The cell was defined 150 years ago

Anthony Hyman and Kai Simons recount how E. B. Wilson described a cell in 1896 as “the basis of the life of all organisms” (Nature 480, 34; 2011). But it was an almost-forgotten German biologist, Max Schultze, who 150 years ago laid an earlier foundation stone for cell biology by defining the cell in terms of what it contained rather than its boundary.

In an 1861 article, 'On muscle-particles and what we should call a cell' (Archiv für Anatomie, Physiologie und wissenschaftliche Medicin 1–27; 1861), Schultze rejects the definition of a cell put forward by Robert Hooke almost two centuries earlier.

On the basis of microscopic observations of sections of cork, Hooke in 1665 had introduced the term cell, after the Latin cella, for 'little room with a rigid wall'. Schultze argued that the existence of an enveloping wall, as found in plants, is not an essential criterion for defining a cell.

Schultze based his conclusion on his comparative studies of protoplasmic material from animal muscle tissue and from protozoans. From his observations of these soft, flexible, living systems, Schultze redefined the cell as a “naked speck of protoplasm with a nucleus” (see A. Reynolds J. Hist. Biol. 41, 307–337; 2008).

It could be argued that this more accurate protoplasm–nucleus description of the cell marked the origin of cell biology as a new scientific discipline, encompassing cells as evolving units of all extant and extinct forms of life.