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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：細胞與溫度
    細胞只能在一定的溫度范圍內(nèi)存活，而進一步保證它們有效工作的溫度范圍就更小了。哺乳動物和鳥類的酶系統(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 溫度都會大大削弱它們的工作效率。盡管溫度變化更大時細胞仍能存活，但機體系統(tǒng)的整體運行能力卻被削弱了。 其它動物對體溫的變化有更強的適應性。 幾個世紀以來，人們就認識到哺乳動物和鳥類調節(jié)體溫的方式與其它動物不同。 隨著時間的推移，人們對這種差異的描述越來越精確和有意義，但是"暖血動物"和"冷血動物"這一古老的分類方式至今仍在大眾詞匯中有所反映。 暖血動物包括哺乳動物和鳥類，其它動物統(tǒng)統(tǒng)被視為冷血動物。 但 是對更多物種進行的研究表明這種分類顯然是不適當?shù)摹?美洲一種小型蜥蜴和沙漠鬣蜥同屬冷血動物，但實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)了恒溫動物(即保持恒定體溫的動物)和變溫動物(即體溫隨外界環(huán)境的變化而改變的動物)這一區(qū)分方式。但這種分類也不恰當。因為有不少哺乳動物在冬眠期間會改變體溫，而許多生活在深海的無脊椎動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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