Louis Pasteur

of the new Faculty of Sciences in Lille. It was on this occasion that Pasteur uttered his oft-quoted remark: ". . . dans les champs de l'observation, le hasard ne favorise que les esprits préparés" (In the field of observation, chance favors only the prepared mind. ) In 1856, he was made administrator and director of scientific studies of the École Normale Supérieure.

Germ theory of fermentation

Pasteur demonstrated fermentation is caused by the growth of micro-organisms, and the emergent growth of bacteria in nutrient broths is not due to spontaneous generation, but rather to biogenesis (Omne vivum ex vivo "all life is from life").

He exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths unless the flasks were broken open; therefore, the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. This was one of the last and most important experiments disproving the theory of spontaneous generation. The experiment also supported germ theory.

While Pasteur was not the first to propose germ theory (Girolamo Fracastoro, Agostino Bassi, Friedrich Henle and others had suggested it earlier), he developed it and conducted experiments that clearly indicated its correctness and managed to convince most of Europe it was true

Today, he is often regarded as the father of germ theory and bacteriology, together with Robert Koch.

Pasteur's research also showed the growth of micro-organisms was responsible for spoiling beverages, such as beer, wine and milk. With this established, he invented a process in which liquids such as milk were heated to kill most bacteria and moulds already present within them. Claude Bernard and he completed the first test on April 20, 1862. This process was soon afterwards known aspasteurization.

Beverage contamination led Pasteur to the idea that micro-organisms infecting animals and humans cause disease. He proposed preventing the entry of micro-organisms into the human body, leading Joseph Lister to develop antiseptic methods in surgery.

In 1865, two parasitic diseases called pébrine and flacherie were killing great numbers of silkworms at Alais (now Alès). Pasteur worked several years proving it was a microbe attacking silkworm eggs which caused the disease, and eliminating this microbe within silkworm nurseries would eradicate the disease.

Pasteur also discovered anaerobiosis, whereby some micro-organisms can develop and live without air or oxygen, called the Pasteur effect.

Immunology and vaccination

Pasteur's later work on diseases included work on chicken cholera. During this work, a culture of the responsible bacteria had spoiled and failed to induce the disease in some chickens he was infecting with the disease. Upon reusing

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