Louis Pasteur
Louis Pasteur; drawing by David Levine

There is a real world independent of our senses; the laws of nature were not invented by man, but forced upon him by that natural world. They are the expression of a rational world order.”

—Max Planck,
The Philosophy of Physics

Louis Pasteur was the father of modern hygiene, public health, and much of modern medicine. He was born in 1822 at Dole, halfway between Dijon and Besançon in eastern France, where his father owned and ran a small tannery. He attended school in nearby Arbois, obtained his first science degrees in Besançon, and in 1847 graduated with a doctorate in science from the Ecole Normale Supérieure in Paris. Scientists at that time believed that the fermentation of grapes, or the souring of milk, or the putrefaction of meat, were all purely chemical processes unrelated to microorganisms.

The causes of infectious diseases were unknown. Malaria was believed to arise from “miasmas” emanating from swampy ground; outbreaks of plague were attributed to unfavorable constellations, to comets, to the wrath of God, or even to the poisoning of wells by Jews, who often paid for it with their lives. The “animalcules” first observed by the Dutchman Anton van Leeuwenhoek in the seventeenth century were believed to arise spontaneously in decaying meat or vegetable matter; they had not as yet been connected with disease. In the eighteenth century Edward Jenner had introduced vaccination against smallpox with liquid drawn from the pustules of pox-infected cows, but the infectious agents involved were unknown, and vaccination against other diseases did not exist.

Pasteur revolutionized science by proving that fermentation and putrefaction are organic processes invariably linked to the growth of micro-organisms; that these never arise spontaneously from inanimate matter but only by reproduction of their own kind; that they are ubiquitous in the environment, but can be killed by subjecting them to heat, the process now known as pasteurization. He showed that infectious diseases of silkworms, animals, and human beings are caused by microorganisms and he devised ways of preventing them by vaccination. His discoveries inspired Joseph Lister in London to introduce antiseptics into surgery, which reduced mortality to a fraction of what it had been. Shortly before his death in 1895 two of Pasteur’s pupils discovered that bubonic plague is caused by bacteria which are transmitted by fleas from dead rats to man, a discovery that helped to eliminate plague from much of the world.

Pasteur led a simple family life and devoted all his time to research. To generations of Frenchmen and to many others, Pasteur’s has been the image of the selfless seeker after the truth who was intent on applying his science for the benefit of mankind. In The Private Science of Louis Pasteur, Gerald L. Geison, a historian of science, claims to have deconstructed Pasteur, and to have produced “a fuller, deeper and quite different version of the currently dominant image of the great scientist.” I propose to deconstruct his deconstruction and restore the rightly dominant image.

Geison analyzes Pasteur’s major discoveries: the asymmetry of biological compounds; fermentation; the vaccines against anthrax and rabies; and his demonstration that life is not generated spontaneously from non-living matter. By a painstaking comparison of Pasteur’s notebooks with his publications, Geison claims to have found him guilty of deception, of stealing other peoples’ ideas, and of unsavory and unethical conduct. Some of these claims are scientifically flawed, while others defy common sense.

Geison’s argument follows the line laid down by certain social theorists who assert that scientific results are relative and subjective, because scientists interpret empirical facts in the light of their political and religious beliefs, and under the influence of wider social and cultural pressures. They allege that instead of admitting their preconceptions, scientists misrepresent their findings as absolute truths in order to establish their power.

Pasteur transformed medicine, but he started out as a chemist and devoted the first ten years of his career to the study of a seemingly recondite matter, the relationship between the crystalline forms of certain salts of tartaric acid, a compound found in wine gone sour, and the effects of solutions containing them on polarized light transmitted through them. Acute observation and brilliant reasoning led him to discover that tartaric acid can exist in two alternative forms which are chemically indistinguishable, but which have their component atoms arranged asymmetrically in space so that they are mirror images of each other, like left and right hands. Since such asymmetries had never been observed in compounds synthesized in the laboratory, Pasteur reasoned that the capacity to produce them must be an intrinsic property of the living cell and soon proved his point with other examples. This was one of the great discoveries in chemistry and immediately established Pasteur’s reputation. Since tartaric acid is a product of fermentation, the discovery led him to the study of fermentation as such and to research on disease.


