JOHN H. NORTHROP AND PAUL H, DE KRUIF 



657 



the isoelectric point of globin. Agglutination again occurs whenever 

 the potential is less than 15 millivolts. 



The effect of normal and immune serum on the pH curves of 

 Bacillus typhosus is shown in Fig, 3.^ The result is very similar to 

 egg albumin. It will be noted that there is no marked difference be- 

 tween the immune and the normal serum and also that the isoelectric 

 point is shifted to a pH of 4.7 in both cases. This was an unexpect- 

 ed result, since the isoelectric point of blood globulin is given by Mi- 



+ 6 



+ 4 ^HQ 



o 



> 



-6 



45 



5.5 

 pH 



6.5 



Fig. 2. Effect of the concentration of globin on the potential and agglutina- 

 tion of Type D at different pH. Acetate buffers. 



chaelis* as 5.4 and the antibodies are known to be associated with the 

 globulins. According to the present experiment, however, the sub- 

 stance in the serum which has the greatest effect on the charge of the 



' Similar experiments have been made by Kosaka and M. Scki, Communication 

 to the Okayama Medical Society, Okayajna-I gakkwai Zasshi, 1922, No. 386. 



^Michaelis, L., Die Wasscrstoffionenkonzentration, Berlin, 1914. It is doubt- 

 ful if this can be considered the isoelectric point of pure imnuino body since 

 traces of foreign proteins have such a marked effect. 



