CARBOHYDRATES. 67 



Does the latter become changed into glyco'gen, does it form a particular 

 glycogen of its own, or is the fructose first changed into d-glucose, 1 and 

 then, in common with the other glucoses, changed to glycogen? Until 

 recently it was quite generally assumed that the last-mentioned process 

 was carried out, but now certain facts have become known which will 

 perhaps lead us to another conception. It has been established that, 

 after the extirpation of the pancreas in dogs, not only does sugar appear 

 in the urine, but at the same time the formation of glycogen in the liver is 

 interfered with, and as a matter of fact this disturbance is much more 

 pronounced when d-glucose is fed to the dog than in the case of fructose. 

 The exact significance of this result is at present not clear. 



When the food is rich in carbohydrates the liver cannot retain all of 

 it as glycogen. The glycogen stored in the liver of man amounts at the 

 most to 150 grams. The muscles can take up an equal amount provided 

 they did not originally contain considerable. As this is often the case 

 under normal conditions, however, we must answer the question as to 

 what becomes of the sugar which is not disposed of as glycogen. A direct 

 consumption of large amounts of sugar is not to be thought of; and on the 

 other hand the sugar content of the organs, and of the blood especially, 

 never exceeds certain well-established limits when the storage places for 

 glycogen have been filled. Here for the first time, we meet with the 

 question of the transformation of one food-stuff into another. Sub- 

 sequently we shall have to study this closely, but at present we will merely 

 mention that the excess of sugar is evidently disposed of as fat, a phenom- 

 enon which we meet with in the vegetable kingdom, and one which plays 

 an important part in the depositing of nutriment in latent seeds, and 

 conversely in its utilization at the time of germination. 



Now what becomes of this stored-up glycogen? As we have seen, the 

 glycogen gradually disappears if nourishment is withheld or work is 

 performed. It was Claude Bernard 2 who first showed this relation between 

 glycogen and muscular work. He found that the livers of hibernating ani- 

 mals during their winter's sleep contained large amounts of glycogen, and 

 not only was the glycogen contained in the liver cells, but also in the 

 muscular tissue and in the lungs. As soon as the animals awoke and 



1 Such a transformation is explained to us by the work of C. A. Lobry de Bruyn and 

 W. Alberda van Ehenstein, Ber. 28, 3078 (1895), and Rec. trav. chim. 14, 103, 156. 

 These two authors have shown that glucose, fructose, and mannose can be easily trans- 

 formed into one another in alkaline solution. The transformation of mannose into 

 glucose is equally interesting as that of fructose into glucose, for the former is used 

 as material for the formation of glycogen. Thus in Japan a natural manna is found 

 which serves the inhabitant in the same way as starch does for us. Cf. Low and Tsuji: 

 Landwirtschaftliche Versuchstationen, 45, 433. Also Haycraft: Z. physiol. Chem. 19, 

 137 (1894). 



2 Compt. rend. 48, 673 (1859). 



