THE COLLOIDAL BEHAVIOR OF PROTEINS. 



By JACQUES LOEB. 



{From the Laboratories of The Rockefeller Institute for Medical Research) 

 (Received for publication, January 31, 1921.) 



Colloids show a number of peculiarities which at first appearance 

 seem to be lacking in crystalloids, and these properties are generally 

 accounted for by differences in the degree of dispersion. We have 

 repeatedly discussed these pecuHarities in our analysis of the chemical 

 behavior of proteins, e.g. the depressing effect of neutral salts on the 

 osmotic pressure, swelling, and viscosity of certain proteins; the 

 pecuHar influence of the hydrogen ion concentration of the solution 

 on these properties; and finally the peculiar influence of the valency 

 of the ion with which the protein is in combination and the apparent 

 lack of influence of the other chemical properties of the ion except 

 valency and sign of charge. ^ The dispersion theory accounts for 

 these difliculties by the assumption of differences in the degree of 

 aggregation of the protein particles. If, for example, the addition of 

 some salt to a protein solution of a definite pH lowers its osmotic 

 pressure, the assumption is made that the salt diminishes the degree 

 of dispersion of the colloidal particles in solution. It is not possible 

 to submit the dispersion theory to a quantitative test since we can- 

 not measure the degree of dispersion of a protein. 



A second theory to account for the influence of salts and hydrogen 

 ion concentration is Pauli's ionization theory which ascribes the os- 

 motic pressure, the swelhng, and viscosity chiefly to the hydratation of 

 ionized protein, while the non-ionized protein molecule is assumed not 

 to be hydrated. The idea of such a hydratation of protein ions 

 has become doubtful in view of recent experimental and theoretical 

 investigations by Lorenz^ and by Born,^ and, moreover, the writer 



iLoeb, J., /. Gen. Physiol, 1920-21, iii, 85, 247, 391; Science, 1920, Hi, 449. 

 ^ Lorenz, R., Z. Elektrochem., 1920, xxvi, 424. 

 ^ Born, M., Z. Elektrochem., 1920, xxvi, 401. 



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