Wilson da Silva

Science journalist, feature writer and editor.

Nov 1, 2001
18 min read
Louis Pasteur (1822-1895), microbiologist and chemist

His dream had been to teach painting, but Louis Pasteur became instead the man who not only proved microbes caused  disease, but that they could be stopped. By the end of his career, his work had guaranteed the salvation of millions.

By Wilson da Silva

LOUIS PASTEUR  was a bright young Frenchman from humble background. And although he was to have a profound impact on medical and veterinary science, and revolutionize the way we treat disease, he never really wanted to study science. What he really wanted to do was to paint. And he was quite good at it, too.

Born in 1822 to Jeanne-Ettiennette Roqui and Jean Joseph Pasteur, a family of tanners in the French town of Dôle, north of Lyon, he was the second of four children. Throughout his life he remained fiercely proud of his agrarian heritage, and liked to visit the beech forests, vineyards and alpine pastures of his youth whenever he could.

As a child, Pasteur had always enjoyed drawing, copying engravings from his school books in charcoal and pencil. When he began attending school in Arbois, his teacher commented on his talent and encouraged it. He expanded his skills to pastel portraits, using  friends, his parents and three sisters as models. A portrait of his mother painted at the age of 13 still survives, showing her dressed in a plaid dress, her head covered in a white bonnet and with brown curls and pale blue eyes showing. 

He had a classicism of line and a cold precision of observation that earned him recognition in art circles around the Franche-Comté region, near the border with Switzerland. Had he not gone into science, he might have risen to prominence as a painter; the French art critic Durand Gréville praised the accuracy and honesty of his paintings, remarking in 1888: “If he had wanted to, he would have held his own among the painters and – who knows? – become a very great painter.” 

Until the age of 14, Pasteur was an average student with more interest in sliding in the snow or fishing off a bridge than schoolwork. His father, a veteran of Napoleonic wars, often sat with his young son after his grueling workday tanning hides, and they would discuss patriotism, honour, justice and duty to society. It was his father who first taught him to read, prompting Pasteur years later to remark: “In teaching me to read, [he] made sure that I learned about the greatness of France.”

Driven by a committed teacher who saw promise in the young Pasteur, he attended college at the Royal College in nearby Besançon, studying hard to pass his baccalauréat examinations, and developing a deeper interest in science. Writing to his parents in 1840, at the age of 17, he said: “Once one is used to working, one can no longer live without it. And of course, everything in the world depends on it; in science, one is happy; in science one rises above all others.” 

Jean-Joseph Pasteur saw the young man’s painting as a dalliance; his great hope was that his son might land a teaching position at a local college. But young Pasteur was developing other ideas, as well some ambition. Terribly shy, provincial and a little naïve, he learned how to get along with people through his art.

Portrait of Pasteur’s father, Jean-Joseph Pasteur, completed in 1842; and one of Sophie Roch in 1839, both by Louis Pasteur(Pasteur Museum, Institut Pasteur)

Painting portraits of the principal and senior staff earned him the attention of superiors, as well as recognition among his schoolmates. He wrote home of scandals in Besançon and unruly behaviour among students; although the young Pasteur was to grow into a radical in his scientific thinking, socially he was cautious, conservative and concerned with being respectable. 

Pasteur attained his baccalauréat in letters (bachelor of letters) in 1840, excelling in science but scoring mediocre marks in geography and history, although he passed adequately in philosophy, Greek, Latin and rhetoric. His confidence nevertheless bolstered, he studied for another year so he could sit for a baccalauréat in science, which would allow him to apply for one of the competitive places at the École Normale Supérieure, a highly prestigious teacher’s college in Paris. By now he was building vision of his future that might carry him beyond the provincial confines of Franche-Comté. 

The once disinterested student now studied with zeal. When he wasn’t studying, he worked part-time as a substitute teacher at Besançon. In his many letters home, he implored his sisters to also study and make a career for themselves, and for his mother to release them from housework so they could do so. “Will power, work and success are the mainstays of human existence: wi0ll power opens the doors to brilliant and happy careers; work allows us to pass through them, and once we have run the course, success will crown our achievement,” he wrote. Pasteur even offered to pay for the education of his sister Joséphine, at the time in boarding school at Lons-le-Saunier, by taking on some extra tutoring.

