Louis Pasteur was a French biologist and chemist who made enormous contributions to germ theory, to prevention of food spoilage, and to the control of disease.
Pasteur discovered that the fermentation process could be stopped by passing air (oxygen) through the fermenting fluid, a process known today as the Pasteur effect. This led to his introduction of the terms aerobic and anaerobic to designate organisms that live in the presence or absence of oxygen, respectively. He further proposed that the phenomena occurring during putrefaction (rotting) were due to specific germs that function under anaerobic conditions.
Pasteur applied his knowledge of microbes and fermentation to the wine and beer industries in France, effectively saving the industries from collapse due to problems associated with production and with contamination that occurred during export. To prevent contamination, Pasteur used a simple procedure: he heated the wine to 50–60 °C (120–140 °F), a process now known universally as pasteurization. Today pasteurization is seldom used for wines that benefit from aging, since it kills the organisms that contribute to the aging process, but it is applied to many foods and beverages, particularly milk. Pasteur also devised a method for the manufacturing of beer that prevented deterioration of the product during long periods of transport on ships.
Pasteur also showed that beef broth could be sterilized by boiling it in a “swan-neck” flask, which has a long bending neck that traps dust particles and other contaminants before they reach the body of the flask.
However, if the broth was boiled and the neck of the flask was broken off following boiling, the broth, being re-exposed to air, eventually became cloudy, indicating microbial contamination.
These experiments proved that there was no spontaneous generation, since the boiled broth, if never re-exposed to air, remained sterile.
Louis Pasteur soon became an expert silkworm breeder and identified organisms that caused the silkworm disease. He saved the silk industry through a method that enabled the preservation of healthy silkworm eggs and prevented their contamination by the disease-causing organisms.
Pasteur developed the overall principle of vaccination and contributed to the foundation of immunology, too. Pasteur’s first important discovery in the study of vaccination came in 1879 and concerned a disease called chicken cholera. He inoculated chickens with the attenuated form and demonstrated that the chickens were resistant to the fully virulent strain.
Pasteur began investigating anthrax in 1879. Pasteur wanted to apply the principle of vaccination to anthrax. The vaccination procedure involved two inoculations at intervals of 12 days with vaccines of different potencies.
One vaccine, from a low-virulence culture, was given to half the sheep and was followed by a second vaccine from a more virulent culture than the first. Two weeks after these initial inoculations, both the vaccinated and control sheep were inoculated with a virulent strain of anthrax. Within a few days all the control sheep died, whereas all the vaccinated animals survived. This convinced many people that Pasteur’s work was indeed valid.
His investigations of animals infected by pathogenic microbes and his studies of the microbial mechanisms that cause harmful physiological effects in animals made him a pioneer in the field of infectious pathology.
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