In the 1840s the Vienna General Hospital was one of the great centres of European medicine, yet many mothers died of ' childbed fever.' Ignaz Semmelweis set out to find the cause of this disease.

In the small French town of Arbois stand the graves of Louis Pasteur 's three young daughters. Two had died from typhoid, one from an inoperable tumour-a stark reminder of the background to his struggle to find the cause of disease.