DIGESTIVE ACTIVITY OF MESENCHYME 459 



mesenchymal cells within the tumor graft and around it pro- 

 hferate and undergo a myeloid metaplasia just as they do in 

 other localities, but to an even greater extent. At a certain 

 stage the tumor is surrounded and partly infiltrated by a great 

 number of ameboid cells — hemoblasts (fig. 6). These cells 

 were probably described by Murphy as 'round-cell infiltration' 

 and were later mistaken by him for small lymphocytes. The 

 hemoblasts proliferate intensely and numerous mitoses are always 

 present. They also differentiate in great numbers into granulo- 

 blasts and finally into the typical granular leucocytes with rod- 

 shaped granulations (fixg. 16). As often observed in centers of 

 sudden intensive proliferative and differentiative processes, 

 the typical mode of differentiation shows slight modifications. 

 Leucocytes with spherically shaped granulation are found among 

 the typical leucocytes with rod-shaped granules. With the 

 increasing number of granular cells formed not only locally, 

 but wuthin the whole organism, the infiltration of the tumor tissue 

 by these cells becomes more and more dense. The capillary net 

 is gorged with granular cells. They accumulate in large groups, 

 mechanically forcing the tumor cells far apart (fig. 6). 



Though no direct ill effect upon the tumor cells can be ob- 

 served, their proliferative ability seems to decline, and mitoses 

 are found less frequently in such grafts. It is also of interest that 

 the tumor cells, especially in parts most intensely infiltrated by 

 granular leucocytes, gradually seem to lose the intense baso- 

 philic character of their cytoplasm always so evident in centers 

 of rapidly growing healthy tumor tissue. Though directly not 

 affecting the tumor cells, the dense leucocytic infiltration seems 

 to be unfavorable for the growth of the tumor tissue and probably 

 affects to a certain degree the metabolism of individual tumor 

 cell, leaving others, as shown by Stevenson, viable and capable 

 of retransplantation into the mouse. Figures 6 and 16 show parts 

 of tumor tissue at various stages of infiltration by granular cells. 

 Their mother cells have been known as large lymphocytes, but 

 an extensive study of their origin and of their further develop- 

 ment has shown them to be in birds and reptiles the common 

 stem cell for all the blood cells (Danchakoff) . Maximoff has 



