78 H. S. SiMMS, B. N. Berg, and D. F. Davies 



age groups was small (56 males in the 70-79 group and 12 

 males in the 80-89 group). 



It will be seen from Fig. 6 that when the data of rat and 

 man are plotted on the same time scale, the curves of the two 

 species are identical in form, except that those of the rat 

 occur much sooner, and are compressed into a much shorter 

 time range, than those of man. This applies not only to one or 

 two diseases of each species, but also to other diseases not 

 reported here. 



It should be pointed out that the rat data were obtained 

 from a fairly homogeneous colony of animals raised under 

 uniform conditions. On the other hand, the human data were 

 obtained from a heterogeneous collection of individuals who 

 had lived under differing conditions. Had the humans been 

 as homogeneous as the rats, their data on these two charts 

 would be characterized by much steeper curves within a much 

 narrower time range — perhaps approximating to the curves 

 of the rats in shape, but not in their location on these charts. 



Hence, we may conclude that the factors which determine 

 the longevity of these two species (rat and man) appear to be 

 identical, except that in one species the lesions of the major 

 diseases have their onset much sooner and over a much 

 shorter range of time, than do those of the other species, when 

 compared on the same time scale. 



That it is possible to alter the age of onset of lesions has 

 been shown by dietary experiments in which rats on a re- 

 stricted food intake were found to have a considerable delay 

 in the onset of their major diseases, as compared with rats 

 receiving as much food as they wanted to eat. This suggests 

 that there may be other methods for modifying lifespan which 

 may result in altering the age of onset of lesions of major 

 diseases. 



Summary 



Observations on the accumulation of lesions in rats in 

 relation to age have shown that the lifespan of these animals 



