In previous communications115 I described the phenomenon of local reactivity to filtrates of cultures of various micro-organisms. The reactivity was induced by the injection of a filtrate into the of a rabbit. When twenty-four hours later an intravenous injection of the same filtrate was given to the rabbit, there appeared an extremely severe hemorrhagic necrosis at the site of the intradermal injection. The determining the local reactivity were termed skin preparatory factors and those responsible for the local injury following the intravenous injection were called In further studies it was shown that the preparatory and the reacting of various biologically and serologically unrelated micro-organisms were able to substitute for each other, provided they had the power of eliciting the phenomenon for themselves. The phenomenon of local reactivity was reproduced with filtrates of cultures of a large number of various micro-organisms.5'11'12 However, in attempts to obtain the necessary from streptococci, considerable difficulties were encountered. At first, cultures of a few strains of nonhemolytic streptococci, of one strain of Streptococcus viridans and of one strain of Streptococcus hemolyticus-pyogenes yielded the toxic factors. In later studies, these strains seemed to have lost the ability to produce them. Strains of Streptococcus hemolyticusscarlatinae were investigated in greater detail. One batch of a filtrate of tryptic digest broth culture yielded powerful preparatory and reacting factors. Filtrates of other cultures of the same strain failed to elicit reactions. The impression gained from these preliminary experiments was that the necessary were in most instances only in weak concentration, this possibly depending on the mode of cultivation of the streptococci and the mode of preparation of the filtrates.