SENSORIMOTOR NEUROLOGY

tissue (e.g. distilled water, alkali) increase the permeability, as shown by the decrease in polarizability. This is a reversible process, as indicated by the effect of some acids and of hypertonic salt solutions after previous swelling of the brain. These experiments support the view that pathological processes which call forth swelling of the brain produce an impairment of the cellsurfaces in that their density is lowered. The transitory increase in permeability of the cell-surfaces, which is, according to modern theories of excitation, an essential part of the excitation process, is thus facilitated, and the threshold of the cells for metabolic or other stimuli is lowered. This explains the mechanism by which swelling of the brain increases convulsive reactivity.