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Sleep has no direct physiological effect on the brain. Because the brain has muscles, it does not get tired. What passes for "brain fatigue" is actually a combination of muscle fatigue and emotional factors, such as anxiety, boredom, or the hypnotic effects of a monotonously repeated task. The muscular and emotional components of sleepiness and wakefulness are almost impossible to sort out. Even the seemingly simple closing of the eyelids has a complex explanation: the eye muscles get tired (so that, in extreme fatigue, focusing becomes impossible), and the cornea must be kept bathed in fluid and protected from dust. Just lying down, with eyes open but with muscles relaxed, has some refreshing and restorative effect. Lying down with eyes closed, to shut out distracting movements, is a bit better. Getting so relaxed as to be half asleep, half awake, beginning to have dreamlike fantasies, is better yet. The last best help to man is sleep itself.
Warm Milk. By whatever mechanism, sleep is the great refresher, or as Shakespeare had it, "Sore labour's bath/Balm of hurt minds." The important thing is to fall asleep at the time of one's choosing. Responsible physicians doubt that there are any universal passports for a quick trip to Nirvana.
The one inviolable rule is: relax-which, of course, is easier said than done. Even the most tightly wound-up businessman can usually do so after 36 holes of golf because his tired muscles do his relaxing for him. But on his workaday routine he may use no more muscle power than it takes to walk to his car. At day's end his muscles are tense, not tired.
The before-dinner drink is a good relaxant, because alcohol depresses nerve cells in the brain, and these help the muscles to relax in their turn. A heavy dinner too late at night, topped by too much liquor, may soon induce a stuporous sleep, but this is likely to be interrupted by hydrostatic pressure in the bladder. At the other extreme, going to bed hungry results in stomach contractions, which keep most people awake. There is much to be said, both physiologically and even psychoanalytically, for Grandma's prescription of a glass of hot milk at bedtime. And for those who feel they have outgrown plain milk, there are soothing substitutes: Ovaltine, Sanka, cocoa or hot buttered rum.
Many men insist that they must have an alcoholic nightcap, but more and more have learned to pass up brandy after dinner, explaining: "It keeps me awake." If, in its place, they take vodka (a mixture of almost pure alcohol and water), they are on the right track. Scotch whisky and gin in moderate amounts are also unlikely to interfere with sleep. The trouble with brandy, bourbon and rye is that, compared with vodka, most brands contain 20 to 30 times as much of the ingredients known to liquor chemists as "congeners." Some of these are the aromatics that give the liquors their characteristic odor, taste and color. Others are chemically different kinds of alcohol, including fusel oil. Even in minute amounts, these congeners keep some people awake.