JOHN H, NOETHROP AND PAUL H. DE KRUIF 653 



suspension since the charge on the bacillus of rabbit septicemia may 

 be reversed by sulfate or NaCl while with Bacillus typhosus suspen- 

 sion the charge is reduced but does not change in sign. 



The experiments in Fig. 6 show clearly the reason for the character- 

 istic difference in the stability of Types D and G of the rabbit septi- 

 cemia bacillus. ^^ Type D which is very stable has a high potential 

 whereas the potential of Type G is very little more than the critical. 



The same figure shows that the acid agglutination zone may be 

 shifted markedly by the addition of other substances. Peptone for 

 instance moves it far to the acid side {cj. Putter^) while immune body 

 brings the isoelectric point to nearly 5. This point will be discussed 

 more fully in the succeeding paper. 



Origin of the Potential. — Loeb has shown/^ in the case of a protein 

 solution separated from a solution of electrolyte by a collodion mem- 

 brane, that the charge on the protein solution can be quantitatively 

 accounted for on the basis of Donnan's theory of membrane potentials. 

 According to this theory, electrolytes affect the potential of a particle 

 in two ways. (1) By combining chemically with the particle (for 

 example hydrogen ions). The ion then becomes part of the molecule 

 of which the particle (membrane) is composed. As a result the con- 

 centration of this ion differs on the opposite sides of the membrane 

 and gives rise to a potential. This potential may be calculated by 

 Nernst's formula from the concentration of the common ion on both 

 sides of the membrane. The membrane behaves as a reversible elec- 

 trode for this ion. (2) Ions which affect the distribution of the 

 common ion without further chemical combination with the mem- 

 brane. This mechanism will suffice to account for all the observations 

 made in the course of this work, if it be supposed that other ions than 

 the hydrogen ion may act by chemical combination.^^ The experi- 

 ments are more complicated than those with a collodion membrane 

 since the organisms are apparently more or less impermeable to ions.^^ 



i^Locb, J., /. Gen. Physiol., 1920-21, iii, 667; 1921-22, iv, 351; Proteins and 

 the theory of colloidal behavior, New York and London, 1922, 120. 



^^ Locb, J., Proteins and the theory of colloidal behavior, New York and London, 

 1922, 164, 165; /. Gen. Physiol., 1921-22, iv, 463; also two papers in this number 

 of the Journal which the writer has had the privilege of reading in manuscript 

 form (y. Gen. Physiol., 1921-22, iv, 741, 759). 



i» Shearer, C, Proc. Cambridge Phil. Soc., 1916-19, xix, 263. 



