Aqueous and methanol extracts of nine traditional Zulu medicinal plants, Cissus quandrangularis L., Cyphostemma flaviflorum (Sprague) Descoings, Cyphostemma lanigerum (Harv.) Descoings ex Wild & Drum, Cyphostemma natalitium (Szyszyl.) J. v. d. Merwe, Cyphostemma sp., Rhoicissus digitata (L. F.) Gilg