SECT. 8] CARBOHYDRATE METABOLISM 1045 



of the central nervous system, the cells of the choroid plexus and the 

 retina. 



Konopacki & Konopacka insisted on the necessity of histo- 

 chemical work as adjuvant to purely chemical investigations, and, 

 as it is true that chemical analyses at present cannot distinguish 

 between regions such as the three germ layers, for instance, they were 

 quite right. But what they did not emphasise was the fact that histo- 

 chemical methods are much more uncertain than purely chemical 

 ones. 



Faure-Fremiet & Dragoiu paid some attention to the glycogen in 

 the developing frog's egg. Using the Bierry-Gruzevska method, they 

 found 3-31 gm. percent, (wet weight) glycogen in the unfertilised egg, 

 or 7-81 per cent, dry weight, and in absolute figures 0-135 mgm. 

 per egg. At hatching the glycogen had diminished to 1-75 per 

 cent, wet weight, or 0-079 n^gm- per ^gg, so that between fertilisation 

 and hatching each egg had lost 0-056 mgm. of glycogen. It would 

 thus appear that over the whole period there is a loss of glycogen, 

 amounting to 41 per cent, of the amount originally there. Evidently 

 the mechanisms at work in the frog's egg differ considerably as 

 regards glycogen from those at work in the hen's. The fall in glycogen 

 added to the fall in fat was found by Faure-Fremiet & Dragoiu 

 not to account for the fall in dry weight and calorific value, so they 

 postulated a fall in protein as well. At the end of the larval yolk-sac 

 period, these workers could find only traces of glycogen. Over the 

 whole period a dry weight loss of 17-3 per cent, was observed, of 

 which 3-2 per cent, was contributed by glycogen, for Faure-Fremiet 

 & Dragoiu did not envisage the possibility that the glycogen might 

 have been transformed into some other substance. 



This, however, was found to happen by Needham. Table 129 

 gives the results obtained, setting side by side with them the data 

 of all the observers who have ascertained the loss in dry weight and 

 the big gain in wet weight which the frog embryo has before hatching. 

 It can thus be seen that, although Faure-Fremiet & Dragoiu found 

 that the egg has only 58-5 per cent, of its glycogen left at the end 

 of development, it has 92-8 per cent, of its total carbohydrate, 

 and the conclusion must be that the glycogen has been transformed 

 into some other kind of carbohydrate, not, as Faure-Fremiet & 

 Dragoiu thought, that it has been combusted to provide energy for 

 the embryo. 



