678 



FLOCCULATION OF BACTERIA BY PROTEINS 



to pH 6.4), As we have observed that when we added a 1 per cent 

 pure oxyhemoglobin sokition to two or three volumes of Bacterium coli 

 suspension, flocculation occurred without any adjustment of reaction, 

 we suspected that salts interfered with the agglutination near the 

 isoelectric point of the hemoglobin. In one experiment, where H ion 

 concentrations were determined electrometrically, flocculation of the 

 bacteria occurred in the absence of salt at pH 6.71 and points acid to 

 this, the concentration of hemoglobin being 1 :400. 



It is also to be noted in Table VII that there is no pro-zone with the 

 higher concentrations of hemoglobin, such as we have uniformly 



TABLE VII. 



Bacterium coli Suspension with Guinea Pig Oxyhemoglobin. 

 1.0 cc. buffer mixture + 0.5 cc. oxyhemoglobin solution + 0.5 cc. coli suspension. 



Temperature = 20°C. X = agglutination within 1 hour. + = agglutina- 

 tion within 12 hours. 



found with the other proteins studied. We did not extend the series 

 more acid than pH 4.4, because the greenish brown color of the solu- 

 tions showed that we no longer had oxyhemoglobin. When Diplo- 

 coccus pneumonicB suspensions were used instead of Bacterium coli, a 

 pro-zone was obtained ; when the hemoglobin concentration was 1 : 400, 

 the bacteria were charged positively at pH 5.0 and reactions acid to 

 this, and remained non-agglutinated. When, instead of bacteria, we 

 used an aqueous suspension of cellulose nitrate as substrate, hemo- 

 globin in dilutions of 1:2,000 to 1:10,000 caused agglutination of the 

 cellulose nitrate at reactions between pH 6.2 to 7.0 (in the absence of 

 salt); with higher dilutions of hemoglobin, flocculation took place at 

 more acid reactions. 



