part 8

70 Everybody needs air; we breathe in air from outside our bodies in every breath. When you put your face under water you cannot keep it there long. Swimmers can't swim under water very long. They need air. Good swimmers may swim with their faces in the water; if so, they keep turning their heads to take a breath through their mouths. Swimmers do not take in air through their noses under the water because water would get in through the nose with the air and go to the lungs. With water in the lungs a person can't go on living.

每个人都需要空气；我们每一次呼吸都从体外吸入空气。 当你把脸放在水里时，你不可能长时间呆在那里。 游泳者不能在水下游很长时间。 他们需要空气。游泳好手会把脸埋在水里游泳；如果是这样，他们会不停地转头，用嘴呼吸。 游泳者在水下不通过鼻子吸入空气，因为水会随着空气通过鼻子进入肺部。 肺里有水，人就不能活下去。

71 Here is a picture of a man's lungs. They are soft like sponges with thousands of little pipes going through them. The pipes keep branching like the branches of a tree so that they go through every part of each lung. Our lungs are in the upper part of our chest. We have two of them. The air we breathe goes right in to every part of the lungs through these branching pipes. They take it to the blood which is moving all the time through the lungs and round to every part of our bodies. The blood makes a journey round the body and back to the lungs in a very short time.

这是一张男人肺部的照片。 它们像海绵一样柔软，有成千上万的小管子穿过它们。 这些管道像树的树枝一样不断地分叉，所以它们穿过每个肺的每个部分。 我们的肺在胸腔的上部。 我们有两个。我们呼吸的空气通过这些分支管道直接进入肺部的每个部位。 它们把它带到血液中，血液一直在通过肺部循环到我们身体的每一个部位。 血液在很短的时间内绕着身体回到肺部。

72 What is blood? It is the red liquid which comes out of your finger when you cut it. There are about thirteen pints of blood in a person's body. We can give a pint of blood at a time to a blood bank for the use of others who may need it. A healthy body makes up the pint of blood quickly. What does our blood do for us? It takes food to all parts of our bodies and takes waste away from them. All the parts of our bodies are made up of cells. These cells, which are very small, all need food all the time.

什么是血？它是当你割伤手指时从手指中流出的红色液体。 一个人的体内大约有13品脱的血。 我们可以一次捐一品脱血给血库，以供其他需要的人使用。 一个健康的身体能迅速补充这一品脱的血液。 我们的血对我们有什么用？ 它把食物运送到我们身体的各个部位，并把废物带走。 我们身体的所有部分都是由细胞组成的。 这些细胞非常小，一直都需要食物。

73 Here are some cells, thousands of times the size they are in the body. Each different sort of cell has its own work to do, different from the work other sorts of cells do. No one had seen cells before the invention of the microscope and its development in the sixteenth and seventeenth centuries. Before then no one could make pictures of cells because no one could see them.

这是一些细胞，它们的大小是它们在体内的几千倍。 每种不同类型的细胞都有自己的工作，不同于其他类型的细胞。 在十六、十七世纪显微镜发明和发展之前，没有人见过细胞。 在那之前，没人能给细胞拍照，因为没人能看到它们。

74 Cells are like little flames. A flame needs food. We get a quick flame—for a fire or a cigarette—by lighting a match or using a lighter. The flame of the match burns the match and the flame of the lighter burns the liquid in the lighter, if there is air for them to burn in. All fires burn something. What they burn is their fuel. Fuel is food for fire.

细胞就像小小的火焰。 火焰需要食物。我们通过点燃火柴或打火机来获得快速的火焰——用于生火或点烟。 火柴的火焰燃烧火柴，打火机的火焰燃烧打火机里的液体，如果有空气让它们燃烧的话。 所有的火都会烧到一些东西。他们燃烧的是燃料。 燃料是生火的食物。

75 The blood is like a stream. The cells take what they need, their fuel, out of the blood stream, as plants and fishes take their food out of water. The blood stream carries food and the oxygen which it has taken up in our lungs to all the cells in the body. Old cells die and give place to new cells in the body as plants and fish and other living things in the world about us die and give place to others. Three million of your red blood cells die every second and other cells take their place. The red cell population of your body changes completely in about three months.

血就像一条小溪。 细胞从血液中获取所需的燃料，就像植物和鱼类从水中获取食物一样。 血液将肺部吸收的食物和氧气运送到身体的所有细胞中。 就像我们周围的植物、鱼类和其他生物死亡并让位给其他生物一样，体内的老细胞死亡并让位给新细胞。 每秒钟有300万个红细胞死亡，其他细胞取而代之。 你体内的红细胞数量在大约三个月内完全改变。