THE MALE AND FEMALE REPRODUCTIVE ORGANS 1133 



copious secretion of vaginal fluid and mucus. These premonitory 

 symptoms are followed by a hemorrhagic oozing and later on by a 

 period of restitution which occupies almost two weeks. Consequently, 

 only a few days of absolute functional rest intervene between the 

 successive menstrual cycles. 



The division of this process into the periods of premenstruation, 

 menstruation, restitution, and complete rest leads us to suspect that 

 the endometrium of the uterus retains a comparatively normal appear- 

 ance only during the last stage of restitution and the succeeding period 

 of rest.^ During the premenstrual state it presents distinct evidences 

 of proliferation, swelling and hypersecretion. The cells of the stroma 

 lose their elongated shape and become more rounded. The capillaries 

 are greatly distended with blood which in turn gives rise to a hyper- 

 plasia of the uterine glands. A few days later blood begins to escape 

 from the superficial vessels and forces its way into the lumen of the 

 uterine canal, and through the constricted orifice of the cervix into 

 the vagina. But this hemorrhagic extravasation is not associated with 

 any considerable destruction of tissue; in fact, the uterine lining re- 

 mains rather intact, although it may be perforated here and there and 

 even partially loosened from the under-lying layers by spaces which are 

 filled with blood. In most instances this congestion also involves 

 the tubes, ovaries and external genitals, but these organs do not con- 

 tribute to the hemorrhagic discharge and hence, menstruation is to 

 be regarded essentially as a phenomenon of the uterus. The quantity 

 of blood lost during this period may amount to as much as 100 to 300 

 grams. 2 Under ordinary conditions, however, it is mixed with consid- 

 erable quantities of mucus, which substance tends to preserve the 

 thrombocytes and, therefore, to prolong the coagulation-time. Men- 

 strual blood as such clots as readily as any other type of blood. 



The phenomenon of heat exhibited by the lower mammals is the homologue 

 of menstruation. It is commonly divided into four periods, namely : (a) the pro- 

 estrum, during which the organs become congested and bleed, (6) the estrum, or stage 

 of sexual desire, (c) the metestrum, or period of restitution, and (d) the anestrum, 

 or stage of rest. Contrary to the human female, those of the other mammals take 

 the male only during the estrus. If sexual union or conception is prevented at 

 this time, the period for sexual intercourse gives way to the period of restitution, 

 but recurs again after a definite interval which in bitches is 12 to 16 weeks, in the 

 cow 3 to 4 weeks, in the sheep 2 to 4 weeks, in monkeys about 4 weeks, and in the 

 sow 9 to 18 days. 



Relation Between Menstruation and Ovulation. — Among the 

 many theories proposed to explain the cause of menstruation is the 

 older view that the menstrual flow is the female fluid of fertilization. 

 Subsequent to the establishment of the fact that menstruation occurs 

 in periodic cycles, it was then believed that it is brought on by the ma- 



1 Findley, Anat. of the menstr. uterus. Am. Jour. Obst., xlv, 1902, and Hitsch- 

 mann and Adler, Bau der Uterusschleimhaut, Manatsh. fiir Geb. und Gyn., xxvii, 

 1907. 



2 Hoppe-Seyler, Zeitschr. fur physiol. Chemie, xlii, 1904, 545. 



