1. Fatal Type I pneumococcal meningitis may be produced in rabbits by intracisternal injection of pneumococci.

2. When organisms are of high virulence, the rabbit does not tend to localize them in the meninges, but an early septicemic process results. Death is septicemic rather than meningeal.

3. In such instances very little cellular reaction occurs in the meninges.

4. Active or passive immunization previous to intracisternal infection inhibits partially the septicemia and permits the development of reactional processes in the meninges.

5. The immunization likewise retards the meningeal disease, but multiplicity of factors prevents us from stating precisely to what this retardation is due. It is not correlated with the presence of agglutinins in the spinal fluid at the time of infection.

6. The rapidity of production of meningitis is influenced by the phase of growth of the culture used, and likewise by the growth activity of that culture.

7. To some extent in the partially immune rabbit the meningeal spaces constitute a relatively non-immune reservoir, constantly feeding the blood stream and breaking down systemic resistance.

8. Intrathecal serum treatment causes rapid agglutination and phagocytosis of pneumococci, and has very rarely, possibly, resulted in cure. Essentially no phagocytosis occurs in the absence of immune serum.

9. Phagocyted pneumococci stained supravitally take up the neutral red stain and are therefore probably injured.

10. The treatment employed subsequent to infection only slightly prolongs life in the majority of cases. It does retard septicemia.

11. The treatment improves the cellular reactional processes in the meninges.

12. A study of the pathology of rabbit pneumococcal meningitis shows that the location of pneumococci precludes complete contact with serum introduced intrathecally, and that these locations provide isolated foci, from which organisms may reinfect the meningeal spaces as rapidly as they are removed by lavage or antibody injections.

13. In recovered rabbits postmeningeal symptoms, weakness, ataxia, nystagmus, and paralyses arise.

14. In our opinion there is some objective evidence of benefit of serum therapy. The rabbit is too susceptible, however, and conditions too artificial to admit of definite conclusions.

15. Rough Type I pneumococci introduced in large quantity cisternally may kill and may be recovered 24 hours after infection, from spinal fluids. In a series of eleven passages, no reversion to smooth type occurred. In all animals injected with rough forms, transient bacteremia resulted.

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