Source, Etc

The deadly nightshade, or belladonna, Atropa Belladonna, Linne (N.O. Solanaceœ), is a tall branching herb with a perennial root widely distributed over central and southern Europe; in England it is confined chiefly to the southern counties; it also widely cultivated not only in this country but also on the continent, in India, in the United States, etc.

The poisonous properties of belladonna were certainly known towards the end of the fifteenth century, probably much earlier. The leaves were introduced into the London Pharmacopoeia of 1809, the root coming into use much later.

The fresh leaves and branches of the plant are used for preparing the juice and green extract of belladonna but only the dried leaves are official. Considerable quantities are dried in this country; much is also imported. .

Description

The stem of the belladonna plant divides usually a little above the ground into three large branches, each of which branches again freely. The lower leaves are solitary, but the upper are arranged in pairs, consisting of a large and a small leaf, the latter being really a leafy bract. The flowers are solitary and pendulous; they have a dull purplish, campanulate corolla and superior, two-celled, many-seeded ovary, which develops into a purplish black, pulpy fruit. The leaves vary from 8 to 20 cm. in length, They are ovate or broadly ovate, acute, entire, tapering towards the base, and glabrous or nearly so, except when quite young, when, in common with the young stems, they are softly pubescent. Both the midrib and the lateral veins are prominent on the under surface.

The dried leaves are thin, papery, and brittle; they are usually of a dull green colour, paler below. Their surface exhibits under the lens numerous whitish elevated points; these are caused by-cells filled with calcium oxalate, which produce, when the tissue of the leaf dries and shrinks, the appearance described. Neither all specimens of the drug nor both surfaces exhibit this character equally well.

The leaves should be collected when the plant is in flower, as they are then richest in alkaloid. For the preparation of the extract the larger stalks should be rejected, as it has been shown that the extract prepared from them contains less alkaloid than that prepared from the leaves (Ranwez, 1897). For the same reason the dry drug should be as free as possible from stalk.

Fig. 30.   Belladonna, showing leaves in unequal pairs. Reduced.

Fig. 30. - Belladonna, showing leaves in unequal pairs. Reduced.

Microscopical Characters

The transverse section of the midrib exhibits strands of bast both above and below the wood (bi-collateral bundles), a feature common in Solanaceae and in a few other orders, but by no means of frequent occurrence, and hence of use in identifying the leaves. There are no bast-fibres or sclerenchymatous cells. Some of the cells of the mesophyll are filled with numerous, minute crystals of calcium oxalate, best seen when portions of the leaves are warmed with solution of chloral hydrate (5 parts) in water (2 parts), or with a mixture of cresol (2 parts) with glycerin (1 part), and examined under the microscope. This is an important character, as it enables these leaves to be distinguished from stramonium, henbane, foxglove, and many others. Each stoma is surrounded by three or four cells, one of which is smaller than the others; the epidermal cells have sinuous walls and striated cuticle.

The student should observe

(a) The upper leaves in unequal pairs,

(b) The glabrous surface,

(c) The presence of whitish raised points (on the dried leaves); and should compare the dried leaves with

(i) Stramonium leaves, which curl and twist as they dry, have a characteristic odour and sinuate -dentate outline,

(ii) Foxglove leaves, which are hairy,

(iii) Henbane leaves, which are hairy.

Constituents

The chief constituents of the drug are the alkaloids hyoscyamine and atropine. Good samples contain about 0.4 per cent, of total alkaloid, but as much as 1 per cent, has (exceptionally) been found. The alkaloids are contained in all parts of the plant; in the calices and young ovaries 0.79 per cent, has been found, in the ripe seeds 0.83 per cent., in the root 05 per cent., and in fresh fruit 0.12 per cent.

Belladonna leaves also contain a fluorescent substance, β-methyl-sesculetin (scopoletin, chrysatropic acid), and yield about 14 per cent, of ash.

Hyoscyamine, C17H13N03, forms colourless crystals melting at 108.5°; it is lsevorotatory [a]D = - 29°.97), and is converted by heating to 110° into its isomer atropine. Atropine differs from hyoscyamine in having a higher melting-point, viz. 115°, and in being optically inactive: it is the racemic modification and can be resolved into laevo- and dextro -hyoscyamine, the latter being much less active than laevo-hyoscyamine. Both hyoscyamine and atropine yield tropine and tropic acid when hydrolysed by heating with baryta water. Hyoscyamine crystallises less readily than atropine, is more soluble in water and dilute alcohol, and yields with gold chloride an aurichloride (C17H13N03,HCl,AuCl3), crystallising in brilliant yellow scales, melting at 160°, whereas the corresponding atropine gold salt crystallises in dull warty prisms melting at 136°. Other alkaloids (belladonnine, apoatropine) may possibly also be present, but it is more probable that these are formed from hyoscyamine during the process of extraction. Hyoscyamine is also found in Hyoscyamus niger, in Hyoscyamus muticus (see p. 53), in Datura Stramonium, as well as in other species of Datura, and is often accompanied by scopolamine (hyoscine) (compare ' Belladonna Root'). For the distribution of the alkaloid in the various parts of the plant compare ' Stramonium Leaves.'

Fig. 31.   Belladonna leaf. Under surface, showing the venation. Natural size.

Fig. 31. - Belladonna leaf. Under surface, showing the venation. Natural size.

Duboisine, the alkaloid from the Australian Duboisia myoporoides appears to consist of hyoscyamine or scopolamine according to the variety of drug from which it is obtained.

Adulterations

(1) The leaves of Scopola carniolica, Jacquin, a Solanaceous plant widely distributed in Hungary; they closety resemble belladonna leaves, but are more lanceolate, more translucent, brighter in colour, and with more distinct veinlets; the crystal cells are less numerous, hairs are absent, and stomata occur on the under surface only; they are usually accompanied by the fruit which is a nearly spherical pyxis almost completely covered by the papery calyx, that of belladonna being a berry; they contain hyoscyamine and scopolamine (0.5 per cent).

(2) The leaves of Phytolacca decandra, Linne; these may be distinguished by containing acicular crystals of calcium oxalate, and by the epidermal cells which are elongated and straight-walled.

(3) The leaves of Ailanthus glandulosa, Desfontaines (N.O. Simaru-beai); these have cluster-crystals of calcium oxalate along the veins.

Other leaves have also been found in the commercial drug, but the microscopical characters of the true drug generally suffice for its identification.

Uses

Belladonna acts as a local anaesthetic and anodyne, and is used externally to relieve pain. Internally, it is given to check the sweating in phthisis, as a sedative to the respiratory nerves, to relieve spasmodic cough, and in numerous other cases.