Morphological Aspects of Ageing in the Placenta 107 



sey, 1948; Wislocki, 1955). It has been compared at the two 

 periods with respect to the localization and amount of nucleo- 

 proteins, enzymes, carbohydrates and lipids which it contains. 

 Electron microscopy has also revealed significant cytological 

 differences between the placenta of the first trimester and at 

 full term (Wislocki and Dempsey, 1955a). 



The cytological and cytochemical changes in the human 

 placenta involve both the nuclei and cytoplasm of the 

 trophoblast (Wislocki, 1955). Mitotic division decreases and 

 various cytoplasmic structures and substances diminish in 

 size and amount. The lipid droplets and mitochondria of the 

 trophoblastic syncytium decrease both in size and number. 

 The brush border of the syncytium seen with the daylight 

 microscope, and the equivalent microvilli observed with the 

 electron microscope, diminish in length. Glycogen gradually 

 disappears from the foetal placenta. Cytoplasmic ribonucleo- 

 protein, seen in the syncytium as cytoplasmic basophilia in 

 the daylight microscope and as ergastoplasmic vesicles in 

 the electron microscope, decreases. On the other hand, acid 

 and alkaline phosphatases increase. The stroma of the villi 

 becomes less cellular and more fibrous. 



Biochemical methods afford another means of determining 

 the amount and direction of placental changes during gesta- 

 tion. Thus, in the human placenta, Villee (1955) reports a 

 gradual decline in the amount of placental glycogen, in the 

 degree of anaerobic glycolysis, and in the rate of oxygen 

 consumption. With respect to the decline in glycogen, the 

 histochemical and biochemical observations are in agreement. 



A recent study of the enzymatic reactions of the rat's 

 placenta from the 13th day of gestation until full term 

 reveals a number of changes (Padykula, 1955, 1956). Adeno- 

 sine triphosphatase and glycerophosphatase (pH9-4), acid 

 phosphatase, esterase (Pearse's method) and succinic dehydro- 

 genase (Seligman and Rutenburg's method) were investigated 

 in frozen, cryostat sections. Homogenized visceral yolk sac 

 was also assayed biochemically for succinic dehydrogenase, 

 adenosine triphosphatase and glycerophosphatase activities. 



