Louis Pasteur: A biographic essay
Since the time of Hippocrates, diseases had been attributed to abstract imbalances of the internal humors of the human body. It was not until the 19th century that, thanks to brilliant researchers such as Louis Pasteur and Robert Koch, that the theory of the microbial origin of infectious diseases was firmly established, according to which these are caused by pathogenic environmental germs that change the healthy body. The determination of the concrete and safe causes of a wide range of afflictions supposed the beginning of the current scientific medicine. Louis Pasteur was a French chemist and bacteriologist, often labeled as “father of modern hygiene, public health and much of modern medicine, as well as the father of microbiology and immunology” (Ligon 2002:134).
Pasteur gave a decisive boost to the development of vaccines, being especially remembered for the success of his vaccine against rabies (1885). His work is remembered for his enormous contributions to the prevention and treatment of diseases, allowing the creation of vaccines, his contributions to various industries and his theoretical basis for the subsequent development of the areas where he worked, in addition to the pasteurization technique, of course.
Early life and first
Louis Pasteur was born on December 27, 1822, in Dole, department of Jura, France. He was the son of a tanner who had been a soldier of Napoleon and grew up in the city of Arbois. He attended secondary school at the Lyceum of Besançon, where he obtained a bachelor's degree in letters in 1840 and science in 1842. He studied chemistry under the direction of Dumas and Balard at the École Normale Supérieure in Paris, and in 1847 he received his Ph.D. in physics and chemistry. He graduated as a chemistry professor at the University of Strasbourg, giving chemistry classes there and in Dijon, between 1847 and 1853.
The following year, his research on racemic acid, and then on tartaric acid, led him to formulate a theory about molecular dissymmetry; he thought he had discovered a demarcation line between the organic substances elaborated by living beings (with dissymmetric molecular structure) and those prepared in laboratories (with symmetric structure). Indeed, Pasteur discovered that tartaric acid paratartaric acid was, in reality,
A mixture of two different tartaric acids possessing equal optical activity, except for the fact that one (the right or dextro form) rotated a polarized beam of light to the right, whereas the other (the left or levo form) rotated light to the left. (Dubos 1950:33)
He managed to manually separate the crystals from these two chemical species and found that each one formed an aqueous solution capable of diverting the polarized light at the same angle but in an opposite direction. Although Pasteur's explanations for this phenomenon were not entirely correct, this discovery allowed other scientists to establish the asymmetric structure of the carbon atom, which was the basis of modern organic chemistry. Such studies have validated Pasteur as the founder of stereochemistry, a branch of chemistry that describes the three-dimensional structure of molecules.
From fermentation to spontaneous generation
In 1848 he was appointed professor of physics and chemistry at the Lycée of Dijon, and three months later alternate in the chair of chemistry of the University of Strasbourg, chair of which he would be holder of in 1852, to later (1854-1857) to the University of Lille as professor of chemistry and dean of the Faculty of Sciences. With a mainly practical orientation, aimed at solving some difficulties encountered by the wine and brewing industries of the region, Louis Pasteur undertook in Lille his well-known studies on fermentation.
His research led him to corroborate, on the one hand, the idea that yeasts were responsible for the production of alcohol in fermentation, and on the other, to discover that the production in the process of fermentation of certain acids and undesirable substances (that sour wine or beer) was due to the action of microorganisms such as bacteria. Pasteur realized that “if the finished wine were heated to 50–60 degrees centigrade for an hour, the development of the harmful microorganisms could be significantly reduced” (Robbins 2001:51). Bacteria were thereby eliminated, thus preventing the acidification of the final product.
The illustrious French scientist would apply this same system to the field of food preservation: heating the milk at high temperature before bottling it, destroying the pathogenic bacteria that it may contain and preventing its fermentation without altering its structure or its components. This process is now called pasteurization.
Meanwhile, in a harsh struggle with the French biologist Felix Pouchet and the theologizing physiologists, he developed his great battle against spontaneous generation. The old idea that some living beings do not derive from the reproduction of others, but that they are formed spontaneously, was based on an inaccurate empirical observation (of rotting flesh, for example, dipterous larvae emerge) and had maintained its validity during centuries, to be sustained by authorities like Aristotle. Although the experiments of Francesco Redi (1626-1698) confused that particular example, the subsequent discovery of microorganisms resurrected this controversy, one of the most relevant in the history of biology.
