By means of the reaction to intracutaneous inoculation with bacterial suspensions in amounts of 0.2 cc., bacterial allergy was demonstrated in rabbits into which had been implanted agar foci containing either gonococci, meningococci, M. catarrhalis, or Bact. lepisepticum. The criterion of hypersensitiveness was the relative size and intensity of reaction evoked by an identical dose in "agar focus" and control rabbits. Rabbits sensitized to gonococci or meningococci usually reacted indistinguishably to either of these organisms, but were less allergic to M. catarrhalis. Similarly, animals sensitized to M. catarrhalis gave moderate but not maximal responses to the two former organisms. Cross-reactions did not occur between Bact. lepisepticum and any of the three Neisseriae. Animals sensitized to the four organisms mentioned reacted no more intensely than did controls to hemolytic streptococci, staphylococci, and rough pneumococci.
The hypersensitive state was found to begin early in the 2nd week and to end usually by the 4th week, being at its height in most instances on the 10th to 12th days. The number of organisms contained in the agar focus determined the success of the sensitization only to this extent, that very small and very large inocula failed to evoke the allergic state.
Rabbits immunized by intravenous injection of live organisms developed cutaneous reactions indistinguishable from those in controls.
The "secondary rise" of Andrewes, Derick, and Swift was rarely observed.