No. 646] THE DURATION OF LIFE 



years. This fact, however, offers no insuperable diffi- 

 culty to the comparison. What is needed is to superim- 

 pose the two curves so that at least two biologically 

 equivalent points coincide. The best two points would 

 be the beginning and the end of the life span. But in 

 the case of Drosophila our life tables start with the be- 

 ginning of imaginal life only. The larval and pupal 

 durations are omitted. In our preliminary comparison 

 (27) we took human age 15, as the point corresponding 

 biologically to the beginning of imaginal life in Droso- 

 phila. 



I think we can get at this starting point more exactly 

 by putting the human and Drosophila h curves together 

 as a starting point at the age for each organism where 

 the instantaneous death rate qx is a minimum. In the 

 case of Drosophila, I think we are safe in concluding, on 

 the basis of the work of Loeb and Northrop (14-17) as 

 well as frgm our own observations, that this point is at 

 or very near the beginning of imaginal life. We shall 

 accordingly take Drosophila age 1 day as this point. 

 Our life tables show that certainly after this time q» 

 never again has so low a value. Indeed the fundamental 

 law of mortality in Drosophila imagoes was stated in 

 (27) in this way (p. 492): ''the instantaneous death 

 rate increases with age as a modified logarithmic func- 

 tion of a;.'* 



The latest edition of Glover's (51) United States Life 

 Tables gives (p. 68) for white males in the original 

 registration states the following values for q^: for age 

 11-12 2.28, and for age 12-13, 2.29. We may, therefore, 

 with sufficient accuracy take exactly 12 years as the 

 minimum point, particularly as the h figures we shall 

 have to use are tabled as of the beginning of the age 

 interval. 



For the other end of the life span we may conveniently 

 take the age at which there is left but one survivor out 

 of 1,000 starting at age 1 day for Drosophila and age 

 12 years for white males. This age for wild type Droso- 



