时差N小时 为什么要流眼泪?（在线收听）

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.

切洋葱或者痛哭之后你会注意到自己流泪了，但事实上，泪薄膜使你的眼睛常常保持湿润这种状态。

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

泪薄膜由三个不同的层面组成：外层是防止蒸发的油脂层，中层是眼泪的主要成分——泪腺液体，内层是粘膜层。每当你眨一次眼睛，这三层薄膜就得到补充，这为你的眼睛提供必要的保护。

Most of your body is protected by skin of course, and your outer layer of skin is made of dead cells and keratin, an opaque, 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.

当然你身体的大部分是由皮肤来保护，皮肤外层是由死细胞和角蛋白（即一种不透明的防护物质）组成。然而，眼睛却需要透明的保护层；在眼睛表面不能覆盖有死细胞或者角蛋白。因此眼泪的一个主要的功能就使这些细胞保持活力。

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 from turning into cells similar to skin cells.

眼泪含有电解的盐类物质，这类化学物质在你身体的深处也存在。这些盐类物质将外眼细胞与外界隔离，防止它们变得类似于表皮细胞。

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

眼泪也能从其他方面保护眼睛。当一粒灰尘进入眼睛时，眼白部分的腺体就会分泌粘液将它包裹起来，然后随多余的液体从泪腺中流出。泪腺是产生眼泪的主要腺体。

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 your cornea. Without tears, tiny irregularities in your eye would give you constantly fuzzy vision.

为了保护眼睛不受细菌侵袭，眼泪中也含有抗细菌酶。更重要的是，眼泪能够帮助抚平微小不均匀的细胞角膜，从而形成一个良好的视觉表面。没有眼泪，那些微小不规则的角膜就会使视线变得模糊。

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

尽管只有在哭泣的时候才见眼泪，但它的确是日常生活中不可缺少的一部分。