Louis Pasteur was the scientist who made the link between germs and disease, and then continued his work by making vaccines for diseases like chicken cholera. This post explores Pasteur's journey to his discovery, and how other scientists followed on from it.
History - Medicine through time - Fighting infectious disease
Science at that time: science was propelled forward by advances that came before and with the industrial revolution. These include the invention of the thermometer (by Fahrenheit in 1709 and Celsius in 1742) and the invention of the microscope as early as 1683 (by van Leeuwenhoek). Microbes were known of at this point, but they were not believed to be the cause of disese, only the result of it. This theory is called spontaneous generation. This theory was only applied to microscopic organisms by this time because of the experiments of Francesco Redi in 1668, who showed that maggots did not spontaneously generate but came from eggs laid by flies. Pasteur was to disprove the theory of microscopic spontaneous generation.
Pasteur was an industrial scientist, not a doctor or pathologist (someone who investigates the cause and effect of disease). This meant that he dealt with the sientific problems facing big businesses. He made his discovery while investigating the reason why sugar beet mysteriously went sour during fermentation in 1857.
He believed that microbes were growing in the sugar beet and causing it to go sour. He proved this with the famous swan-necked flask experiment. In a swan necked flask, microbes cannot get in because they have to travel against gravity to go up the swan neck. Using this knowledge, he set his experiment as follows:
He took two sets of swan necked flasks and filled them with broth, which microbes love to feed on. He then strongly heated the broth in all of the flasks so that no germs would start inside the flasks. Since they couldn't enter through the swan neck, they would have to spontaneously generate to get in. He broke the swan necks of half of the flasks, which would allow microbes to float in on dust particles. After a while, all of the flasks with broken necks had lots of bacterial growth, but those with te swan necks had none. Since no microbes started in any of the flasks, this proved that microbes didn't spontaneously generate. He confirmed his idea in 1865-7 when studying a silkworm disease called pébrine.
Pasteur's ideas were followed up by other scientists such as Robert Koch, who started using this information to single out which microbes cause which diseases and then make a vaccine against that microbe. Pasteur followed this trend that resulted from his own idea by investigating the diseases anthrax, tuberculosis, cholera and others. This is explored in another post.
Important note: Jenner created the first vaccine against smallpox, so it would be unfair to claim that Pasteur and Koch began the trend entirely. However, Jenner created his vaccine without knowledge of why it worked, and so Pasteur's discovery is important because it represents the knowledge behind why vaccines work.
In summary, Pasteur was an industrial scientist who did not discover microbes, but proved that they did not spontaneously generate and also that they caused disease. He began and continued a trend of identifying microbes for the diseases they caused and creating vaccines for them.
Further reading:
http://bcs.whfreeman.com/thelifewire/content/chp03/0302003.html
