ABSORPTION FROM THE SMALL INTESTINE 73 



Salts, like sodium iodide, are not at all absorbed in dilute solu- 

 tions, but when the concentration reaches 3 per cent., absorption 

 becomes pronounced. Normally salts never reach this degree 

 of concentration. It has been found that the absorption of 

 sodium iodide is greatly increased by mustard, pepper, and 

 alcohol, which act either by congesting the mucous membrane 

 or perhaps by stimulating the epithelial cells to greater activity. 



Absorption from the Small Intestine. The food in its passage 

 along the intestine moves slowly, requiring from nine to twenty- 

 three hours after ingestion to appear at the end of the small 

 intestine. The latter, moreover, presents a vast surface for 

 absorption by reason of the villi and the valvulse conniventes. 

 Both of these structures favor absorption. As a matter of 

 fact, 85 per cent, of the protein has been found to disappear. 

 That proteoses and peptones are absorbed directly by the 

 blood is shown in ligating the thoracic duct, which does not 

 interfere with their disappearance. Nevertheless, they do not 

 appear in the blood as such, and if present, act as poisonous 

 bodies which cannot be used by the tissues and are immediately 

 excreted by the kidneys. It is probable that they are changed 

 in their passage through the epithelial walls under the influence 

 of erepsin. The direct way of determining the facts would 

 be to examine the blood during the absorption of proteins; 

 but the flow of blood is so great, the quantity of absorbed 

 products so small, and their removal by the tissues probably 

 so rapid, that certain results have not been ascertained. It 

 may be accepted, however, that during absorption there is 

 an increase in the nitrogenous substances of the blood which 

 are not precipitated by tannic acid, and are, therefore, neither 

 native proteins nor proteoses. Urea accounts for one-half 

 of the increase, so that the rest is probably in the form of amino 

 acids. 



Carbohydrates, which are changed to diffusible sugars, 

 dextrose and levulose, are also absorbed directly into the blood, 

 and as a consequence the portal vein has been found to show 

 an increased percentage of sugar after meals. The lymph 

 of the thoracic duct shows no such increase unless excessive 

 quantities have been taken. 



Fats, it is conceivable, may be absorbed in an emulsified 

 condition, or, as glycerin, fatty acids, and soaps. Experi- 



