434 THE PHYSIOLOGY OF REPRODUCTION 



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 fcetal 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 placentae 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, 1 glucose 

 passes from the maternal to the foetal circulation by diffusion. 

 But these investigators have only proved that it diffuses when 

 a hyperglycaemia exists in the mother. Under similar con- 

 ditions glucose passes into the urine and liquor amnii in Man, 

 but it does not pass normally. 2 Hence it has not been proved 

 that the sugar of the maternal blood is diffused unchanged 

 through the trophoblast. It is more probable that the trans- 

 ference of sugar is not effected by a purely physical process, 

 since the serum of the fcetal rabbit contains laevulose, while 

 the serum of the mother has none (Pa ton, Kerr, and Watson 3 ). 



Between the glycogen metabolism and the growth of the 

 foetus there is a distinct relationship, which probably depends 

 directly on the uses to which glycogen is put. Part of it is 

 accounted for by the intense carbohydrate metabolism which 

 proceeds in the foetus (Bohr 4 ). The glycogen, which is thus 

 katabolised, furnishes thereby the energy necessary for the 

 formation of new tissues, the " Entwicklungsarbeit " of Tangl. 5 

 The question arises whether glycogen also performs anabolic 



1 Cohnstein and Zuntz, " Weitere Untersuchungen zur Physiologic der 

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



2 Even in the hyperglycaemia of diabetes the figures do not support the 

 theory of the mere diffusion of glucose. Offergeld found 0'8 per cent, of sugar 

 in the maternal blood, and 2*2 per cent, in the foetal blood in diabetic coma 

 (" Ueber das Vorkommen von Kohlehydraten im Fruchtwasser bei Diabetes," 

 Ze.it. f. Geb. u. Gynak., vol. li.). 



3 Paton, Kerr, and Watson (B. P.), "On the Source of the Amniotic and 

 Allantoic Fluids in Mammals," Trans. Roy. Soc. Edinburgh, vol. xlvi., 1907. 



4 Bohr, "Die respiratorische Stoffwechsel des Saugetierembryos," Skand. 

 Arch. f. Phys., vol. x., 1900. See also vol. xv., 1904. 



6 Tangl, " Beitrage zur Energetik der Ontogenese," Pjluger's Arch., 

 vol. xciii., 1903. 



