MENSTRUATION 335 



five or six days preceding the flow, the uterine mucous mem- 

 brane gradually thickens, the glands become longer and more 

 tortuous, the connective tissue cells multiply and the blood-ves- 

 sels are greatly increased in size. This is apparently a prep- 

 aration for the reception of the impregnated ovum. A short 

 time before the flow begins there is hemorrhage into the subepi- 

 thelial tissue, possibly by diapedesis, possibly by rupture. In a 

 day or so the superjacent mucous membrane becomes disinte- 

 grated and is discharged with the included parts of the glands. 

 The underlying vessels, being thus exposed, rupture and the san- 

 guineous discharge carries away the debris. 



For three or four days subsequent to the cessation of the flow 

 the uterine mucosa is being repaired. The deeper layers, in- 

 cluding the deeper portions of the glands, were not cast off, and 

 the whole is reconstructed from the intact parts. Following the 

 reconstructive period there is a stage of quiescence lasting some 

 two weeks, until six or seven days prior to the next menstruation. 



At the beginning of each menstrual flow there is general con- 

 gestion of the pelvic viscera and mammary glands, accompanied 

 usually by headache and a sense of pelvic oppression. The 

 congestion and discomfort begin to disappear when the flow is 

 established. 



Ovulation probably in most cases takes place just before the 

 menstrual flow begins, but neither occurrence is dependent upon 

 the other. Ovulation has frequently been shown to take place 

 in the inter-menstrual period, but the congestion of the repro- 

 ductive organs incident to menstruation probably hastens the 

 rupture of any Graanan follicle which at that time happens to 

 be near the completion of its development. 



The relations between ovulation, menstruation and impregna- 

 tion are not definitely determined. Pregnancy lasts for ten 

 lunar months and dates from the time of impregnation (concep- 

 tion), but that time cannot in any case be fixed upon with pre- 

 cision. The vitality of the ovum is thought not to last longer 



