The seeds are disposed in vertical rows on 3 thick parietal placentæ, which project to the centre of the fruit, then divide and turn back, forming two branches directed towards one another. Owing to this structure, the fruit easily breaks up vertically into 3 wedges in each of which are lodged 2 rows of dark brown seeds. The seeds, of which a fruit contains from 200 to 300, are of flattened ovoid form, ³/₁₀ of an inch long by ²/₁₀ broad, not bordered. The testa which is hard and thick, having its surface minutely granulated, is marked on each side of its more pointed end by two furrows directed towards the hilum. The seed, as in other Cucurbitaceæ, is exalbuminous, and has thick oily cotyledons, enclosing an embryo with short straight radicle directed towards the hilum.
Colocynth fruits are mostly supplied by wholesale druggists, broken up and having the seeds removed, the drug in such case being called Colocynth Pulp or Pith.
Microscopic Structure—The pulp is made up of large thin-walled parenchymatous cells, their outer layer consisting of rows of smaller cells more densely packed. The tissue is irregularly traversed by fibro-vascular bundles, and also exhibits numerous large intercellular spaces. The cells contain but an insignificant amount of minute granules, to which neither iodine nor a persalt of iron imparts any coloration. The tissue is not much swollen by water, although one part of the pulp easily retains from 10 to 12 parts of water like a sponge.
Chemical Composition—The bitter principle has been isolated in 1847 by Hübschmann.[1133] He observed that alcohol removes from the fruit a large amount of resin. By submitting this solution to distillation, the bitter principle remains partly in the aqueous liquid, partly in the resin, from which the “Colocynthin” is to be extracted by boiling water. The whole solution was then concentrated and mixed with carbonate of potassium, when a thickish viscid liquid separated. Hübschmann dried it and redissolved it in a mixture of 1 part of strong alcohol and 8 parts of ether. After treatment with charcoal, the solvents were distilled and the remaining bitter principle removed by means of water. This on evaporating afforded 2 per cent. of the pulp of a yellow extremely bitter powder, readily soluble in water or alcohol, not in pure ether. Colocynthin is precipitated from its aqueous solution by carbonate of potassium. Colocynthin was further extracted by Lebourdais (1848) by evaporating the aqueous infusion of the fruit with charcoal, and exhausting the dried powder with boiling alcohol.
Again, another method was followed by Walz (1858). He treated alcoholic extract of colocynth with water, and mixed the solution firstly with neutral acetate of lead, and subsequently with basic acetate of lead. From the filtered liquid the lead was separated by means of sulphuretted hydrogen, and then tannic acid added to it. The latter caused the colocynthin to be precipitated; the precipitate washed and dried was decomposed by oxide of lead, and finally the colocynthin was dissolved out by ether.
Walz thus obtained about ¼ per cent. of a yellowish mass or tufts, which he considered as possessing crystalline structure and to which he gave the name Colocynthin. He assigns to it the formula C₅₆H₈₄O₂₃, which in our opinion requires further investigation. Colocynthin is a violent purgative; it is decomposed according to Walz by boiling dilute hydrochloric acid, and then yields Colocyntheïn, C₄₄H₆₄O₁₃, and grape sugar. The same chemist termed Colocynthitin that part of the alcoholic extract of colocynth which is soluble in ether but not in water. Purified with boiling alcohol, colocynthitin forms a tasteless crystalline powder.
The pulp perfectly freed from seeds and dried at 100° C., afforded us 11 per cent. of ash; the seeds alone yield only 2·7 per cent. They have, even when crushed, but a faint bitter taste, and contain 17 per cent. of fat oil.
The fresh leaves of the plant if rubbed emit a very unpleasant smell.
Commerce—The drug is imported from Mogador, Spain and Syria.
Uses—In the form of an extract made with weak alcohol, and combined with aloes and scammony, colocynth is much employed as a purgative. The seeds, roasted or boiled, are the miserable food of some of the poorest tribes of the Sahara.[1134]