109. Salix, Linn.—Willow.
Sex. Syst. Dioecia, Diandria.
(Cortex e speciebus salicis diversis; cortex Salicis, offic.)
History.—Dioscorides [Lib. i. cap. 136.] speaks of the astringent qualities of the ιτέα, or willow (Salix alba?), which was employed in medicine by the ancients. For a long series of years it fell into disuse, but was again brought into notice in 1763, by the Rev. Mr. Stone, [Phil. Trans. vol. liii. p. 195.] who published a paper on the efficacy of the bark of Salix alba, as a remedy for agues. The broad-leaved willow bark (Salix Caprea) was subsequently introduced into practice by Mr. James, [Observations on a particular Species of Willow, 1792.] whose observations on its efficacy were afterwards confirmed by Mr. White [Observations and experiments on the Broad-leaved Willow Bark. 8vo. Bath, 1798.] and Mr. G. Wilkinson. [Experiments and Observ. on the Cortex Salicis Latifoliae, 8vo. Newcastle-upon-Tyne .]
Botany. Gen. Char.—Flowers dioecious, or rarely monoecious, amentaceous; scales imbricated; a gland surrounding the stamens or ovary. Males: Stamens 2 to 5, usually 2, sometimes the 2 united into 1, and then the anther is 4-celled. Females: Seeds comose; the radicle inferior (Bot. Gall.).
Species.—Sir J. E. Smith [Engl. Flora, iv.] mentions sixty-four indigenous species of Salix; but pharmacological and botanical writers are not agreed as to which species possesses the most medicinal power. The best practical rule to follow is this: Select those whose barks possess great bitterness, combined with astringency. The following are those which are in the greatest repute:—
1. Salix Russelliana, Smith; the Bedford Willow.—Leaves lanceolate, tapering at each end, serrated throughout, very smooth. Footstalks glandular or leafy. Germen tapering, stalked, longer than the scales. Style as long as the stigmas (Smith).—A tree. In marshy woods, wet meadows, &c, in various parts of Britain. Flowers in April and May. Its bark abounds in tannic acid. On account of its astringency, Sir J. E. Smith regards it as the most valuable officinal species; and he observes, that if it has occasionally disappointed medical practitioners, they probably chanced in such cases to give the S. fragilis.
2. Salix alba, Linn.; the Common White Willow.—Leaves elliptic-lanceolate, pointed, serrated, silky on both sides; the lowest serratures glandular. Stamens hairy. Germen smooth, almost sessile. Stigmas deeply cloven. Scales rounded (Smith).—A tall tree. River-sides, moist woods, &c., in various parts of Britain. Flowers in May. Its bark, called cortex salignum, or cortex anglicanum of some writers, is astringent, but less so than that of the preceding species.
3. Salix Caprea, Linn.; Salix latifolia rotunda, Bauhin; Great Round-leaved Willow.—Stem erect. Leaves roundish-ovate, pointed, serrated, waved; pale and downy beneath. Stipules somewhat crescent-shaped. Catkins oval. Germen stalked, ovate, silky. Stigmas nearly sessile, undivided. Capsules swelling (Smith).—A tree. Indigenous, very common; growing in woods and hedges. Flowers in April. Its bark is the broad-leaved willow bark (cortex Salicis latifoliae) recommended by James, White, and Wilkinson (see ante, p. 314).
4. Salix fragilis, Linn.; the Crack Willow.—Leaves ovate-lanceolate, pointed, serrated throughout, very smooth. Footstalks glandular. Germen ovate, abrupt, nearly sessile, smooth. Scales oblong, about equal to the stamens and pistils. Stigmas cloven, longer than the style (Smith).—A tree. Indigenous; about the banks of rivers. Flowers in April and May.
5. Salix pentandra, Linn.; Sweet Bay-Leaved Willow.—This species is officinal in the Prussian Pharmacopoeia, and is preferred by Nees von Esenbcck to all other species. Its bark is the cortex Salicis laureae of some pharmacologists.
6. Salix purpurea, Linn.; Bitter Purple Willow.—This species deserves notice on account of the intense bitterness of its bark.
Description.—Willow bark (cortex salicis) varies, in its appearance and qualities, according to the species and the age of the tree from which it is procured. In the dried state it is usually quilled and odourless. It should have a bitter and astringent taste.
Composition.—The bark of Salix alba was analyzed by MM. Pelletier and Caventou, [Journ. de Pharm. t. vii. p. 123.] who obtained the following results: Bitter yellow colouring matter, green fatty matter similar to that found in cinchona, tannin, resinous extract, gum, wax, woody fibre, and a magnesian salt containing an organic acid.
These celebrated chemists failed to isolate salicine, which must have been contained in their bitter yellow colouring matter, either mixed or combined with some other matter. Their resinous extract is probably identical with what Braconnot calls corticin.
1. Tannic Acid.—This is the astringent principle of willow bark. Sir H. Davy [Elements of Agricultural Chemistry, 4th edit. p. 83.] gives the following as the quantities of tannin [impure tannic acid] in the bark of two willows:—
|480 lbs. of bark.||lbs. of tannin.|
|Leicestershire Willow (Salix Russelliana) large size||33|
|Common Willow (Salix ?) large||11|
2. Salicine—See p. 316.
Chemical Characteristics.—A decoction of the bark, made with distilled water, is coloured dark green (tannate of iron) by sesquichloride of iron; but, made with spring water, dark purple. Solution of gelatin produces a precipitate (tannate of gelatin) in the decoction, but tincture of nutgalls causes no turbidness. A strong decoction of willow bark, containing much salicine, is reddened by concentrated sulphuric acid.
