1. A simple method for the purification of diphtheria toxoid has been presented.

  2. The products have been evaluated with respect to purity, antigenicity, and stability.

  3. Preparations having a purity in excess of 2000 Lf per mg N have been obtained.

  4. Evidence has been presented which indicates that the antigenicity per Lf increases with the purity of the toxoids studied.

  5. A linear logarithmic relationship between the flocculation time and titer at the toxoid-antitoxin equivalence point has been shown.

  6. Various relations between Lf, Kf, purity, and antigenicity have been studied.

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