Here is the detailed information on Germ Theory of Disease



There are two scientists behind the Germ theory: Louis Pasteur and Robert Koch. We now know that infectious diseases such as flu, chickenpox, and pneumonia are due to microscopic organisms like viruses and bacteria. Without this information, we could not have developed methods to treat and prevent these types of infections. However, understanding these is called the ‘germ theory’ of disease, which is a remarkable discovery.

Many scientists made research which caused the formulation of the germ theory. But, the scientific proof of this theory was achieved by two European scientists: Louis Pasteur, who was a Frenchman, and Robert Koch, a German.

The Birth of Pasteurization:

Louis Pasteur, a chemist by profession, while starting his research, focused on the study of crystals. In 1854, he was appointed the Head of the Science Faculty in Lille, during which he was influx with demands from the local wine industry to research the science of fermentation. This was for the first time, he discovered that this process was caused by a living organism, he called it ‘ferment’. This was a turning point in his career; he then began to apply his experimental methods to biological questions.

He had many questions in mind; what did the organism ‘ferment’ consist of, where did it come from, and many more. Other scientists of the time thought that these microorganisms appeared out of thin air, they called it the ‘spontaneous generation’ theory.

One opinion was that the microorganisms appeared from similar microscopic beings which were alike. Pasteur conducted a series of experiments that eventually resolved the debate.

One important test conducted by him made use of an unusual glass flask with a long, thin, bent tube attached to the neck. Pasteur called it a swan-necked flask. He used these flasks to boil liquids which killed the microorganisms in it. He then left it to cool. The design of the flask allowed this liquid to be in contact with the atmosphere, which prevented dust and dirt from entering it.

Pasteur tested a variety of liquids in the same way; including some liquids which are easily fermented. He discovered that none of them were fermented after being boiled. He concluded that both, the processes of fermentation and decay are caused by microorganisms that are present in the air; he also concluded that the microorganisms can be killed by the process of heating.

He applied this concept to the local industries in Lille; he developed the simplest way of preventing contamination in wine that was being caused by unwanted microorganisms. The process involved heating the wine to reach a temperature of about 60°C; this technique is now famous as pasteurization, a term coined after him. It is used in the production of many food products even today. It is also known as louis pasteur germ theory.

Proving a point:

The main task of matching the microorganism to the disease that they cause was to be taken up. Nearly ten years following the famous fermentation experiments by Pasteur, a German microbiologist called Robert Koch moved ahead with this task. He conducted his research in a small laboratory in his place, in the countryside near Berlin.

The first disease he started studying was anthrax, which was common among the farm animals around the place he lived. The anthrax bacterium was already discovered, but there was no proof that this bacterium was the reason behind the disease in the animals.

Koch collected samples of anthrax bacteria from the farm animals which died due to the disease. He used the sample to infect healthy mice. He carried a control experiment, by making use of the same method but he substituted the anthrax bacilli with blood of the healthy farm animals. The anthrax-infected mice developed the disease which resulted in their deaths and the control mice stayed healthy. It was evident that the anthrax bacteria caused the disease. He now had proof that the anthrax bacteria caused the disease.

The outcomes were published and recognized as it had reached consequences for microbiology. Based on this work, he initiated new ways to grow more pure samples of bacteria and stain them so they are seen under the microscope.

Koch is still known for the universal method to test if a bacterium causes a specific disease; it is called “Koch’s postulates”. By this process, he discovered the bacterium which caused tuberculosis and was a major killer of the 19th century. 

By 1900, the discoveries made by Pasteur and Koch, and the work of other scientists, led to the identification of about 20 disease-causing micro-organisms in two decades.

Frequently Asked Questions:

  1. How many postulates were proposed by Robert Koch?
    Robert Koch proposed four postulates to identify a particular micro-organism causing a specific disease.
  1. Who is the “Father of Bacteriology”?
    Louis Pasteur is famous as the Father of Bacteriology.


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