776 



THERMOLABILITY OF COMPLEMENT 



which has been noted by all observers, to make accurate comparison 

 only of the relative degrees of inactivation at the different reactions. 

 In all experiments it was found that the destruction of complement 

 is least at a point between pH 6.1 and 6.4. Within this narrow range 

 from 20 per cent to 50 per cent of the original, activity may be retained 

 when the complement is heated to 50°C. for 10 minutes. On either 

 side of the optimal reaction the drop in activity is rapid. The 

 curves run approximately parallel for all temperatures of heating. 

 At 53°C. a very small degree of hemolytic activity is retained at the 

 optimal reaction; when heated to 55°C. for 10 minutes all comple- 

 mentary power is lost, when referred to the small amount of sen- 

 sitizer used here, at all reactions. 



50 







pH 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 5.8 5.6 5.4 5.2 



Fig. 3. The complementary activity of the euglobuHn fraction in the presence 

 of added end-piece, after heating whole serum to 50°C. in distilled water at the 

 pH values given, and then separating the euglobuhn. 



If after heating the serum dilution the euglobulin is separated 

 by bringing the reaction in all the tubes to pH 6.3 and removing 

 the sediment by centrifugation, the complementary power of this 

 euglobulin in the presence of the titer amount of end-piece follows 

 the curve given in Fig. 3. It is evident then that the preservation 

 of the complementary power at pH 6.1 to 6.4 depends upon preser- 

 vation of the mid-piece function at these reactions. 



A second maximum in the preservation of the complement was 

 found in numerous experiments at pH 6.9, as shown in the lower 

 curve in Fig. 4, from a typical experiment. The importance of this 

 particular reaction was not appreciated in the early experiments 



