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Pasteur's Experiment

The steps of Pasteur's experiment are outlined below:

First, Pasteur prepared a nutrient broth similar to the broth one would use in soup.

Next, he placed equal amounts of the broth into two long-necked flasks. He left one flask with a straight neck. The other he bent to form an "S" shape.

Then he boiled the broth in each flask to kill any living matter in the liquid. The sterile broths were then left to sit, at room temperature and exposed to the air, in their open-mouthed flasks.

After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

He concluded that germs in the air were able to fall unobstructed down the straight-necked flask and contaminate the broth. The other flask, however, trapped germs in its curved neck,­ preventing them from reaching the broth, which never changed color or became cloudy.

If spontaneous generation had been a real phenomenon, Pasteur argued, the broth in the curved-neck flask would have eventually become reinfected because the germs would have spontaneously generated. But the curved-neck flask never became infected, indicating that the germs could only come from other germs.

Pasteur's experiment has all of the hallmarks of modern scientific inquiry. It begins with a hypothesis and it tests that hypothesis using a carefully controlled experiment. This same process — based on the same logical sequence of steps — has been employed by scientists for nearly 150 years. Over time, these steps have evolved into an idealized methodology that we now know as the scientific method. After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

Let's look more closely at these steps.

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Science News

Louis pasteur’s devotion to truth transformed what we know about health and disease.

Louis Pasteur demonstrated, more dramatically than any other scientist, the benefit of science for humankind.

Sam Falconer

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By Tom Siegfried

November 18, 2022 at 7:00 am

Great scientists become immortalized in various ways.

Some through names for obscure units of measurement (à la Hertz, Faraday and Curie). Others in elements on the periodic table ( Mendeleev , Seaborg, Bohr , among many others). A few become household names symbolizing genius — like Newton in centuries past and nowadays, Einstein . But only one has been honored on millions and millions of cartons of milk: the French chemist, biologist and evangelist for experimental science Louis Pasteur.

Pasteur was born 200 years ago this December, the most significant scientist birthday bicentennial since Charles Darwin’s in 2009 . And Pasteur ranked behind only Darwin among the most exceptional biological scientists of the 19th century.

Pasteur not only made milk safe to drink, but also rescued the beer and wine industry. He established the germ theory of disease, saved the French silkworm population, confronted the scourges of anthrax and rabies, and transformed the curiosity of vaccination against smallpox into a general strategy for treating and preventing human diseases. He invented microbiology and established the foundations for immunology.

Had he been alive after 1901, when Nobel Prizes were first awarded, he would have deserved one every year for a decade. No other single scientist demonstrated more dramatically the benefit of science for humankind.

He was not, however, exactly a saint. A Pasteur biographer, Hilaire Cuny, called him “a mass of contradictions.” Pasteur was ambitious and opportunistic, sometimes arrogant and narrow-minded, immodest, undiplomatic and uncompromising. In the scientific controversies he engaged in (and there were many), he was pugnacious and belligerent. He did not suffer criticism silently and was often acerbic in his responses. To his laboratory assistants, he was demanding, dictatorial and aloof. Despite his revolutionary spirit in pursuing science, in political and social matters, he was conformist and deferential to authority.

And yet he was a tireless worker, motivated by service to humankind, faithful to his family and unwaveringly honest. He was devoted to truth, and therefore also to science.

How Pasteur developed pasteurization

In his youth, Pasteur did not especially excel as a student. His interests inclined toward art rather than science, and he did display exceptional skill at drawing and painting. But in light of career considerations (his father wanted him to be a scholar), Pasteur abandoned art for science and so applied to the prestigious École Normale Supérieure in Paris for advanced education. He finished 15th in the competitive entrance examination, good enough to secure admission. But not good enough for Pasteur. He spent another year on further studies emphasizing physical sciences and then took the École Normale exam again, finishing fourth. That was good enough, and he entered the school in 1843. There he earned his doctoral degree, in physics and chemistry, in 1847.

