60 



P. C. Williams 



although retaining an endocrine function as shown by histo- 

 chemistry (Dempsey and Bassett, 1943; Claesson and Hillarp, 

 1947; Deane, 1952) and X-irradiation studies (Brambell and 

 Parkes, 1927; Parkes, 1927), are not so prominent as in other 

 species, for example in the rabbit, where they hypertrophy to 

 form an interstitial gland. Thus the fate of the redundant 

 follicle is partly to disappear completely, partly to persist to 

 form part of the endocrine tissue of the ovary. 



Now to come to the history of atresia. It has been stated 

 that atresia occurs in cycles in the guinea pig (Aron and Aron, 

 1953) and mouse (Engle, 1927), being most marked after 

 ovulation in the guinea pig, and during the first day of di- 

 oestrus in the mouse, though no such cycle has been proved 

 in the rat (Mandl and Zuckerman, 1950). If there is such a 

 correlation, then it is some evidence that atresia is conditioned 

 by hormonal changes and it is this aspect of the subject I wish 

 to discuss. 



First of all I should like to recapitulate some old work on the 

 direct effects of oestrogen on the ovary (Williams, 1944). If 

 an immature rat is hypophysectomized the ovaries atrophy. 

 This atrophy can be at least partly prevented by treatment 

 with oestrogen starting at the time of operation. Table I 



Table I 

 Ovarian Weight in Immature Rats after Hypophysectomy, or Hypo- 



PHYSECTOMY AND THE IMPLANTATION OF A STILBOESTROL TABLET 



5 rats per group. Ovarian weight in 20 normal immature rats =8 -2 mg. 



