History and Fate of Redundant Follicles 63 



Aron, 1953; Aron and Aron, 1953) that a single injection of 

 a crude extract of beef anterior hypophysis produces at a 

 certain dose level atresia of virtually all the follicles in the 

 ovary of the guinea pig. As the dose injected is increased 

 these effects are produced; firstly, follicle stimulation; with a 

 larger dose, atresia; with a still larger dose, luteinization ; 

 and with the highest doses, atresia again. Within the limits 

 producing atresia, the higher the dose the quicker the effect. 

 At first sight, this observation seems to conflict with the 

 increase in atresia produced by hypophysectomy in the 

 immature rat — but I am not sure that there is a conflict. 

 I believe that the operation of hypophysectomy releases 

 gonadotropin into the circulation. The figures in Table I 

 suggest that there is an interruption in the ovarian weight loss 

 on the 3rd day after hypophysectomy. The difference in 

 ovary weight at this point is not statistically significant but 

 I think it is a real one, and Lane and Greep (1935) made a 

 similar observation. There is some supporting evidence for 

 the suggestion that this temporary, slight recovery of ovarian 

 weight is real and a reflection of endogenous gonadotrophin. 

 When a single dose of the gonadotrophin from pregnant mares' 

 serum is given 3-4 days after hypophysectomy to immature 

 rats, the ovarian response is greater than it is if the injection 

 is made before or after this time (Williams, 1945). I think it 

 may well be that gonadotrophin hastens the follicular atresia 

 which certainly occurs, however, in its absence — 21 days 

 after hypophysectomy there are still some follicles in the ovary 

 and some of these are undergoing atresia though the propor- 

 tion (only about 15 per cent) seems to be subnormal. 



When we study the ovaries of the oestrogen-treated, 

 hypophysectomized rats there is a different picture. During 

 the first four days after operation there are less atretic 

 follicles than there are in the untreated animal — there are 

 6-12 instead of 20-30. Apparently oestrogen retards atresia. 

 But on the 5th day something new appears. Fragmentation of 

 the membrana granulosa occurs resembling, so far as one can 

 see from a haematoxylin-eosin preparation, the preliminary 



