104 



HUMAN BIOLOGY 



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, 

 FIG. 97. LINING OF .. . . , , , 



SMALL INTESTINE, and enormously increase the absorb- 



magnified, showing villi jfjg Surface. 



and mouths of intestinal _ ,, _ , .. 



g i ands 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 starch, most of the proteid, and all of the 

 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, flat, pinkish gland 

 situated behind the 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, 



