1. A quantitative turbidimetric method for the estimation of hyaluronidase activity, based on the ability of the enzyme to decrease the capacity of the polysaccharide to precipitate acidified protein has been developed. Two units of hyaluronidase, by this method, are equivalent to one viscosity-reducing unit.

2. Hyaluronidase added to a phagocytic system containing defibrinated human blood, immune or non-immune, greatly increases the rate of phagocytosis of group A streptococci. Phagocytosis of Type I pneumococci is not affected by hyaluronidase under the same conditions.

3. The bactericidal activity of non-immune blood against group A streptococci is increased by hyaluronidase; the activity of immune blood is, however, somewhat inhibited by the enzyme. Killing of pneumococci is not affected by the presence of the enzyme.

4. Mice can be protected against group A streptococcal infection by frequent treatment with 200 turbidity-reducing units of hyaluronidase; the protective action of the enzyme is removed by heating at 60°C. for 1 hour. Mice infected with Type I pneumococcus and treated with hyaluronidase die somewhat sooner than the untreated controls.

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