148 INTERNAL SECRETIONS OF THE OVARY 



p. 126). The difficulties in the way of explaining the periodicity 

 of oestrus on the ground that the ovary regulates its own 

 periodicity, complicated the explanation of the results of X-ray 

 sterilization. Recently, however, the discovery of the pituitary- 

 ovary mechanism has made possible a simpler explanation. 



Synchronization of oestrus and follicular maturation. It was 

 originally thought from the X-ray experiments that the 

 oestrus-producing hormone caused the maturation of the follicle 

 as the oestrous change in the ovary, in the same way as it caused 

 oestrous changes in the accessory organs. This possibility was 

 supported by the discovery that in the mouse the maturation 

 growth of the follicle does not start until the cestrus-producing 

 stimulus has become active (see p. 136). On this view the 

 oestrous changes in the accessory organs and the maturation of 

 the follicle would be synchronized by their both being 

 due to a common stimulus, namely the oestrus-producing hor- 

 mone. It has not been possible, however, to substantiate this 

 hypothesis, owing to the fact that follicular maturation cannot 

 be induced by the injection of the oestrus-producing hormone at 

 times when it would not otherwise occur, such as during the 

 lactation dioestrus, during pseudo-pregnancy, or during preg- 

 nancy (see p. 119). 



{d) OCCURRENCE OF FOLLICULAR MATURATION 

 WITHOUT (ESTRUS 



The opposite result to the occurrence of oestrus after follicular 

 ablation, i.e. the occurrence of follicular maturation without 

 oestrus, has been very ingeniously produced by Zondek (647), 

 who, by feeding thallium to mice, was able to suppress all cyclic 

 changes in the accessory organs. This suppression probably 

 means that the production of cestrin was inhibited; but never- 

 theless the histological ovarian cycle was unaffected, ovulation 

 and the formation of corpora lutea taking place. The matura- 

 tion of the Graafian follicle in these animals, therefore, cannot 

 have been dependent upon the production of oestrin. It is thus 

 possible to reach the conclusion that the production of oestrin 

 is not dependent upon the maturation of the Graafian follicles, 

 and, conversely, that the maturation of the Graafian follicles is 



