FOETAL NUTRITION: THE PLACENTA 433 



zone of separation. The foetal part includes the peninsulje of 

 decidual tissue which form the intermediary zone ; the glycogen 

 contained in it belongs whoUy to these peninsulas and represents 

 the fraction most intimately related to the trophoblast. It may 

 on that account be termed the proximal glycogen, while that 

 of the maternal part is the distal glycogen. On the fourteenth 

 day the distal glycogen forms over 4 per cent, of the weight of 

 the maternal part, and it gradually increases till the eighteenth 

 day, when it forms 5'5 per cent. ; it remains nearly constant tiU 

 the twenty-second day, and then there is a continuous decrease 

 each day tiU the end of pregnancy. On the day before labour 

 it amounts to shghtly over 1 per cent., and practically the whole 

 of it is situated at the zone of separation. This last is probably 

 not destined for the foetus. 



The variations in the proximal glycogen are similar. At the 

 twenty-ninth day there is no glycogen left in the intermediary 

 region. 



In the foetal liver traces of glycogen are present at the 

 eighteenth day, though none can be demonstrated histologi- 

 cally till four days later. Up to the twenty-fourth day the 

 percentage gradually increases, but is still very small. Next 

 day it rises for the first time above the glycogen percentage in 

 the rest of the festal body, and then there is a rapid increase til), 

 on the twenty-ninth day, half of the foetal glycogen is stored in 

 the hver. Hence it may be concluded that, although the hver 

 contains glycogen in the earher stages, a change occurs at the 

 twenty-fifth day of pregnancy. Only then does it store more 

 than its proportion of glycogen by weight, and thus may be 

 said to be capable of carrying on the glycogenic function for 

 the foetus. Before that date the only store of glycogen avail- 

 able is contained in the maternal placenta. " The glycogen 

 metabohsm of the placenta and foetus shows a regular suc- 

 cession of changes which proceed almost regardless of external 

 conditions, and which are independent to a great extent of the 

 glycogen metabohsm of the mother " (Lochhead and Cramer). 



There can be httle doubt that the glycogen stored in the 

 decidual ceEs is absorbed by the trophoblast. It is situated in 

 the maternal peninsulee which are surrounded by foetal tissue, 

 and it gradually decreases in amount while it increases in the 



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