But in 1841, he failed his science baccalauréat. Crestfallen, he nevertheless studied even more feverishly and sat for it again in 1842. Although he reported to his parents that the exams had been harder than the year before, he passed with flying colours. His eyes now firmly on Paris, he sat the entry exams to the École Normale, passing the first tests but, unhappy with his score, sat for it a second time. He was accepted. 

In Paris, a whole new world opened up before him: he regularly attended lectures by Jean-Baptiste Dumas, credited as France’s first analytical chemist and an inspiring teacher in his early forties who was popular with students and a respected figure in Parisian society. Pasteur tutored in mathematics early in the morning, and studied during the day. With his meager earnings, he lived a spartan life in a dormitory and spent every Sunday afternoon at Dumas’ laboratory, taking private lessons with  Dumas’ assistant. 

He became licencié ès sciences (master of science) in 1845. But he didn’t leave for home as his father had hoped. Although he disliked Paris – “squalid, sordid, disgusting,” is how he often described it to Besançon classmates in letters – he was excited by the intellectual stimulation of the capital. 

Pasteur was still a student when he made his first discovery with an experiment in crystallography. He noted that the organic compound, when synthesised in the laboratory, was optically inactive, or unable to rotate the plane of polarised light. And yet, natural tartrate, an acid formed in grape fermentation, could. Why? Already Pasteur possessed the most important qualities of a scientist: the ability to survey all the known data and link them with possible hypotheses, and the patience and drive to conduct experiments under strictly controlled conditions until he had proven or disproven each hypothesis. 

Louis Pasteur examining a patient surrounded by portraits of other patients

After much research, he theorised that synthetic tartrate was composed of two optically asymmetric crystals – a ‘right-handed’ one and a ‘left-handed’ one. Through trial and error, he succeeded in separating the two from each other and showed that each, individually, recovered their optical ability. He then hypothesized that this molecular asymmetry is one of the mechanisms of life. In other words, only living organisms can produce molecules that are always optically active. 

He was right. And although his discovery may sound obscure, it opened the door to a truly powerful idea: some chemical processes were not just chemical at all – they required the intervention of living things. But nine years were to pass before he could take this seemingly innocuous discovery to its final conclusion: that we are surrounded by tiny micro-organisms that are responsible not only for making many organic compounds, but for disease, decay and fermentation.

Pasteur obtained his docteur ès sciences (PhD in science) in 1847. Now working as a professor of physics at the Dijon Lycée secondary school, he presented his work on crystallography at Paris’ Academy of Sciences in 1848. It earned him, at the age of 27, the offer of the position of professor of chemistry at the University of Strasbourg. A year later, aged 28, he married Marie Laurent, the 23-year-old daughter of university’s rector. She encouraged his work, spending evenings taking dictation and was called by some Pasteur’s best collaborator. 

Soon, the world began to open up for him. In 1854, he became dean of the new science faculty at the University of Lille, a growing industrial city. Pasteur established night classes for young working men, and conducted research in partnership with industry: in response to requests from industrialists about the production of alcohol from grain and beet sugar, he began to study fermentation.

Sure enough, Pasteur found that fermenting solutions contained optically active compounds. Therefore, he reasoned, alcoholic fermentation was a biological process carried out by micro-organisms. 

But he truly came to prominence three years later when he accepted an appointment as director of scientific studies at the École Normale Supérieure in Paris, his alma mater. Following his work on fermentation, he had been developing what he called ‘germ theory’– that the minute organisms that cause fermentation are always present, and when fermentation fails, it is because the necessary organism was either absent or it was prevented from growing properly. It was while back in Paris that announced his hypothesis.

Pasteur in his laboratory

His theory was so dramatically different to the prevailing scientific dogma that it caused an uproar. For 2000 years, scholars had believed that life could arise spontaneously in organic materials, and was therefore responsible for a range of processes, including fermentation.

Pasteur argued that microbes caused fermentation, they were in the environment, and they could be stopped by filters. Some microbes could also live without air at all (as anaerobic yeast does), and it was they that were responsible for fermentation: "Fermentation is the consequence of life without air", he wrote.  This directly challenged the accepted theory of ‘spontaneous generation’.

But although he encountered at times violent opposition, the truth was that all previous explanations for fermentation failed to match experimental data. Pasteur’s germ theory was matched by many elegant experiments that seemed  to show unequivocally the existence of microbes and their effect on fermentation.

Although no-one knew at the time, germ theory would the foundation of a revolution. Pasteur and other researchers began to theorise that, if microscopic creatures in the air and soil were the cause of fermentation, they might also be the cause of contagious diseases – which also seemed to ‘spontaneously generate’. 

