CORTEX PRUNI SEROTINÆ.
Cortex Pruni Virginianæ; Wild Black Cherry Bark.
Botanical Origin—Prunus serotina Ehrhart (P. virginiana Miller non Linn., Cerasus serotina DC.)—A shrub or tree, in favourable situations growing to a height of 60 feet, distributed over an immense extent of North America. It is found throughout Canada as far as 62° N. lat., and from Newfoundland and Hudson’s Bay in the east, to the valleys west of the Rocky Mountains.[966] It is also common in the United States.
The tree is often confounded with P. virginiana L., from which, indeed, it seems to be separated by no fixed character, though American botanists hold the two plants as distinct. It is also nearly allied to the well-known P. Padus L. of Europe, the bark of which had formerly a place in the Materia Medica.
History—Experiments on the medicinal value of Wild Cherry Bark were made in America about the end of the last century, at which time the drug was supposed to be useful in intermittent fevers.[967] The bark was introduced into the United States Pharmacopœia in 1820. An elaborate article by Bentley[968] published in 1863 contributed to bring it into notice in this country, but it is still much more employed in America than with us.
Description—The inner bark of the root or branches is said to be the most suitable for medicinal use. That which we have seen is evidently from the latter; it is in flattish or channelled pieces, ⅒ to ¹/₂₀ of an inch in thickness, ½ an inch to 2 inches broad, and seldom exceeding 5 inches in length. From many of the pieces, the outer suberous coat has been shaved off, in which case the whole bark is of a deep cinnamon brown; in others the corky layer remains, exhibiting a polished satiny surface, marked with long transverse scars. The inner surface is finely striated, or minutely fissured and reticulated. The bark breaks easily with a short granular fracture; it is nearly without smell, but if reduced to coarse powder and wetted with water it evolves a pleasant odour of bitter almonds. It has a decided but transient bitter taste.
The bark freshly cut from the stem is quite white, and has a strong odour of bitter almonds and hydrocyanic acid.
Microscopic Structure—The chief mass of the tissue is made up of hard, thick-walled, white cells, the groups of which are separated by a brown fibrous prosenchyme. The liber is crossed in a radial direction by numerous broad medullary rays of the usual structure. The parenchymatous portion is loaded both with very large single crystals, and crystalline tufts of calcium oxalate. There is also an abundance of small starch granules, and brown particles of tannic matters. Thin slices of the bark moistened with perchloride of iron, assume a blackish coloration.
Chemical Composition—The bitterness and odour of the fresh bark depend no doubt on the presence of a substance analogous to amygdalin, which has not yet been examined. Hydrocyanic acid and essential oil are produced when the bark is distilled with water, and must be due to the mutual action of that substance alluded to, and some principle of the nature of emulsin. From the fact that an extract of the bark remained bitter although the whole of the essential oil and hydrocyanic acid had been removed, Proctor inferred the existence of another substance to which the tonic properties of the bark are perhaps due.
The fresh bark was found by Perot[969] to yield ½ per mille of hydrocyanic acid in April, 1 per mille in June, and 1·4 in October. The best time for collecting the bark is therefore the autumn.