THE FOOD AND DIGESTION 359 



genous part forming ammonia compounds, probably carba- 

 mate of ammonia 



o 



H ,! 



\N C 0- 



H 



H 

 H 



Its non-nitrogenous part -probably yields carbohydrates, 

 since a proteid diet may lead to the accumulation of these 

 substances in the liver. The ammonia compounds are car- 

 ried to the liver and there changed to urea, and excreted 

 as such. Thus the entrance of an excess of nitrogen into the 

 tissues is prevented. 



It has been pointed out that gastric juice does not dissolve 

 the nucleo-proteids, but that they are dissolved by the 

 pancreatic juice. Phosphorus is undoubtedly absorbed in 

 organic combination, but the mode of absorption and the 

 channels by which it passes from the intestine have not been 

 investigated. 



2. Carbohydrates. Although the chief monosaccharid 

 formed in digestion is dextrose, others are also produced 

 laevulose from cane sugar, and galactose from milk sugar. 

 All these are absorbed in solution, and are carried away in 

 the blood by the portal vein. 



3. Fats. It was for long thought that the fats are absorbed 

 as a fine emulsion ; but the most recent investigations seem 

 to indicate that after being split up into the component acids 

 and glycerin, they pass, as soluble soaps or as fatty acids 

 soluble in the bile, through the borders of the intestinal 

 epithelium. Here they appear to be again converted into 

 fats by a synthesis of the acid with glycerin. Fine fatty 

 particles are found to make their appearance in the cells 

 at some distance from the free margin and to increase in 

 size. They are passed on from the cells, through the lymph 

 tissue of the villi, into the central lymph vessels, and thus 

 on through the thoracic duct to the blood-stream. Unlike 

 the proteids and carbohydrates, they are not carried directly 

 to the liver. 



