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Our story is about a girl named Iris.

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Iris is very sensitive.

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(Bird cawing)

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So much that she is always in tears.

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She cries when she's sad,

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when she's happy,

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(Godzilla roars)

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and even tears up[br]when things just get to her.

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She has special lacrimal glands[br]to make new tears

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and special tubes, called lacrimal puncta,

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to drain old ones away.

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And she cries so much[br]that she goes through

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ten ounces of tears per day,

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thirty gallons a year!

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In fact, if you look closely,

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you'll see that she's crying[br]a little bit all the time.

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The basal tears that Iris[br]constantly produces

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form a thin coating of three layers

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that cover her and keep[br]dirt and debris away.

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Right next to Iris is the mucus layer,

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which keeps the whole[br]thing fastened to her.

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On top of it is the aqueous layer,

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which keeps Iris hydrated,[br]repels invasive bacteria,

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and protects her skin,[br]or cornea, from damage.

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And, finally, there is the lipid layer,

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an oily outer film that keeps[br]the surface smooth

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for Iris to see through,

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and prevents the other[br]layers from evaporating.

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Normally, Iris goes about her day

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without really noticing[br]the basal tears doing their thing.

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That's kind of their whole point.

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But one day, she meets a girl named Onion.

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Iris is immediately smitten.

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Onion looks gorgeous in her[br]bright purple jacket,

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and she smells terrific.

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So, Iris invites Onion[br]to her house for dinner.

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But when she comes in[br]and takes off her jacket,

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something terrible happens.

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You see, when Onion's jacket is removed,

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a chemical reaction happens,

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converting the sulfoxides[br]that make her smell so great

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into sulfenic acid,

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which then becomes a nasty[br]substance with a long name:

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syn-Propanethial S-oxide.

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The gas stings Iris,[br]and suddenly, she can't help it,

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she starts weeping uncontrollably.

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These reflex tears are different[br]from the basal tears

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that Iris is used to.

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Because they're designed

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to wash away harmful[br]substances, or particles,

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they're released in much larger amounts,

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and their aqueous layer[br]contains more antibodies

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to stop any microorganisms[br]that may be trying to get in, as well.

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Both Iris and Onion are devastated.

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They know they can't continue[br]their relationship

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if Iris is going to hurt and cry[br]every time Onion takes off her jacket.

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So, they decide to break up.

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As Onion walks out the door,[br]Iris stops crying.

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And immediately starts again.

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Only now, she's not crying[br]reflex tears but emotional tears.

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When someone is either[br]too sad or too happy,

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it feels like a loss of control,

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which can be dangerous.

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So, emotional tears are sent in[br]to stabilize the mood

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as quickly as possible,

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along with other physical reactions,

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such as an increased heart rate[br]and slower breathing.

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But scientists still aren't sure

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exactly how or why the tears[br]themselves are helpful.

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They may be a social mechanism[br]to elicit sympathy or show submission.

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But some studies have also found

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that emotional tears contain[br]higher levels of stress hormones,

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such as ACTH and enkephalin,

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an endorphin and natural pain killer.

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In this case, emotional tears[br]are also directly calming Iris down,

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as well as signaling[br]her emotional state to others.

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Sorry things didn't work out[br]with Onion, Iris,

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but don't worry.

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As long as you have[br]all three kinds of tears

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working to keep you balanced[br]and healthy, it will get better.

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You'll see.