The experimental pathogenicity of 14 isolates of Nocardia brasiliensis, 15 of N. asteroides, and 5 of N. caviae was investigated for the white Swiss mice inoculated intraperitoneally and in the foot pad, and for the guinea-pig and the hamster (Mesocricetus auratus) both inoculated intratesticularly. The guinea-pig was remarkably sensitive to N. asteroides, with an apparent relationship between pathogenicity and thermotolerance, confirming previous observations. Mice were in general less susceptible to this species. In both guinea-pigs and hamsters it was possible to observe typical granules with or without clubs. N. caviae was highly pathogenic for the guinea-pig and the hamster but no mycetomas were produced in the mice inoculated in the foot pad. Isolates of N. brasiliensis from natural sources were scarcely virulent for the different animals. Those of human origin produced significant lesions in the mice inoculated intraperitoneally with granules. Foot pad inoculation of mice with N. brasiliensis caused mycetomas in several animals.
