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    Bacteria
    Bacteria are extremely small living things. While wemeasure our own sizes in inches or centimeters, bacterial size ismeasured in microns. One micron is a thousandth of a millimeter: a pinhead isabout a millimeter across.Rod-shaped bacteria are usually from two tofour microns long, while rounded ones are generally one micronindiameter. Thus if you enlarged a rounded bacterium a thousand times, itwould be just about the size of a pinhead.An adulthuman magnified by the same amount would be over a mile (1.6 kilometers)tall.Even with an ordinary microscope,you must look closely to seebacteria. Using a magnification of 100 times, onefinds thatbacteria are barely visible as tiny rods or dots. One cannot make out anythingof their structure. Using special stains, one can see that some bacteria haveattached to them wavy-looking "hairs" called flagella. Others haveonly one flagellum. The flagella rotate, pushing the bacteria through thewater. Many bacteria lack flagellaand cannot move aboutby their own power, whileothers can glide along oversurfaces by some little-understood mechanism.Fromthe bacterial point of view, the world is a very different place from what itis to humans. To a bacteriumwater is as thick as molasses is to us.Bacteria are so small that they are influenced by themovements of the chemical moleculesaround them. Bacteria under the microscope, even thosewith no flagella, often bounce about inthe water. This is because theycollide with the water molecules and are pushed this way and that. Moleculesmove so rapidly that within a tenth of a second the molecules around abacterium have all been replaced by new ones; even bacteria without flagellaare thus constantly exposed to a changing environment.
    全文翻译：细菌
    细菌是极其微小的生物体。我们用英寸或厘米来测量自己的大小，而测量细菌却要用微米。 一微米等于千分之一毫米。 针头直径大约一毫米。 棒状细菌通常有 2～4 微米 长，而圆形细菌的直径一般只有 1 微米。因此，即使你把一个圆形细菌放大 1000 倍，它也 不过一个针头那么大。可是如果把一个成年人放大 1000 倍，就会变成 1 英里(或 1.6 公里) 多高。 用一般的显微镜观察细菌时，你必须仔细观察才能看见它们。使用 100 倍的显微镜时，你会发现细菌不过是隐约可见的小细棒或小点点，而它们的结构你却根本看不出来。 使 用特殊的着色剂后，你会发现有的细菌上长着不少波状的"毛发"即鞭毛，而有的细菌只有一 根鞭毛。鞭毛的旋转可以推动细菌在水中行进。不少细菌没有鞭毛，因而不能自己行进。还有些细菌却能通过某些鲜为人知的机制沿物体表面滑动。我们所熟知的世界在细菌眼中 完全是另一个样子。对于细菌来说，水就同糖浆之于人类一样稠密。细菌是如此的微小，周围化学分子的一举一动都会对它们产生影响。在显微镜下，细菌，甚至包括那些没有鞭 毛的细菌，经常在水中跳来跳去。这是因为它们与水分子相撞后，被弹向各个方向。分子移动很迅速，仅0.1秒之隔，一个细菌周围的分子就会完全更新。因此，即使是没有鞭毛的细菌也暴露在一个不断变化的环境中。