452 VERA DANCHAKOFF 



factors, the myeloid metaplasia and the prehatching changes in 

 the allantois, are added. A special series of experiments were 

 required in which the two tissues could be implanted in perfect 

 contact and in which the reaction, if it depended solely on the 

 physicochemical constitution of the two tissues, could develop 

 immediately, before any other factor became active. The 

 account of this series of experiments is given in the following 

 section. 



5. GROWTH RESTRAINT OF TUMOR IN A MIXED GRAFT OF TUMOR 



AND ADULT SPLEEN 



It is only the study of mixed grafts of tumor and adult splenic 

 tissue in the allantois which gives full evidence of the phagocytic 

 activity of the adult mesenchyme of the spleen against the 

 tumor cell. The net result of an eight to ten days' growth of 

 mixed grafts in most instances is the full disappearance of tumor 

 tissue, but this fact alone does not permit of any conclusion 

 regarding factors involved in this disappearance. Small lympho- 

 cytes, splenic reticular tissue, or even special chemical substances, 

 which may be present in the adult spleen, may equally well 

 be involved in the disappearance of tumor tissue in the 

 double graft. It is necessary to determine whether the tumor 

 foci within the splenic tissue have failed to grow and have be- 

 come necrotic, or whether their growth has been inhibited and 

 finally stopped by the concomitant growth and differentiation 

 of the splenic tissue, or, finally, whether the tumor tissue has 

 been destroyed by some active process exercised by one of the 

 constituent cellular elements of the spleen. . Only a detailed 

 microscopic study of a great number of double grafts, examined 

 at various stages of their development, can furnish definite data 

 concerning these possibilities. 



The typical results of one series of mixed graft growths of 

 adult spleen and Ehrlich sarcoma was as follows : 



Incubated, 60 eggs; unfertile, 12; grafted, 48; died before the end of 

 the eighth day, 12; no graft developed in 4; 32 grafts were collected, 

 four of which were fixed daily from the second day of growth on. 



