346 



DISCUSSION 



reaction predominates strongly and/or precedes the rejection reaction, 

 the animal will be protected and will survive (Fig. 3) ; if the facihtation 

 reaction predominates "weakly", the animal will be partially or tardily 

 runted. 



If the animal survives without apparent runting or with a moderate 

 runting, phase II will take place. 



fc,nV'9enic Stimuli, ^ 

 Rejection Reaction 



Facilitation Reaction 



®. 



(PHASE I) 



Facilitation predominates over Rejection 



^ no Runting 



Fig. 3 (Voisin). Phase I (cells versus host). Predominance of the facilitation 

 reaction over the rejection reaction; protection against runting. 



During phase II, if the rejection reaction of the young mouse toward 

 the homologous cells predominates, the animal will reject the cells and 

 will not be tolerant (Fig. 4). If the facilitation reaction predominates 

 and/or precedes the rejection reaction, the cells will be protected and 

 survive (Fig. 5) : a state of active immunological equilibrium will be 

 reached, which will possibly include a weak reciprocal rejection re- 

 action. But the important thing is that this rejection reaction, if it 

 exists, will be preceded and continuously counteracted by a strong 

 reciprocal facilitation reaction, and the animal can then be considered as 

 tolerant to the injected cells and other cells of the same strain which 



