GROWTH AND REPRODUCTION 769 



The human uterus is a more or less pear-shaped muscular organ 

 about 3 inches long. It consists of the main upper part, or body, and 

 of the neck, or cervix. The internal cavity is about 2 inches long. 

 It is lined by a mucous membrane consisting of a single layer of 

 epithelium and numerous mucous glands resting upon a fibrous sub- 

 mucous coat. Normally, especially in those who have not had children, 

 the cavity is almost absent, being more or less of the nature of a 

 narrow channel. The oviducts enter into the upper part of the body; 

 the cervix connects with the vagina below. 



The vaginal canal is noteworthy for its power of extensibility 

 during parturition. It is lined by a mucous membrane. This is 

 thrown into rugae, or ridges. The channel is lined by a stratified 

 epithelium. In the mucous membrane are glands which pour out a 

 faintly acid secretion. 



The Sexual Life of the Female. In woman, the period of sexual 

 activity begins about the twelfth to seventeenth year of age, varying 

 with race and climate, being earlier in Southern and later in Northern 

 races. In the temperate zone the age is about thirteen to fifteen. 

 Besides the acquisition of the secondary female characteristics, the 

 beginning of sexual life is betokened by the onset of menstruation, a 

 monthly loss of blood from the uterus -the menses. This lasts from 

 two to six days, and usually from 100 to 200 c.c. of fluid, partly blood, 

 partly mucous uterine secretion, are lost. The mixture is dark in 

 colour, and clots very slowly or not at all. 



Just previous to each period of menstruation the whole genital 

 tract becomes more richly supplied with blood, especially the uterus. 

 The mucous membrane of this organ becomes swollen, partly by 

 congestion of blood and lymph, and partly by a certain amount 

 of cell proliferation. This, known as the constructive stage, is 

 followed by the destructive stage. The bloodvessels rupture and 



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form ha3matoma below the mucous membrane, the epithelium of which 

 eventually ruptures, and menstruation proper then ensues. At the 

 cessation of menstruation there is a period of repair (about seven days), 

 in which the uterus returns to its normal state. Then follows a period 

 of rest, or quiescence, generally lasting about twelve or fourteen 

 days. 



The exact relationship of menstruation to ovulation is not known. 

 The shedding of the ovum is usually believed to precede menstruation. 

 The two processes are intimately related, and depend upon the presence 

 of the ovary. When these are removed, menstruation ceases. Men- 

 struation also ceases during pregnancy and during the puerperium 

 the six weeks after child-birth. During lactation, also, it is usually 

 absent. Women of the poorer classes often suckle their children more 

 than a year, in the hope of deferring its return, and therefore the 

 chance of fertilization. This is not necessarily the case. Pregnancy 

 may take place soon after the birth of a child, even before the onset of 

 menstruation. 



The first stage of menstruation is attended with a certain amount 

 of physical discomfort, amounting in some cases to pain, which 



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