Abstract
The experiments previously reported 1 have shown that rat embryos possess the potency to undergo a development of their tissues when implanted in strange surroundings. In order to test further the capacity of the embryonic parts for differentiation, transplantations of 8 and 9 day rat embryos have been made to the chorioallantoic membrane of the chick. This experiment was first performed by Hiraiwa 2 using rat embryos of a considerably older stage of development. He found that there was a considerable degree of self-differentiation in this form.
Up to the present about 200 such transplantations have been made; the eggs have been incubated from 7 to 9 days after transplantation (9 day hosts) and the grafts studied. In many cases the transplant causes only a minor reaction which is indicated by a slight thickening of the membrane on the site of the operation and a slight increase in the vascular field. This is the so-called membrane reaction. In some cases a distinct nodule of tissue is found which upon section shows degenerating embryonic tissue. In these cases there are no embryonic parts except isolated tissue fragments.
In the positive series, containing embryonic parts, there are two groups: (1) those in which there is rapidly differentiating tissue and (2) those in which the tissues have developed exceedingly well but have undergone subsequent degeneration. So far we have had the opportunity to study the sectional material from 6 of these cases. Of these only one shows tissues undergoing differentiation at a rapid rate with a negligible amount of degeneration; 4 cases show the mixed type in which some of the tissues are undergoing differentiation and some are degenerating, while the sixth case shows practically complete embryonic degeneration.
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