Louis Pasteur Experiments

Louis Pasteur 's work on Anthrax

After Louis Pasteur recovered from his depression, he was back at work again, Pasteur turned his attention to another disease that threatened both the health and economy of his nation -anthrax. "Do not think too much about things that have already been accomplished," he said. Better to move on to new challenges. 

The primary victims of anthrax were sheep but it could infect other animals and occasionally people. The disease was threatening half the livestock of France. One moment a sheep would be healthy, the next minute it would be lagging behind the flock, its limbs shaking and blood spurting from its mouth. The farmers knew that in just a few hours there would be convulsions and then death.

Louis Pasteur 's work on cholera

While he studied anthrax, Louis Pasteur also began exploring chicken cholera, which was also epidemic in France. Every morning poultry farmers would walk into their coops, only to find dead hens collapsed on their nests, and roosters that had been strutting proudly the day before, now lying motionless in the dust. It was Louis Pasteur 's experiments with chicken cholera that led to a mistake that would prove an important key to his immunization discoveries.

Louis Pasteur 's mistake in experiments

The mistake happened in his laboratory when Louis Pasteur was injecting hens with the bacillus that caused cholera. By accident he injected them with an old culture instead of a new one. The old culture had been exposed to oxygen and its microbes had been weakened, so the hens didn't get the disease, as planned. But more importantly, they didn't get the disease when he later ingested them with a fresh culture.

Louis Pasteur and Attenuation

The first, weak injection had made them immune. It was the most important discovery of Louis Pasteur's life and the one on which all modern vaccinations are based. The concept is called attenuation - it means simply that a virus is diluted or weakened; is then injected in a body; and the body fights it off without becoming ill but develops a resistance to further exposure of the same virus. Edward Jenner had pioneered the idea of immunization the century before Louis Pasteur. It was Louis Pasteur who expanded and perfected the idea for broader, more effective use. Jenner had used cowpox to prevent smallpox in humans - Louis Pasteur showed that the microorganism itself could protect against the disease it caused.

Louis Pasteur and the cure for Anthrax

Confident over his results with chicken cholera, Pasteur now decided to try the same technique on anthrax. Louis Pasteur gathered 25 sheep on a farm in the French countryside near Chartres and invited his critics and opponents to witness an experiment. Scientists, doctors, and journalists from around the world gathered to see whether Louis Pasteur would triumph or fail. Louis Pasteur vaccinated half the sheep with a weakened form of the anthrax virus and the other half he left alone. His plan was to return after three weeks and give all the sheep an injection of anthrax that would normally be fatal. The spectators were invited to return and see the results.

They did return. There was a lot of excitement in the air that day in May of 1881, when Louis Pasteur gathered the sheep and gave them each a deadly injection of anthrax. He first announced: "The 25 unvaccinated sheep will all perish. The 25 vaccinated ones will survive." Now everyone waited to see if he was right. Louis Pasteur was confident enough to make such a bold statement because Louis Pasteur knew his theory was supported by years of study, experiment, and proof. It was the way he always worked - steadily and patiently, checking and re-checking every detail, conducting experiment after experiment, and never making a claim or a statement that he didn't know he could fully support with hard scientific evidence. By the time Louis Pasteur said something was true, there was little chance of error.

Still, the first night on the farm was a hard one for Louis Pasteur. Someone had mistakenly told him that one of the vaccinated sheep was dying and he spent a restless night trying to understand what had gone wrong. But the next morning when he arrived at the farm, everyone burst into cheers and applause, even his critics. Twenty-three of the unvaccinated sheep were already dead and the other two were dying. But all of the vaccinated sheep were as healthy as before. The inoculations had worked. A disease that had long plagued farmers and ranchers had been vanquished. And there was hope many other diseases could be vanquished by the same method. Only the suffering of the sheep that had been forced to sacrifice their lives so that thousands of others might live dimmed Louis Pasteur 's happiness.