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TED科普：我们为什么会哭？眼泪的三种类型
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我们伤心时流泪，喜悦时流泪，愤怒到某种程度也会流泪，打个哈欠又流泪了……眼泪是怎样生成的？一年我们要哭掉多少水分？这则4分钟的可爱动画向你展示眼泪对人有多重要。
演讲题目：我们为什么会哭？眼泪的三种类型
我们的故事是关于一个名叫虹膜的女孩。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，她开心的时候也会哭，甚至被惹恼了，还是会哭。 She has special lacrimal glands to make new tears and special tubes, called lacrimal puncta, to drain old ones away.她特殊的泪腺可以分泌新的泪水，还有特殊的管道，叫做泪道，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（注：盎司，重量单位，1盎司相当28.35克），一年三十加仑（注：加仑，容积单位，1加仑大约4L）!
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，你会发现她无时不刻都流点眼泪。 The basal tears that Iris constantly produces form a thin coating of three layers that cover her and keep dirt and debris away.虹膜不断产生一点基底眼泪形成薄薄的三层外膜以防止她接触灰尘、碎屑。 Right next to Iris is the mucus layer, which keeps the whole thing fastened to her.紧挨着虹膜外面的是粘液层。给她固定整个组织。 On top of it is the aqueous layer, which keeps Iris hydrated, repels invasive bacteria, and protects her skin, or cornea, from damage.在她上面的是眼房水层，用来保持虹膜湿润， 排斥侵入性细菌，并保护她的皮肤，也叫角膜，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, and prevents the other layers from evaporating.并且，最后，还有脂质层，一层保持表面平滑的油性外膜方便虹膜透视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，虹膜整天也没有注意过基底眼泪在默默的工作。
That's kind of their whole point. But one day, she meets a girl named Onion.某种程度上说，这是它们的存在价值。直到有一天，她遇到了一个叫做“洋葱”的女孩。 Iris is immediately smitten. Onion looks gorgeous in her bright purple jacket, and she smells terrific.虹膜倍受打击。洋葱在她明亮的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，可怕的事情发生了， You see, when Onion's jacket is removed, a chemical reaction happens, converting the sulfoxides that make her smell so great into sulfenic acid, which then becomes a nasty substance with a long name: syn-Propanethial S-oxide.你看，当洋葱脱下外套，一个化学反应发生了，把让她闻起来有浓烈味道的亚砜，转化成次磺酸，进而变成一个有巨长名字的讨厌的物质：丙硫醛-S-氧化物。
The gas stings Iris, and suddenly, she can't help it, she starts weeping uncontrollably.这种气体刺激着虹膜，来势汹汹，她无力阻止，于是她开始控制不住地大哭。 These reflex tears are different from the basal tears that Iris is used to.这种反应性的眼泪与虹膜经常流的基底眼泪不同。 Because they're designed to wash away harmful substances, or particles, they're released in much larger amounts, and their aqueous layer contains more antibodies to stop any microorganisms that may be trying to get in, as well.因为，它们是为了冲掉有害的物质或颗粒。它们的流量更大，并且水层中包含大量抗体也为了阻止可能进入眼睛的微生物。 Both Iris and Onion are devastated. They know they can't continue their relationship if Iris is going to hurt and cry every time Onion takes off her jacket.虹膜和洋葱都震惊了。她们知道将无法继续做好朋友了，如果虹膜会受到伤害和哭泣，在每次洋葱脱下外套的时候。
So, they decide to break up. As Onion walks out the door, Iris stops crying.于是，她们决定绝交。当洋葱走出房门时，虹膜停止了哭泣，
And immediately starts again. Only now, she's not crying reflex tears but emotional tears.紧接着她又开始哭，但是这次，她并不是反射性流泪，而是动情落泪。
When someone is either too sad or too happy, it feels like a loss of control, which can be dangerous.当一个人太难过或是太开心的时候，就会感到失控，这是很危险的。 So, emotional tears are sent in to stabilize the mood as quickly as possible, along with other physical reactions, such as an increased heart rate and slower breathing.因此，留下动情的泪水可以稳定情绪，尽快地，和其他物理反应一起作用，比如加快心率和减缓呼吸。
But scientists still aren't sure exactly how or why the tears themselves are helpful.但是科学家们仍无法确定眼泪是为什么或如何起到效用的。 They may be a social mechanism to elicit sympathy or show submission.可能是一种社会机制 来博取同情，或者表达意见。 But some studies have also found that emotional tears contain higher levels of stress hormones, such as ACTH and enkephalin, an endorphin and natural pain killer.但是某些研究也发现动情留下的泪水中包含较高浓度的应激激素，比如促肾上腺皮质激素和脑啡肽，一种内啡肽，可以自然止痛。 In this case, emotional tears are also directly calming Iris down, as well as signaling her emotional state to others.在这种情况下，情感泪水也可以让虹膜冷静下来，以及向别人传递她的情绪， Sorry things didn't work out with Onion, Iris, but don't worry.很抱歉，虹膜，你不能和洋葱做朋友了，但是别担心。 As long as you have all three kinds of tears working to keep you balanced and healthy, it will get better.只要你拥有这三种泪水来保持你的健康均衡，一切都会好起来。
You'll see.你会看到的。
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