Pasteur, the son of a tanner, was not a physician but became the most important medical scientist working in the 19th century. His earlier work which led to the discovery of the molecular asymmetry of tartaric and racaemic acid had a profound consequence for structural chemistry. The crystals of tartaric and racaemic acid had the same chemical structure but had different effects on polarised light. By 1856 he had begun his work on fermentation beginning with fermentation of milk into lactic acid. He reported the presence of micro-organisms which continued to bud and multiply. He was able to declare that the multiplication of the micro-organism resulted in …