JACQUES LOEB 85 



quantities of water whereby the relative volume occupied by the 

 gelatin in the solution is enormously increased. That this interpreta- 

 tion is correct is proved by experiments on the viscosity of solutions 

 of casein chloride which have no tendency to set to a jelly but which 

 contain, side by side with isolated casein ions and molecules, small 

 particles in suspension, occluding water and capable of swelling. 



4. It has already been shown in a preceding paper that the pH 

 influences the viscosity of casein solutions in a similar way as it influ- 

 ences the viscosity of gelatin solutions, and we have convinced our- 

 selves that the addition of neutral salts has a similar depressing effect 

 on the viscosity of casein chloride solutions as it has on the viscosity 

 of solutions of gelatin chloride. Yet casein solutions have no tend- 

 ency to set to a jelly (as far as the writer has been able to observe) 

 and we cannot therefore attribute the influence of electrolytes on 

 the viscosity of casein chloride solutions to a second type of viscosity. 

 But in the case of casein chloride solutions we can prove directly 

 that the influence of electrolytes on the viscosity has its source in 

 the swelling of casein particles. 



The material used in our experiments was a fine dry powder of 

 nearly isoelectric casein prepared after VanSlyke and Baker.® Parti- 

 cles of equal size of grain (between mesh 100 and 120) were sifted out 

 and 1 gm. of such powder was put into 100 cc. each of solutions of 

 HCl of different concentration to bring the casein to varying pH.'' 

 A microscopic examination of the granules showed that they 

 underwent a swelling which was a minimum at the isoelectric 

 point, which increased with increasing hydrogen ion concentration 

 until it reached a maximum and which then diminished again with 

 a further increase in the hydrogen ion concentration. Hence the 

 volume of the casein particles suspended in the HCl varied in a 

 similar way with the pH as the volume of suspended particles of 

 gelatin. 



This swelling could also be observed when the suspension was put 

 into 100 cc. graduates and the suspended particles were allowed to 

 settle. The volume of the sediment was a minimum at the isoelectric 



« Van Slyke, L. L., and Baker, J. C, J. Biol. Chem., 1918, xxxv, 127. 

 'Loeb, J., J. Gen. Physiol, 1920-21, iii, 547. 



