Scientists and their contributions to Germ Theory
The germ theory is a fundamental tenet of medicine that states that microorganisms, which are
too small to be seen without the aid of a microscope, can invade the body and cause certain
diseases. Until the acceptance of the germ theory, people believed that one became ill because
of foul odors from sewage or bad air. With the invention of the microscope and the
improvement of it by Robert Hooke and Anton van Leeuwenhoek in the seventeenth century
gave scientists the means to observe these microorganisms.
Despite this ability they still believed in spontaneous generation, a belief that living organisms
develop from non-living matter. However, Francisco Redi demonstrated that decaying meat in a container covered with
a cloth did not produce maggots.
In the 1700’s English physician Edward Jenner noticed that treating healthy people with pus from
individuals suffering from cowpox protected them from the terrible effects of smallpox without
actually contracting the more deadly form of smallpox. This discovery revolutionized the practice of
giving vaccines which humans still benefit from today.
The debate over the germ theory continued however. In 1848, Ignaz Semmelweis discovered that fatal
infections that occurred in maternity hospitals in Europe could be prevented with simple hand washing.
He ordered medical students to wash their hands in chlorinated lime water and significantly decreased
the infection rate.
The argument took an important turn in 1857 when French chemist Louis Pasteur discovered the diseases of wine and
beer. He suggested to the brewers that they heat their product enough to kill bacteria but not yeast in process call
pasteurization. Pasteur also conducted experiments with flasks that contained boiled beef broth. He filled flasks with
the broth and sealed them. The sealed containers remained free of bacteria while the open flasks were contaminated
within a few days. He then used long neck flasks bending them into S-shaped curves. Even months after cooling, the
uncapped flasks remained uncontaminated. Pasteur explained that the curved neck trapped airborne microorganisms
before they could contaminate the broth.
The notion of spontaneous generation received another blow in 1858, when Rudolf Virchow introduced the cell theory
which states:
1. All living things are composed of cells
2. Cells are the basic units of structure and function in living things
3. All cells are produced from other cells
It was not until 1876 that German physician Robert Koch proved that bacteria can cause
diseases. Koch showed that the bacterium Bacillus anthracis was the cause of anthrax
and discovered the organism that causes tuberculosis. He developed a guideline for
determining the cause of infectious diseases now known as Koch’s postulates which
states:
1.
The organism must be present in every case of the disease.
2.
The organism must be isolated from a host with the corresponding disease and
grown in pure culture.
3.
Samples of the organism removed from the pure culture must cause the
corresponding disease when inoculated into a healthy animal
4.
The organism must be isolated from the inoculated animal and identical to the
original organism isolated from the original host.
Koch’s postulate introduced the “Golden Era” of medical bacteriology isolating the
causes of typhoid fever, diphtheria, pneumonia, tetanus, meningitis, gonorrhea, and
many others.
In 1928 Sir Alexander Fleming accidently discovered that the Penicillium mold was killing the
bacteria Staphylococcus that he was studying. However, it was not until the 1940’s that Howard
Florey and Ernst Chain were able to create a powdery form of Penicillin and create it into a
medicine. This lead to a mass production and distribution of penicillin, which in turn lead to a
bacteria evolving and becoming resistant to the medicine.
Starting with knowledge of bacteria spreading, scientists also discovered other pathogens. With the
invention of even bigger and better microscopes even more knowledge was gained about the smallest of
organisms (even though scientists do not consider them “alive”) such as viruses and prions.
On a separate sheet of paper answer the following questions: Remember to answer using complete sentences.
1.
2.
3.
4.
5.
What is spontaneous generation?
Explain Redi’s experiment.
What other product do we pasteurize that many drink every day?
Give the modern addition to the cell theory.
After reading the above and seeing how each invention and observation of various scientists helped discover the
germ theory, which scientist(s) best illustrates the importance of each of the following and why:
A. Independent research
B. Replication of results
C. Collaborative efforts among scientists
D. Recent improvements in the scientific method.
6. What invention during World War II further helped mankind in their battle with pathogens?