After vaccination with one or 3 doses of a phenolized suspension of Bacterium tularense white mice developed maximal agglutinative titers of 1:40 to 1:80 at 3 to 4 weeks, the levels slowly declining thereafter. The antibody level was somewhat higher and persisted longer in those animals that had received 3 doses. Following a single booster dose there occurred a slight negative phase followed by a rapidly rising titer. The peak of 1:640 to 1:1280 was reached in about a week when the stimulating

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... ose was administered between 6 and 7 weeks after the initial vaccination. Despite this improved antibody response mice failed to develop any resistance to small numbers of living, virulent organisms when they were challenged intraäbdominally, intracerebrally or subcutaneously at the time of peak antibody titers. The completely susceptible and wholly nonresistant white mouse is an unsuitable test animal for experiments of this nature.