_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.
[1466] Murray, _Apparatus Medicaminum_, ii. (1794) 64-81.
[1467] Microscopic structure of the leaves, see Pocklington, _Pharm.
Journ._ v. (1874) 301.
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.
[1468] Gmelin, _Chemistry_, xvi. (1864). 28.
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.