ERICACEÆ.
FOLIA UVÆ URSI.
Bearberry Leaves; F. Feuilles de Busserole; G. Bärentraubenblätter.
Botanical Origin—Arctostaphylos Uva-ursi Sprengel (A. officinalis Wimmer et Grabowsky, Arbutus Uva-ursi L.), a small, procumbent, evergreen shrub, distributed over the greater part of the northern hemisphere. It occurs in North America, Iceland, Northern Europe, and Russian Asia, and on the chief mountain chains of Central and Southern Europe. In Britain it is confined to Scotland, the north of England, and Ireland.
History—The bearberry was used in the 13th century by the Welsh “Physicians of Myddfai,” described by Clusius in 1601, and recommended for medicinal use in 1763 by Gerhard of Berlin and others.[1466] It had a place in the London Pharmacopœia for the first time in 1788.
Description—The leaves are dark green, ¾ to 1 inch in length by ²/₈ to ⅜ of an inch in breadth, obovate, rounded at the end, gradually narrowed into a short petiole. They are entire, with the margin a little reflexed, and in the young state slightly pubescent, otherwise the whole leaf is smooth, glabrous, and coriaceous; the upper surface shining, deeply impressed with a network of veins; the under minutely reticulated with dark veins.[1467] The leaves have a very astringent taste, and when powdered a tea-like smell.
Chemical Composition—Kawalier (1852) has shown that a decoction of bearberry treated with basic acetate of lead yields a gallate of that metal, thus proving that gallic acid exists ready-formed in the leaves. When the filtrate, freed from lead by sulphuretted hydrogen, is properly concentrated, it deposits acicular crystals of Arbutin, a bitter neutral substance, easily soluble in hot water, less so in cold, dissolving in alcohol, but sparingly in ether.
By contact for some days with emuslin, or by boiling with dilute sulphuric acid, arbutin is resolved, according to Hlasiwetz and Habermann (1875), as follows:—
| C₂₅H₃₄O₁₄ + 2 OH₂ = | C₆H₁₂O₆ | · C₆H₄(OH)₂ | · C₆H₄(OH·OCH₃) |
| Arbutin. | Glucose. | Hydrokinone. | Methyl- hydrokinone. |
Yet possibly arbutin is a mixture of the glucoside compounds of both hydrokinone and methyl-hydrokinone.
By heating arbutin with peroxide of manganese and dilute sulphuric acid, on the other hand, Kinone, C₆H₄O₂, and formic acid are produced. If a concentrated decoction of the leaves is allowed to stand for some months, a decomposition of the arbutin takes place, and a certain quantity of hydrokinone can be isolated by shaking the liquid with ether.
Arbutin is apparently widely distributed among the plants belonging to the order Ericaceæ. Maisch in 1874 showed it to occur in Arctostaphylos glauca Swindley, Gaultheria procumbens L. (Wintergreen) and several other allied American plants. Kennedy (1875) isolated arbutin from Kalmia latifolia L. (Spoonwood), where it occurs in smaller quantity than in bearberry leaves.
Kinic acid (see p. 363) is probably absent in all these plants containing arbutin.
Uloth (1859) had already noticed pyrocatechin (p. 244) and hydrokinone among the products of the distillation of an aqueous extract of bearberry leaves. Arbutin itself also yields hydrokinone by means of dry distillation. Hydrokinone forms colourless crystals, melting at 169° C.
In the mother-liquor from which the arbutin has crystallized, there remains a small quantity of the very bitter substance called Ericolin, occurring in greater abundance in Calluna, Ledum, Rhododendron, and other Ericaceæ. Ericolin is an amorphous yellowish mass, softening at 100° C. and resolved, when heated with dilute sulphuric acid, into sugar and Ericinol, a colourless, quickly resinifying oil of a peculiar, not disagreeable odour; its composition[1468] agrees with the formula C₁₀H₁₆O. The same, or C₂₀H₃₂O₂, is to be assigned to Ursone, which H. Trommsdorff, in 1854, obtained from bearberry leaves by exhausting them with ether (in which however it is but slightly soluble). Ursone is a colourless and tasteless crystallizable substance. It melts at 200° C., and sublimes apparently unchanged. Tonner (1866) met with it in the leaves of an Australian Epacris, a plant of the same order as the bearberry.
Lastly, tannic acid is present in the leaves under notice; their aqueous infusion is nearly colourless, but assumes a violet hue on addition of ferrous sulphate. After a short time a reddish precipitate is produced, which quickly turns blue. By using ferric chloride, a bluish black precipitate immediately separates.
Adulteration—The leaves of Vaccinium Vitis-idæa L., called Red Whortleberry or Cowberry, have been confounded with those of bearberry, which in form they much resemble. But they are easily distinguished by being somewhat crenate towards the apex, dotted and reticulate on the under surface and more revolate at the margin.
Uses—An astringent tonic used chiefly in affections of the bladder.