Abstract
LONDON Royal Society, February 13. L. HOGBEN and D, SLOME: The pigmentary effector system. (7) The chromatic function in Elasmobranch fishes. (8) The dual receptive mechanism of the amphibian background response. Experiments, in which the effects of illumination from above and below, and of illumination with monochromatic lights of different wavelengths, have been compared, show that the visual chromatic (‘background’) response of vertebrates depends on distinct localised retinal elements. The ventral photoreceptors involved in the black background response activate the archaic pituitary mechanism present in Cyclostomes, Elasmobranchs and Amphibia, in all of which removal of the whole gland or part (neurointermediate lobe in Elasmobranchs and Amphibia) abolishes the black background response. The black background response can be evoked in hypophysectomised Elasmobranchs or Amphibia by extracts of which the active constituent is not identical with the pressor or oxytocic substances. Quantitative estimates based on the melanophore index show that more extreme pallor results from removal of the neurointermediate lobe alone than from removal of the neurointermediate lobe along with the pars tuberalis. This reinforces evidence previously adduced to support the existence of a second humoral component, the TF-substance in the pars tuberalis of Amphibia. Removal of the pars glandularis of Elasmobranchs abolishes the white-background response, as does the removal of the pars tuberalis in Amphibia. This points to the conclusion that the same dual mechanism of endocrine control exists in the cartilaginous fishes. C. H. WADDINGTON, J. NEEDHAM and JEAN BRACKET: Studies on the nature of the amphibian organisation centre. (3) The activation of the evocator. The power of performing an induction can be caused to appear in those parts of the amphibian gastrula which do not normally possess it (such as the ventral ectoderm) by exposure to a temperature of 100° C., or treatment with organic solvents. It is now shown that the same effect can be brought about by the action of a respiratory catalyst such as methylene blue upon the isolated ectoderm. Subsequent implantation of these isolated pieces next to competent tissue leads to the formation of a neural tube, or to lesser degrees of neuralisation, in the host or in the graft, or in both simultaneously. This is interpreted as signifying the liberation of the natural evocator from previously inactive combination. The nature of this inactive combination is discussed and the suggestion is made that it is a complex of the type protein-glycogen-evocator. From this point of view the present position of our knowledge of the metabolism of the organisation centre, especially with regard to glycogen, is critically considered. Preliminary measurements of the oxygen uptake of the dorsal lip of the blastopore and ventral ectoderm in a micro-respirometer indicate that only a very small, if any, difference in respiratory rate exists between these regions. The significance of this in relation to other findings on the metabolism of the gastrula may be considerable. C. H. WADDINGTON, J. NEEDHAM, W. W, NOWTNSKI, R. LEMBERG and A. COHEN: Studies of the nature of the amphibian organisation centre. (4) Further experiments on the chemistry of the evocator. The presence of an evocator substance in the digitonin precipitate of the unsaponifiable material of ethereal extracts of crude glycogen from mammalian liver is confirmed. Atempts at fractionation of the sterolic portions of the unsaponifiable material of adult mammalian liver are described. It is shown that acetone extracts of adult mammalian brain, which should contain no kephalin, may be active, and that the activity of kephalin preparations may persist after the destruction of the lipin by saponification.
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Societies and Academies. Nature 137, 334–336 (1936). https://doi.org/10.1038/137334a0
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DOI: https://doi.org/10.1038/137334a0