Rhubarb. The root of one or more undetermined species of Rheum. Nat. Ord. Polygonaceae. Linn. Syst. Enneandria Monogynia. Source, various, principally China, Thibet, and Tartary.
Med. Prop. and Action. Dr. Pereira enumerates eleven species of Rheum yielding the Rhubarb of commerce, and describes twelve different sorts which are met with; for the particulars of which the reader is referred to his valuable work, and also to that of Prof. Royle, on Materia Medica. Their medicinal properties are very similar, although they differ in strength and activity. The English Rhubarb is hardly so purgative, in the same doses, as the Russian and Chinese varieties; and the Himalayan is almost equal to the Russian, but less aromatic, though more astringent. The following are the characters of Rhubarb, as given in the British Pharmacopoeia: - " Trapezoidal, roundish, cylindrical or flatfish pieces, frequently bored with one hole, yellow externally, internally marbled with fine waving greyish and reddish lines, finely gritty under the teeth; taste bitter, faintly astringent, and aromatic; odour strong and very peculiar." The tests for its purity are, that it be free from brown specks externally and internally, and without cavities, and that Boracic Acid does not turn the yellow exterior brown. Impurities are detected in the powder with difficulty. It should be of a fine bright buff-yellow colour. When chewed, Rhubarb should impart to the saliva a deep saffron tinge, and it should not prove slimy or mucilaginous in the mouth. It contains a peculiar crystalline principle, Rheine, or Chryso-phanic Acid, C20H8O6, several resins, a bitter principle, and astringent matter (Tannic and Gallic Acids). Oxalate of Lime in crystals (raphides) exists in varying quantities in Rhubarb. From Russian Rhubarb Mr. Queckett obtained from 35 to 40 per cent. of Oxalate of Lime. Its purgative principle has not yet been isolated. When taken internally, Rhubarb is absorbed into the system, communicates a deep yellow or red colour to the urine, the odour
* Gaz. Med. de Paris, Sept. 5, 1840. Journ. de Chirurg., 1846.
Journ. des Connaiss. Med.-Chir., Sept. 1853.
may be detected in the cutaneous secretion, and the milk of a nurse is rendered purgative. That it exercises a specific action on the intestines is shown by Alibert,* who found that frictions with Rhubarb, or a Rhubarb cataplasm placed over the abdomen, produced a brisk purgative effect, although he was unable to detect it in the urine. " It operates," observes Dr. Garrod,t "more by an increase of the peristaltic motions of the canal, than by augmenting the intestinal secretions; the stools which it produces are accordingly feculent; and, since the drug contains astringent principles, its operation is followed by a more or less confined condition of the bowels." Its purgative action is increased by the addition of the Sulphate of Potash. It is particularly adapted as an aperient for children; but in cases of habitual constipation, it is inadvisable, on account of its subsequent astringent effect.
Offic. Prep. 1. Extractum Rhei (Rhubarb, sliced or bruised, lb. j.; Rectified Spirit fl. oz. x.; Distilled Water Ov. Prepared by macerating the Rhubarb in the Spirit and Water for four days, and subsequent evaporation at a temperature not exceeding 160°). Dose, gr. iij. - gr. x.