1. We have produced arthritis in 50 per cent. of the rabbits injected with Streptococcus mitis.
2. The character of the arthritis is identical with that produced by Micrococcus rheumaticus.
3. The exudate in and about the joints partakes of the same nature as that caused by Streptococcus rheumaticus.
4. Bacteriological studies show that Streptococcus mitis can be recovered from about one third of the affected joints.
5. Arthritis produced by other types of streptococci differs by reason of greater destruction of tissue, by being more permanent in character, and by the exudate containing large numbers of polymorphonuclear leucocytes.
6. The deduction of a distinct variety or species of streptococcus based upon the power to cause arthritis in rabbits is unwarranted.