History of the Cell: http://www.ifcbiol.org/Dotcweb/index.html
Waddington (1968), for all his outstanding contributions to biology in the middle and later part of the 20th century, failed to mention the cell as a concept in his paper 'Main biological conceptions'. The cell to him was a reality, an object for investigation, a fact. Only such a fundamental notion can so present itself to one's consciousness that one considers it "something that goes without saying" - an objective phenomenon, like the sea or the stars. But the cell, a concept that took many years to emerge, was by no means an "obvious fact" to all concerned at the outset. The cell concept probably had a no less painful birth than many other concepts that now are considered fact, such as the heliocentric nature of our solar system (Galileo, 1612-32). That birth (not literally of the cell, but of the concept of the cell) has been the subject of much intensive research, compiled as one fascinating, highly erudite but complex treatise in Harris (2000). We might all concede that there is a "unit of life", and might be prepared to call it a cell, but there is no precise, unambiguous and generally agreed definition of "a cell".