Some observations on the relative dehydration rates of negative stains and biological objects

In an attempt to explain the possible mechanism of negative staining a series of experiments are described in which the relative drying rates of two commonly used negative stains and two biological specimens were measured. Turnip yellow mosaic virus and phosphatidyl-L-serine were used to represent biological specimens and their dehydration rates were measured against potassium phosphotungstate or ammonium molybdate after tritiated water had been added to the solutions containing protein, lipid, negative stains or mixtures of both. From these experiments it was possible to demonstrate that the protein or lipid retains water for longer periods than the negative-staining material. The results are in agreement with an earlier proposal that some negative stains set in a rigid 'glass' and thus preserve the biological structures before the latter are completely dehydrated either in air on the supporting films, or when finally dried in the vacuum of the electron microscope.