JACQUES LOEB 661 



the concentration of the CaCl2 solution. The CeCla has therefore 

 caused a reversal in the sign of charge of the membrane making the 

 latter positive. This made it possible for the CaCla solution to in- 

 crease the rate of diffusion of water through the membrane into the 

 solution. The pH of the solutions varied between 5.1 (in the lowest 

 concentration of CaCl2) and 5.9 (for the highest concentration); i.e., 

 the solutions were all on the alkaline side of the isoelectric point of 

 gelatin. 



Experiments with electrical endosmose confirmed the conclusion 

 that in the presence of CeCls the membrane assumes a positive charge 

 when the membrane had previously been treated with gelatin, but 

 that the membrane remains negatively charged when it has not been 

 treated with a protein. In these experiments with electrical endos- 

 mose the solutions inside and outside the collodion bag were solutions 

 of CeCls of identical concentration. 



II. 



We have shown in another paper^ in this number of the Journal 

 that in the case of collodion membranes treated with gelatin and 

 rendered positive by acid the rate of diffusion of water from the side 

 of pure water through the membrane to the solution is raised by 

 cations in the order K < Na < Li < divalent cations < trivalent 

 cations. Since the Ce ions render the gelatin film of the collodion 

 membrane positive the influence of different cations on the attraction 

 of water should increase in the same order as when the membrane 

 is rendered positive by acid; and the attraction of water by the solution 

 should be a minimum in the case of K. Fig. 2 shows that this is 

 true. In these experiments different concentrations of the four 

 salts, KCl, NaCl, LiCl, and CaCl2, from m/2,048 to 1m were made in 

 m/1,024 CeCls. The H2O surrounding the collodion bags containing 

 the solutions was replaced by m/1,024 CeCls to eliminate the osmotic 

 effect of CeCls in the experiments. The experiments show that the 

 attraction of water by the four salts follows the order we should ex- 

 pect if Ce caused the membrane to assume a positive charge; i.e., 

 K < Na < Li < Ca. The pH in these experiments varied from 



2 Loeb, J., /. Gen. Physiol., 1919-20, ii, 673. 



