68 Discussion 



follicles luteinized, and we have seen a number of cases where only a part 

 of the small follicle was luteinized, forming a little partial accessory 

 corpus luteum one side of a tiny follicle. The other side of that follicle 

 was in full atresia. 



I have formed the notion that a process of partial atresia, or something 

 very much like it, is an essential step in the conversion of granulosa 

 cells into granulosa lutein cells. 



Amoroso : That may also be the case in the ovary of the foetal giraffe 

 where atresia is widespread and is accompanied by the conversion of 

 granulosa cells into granulosa lutein cells. 



Dempsey: Is there any possibility that there are at least two types of 

 atresia ? I was struck by Mr. Williams' pictures of his oestrogen-treated 

 animals which showed an atresia occurring at the base of the follicle as 

 opposed to the generally occurring location near the antrum. Then, 

 there was the phenomenon Dr. Parkes mentioned, that these eggs were 

 extraordinarily well preserved in the atretic follicles, whereas in the 

 atresia that occurs after ovulation in the guinea pig ovary it is my 

 impression that the egg shows changes very rapidly indeed. So, is 

 it possible that we are confusing perhaps two different physiological 

 mechanisms ? 



Williams: The process of atresia in the oestrogen-treated animal is 

 obscure to me. You don't seem to see the intermediate stages. Un- 

 fortunately my material is very scanty between the fifth and the tenth 

 day after hypophysectomy and oestrogen treatment. You do see what 

 are obviously remnants of atretic follicles, which have obviously under- 

 gone atresia since treatment started. The general appearance is rather 

 different from those in the normal animal. I think this is a different 

 form of atresia. 



Strauss: Is not atresia the normal fate of an egg follicle, and matura- 

 tion and ovulation only the exception? In humans, for example, the 

 400 eggs, approximately, which ovulate during the fertile period are 

 unimportant compared with the 400,000 primary follicles. Therefore, 

 there are many more atretic follicles than ripening follicles. What sig- 

 nificance do such atresia and atretic follicles have? 



Harrison: I was interested to hear you say that you thought granu- 

 losa cells had only a short life. Some years ago I carried out some ex- 

 periments in puncturing mature follicles of the rabbit ovary and with- 

 drawing granulosa cells and then culturing them. They grew, interest- 

 ingly enough, into a series of spheres for two, three or four days; I could 

 never get them to grow longer than that. If, however, minute quantities 

 of a water-soluble oestrogen were added, then the spheres increased in 

 size and would live for several days longer. 



Williams: That would fit perfectly well with what I think happens. 

 By giving oestrogen you increase the life of the follicle cells for perhaps 

 a few days but no longer. Perhaps there is an analogous situation in the 

 ovarian interstitial cells in Prof. Zuckerman's X- irradiated animals. 

 It may be that these cells too have a limited life, and in fact vaginal 

 cornification may cease because there is no continual renewal of 

 interstitial tissue from atretic follicles in the X-irradiated animals. 



