Electron Microscopy of the Human Placenta

Sections of two human placentas (full term and 3 months in pregnancy) are studied with electron microscope, and the following results are obtained. 1) The free suface of syncytial cells touching the inter-villous space is covered with many club-shaped microvilli. Although no apparent cellular border is detected among syncytial cells, there are intercellular bridges between syncytial cell and Langhans' cell. 2) The picture, which syncytial cells are in contact with basement membrane directly, is also seen. 3) The endoplasmic reticula are in vesicule ca. 3 in diameter in the early placenta, and become to ca. 2 vacuole in the full term placenta. 4) The osmiophilic lipid granules are seen in syncytial cells, but hardly in Langhans' cells. 5) Besides vacuoles under microvilli, we recognize the macular substances in the cytoplasm of the early placenta, which appear in the somewhat highly election dense and structureless. 6) The nuclear difference between the syncytial and Langhans' cells, which was reported by Boyd and Hughes, should be interpreted as the autolytic change. On this point, I agree with the Isomura's opinion that ether of them is composed of homogeneous fine granular particles. 7) The cellular border of the Langhans' cells is distinct, and simpler than synytial cell in fine structures of cytoplasma; a fewer endoplasmic reticula and almost no lipid granules. 8) The capillary endothelial cells arranged stratiform, and cytoplasmic protuberances from its outer surface are noticed.