INTESTINAL DIGESTION 215 



brush, but their scale is more like that of the nap on 

 velvet. The result of their existence is that the number 

 of epithelial cells in contact with the food is vastly 

 augmented. 



The details of the act of absorption are full of dif- 

 ficulty. We cannot deal with them beyond emphasizing 



FIG. 50. Use is made here of a perspective artifice as in Fig. 9. A 

 bit of the lining of the small intestine is shown cut through and ex- 

 tending away from the observer. The eminences are villi with capil- 

 lary nets inside; the slender pits are glands. 



a few points. We are to think of the fluid contents of 

 the intestine on one side of a membrane composed of 

 living cells. On the other side of the membrane is lymph 

 in the spaces of a loosely knit tissue. Blood is moving 

 steadily through the vicinity in capillary vessels the walls 

 of which permit free exchanges. One might expect a 

 certain movement of water and dissolved substances be- 

 tween the blood and the intestine what is colloquially 

 called a " soaking through." But this simple conception 

 does not carry us far. 



We find that the intestinal lining behaves v quite 

 differently from any simple membrane with which it 

 might be natural to compare it. The largest allowance 

 must be made for its living state. Because each of 



