SECTION III. 

 ABSORPTION OF FOOD 



1. State in which Food leaves the Alimentary Canal- 



(1) The carbohydrates generally leave the alimentary canal 

 as monosaccharids ; but some resist the action of digestion 

 more than others. Lactose seems to be broken down in the 

 intestine only when the special enzyme, lactase, is present in 

 the succus entericus, but in all cases it is broken down before 

 it reaches the liver. Cane sugar, when taken in large excess, 

 may also be absorbed unchanged, and it is then excreted by 

 the kidneys. 



(2) The proteins are absorbed as amino-acids, formed by the 

 action of trypsin and erepsin (pp. 320 and 328). Native pro- 

 teins may be absorbed to a small extent unchanged, as is shown 

 by the fact that the administration of very large amounts of 

 egg albumin may cause its appearance in the urine. Egg- 

 white, when injected into the pelvic colon isolated from the 

 rest of the intestine, and hence free of proteolytic enzymes, 

 may disappear, probably as the result of bacterial action ; 

 but in carnivora the amount absorbed, as indicated by the 

 increased excretion of nitrogen, is trivial. In the horse 

 absorption in the colon is more complete (p. 344). 



(S) Non-protein nitrogenous material may be absorbed 

 as amino-acids, the form in which it is largely present in the 

 food, or may be acted upon by bacteria prior to absorption 

 (p. 340). 



(4) The fats are chiefly absorbed as soaps and as fatty 

 acids, 



(5) The results of the digestion of cellulose are absorbed 

 as salts of organic acids (p. 840). 



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