Mezereon Bark; F. Ecorce de Mézéréon, Bois gentil; G. Seidelbast-Rinde.
Botanical Origin—Daphne Mezereum L., an erect shrub, 1 to 3 feet high, the branches of which are crowded with purple flowers in the early spring, before the full expansion of the oblong, lanceolate, deciduous leaves. The flowers are succeeded by red berries. It is a native of the hilly parts of almost the whole of Europe, from Italy to the Arctic regions, and extends eastward to Siberia. In Britain it occurs here and there in a few of the southern and midland counties, and even reaches Yorkshire and Westmoreland, but there is reason to think it is not truly indigenous. Gerarde, who was well acquainted with it, did not regard it as a British plant.
History—The Arabian physicians used a plant called Mázariyún, the effects of which they compared to those of euphorbium; it was probably a species of Daphne. The word mázariyún is, we are told by competent Arabic scholars, not of Arabic origin, but in all probability derived from the Greek idiom, in which however we are unable to trace its origin. D. Mezereum was known to the early botanists of Europe, as Daphnoides Chamælæa, Thymelæa, Chamædaphne. Tragus described it and figured it in 1546 under the name of Mezereum Germanicum. The bark had a place in the German pharmacy of the 17th century under the name of cortex Coccognidii s. Mezerei; the berries were the Cocca gnidia s. knidia of the old pharmacy.
Description—Mezereon has a very tough and fibrous bark easily removed in long strips which curl inwards as they dry; it is collected in winter and made up into rolls or bundles. The bark, which rarely exceeds ¹/₂₀ of an inch in thickness, has an internal greyish or reddish-brown corky coat which is easily separable from a green inner layer, white and satiny on the side next the wood. That of younger branches is marked with prominent leaf-scars. The bark is too tough to be broken, but easily tears into fibrous strips. When fresh, it has an unpleasant odour which is lost in drying; its taste is persistently burning and acrid. Applied in a moist state to the skin, it occasions, after some hours, redness and even vesication.
Microscopic Structure—The cambial zone is formed of about ten rows of delicate unequal cells. The libre consists chiefly of simple fibres alternating with parenchymatous bundles, and traversed by medullary rays. The fibres are very long,—frequently more than 3 mm., and from 5 to 10 mkm. in diameter, their walls being always but little thickened. In the outer part of the liber there occur bundles of thick-walled bast-tubes, while chlorophyll and starch granules appear generally throughout the middle cortical layer. The suberous coat is made up of about 30 dense rows of thin-walled tabular cells, which examined in a tangential section, have an hexagonal outline. Small quantities of tannic matter are deposited in the cambial and suberous zones.
Chemical Composition—The acrid principle of mezereon is a resinoid substance contained in the inner bark; it has not yet been examined. The fruits were found by Martius (1862) to contain more than 40 per cent. of a fatty, vesicating oil, which appears to be likewise present in the bark.
The name Daphnin has been given to a crystallizable substance obtained by Vauquelin in 1808 from Daphne alpina, and afterwards found by C. G. Gmelin and Baer in the bark of D. Mezereum. Zwenger in 1860 ascertained it to be a glucoside of bitter taste, having the composition C₁₅H₁₆O₉ + 2 OH₂, the same as that of Æsculin, the fluorescing principle occurring in the bark of Æsculus Hippocastanum and the root-bark of Gelsemium nitidum Michaux (G. sempervirens Aiton).—Coccognin, isolated in 1870 by Casselmann from the fruits of D. Mezereum, appears to be closely allied to if not identical with daphnin.
When daphnin is boiled with dilute hydrochloric or sulphuric acid, it furnishes Daphnetin, C₉H₆O₄ + OH₂, described by Zwenger as crystallizing in colourless prisms. By dry distillation of an alcoholic extract of mezereon bark, the same chemist obtained Umbelliferone (p. 322).
Uses—Mezereon taken internally is supposed to be alterative and sudorific, and useful in venereal, rheumatic and scrofulous complaints; but in English medicine it is never now given except as an ingredient of the Compound Decoction of Sarsaparilla. An ethereal extract of the bark has been introduced (1867) as an ingredient of a powerful stimulating liniment. On the Continent, the bark itself, soaked in vinegar and water, is applied with a bandage as a vesicant.
Substitutes—Owing to the difficulty of procuring the bark of the root of D. Mezereum, the herbalists who supply the London druggists have been long in the habit of substituting that of D. Laureola L., an evergreen species, not uncommon in woods and hedge-sides in several parts of England. The British Pharmacopœia (1864 and 1867) permits Cortex Mezerei to be obtained indiscriminately from either of these species, and does not follow the London College in insisting on the bark of the root alone. That of the stem of D. Laureola corresponds in structure with the bark of the true mezereon, but wants the prominent leaf-scars that mark the upper branches of the latter; it is reputed to be somewhat less acrid than mezereon bark. The mezereon bark of English trade is now mostly imported from Germany, and seems to be derived from D. Mezereum.
In France, use is made of the stem-bark of D. Gnidium L., a shrub growing throughout the whole Mediterranean region as far as Morocco. The bark is dark grey or brown, marked with numerous whitish leaf-scars, which display a very regular spiral arrangement. The leaves themselves, some of which are occasionally met with in the drug, are sharply mucronate and very narrow. As to structural peculiarities, the bark of D. Gnidium has the medullary rays more obvious and more loaded with tannic matters than those of D. Mezereum; but the middle cortical layer is less developed. The bark, which is called Ecorce de Gaoru, is employed as an epispastic.