A Routine Method for Obtaining High Contrast Without Staining Sections

Immersion of tissue in aqueous uranyl acetate be- for giving some degree of contrast to components fore embedding is commonly practiced to increase such as membranes when they extend through the the contrast on sections which are subsequently thickness of the section parallel to the electron stained (2, 3, 5). The treatment is only satisfactory beam. A simple modification of current practice 540 THE JOURNAL OF CELL BIOLOGY • VOLUME 50, 1971 • pages 540-544All figures are printed on Kodabromide F3 paper under standard conditions for comparing contrast. Figures 1-4 have only been stained in uranyl acetate before embedment. FIGURE 1 The contrast obtained by treating with 2 % uranyl acetate in absolute ethanol for 2 hr at room temperature. Organelles are discernible but the contrast is inadequate for viewing. X 26,000. FIGURE 2 The contrast obtained by treating tissues with 2 % uranyl acetate in absolute ethanol for 13 hr at 60°C. Contrast is now equal to that obtained by staining sections. Figs. 1 and 2: Fat body from Calpodes larvae. n, nucleus; mi, microbodies; g, Golgi complex. X 26,000. FIGURES 3 and 4 The contrast obtained by treating tissues with 2 % aqueous uranyl acetate for 20 hr at 60 •C. Contrast is satisfactory for viewing and photography of sections suitable for both survey and high magnification. There is no deleterious tissue extraction or stain precipitation. T. S. nerve cord from Calpodes larva. m, microtubules in sheath cells; a, axons; arrows, microtubules with dense central cores.