DIGESTIVE ACTIVITY OF MESENCHYME 457 



Even if there existed no information concerning the presence 

 of enzymes in the mesenchymal cells or their derivatives, the 

 study of the gradual disappearance of tumor cells within the 

 mesenchymal capsules would furnish such evidence. 



An enzyme working in an acid medium has been demonstrated 

 by Opie in the fowl's spleen. At first glance it would seem diffi- 

 cult to reconcile the results of the present observation with the 

 fact that only an enzyme with proteolytic power in acid medium 

 has been found to exist in the spleen of the fowl ; the ground pulp 

 of the organ is approximately neutral (pH =6.89) when freshly 

 removed from the body. Hedin and Rowland state that the 

 reaction is acid, but their work was done on slaughter-house 

 material, and the methods used were not so delicate as more 

 modern procedures. From the description of the process of 

 tumor destruction it will be seen that actual digestion takes 

 place within closed vacuoles, and that an analogy exists be- 

 tween the activity of the mesenchymal plasmodia against the 

 tumor cells and the well-known digestive power of macrophages 

 known to possess enzymes working in acid medium. 



The gradual dissolution of the tumor cells is easily followed 

 within the mesenchymal digestive zone around the actively 

 growing tumor focus. The farther away from the healthy 

 tumor region, the greater are the changes of the tumor cells. 

 In the extreme peripheral zone still recognizable as belonging to 

 the tumor focus in which the tumor tissue is intimately inter- 

 mingled with the splenic mesenchyme, only very small particles 

 of entirely structureless protein can be discerned. The series of 

 gradual changes from an apparently healthy tumor cell to a 

 small amount of structureless protein can be easily made out in 

 figures 5, 7, 9, 11, 12, 13, 14, and 15. 



6. GROWTH RESTRAINT OF TUMOR IN DOUBLE GRAFTS OF TUMOR 

 AND ADULT SPLEEN WIDELY SEPARATED 



As shown in the two preceding series of experiments, the tumor 

 cells begin to show regressive changes in their structure only 

 when in direct contact with splenic adult mesenchymal cells. 

 In contrast to the embryonic allantoic mesenchyme, the adult 



