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The Cell Theory
What level of complexity is necessary for life?
Aristotle (384 - 322BC)
From the C17th microscopists discovered tissues were made of cells (Hooke 1665 and Leeuwenhoek 1677).
Research in the C18th and C19th showed that tissues were made of cells and that the cells of a particular tissue had a common structure.
Xavier Bichat (1771 1802): An organ is composed of different tissues and several organs can be grouped together as an organ system (e.g. the digestive system).
Purkinje (1835) Observed a fertilised hen's egg (a single cell) could develop into an embryo (many specialised cells in a compact mass).
C19th botanists showed that plant tissues consist of many different types of cells.
The Cell Theory
Matthias Schleiden (1838) working on plants and Theodor Schwann (1839) working on animals came to the same basic conclusion: ...The cell is the basic unit of living tissue.
The cell is an autonomous unit ("a citizen") grouped together to form an organism ("the society").
Rudolf Virchow (1858) a pathologist noted that all cells come from pre-existing cells. A fact that was particularly clear when studying the growth of tumours.
The Organismal Theory
The counter argument to the cell theory developed during the later part of the C19th.
Reichert a morphologist: Argued that an organism has a structured plan.
Strasberger a cytologist: Cells are connected in an organism sometimes by cytoplasmic bridges (plant cell plasmodesmata).
Sherrington and Pavlov neurophysiologists: Cells communicate with one another and they are co-ordinated in their actions.
Cell Structure and Microscopy
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