Complement-mediated immune lysis was first described by Pfeiffer after observing an immune reaction against Vibrio cholerae. Application of this reaction in agar gel, with viable vibro organisms, gave results which were unique compared to the red blood cell or enterobacterial systems. Among these was the lack of a detectable "background," a lengthened latent period and differentiable results among the three major cell wall antigens characteristic of this bacterial groups.