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7.34 History of a Mind


Pasteur - The History of a Mind, a perspective

Author: M. Crasnier-Mednansky, Ph.D., D.Sc.
Copyright © 2005, Mednansky Institute, Inc.

"Pasteur: The History of a Mind" was written by Emile Duclaux (1840-1904) and published in France one year after Pasteur's death in 1895.  Emile Duclaux followed the teachings of Pasteur, entered his laboratory as his assistant, was later his collaborator and actively participated in the founding of the Pasteur Institute.  As his readers we are indebted to him for achieving the difficult task of giving posterity the most accurate genesis of Pasteur's discoveries.

Pasteur's rare gift was his vision of the world, which he transformed by demolishing dogmas, stamping out erroneous views and fiercely imposing his own insightful ideas.  At least the reader of "Pasteur - The History of a Mind" can grasp Pasteur's intuitive imagination and extraordinary skill for experimentation.  The reader can further apprehend the genius in Pasteur by evaluating the colossal advancement in biological knowledge resulting from his studies on crystals, lactic and alcoholic fermentation, spontaneous generations, wines and vinegars, diseases of silkworms, manufacture of beer, etiology of microbial diseases, and vaccines.

In the early years of his life as chemist, while doing research on the left-right molecular asymmetry and its mode of action on polarized light, Pasteur was introduced to the realm of life.  A living fermentative organism became a "laboratory of dissymmetrical forces" and, as Pasteur soon discovered, could differentiate between the left- and right-handed activities of a molecule, and utilize one form without touching the other.  Naturally the young savant approached the question of fermentations and later spontaneous generations.

At the time Pasteur initiated his studies on fermentations there was quite a confusion of ideas and a multitude of arguments, particularly it was largely accepted that yeast was not involved in fermentation.  Carried by the knowledge gained during the course of his studies on asymmetry, Pasteur immediately considered fermentation as "a vital act".  A series of brilliant experiments followed leading Pasteur to discover the reproduction of "ferments", the effect of acidity on fermentation, the use of antiseptics to separate ferments, the products of fermentation and finally the division between aerobic and anaerobic life.  Now Pasteur could no longer believe in spontaneous generations as it denied the notion of specificity he had just introduced with his studies on fermentation.

Before Pasteur, the debate on spontaneous generations was mislead by experiments lacking reproducibility.  Pasteur who had ingeniously defined a clear medium to study his ferments was ready to enter the arena.  Experiments confirmed his previous belief and the partisans of spontaneous generations were given correct reasons for their experimental failure.  Thereafter heated debates occurred in front of committees named by the Academy of Science and, despite the fact that some experimental results were given improper explanations, the recognition of the "germ theory" prevailed.  From this resulted safe conditions in conducting experiments by the introduction of autoclaves as well as techniques such as sterilization by flaming.

Pasteur's discovery of the bacterial action in the production of wines and vinegars had also practical consequences.  Industrial methods in the production of wines and vinegar were greatly improved and the concept of pasteurization, the protection against microbes by the action of heat, then introduced.  What remains distinctive is Pasteur's classical demonstration of the action of oxygen on wine.

In 1865, Pasteur's destiny shifted towards a new course when he accepted to study the disease of silkworms to which he devoted six years.  He discovered that diseases may result from the development of a microbe in healthy tissues of its host.  Pasteur's orientation towards pathology would ultimately lead him to make a connection between contagion and heredity.  By studying the contagious diseases of the silkworms he addressed for the first time the question of "receptivity to germs".  He was on the path leading towards immortal fame.

The consecutive study -the manufacture of beers- was started by Pasteur with the motivation of raising the quality of French beers to German standards.  Ultimately Pasteur's book on brewing will reflect the fact that his mind was at that time preoccupied by questions more crucial to him than the problems of the French brewers.  The specificity of his germ theory had been attacked by the partisans of the transformation of microscopic species.  The notion of spontaneous generation of yeast was resurfacing.  It is one more time by experimentation that Pasteur demonstrated that a microscopic species does not transform into another thereby establishing the specificity of microbial diseases.  Furthermore he described the adaptation of microscopic species to aerobic or anaerobic conditions giving birth to the physiological theory of fermentation.

Pasteur had now studied his microbes for twenty years.  The general current of ideas about diseases did not support the germ theory, and diseases were generally considered the results of "forces of the physico-chemical order".  Anthrax, despite Davaine's pioneer work and Koch's brilliant demonstration of the role of the spore in the etiology of this disease, was still not regarded as a bacterial disease.  Pasteur demonstrated unequivocally the bacterial origin of anthrax and by doing so gave the world the magnificent power to "act on disease".  He further discovered the secretion of bacterial toxins and their action in the host, the strict anaerobic character of the "septic vibrio" and its role as agent in septicemia, and general conditions for the establishment of specific bacterial diseases.  During his time, Pasteur forcibly imposed the sterile surgical practices already followed by Lister in England.

In his final studies, Pasteur developed vaccines for chicken cholera, anthrax and rabies.  As he gained public confidence his popularity increased thereby allowing the creation of the Pasteur Institute.  By studying the transmission of bacterial diseases he gave a meaning to the notions of attenuation and virulence.  He apprehended the concept of natural immunity and finally foresaw the cellular theory of immunity later demonstrated by Metchnikoff and his discovery of the white corpuscles of the blood.

Pasteur was a savant, a man of the laboratory.  His life echoed Alfred Lord Tennyson's poem "Ulysses" [1842] in his final verse:

"To strive, to seek, to find, and not to yield."


Suggested Reading:

Scientific papers by Louis Pasteur, in The Harvard Classics, Volume 38, Part 7

On the antiseptic principle of the practice of surgery by Joseph Lister, in The Harvard Classics, Volume 38, Part 6

The Pasteur Institute by François Jacob, 1998, at

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