Control of body fluid volume: Some observations and a hypothesis

Conclusions based on observations of the changes in fluid intake and output and body weight made on 265 patients are reviewed. These patients were suffering from conditions in which there was a disturbance of body fluid volume regulation. On the basis of these observations a hypothesis depending on the concept of “open” systems is developed and discussed. This hypothesis envisages the fluid storage of the body as a continuous flow system with a control mechanism sensitive to changes in both volume and osmotic pressure of some part of the stored fluid. Some applications of this hypothesis are considered.