DIGESTION AND ABSORPTION 313 



ive juice and place in it a small amount of cooked starch. (2) In a 

 second tube, place a small amount of white of egg or other proteid 

 with the artificial digestive juice. (3) In a third, place a few drops of 

 olive oil and artificial digestive juice. Leave these preparations in a 

 water bath or oven at 98° F. for 12 hours and note results. 



When the food is thoroughly dissolved it has reached the 

 last stage of digestion. It is now ready for absorption. 



Absorption. — ^We have learned that the blood carries food 

 to the deep seated cells of the body. The transfer of the 

 digested food through the walls of the intestine to the blood 

 is called absorption. 



The sole object of absorption is to get the digested food 

 into the blood. This takes it through the walls of the villi. 

 Fig. 161 represents a series of villi cut through to show the 

 loose network of blood capillaries and lymphatic capillaries 

 (lacteals) within each one. Lymphatic vessels are like blood 

 vessels in some ways but they carry a milky fluid and not 

 red blood. The mucous membrane of the intestine is 

 bathed by the digested food. To reach the blood and 

 lacteals, this digested food must pass through the mucous 

 membrane of the villi and the thin walls of the capillaries 

 and lacteals. 



This is accomplished by osmosis (see page 298). Only 

 soluble substances can mix by osmosis, hence it is that starch, 

 proteids and other foods must be dissolved or digested before 

 they are ready for absorption. 



Where absorption takes place. — A minute quantity of 

 peptone (derived from proteids) may be absorbed in the 

 stomach, and a small amount may pass into the large in- 

 testine and become absorbed there, but most of it passes 

 through the walls of the villi of the small intestine into the 

 blood. 



The sugar (derived from carbohydrates) is absorbed into 

 the blood through the villi also. 



The fats (as emulsions or soaps) pass into the lacteals. 



