1. Proteolytic enzymes destroy the type-specific M antigen of group A hemolytic streptococci not only when the M substance is contained in cell-free extracts but also when it is a component of the living cell.
2. The injection of enzyme-treated cultures into rabbits fails to induce the formation of M antibodies, but does result in the production of T antibodies and, therefore, provides a method of preparing anti-T sera free from M antibodies.
3. Exposure to these enzymes does not kill the bacteria. Virulence and the ability to form M substance are restored on subculture and animal inoculation.
4. The study of the effect of proteolytic enzymes on group A hemolytic streptococci provides new techniques for analyzing the antigenic composition of these microorganisms.