Pus from a lumbar abscess in a boy, aged 10 years, produced severe general tuberculosis in a guinea-pig. A culture from this guinea-pig resembled a bovine strain in primary culture on egg and a eugonic human strain in subculture on glycerine egg and glycerinated potato. The virulence of the strain was high for the guinea-pig and irregular for the rabbit. For some rabbits the pathogenic effects of the strain were much more severe than those of typical human bacilli and approached, but did not equal, those of bovine bacilli. The results in other rabbits were similar to those of eugonic human bacilli. Cultures recovered from the rabbits resembled in characters the original strain, which was therefore not a mixture of the human and bovine types of tubercle bacilli. The strain cannot be described as ‘human’ or ‘bovine’ according to the usually accepted distinction between these types in the rabbit, but according to the results in the vole could be classified as belonging to the human type.