ON THE INFLUENCE OF AGGREGATES ON THE MEM- 

 BRANE POTENTIALS AND THE OSMOTIC PRESSURE 

 OF PROTEIN SOLUTIONS. 



By JACQUES LOEB. 

 {From the Laboratories of The Rockefeller Institute for Medical Research.) 

 (Received for publication, May 25, 1922.) 



I. 



When a protein chloride solution is separated by a collodion mem- 

 brane from a dilute HCl solution free from protein, under suitable 

 experimental conditions an osmotic equilbrium is reached after about 

 6 hours. When at that time the hydrogen ion concentrations 

 of the protein solution and the outside solution are measured, it 

 is found that the hydrogen ion concentration of the outside solution 

 is higher than that of the protein solution, while the chlorine ion 

 concentration is higher in the protein solution than outside.^ This 

 unequal concentration of the oppositely charged H and CI ions inside 

 and outside leads to a membrane potential and modifies the 

 osmotic pressure of the protein solution. The values of both 

 effects can be calculated from the differences in the pH (or pCl) 

 inside and outside on the basis of Donnan's equation for membrane 

 equilibria. The agreement between observed and calculated values 

 on the basis of Donnan's equilibrium equation is excellent for the 

 membrane potentials and equally good for the osmotic pressure, 

 except that a slight difference in pH (in the second decimal) has a 

 much greater influence on the calculated values of osmotic pressure 

 than of the p.d. These facts were based on the writer's observations 

 on solutions of gelatin and crystalline egg albumin^ and they were 

 confirmed by Hitchcock's observations on solutions of edestin.- 



The writer has shown that if in a solution of gelatin chloride 

 of a certain pH, part of the gelatin in solution is replaced by the 



' Loeb, J., Proteins and the theory of colloidal behavior. New York and London, 

 1922; /. Gen. Physiol, 1920-21, iii, 667, 691. 



2 Hitchcock, D. L, /. Gen. Physiol, 1921-22, iv, 597. 



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