448 VERA DANCHAKOFF 



ing upon the direct activity of the adult spleen are now to be 

 considered. 



As soon as contact between the cellular elements of the tumor 

 and adult splenic tissue is established, not only do the tumor 

 cells begin to undergo a profound change, but those of the adult 

 splenic tissue are also affected. In order to appreciate the 

 changes which take place in these tissues in a double adjacent 

 graft, the development and proliferation of a single graft of each 

 of them on the allantois must be borne in mind. As described in 

 the preceding section, one of the most important features of a 

 single tumor graft was an entire absence of reaction between 

 the mesenchyme of the host and the tumor cells. The growth 

 of adult splenic tissue on the allantois has been made the subject 

 of a previous paper^ and only the more important characters in 

 the process will be mentioned here. 



The grafted splenic mash is a mixture of free cells and groups 

 of cells in a syncytial or plasmodial arrangement. The free 

 cells are erythrocytes, wandering cells of various origin, small 

 lymphocytes, scanty granulocytes, and hemoblasts, disconnected 

 endothelial cells and cells of the splenic reticulum. Among them 

 only cells of endothelial and reticular origin proliferate intensely 

 in a splenic graft. These cells display, moreover, an intensive 

 phagocytic and digesti,ve activity against erythrocytes and 

 granular leucocytes. The small lymphocytes leave in great 

 numbers the parts of the graft most remote from the allantois and 

 are found among the mesenchymal cells of the allantois. Con- 

 ditions here are not very favorable for their further maintenance, 

 and, if not transformed into histiotopic wandering cells, they^ 

 disintegrate and are ingested by the embryonal mesenchymal cells. 

 The fate of the small foci of the splenic tissue which are not sepa- 

 rated into single cells is interesting. Such foci sometimes survive 

 in numbers and become centers of proliferation and further 

 differentiation. The individual cells of the reticulum in such foci 

 hypertrophy, and the tissue, originally in a loose syncytial 

 arrangement, is transformed into true plasmodia with no de- 

 limitation of the constituent cells. Many or all of these cells 

 separate as do hemoblasts from blood-islands, and large groups 



