Abstract
In the preceding articles of this series1 we have discussed in detail some of the factors that underlie alterations in capillary permeability. We have emphasized that the endothelial cell of the capillary wall, quite apart from any adventitious muscular elements, is as every cell possessed of the property of changing the state of the cell membrane, becoming either more or less permeable as the case may be. This change is associated by coincident changes in the caliber of the capillary, for the cell membrane that is permeable limits a cell that is softer and less rigid; such cells when forming a tube (as a capillary) will be more readily pushed and stretched by any force on the inside of the tube. This leads to the dilation of the capillary. Such changes in the cell membrane depend (a) on the hydrogen ion concentration of the tissues and fluids concerned; this in