THE FEMALE REPRODUCTIVE ORGANS. 845 



luteum furnishes the secretion which stimulates the uterus to the 

 augmented growth that takes place in the premenstrual period. 

 This view, as well as other most important functions which this 

 author attributes to the specific tissue of the corpus luteum, have 

 not been conclusively demonstrated. At present perhaps it is 

 wiser to adopt the more cautious theory that some element in the 

 ovary furnishes an internal secretion which is normally necessary 

 to the nutrition of the uterus, and whose augmentation during the 

 growth of a Graafian follicle leads to the greater metabolism charac- 

 teristic of the premenstrual period. 



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.* This view is 

 probably the one most generally accepted to-day, and falls in with 

 the belief that ovulation normally precedes menstruation 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 menstrua- 

 tion occurs before the ovum reaches the uterus and that its physio- 

 logical value lies in the fact that a raw surface is thus made upon 

 which the ovum is grafted. Menstruation, according to him, is 

 an operation of nature for the grafting of the fertilized ovum upon 

 the maternal organism. This view finds some support in the fact 

 that in some of the lower animals (dogs) the flow of blood precedes 

 fertilization. 



The Effect of the Menstrual Cycle on Other Functions. It 

 is natural to suppose that such marked changes as occur in the 



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

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

 ological homologue of parturition," Jacobi. 



