That man who regularly and soundly sleeps his eight or nine hours a day should be the man capable of large physical or mental work; moreover, he is the man who lasts longest; his system becomes daily recuperated, and he has the largest prospect of reaching his threescore and ten, while yet his system is in a degree of health; while his neighbor, less favored in this respect, becomes old at sixty if he chances to live so long. It is not intended to imply that there may not be exceptions to this rule. There have been some who could do with four or five hours' sleep for many years and do good work, and there are probably such men to-day, but they are using up the nervous energy and strength with which they have been endowed far too rapidly; and they are exceptions to the mass of people, who require much more sleep in order to enjoy good mental health. Sleep is to the brain what rest is to the body: "Sleep, that knits up the ravelled sleeve of care, The death of each day's life, sore labor's bath, Balm of hurt minds, great Nature's second course, Chief nourisher in life's feast." No words could paint more beautifully or effectively the office of sleep, than these of England's greatest poet. But we need not turn to the writers of prose or poetry in the past for instruction in this matter; all nature teaches the importance of sleep. Every tree, and shrub, and vine, has its period of sleep, and, if stimulated into ceaseless activity, would soon die; and every portion of the human system is subject to the same great law of necessity. The stomach must have its periods of inactivity and rest; and there are periods during every twenty-four hours when the kidneys secrete very little, if any, urine. It is sometimes said the heart is an exception to this rule; that its beat never ceases from more than six months before birth until nature's last great debt is paid in death. But, in truth, it is at entire rest nearly if not quite one third of the whole time. Its action consists of a _first_ and a _second_ sound, covering the contraction of right and left auricles and ventricles, and then a rest,--and so far as we know a perfect one. Reckoning this at one third the time occupied in each full action of the heart, and we have more than twenty years of perfect quiet out of the threescore and ten. The same is true to even a larger extent of other involuntary processes and movements; for instance, that of respiration. The muscles concerned in this operation are at entire rest during more than one third of the time, and if the process of respiration be much quickened in frequency for any considerable period of time, weariness and languor ensue.