Germ Theory Of Disease

In medicine, the theory that states the cause of diseases to be microorganisms is called germ theory or the germ theory of disease. The English, Joseph Lister, German Robert Koch and French chemist Louis Pasteur are credited with the development of the germ theory of disease. The Louis Pasteur germ theory came into being when the French chemist showed processes such as putrefaction and fermentation occur due to the presence of organisms which thrive in air.  The surgical practice was revolutionised by Lister in the 1860s by the use of carbolic acid to exclude germs. This prevented putrefaction. In 1880 these organisms were recognised to cause cholera and T.B.

History Of Germ Theory Of Disease

Louis Pasteur gave the germ theory. The Miasma theory was prevalent and widely accepted until the germ theory came into being. During the 17th century, Francesco Redi proved the spontaneous generation theory. The spontaneous generation theory was another archaic theory. The spontaneous generation theory states living things arise from non-organic matter.  The spontaneous generation theory was proved with the help of experiments that involved keeping meat and egg in three different jars. The first jar was kept uncovered, and it was found that maggots infested the egg and meatloaf. The second jar was sealed tightly, and no  more worms were found. The third jar was concealed with gauze, and it was seen that no worms were present inside but on the top of the gauze. This caused Redii to disagree with the theory of spontaneous generation. 

Experiments Supporting Germ Theory Of Disease

Louis Pasteur conducted experiments to prove the germ theory. A freshly boiled broth was kept exposed to air under different conditions. The vessel contained a growth medium to restrict the entry of particulates. The growth medium was kept without a filter in a vessel and was left exposed to the room air. A vessel containing a growth medium was also exposed to room air with the help of a long tube to prevent dust particles from entering. Louis observed that the broth which had been left exposed to air without a filter led to the development of microorganisms. John Snow, Ignaz Semmelweis and Robert Koch also contributed to the germ theory of disease. 

Germ Theory Of Fermentation 

The experiments which Louis Pasteur conducted led to the conclusion that microbes are present in the air which cause the fermentation broths to get spoiled. He also carried out further processes of fermentation in compounds like butyric acid, lactic acid, and others. This led to the development of the germ theory of fermentation. This theory states that specific microbes are responsible for bringing about the process of fermentation. The theory was later expanded to include human as well as animal diseases. Pasteur observed that diseases are also caused by these microbes within or outside the body. The germ theory also led to the postulation of germ theory of disease and protection. It was recognised that the immune system had two parts which provided protection from certain types of pathogens.

Koch's Postulates

It was Robert Koch who postulated that a specific kind of organism causes a particular type of disease. Anthrax was isolated from a disease host, and Koch conducted experiments on it. Certain postulates were then formed which were made based on four rules. First, the microorganism must be detected in the diseased person and not the healthy person. Second, the microorganism must be isolated from the person and then cultured. Third, the cultured microbe should, in turn, cause the same disease when it is introduced in a person who is healthy. Finally, the microorganism must be isolated once again from the host who is part of the experiment, and it should be the same as the original host. 

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Solved Examples

1. Who Proposed the Germ Theory of Disease?

Ans: Louis Pasteur proposed the germ theory in the 1850s when he conducted experiments that proved the presence of microorganisms and their role in fermentation and other processes.

Did You Know? 

"Germ" may not just mean a bacterium but can refer to any microorganism or pathogens that are non-living but may become a cause of disease. Examples of such pathogens are prions, or viroid, protists, viruses. Diseases that are caused by such pathogens are called infectious diseases. Although a pathogen may become the principal cause of a disease, other factors need to be considered. Hereditary and environmental factors often have influence over the severity of the disease.

FAQ (Frequently Asked Questions)

1. Explain the Germ Theory of Disease.

Ans: The currently accepted scientific theory that explains many diseases is the germ theory of disease. This theory states that germs, also called pathogens, which are microorganisms, are responsible for causing various diseases among individuals. They are called microbes because their size is so small that they are imperceptible without the use of magnification or microscope. These organisms invade other plants and animals to grow and reproduce, which causes diseases in their hosts. This theory replaced the earlier Miasma theory that dominated the theory of disease transmission before. Robert Koch and Louis Pasteur are mainly responsible for the development of this theory.

2. How did Koch and Pasteur Contribute to the Germ Theory?

Ans. In 1861, Pasteur published the germ theory after experimentation and proved that bacteria caused diseases. Robert Koch in Germany also began pursuing the same idea and began isolation of specific bacteria causing various diseases like cholera. Koch discovered antibodies helped in fighting pathogens and hence ailments. However, it was the French Louis Pasteur who came up with the first vaccines since Jenner, with vaccines for rabies, anthrax and chicken cholera. Koch was a pioneer in using stains to observe bacteria more clearly under a microscope. His assistant, Julius Petri, devised the use of the Petri dish to help in this process.