SECT. 8J 



CARBOHYDRATE METABOLISM 



1031 



thereafter rises with the others (see Fig. 221). This was interpreted 

 as illustrating the importance of carbohydrate as an architectural 

 material in the youngest stages, an importance which was, however, 

 only transitory, and gave way 

 before development was half 

 complete to the predominance 

 of protein and fat found in the 

 adult. The data for the free 

 glucose made it possible to deter- 

 mine to which of the carbohy- 

 drate fractions the total carbo- 

 hydrate concentration curve 

 owed its preliminary peak. With- 

 out doubt it is the great amount 

 of mucoprotein glucose present '^' "^ ^' 



in the embryo in the initial stages which causes this effect. 



Since we know the glycogen present in the embryo each day, a 

 glycogen/glucose ratio can be constructed. As Fig. 285 shows, it 

 remains steady till the middle of incubation, after which it rather 

 suddenly rises, and acquires a 

 new steady value. The point 

 which is important here is the 

 peak in the curve representing 

 the free glucose in percentage of 

 the total glucose, and, at exactly 

 the same time, the rapid change 

 in the glycogen/glucose ratio. 

 Why should there be a higher 

 proportion of free glucose in the 

 embryo then than at any other 

 time ? The answer must surely be 

 that the free glucose goes on increasing until a point is reached at 

 which the production of insulin overhauls it and a control of the 

 proportion of free and combined sugar can be attained. Fig. 285 shows 

 diagrammatically the part played by the pancreas in this mechanism. 

 In early embryonic life there are one and a half times as much glucose 

 as glycogen, but after the critical i ith day there are one and a half 

 times as much glycogen as glucose. In this way the embryo rather 

 quickly approximates to the adult condition, once the time has come 



N E II 66 



Fig. 285. 



