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.