Iris is very sensitive. So much that she is always in tears. 虹膜很敏感，以至于总是以泪洗面。

　　She cries when she's sad, when she's happy, and even tears up when things just get to her. 她难过的时候会哭，开心的时候也会哭，甚至被惹恼了，还会哭。

　　She has special lacrimal glands to make new tears and special tubes, called lacrimal puncta, to drain old ones away. 她的特殊泪腺可以分泌新泪水，它还有叫做泪道的特殊管道，用来排走眼泪。

　　And she cries so much that she goes through ten ounces of tears per day, thirty gallons a year! 她哭得很厉害，每天会流掉十盎司的泪水，一年就是三十加仑！

　　In fact, if you look closely, you'll see that she's crying a little bit all the time. 事实上，如果你仔细观察，会发现她无时不刻都流点儿眼泪。

　　The basal tears that Iris constantly produces form a thin coating of three layers that cover her and keep dirt and debris away. 虹膜不断产生的基底眼泪，形成薄薄的三层外膜，防止她接触灰尘、碎屑。

　　Right next to Iris is the mucus layer, which keeps the whole thing fastened to her. 紧挨着虹膜的是粘液层，它给她固定了整个架构。

　　On top of it is the aqueous layer, which keeps Iris hydrated, 黏液层上面的是水层，用来保持虹膜湿润，

　　repels invasive bacteria, and protects her skin, or cornea, from damage. 赶走侵入性细菌，并保护她的皮肤或角膜，保护她免受侵害。

　　And, finally, there is the lipid layer, an oily outer film that keeps the surface smooth for Iris to see through, 最后还有脂质层，它是一层保持表面平滑的油性外膜，方便虹膜透视，

　　and prevents the other layers from evaporating. 也防止其他层的蒸发。

　　Normally, Iris goes about her day without really noticing the basal tears doing their thing. 通常情况下，虹膜整天都没注意默默工作的基底眼泪。

　　That's kind of their whole point. 某种程度上说，这是它们的存在价值。

　　But one day, she meets a girl named Onion. 直到有一天，她遇到了一个叫做“洋葱”的女孩。

　　Iris is immediately smitten. 虹膜倍受打击。

　　Onion looks gorgeous in her bright purple jacket, and she smells terrific. 洋葱在她明亮紫色外套的烘托下看起来很华丽，并且闻起来棒极了。

　　So, Iris invites Onion to her house for dinner. 于是，虹膜邀请洋葱来家里吃晚餐。

　　But when she comes in and takes off her jacket, something terrible happens. 当洋葱进屋并且脱下外套时，可怕的事情发生了。

　　You see, when Onion's jacket is removed, a chemical reaction happens, 你看，当洋葱脱下外套时，一个化学反应发生了，

　　converting the sulfoxides that make her smell so great into sulfenic acid, 让她很好闻的亚砜转化成了次磺酸，

　　which then becomes a nasty substance with a long name: syn-Propanethial S-oxide. 进而变成一个有巨长名字的讨厌物质：丙硫醛-S-氧化物。