Circulation in the Cell

THE rapidity with which cells respond to the presence of solutes or suspensoids in their immediate vicinity has made the problem of the permeation of the cell a matter of major interest, but the question of how substances are distributed once they have entered the cell has not commanded nearly so much attention. I shall propose that the rapid distribution of nutrilites and reactants within the microcosm of the protoplast (that is, inside the plasma membrane) is effected by an active circulatory apparatus, by which fluid is forced through pores by hydrostatic pressure, somewhat analogous to the apparatus by which a corresponding circulatory distribution is effected in the macrocosm of the animal body. The concept of the cell-circulation is based almost exclusively on work with the yeast cell; but there are many indications which suggest that the conclusions are generally applicable. Many cellular membranes, which were previously thought to be intact, have been shown by electron microscopy to possess systems of pores. Pores which have been first observed by electron microscopy have been afterwards observed by direct light microscopy.