Louis Pasteur, 200 years old: understand how the scientist, full of competitive spirit, changed the course of history

The list of scientific revolutions attributed to the Frenchman Louis Pasteur (1822-1895) is gigantic. He would have been responsible for demonstrating, among other things, that living beings do not arise by spontaneous generation, that infectious diseases are caused by microbes and that it was possible to develop a reliable methodology for manufacturing vaccines against several of these diseases.

The bicentenary of his birth, this December 27th, would be the perfect occasion to show how a single scientist is capable of changing the course of history.

In fact, all items on the list had important participation by Pasteur, but, in many cases, the scenario that led to the transformation of the researcher into an icon was much more complex and interesting than that of isolated genius discoveries.

He managed to make his mark thanks in part to a relentless competitive spirit, an ability to marshal public and private resources, and a knack for personal marketing, carefully cultivating his image.

Pasteur also gained a lasting reputation for not attaching much importance to the supposed separation between “pure” science and applied research. In several cases, his work combined the attempt to find specific answers to economic problems in France in the 19th century with much deeper developments —the origin of living beings and diseases, for example.

According to Andrew Mendelsohn, historian of science at Queen Mary University of London, it is possible that this relatively “hands-on” approach is linked to Pasteur’s origins in rural France, in the small town of Dole (east of the country), today with little more than 20 thousand inhabitants. His father had a modest tannery, which may have stimulated his interest in manufacturing processes involving products from the region.

In childhood and early adolescence, however, little Louis did not show great interest in school, preferring to draw and fish. By leaps and bounds, including a few failures, he began to show an interest in mathematics, physics and chemistry, and was eventually admitted to the École Normale Supérieur in Paris, where, after graduation, he spent some time as a laboratory assistant.

He was accepted as professor of chemistry at the University of Strasbourg in 1848, where he met his future wife, Marie Laurent, daughter of the rector. The couple had five children, but only two of them reached adulthood – the rest died of typhoid fever, a type of bacterial infection.

At first, nothing indicated that Pasteur would become one of those responsible for elucidating the relationship between microbes and animal and plant organisms. His first scientific works dealt with the structure of crystals formed by different chemical compounds.

Several of these substances, however, were relevant to the nascent food industry and to French winemakers. Some of them began to seek the researcher’s help to face prosaic problems, such as cases in which the wine turned sour.

At the time, it had already been demonstrated that beer fermentation was caused by living organisms. In a series of works, Pasteur helped to generalize this idea, showing that different microbes were also present in the fermentation of wine and also when it went bad, as well as in milk that turned sour. From this, he developed the processes now known as pasteurization, which, through heating, prevent most microbes from subsisting in these beverages.

And it was precisely the ability to connect the different findings on the action of microbes on fruits, grains and beverages that led the researcher to become involved in the debate on the so-called spontaneous generation —the idea that microorganisms could appear “out of nowhere” under certain conditions, colonizing decaying organic matter, for example.

It so happens that Pasteur and his collaborators had demonstrated, for example, that sterilized grapes, or whose juice was obtained through sterilized syringes, were incapable of fermenting. The findings provoked controversy, which led the French Academy of Sciences to offer a cash prize to anyone who could obtain conclusive evidence for or against the idea of ​​spontaneous generation.

Pasteur achieved this goal with experiments such as the “col de cygne” (“swan neck”) containers, basically a bottle whose tip is a very long horizontal glass tube. A nutritious broth was placed inside the container, which was then boiled, in order to kill all the microbes inside it.

Dust particles carrying microorganisms from the air could enter the tip of the tube, but would only come into contact with the broth if the bottle was tilted. Without it, the broth wouldn’t go bad, demonstrating that the microbes had to come from somewhere, not “spring out of nowhere.” Thus, Pasteur was declared the winner of the dispute.

In the following decades, also initially thanks to his contact with rural producers who sought to solve everyday problems, the researcher became involved in the development of what he would later call vaccines (at the time, the term “vaccination” was applied only for the rudimentary vaccine against smallpox, the only one that existed). It would be the area that most cemented his fame and, at the same time, the one that most seems to have involved questionable attitudes.

His work first involved avian cholera (which affects chickens, caused by a bacterium later named in his honor, the Pasteurella multocida) and, shortly after, anthrax, which affected cattle, sheep and goats. In these studies, Pasteur began to formulate the so-called principle of attenuation, according to which it would be possible to use methods such as passing a strain of bacteria through different hosts (of different species, for example) to make them become less aggressive.

With this, it would be possible to use these attenuated strains as vaccines, infecting potential victims and preparing their body’s defense system for contact with the “violent” versions of microorganisms.

He put this principle into practice with both animal diseases, with several apparent initial successes, but later analysis showed that he had claimed victory too soon—the vaccines against avian cholera and anthrax were not reliable enough. Furthermore, analyzes of his laboratory notebooks showed that he had used a method similar to that of a competitor he criticized, without disclosing this to the public.

Pasteur’s final triumph with vaccines came with his work on rabies, a disease that is virtually incurable to this day. In July 1885, Pasteur received, in his laboratory in Paris, a visit from a mother desperate for him to try to save her son’s life. The nine-year-old boy, named Joseph Meister, had been bitten by a rabid dog on several parts of his body.

Pasteur, in previous years, had developed a method in which he dried the spinal cord of rabbits infected with rabies and inoculated the nervous tissue in healthy dogs. He found that the marrow fragments were less and less likely to cause disease after they had been allowed to dry for a long time.

As he injected more and more “fresh” nerve tissue into dogs that had already received previous injections, they became more protected, until a last injection from the medulla of a recently sacrificed rabbit did not cause any negative effects.

Pasteur used the same approach on Joseph Meister. The boy not only survived, but as he grew up, he went on to work at the Pasteur Institute. His end was tragic—when the Nazis occupied Paris in World War II, they made him open Pasteur’s tomb for them to visit. Ashamed, Meister committed suicide.

The methodology originally created was also unreliable by today’s standards: one in every 200 people who received the rabies vaccine became paralyzed and died because of their organism’s reaction to the injected nervous tissue.

According to historian of science Bert Hansen, from the State University of New York, Pasteur cultivated close relationships with the press to publicize all these results, also posing for painters and photographers who recorded him in action in the laboratory. This gave him celebrity status and ensured constant donations to the Pasteur Institute, opened in 1888 —one of the donations even came from the Brazilian Emperor Dom Pedro II.