774 



THERMOLABILITY OF COMPLEMENT 



in a salt-poor medium. After bringing the serum dilution to the 

 desired reaction it was left standing 1 hour on ice and the flocculent 

 precipitate brought down by centifugation. The supernatant fluid 

 was decanted, the inner walls of the tube wiped dry with a clean 

 cloth and the sediment representing the mid-piece used at once or after 

 a single washing with distilled water of pH 6.0. The supernatant 

 fluid from the first sedimentation was used as the end-piece dilution. 

 The final preparation of mid-piece was made by carefully emulsifying 

 the sediment in distilled water, or by subsequently bringing it into 

 solution by the addition of NaOH to pH 7.4. 



10 



pM 7.2 7.0 6.8 6.6 6.4 6.2 6.0 5.3 



Fig. 1. The complementary activity of the supernatant fluid alone, after 

 precipitation of the euglobulin at different reactions. One experiment is repre- 

 sented by the lower curve and two by the upper curve. 



Many workers have had difficulty in separating completely the 

 fractions of complement. The extent to which the completeness of 

 separation depends upon the hydrogen ion concentration at which 

 the separation takes place, is shown by the curve. Fig. 1. This 

 records the complementary activity of the supernatant fluid alone 

 separated at different reactions from the euglobulin sediment. 



After adding the amounts of acid or alkali necessary to produce 

 the desired reaction, to a series of tubes containing the different com- 

 plement dilutions, the tubes were heated in all cases for 10 minutes in 

 a water bath, then cooled by placing in ice water. The fluids in the 

 tubes were all brought to the same reaction (pH 7.3 in the case of whole 



