JACQUES LOEB 669 



V. 



The experiments represented in Figs. 5 and 6 seem to show that 

 the efficiency of ions in causing the reversal of the sign of charge is 

 as great in the case of hydrogen ions as in the case of trivalent 

 cations; while the influence on the rate of difTusion of water is 

 considerably greater in the case of tri\'alent cations than in the 

 case of hydrogen ions. Fig. 7 permits a comparison of the attraction 

 of water by solutions of equal concentration of HCl, LaCls, AI2CI6, 

 and ThCU through membranes treated with gelatin. On one side of 

 the membrane was the solution, on the other pure water. If we con- 

 sider only concentrations up to m/32 this attraction is very slight in 

 the case of HCl as compared with LaCls or AI2CI6. (It should be 

 stated that in the experiments with HCl the level of the water was 

 considerably higher at the beginning of the experiment than in the 

 other solutions.) 



Theoretical Remarks. 



The experiments have shown that a reversal of the sign of charge 

 of a collodion membrane can be brought about by acids and by 

 "neutral" salts with trivalent cation after the inside of the membrane 

 has been in contact for an hour or more with a sufficiently strong 

 solution of a protein whereby apparently a protein film is formed on the 

 inside of the membrane. Collodion membranes not treated are always 

 negatively charged in contact with water, no matter whether or not 

 hydrogen ions and trivalent cations are present in sufficient con- 

 centration. Collodion membranes when treated with a protein are 

 also negatively charged when the reaction of the solution is on the 

 alkaline side of the isoelectric point of the protein and when the 

 solution is free from trivalent or tetravalent cations. In this case 

 the protein exists in the form of a metal proteinate dissociating into 

 a positive metal ion, the protein adhering to the inside of the col- 

 lodion membrane. This might suggest that the membrane becomes 

 negative in contact with water on account of these metal ions dissolv- 

 ing in water, while the solid film of protein anions adhering to the 

 membrane is negatively charged. When the h3"drogen ion concen- 

 tration is raised sufficiently to cause the transformation of the protein 



