1. The intradermal injection of H. influenzae in the abdominal wall of rabbits induces inflammation, frequently combined with a central pustule. The corresponding injection of H. pertussis causes a bluish violet discoloration of the skin area involved which undergoes slight hemorrhagic necrotic changes within a few days.
2. The intravenous injection of living H. influenzae, 24 hours after the intradermal inoculation with living H. influenzae, is able to transform the respective skin areas into severe hemorrhagic necrotic lesions within 3 to 5 hours.
3. Heat-killed H. influenzae, if injected intravenously, may produce hemorrhagic-necrotic lesions in areas previously prepared with living or heat-killed H. influenzae.
4. H. pertussis, if injected intravenously, may cause, perhaps to a lesser extent, hemorrhagic necrotic lesions in skin areas 24 hours previously injected with H. influenzae.
5. The normal course of the infection of rabbit skin with H. pertussis is not, or not essentially, influenced by intravenous reinjection of living or killed H. influenzae or H. pertussis.
6. The agar washing filtrate of B. typhosus, if injected intravenously, can produce hemorrhagic necrotic lesions in rabbit skin prepared intracutaneously with living as well as with heat-killed H. influenzae. The intravenous injection of B. typhosus agar washing filtrate has no influence on areas prepared with H. pertussis.
7. Conversely, H. influenzae as well as H. pertussis, if injected intravenously, are able to produce hemorrhagic necrotic lesions in rabbit skin prepared 24 hours previously with B. typhosus agar washing filtrate.
8. The effectiveness of suspensions of H. influenzae apparently is confined to the bacteria themselves rather than to the supernatant fluids. This does not exclude the possibility of producing effective exotoxins under special experimental conditions.