Laurocerasi Folia.—Cherry-Laurel Leaves.
The leaves of Prunus Laurocerasus, Linné (Cerasus Laurocerasus, Lois).
COMMON NAME: Cherry-laurel.
ILLUSTRATIONS: Bentley and Trimen, Med. Plants, Plate 98; Woodville's Med. Bot., Plate 185; Artus' Hand Atlas, Vol. I, p. 205.
Botanical Source and Description.—Cherry-laurel is a small evergreen tree, native of Asia Minor, and often cultivated as an ornamental shrub in the southern part of Europe. The flowers are small, white, and disposed in axillary racemes, which are shorter than the leaves. The fruit is an ovate, acute, purple drupe, with a globular stone. The leaves are very thick and leathery, about 6 inches in length, and one-third as broad, tapering at the apex to a sharp point, and at the base to a short leaf-stalk. The margin is denticulated with sharp, appressed, rather distant, serrate teeth. The upper surface of the leaf is of a bright-shining green color; the lower pale and dull. The tree belongs to the section Cerasus (Jussieu), which, by many botanists, is considered distinct from Prunus, chiefly on account of the globular fruit-stone.
History.—The leaves are employed in medicine. When fresh and bruised, they evolve hydrocyanic acid, but the unbroken fresh leaf is odorless. If the perfect leaves are dried and then powdered, they do not give rise to hydrocyanic acid, but the addition of a little water at once develops the acid (Hanbury). At a meeting of the Pharmaceutical Society of Paris, December 6, 1871, Mr. Marais stated that a temperature of -22° C. (-7.6° F.), applied to the leaves and twigs prevented subsequent formation of hydrocyanic acid, although other volatile products were formed.
Chemical Composition.—The leaves of the cherry-laurel, as well as the bark and the seeds of the tree, when distilled with water, yield a distillate of hydrocyanic acid, and benzoic aldehyde (benzaldehyde, bitter almond oil, C6H5.CHO). W. A. Tilden (Pharm. Jour. Trans., Vol. V, 1875, p. 761), finds that the essential oil of cherry-laurel is not absolutely identical with that of the bitter almond; it consists mainly of benzoic aldehyde, and is accompanied by hydrocyanic acid, possibly some benzoic alcohol (C6H5.CH2OH), and minute quantities of a resin having the peculiar odor of the cherry-laurel leaf. Both substances constitute the medicinal principles of Aqua Laurocerasi (Br.) or cherry laurel water (see Aqua Laurocerasi).
The formation of these substances suggests the presence of amygdalin in these parts of the plant (see Amygdalus). Lehmann (1874), testing the leaves for amygdalin, obtained 1.3 per cent of crystallizable but deliquescent bitter laurocerasin, which behaved toward the ferment emulsin exactly like amygdalin, yielding hydrocyanic acid, benzaldehyde, and dextrose. The similarity also holds good in the products obtained from both when boiled with baryta water; ammonia is split off in both cases, and the barium salt of amygdalic acid (C20H28O13) is formed, which must not be confused with mandelic acid (C8H8O2). With laurocerasin, however, 2 molecules of amygdalic acid were formed for each molecule of ammonia, while amygdalin yielded but one. Hence, Lehmann accepts that 1 molecule of laurocerasin (C40H67NO30) is composed of equal molecules of amygdalin (anhydrous, C20H27NO11), amygdalic acid (C20H28O13), and 6 molecules of water. Laurocerasin is believed also to exist in the unripe bitter almonds, and to evolve amygdalin during the process of maturing. It is also contained in the bark of Prunus padus, the bird-cherry tree, while in its seeds, as well as those of cherry-laurel, amygdalin is present. The theoretical yield of hydrocyanic acid from laurocerasin (C40H67NO30) is only about one-half of that from crystallized amygdalin (C20H27NO11+3H2O). Flückiger (Pharmacognosie, 3d ed., 1891, p. 766), obtained on an average 0.12 per cent of hydrocyanic acid in the distillate of bruised fresh leaves. The yield also varies with the season, being highest in the spring and lowest late in the fall, being then reduced to about one-half The leaves also contain reducing sugar, an iron-greening tannin, and a fatty or waxy matter. Bougarel (1877) isolated from the leaves crystallizable phyllic acid, soluble in alcohol and ether, insoluble in water, and melting at 170° C. (338° F.). It also occurs in the leaves of the apple tree, maple, peach, almond, etc. Young leaves incinerated, yielded to Flückiger about 7 per cent of ash.
Action, Medical Uses, and Dosage.—(See Aqua Laurocerasi.) The bruised leaves are anodyne.