Louis Pasteur, Biological Physicist

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Pasteur’s next step toward biology came when he was a young professor at the University of Lille.

At the beginning of the academic year 1856, an industrialist of Lille, M. Bigo, whose son Emile was taking Pasteur’s course at the Faculty of Sciences, came to see him. Many manufacturers of beet root alcohol, he said, were having problems with their production…

This led to Pasteur’s research on fermentation, when a microorganism such as yeast brings about a change to a food or beverage, such as producing alcohol. Fermentation and light polarization do not appear to have much in common, but they do.

The findings Pasteur presented to the Academy of Sciences of Lille, and subsequently that of Paris, seemed very different from the studies he had undertaken previously. He was known as a specialist on crystals, and now he had become a theoretician of fermentation. Ranging from polarized planes of light to culture media, his reagents had little in common. Yet the preoccupations that guided Pasteur’s thinking at that period were not really different from those that had haunted him for a long time: he wanted to understand the relationship between life and molecular asymmetry.

The idea that a living microscopic organism was responsible for fermentation was one of Pasteur’s key insights. In fact, there were two types of yeast involved in beet root fermentation. The desirable one produced alcohol. The undesirable one, that led to all the problems, produced lactic acid. Debré concludes

A few years after the request of industrialist Bigo, Pasteur had thus established beyond a doubt that the lactic acid in the vats in the rue d’Esquermes came from an unfortunate contamination with this yeast. He even suggested the means to get rid of this contamination… Pasteur’s research on fermentation created microbiology.

Pasteur’s work on fermentation led to the related question of spontaneous generation. Many scientists at the time thought that living organisms could spontaneously arise in dead and decaying tissue, but Pasteur showed that such decay was always due to germs that entered the tissue from the air.

Pasteur’s transition to biology became complete after Jean-Baptiste Dumas asked him to investigate a disease that was destroying the silkworm industry in France. To address this issue, he needed to learn more biology.

Pasteur came from crystals. Owing to his scant knowledge of animal biology, he was somewhat apprehensive about experiments on animals. As soon as he accepted Dumas’s assignment, he therefore went, along with his assistant Emile Duclaux, to the physiology course taught by Claude Bernard at the Sorbonne. There he took notes and humbly relived his years of training in the halls of the university. But he found it difficult to learn a whole new field; and indeed, since he had neither the time nor the patience to do this, he soon preferred to form his own ideas on the problem at hand.

Once again, Pasteur was successful in addressing a biological problem; this time bacteria infecting silkworms (they are not really a worm, but a caterpillar).

The caterpillar of Alés led Pasteur from microbiology to veterinary science to medicine… When Pasteur revolutionized the science of his era by discovering the germs and their role, it was only natural that he should become interested in medicine and hygiene.

At this point, Pasteur had essentially completed his transition from physics to biology and medicine. I won’t discuss his later work on the use of antiseptics in surgery, pasteurization, anthrax infection in sheep, or the development of a rabies vaccine. Debré summarizes,

In his last studies, Pasteur recalled that he had started out as a chemist. First in the laboratory of the rue d’Ulm and then in his Institute, his ultimate experiments indicate that he was trying to understand how the same microbe can either kill a person or stimulate his or her resistance. This is where bacteriology merged into immunology. Pasteur brought these neighboring disciplines together. Understanding the role of the molecules, the toxins, and the antitoxins involved both chemistry and biology.

So what do I conclude about Pasteur’s transition from the physical to the biological sciences? It wasn’t part of a long-range plan. Nor was it primarily motivated by the desire to help the sick, at least initially. I see two key points. First, the rotation of polarized light when passed through an organic substance led him naturally from physics to biology; scientific problems don’t always respect academic boundaries. Second, requests to address industrial problems further accelerated this transition, and those problems happened to be biological in nature. There seems to be a lot of chance involved in this transition (I think there often is for many scientists). But, as Pasteur famously said, chance favors the prepared mind. 

 

https://www.youtube.com/watch?v=OXdbQ1JkX7c
 

 https://www.youtube.com/watch?v=1lLNZQVPpQA