Geison insinuates that Pasteur cheated because the effects on polarized light of his right- and left-handed salts of tartaric acid, which according to Pasteur’s interpretation should have been exactly equal and opposite, were in fact slightly different. Geison writes:

Pasteur minimized the difference—in effect, he explained it away—by pointing to the difficulty of completely separating the two…forms [of crystals]. The deviation would “probably be the same for very well-chosen crystals” he now claimed.

I challenge Geison to go to the chemistry department at Princeton University, where he is a professor of history, and to repeat Pasteur’s experiment. He will have a hard time getting as close an agreement between the two measurements as the very skillful Pasteur did. Later experiments by others proved Pasteur’s explanation of the small discrepancy exactly right; but it seems that, because references to right and wrong would imply the existence of objective truth, they have been eliminated from the vocabulary of Geison’s school of sociologists of science.

Geison also accuses Pasteur of concealing the guidance he had received from his teacher, Auguste Laurent, because such acknowledgment might have implied sympathy with Laurent’s radical political views and could have been damaging to Pasteur’s career. But Geison’s own book shows that Laurent’s ideas on the relationship between the crystalline forms of tartaric acid and the transmission of polarized light when they are dissolved were misleading, confirming Pasteur’s statement that under Laurent’s guidance he “was enveloped by hypotheses without basis.” Politics had nothing to do with the judgment, and Geison’s accusation of opportunism is unjustified.

Pasteur’s turn from molecular asymmetry to fermentation has often been attributed to his having some connections with the brewing industry while he worked at Lille, but Geison writes that Pasteur’s notebooks confirm his statement that “the ‘inflexible’ internal logic of his work” led him to it. Fermentation of grapes produces an alcohol that does not affect polarized light; but Pasteur discovered that other products of fermentation included an alcohol that did. Since he associated that property with living organisms, he concluded that fermentation must be an organic process performed by microorganisms rather than a purely chemical one, as the great chemists Jöns Jakob Berzelius and Justus von Liebig maintained, and he demonstrated this in a series of brilliant experiments which convinced everyone except Liebig, who stuck to his wrong theory.

Pasteur next asked if these micro-organisms arose spontaneously from inanimate matter, as was then widely believed. He answered this question in a brilliant lecture in the grand amphitheatre of the Sorbonne before a distinguished audience. After linking spontaneous generation to the kind of materialism in which there is no need for a divine creator, a doctrine abhorrent to himself, and, as he knew, also to the Church and the royal family, he stressed that “neither religion, nor philosophy, nor atheism, nor materialism, nor spiritualism has any place here…. It is a question of fact. I have approached it without preconceived idea.” Geison disputes this and alleges that his “approach to the question…was strongly conditioned by an intertwined set of philosophical, religious, and political interests.” But he does not give any clear evidence for the claim.

The experiments Pasteur described in that lecture were stimulated in part by Félix-Archimède Pouchet, a biologist in Rouen who claimed that living eggs are generated spontaneously by a “plastic force” in dead plant and animal debris, and that microorganisms arise spontaneously in liquid extracts (or “infusions”) made from boiling hay, even when they are exposed to chemically produced, hence sterile, oxygen. By contrast, Pasteur demonstrated that sugared yeast water, boiled briefly, would not ferment when exposed to sterile air. As a final demonstration, he took sterile sugared yeast water to the Mer de Glace above Chamonix and opened the bottles there. As he expected, the air was germ-free and no fermentation occurred. To disprove him, Pouchet took his boiled-hay infusions up a glacier in the Pyrenees and found that they fermented. Pasteur dismissed this finding as the result of sloppy work in preparing the boiled hay—unjustly, as it later turned out.

