The Digestion of Food 117 



is, it separates from the blood material that is of no further 

 use to the body and casts it out. 



Of the various ingredients of the bile, only the bile salts 

 are of use in digestion. When mixed with pancreatic juice 

 they play an important part in aiding the emulsification and 

 saponifi cation of fats and their subsequent absorption. 

 ^176. Glycogenic Function of the Liver. The third func- 

 .tion of the liver is different from those already described. 

 It is found that the liver of an animal well and regularly 

 fed, when examined soon after death, contains a quantity 

 of a carbohydrate substance not unlike starch. This sub- 

 stance, extracted in the form of a white powder, is really 

 an animal starch. It is called glycogen, or liver sugar, and 

 is easily converted into grape sugar or dextrose. 



The hepatic cells appear to manufacture this glycogen 

 and to store it up from the products of digestion brought 

 by the portal blood. It is also thought that the glycogen 

 thus deposited and stored up in the hepatic, cells is little 

 by little changed into sugar. Then, as it is wanted, the 

 liver deals out this stored-up material by carrying it to 

 the tissues, as their needs demand, to supply them, with 

 material which can be oxidized to yield heat and motion. 



/ 177. Formation of Urea by the Liver. There is evidence 

 to show that the liver has the power to make urea as well as 

 glycogen. Urea is the nitrogenous waste product which results 

 from the breaking down of proteid. An excess of proteid food 

 is probably broken up in the liver into glycogen and urea. 

 The glycogen is utilized, as we have stated, and the urea is got 

 rid of through the kidneys. 



y 178. The Pancreas. The pancreas, or sweetbread, is a 

 gland from six to eight inches long, weighing from three 

 to four ounces, and is often compared in appearance to a 

 dog's tongue. 



