ABSORPTION. 225 



new materials are taken out of the alimentary canal and transferred 

 into the lymph-spaces, in the body of the villi, from which they are 

 subsequently removed by the blood-vessels and lymphatics. As to 

 the mechanism by which the epithelial cells accomplish this result, 

 nothing definite can be asserted. Inasmuch as the absorption of 

 food does not take place in accordance with the laws of osmosis as at 

 present understood, it has been suggested that the cells possess a 

 "selective action" dependent on their organization and living con- 

 dition, an action which is to a great extent conditioned and limited 

 by the degree of diffusibility of the substances to be absorbed. 



Absorption of Water and Inorganic Salts. Water and inorganic 

 salts after their absorption from the intestine and transference into 

 the lymph-spaces of the villi pass through the walls of the capillary 

 blood-vessels and are carried by the way of the portal vein into the 

 liver. Unless water be present in excessive amounts, there is no 

 appreciable absorpion of water by the lymphatics. 



Absorption of Sugar. As previously stated, all the carbohydrates, 

 with the exception possibly of lactose, are transformed by the diges- 

 tive fluids into either dextrose or levulose, under which forms they 

 are absorbed by the epithelial cells. It is possible, however, that 

 soluble dextrin may also be absorbed./t Whatever the form ^pder 

 which the carbohydrates are absorbed, they/never leave the epithe- 

 lial cells except as dextrose and levulose. /^Direct experimentation 

 has shown that the sugars are taken up by the capillary blood-vessels 

 and carried direct to the liver. Analysis of the blood of the portal 

 vein after the ingestion of large quantities of sugar may reveal an 

 increase of 0.25 per cent.; while after the injection of sugar into the 

 intestine the percentage may rise as high as 0.4. As chemic analysis 

 of lymph obtained from the thoracic duct shows -no increase in the 

 percentage of sugar beyond that normally present (o.i per cent.), it 

 is assumed that sugar is not removed from the villi by the lymphatics. 



Absorption of Proteids. Since most of the proteids are transformed 

 through hydration and cleavage by the action of the gastric and pan- 

 creatic enzymes into peptones, there is reason to believe that this 

 change is necessary to their complete and rapid absorption. Never- 

 theless it has been shown by the results of experimentation that 

 unchanged native proteids, such as egg-albumin, and partially 

 digested proteids, such as acid and alkali albumin, albumoses, may 

 likewise be absorbed from the small intestine, though in far less 

 amounts. It has also been demonstrated that native proteids can 

 be absorbed from the large intestine. Inasmuch as chemic analysis 

 has failed to detect more than a trace of either peptone or native pro- 

 teid in the portal blood or in the lymph of the thoracic duct, it must 

 be assumed that the epithelium after absorbing must also synthetize 

 them into some form of coagulable proteid (serum-albumin) which is 

 15 