Among his special interests at the École Normale was crystallography. In particular he was drawn to investigate tartaric acid. It’s a chemical found in grapes responsible for tartar, a potassium compound that collects on the surfaces of wine vats. Scientists had recently discovered that tartaric acid possesses the intriguing power of twisting light — that is, rotating the orientation of light waves’ vibrations. In light that has been polarized (by passing it through certain crystals, filters or some sunglasses), the waves are all aligned in a single plane. Light passing through a tartaric acid solution along one plane emerges in a different plane.

Even more mysteriously, another acid (paratartaric acid, or racemic acid), with the exact same chemical composition as tartaric acid, did not twist light at all. Pasteur found that suspicious. He began a laborious study of the crystals of salts derived from the two acids. He discovered that racemic acid crystals could be sorted into two asymmetric mirror-image shapes, like pairs of right-handed and left-handed gloves. All the tartaric acid crystals, on the other hand, had shapes with identical asymmetry, analogous to gloves that were all right-handed.

Pasteur deduced that the asymmetry in the crystals reflected the asymmetric arrangement of atoms in their constituent molecules. Tartaric acid twisted light because of the asymmetry of its molecules, while in racemic acid, the two opposite shapes canceled out each other’s twisting effects.

Pasteur built the rest of his career on this discovery. His research on tartaric acid and wine led eventually to profound realizations about the relationship between microbes and human disease. Before Pasteur, most experts asserted that fermentation was a natural nonbiological chemical process. Yeast, a necessary ingredient in the fermenting fluid, was supposedly a lifeless chemical acting as a catalyst. Pasteur’s experiments showed yeast to be alive, a peculiar kind of “small plant” (now known to be a fungus) that caused fermentation by biological activity.

Pasteur demonstrated that, in the absence of air, yeast acquired oxygen from sugar, converting the sugar to alcohol in the process. “Fermentation by yeast,” he wrote, is “the direct consequence of the processes of nutrition,” a property of a “minute cellular plant … performing its respiratory functions.” Or more succinctly, he proclaimed that “fermentation … is life without air.” (Later scientists found that yeast accomplished fermentation by emitting enzymes that catalyzed the reaction.)

Pasteur also noticed that additional microorganisms present during fermentation could be responsible for the process going awry, a problem threatening the viability of French winemaking and beer brewing. He solved that problem by developing a method of heating that eliminated the bad microorganisms while preserving the quality of the beverages. This method, called “pasteurization,” was later applied to milk, eliminating the threat of illness from drinking milk contaminated by virulent microorganisms. Pasteurization became standard public health practice in the 20th century.

Incorporating additional insights from studies of other forms of fermentation, Pasteur summarized his work on microbial life in a famous paper published in 1857. “This paper can truly be regarded as the beginning of scientific microbiology,” wrote the distinguished microbiologist René Dubos, who called it “one of the most important landmarks of biochemical and biological sciences.”

The germ theory of disease is born

Pasteur’s investigations of the growth of microorganisms in fermentation collided with another prominent scientific issue: the possibility of spontaneous generation of life. Popular opinion even among many scientists held that microbial life self-generated under the proper conditions (spoiled meat, for example). Demonstrations by the 17th century Italian scientist Francesco Redi challenged that belief , but the case against spontaneous generation was not airtight.

In the early 1860s Pasteur undertook a series of experiments that should have left no doubt that spontaneous generation, under conditions encountered on Earth today, was an illusion. Yet he was nevertheless accosted by critics, such as the French biologist Charles-Philippe Robin, to whom he returned verbal fire. “We trust that the day will come when M. Robin will … acknowledge that he has been in error on the subject of the doctrine of spontaneous generation, which he continues to affirm, without adducing any direct proofs in support of it,” Pasteur remarked.

It was his work on spontaneous generation that led Pasteur directly to the development of the germ theory of disease.

