124 APPLIED IMMUNOLOGY 



mains to take part in hsemolysis of the sheep's cor- 

 puscles by the amboceptor. The corpuscles will have 

 settled to the bottom of the tube, leaving colorless fluid 

 above. In case of a negative result, complete haemol- 

 ysis will have occurred in this tube, because there being 

 no " reagin " in the serum to fix complement with the 

 antigen, complement remains free to act with the 

 hsemolytic system during the second incubation. 

 Hsemolysis is shown by a disappearance of the cloudi- 

 ness due to the corpuscles and the fluid becoming a 

 transparent red color. 



In Tube 2 of the jront row, containing known 

 syphilitic serum, we should get inhibition of hsemol- 

 ysis for the same reason that we obtained it in case of a 

 positive result in Tube 1. 



In Tuhe 3 of the front row, containing non-syphi- 

 litic serum, we should get complete hsemolysis, for the 

 same reason that we obtained it in case of a negative 

 result in Tube 1. 



In all tubes of the hack row, there should be com- 

 plete hsemolysis, because these tubes contain no anti- 

 gen, and therefore no complement-fixation could have 

 taken place during the first incubation, tlie comple- 

 ment remaining free to combine with the haemolytic 

 system. Occasionally, in the serum to be tested, there 

 are substances capable of fixing part or all of the com- 

 plement in the absence of antigen. In these cases, the 



