EXPERIMENTAL EPIDEMIOLOGY OF TUBERCULOSIS : THE EFFECT OF A PRIMARY INFECTION ON CONTACT TUBERCULOSIS IN RABBITS

73 per cent of normal rabbits exposed for about 1 year to cage mates infected with tubercle bacilli of bovine type acquired a respiratory or alimentary tuberculosis, which was fatal in 50 per cent of the cases. 63.6 per cent developed tuberculosis during the first 6 months. Of rabbits vaccinated with tubercle bacilli of human type and exposed in the same cages at the same time only 36.8 per cent acquired tuberculosis during the first 6 months. Later this resistance waned, and by the end of the year altogether 60 per cent had developed tuberculosis, of which 38 per cent succumbed. The disease in the vaccinated rabbits was shown to be of exogenous origin by the isolation in pure culture from the same rabbit of the human type bacillus from the primary infection, and of the bovine type bacillus from the naturally acquired lesion. The vaccination reduced the incidence, extent, and mortality of the disease, affected the route of infection, changed its pathological character, and retarded its progress. The disease acquired by vaccinated rabbits shared many characteristics with adult type tuberculosis in man. It is suggested that this method may be used with relative ease in studying many phases of naturally acquired tuberculosis in small laboratory animals.