Causative organism of cerebrospinal meningitis and cerebrospinal fever, N. meningitidis is characteristically seen as an intracellular Gram-negative diplococcus in the neutrophilic pus cells of infected CSF. Cultures are derived from CSF and blood, from the nasopharynx of carriers, rarely from other sites (e.g., lung). The organism grows best on serum-or blood-agar in air plus 5 per cent CO2 ; colonies may be recognized by the oxidase reaction. Final identification is by carbohydrate fermentation and agglutination with type sera. There are 4 serological types (A,B,C,D); that concerned with active cases is most frequently Type A. The organism is susceptible to sulphonamides and antibiotics.