Microbiology

Microbiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes eukaryotes such as fungi and protists, and prokaryotes such as bacteria and certain algae. Viruses, though not strictly classed as living organisms, are also studied.Microbiology is a broad term which includes many branches like virology, mycology, parasitology and others. A person who specializes in the area of microbiology is a microbiologist.
Although much is now known in the field of microbiology, advances are being made regularly. We have probably only studied about 1% of all of the microbe species on Earth.Thus, despite the fact that over three hundred years have passed since the discovery of microbes, the field of microbiology could be said to be in its infancy relative to other biological disciplines such as zoology, botany and entomology.

History
Pre-Microbiology
The existence of microorganisms was hypothesized for many centuries before their actual discovery in the 17th century. The first theories on microorganisms was made by Roman scholar Marcus Terentius Varro in a book titled On Agriculture in which he warns against locating a homestead in the vicinity of swamps:
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...and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases.
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This passage seems to indicate that the ancients were aware of the possibility that diseases could be srpead by yet unseen organisms.
In The Canon of Medicine (1020), Abū Alī ibn Sīnā (Avicenna) stated that bodily secretion is contaminated by foul foreign earthly bodies before being infected.He also hypothesized on the contagious nature of tuberculosis and other infectious diseases, and used quarantine as a means of limiting the spread of contagious diseases.
When the Black Death bubonic plague reached al-Andalus in the 14th century, Ibn Khatima hypothesized that infectious diseases are caused by "minute bodies" which enter the human body and cause disease.
In 1546 Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact or even without contact over long distances.
All these early claims about the existence of microorganisms were speculative in nature and not based on any data or science. Microorganisms were neither proven, observed, and correctly and accurately described until the 17th century. The reason for this was that all these early inquiries lacked the most fundamental tool in order for microbiology and bacteriology to exist as a science, and that was the microscope.