The First observations:
One of the most important discoveries in the history of Microbiology occurred in 1665 with the help of a relatively crude microscope. After observing a thin slice of cork, an English man, Robert Hooke, reported to the world that life's smallest structural units were "Little boxes" or "Cells" as he called them. This discovery marked the beginning of Cell theory. Though Hooke's microscopes were capable of showing cells, he lacked the staining techniques that would have allowed him to see the microbes clearly. The Dutch merchant, Anton Van Leeuwenhoek, was probably the first to actually observe living microbes through magnifying glasses. Between 1673 and 1723, he wrote a series of letters, to the Royal Society of London, describing the "Little animalcules" he saw through his simple, single-lens microscope. He also made detailed drawings of them he found in rainwater, his own feces, and in material he scraped from his teeth.
The Spontaneous Generation:
Until the second half of the 19th century, many scientists and philosophers believed that some forms of life could arise spontaneously from non living matter. They called this hypothesis as "The spontaneous generation". Not much more than 100 years ago, people believed that toads, snakes and mice could be born of moist soil; that flies could emerge from manure; and that maggots could arise from decaying corpses. A strong opponent for spontaneous generation, the Italian physician Fransesco Redi, set out in 1668 to disprove the theory by demonstrating that maggots did not arise spontaneously from decaying meat.