662 



STABILITY OF BACTERIAL SUSPENSIONS, III 



the difference between the normal and the immune serum becomes 

 less and less marked as the pH approaches that of the acid agglutina- 

 tion zone of the organism. 



Fig. 4 shows the effect of immune serum on the charge and aggluti- 

 nation of Types D and G. As in all the experiments, the agglutina- 

 tion becomes complete as soon as the charge is reduced below 15 

 millivolts. The figure shows that Type D is difficult to agglutinate 

 because it has a fairly high charge at a pH of 7.2 and the effect of the 

 immune serum is insufficient to reduce this to the critical value. 

 Type G, however, has a lower charge and is much more readily 

 agglutinated. Type D at a pH of 4.5 is easily agglutinated since at 

 this pH the serum has a much greater effect on the charge. 



The Effect of Salts. 



Bordet^i showed that salt greatly increased agglutination with 

 immune serum. Porges,^^ however, found that with very powerful 

 immune serum agglutination occurred even though the serum was 

 dialyzed and no salt was present. 





10'* 10-^ 10"^ 



Concentration o|* serum 



Fig. 5. Effect of dialyzed normal and immune serum on the potential and 

 agglutination of B. typhosus. Upper curves show the effect in the presence of 

 0.3 N NaCl. The potential in these two curves is identical but they have been 

 separated slightly in the figure in order to show the difference in the agglutination. 



^^ Bordet, J., Traite de I'immunite dans les maladies infectieuses, Paris, 1920. 

 12 Porges, O., Centr. Bakt., 1 te Abt., Orig., 1905, xl, 133. 



