The Study of the Ageing of Cells 41 



these cells which we should expect to be important from the 

 point of view of the study of ageing. 



We may also note that if a change takes place favouring 

 proliferation (curve A), then the new cell line will outpace the 

 original stock and ultimately exclude it if serial subculturing 

 is used. This corresponds to formation of a tumour. 



Finally, we should recall that few if any cells in a higher 

 animal are undergoing continuous proliferation. In many 

 tissues cell division may occur seldom or never, so that deleter- 

 ious changes can accumulate. In other tissues, although cell 

 division is common, it is based upon the division of stem-line 

 cells which are retained: in these circumstances deleterious 

 changes will accumulate in the stem-line cells. 



Thus we see that, whereas in a continuously proliferating 

 culture deleterious changes tend to be eliminated, in the cells 

 of higher animals they tend to accumulate. Consequently our 

 studies should be based upon cells which either are not pro- 

 liferating, or which are stem-line cells. 



Functions to be studied 



Although qualitative differences between cells serve as a 

 valuable guide to what should be studied quantitatively, 

 qualitative studies are usually too subjective to be of great 

 value in themselves. It is desirable to concentrate upon those 

 cellular functions which can be measured. We may include: 



(1) ability to grow and divide under standard conditions; 



(2) ability to synthesize normal cell products, such as 

 enzymes, hormones, and connective tissue fibres; 



(3) ability to respond to stimulation, e.g. by hormones such 

 as adrenaline and testosterone; 



(4) ability to resist abnormal conditions, such as anoxia, 

 extremes of temperature, malnutrition, bacterial toxins 

 and toxic drugs. 



At King's College we have recently begun such an investiga- 

 tion using Amoeba proteus. Studying point (1), Miss A. 





