Formalin induces a considerable change in meningococcus culture filtrates. This consists of a marked decrease in toxidty as concerns both the Shwartzman phenomenon and the lethal effect, with relative preservation of the antibody-combining capacity and antigenicity.

A similar modification occurs spontaneously in meningococcus culture filtrates on standing.

Inasmuch as these changes parallel those occurring in the conversion of diphtheria toxin into toxoid, it is justifiable to consider such altered meningococcus toxin as meningococcus toxoid.

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