HISTOCHEMISTRY OF PLACENTA 



891 



Pearse procedure. Gomori (1945) devised 

 a method for lipase which has been applied 

 to placentas of several different groups. 



E. IRON AND SULFHYDRYL AND AMINO 

 GROUPS OF PROTEINS 



]\Iicroincineration of tissue sections 

 (Scott, 1933) is a well known means of 

 demonstrating minerals in cells. It was used 

 for the identification of placental iron by 

 Dempsey and Wislocki (1944). Placental 

 iron is also demonstrable in tissue sections 

 by various methods invoh'ing the Prussian 

 blue reaction. 



Protein-linked sulfhydryl groups have 

 been demonstrated in the human placenta 

 in the present study by the method of Barr- 

 nett and Seligman (1952). 



Amino groups of proteins were demon- 

 strated in the granular cells of the metrial 

 gland of the rat by the method of Weiss, 

 Tsou and Seligman (1954). 



III. The Placentas of Man 

 and Rhesus Monkey 



A. TOPOGRAPHY AND GENERAL HISTOLOGY 



The comparative placentation of primates 

 has been extensively studied by Wislocki 

 (1929), Hill (1932), and Stieve (1944). The 

 placentation of the rhesus monkey {Macaca 

 mulatta) has been described in detail by 

 Wislocki and Streeter (1938). 



The human placenta in its earliest stages 

 has been the subject of recent observations 

 by Hertig and Rock (1941, 1945), Rock and 

 Hertig (1948), Hertig, Rock and Adams 

 (1956). In subsequent stages it has been in- 

 vestigated by Grosser (1925a), Spanner 

 (1935a, b, 1940), Stieve (1940, 1941), Stieve 

 and von der Heide (1941), Wislocki and 

 Bennett (1943), and Hamilton and Boyd 

 (1951, 1960). 



The chorion, or outer membrane sur- 

 rounding the developing implanted egg, 

 unites with the vascular, allantoic body 

 stalk in man, apes, and monkeys to give 

 i-ise to the definitive placenta which is hemo- 

 chorial and villous in form. The essential 

 cells or parenchyma of the chorion and pla- 

 centa are collectively called the trophoblast, 

 a term introduced by the Dutch embryolo- 

 gist Hubrecht, signifying "nutritive layer." 



At the site of implantation of the devel- 



oping blastocyst in the uterine endome- 

 trium, cords of trophoblast grow out from 

 the initially smooth surface of the chorion. 

 These tongues which penetrate and erode 

 the endometrium are called the primary 

 chorionic villi. On approximately the 15th 

 day after fertilization of human and rhesus 

 monkey eggs, mesoderm begins to appear in 

 the proximal, attached portions of the villi 

 and differentiates progressively toward 

 their growing distal ends. The differentia- 

 tion of mesoderm in this manner converts 

 the primary chorionic villi into secondary 

 villi. With the development of embryonic 

 blood vessels in them, the secondary villi 

 become converted into tertiary or definitive 

 placental villi. The secondary and tertiary 

 villi are covered by a mantle of trophoblast 

 differentiated into an inner layer of large, 

 vesicular trophoblastic cells or trophoblasts 

 designated as Langhans cells after their dis- 

 coverer, and an outer layer of syncytially 

 transformed cells referred to as the syncy- 

 tial trophoblast or syncytium. The latter, 

 as the name implies, consists of a continu- 

 ous mass of cytoplasm devoid of cell boun- 

 daries and containing small, darkly stained 

 nuclei (Fig. 15.9). 



The distal ends of the chorionic or pla- 

 cental villi continue to grow for a consider- 

 able period in the form of columns of cyto- 

 trophoblast preceding the differentiation of 

 mesoderm in them. These are designated as 

 the trophoblastic cell columns. The distal 

 tips of these columns unite on the periphery 

 of the growing placenta to constitute the 

 trophoblastic shell. These structures will be 

 referred to collectively as the peripheral 

 cytotrophoblast, and the cells comprising 

 them as peripheral trophoblasts, in contra- 

 distinction to the Langhans cells associated 

 with the secondary and tertiary villi. As 

 will be shown, the peripheral trophoblasts 

 have numerous cytologic and histochemical 

 properties which distinguish them from the 

 Langhans cells. The beginning of many of 

 these features can be seen in a human blas- 

 tocyst on the 16th day following fertiliza- 

 tion (Fig. 15.2) and their further develop- 

 ment is illustrated in a placenta of a rhesus 

 monkey of the 29th dav of gestation (Fig. 

 15.3). 



Placental villi grow initially everywhere 

 over the circumference of the human cho- 



