290 GUY A. VOISIN AND RADSLAV KINSKY 



Newborn A's are followed and examined in the first weeks for 

 rimting and over several months for acquired tolerance. 



MATERIAL AND METHODS 



I. Material 



A. Animals 



The present experiments involved loi Utters (577 newborn 

 mice). About 300 adult mice were used as donors of spleen cells, 

 as skin donors, as breeders, as producers of antisera, or as donors 

 of red cells. In addition 50 newborn mice were used to test the 

 toxicity of the sera utilized. Inbred strains of mice were used. 

 The CBA and A/Jax strains were supplied by the Roscoe B. 

 Jackson Memorial Laboratory, Bar Harbor, Maine, and a stock of 

 CBA mice was kindly supplied by Prof. P. B. Medawar from 

 London in 1958. Both strains were bred in our laboratory. 



Isografts performed on the CBA strains of Bar Harbor and 

 London origin demonstrated a 100 per cent tolerance between the 

 two stocks. The mice supphed by Prof. Medawar and their 

 offspring proved to be easier to handle and more resistant. The 

 animals were kept on a standard diet; food was supplied by a 

 French commercial firm (U.A.R.). All the newborn mice used 

 were treated before the 24th hour after birth. 



B. Injected materials 



These were tissues presumed to contain enhancing antigens, 

 presumed enhancing antisera and cells used to induce acquired 

 tolerance. 



(i) Tissues presumed to contain enhancing antigens 



Two kinds of tissue were used. 



(a) Nexvhorn A mice: killed less than 24 hours after birth. Guts 

 and lungs were discarded and the bodies weighed. Four ml. of 

 physiological saline was added to i g. of newborn. Five freezings 



