Louis Pasteur was born on December 27, 1825, in Dole, located in the Jura region of France.The couple had five children, though only two survived to adulthood, which fueled Pasteur's lifelong quest to prevent infectious diseases.Pasteur observed that while solutions of both substances rotated the plane of polarized light, only the tartaric acid formed crystals that could be separated by hand.With the assistance of his mentor, Jean-Baptiste Biot, he discovered that these crystals were optically active, existing in two forms that were mirror images of each other.