Lettuce is the fresh, flowering herb, Lactuca virosa Linn. (N.O. Compositae), a biennial plant, indigenous to and cultivated in Britain, as well as in Germany, France, etc. The plant has a solid stem, 2 to 4 feet high, prickly near the base, branching above, and producing more or less leafy panicles of small, pale yellow flower-heads. The leaves are lanceolate to broadly oblong in shape, the lower leaves being sessile and the upper leaves amplexicaul, with coarsely toothed, or more or less deeply lobed, margin, and bearing stiff bristles or prickles on the under surface of the midrib and lateral veins. The florets number six to twelve; the fruit is small, flattened, and bears a slender beak about as long as the fruit. Both leaves and stem exude when incised a copious, white, bitter latex, which is contained in an anastomosing system of laticiferous vessels in the bast.
Constituents.—In addition to the constituents of the latex, as described under Lactucarium, lettuce contains traces of hyoscyamine, to which the sedative action of the drug is probably due.
Action and Uses.—Lettuce is a mild sedative and hypnotic, and is used chiefly in irritable cough. Lozenges and pastilles are prepared containing 30 or 60 milligrams (½ or 1 grain) of extract in each, sometimes combined with borax.
- Extractum Lactucae, B.P., 1885.—EXTRACT OF LETTUCE.
- Lettuce, fresh, 100. Press out the juice from the fresh herb, heat it to 54°, and strain through calico to remove the chlorophyll. Heat the strained liquor to 93°, remove the coagulated albumin by filtration, evaporate the filtrate to a thin syrup by the heat of a water-bath, add the previously separated chlorophyll after passing it through a hair sieve, stir, and evaporate to a soft extract at a temperature not exceeding 60°. It is prescribed in pill form for its mild hypnotic properties. It is sometimes used with calomel, instead of extract of henbane. Extract of lettuce is an ingredient of soothing lozenges and pastilles for use in coughs. Dose.—3 to 10 decigrams (5 to 15 grains).
Lactucarium is the dried latex of Lactuca virosa, Linn., and other species of Lactuca (N.O. Compositae). It is official in the U.S.P. It is obtained by cutting off the upper portion of the stem, thus allowing the latex to exude, so that it can be transferred to a small cup. After twenty-four hours a thin slice is removed from the cut surface and the operation repeated. The collected latex soon solidifies, and is then removed from the cup, cut into pieces, and dried, gradually acquiring a dull brownish colour during the process. The drug occurs in hard, opaque, irregular pieces, often curved on one side. They are dull brown in colour, but the interior, in recent pieces, may still be whitish and soft. The odour is characteristic, recalling that of opium; taste, bitter. The cooled decoction should not be coloured blue by iodine.
Constituents.—One of the chief constituents of lactucarium is a colourless, tasteless, crystalline substance named lactucerin or lactucone (44 per cent.); this is accompanied by the bitter principles lactucin and lactucic acid, which are crystalline, and lactucopicrin, which is amorphous. Marmite, sugar, and caoutchouc are also present, but the alkaloid hyoscyamine cannot be detected in lactucarium, although traces are said to be contained in the fresh herb.
Action and Uses.—Lactucarium is employed as a sedative in irritable cough and as a mild hypnotic in insomnia. The syrup is much used abroad. Pastilles and lozenges containing lactucarium are prepared for local use against cough, 30 milligrams (1 grain) in each.
Dose.—3 to 10 decigrams (5 to 15 grains).
- Syrupus Lactucarii, U.S.P.—SYRUP OF LACTUCARIUM.
- Tincture of lactucarium, 10; glycerin, 20; citric acid, 0.1; orange-flower water, undiluted, 5; syrup, sufficient to produce 100. Mildly sedative, and is used in irritable cough. Average dose.—8 mils (2 fluid drachms).
- Tinctura Lactucarii, U.S.P.—TINCTURE OF LACTUCARIUM.
- Lactucarium, in coarse powder, 50; glycerin, 25; alcohol (70 per cent), 70; purified benzin, a sufficient quantity; alcohol (45 per cent.), sufficient to produce 100. This tincture is used chiefly for the preparation of Syrupus Lactucarii. Dose.—1 to 2 mils (15 to 30 minims).