National Academies Press: OpenBook

Science, Medicine, and Animals (2004)

Chapter: A Theory of Germs

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Suggested Citation:"A Theory of Germs." National Research Council. 2004. Science, Medicine, and Animals. Washington, DC: The National Academies Press. doi: 10.17226/10733.


Today, it is hard for us to fully appreciate the great revolution in medicine known as “germ theory” and the role that animal research played in its development. It seems impossible that people once believed that foul odors could create disease or that “evil spirits” could cause a person to become ill. We have also forgotten how rare it was for parents to see all of their children survive to adulthood. Still, it has been little more than a century and a half since Robert Koch made the discoveries that led Louis Pasteur to describe how small organisms called germs could invade the body and cause disease.

In the final decades of the 19th century, Koch conclusively established that a particular germ could cause a specific disease. He did this by experimentation with anthrax. Using a microscope, Koch examined the blood of cows that had died of anthrax. He observed rod-shaped bacteria and suspected they caused anthrax. When Koch infected mice with blood from anthrax-stricken cows, the mice also developed anthrax. This led Koch to list four criteria to determine that a certain germ causes a particular disease. These criteria are known as Koch’s Postulates and are still used today. Integral to these criteria is Postulate #3, “The disease must be reproduced when a pure culture is inoculated into a healthy, susceptible host.” Even today, with all of the advances in modern science, it would be impossible to prove that a specific germ is responsible for a disease without the use of laboratory animals. Anthrax

ANTHRAX—A disease caused by Bacillus anthracis bacteria. Can cause skin lesions (cutaneous anthrax), breathing difficulties and shock (inhalation anthrax), or severe vomiting and diarrhea (gastrointestinal anthrax).

CULTURE—Micro-organisms, tissue cells, tissue, or other living matter grown in a specially prepared nutrient medium. Also refers to the cells grown, i.e., a culture of bacteria. GERM—A disease-causing organism, such as a bacteria, parasite, or virus, usually single celled.

Suggested Citation:"A Theory of Germs." National Research Council. 2004. Science, Medicine, and Animals. Washington, DC: The National Academies Press. doi: 10.17226/10733.

overcoming disease

Until the 20th century, it was common to lose a child to disease. Smallpox, polio, diphtheria, whooping cough, tetanus, measles, and mumps maimed and killed thousands of children every year. But due to the development of vaccines, there has not been a single natural case of smallpox in the world since 1977, polio has been eradicated in the Western Hemisphere, and whooping cough, tetanus, and mumps are rarely seen in developed countries.

Smallpox causes blisters similar to chickenpox. Smallpox is easily spread through coughing or sneezing, or through contact with contaminated clothes or bed linen. Twelve and 14 days after exposure, the patient develops a fever with severe aches and pains. A rash then appears over the entire body including the palms of the hands and soles of the feet. Death occurs in 30% of patients due to a massive immune response that causes clotting of the blood and organ failure. Vaccination before exposure to smallpox prevents the illness. There is no known treatment; however, vaccination up to 5 days after the exposure may help to prevent death.

Polio is caused by a virus that enters through the mouth and is easily transmitted from person to person, particularly between children during the summer months. It causes headache, fever, and aches before entering the bloodstream and infecting the nerves controlling movement. The disease causes paralysis in the arms and/or legs (spinal polio), throat, eyes, face, heart, or lungs (bulbar polio), or both (bulbospinal polio). It can lead to suffocation and death caused by paralysis of the lung muscles. Before the invention of the “iron lung,” about half of children with bulbar or bulbospinal polio died. disease

“In 1736 I lost one of my sons, a fine boy of four years old, by the small-pox, taken in the common way. I long regretted bitterly, and still regret that I had not given it to him by inoculation [had his son vaccinated]. This I mention for the sake of parents who omit that operation, on the supposition that they should never forgive themselves if a child died under it; my example showing that the regret may be the same either way, and that, therefore, the safer should be chosen.”

Benjamin Franklin, His Autobiography: 1706-1757

Suggested Citation:"A Theory of Germs." National Research Council. 2004. Science, Medicine, and Animals. Washington, DC: The National Academies Press. doi: 10.17226/10733.
Page 7
Suggested Citation:"A Theory of Germs." National Research Council. 2004. Science, Medicine, and Animals. Washington, DC: The National Academies Press. doi: 10.17226/10733.
Page 8
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Science, Medicine, and Animals explains the role that animals play in biomedical research and the ways in which scientists, governments, and citizens have tried to balance the experimental use of animals with a concern for all living creatures. An accompanying Teacher’s Guide is available to help teachers of middle and high school students use Science, Medicine, and Animals in the classroom. As students examine the issues in Science, Medicine, and Animals, they will gain a greater understanding of the goals of biomedical research and the real-world practice of the scientific method in general.

Science, Medicine, and Animals and the Teacher's Guide were written by the Institute for Laboratory Animal Research and published by the National Research Council of the National Academies. The report was reviewed by a committee made up of experts and scholars with diverse perspectives, including members of the U.S. Department of Agriculture, National Institutes of Health, the Humane Society of the United States, and the American Society for the Prevention of Cruelty to Animals. The Teacher’s Guide was reviewed by members of the National Academies’ Teacher Associates Network.

Science, Medicine, and Animals is recommended by the National Science Teacher's Association.


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