1. A strain of Streptobacillus moniliformis isolated from a case of rat bite fever in man has been found to produce infection of the developing chick embryo following inoculation of the chorio-allantois.
2. The disease in embryos is characterized by invasion of the blood stream and an almost exclusive localization of the infectious process to the synovial lining of the joints.
3. In the early stages of the development of the joint lesions the Streptobacillus moniliformis behaves as a facultative intracellular parasite within the cytoplasm of the synovial lining cells. Conditions favorable for the growth of the microorganisms are maintained only temporarily. The infection appears to be self-limiting in nature.