SECT. 8] CARBOHYDRATE METABOLISM 1039 



Some other experiments on glycogen in embryonic life are worth 

 mentioning. Driessen's histological work showed that the early ovum 

 of the rabbit, the mouse, and man (from the 3rd to the 6th week 

 in the latter case) is surrounded by a layer of cells very rich in 

 glycogen. This is probably significant for the nourishment of the 

 embryo, and brings to mind the observation of Zavattari that the 

 test cells of ascidian eggs are full of glycogen granules also. M. R. 

 Lewis studied the cells of early embryos of the chick and the minnow 

 in tissue cultures. Glycogen was always present according to histo- 

 chemical test in the latter case, but only for the first 48 hours of 

 development in the former. This is in agreement with Kiilz's work 

 already mentioned, where 5000 6-hour cicatriculae were taken and 

 worked up for glycogen. 



Another analogous line of investigation is that of Vastarini-Cresi, 

 who has studied histochemically the appearance and distribution 

 of glycogen in the chick embryo. The first traces appear, according 

 to him, in the heart at the 2nd day of development, i.e. at the be- 

 ginning of pulsation. He considers that the canaHsation of vessels 

 and spaces is specially associated with glycogen metabolism. He 

 divides organogenesis into three phases: (i) Active cell multiplica- 

 tion in all directions to form a bud; here no glycogen can be found 

 in them. (2) A period of glycogenic infiltration followed by one of 

 canalisation or cellular dissolution. The inside cells become so full 

 of glycogen that they cytolyse, and so form cavities. (3) Removal 

 of the glycogen to other places. 



8-9. Embryonic Blood sugar 



The question of embryonic blood sugar and what happens to it 

 must now be taken up. As long ago as 1875 Moriggia gave figures 

 for foetal blood sugar in many animals. 



Hanan's figure for the embryonic blood sugar of the chick at the 

 15th day is not in agreement with the later one of Vladimirov & 

 Schmidttj who also used the Hagedorn-Jensen method, but probably 

 worked on chicks of a different breed. They found a constancy until 

 just before hatching, and considered that from the nth day onwards 

 insulin was an effective agent in regulating the blood sugar leveP (see 



1 Vladimirov has also studied the effect of adrenalin, asphyxia, etc. on the embryonic 

 blood sugar of the chick. The results of Riddle & Honeywell agree with Vladimirov & 

 Schmidtt rather than with Hanan, for they found the blood sugar of the embryo to be 

 always less than that of the adult (3 species of pigeons) . 



