1. Precipitation of diphtheria-toxoid by alum depends on the pH under which the precipitate is formed.

  2. Purified toxoid requires much less amounts of alum to be precipitated than the original toxoid.

  3. One-eighth by volume of 4 per cent solution of alum seems to be sufficient for toxoid purified with calcium-phosphate to precipitate the greater part of the active principle from it.

  4. The superiority of the alum-toxoid as an immunizing agent was shown with toxoids purified with calcium-phosphate.

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