For centuries people had suspected that some diseases must be transmitted from person to person by close contact. But determining exactly how that happened seemed beyond the scope of scientific capabilities. Pasteur, having discerned the role of germs in fermentation, saw instantly that something similar to what made wine go bad might also harm human health.

After disproving spontaneous generation, he realized that there must exist “transmissible, contagious, infectious diseases of which the cause lies essentially and solely in the presence of microscopic organisms.” For some diseases, at least, it was necessary to abandon “the idea of … an infectious element suddenly originating in the bodies of men or animals.” Opinions to the contrary, he wrote, gave rise “to the gratuitous hypothesis of spontaneous generation” and were “fatal to medical progress.”

His first foray into applying the germ theory of disease came during the late 1860s in response to a decline in French silk production because of diseases afflicting silkworms. After success in tackling the silkworms’ maladies, he turned to anthrax, a terrible illness for cattle and humans alike. Many medical experts had long suspected that some form of bacteria caused anthrax, but it was Pasteur’s series of experiments that isolated the responsible microorganism, verifying the germ theory beyond doubt. (Similar work by Robert Koch in Germany around the same time provided further confirmation.)

Understanding anthrax’s cause led to the search for a way to prevent it. In this case, a fortuitous delay in Pasteur’s experiments with cholera in chickens produced a fortunate surprise. In the spring of 1879 he had planned to inject chickens with cholera bacteria he had cultured, but he didn’t get around to it until after his summer vacation. When he injected his chickens in the fall, they unexpectedly failed to get sick. So Pasteur prepared a fresh bacterial culture and brought in a new batch of chickens.

When both the new chickens and the previous batch were given the fresh bacteria, the new ones all died, while nearly all of the original chickens still remained healthy. And so, Pasteur realized, the original culture had weakened in potency over the summer and was unable to cause disease, while the new, obviously potent culture did not harm the chickens previously exposed to the weaker culture. “These animals have been vaccinated,” he declared.

Vaccination, of course, had been invented eight decades earlier, when British physician Edward Jenner protected people from smallpox by first exposing them to cowpox, a similar disease acquired from cows. (Vaccination comes from cowpox’s medical name, vaccinia, from vacca , Latin for cow.) Pasteur realized that the chickens surprisingly displayed a similar instance of vaccination because he was aware of Jenner’s discovery. “Chance favors the prepared mind,” Pasteur was famous for saying.

Because of his work on the germ theory of disease, Pasteur’s mind was prepared to grasp the key role of microbes in the prevention of smallpox, something Jenner could not have known. And Pasteur instantly saw that the specific idea of vaccination for smallpox could be generalized to other diseases. “Instead of depending on the chance finding of naturally occurring immunizing agents, as cowpox was for smallpox,” Dubos observed, “it should be possible to produce vaccines at will in the laboratory.”

Pasteur cultured the anthrax microbe and weakened it for tests in farm animals. Success in such tests not only affirmed the correctness of the germ theory of disease, but also allowed it to gain a foothold in devising new medical practices.

Later Pasteur confronted an even more difficult microscopic foe, the virus that causes rabies. He had begun intense experiments on rabies, a horrifying disease that’s almost always fatal, caused usually by the bites of rabid dogs or other animals. His experiments failed to find any bacterial cause for rabies, leading him to realize that it must be the result of some agent too small to see with his microscope. He could not grow cultures in lab dishes of what he could not see. So instead he decided to grow the disease-causing agent in living tissue — the spinal cords of rabbits. He used dried-out strips of spinal cord from infected rabbits to vaccinate other animals that then survived rabies injections.

Pasteur hesitated to test his rabies treatment on humans. Still, in 1885 when a mother brought to his lab a 9-year-old boy who had been badly bitten by a rabid dog, Pasteur agreed to administer the new vaccine. After a series of injections, the boy recovered fully. Soon more requests came for the rabies vaccine, and by early the next year over 300 rabies patients had received the vaccine and survived, with only one death among them.

