STUDIES ON THE BIOLOGY OF STREPTOCOCCUS : V. ANTIGENIC RELATIONSHIPS BETWEEN STRAINS OF STREPTOCOCCUS FROM SCARLET FEVER AND ERYSIPELAS.

1. Strains of hemolytic streptococci isolated from cases of erysipelas agglutinate in a high percentage of instances with erysipelas immune sera. When agglutination occurs with one serum, the strain usually agglutinates with all other erysipelas sera. 2. Erysipelas immune sera agglutinate strains from erysipelas in a higher percentage of instances than they agglutinate scarlatinal strains. 3. Strains from miscellaneous pyogenic infections may agglutinate in these sera, but the percentage of positive reactions is low and a strain usually agglutinates in but one or two of several sera. 4. Erysipelas strains which agglutinate in immune sera are not necessarily identical, although identical strains may occur. Similarly, identical strains may occur among scarlatinal strains agglutinated by scarlatinal immune sera. 5. Erysipelas strains form a closely related group of hemolytic streptococci. Scarlatinal strains form an equally compact group. The two groups are related antigenically but less closely related than the strains within the groups. These groups are related to pyogenic strains, but less closely than they are related to each other. 6. Erysipelas, scarlatinal, or pyogenic strains which agglutinate in erysipelas or scarlatinal sera are capable of absorbing the agglutinin for all other strains except the homologous strain and strains identical with it. Strains identical with the homologous strain absorb the agglutinin completely. 7. Erysipelas or scarlatinal strains may absorb the common group agglutinin from their respective sera, when they are incapable of agglutination in these sera. 8. The agglutinogen is probably of complex or composite nature, with characteristic variations in the scarlet fever and erysipelas groups.