MENSTRUATION. 317 



the resting mucosa, about seven days. The times given are approximative only. 

 The whole cycle of changes covers about sixteen days. Since the monthly 

 period is about four weeks, the period of rest, as thus calculated, is only about 

 twelve days. 



1. Tumefaction. — A few days before the menstrual flow the mucosa gradu- 

 ally thickens; the surface becomes irregular; the openings of the glands lie in 

 depressions. The connective-tissue cells are increased in number, and it is said 

 by some authors in size, but the increase in size is doubtful ; the number of round 

 cells increases; the glands expand and become more irregular in their course; a 

 short time before hemorrhage begins, the blood-vessels, especially the capillaries 

 and veins, become greatly distended. We must assume that the connective- 

 tissue cells proliferate, but we have no satisfactory observations upon their divi- 

 sion. It was formerly asserted that the menstrual decidua contains decidual 

 cells, but in all the specimens the author has studied there were none present. 



2. Menstruation. — When the changes just described are completed, the 

 decidua menstrualis is fully formed, and its partial disintegration begins. The 

 process commences with an infiltration of blood into the subepithelial tissues; 

 this infiltration has hitherto been commonly explained as due to the rupture of 

 the capillaries; but as no ruptures at this period have been observed, we may 

 justly regard this explanation as inadmissible, and account for the infiltration per 

 diapedesin. It lasts for a day or two, and is apparently the immediate cause of 

 a very rapid molecular disintegration of the superficial layers of the mucosa, 

 which in consequence are lost; the superficial blood-vessels are now exposed, 

 and, by rupturing, cause the well-known hemorrhagia of menstruation. By the 

 disappearance of its upper portion the mucosa is left without any lining epithe- 

 lium and is very much (and abruptly) reduced in thickness. Its surface is 

 formed by connective tissue and exposed blood-vessels. 



3. Restoration of the Mucosa. — At the close of menstruation the mucosa is 

 2 or 3 mm. thick ; the regeneration of the lost layers begins promptly and is com- 

 pleted in a variable time, probably from five to ten days. The hyperemia rapidly 

 disappears; the extravasated blood-corpuscles are partly resorbed, partly cast 

 off; the spindle-cell network grows upward, while from the cylinder epithelium 

 of the glands young cells grow and spread up and out so as to produce a new 

 epithelial covering; new subepithelial capillaries appear. The details of these 

 changes are imperfectly known; they effect the return of the mucosa to its 

 resting-stage. 



Decidua Menstrualis. — Specimens from the first day of menstruation are the 

 most instructive. They should be preserved in Zenker's fluid; sections may be 

 made perpendicular to the decidual surface from blocks io to is mm. cube, and 



