CALVIN B, COULTER 



775 



serum, pH 6.3 in the case of the fractions) the volumes equalized, 

 and where distilled water had been used as the diluent, isotonicity 

 was restored by the addition of one-tenth volume of 8.5 per cent NaCl 

 solution. The original dilution was 1 to 20 in all cases, and the frac- 

 tions were used in the same corresponding dilution. Between ma- 

 nipulations the tubes were placed in ice water and protected from 

 sunhght. 



pH 74 7.2 70 6.8 6.6 6.4 6.2 6.0 5.8 5.6 5.4 5.2 



Fig. 2. The complementary activity retained by whole serum diluted in dis- 

 tilled water and heated at different temperatures, at varying reactions. 



The complementary activity in percentages of that of the unheated 

 control retained by whole serum diluted 1 to 20 in distilled water 

 and heated at varying reactions at different temperatures, is shown 

 in Fig. 2. The experiments recorded gave the highest values observed 

 in many similar experiments. The value at any given pH relative 

 to the unheated control varies with different specimens of serum, 

 so that each curve is given to represent a single experiment. Al- 

 though the amount of destruction increases with the temperature 

 it is possible on account of this individual variation in thermolabihty. 



