460 VERA DANCHAKOFF 



found the same to be true for the mammals. Again in figure 6 

 a number of such stemcells are seen to differentiate into granulo- 

 blasts, round acidophilic granules appearing in their cytoplasm. 

 Figure 16 shows to what an extent the granulocytic infiltration 

 can develop. Occasionally tumor cells are found surrounded by 

 heavy capsules of granulocytes. It is rather remarkable that 

 the tumor cells, though seemingly entirely cut off from the nu- 

 tritive substance by the heavy coats of granular cells, do not 

 easily show regressive changes, as is the case when they are 

 surrounded by mesenchymal cells. This ma}^ be explained by 

 the findings of Opie,^" w^ho proved the leucocytes of the birds to 

 be free from the proteolytic enzymes analogous to that found in 

 the granular leucocytes of mammals. Accordingly, even in the 

 case where leucocytes surround a tumor cell and are retained 

 around it, no marked ill effect on the tumor cell is produced. 



No doubt, the intensive granulocytic infiltration does exer- 

 cise a noticeable restraint on the proliferative ability of the tumor 

 cell in such grafts. It is difficult, however, to decide whether 

 this unfavorable effect is due to a consumption of the available 

 nutritive material by the rapidly proliferating myeloid tissue 

 or, possibly, to certain products of the specific metabolism of 

 the granular cells, which are now added to the milieu in which 

 the tumor cells live. 



7. GROWTH OF EHRLICH SARCOMA IN DOUBLE GRAFTS OF TUMOR 



AND EMBRYONIC SPLEEN 



The study of the growth of a single Ehrhch sarcoma graft 

 within the allantoic membrane (section 3) has already shown 

 that tumor cells and those of the allantois at least may live and 

 grow in proximity without any ill effect upon each other. It 

 would not be permissible, however, to assume that all embrj^onic 

 mesenchyme in contradistinction to the adult splenic mesen- 

 chyme has no power to destroy tumor cells. Regional differ- 

 ences may arise in the course of its development and parts of 

 embryonic splenic mesenchyme may acquire properties different 

 from those characteristic of the mesenchyme of other regions of 

 the body. Moreover, the tumor cells in a mixed graft of tumor 



