The Nature and Criteria of Senescence 



the lip make subsequent cracking more likely (Brown and 

 Flood, 1947). 



It is convenient to treat survival curves such as those of man 



• Annealed glass tumblers 

 © Toughened glass tumblers 



Fig. 8. — Survival curves for cafeteria tumblers. 



A = 549 annealed glass tumblers • — • 

 B = 241 toughened glass tumblers — 



Time: 1 scale division = 2 weeks for Curve A, 5 weeks for curve B. 



(Drawn from the data of Brown and Flood, 1947) 



or Drosophila as combinations of the log-linear 'environmental' 

 curve, found where the standing death-rate is high, with a 

 terminal rectangular decline due to senescence, since it is evi- 

 dent that not all those individuals who die in middle life 



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