DECIDUA SEROTINA AT SEVEN MONTHS. 357 



the villi, and here and there are converted into canalized fibrin. (3) The prolifera- 

 tion islands are converted into canalized fibrin and at the same time grow and 

 fuse, forming larger patches, particularly on the larger stems. In this manner are 

 produced the large areas and columns of fibrin such as appear in our section. (4) 

 Over the tips of the villi, where they are imbedded in the decidua serotina, 

 the epithelium apparently degenerates and becomes hyaline tissue, but without 

 canalization. The mesoderm exists in two principal forms, adenoid tissue and 

 fibrillar tissue around the blood-vessels. The adenoid tissue (Fig. 237) may be 

 considered as the proper tissue of the villus. It consists of a network of proto- 

 plasmic threads, which start from nucleated masses. There are many large meshes, 

 which are partly occupied by the very large, coarsely granular cells, /, I, which gen- 

 erally are widely scattered, but sometimes are present in large numbers. These free 

 cells are extravasated blood-corpuscles, which have increased in size. Probably 

 they are dead or at least dying and have swollen by imbibition. They undergo 

 disintegration, their protoplasm, becoming vacuolated; the 1 vacuoles increase in size 

 as the protoplasm is dissolved, until finally the cell-body entirely disappears. About 

 the capillary blood-vessels, v, the network is more finely spun. Around the larger 

 blood-vessels the mesoderm has a distinct intercellular substance with a ten- 

 dency to fibrillar differentiation in quite a wide zone around the blood-vessels. In 

 this zone the cells become elongated or irregularly fusiform. Around the larger 

 vessels the cells are grouped in laminae, and apparently are contractile, so that they 

 must be looked upon as an imperfectly differentiated form of smooth muscular 

 tissue. 



Decidua Serotina at Seven Months. 



Specimens may be treated as described for the placenta in situ (page 352). 

 If, however, the best results are desired, the whole of the uterus should be cut 

 through and the placenta divided into smaller pieces from i to 2 cm. in diameter, 

 so as to allow a freer penetration of the preserving fluid. Either Zenker's or 

 Tellyesnicky's fluid is recommended. In a normal uterus about seven months 

 pregnant we find the following relations : The serotina is about i . 5 mm. thick, 

 and contains an enormous number of decidual cells (Fig. 238); the cavernous, 

 D' ', and compact, D", layers, are very clearly separated; the mucosa is sharply 

 marked off from the muscularis, although scattered decidual cells have penetrated 

 between the muscular fibers. The muscularis is about 10 mm. thick and is 

 characterized by the presence of quite large and' numerous venous thrombi, espe- 

 cially in the part toward the decidua. The decidua itself contains few blood-vessels. 

 Upon the surface of the decidua can be distinguished a special layer of denser 

 decidual tissue, which in many places is interrupted by the ends of the chorionic 

 villi which have penetrated it, as is well shown in the accompanying figure. The 

 gland cavities of the spongy layer, D' ', are long and slit-like; they are filled for 

 the most part with fine granular matter, which stains light blue with hematoxylin; 



