ONSET OF DISEASE AND THE 

 LONGEVITY OF RAT AND MAN 



Henry S. Simms, Benjamin N. Berg, 

 and Dean F. Davies 



Department of Pathology, College of Physicians 

 and Surgeons, Columbia University, New York 



It is self-evident that the longevity of any species, such as 

 the rat or man, depends upon the age range at which the 

 major diseases of that species result in death. This, in turn, 

 depends upon three factors : 



First, the ages at which early lesions of the major diseases 

 are most likely to appear in individuals of the species. (This 

 we call the "probable age of onset.") 



Second, the time required for lesions to develop from the 

 early stages to the severe lesions that cause death. 



Third, the effect of advancing age on the onset of lesions in 

 that species. 



The combined action of these three factors results in the 

 mortality curves with which we are familiar (Fig. 1). 



One hundred and thirty-four years ago Gompertz (1825) 

 published his law relating mortality with age. More than one 

 hundred years later this law was rediscovered by one of the 

 present authors — and this started him on a career in gerontol- 

 ogy. The law may be expressed in the following form : 



Log Pm - Log Pmo = ^W 

 where P^ is the probability of death (mortality rate) at age t, 

 P^Q is the (extrapolated) probability of death at the age of 

 birth, and k^ is a constant having a positive value. 



Fig. 1 shows a plot of the logarithm of mortality rate against 

 age. This is seen to be approximately a straight line through- 

 out adult life. The equation of this line is the one just given. 



72 



