For the preparation of the officinal elaterium, the fruit has to be employed while still somewhat immature, for the simple reason that it would be impossible to gather it so as to retain its all-important juice if left till quite ripe. When it is sliced longitudinally as in making elaterium, some of the juice is expelled by virtue of the endosmotic action already described, as can easily be seen on examining the contracted lining of the sliced fruit.
Pereira observes[1124] that if the juice of a fruit is received on a plate of glass, it is seen to be nearly colourless and transparent. In a few minutes however, by exposure to the air, it becomes slightly turbid, and small white coagula are formed in it. By slow evaporation, minute rhomboidal crystals make their appearance: these are elaterin.
Hot, dry weather favours the development of the active principle of the drug.[1125]
Microscopic Structure—The middle layer of the fruit is built up of large somewhat thick-walled cells, traversed by a few fibro-vascular bundles. The former abound in small starch grains, and also contain granules of albuminous matter.
Chemical Composition—The experiments of Clutterbuck (1819) proved that the active properties of the elaterium plant reside chiefly, though not exclusively, in the juice that surrounds the seeds; and it is to this juice and to the medicinal product which it yields, that the attention of chemists has been hitherto directed.
The juice obtained by lightly pressing the sliced fruits is at first greenish and slightly turbid. After having been set aside a few hours, it yields a deposit, which has to be collected on calico, rapidly drained with gentle pressure between layers of bibulous paper and porous bricks, and dried in a warm place. The substance thus obtained is the Elaterium of pharmacy.[1126] The method recommended by Clutterbuck[1127] involves no pressing. The juice of the sliced fruit is saved, and the pulp, scooped out by the thumb of the operator, is thrown on a sieve and slightly washed with pure water. From these liquors, elaterium is deposited.
Elaterium occurs in irregular cake-like fragments, light, friable, and opaque; when new, of a bright pale green, becoming by age greyish and exhibiting minute crystals on the surface. It has a herby tea-like odour and a very bitter taste. The produce is extremely small: 240 lb. of fruit gathered at Mitcham, 1Oth August 1868, yielded 4⅝ ounces of elaterium = 0·123 per cent.
Elaterium consists, according to Pereira, of Elaterin, to which the activity of the drug is due, contaminated with green colouring matter, cellular tissue, and starch, together with a little of the residue of the bitter liquor from which these substances were deposited. Yet, in our opinion, this description is not applicable to the best varieties of elaterium. We have examined elaterium carefully prepared in the laboratory of Messrs. Allen and Hanburys, London, and a fine specimen imported from Malta. Both are devoid of starch, as well as of cellular tissue, but were seen to be largely made up of crystals. The first sample contained 12 per cent. of water, and yielded after drying, 8·4 per cent. of ash.
The most interesting principle of elaterium is Elaterin, C₂₀H₂₈O₅, discovered about the year 1831 by Morries, and independently by Hennell. The best method of obtaining it, according to our experience, is to exhaust elaterium with chloroform. From this solution, a white crystalline deposit of elaterin is immediately separated by addition of ether. It should be washed with a little ether, and recrystallized from chloroform. We have thus obtained 33·6 per cent. of pure elaterin from the above-mentioned elaterium of London, and 27·6 per cent. from that of Malta. Elaterin crystallizes in hexagonal scales or prisms; it has an extremely bitter, somewhat acrid taste. It is readily soluble in boiling alcohol, amylic alcohol, bisulphide of carbon, or chloroform. Its alcoholic solutions are neutral and are not precipitated by tannin, nor by any metallic solution. It is but very little coloured by cold concentrated sulphuric acid.
Elaterin is the drastic principle of Ecballium; if to its boiling alcoholic solution, solid caustic potash is added, the liquid thus obtained is stated by Buchheim (1872) to be no longer precipitable by water. The elaterin is then in fact converted into an acid body, which may be separated by supersaturating the solution with a mineral acid. The principle thus obtained has been found by Buchheim to be devoid of drastic power.