His ideas electrified those who read them, and triggered an avalanche of more research. After studying the characteristics of germs that caused disease – or bacteria and viruses, as we came to know them – he and others found that manipulating them in the lab could immunise animals against them. This was a truly stupendous discovery: suddenly, there was a powerful new weapon to fight disease – vaccines. And while he wasn’t the only one to develop vaccines for human and animal immunisation, he was not only the springboard for these discoveries, he stayed at the forefront of its exploitation.

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Elected to France’s Academy of Sciences in 1862, he went on to apply germ theory solutions to potentially devastating problems in the wine and silk industries. His work on fermentation for the British beer industry allowed it to be shipped as far as India for the first time, and his application to problems in milk production earned his solution the name ‘pasteurisation’ – the destruction of harmful microbes by heat, making it possible to produce, preserve and transport wine, beer and milk without spoilage. At the 1867 Paris Exhibition, Pasteur was conferred the Grand Prize Medal for his work on wine.

Partially paralysed by a stroke the following year, he nevertheless continued to make gains with his work in microbiology. Although he worked alongside many medical practitioners, it was not until he was elected to France’s Academy of Medicine in 1873 that his controversial work in infectious diseases gained approval in the medical and veterinary community. 

Between 1877 and 1887, he discovered three new species of bacteria that he proved were responsible responsible for human illnesses: staphylococcus, streptococcus and pneumococcus. In 1881 he perfected a technique for reducing the virulence of many disease-producing microbes, and succeeded in vaccinating a whole herd of sheep against anthrax. Later he immunised chickens and ducks from chicken cholera. In this he was now following the example of English physician Edward Jenner, who had developed a vaccination for animals against cowpox. 

But it was in 1885 that his work would capture the public’s attention. He had been experimenting for years with rabies, and after numerous inoculations of animals with the saliva of other infected animals, concluded that a virus was the cause, and that it was also present in the brain. Taking a slice of brain tissue from a rabid dog, he injected into the body of a healthy animal and, sure enough, it developed rabies. He spent time trying to develop a weakened form of the rabies virus he could use as a vaccine. 

On 6 July that year, he faced an ethical dilemma. A mother, whose nine-year-old son had been bitten 12 times by a rabid dog, begged Pasteur to save his life. Reluctant to test his vaccine so soon, he nevertheless agreed. He had no data on what dosages and frequencies might suffice, so he guessed, inoculating the boy with 12 injections in 10 days. The boy failed to develop the dreaded brain-ravaging disease. News flashed around the world, and people who had been bitten by rabid dogs began to flock to Paris to receive Pasteur’s treatment. 

The following year, in a speech to the Academy of Sciences, Pasteur called for the creation of a research centre for infectious diseases such as rabies. The French government backed the initiative and with a host of private money, the Pasteur Institute was opened in Paris in 1888, with Louis Pasteur as its director. At its opening, he pleaded the case for science: “I beseech you to take interest in these sacred domains so expressively called ‘laboratories’. Ask that there be more, and that they be adorned, for these are the temples of the future, of wealth and of well-being.”

The Pasteur Institute grew to become one of the world’s most celebrated medical institutes, producing the BCG vaccine for tuberculosis, the first sulfonamide drug, the first antihistamine and it was the first to identify HIV, the human immunodeficiency virus.

“Hommage à Louis Pasteur” by Jules Scalbert

By a sad twist of fate, his work on vaccines and immunisation came too late for his own family. Pasteur had had five children with his wife – four daughters and a son –  but three of his daughters ultimately died from infections: typhoid. In November 1894, Pasteur himself became ill with kidney failure, and gradually grew weaker until he eventually died on 28 September 1895, at the age of 73. 

Thanks to Louis Pasteur, we came to understand that germs that caused septicemia and gangrene, among the many infections that used to ravage hospitals, where nearly a third of women once died from childbirth infections. And thanks to Pasteur, techniques could be devised to kill microbes and to control contamination and infection. 

Louis Pasteur’s remains were entombed at the Pasteur Institute. And there’s an ironic twist: in 1940, when German forces occupied Paris, a Nazi officer searching the Pasteur Institute demanded Louis Pasteur’s tomb be opened. The French soldier guarding it refused, and shot himself.

That man was Joseph Meister, whom as a young man Pasteur had saved from rabies with his experimental inoculations.