[] [From the Pathological Laboratory of the Johns Hopkins Hospital and University.] The literature of the bacillus pyocyaneus with especial reference to its pathogenic effects in human beings was reviewed. Especial reference was made to the experimental work of Charrin on animals and to the human infections reported by Oettinger, Ehlers, Jad kewitch, Neumann, Schaefer, Karlinsky, Ledderhose-Jakowski, Gruber, Martha, Krannhals, Calmette, Mon, nier, Ernst, Fowler, Adami and Williams, Kossel-Blumer, Williams and Cameron, Lavender, Pes and, Gradenigo, and Le Noir. There can no longer be any doubt that in addition to the more or less accidental appearance of blue pus in surgical cases that the bacillus pyocyaneus is capable of entering the human organism and setting up disease processes of variable intensity sometimes of a violence leading to a fatal issue. The writer reported eleven such cases which had come under his personal observation. These eleven cases were independent of the