CORTEX ULMI.
Elm Bark; F. Ecorce d’Orme; G. Ulmenrinde, Rüsterrinde.
Botanical Origin—Ulmus campestris Smith, the Common Elm, a stately tree, widely diffused over Central, Southern and Eastern Europe, southward to Northern Africa and Asia Minor, and eastward as far as Amurland, Northern China, and Japan. It is probably not truly indigenous to Great Britain; but the Wych Elm, U. montana With., is certainly wild in the northern and western counties;[2063] the latter is, according to Schübeler, the only species indigenous to Norway.
History—The classical writers, and especially Dioscorides, were familiar with the astringent properties of the bark of πτελέα, by which name Ulmus campestris is understood. Imaginary virtues are ascribed by Pliny to the bark and leaves of Ulmus. Elm bark is frequently prescribed in the English Leech-books of the 11th century, at which period a great many plants of Southern Europe had already been introduced into Britain.[2064] Its use is also noticed in Turner’s Herbal (1568) and in Parkinson’s Theater of Plants (1640), the author of the latter remarking that “all the parts of the Elme are of much use in Physicke.”
In the Scandinavian antiquity the fibrous bark of Ulmus montana used to be made up into ropes.[2065]
Description—Elm bark for use in medicine should be removed from the tree in early spring, deprived of its rough corky outer coat, and then dried. Thus prepared, it is found in the shops in the form of broad flattish pieces, of a rusty yellowish colour, and striated surface especially on the inner side. It is tough and fibrous, nearly inodorous, and has a woody, slightly astringent taste.
Microscopic Structure—The liber, which is the only officinal part, consists of thick-walled, tangentially-extended parenchyme, in which there are some large cells filled with mucilage, while the rest contain a red-brown colouring matter. The mucilage forms a stratified deposit within the cell. Large bast-bundles, arranged in irregular rows, alternate with the parenchyme, and are intersected by narrow, reddish, medullary rays consisting of 2 or 3 rows of cells. The bast-bundles contain numerous long tubes about 30 mkm. thick, with narrow cavities; and besides these, somewhat larger tubes with porous transverse walls (cribriform vessels). Each cubic cell of the neighbouring bast-parenchyme encloses a large crystal, seldom well defined, of oxalate of calcium.
Chemistry—The chief soluble constituent of elm hark is mucilage with a small proportion of tannic acid, the latter, according to Johanson (1875), probably agreeing with that of oak bark and bark of willows. The concentrated infusion of elm bark yields a brown precipitate with perchloride of iron; the dilute assumes a green coloration with that test. Starch is wanting, or only occurs in the middle cortical layer, which is usually rejected.
Elms in summer-time frequently exude a gum which, by contact with the air, is converted into a brown insoluble mass, called Ulmin. This name has been extended to various decomposition-products of organic bodies, the nature and affinities of which are but little known.[2066]
Uses—Elm bark is prescribed in decoction as a weak mucilaginous astringent, but is almost obsolete.