l68 MICHAEL FELDMAN AND DAVID YAFFE 



metastasis developed. The SBLi homograft did grov^ in spleen 

 cell chimeras, but metastasis appeared only in foetal-cell treated 

 animals, v^here the immune response is reduced. Whether the 

 promotion of metastasis in isologous systems is also due to some 

 kind of reduced host resistance, is still an open question. 



The formation of metastasis in X-irradiated isologous systems 

 could theoretically be attributed to either of the follow^ing pro- 

 cesses: (i) that the destruction of the lymphatic tissue by X- 

 irradiation furnishes favourable physiological conditions for 

 tumour cell migration, v^hich is restricted in animals with 

 normal lymphatic tissue; or (2) that cell migration from the 

 original implant, via the lymphatics, takes place even in normal 

 animals, but that the progressive growth of the tumour cells 

 within the normal lymph nodes is suppressed. The X-irradiation 

 accordingly alleviates a suppressing effect exerted by the 

 organized lymph nodes. To test these two assumptions, tumours 

 were grafted subcutaneously into isologous C57BL animals, the 

 lymph nodes were extirpated at various time intervals following 

 grafting, and nodal cell suspensions from individual hosts were 

 injected intramuscularly into other isologous animals. It was 

 found that re-inoculation of lymph node cell suspensions from 

 each of the primary hosts 25 days following subcutaneous trans- 

 plantation of SBLi, resulted in tumour growths in all secondary 

 hosts. Hence, metastatic migration takes place even in non- 

 irradiated normal animals, but within the organized normal 

 lymph nodes the progressive growth of such tumour emboh is 

 suppressed. This suppressive effect is abolished by X-irradiation. 



The formation of metastasis in radiation chimeras was also noted 

 by Barnes et al. (1957). In non-irradiated animals, cortisone was 

 found to activate the formation of metastasis in otherwise non- 

 metastatic tumours (Agosin et al., 1952; Baserga and Shubik, 

 1954). Furthermore, Baserga and Shubik have shoMOi that 

 cortisone, like X-irradiation, has in fact ehcited the progressive 

 growth of pre-existing metastatic emboH. In view of the simi- 



