Experimental studies on the differentiation of embryonic tissues growing in vivo and in vitro .—I. The development of the undifferentiated limb-bud (a) when subcutaneously grafted into the post-embryonic chick and (b) when cultivated in vitro

Abstract

One method by which the problem of the differentiation of animal tissues may be approached is by studying the behaviour of simple embryonic tissues when growing in an abnormal environment, such as that produced by grafting into atypical situations in vivo or by cultivation in vitro . It is along these lines that the investigations of the present writers are being conducted. The work so far completed, the results of which are recorded in the present communication, consists of a study of the development of the undifferentiated, embryonic limb-bud of the fowl when grafted subcutaneously into a postembryonic chick and when cultivated vitro. A preliminary investigation of the histogenesis of cartilage and bone in the limbs of the embryonic fowl was carried out by one of the writers (Fell, 1925) in order to provide normal standards with which to compare the experimental material. Rous (1910, 1911), Fichera (1909) and many others have successfully grafted foœtal and embryonic tissues into young and adult animals, usually in connection with the study of tumour growth ; a bibliography and summary of the earlier work is given in Fichera’s paper. Almost all the work on the development of grafts of the undifferentiated limb-buds has been carried out on the embryonic Amphibia by Braus, Harrison (1907, 1918, 1921), Detweiler (1918, 1925), Nicholas (1924) and others. Spurting (1923) describes a case of accidental but successful autotransplantation of the posterior limb-bud in a fowl embryo. Murray and Huxley (1925) record two experiments in which part of the limb-bud of a four-days’ embryo was successfully grafted on to the chorioallantoic membranes ; in one case “ a highly differentiated and very easily recognizable femur ” showing early ossification was found after 5 days’ growth.