112 OSMOTIC PRESSURE AND VISCOSITY 



On the other hand, the high viscosity of gelatin solutions, e.g., 

 that part of the viscosity which is due to the volume occupied by the 

 sohd particles of jelly, is entirely regulated by the Donnan equilib- 

 rium. The dispersion theory was not able to account for the influ- 

 ence of electrolytes on the viscosity and osmotic pressure of protein 

 solutions while this influence is accounted for mathematically by the 

 Donnan theory. 



SUMMARY AND CONCLUSIONS. 



1. These experiments confirm the conclusion that protein solutions 

 are true solutions consisting of isolated ions and molecules, and that 

 these solutions may or may not contain in addition solid submicrc- 

 scopic particles capable of occluding water. 



2. The typical influence of electrolytes on the osmotic pressure of 

 protein solutions is due to the isolated protein ions since these alone 

 are capable of causing a Donnan equilibrium across a membrane 

 impermeable to the protein ions but permeable to most crystalloidal 

 ions. 



3. The similar influence of electrolytes on the- viscosity of protein 

 solutions is due to the submicroscopic solid protein particles capable 

 of occluding water since the amount of water occluded by (or the 

 amount of swelling of) these particles is regulated by the Donnan 

 equilibrium. 



4. These ideas are supported by the fact that the more the sub- 

 microscopic solid particles contained in a protein solution or suspen- 

 sion are transformed into isolated ions {e.g., by keeping gelatin solu- 

 tion for 1 hour or more at 45°C.) the more the viscosity of the solution 

 is diminished while the osmotic pressure is increased, and vice versa. 



