cytology, in biology, the study of the structure of all normal and abnormal components of cells and the changes, movements, and transformations of such components. The discipline includes cytogenics, cytochemistry, and microscopic anatomy, which involve investigations employing various microscopes, such as light, phase, interference, and electron microscopes. Cells are studied directly in the living state (phase microscopy) or are killed (fixed) and prepared for viewing (embedded, sectioned, and stained) on light or electron microscopes.

Study of cells. Its earliest phase began with Robert Hooke's microscopic investigations of cork in 1665, during which he introduced the term cell to describe dead cork cells. Mathias Jacob Schleiden (in 1838) and Theodor Schwann (1839) were among the first to state clearly that cells are the fundamental units of both plants and animals. This pronouncement (the cell theory) was confirmed and elaborated by a series of discoveries and interpretations. In 1892 Oscar Hertwig (1849–1922) suggested that processes at the organism's level are reflections of cellular processes, thus establishing cytology as a separate branch of biology. Seealso physiology.

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