Almost one hundred years ago, Cohn (1872) suggested that the
resistance of bacteria to attack by acids and alkalies was due to the
presence of a rigid structure surrounding the cell. The phenomenon of
plasmolysis, first observed twenty years later by Fischer (1891), produced
the first visual evidence for a cell wall. During plasmolysis the cytoplasm
loses water and retracts from an apparently rigid cell wall. The suggestion
that the retracted cytoplasm is itself surrounded by a membrane respon￾sive to osmotic changes followed naturally from Fischer’s observations.
Although some evidence for this membrane was obtained from observa￾tions with the light microscope, conclusive visual evidence came only
with the advent of electron microscopy and the allied thin-section
techniques (Kellenberger and Ryter, 1958; Glauert, 1962). This mem￾brane has been variously termed a “cytoplasmic membrane”, a “plasma
membrane”, a “protoplast membrane” and more recently a “plasma￾lemma”. In this review it is proposed to use the term cytoplasmic
membrane.