114 BIOLOGY OF DEATH 



been possible to calculate the specific death rates for each 

 of the 189 causes of death of the International List, for 

 each sex separately, and for each age in 5 year groups, 

 for the United States Registration Area, exclusive of 

 North Carolina, in 1910. These results have been put 

 together in the biological scheme of classification and may 

 be presented briefly in the form of diagrams. 



The summary table from which these curves are plot- 

 ted is given as Table 9. 



Let us first consider deaths from all causes taken 

 together, in order to recall to mind the general form of 

 a death rate curve. It will be noted, at once, that the 

 rates are plotted along the vertical axis on what strikes 

 one at first as a peculiar scale. The scale is logarithmic. 

 The horizontal lines are spaced in proportion to the 

 logarithms of the numbers at their left, instead of in pro- 

 portion to the numbers themselves. The advantages of 

 this method of plotting in the present case are two-fold. 

 First, it is possible to get a much wider range of values 

 on the diagram ; and second the logarithmic scale permits 

 direct and accurate estimation of the rate of change of a 

 variable. A straight line forming an angle with the hor- 

 izontal on a logarithmic scale means that the variable 

 is increasing or decreasing, as the case may be, at a con- 

 stant rate of change. 



Figure 27 gives the specific death rates for the com- 

 bined total of all causes. The curve in general has the 

 form of a V, with one limb much extended and pulled over 

 to the right. Examining it more in detail, we note that 

 in the first year of life, the specific death rate, or, as we 

 may roughly call it, the force of mortality, bears heav- 

 ier on female infants than on the males. Out of a thou- 

 sand exposed to risk, 124 male babies die in that year, 



