To illustrate the structure of nerve fibers. Labels: A, nerve fiber examined fresh; n, node. B, nerve fiber with axis cylinder shaded, and medulla represented by dark lines; n.c, nucleus; p, granular cell substance near the nucleus. C, more highly magnified: m, medulla; n, node. D, nerve treated with reagents to show the axis cylinder: n.x, surrounded by medulla, m. E, nerve treated with reagents to show n.c, nucleus with fine line over it representing the neurilemma, and outside this fine connective tissue, c: n.c', nucleus lying in the fine connective tissue. F, nerve fiber deprived of its neurilemma showing medulla broken up into fragments, m, surrounding the axis cylinder, n.x.