CHAPTER XV. 



THE ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM 



(Continued). 



5. The Absorption of Water. What has gone before in- 

 dicates how osmotic pressure is one of the forces which deter- 

 mines the movement of dissolved substances. It will be 

 shown now that under proper conditions it becomes a force 

 which determines the movement of water, and that it is in 

 part responsible for the absorption of this substance in the 

 living organism. The amount of water that can be absorbed 

 from the alimentary tract is enormous. It is ordinarily 

 stated that 4 or 5 liters of pure water may be absorbed in the 

 course of a day. This does not, however, indicate all that 

 can be absorbed. FRIEDRICH MULLER once showed in his clinic 

 in Munich a man who not infrequently consumed between 20 

 and 30 liters of beer in twenty-four hours without having a 

 diarrhoea. Beer does not, of course, represent pure water, 

 and the limits for this substance may be lower. 



Osmotic pressure becomes effective in determining the 

 absorption of water when the diffusion of the dissolved parti- 

 cles to regions of a lower concentration is prevented by a 

 semi-permeable membrane. This may be illustrated by the 

 accompanying diagram (Fig. 28). A represents in cross- 

 section a PASTEUR-CHAMBERLAND filter, in the wall of which 

 is deposited a semipermeable precipitation membrane M, such 

 as copper ferrocyanide, made as described above (page 255). 

 The osmotic cell, as such an apparatus is called, is closed with a 

 rubber stopper, C, through which passes the glass manometer 



262 



