THE PERIODICITY OE CESTRUS 149 



not dependent upon the production of oestrin. Zondek (647) 

 draws attention to this absence of correlation as follows: ' Wir 

 haben also festgestellt: das Ei beherrscht nicht das Hormon, das 

 Ovarialhormon beherrscht aber auch nicht das Ei. Ei und 

 Ovarialhormon stehen nebeneinander, sind koordiniert, sind 

 gleichberechtigt. Sie stehen aber unter der Herrschaft einer 

 zentralen Regulation. . . .' 



x-\ll this initial work paved the way for the discovery of 

 the influence exerted on the ovary by the anterior pituitary 

 body, and it is possible to assert definitely at this stage that the 

 regulation of ovarian periodicity is controlled by the anterior 

 pituitary, and that ovarian regulation is therefore external to 

 the ovary itself. The same conclusion is indicated by numerous 

 experiments on ovarian grafts. 



(e) REASONS FOR SUPPOSING 0\^\RIAN REGULATION 

 TO BE EXTERNAL 



The hypothesis that the periodicity of ovarian endocrine 

 activity depended upon the periodicity of its cyclic structures 

 seemed so well-founded that small attention was originally 

 paid to the facts which implied that the regulation of the ovary 

 might be to some extent external. Recent work on the mechanism 

 of the oestrous cycle, however, has brought these experiments 

 into prominence. 



Ovarian grafts. As long ago as 1900 it was shown by Foa (207) 

 that extraordinary effects were obtained by grafting the ovaries 

 from one animal into an animal of a different age. He found 

 that the ovary of the immature animal grafted into an ovariec- 

 tomized adult underwent rapid development and attained a 

 state of maturity long before it would have done so in its 

 original environment. Many experiments have been made in 

 confirmation of Foa's original observations (365, 367) ,and further 

 details have been added. Converse experiments have show^n that 

 an adult ovary grafted into an ovariectomized immature female 

 loses both its histological and endocrine cyclic activity. Control 

 operations have shown quite adequately that neither effect is 

 due to manipulation, and it must be concluded, therefore, that 

 the ovarian age is regulated by that of the soma. Parallel 



