Hibernation
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[ks around. When he sees that the snow is still thick on the ground, he quickly goes to sleep again.
[点评]
此文是一篇非常好的背景材料。有关动物冬眠我们或许有所了解，但也许是一知半解。文章先叙述了动物冬眠时的状况，而后详细说明了为什么有些动物能做到冬眠，最后还举例说明了半冬眠动物熊的情况，使读者丰富了这方面的知识。
[参考译文]
冬眠
冬眠不仅仅是睡眠，而是一种沉睡。动物的体温降到刚好在零摄氏度以上，心脏跳动非常缓慢。人们看到处于冬眠状态的动物，常常以为它们是死的：身体摸上去冰凉，可能每5分钟才呼吸一次。冬眠的动物感觉不到任何疼痛。你可以摸它，拉它的尾巴，也不能使它动一动或醒过来。当它处于冬眠状态时，甚至可以长时间地生活在有毒空气中而无任何不良后果。
用这样的方式越冬，动物可以睡过整个冬天。你或许会觉得奇怪，它好几个月不吃东西，怎么活过来的呢?可以从两方面的事实中得到答案。第一，在夏秋季节，动物体内储存大量的脂肪。第一是与食物对身体的主要用途，即食物供给身体活动所需的能量有关。我们已经知道，冬眠的动物把活动量减少到大大低于一般的水平。甚至心肺的活动量也大大减少了。冬眠的动物几乎没有什么活动，几乎也不消耗什么能量。因此它也几乎不需要什么食物。
有些动物，包括有些熊，只是半冬眠。就是说，每到冬天它就睡觉，不过他们睡得不那么沉，因为他们属温血运动，所以体温不下降。在秋天，熊吃了又吃长得真是肥极了。它身上的毛也长得更长了，很快全身就包满了一层厚厚的脂肪和毛。到了11月，它找个地方躺下睡觉了。在冬天暖和的日子里，它可能以为春天已经来到了，便起来四处走走，当它看到地上积雪仍然很厚时，它很快又去睡了。