Vigyan Prasar Science Portal
For anything and everything on science from India
Louis Pasteur
A Great Benefactor of Humanity
Dr Subodh Mahanti


“I was born to a tanner. He was a worker but was always eager to learn. He was my first teacher and it was he who inspired in me the love for work, as a direction for my work, instilled in me the love for my country. May your work also be governed by these two passions.”

Louis Pasteur

Where does genius come from? Often, we are contented with attributing it to a unique, exceptional and mysterious resource of mind. On the contrary, in the case of Pasteur, we see clearly that the power of his genius comes from multiple sources, very much in opposition to his intelligence, character and temperament. He was an artist and a dreamer. He would allow himself to be fascinated by mirages of an imagination which always tended to go beyond the horizons of knowledge. He was ambitious and dominating and would be satisfief only with real and complete victories. He was rigorous and demanding towards himself. At the same time he would spare no efforts to be severe and disciplined.

Jacques Monod while speaking on the occasion of the celebration of the 150 birth anniversary of Lois Pasteur in 1973.


“Pasteur has done much more than create the science of microbes : he inaugurated the era of scientific medicine … Pasteur opened medicines to science : he introduced into the medical body the notion of germ – non-microbial – which brought in a permanent revolution. Preserver in all fields other than science, preserver by nature with great respect for order, traditions and institutions, Pasteur - “who was not even a doctor” – was to force open the doors of the sacrosanct temple of medicine, to clear the fog of scholastic learning and destroy the existing idols; doctors where going through scientific training, doctrines ceased to be frozen into dogmas, the prevailing mentalities and attitudes were transformed.

Claire Salomon-Bayet

Louis Pasteur is regarded as one of the greatest biologists of all times. Isaac Asimov, the prolific science writer, said : “In biology it is doubtful that any one but Aristotle and Darwin can be mentioned in the same breath with him.”

Pasteur solved the mysteries of rabies, anthrax, chicken cholera, and silkworm diseases and contributed to the development of the first vaccines. Pasteur was responsible for some of the most important theoretical concepts and practical applications of modern science. Although not a physician, Pasteur was undoubtedly the most important medical scientist working in the 19th century. He gave a new meaning to medicine. He was one of the forerunners in the study of microorganisms. He not only explained the causes for contagious diseases but also recommended ways of avoiding them. Pasteur was a founder of the germ theory. He laid the foundations of three distinct sciences- Immunology, microbiology and stereochemistry. It was Pasteur who brought to an end the debate on spontaneous generations which had continued for centuries. He clearly demonstrated that spontaneous generation was not possible. And doing so Pasteur set the stage for modern biology and biochemistrty. Psteur described the scientific basis for fermentation—the process of production of wine, beer and vinegar. He clearly demonstrated that the nature of fermentation was organic (a product of a certain type of living organism) and not inorganic, as proposed and defended by Justus von Liebig. Pasteur developed a vaccine against anthrax, a particularly deadly, highly communicable disease of domestic animals.

The name of Louis Pasteur became a household word for his two inventions: pasteurization process for sterilizing dairy foods and a vaccine for rabies. While these two inventions are hallmarks of his long, rich career but he achieved much more. In public mind the name of Pasteur is associated with rabies to such an extent – that his main discoveries are often forgotten.
Science was the main passion of his life and his whole life was devoted to it. Pasteur said; “Science…it is my life…it has brought me a deepness of pleasure that I have always known yet never realized.” Pasteur was a great hero in his own times and he remains so to this day.

Pasteur was born on 27 December 1822 in Ole in France and grew up in the nearby town of Arbois. His father Jean Pasteur was a tanner without much education. Pasteur was very much influenced by his father. In one of his letters to his father Pasteur wrote: “You (Pasteur’s father) might not remember how important your influence on me was in developing my mind… It was you who helped me decide to study natural sciences—undoubtedly because of your own interest in the subject rather than your conviction regarding my aptitude. Enthusiasm and mother’s presence of mind were all passed on to me by you. If I have always associated the grandeur of our country it is because of the feelings that you inspired in me.”

