324 GUY A. VOISIN AND RADSLAV KINSKY 



tentative explanation would lead to considerations which would 

 be highly speculative. 



Part of these will be detailed at the Prague symposium (Voisin, 

 1962). Possibly the most significant point is that the preceding 

 results can hardly be accounted for by generally accepted views on 

 immunological tolerance to living cells. There is an approach 

 suggested by the first part of the reported experiments (on 

 runting) : passive facilitation of the newborn mice brings about 

 something which is indistinguishable from a state of tolerance 

 induced in homologous injected spleen cells toward the recipient. 

 The only suggestion that we would like to make is that it might 

 not be necessary to make that distinction. This state of tolerance 

 is not necessarily a permanent one ; the tolerance may be broken 

 even after several weeks and the animal may die of runting disease : 

 this seems to be the explanation why proportionally more 

 passively protected animals died after grafting (between day o and 

 day 99 after grafting) than did unprotected animals (16 out of 88, 

 i.e. 18 per cent, versus 3 out of 38, i.e. 8 per cent). If facilitation 

 leads actually to a state indistinguishable from tolerance, it might 

 be of very great theoretical (and practical !) importance. This 

 problem is at present under experimental study, but the results are 

 not ready to be reported as yet. 



SUMMARY 



Each of 75 htters comprising 450 newborn mice was divided 

 into three parts leading to three series. The first series (197 

 newborns) received adult CBA spleen cells plus immune serum 

 prepared by immunizing adult CBA against either lyophilized 

 newborn strain-A mice or against living strain-A tumour (accord- 

 ing to a technique similar to the one used to obtain antibodies 

 enhancing the growth of tumour tissues). The second series (170 

 newborns) received the same number of CBA spleen cells from 

 the same preparation and the same amount of normal CBA serum. 



