The results obtained in this study show that when two separate immunological systems are combined, mixed agglutination is obtained in relatively high concentrations of the sera but homologous aggregation alone results with sufficient dilution. Where mixed agglutination occurs, it is due largely or entirely to nonspecific serum factors acting on the sensitized red cells. These non-specific factors are of the nature of conglutinin, or are identical with conglutinin. The possibility that antibody per se under certain conditions in the system studied may also produce the mixed agglutination effect has not been eliminated.

Whole normal human serum, its various fractions, or gum acacia, all of which showed conglutinating activity, increased the percentage of mixed agglutination when added in adequate concentrations to the system.

These findings suggest that, in essence, both the Bordet and the lattice theories are substantially applicable to the mechanism of agglutination, the lattice theory best explaining the specific union of antibody with antigen to bring about aggregation, and the Bordet theory offering a reasonable basis for many side effects involving non-specific constituents of serum.

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