DIGESTIVE ACTIVITY OF MESENCHYME 455 



4. A remarkably large graft of splenic tissue only is found. In 

 parts of the graft giant-cells and accumulations of condensed cellular 

 reticulum are found, possibly foci of former activity' against tumor. 



Grafts of eight days: 1. A remarkably large graft of only splenic 

 tissue is present. 



2. A very large graft of splenic tissue is found, but no tumor cells. 



3. A medium-sized graft of healthy dense splenic tissue is present; 

 there are no tumor cells. 



4. A good-sized graft of splenic tissue only is present. 



The close analysis of these thirty-two grafts indicates that 

 had all of them been allowed to grow eight days or more, very 

 few would have contained tumor tissue at that period. Only 

 in those mixed grafts, in which the contact between the tumor 

 and splenic tissue had been incompletely effected would tumor 

 still be growing. 



The purpose of my further study is an analysis of the factors 

 involved in the disappearance of tumor in grafts in which a 

 complete contact between tumor and adult spleen tissue has 

 been effected at an early period of the graft growth. 



The failure to find tumor tissue in a mixed graft of eight days ' 

 growth does not depend upon absolute failure of the tumor tissue 

 to grow in such grafts, because at an early stage (two to four 

 days, more particularly three days) actively growing tumor 

 tissue is found. Even in later stages, as for example in a seven 

 day graft, tumor tissue has been found in the graft, but in such 

 cases, even better than in cases of complete disappearance of the 

 tumor, does the effect of the destructive activity of the mesen- 

 chyme appear. Only in those parts in which a direct contact 

 of both tissues is effected are the tumor cells, no matter whether 

 in mitosis or in the resting stage, encircled and destroyed. If 

 in contact with the allantoic mesenchyme however, the tumor 

 cells grow unhampered. 



The difference between adult splenic mesenchyme and that 

 of the embryonic allantois appears very clearly in these experi- 

 ments. A positive tropism to the heterogeneous Ehrlich 

 sarcoma cell is shown by the adult splenic mesenchymal cell, 

 and is entirely lacking in the allantoic mesenchymal cell. This 

 affinity of the adult mesenchymal cell, probably of chemical 



