THE PREGNANT UTERUS. 319 



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

 tive-tissue stain will demonstrate the fibrillar tissue in the decidua and the very 

 large amount of the same in the muscularis. 



The accompanying figure is from a uterus in active menstruation. The 

 decidual membrane is from i.i to 1.3 mm. thick; its surface is irregularly tume- 

 fied; 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 de- 

 cidua 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 numerous more or less 

 separate small masses. Some of the blood-vessels are ruptured. The super- 

 ficial 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 hematox- 

 ylin, 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 protoplasmatic bodies. 

 There is no indication of any enlargement of the cells, such as occurs in the pro- 

 duction 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 re- 

 flexa. For an account of this process see pages 118 to 120, where also proper 

 definitions of the terms decidua reflexa, serotina, and vera are given. As the 

 ovum increases in size the decidua reflexa also increases, and gradually becomes 

 thinner and thinner, until it ultimately disappears. The exact date of its disap- 

 pearance is not known; it falls somewhere within the fifth month. Accord- 

 ingly, we may divide the period of pregnancy into two phases or stages, each 

 comprising about half of the whole period. During the first stage the decidua 

 reflexa is present, during the second stage it is absent, so that the chorion laeve 

 comes into direct contact with the decidua vera. In the following sections a 

 typical uterus of the first and second stages each is described. 



Human Uterus Three Months Pregnant. 



The uterus measures about 34 inches in transverse diameter, and shows 

 well-marked venous sinuses on its external surface. It should be opened by a 



