Perhaps we ask, “What is it then that goes out of business, what is it that rests when we call ourselves asleep? Scientists answer the question by saying that the space between sleeping and waking is very hazy; that the border line is dim; that certain neurons are busy in our dreams; that other neurons keep the organs of the body active, but that the part of the brain which most truly sleeps is that part which knows things - the part that can say, "Yes, I see, I think, I feel."

Evidently, then, sleep is the rest time for our thinking neurons. It is for the sake of what they must do for us when we are awake that we are careful to give them definite hours of sleep. In a way it is a selfish matter. We treat them well at night because we wish them to treat us well by day.

As a rule, human beings need to sleep according to their age and according to their vigor. Bear in mind. two points: 1. The younger the child, the more sleep does he need in order to secure good service from his neurons. 2. The weaker the person, the more sleep does he need.1

Whenever we are tired we prove within ourselves that the cells of the body have been breaking down faster than they could build up. Exercise breaks them down, whereas rest, especially during sleep, builds them up

1 The hours of sleep for different ages are given in Good Health, page 54.

again. Every living creature should manage to keep the two conditions balanced. Those railroad accidents occurred because the balance was not kept.

He who wishes to do good work should rise in the morning with a feeling of being rested. The man or woman or child who gets up tired and goes to work in that condition is losing the balance of things; he is getting too little sleep; he is doing all he can to wreck the engine that pulls his train, and he will probably succeed in doing it.

CHAPTER XVIII

OUR SYMPATHETIC GANGLIA

In the spring of 1907, at an athletic meet for the public school boys of New York City, we watched the relay race. Four boys started abreast, and as they ran they seemed to command legs, feet, and bodies to strive to their utmost.

Every muscle responded. The boys fairly flew over the ground until, with outstretched arms and straining fingers, they touched the straining fingers of the outstretched arms of other boys who were to fly across the next curve of the huge, oval track.

At the end of the flight one of the boys fainted away for a moment and fell into the arms of his friends. Why did he faint? Because leg muscles, arm muscles, body muscles had, as it were, robbed the brain of blood. They had needed so much for their own work that they clamorously demanded it, and certain neurons had met the demand by issuing command after command to the heart to work faster and harder.

The heart had no choice. It had to obey. In the meantime, however, the neurons which govern the heart were.

getting overtired. I suppose the nuclei were shriveling, for the results proved that the commands were growing fainter and weaker. The heart was doing all it could, but even with its utmost endeavor it finally failed to pump as much blood into the brain as certain neurons up there needed. They accordingly had to stop working

for lack of it, and at that instant the boy became unconscious. He fainted. When this condition overtook him his brain was probably even paler than that of the pigeons that were exhausted by their flight from Bologna to Turin.

The point to bear in mind just here is that, as a rule, a person who faints during exercise proves that he has

not been properly trained. The trained runner does not faint, for a healthy heart, like any other part of a healthy body, learns through practice to do the work which is required of it.

Exercise is all-important for each of us, but when it is so violent that a set of untrained neurons has to be overworked, it becomes harmful and not helpful.

An overworked bicycle rider is the one who is most apt to have trouble with his heart. His thinking neurons are able to force the neurons which control his heart to work so persistently that, in time, the heart is overstretched; that is, it has become too large to do faithful, everyday work. The man is then said to have "heart trouble."

Pause just here and test yourself in two ways. First, try with all your might to make your heart stop beating. Try to prevent the great arteries from expanding and contracting as the blood surges through them in pulses. See whether, by thinking and willing hard enough, you can prevent your sweat glands and oil glands from manufacturing salt water and oil. Will your stomach obey you when you command it to stop digesting your food?

Now turn the tables. Say to your heart as it pounds steadily along: "Beat faster. Beat faster. You must beat faster." Will it obey you? No; it goes neither faster nor slower by the fraction of a second. Your commanding neurons and your heart seem to be as