SECTION XXVII 

 ABSORPTION 



CHAPTER LXXXV 



THE ABSORPTION OF THE REDUCED FOODSTUFFS FROM 

 THE ALIMENTARY CANAL 



General Discussion. — The term absorption refers more particu- 

 larly to the process by means of which the simplified foodstuffs are 

 transferred from the lumen of the alimentary canal into the absorbing 

 channels, i.e,, into the blood-capillaries or the lacteals. It is to be 

 remembered, however, that certain animals also take in materials 

 through their skin, and that absorption from the different body-cavi- 

 ties is a common phenomenon. If we confine ourselves at this time 

 to the foodstuffs, it is to be noted first of all that water, salts, and the 

 simple sugars are dialyzable without digestion, whereas others must 

 be changed so as to be able to pass through the intestinal epithelium. 

 This brings in a definite element of time; digestion and absorption 

 going on side by side, because certain substances begin to pass into the 

 body long before the chemical and mechanical reductions of all the 

 different foodstuffs have actually been completed. Moreover, while 

 some of the digested material may be taken up in the mouth, stomach, 

 and large intestine, by far the largest amount is absorbed in the small 

 intestine. 



In endeavoring to obtain an idea regarding the factors concerned 

 in absorption, we find first of all that they are resident in a layer of 

 epithelial cells, which, physiologically considered, really form a part 

 of the external envelope of the body. Through these the simplified 

 foodstuffs must pass in order to gain access to the fluids of the body. 

 Until not so many years ago it was believed that the forces by means of 

 which this transfer is effected, consist of filtration, diffusion, and 

 osmosis. In the course of time, however, it has become evident that 

 many of these phenomena cannot be explained upon this basis 

 and hence, physiologists finally took recourse to a purely vitalistic 

 hypothesis. As emphasized repeatedly on previous occasions, it is for 

 us to accept an intermediate view which not only acknowledges the 

 above physical principles, but also recognizes the occurrence of certain 

 intracellular processes, regarding which our knowledge is as yet ex- 



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