OTHEK SOURCES OF GLYCOGEK 143 



red color instead of the blue color of ordinary starch. 

 The manner in which this glycogen is formed from the 

 grape sugar of the portal vein is explained as follows: 

 The protoplasm of the liver cells causes the sugar to lose 

 water, and the result is a chemical change resulting in 

 glycogen. 



It has been demonstrated that blood which contains 

 over a certain proportion of grape sugar throws off this 

 excess through the kidneys, and it is thus lost to the 

 body as a nutrient. To avoid this loss the liver cells take 

 up this sugar and convert it into glycogen, which they 

 store in the body of the cell and feed out to the tissue- 

 supply system as it is needed. Before they feed it out 

 they reconvert it into grape sugar, and thus the amount 

 of sugar contained in the blood which supplies the tissues 

 never exceeds a certain proportion (0.1% to 0.2%). The 

 liver, therefore, acts as a storehouse of the carbohydrate 

 or energy supplying nutrient of the body. How it changes 

 the glycogen back to sugar is not fully known, but it is 

 supposed that the liver cells contain an enzyme similar 

 to diastase, which performs this action, as needed. When 

 we consider that the carbohydrates furnish the main 

 part of the energy of the body, this regulative action of 

 the liver becomes very important to the activity of the 

 body. 



Other Soueces of Glycogen. 



Experiments have demonstrated that, to some extent, glycogen 

 may be formed also from proteids. For example, when a person 

 suffering from diabetes is fed upon purely proteid foods, all carbo- 

 hydrates being excluded from his diet, sugar is still formed. 

 This can be explained only on the assumption that it is manu- 

 factured from proteid. This manufacture is believed to take 



