REACTIONS OF RABBITS TO INTRACUTANEOUS INJECTIONS OF PNEUMOCOCCI AND THEIR PRODUCTS : I. THE ANTIBODY RESPONSE.

1. Sixty rabbits were immunized by the repeated injections into the skin of small doses of suspensions of heat-killed Type I pneumococci. In 53 of the rabbits no type-specific antibodies appeared in the serum, and in the remaining seven the titre of these antibodies in the serum was very low. In all cases, however, the sera possessed a high titre of species-specific antibodies. 2. Forty-five rabbits similarly immunized by injections of heat-killed Type III pneumococci also failed to form type-specific antibodies but did form species-specific antibodies. 3. Suspensions of heat-killed R pneumococci and solutions of bacterial substances when injected into the skin stimulated the production of species-specific antibodies, although they failed to stimulate the production of any type-specific antibodies. 4. Animals which had been immunized by intracutaneous injections still possessed the ability to form type-specific antibodies when they were subsequently given intravenous inoculations of type-specific pneumococci.