Differentiation of Bacteria. 



121 



the different species are especially marked in the case of the 

 typhoid-colon group. Schidorsky and Reim claim to have had 

 considerable success in the practical diagnosis of typhoid using 

 this method. 



Jaff6, working with a number of strains in the typhoid-colon 

 group, obtained constants differing somewhat from those of 

 Michaelis, and observed also several strains of each species which 

 showed markedly different behavior toward the reagents from 

 that of the general average. 



In my investigations I made use of six strains of B. typhosus 

 and four of B. coli. In two sets of experiments, using in one case, 

 acetic acid and sodium acetate, and in the other, lactic acid and 

 sodium lactate, the behavior of five strains of B. typhosus was shown 

 to be the same toward both of these reagents. Three of the strains 

 regularly failed to agglutinate at all even when concentrations of 

 hydrogen ion varying between .7 and 900 X 10- 5 were used. 

 The other two strains agglutinated about equally in all the con- 

 centrations between 14 and 200 X 10- 5 . Variations in the con- 

 centrations of salt present between N/40 and N/200 made no 

 noticeable difference. 



Using acetic and lactic acids without the presence of the 

 salt, the same three strains failed to agglutinate, the other two, 

 however, showing agglutination between the values of 60 and 

 300 X 10- 5 . The hydrogen ion concentrations in these cases were 

 calculated from the formula 



Ch = V^&'Cacid" 



Comparing these acids with the strong acid HC1, which can be 

 assumed to be completely dissociated in dilutions above N/100, 

 it was found that the three strains which showed resistance 

 toward the weaker acids were partially agglutinated by values of 

 Ch of from 50 to 500 X 10- 5 while the other two were completely 

 agglutinated by these concentrations. A sixth strain also showed 

 partial agglutination by the same values. 



The conclusions to be drawn from these results would seem to 

 be, first, that the hydrogen ion concentrations necessary to bring 

 about agglutination in suspensions of typhoid bacilli may differ 

 considerably with the way in which these concentrations are ob- 



