FROM THE SMALL INTESTINE 647 



in absorption is due to a change in the vital activity and not in 

 a physical condition of the cells. 



We have still to answer the question whether the uptake of 

 water is, or is not, conditioned solely .by the difference of osmotic 

 pressure maintained on the two sides of the intestinal epithelium. 

 Leubuscher answered this in the negative, because he found that 

 a -25 per cent, or a '5 per cent, solution of NaCl was absorbed 

 more rapidly than distilled water. But Reid has shown that 

 distilled water damages the epithelium and destroys its one-sided 

 permeability, which amply accounts for Leubuscher's result. 

 Reid, also, believes that when the gut is absorbing a solution, 

 which does the epithelium no damage, the uptake of water is 

 independent of the initial and final concentrations of the solution. 

 He quotes the observation that water is absorbed at the same 

 rate from 2 per cent, solutions of dextrose and maltose, although 

 both substances are absorbed at the same rate, and the osmotic 

 pressure of the dextrose solution on an impermeable membrane is 

 about double that of the maltose solution. On the other hand, 

 there are results among Reid's experiments which point just as 

 much to the opposite conclusion. For instance, he found that, 

 after a loop had been washed out with a '9 per cent. NaCl 

 solution, distilled water was absorbed more rapidly than a '9 per 

 cent. NaCl solution. Again, he found that water was absorbed 

 more rapidly from a 2 per cent, solution of dextrose with a final 

 A = -440 than from a solution of the same percentage of 

 dextrose in a '6 per cent. NaCl solution with a A = -550. 



After a brief consideration of the available evidence we are 

 bound to believe that osmosis does play a considerable part in 

 the absorption of water. And although it is impossible to look 

 upon the intestinal epithelium as a simple osmotic membrane, it 

 is equally impossible to say how far these cells have the power 

 of sucking up fluid and passing it over to the blood in defiance 

 of osmosis. 



Waymouth Reid's Experiment. Like Heidenhain and Cohnheim, 

 Reid has come to the conclusion that absorption is not a purely 

 physical process, but depends upon a physiological factor as well. 

 His experiments are of very unequal values, and we must con- 

 sider how far they necessarily bear the interpretation he has put 

 upon them. He has compared the diffusion velocities of peptone 

 and dextrose through parchment into serum with the rates at 



