THE UNIQUENESS OF THE INDIVIDUAL 



matter, it certainly does not depend upon any use which the 

 matter may later be put to. If it did, the life of the cell outside 

 the body, in tissue culture, would not be possible. Perhaps the 

 nuclear substances discharged by cells have to do with the 

 control of growth, for tissues maintained by culture and sub- 

 culture outside the body, in media constantly renewed, indulge 

 in unlimited growth; perhaps the reaction which occurs when, 

 in homografting, nuclear substances of slightly the wrong kind 

 enter the lymph nodes and other centres of response is a tell- 

 tale aberration of some deeply important regulatory mechan- 

 ism, essentially of an immunological character, by which these 

 substances are dealt with in ordinary life. Several scientists 

 have thought along such lines and are seeking evidence of an 

 essentially immunological control of growth. Might not the 

 nuclear particles I am discussing be its agents? 



Unfortunately, I do not think these nuclear particles will 

 fill the bill. Substances which control the growth of particular 

 tissues — of one tissue, that is, but not necessarily of another — 

 must surely be specific to and characteristic of those tissues; 

 but within any one individual the nuclear antigens are common 

 to them all. I incline to the more homely view that the emission 

 of nuclear particles is excretory in nature. No one doubts that 

 the nucleus administers the activity of the outl3dng parts of 

 the cell, but no one knows exactly how it makes its wishes 

 known. It is likely (though this is only one possibility among 

 several) that genetically specific matter leaves the nucleus and 

 enters the cytoplasm, though not at all likely that, having done 

 so, it goes back; it may simply be discharged through the 

 surface of the cell, eventually to reach the lymph nodes or other 

 clearance centres and to be broken down. Something of the 

 kind has long been thought to happen in nerve cells, for the 

 integrity and working order of a nerve fibre is absolutely 

 dependent upon the presence of the nucleus in the cell-body 

 from which the fibre arises. The dependence of the nerve fibre 



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