Popularly hailed as a hero, Pasteur was also vilified by some hostile doctors, who considered him an uneducated interloper in medicine. Vaccine opponents complained that his vaccine was an untested method that might itself cause death. But of course, critics had also rejected Pasteur’s view of fermentation, the germ theory of disease and his disproof of spontaneous generation.

Pasteur stood his ground and eventually prevailed (although he did not turn out to be right about everything). His attitude and legacy of accomplishments inspired 20th century scientists to develop vaccines for more than a dozen deadly diseases. Still more diseases succumbed to antibiotics, following the discovery of penicillin by Alexander Fleming — who declared, “Without Pasteur I would have been nothing.”

Even in Pasteur’s own lifetime, thanks to his defeat of rabies, his public reputation was that of a genius.

Pasteur’s scientific legacy

As geniuses go, Pasteur was the opposite of Einstein. To get inspiration for his theories, Einstein imagined riding aside a light beam or daydreamed about falling off a ladder. Pasteur stuck to experiments. He typically initiated his experiments with a suspected result in mind, but he was scrupulous in verifying the conclusions he drew from them. Preconceived ideas, he said, can guide the experimenter’s interrogation of nature but must be abandoned in light of contrary evidence. “The greatest derangement of the mind,” he declared, “is to believe in something because one wishes it to be so.”

So even when Pasteur was sure his view was correct, he insisted on absolute proof, conducting many experiments over and over with variations designed to rule out all but the true interpretation.

“If Pasteur was a genius, it was not through ethereal subtlety of mind,” wrote Pasteur scholar Gerald Geison. Rather, he exhibited “clear-headedness, extraordinary experimental skill and tenacity — almost obstinacy — of purpose.”

His tenacity, or obstinacy, helped him persevere through several personal tragedies, such as the deaths of three of his daughters, in 1859, 1865 and 1866. And then in 1868 he suffered a cerebral hemorrhage that left him paralyzed on his left side. But that did not slow his pace or impair continuing his investigations.

“Whatever the circumstances in which he had to work, he never submitted to them, but instead molded them to the demands of his imagination and his will,” Dubos wrote. “He was probably the most dedicated servant that science ever had.”

To the end of his life, Pasteur remained dedicated to science and the scientific method, stressing the importance of experimental science for the benefit of society. Laboratories are “sacred institutions,” he asserted. “Demand that they be multiplied and adorned; they are the temples of wealth and of the future.”

Three years before his death in 1895, Pasteur further extolled the value of science and asserted his optimism that the scientific spirit would prevail. In an address, delivered for him by his son, at a ceremony at the Sorbonne in Paris, he expressed his “invincible belief … that science and peace will triumph over ignorance and war, that nations will unite, not to destroy, but to build, and that the future will belong to those who will have done most for suffering humanity.”

Two hundred years after his birth , ignorance and war remain perniciously prominent, as ineradicable as the microbes that continue to threaten public health, with the virus causing COVID-19 the latest conspicuous example. Vaccines, though, have substantially reduced the risks from COVID-19, extending the record of successful vaccines that have already tamed not only smallpox and rabies, but also polio, measles and a host of other once deadly maladies .

Yet even though vaccines have saved countless millions of lives, some politicians and so-called scientists who deny or ignore overwhelming evidence continue to condemn vaccines as more dangerous than the diseases they prevent. True, some vaccines can induce bad reactions, even fatal in a few cases out of millions of vaccinations. But shunning vaccines today, as advocated in artificially amplified social media outrage, is like refusing to eat because some people choke to death on sandwiches.

Today, Pasteur would be vilified just as he was in his own time, probably by some people who don’t even realize that they can safely drink milk because of him. Nobody knows exactly what Pasteur would say to these people now. But it’s certain that he would stand up for truth and science, and would be damn sure to tell everybody to get vaccinated.

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Spontaneous generation

Work with silkworms.

