FCETAL NUTRITION: THE PLACENTA 



439 



occurs in the crypts and the tissues outside them, and also, according 

 to Assheton, in the maternal blood-stream. It is not yet possible 

 to explain the exact significance of these changes. The iron-free 

 pigment is apparently a waste product, and the iron-containing part 

 is stored in the foetal organs. Whether the foetus subsequently 

 synthesises part of the organic iron compound into hemoglobin, or 

 absorbs minute quantities of haemoglobin as such, according to its 

 requirements, is unknown. 



The cotyledonary and inter-cotyledonary parts of the placenta 

 present differences both anatomically and physiologically. In the 

 inter-cotyledonary region are the glands, and here only are found 

 the gland-secretion and the " cellular " 

 secretion. In the cotyledonary parts the 

 glands are absent. Here the villi are 

 formed, and they effect an attachment to 

 the mucosa by the greater activity of the 

 trophoblast. Assheton has suggested that 

 this hyper-activity may be stimulated by 

 the absence of glands and consequently of 

 uterine milk in the cotyledons, the foetal 

 ectoderm attacking the mucous membrane 

 more vigorously in order to obtain food. 

 The blood effusions are also cotyledonary, 

 and the eosin and iron reactions are 

 obtainable in the adjacent trophoblast, 

 and not at other places. Finally, it is 

 probable that the exchange of oxygen 

 and carbonic dioxide is carried out in 

 the cotyledons. Here the maternal capillaries are more dilated 

 than outside the burrs, and they come close up to the surface, 

 some of them even impinging on the lining membrane of the 

 crypts. Between them and the allantoic vessels in the villi inter- 

 vene only a small amount of mesoblast, the cellular trophoblast, and 

 the lining of the crypts which, according to Assheton, corresponds 

 to the plasmodiblast of the bat. In the inter-cotyledonary regions, 

 on the other hand, the foetal vessels are related to the orifices of the 

 glands, and appear to be concerned principally with the absorption of 

 their secretion. As already mentioned, the villi may also be concerned 

 with the excretion of waste products of haemoglobin. 



Bonnet was the first to show that the trophoblast in Ruminants 

 was actively phagocytic and absorbed the constituents of the uterine 

 milk (Fig. 120). He demonstrated the presence of fat globules, 

 haemoglobin and its derivatives, degenerated leucocytes and "Stabchen " 

 (Fig. 121) in short, all the histologically demonstrable constituents 



FIG. 120. Ingestion and dis- 

 integration of red blood 

 corpuscles by the tropho- 

 blast of the sheep. (From 

 Jenkinson's " Notes on the 

 Histology and Physiology 

 of the Placenta in Ungu- 

 lata," Proc. Zool. Soc,., Lon- 

 don, vol. i., 1906.) 



