254 DIGESTIVE SYSTEM. 



and jejunum) ; but as they approach the ileum their progress 

 seems slower, they begin to mingle together, and finally are 

 found accumulated at the lower end of the small intestine. 

 As they are subjected to absorption during this passage, they 

 may be said to move more slowly in proportion as their con- 

 sistency increases and their quantity diminishes. 



IV. ABSORPTION. 



A. .Absorption in general, role of the epitheliums, function 

 of the villosities. 



We have seen that the stomach absorbs no part of its con- 

 tents, and that the phenomenon of rejection (refus) is caused 

 by the vitality of the epithelium which lines the mucous coat. 

 In the intestine, on the contrary, absorption takes place very 

 rapidly, and we shall also find that the phenomenon of pas- 

 sage is solely dependent on the characteristic vitality of the 

 intestinal epithelium. 



Setting aside the property of the epitheliums, the phenom- 

 ena of absorption may be generally considered as phenomena 

 of diffusion. These are known to everybody. Most people 

 have tried the experiment of pouring red wine upon water 

 contained in a glass, pouring it so slowly as to prevent the 

 wine mixing with the water. The colored wine is then seen 

 to rest upon the surface of the water, the latter remaining 

 colorless, as the wine is lighter than the water; and the two 

 layers are so distinct that one would imagine that they could 

 never mingle. After a short time, however, though remain- 

 ing quite undisturbed, the two fluids mix, and become homo- 

 geneous ; the water has passed into the wine, or is diffused 

 into it. Something similar takes place in absorption, looked 

 at from a general point of view. Indeed, the organism being 

 composed of four-filths of water to one-fifth of solid matter, 

 may be compared to a sponge soaked in water. Now, if a 

 sponge soaked in water be placed in alcohol, the latter w r ill 

 penetrate the water in its turn, intermingling with it; in 

 this case the sponge may be left out of the account, the 

 essential feature of the phenomenon being an act of diffusion 

 between the alcohol and the water (contained in the meshes 

 of the sponge). The fact of the circulation of the blood is 

 only accessory. A frog may be deprived of its circulation, 

 and yet if one of its limbs be dipped into a solution of strych- 

 nine, the poison will be diffused throughout its whole body, 

 will reach the spinal marrow, and kill it in the convulsions 



