This volume collects the contributions made by the participants in a conference held at the New York Academy of Medicine with the aid of a grant from the National Science Foundation. The general reader will find the contents of this book an enjoyable means of becoming acquainted with the nature and scope of immunology as it has developed in recent times. The contents comprise a wide variety of topics including: the cellular origins, biosyntheses and metabolism of antibody; the acquisition of tolerance to and rejection of foreign tissues; allergic encephalomyelitis; the Shwartzman reaction; agammaglobulinemia; and serum sickness and related states.