The germ theory of disease states that many diseases are caused by microorganisms such as bacteria, viruses, protozoa, or fungi. These diseases are caused by the growth and replication of microorganisms.
The germ theory of disease was devised by Louis Pasteur. He also performed various experiments to demonstrate the relationship between microorganisms and diseases.
History of Germ Theory of Disease
Until germ theory was accepted, the Miasma theory was prevalent which stated that the disease was caused by the decomposition of organic matter which released poisonous air carrying disease-causing agents.
During the 1600s, the concept of spontaneous generation of diseases was proved wrong by the experiments performed by Francesco Redi. In his experiments, he placed a loaf of meat and an egg in three distinct jars:
- The first jar was left uncovered. It was observed that the maggots covered the meatloaf and the egg.
- The second jar was sealed tightly with a lid. No maggots were observed.
- The third jar was covered only with gauze. It was observed that no maggots were inside the jar but were present on the top of the gauze.
Thus Redi refuted the concept of spontaneous generation.
Anton Van Leeuwenhoek, the first microbiologist to observe the microorganisms under a microscope, also supported the germ theory of disease. Richard Bradley later postulated that diseases were caused by microorganisms which were later supported by Marcus Antonius Von Plenzic.
Also read: Microbes and Disease
Experiments in support of Germ Theory of Disease
The freshly boiled broth was exposed to air under the below-mentioned conditions:
- The growth medium was kept in a vessel containing a filter to prevent the entry of particulates.
- The growth medium was kept in a vessel without a filter and was exposed to room air.
- The growth medium was kept in a vessel and was exposed to room air through a long tube to prevent the entry of any dust particles.
Pasteur observed that the broth which was exposed to the room air without a filter developed microorganisms. In addition to him, Ignaz Semmelweis, John Snow and Robert Koch are also some important contributors to the germ theory of disease. However, the experiments conducted by Louis Pasteur and Robert Koch provided accurate prooves in support of the germ theory of disease.
Germ Theory of Fermentation
The experiments performed by Louis Pasteur made him conclude that the microbes present in the air spoiled the fermentation broths. He performed various other fermentation processes for compounds like lactic acid, butyric acid, etc. Thus he postulated the germ theory of fermentation which states that every fermentation process is acted upon by certain microbes.
He further extended the theory to animal and human diseases. He observed that the diseases are also caused by the germs present in or around the body.
Also read: The Origin Of Life On Earth
Robert Koch stated that a specific disease is caused by a particular organism. He isolated anthrax from a diseased host and conducted experiments on it. He then formulated certain postulates that were based on the following four rules:
- The microorganism must be identified only in the diseased individual and not in the healthy individual.
- The microorganism should be isolated from the diseased individual and cultured.
- The cultured microorganism should cause disease when introduced to a healthy individual.
- The microbe should be isolated again from the experimental host and should be identical to the original organism.
The final proof of the germ theory of disease came when Louis Pasteur grew anthrax bacillus in culture. He extracted blood from a sheep suffering from anthrax and placed it in sterile culture, and allowed the bacilli to grow. He repeated the process until all the original cultures were eliminated from the final dish. The final culture when injected into the sheep produced anthrax. This proved that the bacillus was responsible for the disease.
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