DIGESTIVE ACTIVITY OF MESENCHYME 437 



It is difficult on the basis of these experiments, to be sure that 

 in the presence of the adult splenic graft the allantoic mesen- 

 chymal cells themselves do not begin at least to take part in the 

 described activity. No definite morphological criteria exist 

 which would permit of a sure identification of allantoic and 

 splenic mesenchymal cells, for both are characterized by the 

 same structural features. It is possible, however, to demon- 

 strate by another series of experiments that the embryonic 

 mesenchymal cells are incapable of destroying the tumor by 

 phagocytic activity whether adult splenic tissue is present or 

 not in the host. If tumor tissue and adult splenic tissue are 

 grafted, widely separate, as described in section 6, the growth of 

 the tumor is not affected by the activity of any mesenchymal 

 elements. It is true that the tumor does not always grow as well 

 as if grafted alone, but, as the analysis of the conditions will 

 show, the factor damaging the growth of the tumor in this 

 case is the myeloid metaplasia of the embryonic mesenchyme 

 following a single spleen graft. 



The existence of a phagocytic destructive power in the em- 

 bryonic splenic mesenchyme similar to that revealed by the 

 adult splenic tissue against the living Ehrlich sarcoma cell, 

 though made improbable by the lack of resistance .in the embryo, 

 is not, however, altogether precluded. On the other hand, the 

 cells of the embryonic allantois itself might have been stimulated 

 to a similar digestive activity by extracellular substances brought 

 in with the adult splenic tissue. In order to obtain some defi- 

 nite information concerning the phagocytic digestive capacity 

 of the embryonic mesenchyme, two other series of experiments 

 were made and are described in section 7. On the one hand, the 

 Ehrlich sarcoma thoroughly mixed with splenic tissue of em- 

 bryos up to the hatching period was grafted; on the other, grafts 

 of the Ehrlich sarcoma mixed with aseptic dead splenic tissue 

 only and together with embryonic spleen were made. The 

 tumor grew well in both cases, and no mesenchymal reaction 

 developed around the tumor cells. 



It seemed desirable, finally, to approach the question whether 

 the destructive power of the adult splenic mesenchyme of the 



