part 1 ：眼泪。那些你也许不知道的事~ hints: the River Thames Greenwich antiseptics

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 one 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 six 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.

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