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Bacteria

細(xì)菌

Bacteria are extremely small living things. While we measure our own sizes in inches or centimeters, bacterial size is measured in microns. One micron is a thousandth of a millimeter: a pinhead is about a millimeter across. Rod-shaped bacteria are usually from two to four microns long, while rounded ones are generally one micron in diameter. Thus if you enlarged a rounded bacterium a thousand times, it would be just about the size of a pinhead. An adult human magnified by the same amount would be over a mile tall.

細(xì)菌是極其微小的生物體。我們用英寸或厘米來(lái)測(cè)量自己的大小，而測(cè)量細(xì)菌卻要用微米。一微米等于千分之一毫米。針頭直徑大約一毫米。棒狀細(xì)菌通常有2-4微米長(zhǎng)，而圓形細(xì)菌的直徑一般只有1微米。因此，即使你把一個(gè)圓形細(xì)菌放大1000倍，它也不過(guò)一個(gè)針頭那么大。可是如果把一個(gè)成年人放大1000倍，就會(huì)變成1英里(或1.6公里)多高。

Even with an ordinary microscope, you must look closely to see bacteria. Using a magnification of 100 times, one finds that bacteria are barely visible as tiny rods or dots. One cannot make out anything of their structure. Using special stains, one can see that some bacteria have attached to them wavy-looking "hairs" called flagella. Others have only one flagellum. The flagella rotate, pushing the bacteria through the water. Many bacteria lack flagella and cannot move about by their own power, while others can glide along over surfaces by some little-understoodmechanism.

用一般的顯微鏡觀察細(xì)菌時(shí)，你必須仔細(xì)觀察才能看見(jiàn)它們。使用100倍的顯微鏡時(shí)，你會(huì)發(fā)現(xiàn)細(xì)菌不過(guò)是隱約可見(jiàn)的小細(xì)棒或小點(diǎn)點(diǎn)，而它們的結(jié)構(gòu)你卻根本看不出來(lái)。使用特殊的著色劑后，你會(huì)發(fā)現(xiàn)有的細(xì)菌上長(zhǎng)著不少波狀的"毛發(fā)"即鞭毛，而有的細(xì)菌只有一根鞭毛。鞭毛的旋轉(zhuǎn)可以推動(dòng)細(xì)菌在水中行進(jìn)。不少細(xì)菌沒(méi)有鞭毛，因而不能自己行進(jìn)。還有些細(xì)菌卻能通過(guò)某些鮮為人知的機(jī)制沿物體表面滑動(dòng)。

From the bacteria point of view, the world is a very different place from what it is to humans. To a bacterium water is as thick as molasses is to us. Bacteria are so small that they are influenced by the movements of the chemical molecules around them. Bacteria under the microscope, even those with no flagella, often bounce about in the water. This is because they collide with the watery molecules and are pushed this way and that. Molecules move so rapidly that within a tenth of a second the molecules around a bacteria have all been replaced by new ones; even bacteria without flagella are thus constantly exposed to a changing environment.

我們所熟知的世界在細(xì)菌眼中完全是另一個(gè)樣子。對(duì)于細(xì)菌來(lái)說(shuō)，水就同糖漿之于人類一樣稠密。細(xì)菌是如此的微小，周圍化學(xué)分子的一舉一動(dòng)都會(huì)對(duì)它們產(chǎn)生影響。在顯微鏡下，細(xì)菌，甚至包括那些沒(méi)有鞭毛的細(xì)菌，經(jīng)常在水中跳來(lái)跳去。這是因?yàn)樗鼈兣c水分子相撞后，被彈向各個(gè)方向。分子移動(dòng)很迅速，僅0.1秒之隔，一個(gè)細(xì)菌周圍的分子就會(huì)完全更新。因此，即使是沒(méi)有鞭毛的細(xì)菌也暴露在一個(gè)不斷變化的環(huán)境中。

Sleep

睡眠

Sleep is part of a person's daily activity cycle. There are several different stages of sleep, and they too occur in cycles.

睡眠是人每天日常活動(dòng)循環(huán)的一部分。人的睡眠分幾個(gè)階段，而這些階段也是循環(huán)發(fā)生的。

If you are an average sleeper, your sleep cycle is as follows. When you first drift off into slumber, your eyes will roll about a bit, your temperature will drop slightly, your muscles will relax, and your breathing well slow and become quite regular. Your brain waves slow down a bit too, with the alpha rhythm of rather fast wavespredominating for the first few minutes. This is called stage 1 sleep. For the next half hour or so, as you relax more and more, you will drift down through stage 2 and stage 3 sleep. The lower your stage of sleep, the slower your brain waves will be. Then about 40 to 60 minutes after you lose consciousness you will have reached the deepest sleep of all. Your brain waves will show the large slow waves that are known as the delta rhythm. This is stage 4 sleep.

