214 BIOLOGY L OF DEATH 



265,500 calories. Small animals, with an intensive meta- 

 bolism live a relatively short time; large animals with 

 more sluggish metabolism live a longer time. Rubner's 

 view is that a definite sum of living action (energy trans- 

 formation) determines the physiological end of life. 

 This is precisely the view suggested here except that it 

 is here postulated that the definite sum, for individual 

 or species, is fundamentally determined, by heredity, 

 working through the structural make-up. 



If we may be permitted to make a suggestion regard- 

 ing the interpretation of Loeb and Northrop 's results in 

 conjunction with our own on Drosophila, it would be to 

 this effect. Any given genetically pure strain of Droso- 

 phila is made up of individual machines, constructed to 

 turn out, before breaking down, a definite limited amount 

 of energy in the form of work, mechanical, chemical and 

 other. This definitely limited total energy output is 

 predetermined by the hereditary constitution of the indi- 

 vidual which fixes the kind of physico-chemical machine 

 that that individual is. But the rate per unit of time of 

 the energy output may be influenced between wide limits 

 by environmental circumstances in general and tempera- 

 ture in particular, since increased temperature increases 

 rate of metabolic chemical changes in about the same 

 ratio, as demonstrated by a wealth of work on tempera- 

 ture coefficients, as it increases other chemical changes. 

 But if the rate of energy output per unit of time is changed, 

 the total time taken for the total output of a predeter- 

 mined amount of energy, as work, must change in inverse 

 proportion to the change of rate. So we should expect 

 just precisely the results on duration of life that Loeb 

 and Northrop got, and so far from these results being in 

 contradiction to ours upon heredity, they may be looked 



