddish and yellowish veins intermingled with white, of an odor decidedly aromatic, of a bitter and astringent not mucilaginous taste, feeling gritty and staining the saliva yellow when chewed, and affording a powder either bright yellow, or yellow with but a slight reddish-brown tinge. When very light, rhubarb is usually rotten or worm-eaten; when very heavy and compact, it is of inferior species, culture, or preparation. Rotten, worm-eaten, or otherwise inferior rhubarb is often powdered, and colored yellow with turmeric, and the shavings left when Chinese rhubarb is trimmed for powdering, or to imitate the Russian, are applied to the same purpose. The stellate markings observed in the cut or broken surface of the Chinese rhubarb has been believed by various pharmacologists to be of great practical value in determining the true character of the rhizome and especially in enabling a distinction between the Chinese and European rhubarb to be made. There has been a general concurrence with the statements of Tschirch that the star spots are never present in the root, occurring only in the rhizome. In an elaborate re-examination of this subject by Jakabhasy, however, the star spots were found in the root as well as in the root stock and also in the European as well as in the Asiatic rhubarb. Nevertheless, Jakabhasy states that it is possible to distinguish the two rhubarbs by the fact that in the European Rhubarb the star spots occur in greater number on the longitudinal section while in the Chinese rhubarb they are present on the transverse section, where they form a circle. He believes also that the superabundance of starch and the lack of crystals in the star spots are diagnostic of the European drug. When the rhubarb is powdered these characteristics are not available, under which circumstances the percentage of ash seems to be valuable. The Chinese rhubarb, unless of very inferior quality yields from 8 to 25 per cent.; the European 1.3 to 6 per cent. of ash. According to Jakabhasy, Shensi is the best, Shanghai the poorest, and Canton the intermediate variety of Chinese rhubarb. Of the European the English is the most, the French next, and the Austrian the least active.
Chemical Properties.—Rhubarb yields all its activity to water and alcohol. The infusion is of a dark reddish-yellow color, with the taste and odor of rhubarb, and the residue, after sufficient maceration, is whitish, inodorous, and insipid. By long boiling the virtues of the medicine are impaired. The first examination of rhubarb yielding results of value was that of Schlosberger and Dopping. Besides extractive, tannic and gallic acids, sugar, starch, pectin, lignin, calcium oxalate and various inorganic salts, they discovered three coloring principles, holding an intermediate place between resin and extractive matter, being freely soluble in alcohol, and slightly so in water. Two of these were uncrystallizable, and denominated brown resin and red resin, or phaeoretin and erythroretin; the other, crystallizable in granular crystals, and identical with chrysophanic acid; previously discovered by Rochleder and Heldt in the yellow lichen, or Parmelia parietina of Sprengel. Chrysophanic acid crystallizes in golden-yellow needles or plates melting at 102° C. (215.6° F.), and is soluble in ether, alcohol, or benzene. Alkalies also dissolve it, forming fine dark red solutions. Its formula is C15H10O4, and it is now: recognized as a derivative of anthracene, C14H10, and as closely related to alizarine, C14H8O4. It bears to methyl-anthracene, C14H9(CH3), the same relation that alizarine bears to anthracene. Hence, on distilling it with zinc dust, methyl-anthracene is formed from it by reduction.
De La Rue and Muller (J. Chem. S., x, 298) extracted from rhubarb emodin, which crystallizes in orange-colored prisms. Its formula is C15H10O5. and it is a trioxymethylanthraquinone. The relations of both this compound and chrysophanic acid to alizarine and anthracene will be better shown by writing their molecular formulas, as follows:
- C14H10 - Anthracene.
- C14H6(OH)2O2 - Alizarine.
- C14H5(CH3)(OH)2O2 - Chrysophanic Acid.
- C14H4(CH3)(OH)3O2 - Emodin.
Kubli (Ph. Z. R., 6, p. 603) obtained results both confirmatory and explanatory of those already given. He found a glucoside, chrysophan, C27H30O14, which, under the influence of dilute acids or ferments, splits up into chrysophanic acid and sugar, according to the reaction C27H30O14 + 2H2O = C15H10O4 + 2C6H12O6 also a characteristic tannic acid, rheotannic acid, C27H30O14, which is decomposed by dilute acids into rheumic acid, C20H16O9, and sugar. Chrysophan is a yellowish powder, abundantly present in rhubarb, soluble in water or alcohol, not in ether; rheotannic acid is a reddish brown powder, sparingly soluble in cold water. Kubli found further a colorless neutral compound, sparingly soluble in hot water, of the formula C10H12O4, which he did not name. He stated that chrysophanic acid is not found in rhubarb, but is produced when the root is digested in water through the breaking up of the glucoside chrysophan, probably under the action of a ferment. This ferment he believes to be soluble in water, but insoluble in alcohol, and that on this account an alcoholic extract of the root can be evaporated without the formation of chrysophanic acid. On the other hand, it is to the presence of this ferment that he attributes the progressive deposition of chrysophanic acid from an extract of rhubarb prepared with diluted alcohol. (Ph. Z. R., xxiv, 193.) O. Hesse (Proc. A. Ph. A., 1896, 549) found in addition to chrysophanic acid, C15H8O2(OH)2, and emodin, C15H7O2(OH)3, a third crystalline principle, which he named rhein, and ascribes to it the formula C15H6O2(OH)4. Hesse calls attention to the relation these formulas bear to one another. Rhein forms microscopic yellowish-brown scales, is insoluble in water, ether, and benzene, but sparingly soluble in alcohol. It dissolves readily in aqueous solutions of the alkalies and alkaline carbonates, forming deep purple-red solutions. Hesse also finds an amorphous resinous substance, upon which, he states, the entire activity of rhubarb depends. Dragendorff states that from 11 to 17 per cent. of arabic acid and pectose are present in rhubarb. Hunkel (Ph. Archiv., Nov., 1900, 201) reviewed the investigations of various chemists and isolated tanoid by the process of Lowe and a phenolic body (unnamed) which had not been previously described.
