DAVID I. HITCHCOCK 615 



2. The potential difference developed between a solution of edestin 

 chloride or acetate separated by a collodion membrane from an acid 

 solution free from protein was found to be influenced by salt con- 

 centration and hydrogen ion concentration in the way predicted by 

 Donnan's theory of membrane equilibrium. 



3. The osmotic pressure of such edestin-acid salt solutions was 

 found to be influenced by salt concentration and by hydrogen ion 

 concentration in the same way as is the potential difference. 



4. The colloidal behavior of edestin is thus completely analogous 

 to that observed by Loeb with gelatin, casein, and egg albumin, and 

 may be explained by Loeb's theory of colloidal behavior, which is 

 based on the idea that proteins react stoichiometrically as ampho- 

 teric electrolytes and on Donnan's theory of membrane equilibrium. 



The writer wishes to acknowledge his indebtedness to Dr. Jacques 

 Loeb, at whose suggestion and under whose direction this work was 

 done, and to Dr. John H. Northrop, whose advice has been of great 

 assistance. 



