270 



H. J. CURTIS AND CATHRYN CROWLEY 



following the insult, and took a large fraction of the total life-span before it 

 became manifest, clearly demonstrates that this factor is not a dominant one 

 in the ageing process. 



60 



100 140 



ISO 220 260 300 340 380 420 460 

 Age (days) 



Fig. 4. Weight curves for normal and mercury-poisoned mice. 



The nature of at least one of the other factors involved in the ageing 

 process is suggested by other work. It has been shown (Stevenson and Curtis, 

 1961; Curtis and Crowley, 1962) that chromosomal aberrations in regenerat- 

 ing liver ceUs increase steadily with age and undoubtedly form part, but by 

 no means aU, of the ageing j^rocess. In the present experiment, the kidney 

 was damaged when the animals were young and their cells were quite free of 

 aberrations. The damage caused scarring which could be compensated for by 

 an over-activity of normal cells. As these normal cells accumulated spontan- 

 eous mutations with age, they were less well able to perform this function, and 

 there were no reserve cells to take over. Functional failure was followed by 

 organ failure and death. This is an attractive hypothesis, and while the 

 present experiment does not prove it, it does give it positive support. 



REFERENCES 



CuBTis, H. J., and Crowley, Cathryn (1962). This volume p. 2.51. 



Curtis, H. J., and Gebhard, K. L. (1959). Froc. 2nd U.N. Conference on Peaceful Uses 



of Atomic Energy 22, 53. 

 Curtis, H. J., and Healey, Ruth (1956). In "Radiobiology", p. 261. Oliver and Boyd, 



Edinburgh. 



