THE HORMONES IN HUM AN REPRODUCTION 



obtained bleeding by estrin deprivation in monkeys from 

 which he had removed the whole pituitary gland. Adrenin 

 has been thought of, but Edgar Allen succeeded in producing 

 estrin-deprivation bleeding in monkeys from which the adrenal 

 glands had been removed. This experiment is not quite conclu- 

 sive, for monkeys may possibly have other sources of adrenin 

 beside the adrenal gland. Up to the present, at least, this 

 hypothesis has yielded no valuable clues. 



Hypothesis 4. George Van S. Smith and 0. W. Smith have 

 suggested that the bleeding of menstruation is caused by 

 conversion of estrogenic hormone into a non-estrogenic by- 

 product which is toxic to the endometrium. This hypothesis 

 could perhaps explain ovulatory cycles, but it cannot be fitted 

 very well to simple estrin-deprivation bleeding; in any case 

 it will be acceptable only when somebody comes forward with 

 chemical derivatives of the estrogenic hormones that are 

 especially toxic to the endometrium (Appendix II, note 14). 



These are the most plausible current guesses about the im- 

 mediate cause of uterine bleeding after hormone deprivation. 

 None of them has been proved or even rendered likely, by 

 experiment. It is indeed vexatious that we cannot clear up 

 this important problem. 



The modern concept of the cycle. By way of summary, let 

 us now set forth a concise description of the primate cycle 

 as revealed by recent research. What follows will, I think, be 

 accepted by most of the American investigators, and also the 

 British, although a die-hard English gynecologist a few years 

 ago dubbed it "the American theory." 



We begin by suggesting that there is a basic tendency to 

 cyclical function of the ovaries, and that this is produced by 

 a sort of reciprocal "push-pull" reaction between the pitui- 

 tary and the ovarian hormones, as explained in full earlier 

 in this chapter. In most cycles of fully mature human females, 

 the pituitary gonadotropic hormones cause the ripening of 



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