In his early school days Pasteur was not an outstanding student. The young Pasteur preferred fishing and painting to studies. He showed great talent for drawing. He made a series of portraits of his family members, classmates and neighbours. Several of his portraits are exhibited at the Pasteur Museum. On his portraits Pasteur wrote to his parents: “Some students told me that people in Besancon were talking about a schoolboy who draws his classmates. The fact is, as I already told you, my first portrait was exhibited in the reception area where people come to see students. However, all this is not going to fetch me a seat in Ecole Normale. I would prefer a first place in the college to the ten thousand praises that are loosely showered in general conversations.” Though Pasteur could easily become a superior portrait artist but fortunately for science he did not pursue this career. Pasteur himself became interested in scientific subjects particularly in chemistry. Pasteur’s father was not in favour of his son ending up as an artist. He wanted that his son after completing his education become a professor in the college at Arbois. However, the headmaster the local school recognized Pasteur’s potential and convinced his father to send young Pasteur to Ecole Normale Superiuere in Paris, the most prestigious university founded specifically to train outstanding students, for careers in higher education in science and humanities. On 26 August 1842 Pasteur qualified for admission to the Ecole Normale and among the twenty-two candidates selected Pasteur ranked fifteenth. His physics was classed as “passable”’ and chemistry “mediocre”. Not satisfied with the result Pasteur decided to appear for the entrance examination the next year again. In the second attempt he was ranked 4th. As a part of his preparation for his second attempt Pasteur attended Dumas’s lectures on chemistry . He developed a special fascination for chemistry and all his future work showed a chemical approach, even to biological problems. Pasteur was deeply attached to Ecole Normale. In the notes furnished by Pasteur in 1895 for the publication brought out on the occasion of the centenary of the Ecole Normale Pasteur wrote: “”when I was a student of the College in Arbois, the words Ecole Normale would light up my soul…The surroundings were so dark and gloomy; the only source of light in dingy hall was from the north; the laboratories would not satisfy a single school today; yet, it was here that many ideas flourished; there was a passion for work which, even after fifty years here, draws me into its frenzy…Do you realize that the authors of these notes has always been fondly attached to the Ecole Normale? It is here that he met some great scientists and hundreds of very fine people, found wonderful friends and had the joy of seeing students become teachers.”

It was at Normale Ecole that Pasteur carried out most of his investigations. Emile Roux while commenting on Pasteur’s working style wrote: “In order to be closer to the work place, both the master and his pupils stayed at the Ecole Normale itself. Pasteur used to come first always….As soon as he entered, he would get down to work with a cardboard piece and a pencil in hand. He would observe the cultures and go down to the basement to see animals being experimented upon. Then, we used to do autopsies, showing, microscopic examinations, etc. You must see Pasteur at his microscope in order to have an idea of the patience with which he examined the preparation. Moreover, he observed everything with the same degree of care: nothing escaped his eye (even though he was short sighted!) and we used to joke that he used to see microbes grow in the broth. Later, Pasteur wrote down whatever observed…”

Over the course of 50 years – the second half of the 19th century – Pasteur’s discoveries revolutionized chemistry, agriculture, industry, medicine, surgery and hygiene. These discoveries greatly improved the human condition.

Pasteur was a chemist. He launched his memorable scientific career by studying the shapes of crystals of tartaric acid, an organic acid. He wanted to know why tartaric and paratartaric or racemic acids, which had the same chemical composition exhibited different optical properties in solution. Pasteur had observed that tartrate (salt of tartaric acid) synthesized in laboratory was optically inactive that it was unable to rotate the plane of polarized light but tartrate from grapes could easily rotate a beam of polarized light to the right. He was convinced that the internal structures of the two compounds must be different and this difference would show in their crystal forms. Upon careful examination under a microscope Pasteur found that crystals of tartaric acid looked alike. They possessed an identical asymmetry – which could rotate a beam of polarised light to the right. However, when Pasteur examined the crystals of the paratartic acid he found that there were two types of crystals. Both the types were asymmetrical. But one type was mirror image of the other, in the same way as the right hand mirrors the left.. Pasteur then performed a simple and elegant experiment, perhaps the most simplest and yet the most elegant in the annals of chemistry. Pasteur first separated the two types of crystals in two piles. For separation he only needed a dissection needle and a microscope. After the separation he could then demonstrate that in solution one form rotated the light to the right and the other form to the left. Based on this experiment Pasteur suggested that the optical property shown by a molecule is the result of the internal arrangement of atoms in space. The experiment was the beginning of a new science, which we call stereochemistry—the branch of chemistry dealing with the arrangement of atoms or groups of atoms that make up molecules. Pasteur’s simple experiment demonstrated that organic molecules with the same chemical composition can exist in space in unique stereospecific forms. Pasteur did not stop at proposing that different optical properties in solution is the result of the difference in structure in space. He went a step ahead. He proposed that asymmetrical molecules were indicative of living processes. In other words, living organisms only produce molecules that are of one specific orientation and which are always optically active. The proteins in higher animals are made up of only left-handed amino acids and not their mirror images or the right hand forms. Our body cells only burn the right-handed form of sugar to produce energy and not the left-handed form.