Physiological Effects.—Willow bark possesses both bitterness and astringency. It belongs, therefore, to the astringent bitters, whose effects have been already noticed (see vol. i., p. 241). It is less apt to disturb the stomach than cinchona, but its tonic and febrifuge powers are less than the latter. Vogt [Pharmacodynamik, Bd. i. S. 658.] ascribes to it balsamic properties.
Uses.—It has been employed as an indigenous substitute for cinchona. The indications for its use, therefore, are the same as those for the latter. It is given in intermittents, dyspeptic complaints accompanied with, or dependent on, a debilitated condition of the digestive organs, passive hemorrhages, chronic mucous discharges, in the stage of convalescence after fever, and as an anthelmintic. As a local astringent, the powder or infusion is sometimes employed, but there are many more efficient remedies of this kind.
Administration.—The dose of the powder is ʒss to ʒj. The infusion or decoction (prepared with ℥j of the bark and Oj of water) may be given in doses of from f℥j to f℥iij.
SALICINUM; Salicine.—Obtained in a more or less impure state by Brugnatelli, Fontana, [Journ. de Chim. Méd. t. i. p. 216, 1825.] in 1825, and Buchner [Repert. für d. Pharm. Bd. xxix. S. 411, 1828. Also Journl. de Pharm. xvi. 242.] in 1828, and in a pure state by Leroux [Ann. de Chim. et de Phys. t. xliii. p. 440. Also Journ. de Chim. Méd. t. vi. p. 340, 1830.] in 1829. Has been found in about fourteen species of Salix and eight species of Populus. [Herberger, Pharmaceutisches Central-Blatt für 1838, S. 848.] It has been detected in the bark, leaves, and flowers. Herberger obtained 250 grains, Merck 251 grains, from 16 ounces of the bark and young twigs of Salix Helix; Erdmann, however, procured, by another process, 300 grains from the bark of Salix pentandra. [Ibid. S. 852.] Merck's process for obtaining it, as stated by Liebig, [Turner's Chemistry, 7th edit. p. 816.] is as follows:—
"Dried or fresh willow bark is cut small, and exhausted by repeated boiling with water. The decoctions are concentrated, and while boiling treated with litharge till the liquor appears nearly colourless. The dissolved oxide of lead is removed, first by sulphuric acid, afterwards by sulphuret of barium, and, after the separation of sulphuret of lead, evaporated, when salicine crystallizes; and is purified by repeated solution and crystallization (Merck). From willow bark, which is fresh and rich in salicine, it may be obtained by cautious evaporation of the cold aqueous infusion (Merck). The oxide of lead removes from the solution gum, tannin, and extractive matter, which would impede the crystallization of the salicine. It also combines with the salicine, forming a kind of salt which is decomposed by the sulphuric acid and sulphuret of barium. If the latter be carefully added, neither sulphuric acid nor baryta remain in the solution; and the sulphuret of lead, which separates, acts as a decolorizing agent."
Salicine crystallizes in silky needles and laminae. It is white, very bitter, inodorous, neutral to vegetable colours, fusible at 230° F., and combustible at a higher temperature. It rotates to the left a ray of plane polarized light. It is much more soluble in boiling than in cold water, 100 parts of which dissolve only 5.6 parts of salicine. It is also soluble in alcohol, but not so in ether or the volatile oils. It is not precipitated by any agent. Oil of vitriol colours it blood-red. [Phloridzin, veratria, piperin, oil of bitter almonds, &c. are also coloured red by oil of vitriol.] By this test the presence of salicine is detected in its solutions, and in decoctions of willow and poplar barks. Chromic acid (or a mixture of bichromate of potash and sulphuric aeid) converts salicine (C26H18O14) into hydruret of salicyle (also called salicylous acid), C14H5O4, H (oil of meadow-sweet) carbonic acid and formic acid. Hence this acid may be employed as a test for salicine. For this purpose 3 parts of salicine, 3 of bichromate of potash, and 24 of water, are to be dissolved in water, and to the solution 4 ½ parts of oil of vitriol diluted with 12 parts of water are to be added. On the application of heat, the well-known odour of the flowers of meadow-sweet (Spiraea ulmaria) is evolved. If diluted hydrochloric or sulphuric acid be boiled with a solution of salicine, the fluid becomes suddenly turbid, and deposits a precipitate of saliretine, glucose being at the same time formed.
By the prolonged action of heat, saligenine loses the elements of water (2HO) and becomes saliretine (C14H6O2).
Salicine has been repeatedly subjected to analysis.
|Atoms.||Eq. Wt.||Per Ct.||Piria.[Ann. de Chim. et de Phys. 3me Sér. t. xiv. p. 357, 1845.]|
Salicine possesses tonic properties analogous to disulphate of quina, than which it is less liable to irritate the stomach. In its passage through the system salicine undergoes oxidation, and is converted into hydruret of salicyle, which is found in the urine. Its presence is detected by a persalt of iron, which strikes an intense violet colour with urine containing it. [Laveran and Millon. Comptes Rendus, t. xix. p. 347; and Annuaire de Chimie, p. 585, 1845. These writers state that salicylic acid was also produced; but Wöhler and Frerichs found that hydruret of salicyle did not become changed into salicylic acid in its passage through the system.] It is employed in dyspepsia, intermittents, and other diseases for which cinchona and disulphate of quina are usually exhibited. In the event of the latter becoming scarce, salicine would prove an exceedingly valuable substitute. The dose of it is from 10 to 30 grains. It may be given in powder mixed with sugar or dissolved in some aromatic water. [Blom, Beobacht. u. Beitr. ü. die Salicine, Potsamd, 1835.] Its quickest action in intermittents is said to be obtained when it is given in powder. [Lond. Med. Gaz. Feb. 28, 1840.]