Throughout history, people have created explanations for disease. Some
have held that disease has spiritual causes, but the most persistent biological
theory over the centuries was that illness resulted from an imbalance in
the body fluids. The introduction of germ theory by Louis Pasteur and others
in the 19th century led to the modern belief that many diseases are caused
by microorganisms--bacteria, viruses, yeasts, and parasites.
See Content Standard G History and
Nature of Science (grades 9-12): Historical Perspectives.
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