980 THE PHYSIOLOGY OF REPRODUCTION. 



most fully perhaps by Fraenkel,* who believes that this internal 

 secretion is furnished by the yellow cells of the corpus luteum. 

 This observer, from the results of operations upon women, believes 

 that the ovum is normally discharged two weeks before menstrua- 

 tion, and the resulting increased activity of the cells of the corpus 

 luteum is responsible for the secretion which stimulates the uterus 

 to the augmented growth that takes place in the premenstrual 

 period. Whether or not the monthly change in the endometrium 

 is directly dependent upon an internal secretion from the ovary or 

 is an independent cyclic process peculiar to this tissue, there seems 

 to be no doubt that the physiological integrity of the uterus as a 

 whole is dependent upon the ovaries. Removal of the ovaries 

 in the young prevents the normal development of the uterus, 

 while removal in the adult causes a degeneration of the uterus, 

 which, however, can be averted by a successful transplantation 

 of ovarian tissue, f In the lower animals Marshall and Jolly | 

 have been able to show that extracts of the ovaries, taken from 

 an animal in or just before heat (procestrous or oestrous period), 

 when injected into an animal during the anoestrum bring on a 

 transient condition of heat. These authors do not believe, how- 

 ever, that the chemical stimulus (hormone) formed in the ovary 

 is developed by the cells of the corpus luteum, since according 

 to their observation on cats and dogs ovulation does not occur 

 until after heat has begun (procestrum) ; nor does it depend upon 

 the mere maturation of the follicles, since when these are opened 

 by puncture, some time before maturation, heat appears in due 

 season. 



The Physiological Significance of Menstruation. — Naturally 

 many views have been proposed to explain the significance of men- 

 struation. According to the Mosaic law, it is a process of purifica- 

 tion; others have seen in it a mechanism to remove an excess of 

 nutriment in the body ; but since the period in which our knowl- 

 edge of the structure of the organs concerned and of the histo- 

 logical changes during the act became more definite, theories of the 

 meaning of menstruation have usually assumed that it is a prepara- 

 tion for the reception of the fertilized ovum. These views have 

 taken two divergent forms according as the act of ovulation was 

 believed to precede or to happen simultaneously with or subse- 

 quently 10 the act of menstruation. According to one view, the 



* Fraenkel, "Archiv f. Gynakologie," 68, 2, 1903. See also Ihm, "Monat- 

 schrift f. Geburtshtilfe u. Gynakol.," 21, 515, 1905, for discussion and extensive 

 literature. 



t Carmichael and Jolly, "Proc. Roy. Soc," B, 79, 1907, and Marshall 

 and Jolly, "Roy. Soc. Edinb.," 45, 589, 1907. 



t Marshall and Jolly, "Philosophical Transactions, Royal Society," 

 London, 1905, B. cxcviii., 99; also Marshall and Runciman, "Journal of 

 Physiology," 49, 17, 1914. 



