744 TEXT-BOOK OF PHYSIOLOGY 



maturation. As the nucleus is regarded as the part of the ovum which 

 transmits parental characteristics it is assumed that the extrusion of a por- 

 tion of the nuclear material is a means by which an excess of inherited 

 substance is prevented. 



Menstruation. Menstruation is a periodic discharge of blood and 

 mucus from the surface of the mucous membrane of the uterus, and occurs 

 about every twenty-eight days. The duration of the menstrual period ex- 

 tends over four or five days and the amount of blood discharged varies 

 from 180 c.c. to 200 c.c. Menstruation is usually an accompaniment of 

 ovulation, though the latter process may take place independently of the 

 former. It is characterized by both local and systemic changes. The 

 local changes are most marked in the uterus, the mucous membrane of which 

 increases in thickness from a proliferation of the connective tissue and a 

 hyperemic condition of the blood-vessels. Subsequently to these changes 

 the epithelial surface, as well as the more superficial portions of the connec- 

 tive tissue, undergo degeneration and exfoliation, after which the finer 

 blood-vessels rupture and permit of an escape of blood into the uterine 

 cavity. At the end of the menstrual period regenerative changes set hi 

 which continue until the normal condition of the mucous membrane is 

 reestablished. 



The Corpus Luteum. With the rupture of the Graafian follicle there is 

 an effusion of blood into the follicular cavity which soon coagulates, loses its 

 color and assumes the characteristics of fibrin. The walls of the follicle, 

 which have become thickened from the deposition of a reddish-yellow glutin- 

 ous substance, now become convoluted and undergo a still further hypertrophy, 

 until they encroach upon and almost obliterate the follicular cavity. In a 

 few weeks the mass loses its red color and becomes decidedly yellow, when it 

 is known as the corpus luteum. With the continuance of reparative changes 

 this body gradually disappears until at the end of two months nothing 

 remains but a small cicatrix on the surface of the ovary. Such are the 

 changes in the follicle if the ovum has not been impregnated. 



The corpus luteum, after impregnation has taken place, undergoes a 

 much slower development, becomes larger, and continues during the entire 

 period of gestation. The difference between the corpus luteum of the un- 

 impregnated and pregnant condition is expressed in the following table by 

 Dalton: 



CORPUS LUTEUM OF MENSTRUATION. CORPUS LUTEUM OF PREGNANCY 



At the end of three Eighteen millimeters in diameter; central clot reddish; convoluted wall 



weeks. pale. 



One month Smaller; convoluted wall bright | Larger; convoluted wall bright yellow; 



yellow; clot still reddish. 

 Two months Reduced to the condition of an 



insignificant cicatrix. 



Four months Absent or unnoticeable . . . 



clot still reddish. 



Twenty millimeters in diameter; con- 

 voluted wall bright yellow; clot perfectly 

 decolorized. 



Twenty millimeters in diameter; clot 



pale and fibrinous; convoluted wall dull 

 yellow. 



Six months Absent Still as large as at the end of second 



month; clot fibrinous; convoluted wall 

 paler. 



Nine months Absent. 



Twelve millimeters in diameter; central 

 clot converted into a radiating cicatrix; 

 external wall tolerably thick and convo- 

 luted, but without any bright yellow 

 color. 



