1. An improved method is outlined for the isolation and purification of the pneumococcal transforming substance. This method makes use of the fact that citrate inhibits the destructive action of the enzyme, desoxyribonuclease, which is released together with the active material during lysis of the living bacterial cells. A fivefold greater yield of purified transforming agent is obtained by the present method than by the procedure previousiy described.

2. The specific transforming substance has been isolated from pneumococci of types II and VI, in addition to Type III. In each instance the biologically active material has been found to consist of desoxyribonucleic acid.

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