l40 ABSORPTION 



carried into the small intestine with the chjTue. In the 

 small intestine, therefore, is found the main seat of proteid 

 absorption. A little may pass into the large intestine and 

 be absorbed there, but this represents a very small amount 

 of the whole, less in fact than in the stomach under ordi- 

 nary conditions. Wherever it is absorbed it passes into 

 the blood and never into the lymphatics or lacteal system. 

 The reason for this selection is another of the facts not 

 yet explained. In passing through the mucous mem- 

 brane cells, as already mentioned, the protoplasm of those 

 cells breaks down the peptone into a simpler form of 

 proteid and delivers it in that form to the blood. While 

 this action of the protoplasm is not yet fully explained, 

 indications are that the change talces place in the mucous 

 membrane cells, and is due to an enzyme present in the 

 protoplasm. At present we know nothing of what this 

 enzyme is or its composition. In view of the poisonous 

 action of peptone upon the blood and the system, its 

 importance is evident. 



Starch and sugar. By the time digestion is completed 

 in the small intestine, starches and sugars have all been 

 changed to grape sugar, and this substance passes into 

 the blood without change. AA'hile some may be absorbed 

 in the stomach and large intestine, the main seat of 

 absorption is the small intestine, as in the case of proteid. 

 Like proteid, grape sugar enters the blood, and not the 

 lacteals. 



Fats. Fats are absorbed either as emulsions or soaps, 

 and instead of entering the blood they are the only form 

 of nutrient that passes into the lacteals. In passing 

 through the mucous cells of the villi the soaps are changed 

 back into emulsions so that the fat which enters the lac- 