如果你是一個(gè)正常的睡眠者，你的睡眠循環(huán)會(huì)這樣進(jìn)行。在你開(kāi)始昏昏入睡時(shí)，你的眼睛會(huì)滾動(dòng)幾下，體溫略有下降，肌肉放松，呼吸變得緩慢而有節(jié)奏。除了開(kāi)始幾分鐘比較快的α節(jié)奏外，腦電波也稍有減緩。這被稱為第一階段睡眠。在隨后約半小時(shí)內(nèi)，你進(jìn)一步放松，進(jìn)入第二和第三階段睡眠。睡眠越深入，腦電波就越緩慢。大約在開(kāi)始睡眠后的40到60分鐘，你將進(jìn)入沉睡狀態(tài)。這時(shí)的腦電波表現(xiàn)為巨大的緩波，被稱為δ節(jié)奏。這就是第四階段睡眠。

You do not remain at this deep fourth stage all night long, but instead about 80 minutes after you fall into slumber, your brain activity level will increase again slightly. The delta rhythm will disappear, to be replaced by the activity pattern of brain waves. Your eyes will begin to dart around under your closed eyelids as if you were looking at something occurring in front of you. This period of rapid eye movement lasts for some 8 to 15 minutes and is called REM sleep. It is during REM sleep period, your body will soon relax again, your breathing will grow slow and regular once more, and you will slip gently back from stage 1 to stage 4 sleep - only to rise once again to the surface of near consciousness some 80 minutes later.

但你并不是整夜都保持這種沉睡狀態(tài)。入睡后約80分鐘左右，你的大腦運(yùn)動(dòng)水平會(huì)再度略有提高。δ節(jié)奏消失，并被腦電波的運(yùn)動(dòng)圖形取代。你的眼睛會(huì)在閉著的眼瞼下迅速轉(zhuǎn)動(dòng)，就好象你在看著眼前發(fā)生的什么事情。這種迅速的眼球運(yùn)動(dòng)持續(xù)約8-15分鐘，這一階段睡眠被稱之為快速眼動(dòng)(REM)睡眠。在REM睡眠階段，你的肢體會(huì)很快再度放松，呼吸也再次放慢并變得有節(jié)奏，你會(huì)輕松地從第一階段滑入第四階段睡眠——直到大約80分鐘后重新接近清醒狀態(tài)。

Cells and Temperature

細(xì)胞與溫度

Cells cannot remain alive outside certain limits of temperature, and much narrower limits mark the boundaries of effective functioning.

細(xì)胞只能在一定的溫度范圍內(nèi)存活，而進(jìn)一步保證它們有效工作的溫度范圍就更小了。

Enzyme systems of mammals and birds are most efficient only within a narrow range around 37℃; a departure of a few degrees from this value seriously impairs their functioning. Even though cells can survive wider fluctuations, the integrated actions of bodily systems are impaired. Other animals have a wider tolerance for changes of bodily temperature.

哺乳動(dòng)物和鳥(niǎo)類的酶系統(tǒng)只能在37℃左右的很小范圍內(nèi)才能有效工作。與此相差僅幾度的溫度都會(huì)大大削弱它們的工作效率。盡管溫度變化更大時(shí)細(xì)胞仍能存活，但機(jī)體系統(tǒng)的整體運(yùn)行能力卻被削弱了。其它動(dòng)物對(duì)體溫的變化有更強(qiáng)的適應(yīng)性。

For centuries it has been recognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of characterizing the difference have become more accurate and meaningful over time, but popular terminology still reflects the old division into "warm blooded" and "cold blooded" species; warm-blooded included mammals and birds whereas all other creatures were considered cold-blooded. As more species were studied, it became evident that this classification was inadequate. A fence lizard or a desert iguana-- each cold-blooded -- usually has a body temperature only a degree or two below that of humans and so is not cold.

幾個(gè)世紀(jì)以來(lái)，人們就認(rèn)識(shí)到哺乳動(dòng)物和鳥(niǎo)類調(diào)節(jié)體溫的方式與其它動(dòng)物不同。隨著時(shí)間的推移，人們對(duì)這種差異的描述越來(lái)越精確和有意義，但是“暖血?jiǎng)游铩焙汀袄溲獎(jiǎng)游铩边@一古老的分類方式至今仍在大眾詞匯中有所反映。暖血?jiǎng)游锇ú溉閯?dòng)物和鳥(niǎo)類，其它動(dòng)物統(tǒng)統(tǒng)被視為冷血?jiǎng)游?。但是?duì)更多物種進(jìn)行的研究表明這種分類顯然是不適當(dāng)?shù)摹Ｃ乐抟环N小型蜥蜴和沙漠鬣蜥同屬冷血?jiǎng)游?，但?shí)際上它們的體溫通常只比人類的體溫低1-2度，因此并不是真正的冷血。

Therefore the next distinction was made between animals that maintain a constant body temperature, calledhomeotherms, and those whose body temperature varies with their environment, called poikilotherms. But this classification also proved inadequate, because among mammals there are many that vary their body temperatures during hibernation. Furthermore, many invertebrates that live in the depths of the ocean never experience changes in the chill of the deep water, and their body temperatures remain constant.

因此又出現(xiàn)了恒溫動(dòng)物(即保持恒定體溫的動(dòng)物)和變溫動(dòng)物(即體溫隨外界環(huán)境的變化而改變的動(dòng)物)這一區(qū)分方式。但這種分類也不恰當(dāng)。因?yàn)橛胁簧俨溉閯?dòng)物在冬眠期間會(huì)改變體溫，而許多生活在深海的無(wú)脊椎動(dòng)物在寒冷的深海水域中體溫并不變化，而是恒定的。

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