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Fermentation and putrefaction were often perceived as being spontaneous phenomena, a perception stemming from the ancient belief that life could generate spontaneously. During the 18th century the debate was pursued by the English naturalist and Roman Catholic divine John Turberville Needham and the French naturalist Georges-Louis Leclerc, count de Buffon . While both supported the idea of spontaneous generation , Italian abbot and physiologist Lazzaro Spallanzani maintained that life could never spontaneously generate from dead matter. In 1859, the year English naturalist Charles Darwin published his On the Origin of Species , Pasteur decided to settle this dispute. He was convinced that his germ theory could not be firmly substantiated as long as belief in spontaneous generation persisted. Pasteur attacked the problem by using a simple experimental procedure. He showed that beef broth could be sterilized by boiling it in a “swan-neck” flask, which has a long bending neck that traps dust particles and other contaminants before they reach the body of the flask. However, if the broth was boiled and the neck of the flask was broken off following boiling, the broth, being reexposed to air, eventually became cloudy, indicating microbial contamination. These experiments proved that there was no spontaneous generation, since the boiled broth, if never reexposed to air, remained sterile . This not only settled the philosophical problem of the origin of life at the time but also placed on solid ground the new science of bacteriology , which relied on proven techniques of sterilization and aseptic manipulation.

In 1862 Pasteur was elected to the Académie des Sciences , and the following year he was appointed professor of geology, physics , and chemistry at the École des Beaux-Arts (School of Fine Arts). Shortly after this, Pasteur turned his attention to France’s silkworm crisis. In the middle of the 19th century, a mysterious disease had attacked French silkworm nurseries. Silkworm eggs could no longer be produced in France, and they could not be imported from other countries, since the disease had spread all over Europe and had invaded the Caucasus region of Eurasia, as well as China and Japan. By 1865 the silkworm industry was almost completely ruined in France and, to a lesser extent, in the rest of western Europe. Pasteur knew virtually nothing about silkworms, but, upon the request of his former mentor Dumas, Pasteur took charge of the problem, accepting the challenge and seizing the opportunity to learn more about infectious diseases . He soon became an expert silkworm breeder and identified the organisms that caused the silkworm disease. After five years of research, he succeeded in saving the silk industry through a method that enabled the preservation of healthy silkworm eggs and prevented their contamination by the disease-causing organisms. Within a couple of years, this method was recognized throughout Europe; it is still used today in silk-producing countries.

In 1867 Pasteur resigned from his administrative duties at the École Normale Supérieure and was appointed professor of chemistry at the Sorbonne, a university in Paris . Although he was partially paralyzed (left hemiplegia ) in 1868, he continued his research. For Pasteur, the study of silkworms constituted an initiation into the problem of infectious diseases, and it was then that he first became aware of the complexities of infectious processes. Accustomed as he was to the constancy and accuracy of laboratory procedures, he was puzzled by the variability of animal life, which he had come to recognize through his observation that individual silkworms differed in their response to disease depending on physiological and environmental factors. By investigating these problems, Pasteur developed certain practices of epidemiology that served him well a few years later when he dealt with animal and human diseases.

Louis Pasteur’s scientific discoveries in the 19th century revolutionized medicine and continue to save the lives of millions today

Regents' Professor of Clinical Laboratory Science, Texas State University

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Rodney E. Rohde has received funding from the American Society of Clinical Pathologists (ASCP), American Society for Clinical Laboratory Science (ASCLS), U.S. Department of Labor (OSHA), and other public and private entities/foundations. Rohde is affiliated with ASCP, ASCLS, ASM, and serves on several scientific advisory boards. See https://rodneyerohde.wp.txstate.edu/service/ .

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Some of the greatest scientific discoveries haven’t resulted in Nobel Prizes.

Louis Pasteur , who lived from 1822 to 1895, is arguably the world’s best-known microbiologist. He is widely credited for the germ theory of disease and for inventing the process of pasteurization – which is named after him – to preserve foods. Remarkably, he also developed the rabies and anthrax vaccines and made major contributions to combating cholera .

