A series of observations on the blood of patients acutely ill with scarlet fever 
has shown that a toxic substance can be demonstrated in the serum by means of 
intracutaneous injections of the serum in persons who have not had scarlet fever 
and whose serums fail to blanch the rash in scarlet fever. The reaction caused 
by this substance consists of a bright red local erythema, varying from 20 to 70 
mm. in diameter, of 1 to 4 days duration. The severer reactions are moderately 
indurated and tender, and are followed bypigmentation and desquamation. Control 
injections in persons whose serums blanch the rash in scarlet fever cause no 
reaction. The toxic substance is not neutralized by mixture with a human serum 
which gives a negative blanching test but is readily neutralized by a human 
serum which gives a positive blanching test. It is not neutralized by normal 
horse serum, but is completely neutralized by Dochez's scarlatinal 
antistreptococcic serum. In a limited number of observations on the urine of 
patients with scarlet fever a similar toxic substance has been found in two out 
of five cases studied. Since the toxic substance described appears to resemble 
the toxic substance found in the filtrates of scarlatinal hemolytic 
streptococcus cultures by Dick and Dick and since it is neutralized not only by 
a blanching human serum but also by Dochez's scarlatinal antistreptococcic horse 
serum, the experiments reported support the conception that scarlet fever is a 
local infection of the throat by a particular type of Streptococcus haemolyticus 
capable of producing a toxin which is absorbed and is the cause of the general 
manifestations of the disease.