The most important researches upon the constituents of rhubarb were made by Tschirch and Heuberger (A. Pharm., Nov. 21, 1902, 596, 630, and Ph. Ztg., Aug. 3, 1904, 651). Their conclusions are that rhubarb contains primarily two classes of substance's. 1. Tannoglucosides; 2. Anthraglucosides. These two classes cannot be sharply separated from each other and are therefore associated together in all extractions. Both of these are characterized by their ready decomposition and conversion into secondary products, such conversion resulting even during the treatment of the drug with ordinary solvents. Thus, the ether extraction has been found to contain the products of the hydrolysis of the anthraglucosides, namely, chrysophanic acid, emodin and rhein. It is however not proven (indeed not even probable) that the tannoglucosides combine with the anthraglucosides to form so-called double glucosides. On the contrary, the indications are that these two classes of glucosides occur beside each other; furthermore, the relatively large quantity of tannoglucosides and their hydrolytic products is noteworthy and that, therefore, the activity of rhubarb is not attributable solely to the anthraglucosides; but the activity of the latter must be materially modified by that of the tannoglucosides. To what degree the primary tanno- and anthraglucosides have become hydrolyzed in the drug itself, it is difficult to determine; it is certain, however, that the drug contains a considerable quantity of free oxy-methylanthraquinones, while it is probable that the formation of the secondary glucosides results during the extraction and manipulation of the extract.
Tschirch sums up the results of the investigation as follows: Aweng's Double Glucoside is in its essentials identical with tannoglucoside, but contains some anthraglucoside. Aweng's Frangulic Acid is a secondary product of the decomposition of tannoglucoside, containing variable quantities of anthraglucoside as impurity. Kubli's Rheumtannic Acid and Hunkel's Tanoid are identical with tannoglucoside, but less pure. Kubli's and Hunkel's Rheum Acid is identical with rheum red, and therefore a product of the hydrolysis of tannoglucoside. Schlossberger and Dopping's Aporetin and Phaeoretin are impure, difficultly soluble tannoglucoside. Erythroretin is a mixture of chrysophanic acid, emodin and rhein. Garot's Erythrose is chrysamic acid. Rhein, yielding only a diacetyl derivative, cannot be regarded as being tetraoxymethyl-anthraquinone. It has the composition C15H8O6 (not C15H10O6, Hesse) which formula corresponds to a methylene ether of a tetraoxyanthraquinone. Dragendorff's, Greenish's and Elborne's Cathartic Acid is an impure tannoglucoside, containing anthraglucosides and some albuminoid substances. Gilson's Chrysophan belongs to the anthraglucosides. Aweng's Secondary Glucosides are secondary, mostly difficultly soluble hydrolytic products of the primary tanno- and probably also of the anthraglucosides.
Finally, Tschirch determined that rhubarb contains no resins whatever; that the rheo-tannoglucosides and their products of decomposition and hydrolysis are devoid of purgative activity, and that such activity is due solely to the anthraglucosides and their derivatives. Rhubarb contains no other body besides the latter that has peristaltic effect on the intestinal tract.
As regards the rheo-tannoglucoside, its medicinal activity is confined to the tonic and mildly astringent effect produced on administering the drug. Tschirch (Ph. Ztg., Aug. 3, 1904, 651) recommended a method for assaying rhubarb based on the volumetric estimation of the free oxymethylanthraquinones, dependent on the ease with which the anthraglucosides can be hydrolyzed with sulphuric acid. See also Proc. A. Ph. A., 1905, 627.
There are other interesting principles in rhubarb. Some have been disposed to ascribe its odor to a volatile oil, but this has not been isolated. The calcium oxalate is interesting from its quantity, and from the circumstance that, existing in distinct crystals, it occasions the grittiness of the rhubarb between the teeth. The proportion seems to vary exceedingly in different specimens. According to Scheele and Henry, it constitutes nearly one-third, and Queckett found between 35 and 40 per cent., while Brandes obtained only 11, Schrader only 4.5 parts in the hundred, and Dragendorff, in five samples analyzed, from 1.2 to 5.6 per cent. Little or no difference of composition has been found between the Russian and the Chinese rhubarb. The European contains but a small proportion of calcium oxalate, and is therefore less gritty when chewed. It has, however, more tannin and starch than the Asiatic.
