822 PHYSIOLOGY OF DIGESTION AND SECRETION. 



days, the blood retains a practically constant composition in sugar 

 indicates that this material is being formed from either the protein 

 or fat-supply of the body. Other considerations tend to exclude the 

 fat, and we are, therefore, led to the belief that the protein can give 

 rise to sugar in the body. 



Effect of Fats upon Glycogen Formation. — ^A large number of 

 substances have been found by some observers to increase the store 

 of glycogen in the liver. In some of these cases at least it is evident 

 that the substance is not a direct glycogen-former in the sense that 

 the material is itself converted to glycogen. It may increase the 

 supply of liver glycogen in some indirect way, — for example, by 

 diminishing the consumption of glycogen in the body. The most 

 important substance in this connection from a practical standpoint 

 is fat. Whether or not the body can convert fats into sugar or 

 glycogen is a question about which at present there is a difference 

 of opinion, but the balance of evidence is against the possibility 

 of the conversion of the fats (fatty acids) to sugar. Cremer, 

 however, has furnished apparent proof that glycerin acts as a 

 direct glycogen or sugar-former. When fed, especially in the dia- 

 betic condition, it causes an increase in the sugar which cannot 

 be explained as a result of protein metabolism. Since in the body 

 neutral fats are normally split into glycerin and fatty acid, the fact 

 that glycerin can be converted to sugar seems to carry with it the 

 admission that fats maj^ contribute directly to sugar production. 

 Whether the synthesis of sugar (or glycogen) from glycerin is, 

 so to speak, a normal process or occurs only under special condi- 

 tions, cannot be decided at present. Since, however, the glycerin 

 radicle constitutes but a small fraction of the fat molecule, the 

 quantitative importance of a change of this kind cannot be very 

 great under any circumstances. 



The Function of Glycogen— The Glycogenic Theory.— The 

 meaning of the formation of glycogen in the liver has been the 

 subject of much discussion. The view advanced first by Ber- 

 nard is the one now most generally accepted. According to 

 Bernard, glycogen forms a temporary reserve supply of carbo- 

 hydrate material that is laid up in the liver during digestion and 

 is gradually made use of in the intervals between meals. During 

 digestion the carbohydrate food is absorbed into the blood of the 

 portal system as dextrose or as dextrose, levulose, and galactose. 

 If these sugars passed through the liver unchanged, the contents 

 of the systemic blood in sugar would be increased perceptibly, 

 giving the condition designated as hyperglycemia and the excess of 

 sugar would be excreted by the kidneys. But as the blood from 

 the digestive organs passes through the liver the excess of sugar is 

 abstracted by the liver cells, is dehydrated to make glycogen, and is 



