THE HORMONES IN HUMAN REPRODUCTION 



THE UNKNOWN SIGNIFICANCE OF MENSTRUATION 



In all this discussion of the nature and the course of men- 

 struation, we have had nothing to say about the significance 

 and possible usefulness of the periodic breakdown and hemor- 

 rhage. The human mind has an intractable desire that natural 

 phenomena shall be useful. We are not comfortable in the 

 presence of useless or undirected activity. Menstruation in 

 particular ought to have a practical reason for its occur- 

 rence, for otherwise it seems a totally wasteful, destructive, 

 and vexatious business. Up to the present, however, no one 

 has been able to demonstrate such a meaning. There are in 

 fact only two guesses that are even worth talking about. 



The late Walter Heape of Cambridge, England, one of the 

 pioneers in the study of the reproductive cycle, proposed in 

 1900 that menstruation is the same thing as a period of 

 bleeding that occurs in female dogs when they are going into 

 heat, i.e. in the week preceding ovulation. A somewhat similar 

 proestrous bleeding occurs in cows, particularly in heifers. 

 Such bleeding is easily explained, for it is clearly due to 

 engorgement of the blood vessels produced by a strong action 

 of the estrogenic hormone. Under the microscope it does not 

 resemble menstruation ; the blood oozes from superficial blood 

 vessels and there is little or no breakdown of the tissues. When 

 Heape wrote, nothing was known of the time of ovulation in 

 the primate cycle, nor of the premenstrual endometrium and 

 its dependence upon the corpus luteum. In the primates, on 

 his theory, ovulation would be expected to occur during men- 

 struation, or immediately after the flow, just as in the bitch 

 and cow ovulation occurs about the end of the proestrous 

 bleeding. Since we know now that ovulation takes place a 

 week to ten days after the cessation of menstruation, we can 

 reconcile Heape's theory with the facts only by supposing 

 that in the menstruating primates there is first proestrous 

 bleeding, then a delay unknown in the other animals, and 



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