大众英语80篇背诵阅读带翻译(二十五)
"50 Cells and Temperature
Cells cannot remain alive outside certain limits of temperature, and much narrower limits mark the boundaries of effective functioning. 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. 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. Therefore the next distinction was made between animals that maintain a constant body temperature, called homeotherms, 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 a change in the chill of the deep water, and their body temperatures remain constant.细胞与温度细胞只能在一定的温度范围内存活，而进一步包管它们有效义务的温度范围就更小了。哺乳动物和鸟类的酶系统只能在 37℃阁下的很小范围内本领有效义务。与此相差仅几度的温度都会年夜年夜削弱它们的义务苦守。虽然温度转变更年夜时细胞仍能存活，但机体系统的团体运转本领却被削弱了。别的动物对体温的转变有更强的适应性。几个世纪以来，人们就认识到哺乳动物和鸟类调理体温的体例与别的动物不合。跟着时候的推移，人们对这种差异的描绘越来越精确和存心义，可是"热血动物"和"冷血动物"这一陈腐的分类体例至今仍在民众词汇中有所反应。热血动物包括哺乳动物和鸟类，别的动物完整被视为冷血动物。可是对更多物种举行的钻研表明这种分类显然是不得当的。美洲一种小型蜥蜴和戈壁鬣蜥同属冷血动物，但理想上它们的体温每每只比人类的体温低 1～2度，因此并不是真正的冷血。因此又出现了恒温动物(即连结恒定体温的动物)和变温动物(即体温随外界情况的转变而窜改的动物)这一区分体例。但这种分类也不得当。因为有不少哺乳动物在蛰伏期间会窜改体温，而良多糊口在深海的无脊椎动物在严冷的深海水域中体温并不转变，而是恒定的。

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