_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.
[966] Hooker, _Flora Boreali-Americana_, i. (1833) 169.
[967] Schöpf, _Materia Medica Americana_, Erlangæ 1787; 77.—Also
Barton, _Collections for Mat. Med. of U.S._, Philad. 1798. 11.
[968] _Pharm. Journ._ v. (1864) 67.—Also Bentley and Trimen, _Med.
Plants_, part 3; (1878).
=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.
=Uses=—In America, wild cherry bark is held in high estimation for
its mildly tonic and sedative properties. It is administered most
appropriately in the form of cold infusion or syrup, the latter being
a strong cold infusion, sweetened; a fluid extract and a dry resinoid
extract are also in use. The bark is said to deteriorate by keeping,
and should be preferred when recently dried.