the tissues affects the nerves. We are rested and strong when these wastes are removed and the tissues are supplied with fresh food and oxygen. Work causes the accumulation of carbon dioxid, which is nature's narcotic.[1] The drowsy feeling that ensues is more pleasant than the drowsy feeling from alcohol or opium. Those who do not employ nature's narcotic but free themselves of it by hurried, anxious breathing become restless and crave artificial narcotics.
Fatigue without work occurs with people who are idle. The oxidation in their cells is not complete, and poisonous products of the incomplete burning result. This is known as self-poisoning (auto-toxemia). The poisons are taken by the blood to the nerves and brain, and give a tired feeling as effectually as does hard work; or the food may ferment in the food tube and form poisons which increase the tired feeling. Such persons are usually irritable, while persons who are fatigued by useful labor are likely to be dull and drowsy.
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Fig. 118.—The Situation of Headaches with reference to their causes.
Headaches are caused by poisons in the blood or by pressure of blood congested in the head. Like all other pains they should be a source of benefit in
- ↑ It has been found that it is injurious to rebreathe expired air containing one per cent of carbon dioxid, but a far greater percentage is harmless if introduced into fresh air, thus indicating that the injury from poor ventilation comes chiefly from the "crowd poison," or organic particles thrown off.
