Botanical Source and History.—This tree attains the height of 20 to 50 feet, with a diameter of 8 to 12 inches. It is covered with a smooth, greenish-white bark, except on the trunks of very old trees. The leaves are orbicular-cordate, abruptly acuminate, dentate-serrate, smooth on both sides, pubescent at the margins, dark-green, 3-nerved, 2 to 2 1/2 inches long, and 1 1/4 as wide, on long, slender, and laterally compressed petioles, which accounts for the continual agitation of the leaves by the slightest breeze. The aments are plumed with silken hairs, and are about 2 inches long and pendulous, appearing in April, long before the leaves. The scales are cut into 3 or 4 deep, linear divisions, and fringed with long hairs (W.—G.). This tree is common in lower Canada and in the northern and middle states. The bark is the medicinal part, and should be collected in the spring, just as the sap begins to rise. Its virtues are imparted to alcohol, water, or acetic acid. There are several varieties of this tree, all of which possess similar properties, as the Populus grandidentata, Michaux; P. candicans, Aiton, etc.
Chemical Composition.—The glucosids, populin and salicin, are constituents common to the barks of nearly all species of Populus, as P. tremuloides, P. tremula, P. alba (for the latter, see analysis by M. F. Schaak, Amer. Jour. Pharm., 1892, p. 226). The leaf-buds of P. nigra, P. dilatata (P. pyramidalis), and P. balsamifera, were found by Piccard (Jahresb. der Pharm., 1865, p. 24; and 1873, p. 39) to contain a yellow coloring matter, chrysin (acetyl-benzoyl-phloroglucin [C15H20O8]), tectochrysin (C16H12O4), salicin and populin, resin and essential oil, which he believes (ibid., 1875, p. 70) to contain dipentene (C10H16). The buds of the American aspen (Populus tremuloides), according to R. Glenk (Amer. Jour. Pharm., 1889, p. 240), contain an acid resin of a hop-like odor, soluble in alcohol, caustic potash, glacial acetic acid, acetic ether, and amyl alcohol; slightly soluble in chloroform, ether, carbon disulphide, oil of turpentine, and benzol; insoluble in water. For description of the bitter glucosid, salicin (C13H18O7, or C6H4O.[C6H11O5]), see Salicinum.
Populin (benzoyl-salicin, C20H22O8.2H2O, or C13H17.[C7H5O]O7.2H2O) was discovered, in 1831, by Braconnot, and occurs, together with salicin, in the bark and the leaves of several species of Populus. The leaves of P. tremula contain more populin than the bark, and may be employed to advantage in its isolation. To prepare both, an aqueous decoction of the bark is precipitated by subacetate of lead, the filtrate freed from lead by carefully adding sulphuric acid, filtered again, treated with charcoal, and evaporated to a smaller bulk. The salicin, upon cooling, crystallizes out; the filtrate, upon the addition of potassium carbonate, yields a precipitate of populin, which is obtained pure by recrystallization from water. Populin is a very light substance, snow-white, with a sweetish taste not unlike that of liquorice. It requires about 2000 times its weight of cold and about 70 times its weight of boiling water to dissolve it. Alcohol, when boiling, dissolves it, depositing the populin on cooling in the form of a crystalline magma. It is soluble in acetic, nitric and phosphoric acids, from which solutions it is precipitated by alkalies. It is hardly soluble in ether. Boiling with diluted mineral acids decomposes it into dextrose, benzoic acid and saligenin (C6H4OH.CH2OH), which is further converted into resinous saliretin. Concentrated sulphuric acid gives with populin a purple-red solution. When heated on platinum foil it burns with a strong flame, emitting an aromatic odor. By oxidation with a mixture of sulphuric acid and potassium bichromate, the odor of salicylic aldehyde (C6H4.OH.CHO), the principal constituent of the oil of Spiraea Ulmaria, is evolved.
Action, Medical Uses, and Dosage.—Poplar bark is tonic and febrifuge, and has been used in intermittent fever with advantage. An infusion of it is reputed a valuable remedy in emaciation and debility, after protracted fevers and reproductive disorders of the nervous and hysterical, lumbricoid worms, impaired digestion, chronic diarrhoea, intermittent fevers, etc. As a diuretic, it has been beneficially used in urinary affections, gonorrhoea, gleet, etc. Both populus and populin have a decided affinity for the genito-urinal tract. It is thought to aid the recuperative powers of the kidney when undergoing granular degeneration. In tenesmic vesical irritation and in tenesmus after urination it is decidedly effective. Minute doses—fraction of a drop—are most beneficial here. It is suggested by Prof. Webster for trial in stubborn uterine congestion and prostatic hypertrophies. The Large aspen, P. grandidentata, is said to be the most active and bitter. Dose of the powdered bark, 1 drachm, 2 or 3 times a day; of a saturated tincture of the fresh bark, from a fraction of a drop to 30 drops; of populin, 1 x trituration, 1 grain every 2 or 4 hours.
Specific Indications and Uses.—Marked debility with impairment of digestion; tenesmic vesical irritation; tenesmus after micturition.
Related Species.—Several species of Populus besides American poplar have been employed more or less in medicine, and probably most of them depend upon both salicin and populin for their virtues. Among those employed are Populus nigra, or European black poplar; Populus tremula, European aspen; Populus alba, silver-leaf poplar, etc. (See the above-named species for chemical composition.)
Populus balsamifera, Linné, Balsam poplar.—This tree, also called Tacamahac, or Tacamahac poplar, attains the height of 50 to 70 feet, with a trunk about 18 inches in diameter. Branches smooth, round, deep-brown; buds acuminate, smooth, covered in the spring with an abundance of fragrant, viscid, balsamic juice. Leaves ovate, gradually tapering and pointed, smooth on both sides, with fine glandular serratures, deep-green above, whitish and reticulate-vein beneath, on long petioles; sometimes 2 glands at the apex of the petiole. Scales dilate slightly hairy (L.—W.). This tree is found in Canada, the northern parts of the United States, and in Siberia. In this country it is in blossom in April. The leaf-buds are the medicinal parts, and should be collected in the spring; they are covered with a fragrant resinous matter, which may be separated in boiling water, and upon which their virtues depend. They have an agreeable, incense-like odor, and an unpleasant, bitterish taste. The balsamic juice is collected in Canada in shells, and sent to Europe, under the name of tacamahaca. Alcohol or spirits is the proper solvent. (For chemical composition, see Piccard, loc. cit.).
Populus candicans, Aiton.—The buds of the Populus candicans, Aiton, or Balm of Gilead, possess virtues similar to the above. The tree is of less stature than the P. balsamifera, the leaves are broader, and heart-shaped, with a distinct sinus at the base; the petioles are hairy and the branches terete (G.) Poplar buds are reputed stimulant, tonic, diuretic, and antiscorbutic. A tincture has been beneficially employed in affections of the chest, stomach, and kidneys, and in rheumatism and scurvy. With lard or oil they form a useful external application in bruises, swellings, wounds, some cutaneous diseases, rheumatic pains, etc. Added to ointments they prevent, in a great measure, their liability to become rancid, but in this respect are not equal to paraffin, which will wholly prevent rancidity in cerates and ointments prepared with it, discovered by Prof. E. S. Wayne. The bark is said to be tonic and cathartic, and to have prove of service in gout and rheumatism. Dose of a tincture of the buds, from 1 to 4 fluid drachms; this is excellent for colds and pain in the chest. An extract of the bark made with diluted acid, in the dose of from 5 to 15 grains, 3 times a day, is a useful tonic in debility, intermittent fever, rheumatism, etc.
King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.