FUNCTIONS OF THE LIVER 79 



Glycogenic Function of the Liver. Glycogen, or ani- 

 mal starcli can be detected by the microscope in the 

 cells of the liver, increasing after meals and decreasing 

 during the hours of fasting, and varying with the kind 

 and quantity of food, exercise, etc. The amount in the 

 liver varies between 1.5 and 4 per cent of the weight of 

 the liver. Glycogen is chiefly derived from starchy 

 foods, though proteins may furnish small amounts. Fats 

 seem to increase the amount of glycogeii in the liver by 

 preventing its consumption in other parts of the body. 



GLYCOGEN THEORY. The theory of this function of the 

 liver is that it maintains the sugar equilibrium of the 

 body; that is, that an increase of carbohydrate food 

 would always be followed by an increase of sugar in 

 the blood if the liver did not convert the dextrose and 

 other sugars into animal starch which it stores up until 

 a fasting period, or at least decrease of the normal 

 sugar content of the blood, calls for a renewal of the 

 supply, when the stored glycogen of the liver is recon- 

 verted into sugar and given up to supply the deficiency. 

 This conversion appears to be accomplished by a special 

 enzyme formed for the purpose, in the liver. 



The liver is not the only store house for glycogen. 

 It is estimated that the red muscles of the body contain 

 as much of this starch as the liver itself, and that it is 

 used up more rapidly when the muscle is active than 

 when passive. 



Urea-Forming Function of the Liver. Urea is the 

 chief form in which nitrogen is removed from the body. 

 This product of protein food is eliminated from the 

 blood by the kidneys, but it is formed in the liver and 

 sent to the kidneys only to be extracted. No doubt the 

 liver is not the only source of urea, but it is at least 

 a demonstrated source of this end product of protein 

 digestion. 



