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Koch’s 3rd postulate requires the same disease to be produced in a healthy host using a pure culture. Koch himself said this was the only way to obtain direct proof of causation.
So why abandon that logic when the test failed?
For cholera, Koch could satisfy only Postulate #2 (pure culture). He failed #1 (bacterium found in healthy people) and #3 (pure cultures could not reproduce cholera in animals). Yet he still declared Vibrio cholerae the cause. If the defining test fails, what’s left but belief?
Max von Pettenkofer, Dr. Emmanuel Klein, and Ilya Metchnikoff all drank pure cultures of Vibrio cholerae and stayed perfectly healthy. Koch knew neither animals nor humans could be made sick experimentally—yet still asserted causation without direct proof.
Modern “revisions” to Koch’s Postulates exist for one reason: the original, falsifiable criteria were not met. Instead of admitting the hypothesis failed, the standards were changed.
Science moves forward by confronting failed predictions—not rewriting the rules to protect them.
For more on Koch's Cholera Catastrophe:
1.
For more examples of direct human exposure to "deadly pathogens" that failed to cause disease and falsified the germ hypothesis:
Related Notes:
Koch's 1st Postulate
Koch’s 2nd Postulate
