1. Following repeated intracutaneous injections of heat-killed pneumococci rabbits acquire an increased skin reactivity.
2. The increased skin reactivity reaches a maximum after 4 to 6 injections have been made, after which it becomes greatly diminished.
3. The relationship of increased skin reactivity to active resistance to infection by Pneumococcus, and to the presence of species-specific antibodies in the blood, is still obscure.
4. The increased skin reactivity is not transferable by serum from a highly reactive to a normal rabbit.
5. After regression of the reaction to the first injection of Pneumococcus into the skin, there frequently follows a recrudescence, or exacerbation, of the reaction.
6. The increased skin reactivity and secondary reactions are incited alike by all types and all forms of Pneumococcus.