THE HORMONES IN HUMAN REPRODUCTION 



settles gently and inconspicuously back to the state it was 

 in before the follicles matured. 



Theories about the menstrual cycle. There is no need to 

 discuss outmoded theories of the cycle here, except to exclude 

 one or two ancient fallacies that still crop up occasionally. 

 For example, some people still consider that menstruation is 

 equivalent to estrus. This is a common notion among farmers. 

 Because menstruation is the most prominent event in the 

 human cycle, and estrus the most conspicuous phenomenon 

 in the cycle of the barnyard animals, they are wrongly con- 

 sidered to be fundamentally alike. It would follow from this 

 that in humans the egg is shed from the ovary at the time 

 of menstruation, a notion which is absolutely incorrect, as 

 will be seen from our previous discussion. Menstruation is 

 the last stage, not the first, of the corpus luteum phase of 

 the cycle. 



Another false view, which prevailed widely among Euro- 

 pean gynecologists from 1880 to 1910, asserted that there 

 is no chronological relation whatever between ovulation and 

 menstruation. The egg may be shed at any stage of the cycle. 

 This conclusion was drawn by surgeons who knew very little 

 about other species, and who moreover usually saw at the 

 operating table not normal pelvic organs, but those of 

 patients with gynecological ailments, often subject to dis- 

 turbances of the cycle. 



When it began to be understood clearly that the ovary 

 is an organ of internal secretion, a group of first-class 

 German gynecologists, including especially Robert Schroeder, 

 Robert Meyer, and Ludwig Fraenkel (the latter two now in 

 exile) developed a theory which had been vaguely outlined 

 a generation earlier, that the corpus luteum is in some way 

 associated with the menstrual cycle. Gradually their views, 

 clarified by intensive observation of human material, ar- 

 ranged themselves into a theory of the cycle which was very 

 plausible and which has turned out to be partly correct. 



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