Singer and Nicholson (1972) proposed the fluid mosaic model of cell membrane. According to this model cell membranes are quasifluid with a viscous lipid bilayer having mosaic of proteins on the surface and inside. Robertson (1959) proposed the unit membrane model for cell membrane. It states that all biomembranes have a trilaminar structure with an electron transparent lipid bilayer lying sandwithched between electron dense protein layers. Danielli and Davson states that in plasma membrane a double phospholipid layer is surrounded on the either side by a layer of hydrated globular proteins or P−L−L−P. Huxley (1868) called the protoplasm as physical basis of life.