1. Histological examination of sections of the eyes and joints of large numbers of rabbits injected with hemolytic streptococci has clearly demonstrated that when arthritis or cyclitis occurs, the synovial villi and ciliary processes are the most frequent and usually the primary sites of inflammation.
2. By special methods for demonstration of bacteria, it has been shown that bacteria which found lodgement in either an eye or a joint were demonstrable first in the vessels of ciliary processes or synovial villi.
3. A localized synovitis or iridocyclitis is brought about by the localization of bacteria in the synovial villus and ciliary process.
4. These experiments, which give a clearer insight into the pathogenesis of infectious arthritis and iritis, explain why both may occur in association with certain infectious diseases.