Having worked under Sir Alexander Fleming and published three papers to correct myths and misinformation about penicillin's discovery, I wish to comment on John Waller's article.
Waller's statement that Fleming gave "neither help nor encouragement" to the biochemists who tried to extract purified penicillin from the mould broth is wrong. In 1928-29, Fleming had two assistants, Frederick Ridley and Stuart Craddock, working on this at St Mary's Hospital. They were newly qualified medical graduates, but only Ridley had some biochemical knowledge. By sheer determination, they achieved a partially purified extract with a penicillin titre of 1 in 3,000. Fleming had no chemical knowledge, but he helped by doing bacteriological assays on the extracts. Both left St Mary's in 1929.
In 1934, Fleming asked Lewis Holt to try to purify and concentrate the extract from the mould broth. Using direct solvent extraction, he got further than Ridley and Craddock, but he finally extracted into too alkaline a solution and lost the purified penicillin. He gave up after this.
He got very close to the result that Howard Florey, Ernst Chain and Norman Heatley achieved in 1940 using more modern methods. The reason Fleming got all the attention was that Florey refused to speak to journalists.
Francis Diggins
Bexhill-on-Sea, East Sussex