226 BIOLOGY OF DEATH 



part in determining the duration of life largely, if not 

 in principle entirely, by influencing the rate at which the 

 vital patrimony is spent. If we live rapidly, like Loeb 

 and Northrop 's Drosophila at the high temperatures, our 

 lives may be more interesting, but they will not be so 

 long. The fact appears to be, though reservation of 

 final judgment is necessary till more returns are in, 

 that heredity determines the amount of capital placed in 

 the vital bank upon which we draw to continue life, and 

 which when all used up spells death ; while environment, 

 using the term in the broadest sense to include habits 

 of life as well as physical surroundings, determines the 

 rate at which drafts are presented and cashed. The 

 case seems in principle like what obtains in respect of the 

 duration of life of a man-constructed machine. It is 

 self-evident that if, of two automobiles of the same make 

 leaving the factory together new at the same time, one is 

 run at the rate of 1,000 miles per year and the other at 

 the rate of 10,000 miles per year, the useful life of the 

 former is bound to be much longer in time that that of 

 the latter, accidents being excluded in both cases. Again, 

 a very high priced car, well-built of the finest material, 

 may have a shorter duration of life than the poorest 

 and cheapest machine, provided the annual mileage output 

 of the former is many times that of the latter. 



The first three of these conclusions seem to be firmly 

 grounded. The last rests, at present, upon a less secure 

 footing. Because it does, it offers an extremely promis- 

 ing field for both statistical and experimental research. 

 We need a wide variety of investigations, like those of 

 Loeb and Northrop, of Slonaker and of Rubner, on the 

 experimental side. On the statistical side, well-conceived 



