80 BIOLOGY OF DEATH 



beginning, however, of its proper mathematical and bio- 

 logical analysis. If biologists had been furnished with 

 data of anything like the same quantity and quality for 

 any other organism than man it is probable that a vastly 

 greater amount of attention would have been devoted to 

 them than ever has been given to vital statistics, so-called, 

 and there would have been as a result many fundamental 

 advances in biological knowledge now lacking, because 

 material of this sort so generally seems to the profes- 

 sional biologist to be something about which he is in no 

 way concerned. 



Let us examine some of the general facts about the 

 normal duration of life in man. We may put the matter 

 in this way : Suppose we started out at a given instant of 

 time with a hundred thousand infants, equally distributed 

 as to sex, and all born at the same instant of time. How 

 many of these individuals would die in each succeeding 

 year, and what would be the general picture of the changes 

 in this cohort with the passage of time? The facts on this 

 point for the Eegistration Area of the United States in 

 1910 are exhibited in Figure 18, which is based on 

 Grlover's United States Life Tables. 



In this table are seen two curved lines, one marked I x 

 and the other d^. The l^ line indicates the number of 

 individuals, out of the original 100,000 starting together 

 at birth, who survived at the beginning of each year of 

 the life span, indicated along the bottom of the diagram. 

 The dx line shows the number dying within each year 

 of the life span. In other words, if we subtract the num- 

 ber dying within each year from the number surviving 

 at the beginning of that year we shall get the series of 

 figures plotted as the Ix line. We note that in the very 

 first year of life the ariginal himdred thousand lose over 



