Abstract
Three methods of preparing cold agglutinin from sera are described. The most concentrated material so obtained was studied electrophoretically, and ultracentrifugally, and the sedimentation constant, electrophoretic mobility, and approximate isoelectric points are given. Quantitative studies of the reaction of cold agglutinin with erythrocyte stromata are presented. An immunochemical study demonstrates that cold agglutinin is not identical with normal serum gamma globulin.