The direct inoculation of a sarcoma of the fowl into the developing chick embryo or its membranes has yielded growths in many cases. The best results have been obtained with grafts of the living tumor tissue, but, as in the adult, growths can be engendered with dried tissue or with the Berkefeld filtrate of a tumor extract. When living tumor tissue is used, an actual transplantation occurs.
The neoplasms developing are spindle-celled sarcomata, remarkably uniform in structure, and similar to those in the adult fowl, except that in the embryo the neoplastic cells are often extremely long and slender, and the structure of the growth is very loose. The membranes adapt themselves in a remarkable way to the support of the tumors. In them, the growth is seldom invasive; and while regional metastases are occasionally seen, none occur by the bloodstream, despite the predilection of the growth for this path of distribution in adult hosts. In the more resistant structures of the embryo itself, an invasive extension of the sarcoma occurs. Growths originally in the yolk-sac outside the chick may be carried into the latter during the course of development. Secondary growths in the viscera may cause the death of the host some weeks after hatching.
In order to produce tumors in the embryo, the sarcoma cells or the agent engendering the growth must be brought into a direct association with the mesodermal tissues. This necessity is responsible for interesting differences in the location of the growths in the various membranes.
The sarcoma will grow in the membranes of pigeon or duck embryos, whereas in adults of these species it will not do so; and in chicken embryos of different varieties, it grows uniformly well, a finding not obtained in adults. In embryo hosts of all the sorts mentioned, there is a total absence of the cellular reaction which in adults indicates resistance to the tumor's development. Relatively speaking, the embryo seems much more favorable than the adult as a host for the sarcoma.