(vii.) If all these are useless, be quite resigned; try not to get irritated, do not toss about if you can avoid it. Do not think about interesting things. In fact, if you cannot sleep, take as much rest as you can. Lie utterly relaxed and breathe deep. Finally, with regard to the number of hours of sleep required, it must remain a personal question. Some people do not need more than between five or six, especially in later life, others seem positively to need not less than eight. But the chances are that everyone requires from about five and a half to eight. Less than that minimum is probably insufficient in the long run, more than eight probably unnecessary for anyone in good health. Nor must it be forgotten that in itself the desire for much sleep is not a healthy sign; it may easily point to a sluggish liver. This brings us to the second division of the subject--namely Rest, which does not only largely diminish the ill-results of not sleeping at night, but is probably good for all hard workers either of mind or body, at certain times during the day, in particular after a long continued stretch of brain-work, when an interval should be taken by the mind; after a meal, when quiescence on the part of the body leaves the digestion more energy to do its work; and after physical exercise, when those limbs which have borne the brunt of it should be left quiescent. A flat or semi-recumbent position is the best, one in which the body is completely supported, and no muscular effort is needed to retain it in its position; and the deep breathing of sleep may be at first imitated and will soon be acquired. The reason for this is that since slow, long breath is the means naturally adopted by the lungs in sleep, it is probably the best method of resting the breathing muscles even when awake. It is a mistake to spend too long over these rests; if two a day are taken, a quarter of an hour, provided it be real rest, is likely to be sufficient to freshen one up again completely, while if the muscles are left too long relaxed, they will be disinclined to begin work again. Now sleep and rest are widely different from relaxation, the third means of recuperation mentioned above, since the first two are purely natural, and require merely passivity as a condition, whereas intentional relaxation is at first purely artificial, and requires, even when it has become easy with practice, certain voluntary efforts. It has therefore this initial disadvantage, and in addition this further one, that in the young it is seldom if ever required, since the natural means of recuperation, Sleep and Rest, supply all that is wanted. Unless habits are acquired in childhood or youth, however, there are few people who will ever spare the time to acquire them at all. It requires also an exercise of imagination--rest, that is to say, has to be attained self-consciously.