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Cellsand Temperature
Cells cannot remain alive outside certain limits oftemperature, and much narrower limits mark the boundaries ofeffective functioning. Enzyme systems of mammals and birds are mostefficient 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 widertolerance for changes of bodily temperature. For centuries it has beenrecognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of characterizing the difference havebecome more accurate and meaningful over time, butpopular terminology still reflects the old division into "warm blooded" and "cold blooded" species; warm-blooded includedmammals and birds whereas all other creatures were considered cold-blooded. Asmore species were studied, it became evident that this classification wasinadequate. A fence lizard or adesert iguana -- each cold-blooded -- usuallyhas a body temperature only a degree or two below that of humans and so is notcold. Therefore the next distinction was made between animals that maintain aconstant body temperature, called homeotherms, and those whose bodytemperature varies with their environment, called poikilotherms. But thisclassification also proved inadequate, because among mammals there aremany that vary their body temperatures during hibernation. Furthermore,many invertebrates that live in the depths of the ocean never experience achange in the chill of the deep water, and their body temperatures remainconstant.
全文翻譯：細(xì)胞與溫度
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。哺乳動(dòng)物和鳥類的酶系統(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。 幾個(gè)世紀(jì)以來，人們就認(rèn)識(shí)到哺乳動(dòng)物和鳥類調(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越精確和有意義，但是"暖血?jiǎng)游?和"冷血?jiǎng)游?這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)物和鳥類，其它動(dòng)物統(tǒng)統(tǒng)被視為冷血?jiǎng)游铩?但 是對(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?美洲一種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。 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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