In 1854 Pasteur joined the Faculty of Sciences in Lille as Dean and Professor of Chemistry. It is here that his attention was drawn to the problem of alcoholic fermentation. Lille was an industrial town with a number of distilleries and factories. One distiller named M. Bigot, father of one of Pasteur’s students in chemistry, sought Pasteur’s help in overcoming his difficulties in manufacturing alcohol by fermentation. This was in summer of 1856. Bigot’s problem was that often his fermentation yielded lactic acid instead of alcohol. At the time it was believed that the process of fermentation leading to production of wine, beer and vinegar was a straightforward chemical breakdown of sugar to the desired molecules.

At Bigot’s factory the following observations of Pasteur led him to solve the puzzle of alcoholic fermentation:
i) The yeast cells found in the fermenting vats of wine remained healthy as long as normal production of alcohol continued but when lactic acid formed the yeast cells were found to be mixed with rod-like microbes. It may be noted here that before Pasteur explained the fermentation process scientists believed that yeasts were simply to be either a product of fermentation or catalytic agent that helped the fermentation proceed smoothly.

ii) Alongwith alcohol (that is ethyl alcohol) other complex organic compounds were found to ber produced during the fermentation. This could not be explained by the simple catalytic breakdown of sugar shown by Lavoisier. There must be other additional processes involved.

iii) Some of the organic compounds produced during the fermentation were found to be asymmetric that is they rotated plane of polarized light. Pasteur believed that living cells only produced asymmetric molecules.

Based on the above observations Pasteur concluded that the fermentation process was carried out by living cells, the yeasts. The fermentation turned sour when the yeast was contaminated with other microorganisms. In this way Pasteur won the battle against Justus von Liebig, who believed that fermentation was a purely a chemical reaction involving non-living oraganisms.

To prevent the fermentation from going sour Pasteur suggested that while the yeast, the organism which produced fermentation, should be allowed to work but not other microorganisms. To achieve this Pasteur suggested to heat the wine slightly to kill the contaminated organism after the fermantation was complete and to close the container. This process of killing undesirasble microorganisms is now called pasteurization. Pasteur’s findinds not only transformed the vinegar, the wine and the beer industry but also changed the bread, milk and cheese industry. Pasteur described his conclusion in the following way: “…I arrived at the conclusion that all diseases concerning wine, at least those that are known presently are determined by microscopic plants which are like ferments. In this way, one can say that when wine is bottled, the germ leading to its disease is also sealed inside. In order to preserve wine, it became necessary to find a way killing such germes. I first tried adding chemical substances which gave me some interesting results. But, they did not satisfy me for several reasons. Finally, I tried the effect of heat and I think I arrived at a very practical processs. All that needs to be done is to keep the wine temperature ranging between 60 to 100 0C, in closed containers, for an hour or two.”

Pasteur’s research on fermentation created great excitement and controversy. His experiments were criticized by those who believed in the theory of spontaneous generation, a subject speculated from Greek ans Roman times, was still debated in the exalted French Academy of Sciences. This made Pasteur to turn his attention to the question of where microorganism came from. To Pasteur, it became obvious, that yeasts and other microorganisms found during fermentation and putrefaction came from the outside. He pointed out that dust of the air was the carrier of contamination.

In 1865 Pasteur was asked to investigate a new disease devastating the silkworms of Southern France. Before taking up the work of investigating the disease, Pasteur knew nothing of silkworms. In fact in his own words, ‘he had never even seen a silkworm.’ A considerable confusion was caused by the presence of two quite independent infectionsss. Pebrine, in which black spots and corpuscles were generally, but not always, present on the worm. The worms affected by this disease often died within the cocoons. In the second type of the disease, flacherine, the worms exhibited no corpuscles or spots but failed to spin cocoons. During investigating the silk-worm disease Pasteur suffered a stroke which partially paralysed his left side. However, Pasteur managed to complete his experiments, analysis and conclusions of the problems plaguing the development of heralthy silkworms. He provided a comprehensive analysis of the disease and its promotion. Pasteur suspected that pebrine corpuscles were responsible for the failure of the worms. By examining the silkworms under the microscope Pasteur was able to identify those free of pebrine and he used only their eggs for breeding. He also excluded from breeding eggs from worms with flacherine, whom he identified by their sluggish behaviour in climbing leaves when about to construct cocoon. Silk-worm farmers were instructed and Pasteur’s methods of selection and how to use the microscope to detect sickness in the worms. In this way the silk industry in France returned to health.

