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.
Alexandrian senna consists of the leaflets of Cassia acutifolia, Delile (N.O. Leguminosae), a small shrub from 1 to 1.5 metres in height, indigenous to and cultivated in the middle and upper Nile territories, and cultivated also in India. The medicinal value of the pods and leaves of the plant was known to the Arabian physicians of the tenth and eleventh centuries, through whom European physicians probably became acquainted with the drug.
Alexandrian senna is collected by Bedouins, chiefly from wild plants between Suakin and Kassala, the shrubs being cut down and dried. The drug is either cleaned in the Soudan or sent in the crude state to Cairo, Alexandria or Suez and there cleaned and sorted from stalks, stones, etc. It is exported from Alexandria.
Fig. 20. - Alexandrian Senna leaves. Natural size.
The plant produces a paripinnate compound leaf about 10 cm. in length. The leaflets average about 25 cm. in length, seldom exceeding 4 cm., and, when dried, are of a pale greyish green colour, thin, and brittle, lanceolate to ovate-lanceolate in outline, with an entire margin and acute, mucronate apex. They are decidedly unequal at the base, and on the under surface the veins are distinct. When examined with a lens both surfaces of the leaf are seen to be pubescent, small hairs being distinctly visible, especially near the veins.
The leaves frequently appear in commerce in a more or less broken condition due to their brittle, papery texture. They curl slightly as they dry, and, being loosely packed, retain this appearance; Indian senna leaves, on the other hand, being pressed into bales, are commonly flat and bear other evidence of the pressure to which they have been subjected.
Alexandrian senna has a faint but characteristic odour and a mucilaginous, mawkish, unpleasant taste.
The epidermal cells of both surfaces have straight walls and many contain mucilage; the stomata are surrounded by two cells with their long axes parallel to the ostiole; the hairs are one-celled, thick-walled, warty, and often curved. Both surfaces possess long, narrow palisade cells. The midrib contains abundant pericyclic fibres, abutting on which are cells containing prismatic crystals of calcium oxalate, cluster crystals of which occur in the mesophyll.
The student should observe
(a) The predominating asymmetrical, lanceolate or ovate-lanceolate shape,
(b) The veins distinct on the under surface,
(c) Both surfaces more or less distinctly pubescent; and should compare the leaves with
(i) Mecca senna leaves, which are elongated lanceolate, (ii) Indian senna leaves, which are yellowish green in colour, less conspicuously asymmetrical, and less pubescent.
Fig. 21. - Obovate Senna leaves (C. obovata). Natural size.
According to the very exhaustive researches of Tutin the chief constituents of Alexandrian senna are rhein, aloe-emodin, kaempferol and isorhamnetin, all four substances occurring both free and in the form of glucosides; myricyl alcohol and a phyto-sterolin (phytosterol glucoside) are also present. The leaves contain in addition mucilage, calcium oxalate, resin, and amorphous glucosidic material.
Aloe-emodin, C14H502(OH)2CH1OH, brownish green needles, is hydroxymethyldihydroxyanthraquinone and is the primary alcohol corresponding to chrysophanic acid (better termed chrysophanol) which is dihydroxymethylanthraquinone. Rhein, C14H502(OH)2COOH, orange needles, is the corresponding carboxylic acid and may be formed by the oxidation of aloe-emodin. Both aloe-emodin and rhein exist in the free state and in the form of glucosides.
Kaempferol, C15H602(OH)4, is 1:3:4-trihydroxyflavonol (bright yellow needles), and is yielded together with dextrose by the hydrolysis of kaempferine, C27H30O16,6H1O, which is also present in senna.
Isorhamnetin, C6H1207, yellow needles, was first obtained from yellow wallflowers.
Of these constituents aloe-emodin and its glucoside appear to be the only purgative ones. The total amount of methylanthraquinone derivatives present in senna has been variously estimated at 10 to 4.0 per cent, a proportion that is not consistent with the purgative action of the drug and the true active constituent is apparently still unknown.
Recent investigations have revealed the presence of oxymethylanthra-quinones in a number of laxative drugs, which, therefore, form a natural group allied by the similarity of their constituents. The following are the most important members of the group:
Senna, which contains aloe-emodin, and rhein.
Cascara Sagrada, the bark of Rhamnus Purshianus, de Candolle (N.O. Rhamnaceae), which contains emodin and frangula-emodin.
Alderbuckthorn Bark, from Rhamnus Frangula, Linne, which contains frangulin and frangula-emodin.
Rhubarb, the rhizome of Rheum officinale, Baillon, etc. (N.O. Polygonacece), which contains or yields chryso-phanic acid, emodin, aloe-emodin, and rhein.
Aloes, from various species of Aloe (N.O. Liliaceae), which contains and yields aloe-emodin. Cassia Pulp, an aqueous extract of the fruit of Cassia Fistula, Linne, which contains unidentified oxymethylanthra-quinones.
Senna stimulates the muscular coat of the intestine and produces purgation, which is not followed, as is commonly the case, by constipation; it is therefore one of the most useful of purgatives, especially in cases of habitual constipation.
Senna pods, the fruits of Cassia acutifolia; occasionally found mixed with the senna, and imported as a separate article of commerce; very flat legumes. (See p. 100).
Cassia obovata (dog senna), Upper Egypt; formerly highly valued as a drug, and cultivated in Italy and sometimes termed Italian senna; leaves broadly obovate, apex abruptly tapering venation, pinnate, distinct; constituents similar to those of senna; total oxymethylanthraquinones 3.8 per cent.; about equal to senna in activity. The leaves are sometimes broken up and mixed with broken Alexandrian senna, they may be recognised by the papillose cells of the lower epidermis.
Argel leaves, Solenostemma Argel, Hayne (N.O. Asclepiadeae); resemble senna in colour and outline, but distinguished by their thick, rigid texture and peculiarly curled, curved, or twisted appearance; surface finely wrinkled; veins not evident; leaf equal at the base; hairs three-celled; taste distinctly bitter; formerly regularly mixed with the senna but now of rare occurrence.
Fig. 22. - Argel leaves. a, showing the shape of the leaf; b, c, d, showing the curled appearance of the dried leaves. Natural size.
Arabian, Mecca, or Bombay senna, obtained from wild plants of C. angustifolia; collected in Southern Arabia and sometimes shipped via Bombay, or now more commonly by the Red Sea route, to London; elongated lanceolate, often discoloured and mixed with stalks; frequently mixed with Alexandrian senna, but may be distinguished by the shape; contain about 2.5 per cent, of total oxymethylanthra-quinones.
Leaves of the following plants have also been imported as senna, or have occurred in commercial senna:
Cassia holosericea, Fresenius; smaller, more obtuse, hairy.
Cassia montana, Heyne; darker, rounded apex, dark network of veins.
Tephrosia apollinea, de Can-dolle; obovate-oblong, pubescent, emarginate lateral veins straight and parallel; fruits narrow - cylindrical; recently (1918) found in Alexandrian senna.
Colutea arborescens, Linne; green, very thin.
Globularia Alypum, Linne; spathulate, rounded apex, mucronate.
Coriaria myrtifolia, Linne; ovate-lanceolate, greyish-green, two prominent lateral veins, conspicuous midrib.
Fig. 23. - Arabian Senna leaves. Natural size.