CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 545 



the bodies of the columnar cells of the villi. It has, it is true, 

 been maintained by some that they pass betiveen the cells and 

 not into them; but the evidence is distinctly against this view. 

 The cells may again and again be seen crowded with fat, and 

 the cases in which the fat has been seen between the cells and 

 not in them are due to the extrusion of the fat, during the shrink- 

 ing of the villus in the course of preparation, from the cells into 

 spaces between the cells. In the frog, in which there are no villi, 

 and in which the folds of mucous membrane serving the purposes 

 of villi do not so readily shrink, the presence of fat globules in the 

 cells after a fatty meal can always be easily demonstrated by 

 osmic acid preparations. Since no such collections of fat globules 

 are seen in the cubical cells of the glands of Lieberkiihn we infer 

 that these have nothing to do with the absorption of fat. 



How the fat enters into the substance of the cell we do not 

 know. We may presume that the striated border plays some part, 

 but what part we do not know. Though, as we have seen, the rods 

 making up the border appear able, to move, to change their form, 

 we have no evidence that the fat is introduced into the cells by 

 means of any movements of these rods. We may imagine that the 

 globules pass into the cell substance by help in some way of these 

 rods, through amoeboid movements comparable with the ingestive 

 movements of the body of an amoeba; but we have no positive 

 evidence to support this view. We said ( 247) that bile promotes 

 the passage of fat through membranes, possibly by in some way 

 promoting a closer contact between the particles of fat and the 

 substance of the membrane ; but even if bile has this effect on the 

 surface of the cells, its action in this respect can be subsidiary only. 



Within the columnar cell the fat may be seen, both in osmic 

 acid preparations, and in fresh living cells, to be disposed in 

 globules of various sizes, some large and some small, each globule 

 placed in a space of the protoplasmic cell substance. It does not 

 follow that the fat actually entered the cell exactly in the form of 

 these globules ; it may be that the fat passes the striated border 

 in very minute spherules which, reaching the body of the cell, 

 run together into larger globules ; but whether this is so or not 

 we do not know. The view has been put forward that all the 

 fat is split up into fatty acids, and as fatty acid or as soap passes 

 into the substance of the cell, where it is immediately synthe- 

 sized by the action of the cell into neutral fat. But the evidence 

 for this view is not conclusive; it is based on the one hand on 

 the fact that fat when it is administered in food as fatty acid 

 is found in the cells as neutral fat, and on the other hand on 

 the consideration that a fatty acid or a soap being soluble could 

 more readily pass into the" substance of the cell than can a 

 neutral fat. 



From the columnar cell the fat passes into the spaces of the 

 reticular tissue of the villus. It has. it is true, been contended 



