THE STUDY OF THE AGEING OF CELLS 



J. F. Danielli 



Department of Zoology, King's College, London 



That the senescence of mammals is in any way due to the 

 ageing of cells is an assumption. The phenomena responsible 

 for senescence as we know it may all occur at the supercellular 

 level, and the differences which are observed between the 

 cells of healthy adults and senescent adults may be secondary. 

 However, there is no doubt that cells do senesce in themselves, 

 and that even if senescence as we see it in mammals is not 

 primarily due to senescence at the cellular level, nevertheless 

 when other causes of senescence have been counteracted there 

 will remain senescence of purely cellular origin. 



In view of this position the essential aim of the study of the 

 ageing of cells must be to detect the primary changes respon- 

 sible for the senescence of cells, and then to devise methods for 

 detecting such changes in somatic cells. 



The cells to be studied 



The first point which I wish to emphasize is that if one is to 

 study senescence in cells, one must have cells which really are 

 old. In some peculiar way this necessity has often escaped 

 notice, and we find it said that studies on tissue cultures and 

 on protozoan or bacterial cultures have shown that cells are 

 potentially immortal. For the most part this is based on a 

 fallacy. To begin with, if cells are continually growing and 

 dividing, as they usually are in the experiments referred to, 

 then they are not in any case old cells. For example, if the 

 cells divide regularly at intervals of two days, then immediately 

 after a division at worst half of the cell is two days old, one- 

 quarter is four days old, one-eighth is six days old, and so 

 on. The cell only becomes really old if its multiplication is 



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