Source, Etc

The castor-oil plant, Ricinus communis, Linne (N.O. Euphorbiaceoe), is a native of India, but is diffused now over all tropical and subtropical countries. In India it may attain a height of 40 metres and be a perennial tree, but in cooler climates it is either a shrub or an annual herb. The plant, and with it the seed, is subject to much variation, the larger, arborescent forms yielding large seeds, the small, annual varieties small seeds.

The oil pressed from the seeds was well known to the Egyptians, Greeks, and Romans, and employed both as a medicine and illuminant, as well as for various technical purposes. It was used in Europe during the early Middle Ages, but subsequently fell into disuse, being re-introduced from the West Indies toward the end of the last century. The supplies of seeds came then chiefly from Jamaica, but the exports from India increased with great rapidity. The market is now chiefly supplied from India and South America, but considerable quantities of the seed are raised in other countries', as, for instance, in Italy.

Description

The fruit of the plant is a three-celled, three-seeded, thorny capsule. The seeds are oblong in outline, somewhat flattened, and from about 8 to 15 mm. long. The seed-coat is quite smooth and glossy, and varies in colour from a greyish brown to a beautiful grey marbled with reddish brown or black spots and stripes. The dorsal surface is arched, the ventral nearly flat; at one extremity is a prominent, usually pale, caruncle, from which a distinct line (raphe) runs along the ventral surface to the other extremity of the seed, where it terminates in a raised point (chalaza), branches and disappears. The caruncle can be easily removed, disclosing a dark spot (hilum) beneath.

The seed-coat is thin and brittle. The marbled outer layer, which, especially after soaking in water, can easily be scraped off, is succeeded by a hard, dark layer. Within is the kernel, consisting of a large, yellowish white, oily endosperm enclosing a small embryo with two papery cotyledons. Surrounding the kernel is a delicate silvery white membrane.

Castor seeds have an almost imperceptible odour and very slightly acrid taste.

The student should observe

(a) The glossy, mottled seed-coat,

(b) The small caruncle,

(c) The oily endosperm and papery cotyledons; and compare the seeds with croton seeds, which have a uniformly dull brown surface.

Constituents

The most important medicinal constituent of castor seed is the fixed oil. It exists in the seed to the extent of about 50 per cent., and may be obtained by pressing the unshelled or shelled seed without heat (' cold drawn castor oil'). Usually the seeds are first graded to size, cracked between rollers, the shells removed by fanning and the kernels pressed; the oil is filtered, steamed to coagulate proteids (see below) and again filtered. The cake still contains 8 to 10 per cent, of oil which can be recovered by extraction with benzene. Much is thus produced in Italy, Marseilles, London, Hull, Belgium, etc. Considerable quantities are also produced in India and elsewhere by pressing the seeds between hot plates, or by boiling the crushed seeds and skimming off the oil, but such oil has a dark colour and disagreeable odour, and is unsuitable for medicinal use.

The cake left after the expression of the oil contains ricinine (Tuson, 1864), a crystalline principle melting at 201.5°, but present in small quantity only (about 0.2 per cent.), ricin (Stillrnark, 1889), a toxin similar in nature to the bacterial toxins, and also (ripe seeds) a very active lipase (fat-splitting enzyme) and other enzymes.

Both castor seeds and the cake left after the expression of the oil act as violent purgatives, a property probably due to the ricin contained in them.

Castor oil consists chiefly of the glycerides of ricinoleic, isoricinoleic dihydroxy-stearic, and other acids. It owes its purgative action in all probability to the ricinoleic acid. It is characterised by its specific gravity (0.958 to 0.970), solubility in alcohol (1 in 3.5), insolubility in petroleum spirit (which, however, disappears if other vegetable oils are present) and by its high acetyl value (150).

Constituents 154Fig. 98.   Fruit and seed of Ricinus communis. Natural size. (Bentley and Trimen.)

Fig. 98. - Fruit and seed of Ricinus communis. Natural size. (Bentley and Trimen).

It is much used for lubricating hot machinery, and for illuminating purposes. See also ' Castor Oil.'

Ricin is extremely poisonous, 0.002 of a milligramme per kilo, being fatal to rabbits. It is capable of producing an antitoxin (antiricin) in the body, and it is interesting to note that Ehrlich's researches on this property led to the preparation of antidiphtheritic and other sera (Muller, 1899). Ricin is probably identical with Bubnow and Dixon's ricinone (Finnemore and Deane, 1905); its activity is destroyed by heating to 100°. It forms with abrin (Abrus precatorius, Linne), crotin (Croton Tiglium, Linne), curcin (Jatropha Curcas, Linne), and two or three others a group of toxins (toxalbumoses, phytalbumoses) possessing similar properties; being insoluble in oil it is left in the cake when the seeds are pressed and renders the cake unfit for cattle food.

The lipase in the seeds has been turned to commercial use as a convenient means of splitting oils into glycerin and fat-acids; any lipase present in the expressed oil is rendered inactive by the steaming.

Uses

The oil expressed from the seeds is valuable as a simple purgative, at once rapid and certain, mild and painless. On account of their violent action the seeds themselves are never employed in this country, though in some countries they are said to be a favourite purgative.

Note

Semina Ricini Majores (Physic Nuts, Purging Nuts, Pignons d'Inde) are the seeds of Jalropha Curcas, Linne; they resemble castor seeds in shape, but are rather large, dull black; surface minutely rugose, with small white patches; they contain a fixed oil, much more purgative than castor oil, and curcin (see above).