THE CARDIOTOXIC ACTION OF PREPARATIONS CONTAINING THE OXYGEN-LABILE HEMOLYSIN OF STREPTOCOCCUS PYOGENES : II. INHIBITION OF CARDIOTOXIC EFFECT BY A SUBSTANCE RELEASED FROM THE FROG'S HEART.

1. The mechanism of sensitization of the isolated frog' heart to a product of the hemolytic streptococcus has been investigated. The sensitization depends upon the release from the isolated heart of a substance which inhibits the action of the cardiotoxin. The inhibitor is released upon the first (sensitizing) administration of cardiotoxin, but not upon the second (contracture-producing) administration. 2. The inhibitor released by the heart neutralizes the lethal factor present in the streptococcal preparation employed. 3. Some of the properties of the inhibitor have been investigated.