【英语时差8,16】我们为什么会哭？

 You notice your tears most after a good cry or while slicing an onion, but actually your eyes are constantly moistened by a thin film of tears.

This film has three distinct layers: an outer, oily layer to prevent evaporation¹; a middle layer of lacrimal fluid, the main ingredient of tears; and an inner, mucous² layer. This three layer film is replenished³ every time you blink, and it provides essential protection for your eyes.

Most of your body is protected by skin of course, and your outer layer of skin is made of dead cells and keratin, an opaque⁴, protective substance. Your eyes need to be transparent,however; they can’t be covered by a layer of dead cells and keratin. One of the main functions of tears therefore, is to keep these cells alive.

Tears are loaded with electrolyte salts, chemicals that are also found deep inside your body. These salts make your outer eye cells feel like they’re inside your body, preventing them from turning into cells similar to skin cells.

Tears help your eyes in other ways too. When a speck⁵ of dust gets in your eye, it’s coated with mucous from glands⁶ in the white of your eye, then washed out with extra fluid from the lacrimal glands, the main tear producing glands above the eye.

To protect your eyes from germs, tears also contain bacteria fighting enzymes⁷. What’s more, tears provide a good optical surface. They smooth out the microscopically⁸ uneven⁹ cells of your cornea. Without tears, tiny irregularities in your eye would give you constantly fuzzy vision.

Although they’re most apparent during a good cry, tears are actually an essential part of everyday life.

1 evaporation   

n.蒸发，消失

参考例句：

• Be careful not to lose too much liquid by evaporation.小心不要因蒸发失去太多水分。
• Our bodies can sweat,thereby losing heat by evaporation.我们的身体能出汗，由此可以蒸发散热。

2 mucous   

adj. 黏液的，似黏液的

参考例句：

• Healthy,skin,mucous membranes,and cilia are natural barriers to many viruses.健康的皮肤，粘膜和纤毛是许多病毒的天然屏障。
• Seromucous glands contain both mucous and serous cells.浆粘液腺既含有粘液性细胞，又含有浆液性细胞。

3 replenished   

补充( replenish的过去式和过去分词 )； 重新装满

参考例句：

• She replenished her wardrobe. 她添置了衣服。
• She has replenished a leather [fur] coat recently. 她最近添置了一件皮袄。

4 opaque   

adj.不透光的；不反光的，不传导的；晦涩的

参考例句：

• The windows are of opaque glass.这些窗户装着不透明玻璃。
• Their intentions remained opaque.他们的意图仍然令人费解。

5 speck   

n.微粒，小污点，小斑点

参考例句：

• I have not a speck of interest in it.我对它没有任何兴趣。
• The sky is clear and bright without a speck of cloud.天空晴朗，一星星云彩也没有。

6 glands   

n.腺( gland的名词复数 )

参考例句：

• a snake's poison glands 蛇的毒腺
• the sebaceous glands in the skin 皮脂腺

7 enzymes   

n. 酶，酵素

参考例句：

• It was said that washing powders containing enzymes remove stains more efficiently. 据说加酶洗衣粉除污更有效。
• Among the enzymes which are particularly effective are pepsin, papain. 在酶当中特别有效的是胃朊酶、木瓜酶。

8 microscopically   

显微镜下

参考例句：

• Microscopically the ores are medium grained to amorphous. 显微镜下，矿石为中粒至非晶质。 来自辞典例句
• He studied microscopically the statistics of trade. 他极仔细地研究了贸易统计数字。 来自辞典例句

9 uneven   

adj.不平坦的，不规则的，不均匀的

参考例句：

• The sidewalk is very uneven—be careful where you walk.这人行道凹凸不平—走路时请小心。
• The country was noted for its uneven distribution of land resources.这个国家以土地资源分布不均匀出名。