430 THE PHYSIOLOGY OF REPRODUCTION 



placenta of the rabbit, a few observations have been made by 

 Eden,^ Maximow, and Masius. Chipman has investigated the 

 subject in greater detail, but he draws no conclusions from the 

 histological data. In reality, the study of fat in the placenta 

 is rendered difficult by its occurrence both as an infiltration 

 and in the degeneration of cells. 



Fat is found in the foetal viscera, hver, heart, and mid-gut, 

 before the allantoic circulation is estabhshed. At this time, 

 the tenth day, the vitelhne circulation is at its height, and the 

 fat probably reaches the embryo by its vessels, as it is also 

 found in the hypoblast of the area vasculosa. It may be de- 

 rived from the absorption by the trophoblast of fat-droplets 

 contained in the giant-ceUs of the peri-placental folds. As the 

 vitelhne circulation diminishes, the fat disappears from the 

 embryonic viscera, and does not reappear till four or five days 

 after the estabhshment of the allantoic circulation. During this 

 interval fat is present in the extra-placental wall of the blasto- 

 cyst, but it probably arises by a degeneration of its cellular 

 protoplasm. 



In the foetal placenta, fat is never found in the mesoblast or 

 capillary walls, but it occurs in the trophoblast, especially 

 where it is in contact with maternal blood or decidua. It in- 

 creases from the twelfth to the sixteenth day, then it decreases, 

 and a week later disappears altogether. In the maternal 

 placenta fat first appears in the decidual cells which are 

 nearest the trophoblast. They show no sign of degeneration 

 at this time, and they probably secrete the fat globules. After 

 increasing for a few days, it diminishes with the atrophy of the 

 decidual cells, and finally appears as fatty debris. Fat is also 

 present in the proliferating endothehum, and later in the fibrin 

 laminae of the uterine sinuses. 



In the new-born fcetus the main store of fat is contained 

 in the subcutaneous tissue. It is remarkable that it does not 

 appear in this situation tiU the greater part of the fat has dis- 

 appeared from the placenta. It is either transmitted to the 

 foetus in a form which does not reduce osmic acid, or formed in 

 the fcetus itself from other substances. At birth the foetal 



1 EdeD, "The Occurrence of Nutritive Fat in the Human Placenta," 

 Proc. Boy. Soc, London, vol. Ix., 1896. 



