THE UNIQUENESS OF THE INDIVIDUAL" 



of how SO simple a molecule can embody a genetical programme, 

 the huge variety of detailed and exact instructions or proposals 

 which are carried out, or disposed, as development unfolds. 

 If this interpretation of the structure of nucleic acids is correct, 

 they can differ one from another only in the ordering of the 

 bases along the length of the chain — a profoundly revolution 

 ary view, because it puts an end to the atomic or particulate 

 conception of the '"gene\ A gene can still be thought of as a 

 particle, but it can no longer be a particle; it is now an ordinal 

 singularity of a nucleic acid molecule, a region in which some 

 unique and distinctive permutation of the organic bases prevails. 



The antigens that cause transplantation immunity, I have 

 said, are probably desoxyribonucleoproteins. It is as if the 

 antigens were genes. I shall now examine three consequences of 

 this interpretation, the first two immediate and concrete, the 

 third intangible and vague. 



The first is this. In theory, one way of making a homograft 

 acceptable to a host which would otherwise have rejected it 

 would be to alter its antigenic constitution, so that it could no 

 longer provoke an immunological reaction from the host. If the 

 antigens are nuclear nucleoproteins, this solution is out of the 

 question, for the antigens are built into the inner genetic 

 substance of the cell. 



The second consequence is rather more encouraging. We are 

 beginning to learn something about the structure of nucleic 

 acids, but of the exact nature of the union between a nucleic 

 acid and a protein that makes a nucleoprotein we are still in 

 doubt. If the antigens of transplantation immunity are nucleo- 

 proteins, tissue grafting should provide us with a direct test of 

 their biological integrity, that is, of the degree to which, after 

 extraction and chemical handling, they retain the properties of 

 their native state. The trouble with the nucleoproteins ex- 

 tracted from higher organisms is that nobody has so far been 

 able to do anything with them except record and ponder 



165 



