The active fibrinolytic principle present in cultures of hemolytic streptococci can be isolated in stable form, and partially purified by the following methods:

1. Precipitation of culture filtrate with 3 volumes of 95 per cent ethyl alcohol.

2. Adsorption upon polyaluminum hydroxide B of Willstätter (5) followed by elution with M/10 sodium phosphate buffer, pH 7.3.

Concentration can be best accomplished by vacuum dialysis (4) of either culture filtrates or preparations obtained by adsorption and elution.

The streptococcal fibrinolysin is characterized by the following properties:

1. It may resist heating to 100°C. for 60 minutes; variations in thermal resistance are described.

2. Partially purified preparations give positive tests for protein. Activity is rapidly and completely destroyed by trypsin or papain.

3. The active principle is demonstrable in dissolved fibrin even after 18 hours incubation.

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