Why? The Science of Athletics

HUMAN MECHANISM inhale fresh air is because stuffy moisture and lack of ventilation cause the mucous membrane to become gorged with blood, susceptible to the attacks of certain microbes, and a "cold in the head" is contracted. The air taken in through the nostrils passes by way of the wind-pipe, which divides at the base into the two bronchial tubes, and enters the lungs. Here, again, Nature has made provision for the exclusion of harmful matter, for there is a further mucous coating and there are also innumerable little lashes, or cilia, moving back– wards and forward rhythmically for the purpose of pre– venting dangerous microbes from entering the lungs. When such microbes do establish themselves on the cilia certain glands at once pour out a copious stream of mucus, which is periodically, and automatically, blown out by the lungs and a cough, or a "cold on the chest", ensues. It is possible for us still to follow the analogy of the blood-stream, for, just as the aorta breaks up into arteries terminating in the capillaries, so the bronchial tubes branch off into the finer bronchioles which, in their turn, end in tiny dilatations, which are sub-divided into minute air-cells. It is on the walls of these air-cells that the necessary interchange of gases takes place. In the two lungs there are something like six millions of these little air-cells, not one of them more than about a tenth of an inch in length. They bring a large volume of air into almost direct contact with the blood approxi– mately fifteen times in each minute. In order that, sleeping or waking, we may go on breathing, Nature has so arranged things that the lowest part of our brain, -the medulla oblongata, contains a nerve c~ntre which is susGeptible to the presence of carbon dioxide in the blood. Stimulated by this C0 2 , the nerve centre is continually sending out orders for activity to the respiratory organs, which keep the lungs working. The necessity of making full use of one's lungs is seen by taking the example of sedentary workers. Such • I