Microscopic Structure—The cortical tissue is covered with a thin suberous coat; the middle layer of the bark is built up of a thin walled parenchyme, through which enormous, hard, thick-walled cells are scattered in great numbers and are visible to the naked eye, as they form large irregular groups of a bright yellow colour. Towards the inner part these stone-cells disappear, the tissue being traversed by undulated medullary rays, loaded with very small starch grains; many of the other parenchymatous cells of the liber contain crystals of calcium oxalate. The longitudinal section of the liber exhibits large but not very numerous laticiferous vessels, containing a brownish mass, the concrete milk juice in which all parts of the tree abound.
Chemical Composition—The first attempts to isolate the active principles of this bark were made by two apothecaries, Scharlée at Batavia[1561] (1862) and Gruppe at Manila[1562] (1872).
In 1875 Jobst and Hesse exhausted the powdered bark with petroleum ether, and then extracted, by boiling alcohol, the salt of an alkaloid, which they called Ditamine. After the evaporation of the alcohol, it is precipitated by carbonate of sodium and dissolved by ether, from which it is removed by shaking it with acetic acid. Ditamine as again isolated from the acetate forms an amorphous and somewhat crystalline, bitterish powder of decidedly alkaline character; the barks yields about 0·02 per cent. of it.
From the substances extracted by means of petroleum ether, as above stated, Jobst and Hesse further isolated (1) Echicaoutchin, C₂₅H₄₀O₂, an amorphous yellowish mass; (2) Echicerin, C₃₀H₄₈O₂, forming acicular crystals, melting at 157° C.; (3) Echitin, C₃₂H₅₂O₂, crystallized scales, melting at 170°; (4) Echiteïn, C₄₂H₇₀O₂, which forms rhombic prisms, melting at 195°; (5) Echiretin, C₃₅H₅₆O₂, an amorphous substance melting at 52° C.
Echicaoutchin may be written thus: (C₅H₈)₅O₂, echicerin (C₅H₈)₆O₂, echiretin (C₅H₈)₇O₂; these formulæ at once point out how nearly the three last named substances are allied. They are probably constituents of the milky juice of the tree.
Lastly, Jobst and Hesse pointed out the existence of another alkaloid in Dita bark.
Harnack (1877) on the other hand is of the opinion that it contains only one alkaloid, which he terms Ditaïne. He used the alcoholic extract of the bark which he treated with ether to which he added a little ammonia. By this process ditamine of Jobst and Hesse would have been removed, but Harnack suggests that only a little ditaïne is dissolved by ether. He then mixed the extract with potash and exhausted it with alcohol, which afforded crystals of ditaïne, answering to the formula C₂₂H₃₀N₂O₄; its physiological action is nearly the same as that of curare. Ditaïne is but sparingly soluble in ether or petroleum ether, but dissolves readily in water, alcohol, or chloroform; it has a decidedly alkaline reaction. It would appear that it is a glucoside.
Dita bark is stated[1563] to yield 5 per cent. of “ditaïne”; but this probably refers not to the pure alkaloid.
Uses—The bark has been recommended as a tonic and antiperiodic, being extravagantly praised as a substitute for quinine.