Germ Theory Science figures out how diseases are spread

Early Theories Miasma  Disease carried by foul air Spontaneous Generation  Decomposers are the result of the process of decay Rotting things change into living organisms

Little Things Leeuwenhoek  Built an early microscope and examined everything Noticed small living organisms in everything he examined  In food, water, excreta, plaque He did not know what function they played

Francisco Redi (1688) Showed that maggots could only come from adult flies.

Opponents still insisted that microorganisms could still form spontaneously.

Ignaz Semmelweis (1847) Discovered that midwives who washed their hands before delivering babies had fewer infant deaths Made doctors at his hospital start washing their hands Infant Death Rate dropped to 1% from 10% before the hand washing.

Pasteur’s Germ Theory Louis Pasteur ( )  A Scientist (not a doctor) Brewery in France asked Pasteur to investigate why some vats of alcohol would go bad His theory: A growing, living organism caused the problem

His solution to the problem was to boil the liquid to kill the germs  Pasteurisation Applied to milk, beer, wine, vinegar It worked! Under sterile conditions, life did NOT spontaneously generate.

Pasteur battles Spontaneous Generation Theory French Academy launches competition to prove or disprove Spontaneous Generation in 1860 Pasteur devises experiments to show that microbes existed in the air

Some of Pasteur’s experiments are still sterile!

Linking Germs to Disease “If wine and beer are changed by germs, then the same can and must happen sometimes in men and animals”

Pasteur gave three ways to stop germs 1. Heat them 2. Filter them 3. Expose them to chemicals that can kill them

Joseph Lister (1867) British Surgeon Knew you couldn’t heat or filter humans, so experimented with chemicals to kill germs. Developed sterile surgery techniques, including using weak acids to clean everything, using sterilized gloves, and not using same instruments between patients. Immediate success!

Robert Koch (1890) Developed tests to isolate the causes of diseases These tests are still used today Isolated the germs that cause anthrax, tuberculosis and cholera Tests are called Koch’s Postulates

Koch’s Postulates The organism must be: 1. found in all cases of the disease examined 2. isolated and maintained in a pure culture 3. capable of producing the original infection in a new animal 4. retrievable from the new animal and cultured again

Koch finally ended the idea of miasma, which lingered even into the 1950’s because it made sense and was, partly, true. Miasma said that the dirt and bad air made people sick; Koch (and the others who came before him) showed that it was microorganisms in the air that made people sick

“Common Sense” vs. Science Miasma was “common sense”; bad air caused disease.  Observation  Conclusion Germ Theory is science; microorganisms in the air (and elsewhere) caused disease.  Observation  Research  Hypothesis  Experiment  Conclusion  Peer Review