1. By the intravenous injection into rabbits of Streptococcus mitis, we have produced focalized myocardial lesions which are identical with those caused by the injection of Streptococcus rheumaticus, and with those produced by Bracht and Wächter with Streptococcus viridans.
2. The lesions differ from those which we produced by injections of streptococci from the Chicago epidemic of sore throat (epidemic streptococcus).
3. The lesions are not identical with Aschoff bodies and are easily differentiated from them. They also differ from the foci produced by Jackson and Coombs, who describe their lesions as being either Aschoff bodies or similar formations.
4. The myocardial lesions of the rabbit appear to be caused by toxins liberated by the streptococci injected and not by the living organisms themselves.
5. The only point of similarity between the experimental lesions and those found in cases of rheumatic carditis in man is their focalized nature.