“…The method has been found useful for studying enzymes including esterases (184, 360, 361, 849), proteolytic enzymes (693), fibrinolysin (180), and pepsinogen (38). It has been applied to milk (4, 269, 771), to cerebrospinal fluid (203,204,297), and to various biological fluids (5,18,365,460,478,479,851) as well as to tissue extracts including those from pituitary (140, 946) and adrenal ( 549 It has also been used for investigating proteins that have been separated or modified by chemical reactions (141, 543, 561,652, 673, 713, 850). The specificity of immunological reactions permits the demonstration of relationships between antigens from different sources in a way that is not possible by ordinary chemical methods; as examples it has been shown that some tissue and serum proteins are identical (758,805,806), that livetins in egg yolk are identical with some hen serum proteins (922), that conalbumin and transferrin differ only in the carbohydrate moiety (923), that protein distributions in serum and ascitic fluid from mice differ only with respect to the absence of a prealbumin in the latter fluid (407), that most mammals have related alpha-and beta-protein fractions (762), that apes and men have many serum proteins in common (899), that there are inherited variations in human serum proteins (169), and that tissue transplant rejection causes variations in serum proteins (913).…”