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were 88.6 and 89.7 per cent respectively. These figures differ by con- 

 siderably less than the probable error and are therefore to be consid- 

 ered identical. In the remaining experiments the acid was allowed to 

 act for about 30 minutes (the time varying by not more than | minute 

 in any one experiment) so that there could be no doubt that it would 

 have its full effect. 



4.0 pH 



Fig. 1. The effect of temporary acidulation upon the subsequent efficiency of 

 radiated and normal complement. The ordinates represent efficiency in per 

 cent of that of the corresponding unacidulated complement, and the abscissae 

 represent the pH to which the complement was exposed during the period of 

 acidulation. Open circles, normal complement; solid circles, radiated complement; 

 where these coincide the circles are shaded. 



The relation between the true reaction during acid treatment and 

 the hemolytic activity after the restoration of the normal reaction of 

 serum (pH = 7.6) will be most easily grasped by a study of Fig. 1 

 in which relative efficiencies are plotted as ordinates against hydrogen 

 ion concentration in terms of pH. These values of pH are accurate 



