462 THE PHYSIOLOGY OF REPRODUCTION 



the fourteenth day the distal glycogen forms over four' 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 till the twenty-second day, and then there is a continuous 

 decrease each day till the end of pregnancy. On the day before 

 labour it amounts to slightly over one per cent., and practically the 

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

 probably Twt 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 histologically 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 foetal body, and 

 then there is a rapid increase till, on the twenty-ninth day, half of 

 the foetal glycogen is stored in the liver. . Hence it may be concluded 

 that, although the liver contains glycogen ' in the .earlier 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 available is 

 contained in the maternal placenta. " The glycogen metabolism of the 

 placenta and foetus shows a regular succession of changes which 

 proceed almost regardless of external conditions, and which are 

 independent to a great extent of the glycogen metabolism of the 

 mother " (Lochhead and Cramer). 



There can be little doubt that the glycogen stored in the deqidual 

 cells is absorbed by the trophbblast. It is : situated in the maternal 

 peninsulse which are surrounded by foetal tissue, and it gradually 

 decreases in amount while it increases in the foetus. That none can 

 be demonstrated in the trophoblast may be due to a transformation 

 into sugar before it is absorbed. Glycerine extracts of both the 

 maternal and the foetal part of the placenta possess an enzyme which 

 has a powerful hydrolytic action on glycogen. On the other hand, 

 the enzyme action is markedly weaker, or absent altogether, in the 

 placentte of Ruminants, in which the glycogenic changes are known 

 to be insignificant. 



It is not easy to determine why such a complex mechanism is 

 necessary if, as is stated by Cohnstein and Zuntz,^ glucose passes 

 from the maternal to the foetal circulation by diffusion. But these 

 investigators have only proved that it diffuses when a hyperglycsemia 



1 Colmsteiii and Zuntz, "Weitere Untersucliungen zur Physiologie der 

 Saugetierfotus," Pflilger's Arch., vol. xlii., 1888. 



