58 EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 



outlines, but as gestation advances their cytoplasm shrinks so that they appear as 

 narrow sheaths around the capillaries and the prominent giant cells. 



The placental labyrinth of the cat is stained very deeply by trypan-blue. The 

 dye appears in both types of cells composing the chorionic ectoderm just referred to 

 (figs. 14 and 15). In the giant cells it is particularly striking, filling the cytoplasm 

 with numerous bright blue granules. In the smaller epithelial cells constituting the 

 lamella- it is no less abundant but tends to appear in clumps. It is also observed in 

 the cytoplasm of many of the endothelial cells lining the maternal capillaries, but 

 none of it occurs in the fetal mesoderm or in the endothelium of the embryonic blood- 

 vessels. In the masses of chorionic ectoderm at the junction of the chorion and 

 spongiosa very little trypan-blue is found. One receives the impression that this 

 is due solely to the fact that these cells are too remote from the maternal vessels in 

 which the dye is circulating to participate in its absorption. No dye is seen in the 

 epithelium of the remains of the uterine glands or in the detritus in their lumen. 

 Macrophages, heavily laden with trypan-blue, are present in large numbers in the 

 stroma surrounding the gland and in the uterine musculature. 



The only other noteworthy deposit of dye is found in the chorionic ectoderm 

 along the borders of the placenta. In carnivora the maternal blood extravasates 

 into the space between the uterine epithelium and the chorion along the margins of 

 the placenta; hence this region in the dog has been termed the green border and 

 in the cat the brown border. The chorionic villi which dip into this mass of blood 

 are actively engaged in its resorption, and the epithelial cells covering them are seen 

 under the microscope to contain numerous entire and fragmented red blood-cor- 

 puscles, besides abundant pigment. It is thought that in this way the fetus obtains 

 the iron necessary for its growth. In the cat the chorionic villi in this region are 

 covered by a single layer of high columnar epithelial cells which have club-shaped 

 distal ends and nuclei situated close to the basement membrane. The distal, broad 

 end of the cell contains numerous whole or fragmented erythrocytes, whereas 

 deposits of finely granular brown pigment are seen in the middle and proximal 

 portion of the ceil. In the vitally stained animal numerous granules of trypan-blue 

 are distributed throughout the central and proximal portions of these same cells 

 (fig. 4) . The chorionic ectoderm over the poles of the fetus is unstained. 



The observations made upon pregnant cats may be briefly summarized as 



follows: 



1 . Trypan-blue is incapable of passing from the maternal blood-stream through 

 the placenta and membranes into the fetus or even into the amniotic or allantoic 



fluids. 



2. Trypan-blue, injected into the maternal blood-stream, reaches the placenta, 

 where it is absorbed and stored, principally by the chorionic ectoderm of the laby- 

 rinth. It is stored in the cytoplasm of the chorionic cells in the form of granules. 



3. The endothelium winch lines the maternal capillaries of the placental laby- 

 rinth absorbs and stores the dye in the same manner as the chorionic ectoderm. 



4. Trypan-blue is also deposited in the chorionic epithelium of the brown 

 border. 



