ABSORPTION OF CARBOHYDRATES BY THE INTESTINES 417 



tein is often protected from the action of the digestive enzymes, there may 

 be 10 to 15 per cent. loss. Analysis of the total lymph discharged by the 

 thoracic duct fails to show any increase of proteins during active digestion, 

 from which it is inferred that proteins pass by way of the liver. 



The non-nitrogenous residue is oxidized or temporarily stored as glycogen. 



From 12 to 15 per cent, of the protein remains in the food as it passes the 

 ileocecal valve. This amount, less the loss in the feces, is absorbed in the 

 large intestine. 



Absorption of Carbohydrates by the Intestines. Carbohydrates 

 are broken down to dextrose, levulose, etc., and are absorbed as such. Even 



FIG. 284. Section of the Villus of a Rat Killed during Fat Absorption, ep, Epithelium; 

 sir, striated border; c, lymph cells; c', lymph cells in the epithelium; /, central lacteal con- 

 taining disintegrating lymph corpuscles. (E. A. Schafer.) 



the soluble cane-sugar is split by the invertase of the intestine into the mono- 

 saccharides, dextrose and levulose. Starch is the source of most of the 500 

 grams of dextrose absorbed in an average diet per day. During the absorp- 

 tion of a carbohydrate meal the percentage of dextrose in the blood of the 

 portal vein is increased over the normal, which is o . i to 1.5 per cent. This 

 excess of dextrose passes through the liver and is temporarily stored in the 

 liver cells as glycogen. In the case of a fistula in the receptaculum chyli. 

 the chyle contained less than a half per cent, of the total dextrose absorbed. 



Experiments on the rate of absorption of the different sugars seem to 

 indicate that their absorption does not follow known physical laws and that 

 we must assume an unknown chemical factor in the living protoplasm. 



Dextroses are absorbed readily by the large intestine. 



