Koch's postulates
Etiological discovery in medicine has a history in Robert Koch's demonstration that the tubercle bacillus ("Mycobacterium tuberculosis" complex) causes the disease tuberculosis, "Bacillus anthracis" causes anthrax, and "Vibrio cholerae" causes cholera. This line of thinking and evidence is summarized in Koch's postulates. But proof of causation in infectious diseases is limited to individual cases that provide experimental evidence of etiology.