The foremost representative of classical Greek medicine was Hippocrates whose most famous works was the treatise Airs, Waters, and Places, an early primer on environmental medicine. In western Europe, monks played an important role in Christian healing as well as in the collection and preservation of medical manuscripts. As the Islamic Empire gradually expanded, a comprehensive body of Greco-Roman medical doctrine was adopted together with an extensive Persian and Hindu drug lore. The early-sixteenth-century findings of Andreas Vesalius of Padua, based on meticulous and systematic dissections that established the foundations of modern anatomy in the West, contradicted Galen's descriptions. This chapter talks about Renè Descartes's mechanical theory, and William Harvey's experimental discovery of the blood circulation. The French medical revolution was ushered in by an important change in approach. With the existence of microscopic germs and some of their actions firmly established, researchers such as Pasteur and the German physician Robert Koch began to study specific diseases.