History and Fate of Redundant Follicles 61 



shows the progressive loss of weight in the ovaries after 

 hypophysectomy and the maintenance of weight if a stilb- 

 oestrol tablet is implanted at the time of operation. The 

 same effects can be produced by daily injections of 50-100 [ig. 

 of oestrone. 



The histological effects of the treatment are striking. The 

 ovary of the normal immature rat (Fig. 5) contains follicles 

 in various stages of development and atresia, and almost 

 all with a mean diameter greater than 200 \i are vesicular. 

 (Hereafter, it is only follicles of this size that are counted and 

 discussed.) There is little change in the general appearance 

 during the first five days after operation in the untreated 

 animal though more of the vesicular follicles are now atretic, 

 and by the 15th day (Fig. 6) the follicular apparatus is almost 

 non-existent. If oestrogen treatment is started at operation 

 then by the 5th day the ovary is full of medium-sized follicles 

 almost all of which are solid — suggesting that oestrogen 

 stimulates proliferation of the membrana granulosa — and 

 this condition persists until the 15th day at least (Fig. 7), 

 though by this time the follicles are not quite such a pro- 

 minent feature of the ovary as they were at the 5th day. If 

 oestrogen treatment is delayed until seventeen days after 

 operation there is no recovery of ovarian weight, though some 

 remaining rudimentary follicles are stimulated and enlarge 

 (Fig. 8). I think this proves that the stimulation depends upon 

 the presence in the ovary of follicles already possessing a 

 membrana granulosa (it does not effect primordial follicles) 

 but does not depend upon the presence of gonadotrophin in 

 the circulation. Quantitative study of the immediate effects 

 (Table II) shows that the number of follicles per ovary with a 

 diameter of more than 200 \i is actually increased by the 

 oestrogen treatment, that most of these follicles are solid 

 (and in fact those called vesicular mostly show only that 

 localized fragmentation of the membrana granulosa that is 

 the first sign of antrum formation), and that the size of the 

 largest follicle in each ovary remains more or less constant. 

 In the untreated animal the number of follicles of this size 



