IMMUNITY AND THE POWER OF DIGESTION. 2O7 



chyme, the adult mesenchymal cells, once close to the tumor 

 cell, will not indifferently pass by, but together with other 

 mesenchymal cells, will tightly surround it. The tumor cell, in 

 response to the approach of the adult mesenchymal cell, with- 

 draws its cytoplasmic processes, becomes immobile and assumes 

 soon a spherical shape. The Figure I illustrates a tumor focus 

 in which the cells still intensely proliferate in the center as may 

 be seen from numerous mitoses present. The tumor focus is 

 however surrounded by a zone of mesenchymal syncytium of 

 splenic origin. The cells of this tissue encircle the tumor cells 

 at first surrounding them very tightly (Figs. I and 2, x). The 

 adult splenic mesenchymal cells of the fowl treat a heterogeneous 

 mammalian tumor cell, which, if present alone in the embryonic 

 allantois, would live and proliferate in no other manner than if 

 it were a block of dead protein. They gather around the tumor 

 cells and enclose them into a capsule and then secrete a fluid 

 within the little cavity occupied by the tumor cell. The nature 

 of this fluid is such that a disintegration of the tumor cell takes 

 place and a complete splitting of its proteins, it must therefore 

 contain proteolytic enzymes. The tumor cell gradually loses its 

 structure (TV, Figs. 1,2,3 and 4) is transformed into a block of 

 structureless protein (TV, Figs, i, 2, 3 and 4) and finally disap- 

 pears completely. Tumor cell after tumor cell is digested in this 

 manner. In the case of the Ehrlich sarcoma, the rate of digestion 

 of the tumor cells by the splenic mesenchyme is higher than the 

 rate of proliferation of the tumor cells, and the grafted tumor, even 

 after a good start of development, disappears. The same process 

 is observed in relation to the sarcoma 180. Only in this case the 

 rate of proliferation of these tumor cells is higher than the rate 

 of their digestion by the splenic mesenchyme, and the tumor 

 still grows in spite of the existence of a peripheral zone around it, 

 in which the process of digestion of tumor cells by mesenchymal 

 cells is most evident. 



The study of microscopical preparations allows us to follow 

 the gradual changes which the tumor cells undergo within the 

 vacuoles surrounded by mesenchymal cells, changes which lead 

 to the full disappearance of the tumor cells. Figures 2, 3 and 4 

 show very clearly how healthy tumor cells H Tc are cut off from 

 the tumor focus, the tumor cells withdrawing their processes 



