THE UNIQUENESS OF THE INDIVIDUAL 



no danger that the attempt to make homografts permanently 

 acceptable is going to brush aside some prudent natural safe- 

 guard against compounding individuals of cells of different 

 origins. There is only one special circumstance in which we 

 need expect trouble: when the host will accept the graft but 

 the graft will not accept the host. My colleagues have shown 

 that this danger is not merely theoretical. 



Skin homografts are destroyed by what is technically known 

 as an ""actively acquired** immunity reaction; there is no ready- 

 made resistance against homografts, in the sense in which an 

 individual of blood group O is ready equipped with antibodies 

 capable of agglutinating red blood corpuscles from donors of 

 groups A or B. Resistance to homografts develops in the course 

 of, and as a consequence of, exposure to the foreign substances, 

 antigens^ contained within them. At first, as I have already 

 said, a skin homograft behaves just like skin merely transposed 

 from one part to another of a single individual: it heals on just 

 as soundly, it is as quickly and as richly re-equipped with a 

 working vasculature, and it undergoes just the same processes 

 of internal reorganization and repair. It may even survive long 

 enough to grow new skin glands and a new crop of hair. But 

 sooner or later, a reaction overtakes it. Just how soon that 

 happens depends upon many variables, e.g. the quantity of 

 foreign tissue that is grafted, for the more that is grafted, the 

 sooner will it be destroyed. There is, however, one variable 

 whose influence overrides all others, the genetical relationship 

 between the donor and the host, and this is worth a momenfs 

 notice. 



Philosophers make a distinction between differences of 

 degree and of kind, but the inborn differences between indi- 

 viduals cannot be classified in either way. The differences 

 between individuals are combinational, or, as mathematicians 

 say, combinatorial differences; one individual differs from all 

 others not because he has unique endowments but because he 



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