The Scientific Method
Observation
Hypothesis
Experiments to test Hypothesis
Interpretation of test results
Conclusion to prove or disprove the hypothesis
Anton van Leeuwenhoek (1632-1723)
First to see "animalcules" or protozoa in 1674
Reported existence of bacteria in 1674
Made his own microscopes for inspecting the cloth he bought and traded. He created the first microscope able to see microbes. Unfortunately he did not teach anyone his trade, so the method to make these microscopes died with him.
No link was made between "animalcules" and illness
Spontaneous Generation
Doctrine that lifeless substances give rise to living organisms (see Controversy over Spontaneous Generation
Scientists Redi, Needham, Spallanzani and Pasteur all dealt with this phenomena
First observations:
wheat bran + rags = mice
meat + time = maggots
Created experiment that proved that flies were required for the formation of maggots on meat by using lace to cover a jar of meat.
Needham (1748)
Used two cork flasks, one slightly heated, one not. He observed that after sitting for some time both still had microorganisms in them.
Problem: He did not heat the one enough to kill anything, and he did not know how many bacteria he started with in the first place.
Spallanzani (1767)
Used FOUR flasks with mutton boiled infusion.
One open to air
One corked
One heated slightly with cork
One boiled longer, sealed by melting the glass
He revealed that the 4th, boiled and sealed flask did not grow microorganisms.
Needham countered that because Spallanzani had sealed the flask he had deprived it of it's "life force" or oxygen so therefore of course it didn't grow anything.
1. Disproved Spontaneous Generation with his neck flask experiment. Allowed air in but gravity prevented microorganisms from getting into the broth. Once tipped so that the broth touched the dip in the neck, microorganisms grew.
2. Thought of the Germ Theory of Disease
3. Proved that yeast makes wine with grapes
4. Developed a vaccine for rabies
5. Developed immunization techiniques
Robert Koch (1875) pronounced "coke"
1. Proved the Germ Theory of Disease
Created Koch's Postulates: (to prove a microbe is the cause of a disease)
1. Always observe organism in diseased animal
2. Isolate organism in pure culture
3. Inoculate healthy animal and re-create the disease
4. Re-isolate the organism from the experimentally infected animal
2. Developed Pure Culture Technique
Because of Hess, he adapted Agar, used by Hess to make jelly, as his solid culture medium.
Agar is a powder from seaweed; solid at room temp, and it will not be degraded by bacteria.
Finally practices were being used to reduce the transmission of infectious disease:
sterile practices in hospitals
pasteurization of dairy products
insect control
care in preparation of food
sanitation improvements
personal hygiene
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