Abstract
The occurrence in health and disease and the clinical significance of a protein fraction of human plasma characterized by cold-insolubility in combination with heparin was studied by means of an empirical technique of measurement sufficiently reliable to allow quantitative interpretation of serial changes in plasma levels. Data allow the conclusions that normal individuals have low levels of the fraction, and that these levels become greatly increased as a result of most acute inflammatory or necrotizing diseases. The appearance of the fraction in increased amounts represents another reaction in the category of "acute-phase" phenomena. Data support the other items of evidence indicating that the fraction may fulfill a different physiological role from clottable protein. The nature of this function is as yet unrevealed.