THE HUM A N. PLA CEN TA . 



.3.-)!) 



origin, and accordingly have described it as a "decidua subchorialis" The de- 



cidual cells exhibit great variety in their features (Fig. 239). They are nearly 



all oval discs, so that their outlines differ according as they are seen lying in the 



tissue turned one way or another; they vary greatly in size; the larger they are, 



the^more nuclei they contain; the nuclei 



are usually more or less elongated; the 



contents of the cell granular. Some of 



the cells present another type, c; these 



are more nearly round, are clear and 



transparent; the nucleus is round, stains 



lightly, and contains relatively few and 



small chromatin granules; such cells are 



most numerous about the placental margin. 



The Human Placenta. 



Specimens of the fresh normal human 

 placenta may be obtained without diffi- 

 culty from maternity hospitals. The 

 placenta should be thoroughly examined 



FIG. 239. DECIDUAL CELLS FROM THE SECTION 



REPRESENTED IN FIGURE 238. 

 in the fresh State by the Student and c > Multinucleate cell; at a seven blood-corpuscles ha\*e 



all the points in the description below 



verified by him. To make an injected specimen either the starch injection mass 

 or the colored gelatin mass may be used according as*it is desired to demonstrate 

 only the coarser or all the branches of the vessels. The" injection should be made 

 through one of the arteries of the umbilical cord. As there is almost invariably 

 a cross-anastomosis between the two arteries close to the placenta, it is sufficient 

 to inject one of them in order to fill the entire system of vessels. The starch mass 

 may be injected in the cold specimen. If the gelatin mass is used, the specimen 

 must be submerged in warm water until it is sufficiently heated to keep the gelatin 

 mass melted during the process of injection. After the gelatin injection is com- 

 pleted, the placenta may be preserved in 70 per cent alcohol, to every TOO c.c. of 

 which 2 c.c. of hydrochloric acid have been added. After twenty-four hours replace 

 the acidulated alcohol by fresh alcohol of 70 per cent, which should be again 

 changed after another twenty-four hours. Specimens will then keep indefinitely. 

 Such specimens may be used either for sections of the placenta to be made from 

 pieces imbedded in celloidin, or for the study of isolated fragments of the villi, 

 which are pulled out of the placenta by forceps. 



The human placenta is a disc of tissue to which the umbilical "cord of the 

 child is attached by its distal end. As a result of normal labor the amnion 

 and chorion, by which the fetus in utero is surrounded, are ruptured; the child 

 is then expelled, but by means of the long umbilical cord remains attached to the 

 uterus; after an interval the placenta, with which the cord retains its connection, 



