Lobelia, Indian Tobacco; F. Lobelie enflée; G. Lobeliakraut.
Botanical Origin—Lobelia inflata L., an annual herb, 9 to 18 inches high, with an angular upright stem, simple or more frequently branching near the top, widely diffused throughout the eastern part of North America from Canada to the Mississippi, growing in neglected fields, along roadsides, and on the edges of woods, and thriving well in European gardens.
History—Lobelia inflata was described and figured by Linnæus[1460] from specimens cultivated by him at Upsala about 1741, but he does not attribute to the plant any medicinal virtues.
The aborigines of North America made use of the herb, which from this circumstance and its acrid taste, came to be called Indian Tobacco. In Europe it was noticed by Schöpf,[1461] but with little appreciation of its powers. In America it has long been in the hands of quack doctors, but its value in asthma was set forth by Cutler in 1813. It was not employed in England until about 1829, when, with several other remedies, it was introduced to the medical profession by Reece.[1462]
Description—The leaves are 1 to 3 inches long, scattered, sessile, ovate-lanceolate, rather acute, obscurely toothed, somewhat pubescent. The edge of the leaf bears small whitish glands, and between them isolated hairs which are more frequent on the under than on the upper surface. They are usually in greater abundance on the lower and middle portions of the stem.
The stem of the growing plant exudes when wounded a small quantity of acrid milky juice, contained in laticiferous vessels running also into the leaves. The inconspicuous blossoms are arranged in a many-flowered, terminal, leafy raceme. The five-cleft, bilabiate corolla is bluish with a yellow spot on the under lip, its tube being as long as the somewhat divergent limb of the calyx.
The capsule is ovoid, inflated, ten-ribbed, crowned by five elongated sepals which are half as long as the ripe fruit. The latter is two-celled, and contains a large number of ovate-oblong seeds about ¹/₅₀ of an inch in length, having a reticulated, pitted surface.
The herb found in commerce is in the form of rectangular cakes, 1 to 1¾ inches thick, consisting of the yellowish-green chopped herb, compressed as it would seem while still moist, and afterwards neatly trimmed. The cakes arrive wrapped in paper, sealed up and bearing the label of some American druggist or herb-grower.
Lobelia has a herby smell and, after being chewed, a burning acrid taste resembling that of tobacco.
Chemical Composition—Lobelia has been examined by Procter, Pereira (1842), Reinsch (1843), Bastick (1851), also by F. F. Mayer.[1463] The first-named chemist[1464] traced the activity of the plant to an alkaloid which he termed Lobelina, and his observations were confirmed by the independent experiments of Bastick.[1465] Lewis (1878) obtained it by mixing the drug with charcoal and exhausting the powder with water containing a little acetic acid. The liquid is cautiously evaporated to the consistency of an extract and triturated with magnesia, from the excess of which the aqueous solution of lobeline is separated by filtration. It is agitated with amylic alcohol (or ether), which by spontaneous evaporation affords the alkaloid. The latter is again dissolved in water and filtered through animal charcoal; from the dried powder lobeline is to be removed by ether.
Lobeline is an oily, yellowish fluid with a strong alkaline reaction, especially when in solution. In the pure state it smells slightly of the plant, but more strongly when mixed with ammonia. Its taste is pungent and tobacco-like, and when taken in minute doses, it exercises in a potent manner the poisonous action of the drug. Lobeline is to some extent volatile, but its decomposition begins when it is heated to 100° C. either pure or in presence of dilute acids or caustic alkalis. Lobeline dissolves in water, but more readily in alcohol or ether, the latter of which is capable of removing it from its aqueous solution. It neutralizes acids, forming with some of them crystallizable salts, soluble in water or alcohol.
The herb likewise contains traces of essential oil (the Lobelianin of Pereira?), resin and gum. The seeds afforded Procter about 30 per cent. of fixed oil, sp. gr. 0·940, which was found to dry very rapidly. The Lobeliin of Reinsch appears to be an indefinite compound.
In 1871 Enders at our request performed some researches on Lobelia in order to isolate the acrid substance to which the herb owes its taste. He exhausted the drug with spirit of wine and distilled the liquid in presence of charcoal, which then retained the acrid principle. The charcoal was washed with water, and then treated with boiling alcohol. This on evaporation yielded a green extract, which was further purified by means of chloroform. Warty tufts were thus finally obtained, yet always of a brownish colour. The tufts are readily soluble in ether and chloroform, but only slightly in water; they possess the acrid taste of lobelia. This substance, which we may term Lobelacrin, is decomposed if merely boiled with water; by the influence of alkalis or acids it is resolved into sugar and Lobelic Acid. The latter is soluble in ether, water, and alcohol, and is non-volatile; it yields a soluble salt with baryum oxide, whereas its plumbic salt is insoluble in water.
Lewis suggests that lobelacrin is nothing else than lobeliate of lobeline, which he believes to exist ready formed in the plant. From a decoction of the drug, on addition of sulphate of copper, lobeliate of copper is precipitated. By decomposing the latter with sulphuretted hydrogen, concentrating the solution and shaking it with warm ether, Lewis obtained a yellow solution affording on evaporation a crystalline mass of lobelic acid.
Uses—Lobelia is a powerful nauseating emetic; in large doses an acro-narcotic poison. It is prescribed in spasmodic asthma.