126 



METABOLISM AND NUTRITION 



In view of the great variations in the percentage of glycogen in the body, 

 if one is to determine directly the influence of different foodstuffs on its storage, 

 it is necessary first to deprive the animal, as far as possible, of all its glycogen. 

 As appears from Pfliiger's experiment on the dog cited above, a considerable 

 quantity of glycogen may remain in the body even after prolonged fasting. 

 Glycogen is far more completely removed from the body by severe muscular work ; 

 in fact under such circumstances it sometimes disappears almost completely, 

 both from the liver and from muscles, in the course of a few hours. Naturally, 

 the effect of muscular work is assisted by a previous fasting period. 



There are a great number of different substances which have been claimed 

 to bring about an increase in the percentage of glycogen in the liver. Among 





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V. ? 



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PIG. 45. Preparations from the liver of a man, after Frerichs. A, section through the normal 

 liver containing glycogen; B, section through the liver of a diabetic, almost free of glycogen. 

 Both preparations treated with iodine. 



them are several which, at most, act only indirectly, either by stimulating the 

 liver cells to produce glycogen or by diminishing its consumption. We shall 

 pass over these substances and consider here only the true glycogen formers. 



There is no longer any doubt that certain carbohydrates constitute an 

 important source of glycogen:, proofs of this are present on every hand. For 

 example, after feeding with cane-sugar, grape-sugar or starch, 14.7 per cent 

 of glycogen has been found in the liver of hens, 10.5 per cent in that of the 

 goose, and 16.9 per cent in the rabbit's liver. 



It might be supposed that the carbohydrates had not contributed directly 

 to this storage of glycogen, but that they only protect glycogen split off from 

 proteid from being further oxidized. Otto has shown, however, that even if we 

 assume that the greatest possible amount of glycogen has been formed from pro- 

 teid, there always remains a considerable excess which could only have come 

 from carbohydrates. Similarly Popielski found that in dogs in which an Eck 



