776 AGGREGATES AND MEMBRANE POTENTIALS 



equilibria that this difference in concentration of protein ions must 

 give rise to potential differences between the solid particles and 

 the weaker gelatin solution. 



4. The writer had shown previously that when the gelatin in a 

 solution of gelatin chloride is replaced by powdered gelatin (without a 

 change in pH), the osmotic pressure of the solution is lowered the 

 more the more dissolved gelatin is replaced by powdered gelatin. It 

 is therefore obvious that the powdered particles of gelatin do not 

 participate in the osmotic pressure of the solution in spite of the fact 

 that they participate in the establishment of the Donnan equilibrium 

 and in the membrane potentials. 



5. This paradoxical phenomenon finds its explanation in the fact 

 that as a consequence of the participation of each particle in the 

 Donnan equilibrium, a special osmotic pressure is set up in each 

 individual particle of powdered gelatin which leads to a swelling of 

 that particle, and this osmotic pressure is measured by the increase 

 in the cohesion pressure of the powdered particles required to balance 

 the osmotic pressure inside each particle. 



6. In a mixture of protein in solution and powdered protein (or 

 protein micellae) we have therefore two kinds of osmotic pressure, 

 the hydrostatic pressure of the protein which is in true solution, and 

 the cohesion pressure of the aggregates. Since only the former is 

 noticeable in the hydrostatic pressure which serves as a measure 

 of the osmotic pressure of a solution, it is clear why the osmotic 

 pressure of a protein solution must be diminished when part of the 

 protein in true solution is replaced by aggregates. 



