450 VERA DANCHAKOFF 



a vigorous metabolism since they continue to proliferate. 

 Tumor cells in mitosis are encircled by mesenchymal cells, even 

 more readily at the beginning, because at this time they lose 

 their cytoplasmic connections with adjacent cells. The first 

 change in a tumor cell around which mesenchymal cells have 

 accumulated is the withdrawal of its processes; it consequently 

 loses its characteristic fusiform or branched shape and becomes 

 spherical. This process has taken place on. a large scale in the 

 graft from which figure 5 was drawn. Neither cytoplasm nor 

 nucleus shows at this stage any degenerative change. Numerous 

 cells, however, seem to have become immobile as no cytoplasmic 

 processes appear at their periphery. The splenic mesenchymal 

 cells occur singly or accumulate in small groups around such tumor 

 cells and quickly encircle them, thus separating them from the 

 surrounding tissue. They form an entire capsule around the 

 tumor cells, and include them in small cavities of uninterrupted 

 cellular Plasmodium. After being surrounded, the tumor cells 

 undergo a series of physicochemical changes which end only with 

 its complete disappearance. It is gradually transformed by the 

 digestive activity of the surrounding Plasmodium into a small 

 mass of non-living protein. The final jDroducts of digestion are 

 resorbed and assimilated by the surrounding living cells. 



The space within which the tumor cell is found is not a rigid 

 cavity. At the beginning the tumor cell is usually tightly sur- 

 rounded by the Plasmodium; later it lies in a cavity larger than 

 itself, then gradually the cavity becomes smaller, the surrounding 

 cells drawing closer together about the diminishing body of the 

 tumor cell (figs. 7, 9, 11). 



The morphological picture of the gradual changes under- 

 gone by the tumor cells as seen in the several figures varies 

 greatly. Sometimes the cytoplasm is first attacked, its periph- 

 eral zone vacuolized, while a more compact and homogeneous 

 part still remains around the nucleus. In other cases the nuclei 

 seem first to be dissolved, and irregular chromatin particles 

 are found scattered within the cytoplasm. The same parts of 

 the tumor cells do not always disappear first. Sometimes a 

 small chromatic mass, in other cases a clear vacuolized accumula- 



