THE UNIQUENESS OF THE INDIVIDUAL 



upon its nucleus is doubly instructive, (a) because in large 

 animals the nucleus may be several feet away from the most 

 distant part of the fibre, so that the idea of something leaving 

 the nucleus, reaching the farthest tip and then returning home 

 becomes almost impossible to credit: the traffic of nuclear 

 particles can only be one-way; and (b) because it gives the 

 clearest possible evidence of the activity of the nucleus during 

 its so-called ''resting stage**, i.e. between one nuclear division 

 and the next. The nuclei of mature nerve cells do not divide, 

 so that their labours, though doubtless strenuous, are all 

 sabbatical. Fortunately, there is other evidence that nuclei 

 are busy in the intervals between dividing; for example, nuclei 

 isolated from cells seem to be able to incorporate substances 

 from the environment by active metabolism and to enjoy 

 considerable synthetic powers.^ Yet their own substance does 

 not increase until just before the act of division, so that what 

 is made in the nucleus must presumably go elsewhere. I 

 emphasize these points, perhaps to the extent of labouring 

 them, only to make clear that the idea of nuclear substances 

 entering the cytoplasm and then being discharged through the 

 surface of the cell is not at all surprising. What is surprising 

 is that a technique like skin grafting should provide us with 

 evidence that it occurs. 



4. WHAT CAN BE DONE ABOUT IT.? 



It is at present possible to envisage four kinds of ways in 

 which a homograft could be made acceptable to its host: (a) the 

 antigenic constitution of the graft might be changed, so that 

 it no longer stirred up a reaction in its host; (b) the graft might 

 be transplanted in such a way that it could not exercise its 

 antigenic properties; (c) the host might be changed in such a 

 way that its reaction against the graft was enfeebled or done 



1 V. G. Allfrey and A. E. Mirsky, Nature, 176, p. 1042, 1956. 



168 



