Abstract We go backward in time here, but forward in understanding. The preceding chapter has given mixed reviews to bio-logical science around the turn of the century. There was brilliant progress in some areas, but neglect and confusion in relation to cell membranes. Charles Ernest Overton was an exception, someone whose comprehension of cell membrane composition and function was never confused. On the contrary, “prescient ” would in retrospect be a good description. Overton ’s work is outside the main theme of this book, in the sense that he himself never experimented with films of oil on water surfaces, but it establishes a physiological context and shows that some areas of physiology were crying out for just the kind of insight that surface film measurements could provide.