Age Changes in the Ovary 119 



controlling the destructive processes of atresia, but also on 

 stimulating continued division in the cells of the germinal 

 epithelium after they have ordinarily become inactive. 



There is no need to discuss fully the evidence for and against 

 these two views since it has been summarised and criticised 

 in detail by Zuckerman (1951) who supports the older view 

 in his summing up. Two things stand out. The first is the 

 extraordinary paucity of reliable counts of the total number 

 of follicles in the ovary of any species at different ages, and 

 the difficulty of forming a satisfactory picture of oogenesis 

 by piecing together a series of discontinuous histological 

 observations. Second, neoformation, even if it occurs at all, 

 is totally insufficient in women and partly insufficient in other 

 animals to compensate for the atresia that takes place. 



Age changes in the ovum 



However long or short the life of an oocyte before its final 

 maturation may ultimately turn out to be, the ovum certainly 

 does not go on living for very long after ovulation and the 

 present trend of opinion is to reduce even more the interval 

 during which the ovum is thought capable of being fertilised. 

 Probably its entire lifespan is less than twenty-four hours and 

 even within this interval the ovum's capacity to develop into a 

 normal embryo falls off progressively. The work of B landau 

 and of Young (1953) has shown that, in both guinea pigs and 

 rats, the proportion of embryos, with defects of development 

 increases as the time interval between ovulation and fertili- 

 sation is increased. The ability of the ovum to become 

 fertilised is not, however, altered in the same way. The 

 proportion of fertilised ova in the tubes is not changed and 

 it is only in the later stages of implantation and development 

 that the influence of the ovum's age becomes apparent. 

 This finding applies to cattle as well, according to Barrett 

 (1948), who has studied the conception rates in dairy cows 

 artificially inseminated at varying intervals after ovulation. 

 These observations may be of importance in any consideration 

 of the problem of abortion in women since the natural 



