THE EFFECT OF A POLYSACCHARIDE-SPLITTING ENZYME ON STREPTOCOCCAL INFECTION.

1. Confirming the observations of other experimenters, it has been found that group A hemolytic streptococci produce a capsule containing a polysaccharide which is similar to, if not identical with, certain high molecular weight sugars found in the mammalian body. 2. Leech extract possesses a powerful enzyme capable of splitting one of the linkages in this polysaccharide and of decapsulating group A and group C hemolytic streptococci in vitro and in vivo. 3. Mice and guinea pigs can be protected from intraperitoneal infection with a virulent group C streptococcus by the intraperitoneal administration of leech extract. In contrast there is little protective action of leech extract in mice infected with group A hemolytic streptococci. 4. The protective effect of leech extract against streptococcal group C infection is probably due to the removal of the capsule in vivo. 5. The capsule of mouse virulent group C streptococci plays a major rôle in the virulence of that microorganism, while the capsule of certain mouse virulent group A streptococci plays little, if any, rôle in virulence, at least when the infection is intraperitoneal in the mouse.