Tuberculous morbidity in Swiss albino mice immunized with BCG

Study was made of the effect of BCG vaccination on the establishment of experimental tuberculous infection in mice. To this end, mice were infected with small quantities of virulent human bacilli administered by the respiratory route. The quantity of bacilli present for inhalation was so controlled as to permit only a finite percentage of unvaccinated animals to become infected. The relative proportion of mice infected by inhaling these small numbers of virulent bacilli was not found to be lowered by prior BCG vaccination. Thus, pulmonary tissue of immunized mice was not able to prevent the initial lodgement of virulent tubercle bacilli. The growth of virulent organisms in infected lungs, however, was significantly retarded by prior vaccination.