150 The Feeding of Animals 



THE LIVER 



One part of the arterial system of blood-vessels 

 runs to the stomach and intestines and is distributed 

 over their walls in fine divisions. These connect 

 with the capillaries of the portal vein which leads to 

 the liver. During this passage of the blood from 

 one system to the other, part of the digested food 

 is taken up. Now it is very evident that the quan- 

 tity of material thus absorbed must vary greatly at 

 different times according to the nature and amount of 

 food supply and the activity of the digestive processes. 

 If, therefore, the blood from the alimentary canal was 

 allowed to pass directly into the general circulation, 

 the* supply to the tissues of the nutrients, especially 

 the carbohydrates, would be very uneven. Just here 

 comes in a liver function. In that organ there is 

 found a starch -like body known as glycogen, which 

 appears in increased quantity following the abundant 

 absorption of sugar from the intestines. It is believed, 

 because of this and other facts, that the liver acts as 

 a regulator of the carbohydrate supply to the general 

 tissues of the body, storing a temporary excess of the 

 sugar in the form of glycogen and then gradually 

 giving it up to the general circulation as it is needed. 



