（介绍）
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当你半夜醒来 发现黑暗中有双发光的眼睛盯着你 你一定会被吓到
It can be terrifying to wake up in the middle of the night to a pair of glowing eyes staring at you from the darkness,
然后你意识到原来是你的猫
only to realize that it’s just your cat.
你确定么？
… Or is it?
很多动物 像鳄鱼 果蝠和狗 眼睛里都有发光结构 这个可以增强夜视能力
Lots of animals, including alligators, fruit bats, and dogs, all have a shiny structure in their eyes that gives them better night vision,
也可以产生这种诡异的光
which also causes this creepy glow.
眼睛后部有一层薄薄的组织叫做视网膜 由特殊的光敏细胞组成
The layer of tissue at the back of your eyes is called the retina, and it’s made up of special light-sensitive cells.
光线刺激这些细胞会产生电信号 通过视网膜后面的视神经
Light that hits those cells gets turned into an electrical signal that’s sent along the optic nerve, which sits behind the retina.
传递到大脑
That signal travels all the way to the brain.
如果光线接触不到这些细胞 就不能产生信号 也就无法被大脑察觉
And light that misses those cells isn’t turned into a signal, so your brain can’t detect it.
从爬行类到鸟类再到其他哺乳类动物 比如说猫 动物界的多数物种都拥有相同的眼睛结构
Many species across the animal kingdom have this same basic eye structure, from reptiles to birds to other mammals like cats.
有些动物视力较好 是因为眼睛里有更多的光敏细胞
One way animals have evolved to see better is to have more of those light-sensitive cells in each eye.
人类视网膜上有超过九千五百万个光敏细胞
Humans, for example, have over ninety-five million of them per retina.
但是很多需要在夜间捕食的夜行动物 它们有别的方法来捕捉更多的光
But a lot of animals—especially nocturnal animals whose eyes have to work well at night—have another way of detecting more light.
它们眼睛内部有一种叫做反光膜的结构 这个词（tapetum lucidum）在拉丁语中的意思是”明亮的挂毯”
They have a structure called the tapetum lucidum, which is Latin for “bright tapestry.”
这是一层长在视网膜后像镜子一样的组织
It’s a layer of tissue that sits behind the retina and acts like a mirror.
它可以通过反射 让光线再次经过视网膜上的光敏细胞
The tapetum lucidum reflects light that gets through the retina back at those light-sensitive cells
从而再次被光敏细胞捕捉到
giving them another chance to detect it.
但是有一些反射光会穿过这些动物的瞳孔
But some of the reflected light flies back out the animals’ pupils,
使它们的眼睛看起来像是在发光
which is what makes it seem like their eyes are glowing.
而光的颜色 也叫做眼耀 取决于反光膜的组成物质
The color of that glow, also called eyeshine, depends on what the tapetum lucidum is made of.
不同生物的反光膜表面由不同的高度有序的分子和纤维组成
And different critters have different highly ordered molecules or fibers that create a reflective surface.
某些鱼类的反光膜表面含有DNA的化学构建模块鸟嘌呤 会产生白色的眼耀
Some fish eyes use guanine—one of the chemical building blocks in DNA—and have white eyeshine.
羊类反光膜表面含有胶原蛋白 这也是很多动物肌肉和皮肤的结构物质
Sheep have collagen, which also provides structure to muscles and skin in lots of animals,
会发出蓝色或绿色的光
which leads to a blue or green glow.
猫类反光膜含有核黄素和锌 以及一些别的分子
And cats use riboflavin and zinc, among other molecules.
锌的含量决定猫的眼耀是黄色 绿色 或是蓝色
And the amount of zinc does a lot to determine how yellow or green or even blue their eyeshine is.
所以 你家小猫的眼睛可不是手电筒
So your kitty’s eyes aren’t actually like little flashlights;
它们只是在反射你房间里的光
they’re just reflecting some of the ambient light in your room.
但是如果它们开始发射红光或者激光束 或许你就该逃跑了
But if they start glowing red and shooting laser beams, you should probably run.
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