368 ELECTRICAL CHARGES OF COLLOIDAL PARTICLES 



ments with solutions inside collodion bags, it is at least sufficient to 

 leave no doubt that this difference in pH inside and outside causes the 

 p.D. In other words, there is no doubt that the p.d. between the 

 powdered particles and the surrounding liquid with which they are in 

 equilibrium is due to the Donnan equilibrium. 



We have already shown in a preceding paper that the addition of 

 a salt to a solution containing suspended particles of powdered gel 

 of gelatin chloride diminishes the p.d. between the particles and 

 surrounding liquid and that this diminution is due to a diminution of 

 the value pH inside minus pH outside; i.e., to the Donnan 

 equilibrium.^ 



These facts then leave no doubt that the difference in the hydrogen 

 ion concentration between micellae of protein and the surrounding 

 solution which the Donnan equilibrium demands is the only cause of 

 the electrical charges of micellae of proteins or of their models. 



The experiments on the solution of casein chloride published by 

 Robert F. Loeb and the writer in the preceding number of this Journal 

 indicate that aside from the electrical charges osmotic forces may 

 play a role in maintaining the stability of colloidal suspensions.^ 

 These forces are also a consequence of the Donnan equilibrium and 

 hence vary in a similar way as the p.d. No other theory except the 

 Donnan theory can account for this similarity. 



VI. The Origin of the Electrical Charges of Living Cells and Tissues- 



In his first paper on the theory of membrane equilibria Donnan 

 suggested that the membrane potentials postulated by his theory 

 might contribute towards an explanation of the action of nerves and 

 even of electrical fish. In 1911 the writer suggested to Dr. Beutner 

 that he investigate the p.d. between such organs as apples or leaves 

 of the rubber plant and water, instead of the p.d. of muscles or nerves 

 which had usually been used by physiologists for this purpose. In 

 these experiments Dr. Beutner made the important observation that 

 the P.D. between the surface of an apple or a leaf was a maximum 

 when the bounding liquid was pure water, while the p. d. was de- 

 pressed when a salt was added to the water the depressing effect on 



6 Loeb, J., and Loeb, R. F., /. Gen. Physiol., 1921-22, iv, 187. 



