874 THE PHYSIOLOGY OF REPRODUCTION. 



The majority of writers seem to favor the latter view.* Regarding 

 the physiological importance of the corpus opinions also differ. 

 Some regard it as simply a protective mechanism by means of 

 which the empty space in the follicle is filled up by a tissue which is 

 afterward easily absorbed, instead of by scar tissue. Others, how- 

 ever, attribute to the lutein cells secretory functions of the most 

 important character in connection with the subsequent develop- 

 ment of the egg and the activities of the uterus. Some reference 

 will be made to these views farther on. 



Menstruation. The attainment of sexual maturity or puberty 

 is marked by a number of visible changes in the body, but in the 

 female the characteristic change is the appearance of the men- 

 strual flow from the uterus. The age at which this phenomenon 

 occurs shows many individual variations, but the average for 

 temperate climates is given usually at 14 to 15 years. In the 

 warmer countries the age is earlier, 8 to 10 years, and in the cold 

 regions somewhat later, 16 years. The racial characteristic in 

 this respect is said to be maintained, however, after generations of 

 residence hi countries of a different climate, as is illustrated by the 

 relatively early appearance of menstruation among Jews even in 

 the colder countries. After the phenomenon appears it occurs at 

 regular intervals of 28 days, more or less, and hence is known as 

 the monthly period, menses, menstruation, or catamenia. The 

 interval is not absolutely regular, and shows many individual 

 variations within limits which may be placed at 20 to 35 days. 

 Absence of the menstrual flow is designated as a condition of amen- 

 orrhea. Certain premonitory symptoms usually precede the 

 appearance of the menses, such as pains in the back or head or 

 a general feeling of discomfort, although in some cases these symp- 

 toms are absent. When these premonitory symptoms are unusually 

 painful or serious and the flow is difficult or irregular the condition 

 is designated as dysmenorrhea. The flow begins with a discharge of 

 mucus, which later becomes mixed with blood. The quantity of 

 blood lost is subject to individual variations, but it may amount to 

 as much as 100 to 200 gms. The flow continues for 3 or 4 days 

 and then subsides. Under normal conditions this phenomenon 

 occurs regularly throughout sexual life, that is, during the period 

 in which conception is possible. If fertilization occurs the flow 

 ceases normally during pregnancy and the period of lactation. At 

 the forty-fifth to the fiftieth year the flow disappears permanently, 

 and this change marks what is known as the natural menopause, 

 climacteric, or change of life. The change is sometimes abrupt, 

 sometimes very gradual, being preceded by irregularities in 



* For discussion and literature see Marshall, "Quarterly Journal Micro- 

 scopical Science," 1905, xlix., 189; and Loeb, " Journal of the American 

 Medical Association," 1906, xlvi., 416. 



