There is an extensive literature presenting experiments designed to show that the leucocytes play a more active part in ridding the organism of injected bacteria in immunized animals than in normal ones. This qualitative response on the part of the leucocytes has been very carefully studied and is specific. Gay and Claypole (1) have, however, recently described a quantitative response in the leucocytes of immunized animals which they claim is also specific. Upon injecting a normal rabbit intravenously with typhoid bacilli there results first a leucopenia and then a hyperleucocytosis; if a rabbit immunized against typhoid bacilli is similarly injected, they found likewise first a leucopenia and then a hyperleucocytosis, but the hyperleucocytosis in this case was much greater in degree than that called forth in the normal animal. Their table indicates that normal rabbits will show a maximum of about 35,000 to 60,000 leucocytes to the cubic millimeter, while the rabbits immunized against typhoid bacilli yield counts of 60,000 to 150,000.