292 



lotka: a natural population norm 



its equivalent 3), and the defining equation r = (b - d). In 

 actual fact of course 6, d and r are in every instance completely 

 determined. There must therefore be a third relation between 



Fig. 5. Age-distribution at death, England and Wales 1871-1880. 



them. In fact if one male, at age a, gives rise, on an average, to 

 /3m(«) male births per unit of time, we must have 



6m = 



1 I c„, (a) /?„, (a) da 



Cm (a) I3,„ (a) da 

 Jo 



(25) 

 (26) 



