There is present in inflammatory exudates a factor which induces a prompt increase in the permeability of normal capillaries. Its liberation and presence in exudates offers a reasonable explanation for the mechanism of increased permeability of small vessels in injured tissue.
A method for the isolation and purification of this permeability factor has been described. In its essential features, this consists of treating the exudate with pyridine followed by acetone. After separation of the protein fractions further purification can be obtained by prolonged extraction with butyl alcohol or by subjecting the acetone supernatant fraction to low temperature (–20°C.). The latter favors spontaneous separation of the active principle. The purified material is a crystalline doubly refractive nitrogenous substance.
The factor is evidently not a protein, yet it contains amino and carboxyl groups. It gives a positive test for the presence of an indole nucleus in its structure (Adamkiewicz test). The active material is dialyzable; and it is precipitated by concentrated ammonium sulfate. The present evidence indicates that it is an intermediary breakdown product of protein metabolism, probably belonging to the group of relatively simple polypeptides. Further studies are being conducted in an endeavor to determine its precise chemical structure.