The Nature and Criteria of Senescence 



YEARS 



Fig. 13. — Irish Wolfhounds. Survival of 67 individuals from 12 months of 

 age — sexes combined. Line — whole sample, annual totals. Points — 38 in- 

 dividuals whose exact date of death was known, to scale (data from 



Miss D. Gardner). 



histological appearances of many kinds, and estimations of 

 general or special metabolism are of value within sharply- 

 defined limits, but all are subject to considerable variation apart 

 from the general senile process. In retarded Gladocera, for 

 example, where mean life-span is artificially prolonged by post- 

 poning growth, the heart rate fails to decline before death to 

 the low levels normally found in old age (Ingle, Wood and 

 Banta, 1937). Minot (1908), Hertwig and others considered that 

 a steady decrease in the nucleocytoplasmic ratio was a general 

 feature of ageing in organisms, a suggestion which has not been 

 upheld by later work, and which would today require trans- 

 lation into more precise biochemical terms. Dehydration was 

 also formerly regarded as a general senile phenomenon. From 

 a recalculation of older data, however, and from fresh material, 



29 



