All the four types of acid-fast bacilli used in this investigation have proved virulent for the golden hamster. Of the four types the bovine is the most virulent for the species and, after subcutaneous inoculation, gives rise to severe generalized progressive tuberculosis, the lesions containing enormous numbers of tubercle bacilli. The human type is also highly virulent for the hamster and produces general progressive tuberculosis closely resembling that set up by bovine bacilli. Caseation of the lesions in the organs was, however, less extensive in the human than in the bovine infections but there was little difference in this respect between the glandular lesions of the two infections, and multiplication of bacilli was as profuse in one as in the other. Avian bacilli can readily multiply in the tissues of the hamster and cause death, but appear unable to give rise to macroscopic tuberculous lesions. Only one hamster was injected with avian bacilli and the result of this experiment is not in accord with those of Balfour-Jones already quoted. The vole bacillus is less virulent for the hamster than either the bovine or the human type of bacillus. Of the two hamsters injected with this type of bacillus one was killed 152 days later, its general condition then being good and its body showing plenty of subcutaneous fat. Nevertheless the organs were found to contain tuberculosis-like lesions, numerous in the spleen and liver, and the lymphatic glands generally were enlarged. The remaining hamster died 188 days after inoculation and showed generalized disease very similar to that in the last hamster. The glandular and visceral lesions of both hamsters contained very numerous acid-fast bacilli but, in striking contrast to those produced by bovine and human bacilli, showed no evidence of caseation.

Acid-fast bacilli were present in the faeces of all the hamsters; they were numerous in those of hamsters 3, 4, 5 and 2 and relatively sparse in those of hamsters 1 and 6.