412 GENERAL DISCUSSION 



the study of antigens but, relatively speaking, I think progress has 

 been very satisfactory. Two years ago it would have been un- 

 thinkable to use the words "homogeneity" or "purity" in 

 speaking of transplantation antigens, but those words were used 

 several times here by Davies and Kandutsch — though admittedly 

 in a very tentative way. Obviously, a good deal of exchange of 

 thought, and perhaps also exchange of materials, will have to take 

 place before one can sort out the relationship between sensitizing 

 or enhancing antigens so far made manifest by their serological 

 activity alone. 



During the meeting two wholly new conceptions have been 

 put before us : one of them of the crucial importance of the thymus 

 in the development of immunological reactivity; the other raising 

 the possibility that newborn mice can be sensitized, and leading to 

 all kinds of reflections on the relationship between tolerance and 

 paralysis. I am quite sure you don't wish me to summarize the 

 rest of the meeting. We have heard a mass of important infor- 

 mation, backed up by some pretty close reasoning. I think it fair 

 to say that we are making rapid progress in the solution of trans- 

 plantation problems. When this meeting began I said that causes 

 for self-congratulation and self-reproach were about equally 

 balanced, but I think that for a few weeks after this conference we 

 might allow the balance to tilt slightly in favour of self-con- 

 gratulation. 



I would like to thank all of you very much for your extremely 

 strict time-keeping and the liveliness and the pointedness of the 

 discussion, and I would like particularly to thank the non-English- 

 speaking contributors for the efforts they have made to dehver 

 extremely clearly set out and perfectly intelligible papers in a 

 foreign language. And, finally, may I thank the Ciba Foundation 

 on your behalf not merely for making this meeting possible, but 

 for making it possible in surroundings so conducive to thought 

 and to enjoyment. 



