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.

The early 1870s. Although a revolution is under way in the understanding of disease, ignorance and opposition to the new ideas exist at all levels. Can Pasteur or Koch find a practical outcome of their experiments that will convince the sceptics?

On 6 July 1885 young Joseph Meister was brought to Pasteur's laboratory. He had been savaged by a rabid dog and bitten 14 times. Death from rabies seemed certain, unless Pasteur would treat him with an untried and possibly lethal vaccine.