THE PEBMEABILITY OF OBGANIC MEMBEANES 141 



and cell solutes, cause water to enter at almost as great 

 an initial rate as when pure water is the surrounding 

 medium. When, however, the osmotic pressure of the 

 external solution balances the various internal forces, the 

 entrance of water ceases. Any further dilution or con- 

 centration of the liquid on the outside quickly leads to 



M-NaCl 



ZM-NaCl 

 4M-NaCl 



i i i i i i i i i i i i i i i i i i i i i i PI i i i i i i i I i i i i i i i i i i i i i i i i i i 

 24. 48 72 96 120 144 168 192 216 24O 264 288 Hour -3 



FIG. 15. CURVES SHOWING ENTRANCE AND WITHDRAWAL OF WATER 

 IN XANTHIUM SEEDS ON SHITTING FROM WATER TO SALT 

 SOLUTIONS, OR VICE VERSA, AT THREE-DAY INTERVALS. 



The semi-permeability of the membrane is well illustrated by the be- 

 haviour recorded in these curves; Curves 2, 3, and 4 are displaced 

 to the right to avoid confusion. 



a readjustment, water passing in or out till equilibrium 

 is again established. The accompanying figure with legend 

 taken from Shull's paper makes this clear, and illustrates 

 well the efficiency of the coat as a semi-permeable mem- 

 brane. Sodium chloride solutions containing from 1 to 

 4 gramme- molecules per litre were employed. 



It was, in addition, proved by chemical tests that 



