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further developed the compound microscope, including the use of the iris diaphragm. Hooke kept a detailed record of his observations.
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Described unicellular organisms from his observations of a drop of stagnant rainwater as 'animalcules'.
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Discovered bacteria from his observations of salvia
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Noted that the cells of orchids he was observing under the microscope contained a structure inside the cell. He called this the 'nucleus'.
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Formulated the cell theory that all living matter is composed of small units called cells
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Stated that 'where a cell exists there must have been a pre-existing cell, just as the animal arises only from an animal and the plant only from a plant.
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Built the first electron microscope. Transmission electron microscope. Transmission electron microscopes and scanning electtron microscopes were developed in the following decades. Details of internal cell structures were revealed.
