Medicine, the art and science of treating disease. Within the last 150 years medicine has become dominated by scientific principles. Prior to this, healing was mainly a matter of tradition and magic. The Greeks introduced anatomy and physiology and provided the Hippocratic oath, in use today. In the 17th century, William Harvey researched blood circulation and the heart; in the 18th century, Edward Jenner introduced vaccination; in the 19th century, Louis Pasteur proposed the germ theory and anesthesia made advances in surgery possible. Medicine in the 20th century uses new diagnostic techniques (x-rays, CAT scans, MRIs), organ transplants, a better understanding of nutrition and immunity, and new drugs, especially antibiotics.