SECT. 8] CARBOHYDRATE METABOLISM 1043 



was essential and that lack of it led to vacuolation and death in 

 cultures of connective tissue cells from 8-day chicks. Willmer, using 

 intestinal cells from 11 -day chicks, confirmed this and found that 

 the optimal concentration of glucose was rather lower than i per 

 cent., though growth would sometimes proceed well in concentra- 

 tions up to 2 per cent. When, however, Holmes & Watchorn came 

 to make cultures of the embryonic rat kidney, they found that the 

 optimal concentrations were much lower, varying around 0-2 per 

 cent, or even a good deal less, and they suggested that the difference 

 lay between avian and mammalian tissue. They recalled that the 

 amount of glucose in the egg is at certain times quite large, and 

 thought it likely that the chick's tissues might be exposed to greater 

 concentrations of glucose in the egg than those of the rat in the 

 uterus. As will be mentioned in the Section on protein metabolism, 

 Holmes & Watchorn were able to show that glucose exerted a marked 

 protein-sparing action on rat embryonic kidney tissue grown in 

 vitro, as judged by the diminution in ammonia and urea-production. 

 Krontovski & Bronstein, who also worked with embryonic tissues 

 from the rat, were able to demonstrate by microchemical methods 

 a disappearance of glucose from the medium in which the cells were 

 growing!. 



8-10. Carbohydrate Metabolism in Amphibian Development 



We may now consider the movements of the carbohydrate fractions 

 in eggs which have so far been left out of account. The reptiles have 

 been very little investigated, but according to Tomita the 100 mgm. 

 per cent, of free glucose present in the egg of the sea-turtle, Thalasso- 

 chelys corticata, have disappeared entirely by the 30th day of develop- 

 ment. Corresponding with this diminution there is a peak in lactic 

 acid content (see p. 1053). 



As regards amphibia, a histochemical study of the glycogen in the 

 frog embryo and larva was made by Konopacki and by Konopacki & 

 Konopacka. After fertilisation and the formation of the perivitelline 

 space, the amount of glycogen thus estimated diminishes consider- 

 ably, and apparently undergoes no further changes till the gastrula 

 stage. At this time there is little to be seen; only a few cells of the 



1 This was confirmed by Holmes & Watchorn and by Friedheim & Roukhelman. 

 Acidification of the medium may occur owing to the lactic acid produced (Magaih) . 



