Louis Pasteur (1822-1895), French microbiologist and chemist. Louis Pasteur proved the germ theory of disease, which holds that germs attack the body from the outside. This explained diseases such as anthrax and meant that he could develop the first vaccine for rabies. He also showed that organisms such as bacteria were responsible for souring wine and milk and they could be removed by boiling and then cooling the liquid. This process is now known as pasteurisation.