1. An acute purulent meningitis due to the invasion of the meninges by Pfeiffer's influenza bacillus is not a very uncommon disease ininfants and young children. It has a very high mortality.
2. Complement is entirely absent in the cerebrospinal fluid of these cases, and bactericidal experiments suggest that the injection of a specific antiserum will have but slight lethal effect on the organisms unless complement is injected at the same time.
3. Treatment with a mixture of specific antiserum and complement led in some cases to a definite clinical improvement, coincident with sterilization and clearing of the cerebrospinal fluid. But after some days, the patients relapsed and died. Autopsy showed localized abscesses in the vicinity of the base of the brain, the lesions being definitely walled off from the general subarachnoid space. In one case, the patient recovered.
4. Since the walls of the abscesses apparently present an insuperable mechanical obstacle to the action of the antiserum and complement, the possibility of preventing the formation of abscesses is discussed. Earlier diagnosis and more rapid sterilization are the most obvious measures. Bactericidal experiments indicate that the proportion of antiserum to complement may be an important factor in bringing about a more rapid elimination of the bacilli.