16 INTESTINAL ABSORPTION. 



In tes final A bsorption . 



In intestinal absorption the dissolved constituents are 

 absorbed by the blood stream, the particulate by the 

 lacteals. The proteids of chyle are absorbed partly as 

 peptone, partly as alkali-albuminate. They enter the 

 circulation both by the veins and lacteals, but it cannot be 

 stated in what proportion. It is not known whether 

 coagulable albumin is absorbed or not. 



There is reason to believe that most of the dextrose into 

 which all carbohydrates are converted in digestion is 

 absorbed by the veins, but direct evidence is wanting : the 

 remainder undergoes the lactic acid fermentation in the 

 intestine. 



The fats are absorbed both as glycerides in the state of 

 emulsion, and as alkaline soaps and glycerine. The absorp- 

 tion of water, in consequence of which the intestinal content 

 becomes more and more concentrated as it advances, 

 takes place by the capillaries, and is mainly due to " diffu- 

 sion." Consequently it may be diminished or reversed by 

 the presence in the intestinal liquid of salts of high " osmo- 

 tic equivalent." 



Faeces consist of insoluble residues of food and bile, and 

 of insoluble salts ; particularly calcic, magnesic, and am- 

 monio-magnesic phosphates. They yield certain gases, 

 viz., CO 2 , marsh gas and a trace of sulphuretted hydrogen. 

 In human excrement a crystalline body called excretin 

 occurs. 



Diffusion of liquids. When two liquids (of which one A is water, the other 

 B a solution) are separated by a membrane, an exchange takes place between 

 them through the membrane. So long as the two liquids remain unaltered 

 (as would be the case if the liquid on either side of the membrane were con. 

 tinually replaced by fresh of the same quality) the relation between the weight 

 of water which passes from A to B, and of the body in solution which passes 

 from B to A, is constant. This relation is called the osmotic equivalent. If 

 B holds NaCl in solution, the former is greater than the latter, and the 

 equivalent is said to be positive ; if HC1, it is less, and the equivalent is 

 said to be negative. 



