被纸割伤为什么那么疼？真是十指连心？

Paper seems completely harmless, but deployed properly, it can be a serious weapon: paper cuts are just the worst.

纸看起来无害，但合理使用的话，它也能成为犀利的武器：最严重的状况就是被纸割伤。

It’s all to do with nerve endings. To start with, there are lots more pain receptors embedded in your fingertips than almost anywhere else in your body. So while a paper cut on your arm, or thigh, or ankle might still be annoying, it would probably be more trivial than the intense fiery quality that finger-based paper cuts tend to have.

这跟神经末梢有关。首先，指尖的痛觉感受器比其他任何身体部位要多得多。所以，虽然纸割伤胳膊、大腿、脚踝也很疼，但也要比割伤手指那种火辣辣的疼痛感要轻得多。

This actually makes a good deal of evolutionary sense. Fingertips are how we explore the world, how we do small delicate tasks. So it makes sense that we have a lot of nerve endings there. It’s kind of a safety mechanism.

这其实是非常符合进化论的。我们用指尖来探索世界，做精细工作，所以指尖就该有很多神经末梢，这是一种安全机制。

To the naked eye, it might seem as if a paper's edge is fairly straight and smooth. But if you were to zoom in, you’d find that paper is more akin to a saw than to a blade.

肉眼看着好像纸的边缘很直很平，但如果你放大看，会发现纸更像锯而非刀片。

And paper cuts are typically shallow – but not too shallow. They’re deep enough to get past the top layer of the skin, otherwise they wouldn’t hurt. The top layer of skin has no nerve endings. But they don’t slice that deep into your body, which is perhaps why it’s puzzling that they should hurt so much. A deeper wound would result in bleeding. The blood would clot and a scab would develop, beneath which the skin could go about healing free from the continuedassault of the outside world. But the shallow wound of a paper cut doesn't offer such protection.

被纸割出的伤口浅，但也不是太浅。伤口深入到皮肤表层之下，否则就不疼了，皮肤表层没有神经末梢。但他们还不太深，这可能就是为什么人们会疑惑怎么这么疼，更深的伤口会引起出血，血会凝结，然后结痂，下面的皮肤可以不受外界干扰自行修复。但纸割出的浅的伤口就没有这种保护。

Without the cushion of blood, pain receptors are left exposed to the elements, and unless you quickly bandage your paper cut, those neurons will keep on sending the alarm bell. That, after all, is their job.

没有血液的这种保护作用，痛觉感受器被暴露在自然环境之中，除非快速包扎伤口，否则神经元会一直传送警报，毕竟这就是它们的工作。

Unfortunately, each of us is going to face the prospect of enduring a few paper cuts as we go about our lives. Luckily, a thousand paper cuts would really really hurt, but it probably wouldn’t kill you.

不幸的是，我们在生活中都会被纸割伤几次。但幸运的是，被纸割伤一千次可能真的非常非常疼，但也死不了。