Louis Pasteur, the 19th-century French chemist and biologist, is known primarily as the "the father of germ theory," as he was the first scientist to offer formal support for the idea that microbes, or microscopic life forms, were responsible for the pathogenesis (the cause and progression) and transmission of certain diseases in humans, livestock and other animals.
As a consequence, his work in the realm of vaccines and food safety has led many science historians to observe that Pasteur's work has arguably saved more human lives than anyone else in the annals of history.
Pasteur, however, was the architect of a number of other groundbreaking ideas in the world of natural sciences, some of them unrelated or only tangentially related to his work in the area of infectious diseases.
In addition to introducing the concept of molecular asymmetry, Pasteur is credited with virtually saving both the wine and silk industries in his native France.
His ideas about how germs trigger the body to fight back against invaders have led to his being credited as "the father of immunology," making him, in effect, the "parent" of a pair of related yet distinct ideas in microbiology.
Louis Pasteur Biography
Born in Dole, France in 1822, Pasteur, like a lot of renowned figures in the comparative dawn of modern scientific exploration, did not limit himself to a single discipline.
The son of a sergeant major from whom he gained a strong sense of patriotism, Pasteur was reputedly only an average student as a child, though skilled in drawing and painting; some of his works are now displayed in the Pasteur Institute (Institut Pasteur).
The lad's creativity did not hearken to his brilliant future in science, which ultimately led him to receive the Legion of Honour, France's highest decoration.
After attending primary school in Arbois and secondary school (high school) as well as university in Besancon, Pasteur headed to the École Normale Supérieure in Paris – where he would later become director of scientific studies – in 1843, launching his science career in earnest.
Pasteur earned degrees in chemistry, physics and math, and, drawn initially to the first of these, became a professor of chemistry at the University of Strasbourg in 1848.
Three of his five children with his wife, Marie Laurent, whom Pasteur married in 1849, died from illness; many people believe that this was the main factor that prompted him to research diseases and illnesses, the real causes of virtually all of which were unknown at the time.
Molecular Asymmetry: Enantiomers
Perhaps like a future Academy Award-winning actor whose initial film role is obscure yet impressive, Pasteur's first major contribution to the body of scientific knowledge is not something he is widely remembered for. Pasteur produced the concept of molecular asymmetry, or the concept that molecules with the same chemical composition and bonding arrangement were not all actually the same shape.
Via meticulous experiments on the light-scattering properties of the tartaric acid found in wine (a hint of his work to follow), Pasteur's discovery demonstrated that chemically "identical" molecules can actually exist in mirror image – "left-handed" and "right-handed" – forms.
Further, he noted that all molecules in living things were left-handed. This was vitally important for understanding three-dimensional structures, especially in the science of crystallography.
Germs and Spontaneous Generation
Before Pasteur came along, most people believed in the notion of spontaneous generation, the idea that bacteria, microbes, germs and life in general appeared essentially out of nowhere, or from things like dust, dead flesh and even maggots.
The same theory was thus applied to illnesses: Weakness in an individual and the associated internal physical changes was presumed to allow these germs to appear, causing illnesses in an accordingly spontaneous way.
Pasteur, on the other hand, believed that these illnesses must arise from micro-organisms that themselves came from living things. That is, he theorized that "germs" didn't just appear out from scratch; they were living things in their own right. He achieved this through a series of elegant experiments that proved that food spoilage was a result of unseen elements in the air.
People were skeptical because Pasteur was not even a physician, but his work led to the development of antiseptics and revolutionized medicine.
Pasteur's Experiment: Fermentation
In his now-famous work involving fermentation, which is the oxygen-independent conversion of sugar by-products to alcohol and lactic acid, Pasteur showed that yeast is a living thing and an active part of the fermentation process. This was important in that it established fermentation as a biological process and not simply a chemical one.
Pasteur demonstrated that when air was pumped through the fermenting fluid, fermentation stopped. This showed that some kind of living organism that requires an oxygen-free environment has to be a part of the process. He was able to show that different microbes are responsible for different types of fermentation.
The Germ Theory of Disease
Pasteur was not the first to propose that unseen things in the environment could cause disease, but he was the first to offer evidence for the claim.
In experiments with beef broth, Pasteur showed that food would only spoil when exposed to microbes that were already present in the air. He applied these and similar findings to generate an elaborate germ theory of disease, which stated that bacteria and microbes cause disease, and that both diseases and their tiny causes exist in the world just like humans and other animals, rather than arising de novo ("from nothing").
This was no mere academic matter. By isolating a specific physical cause for diseases, Pasteur offered hope that these diseases could be prevented, thereby possibly staving off deaths like those that three of his children and countless others across Europe – for example, in the "Black Death" or bubonic plague of the 14th century, caused by the Yersinia pestis bacteria – had suffered.
Pasteur's Invention: Of Wine and Worms
Having come to understand that food and other things go bad not for mysterious or unpredictable reasons but because of bacteria, Pasteur was ready to address his home country's wine problem.
France had long been economically reliant on wine. Much of it was spoiling in transit because of bacterial contamination, but boiling the wine to kill the bacteria ruined the product. Using his signature methodical approach, Pasteur found that raising the wine to a certain intermediate temperature (55 C, or about 131 F) killed the bacteria without ruining the wine.
This process, now fittingly called pasteurization, has become universal in the food industry.
Pasteur's work with silkworms: Having rescued the wine industry, Pasteur used his knowledge of germ theory and disease to identify a parasite that was causing silkworm diseases. With the help of his wife, he was able to isolate the infected worms to get rid of the disease, thereby saving yet another vital sector of his country's economy.
Pasteur and Vaccines
In 1880, pushing the age of 60 but still as active as ever, Pasteur – who is sometimes erroneously credited with creating the first vaccine – developed the idea of vaccines with chickens. (Edward Jenner had developed a smallpox vaccine at the end of the 1700s, but with zero understanding of the underlying immunological mechanism.)
Pasteur showed that chickens, when inoculated (injected) with a non-virulent (non-disease-causing) form of the bacterial illness called chicken cholera, developed resistance to the virulent (disease-causing) types of cholera.
Pasteur's vaccine and others like it today, because they use living forms of the relevant organism, are called live attenuated vaccines, with "attenuated" meaning "thinned out."
Pasteur went on to use the same principles to produce an anthrax vaccine as well as a rabies vaccine, the latter demonstrating that the creation of vaccines for diseases caused by viruses rather than bacteria was possible, and also protecting against the bite of a rabid dog or other rabid animal.
On the basis of his contributions to both germ theory and immunology, Pasteur may be regarded as the father of microbiology and of preventive medicine in general.
About the Author
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs.com and the editor of "Run Strong," he has written for Runner's World, Men's Fitness, Competitor, and a variety of other publications. More about Kevin and links to his professional work can be found at www.kemibe.com.