Pasteur’s predecessor, the great naturalist Georges Cuvier, had already disputed the idea of spontaneous generation as unproven, and had associated the idea with the philosophers responsible for the French Revolution, on the ground that it denied the divine creation of life. Later, spontaneous generation became associated with materialism and also with Darwinism. Against this background, Geison castigates Pasteur’s conduct in his controversy with Pouchet over fermentation, because some of Pasteur’s own attempts at preventing fermentation of sugared yeast water had not succeeded, and many of his other experiments had also failed. According to Geison, he disregarded these failures because his religious and political views prejudiced him against taking them seriously. Geison implies that Pasteur acted dishonestly by not repeating Pouchet’s experiment with hay infusions, since, according to the orthodox scientific method as he understands it, a single disproof of a hypothesis invalidates all previous supporting evidence. For his part, Pasteur once remarked wisely: “In the observational sciences, unlike mathematics, the absolutely rigorous demonstration of a negation is impossible.” Geison dismisses this as unscientific.


In fact, scientists rarely follow any of the scientific methods that philosophers have prescribed for them. They use their common sense. Having convinced himself by the most rigorous possible experiments that fermentation will not take place under sterile conditions, Pasteur could be confident that any contrary evidence was the result of error and he wasted no time searching for it. He felt sure that the source of the error was bound to emerge eventually. It did indeed fourteen years later when Pouchet’s boiled-hay infusions were found to have contained heat-resistant bacterial spores which boiling would have failed to kill. Geison attributes Pasteur’s immediate victory over Pouchet to his gift for persuasive advocacy rather than to the intelligent judgment of his audience, which Geison dismisses as a scientific elite in league with Pasteur’s quest for power. Now that we have seen that the complexity of life on the atomic scale is vastly greater than that of non-living matter, the idea of spontaneous generation seems even more absurd than it did in Pasteur’s time. But this seems not to be apparent to Geison; the line of thought with which he is associated may define such generation as just an alternative paradigm.

Pasteur’s discovery that all fermentation was caused by the actions of microorganisms convinced him that the same must be true of contagious diseases. He observed that animals which had recovered from a disease became immune to reinfection by the same disease. From there it was only a short step to the idea that if virulent microorganisms could somehow be reduced in potency, they might serve as vaccines that would make animals immune to infection by fully potent forms of the same organisms.

Pasteur and his young collaborator Emile Roux first put this idea into practice in a vaccine against a type of cholera that affects chickens and other domestic birds. Pasteur published his work in 1880, and his new cholera vaccine for poultry became available soon afterward. Pasteur’s and Roux’s next target was anthrax, which was then decimating French sheep and cattle. The vaccine they developed contained live anthrax bacilli, whose effect was “attenuated” so as to render them non-infectious. This was done either by exposing cultures of virulent anthrax bacilli to air at 42°–43° C—i.e., “oxidizing” them—or subjecting them to the process of “passage,” by which one animal that is not susceptible to the disease—say, a mouse—is injected with a small quantity of bacteria, which, after they have multiplied, are injected into a second mouse, and so on.1 Two of Pasteur’s collaborators, Charles Chamberland and Emile Roux, used potassium bichromate, an oxidizing agent, to produce attenuating effects on bacteria that were similar to those from exposure to air, but that were faster and perhaps more drastic. From what we know today, we can conclude that all these treatments probably induced genetic mutations that weakened the bacteria without killing them. Pasteur’s competitor Jean-Joseph Henri Toussaint tested other vaccines consisting of anthrax-infected sheep blood that was heated or treated with carbolic acid, the disinfectant which Joseph Lister in London had introduced to kill bacteria. Toussaint’s vaccines produced variable results, as indeed Pasteur’s did initially.

