Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective functioning. Enzyme1 systems of mammals and birds are most efficient only within a narrow range around 37C;a departure of a few degrees from this value seriously impairs2 their functioning. Even though cells can survive wider fluctuations3 the integrated actions of bodily systems are impaired4. Other animals have a wider tolerance5 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 terminology6 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 inadequate7. A fence lizard8 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 home0therms, and those whose body temperature varies with their environments, called poikilotherms. But this classification also proved inadequate, because among mammals there are many that vary their body temperatures during hibernation9. Furthermore, many invertebrates10 that live in the depths of the ocean never experience change in the depths of the ocean never experience change in the chill of the deep water, and their body temperatures remain constant.
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(diào)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)?。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。
1 enzyme n.酵素，酶
參考例句：
Above a certain temperature,the enzyme molecule will become unfolded.超過一定溫度，酶分子將會展開。
An enzyme that dissolves the fibrin of blood clots.能溶解血凝塊中的纖維的酶。
2 impairs
v.損害，削弱( impair的第三人稱單數(shù) )
參考例句：
Smoking impairs our health. 吸煙會損害我們的健康。 來自《簡明英漢詞典》
Almost anything that impairs liver function can cause hepatitis. 任何有損于肝功能的因素，幾乎都會引起肝炎。 來自辭典例句
3 fluctuations
波動，漲落，起伏( fluctuation的名詞復數(shù) )
參考例句：
He showed the price fluctuations in a statistical table. 他用統(tǒng)計表顯示價格的波動。
There were so many unpredictable fluctuations on the Stock Exchange. 股票市場瞬息萬變。
4 impaired
adj.受損的；出毛病的；有（身體或智力）缺陷的v.損害，削弱( impair的過去式和過去分詞 ) 參考例句：
Much reading has impaired his vision. 大量讀書損害了他的視力。 來自《現(xiàn)代漢英綜合大詞典》
His hearing is somewhat impaired. 他的聽覺已受到一定程度的損害。 來自《現(xiàn)代漢英綜合大詞典》
5 tolerance
n.寬容；容忍，忍受；耐藥力；公差
參考例句：
Tolerance is one of his strengths.寬容是他的一個優(yōu)點。
Human beings have limited tolerance of noise.人類對噪音的忍耐力有限。
6 terminology
n.術(shù)語；專有名詞
參考例句：
He particularly criticized the terminology in the document.他特別批評了文件中使用的術(shù)語。
The article uses rather specialized musical terminology.這篇文章用了相當專業(yè)的音樂術(shù)語。
7 inadequate adj.(for,to)不充足的，不適當?shù)?BR> 參考例句：
The supply is inadequate to meet the demand.供不應求。
She was inadequate to the demands that were made on her.她還無力滿足對她提出的各項要求。
8 lizard n.蜥蜴，壁虎
參考例句：
A chameleon is a kind of lizard.變色龍是一種蜥蜴。
The lizard darted out its tongue at the insect.蜥蜴伸出舌頭去吃小昆蟲。
9 hibernation
n.冬眠
參考例句：
Bears wake up in the spring after a winter of hibernation.熊經(jīng)過一個冬天的冬眠后在春季蘇醒。
The tortoise spends the winter months in hibernation.烏龜在冬眠中度過寒冬季節(jié)。
10 invertebrates
n.無脊椎動物( invertebrate的名詞復數(shù) )
參考例句：
Insects and worms are all invertebrates. 昆蟲和蠕蟲都是無脊椎動物。 來自辭典例句
In the earthworm and many other invertebrates, these excretory structures are called nephridia. 在蚯蚓和許多其它無脊椎動物中，這些排泄結(jié)構(gòu)稱為腎管。 來自辭典例句
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(diào)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)?。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。
1 enzyme n.酵素，酶
參考例句：
Above a certain temperature,the enzyme molecule will become unfolded.超過一定溫度，酶分子將會展開。
An enzyme that dissolves the fibrin of blood clots.能溶解血凝塊中的纖維的酶。
2 impairs
v.損害，削弱( impair的第三人稱單數(shù) )
參考例句：
Smoking impairs our health. 吸煙會損害我們的健康。 來自《簡明英漢詞典》
Almost anything that impairs liver function can cause hepatitis. 任何有損于肝功能的因素，幾乎都會引起肝炎。 來自辭典例句
3 fluctuations
波動，漲落，起伏( fluctuation的名詞復數(shù) )
參考例句：
He showed the price fluctuations in a statistical table. 他用統(tǒng)計表顯示價格的波動。
There were so many unpredictable fluctuations on the Stock Exchange. 股票市場瞬息萬變。
4 impaired
adj.受損的；出毛病的；有（身體或智力）缺陷的v.損害，削弱( impair的過去式和過去分詞 ) 參考例句：
Much reading has impaired his vision. 大量讀書損害了他的視力。 來自《現(xiàn)代漢英綜合大詞典》
His hearing is somewhat impaired. 他的聽覺已受到一定程度的損害。 來自《現(xiàn)代漢英綜合大詞典》
5 tolerance
n.寬容；容忍，忍受；耐藥力；公差
參考例句：
Tolerance is one of his strengths.寬容是他的一個優(yōu)點。
Human beings have limited tolerance of noise.人類對噪音的忍耐力有限。
6 terminology
n.術(shù)語；專有名詞
參考例句：
He particularly criticized the terminology in the document.他特別批評了文件中使用的術(shù)語。
The article uses rather specialized musical terminology.這篇文章用了相當專業(yè)的音樂術(shù)語。
7 inadequate adj.(for,to)不充足的，不適當?shù)?BR> 參考例句：
The supply is inadequate to meet the demand.供不應求。
She was inadequate to the demands that were made on her.她還無力滿足對她提出的各項要求。
8 lizard n.蜥蜴，壁虎
參考例句：
A chameleon is a kind of lizard.變色龍是一種蜥蜴。
The lizard darted out its tongue at the insect.蜥蜴伸出舌頭去吃小昆蟲。
9 hibernation
n.冬眠
參考例句：
Bears wake up in the spring after a winter of hibernation.熊經(jīng)過一個冬天的冬眠后在春季蘇醒。
The tortoise spends the winter months in hibernation.烏龜在冬眠中度過寒冬季節(jié)。
10 invertebrates
n.無脊椎動物( invertebrate的名詞復數(shù) )
參考例句：
Insects and worms are all invertebrates. 昆蟲和蠕蟲都是無脊椎動物。 來自辭典例句
In the earthworm and many other invertebrates, these excretory structures are called nephridia. 在蚯蚓和許多其它無脊椎動物中，這些排泄結(jié)構(gòu)稱為腎管。 來自辭典例句