1. White mice are highly susceptible to infection by inoculation with Bacillus abortus. The susceptibility appears to be as great as that of the guinea pig, and this animal probably can be substituted satisfactorily for guinea pigs in diagnostic work.
2. Both mice and rats are very refractory to feeding infection with Bacillus aborlus. The failure to infect mice in this way was complete, but the feeding of large amounts of culture gave infection in rats. Subcutaneous inoculation resulted in infection of all the animals. The difficulty of infecting rats and mice with Bacillus abortus by feeding makes it very doubtful whether these animals can have any rôle in the propagation and spread of infectious abortion in cattle.