1036 CARBOHYDRATE METABOLISM [pt. iii 



(c) Eleventh day. The insulin about this time attains such con- 

 centration or activity that it is able to stop the relative increase of 

 free glucose, which now passes through its peak. Perhaps the ap- 

 pearance of insulin is sudden, for Pucher & Hanan could not find 

 any in the embryo until the i ith day. The Hver cells, changing the 

 character of their growth, prepare to receive stores of glycogen, 

 and from this point onward do so (Murray; Sakuragi; Potvin 

 & Aron). 



{d) Eleventh day till the end of embryonic development. The control of 

 the free glucose by the insulin continues, so that as per cent, of the 

 total glucose it declines. Synchronously with this process the glycogen 

 of the embryonic liver increases steadily in amount, its origin being 

 partly the glycogen of the transitory liver in the blastoderm and 

 partly the diminishing free glucose. In other tissues also, e.g. the 

 intestinal walls (Maruyama) glycogen steadily increases. The carbo- 

 hydrate systems in the chick are now fully sensitive to the action of 

 insulin. 



The concomitant events outside the embryo may be traced by the 

 curves given above. The most remarkable items seem to be that, 

 when the free carbohydrate is at a maximum in the embryo, it is 

 at a minimum outside, and that the periods of maximum importance 

 of mucoprotein glucose inside the embryo coincide with the periods 

 of maximum catabolism of ovomucoid outside. 



8-8. Embryonic Tissue Glycogen 



A good deal has been said already about the glycogen in the foetal 

 liver at different stages, and the question now arises as to what 

 happens to the glycogen in the rest of the body and its different 

 parts. Fig. 270, embodying the data of Murray and Sakuragi, 

 demonstrates that in the case of the chick the glycogen in the em- 

 bryonic body as a whole rises in a regular curve both absolutely and 

 relatively. In the last half of last century, much importance was 

 for some reason attached to the embryonic glycogen, and it was 

 thought that this substance was in some mysterious way connected 

 with growth and differentiation. This belief died out when it came 

 to be found that glycogen is not present in embryonic tissues to a 

 greater extent than in adult ones. Fig. 287 shows the combined data 

 of various investigators, the abscissa being in all cases conception age. 

 Gage claimed to have seen glycogen histochemically in pig embryo 



