JOHN H. NORTHROP AND PAUL H. DE KRUIF 



665 



It is evident from the foregoing that the agglutination may be con- 

 sidered as caused by the salt, as Bordet stated. The serum, however, 

 does not sensitize the bacteria but protects it from the salt so that the 

 latter does not reduce the cohesive force. If we study the effect of 

 salts and acids on the agglutination and charge of organisms sensitized 

 with immune serum, we should expect then to obtain curves similar 



TABLE V. 



Influence of NaCl Concentration ojt Agglutination with Dialyzed Normal and 



Immune Serum. 



to those given in the preceding paper with the exception that the 

 stable zone in high concentrations of salt would not appear and the 

 agglutination should be found to depend entirely on the potential. 

 A summary of a number of such experiments is given in Fig. 7. The 

 serum concentration was 1 : 500 in all cases; i.e., in excess. The figure 

 shows that with the exception of strong acid solution, complete ag- 

 glutination occurred whenever the potential was reduced below 15 



