This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Lactucarium consists of the dried latex of Lactuca virosa, Linne (N.O. Compositae), and other species of Lactuca. Lactuca virosa is a native of central and southern Europe, but is cultivated in England.
All the plants belonging to the sub-order Ligulifloroe, in which the genus Lactuca is included, contain a system of laticiferous vessels forming an anastomosing network penetrating to all parts of the plant (compare fig. 177). They are especially numerous in the bast of the stem, but are present also in the pith. Hence when the stem of L. virosa is wounded a free exudation of latex takes place in the form of white milky fluid of intensely bitter taste. This latex when dried constitutes the drug. It is collected in Germany near Zell on the Mosel, where most of the commercial drug is produced, by cutting the stem off about a foot below the summit; the latex which exudes is taken off by the finger and transferred to a china cup. It soon coagulates and is then removed from the cup by warming and gently tapping, when it falls out in the shape of a blunt cone which may be dried entire or cut into four pieces and dried. Thin slices are daily taken off the stem and the collection of lactucarium thus proceeds during the summer. The annual production is only about 150 kilograms.
German lactucarium occurs in hard, opaque, irregular, angular pieces, sometimes flat or curved on one or two of their sides, of a dingy brown or reddish brown colour. In the interior they are paler; if quite fresh creamy white and of the consistence of wax; but the colour changes by exposure to a dull brown, the drug becoming at the same time hard. They possess a strong characteristic odour, different from but recalling that of opium, and a bitter taste.
Lactucarium is tough and difficult to powder. Boiled in water it softens to a plastic mass, but only very little of it is soluble. The cooled and filtered liquid should not be coloured blue by iodine, indicating the absence of starch, which has been found in factitious lactucarium, but, as Composite plants contain no starch, this should not be present in the genuine drug. Lactucarium is only partially soluble in alcohol and ether.
It appears doubtful whether lactucarium possesses any particular therapeutic action, although it has been used as a sedative. Lactucin, lactucic acid (crystalline), and lactucopicrin (amorphous) are three bitter principles, the re-examination of which is to be desired. Lactucerin (lactucone), constituting about one-half of the drug, and extracted from it by boiling alcohol, is a crystalline, tasteless, inert, waxy substance, yielding by saponification acetic acid and lactucol (or, according to Hesse, a- and β-lactucerol).
In addition to these constituents, that are apparently peculiar to lactucarium, various other substances commonly found in the latex of plants have been detected, such as caoutchouc, albumen, mannite, certain inorganic substances, etc.
The alkaloid hyoscyamine, which Dymond detected in both wild and cultivated lettuce, especially when the flowering stage is reached, and to which possibly any sedative action of the fresh plant might be due, could not be found in lactucarium.
Lactucarium has been used as a sedative, but is now not much employed.