Salix. Willow-bark. Salix fragilis, Salix purpurea, Salix pentandra.

Salix. U. S. 1880.—Willow-bark. Weidenrinde, G. Ecorce de Saule, Fr. Most of the species of the large genus Salix are possessed of similar medicinal properties. (For elaborate study of various willow barks see Wellcome Chemical Research Laboratory Report, No. 39.) S. fragilis L. or Crack Willow, which has been introduced into this country from Europe, is said by Sir James Smith to be the most valuable species. S. purpurea L., a European species, is stated by Lindley to be the most bitter, and S. pentandra L. is preferred by Nees von Esenbeck. Many native species are in all probability equally active with the foreign.

Salix alba L., the species formerly recognized by the U. S. Pharmacopoeia, is the common European or white willow. It has sparingly escaped from cultivation, growing from New Brunswick and Ontario southward to Pennsylvania. It is a large tree with a rough grayish bark, the twigs being brittle at the base, and in this respect somewhat resembling S. fragilis. The leaves are pubescent on both surfaces and finely serrulate. It hybridizes with other species of Salix. It flowers in April and May, and the bark is easily separable throughout the summer. That obtained from the branches rolls up when dried into the form of a quill, from 0.5 to 1 mm. thick, has a brown, more or less finely warty periderm, is flexible, fibrous, and of difficult pulverization. The inner surface is brownish-white, and smooth, separating in thin layers. Willow bark has a feebly aromatic odor and a peculiar bitter astringent taste. It yields its active properties to water, with which it forms a reddish-brown decoction. Pelletier and Caventou found among its ingredients, tannin, resin, a bitter yellow coloring matter, a green fatty matter, gum, wax, lignin, and an organic acid combined with magnesia. The proportion of tannin is so considerable that the bark has been used for tanning leather. The characteristic constituent of all species of willow, however, is salicin. Robert W. Beck (A. J. P., 1891, 581) has determined the relative percentages of salicin and tannin as follows:

Jowett and Potter made an examination of thirty-three samples of willow and poplar, and found in but one (Salix discolor Muhl.. the related glucoside salinigrin, which Jowett had previously discovered in an unknown sample of willow bark. This compound has the formula C₁₃H₁₆O₇, and on hydrolysis yields glucose and meta-hydroxybenzaldehyde. (Wellcome Chem. Research Laboratory Report, No. 28.) The bark of the willow is feebly tonic, but it is at present never employed in regular medicine.

Salix nigra Marsh. Black Willow.—This is a tree with a dark brown bark, and is noted for its rapid distribution along streams into which its brittle twigs fall, which strike root, forming new plants. It hybridizes with Salix alba. The younger Michaux states that this is a strong bitter, and according to various eclectic practitioners its green aments or floral buds are a very active sexual depressant, useful in spermatorrhea, in all forms of sexual excitement, and in the nervous disturbances of the menstrual period. From twenty to thirty minims (1.3-1.8 mils) of the fluidextract are to be given four times a day.

The Pussy Willow (Salix discolor Muhl.) is a shrub growing in swamps and on moist hillsides of the northern United States. It is well known because of its silky downy catkins which appear in early spring before the leaves.

The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.