One more thing which the body, to be healthy, demands for food is Sun-light, that invaluable medicine for all forms of nervous disease, which Americans, more than any other people, curtain carefully out for fear of fading carpets and furniture. But what are French moquettes, brocade, or satin, compared with rosy cheeks, clear complexions, and steady nerves? If we would only draw up the shades, open the shutters, and loop the heavy curtains out of the way, or, better still, take them down altogether, might we not look for a marked improvement in systems affected by nervous diseases? This want of sun-light may be expected also, of course, most to affect those who remain within doors, and who, even in walking, shade themselves with veils and sun-shades from the life-giving rays of the sun. _Sleep._--To many of the organs of the body there have been allotted seasons of comparative quiet and repose, even during the day. If the rules for food be observed, the stomach, for instance, has, as stomach, its vacations from labor, by means of which it is enabled to prepare for, and perform, its regularly recurring work with vigor. Even with organs where this is not the case, the action is slackened very materially at times, as in the case of the heart and lungs during sleep. They must continue to work, though more slowly, and the part of the nervous system which carries on their involuntary and mechanical action, has also then a partial relief. But the only rest for the thinking brain is to be found in normal sleep. From the instant when, in the morning, we become conscious of the external world, to the instant late at night, or, it may be, early in the morning, when we pass through the gates of sleep, out from companionship, into an utter solitude, it never rests from its work. Whether, by volition, we summon all our intellectual power to the closest attention, and turn, as it were, the whole energy of our being into one thought-channel, till the organs of sense become simply outside appendages which disturb the internal self with no imported knowledge, or whether, lying idly, as we say, on the sofa, we let our thoughts wander as they will, thought still goes on. Coming and going more rapidly than the shortest pendulum can swing, inter-weaving more subtly than the threads of the most complicated lace under the fingers of the skillful worker; "trains of thought" pass and repass through our minds, following, as we mechanically express it, the Laws of Association. Only in losing consciousness, do we cease to destroy the brain cells; it is only in sleep that the brain can rest.