Studies on the nature of the amphibian organization centre. I—Chemical properties of the evocator

Abstract

Abstract During the amphibian egg-laying season of 1933, Needham, Waddington, and Needham (1933, a, b; 1934) obtained evidence that the activity of the organization centre of the newt gastrula is partly due to the presence of an ether-soluble substance. The active ether extracts were found to be capable of evoking the formation of a neural tube from the competent presumptive epidermis of the gastrula. It seems difficult, however, to suppose that they can determine the regional character of the evoked neural plate, as normal living organizers do, and the active substance is therefore spoken of as the evocator, to emphasize the fact that its functions represent only one part of the whole process of embryonic induction. The presence of the evocator could also be demonstrated in ether extracts of adult newt tissues; and in a research carried out at the same time Holtfreter (1933) showed that the evocator is present in a large number, if not in all, adult tissues from animals belonging to nearly all the groups of the animal kingdom. Holtfreter found that evocation occurred after the implantation of adult tissues which had been killed and treated with various solvents, but he showed that a prolonged extraction with ether tended to lessen, though it did not entirely destroy, the evocating power of the tissue. This result, which so far as it went was confirmatory of Needham, Waddington, and Needham’s work, was, however, denied by Fischer and Wehmeier (1934), who, on repeating the extraction experiments, could confirm the fact that the ether extracts were active, but claimed that the evocating ability of the tissues was not much lessened by the extraction. In a more recent communication (1934, a) Holtfreter has repeated his extractions, and finds that the activity of the extracted tissue is only slightly lowered. It is very probable, however, that there will be difficulty in extracting the whole of the active ether-soluble substances from a given mass of tissue. There is general agreement that ether extracts contain an active substance.