Fleming found that penicillin killed staphylococcus, hemolytic streptococcus, pneumococcus, gonococcus, diphtheria bacilli, and other bacteria, but it did no harm to the influenza bacillus. He did not try to develop penicillin into a medicine. To him the influenza bacillus was important enough that he used penicillin to help grow it by killing any contaminating bacteria in the culture. He used penicillin as he said, “for the isolation of influenza bacilli.”