On Pasteur’s work on silk worms Eile Roux wrote: “There are many lessons pertaining to human medicine in this study on disease affecting silkworms!….Without knowing anything about all these doctrines, a chemist, who knew how to use a microscope for experiments, showed that everything boils down to a parasite transmitted by the sick to healthy subjects and by parents to their descendants. The mystery of the contagion is explained in this way…”

In 1880, Pasteur found the cause for boils and Osteomyelitis, a microbe in the form of a “mass of grains” (staphylococcus). He also discovered a microbe in perpetual infection in the form of a “rosary” (streptococcus).

Anthrax, a fatal disease of sheep and cattle, was destroying the sheep industry and economy of France. Robert Koch isolated the anthrax bacillus, which was earlier identified by the French physician Davain, from infected spleens. Koch also showed that under resting conditions the bacillus formed long-lived spores. However, it was not known whether the cultured bacillus, itself, and not something carried along in Kochk’s culture medium caused anthrax in the animals, in which the culture was injected. It was Pasteur, who conclusively proved that it was the anthrax bacillus which was responsible for the disease.
The most celebrated of Pateur’s researches was the development of a vaccine against rabies, also called hydrophobia. Rabies has been known since times immemorial. Democritus is supposed to have been the first to describe rabies, five centuries before Christ. Pliny the Elder in the book VII of his voluminous ‘Natural History’ wrote of “the worm on a dog’s tongue which was thought to be the cause for rabies”. Even during Pasteur’s time rabies was a serious problem in France. The most obvious cause was of course the rabid dog. Many superstitions were associated with the treatment of rabies. The disease had been looked upon with horror. The treatments applied to victims were horrible, for example, cauterizing the bite wounds with a red-hot iron.

In December 1886 Pasteur decided to study rabies. It was not simple. There were no reliable models as well as a methodology which can ensure and renew the transmission of the disease between animals in order to study the disease better. The symptoms of the disease are varitable and it may take weeks to months to develop if they develop at all. In spite of these difficulties Pasteur decided to work on it as he realized that conquest of rabies would be regarded as a great achievement to the world of science and to the public at a large. Pasteur was not alone. A number of scientists in different parts of the world were interested in this disease. After Pasteur entered the field the contagious nature of rabies had been established. This had resulted the beginning of quarantines for dogs coming from a foreign country. Such preventive meausers controlled “local” rabies considerably. But then there was no proven treatment to save people bitten by rabid animals. Pasteur started his research by taking a sample of a saliva of a child who died of rabies and he used it to inoculate rabbits. In less than five years after his research began, he came out with a method to “manufacture” anti-rabies vaccine and a protocol for the vaccination. Initially he demonstrated the efficacy of his vaccine in rabbits and dogs. In 1885 Pasteur used a rabies vaccine developed by him on a badly bitten nine-year old boy, Joseph Meister. Against the advice of his colleagues Pasteur began the course of 14 injection using virus attenuated in the spine of rabbits. Meister survived and he become part of the history of medicine. Joseph Meister later became a caretaker at Pasteur’s Institute.

“I feel that I am harbouring two deep impressions : the first is that science does not have any nation; the second, which seems to be independent of the first, but is still a direct consequence of it, is that science is the highest personification of the nation, as amongst all the peoples, those who march ahead with there thought and inteleligence always lead.”

While presenting the results of his rabies treatment to the Academy of sciences on March 1, 1886 Pasteur called for the creation a rabies vaccine center. Pasteur said : “The cure for rabies resulting from dog bites was well founded. There was the need to create a vaccination for rabies.” The Academ of sciences launched an extensive, international public drive for funding the proposed center and it was able to collect 2,586,680 Frances. With the overwhelming response shown by a number of people it was possible to acquire 11,000 m2 of land on rue Durot. The Institute which bears the name of Pasteur was inaugurated on 14 November 1888 in the presence of French president Sadi Carnot. In his inaugural speech on the occasion Pasteur said: “…It can be said of the immense building which was constructed that, without exception, each stone stands as a material symbol for generosity. All virtues were combined to raise this work structure…My dear colleagues, maintain the enthusiasm that you showed right from the beginning. At the same time, be extremely strict in monitoring. Do not forward anything that cannot be proved in a simple and decisive manner. Adopt a critical mind. By itself, it cannot encourage ideas nor stimulate anything great. But without it, everything is useless. It always has the last word. When I ask of you in this respect and what you will in turn ask of your disciples in the most difficult part for an inventor…” It may be noted that Pasteur became so emotional that he had to ask his son to read out his speech.

