Golden Age of Microbiology
As early as the sixth century BCE scholars wondered whether a disease was passed from person to person via tiny agents that could not be seen. However, no definitive investigation took place for centuries because researchers lacked the tools they needed to study microorganisms, or microbes, organisms too small to be seen without magnification. Initially, hand lenses provided enough magnification to see large, previously unknown unicellular eukaryotic organisms and stimulated further refinement of lenses that eventually lead to the development of microscopes with compound lenses.English physicist and chemist Robert Hooke paved the way for the study of cells (a word that he coined) with his book Micrographia, which was published in 1665. Hooke observed cork cells using a microscope. Around the same time, Dutch scientist Antonie van Leeuwenhoek built a microscope of his own design and used it to observe protozoa, unicellular organisms from the domain Eukarya, in water. This was the first observation made of still-living cells, as well as the first observation of living microbes. Later, van Leeuwenhoek also observed bacteria and documented his observations. His discoveries were published in the Royal Society of England's Philosophical Transactions in 1673, ushering in what is known as the Golden Age of Microbiology. Following van Leeuwenhoek's discovery, scientists flocked to the new scientific discipline of studying the tiny organisms only visible under magnification. In 1796, English physician Edward Jenner observed that survivors of cowpox were immune to smallpox infection. He took fluid from pustules on cows infected with cowpox, a virus closely related to human smallpox, and purposefully infected patients, which led to smallpox immunity. This conferred complete or partial immunity to the majority of the inoculated patients. Jenner did not identify the pathogen responsible for smallpox, but his use of inoculation to protect against infection was invaluable and resulted in his informal title as the "father of immunology." Vaccination, the technique of exposing people or animals to a form of a pathogen to develop immunity to it, is still in use today, although the methods have changed.
Foundations of the Germ Theory of Disease
2. The microorganism must be able to be isolated from a host and grown in pure culture.
3. Samples from the pure culture must be able to produce the disease when inoculated into a healthy, susceptible laboratory animal.
4. The microorganism must be isolated from the laboratory animal and shown to be identical to the microorganism isolated from the original host.