DIGESTIVE ACTIVITY OF MESENCHYME 449 



of free cells arise with the characters of hemoblasts. These 

 cells undergo further differentiation into granuloblasts and 

 granulocytes. Large parts of the adult splenic tissue growing 

 and proliferating in the allantois are transformed into accumu- 

 lations of granuloblastic tissue. This transformation is greatly 

 favored by a rich ingrowth of vessels and markedly inhibited by 

 the failure of the vessels to develop a sufficiently abundant net- 

 work. 



An adult splenic graft begins to develop in a quite similar 

 manner when grafted on the allantois in close proximity with a 

 tumor graft. Only the granuloblastic transformation of its 

 cellular reticulum is less pronounced in the part of the graft 

 adjacent to the tumor tissue. The cells here retain their fusi- 

 form or stellate shape and usually possess numerous slender proc- 

 esses which anastomose with the neighboring cells. A vascular 

 net is regularly found in the peripheral zone of the splenic graft. 

 Numerous round ameboid cells are present in this zone. Hemo- 

 blasts and granuloblasts are the most numerous ; granular leuco- 

 cytes are few at the beginning, but more abundant in later stages; 

 small lymphocytes may also be encountered, but they are 

 always scarce — a fact of great interest in connection with the 

 important role that has been ascribed to them by Murphy. 



The tissue in the extreme outer zone of the splenic graft 

 assumes the form of a loose mesenchyme. This tissue becomes 

 a striking factor not only in limiting the growth of the adjacent 

 tumor graft, but in actively destroying or digesting cell by cell 

 a great part of the tumor tissue. Figure 5 illustrates this proc- 

 ess developing in the zone between tumor and spleen graft as soon 

 as the tissues of both grafts come together. 



The mesenchyme of the periphery of the adult splenic 

 graft manifests a property entirely lacking in the embryonic 

 mesenchyme of the allantois around a single tumor graft. When 

 single tumor cells grow into this zone they appear morphologically 

 unchanged, but the splenic mesenchymal cells are attracted 

 to them at once. They gather around the tumor cells and 

 accumulate in the recesses between their cytoplasmic processes 

 to form small syncytial groups. These tumor cells still possess 



