part 13

120 There are about five million red cells in one cubic millimeter of our blood. One millimeter is a thousandth part of a meter and a tenth of a centimeter. One cubic centimeter—how much space does that take up? Here is a picture of a cube which is one centimeter long, one centimeter wide and one centimeter high. It takes up one cubic centimeter of space. A centimeter is a little less than half an inch.

我们每立方毫米的血液中大约有500万个红细胞。 一毫米是一米的千分之一，也是厘米的十分之一。 一立方厘米——它占了多少空间？ 这是一个一厘米长，一厘米宽，一厘米高的立方体的图片。 它占据了一立方厘米的空间。 一厘米略小于半英寸。

121 You can put a paper cube this size together for yourself, or cut one out of soap or cheese. To make a paper cube, take a pencil and make six one centimeter squares like this: Now take your scissors and cut round the outer lines. Do not cut the broken lines but make folds there. Put the edges together to make a hollow paper cube, as in the picture. Your cube will be a cubic centimeter in size. A cube has six sides; its sides are equal squares. The surface of a one-centimeter cube is six square centimeters. In one cubic centimeter of our blood there are about five billion red cells.

你可以自己做一个这么大的立方体，或者用肥皂或奶酪切一个。 要做一个纸立方体，拿一支铅笔，像这样画六个一厘米的正方形。现在用剪刀把外面的线剪下来。 不要剪断折线，而要在那里折起。 如图所示，把纸的边缘拼在一起，做成一个中空的立方体。 你的立方体的大小是一立方厘米。 立方体有六个面；它的边是等方。 1厘米的立方体的表面是6平方厘米。 在一立方厘米的血液中，大约有50亿个红细胞。

122 Living things are made up of cells, and cells do not grow to be more than twice the size they were at first. But trees can grow to be many thousands of times the size they were as seeds. The tallest tree known is 364 feet high. One great tree in California is as much as 115 feet round its trunk at the thickest point. How does such growth take place if cells do not grow to be more than twice as large as they were at first? It all takes place through division. The cells which make up the organism are able to divide into two and this division goes on and on. When you were born you had as many as 200 billion cells in your body all coming, in nine months, from the division of one cell 1.175th of an inch across.

生物是由细胞组成的，细胞生长后不会超过最初大小的两倍。 但树木可以长到种子时的几千倍大小。 已知最高的树有364英尺高。 在加州，有一棵大树的树干最粗处有115英尺长。 如果细胞没有长到原来的两倍以上，这种生长是如何发生的？ 这一切都是通过除法发生的。 组成生物体的细胞能够分裂成两个，这种分裂会不断地进行下去。 当你出生的时候，你的身体里有多达2000亿个细胞，在9个月的时间里，由一个直径1.175英寸的细胞分裂而来。

123 All organisms which you see in the world about you have grown by cell division. You and I have become what we are through billions of divisions in the cells whose outcome is our cell structure at this minute. In cell division the two halves of the cell (as you see in picture four) become ready to separate. In picture five you see that they have separated. The cell in picture one, by division, has become two separate cells. The daughter cells do in every way the same as their mother cell did. One of the greatest questions scientists are working on is: What keeps the daughter cells doing what they have to do?

在你周围的世界上你所看到的一切生物都是通过细胞分裂而生长的。 你和我是通过细胞的数十亿次分裂才变成现在这个样子的，细胞分裂的结果就是我们现在的细胞结构。 在细胞分裂中，细胞的两半（如图四所示）准备分开。 在图5中你可以看到它们分开了。 图一中的细胞通过分裂，变成了两个独立的细胞。 子细胞在各方面都和母细胞一样。 科学家们正在研究的最大问题之一是：是什么让子细胞做它们必须做的事情？

124 Even the simplest living organism is far more complex than any machines that people have made. Organisms are built up of parts which are themselves more complex than any machine. And these parts in turn are the most complex things the science of chemistry knows. It is because they are so complex that they can work together in an organism in so many different ways. Chemistry is about the different ways in which different materials are built up. For example: Water is made up of oxygen and hydrogen united in a way which may be represented like this. Carbon dioxide is made up of carbon and oxygen in a way which may be represented like this. Chemists make use of the formula H2O for water in their writing. They use formulas to represent the structure of all material things.

即使是最简单的生物体也比人们制造的任何机器复杂得多。 生物体是由部件组成的，这些部件本身比任何机器都要复杂。 而这些部分又是化学科学所知的最复杂的东西。 这是因为它们是如此复杂，它们可以在一个有机体中以许多不同的方式协同工作。 化学是关于不同物质形成的不同方式。 例如：水是由氧和氢结合而成的，可以这样表示。 二氧化碳由碳和氧组成，可以这样表示。 化学家在写作中使用分子式H2O表示水。 他们用公式来表示所有物质的结构。

125 The most important of the materials in our bodies are the proteins (from Greek proteios, meaning "having first place"). Among them are materials with the most complex structures known to the chemist. We can get some idea of how complex proteins are by comparing the formula for one of them with the formula for water (H2O) or for carbon dioxide (CO2). Compare this formula for a protein from milk: with the simple formulas for water: or carbon dioxide: The letter N in this formula represents nitrogen and the letter S represents sulphur.

我们体内最重要的物质是蛋白质（来自希腊语proteios，意思是“居首位”）。 其中有化学家所知道的结构最复杂的材料。 通过将其中一种蛋白质的分子式与水（H2O）或二氧化碳（CO2）的分子式进行比较，我们可以对蛋白质的复杂程度有所了解。 将牛奶中蛋白质的分子式与水或二氧化碳的简单分子式进行比较：这个分子式中的字母N代表氮，字母S代表硫。