Osmotic Pressure of Fixing Solutions

Abstract

IT has long been the custom in many laboratories to make up certain fixatives in saline solutions, but the value of this practice has recently been questioned¹ on the ground that the osmotic pressure of most fixatives, as determined by the freezing point, is already greater than that of the tissues. However, since the particles of the fixative are presumably able to pass more or less freely across the surface membranes of the cells, it seems likely that they do not produce any effective osmotic pressure. If this is so, then the freezing point of a fixing solution is no guide to its physiological osmotic pressure. Further, it is possible that the addition of salts to fixatives is necessary to prevent the distortion which would result from the fact that the particles of fixative differ from those of the tissue fluids in mobility and electrostatic charge.