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Summary: Highly labile factors (I and II) of anthrax toxin were purified from the toxic plasma of guinea-pigs just dead from anthrax by fractionation methods which involved the minimum of inactivation. The final preparations of factors I and II, which still contained constituents of guinea-pig plasma, were toxic when injected together but innocuous when injected separately.
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Stanley et al. (1960) studied this question.
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