Abstract
1. Comparative tests on guinea pigs with B. abortus yield the best results when minute doses are injected subcutaneously and the animal kept at least 4 weeks. 2. B. abortus gradually loses its virulence for guinea pigs under artificial cultivation. 3. Two cultures resembling B. abortus from cattle, isolated from human cases of so called Malta fever, are shown to be in their effect on guinea pigs not identical with the bovine strains. 4. The results of studies of B. abortus from swine indicate a close relation between the porcine strains and the two human strains.