AND FECUNDITY OF WOMEN ACCORDING TO AGE. 489 



according to the age of the mother, also to the frequency of twins and triplets 

 according to the mother's age. But the results of these investigations have been 

 so imperfect or unsatisfactory that I do not now describe them. 



The views hitherto entertained regarding the influence of age on fecundity have 

 been various. " In regard to age (says Burdach*) fecundity is diminished in the 

 first and last portions of the continuance of the aptitude for procreation. The elk. 

 the bear, &c., have at first only a single young one, then they come to have most 

 frequently two, and at last again only one. The young hamster produces only 

 from 3 to 6 young ones, whilst that of a more advanced age produces from 8 to 

 16. The same is true of the pig. This rule appears to be general, since it applies 

 also to the entomostracese ; according to Jurine, the number of the young of the 

 Monoculus pulex is at first from 4 to 5, afterwards rising gradually as high as 

 18. We scarcely ever encounter the births of 3 or 4 children, except in women 

 who have passed the thirtieth year. Precocious marriages are not only less 

 fertile, but the children also which are the result of them have an increased rate 

 of mortality. According to Sadler, every marriage in the families of the peers of 

 England yields 4-40 children when the woman was married below 16 years of 

 age ; 4-63 from this age to 20 ; 5-21 from 20 to 23 ; and 5-43 from 24 to 27." The 

 notions here expressed by Burdach are in the main correct ; but it is evident 

 that they are very indefinite. They are to be regarded, also, more in the light of 

 happy guesses than of well-founded opinions. Burdach evidently places chief 

 reliance on the evidence afforded by the numbers at a birth. From many quar- 

 ters I have received corroboration of Burdach's statements regarding the increase 

 and subsequent decrease of the number produced at a birth by pluriparous animals, 

 and I have received similar information regarding bitches, guinea pigs, the fertility 

 of hens, &c. When I first paid attention to this subject, the plural births of women 

 appeared to me to form a simple key for the determination of the fecundity of 

 women at different ages. But I soon became dissatisfied with the materials I 

 quickly collected. Woman is not a pluriparous animal, neither does she produce 

 so regularly, or according to season, as the animals with which she is compared. 

 In her the occurrence of twins and triplets is an exception to the normal rule, 

 and the number of children born by her cannot be so simple and sure a test of 

 fecundity, as in the case of animals having multiple litters at stated periods. 

 Indeed, it is apparent that the evidence derived from plural births alone in women 

 may positively mislead, for a woman may be more fertile bearing one child at a 

 time frequently than another bearing twins or triplets more seldom. In this 

 place I shall only say, that the numerical study of twins, in reference to the age of 

 the mother, yields interesting results, which do not confirm Burdach's statement 

 , regarding them, yet are not hostile to the conclusions of this paper. Burdach. 

 in his Avork, describes an annual rise and fall in the fecundity of some pluriparous 



* Physiologie, torn. ii. page 117. 



