In 1844 the young Austrian doctor Ignaz Semmelweis was faced with numerous, often lethal cases of puerperal fever. The mortality rate was 2 to 3 times higher in the ward where medical students were being taught than in the ward where midwives were being taught. After investigation, he came to the conclusion that the young doctors were bringing "something" with them from the room where they assisted with dissections of women who had died of puerperal fever and they then passed on this "something" when they examined new women during delivery. He was a fierce advocate of washing hands with chlorine water and by doing so spectacularly reduced the incidence of the infection in his department. And yet he was ignored by most of his colleagues.

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Although various micro-organisms had already been described by Anthony van Leeuwenhoek in Holland (1632-1723), their ability to induce disease was not yet understood. In 1860 Louis Pasteur in France discovered that diseases existed which were caused by small ("micro") living organisms. This discovery had enormous consequences, which reached well beyond medical practice. In 1867 the Englishman Lister realised that bacteria which caused infections could be killed by carbolic acid (phenol). This product was then used to clean instruments and wounds. An initial consequence of this was that the incidence of puerperal fever (streptococcal infection) sharply decreased everywhere. However, a patient who was already infected could not be cured by disinfection. A solution had to be sought.

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Around the turn of the century, syphilis in Europe was a significant problem. There was no effective treatment, but mercury chloride was widely used. In 1903 Elie Metchnikoff demonstrated that the disease could be transmitted to chimpanzees. In 1905 the German Fritz Richard Schaudinn discovered the pathogen. Noguchi Hideyo, a Japanese bacteriologist, also carried out important work on this pathogen. In 1910 the German Jew Paul Ehrlich, together with the chemist Bertheim and his Japanese assistant Kiyoshi Shiga, developed a substance based on arsenic: Salvarsan (606). Initially Salvarsan (=arsphenamine) was developed as a model for the treatment of trypanosomiasis in mice. The step to the treatment of syphilis was due to a wrong assumption by Schaudinn. He thought that treponemes were related to trypanosomas. Inspired by this idea, together with his Japanese assistant Sahachiro Hata, Ehrlich developed a model of chicken treponematosis. Salvarsan was successful. After this it also proved to be active in rabbits infected with T. pallidum. The substance killed syphilis bacteria in man too. The product was rather toxic, but heralded a revolution in treatment and in the medical thinking of the time. Together with the Russian Elie Metchnikoff (discovery of phagocytosis) Ehrlich received the Nobel prize in 1908. However Salvarsan was not active in patients with neurosyphilis. The Austrian von Jauregg (Nobel prize 1927) introduced treatment with vivax malaria. After approximately 12 episodes of fever, quinine was given. He established that high fever has a favourable effect on some chronic processes (T. pallidum is very sensitive to high temperature). He claimed that he recorded an improvement in 67% of patients.

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After the ground-breaking work of the Scot Alexander Fleming in 1928 at St. Mary’s Hospital in London, the German Ernst Chain (later becoming a naturalised Briton) and the Australian Howard Florey (all three shared the Nobel prize in 1945) developed a method in Oxford for preparing penicillin in large quantities from mould cultures. This was to be the final breakthrough in the area of antibiotics at the beginning of the Second World War. Penicillin rapidly replaced Salvarsan for the treatment of syphilis, and is still the drug of choice.