How important was Louis Pasteur

Q. So what was the theory before germs were discovered

A. Doctors in the mid-19th Century still thought diseases were spread by miasma - polluted air.

Q. How did Pasteur change all that

A. Working as a chemist at Lille University, Pasteur was asked by an industrialist about the production of alcohol from beet sugar. He wanted to know why the wine was going sour after fermentation. Pasteur discovered that fermentation involved micro-organisms in yeast - and for the process to produce alcohol rather than lactic acid, the correct type of yeast need to be used.

Q. So that led on to...

A. The process of killing germs. Having discovered that 'bad' wine contained germs that could be seen through a microscope, Pasteur developed a process for killing them by heating the wine to 50C and then cooling it down. He called this process 'pasteurisation'. Pasteur then set about proving that the germs came from the air and could therefore be prevented from entering the liquid in the first place.

Q. How

A. He sealed a liquid in an airtight jar and left another sample exposed to the air. Pasteur now used his discovery to help treat diseases. He knew that the British doctor Edward Jenner had developed vaccination smallpox. Pasteur believed that his germ theory could be used to explain how vaccination worked. He examined the blood of healthy people and compared it with the blood of people with diseases. The difference, he found, was that their blood contained lots of germs.

Q. What else did he discover

A. Apart from pasteurisation - which is used on most dairy products today -he went on to discover vaccinations for chicken pox, cholera, diphtheria, anthrax and rabies. His work with silkworms is also notable.

Q. Silkworms

A. The French silk industry was seriously threatened by a disease that killed silkworms in the mid-1860s and Pasteur was employed by the government to investigate the disease. He found a minute parasite infecting the silkworms and recommended that all infected silkworms be destroyed. His advice was followed and the disease eliminated. His work on treating rabies was also widely acclaimed.

Q. What did he discover

A. In 1882, he demonstrated that the causative micro-organism infects the nervous system. Using the dried tissues of infected animals, he succeeded in obtaining a form of the virus suitable for inoculating of humans. In 1885, Pasteur used the vaccine to save the life of a boy bitten by a rabid dog.

Q. So, a hero all round

A. Yes - although some found him unfriendly. In fact he wasn't - but always refused to shake hands with people... because he feared passing on germs.

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By Steve Cunningham