=== Erythrocytes (red blood corpuscles) ===

Note the staining, size, and shape of these elements. Erythrocytes are biconcave discs that average 7.7μm in diameter and 1.9μm in the greatest thickness. Look at the scanning EM picture (below) to see the three dimensional appearance of erythrocytes. Adult men have an average of 5.5 million RBCs and 8 thousand white blood cells per cubic millimeter of blood; thus, only one leukocyte exists for every six to seven hundred RBCs.

In certain kinds of anemias the RBCs may be larger than normal (macrocytes) or smaller than normal (microcytes). In normal blood the range in size of erythrocytes is very narrow with the differences in diameter usually being less than one micrometer.

=== Leukocytes (white blood cells) ===