Based on newly available documents and others translated for the first time, physician Nicholas Kadar sheds important new light on the thinking of the celebrated Hungarian doctor Ignaz Semmelweis (1818-1865) at the Vienna School of Medicine, where he discovered the cause and prophylaxis of childbed fever, one of the greatest findings in the history of medicine. Drawing a portrait of an era open to the possibilities of antiseptics – vitally important in a world facing Covid-19, Kadar explodes the opposition Semmelweis faced from his contemporaries and explains many aspects of Semmelweis’s hitherto unexplained actions. Kadar’s detailed study demonstrates that supposed champions of Semmelweis’s work destroyed his career prospects in Vienna, and did more harm to his highly effective medical doctrine than any of proclaimed opponents ever did. Step by step, Kadar traces the presuppositions and the deductive logic that led Semmelweis to his discovery of the cause and prophylaxis of childbed fever, giving it proper place in the history of medicine.