Hibernation-冬眠
hibernation is more than sleep. it is a very deep sleep. the animal's temperature drops to just over zero centigrade, and its heart beats very slowly. people who find hibernating animals asleep often think that they are dead: the body feels very cold, and the creature may breathe only once every five minutes. a hibernating animal cannot feel any pain. you can touch it, or even pull its tail, without causing it to move or wake up. in its hibernating state it can even live in a poisonous atmosphere for a long time without any ill effect.
hibernating in this way, the animal can sleep all through the winter. you might wonder how it manages to live without eating for so many months. the answer lies in two facts. the first is that it has stored supplies of fat in its body during the summer and autumn. the second is connected with the main use the body makes or rood――to supply the energy for movement. we have seen that hibernating animal reduces movement to far below the ordinary level. even the movements or the heart and lungs are greatly reduced. the animal hardly makes any movement, hardly use any energy, and hardly needs any rood.
some animals, including some bears only hair hibernate. that is to say, they sleep during the winter, but their sleep is not deep and their body temperature does not drop, as they are warm blooded animals. in the antumn the bear eats and eats and becomes very rat. his hair grows longer. soon he has a thick covering or rat and fur. in november he rinds a place to lie down and goes to sleep. on warm winter days he may think spring has arrived;he gets up and wa
冬眠不僅僅是睡眠，而是一種沉睡。動物的體溫降到剛好在零攝氏度以上，心臟跳動非常緩慢。人們看到處于冬眠狀態(tài)的動物，常常以為它們是死的：身體摸上去冰涼，可能每5分鐘才呼吸一次。冬眠的動物感覺不到任何疼痛。你可以摸它，拉它的尾巴，也不能使它動一動或醒過來。當(dāng)它處于冬眠狀態(tài)時，甚至可以長時間地生活在有毒空氣中而無任何不良后果。
用這樣的方式越冬，動物可以睡過整個冬天。你或許會覺得奇怪，它好幾個月不吃東西，怎么活過來的呢?可以從兩方面的事實中得到答案。第一，在夏秋季節(jié)，動物體內(nèi)儲存大量的'脂肪。第一是與食物對身體的主要用途，即食物供給身體活動所需的能量有關(guān)。我們已經(jīng)知道，冬眠的動物把活動量減少到大大低于一般的水平。甚至心肺的活動量也大大減少了。冬眠的動物幾乎沒有什么活動，幾乎也不消耗什么能量。因此它也幾乎不需要什么食物。
有些動物，包括有些熊，只是半冬眠。就是說，每到冬天它就睡覺，不過他們睡得不那么沉，因為他們屬溫血運動，所以體溫不下降。在秋天，熊吃了又吃長得真是肥極了。它身上的毛也長得更長了，很快全身就包滿了一層厚厚的脂肪和毛。到了11月，它找個地方躺下睡覺了。在冬天暖和的日子里，它可能以為春天已經(jīng)來到了，便起來四處走走，當(dāng)它看到地上積雪仍然很厚時，它很快又去睡了。
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