ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 281 



absorbed formerly. What has been said of dextrose holds 

 also for a number of other substances. 



The different portions of the alimentary tract absorb salts 

 in very different amounts. Under ordinary circumstances 

 the amount of salt absorbed in the mouth or oesophagus is 

 to be looked upon as practically nothing. While certain au- 

 thors believe that considerable amounts of salt are absorbed 

 in the stomach, others question it entirely. The small in- 

 testine absorbs salts freely throughout its entire length, 

 though the jejunun seems to be somewhat more active in this 

 regard than the ileum. The large intestine also takes up salts, 

 but not to the same extent as the small bowel. 



Under certain circumstances one region of the alimentary 

 tract may absorb a salt while another is excreting this same 

 salt. One and the same portion of the intestine may even 

 absorb a salt which under somewhat different conditions it 

 excretes. The character of the changes which take place 

 in the absorbing structure of the alimentary tract to render 

 such phenomena possible are not as yet understood, and the 

 visible alterations (swelling, contraction, coagulation) often 

 observed in the absorbing surfaces still lack a unifying 

 physical explanation. 



