470 VERA DANCHAKOFF 



The fact that W. lUillock found no resistance against hetero- 

 geneous tumor in the rat until two weeks after birth is very 

 significant, for it is at about the same time that the splenic 

 chick mesenchyme develops its characteristic phagocytic and 

 digestive power over the mammalian Ehrlich sarcoma cell. 

 Whether this coincidence should be regarded as accidental or 

 as a consequence of common factors only further research can 

 shoAv. Bullock found that a graft of adult splenic tissue in a 

 new-born rat at a distance from the tumor graft did not 

 result in an induced immunity in the young animal. His results, 

 therefore, though relating to mammals, do not support the 

 lymphocyte hypothesis. 



Murphy further states that he has regularly obtained inhibi- 

 tion of a tumor implant if a bit of adult spleen w^ere grafted 

 together wdth the tumor. "Round-cell infiltration" was ob- 

 served by him around the necrotic tumor tissue, the ''round-cells" 

 being later described as small lymphocytes. Stevenson re- 

 peated these experiments, using the same tumor, and regularly 

 obtained a conjoint grow^th of tumor and spleen. As seen in 

 section four of this paper the tumors employed grew fairly well 

 in double grafts, grafted adjacently or at a distance. Stevenson 

 proved the presence of living tumor cells within grafts by re- 

 grafting them back into mice, and he also described an infiltra- 

 tion of the tumor by granular leucocytes. This infiltration is 

 only one of the expressions of a general myeloid metaplasia 

 which develops in the mesenchyme of the host after adult splenic 

 grafts. These changes in the host depending upon a graft of 

 adult spleen on its allantois seem not to have been observed by 

 Murphy. 



The failure in Murphy's experiment of the tumor to take if 

 grafted adjacent to the splenic tissue or even at a distance is 

 difficult to understand, unless he used a sarcoma in its regressive 

 phase, when a dense infiltration with granulocytes might have 

 produced a sufficiently injurious effect upon it to check the 

 growth. 



There is also little to say in regard to the analogy which has 

 been drawn between the resistance observed in the adult animal 



