480 APPLIED BIOLOGY 



any kind of food, and consequently any food not made ready 

 for absorption while in the stomach is digested by the en- 

 zymes poured into the intestine. The final result is that the 

 starch, proteins, and fat which enter the intestine undigested 

 are prepared for absorption. For this work the intestine 

 is specially adapted, because of the numerous delicate pro- 

 cesses (called villi, singular is villus) which extend from the 

 lining membrane (see Fig. 159). These are richly supplied 

 with blood- and lymph-vessels, into which digested food is 

 absorbed , rapidly. 



402. Details of Digestion in Intestine (Optional). The 

 bile from the liver, the secretion from the glands in the walls 

 of the intestine, and the pancreatic secretion are alkaline, 

 and quickly change the acid food which arrives from the 

 stomach. Of the pancreatic secretion, the enzyme called 

 amylopsin acts like the ptyalin of the saliva and digests starch 

 to sugar ; the enzyme called trypsin acts on proteins much 

 the same as pepsin does in the stomach ; and the enzyme 

 lipase (or steapsin) changes fats to fatty acid and glycerine. 

 The fatty acid easily combines with the alkaline substances 

 in bile and intestinal juice and forms a kind of soap which 

 is absorbable. Since the pancreatic secretion is able to 

 digest rapidly the three kinds of food, it is by far the most 

 important digestive secretion. 



Bile, from the liver, does not itself digest any food, but it 

 has been shown that fats are digested and absorbed better 

 when bile is present. 



The intestinal juice, from the glands of the intestine, has 

 a number of enzymes of which the most important change 

 cane-sugar, milk-sugar, and malt-sugar into glucose or similar 

 sugars. 



(D) It is possible to demonstrate the effect of pancreatic secre- 

 tion upon proteins and starch by performing experiments similar 

 to the previous ones ( 398 and 399) with saliva and gastric juice, 

 but substituting in this case pancreatic secretion. This may be 



