Hans and Zacharias Janssen were the inventors of the first compound microscope.
English physicist Robert Hooke looked at a sliver of cork through a microscope lens and noticed some "pores" or "cells" in it. Robert Hooke believed the cells had served as containers for the "noble juices" or "fibrous threads" of the once-living cork tree. Hooke was the first person to use the word "cell" to identify microscopic structures when he was describing cork.
Francesco Redi, an Italian physician, did an experiment to determine if rotting meat turned into flies. He found that meat cannot turn into flies and only flies could make more flies. This was an important experiment because it helped to disprove the theory of spontaneous generation. It did this by showing that the rotten meat did not turn into flies and only flies could make more flies.
Anton Van Leeuwenhoek
Anton Van Leeuwenhoek was the first to see and describe bacteria.
From 1745 to 1748 John Needham, a Scottish clergyman and naturalist, showed that soup that had been exposed to the air contained many micro organisms. He claimed that there was a "life force" present in the molecules of all inorganic matter, including air and the oxygen in it, that could cause spontaneous generation to occur.
From 1765 to 1767 Lazzaro Spallanzani, an Italian abbot and biologist, tried variations on John Needham’s soup experiments. He determined that soup in a sealed container was sterile and that micro organisms that caused the soup to spoil had entered from the air.
Robert Brown discovered the cell nucleus.
Theodor Schwann and Matthias Jakob Schleiden created what is called the cell theory. The cell theory states that all living things are made up of one or more cells.
Schwann proposed that all organisms are composed of cells. Together with Matthias Schleiden he formulated the cell theory of life. Schwann also discovered the cells, now known as Schwann cells, that form a sheath surrounding nerve axons and conducted experiments that helped disprove the theory of spontaneous generation.
Rudolf Virchow published his now-famous aphorism omnis cellula e cellula ("every cell stems from another cell"). He also stated that all diseases involve changes in normal cells.
Louis Pasteur did an experiment that determined that soup exposed to air only spoiled if the air was not filtered or if the flask containing the soup had an opening that allowed micro organisms to get to the soup. If he used flasks with long S-shaped necks the micro organisms that spoiled the soup settled in the neck and did not spoil the soup.