Metchnikoff has speculated upon the possibility of delaying old age, and I do not see why his method should not be applied to the diurnal need of sleep. No vital process seems to be absolutely fated in itself; it is a thing conditioned and capable of modification. If Metchnikoff is right—and to a certain extent he must be right—the decay of age is due to changing organic processes that may be checked and delayed and modified by suitable food and regimen. He holds out hope of a new phase in the human cycle, after the phase of struggle and passion, a phase of serene intellectual activity, old age with all its experience and none of its infirmities. Still more are fatigue and the need for repose dependent upon chemical changes in the body. It would seem we are unable to maintain exertion, partly through the exhaustion of our tissues, but far more by the loading of our blood with fatigue products—a recuperative interlude must ensue. But there is no reason to suppose that the usual food of to-day is the most rapidly assimilable nurture possible, that a rapidly digestible or injectable substance is not conceivable that would vastly accelerate repair, nor that the elimination and neutralisation of fatigue products might not also be enormously hastened. There is no inherent impossibility in the idea not only of various glands being induced to function in a modified manner, but even in the insertion upon the circulation of interceptors and artificial glandular structures. No doubt that may strike even an adventurous surgeon as chimerical, but consider what people, even authoritative people, were saying of flying and electric traction twenty years ago. At present a man probably does not get more than three or four hours of maximum mental and physical efficiency in the day. Few men can keep at their best in either physical or intellectual work for so long as that. The rest of the time goes in feeding, digesting, sleeping, sitting about, relaxation of various kinds. It is quite possible that science may set itself presently to extend systematically that proportion of efficient time. The area of maximum efficiency may invade the periods now demanded by digestion, sleep, exercise, so that at last nearly the whole of a man’s twenty-four hours will be concentrated on his primary interests instead of dispersed among these secondary necessary matters.