At the beginning of the century, medical scientists made a surprising discovery: that we are (1)_____ not just of flesh and blood but also of time. They were able to (2)_____ that we all have an internal 'body clock' which (3)_____ the rise and fall of our body energies, making us different from one day to the (5)_____. These forces became known as biorhythms: they create the (5)_____ in our everyday life. The (6)_____ of an internal 'body clock' should not be too surprising, (7)_____ the lives of most living things are dominated by the 24-hour night-and-day cycle. The most obvious (8)_____ of this cycle is the (9)_____ we feel tired and fall asleep at night and become awake and (10)_____ during the day. (11)_____ the 24-hour rhythm is interrupted, most people experience unpleasant side effects. (12)_____, international aeroplane travelers often experience 'jet lag' when traveling across time (13)_____. People who are not used to (14)_____ work can find that lack of sleep affects their work performance. (15)_____ the daily rhythm of sleeping and waking, we also have other rhythms which (16)_____.longer than one day and which influence wide areas of our lives. Most of us would agree that we feel good on (17)_____ days and net so good on others. Sometimes we are (18)_____ fingers and thumbs but on other days we have excellent coordination. There are times when we appear to be accident-prone, or when our temper seems to be on a short fuse. Isn't it also strange (19)_____ ideas seem to flow on some days but at other times are (20)_____ nonexistent? Musicians, painters and writers often talk about 'dry spells'.