DIGESTION AND ABSORPTION OF NUTRIENTS 101 



villus, the liquefied food is readily absorbed by the blood 

 current. Within the villi, too, are other thin-walled tubes, 

 called lacteals, which are of great importance in the absorption 

 of fats. As the souplike mass of food is pushed slowly 

 along through the small intestine, it becomes less and less 

 in bulk, and more and more solid, owing to the fact that the 

 dissolved salts, sugars, peptones, and fats are largely taken up 

 by the blood vessels and lacteals within the villi. 



141. Absorption in the large intestine. The amount of absorp- 

 tion in the large intestine is considerably less, of course, for both 

 villi and ridges are wanting. Yet even here considerable absorp- 

 tion takes place. When the mass reaches the lower end of the in- 

 testine, it consists of little but the indigestible cellulose of vegetable 

 foods, some undigested connective tissue, waste substances from the 

 bile, the solids in the mucous secretion, and some raw starch and 

 undigested fats if large quantities of these nutrients have been eaten. 

 This refuse of the food is thrown off from the body. 



VIII. THE LIVER AND ITS FUNCTIONS 



142. Position, form, size. The human liver (Fig. 26) is the larg- 

 est gland of the body, weighing three to four pounds. It lies toward 

 the right side of the body, just beneath the diaphragm, and par- 

 tially covers the pyloric end of the stomach. It consists of several 

 lobes, and on its under surface there is a small, greenish brown sac 

 called the gall bladder. The deep red color of the liver is partly due 

 to the fact that one fourth of all the blood of the body is found 

 within its tissues. 



143. Functions of the liver. The liver performs three important 

 functions. In the first place, it secretes a golden brown liquid 

 called the bik, which is either poured at once through the bile duct 

 into the small intestine or is stored in the gall bladder until needed. 

 If the bile duct becomes stopped up, the bile is absorbed into the 

 blood and gives to the tissues the yellow tint that is characteristic 



