Because almost all cells are microscopic, knowledge of the component cell parts increased proportionately to the development of the microscope and other specialized instruments and of allied experimental techniques. Among those who contributed to early knowledge of cells through their use of the microscope were Antony van Leeuwenhoek, Robert Hooke, and Marcello Malpighi. In the 19th cent. Matthias J. Schleiden and Theodor Schwann developed what is now known as the cell theory. The theory was widely promoted after the pronouncement by Rudolf Virchow in 1855 that “omnis cellulae e cellula” [All cells arise from cells]. The study of cell structure came to be called cytology and that of tissues histology. In the 20th cent. appreciation of the biochemistry of the cell has flourished, along with a better understanding of its structure; cell biology now integrates both chemical and structural information.
