THE MENSTRUAL CYCLE 



the problem in the light of our knowledge of the hormones. 

 To resume this subject where we left off on page 75, there is 

 scarcely any doubt at present that the cycle is somehow 

 produced by interplay of hormones from the ovary and the 

 pituitary gland. 



If we look at the pituitary gland or hypophysis (Plate 

 XIX and Fig. 20) we find that this gland of internal secretion 

 is composed of two major parts, the anterior and the poste- 

 rior lobes. It is the anterior lobe which produces hormones 

 (probably two in number) having the power of stimulating 

 the ovary to produce estrogenic hormones and of promoting 

 the growth of ovarian follicles. They also affect the male 

 organism, causing the testes to grow and produce sperm cells. 

 Because of these actions the hormones we are discussing are 

 called gonadotrophic, a name which signifies "producing 

 growth of the sex glands." From the brilliant work of P. E. 

 Smith, Bennett Allen, H. M. Evans, Zondek and Aschheim, 

 and many others between 1915 and the present time, we have 

 learned (as mentioned in Chapter III) that removal of the 

 anterior lobe of the pituitary stops growth of the ovaries and 

 puts an end to the cycles of the animal. By implanting bits of 

 anterior pituitary, or better by injecting extracts of the gland 

 into immature animals, the ovaries are caused to grow and 

 the cycle to begin. The ovary is thus absolutely dependent 

 upon this action of the pituitary. Removal of the anterior 

 lobe produces all the effects of castration, for without it the 

 sex glands, ovary and testis, deteriorate to inactivity. On the 

 other hand, there is a good deal of evidence that the estro- 

 genic hormone of the ovary represses the production of the 

 pituitary gonadotrophic hormones. After removal of the 

 ovaries, the pituitary gland is found to contain more gonado- 

 trophic potency than before; after injection of estrogenic 

 hormones it contains less (Appendix II, note 11). 



When these facts became known, a fairly clear explanation 

 of the reproductive cycle suggested itself almost simultane- 



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