778 THE REPRODUCTIVE ORGANS 



between periods of heat. Although conception is not confined to the periods 

 of menstruation in the human species, yet it is more likely to occur about a 

 menstrual epoch than at other times. 



The exact relation between the discharge of ova and menstruation is not 

 very clear. In animals, the physiological analogy of menstruation appears to 

 be found in the proaestral processes, which are the preliminary stages of heat, 

 and occur immediately before ovulation. It was formerly believed that men- 

 struation was the result of a congestion of the uterus arising in association 

 with the enlargement and rupture of a vesicular ovarian follicle; but though a 

 vesicular ovarian follicle is, as a rule, ruptured at each menstrual epoch, yet 

 instances are recorded in which menstruation has occurred where no ovarian 

 follicle can have been ruptured, and cases where ova have been discharged in 

 amenorrheic women. It must therefore be admitted that menstruation is 

 not strictly dependent on the maturation and discharge of ova. 



Observations made after death, and facts obtained by clinical investiga- 

 tion, support the view that rupture of a vesicular ovarian follicle does not 

 happen on the same day of the monthly period in all women. In the minor- 

 ity of cases it may occur toward the close or soon after the cessation of a 

 flow. On the other hand, in almost all subjects examined after death, of 

 which there is record, rupture of the follicle appears to have taken place 

 before the commencement of the menstrual flow. 



However, the presence of the ovaries seems necessary for the performance 

 of the menstrual function; for women do not menstruate when both ovaries 

 have been removed by operation. See page 498 for a discussion of the 

 functional effects of removal of the ovary. 



Source and Character of Menstrual Changes. The menstrual periods 

 usually occur at intervals of a lunar month, the duration of each being from 

 three to six days. In some women the intervals are so short as three weeks 

 or even less; while in others they are longer than a month. The periodical 

 return is usually attended by pains in the loins, a sense of fatigue in the lower 

 limbs, and other symptoms, which vary extremely in different individuals. 



The menstrual discharge is a thin sanguineous fluid, and consists of blood, 

 epithelium, and mucus from the uterus and vagina. The menstrual flow 

 is preceded by a general engorgement of all the pelvic organs with blood. 

 The cervix and vagina become darker in color and softer in texture, and 

 the quantity of mucus secreted by the glands of the cervix and body is in- 

 creased. The uterine mucous membrane is swollen and the glands are 

 enlarged. The discharge of blood, the source of which is the mucous 

 membrane of the body of the uterus, is probably associated with uterine 

 contractions. There is great difference of opinion as to whether or not 

 any of the uterine mucous membrane is normally shed during the process 

 of menstruation. John Williams believes that the whole of the mucous 

 membranes of the body of the uterus is thrown off at each monthly period, 



