No general rule can be laid down as to the number of hours which should be passed in sleep, since the need of sleep varies with age, temperament, and the way in which the waking hours have been employed. The infant slumbers away the greater part of its time. Young children should sleep from six to seven in the evening, until morning, and for the first three or four years of their life should also rest in the middle of the day. Up to their fourteenth or fifteenth year the hour of retiring should not be later than nine o’clock, while adults require from seven to nine hours. Some can do with two or three hours less than this, but they are so few that they offer no examples for us to follow. Insufficient sleep is one of the crying evils of the day. The want of proper rest of the nervous system produces a lamentable condition, a deterioration in both body and mind. This sleepless habit is begun even in childhood, when the boy or girl goes to school at six or seven years of age. Sleep is persistently put off up to manhood and womanhood. Persons who are not engaged in any severe work, whether bodily or mental, require less sleep than those who are working hard. Muscular fatigue of itself induces sleep, and the man who labors thus awakes refreshed. But brain work too often causes wakefulness, although sleep is even more necessary for the repair of brain than of muscular tissue. In such cases the attention should be forcibly withdrawn from study for some time before retiring to rest, and turned to some light reading, conversation or rest before going to bed. A short brisk walk out of doors just before bed time may aid the student in inducing sleep. Drugs should be avoided. After a heavy supper, either sleep or digestion must suffer, but the person who goes to bed hungry will not have sound and refreshing sleep. If one works after supper, through a long evening, he should eat a light lunch of some sort an hour or two before bed time. Ordinarily persons do best to retire at ten or eleven, and the habits of society which require later hours are to be regretted. Brain work, however, after midnight is most exhausting, and though sometimes brilliant, would probably be better still if diverted to earlier hours. Whatever be the explanation, it is an undoubted fact that day and night cannot be properly exchanged. About one or two o’clock in the morning the heart’s action sinks, and nature points to the necessity for rest. Sleep in the day time does not compensate for the loss of that at proper time, and slumbers prolonged to a late hour do not refresh the mind or body as does sleep between the hours of eleven and six or seven, the normal period for rest.