I024 



CARBOHYDRATE METABOLISM 



[PT. Ill 



total glycogen per cent, of the placental weight, except at the time 

 (between the i8th and 22nd days) when the maximal placental 

 amounts are present. These facts are in exact agreement with the 

 work of Chipman. 



Fig. 278 should be compared with Fig. 270. It can be seen that 

 they are fundamentally alike — in the case of the chick the rising 

 embryo curve and the falling 

 non-embryo curve cross at the 

 17th day of development; in 

 the case of the rabbit the rising 

 embryo curve and the falling 

 placenta curve cross at the 27th 

 day of development. It is inter- 

 esting to enquire whether these >' 

 cross-over points occur at equal -^ 

 percentages of the whole de- 

 velopmental time, and it is easy 

 to calculate what percentage of 

 the total amount of glycogen 

 in the system is at any given 

 moment in the embryo and 

 what percentage is in the ad- 

 nexa. If this is done a graph is 

 obtained like that in Fig. 279, 

 from which it may be deduced that the mid-point in the assump- 

 tion of the glycogenic function (the "cross-over point") by the 

 embryonic liver occurs when 82 per cent, of the total development 

 is achieved in the case of the chick and 91 per cent, in the case of 

 the rabbit. Another interesting point which emerges from Fig. 278 

 is that the amounts of glycogen in the embryonic liver and the 

 amounts in the placenta would not fall on a horizontal line if added 

 together. This must mean either that some of the placental glycogen 

 is destined for other organs of the embryo than the liver, or that a 

 catabolism of carbohydrate as energy source is going on. The latter 

 possibility fits in, of course, with what has already been said 

 about the energy sources of mammalian embryos (see pp. 729 

 and 993). 



"The most obvious phenomenon in the decidual cells of the rabbit 

 is the presence of glycogen at a time when the foetal liver cells store 



7 18 19 20 21 22 23 24 25 26 27 28 29 

 Days of development 



278. 



