Studies on the nature of the amphibian organization centre IV—Further experiments on the chemistry of the evocator

Abstract

In preceding papers evidence was presented showing that a substance or substances able to bring about the differentiation of competent amphibian ectoderm into neural tissue is found in ethereal extracts of amphibian or mammalian liver. It was further shown that the active material could be traced into the unsaponifiable fraction and was precipitable with digitonin. The suggestion was therefore made that this substance, the evocator, was sterol-like in nature. Further experiments in confirmation and extension of these findings are described in the present communication. During the laying season of 1935 we were much hampered by a diminished breeding activity of the newts owing to the very cold spring; and the quality of the eggs produced was poor, rendering them more suitable for experiments in which chemical preparations were not implanted ( cf . Waddington,1936; Waddington and Wolsky, 1936). However, a sufficiency of material was obtained to permit of the following up of three lines of attack: (1) the digitonin precipitation of ether-extracts of crude glycogen; (2) the fractionation of the total unsaponifiable material of liver; (3) the study of the activity possessed by crude kephalin preparations.