In a rationally constructed complement fixation test the quantity of each reagent should be known and definite. The relative quantities of the different factors used should also be definite and suitable. The reasons why these principles should be respected will be apparent.
First, let us study the properties of hemolytic amboceptor and complement. When present together amboceptor and complement dissolve the blood corpuscles for which the amboceptor used possesses a specific affinity. The process of hemolysis is, however, a quantitative one. To dissolve a given bulk of corpuscles requires a definite amount of amboceptor and complement; and the quantity of these two reagents just sufficient to cause complete hemolysis within a time limit represents the unit of these hemolytic components relatively to each other. Expressed graphically:
1 unit corpuscles + 1 unit amboceptor + 1 unit complement = complete hemolysis.
There exists, however, a peculiar relationship