But because he died in 1895, six years before the first Nobel Prize was awarded, that prize isn’t on his resume. Had he lived in the era of Nobel Prizes, he would undoubtedly have been deserving of one for his work. Nobel Prizes, which are awarded in various fields, including physiology and medicine , are not given posthumously.

During the current time of ongoing threats from emerging or reemerging infectious diseases, from COVID-19 and polio to monkeypox and rabies , it is awe-inspiring to look back on Pasteur’s legacy. His efforts fundamentally changed how people view infectious diseases and how to fight them via vaccines.

I’ve worked in public health and medical laboratories specializing in viruses and other microbes, while training future medical laboratory scientists . My career started in virology with a front-row seat to rabies detection and surveillance and zoonotic agents, and it rests in large part on Pasteur’s pioneering work in microbiology, immunology and vaccinology.

First, a chemist

In my assessment, Pasteur’s strongest contributions to science are his remarkable achievements in the field of medical microbiology and immunology. However, his story begins with chemistry.

Pasteur studied under the French chemist Jean-Baptiste-André Dumas . During that time, Pasteur became interested in the origins of life and worked in the field of polarized light and crystallography .

In 1848, just months after receiving his doctorate degree, Pasteur was studying the properties of crystals formed in the process of wine-making when he discovered that crystals occur in mirror-image forms , a property known as chirality. This discovery became the foundation of a subdiscipline of chemistry known as stereochemistry , which is the study of the spatial arrangement of atoms within molecules. This chirality, or handedness, of molecules was a “ revolutionary hypothesis ” at the time.

These findings led Pasteur to suspect what would later be proved through molecular biology: All life processes ultimately stem from the precise arrangement of atoms within biological molecules.

Wine and beer – from fermentation to germ theory

Beer and wine were critical to the economy of France and Italy in the 1800s. It was not uncommon during Pasteur’s life for products to spoil and become bitter or dangerous to drink. At the time, the scientific notion of “spontaneous generation” held that life can arise from nonliving matter, which was believed to be the culprit behind wine spoiling.

While many scientists tried to disprove the theory of spontaneous generation, in 1745, English biologist John Turberville Needham believed he had created the perfect experiment favoring spontaneous generation. Most scientists believed that heat killed life, so Needham created an experiment to show that microorganisms could grow on food, even after boiling. After boiling chicken broth, he placed it in a flask, heated it, then sealed it and waited, not realizing that air could make its way back into the flask prior to sealing. After some time, microorganisms grew, and Needham claimed victory.

However, his experiment had two major flaws . For one, the boiling time was not sufficient to kill all microbes. And importantly, his flasks allowed air to flow back in, which enabled microbial contamination.

To settle the scientific battle, the French Academy of Sciences sponsored a contest for the best experiment to prove or disprove spontaneous generation . Pasteur’s response to the contest was a series of experiments, including a prize-winning 1861 essay .

Pasteur deemed one of these experiments as “unassailable and decisive” because, unlike Needham, after he sterilized his cultures, he kept them free from contamination. By using his now famous swan-necked flasks, which had a long S-shaped neck, he allowed air to flow in while at the same time preventing falling particles from reaching the broth during heating. As a result, the flask remained free of growth for an extended period. This showed that if air was not allowed directly into his boiled infusions, then no “living microorganisms would appear, even after months of observation.” However, importantly, if dust was introduced, living microbes appeared.

Through that process, Pasteur not only refuted the theory of spontaneous generation, but he also demonstrated that microorganisms were everywhere. When he showed that food and wine spoiled because of contamination from invisible bacteria rather than from spontaneous generation, the modern germ theory of disease was born .

The origins of vaccination in the 1800s

In the 1860s, when the silk industry was being devastated by two diseases that were infecting silkworms , Pasteur developed a clever process by which to examine silkworm eggs under a microscope and preserve those that were healthy. Much like his efforts with wine, he was able to apply his observations into industry methods, and he became something of a French hero .

