How did the idea that germs cause disease come about?
Louis Pasteur, a chemist and biologist, held the belief that scientific research should aid in the development and progression of industries. When beverage manufacturing plants were having problems with liquids spoiling during the mid-1800s, Pasteur used his microscope to observe the fermentation process. When a batch was bad, he found that other microorganisms had mixed with the yeast. He showed that heating liquid to around 60°C (140°F) would kill the microorganisms and sterilize the product to prevent contamination. This heating process is known as pasteurization and is still used today to prevent bacterial growth in milk, juice, and other beverages.
Pasteur’s work with fermentation led him to research the origins of microorganisms, which he believed came out of the air. He performed a simple experiment by collecting air at different altitudes into flasks of yeast- filled liquid. The flasks had long, narrow necks that would allow air to enter but would trap dust and microorganisms. The liquid remained free of microorganisms as long as Pasteur didn’t shake the flask. Once shaken, the liquid would begin to host microorganisms and turn cloudy. This confirmed his hypothesis about where germs came from, but other scientists had to be convinced that substances couldn’t just produce germs on their own—an idea known as spontaneous generation.
With a greater understanding of the origins of germs, Pasteur set about to discover better ways to prevent diseases. He was studying chicken cholera, when he left his lab in the heat of the summer and returned to find that his cultures would no longer make the chickens sick. He grew new cultures and injected those chickens as well as a second batch. The chickens that had been previously injected with the damaged batch of cholera remained well, while the new group of birds grew sick and died. He deduced that the summer heat had made the bacilli noninfectious and learned that he could reproduce the effect by growing it in a warmer environment. He went on to create vaccines for rabies and for anthrax in sheep.
Louis Pasteur led the way for a new era of medicine, in which patients could anticipate a cure for their illnesses. His students and colleagues continued to isolate disease- causing bacteria and develop vaccines. Deeper understanding of these bacteria led to the development of antibiotics, which have had a major impact on modern medicine.
fermentation: the process in which microorganisms, especially bacteria and yeast, break down plant or animal materials
microorganisms: single-celled organisms too small to be seen by the naked eye
bacilli: rod-shaped bacteria
Edward Jenner created the first vaccine in the 1790s when he discovered that injecting patients with cowpox would immunize them from smallpox—a similar virus that could be contracted only once.
Pasteur’s work with fermentation led him to the creation of the germ theory of disease—the idea that microorganisms from outside the body can cause disease within it. It took a long time for the scientific community to accept the idea. It seemed illogical to scientists that something that couldn’t even be viewed without a microscope could cause damage to an organism as large as an animal or a human being.
“Where observation is concerned, chance favors only the prepared mind.” —Louis Pasteur
