Causative organism of gonorrhoea, the gonococcus is morpho¬ logically identical with the meningococcus, the intracellular diplococci occurring in the pus cells of urethral or vaginal discharge, less commonly in peritoneal organs, in the conjunctiva of infants infected at birth, and other sites. Cultures grow slowly (2 – 3 days) on fresh, moist blood agar with added CO2 . In mixed cultures the oxidase reaction permits easy recognition of Neisseria colonies, which grown on heated blood agar develop a purple colour when flushed with 1 per cent tetramethyl-p-phenylenediamine; subcultures from such colonies must be made immediately colour develops. Final identification is by carbohydrate fermentation.