1. Following repeated intracutaneous injections of heat-killed S or R pneumococci, rabbits acquire an increased skin reactivity to the nucleoprotein of both Pneumococcus and indifferent Streptococcus.

2. Rabbits acquire a skin reactivity to the proteins of both the organisms mentioned after receiving intracutaneous injections of heat-killed indifferent streptococci.

3. Injections of pneumococci into the skin are followed in some rabbits by an eye sensitivity to pneumococcus protein but not to streptococcus protein nor to suspensions of either living organism.

4. Injections of indifferent streptococci into the skin are followed, in some rabbits, by an eye sensitivity to suspensions of live indifferent Streptococcus, but not to R Pneumococcus or to the nucleoprotein of either organism. Measured in terms of bacterial specificity therefore, the eye sensitivity possesses a specificity which is not shared by the skin sensitivity.

5. The sera of rabbits injected intracutaneously with pneumococci or indifferent streptococci contain agglutinins for both R Pneurnococcus and indifferent Streptococcus.

6. Only those animals injected with pneumococci acquire resistance to pneumococcal infection.