JACQUES LOEB 



667 



point of gelatin the trivalent cation makes the 

 by combining with gelatin and forming a salt; 

 But, in addition, the salts of trivalent cations 

 and the more the higher their concentration until 

 is reached, as shown in Fig. 4. On the acid side 

 point the protein film cannot react chemically 

 and the membrane is charged positively through 



membrane positive 

 e.g., La gelatinate. 

 attract the water, 

 a certain maximum 

 from the isoelectric 

 with the La or Ce 

 the influence of the 



-I— > 



i 



G 

 o 



"to 



.Z5 



480 

 440 

 400 

 360 

 320 

 280 



T:i 240 



O 



.1—1 

 c 



200 



160 



120 



80 



40 



pn 1 



2 3 4 5 6 7 



Fig. 6. Showing that the critical point for this steep rise varies with the 

 isoelectric point of the protein with which the membrane has been treated. 



acid. In this case the trivalent cation acts apparently by increasing 

 the density of charge of the positive membrane considerably, as was 

 to be expected. 



In order to test this idea further, membranes treated with oxy- 

 hemoglobin instead of with gelatin were tried. The isoelectric point 

 of oxyhemoglobin is at pH = 6.8. In this case the steep rise in the 

 curve with LaCls should be nearer this value than 4.7. The curves 



