Larch bark is obtained from Larix europaea, DC. (N.O. Coniferae), a large tree indigenous to Southern and Central Europe, but cultivated in Britain. The bark is stripped from the trunk and branches, and dried. It occurs usually in flat, curved, or channelled pieces, less frequently in large quills. The outer portion (often largely developed) consists of dark brown fissured outer bark, from which large flakes can easily be split off, disclosing a rose-coloured surface; inner portion, narrow and whitish. The longitudinal section exhibits very large spindle-shaped sclerenchymatous cells, and long narrow cells containing small prismatic crystals of calcium oxalate embedded in a dark brown amorphous mass. The bark has a terebinthinate odour and astringent terebinthinate taste. Young bark, or older bark deprived of its outer portion, is better than the thick old bark usually in commerce, but can seldom be procured. Venice turpentine is the viscid yellowish liquid which exudes when holes are bored in the trunk of Larix europaea. It is entirely soluble in absolute alcohol; and does not readily harden on exposure, or when mixed with one-sixteenth of its weight of magnesia. It yields about 15 per cent. of volatile oil resembling turpentine. The Venice turpentine of commerce is often a factitious substance prepared by dissolving resin in oil of turpentine; it is darker in colour than the genuine substance. Venice turpentine is used in veterinary practice (see Terebinthina Veneta Factitia).
Constituents.—The chief constituent of larch bark is tannin, but it also contains the crystalline bitter principle larixin (larixinic acid), which appears to be allied to pyrocatechin. Larixin is said to be most abundant in the young bark.
Action and Uses.—Larch bark is astringent and diuretic. The tincture is used internally as a stimulating expectorant in chronic bronchitis. Diluted with 20 to 30 parts of water it forms an astringent injection to arrest chronic mucous discharges.
- Tinctura Laricis, B.P. 1885.—TINCTURE OF LARCH.
- Larch bark, in No. 20 powder, 12.5; alcohol, sufficient to produce 100. Add 10 of the alcohol to the drug to moisten it, and proceed with the percolation process. Tincture of larch is used as an expectorant in bronchitis, and, diluted with 30 parts of water, as an astringent lotion in leucorrhoea. Dose.—1 1/2 to 2 mils (20 to 30 minims).
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.