JACQUES LOEB 95 



4. This idea is supported by experiments on solutions and suspensions 

 of casein chloride in which it is shown that their viscosity is chiefly 

 due to the swelling of solid particles of casein, occluding quantities 

 of water regulated by the Donnan equilibrium; and that the breaking 

 up of these solid particles into smaller particles, no longer capable of 

 swelling, diminishes the viscosity. 



5. This leads to the idea that proteins form true solutions in water 

 which in certain cases, however, contain, side by side with isolated 

 ions and molecules, submicroscopic solid particles capable of occluding 

 water whereby the relative volume and the viscosity of the solution 

 is considerably increased. This accounts not only for the high order 

 of magnitude of the viscosity of such protein solutions but also for 

 the fact that the viscosity is influenced by electrolytes in a similar 

 way as is the swelling of protein particles. 



6. We therefore reach the conclusion that there are two sources 

 for the viscosity of protein solutions; one due to the isolated protein 

 ions and molecules, and the other to the submicroscopic solid particles 

 contained in the solution. The viscosity due to the isolated mole- 

 cules and ions of proteins we will call the general viscosity since it is of 

 a similar low order of magnitude as that of crystalloids in solution; 

 while the high viscosity due to the submicroscopic solid protein par- 

 ticles capable of occluding water and of swelling we will call the special 

 viscosity of protein solutions. Under ordinary conditions of hydrogen 

 ion concentration and temperature (and in not too high a concentration 

 of the protein in solution) the general viscosity due to isolated ions 

 and molecules prevails in solutions of crystalline egg albumin and in 

 solutions of metal caseinates (where the metal is monovalent) while 

 under the same conditions the second type of viscosity prevails in 

 solutions of gelatin and in solutions of acid-salts of casein; and also in 

 solutions of crystalHne egg albumin at a pH below 1.0 and at higher 

 temperatures. The special viscosity is higher in solutions of gelatin 

 than of casein salts for the probable reason that the amount of 

 water occluded by the submicroscopic solid gel particles in a gelatin 

 solution is, as a rule, considerably higher than that occluded by the 

 corresponding particles of casein. 



