2. The Germ Theory of Disease (19th Century)
Prior to the 19th century, the dominant belief was the miasma theory—that diseases arose from “bad air.” This changed dramatically with the pioneering work of Louis Pasteur and Robert Koch, who demonstrated that specific microbes cause specific diseases. Their research not only debunked old misconceptions but also revolutionized infection control, sterilization, and medical hygiene. The CDC highlights how germ theory remains central to modern medicine, guiding everything from antibiotics to public health interventions and ongoing research into infectious diseases.
