In the 1890s, Ernest Overton, a physiologist (and, incidentally, a cousin of Charles Darwin), immersed a variety of cells in hundreds of solutions containing various substances. Chemicals soluble in oil tended to enter the cell, he noted, while those insoluble in oil could not get in. The cell membrane must be an oily layer, Overton concluded, although he could not quite explain how a substance such as an ion or sugar, insoluble in fats, might enter or leave the cell.
