Germ theory

In the nineteenth century, Louis Pasteur’s work challenged spontaneous generation—the idea that microorganisms arose spontaneously from decaying material. His investigations helped establish germ theory. Robert Koch identified particular microorganisms responsible for particular diseases.

Pasteur’s germ theory in 1861 provided a new explanation of disease, and Koch subsequently identified bacteria responsible for diseases including tuberculosis and cholera. Over time, germ theory displaced miasma and the four humours as accepted explanations.

Louis Pasteur’s germ theory, published in 1861, strengthened the scientific case for preventing contamination. Acceptance was gradual, however. Public health improvements did not wait until everyone agreed about the causes of disease.