英语听力：自然百科 探索世界奥秘之Life Story(生命物语) Unit12（在线收听）

探索世界奥秘之Life Story(生命物语) Unit12

But if I were to tell you just the science of these changes I would be missing the most important thing of all. Let me show you what I mean. 

This is the amount of tears that an average person cries during a lifetime. Just a fraction under 65 liters, or to put it another way, about 1 million 850 thousand drops. So what do you know about them? Well, each tear weighs 35, 000 th of a gram and is about as salty as this part of the River Thames, at Greenwich.

Tears are produced by a gland just above the eye which is literally squeezed when we cry and the tears come down 6 tiny tubes about the thinness of a human hair. As far as we can tell, of all the animals in the world only humans actually cry when we are hurt or upset, about 28 drops each time. Though they are 99% water, tears also contain around 80 other ingredients, including sugar and antiseptics. 

But what's the most important thing to know if all these were your tears, of course, it's why you cried them. How many of these thousands of droplets were shed in fits of anger? How many in pain, how many in love, in grief, how many in sorrow, how many were shed by a baby and how many by an old man facing the end of life? The truth is, a knowledge of the science of life is only made complete by a knowledge of those living it. The human body is not just a biological machine. It's much more than that. It's a person. 

And in this series, it's people that will tell us what the body's ever changing story really means. Take Zach for example， having already mastered the complexities of crawling, he will be taking his first steps.

words and expressions

antiseptic: A substance that inhibits the growth and reproduction of disease-causing microorganisms.

抗菌剂：抑制致病微生物生长和繁殖的物质

in fits of :（感情的）激发

in a fit of rage

一时气愤