We are unacquainted with Russian lactucarium, which has been quoted at a very high price in some continental lists.
Chemical Composition—Lactucarium is a mixture of very different organic substances, together with 8 to 10 per cent. of inorganic matter. It is not completely taken up by any solvent, and when heated merely softens but does not melt. Nearly half the weight of lactucarium consists of a substance called Lactucerin or Lactucon, which in our opinion is closely allied to if not identical with similar substances occurring in numerous milky juices. Lactucerin as afforded by the drug under examination is probably a mixture of several bodies. It may be obtained by exhausting lactucarium with boiling alcohol sp. gr. 0·830; it is deposited in crystals, which when duly purified have the form of slender colourless, microscopic needles. Lactucerin is an inodorous, tasteless substance, insoluble in water, but dissolving in ether and in oils both fixed and volatile, not quite so readily either in benzol, or in bisulphide of carbon. We found it to melt at 232° C. and to agree with the formula C₁₉H₃₀O; Franchimont (1879) assigns to it the formula C₁₄H₂₄O, melting point 296°.
Euphorbon (see Euphorbium), echicerin (see Cortex Alstoniæ), taraxacerin ([p. 394]), the cynanchol, C₁₅H₂₄O, extracted in 1875 by Buttleroff from Cynanchum acutum L., are remarkably analogous to lactucerin.
In the lactucarium of Zell, we further met with a large amount of a substance which is readily soluble in bisulphide of carbon. It is an amorphous mass, melting below 100°, separating from alcohol as a syrupy mass.
Cold alcohol, as well as boiling water, takes out of lactucarium about 0·3 per cent. of a crystallizable bitter substance, Lactucin, C₁₁H₁₂O₃H₂O, which although it reduces alkaline cupric tartrate, is not a glucoside. It may be best obtained by means of dialyse. Lactucin forms white pearly scales, readily soluble in acetic acid, but insoluble in ether. It loses its bitterness when treated with an alkali.
From the mother-liquors that have yielded lactucin, Ludwig, in 1847, obtained Lactucic Acid, as an amorphous light yellow mass, becoming crystalline after long standing. Lastly lactucarium has further afforded in small quantity an amorphous substance named Lactucopicrin, C₄₄H₆₄O₂₁, apparently produced from lactucin by oxidation; it is stated by Kromayer (1862) to be soluble in water or alcohol, and to be very bitter.
Of the widely diffused constituents of plants, lactucarium contains caoutchouc (40-50 per cent.), gum, oxalic, citric, malic and succinic acids, sugar, mannite, and asparagin, together with potassium, calcium and magnesium salts of nitric and phosphoric acids. We obtained crystals of nitrate of potassium by concentrating the aqueous decoction of lactucarium. On distillation with water, a volatile oil having the odour of lactucarium passes over in very small quantity.
Uses—The soporific powers universally ascribed in ancient times to the lettuce are supposed to exist in a concentrated form in lactucarium. Yet numerous experiments have failed to show that this substance possesses more than very slight sedative properties, if indeed it is not absolutely inert.[1459]