896 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Some days before the flow occurs the mucous membrane of the body of the 

 uterus begins to thicken, partly by an active growth of its connective tissue 

 elements and partly by an excessive filling of its capillaries and veins with 

 blood. The cause of this swelling is not known. It continues until the 

 membrane has doubled or trebled in thickness, and, according to some authori- 

 ties, the uterine cavity becomes a mere slit between the walls. Then occurs an 

 infiltration of blood-corpuscles and plasma, probably largely by diapedesis, 

 although possibly assisted by rupture, through the walls of the swollen capil- 

 laries into the connective-tissue spaces beneath the epithelial lining of the 

 uterine wall. The epithelium is thus pressed up from beneath, and begins 

 rapidly to undergo disintegration (perhaps fatty degeneration) and to disappear. 

 The immediate cause of the degeneration is not definitely known. The con- 

 nective-tissue elements and the upper portion of the glands are involved in 

 the degenerative change. The capillaries, thus laid bare, burst, and the dark 

 blood oozes forth and, mixed with disintegrated remains of the uterine tissues, 

 with the mucous secretion of the uterus and the vagina, and with the escaped 

 lymph, passes away, drop by drop, from the body. There is great difference of 

 opinion as to the extent of the destruction of uterine tissue. On the one extreme 

 side are those who claim that the loss of tissue is normally wholly trivial and 

 secondary, the hypersemia and the bloody glandular discharge being the 

 important events. Other authorities, equally extreme, have observed a disap- 

 pearance of the whole mucous membrane except the deepest layers containing 

 the bases of the glands ; this is probably pathological. From all the evidence an 

 opinion intermediate between these two views seems most reasonable namely, 

 that usually and physiologically only the superficial portion of the mucous 

 membrane disintegrates. Differences in the amount undoubtedly occur. 

 Occasionally it happens that the membrane, instead of disintegrating, comes 

 away in pieces of considerable size. The term decidua menstrualis is applied 

 to the lost coat. The flow continues upon an average four days or more. 

 From observations upon 2080 American women Emmet 1 finds the average 

 duration of the flow at puberty to be 4.82 days, the average in later life 4.66 

 days. The amount of blood discharged can be determined only with great diffi- 

 culty. It probably varies greatly, but is commonly estimated at from 100 

 to 200 cubic centimeters (4-5 ounces). The blood is slimy, with abundant 

 mucus ; usually it does not coagulate. Epithelium cells, red corpuscles, leuco- 

 cytes, and detritus from the disintegrated tissues, occur in it, and it has a cha- 

 racteristic odor. As the flow ceases, a new growth, of connective-tissue cells, 

 capillaries, glands, and from the glands superficial epithelium, begins, and the 

 mucous membrane is restored to its original amount. Whether a resting period 

 follows before the succeeding tumefaction occurs, is not definitely known, but 

 it seems probable. The durations of the various steps in the uterine changes 

 are not well known, and probably vary in individual cases. Minot 2 suggests 

 the following approximate times : 



1 T. A. Emmet: The Principles and Practice of Gynaecology, 2d ed., 1880. 

 a C. S. Minot : Human Embryology, 1892. 



