The thin, shining cork-bark easily exfoliates, showing beneath it the mesophlœum which is rich in chlorophyll. The stalks are mostly hollow, and partially filled with a whitish pith. The wood when dried is about half or one-third as broad as the hollow centre, and the green bark considerably narrower than the wood; the latter has a radiate structure, and in older stems exhibits two or three sharply-defined annual rings. The stems are usually cut into short lengths before being dried for use.
The odour, which is rather fœtid and unpleasant, is to a great extent dissipated by drying. The taste, at first slightly bitter, is afterwards sweetish. The bitter appears to be more predominant in the spring than in the autumn.
Microscopic Structure—The epidermis of younger shoots consists of tabular thick-walled cells, many of them being elevated from the surface as short blunt hairs. The older stems are covered with the usual suberous envelope. The boundary between the mesophlœum and the endophlœum is marked by a ring of strong liber-fibres, some of which also occur in the pith. The woody part is rich in large vessels. In the parenchymatous tissue of bitter-sweet, small crystals of oxalate of calcium, not of a well-defined outline, and minute starch granules are deposited.
Chemical Composition—The taste of bitter-sweet appears due, according to Schoonbroodt (1867), to a bitter principle yielding by decomposition, sugar and Solanine,—the latter in very small amount. Solanine is an alkaloid; it was first prepared in 1820 by Desfosses, a pharmacien at Besançon, from the berries of Solanum nigrum L., and was subsequently detected by the same chemist in the leaves and stalks of S. Dulcamara, and by Peschier in the berries. Winckler (1841) observed that the alkaloid of dulcamara stems can be obtained only in an amorphous state, and that it behaves to platinic and mercuric chlorides differently from the solanine of potatoes. Moitessier (1856) confirmed this observation, and obtained only amorphous salts of the solanine of bitter-sweet.
Zwenger and Kind on the one hand, and O. Gmelin on the other (1859 and 1858), found that solanine, C₄₃H₆₉NO₁₆ (or C₄₂H₈₇NO₁₅, according to Hilger, 1879), is a conjugated compound of sugar and a peculiar crystallizable alkaloid, Solanidine, C₂₆H₃₉NO (or C₂₆H₄₁NO₂?). The latter, under the influence of strong hydrochloric acid, gives up water, and is converted into the amorphous and likewise basic compound, Solanicine.
Wittstein (1852) stated another alkaloid, dulcamarine, to be present in the stems of bitter-sweet. But Geissler (1875) proved that this substance, when perfectly pure, contains no nitrogen, and is not an alkaloid. Geissler obtained his Dulcamarin by warming an aqueous decoction of the drug with charcoal, which he dried and exhausted with boiling alcohol. This on evaporation afforded a yellowish amorphous matter, which was dissolved in water and mixed with a very little ammonia; a substance containing nitrogen then separated. The liquid was evaporated, the residue again dissolved in alcohol, and the alcohol distilled. Dulcamarin thus obtained is a yellowish powder of at first bitter and subsequently permanently sweet taste. It dissolves in water or alcohol, not in ether, chloroform, bisulphide of carbon. By boiling dulcamarin with dilute acids it splits up according to the following equation:—
| C₂₂H₃₄O₁₀ + 2 OH₂ = | C₆H₁₂O₆ | · C₁₆H₂₆O₆. |
| Dulcamarin. | Sugar. | Dulcamaretin. |
Dulcamaretin, a dark brown, tasteless mass, is soluble in alcohol, not in water or ether.
Uses—Dulcamara is occasionally given in the form of decoction, in rheumatic or cutaneous affections; but its real action, according to Garrod, is unknown. This physician remarks[1658] that it does not dilate the pupil or produce dryness of the throat like belladonna, henbane or stramonium. He has given to a patient 3 pints of the decoction per diem without any marked action, and has also administered as much as half a pound of the fresh berries with no ill effect.