CHEMICAL FIXATIVES FOR ELECTRON MICROSCOPY

Abstract

This chapter discusses the chemical fixatives for electron microscopy. The following fixatives have been tried on rat liver tissue: a standard osmium tetroxide solution; pure melted osmium tetroxide; strong osmium tetroxide solutions in carbon tetrachloride, acetone, pyridine, or glycerol; aqueous solutions of potassium, calcium, barium, or zinc permanganate; formaldehyde with or without an osmium post-fixation; and acrolein with or without an osmium post-fixation. Concentrated acrolein was used as a substitution fluid in a freeze-substitution technique when fixing mussel gills. The chapter describes the results of these fixation experiments and provides a short review of some other fixation methods. The variable staining reactions of osmium tetroxide with different techniques are of particular interest. Some of the fixatives tried give a higher contrast than is encountered after the standard osmium fixation and in all cases, the contrast is high enough to permit work on unstained sections. From a cytological point of view, the calcium permanganate fixation gives a more varied and interesting picture of the cytoplasm than the other permanganate fixations. The permanganate fixations make most of the cytoplasmic membranes appear as uniformly thick double layers, whereas some of the osmium fixatives reveal differences in the membranes with regard to thickness, density, and their apparent singleness or doubleness.