112 DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA. 



protoplasm. They stain a deep green and contain a single large basophilic 

 nucleolus. The protoplasm stains a bright green and is extremely rich in minute 

 granular and short, rod-like mitochondria (fig. 4). These are quite uniform in size, 

 the rods rarely being over 2 pin length, and are distributed uniformly through the 

 protoplasm. No other granules are demonstrable. In some areas the protoplasm 

 is finely vacuolated and here the mitochondria are somewhat less numerous. 



The labyrinth consists of a dense network of maternal blood-spaces, inclosed 

 in a thinned-out syncytium, and fetal blood-vessels supported by a small amount 

 of connective tissue. The syncytium resembles endothelium, but retains the rich- 

 ness in mitochondria (fig. 5) characteristic of the border and interlobular syncytium, 

 and also exhibits a similar staining reaction. 



The fetal blood is inclosed in delicate capillaries whose endothelium is similar 

 to that found in other localities. Its nuclei and protoplasm stain a lighter green 

 than do the nuclei and protoplasm of the syncytium and the protoplasm is .about 

 one-fourth as rich in mitochondria as is that of the syncytium. The mitochondria 

 are much more variable in size and many curved rods, 6 to 8 /x long, are seen. 



A section through the roof of the central excavation shows irregular columns 

 of degenerating decidual tissue separated by papillary processes of fetal ectoderm, 

 one or two cells in thickness. The fetal cells are small, cuboidal in shape, and 

 contain relatively large round or oval nuclei which stain deep green and contain 

 basophilic nucleoli. The small amount of green-staining protoplasm is quite rich 

 in small granular and rod-like mitochondria. The cells of the decidua in this 

 locality have highly vacuolated protoplasm and pycnotic nuclei. The mitochondria 

 are limited to a few minute granules lying between the vacuoles in the protoplasm. 



HUMAN PLACENTA. 



The labyrinth of the mature human placenta is made up of chorionic villi sur- 

 rounded by maternal blood-spaces. The fetal blood-vessels occupy the center of 

 each villus and are supported by a rather coarse connective-tissue network. The 

 villi are covered by a syncytium which everywhere separates the fetal vessels from 

 the maternal blood. Just beneath this syncytium are varying numbers of clear 

 Langhans cells. The syncytium is a layer of protoplasm of variable thickness in 

 which no cell boundaries can be made out. The numerous nuclei are usually 

 arranged in a single layer and are quite close together. However, in places where 

 the syncytium is thick, as in the angle or at the junction of two large villi, there may 

 be 4 or 5 layers of syncytial nuclei. They are small, round or oval in shape, stain 

 deep green, and contain a medium-sized basophilic nucleolus. 



The protoplasm of the syncytium takes the green faintly and is usually homo- 

 geneous, though in some areas it is finely vacuolated. It is very rich in minute 

 granular and short rod-like mitochondria (fig. 6). These are distributed uniformly 

 through the protoplasm and are so numerous and crowded that it is difficult to 

 distinguish the individual granules except in very thin, well-differentiated sections. 

 They are somewhat less numerous in the vacuolated areas. 



