152 D. W. H. Barnes and J. F. Loutit 



ten weeks in the case of acquired tolerance to homologous 

 tissue. From indirect evidence of experiments as yet incom- 

 plete we infer that it may be more or less permanent. Chim- 

 aeras, formed bv irradiation of CBA mice with 950 r and 

 treatment with spleen of strain A, have been kept, as noted, 

 routinely until death. Such animals as were available have 

 been challenged with subcutaneous inoculations of the 

 tumour sarcoma-1 ; ten, having survived 18 to 246 days after 

 irradiation, have all "taken" the tumour and succumbed. 



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