JACQUES LOEB 353 



In 1916 J. A. Wilson suggested that the electrical charges of 

 micellae were caused by the establishment of a Donnan equilibrium 

 between the colloidal particle and the surrounding solution.* There 

 were, however, no measurements of membrane potentials available 

 at that time and this was probably the reason that his suggestion 

 was not accepted. 



We may consider a solution of a protein inside a collodion bag 

 surrounded by a watery solution (free from protein) as a model 

 of a micella. The measurements of the p. d. with the aid of a 

 Compton electrometer with saturated calomel electrodes show that 

 the electrical charges of this model vary in the same way as the 

 charges possessed by colloidal particles in general (e.g. coagulated egg 

 albumin) in suspension; namely, (1) The electrical charge of the 

 micella model is zero at the isoelectric point of the protein. (2) 

 The charge of the model is positive on the acid side and negative on 

 the alkali side of the isoelectric point, and increases with the addition 

 of little acid and diminishes with the addition of more acid to iso- 

 electric particles. (3) The charge of the model is depressed by the 

 addition of low concentrations of neutral salts and the depressing 

 action of the salt increases rapidly with the valency of that ion of the 

 neutral salt which has the opposite sign of charge to that of the 

 miceUa.^ 



If these charges are due to the Donnan equilibrium it must be pos- 

 sible to prove that the concentration of the crystaUoidal ions inside 

 the micella (or its model) is different from their concentration in 

 the surrounding liquid and that this difference in the concentration 

 of crystaUoidal ions on the opposite sides of the membrane is able to 

 account quantitatively for the observed p. d. The difference in the 

 concentration of crystaUoidal ions in the two phases (micella and 

 surrounding water) is due to the fact that the protein ion cannot 

 diffuse into the watery solution. When a solution of a protein-acid 

 salt is inside a collodion membrane, the diffusion of the protein ion is 

 prevented by the membrane and when the protein ion forms part of a 

 gel the diffusion of the protein ions is prevented by the forces of 



* Wilson, J. A., J. Am. Chcm. Soc, 1916, xxxviii, 1982. 

 ' Locb, J., J. Gen. Physiol, 1920-21, iii, 667. 



