history of the membrane discovery
Robertson found wide occurrence of such trilaminar composition in most of the membranes of cellular organelles and in 1959, he propounded the concept of the "unit membrane". A unit membrane has the protein-lipid-protein arrangement. In 1938 Harvey and Danielle produced a hypothetical model of the plasma membrane which has shown a biomolecular lipid structure sandwiched by two layers of protein molecules. The electron microscope studies have confirmed this protein-lipid-protein arrangement in the plasma membrane. The trilaminar nature of plasma membrane has been proposed by Danielli and Davson in 1935 by certain indirect evidences.