Abstract
THE aqueous phase of body composition — the total body water and its solutes — includes as its prime component the great working mass of body cells, participating in energy exchange and substrate oxidation for work performance. The body-cell mass is surrounded, infiltrated and bathed by a second watery component, slightly smaller in volume, and concerned with the bulk movement of oxygen, carbon dioxide, metabolites and regulators, via the circulation: the extracellular fluid. Whatever other differences exist between these two reservoirs of body water, none is more clear cut than the fact that within cell water the predominant cation is . . .