Senna consists of the leaflets of several species of Cassia, among which those which yield it most largely are C. acutifolia of Upper Egypt and Nubia, C. obovata of Lower Egypt, Syria, etc., C. elongata of the South of Arabia, cultivated in India, and C. AEthiopica, growing in Fezzan, southward of Tripoli, on the African coast of the Mediterranean. C. lanceolata of Forskhall, growing in Arabia in the neighbourhood of Mecca, probably also yields it. All these species are small shrubs, with pinnate leaves, and leaflets characterized by the obliquity of their base; the angle which the edge of the leaf forms with the midrib at its insertion being different on the two sides. With the leaflets are not unfrequently also gathered portions of the footstalks of the leaves, the flowers, and the fruit, the last of which is a flat membranous legume or pod, in some species curved, and in others nearly straight. There are several commercial varieties of the drug, named from the place of their export or production. The following are brief notices of those in common use.

1. Alexandria Senna (Senna Alexandrina, Br.), so named from the Egyptian port whence it is commercially distributed, is collected mainly in Nubia and Upper Egypt from Cassia acutifolia, and brought down to Boulac on the Nile, in the neighbourhood of Cairo. Here it formerly underwent admixture with certain proportions of the leaflets of Cassia obovata, growing in Lower Egypt, and the leaves of Cynanchum oleaefolium, commonly called argel; and, thus prepared, was repacked, and sent down the Nile to Alexandria. At present, however, these additions are not always, if ever made; and the Alexandria senna now imported generally contains little or none of the argel, and but a comparatively few leaflets of C. obovata. it consists, therefore, mainly of the leaflets of C. acutifolia, with small portions of the footstalks, flowers, pods, etc. These leaflets are almost always less than an inch long, somewhat ovate, and pointed at the end. Those of argel, which are still occasionally to be found among them, are distinguishable by their regular base, that of the senna leaflets being as before stated always oblique, by their much greater length, usually exceeding an inch, their lighter colour, firmer texture, and nearly total absence of lateral veins. The leaflets of the obovate senna are distinguishable, at a glance, by their more rounded form, their greatest breadth near the apex, and their mucronate point. This variety of senna is most highly esteemed.

2 Tripoli Senna derives its name from the Barbary port of Tripoli, whither it is brought by caravans from Fezzan. it consists, in general, exclusively of the product of one species of Cassia, which is believed to be the C. AEthiopica of Guibourt, the leaflets of which closely resemble those of C. acutifolia, though perhaps somewhat smaller and more fragile; and this variety of the drug is characterized chiefly by the great extent to which the leaflets are broken up. it is probably not less efficient than the Alexandria senna, but is less esteemed in consequence of this comminuted state of the leaflet. it is very seldom brought into the United States.

3. India Senna (Senna indica, Br.), though brought from the ports of Hindostan, is mainly produced in the southern parts of Arabia, whence it is taken in the native vessels to Bombay. it is sometimes called Mocha senna, from the Arabian port of that name. it is the product exclusively of the Cassia elongata. This plant has, within a few years, been introduced into India, and cultivated to a considerable extent. A sub-variety of the drug thus produced is called Tinnevelly senna. India senna is distinguished by the great relative length of the leaflets, from one to nearly two inches, and their oblong shape. As ordinarily found in the shops, it has a yellowish hue, and is frequently intermingled with leaves decayed or otherwise injured. it has considerable activity; but is thought to be somewhat inferior in this respect to the Alexandria senna The Tinnevelly senna is much superior in aspect to the ordinary India senna; having a fresher green colour, and being free from any admixture of the footstalks and other fragments of the plant.

A very good senna has, within a few years, been brought into the American market under the name of Mecca senna. The leaflets are in length and shape between those of C. acutifolia and G. elongata, the latter of which, as found in the India senna, they resemble in their yellowish or tawny hue. it is probably derived from C. lanceolata of Forsk-hall.

Sensible and Chemical Properties. Senna has a pale-greenish or yellowish-green colour, a faint peculiar smell, and a sweetish, slightly bitter, somewhat nauseous taste. The powder is greenish. it yields its virtues readily to water and alcohol. The infusion upon standing deposits a precipitate, which is ascribed to the oxidation of its extractive matter, and has been supposed, though probably on insufficient grounds, to increase the griping property of the medicine. infusion of galls, and solution of Subacetate of lead precipitate the active matter of the leaves, and are, therefore, incompatible in prescription. it was at one time supposed that the active principle had been isolated, and the name of ca-thartin was, upon this supposition, conferred on the matter obtained; but further investigation appears to have determined that the substance so named has little purgative power, and is, in fact, of complex composition. Recently Mr. Robert Rau, in this country, and Prof. Dragen-dorff and Mr. Kubly, of Europe, claim to have discovered the active principle of senna in a crystalline substance, for which the first-named chemist proposes the name of sennin, believing it to be neutral, and the two latter that of cathartic acid, as they found it to possess acid properties.*

* Active Principle. Sennin. Cathartic Acid. in an essay on senna and its active principle, by Mr. Robert Rau, of Bethlehem, Penn., contained in the number for May, 1866, of the American Journal of Pharmacy (p. 193), is an account of experiments, from which it would appear that the author had discovered the active principle of senna, so long sought for in vain. According to Mr. Rau, this principle is crystallizable in needles, of a taste at first scarcely perceptible, but in a few minutes becoming nauseous, bitter, and extremely persistent; insoluble in water, cold or hot, and in cold alcohol, but soluble in hot alcohol and in ether, and still more so in chloroform. The ethereal solution was neuter to test paper; and the crystals were insoluble in dilute acetic acid and in alkaline solutions. When strongly heated, they melted, took fire, and left only charcoal, which was entirely consumed at a red heat. The principle obtained is, therefore, organic; and as Mr. Rau found five grains to purge actively in five hours, he seems justified in the conclusion that it was the active cathartic constituent, and in proposing for it the name of sennin. it was obtained by precipitating an infusion of senna with solution of Subacetate of lead, and afterward treating it with sulphuretted hydrogen to throw down the excess of lead. The precipitated sulphuret of lead was boiled with Medical Effects and Uses. Senna was used by the older Arabian physicians; and notices of it are found in their writings so early as in the ninth century, though it was probably used long before. it is a prompt and very efficient cathartic, producing copious watery discharges, and often with considerable griping, but with little irritation of the mucous membrane. I have found it among the cathartics most readily retained by the stomach. The griping property is probably owing, not to that sort of irritation produced by the acrid cathartics, but to the direct and energetic influence of the medicine on the muscular coat of the bowels. it is the combination of this strong operation on the peristaltic movement with the property of increasing secretion into the bowels, that gives senna its peculiar character. it is purely cathartic, having no other special influence, to qualify its operation in this capacity.