THE RÔLE OF MICROBIC VIRULENCE, DOSAGE, AND HOST RESISTANCE IN DETERMINING THE SPREAD OF BACTERIAL INFECTIONS AMONG MICE : III. B. ENTERITIDIS INFECTION

1. Several mouse populations under experimental observation were infected with B. enteritidis typhoid. The infection took the form of periods of low grade mortality interspersed with epidemiform outbreaks. During the periods of low grade mortality, the number of daily deaths was either relatively constant or rhythmic in 9 day intervals. The epidemiform outbreaks were associated invariably with some definite environmental disturbance. 2. The spread of this infection was not influenced by the presence of bacteriophage or the bacterial-dissociation phenomena. 3. The virulence or disease-producing power of B. enteritidis was found to be constant during all pre-epidemic, epidemic, and endemic phases of the infection. 4. The dosage of B. enteritidis available to a population at a given time was found to vary directly with mortality at a time difference approximating that of the incubation period of the disease. 5. The amount and severity of B. enteritidis infection in the populations were controlled experimentally by varying the diet from adequate to optimum constituents and by varying the daily immigrants from a relatively resistant to a susceptible race of mice.