Early osmotic history of the plasma membrane.

The following topics, amonig others, aire conisidered: Pfeffer 's hypothesis of an invisible plasma membrane, to account for similarities in the osmotic behavior of plant cells and artificial osmometers; early doubts as to the reality of Pfeffer's membrane; denial by colloid chemists of the existence of plasma membranes because of the supposed failure of cells to obey osmotic laws; demonstrations of thin, external cell membranes by electrical and micromanipulative methods; use of the plasma membranie in the matheniatical treatment of cell permeability; the niature of so-called "'perfect osmometers"'; the erytbrocyte as anl osmometer; hemolytic evideiece of the existenice of an erythrocyte membraine.