Experiments were undertaken to determine the protein fraction or fractions of antimeningococcus serum with which are associated the agglutinative and precipitative activities and also the neutralizing activity for the toxic substance of the meningococcus which induces the phenomenon of local skin reactivity.

In the method for the concentration of antimeningococcus serum described in a paper by Neal and others (1) concentration of the agglutinative activity was obtained by separation of a water-insoluble globulin after partial removal of euglobulin by saturation of the serum with sodium chloride. Similar results have been obtained in this laboratory with Banzhaf's method (1). It was noted, however, with certain sera, that a lower degree of concentration of potency for group II strains was obtained than for strains of groups I and III. With one serum particularly, potency for group II strains, as determined by the precipitation reaction, was adversely affected by concentration.

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