This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Jalap is obtained from Ipomoea Purga, Hayne (N.O. Convolvulacoe), a plant with climbing, twining stems indigenous to the eastern slopes of the Mexican Andes. It sends out slender runners which are provided at intervals with scaly, cataphyllary leaves in the axils of which are buds; below the buds roots are produced, some of which thicken rapidly and form fusiform or napiform organs, often of considerable size. These tuberous roots (tubercules) are collected and dried in nets over fires, the smaller entire, but the larger longitudinally incised to allow of the free escape of moisture. When fresh they are fleshy and white internally, but by drying, especially in the manner indicated, they darken in colour. Jalap is imported in sacks from the east coast of Mexico, and distinguished as 'Mexican' or 'Vera Cruz ' jalap.
The jalap plant has been cultivated in India and Jamaica but these colonies do not at present compete with Mexico in the supply of the drug.
The Spaniards became acquainted with this and similar purgative Convolvulaceous plants early in the sixteenth century, and exported considerable quantities of them to Europe.
Jalap occurs in pieces of very varying size, most commonly about that of a hen's egg, although sometimes they attain 10 cm. or more in diameter. They vary also much in shape, being sometimes napiform, sometimes fusiform or irregularly oblong. The small are usually entire, but the larger bear gashes that have been made to facilitate the drying. Towards the lower extremity they taper off and show a fractured end where the slender part of the root has been broken off. The surface is dark brown, furrowed and wrinkled (but not conspicuously convoluted), and marked with numerous, paler, elongated transverse scars (lenticels). They are heavy and compact, and so hard as to be broken with difficulty, but softening readily in water. Internally they have a yellowish grey or dingy grey colour, and are very tough or horny, the section exhibiting irregular dark lines often concentrically arranged. These lines are due to the formation of secondary cambiums, an abnormal development that is occasionally, although not often, met with. Under the lens numerous dark resin cells are visible, especially in the cortical portion, but woody tissue is not easily discerned.
Jalap has a distinct and characteristic odour which is often ascribed to the smoke from the fire over which the roots have been dried, but which is, partly at least, inherent in the drug. The taste is at first sweetish, but afterwards disagreeably acrid.
The heat to which the drug is subjected during the drying is generally sufficiently high to gelatinise the starch, especially in the interior of the roots, where the moisture is retained longer than in the outer portions; hence the horny and not starchy appearance of the drug. Roots obtained from cultivated plants in India and Jamaica are usually more carefully dried, and present a mealy, not horny, appearance in the interior.
Powdered jalap is characterised, when examined under the microscope, by the abundant starch which may be intact or in any stage of gelatinisation; the grains are either simple or compound; the former, measuring mostly 25µ to 40µ, are rounded or ovoid and exhibit concentric striae; compound grains may contain 2 to 6 constituents. Numerous globules of resinous emulsion, varying in size, are evident or can be made evident by solution of iodine in potassium iodide. There are occasional sclerenchymatous cells, and fragments of vessels with areolated pits. Cluster crystals of calcium oxalate are frequent.
Fig. 183. - Jalap root. Small specimen, natural size, showing the transverse lenticels.
Fig. 184. - Jalap root. Transverse section. Slightly reduced. (Pharmaceutical Journal).
The principal constituent of jalap is the ' resin ' which can be separated by extracting the root with alcohol, concentrating the tincture, pouring it into water, washing and drying the resinous precipitate. The drug contains in addition colouring matter, sugar, starch, β-methylaesculetin, ipurganol, a phytosterin and calcium oxalate.
The resinous precipitate obtained as described is known as 'jalap resin.' The yield has varied from 2 to 22 per cent. of the drug; 8 to 12 per cent. is often found. It is characterised by its partial solubility (about 10 per cent.) in ether.
Jalap resin is an exceedingly complex mixture, the composition of which is only imperfectly known. Treatment with various solvents in succession has given the following results:
Petroleum Spirit, 1.9 per cent., containing fatty acids and fats, phytosterol, cetyl alcohol.
Ether, 9.7 per cent., containing ipurganol; after treatment with alkali followed by acid, chiefly amorphous substances were obtained, together with a little phytosterol, cetyl alcohol, etc.
Chloroform, 24.1 per cent., containing β-methylaesculetin; after treatment with alkali and acid, formic, butyric and (d-methylethylacetic acids, glucose, convolvulinolic acid (C15H30O3), and a higher homologue were obtained.
Ethyl Acetate, 22 per cent., similar in composition to the chloroform extract.
Alcohol, 38.8 per cent., by treatment with barium hydroxide a water-soluble, non-purgative, 'hydrolysed,' resin was obtained, which, boiled with dilute sulphuric acid, gave glucose, convolvulinolic acid, ipurolic acid (also found in /. purpurea, Roth), formic, butyric and valeric acids.
All these extracts except the petroleum spirit are purgative, and each appears to be only partly glucosidic. Convolvulinolic acid (hydroxypentadecylic acid), and ipurolic acid are crystalline; they appear to exist in the resin in the form of glucosides which can be split up by appropriate treatment.
The portion soluble in ether is assumed to be identical with scammony resin.
Good jalap should yield not less than 10 per cent. of total resin when exhausted with alcohol, the tincture concentrated and poured into 8 volumes of water and the precipitated resin washed and dried. Much of the drug that at present reaches the market contains considerably less, and its exclusion from use in making the official preparations of jalap is ensured by the minimum requirement of 10 per cent. adopted by the British Pharmacopoeia. On the other hand there seems to be little doubt that the quality of the drug has deteriorated during the last twenty-five years, from 12 to 18 per cent. being formerly the usual amount of resin contained in it. Under exceptional circumstances.the quantity has risen in roots cultivated in India to upwards of 20 per cent.
Jalap is a powerful stimulant of the intestinal secretion, producing in small doses a laxative effect, and in large doses active purgation. It is much used as a hydragogue cathartic.
Tampico jalap is afforded by Ipomoea simulans, Hanbury, a plant resembling I. Purga and growing on the eastern slopes of the Mexican Andes. The roots are exported from Tampico (a town on the Gulf of Mexico, about 200 miles north of Vera Cruz), whence it derives its name. This root, which frequently appears on the London market, is distinguished by its irregular shape and remarkable, convoluted surface, which does not exhibit the small transverse scars characteristic of true (Vera Cruz) jalap. It yields about 10 per cent. of resin, which is distinguished from the resin of true jalap by its complete solubility in ether. This resin (tampicin) is probably identical with the ether-soluble resin of jalap and scammony.
Fig. 185. - Tampico Jalap root. Natural size.
Orizaba jalap (light, woody, stalk, or male jalap), is produced by Ipomoea, orizabensis, Ledanois. (See below).