Source, Etc

The chief plants that yield the liquorice root of commerce are Glycyrrhiza glabra, Linne, G. glandulifera, Waldstein and Kitaibel, and G. glabra, var. β-violacea. The British Pharmacopoeia permits the collection from any species of Glycyrrhiza, but the product must comply with the official description.

Glycyrrhiza glabra, Linne (N.O. Leguminosoe), is widely distributed over southern Europe, extending to Central Asia; it is cultivated to a limited extent in England (Yorkshire), but our supplies are derived chiefly from Sicily and Spain.

The plant produces a tall, erect, herbaceous stem, and a stout perennial root, dividing, a few inches below the surface, into several long, straight, descending branches. Near the surface it also throws out long horizontal runners provided with scaly cataphyllary leaves with buds in their axils. In England the plant is dug up in the late autumn, and either sold in the fresh state or cut transversely and dried. The drug consists therefore of both runners and roots, the former constituting the major part.

Spain (Murcia, Aragon and Toledo, valleys of the Ebro, Guadalquivir, &c), Sicily and the south of France furnish considerable quantities of carefully dried liquorice root. In southern Italy large quantities of liquorice root are grown, but it is chiefly converted into extract.

Description. Spanish liquorice is exported in large bales or in bundles of long, straight, cylindrical pieces from 1 to 2 cm. thick. These have a rather dark reddish brown colour, and are usually longitudinally wrinkled. On the surface they also bear small scars of roots, and, on the majority of pieces (the runners), here and there minute dark buds may be seen.

The drug breaks with a fracture that is fibrous in the bark, splintery in the wood; the section exhibits a yellow wood surrounded by a moderately thick yellowish grey bark, the pieces of runner being distinguished by the presence of a small pith. Under the lens the wood is seen to consist of very numerous medullary rays, between which are very narrow, porous wedges of vascular tissue; opposite to these in the bark are radial rows of dark points (groups of bast fibres).

Peeled root (including runner), which alone is official, has a pale yellow, slightly fibrous exterior and exhibits no trace of the small buds; otherwise it resembles the unpeeled.

The drug has a characteristic but not powerful odour, and a very sweet taste without perceptible bitterness or acridity.

Fig. 160.   Spanish Liquorice

Fig. 160. - Spanish Liquorice root. Transverse section of rhizome (runner). a, bark; b, wood; c, pith. Magnified 3 diam. (Berg).

The student should observe

(a) The yellow colour of the section, and fibrous bark,

(b) The minute buds on the unpeeled root,

(c) The pith in most of the pieces,

(d) The characteristic sweet taste, free from acridity; and should carefully compare this (the Spanish) variety with the Russian.

Microscopical Characters

In transverse section the cork-cells are brown and flattened. The cells of the cortex contain small (1.5 to 20) starch grains and prismatic crystals of calcium oxalate. The bast-ring is characterised by the presence of numerous bundles of strongly thickened, striated, yellowish bast fibres accompanied by calcium oxalate cells. The wood contains vessels of varying size (often 100) accompanied by wood fibres closely resembling the bast fibres.

Fig. 161.   Bales of decorticated Liquorice root.

Fig. 161. - Bales of decorticated Liquorice root.

The powder is characterised by the very thick-walled, grouped bast fibres with calcium oxalate cells frequently attached; by the portions of large, thick-walled vessels with closely packed, bordered pits; by the small starch grains and by the prevailing yellowish colour which is changed to orange yellow by sulphuric acid. It should be free from polygonal, brownish cork cells (unpeeled root) and from sclerenchymatous cells (olive-stones, almond shells, &c).

Constituents

The principal constituent of liquorice root is the sweet principle, glycyrrhizin, which, when quite pure, is a white, crystalline, intensely sweet powder, soluble in water. This has been shown to consist of the potassium and calcium salts of glycyrrhizinic acid, a colourless, crystalline acid, slightly soluble in water, but imparting a sweet taste to it in a dilution of 1 in 20,000; it is not a glucoside as was formerly supposed, since it yields on hydrolysis glycyrrhetinic acid and glycuronic acid, but no sugar. Liquorice root contains about 5 to 7 per cent, of it. The drug also contains glucose (1.4 per cent.), sucrose (2.5 per cent.), starch (29 per cent.), an acrid bitter principle, proteids, asparagin, fat, and resin. It yields from 3 to 4 per cent, of ash, and from 15 to 27 per cent, of aqueous extract dried at 100° (official minimum 20 per cent.).

Many other plants are remarkable for their sweet taste, but the presence of glycyrrhizin has been definitely proved only in Periandra dulcis, Martius (N.O. Leguminosoe, Brazil), Pradosia latescens, Radlkofer (Monesia bark, N.O. Sapotaceoe, Brazil). The root of Abrus preca-torius, Linne (Indian liquorice, N.O. Leguminosce), Trifolium alpinum, Linne (mountain liquorice, N.O. Leguminosce, Europe), Astragalus Olycyphyllos, Linne (N.O. Leguminosoe), Polypodium vulgare, Linne (N.O. Polypodi-acece), Myrrhis odorata, Scopoli (N.O. Um-belliferce), Ononis spinosa, Linne (N.O. Leguminosoe), etc, contain sweet principles, possibly glycyrrhizin. The leaves of Eupatorium Rebaudianum (N.O. Compositae), contain eupatorin, and rebaudin said to be 180 times as sweet as sugar.

According to Robert eupatorin is a neutral and rebaudin an acid saponin (compare p. 254). Glycyrrhizin also belongs to the saponins; it has no hemolytic action, but its decomposition product, glycyrrhetinic acid, has; Robert considers that this explains the value of liquorice as a remedy for coughs.

Uses

Liquorice root is a demulcent and expectorant; the liquid extract is frequently employed to mask the taste of nauseous medicines.

Varieties

Russian Liquorice Root. Very large quantities of liquorice root are collected in southern Russia, where the plant grows wild on the banks of the Volga and other rivers, needing no cultivation. The plant that yields this root is G. glandulifera, Waldstein and Kitaibel. Instead of producing numerous runners this plant forms a large rootstock, from which long perennial roots are given off. These are usually freed from the purplish brown cork by scraping.

Nearly all the Russian liquorice root that reaches this country has been peeled, and presents therefore a smooth yellow exterior, to which loose fibres are attached, the larger pieces being often longitudinally split. It attains a much larger size than the Spanish, the crown of the root, which shows the remains of several stems, being occasionally as much as 10 cm. in diameter. The texture is commonly looser and more fibrous than that of the Spanish drug, and the taste, although sweet, is accompanied by a more or less perceptible but not strong bitterness or acridity.

Fig. 162.   Russian Liquorice root. Transverse section. Magnified 1 diam. (Berg.)

Fig. 162. - Russian Liquorice root. Transverse section. Magnified 1 diam. (Berg).