THE RÔLE OF MICROBIC VIRULENCE, DOSAGE, AND HOST RESISTANCE IN DETERMINING THE SPREAD OF BACTERIAL INFECTIONS AMONG MICE : I. PASTEURELLA LEPISEPTICA AND PASTEURELLA AVISEPTICA INFECTIONS

1. Three strains of Pasteurella native to rabbits, introduced into mouse communities failed to spread or survive.

2. One strain of fowl Pasteurella, so introduced, survived for 2 months without causing death, after which, it gave rise to a 5 day epidemic, fatal to 77 per cent of the population. Subsequently, no further deaths from this source occurred and the strain died out completely.

3. At the height of the epidemic, caused by the fowl strain of Pasteurella, 6 cultures were obtained which, on direct inoculation, proved to have a degree of virulence for mice and rabbits equal among themselves and the same as the strain originally employed.