132 INTERNAL SECRETIONS OF THE OVARY 



The most difficult problem in connection with the distribution of 

 oestrin is to explain its abundance in the body fluids during 

 pregnancy, i.e. during the luteal phase, and to explain why this 

 abundance does not result in the appearance of cestrus and 

 abortion. A priori the excess of oestrin during pregnancy 

 suggests strongly that it is responsible for the changes of the 

 luteal phase. Two explanations more in keeping with the mass 

 of evidence discussed above may be put forward: 



(a) In spite of the large amounts of oestrin in the body fluids, 

 the corpus luteum may still be dominant. 



{h) There is some evidence (see p. i88) that the preliminary 

 action of oestrin is necessary for the effective action of 

 the luteal hormone. In this case the presence of oestrin 

 during pregnancy may be a necessary complement to 

 the action of the corpus luteum. 



In either case the idea of a balance between oestrin and the 

 corpus luteum (see p. 182) is a necessary assumption. The 

 refinement of methods for obtaining the luteal hormone from 

 body fluids should enable this point to be decided. The source 

 of the large excess of oestrin during pregnancy has usually been 

 put down to its elaboration by the placenta, but Fellner 

 (194) considers it to be due at least in part to the activity of the 

 ovarian interstitial tissue. 



Significance of occurrence in placenta. The abundance of 

 oestrin in the placenta has led many workers, notably Allen (12) 

 and Aschheim (36) to conclude that elaboration of the hormone 

 is carried on in this organ. It is, however, almost as difficult 

 to assume that oestrin is elaborated by the placenta as to assume 

 the opposite. The only evidence in favour of its elaboration by 

 the placenta is its abundance in the organ, and this is far from 

 conclusive. On the other hand, various workers have shown that 

 the injection of oestrin during pregnancy leads to reabsorption 

 or abortion, and its secretion by the placenta would thus be a 

 definite anomaly. Weight for weight, the placenta contains 

 as much oestrin as the ovaries, and since the weight of the 

 placenta may be anything up to 500 times as much as the ovaries, 

 it contains about 500 times as much oestrin. If the placenta 

 elaborates oestrin, therefore, and at the same rate as the ovaries. 



