In a recent address Lord Horder1 spoke of the reference of the physician, including in this quaint but vivid phrase three duties, namely, to heal the sick, to prevent disease and to gain control of the biologic principles of life in the interest of the public. As physicians, we have been trained to heal the sick as our first duty. Preventive medicine has impressed on us our responsibility in safeguarding the public against the scourge of disease. But in my function as an anatomist engaged in the study of growth and repair, it is toward the control of the biologic principles of life that I wish to direct your attention in this lecture. Macpherson Lawrie2 has pointed out in his recent book that the real tragedy of illness is not the illness of the hospital and the institution, not the illness which the doctor sees, but the illness