Source, Etc

Lobelia or Indian tobacco, Lobelia inflata, Linne (N.O. Campanulaceoe), an erect annual herb with acrid milky juice (latex), is distributed over the eastern States of North America, and cultivated for medicinal use in the States of New York and Massachusetts. The drug was a domestic medicine of the North American Indians, and was introduced into European practice about 1830. The plant is cut as soon as the lower capsules turn brown, and dried; it is sent into commerce either in bales or in oblong compressed packets.

Description

The stem of the plant, which varies in colour from green to yellowish or often purplish, is hairy and winged in the upper part, but quadrangular, channelled, and nearly glabrous below. The leaves are alternate, broadly oval to ovate-lanceolate in outline, and vary in length from about 3 to 8 cm. They are sessile or shortly petiolate, and bear, especially on the veins of the under surface, scattered bristly hairs; the margin is irregularly crenate-dentate.

The flowers, which are arranged in a long leafy raceme, have a pale blue bilabiate corolla, a tubular calyx with five long spreading teeth and an inferior two-celled ovary. The latter develops into an ovoid, inflated, ten-ribbed fruit, about 7 or 8 mm. long, crowned with the remains of the calyx, and containing numerous minute, brown, oval-oblong seeds, which, under the lens, exhibit a beautifully reticulated surface.

In the commercial drug the green hairy and winged or purplish and channelled stems with alternate leaf-scars are easily found. The leaves are mostly in a fragmentary condition, but recognisable by their hairy under surface. The flowers are seldom to be found, but the characteristic inflated fruits containing the very minute seeds are always present.

The stems and leaves contain laticiferous vessels in the bast, a character that can be ascertained by microscopical examination only, but one that may afford valuable aid in identifying doubtful specimens.

The drug has a somewhat irritant odour, and, when chewed, an unpleasant acrid burning taste.

It is said that the plants are sometimes allowed to mature their seeds and are then thrashed, the seeds being sold separately, whilst the herb is pressed into packets. This would account for the frequent absence of the flowers from the drug, and for the presence of numerous capsules but comparatively few ripe seeds.

The student should observe

(a) The hairy winged stem,

(b) The inflated fruits,

(c) The minute oblong reticulated seeds.

Constituents

That lobelia contains a toxic principle is beyond question, but of the nature of that principle there is some doubt. J. U. and C. J. Lloyd (1887) isolated a white, odourless, amorphous alkaloid, lobeline, which gave easily crystallisable salts with acids, and possessed powerful emetic properties. They also found a neutral crystalline inactive substance, inflatin. Other investigators, notably Siebert (1890) have obtained lobeline in the form of a pale yellowish or colourless (Dreser, 1890) syrupy liquid with strongly alkaline reaction, yielding a crystalline hydrochloride and a crystalline platino-chloride. The formula indicated was C18H13N02.

Fig. 107.   Lobelia inflata. 1, upper part of a plant; 2, flower; 3, corolla; 4, flower, cut vertically; 5, ovary, cut transversely; 6, ripe fruit; 7, the same, cut transversely; 8, seed; 9, the same cut longitudinally; 1, slightly reduced; 2 7, enlarged. 8, 9, highly magnified. (Bentley and Trimen.)

Fig. 107. - Lobelia inflata. 1, upper part of a plant; 2, flower; 3, corolla; 4, flower, cut vertically; 5, ovary, cut transversely; 6, ripe fruit; 7, the same, cut transversely; 8, seed; 9, the same cut longitudinally; 1, slightly reduced; 2-7, enlarged. 8, 9, highly magnified. (Bentley and Trimen).

The uncrystallisable lobelacrin of Enders (1871) appears to be lobeline lobelate (Lewis). The drug yields about 10 per cent. of ash.

Uses

Lobeline has an action closely allied to that of nicotine; it first excites the nerve-cells and then paralyses them. The drug relaxes the bronchial muscles, and thus dilates the bronchioles; it is given in spasmodic asthma and in the dyspnoea of chronic bronchitis. Large doses produce vomiting, and may cause collapse through medullary paralysis.