210 VERA DANCHAKOFF 



EXPLANATION OF FIGURES. 



The figures are retouched photographs from original preparations. The Figure 

 i at about 400, the Figure 3, 700 and the Figures 2 and 4, 1000 diameters. 



ABBREVIATIONS. 

 Gr Lc. Granular leucocytes. 

 H Tc. Healthy tumor cells. 



5 Ms. Splenic mesenchyme exercising a phagocytic and digestive activity. 

 Tc'. Tumor cells in various stages of disintegration. 



Tc" . Tumor cells transformed into blocks of almost structureless protein. 

 V. Vessel. 

 X. Tumor cells tightly surrounded by mesenchymal cells. 



The figures illustrate the result of growth of mixed grafts, consisting of mam- 

 malian tumor and adult chick spleen on the allantois. 



PLATE I. 



FIG. i. Actively growing tumor focus of 4 days growth in the allantois. In 

 the center groups of healthy tumor cells with numerous mitoses. The focus of 

 healthy tumor tissue is surrounded by a zone in which the splenic mesenchymal 

 cells encircle the tumor cells and digest them in closed vacuoles. 



FIG. 2. Small area of the peripheral zone around a tumor focus of 4 days growth. 

 Only two tumor cells (H Tc) still exhibit a healthy structure. All the others (Tc' 

 and Tc"} show various changes dependent upon the digestive activity of the splenic 

 mesenchymal syncytium enclosing them in vacuoles. 



