SLEEP.--"About one-third of an average human life is passed in the familiar and yet mysterious state which we call sleep. From one point of view this seems a large inroad upon the period in which our consciousness has its exercise; a subtraction of twenty-five years from the life of one who lives to be seventy-five. Yet we know that the efficiency and comfort of the individual demand the surrender of all this precious time. It has often been said that sleep is a more imperative necessity than food, and the claim seems to be well founded." It is quite likely that some students indulge in too much sleep. This may sometimes be due to laziness, but frequently it is due to actual intoxication, from an excess of food which results in the presence of poisonous "narcotizing substances absorbed from the burdened intestine". This theory is rendered tenable by the fact that when the diet is reduced the hours of sleep may be reduced. If one is in good health, it seems right to expect that one should be able to arise gladly and briskly upon awaking. By all means do not indulge yourself in long periods of lying in bed after a good night's rest. If we examine the physical and physiological conditions of sleep we shall better understand its hygiene. Sleep is a state in which the tissues of the body which have been used up may be restored. Of course some restoration of broken-down tissue takes place as soon as it begins to wear out, but so long as the body keeps working, the one process can never quite compensate for the other, so there must be a periodic cessation of activity so that the energies of the body may be devoted to restoration. Viewing sleep as a time when broken-down bodily cells are restored, we see that we tax the energies of the body less if we go to sleep each day before the cells are entirely depleted. That is the significance of the old teaching that sleep before midnight is more efficacious than sleep after midnight. It is not that there is any mystic virtue in the hours before twelve, but that in the early part of the evening the cells are not so nearly exhausted as they are later in the evening, and it is much easier to repair them in the partially exhausted stage than it is in the completely exhausted stage. For this reason, a mid-day nap is often effective, or a short nap after the evening dinner. By thus catching the cells at an early stage of their exhaustion, they can be restored with comparative ease, and more energy will be available for use during the remainder of the working hours.