1. Rabbits inoculated intradermally with certain strains of green streptococci have well marked lesions which, after reaching a maximum size in 24 to 48 hours and then beginning to retrogress, show in over 50 per cent of the animals a secondary increase in size and other signs of inflammation about 8 or 9 days after inoculation.
2. This secondary reaction may follow the inoculation of a variety of strains of green-producing streptococci from various sources, of indifferent streptococci, and occasionally of pneumococci.
3. The inoculation of hemolytic streptococci, staphylococci, Micrococcus catarrhalis, or Bacillus coli has not been followed by this secondary reaction.
4. The secondary reaction is not due to increased activity of the injected bacteria since the lesions are usually sterile at the time it occurs and since the secondary reaction occurs after inoculation of killed organisms as well as after that of living ones.
5. A second inoculation of green streptococci into a rabbit within 9 weeks of a first injection is followed by a primary but not by a secondary reaction. This inhibition of the secondary reaction is not specific; for the phenomenon of secondary reaction can be completely inhibited by previous inoculations of the rabbit with any living streptococcus and usually with pneumococci. Killed organisms are less effectual.
6. Preliminary injection with staphylococci, Micrococcus catarrhalis, and Bacillus coli has not prevented the appearance of a secondary reaction in response to subsequent injections of green streptococci.
7. The agent responsible for the secondary reaction has not as yet been determined; its nature is discussed. The phenomenon is possibly a form of allergic reaction.