IO4 



HUMAN BIOLOGY 



FIG. 97. LINING OF 

 SMALL INTESTINE, 

 magnified, showing villi 

 and mouths of intestinal 

 glands. 



numerous folds in order to increase the secreting and 

 absorbing surface (Fig. 96). On and between the folds 



are thousands of little threadlike 

 projections called villi (Fig. 97). 

 In each villus are found fine capil- 

 laries and a small lymphatic called 

 a lacteal (colored Fig. 2). The villi 

 are so thick that they make the 

 lining of the intestine like velvet, 

 and enormously increase the absorb- 

 ing surface. 



Digestion in the Small Intestine. - 

 This is by far the most active and 



important of the digestive organs. The mouth digests 

 a small part of the starch, and the stomach digests a 

 small part of the proteid ; the small intestine digests 

 most of the starcJi, most of tJie proteid, and all of tJie 

 fats. The food is in the mouth a few minutes, and in the 

 stomach two or three hours ; it is in the small intestine ten 

 or twelve hours. There are thousands of small glands 

 called intestinal glands that open between the villi (Fig. 

 97) and secrete the intestinal juice, which digests cane 

 sugar. Besides these, there are two very large and active 

 glands, the pancreas and liver, which empty into the 

 intestine by ducts. 



The Pancreas. The small intestine is the most impor- 

 tant of the digestive organs, chiefly because it receives the 

 secretion from the pancreas, the most important of diges- 

 tive glands. The pancreas is a long, fiat, pinkisJi gland 

 situated behind tJie stomach (see Fig. 90). The pancreatic 

 juice contains three powerful ferments > one of which (amy- 

 lopsin) digests the starches, another (trypsin) digests pro- 

 teids, and the third (steapsin),. with the aid of the bile, 



