THE MENSTRUAL CYCLE 



to occur, therefore, when the reproductive tract is preparing 

 for its highest activity or receding from it. My papers de- 

 scribing the monkey cycle set off an active debate among 

 the gynecologists as to whether anovulatory cycles occur 

 in women. After much discussion and a great deal of careful 

 observation, it is generally agreed that anovulatory cycles 

 do occur, though with much less frequency than in monkeys. 

 They seem to be most frequent in young girls and in women 

 approaching the menopause. 



There is no place for menstruation without ovulation, in 

 the theoretical scheme which I have called the German theory. 

 Therefore the savants who had formulated that theory 

 simply declared that anovulatory menstruation is not men- 

 struation at all. The rest of us, however, have gone on trying 

 to find an explanation that fits all the facts. In this search 

 the new knowledge of the ovarian hormones has begun to 

 help us. 



THE HORMONES AND MENSTRUATION 



Experimental uterine bleeding. A simple experiment, made 

 in 1927 by Edgar Allen, opened up the whole problem of the 

 relation of the ovarian hormones to menstruation. Allen 

 found that removal of both ovaries from a mature Rhesus 

 monkey will usually cause within a few days a single period 

 of menstruation-like bleeding. Why the medical profession 

 had failed to discover this fact from human surgical patients 

 is difficult to understand. It has long been known that removal 

 of the ovaries abolishes the menstrual cycles, but the doctors 

 had missed observing the fact that one period of hemor- 

 rhage often follows the operation before the cycles cease 

 permanently. They seldom remove the ovaries except in the 

 presence of disease, when the cycles are already altered, or 

 for tumors which themselves produce bleeding, or as part of 

 a larger operative procedure which may cause surgical 

 hemorrhage from the uterus. Thus bleeding due purely to 



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