FCETAL NUTRITION: THE PLACENTA 435 



functions in the development of the foetus. " The absence of 

 glycogen from some of the growing foetal tissues, and the fact 

 that many of the tissues in which it is present do not contain 

 even as much as the adult ones, leave httle doubt that a definite 

 formative power cannot be attributed to glycogen as such. On 

 the other hand, the scarcity of glycogen in embryonic tissues 

 does not necessarily justify the conclusion that glycogen does not 

 take part in the building up of the tissues. It is well known 

 that embryonic tissues are rich in mucin, which contains a large 

 amount of a carbohydrate group in its molecule. Although 

 glycogen as such has no formative power, it may yield one of 

 the " Bausteine " for the building up of the main protein body 

 of foetal tissues. In this connection it is interesting to consider 

 the conditions in the hen's egg, which contains in itself the 

 material of which the embryo is built up.^ In the ovum carbo- 

 hydrate as such is practically absent. At the same time all the 

 protein substances of the white of egg are distinguished by the 

 presence of a large amount of glucosamine in their molecule. Here 

 the carbohydrate group has entered into the protein molecule, and 

 correspondingly there is a scarcity of free carbohydrate." ^ 



Protein Metabolism. — In so far as the influence of the tropho- 

 blast on proteins has been investigated in the placenta of the 

 rabbit, it may be considered here. It is generally accepted that 

 coUoid substances with large molecules, which are not adapted 

 for difEusion, require a preUminary transformation, by which the 

 size of the molecules is decreased before they can be taken up 

 by the fcetal ectoderm. But the actual observations are against 

 such a general statement. In the sheep the trophoblast can 

 absorb not only haemoglobin, a coUoid, without any prehminary 

 transformation, but even enormously larger masses of proto- 

 plasm in the form of cells. On the other hand, such hydrolysed 

 products of albumen as albumoses and peptone are not present 

 in the fresh placenta, nor can any extra-cellular proteolytic 

 enzyme be extracted.^ Hence there is no evidence of a placental 



^ Compare Emrys-Koberfcs, " A Further Note on the Nutrition of the Early 

 Embryo, with Special Reference to the Chick," Proc. Roy. Soc, London, B., 

 vol. Ixxx., 1908. 



^ Loohhead and Cramer, loc. cit. 



' Loohhead, "On the Transmission of Nitrogenous Compounds from 

 Mother to Fcetus," Trans. Obstet. Soc, Edinburgh, vol. xxxiii., 1907-8. 



