A Note on Inductions by Chick Primitive Streak Transplanted to the Rabbit Embryo

The work of Waddington and Waterman (1933) has shown that it is possible to cultivate young rabbit embryos in vitro, using the normal watch-glass technique and a medium composed of chicken embryo extract and either chick or rabbit plasma. Micro-surgical operations can be performed on such embryos before they are explanted into culture, and the mutual interactions of the various embryonic rudiments can be investigated in this way. It may eventually be possible to obtain as complete an account of the developmental mechanics of the mammalian embryo as Spemann and his school have provided in the Amphibia, but it is probable that operations on the mammalian embryo will always be attended with considerable difficulty. Apart from the laboriousness of the tissue culture technique with its concomitant necessity for absolute sterility, the rabbit embryo, if not every mammalian embryo, is very difficult to handle owing to its transparency, toughness and stickiness. The transparency of the blastocyst and embryonic shield in the primitive streak stage makes it difficult to distinguish exactly the various embryonic organs; the toughness of the tissue hinders neat cutting and operating; while the stickiness of the cells is probably the most annoying characteristic of all, since it results in any fragment of tissue, which may for example be intended for a graft, adhering to the operating knives with such tenacity that it frequently becomes entirely macerated during the attempts made to free it.