CHAPTER XIII 



A RECIPROCAL RELATION BETWEEN THE OSMOTIC 



PRESSURE AND THE VISCOSITY OF GELATIN 



SOLUTIONS 1 



1. The experiments in the preceding chapter have led to the 

 conclusion that proteins form true solutions consisting of isolated 

 protein ions and molecules which may or may not contain in 

 addition to the isolated ions and molecules submicroscopic 

 particles capable of occluding water and giving rise to a Donnan 

 equilibrium. Only when a protein solution contains particles of 

 this latter type do we notice a comparatively high viscosity and a 

 similar influence of electrolytes on viscosity as on osmotic pres- 

 sure. Solutions of crystalline egg albumin of not too high a con- 

 centration have a comparatively low viscosity which is not 

 affected in the typical way by electrolytes and this leads to the 

 conclusion that these solutions consist chiefly of isolated ions and 

 molecules or of particles too small to occlude water. If this con- 

 clusion is justified, we are forced to the further conclusion that the 

 influence of electrolytes on the osmotic pressure of protein solu- 

 tions is determined by the isolated ions of a protein solution and 

 not by the submicroscopic particles capable of occluding water, 

 i.e., the micellae, since solutions of crystalline egg albumin show 

 the influence of electrolytes on their osmotic pressure in a striking 

 way. It would further follow that in case of a gelatin solution 

 where both isolated ions and submicroscopic micellae are sup- 

 posed to exist the isolated ions are responsible for the influence of 

 electrolytes on the osmotic pressure of the solution while the sub- 

 microscopic particles of solid jelly capable of occluding water are 

 responsible for the influence of electrolytes on the viscosity of 

 gelatin solutions. In other words, wherever there exists a rever- 

 sible aggregate formation from isolated protein ions in solution 



1 LOEB, J., J. Gen. Physiol, vol. 4, p. 97, 1921-22, 



232 



