Louis Pasteur (1822 - 1895)

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

Jenner and the Smallpox vaccine

The discovery of a vaccine to guard against smallpox was the first major step in counteracting infectious disease. This post explores the events preceeding the vaccine, the discovery of the vaccine and the public's reaction to it.
History - Medicine through time - 18th/19th Centuries


Vaccination is often confused with inoculation, as they are similar. Before the introduction of vaccines, inoculation was the best way of developing immunity to smallpox. Inoculation involves deliberately infecting someone with the pus from a person who only had a mild form of the disease, and hoping that the body would be able to fight it. By surviving the disease, the person could become immune to future.

The problem with inoculation was that it was very dangerous. People risked contracting a fatal form of the disease. It was introduced to Britain in 1718 by Lady Mary Wortley Montagu, and by the time Edward Jenner (1749-1823) began experimenting with his theories in 1796 many people had become rich by setting up inoculation houses and charging for the service. These people didn't want to lose their business to the new practice of vaccination that was introduced by Jenner, which is one of the reasons he received so much resistance when he introduced it.

How Jenner discovered his vaccine
Jenner was the student of John Hunter, 'the father of modern surgery', who taught him the importance of scientific observation. Jenner lived in the countryside and investigated the rumour that milkmaids, who were exposed to the non-fatal disease cowpox, didn't get smallpox.


This led him to believe that getting cowpox and defeating it somehow gave a person resistance to smallpox as well. He decided to investigate by infecting someone with cowpox, and then testing them with smallpox. He chose a young boy, James Phipps, and tried the experiment. he found that catching and defeating cowpox did indeed give immunity to smallpox. Jenner wrote about his discovery in 1798.


Because cowpox was non-fatal, this was an excellent way to safely give any healthy person immunity to smallpox. He had discovered the vaccine.

Reactions to the vaccine
As prevously said, Jenner's vaccination method would put many people out of business. They attacked his techniques and spread rumours of strange and horrible side effects that could result from Jenner's discovery. The picture in this post shows the fears that some people had about the vaccine's 'side effects'.


However, the vaccine was so effective that the resistance was crushed. Members of the Royal Family were vaccinated, he was given £30,000 by the government (1802-6) and Emperor Napoleon even released a prisoner at Jenner's request!

Vaccines are used to this day since they became compulsory for all children in 1853. They have had an effect of great magnitude on modern preventative medicine.


Further reading:
http://www.jennermuseum.com/edwardjenner.html
http://en.wikipedia.org/wiki/Edward_Jenner
http://www.historylearningsite.co.uk/edward_jenner.htm