320 



DR MATTHEWS DUNCAN ON SOME 



that, after that age, sterility gradually increases according to the greater age at 

 the time of marriage. 



Chapter V. — Expectation of Sterility. 



The main element in the expectation of sterility is the age of the woman at 

 marriage. This has just been described. But, besides this, our statistics suggest 

 to us other laws as to the expectation of sterility. Of these the first is : — 



That the probability of a woman 's being sterile is decided in 3 years of married 

 life. For while a large number are fertile in each of the first three years of 

 married life, only 7 per cent, of the fertile bear after 3 years of marriage, or about 

 1 in 13. 



TABLE II. — Showing the Fertility of Mothers, of different Ages at Marriage, 



COMMENCING AFTER THREE YEARS OF MARRIED LlFE. 



Mother's Age at Marriage, . 



15-19 



20-24 



25-29 



30-34 



35-39 



40-44 



45-49 



Total. ! 



Number of Fertile, 



649 



1905 



809 



251 



96 



10 



2 



3722 



Number commencing Fertility 1 

 after being 3 years married, J 



63 



119 



62 



27 



15 



1 





287 



Percentage commencing Fer- \ 

 tility after being 3 years > 



9-7 



6-2 



7-7 



10-7 



15-6 



10-0 



... 



7-7 





10-3 



160 



13-0 



9-3 



6-4 



100 



... 



13-0 



This same Table affords us a second law of expectation of sterility : — 

 That when the expectation of fertility is greatest, the probability of sterility is 

 soonest decided, and vice versa. For our Tables show that of the wives married 

 from 20 to 24 who are all fertile, only 6 2 per cent, begin to breed after three 

 years of marriage ; while at the other ages, with less fecundity, a greater per- 

 centage commences after the completion of the third year of marriage. 



Chapter VI. — Relative Sterility. 



Here I take into consideration only those who have borne children, only those 

 who are not sterile. Of course all these wives, if they survive in wedlock, will 

 sooner or later become relatively sterile. Now, in a paper lately read to this 

 Society, I showed that the prolongation of fertility was greater according as the 

 age at marriage was less. From this conclusion it is easy to derive one in regard 

 to relative sterility, to the effect that : — 



Relative sterility will soone? arrive according as the age at marriage is greater 