In 1881, Pasteur’s first publications about his air-oxidized anthrax vaccines drew a challenge for a public trial from veterinarians who were upset that a chemist was poaching on their preserve. Twenty-four sheep, one goat, and four cows were given two successive protective vaccinations before the trial; another twenty-four sheep, one goat, and four cows were left unvaccinated. On May 31 all animals received injections of virulent anthrax bacilli. By the day of the public trial, on June 2, all the unvaccinated sheep and the goat were dead and the cows were very sick, while the vaccinated animals were alive and healthy, except for one ewe which died the following day. A post-mortem showed that it carried a fetus that had died about two weeks earlier.

Geison tells us that he found evidence in Pasteur’s notebooks that this triumph was achieved not with Pasteur’s own air-oxidized vaccine, but with Roux’s and Chamberland’s bichromate-oxidized vaccine, which Chamberland had attenuated further by three passages through mice. After the trial, however, Pasteur continued to develop the air-oxidized vaccine; it was soon used successfully by farmers throughout the world. By 1894, 3,400,000 sheep had been vaccinated and mortality from anthrax had fallen to 1 percent, compared to 9 percent for unvaccinated sheep.2

Pasteur did not make a public statement that the trial vaccine had been oxidized by bichromate; but neither did he claim that it had been oxidated by air. All the same, Geison accuses him of having “actively misrepresented the nature of the vaccine actually used” and of “a significant and undeniable element of deception.” (I wonder what difference there is between “misrepresenting” and “actively misrepresenting.”) Geison also accuses Pasteur of taking credit that belonged to his competitor Toussaint, because Toussaint was the first to use an antiseptic, such as carbolic acid, to treat the sheep blood used for vaccines, and Geison regards the potassium bichromate used by Pasteur as just an alternative antiseptic.

Both accusations are based on misconceptions. Carbolic acid (phenol, as it is now called) kills bacteria, while Chamberland’s bichromate treatment kept them alive, as shown by their subsequent passage through mice. One of the empirical findings of immunology, probably discovered by Pasteur himself, is that live attenuated vaccines are more effective than dead ones. (For example, this is why Sabin’s polio vaccine has proved more effective than Salk’s.)

Besides, Pasteur pointed out that Toussaint’s vaccine would be extremely difficult to adapt for practical use because, unlike his own, it could not be propagated in cultures. Therefore Pasteur owed no intellectual debt to Toussaint. There is, moreover, no qualitative difference between the attenuating mutations induced by exposure to bichromate and those induced by exposure to air; both processes have an oxidizing effect. Hence there was no deception about the nature of the vaccine used. Under the pressure of the public trial, Chamberland and Roux apparently decided that the bichromate vaccine was safer, but Pasteur later preferred his own, air-oxidized vaccine. So what? The charge of “active misrepresentation” is ridiculous, especially since Pasteur’s air-oxidized vaccine was used successfully until long afterward.

The next vaccine Pasteur developed, against the rabies virus, was also air-oxidized. In July 1885, a couple from Alsace brought to Pasteur’s laboratory their nine-year-old son Joseph Meister, whose hands and legs had been severely bitten fourteen times by a rabid dog. Rabies has a long incubation period, so that a vaccine given soon after infection still stands a good chance of success. Pierre-Victor Galtier’s earlier transmission of the infectious agent from rabid dogs to rabbits led Pasteur to the idea of attenuating it by repeated passages through rabbits. Pasteur’s young collaborator Emile Roux then thought of attenuating the power of the infection by exposing strips of fresh spinal marrow taken from a rabbit that had died of rabies to dry, sterile air for various lengths of time. A small piece of marrow ground up and suspended in sterilized broth was then used as a vaccine.

Pasteur first gave the boy an injection derived from the most attenuated strips of spinal cord that had been dried longest, and he followed this by injections of less and less attenuated strips of spinal cord that had been dried for successively shorter periods. They saved Joseph Meister’s life and also that of a fifteen-year-old shepherd boy, Jean-Baptiste Jupille, who had been severely bitten while trying to save other boys from being attacked.

