Discussion 



83 



number of deaths due to lung disease in the male. Unexplained 

 deaths were due to vertigo as signs of destruction of one labyrinth 

 were found (9-5 per cent in females, 8-5 per cent in males). Other 

 causes of death which were diagnosed account for about 16 per cent. 

 We have no obvious cases of nephrosis leading to death, but all rats 

 over the age of 10 months have proteinuria and this becomes very 

 high in some very old animals. Very old animals, of about 36 months, 

 generally show no pathological findings which could explain their 

 death. The possibility exists, therefore, that natural death may 



20 n 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 



Age in months (7269) 



Fig. 2 (Verzar). 



occur without obvious illness being suffered. (About 15 per cent of 

 our rats were not autopsied.) 



The survival curves show that after the 10th month "ageing" 

 occurs at the same rate as resistance to external damage (infections) 

 diminishes. This leads to maximal mortality at about 23-5 months, 

 which is also the time of survival of 50 per cent of all individuals. 



Another point is that creatinuria in our rats begins at 500 days, at 

 exactly the same time as the muscular dystrophy in Dr. Berg's rats. 

 Creatinuria is also present with old age in man. 



Rockstein : How much, if at all, did you extend the life of those rats 

 by restricted diets. Dr. Berg ? 



Berg: Lifespan studies have not been completed. At 800 days the 

 survival rate of ad libitum-ied males was 48 per cent as compared 



