You're fast asleep, and nothing is happening. Or is it? In fact, your body is hard at work. Your lungs are taking oxygen from the air, and your heart is pumping blood round your body. Millions of pieces of information are travelling backwards and forwards to your brain all the time. Muscles are repairing themselves, and in your lymph nodes special cells are cleaning germs and waste from the body. You may think that nothing is happening, but in the extraordinary machine that is the human body, it is very busy indeed...

你快速入睡，任何事都沒發生？或者有發生？事實上，你的身體工作的很辛苦，你的肺要從空氣中取氧氣，你的心臟要替整個身體輸血，數百萬條訊息不停在大腦來來回回傳遞，肌肉自動修復，你的淋巴結中的特殊細胞正在清潔體內的細菌和廢物，你可能認為任何事都沒發生，但在名為人體的非凡機器中，的確是非常繁忙。