Pasteur realized later that Roux’s preparation of the vaccine actually killed a progressively greater proportion of the rabies virus instead of merely attenuating its effect; all the same, the vaccine proved effective. In a paper published in 1985 Dr. Hilary Koprowski, formerly president of the Wistar Institute in Philadelphia, wrote:

Young Meister’s treatment took place on 6 July 1885…. By 12 April 1886, 726 people had been treated, 688 after having been bitten by dogs and 38 by wolves. There were four deaths. By 31 October, 2490 had been vaccinated, and since then the Pasteurians have had the last word…. Despite many modifications, confidence in the original product was so strong that it was used until 1953 when the last person was vaccinated at the Pasteur Institute in Paris with Pasteur’s original preparation.3

Nevertheless, Koprowski has written to me that it is hard to say even today whether Pasteur’s vaccine was completely safe for human beings and whether some of the rabies infections that occurred after Pasteur’s original vaccination were from the animal bite or from the vaccine. He reports that a vaccine made from rabies virus grown in cultures of human fibroblast (skin cells) has recently proved both efficacious and safe. It is known as the “human diploid vaccine” and is manufactured at the Mérieux Institute in Lyon for use throughout the world.

Dr. Michel Peter and other physicians accused Pasteur, a mere chemist, of having used an insufficiently tested vaccine. Geison eagerly takes up their case and accuses Pasteur of unethical conduct, because “boldly, even recklessly, Pasteur was willing to apply vaccines in the face of ambiguous experimental evidence about their safety or efficacy.” Pasteur had indeed obtained variable results when he tried to immunize dogs, beginning with the most briefly dried, and therefore least attenuated and most virulent, strips of spinal cord, and then followed that treatment with injections from spinal cords dried for progressively longer periods. But in a subsequent trial on dogs begun forty days before his vaccinations of Meister, Pasteur had reversed that order, and none of the dogs he treated contracted rabies, despite the virulence of the final injection. Twenty-seven days elapsed between that final injection and the first injection he gave Meister—a period that would have been long enough for the dogs to develop rabies symptoms if Pasteur’s second procedure had been faulty. In the face of this evidence, Pasteur would have been timid and heartless to refuse the desperate appeal by Joseph Meister’s father. Geison’s accusation that Pasteur’s successful attempt to save Meister’s life was unethical is without foundation.

In Pasteur’s day there was no way of being sure either that a suspected dog really had rabies or that it had infected its victim. Pasteur’s enemies benefited from these uncertainties, but in 1888 they seem to have been silenced by the report of an English commission which repeated and confirmed the successful vaccinations of dogs and concluded:

From the evidence of all these facts, we think it certain that the inoculations practiced by M. Pasteur on persons bitten by rabid animals have prevented the occurrence of hydrophobia in a large proportion of those who, if they had not been so inoculated, would have died of that disease. And we believe that the value of his discovery will be found much greater than can be estimated by its present utility, for it shows that it may become possible to avert, by inoculation, even after infection, other diseases besides hydrophobia. 4

Pasteur had no medical degree and therefore could not carry out the injections of Meister and Jupille himself. They were done not by Pasteur’s own medical collaborator, Emile Roux, but by two other doctors. From this fact Geison speculates that Roux refused to give the injections because he considered them unsafe, and that he fell out with Pasteur over this issue. But Geison cites no documentary evidence for this claim.

According to Geison, Pasteur’s colleagues supported him against the accusations of Peter and other physicians because Pasteur’s treatment of Meister “was a symbolic rallying point in a wider struggle for cultural authority and power…. Critics of Pasteur’s treatment for rabies…were…pushed aside in pursuit of a larger project: to secure the cultural domination of modern ‘professional science.’ ” Might they not have been pushed aside because Pasteur’s vaccine worked?

