Experiments were made for the purpose of testing the reaction of protection against infection as a measure of potency of antimeningococcic serum.

The results of the experiments were extremely variable and bore no relation to the quality of the sera as determined by the period of immunization of the horses from which they were obtained, or the indications of efficiency based upon their employment in human cases of epidemic meningitis.

The results also failed entirely to conform to the agglutination titer of the sera tested and to be affected by the different type forms of the meningococci.

We regard the protective power for laboratory animals of the antimeningococcic serum as an unsuitable index of its value in human medicine and as inferior to the agglutination titer as a standard of potency.

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