Onset of Disease and Longevity of Rat and Man 73 



For nearly 15 years we have been studying the onset of 

 lesions in rats in relation to age and longevity. For the 

 purpose of these studies we established a special rat colony 

 with conditions that were unusually favourable and uniform. 

 The temperature was kept constant (76° f). The humidity 

 Avas kept at about 60 per cent. The lighting was indirect and 



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V 



Fig. 1. Logarithm of human mortahty, plotted 

 against age (From Simms, 1946). 



Figs. 1-5 reproduced by courtesy of the Editor, Journal of Gerontology. 



was the same in all cages, with 12 hours of light and 12 hours 

 darkness each day throughout the year. The diet was uniform 

 and the quarters were quiet and clean. Data on growth and 

 disease in rats kept under these conditions have been reported 

 by Berg and Harmison (1957). 



Finally, we were able to reduce respiratory infection (and 

 other infections) to such a low level that they were practically 

 non-existent. Under these conditions it was possible to study 



