The valuable paper of Rosenau and Anderson on hypersusceptibility, which was presented at the recent session of the American Medical Association in Boston, and of which the authors' abstract appears in this issue, calls fresh attention to a most important "immunity reaction." We are all familiar with the occasional examples of individual and family hypersusceptibility which may be manifested against many drugs and certain infections. This is a natural hypersusceptibility. Since the time of Koch, however, facts concerning a peculiar acquired hypersusceptibility have been gradually accumulating.
The tuberculous individual, for unknown reasons, acquires a delicate susceptibility to an injection of tuberculin which the non-tuberculous does not possess. Experience in the immunization of animals with toxins and bacteria has brought to light other examples in which the immunizing process resulted in heightened susceptibility to the substance injected, rather than immunity. Animals which have endured prolonged immunization with tetanus or diphtheria toxin