378 DISCUSSION 



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DISCUSSION 



Simonsen: I am very convinced by Dr. Russell's evidence that nothing 

 like complete tolerance of the graft is induced instantaneously in his 

 system, that the graft in fact goes on reacting against the host for some 

 days. The graft-versus-host tolerance which I described occurring in 24 

 hours in the C3H and C3HX ST/ A system, I wouldn't claim was 100 

 per cent tolerance but it was a very marked partial tolerance; my best 

 estimate is that about five-sixths of the reactivity towards ST/ A antigen 

 got lost in the first day. But I think the question of whether the animal 

 is going to die or not may be a very marginal question in terms of cells 

 which continue reacting after the first day. It may very well be that a 

 relatively small fraction of the original graft is decisive. And it may be 

 this fraction which Dr. Russell picks up with his treatment of antiserum 

 or with sensitized cells. If this is true, his test system may in fact be more 



