CELLULAR 



There was, however, no clue to the cause of this 

 deviation. In general the inorganic salts were 

 found to give too much osmotic pressure. 



•The difficulty seemed to be cleared up by the 

 theory of Arrhenius, which states that all the 

 exceptional substances have the power to con- 

 duct the electric current in solution and that 

 they owe this property to the splitting of their 

 molecules into electrically charged ions. This 

 explains why they have abnormally high osmotic 

 pressures, for each ion produces as much osmotic 

 pressure as the molecule itself. 



There remained the problem of finding a 

 generally useful method of measuring the os- 

 motic pressure of living cells, de Vries took this 

 up. Instead of allowing the cell to absorb water, 

 as in Pfeffer's experiments, he employed the 

 opposite method, withdrawing water from the 

 cell. If the cell absorbs water with a certain 

 force we may oppose to it an equal force so that 

 no absorption takes place. If we increase the 

 opposing force, water will flow out of the cell, 

 and this may cause the protoplasm to shrink 

 away from the cell wall. 



