. Physiology, experimental and descriptive . rane of Small Intestine. 220 ABSORP TION — 1 rILMI. Again, while the folds in the lining of the stomach aretemporary, these are permanent. They serve to increase thesurface of the lining, and to retard the passage of the foodmaterial, and so to aid the process of digestion and of absorp-tion. Further, the surface of the mucous membrane is thicklybeset with little cylindrical projections, like the pile on velvet. These pro-jections are calledVilli (singular, vil-lus). The villigreatly increasethe absorbing sur-face of the smallintestine. In eachvillu
. Physiology, experimental and descriptive . rane of Small Intestine. 220 ABSORP TION — 1 rILMI. Again, while the folds in the lining of the stomach aretemporary, these are permanent. They serve to increase thesurface of the lining, and to retard the passage of the foodmaterial, and so to aid the process of digestion and of absorp-tion. Further, the surface of the mucous membrane is thicklybeset with little cylindrical projections, like the pile on velvet. These pro-jections are calledVilli (singular, vil-lus). The villigreatly increasethe absorbing sur-face of the smallintestine. In eachvillus is a networkof Blood Capil-laries, and thebeginning oflymphatic capil-laries called Lac-teals. In the villithe largest partof the work ofabsorption isdone. The fatsare absorbed bythe lymph capil-laries, and the rest of the foods by the blood capillaries. Itshould be carefully noted that nearly all of the foods but thefats go at once to the liver, through the portal vein; but thefats are carried by the main lymph duct (the Thoracic Duct). Capillaries Fig. 65. Plan of Absorption. ABSORPTION. 221 to be emptied into the subclavian vein in the neck, hence donot directly pass through the liver. If a solution of salt and one of sugar are brought into con-tact, they will gradually mix; and this is called Diffusion. If,now, a piece of parchment be tightly tied over the end of atube, and one of the above solutions be placed inside, and theother around the tube, they will still diffuse through the mem-brane, and mingle. This is called Osmosis, or Dialysis; and theparchment is called a dialyzing membrane. In the digestivetube the mucous membrane represents the dialyzing membrane,with blood or lymph on one side, and the contents of thedigestive tube on the other. Soluble materials, such as pep-tones, sugars, etc., pass through the mucous membrane intothe blood. The process of osmosis, and to a lesser extent of filtrationand imbibition, as they are known to occur outside the body,were su
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