Differential Dye Reduction and Reoxidation in Triturus Development

T. HE question whether definite regional or graded differences in rate of respiration or other metabolic activities are characteristic of early embryonic amphibian development has received considerable attention during recent years. Various investigators have attempted to throw light on the problem of the nature of neural induction by the dorsal inductor region, the so-called "organizer," by studies on the metabolism of this region as compared with other parts of the embryo. More than twenty years ago differences in susceptibility to various agents, indicating a decrease from the anterior (animal) pole and a higher susceptibility appearing on the dorsal side and attaining a maximum in the dorsal lip of the blastopore were observed in the frog embryo (Bellamy, 19I9). More recently determinations of oxygen consumption, CO, production, respiratory quotients, glycolysis, and some data on distribution of glycogen and sulphydryl proteins have appeared. Since these have recently been discussed at some length with a bibliography (Child, 1941, PP. 151-58), extended consideration is not necessary here. Although the different lines of evidence from these investigations are not in complete agreement, they do indicate the