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 



4.388 



P 



SERVIA 



..L.4-T- 



1700 20 4O 60 60 1800 20 40 6O 6O I9OO 2O 4O 60 80 2000 2O 4O 6O 60 2JOO 



YEARS 

 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- 



