JACQUES LOEB 619 



isoelectric point of the protein solution. It was suspected that this 

 was due to the uncertainty in the measurements of the pH of the 

 outside aqueous solution near the isoelectric point. This turned out 

 to be correct, since it is shown in this paper that the discrepancy dis- 

 appears when both the inside and outside solutions contain a buffer 

 salt. 



2. This removes the last discrepancy between the observed p.d. and 

 the p. D. calculated on the basis of Donnan's theory of p.d. between 

 membrane equilibria, so that we can state that the p.d. between protein 

 solutions inside collodion bags and outside aqueous solutions free from 

 protein can be calculated from differences in the hydrogen ion con- 

 centration on the opposite sides of the membrane, in agreement with 

 Donnan's formula. 



