FCETAL NUTRITION: THE PLACENTA 487 



existence of an infcra-cellular proteolytic enzyme ''■ and de- 

 composition products of the proteins in the placenta also 

 point to the occurrence of a trophoblastic metabohsm of 

 proteins. 



The carbohydrates undergo changes which appear to be 

 the result of trophoblastic activity. In the rabbit, the glycogen 

 which is " swallowed " along with the decidual cells by the 

 Plasmodium (Chipman) is not found as glycogen. A hydrolytic 

 transformation to sugar probably takes place (see p. 434). In 

 addition the foetal serum contains laBvulose, which must be 

 formed in some part of the fertihsed ovum, since it is absent in 

 the mother. Fats may also be transformed by the trophoblast 

 (see Chap. XI., p. 512). 



It is generally, supposed that many syntheses occur in the 

 fertihsed ovum, though direct evidence is difficult to obtain in 

 Mammals. In the chick hsemoglobin is synthesised, and the same 

 almost certainly occurs in Man and other animals, part of the 

 synthesis being effected by the trophoblast (see p. 480). The 

 nucleoproteins of the foetal cotyledons in the sheep appear to 

 be formed there, since they differ in composition from the nucleo- 

 proteins of the cotyledonary burrs. The glycoprotein mucin 

 is a characteristic constituent of the inter-cellular ground- 

 substance of the whole foetal organism, and is apparently built 

 up by the ovum.^ The chondroproteins, a special group of 

 glycoproteins, which yield on hydrolysis proteins and the 

 carbohydrate-containing chondroitin-sulphuric acid, are also 

 found chiefly in the fcstus as constituents of the cartilage and 

 tendons. 



A consideration of these and similar facts leads us to beheve 

 that the new organism owes its development in large part to 



^ The enzyme has been found only in the human, placenta. It is desirable 

 that its presence in the trophoblast should be established, and this can only 

 be done In such animals as the sheep and rabbit, in which the foetal placenta 

 can be detached from the maternal, and investigated separately. As was 

 previously mentioned, the placenta contains no extra-cellular proteolytic 

 enzyme. 



' In the placenta of the cow, Jenkinson has described cells resembling 

 goblet-cells in the lining of the cotyledonary crypts, and ascribes to them a 

 maternal origin (Proc. Zool. Soc, London, vol. i., 1906). They may supply 

 mucin to the uterine milk, and so to the trophoblast. According to Assheton, 

 these lining cells are trophoblastic in the sheep. 



