G. F. FUEGER Among the many processes in Physiology few appear mo~e inviting to be studied by tracers and external imaging than the variety of the routes of migratory (blood) cells in health and disease. Much emphasis has been placed lately on the methods of labelling of the white blood cells. It is obviously quite important and necessary to refine the methods of leucocytic labelling, particularly to search for ways to label selectively a specific group of white blood cells, but there is also the need to review and keep abreast with the developing knowledge of the white blood cells...