METABOLISM, NUTRITION AND DIETETICS 449 



While the liver in the adult (containing as it does from 2 to 10 

 per cent of glycogen, or even more with a diet rich in sugar or starch) 

 may be looked upon as the main storehouse of surplus carbo-hydrate, 

 depots of glycogen seem to be formed, both in adult and fcetal life, 

 in other situations where the strain of function or of growth is excep- 

 tionally heavy in the muscles of the adult (0-3 to 0-5 per cent, of the 

 moist muscle), in the placenta, in many developing organs in the 

 embryo (lungs, epithelium of the trachea, oesophagus, intestine, ureter, 

 pelvis of kidney, and renal tubules.) In the embryonic muscles the 

 glycogen may constitute as much as 40 per cent, of the solids. 



Although it cannot be doubted that much of the hepatic glycogen 

 leaves the liver as sugar, there is no proof that it all does so. It is known 

 that fat maybe formed from carbo-hydrates (p. 458); and globules of 

 oil are often conspicuous among the contents of liver-cells, side by side 

 with glycogen. It is possible, therefore, that some of the glycogen 

 may represent a half-way house between sugar and fat, or, since fat 

 can also be formed from proteid, and a purely proteid diet produces 

 some glycogen, a half-way house between proteid and fat. The 

 so-called ' liver dextrin/ a nitrogenous substance containing a carbo- 

 hydrate group, which reduces cupric oxide and yields a reducing 

 sugar on being heated with dilute acid, may be an intermediate 

 stage in the conversion of proteid into sugar. According to Seegen, 

 its discoverer, the amount of this body in the liver sometimes 

 exceeds that of the glycogen and sugar put together. That glycogen 

 may be produced from proteids even during starvation is shown by 

 the following experiment : A fasting animal was put under the 

 influence of strychnia to remove all glycogen from the liver. Then 

 the strychnia spasms were cut short by chloral, and the animal 

 allowed to sleep for eighteen hours. At the end of that time a 

 considerable amount of glycogen was found in the liver and muscles, 

 and this must have come from the proteids of the body. 



Pavy has put forward the heterodox view that the glycogen formed 

 in the liver from the sugar of the portal blood is never reconverted 

 into sugar under normal conditions, but is changed into some other 

 substance or substances, and he denies that the post-mortem forma- 

 tion of sugar in the hepatic tissue is a true picture of what takes 

 place during life. But in spite of the brilliant manner in which he 

 has defended this thesis both by argument and by experiment, it 

 must be said that the older doctrine of Bernard, which in the main 

 we have followed above, is attested by such a cloud of modern 

 witnesses that it seems to be firmly and finally established. 



Fate of the Sug-ar, What, now, is the fate of the sugar 

 which either passes right through the portal circulation 

 from the intestine without undergoing any change in the 

 liver, or is gradually produced from the hepatic glycogen? 

 When the proportion of sugar in the blood rises above a 

 certain low limit (about 3 parts per 1,000), some of it is 

 excreted by the kidneys (Practical Exercises, p. 526). 



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