Research on fermentation had led Pasteur to wonder if those microorganisms that intervened in it formed spontaneously or came from the environment. To solve the question, he devised an experiment consisting in introducing nutritive material sterilized by heat in various containers; all of them were sealed to prevent contamination by local air.
The results were unequivocal: in the containers in which humid air was introduced, a rapid putrefaction of the organic matter took place; on the other hand, in the containers where the introduced air contained little humidity, there was practically no alteration of the original material. Pasteur deduced that the air is loaded with germs of microorganisms that develop in contact with an organic matter under the right environmental conditions. The publication of the conclusions in his 1860 report titled “Memoir on Organized Corpuscles that Exist in Suspension in the Atmosphere: An Examination of the Doctrine of Spontaneous Generation.” supposed the definitive liquidation of the theory of spontaneous generation (Robbins 2001:47).
Microbial theory and vaccines
Previous studies, in fact, suggested to Pasteur an analogy between disease and fermentation: in the same way that the action of external microorganisms is the cause, for example, of the deterioration of milk, these same microorganisms could invade a healthy body and cause the conditions. He thus came to establish, as a consequence of his work, the so-called microbial or germ theory of diseases, according to which “the secret to the mysteries of both fermentation and disease lay in the action of microscopic organisms, also called ‘microbes’” (Robbins 2001:70). Despite the incomprehension that arose (derived in a way from common sense, for which it is surprising that microscopic beings can kill infinitely larger ones), the results of their further investigations would endorse their hypothesis.
Meanwhile, the civil war that was raging in Paris in 1871 forced Pasteur to leave the city. In those years and until his death, Louis Pasteur directed his activity towards the study of contagious diseases (assuming that they were due to germs that passed from one organism to another), not only confirming his theory but also developing vaccination as a preventive method. Known since ancient times, the mechanism of vaccination is simple: to stimulate the immune system by exposing it to the microorganism responsible for a certain disease, so that in the future it can respond immediately to an eventual infection.
In 1879, while conducting experiments with chickens affected by the cholera of chickens, Pasteur warned that some animals infected with a crop preserved in poor condition, and therefore deteriorated, were protected from the disease; he had discovered that, under certain conditions, germs were less pathogenic, but that inoculating them into a healthy individual also gave rise to a defensive response that protected against virulent germs. (Dubos 1950:278).
The continuation of his research allowed him to develop the vaccine to prevent rabies, a contagious disease also called hydrophobia in man and against which there was no palliative, resulting fatally in most of the cases. After long studies and experiments tested since 1880, he found a safe method to attenuate the virus: to inoculate the disease in rabbits and, after his death, to desiccate the marrows of rabbits, from which less virulent extracts could be obtained as the drying time progressed.
The effectiveness of this vaccine, its last great contribution to the field of science, was successfully tested on July 6, 1885 in a nine-year-old Alsatian boy, Joseph Meister, who had received fourteen bites from a rabid dog and who, thanks to a patient treatment for ten days, he did not develop the disease. This spectacular success had a great resonance, as well as practical consequences for Pasteur, who until then had worked with rather precarious means.
Popular support made possible the construction of the Pasteur Institute, founded in 1888, which would enjoy a justified international prestige thereafter. With his health greatly weakened (he had been suffering from a hemiplegia since 1868), in 1892 he received a solemn tribute at the Sorbonne on the occasion of his seventieth birthday; Three years later, the distinguished scientist died in Marnes-la-Coquette.
Dubos René J. 1950. Louis Pasteur, Free Lance of Science. Boston: Little, Brown.
Robbins, Louise. 2001. Louis Pasteur: and the Hidden World of Microbes. New York: Oxford University Press.
Ligon, B. lee. 2002. “Biography: Louis Pasteur: A Controversial Figure in a Debate on Scientific Ethics.” Seminars in Pediatric Infectious Diseases 13(2):134–41.