The anthelmintic virtues of koso were investigated by Brayer, a French physician of Constantinople, to which place parcels of the drug are occasionally brought by way of Egypt, and he published a small pamphlet on the subject.[979] Several scattered notices of koso appeared in 1839-41, but no supply of it reached Europe until about 1850, when a Frenchman who had been in Abyssinia obtained a large stock (1,400 lb., it was said), a portion of which he endeavoured to sell in London at 35s. per ounce! The absurd value set upon the drug produced the usual result: large quantities were imported, and the price gradually fell to 3s. or 4s. per lb. Koso was admitted a place in the British Pharmacopœia of 1864.
Description—The flowers grow in broad panicles, 10 to 12 inches in length. They are unisexual, but though male and female occur on the same tree, the latter are chiefly collected. The panicles are either loosely dried, often including a portion of stalk and sometimes a leaf, or they are made into cylindrical rolls, kept in form by transverse ligatures. Very often the panicles arrive quite broken up, and with the flowers in a very fragmentary state. They have a herby, somewhat tea-like smell, and a bitterish acrid taste.
The panicle consists of a zigzag stalk, which with its many branches is clothed with shaggy simple hairs, and also dotted over with minute stalked glands; it is provided at each ramification with a large sheathing bract. At the base of each flower are two or three rounded veiny membranous bracts, between which is the turbinate hairy calyx, having ten sepals arranged in a double series. In the male, the outer series consists of much smaller sepals than the inner; in the female, the outer in the ultimate development become enlarged, obovate and spreading, so that the whole flower measures fully ½ an inch across. In both, the sepals are veiny and leaf-like. The petals are minute and linear, inserted with the stamens in the throat of the calyx. These latter are 10 to 25 in number, with anthers in the female flower, effete. The carpels are two, included in the calycinal tube; and each surmounted by a hairy style. The fruit is an obovate one-seeded nut.
Koso as seen in commerce has a light brown hue, with a reddish tinge in the case of the female flowers, so that panicles of the latter are sometimes distinguished as Red Koso.
Chemical Composition—Wittstein (1840) found in koso, together with the substances common to most vegetables (wax, sugar, and gum), 24 per cent. of tannin, and 6·25 of an acrid bitter resin, which was observed by Harms (1857) to possess acid properties.
The researches of Pavesi (1858), and still more those of Bedall[980] have made us acquainted with the active principle of the drug, which has been named Koussin or Kosin. It may be obtained by mixing the flowers with lime, exhausting them with alcohol and then with water; the solutions mixed, concentrated, and treated with acetic acid, deposit the kosin. We are indebted to Dr. Bedall for a specimen of it, which we find to consist chiefly of an amorphous, resinoid substance, from which we got a few yellow crystals by means of glacial acetic acid.
Mr. Merck favoured us with kosin prepared in his laboratory at Darmstadt. It is a tasteless substance of a yellow colour, forming fine crystals of the rhombic system,—readily soluble in benzol, bisulphide of carbon, chloroform or ether, less freely in glacial acetic acid, and insoluble in water. We found a solution of kosin in 20 parts of chloroform to be destitute of rotatory power. Of alcohol, sp. gr. 0·818, 1000 parts dissolve at 12° C. only 2·3 parts of this kosin. It is abundantly soluble in alkalis, caustic or carbonated, yet has nevertheless no acid reaction, and may be precipitated from these solutions by an acid without having undergone any alteration. It is then however a white amorphous mass, which yields the original yellow crystals by re-solution in boiling alcohol, in which it dissolves readily. The analysis which we have performed of kosin assigns it the formula C₃₁H₃₈O₁₀.
Kosin fuses at 142° C., and remains after cooling an amorphous, transparent yellow mass; but if touched with alcohol, it immediately assumes the form of stellate tufts of crystals. This may be repeated at pleasure, kosin not being altered by cautious fusion.
Kosin is not decomposed by boiling dilute acids. It dissolves in strong sulphuric acid, giving a yellow solution which becomes turbid by the addition of water, white amorphous kosin being thrown down. At the same time a well-marked odour exactly like that of Locust Beans, due to isobutyric acid, CH₃·CH₃·CH·COOH, is evolved. It would thus appear that in all probability kosin is a compound ether of that acid. It is very remarkable that the active principle of fern root, the filicic acid (see Rhizoma Filicis), by decomposition yields butyric acid. If the sulphuric solution of kosin is allowed to stand for a week, it gradually assumes a fine red; and then yields, on addition of much water, an amorphous red mass which after drying is not soluble in bisulphide of carbon, and may thus be purified. We have not succeeded in obtaining this red derivative of kosin in a crystalline state.[981]
In its anthelmintic action, kosin is nearly allied with filicic acid.[982]