ABSORPTION FROM THE ALIMENTARY CANAL. 329 



The Mechanism of Absorption. 



263. The absorption of fats. We have now to consider the manner in 

 which these several substances pass into either the lacteal radicle or the 

 capillary bloodvessels. It will be convenient to begin with the absorption 

 of the fats. 



We have seen reason ( 241), to think that the fats, remaining chiefly as 

 neutral fats, are emulsified in the intestine by means of the bile and pan- 

 creatic juice, the small quantity of soap which is formed probably serving 

 simply the purpose of facilitating the ernulsification. 



The neutral fats so emulsified pass in the first instance into the bodies of 

 the columnar cells of the villi. It has, it is true, been maintained by some 

 that they pass between the cells and not into them ; but the evidence is 

 distinctly against this view. Since no such collections of fat globules are 

 seen in the cubical cells of the glands of Lieberkuhn 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 in- 

 troduced 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 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. 



When fatty acids are ingested neutral fats appear in the chyle, indicating 

 a synthesis of fatty acids into neutral fats in the epithelium of the villi. 



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

 rations 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 proto- 

 plasmic 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. 



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

 tissue of the villus. It has, it is true, been contended that it passes along 

 the substance of the bars of the reticulum ; but in carefully prepared osmic 

 acid specimens of a villus in active digestion of fatty food, the fat may be 

 distinctly recognized as largely filling up, still in the form of globules of 

 various sizes, the spaces in the meshes of the reticulum which are not occu- 

 pied by the leucocytes or allied wandering cells. The bases of the columnar 

 cells, through the gaps in the basement membrane, directly abut upon the 

 labyrinth of spaces ; and the fat once out of the base of the cell is free in 

 the spaces of the labyrinth. How it issues from the cell we do not exactly 

 know ; possibly by a process analogous to the excretion of solid matters by 

 an amoeba. 



From the labyrinth of spaces of the reticulum of the villus the fat passes 

 into the cavity of the lacteal radicle ; and it is worthy of note that in the 

 passage it undergoes a change. In the interior of the intestine, in the sub- 

 stance of the columnar cell, and apparently in the labyrinth of the reticu- 



