458 VERA DANCHAKOFF 



splenic mesenchymal cell of the fowl manifests a well-pronounced 

 tropism toward the healthy tumor cells of the heterogeneous 

 Ehrlich sarcoma, which enables it to approach the tumor cell or, 

 if the approach be accidental, to keep in touch with it. No 

 immune state is produced by the presence of the adult splenic 

 tissue in the organism of the host, for even that part of the tumor 

 separated from the adult splenic tissue by the width of a few 

 cells only often proliferates as intensely, as if it were grafted 

 alone. The lack of resistance in the embryo is even more appar- 

 ent in experiments in which the two grafts are placed at a dis- 

 tance from one another of 2 to 3 cm. Under these conditions 

 the tumor graft grows unhampered for about four days, the tumor 

 cells being in contact only with embryonic allantoic mesen- 

 chymal cells. Both tissues follow their course of development 

 without any apparent reaction between them. 



The graft of splenic tissue, separated from the tumor graft 

 by 2 to 3 cm. grows and develops within the allantois in the 

 manner described in section 4. 



The presence of a graft of adult splenic tissue within the allan- 

 tois soon calls forth extensive changes in all of the embryonic 

 mesenchyme of the host, including the mesenchyme of the allan- 

 tois itself. These changes as I have described consist in a stimula- 

 tion of proliferative processes in the mesenchyme. The host's 

 spleen grows to be an organ many times exceeding its normal 

 volume. The delicate strands of connective tissue between the 

 muscle bundles or the nephric tubules, or the testis cords, etc., 

 become transformed into heavy masses of mesenchyme and such 

 derivatives as granuloblasts and granular leucocytes. The 

 allantois itself shows innumerable foci of mesenchyme prolifera- 

 tion. The mesenchymal cells of the vascular adventitia espe- 

 cially proliferate in an intensive way. The proliferating 

 mesenchymal cells are gradually transformed into great masses 

 of ameboid cells — hemoblasts which differentiate into granulo- 

 blasts (myelocytes) and granular leucocytes. 



At this time the tissue in the tumor graft, when separated 

 frojTi the splenic graft by a distance of several centimeters, ac- 

 quires an interesting appearance. The embryonic allantoic 



