Whether it operates by contact with the inner surface of the alimentary canal, or through the medium of absorption, has not been certainly determined; but it is not improbable that it conjoins both modes of action. That its cathartic principle is absorbed may be inferred from the asserted fact, that the milk of nursing women, under the influence of the medicine, operates upon the bowels of the infant; and, if the experiment can be relied on, in which the infusion, injected into the veins of a man, produced vomiting and purging, we must admit that it may be capable ether, which, after spontaneous evaporation, left behind the principle just described, in the form of acicular crystals, interlaced, and of a dirty-white colour. in this state it was probably not quite pure.

Prof. Dragendorff, and Mr. Kubly, of Dorpat, have extracted from senna a crystalline substance which they deem the active principle, by treating a syrupy extract prepared by evaporating in vacuo a strong watery infusion of the leaves with successive portions of absolute alcohol, throwing away the first precipitate thus obtained, collecting the rest, and purifying them by repeated solution in water, and reprecipitation with absolute alcohol. The principle is said to be insoluble in water, strong alcohol, and ether, but is dissolved by water when combined with alkaline and earthy bases, and thus is taken up from senna by infusion. it is believed to be an acid, containing both nitrogen and sulphur, but is also a glucoside, splitting into another acid and glucose when treated with acids at a high temperature. The minimum dose of the pure acid is one and a half grains, which purge with griping. (See Am. Journ. of Pharmacy, July, 1866, p. 374, from the Druggists' Circular, June, 1866.) i cannot but think that there is some incongruity between the mode of preparing cathartic acid above given, and the chemical properties ascribed to that principle. Supposing this extremely insoluble substance to be readily extracted from senna by water in consequence of its union with alkaline or earthy bases, it does not seem to me clear how it should be separated from this combination simply by the successive action of water and alcohol. Perhaps something in the original may have escaped notice in the translation which might throw light on the subject. in the mean time, however, I am disposed to ascribe the credit of having isolated the active principle rather to Mr. Rau than to the chemists last mentioned. [Note to the third edition.) of producing its special effect on the bowels through the circulation. Besides, senna imparts to the urine the property of being reddened by ammonia; and Dr. E. Hardy detected this change twenty-one minutes after the senna had been taken, increasing afterwards, and at its height in half an hour. {Journ. de Pharm. et de Chim., 3e sér., xliv. 161.)

From its purely cathartic character, its promptness and efficiency, and its influence at once on the peristaltic motion and secretory function of the bowels, it may be used in all cases requiring active purgation, whether the indication be merely to evacuate the bowels, or to produce a depletory effect, or to obtain both effects at the same time.

It is an excellent cathartic for acute inflammatory affections, and generally for fevers when the circulation is vigorous, and the state of the system sthenic. in these cases, it is very usefully associated with the saline cathartics.

The combined power above mentioned peculiarly adapts it to cases of obstinate constipation from fecal accumulation, in which watery secretion is wanted in order to soften and break up the consolidated mass, and energetic contraction of the muscles to expel it.

It is also admirably adapted to cases of bilious colic, after the administration of calomel, and when other cathartics are rejected from the stomach. I have generally found, under these circumstances, small doses of a compound infusion of senna, such as will be recommended below, say one or two fluidounces, repeated every two hours, retained well by the stomach, and efficient as a cathartic.

Senna given in small doses, suitably combined, answers also very well as a laxative, proving its want of any considerable irritant property.

It is much employed, in conjunction with spigelia, or other anthelmintic, for the expulsion of worms, to which the energy of the muscular contraction it produces well adapts it.

The griping quality may be in a considerable degree modified by administering senna in connection with aromatics; and it is thought that the purgative salts, such as bitartrate of potassa, tartrate of potassa, and sulphate of magnesia, not only aid its operation, but, by a chemical influence upon the senna itself, or its active principle, alter it in such a manner as to diminish its disposition to gripe. Of the effect of this combination, in modifying the operation of senna, there is no doubt; but I am disposed to ascribe it to the physiological rather than the chemical influence of the salt used.

The same property of producing energetic peristaltic contraction, which renders it so efficient as a cathartic when taken by the stomach, adapts it also for use by enema, in cases of peculiar obstinacy.

Administration

Senna is not often given in powder, in consequence of its bulk. The dose of it, in this state, is from half a drachm to two drachms. Occasionally, I have known the powder to be taken as a laxative, mixed, in very small proportion, with stewed prunes, used as an article of diet. The taste is little perceived, especially when the fruit is prepared with molasses.

Confection of Senna (Confectio Sennae, U. S., Br.; Electuarium Sennae, Ed.), often called lenitive electuary, is another preparation in which senna is used in substance. The mode of preparing it is somewhat changed in the present Pharmacopoeia, though the ingredients and the result are essentially the same. Purging cassia, tamarinds, prunes, and figs, suitably comminuted, are first digested with water for three hours, and then, the coarser parts having been separated by the hand, are pressed through sieves, so as to make a uniform pulp. The process is repeated with the residue. The pulps are then mixed, sugar is added, and, the superfluous water having been evaporated, the preparation is completed by incorporating powdered senna and coriander thoroughly with the soft mass. This is an excellent compound laxative, with little or no unpleasant flavour, operating very kindly, and well adapted to the costiveness of pregnant women, that of convalescence, and that accompanying hemorrhoidal affections. it is not suited to dyspeptic cases. The dose is about two drachms, which may be most conveniently taken at bedtime.