All these early claims about the existence of microorganisms were speculative and were not based on any data or science. Microorganisms were neither proven, observed, nor correctly and accurately described until the 17 th century. The reason for this was that all these early studies lacked the microscope. Antonie van Leeuwenhoek — was one of the first people to observe microorganisms, using a microscope of his own design, and made one of the most important contributions to biology.
Robert Hooke was the first to use a microscope to observe living things. Van Leeuwenhoek did not make the connection between these processes and microorganisms, but using a microscope, he did establish that there were forms of life that were not visible to the naked eye.
Lazzaro Spallanzani — found that boiling broth would sterilize it and kill any microorganisms in it. He also found that new microorganisms could settle only in a broth if the broth was exposed to the air.
He also did this in vessels with no filter at all, with air being admitted via a curved tube that prevented dust particles from coming in contact with the broth. Robert Hooke was the first to use a microscope to observe living things. Van Leeuwenhoek did not make the connection between these processes and microorganisms, but using a microscope, he did establish that there were forms of life that were not visible to the naked eye. Lazzaro Spallanzani — found that boiling broth would sterilise it and kill any microorganisms in it.
He also found that new microorganisms could settle only in a broth if the broth was exposed to the air. He also did this in vessels with no filter at all, with air being admitted via a curved tube that prevented dust particles from coming in contact with the broth. By boiling the broth beforehand, Pasteur ensured that no microorganisms survived within the broths at the beginning of his experiment.
This meant that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory instead. Louis Pasteur. His classification of bacteria into four groups based on shape sphericals, short rods, threads, and spirals is still in use today. Among other things Cohn is remembered for being the first to show that Bacillus can change from a vegetative state to an endospore state when subjected to an environment deleterious to the vegetative state.
His studies would lay the foundation for the classification of microbes and gave some of the first insights into the incredible complexity and diversity of microbial life. In , Robert Koch — established that microbes can cause disease. He found that the blood of cattle who were infected with anthrax always had large numbers of Bacillus anthracis. Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, and this caused the healthy animal to become sick.
He also found that he could grow the bacteria in a nutrient broth, then inject it into a healthy animal, and cause illness. Although these postulates cannot be applied in all cases, they do retain historical importance to the development of scientific thought and are still being used today.
Spontaneous generation is an obsolete body of thought on the ordinary formation of living organisms without descent from similar organisms. Typically, the idea was that certain forms such as fleas could arise from inanimate matter such as dust or that maggots could arise from dead flesh.
A variant idea was that of equivocal generation, in which species such as tapeworms arose from unrelated living organisms, now understood to be their hosts. Doctrines held that these processes were commonplace and regular.
Such ideas were in contradiction to that of univocal generation: effectively exclusive reproduction from genetically related parent s , generally of the same species. The doctrine of spontaneous generation was coherently synthesized by Aristotle, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia.
Today spontaneous generation is generally accepted to have been decisively dispelled during the 19 th century by the experiments of Louis Pasteur. He expanded upon the investigations of predecessors, such as Francesco Redi who, in the 17 th century, had performed experiments based on the same principles.
In summary, Pasteur boiled a meat broth in a flask that had a long neck that curved downward, like a goose. The idea was that the bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth quickly became clouded.
In detail, Pasteur exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths unless the flasks were broken open, showing that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth.
This was one of the last and most important experiments disproving the theory of spontaneous generation. Upon exposure to the outside environment, Pasteur observed the putrefaction of the food source bottom panel.
This strongly suggested that the components needed to create life do not spontaneously arise. Despite his experiment, objections from persons holding the traditional views persisted. Many of these residual objections were routed by the work of John Tyndall, succeeding the work of Pasteur.
Ultimately, the ideas of spontaneous generation were displaced by advances in germ theory and cell theory. Disproof of the traditional ideas of spontaneous generation is no longer controversial among professional biologists. His work also encouraged the belief that microorganisms were in the air and could cause disease. Pasteur postulated the germ theory of disease , which states that microorganisms are the causes of infectious disease. Pasteur's attempts to prove the germ theory were unsuccessful.
However, the German scientist Robert Koch provided the proof by cultivating anthrax bacteria apart from any other type of organism.
He then injected pure cultures of the bacilli into mice and showed that the bacilli invariably caused anthrax. The procedures used by Koch came to be known as Koch's postulates Figure. They provided a set of principles whereby other microorganisms could be related to other diseases.
The development of microbiology. In the late s and for the first decade of the s, scientists seized the opportunity to further develop the germ theory of disease as enunciated by Pasteur and proved by Koch. There emerged a Golden Age of Microbiology during which many agents of different infectious diseases were identified. Many of the etiologic agents of microbial disease were discovered during that period, leading to the ability to halt epidemics by interrupting the spread of microorganisms.
Then, after World War II, the antibiotics were introduced to medicine. The incidence of pneumonia, tuberculosis, meningitis, syphilis, and many other diseases declined with the use of antibiotics. Work with viruses could not be effectively performed until instruments were developed to help scientists see these disease agents. In the s, the electron microscope was developed and perfected.
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