þÿLouis Pasteur s Experiment
Like many other scientific breakthroughs, the discovery of immunization happened by accident.
In 1880 Louis Pasteur was trying to protect chickens from cholera. To study the disease, Pasteur and his assistants gave injections of cholera bacteria to several groups of chickens. The chickens usually died from cholera after being injected with the bacteria. However, one group of chickens survived. Pasteur noticed that these chickens had been injected with a six-week-old batch of cholera bacteria.
Pasteur s assistants prepared new colonies of cholera bacteria and injected these chickens a second time. They also injected a group of chickens that had not been previously injected. Pasteur was surprised that the chickens that had been injected previously with the old bacteria remained healthy, while all the chickens in the second group became sick and died.
This is how Pasteur came to discover that exposure to weakened pathogens can provide immunity from disease. The idea was later used to protect animals from other serious diseases. Today immunizations help protect people from many illnesses.