THE UNIQUENESS OF THE INDIVIDUAL 



For these and other reasons, most of us are now convinced 

 that antibodies play no necessary part in the reaction that 

 destroys skin homografts and most other homografts of soUd 

 tissues. With homografts of isolated cells, and more particu- 

 larly of leukaemic tumours, it may be a different story. By 

 'antibodies'* I must be assumed to mean the ordinary, orthodox 

 antibodies that circulate freely in solution in the blood stream 

 and can be recovered in serum free from cells. Perhaps the cells 

 that do destroy homografts are transporters of antibodies and 

 perhaps they liberate them exactly where they can do most 

 damage, that is, in the immediate neighbourhood of the grafts; 

 but if that proves to be the case, I suspect that the antibodies 

 will turn out to be so far different from ordinary antibodies as 

 to deserve some different name. 



I now come back to the problem Avhich I should have begun 

 with: what are the antigens, i.e. the substances in homografts 

 that actually set the immunity reaction going? This may be 

 said at once: that whatever the antigens are, there are a great 

 many of them and they are under very exact genetical control. 

 So much was made clear by the pioneer work of C. C. Little, 

 developed to a remarkable degree of refinement by the school 

 of research which he created in Bar Harbor, Maine (notably 

 by G. D. Snell), and by P. A. Gorer at Guy''s Hospital. But the 

 researches which have made it possible for antigens to be 

 labelled, traced through their Mendelian evolutions, and 

 separated by purely genetical methods has left entirely open 

 the question of what they are. Without recourse to any kind 

 of physical or chemical analysis, it can at least be said that the 

 antigens cannot be substances which are in any way peculiar 

 to any one kind of living cell. All the antigens belonging to 

 that combination which distinguishes a particular individual 

 are to be found in all the living tissues of which his body is 

 composed. Analysis by methods making use of the principle of 

 'tolerance** (Section 5) shows that the skin cells of a particular 



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