Louis Pasteur was born in 1822 in Dole, France. His discovery that most infectious diseases are caused by germs, also known as the germ theory of disease, is one of the most important in medical history. His work became the foundation for the science of microbiology, and a cornerstone of modern medicine. As Pasteur was growing up, his teachers thought that Louis was not fit for advanced studies, and felt he should carry on the work of his father as a tanner of leather.