878 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. In the lower animals Marshall and Jolly f have been able 

 to show that extracts of the ovaries, taken from an animal in or 

 just before heat (prooestrous or oestrous period), when injected into 

 an animal during the anoestrum bring on a transient condition of 

 heat. These authors do not believe, however, that the chemical 

 stimulus (hormone) formed in the ovary is developed by the cells 

 of the corpus luteum, since according to their observations on cats 

 and dogs ovulation does not occur until after heat has begun (pro- 

 oestrum) . 



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

 swelling and congestion of the membrane constitute a prepara- 

 tion for the reception of the fertilized ovum. If the ovum fails of 

 fertilization, then degenerative changes ensue, and the membrane 

 or a portion of it is cast off in the menstrual flow, while the re- 

 mainder is absorbed. According to this view, menstruation is an 

 indication that fertilization has not taken place. J This view 

 falls in with the belief that ovulation normally precedes menstrua- 

 tion by a considerable interval. The other point of view was 

 advocated especially by Pfliiger in connection with his theory of the 

 common cause of ovulation and menstruation. He assumed that 

 menstruation occurs before the ovum reaches the uterus and that 



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

 " Monatsschrift f. Geburtshiilfe u. Gynakol.," 21, 515, 1905, for discussion 

 and extensive literature. 



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

 London, 1905, B. cxcviii., 99. 



J This view finds expression in the aphorisms: "Women menstruate 

 because they do not conceive," Powers, and "The menstrual crisis is the 

 physiological homologue of parturition," Jacobi. 



