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.

血液在各处做两件事：为细胞提供食物和氧气，并带走废物。 这就好像血液使细胞里的小火继续燃烧，带走了灰烬。 细胞里燃烧的燃料是由我们吃的食物提供的。 没有氧气它就不能燃烧。 这种气体对所有生物都是必需的，就像燃烧木头或煤一样。 燃烧是氧气和燃料结合时发生的变化。 煤、木材和其他燃料（例如烹饪用煤气）通过从空气中吸收氧气燃烧。

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.

当你看到有人在满是人的房间里打开窗户时，你就知道那是为了让外面的空气进来。 当好的空气从窗户进来时，含有更多二氧化碳和水而较少氧气的坏的、用过的空气就出去了。 我们说好空气就是新鲜空气。 新鲜空气是干净的，很好呼吸，有足够的氧气在它为我们的需要。

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.

这些男孩在外面呼吸新鲜空气，深深地呼吸着，而他们的老师正在对他们的每一次呼吸说：in OUT。 如果你能观察它们，你会看到它们的胸部先是变大，然后变小，因为它们的肺吸入和呼出空气。 无论我们是醒着还是睡着，呼吸都在继续。 大多数时候，我们都没有意识到自己的呼吸。 我们呼吸时肺的运动是自动的。 呼吸是自己进行的，肺每分钟吸入新鲜空气，排出旧空气约18次。 这是常见的呼吸频率。 如果有什么东西把空气与我们隔绝，使我们无法获得足够的氧气来满足我们的需要，我们就会意识到自己的呼吸。

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.

闭上你的嘴，用大拇指和另一个手指夹住鼻子，这样你就把空气呼出来，把气吸进去。 你能屏住呼吸多久？ 你最好不要握着它超过一分钟。 如果一个人长时间不供氧，他就会失去知觉。 当人们因为水或烟雾进入肺部而失去知觉时，让他们重新呼吸是非常重要的。 这是通过把他们的脸朝下（在他们的牙齿之间放一些东西来保持嘴巴张开），然后让他们的肺部开始呼吸。

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.

我们飞得越高，空气的压力就越小，因为我们上方空气的重量就越小。 当气压变小（空气变薄），我们一次呼吸的氧气量就变少了。 我们必须吸入更多的空气才能获得等量的氧气。 我们用来测量空气压力的仪器是气压计。

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.

1953年，人类登上了世界最高峰——珠穆朗玛峰。 他们在高空时必须使用氧气。 他们必须控制他们使用的氧气量。 他们无法从下面的人那里得到更多的补给。 这个人正在攀登一座高山，他正在使用储存在他背上的那些罐子里的氧气供应。 通过打开和关闭阀门，他可以控制自己吸入的氧气量。 气体被泵入罐内的小空间。 它在那里受到压力，当阀门打开时它就出来了。