It is remarkable that Pasteur achieved his phenomenal practical successes while his theoretical concepts were still far from accurate. At first he thought his live, attenuated vaccines caused immunity by consuming the nutrients in the host, leaving none for virulent bacteria. Later he changed his mind and believed that the attenuated bacteria released a toxin that stopped further bacterial growth, but in 1890 Emil Behring and Shibasaburo Kitasato in Berlin discovered that the toxin was released not by the bacteria but by the defenses of the host animal in the form of antibodies.

Yet Geison has little to say about the correct explanations for the efficacy of vaccines, or for other phenomena, perhaps because his ideological approach denies their very existence. According to him, “Pasteur shared with many of his peers a rather simpleminded and absolutist notion of scientific truth, rarely conceding the possibility of its being multifaceted and relative.” According to Geison, Pasteur’s “scientific beliefs and modus operandi were sometimes profoundly shaped by his personal concerns, including his political, philosophical and religious instincts,” while “…the real individual scientist…tries to navigate a safe passage between the constraints of empirical evidence on the one hand and personal or social interests on the other.”

Had Michael Faraday’s discovery of electromagnetic induction been “multifaceted and relative,” there would be no electric power; had Albert Einstein’s concept of the relation between mass and energy and James Chadwick’s discovery of the neutron been relative, there would be no nuclear power and no atomic bombs; had Erwin Schrödinger’s wave equation been relative, there would be no computers. Nor is there a shred of evidence that any of these scientists, or Ernest Rutherford, or Alexander Fleming, or James Watson, or Francis Crick, had to “navigate a safe passage between the constraints of empirical evidence on the one hand and personal and social concerns on the other.” Such concerns may have made Galileo and Darwin hesitate to publish their revolutionary ideas, and they may affect some of today’s scientists who try to disentangle the respective influences of nature and nurture on human behavior; but these are exceptions. I cannot think of any Nobel Prize-winning discovery in physics, chemistry, or medicine that was based on anything other than empirical evidence or mathematical insight.

According to Geison, it is now a commonplace among historians and sociologists of science that science, no less than any other form of culture, depends on rhetorical skills. I have known scientists who possessed great rhetorical skills which failed to conceal the shallowness of their research from their peers. On the other hand, Alexander Fleming’s lectures put everyone to sleep, while his discovery of penicillin made him one of this century’s most famous scientists. Good research needs no rhetoric, only clarity. The entire approach emphasizing “relative” truth seems to me a piece of humbug masquerading as an academic discipline; it pretends that its practitioners can set themselves up as judges over scientists whose science they fail to understand.

Toppling great men from their pedestals, sometimes on the slenderest of evidence, has become a fashionable and lucrative industry, and a safe one, since they cannot sue because they are dead. Geison is in good company, but he, rather than Pasteur, seems to me guilty of unethical and unsavory conduct when he burrows through Pasteur’s notebooks for scraps of supposed wrongdoing and then inflates these out of all proportion, in order to drag Pasteur down. In fact, his evidence is contrived, and does not survive scientific examination.

Pasteur may have been domineering, intolerant, pugnacious, and, in his later years, a hypochondriac who searched every slice of bread for bacteria before eating it; but he was courageous, compassionate, and honest, and his scientific achievements, which have much reduced human suffering, make him one of the greatest benefactors of mankind. Joseph Meister became the proud janitor of the Pasteur Institute in Paris. He killed himself in June 1940 rather than open the crypt where Pasteur lies buried to the invading Germans. In 1922, the French Ambassador to the United States, Jules Jusserand, said in a speech: “In the course of its history, France has produced many great men. There is no one of whom we are prouder than Pasteur…. Some years ago, before the war, a newspaper organized a kind of plebiscite and asked its readers who in their view were France’s greatest sons. 2,300,000 replies came, and in this militaristic nation of ours…the emperor Napoleon came seventh and Pasteur came first.”5

This Issue

December 21, 1995