 The characterization of protoplasm as just a viscous substance existing on its own was complicated by the identification of the cell membrane as a structure distinct from the cell wall and, as discussed below, of membrane-bound organelles. In the end, most biologists acquiesced in some version of Schultze’s (1861: 11; as translated by Hall, 1951: 451) compromise position that raised protoplasm to be one defining feature of cells when he defined a cell as “a lump of protoplasm inside of which lies a nucleus”. Those who adopted such a compromise position often invoked a metaphor, originating with Raspail, according to which the cell is “a kind of laboratory within which all tissues organize and grow” (1843: 28; as translated by Harris, 1999: 32). The laboratory metaphor encouraged attempts to develop chemical explanations for all the reactions occurring in cells. There were a number of variants on this theme. Unger analogized the plant cell with a “mächtige chemische Werkstätte” (powerful chemical workshop) (1851: 23) and Virchow stated that “starch is transformed into sugar in the plant and animal just as it is in a factory” (1858: 107). 