Introduction

Abstract

By the 1930s, chemical analyses of vertebrate tissues—chiefly muscle—and of isolated cells—chiefly red blood cells—had demonstrated a peculiar and puzzling asymmetry. Tissues and cells generally contained high concentrations of potassium ions (K⁺) relative to sodium ions (Na⁺); by contrast, the environments of these tissues and cells, such as the blood plasma, contained the opposite concentration ratio: high Na⁺/low K⁺. Meanwhile, studies on the changeable contents of tissues and cells suggested that a membrane, although not visible by the microscopy of that time, surrounded each cell. Such a membrane could then have different permeabilities to solutes such as Na⁺ and K⁺. And investigations of excitable tissues, such as nerve and muscle, also focused on Na⁺ and K⁺ contents, with the electrical activity explained by some in terms of varying permeabilities to ions.