NATURAL DEATH, PUBLIC HEALTH 253 



accurate population data exist, furnish a cogent demon- 

 stration of the essential soundness and accuracy of this 

 theory of population growth. Indeed, the facts warrant, 

 I believe, our regarding this as a first approximation to 

 the true natural law of population growth. We now are 





I 



mo m 40 60 eo eoo 20 40 60 



1900 20 40 60 eO 20O0 20 40 eO go 2100 



VZARS 

 Fig. 63. — Showing the curve of growth of the.population of Serbia. 



approaching the proper mathematical foundation on 

 which to build sociological discussions of the problem 

 of population. 



As a further demonstration of the soundness of this 

 theory of population growth, let attention be directed for 

 a moment to an example of its experimental verification. 

 To a fruit fly (Drosophila) in a half pint milk bottle, such 

 as is used in experimental work on these organisms, the 

 interior of the bottle represents a definitely limited uni- 

 verse. How does the fly population grow in such a uni- 

 verse? We start a bottle with a male and female fly, 

 and a small sample, say 10, of their offspring of different 

 ages (larvae and pupae). The results are shown in Fig- 



