_Larch Bark._
=Botanical Origin=—_Pinus Larix_ L.—see p. 609.
=History=—The bark of the larch has long been known to possess
astringent properties; hence it has been used in tanning.
Gerarde,[2288] who wrote near the close of the 16th century, likened it
to that of the pine, which he described to be of a binding nature; but
there is no evidence that it was an officinal drug.
About the year 1858 larch bark was recommended by Dr. Frizell of
Dublin, and afterwards by other physicians, as a stimulating astringent
and expectorant. In consequence of the favourable effects which have
resulted from its use it has been included in the _Additions to the
Pharmacopœia of 1867_.
=Description=—The bark that we have seen is in flattish pieces or
large quills, externally reddish-brown. In those taken from older wood
there is a large amount of an exfoliating corky coat, displaying as
it is removed bright rosy tints, while the liber is of a different
texture, slightly fibrous and whitish. The inner surface is smooth
and of a pinkish-brown, or pale yellow. The bark breaks with a short
fracture, exhaling an agreeable balsamic terebinthinous odour; it has a
well-marked astringent taste. For medicinal use the inner bark is to be
preferred.
=Microscopic Structure=—A transverse section exhibits resin-ducts, but
far less numerous than in the bark of many allied trees. The medullary
rays are not very distinct. Throughout the middle layer of the bark
large isolated thick-walled cells of very irregular shape are scattered.
=Chemical Composition=—Larch bark has been examined by Stenhouse,[2289]
who finds it to contain a considerable amount of a peculiar tannin,
yielding olive-green precipitates with salts of iron. The same chemist
also discovered[2290] in larch bark an interesting crystallizable
substance called _Larixin_ or _Larixinic Acid_, which has the
composition C₁₀H₁₀O₅. It may be obtained by digesting the bark in
water in 80° C. and evaporating the infusion to a syrupy consistence.
From this, by still further cautious heating in a retort, the larixin
may be distilled, during which operation some of it crystallizes on
the inner surface of the receiver, the remainder being dissolved in
the distilled liquor. From the latter it may be obtained in crystals
by evaporation. The substance forms colourless crystals, sometimes
as much as an inch long; it volatilizes even at 93° C., and melts at
153°. It requires about 88 parts of water for solution at 15° C., but
more freely dissolves in boiling water or in alcohol. From ether, in
which it is but sparingly soluble, it separates in brilliant crystals.
The solutions have a bitterish astringent taste and a slightly acid
reaction, and assume a purple hue on addition of ferric chloride. When
a solution of baryta is added to a concentrated solution of larixin,
the latter being in excess, a bulky gelatinous precipitate falls; it
is readily soluble in boiling water and is deposited again on cooling.
Stenhouse failed to obtain it either from the bark of _Pinus Abies_ L.,
or from that of _P. silvestris_ L.
[2288] _Herball, enlarged by Johnson_, Lond. 1636. 1366.
[2289] _Proceedings of the Royal Society_, xi. (1862) 404.
[2290] _Phil. Trans._, vol. 152 (1862) 53.—We write the name _Larixin_
instead of _Larixine_, with the concurrence of Dr. Stenhouse.
=Uses=—Larch bark, chiefly in the form of tincture, has been prescribed
to check profuse expectoration in cases of chronic bronchitis; it has
also been found useful in arresting internal hæmorrhage.