Uses—Jalap is employed as a brisk cathartic.
Other kinds of Jalap.
Besides true jalap, the roots of certain other Convolvulaceæ of Mexico have been employed in Europe, either in the form of jalapin, or as adulterants of the more costly, legitimate drug. The two following have been extensively imported and have been traced to their botanical source; but there are others, of more occasional occurrence, the origin of which has not been ascertained.[1644]
1. Light, Fusiform, or Woody Jalap, Male Jalap, Orizaba Root, Jalap Tops or Stalks, Purgo macho of the Mexicans.
This drug is derived from Ipomœa orizabensis Ledanois,[1645] a plant of Orizaba, which is but imperfectly known. It is described as a pubescent climber, having a spindle-shaped root about two feet long of woody and fibrous texture. The drug occurs in irregular rectangular or block-like pieces, evidently portions of a very large root, divided transversely and longitudinally. Sometimes it is more like true jalap, being in entire roots, of smaller size, spindle-shaped, not spherical. It has a somewhat lighter colour than jalap, and much deeper longitudinal wrinkles. The larger pieces often exhibit deep cuts from an axe or knife; transverse slices are of rare occurrence. Although generally less ponderous than jalap, the Orizaba drug is nevertheless of a compact and often horny texture. From jalap it is easily distinguished by its radiated transverse section, and the numerous thick bundles of vessels which project as woody fibres from the fractured surface.
In chemical constitution Orizaba root is closely parallel to jalap. The resin was named by Mayer Jalapin; it is the Jalapin of Gmelin’s Chemistry (xvi. 405), and perhaps the jalapin of English pharmacy.[1646]
In the pure state it is a colourless amorphous translucent resin, dissolving perfectly in ether,[1647] thus differing from convolvulin the corresponding resin of jalap. We find that it is readily soluble also in acetone, amylic alcohol, benzol and phenol, not in bisulphide of carbon. It has the composition of C₃₄H₅₆O₁₆, so that it is homologous with convolvulin; the decomposition-products of jalapin obtained by similar treatment, namely jalapic acid, jalapinol, and jalapinolic acid, are likewise homologous with the corresponding substances obtained from convolvulin. All these bodies when treated with nitric acid yield ipomœic acid. Jalapin has the same fusing point as convolvulin, and behaves in the same manner with alkalis.
The root afforded us 11·8 per cent. of resin dried at 100° C. When perfectly washed, decolorized and dissolved in two parts of alcohol, this resin turned the plane of polarization of a ray of light 9·8° to the left, in a column of 50 mm. long. Convolvulin under the same conditions turned it only 5·8°. The resin of Orizaba root is held by chemists to be identical with that of scammony, of which it has the drastic action.
2. Tampico Jalap,—Purga de Sierra Gorda of the Mexicans. The plant which affords this drug has been described by one of us (1869) under the name of Ipomœa simulans.[1648] It is closely related to I. Purga Hayne, from which by its foliage it cannot be distinguished, but it has a bell-shaped corolla and pendulous flower-buds, which are very different. I. simulans Hanbury grows in Mexico along the mountain range of the Sierra Gorda in the neighbourhood of San Luis de la Paz, from which town and the adjacent villages its roots are carried down to Tampico. It has also been found on the lofty Cordillera near Oaxaca, but whether there collected we know not.
The drug, to which in trade the name Tampico Jalap is commonly applied, has been imported during the last few years in considerable quantities. In appearance it closely approaches true jalap, but the roots are generally smaller, more elongated or finger-like, more shrivelled and corky-looking, wanting in the little transverse scars that are plentifully scattered over the roots of true jalap. Many pieces occur however which it is impossible to distinguish by the eye from true jalap, with which it agrees also in odour and taste.