JACQUES LOEB 757 



similar to that in which acids or alkalies act, inasmuch as in low 

 concentrations the positive charge of isoelectric gelatin increases 

 with the concentration of the LaCls solution until a maximum is 

 reached at a concentration of LaCU of about m/8,000; from then on 

 a further increase in the concentration of LaCls diminishes the charge 

 again. It is shown that the same is true for the action of 

 Na4Fe(CN)6. From this it is inferred that the charge of the iso- 

 electric gelatin under the influence of LaCls and Na4Fe(CN)6 at the 

 isoelectric point is due to an ionization of the isoelectric protein by 

 the trivalent or tetravalent ions. 



4. This ionization might be due to a change of the pH of the solu- 

 tion, but experiments are reported which show that in addition to this 

 influence on pH, LaCls causes an ionization of the protein in some 

 other way, possibly by the formation of a complex cation, gelatin-La. 

 Na4Fe(CN)6 might probably cause the formation of a complex anion 

 of the type gelatin-Fe(CN)6. Isoelectric gelatin seems not to form 

 such compounds with Ca, Na, CI, or SO4. 



5. Solutions of LaCla and Na4Fe(CN)6 influence the osmotic 

 pressure of solutions of isoelectric gelatin in a similar way as they 

 influence the p.d., inasmuch as in lower concentrations they raise the 

 osmotic pressure of the gelatin solution until a maximum is reached 

 at a concentration of about m/2,048 LaCU and m/4,096 Na4Fe(CN)6. 

 A further increase of the concentration of the salt depresses the 

 osmotic pressure again. NaCl, LiCl, MgCl2, CaCU, and Na2S04 do 

 not act in this way. 



6. Solutions of LaCls have only a depressing effect on the p.d. and 

 osmotic pressure of gelatin chloride solutions of pH 3.0 and this 

 depressing effect is quantitatively identical with that of solutions of 

 CaCl2 and NaCl of the same concentration of CI. 



