THE DIGESTION OF FOOD 117 



The ingested proteins are changed in the stomach and 

 intestines to peptones, and in part, perhaps mainly, to 

 amino acids resulting from the cleavage of peptones. The 

 fats are split partly, or entirely, into fatty acids and glyc- 

 erin, with the subsequent formation of soaps by the union 

 of the free acids with alkaline bases. It has been held that 

 in the passage of these new compounds through the walls 

 of the intestine changes occur of a synthetical character, 

 with a partial or total reconstruction of the proteins and 

 fats into forms similar to those in the ingested food. This 

 view as to the proteins has been modified somewhat by 

 the demonstration of the existence of amino acids in the 

 blood showing that, if a synthesis of proteins occurs in the 

 intestinal walls, it is at least not complete. Amino 

 acids may exist in the blood even if synthesis occurs in 

 the intestinal walls. The rebuilding of fats and their 

 transference into the lacteals is regarded as being 

 accomplished through the activity of cells lying in the 

 mucous lining of the intestine. This seems to be proven. 

 It seems, then, that the vital forces residing in these 

 cells probably play a part in the transfer of the nutrients 

 into the blood circulation, and that this absorption 

 can not be explained wholly on the basis of osmotic 

 pressure. 



172. Place of maximum absorption of food. Absorp- 

 tion of digested food takes place to a limited extent 

 from the stomach of man and the dog, but not from the 

 stomach of the herbivora. The main transference of the 

 products of digestion into the blood is from the intestines, 

 particularly the small intestine. Much of the water that 

 passes into the large intestine is absorbed there, together 

 with the products of digestion not already absorbed and 

 those products that result from bacterial action. 



