Source, Etc

The common or spotted hemlock, Conium1 macu-latum, Linne (N.O. Umbelliferoe), is a biennial plant widely spread throughout temperate Europe and generally distributed over Great Britain. It is distinguished by its smooth hollow stem with purple spots, the general and partial involucres on the inflorescence, its glabrous, decompound leaves and ovoid fruit without vittae but with deeply grooved endosperm (compare also the details given under ' Hemlock Herb '). This plant was in all probability the one employed by the Greeks in the preparation of poisonous draughts. It was used in Anglo-Saxon medicine, but has latterly lost much of its reputation owing to the uncertain action of its preparations. Researches have indicated the reason of this and suggested a remedy.

The fruits should be gathered from wild plants when full-grown, but before they ripen - that is, before the colour changes from green to yellow - and thoroughly dried; if carefully preserved quite dry they will long retain their activity unimpaired.

Description

Hemlock fruits, gathered when unripe, possess, after drying, a distinct greenish grey colour, which changes by long keeping to yellowish grey. They are small (about 3 mm. long), broadly ovoid and slightly compressed laterally. They are crowned with small stylopods bearing the remains of the stigmas. In the commercial drug the mericarps are usually separate and freed from the stalks. Each mericarp is glabrous and exhibits five paler sharply prominent primary ridges, which, from the presence of small protuberances, are irregularly crenate and wavy, a character not equally well shown by all fruits, and more conspicuous in the fresh than in the dried. Cut -transversely and examined with a strong lens, the endosperm exhibits a deep furrow or groove on its commissural surface (fig. 61, C). This furrow, being filled with the tissue of the pericarp, is not visible on the commissural surface of the mericarp, but only on the transverse section; its presence should be carefully noted, as it indicates that the fruits are derived from a plant belonging to the suborder Campylospermeoe, and distinguishes them at once from anise, fennel, etc, that have an endosperm nearly flat on its commissural surface (suborder Orthospermeoe), and from coriander and other fruits that have an endosperm strongly curved in both radial and transverse section (suborder Ccelospermeoe). The pericarp contains no vittae, and this is also an important character, but one hemlock, and should be pronounced Conium.

1 This pronunciation, though well established, is not strictly correct. The word is derived from the Greek that can be ascertained only by subjecting a transverse section to examination under the microscope.

Description 90

The fruit has scarcely any odour or taste, but when to the crushed fruit a solution of caustic potash is added a strong mouse-like odour is developed.

The student should observe

(a) The glabrous surface,

(b) The irregular crenate ridges,

(c) The grooved endosperm, and, if possible, under the microscope, the absence of vittoe; and should compare the fruits with anise fruits, which are distinguished by the short bristly hairs with which they are provided, by the presence of numerous vittae, and by the endosperm, which is not grooved, the latter being the most definite character visible under a lens.

Fig. 61.   Hemlock fruit. A, side view of entire fruit. B, longitudinal section of the same, showing endosperm and embryo, magnified 3 diam. D, half of the same, further enlarged; 3, embryo. C, transverse section: v, commissural surface; k, ridges; 2, endosperm magnified 14 diam. E, portion of the same, further enlarged; i, pericarp; t, seed coat. (Berg.)

Fig. 61. - Hemlock fruit. A, side view of entire fruit. B, longitudinal section of the same, showing endosperm and embryo, magnified 3 diam. D, half of the same, further enlarged; 3, embryo. C, transverse section: v, commissural surface; k, ridges; 2, endosperm magnified 14 diam. E, portion of the same, further enlarged; i, pericarp; t, seed-coat. (Berg).

Constituents

The principal constituent of hemlock fruits is the poisonous, volatile, liquid alkaloid coniine, of which they may contain, when collected at the proper time and dried, as much as 2.77 per cent. (Farr and Wright, 1904), the average being 1.65 per cent. This alkaloid is the source of the strong odour produced when hemlock fruits are crushed and mixed with caustic potash, the alkali liberating the alkaloid which was previously combined with acids.

The proportion of coniine present attains its maximum when the fruits are full or nearly full grown, but before the colour changes from green to yellow; during this change (the ripening of the fruit) the proportion of coniine rapidly diminishes. Commercial fruits yield from 0.5 to 1.3 per cent, of coniine.

It is accompanied in the fruit by small quantities of methylconiine, which is oily and resembles coniine, and by conhydrine, which is colourless and crystalline. Ethyl piperidine and pseudoconhydrine are also present.

Pure coniine, C8H17N, is a-propyl-piperidine. It is a colourless, oily, very poisonous liquid with an extremely unpleasant odour. It boils at 163.5° without decomposition in an atmosphere free from oxygen; but exposed to the air, even at ordinary temperatures, it rapidly assumes a brown colour. It yields crystalline non-volatile salts. It may be produced from a-picoline, C5H4(CH3)N, one of the constituents of coal tar, by heating it to 250° for 10 hours with acetic aldehyde, by which it is converted into a-allyl pyridine C5H4(C3H5)N; this by reduction with sodium yields coniine C5H9(C3H7)NH. Coniine thus prepared is, however, optically inactive, whereas natural coniine is dextrorotatory; it can be separated into the dextro- and laevo-rotatory alkaloids by inducing crystallisation of the tartrate by means of a crystal of natural coniine tartrate.

Assay

Percolate 10 gm. of the finely produced fruit with 70 per cent, alcohol until exhausted, add 20 c.c. N/10 sulphuric acid and evaporate off the alcohol. Transfer to a separator, wash twice with chloroform, make alkaline with solution of potash and shake out with three successive 5 c.c. of chloroform. Transfer the alkaloids to acidified water and back to chloroform. Repeat this purification twice. Finally shake the chloroformic solution of the alkaloids with three drops of fuming hydrochloric acid, wash the separator with a little alcohol, evaporate, dry at 90° and weigh. The weight of the alkaloidal hydrochlorides multiplied by 0.777 gives the weight of alkaloid in 10 gm. of the fruit.

Uses

Hemlock is used in spasmodic and convulsive diseases, such as tetanus, chorea, and epilepsy; in asthma, whooping-cough, and spasmodic affections of the larynx. Coniine depresses the medulla and motor nerve endings, excessive doses resulting in death from respiratory paralysis.