[Characteristics of artefacts following fixation with glutaraldehyde and osmium tetroxide]

In the myocard and kidney of rats perfused with Karnovsyk's solution for 5--10 minutes then fixed for two more hours and postfixed in 1 per cent solution of osmium tetroxid in Millonig buffer, characteristic electrondense granules were observed. The structure of the organ appeared to be normal. Although the granules appeared to be diffuse, they presence was most marked on the membranes, on the surface of erythrocytes and in the pinocytic vacuoles both on counterstained slides and on those of without counterstaining. When postfixation was carried out with osmium-tetroxide solved in Veronal buffer artefacts did not occur. To avoid artefacts fixation in glutaraldehyd should not be followed by a postfixative containing phosphate buffer.