MENSTRUATION. 341 



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

 appearance of its upper portion the mucosa is left without any lining epithelium 

 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 extra vasated 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 10 to 15 mm. cube, and 

 stained with alum hematoxylin and eosin. The use of Mallory's triple connective- 

 tissue stain will demonstrate the fibrillar tissue in the decidua and the very large 

 amount of the same in the muscularis. 



The accompanying illustration (Fig. 226) is from a uterus in active menstrua- 

 tion. The decidual membrane is from i.i to 1.3 mm. thick; its surface is 

 irregularly tumefied; the gland openings lie for the most part in the depressions. 

 In the cavity of the uterus there was a small blood-clot. The demarcation 

 between the decidua and the muscularis is sharp. The upper fourth, d, of the 

 decidua is broken down and very much disintegrated; its cells stain less readily 

 than those of the. deep portion of the membrane; the tissue is divided into numer- 

 ous more or less separate small masses. Some of the blood-vessels are ruptured. 

 The superficial epithelium, ep, is loosened everywhere; in places fragments of it 

 have fallen off, and in some parts it is gone altogether; it stains readily with 

 alum hematoxylin, differing in this respect from the underlying connective tissue. 

 The deeper layer of the decidua is dense with crowded well-stained cells, which 

 lie in groups and are probably proliferated connective-tissue cells. They have 

 small oval or elongated darkly stained nuclei, with very small granular protoplas- 

 matic bodies. There is no indication of any enlargement of the cells, such as 

 occurs in the production of true " decidual" cells. There are very few leucocytes. 

 The glands are enlarged somewhat, and are lined by a normal cylinder epithelium, 

 which offers no obvious change as compared with that of the glands of the resting 

 uterus. 



. 



The Pregnant Uterus: the Two Stages. 



When the ovum implants itself in the uterine wall, it becomes covered by a 



growth of the mucous membrane or decidua which we know as the decidua 



reflexa. For an account of this process see pages 124 to 127, where also proper 



