ABSTRACT
It is shown that pieces of presumptive epidermis (ventral ectoderm of the gastrula), when isolated into weak solutions of several dyes, will undergo neural differentiation. Dyes such as Janus green and neutral red, which are not known to accelerate cell respiration, appear to have this effect, as well as methylene blue, the accelerating action of which on cell respiration is well known.
Measurements of the oxygen consumption of isolated pieces of the gastrula by the Cartesian Diver method show that methylene blue, if in weak concentration, has an accelerating action of about 45 %. In stronger concentrations it is inhibitory.
The experiments of Marston (1923) and Commoner (1938) on the formation of dye-protein complexes render the expectation that dyes could liberate the organizer substance from its inactive precursor by competitive complex-formation not without plausibility.
In order to make sure that no piece of tissue approaching the limits of the organizer region had been taken, each gastrula was carefully examined after the explant had been removed from it.
