These two micrographs show the outer cell surface of the epithelial cell border in intestine (upper) and stomach (lower) tissue. This surface, called the glycocalyx, is composed of negatively charged acidic polysaccharides, which here, have been stained by binding a polycationic derivative of ferritin. High iron content causes electron scattering, and thus, regions to which the ferritin have bound appear dark in these images. These images, courtesy of Susumu Ito, are Figures 20 (upper) and 21 (lower) from Chapter 1 (The Cell Surface) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.