As his research scholar at the time V. D. Allison recalled, Fleming was not a tidy researcher and usually expected unusual bacterial growths in his culture plates. Fleming had teased Allison of his "excessive tidiness in the laboratory", and Allison rightly attributed such untidiness as the success of Fleming's experiments, and said, "[If] he had been as tidy as he thought I was, he would not have made his two great discoveries."

In late 1921, while Fleming was maintaining agar plates for bacteria,