COMPARISON OF THEORIES 



(ii) The persistence of immunological ' memory ' over many 

 years — for example, Davenport's phenomenon (Daven- 

 port and Hennessey, 1956). 

 In addition, there is (iii), an accepted principle derived 

 largely from modern work on adaptive enzyme formation in 

 bacteria that the 'code' determining the pattern of all 

 functional proteins is genetically provided. 



The last of these is perhaps not to be regarded as a cate- 

 gorical requirement until a great deal more is known about 

 genetic aspects of differentiation, but it would seem most 

 unwise to disregard the principle unless absolutely forced to 

 do so. 



If we adopt it, we can in the first place accept some of the 

 differences between individuals in the type or amount of 

 antibody produced as being related to inborn genetic 

 differences. Qualitative differences amongst gamma globulin 

 molecules produced by the same individual may be ascribed 

 {a) to the process of embryonic differentiation, {b) to somatic 

 mutation at any time during life. The equally or more im- 

 portant differences in the relative numbers of different types 

 of gamma globulin molecule can be ascribed to {a) selective 

 proliferation of cells of certain clones as a result of specific 

 stimulation, (b) activation to produce and liberate globulin 

 of cells of appropriate clones, {c) transfer of genetic character 

 from cells of one clone to those of another by some process 

 of transduction in the broad sense. 



Any hypothesis to incorporate such a point of view must 

 take the form of a clonal selection theory. That can hardly 

 be a matter for controversy. The principal difference of 

 opinion will be whether it is or may become necessary to 

 accept more active participation of foreign antigens in 

 determining the emergence of antibody-producing clones — 

 in other words, to graft something of the indirect template 

 theory on to the clonal selection hypothesis. The possibility 

 cannot be eliminated and if new experiments make it necessary 

 to adopt such a point of view, the remoulding of genetic 



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