1. Hemolytic streptococcus has been found in 100 per cent of the throats of patients with scarlet fever during the 1st week of the disease.
2. The average length of time that these organisms are present in the throat varies from 10 to 20 days.
3. No morphological or cultural characteristics peculiar to the hemolytic streptococcus from scarlet fever can be demonstrated.
4. Ten immune sera have been prepared from different strains of scarlet fever streptococci and each of the sera agglutinated more than 80 per cent of the strains isolated from scarlatinal throats. On the other hand, scarlatinal streptococci are not agglutinated by immune sera prepared from hemolytic streptococci isolated from other pathological sources.
5. Serum from patients convalescent from scarlet fever agglutinates weakly or not at all the homologous strain of hemolytic streptococcus.
6. The specificity of the agglutination reaction of scarlatinal streptococci is confirmed by absorption experiments.
7. Scarlatinal antistreptococcic serum affords some degree of protection against virulent scarlet fever streptococci but has no protective power against hemolytic streptococci from other diseases.
8. In a small epidemic of scarlet fever a healthy carrier of hemolytic streptococcus was detected; the organism carried was identical in its serological reactions with strains of hemolytic streptococci isolated from active cases of scarlet fever.
9. In a study of a number of contacts with a case of scarlet fever, in only one instance was a scarlatinal type of hemolytic streptococcus recovered from the throat.