Semen Crotonis; Croton Seeds; F. Graines de Tilly ou des Moluques, Petits Pignons d’Inde; G. Purgirkörner, Granatill.
Botanical Origin—Croton Tiglium[2095] L. (Tiglium officinale Klotzsch), a small tree, 15 to 20 feet high, indigenous to the Malabar Coast and Tavoy, cultivated in gardens in many parts of the East, from Mauritius to the India Archipelago. The tree has small inconspicuous flowers, and brown, capsular, three-celled fruits, each cell containing one seed. The leaves have a disagreeable smell and nauseous taste.
History—In Europe, the seeds and wood of the tree were first described in 1578 by Christoval Acosta—the former, with a figure of the plant, appearing under the name of Piñones de Maluco.[2096] The plant was also described and figured by Rheede (1679)[2097] and Rumphius (1743).[2098] The seeds, which were officinal in the 17th century, but had become obsolete, were recommended about 1812 by English medical officers in India,[2099] and the expressed oil by Perry, Frost, Conwell and others about 1821-24. The oil then in use was imported from India, and was often of doubtful purity, so that some druggists felt it necessary to press the seeds for themselves.[2100]
Description—Croton seeds are about half an inch long, by nearly ⅖ of an inch broad, ovoid or bluntly oblong, divided longitudinally into two unequal parts, of which the more arched constitutes the dorsal and the flatter the ventral side. From the hilum, a fine raised line (raphe) passes to the other end of the seed, terminating in a darker point, indicating the chalaza. The surface of the seed is more or less covered with a bright cinnamon-brown coat, which when scraped shows the thin, brittle, black testa filled with a whitish, oily kernel, invested with a delicate seed-coat. The kernel is easily split into two halves consisting of oily albumen, between which lie the large, veined, leafy cotyledons and the radicle. The taste of the seed is at first merely oleaginous, but soon becomes unpleasantly and persistently acrid.
Microscopic Structure—The testa consists of an outer layer of radially arranged, much elongated and thick-walled cells; the inner parenchymatous layer contains small vascular bundles. The soft tissue of the albumen is loaded with drops of fatty oil. If this is removed by means of ether and weak potash lye, there remain small granules of albuminoid matter, the so-called Aleuron, and crystals of oxalate of calcium.
Chemical Composition—The principal constituent of croton seeds is the fatty oil, the Oleum Crotonis or Oleum Tiglii of pharmacy of which the kernels afford from 50 to 60 per cent. That used in England is for the most part expressed in London, and justly regarded as more reliable than that imported from India, with which the market was formerly supplied. It is a transparent, sherry-coloured, viscid liquid, slightly fluorescent, and having a slight rancid smell and an oily, acrid taste. Its solubility in alcohol (·794) appears to depend in great measure on the age of the oil, and the greater or less freshness of the seeds from which it was expressed,—oxidized or resinified oil dissolving the most readily.[2101] We found the oil which one of us had extracted by means of bisulphide of carbon to be levogyre.
Croton oil consists chiefly of the glycerinic ethers of the common fatty acids, such as stearic, palmitic, myristic and lauric acids. They partly separate in the cold; the acids also may partly be obtained by passing nitrous acid through croton oil. There are also present in the latter, in the form of glycerinic ethers, the more volatile acids, as formic, acetic, isobutyric and one of the valerianic acids.[2102] The volatile part of the acids yielded by croton oil contains moreover an acid which was regarded by Schlippe (1858) as angelic acid, C₅H₈O₂. Yet in 1869 it was shown by Geuther and Frölich to be a peculiar acid, which they called Tiglinic acid. Its composition answers to the same formula, C₄H₇COOH, as that of angelic acid; but the melting points (angelic acid 45°, tiglinic 64° C.) and boiling points (angelic acid 185°, tiglinic 198°·5) are different. Both these acids have been mentioned in our article on Flores Anthemidis, at page 386. Tiglinic acid may also be obtained artificially; it is the methylcrotonic acid of Frankland and Duppa (1865).
Schlippe also stated croton oil to afford a peculiar liquid acid termed Crotonic Acid, C₄H₆O₂. According to Geuther and Frölich, however, an acid of this formula does not occur at all in croton oil. By synthetic methods three different acids of that composition are obtainable.
The drastic principle of croton oil has not yet been isolated. Buchheim[2103] suggested that the action of the oil depends upon “Crotonoleic acid,” which however he failed in isolating satisfactorily. It is remarkable that the wood and leaves of Croton Tiglium appear to partake also of the drastic properties of the seeds.
Schlippe asserts that he has separated the vesicating matter of croton oil: if the oil be agitated with alcoholic soda, and afterwards with water, the supernatant liquor will be found free from acridity, while the alcoholic solution will yield, on addition of hydrochloric acid, a small quantity of a dark brown oil, called Crotonol, possessing vesicating properties. We have not succeeded in obtaining it, nor, so far as we know, has any other chemist except its discoverer.