462 VERA DANCHAKOFF 



twentieth day of incubation were grafted in mixture with Ehr- 

 lich sarcoma. The spleen in all these stages is very small, but 

 nevertheless good mixtures were obtained by sacrificing a great 

 number of embryos. The study of such double grafts has 

 shown that they consist of embryonic splenic mesenchyme and 

 tumor tissue intimately intergrown. Strands of mesenchymal 

 cells were seen to traverse the tumor tissue in all directions. 

 Wherever the splenic tissue remained in the graft as larger parti- 

 cles, it underwent a rapid and thorough granuloblastic trans- 

 formation (fig. 17, lower part). Though in direct apposition with 

 tumor cells, none of the splenic embryonic cells seemed to mani- 

 fest an activity similar to that displayed by the adult splenic 

 mesenchyme on coming into contact with tumor cells. An 

 infiltration by granular leucocytes in a moderate degree is ob- 

 served in late stages; it never attains, however, the same degree 

 as in the case of the myeloid metaplasia of the host's mesen- 

 chyme, remains always more or less confined to the region in 

 which both tissues come together, and is not followed by any 

 noticeably injurious effect upon the tumor growth. This analy- 

 sis refers to conjoint growth of tumor and embryonic spleen in 

 all of the stages used, i.e., at the seventh, the fifteenth, and the 

 twentieth day of incubation. 



This observation seems to be of particular interest in relation 

 to an inhibiting power on heteroplastic grafting ascribed by 

 Murphy to the small lymphocytes which develop in the spleen 

 in the last stages of incubation. According to Murphy, these 

 small lymphocytes would confer on the whole organism the 

 power of inhibiting heteroplastic grafts in any of its parts. The 

 results of my experiments, in which the embryonic splenic tissue 

 of embryos at the twentieth day of incubation was grafted in 

 close apposition with the tumor, have, however, demonstrated 

 that even the direct contact between the small lymphocytes of 

 the embryonic spleen and the tumor tissue does not exercise 

 inhibiting effects upon the tumor cells. 



Other factors than the development of the small lympho- 

 cytes must, therefore, determine the striking difference between 

 the results of a tumor-embryonic spleen graft and a tumor- 

 adult spleen graft. 



