1. A minority only of scarlatina streptococci are agglutinated by antisera for individual strains and no group agglutination has been observed.
2. Absorption tests reveal the existence of common or generalised agglutinogenic constituents but these are not restricted to scarlatina strains and can be recognised among the majority of the haemolytic streptococci isolated from various sources.
3. Though certain serological groups among scarlatina streptococci may be recognised as corresponding generally to “types” described by Smith and Griffith, there is such considerable antigenic overlap among the different groups that the differentiation and relationship of strains cannot be expressed satisfactorily by formulating definite serological types.
4. A system of serological analysis of scarlatina and other haemolytic streptococci is suggested (see Table IV).
5. While strains presenting particular serological characters may be associated more frequently with scarlatina, haemolytic streptococci with common serological characters occur both in scarlatina and other conditions. No essential serological distinction can be drawn between scarlatinal and other haemolytic streptococci and a “Streptococcus scarlatinae” group cannot be defined by serological methods.
6. Among the haemolytic streptococci derived from conditions other than scarlatina no relationship exists between serological characteristics and toxigenic properties (as evidenced by cutaneous reactions to culture nitrates).
We have to thank Drs J. Smith and F. Griffith for cultures of the type strains referred to in the text.