JACQUES LOEB 775 



gelatin and the solution of gelatin inside the collodion bag, and a 

 second one between the gelatin solution inside the collodion bag and 

 the outside aqueous solution free from gelatin. 



This explains why the powdered particles of protein contained in a 

 gelatin solution participate in the Donnan equilibrium and the mem- 

 brane potential of the solution without adding to the osmotic pressure 

 of the solution as measured by the hydrostatic pressure required to 

 equalize the rate of diffusion of water in opposite directions through 

 the membrane. The participation of the solid particles in the Don- 

 nan equilibrium leads to an osmotic pressure inside of each solid 

 granule, but this osmotic pressure is measured in terms of cohesion 

 pressure of the swollen particles. 



This swelling of the solid particles increases the viscosity of the 

 solution, and the writer has shown that this fact is a further support 

 of the explanation of colloidal behavior on the basis of the theory 

 of membrane equilibria.* 



SUMMARY AND CONCLUSIONS. 



1 . It is shown that when part of the gelatin in a solution of gelatin 

 chloride is replaced by particles of powdered gelatin (without change 

 of pH) the membrane potential of the solution is influenced com- 

 paratively little. 



2. A measurement of the hydrogen ion concentration of the gelatin 

 chloride solution and the outside aqueous solution with which the 

 gelatin solution is in osmotic equilibrium, shows that the membrane 

 potential can be calculated from this difference of hydrogen ion 

 concentration with an accuracy of half a millivolt. This proves that 

 the membrane potential is due to the establishment of a membrane 

 equilibrium and that the powdered particles participate in this 

 membrane equilibrium. 



3. It is shown that a Donnan equilibrium is established between 

 powdered particles of gelatin chloride and not too strong a solution 

 of gelatin chloride. This is due to the fact that the powdered gelatin 

 particles may be considered as a solid solution of gelatin with a 

 higher concentration than that of the weak gelatin solution in which 

 they are suspended. It follows from the theory of membrane 



