DISCUSSION 



347 



will further benefit by the same immunologically balanced reactions. 

 Various factors, among which the strain combination is certainly the 

 most important, will determine which type of reaction will predomi- 

 nate at phase I and at phase II. 



The logical consequences of this concept (namely the possibility of a 

 homologous injection of spleen cells into a newborn mouse resulting 



^^ V.genic St/mp^ ^^ 





( PHASE n ) 



Injected cells (Rejection predominates ^ 

 Rejected *• — j over Facilitation J 



''(no tolerance) 



Fig. 4 (Voisin). Phase II (host versus cells). Predominance of the rejection 

 reaction over the faciHtation reaction: cells are rejected; the mouse is not 



tolerant. 



either in homologous disease or in immunological tolerance, or in no 

 obvious modification) precisely coincide with what is actually observed 

 in current experimentation. 



It must be understood that phase I is not a prerequisite for phase II to 

 take place. If one succeeded in injecting adult Hving, surviving, ex- 

 clusively immunologically incompetent cells into a newborn animal, 

 the immunological story would start directly at phase II with immuno- 

 logical reaction only on the part of the host, thus without any risk of 

 rimting. On the other hand, if one injects spleen or Hver cells from a 



