PROTECTION AGAINST RUNTING 293 



directly on a Kline agglutination plate, using precautions to avoid 

 drying (Gorer mixed the serum dilutions with RBC in tubes and 

 placed a drop from each tube on a separate slide for microscopic 

 observation). The examination was made under a binocular 

 magnifying glass and the results graded as - , ± , and + to 

 + + + + . The highest dilution giving + is taken as the strength 

 of the serum, and the dilutions giving the strongest agglutination 

 are recorded in parentheses. This leads to notations such as 

 512 (+ + -f + 64-128). 



(2) In vivo 



Sera were tested both for cytotoxicity and enhancing power. 

 Dilutions of sera corresponding to volumes of pure sera ranging 

 from o- 20 to 2- 00 mm.^ were injected intravenously in newborn 

 A mice. 



(a) Cytotoxicity was studied by weight curve and mortality rate 

 of A newborns injected v^th sera alone. 



(b) Enhancing power was evaluated by the ability of sera to 

 protect A newborns against runting by homologous (CBA) 

 adult spleen cells. Protection was judged by weight curve and 

 mortahty rate of the treated animals as compared to animals 

 having received the same amounts of CBA cells and normal CBA 

 serum. 



C. Injections of the newborns with homologous cells 



Doses of 7± I million CBA adult spleen cells were injected 

 in a volume of 0-05 ml. into the orbital branch of the anterior 

 facial vein of newborn A mice according to Billingham, Brent 

 and Meda war's technique (Billingham and Brent, 1956). 

 Paraffin oil was applied over the retro-orbital region in order to 

 increase the transparency of the skin as well as to magnify the vein. 

 A total of 471 newborn A mice were injected intravenously during 

 the present experiments. Occasional post-injection breathing 

 troubles were overcome in most cases by repeated gentle pressure 



