Diffusion, perfusion and the exclusion principles in the structural and functional organization of the living cell: reappraisal of the properties of the `ground substance'

The thesis is presented that only within very small microdomains of the cell internum might diffusion operate in the sorting of molecular affinities. Much of cell metabolism is guided and controlled in rate by the speed with which molecules that have to interact encounter one another. What is clear, however, is that the cell does not have a single 'modus operandi' but has the choice of many different strategies, each of which can contribute in different proportion to the rate of ongoing activity. It is probably our own desire to simplify things and use the most (or more) probable strategy that confines our appreciation of the overall robustness of the cell as a 'survival machine'. The main operative process at any given time (perfusion, diffusion or whatever) has always to be considered very carefully in relation to the organisational structure of the cell, which can be transient and fickle but nevertheless has been seen as involving an extensive cytomatrix, a ground substance, within an aqueous environment in which the degree of water structuring is even more fickle.