1. Normal serum, used in cultures for preparation of the streptolysin, modifies the properties of the streptolysin, causing delayed hemolysis, increased filterability, resistance to oxidation or reduction, and absence of antigenicity.
1. Streptolysin prepared without serum is an active antigen.
3. Similar temperatures are required to destroy the antigenic activity of serum-free streptolysin and the skin reactivity of Dick toxin.
4. Scarlet fever antitoxin contains antistreptolysin which does not neutralise serum streptolysin and which can be detected only by titration against serum-free streptolysin.
5. The antihemolysin which neutralises serum-free streptolysin is species-specific but not type-specific.