CELLULAR 



not to sugar: if a sugar solution is placed inside 

 and the cup is then immersed in water the latter 

 is absorbed and the manometer registers an in- 

 crease of pressure. 



Pfeffer regarded the copper ferrocyanide 

 membrane as analogous to the protoplasmic sur- 

 face of the cell, the sugar solution in the interior 

 corresponding to the solution of sugars, and 

 other food substances, contained in the central 

 vacuole. 



The question with which Pfeffer started out 

 was apparently answered. Since the artificial 

 model could produce as much pressure as the 

 plant cell the mechanism might be regarded as 

 satisfactorily explained. Pfeffer, however, went 

 further, investigating the effects of concentra- 

 tion and temperature and coming to the con- 

 clusion that the pressure is directly proportional 

 to the concentration, and that it increases about 

 1/273 when the temperature rises 1° C. 



In the meantime van't Hoff became interested 

 in the attraction between water and other sub- 

 stances, a problem which is intimately connected 

 with osmosis. One day as he left his laboratory, 



