part 9

80 Everywhere the blood stream does two things: supplies the cells with food and oxygen and takes away waste. It is as if the blood kept the little fires in the cells burning and took away the ashes. The fuel for the fires in the cells is given us by the food we eat. It cannot burn without oxygen. This gas is as necessary to all living things as it is necessary to the burning of fires made of wood or coal. Burning is the change which takes place when oxygen and fuel unite. Coal, wood and other fuels (cooking gas, for example) burn by taking oxygen from the air.

81 When you see someone opening a window in a room full of people, you know that is to let in air from outside. As good air comes in through the window, bad, used air, with more carbon dioxide and water in it and less oxygen, goes out. We say good air is fresh air. Fresh air is clean and good to breathe and has enough oxygen in it for our needs.

82 These boys are outside in the fresh air, breathing deeply while their teacher is saying: IN OUT for every breath which they take. If you could watch them you would see their chests becoming first larger, then smaller in size, as their lungs breathed air in and out. Breathing goes on when we are awake and when we are sleeping. Most of the time we are not conscious of our breathing. The motion of our lungs as we breathe is automatic. It goes on by itself, the lungs taking fresh air in and letting used air out about eighteen times a minute. This is the common rate of breathing. We become conscious of our breathing if anything shuts the air off from us, so that we do not get enough oxygen for our needs.

83 Keeping your mouth shut, take your nose between your thumb and one finger, so that you shut the air out and shut your breath in. How long can you hold your breath? You will be wise if you do not try to hold it more than a minute. If oxygen is kept from a person for long he will become unconscious. When people become unconscious through getting water or smoke in their lungs it is very important to start them breathing again. This is done by turning them face down (putting something between their teeth to keep their mouths open) and then working their lungs to start them breathing.

84 The higher up we go the less is the pressure of the air, because the weight of the air above us is less. As the pressure becomes less (air gets thinner) the amount of oxygen we get in one breath becomes less. We must take in more air to get the same amount of oxygen. The instrument we use to measure the pressure of the air is the barometer.

85 Men have been able (1953) to get to the top of the highest mountain in the world, Mount Everest. They had to use oxygen when they got up high. They had to keep control over the amount of oxygen they used. They could get no more supplies from those below. This man, who is going up a high mountain, is using a supply of oxygen which is stored in those cans he is carrying on his back. By opening and shutting a valve, he controls the amount of oxygen he breathes in. The gas has been pumped into the small space inside the cans. It is under pressure in there and comes out when the valve is opened.