The pH of this buffer is 7.4 (0.1M); the osmolarity is 440 mosmols, so this buffer is hypertonic to most body fluids. Millonig recommended to use this buffer for the fixation of very hydrated tissues with osmium tetroxide. For marine organisms, a higher concentration of sodium chloride (3%) is recommended. We supply it in a double strength (0.2M), pH 7.4. Dilution is needed before use.