_Slippery Elm Bark._
=Botanical Origin=—_Ulmus fulva_ Michaux, the Red or Slippery Elm, a
small or middle-sized tree,[2067] seldom more than 30 to 40 feet high,
growing on the banks of streams in the central and northern United
States from Western New England to Wisconsin and Kentucky, and found
also in Canada.
=History=—The Indians of North America attributed medicinal virtues to
the bark of the Slippery Elm, which they used as a healing application
to wounds, and in decoction as a wash for skin diseases. It is the
“Salve Bark” or “Cortex unguentarius” of Schöpf.[2068] Bigelow, writing
in 1824, remarks that the mucilaginous qualities of the inner bark are
well known.
=Description=—The Slippery Elm Bark used in medicine consists of the
liber only. It forms large flat pieces, often 2 to 3 feet long by
several inches broad, and usually ¹/₂₀ to ²/₂₀ of an inch thick, of
an extremely tough and fibrous texture. It has a light reddish-brown
colour, an odour resembling that of fenugreek (which is common to the
leaves also), and a simply mucilaginous taste.
In collecting the bark the tree is destroyed, and no effort is made
to replace it, the wood being nearly valueless. Thus the supply is
diminishing year by year, and the collectors who formerly obtained
large quantities of the bark in New York and other eastern states have
now to go westward for supplies.[2069]
[2066] Gmelin, _Chemistry_, xvii. (1866) 458.
[2067] Fig. in Bentley and Trimen’s _Med. Plants_, part 34 (1878).
[2068] _Mat. Med. Americ._, Erlangæ, 1787. 32.
[2069] _Proceedings of the American Pharmaceutical Association for
1873_, xxi. 435.
=Microscopic Structure=—The transverse section shows a series of
undulating layers of large yellowish bundles of soft liber-fibres,
alternating with small brown parenchymatous bands. The whole tissue
is traversed by numerous narrow medullary rays, and interrupted by
large intercellular mucilage-ducts. In order to examine the latter,
longitudinal sections ought to be moistened with benzol, aqueous
liquids causing great alteration. In a longitudinal section, the
mucilage-ducts are seen to be 70 to 100 mkm. long, and to contain
colourless masses of mucilage, distinctly showing a series of layers.
Crystals of calcium oxalate, as well as small starch grains, are very
plentiful throughout the surrounding parenchyme.
=Chemical Composition=—The most interesting constituent of the bark is
mucilage, which is imparted to either cold or hot water, but does not
form a true solution. The bark moistened with 20 parts of water swells
considerably, and becomes enveloped by a thick neutral mucilage, which
is not altered either by iodine or perchloride of iron. This mucilage
when diluted, even with a triple volume of water, will yield only a
few drops when thrown on a paper filter. The liquid which drains out
is precipitable by neutral acetate of lead. By addition of absolute
alcohol, the concentrated mucilage is not rendered turbid, but forms a
colourless transparent fluid deposit.
=Adulteration=—Farinaceous substances admixed to the powdered drug may
be detected by means of the microscope.
=Uses=—Slippery Elm Bark is a demulcent like althæa or linseed. The
powder is much used in America for making poultices; it is said to
preserve lard from rancidity, if the latter is melted with it and kept
in contact for a short time.