Louis Pasteur

Louis Pasteur is best known for two things: pasteurization and vaccination. This brilliant scientist accomplished an enormous amount during his lifetime, with several important discoveries to his credit.

Chirality is a property of certain molecules which essentially means they can exist in one of two mirror image formations. Chemically they are identical, despite this structural difference. They also reflect light differently, and it is this property which led Pasteur to discover the existence of chiral molecules.

Spontaneous generation, also known as abiogenesis, is the belief that living organisms are generated by the decay of organic matter. This was a fairly commonly-held belief in history: Aristotle, for example, noted that it was common to see mice arising from dirty hay, and crocodiles from rotting logs in bodies of water.

In the mid-sixteenth century, physician Girolamo Fracastoro theorized that diseases might be caused by tiny particles, and following this several other noted scientists formulated similar theories. However, it was not until 1861 that Louis Pasteur confirmed this theory. Pasteur’s experiments involving boiling nutrient-rich broth, and then exposing the broth to air which was filtered to prevent the entry of any particles. Nothing grew in the broth, thus proving that the organisms which grew in such media had not spontaneously generated from the broth itself.

Other experiments Pasteur conducted showed that fermenting beverages could be contaminated by certain microorganisms. After establishing this fact, he invented a process which would kill the contaminating microbes: pasteurization, in which liquid was heated to kill bacteria and other microorganisms.

Later in life, Pasteur worked with diseases such as cholera in chickens. During the course of this work, he attempted to infect chickens with a culture of the cholera bacteria which had, unbeknownst to him, spoiled. The chickens did not become diseased, and Pasteur re-used them in a later experiment. However, although they were this time exposed to an infectious culture of cholera, the chickens again failed to contract the disease.

Pasteur realized that the chickens might now be immune to cholera, after having been exposed to a strain which was too weak to cause severe disease. This was not a new concept – Edward Jenner had previously discovered, in the 1790s, that an infection with cowpox could provide cross-immunity to smallpox.

However, Pasteur’s work was particularly important because it showed that an artificially-weakened disease-causing organism could provide protection, meaning there would be no need to locate naturally weak disease forms which could provide cross-immunity.

It was also Pasteur who produced and tested the first rabies vaccine, and who also risked serious legal implications during the testing. The vaccine was made from rabies virus which had been grown in rabbits. Nerve tissue of the rabbits was then harvested and dried, to weaken the virus.

On July 6, 1885, a nine-year-old boy named Joseph Meister was attacked by a rabid dog. The young boy faced almost certain death, but even so, using the vaccine was a serious personal risk for Pasteur, who was not a licensed physician and might therefore have faced prosecution if the boy had died.

Luckily for Pasteur, and for immunological research, the boy’s treatment was a huge success – Joseph Meister made a fulll recovery, Pasteur was a hero, and the legal implications of the episode were ignored.