Onset of Disease and Longevity of Rat and Man 79 



is directly related to the age of onset of lesions of the major 

 diseases of this species. The age of onset of these lesions, when 

 plotted against age, gives smooth curves which are character- 

 istic of the diseases in question. 



Data on human lesions, found from autopsy data at dif- 

 ferent ages, give curves similar to those of rats, except that 

 the onset of the human diseases does not occur until many 

 years later than is the case with the rats. This indicates that 

 there is a mechanism for the deferment of onset of lesions, 

 which accounts for the difference in lifespan between the 

 species. 



REFERENCES 



Berg, B. N. (1956). J. Geront, 11, 134. 



Berg, B. N., and Harmison, C. R. (1957). J. Geront.y 12, 370. 



GoMPERTZ, E. (1825). Phil. Trans., 115, 513. 



SIMMS, H. S. (1946). J. Geront, 1, 13. 



SIMMS, H. S., and Berg, B. N. (1957). J. Geront.y 12, 244. 



DISCUSSION 



Gerking: The curve showing the age distribution of onset of dis- 

 ease in your rats was a normal, or nearly normal distribution. The 

 right-hand portion of the curve of deaths that Dr. Benjamin showed 

 us, indicating senescence in the human, was also the normal distri- 

 bution. These both occurred late in life and they may actually reflect 

 the same phenomenon. 



Berg: That is true. We find the same type of distribution curve for 

 the onset of lesions as for mortality — in both rat and man. This is 

 because the period for the full development of the disease, from the 

 time of the early lesion to the late lesion, does not change with age. 



Gerking: The correspondence between the shape of these ciu'ves, 

 over a wide range of ages, is very remarkable. 



GriXneherg: I have some confirmatory evidence on what you said 

 about the relation between the age of onset of the disease and the 

 environment. In mice of the A strain, in animals above a certain age, 

 nearly all individuals suffer from the deposition of a substance called 

 amyloid in the kidneys and various other organs. A group of in- 

 vestigators in the National Institutes of Health, Bethesda, has suc- 

 ceeded in influencing this condition by a change of diet. If these 

 animals are fed on a protein-poor diet the onset of the condition is 

 delayed and the total incidence is greatly reduced. Still more in 



