Louis Pasteur, French chemist and microbiologist, c 1870s.
© Science Museum / Science & Society Picture Library
Engraving by C H Jeens of Louis Pasteur (1822-1895). Pasteur carried out experiments in the 1860s which proved that germs present in the air are responsible for disease and decay. In 1884 he was appointed Profesor of Chemistry at the University of Lille where he researched the reasons why some alcohols turn sour. He discovered that by heating liquid to a certain temperature the bacteria were killed. This proces is used to kill pathogens in milk, wine and foods, and is known as pasteurisation. Pasteur went on to produce vaccines against anthrax and rabies, and in 1888 the Pasteur Institute was established in Paris for the treatment of rabies.