Germ Theory

Thomas Wakley...all is darkness and confusion, vague theory, and a vain speculation. Is it a fungus, an insect, a miasm, an electrical disturbance, a deficiency of ozone, a morbid off-scouring from the intestinal canal? We know nothing; we are at sea in a whirlpool of conjecture.

Miasma Theory

Blood Generation Theory

Germ Theorycontagium vivum

Friedrich Henle The material of contagions is not only an organic but a living one and is indeed endowed with a life of its own, which is, in relation to the diseased body, a parasitic organism.

John Snow

Louis Pasteur (1822-95)

Robert Koch(1843-1910)

anthrax spores

Koch's postulates

1. the pathogen must be found in every individual who has the disease.

2. the pathogen must be isolated from a diseased individual and grown separately in a pure culture.

3. the disease must be induced in an experimental animal by transferring the pathogen from the pure culture.

4. the same pathogen must be isolated from the experimental animal after it has contracted the disease.