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GUY A. VOISIN AND RADSLAV KINSKY 



Group 4: animals which retained perfect grafts for at least 100 

 days and never rejected them during their lifetime were classi- 

 fied as permanently tolerant. 



Table IV 



Increase in proportion and quality of tolerance to skin grafts by specific 



treatment (facilitation) of newborn mice. numbers and percentages of 



grafts rejected or variously tolerated 



All differences — or absence of difference — statistically significant (significance of the 

 difference in rate of normal rejection evaluated by the method of binomial expansion). 



It was found that only the animals which received homologous 

 cells plus normal serum were capable (in 4 cases out of 37, 10 • 8 

 per cent) of giving a normal rejection, while animals which 

 received facilitating serum instead of normal serum were in no 

 instance capable of a normal rejection. It was also found that the 

 animals treated with facilitating serum were able to develop 

 permanent tolerance in 69 cases out of 79 (87- 3 per cent) while the 

 animals treated with normal serum developed it in 21 cases out of 

 37 (56- 8 per cent). The percentage of undetermined tolerance is 



