Ten years later, in 1938, Howard W Florey, Professor of Pathology at the University of Oxford, was looking for a substantial project for his group of research workers (which initially included Ernst Boris Chain and Norman Heatley). He decided to research the phenomenon of ‘antibiosis’ (the process whereby micro-organisms produce substances that kill or inhibit other micro-organisms). From compiling a list of about 200 known examples of antibiosis, Florey and Chain decided to investigate just three. The first of this three was the substance produced by Penicillium notatum, described by Alexander Fleming.

Dr Norman George Heatley, played a vital role in this work. His task was to produce as much ‘mould juice’ as possible for the others to study. He also devised the essential step that allowed the partial purification of the drug penicillin, built the apparatus to carry out this purification process, and developed the method to measure how much of the drug penicillin was present in any sample. This method forms the basis of the assessment of the sensitivity of micro-organisms to antibiotics to this day.