Invisible microbes cause sickness by setting up home in our bodies and multiplying - fast Follow the hunt for these tiny killers over thousands of years and the fight to outwit and eliminate them. Smallpox and tuberculosis came from cattle Cholera made the skin shrivel and turn blue Hospitals caused fatal diseases Find out how the French scientist Louis Pasteur unmasked germs living in the air the German doctor Robert Koch proved that they caused disease and the British surgeon Joseph Lister pioneered surgery in super-clean conditions - some of the greatest victories in the battle against disease.