Throughout history, people have created explanations for disease. Some have held that disease has supernatural causes. Others have used careful observation and reasoning to propose natural causes.
Learning Goal 2bc
French chemist Louis Pasteur demonstrated that spoilage and fermentation occur when microorganisms enter from the air, multiply rapidly, and produce waste products. He showed that spoilage could be avoided by keeping germs out or by destroying them with heat.
Learning Goal 2d
German physician Robert Koch used a set of criteria to evaluate whether specific germs caused anthrax. He and others then used the criteria to identify the germs that cause numerous other diseases.
Learning Goal 3
Pasteur found that infection by disease organisms (germs) caused the body to build up an immunity against subsequent infection by the same organisms. He then produced vaccines that would induce the body to build immunity to a disease without actually causing the disease itself.
Learning Goal 4
Investigations of the germ theory by Pasteur, Koch, and others in the 19th century firmly established the modern idea that many diseases are caused by microorganisms. Acceptance of the germ theory has led to changes in health practices.
Learning Goal 5
In medicine, as in other fields of science, discoveries are sometimes made unexpectedly, even by accident. But knowledge and creative insight are usually required to recognize the meaning of the unexpected.
Learning Goal 6
The improvement of microscope lenses and design in the 1600s led to discovery of a vast new world of microscopically small plants and animals, among them bacteria and yeasts. Because most microorganisms do not cause disease, they are present even in healthy individuals. Therefore, the discovery of those microorganisms did not suggest what effects they might have on humans and other organisms.
Learning Goal 7
Current health practices emphasize sanitation, the safe handling of food and water, the pasteurization of milk, isolation, and aseptic surgical techniques to keep germs out of the body; vaccinations to strengthen the body's immune system against subsequent infection by the same kind of microorganisms; and antibiotics and other chemicals and processes to destroy microorganisms.
Learning Goal 8
After the discovery of germs, biologists turned to the identification and investigation of microorganisms, discovering thousands of different bacteria, viruses, yeasts, and parasites and gaining a deeper understanding of the interactions between organisms.