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Fingernails. They’re good for scratching, biting, clipping, and polishing. But what are they, in fact?
手指甲可以被用来划，咬，剪，磨。但是事实上，它们究竟是什么呢？

Although nails may look simple, they actually have various parts: a root buried beneath the skin at the base of the nail, the nail matrix, part of which is seen through the nail body as the white, half-moon shape where the nail meets the skin, the nail body–the part on the outside–and a nail bed that connects the nail to underlying¹ tissue.
虽然指甲看起来很简单，但是实际上它们由几个不同的部分组成：深埋在甲根处皮肤下的根基、指甲基质（指甲基质部分由甲体上的白色部分组成，也就是指甲和皮肤连接处的半月形状）、甲体（也就是我们能看到的外面的部分）以及甲床（连接指甲和底部组织的部位）。

Nail growth begins at the root, which produces the cells that form the nail body. As these cells form they produce keratin, the substance that makes the nail body hard and durable². As new cells form, the existing keratin-filled cells are pushed forward, away from the root. When these cells lose contact with the root and form the nail body, they die. That’s why it doesn’t hurt when you trim your nails.
指甲的生长从根基处开始，那里可以产生形成甲体的细胞。这些细胞形成后会产生角蛋白，正是这种物质使得我们的指甲坚固且耐用。随着新细胞的形成，被角蛋白 填充的已有的细胞被向前推进，逐渐远离根基。当这些老化的细胞失去和根基的联系时，它们便形成了甲体，此时它们已经死亡。这就是你修剪指甲时不会感觉到痛 的原因。

Once nails start growing, they don’t stop. Nails grow continuously, and if not trimmed can become extremely long. Nails protected from wear will eventually grow in long, twisted shapes, like a ram’s horn.
指甲一旦开始生长便不会停止。指甲不断地生长，如果不修剪的话会变得非常的长。耐磨损的指甲最终会长成长而弯的形状，就像羊角一样。

When kept at a proper length, nails can be useful in many ways, including acting³ as a barometer⁴ of a person’s health. Because the nail root is sensitive to changes in the body, the appearance of nails can sometimes provide clues to certain illnesses.
如果被修剪成适当的长度，指甲也会有很多的用途。例如，指甲可以作为健康的晴雨表。因为指甲的根基对于身体的变化非常敏感，所以指甲的外观有时候可以告诉我们是否患有某种疾病。

During extreme stress, extended fever, or in response to poisonous drugs, fingernails can crack, become thinner or thicker, and can even be shed.
在承受极大压力时，高烧持续不断时，或者人体是对有毒药物作出反应时，手指甲会破裂，变得更薄或者更厚，甚至有可能会脱落。