Principles Governing the Practical Application of Complement-Fixation Tests,

Summary Data on experiments with syphilitic serum and cardiolipin antigen are presented supporting a treatment of complement fixation based on the mass law under the assumption that the interaction between complement and immune complex is chemical in nature. Data are given showing good agreement with equations derived from the proposed assumptions. It is pointed out (19, 21) that such a model should serve as only an approximation on the road to a more adequate definition of this complex phenomenon. The fixation of complement is a direct linear function of the amount of immune complex when the amount of antigen is adjusted to yield maximum fixation and an amount of complement is used just sufficient to leave a constant quantity of complement free in each test. The correlation between the experimental data and the theoretical relationships presented lends support to the use of the linear relationship between complement and serum employed in the technic of Wadsworth, Maltaner and Maltaner for the determination of antibody titer. The use of an endpoint based on the adjustment to leave approximately one unit of complement free in solution has been shown to have the advantage of allowing a simple estimation of complement free in solution. The authors wish to express their appreciation to Dr. W. R. Thompson for valuable discussions and useful suggestions.