<P> With the development of radioactive tracers, it was shown that cells are not impermeable to Na . This was difficult to explain with the membrane barrier theory, so the sodium pump was proposed to continually remove Na+ as it permeates cells . This drove the concept that cells are in a state of dynamic equilibrium, constantly using energy to maintain ion gradients . In 1935, Karl Lohmann discovered ATP and its role as a source of energy for cells, so the concept of a metabolically - driven sodium pump was proposed . The tremendous success of Hodgkin, Huxley, and Katz in the development of the membrane theory of cellular membrane potentials, with differential equations that modeled the phenomena correctly, provided even more support for the membrane pump hypothesis . </P> <P> The modern view of the plasma membrane is of a fluid lipid bilayer that has protein components embedded within it . The structure of the membrane is now known in great detail, including 3D models of many of the hundreds of different proteins that are bound to the membrane . These major developments in cell physiology placed the membrane theory in a position of dominance and stimulated the imagination of most physiologists, who now apparently accept the theory as fact--there are, however, a few dissenters. (citation needed) </P> <P> In 1956, Afanasy S. Troshin published a book, The Problems of Cell Permeability, in Russian (1958 in German, 1961 in Chinese, 1966 in English) in which he found that permeability was of secondary importance in determination of the patterns of equilibrium between the cell and its environment . Troshin showed that cell water decreased in solutions of galactose or urea although these compounds did slowly permeate cells . Since the membrane theory requires an impermanent solute to sustain cell shrinkage, these experiments cast doubt on the theory . Others questioned whether the cell has enough energy to sustain the sodium / potassium pump . Such questions became even more urgent as dozens of new metabolic pumps were added as new chemical gradients were discovered . </P> <P> In 1962, Gilbert Ling became the champion of the bulk phase theories and proposed his association - induction hypothesis of living cells . </P>

Who suggested that all cells come from preexisting cells by the process of cell division