PROTECTION AGAINST RUNTING 297 



US to discard 8 litters, amounting to 46 newborns among which 

 35 were injected. 



(c) Some of the normal controls (25 per cent) received intra- 

 venous injections of physiological saline at birth, in the same 

 volume as experimental animals received sera + cells. 



(d) From repeated prehminary experiments it was known that 

 A newborns injected with isologous adult spleen cells behave (as 

 far as their state of health, weight curve and survival were 

 concerned) the same way as uninjected newborns or newborns 

 injected with saline. It was therefore not deemed necessary to add 

 that type of control to litters already divided into three series. 



RESULTS 



Each of 1 01 htters comprising 577 newborns of strain A 

 was divided into 3 series. The first series (250 newborn mice) 

 received adult CBA spleen cells plus immune serum prepared by 

 immunizing adult CBA against A-strain tissues. The second series 

 (221 newborn mice) received the same number of CBA spleen 

 cells and the same amount of normal CBA serum. The third 

 series (106 newborn animals) received nothing or physiological 

 saline and was followed as normal controls. It must be remem- 

 bered that 18 litters (81 newborn animals) were lost before the 7th 

 day owing to the cannibalism of the parents ; 8 more litters (46 

 newborns) were discarded because one or more of the normal 

 controls included in these litters died during the experiments. 

 Finally 75 litters comprising 450 newborn animals were considered 

 as satisfactory and were utihzed for this study. They were 

 followed and studied for occurrence of runt disease and, later, for 

 specific tolerance to CBA skin. The immune sera utilized to 

 treat these animals were also studied. 



The experimental results will be reported in three sections: 

 the study of runting and its prevention; the immunologically 

 specific properties of the immune sera; and the study of tolerance 

 and its enhancement. 