When powdered rhubarb is heated, odorous yellow fumes rise, which are probably in part the vapor of chrysophanic acid. Its infusion is reddened by the alkalies, in consequence of their union with this acid, and their reaction on the other coloring principles. It yields precipitates with gelatin, most of the acids, ferric salts, lead acetate, mercurous nitrate, silver nitrate, stannous chloride, lime water, and solutions of quinine. Nitric acid occasions at first a turbidness, and afterwards the deposition of a yellow precipitate. The substances producing precipitates may be considered as incompatible with the infusion.
For a method of detecting the presence of turmeric in powdered rhubarb by the influence of chloroform on the coloring principles of each of these substances, and of distinguishing through the same agency between the true Chinese rhubarb and that of European origin, the reader is referred to a paper, by W. L. Howie, contained in A. J. P. (Jan., 1874, 16), from P. J. (Nov. 15, 1873); see also P. J., 1898, 126.
Uses.—Rhubarb contains cathartic principles of the anthraquinone series. It differs from drugs of this group—such as aloes, cascara, etc. —in that it has a larger percentage of tannic acid. On account of the considerable quantity of tannin its purgative action is often followed by constipation. This sequence of effects has led to its use in the treatment of diarrheas, especially of the inflammatory type, on the theory that the catharsis it caused would evacuate the irritant materies morbi, and that its subsequent astringency would check the excessive secretion. The logic is plausible, but erroneous. As the action of its cathartic principles is limited to the lower bowel it has very little influence in cleaning out the smaller bowel which is the more frequently involved in acute diarrheas. In inflammations of the colon, such as dysentery, its use might appear more reasonable, but even here it is greatly inferior to less irritant laxatives because it acts chiefly by virtue of its local irritant influence. Rhubarb is also widely prescribed in atonic dyspepsia attended with constipation. It is frequently combined with an alkali, either magnesia or soda.
It sometimes occasions griping. Its coloring principle is absorbed, and may be detected in the urine. By its long-continued use the perspiration, especially that of the axilla, is said to become yellow, and the milk of nurses cathartic. It gives a yellow color to the alvine discharges.
By the roasting of rhubarb its cathartic property is diminished, probably by the volatilization of the purgative principle, while its astringency remains unaffected. When so treated it is termed torrefied rhubarb. This mode of treatment has been sometimes resorted to in cases of diarrhea. By long boiling the same effect is said to be produced.
Powdered rhubarb has been usefully applied to indolent and sloughing ulcers. It is said to have proved purgative when sprinkled over a large ulcerated surface, and the same effect is asserted to have been produced by rubbing it, mingled with saliva, over the abdomen.
European rhubarb must be administered in double or treble the dose of true rhubarb to produce an equal effect. Few medicines are used in a greater variety of forms. It is most effectual in substance. It is frequently given in the shape of pill, combined with an equal proportion of soap when its laxative effect is desired. The infusion is much used in cases of delicate stomach, and is peculiarly adapted to children. The syrup, tincture, and fluidextract are also useful preparations. They are all official. The formula for mixture of rhubarb and soda which was largely used in New York at one time will be found in the National Formulary IV. The name was changed to Mistura Rhei Composita.
Dose, as a purgative, from twenty to thirty grains (1.3-2.0 Gm.); as a laxative and stomachic from five to ten grains (0.32-0.65 Gm.).
Off. Prep.—Fluidextractum Rhei, U. S.; Extractum Rhei, U. S., Br.; Infusum Rhei, Br.; Liquor Rhei Concentratus, Br.; Pilulae Rhei Compositae, U. S. (Br.); Pulvis Rhei Compositus, U. S; Br.; Syrupus Rhei (from Fluidextract), U. S; Br.; Syrupus Rhei Aromaticus (from Aromatic Tincture), U. S.; Tinctura Rhei, U. S. (Br.); Tinctura Rhei Aromatica, U. S.; Tinctura Rhei Composita, Br.; Elixir Catharticum Compositum (from Fluidextract), N. F.; Fluidglyceratum Rhei, N. F; Mistura Opii et Rhei Composita (from Tincture), N. F.; Mistura Rhei Alkalina (from Fluidextract), N. F.; Mistura Rhei Composita (from Fluidextract), N. F.; Pilulae Antiperiodica;, N. F.; Pilulae Antiperiodicae sine Aloe, N. F.; Pilulae Rhei, N. F.; Pulvis Rhei et Magnesiae Anisatus, N. F.; Syrupus Sennae Aromaticus, N. F.; Syrupus Sennae Compositus (from Fluidextract), N. F.; Tinctura Antiperiodica, N. F.; Tinctura Antiperiodica sine Aloe, N. F.; Tinctura Rhei Aquosa, N. F.; Tinctura Rhei Dulcis, A. F.; Tinctura Rhei et Gentianae, N. F.; Tinctura Zedoariae Amara, N. F.; Vinum Rhei Compositum (from Fluidextract), N. F.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.