In accordance with Pasteur’s wishes the institute was founded as a clinic far rabies treatment, a research center for infection disease and a teaching center. It became one of the premier international biological research. The 1891, the first Pasteur Institute was founded in Saigon (later rebamed HOCHIMINH City) in Vietnam launching but was to become a vast international network of Pasteur Institute. The Institute become so popular both in France and Abroad that it become a symbol of the country.

Pasteur work is not simply the sum of his discoveries. It also represented the revolution of scientific methodology. Pasteur superimposed two indispensable rules of modern research, the freedom of creative imagination necessarily subjected to rigorous experimentation. He would teach his disciples. “…It is an art to propose conclusive experiments without leaving anything to the imagination of the observer. In the beginning any experimental research on a specific subject, imagination should give wings to the thought. At the time of concluding and interpreting the fats that were collected observation, the imagination should be dominated and prevailed over by concrete results of experiments.” In fact Pasteur brought in a revolution, the pasteurian revolution, in science. And when Pasteur died it was not just the world of science and health that were no longer the same, the world itself became so different.”

Pasteur possessed the most important qualities of a true scientist. He had the ability to survey all the known facts about a particular problem and link them for all possible hypotheses; he had the necessary patience and drive to carry out experiments under the strictly controlled conditions and above all the brilliance to draw the correct conclusion from the experimental results. While explaining the importance of experimentation Psteur said: “imagination should give wings to our thoughts but we always need decisive experimental proof, and when the moment comes to draw conclusions and interpret the gathered observations, imagination must be checked and documented by the factual results of the experiment.” Further Pasteur said: “Preconceived ideas are the beacons which light up the path of experimenter and guide him in probing into nature. They become a danger only when they are transformed into fixed ideas. This is the reason why I wanted to see the following words inscribed at the entrance of any temple of science: the greatest mischief of the mind is to believe certain things, as by believing we would want them to be so.”
Louis Pasteur was a great humanist. He never filed any patents for his inventions. He could have easily amassed great wealth. His only ambition was to be useful. He emphasized the importance of research. Pasteur said: “I beseech you to take interest in these sacred domains called laboratories. Ask that there be more and that they be adorned for these are the temples of the future, wealth and well-being. It is here that humanity will learn to read progress and individual harmony in the works of nature, while humanity’s own works are all too often those of barbarism, fanaticism and destruction.” Pasteur was a great patriot. His feelings for his motherland are expressed in his following words: “Science was the main passion of my life. My whole life is devoted to it. In difficult moments, that cannot be separated from long hours of work, the thought of my motherland would encourage me. I used to associate her grandeur with the grandeur of scienc.”

Pasteur died on 28 September 1895. The French Government honored Pasteur with a national funeral, which was held on 5 October 1895. His funeral was attended by thousands of people, who gathered in silence. People were seen crying out of emotion and gratitude. Louis Pasteur was initially cremated in the Cathedral of Notre Dame but it was transferred to a permanent crypt in the Pasteur Institute. The crypt was made of mosaic represents the principal periods of his work. In 1940 the invading Germans ordered Joseph Meister to open the crypt for inspection, but Meiser chose to kill himself rather than to so.

We would like to end this article by quoting what Francois Jacob said of Pasteur on the occasion of the centenary celebration of the Pasteur Institute: “ … Pasteur left his mark, through his very style, not only on his students and Institute but on experimental biology as a whole. All the research activities of present day biologists tends to reformulate highly varied problems into issues that can be handled in the laboratory. Their efforts are geared towards finding answers through experiments. This trend in the field of modern medicine, and what we call public health today started with Pasteur and his strategy….”

For Further Reading

1. Louis Pasteur by Beverly Birch, Garth Stevens, Inc., Milwanke W1, 1989.
2. Pasteur and Modern Science by Rene Dubos, Doubleday and Co., Inc. New York, 1960.
3. Life of Pasteur by Vallery-Radot, Doubleday, Page and Co., New York, 1919