The criteria for toxicity were: (a) production of inflammatory skin reactions in guinea pigs; (b) induction of weight loss in mice by intraperitoneal injection; and (c) depression of resistance to staphylococcus infections in mice.

Allergenicity of a preparation was investigated by (a) its ability to evoke a hypersensitive skin response in guinea pigs previously sensitized with whole tubercle bacilli; and (b) its capacity to induce hypersensitivity to one or more of its components when injected under appropriate conditions into guinea pigs.

Fraction F I, a preparation precipitated from methanol extract by slow concentration at 45°C., was found to possess some toxicity and some allergenicity by all of the criteria employed.

Subfraction F I-P, precipitated from aqueous suspensions of F I by 33 per cent ethanol and 0.5 per cent NaCl, was apparently the F I component responsible for these activities. The saline-ethanol-soluble subfraction, F I-S, was neither toxic nor allergenic by the tests performed.

These findings were considered of particular interest inasmuch as F I-S, despite its small yield, had been shown earlier to be the most active single substance used as vaccine to increase resistance to experimental tuberculosis in mice.