146 HOWARD, MICHIE AND WOODRUFF 



menon was regularly repeatable in each of a series of 17 tests 

 involving 3 different strain combinations. Two of the tests 

 included an additional type of control, namely litter-mates 

 treated at birth with isologous in place of homologous irradiated 



0-3 



02 



c 



c 

 «} 



to 



0-1 



00 



2x10^^ 2x10^ 



Neonatal dose of (A x CBA )F| 



2x10*^ 2x10^ 



Spleen cells ( i. p.) 



Fig. 3. Specimen test of the power of varying doses of (Ax CBA) F^ 

 spleen cells, injected i.p. into newborn A-strain mice, to modify spleno- 

 megaly developed in response to challenge on day 2 with 2 x 10' CBA 

 spleen cells i.p. (Data from Howard and Michie, 1962.) 



cells. As shown in Table III, no resistance to challenge was 

 exhibited by such animals, as predicted by the hypothesis that 

 the phenomenon is immunological in nature. Further confirma- 

 tion that the active principle in the resistance-inducing inoculum 

 could be identified with specific transplantation antigens was 

 obtained by extensive tests in which the neonatal and the 

 challenging inoculum offered only a weak antigenic provocation 



