FIXATION OF COMPLEMENT 123 



finger can be used as a stopper for the tube while mix- 

 ing, provided that contamination from one tube to 

 another is avoided by using a different finger for each 

 case. The tubes are then incubated for one hour at 

 37° C. to assist in fixation of complement. At the end 

 of this time, no alteration in the appearance of the con- 

 tents is manifest, though complement-fixation will 

 have taken place in the tubes containing syphilitic 

 serum and antigen. In the negative cases there will be 

 no complement-fixation. The occurrence or non-oc- 

 currence of complement-fixation is now determined by 

 the addition of the hemolytic system and re-incubation 

 of the tubes. To each tube is added 1 c.c. of a 1-1000 

 dilution of anti-sheep hemolytic amboceptor and 1 c.c. 

 of a 5 per cent, suspension of sheep's corpuscles. The 

 contents of the tubes are again thoroughly mixed, and 

 the tubes incubated for one and a half to two hours. 

 At the end of this time a preliminary reading of the 

 results may be made, but final reading should be de- 

 ferred until next morning after the tubes have re- 

 mained all night in the ice-box.^ 



Reading of Besults, — In case of a positive result, 

 in Tube 1 of the front row there should be no hsemol- 

 ysis, because complement being fixed by the action of 

 the antigen on the syphilitic serum, no complement re- 



^ The time consumed in incubating the tubes may be materially lessened 

 by placing them in a water-bath heated to 37° C. instead of in the air incubator, 

 only one-half the time being required for each incubation in the water-bath. 