Even with failing health from a severe stroke that left him partially paralyzed, Pasteur continued his work. In 1878, he succeeded in identifying and culturing the bacterium that caused the avian disease fowl cholera . He recognized that old bacterial cultures were no longer harmful and that chickens vaccinated with old cultures could survive exposure to wild strains of the bacteria. And his observation that surviving chickens excreted harmful bacteria helped establish an important concept now all too familiar in the age of COVID-19 – asymptomatic “healthy carriers” can still spread germs during outbreaks.

After bird cholera, Pasteur turned to the prevention of anthrax , a widespread plague of cattle and other animals caused by the bacterium Bacillus anthracis . Building on his own work and that of German physician Robert Koch , Pasteur developed the concept of the attenuated, or weakened, versions of microbes for use in vaccines.

In the late 1880s, he showed beyond any doubt that exposing cattle to a weakened form of anthrax vaccine could lead to what is now well known as immunity, dramatically reducing cattle mortality.

The rabies vaccine breakthrough

In my professional assessment of Louis Pasteur, the discovery of vaccination against rabies is the most important of all his achievements.

Rabies has been called the “ world’s most diabolical virus ,” spreading from animal to human via a bite .

Working with rabies virus is incredibly dangerous, as mortality approaches 100% once symptoms appear and without vaccination. Through astute observation, Pasteur discovered that drying out the spinal cords of dead rabid rabbits and monkeys resulted in a weakened form of rabies virus. Using that weakened version as a vaccine to gradually expose dogs to the rabies virus, Pasteur showed that he could effectively immunize the dogs against rabies.

Then, in July 1885, Joseph Meister, a 9-year-old boy from France, was severely bitten by a rabid dog. With Joseph facing almost certain death, his mother took him to Paris to see Pasteur because she had heard that he was working to develop a cure for rabies.

Pasteur took on the case, and alongside two physicians, he gave the boy a series of injections over several weeks. Joseph survived and Pasteur shocked the world with a cure for a universally lethal disease. This discovery opened the door to the widespread use of Pasteur’s rabies vaccine around 1885, which dramatically reduced rabies’ deaths in humans and animals .

A Nobel Prize-worthy life

Pasteur once famously said in a lecture , “In the fields of observation, chance favors only the prepared mind.”

Pasteur had a knack for applying his brilliant – and prepared – scientific mind to the most practical dilemmas faced by humankind.

While Louis Pasteur died prior to the initiation of the Nobel Prize, I would argue that his amazing lifetime of discovery and contribution to science in medicine, infectious diseases, vaccination, medical microbiology and immunology place him among the all-time greatest scientists.

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Louis Pasteur stepped onto the world stage with a famous experiment borne out of necessity. In July 1885, a rabid dog attacked a boy named Joseph Meister. At a time when this would have been a death sentence from rabies, Joseph’s mother asked for help from Louis Pasteur, who she heard was working on a cure for rabies. Pasteur inoculated the child with 13 increasingly strong doses of an experimental rabies vaccine. At the end of the treatment, the child did not develop rabies, and a new era of vaccination began.

The rabies vaccine was not Louis Pasteur’s only achievement, though it was lauded the world over because there was no treatment and cure of rabies at the time. By the time of his experiment on Joseph Meister, Pasteur had already developed a vaccine against chicken cholera and anthrax in cattle. He had also shown that spontaneous generation was non-existent, proving that food spoiled from something landing on it from the environment. And his work on vaccines solidified the main tenets of germ theory . Instead of believing that bad air caused disease, scientists changed their focus to diseases -- especially communicable ones -- being caused by a germ of some kind.

Pasteur received many accolades for his work. Among them, he was named a Foreign Member of the Royal Society in 1869. He was elected to the Académie Nationale de Médecine in 1873. The Royal Netherlands Academy of Arts and Sciences named him a foreign member in 1883. By the time of his death, Louis Pasteur asked that his extensive notes on his laboratory methods and experiments be kept private. They were not released to the public until 1964.