Acocanthera.—The Wa Nyika, the Wa Gyriama, and the Wa Kamba tribes of Eastern Africa, and the natives of Obok on the Gulf of Aden, prepare vegetable arrow poisons probably from different species of plants, although the names wabayo and ouabain seem to have been used as synonyms by missionaries and others sending the extract to Europe.
The botanical sources of these arrow poisons are uncertain. It is certain that several species of the apocynaceous genus Acocanthera are used for arrow poisons by the natives of Africa. Of the four principal species, A. schimperi B. and H. is found abundantly in the highlands of Abyssinia and throughout a great portion of Eastern Africa; A. deflersii Schwf., which resembles the last-named. species closely, but, according to Schweinfurth, differs in that its flowers are larger, sweet-smelling and pure white, has been found in the neighborhood of Yemen; A. ouabaio Arnaud is a native of Somaliland, and A. venenata Don, of South Africa. For details, see A. de S., cvii, p. 1162; abs. in J. P. C., 1889, p. 245. From Acocanthera abyssinica is prepared Shashi-poison of German Eastern Africa.
In 1882 Arnaud obtained from an unidentified species of the genus Acocanthera (which he named provisionally A. Ouabaio), a crystalline glucoside, and in 1893 Lewin separated from the Acocanthera Deflersii an amorphous glucoside.
Owing to the imperfect identification of the plants from which the principles have been obtained, there has been much confusion in the names which have been applied to the principles which various investigators have separated from these arrow poisons. According to Lewin (B. K. W., 1906, p. 1583), there are two glucosides found in the various species of acocanthera, one of which is crystalline, and the other amorphous. The amorphous substance, or, as it is generally known, amorphous ouabain, corresponds to the abyssinin of Briege (A. I. P. T., 1903), and the carissin prepared by Bancroft from the Carissa ovata R. Br. (Fam. Apocynacece), an Australian plant. The acocantherin of Frazer he regards as identical with the crystalline ouabain of Arnaud, and probably is isomeric with the amorphous variety. It is generally conceded that the crystalline ouabain is chemically identical with the glucoside discovered by Thoms in the Strophanthus gratus (see page 1068). Its action seems to be precisely the same as that of strophanthus. Ouabain was apparently first employed clinically by Stadelmann (B. K. W., 1906, vol. xliii, p. 1586), and has more recently been used by others with more or less success in the treatment of various forms of cardiac weakness. Stadelmann used an amorphous glucoside prepared by Merck from the wood of the Acocanthera Schimperi, in doses of from one three-hundredth to one two-hundredth of a grain (0.0002-0.0003 Gm.) three times a day.