Related entry: Lactucarium (U. S. P.)—Lactucarium
The flowering herb of Lactuca virosa, Linné, and other species of Lactuca.
COMMON NAME: Strong-scented lettuce.
ILLUSTRATION: Bentley and Trimen, Med. Plants, 160 and 161.
Botanical Source.—Lactuca virosa has a tap-shaped root, with a solitary stem, 2 or 3 feet high, erect, round, smooth, sparingly leafy, scarcely branched, panicled at the top, and a little prickly below. The leaves are horizontal, nearly smooth, and finely toothed; the radical ones numerous, obovate, undivided, depressed; those of the stem smaller, often lobed; arrow-shaped, clasping at their base; the midrib of all more or less beset underneath with prominent prickles, such as often occur on the margin also. The flower-heads are numerous and panicled, with an abundance of small, heart-shaped, pointed bracteas. Involucral scales downy at the tip, destitute of any keels or ribs. Corolla small and light-yellow. Pappus rough (L.). There are many varieties of lettuce; they all have large leaves, often corrugated, and containing more or less of a whitish juice, the lactucarium. Their stems are round and corymbose at the summit; the leaves suborbicular and runcinate; cauline ones cordate or obovate; flowers Yellow.
Lactuca sativa has an annual, tap-shaped root, with a corymbose Stem, 2 or 3 feet in height, and suborbicular leaves; cauline ones cordate. Heads numerous and small, with yellowish corolla (W.). It is not so rank in odor as the L. virosa, has not blood-red spots on its stems, and no prickles on the keel of its leaves. Previous to the appearance of the flowering stems, the garden lettuce contains a pleasant, sweet, watery juice, and in this condition the plant is employed as a salad; but in both species, no sooner does the flowering stem rise above the early leaves than the juice grows milky, very bitter, and of a strong, peculiar, rank odor, not unlike that of opium (see Chemical Composition).
Lactuca Scariola, Linné, differs from L. virosa in having vertical, spinescent, toothed, deeply-out, or pinnatifid leaves.
History.—The Lactuca virosa, Linné, is the only species recognized by the Br. Pharm. 1885, and is directed by the U. S. P. as the source of Lactucarium (see Lactucarium). Several other species, however, yield this product. Lactuca sativa, or common lettuce of the gardens, is supposed to be a native of the East Indies; it is extensively cultivated in Europe and this country. According to Prof. J. M. Maisch, the L. canadensis, var. elongata (wild lettuce), of our country possesses narcotic principles similar to the others. Mr. H. Flowers (Amer. Jour. Pharm., 1879, p. 343) observed in a growing specimen of this plant a strong, narcotic odor of the milky juice, but a remarkable change in the taste, from sweetish to bitter, took place later in the season. Lactucarium, or lettuce-opium, so-called, is obtained from the plants "by cutting the stem of the lettuce at the time of flowering, imbibing the milky juice that flows out by a sponge or by cotton, and squeezing it out into a vessel containing a little water. It is then left in a dry place until it concretes into a solid mass" (Thompson's Org. Chem.). The juice, in drying, loses about half its weight of water. By making another cut a short distance below the first, and so proceeding several times daily, the whole of the juice contained in the plant may be collected. There are several other modes recommended for procuring the lactucarium, but no one of them obtains an article equal to that collected by the above plan. After the middle period of inflorescence, the juice, becomes thicker, but deteriorates in its medicinal principles. A single plant of L. sativa is said to yield 17 grains of lactucarium, while a plant of L. virosa gives 56 grains. L. Scariola, or prickly lettuce, yields 25 grains. As found in commerce, lactucarium is in roundish, compact, rather hard masses, weighing several ounces, of a reddish-brown color externally, of a bitter, narcotic, and somewhat acid taste, and an odor approximating that of opium. It is asserted that two species—L. Scariola, Linné, and L. altissima, Bieberstein.furnish a superior article of lettuce-opium. Fairgrieve, of Scotland, cultivated the L. virosa, var. montana, and Aubergier, of France, the L. altissima.
Chemical Composition.—The chief constituent of lactuca is lactucarium (see Lactucarium). Potassium nitrate is an additional constituent. Mr. T. S. Dymond (Pharm. Jour. Trans., 1891, Vol. XXII, p. 449), having observed mydriatic action with extracts of Lactuca sativa (common garden lettuce) and L. virosa, the former being collected while flowering, succeeded in isolating therefrom an alkaloid (not exceeding 0.02 per cent), which he identified as hyoscyamine. Specimens of English and German lactucarium, on the other hand, did not contain a trace of the alkaloid. The occurrence of an alkaloid in so widely-used a vegetable need not, however, cause alarm. It is probably in insignificant quantity in the early stages of growth of the vegetable.
Medical Uses.—(See Lactucarium.)