NATURAL DEATH, PUBLIC HEALTH 247 



The first thing obviously needed in any scientific 

 approach to the problem of population is a proper mathe- 

 matical determination and expression of the law of popu- 

 lation growth. It has been seen that the most devastating 

 calamities make but a momentary flicker in the steady 

 progress of the curve. Furthermore, population growth 

 is plainly a biological matter. It depends upon, in last 

 analysis, only the basic biological phenomena of fertility 

 and mortality. To the problem of an adequate mathe- 

 matical expression of the normal growth of populations, 

 my colleague, Dr. Lowell J. Reed, and I have addressed 

 ourselves for some time past, The known data upon which 

 we have to operate are the population counts given by 

 successive censuses. Various attempts have been made 

 in the past to get a mathematical representation of these 

 in order to predict successfully future populations, and 

 to get estimates of the population in inter-censal years. 

 A noteworthy attempt of this sort is Pritchett's fitting 

 of a parabola of the third order to the United States popu- 

 lation from 1790 to 1880 inclusive. This gave a fairly 

 good result over the period, but was obviously purely 

 empirical, expressed no real biological law of change, 

 and in fact failed badly in prediction after 1890. 



We have approached the problem from an a priori 

 basis, set up a hypothesis as to the more important 

 biological factors involved, and tested the resulting 

 equation against the facts for a variety of countries. 

 The hypothesis was built up around the following 

 considerations : 



1. In any given land area of fixed limits, as by 

 political or natural boundaries, there must necessarily be 

 an upper limit to the number of persons that can be sup- 

 ported on the area. To take an extreme case, it is obvious 



