Figure 1.

Ellermann and Bang's drawings of normal chicken bone marrow (left) and leukemic chicken bone marrow (right). The normal marrow contains dense, dark trabeculae of bone. The cells in the spaces between trabeculae are nucleated erythrocytes (red blood cells). The leukemic marrow contains little bone, many immature leukocytes (white blood cells, later shown to be B lymphocytes), and very few erythrocytes. (Reprinted from Ellermann V, Bang O. 1909. Z Hygeine Infektionskrakheiten 63: 231–273.)