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.
Senega root is obtained from Polygala Senega, Linne (N.O. Polygaleoe), a small plant producing a perennial knotty rootstock, from which numerous slender stems 15 to 30 cm. high arise. It is widely distributed over the United States and the southern parts of British America, the root being collected largely in Minnesota and Manitoba (western senega) and in the north-western of the United States (northern senega). It was formerly collected in the more southern States, but is now nearly exterminated there. The root was used by the Seneca Indians as a remedy for snake-bite, and was introduced into medicine about the middle of the eighteenth century.
Senega root consists of a slender, greyish or brownish yellow root surmounted by a knotty crown, to which are attached the remains of numerous slender aerial stems and small shoots beset with the scars or remains of purplish scaly leaves. The root is usually about 3 to 6 mm. thick at its upper extremity, but it soon divides into two or three spreading branches. It is frequently curved and contorted, and is longitudinally and sometimes, especially near the crown, transversely wrinkled. Very frequently, but not always, it exhibits a prominent keel resembling a contracted sinew and following a gently spiral course; this keel may generally be found on the concave surface of the curves of the tap-root, and often extends a considerable distance.
The root breaks with a short fracture, the fractured surface exhibiting a whitish wood and yellowish translucent bark. The former frequently presents an abnormal appearance. Instead of a complete circle of wood a wedge-shaped portion, or sometimes two, of varying extent, is replaced by parenchymatous tissue, and the wood therefore appears to have had a segment cut out of it. This appearance varies in different parts of the same root, the segment that is missing being sometimes narrow and wedge-shaped or occasionally increasing to nearly a semicircle, thus reducing the wood to one-half its normal amount. If a keeled root is soaked in water and the bark stripped from it, the wood will be seen to have transverse cracks or a longitudinal fissure on the convex surface, the latter usually extending for some distance and widening from a narrow crack into a broad fissure. These cracks and fissures are filled with easily removable parenchymatous tissue.
The concave sides of the curved roots bear the keels, and these are seen in the transverse sections to be due to a largely developed bast; the keels do not arise from any abnormal development of the wood. The root has a distinct odour, recalling wintergreen; the taste is at first somewhat sweet, but soon becomes sour and acrid. The powdered root is very irritating to the throat and nostrils when inhaled, and imparts to water the property of frothing.
Fig. 156. - Senega root. 1 and 2, roots,showing the keel; 3, transverse section. Natural size. (Vogl).
The student should observe
(a) The prominent keel,
(b) The irregular wood in transverse sections, and should strip the bark from the root and examine the wood.
Senega root contains as principal constituents senegin and polygalic acid. These substances are both glucosides, and resemble, but are not identical with, quillaja-sapotoxin and quillajic acid, constituents of quillaja bark, their action being qualitatively the same, but quantitatively different (Atlass, 1890). Polygalic acid is sternutatory, and imparts to water the property of frothing. Senegin is decidedly toxic. Both these bodies require, however, further investigation.
Fig. 156a. - Senega root. A, transverse section of normally developed root; B, C, D, of abnormally developed roots, a, bark; b, wood; v, bast. Magnified. (Berg).
The drug often contains a small percentage of methyl salicylate (oil of wintergreen), probably produced by the gradual decomposition of an unknown glucoside; its presence has been utilised as a test of the identity of the drug, but it is unreliable. Senega root also contains about 5 per cent, of fixed oil, but is free from starch; it yields about 4 per cent, of ash.
Senega is used as a stimulant expectorant in bronchitis.
Northern senega, collected in the north-western States, is considerably larger than the usual variety (western senega), and darker in colour; it is less contorted and shows the keel less distinctly, but it has a very acrid taste, and is undoubtedly a good senega. It is said to be derived from Poly gala Senega, var. latifolia.
White senega, from Polygala alba, Nuttall, is collected to some extent in the southern States. The root is more slender than western senega, has descending branches rather than spreading, and is lighter in colour. It has no keel and a normal wood. The taste is much less acrid than that of western senega, and it is presumably less active.
Senega stems; these are about 2 mm. thick, rounded, hollow; they contain non-lignified bast fibres by which they may be identified in the powder.
Other roots occasionally find their way into parcels of senega, frequently as a result of careless collection, but the characters given sufficiently distinguish the genuine drug.