It has been shown by our experiments that the serum of rabbits treated with emulsions of Treponema pallidum contains agglutinating substances.

Normal rabbit serum also possesses agglutinating power for this organism, but, as in the case of normal bacterial agglutinins, to an extent very much inferior to that possessed by the sera of immunized animals. Normal human sera will agglutinate similar pallidum emulsions, as will the sera of certain syphilitic patients with positive Wassermann reactions. Whether or not there is a quantitative difference of diagnostic value between the sera of normal human beings and those of syphilitics remains to be seen.

The sera of rabbits immunized with strain A agglutinate Noguchi's strain 9 in dilutions as high as 1 to 500.

We regard as the most important result of these experiments the demonstration of definite antibodies in the circulation of animals treated with dead emulsions of Treponema pallidum. Since it is our belief that the agglutinating effect is due to an antibody essentially the same as that which produces bactericidal, precipitating, and opsonic effects, i. e., that there is probably one type of antibody only, we believe that the demonstration of agglutinins establishes the fact that in syphilis as in bacterial diseases the host responds by the formation of antibodies or sensitizers specific for the treponema.

Spirocheticidal experiments with these sera, both in vitro and in vivo, are in progress.

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