THE effectiveness of penicillin in the treatment of many varieties of pneumococcal infections is well established. Since it is believed that its effectiveness in a proved case of pneumococcal pericarditis is worth recording, the following case is presented.F. D., a 30-year-old shipyard office worker, was admitted to the Northern Permanente Foundation Hospital on April 8, 1945, complaining of severe knifelike chest pains and dyspnea. Four weeks prior to admission he developed pleuritis on the left side, associated with some coughing, which was relieved by heat and strapping. Three weeks prior to admission he developed substernal pain, which was made . . .