時差N小時:為什么要流眼淚?

You notice your tears most after a good cry or whileslicing an onion, but actually your eyes areconstantly moistened by a thin film of tears.

切洋蔥或者痛哭之后你會注意到自己流淚了，但事實上，淚薄膜使你的眼睛常常保持濕潤這種狀態(tài)。

This film has three distinct layers: an outer, oilylayer to prevent evaporation; a middle layer oflacrimal fluid, the main ingredient of tears; and aninner, mucous layer. This three layer film isreplenished every time you blink, and it providesessential protection for your eyes.

淚薄膜由三個不同的層面組成：外層是防止蒸發(fā)的油脂層，中層是眼淚的主要成分——淚腺液體，內(nèi)層是粘膜層。每當(dāng)你眨一次眼睛，這三層薄膜就得到補(bǔ)充，這為你的眼睛提供必要的保護(hù)。

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

當(dāng)然你身體的大部分是由皮膚來保護(hù)，皮膚外層是由死細(xì)胞和角蛋白(即一種不透明的防護(hù)物質(zhì))組成。然而，眼睛卻需要透明的保護(hù)層;在眼睛表面不能覆蓋有死細(xì)胞或者角蛋白。因此眼淚的一個主要的功能就使這些細(xì)胞保持活力。

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 fromturning into cells similar to skin cells.

眼淚含有電解的鹽類物質(zhì)，這類化學(xué)物質(zhì)在你身體的深處也存在。這些鹽類物質(zhì)將外眼細(xì)胞與外界隔離，防止它們變得類似于表皮細(xì)胞。

Tears help your eyes in other ways too. When a speck of dust gets in your eye, it's coated withmucous from glands in the white of your eye, then washed out with extra fluid from the lacrimalglands, the main tear producing glands above the eye.

眼淚也能從其他方面保護(hù)眼睛。當(dāng)一粒灰塵進(jìn)入眼睛時，眼白部分的腺體就會分泌粘液將它包裹起來，然后隨多余的液體從淚腺中流出。淚腺是產(chǎn)生眼淚的主要腺體。

To protect your eyes from germs, tears also contain bacteria fighting enzymes. What's more,tears provide a good optical surface. They smooth out the microscopically uneven cells of yourcornea. Without tears, tiny irregularities in your eye would give you constantly fuzzy vision.

為了保護(hù)眼睛不受細(xì)菌侵襲，眼淚中也含有抗細(xì)菌酶。更重要的是，眼淚能夠幫助撫平微小不均勻的細(xì)胞角膜，從而形成一個良好的視覺表面。沒有眼淚，那些微小不規(guī)則的角膜就會使視線變得模糊。

Although they're most apparent during a good cry, tears are actually an essential part ofeveryday life.

盡管只有在哭泣的時候才見眼淚，但它的確是日常生活中不可缺少的一部分。