托福閱讀資料之What Are Calluses And How Are They Formed?

　　These extra-tough patches of skin are generally quite useful–we might even say handy–because they act like a kind of natural armor, protecting areas of skin that get an unusual amount of wear and tear. Have you ever wondered exactly what a callus is, or how it forms on your skin?

　　Callus formation is triggered by pressure or abrasion. The heel of your foot as it rubs inside your shoe, or the palm of your hand if you’re doing a lot of manual labor are good examples of this.

　　While it might feel like a callus is something extra, added to your skin, it’s actually just a build-up of what’s already there.

　　Here’s How It Works

　　Your skin has a number of layers of different types of cells.

　　The outermost is a layer of hardened, dead cells. This top layer is usually about twenty-five cells thick, and it constantly replaces itself as the outermost cells flake off to be replaced by new hardened, dead cells underneath.

　　All About Friction

　　If your skin is subject to an unusual amount of friction, this layer of dead cells increases. New dead cells are added faster than the old ones slough away. This can build up the outer layer from twenty-five cells thick to over a hundred cells thick. You’ve grown a callus.

　　While calluses are generally useful, if the process continues unchecked a callus can thicken into a cone-shaped structure called a corn. These super calluses can be quite painful, and may require the attention of a doctor.

　　譯文

　　對于“老繭”，我們都很熟悉。

　　這些皮膚上突出的硬皮是很有用的，也可以說是方便，因為他們扮演著保護常磨損皮膚的天然盔甲的角色。你是否思考過什么是老繭?他又是怎樣形成的?

　　老繭是由壓力和摩擦而形成。腳后跟的繭是由其在鞋里摩擦而形成，正如手繭是在大量的勞動過程中形成。

　　盡管看起來似乎是皮膚上多出的部分，然而事實是已經(jīng)存在的皮膚角質(zhì)的累積。

　　形成過程

　　皮膚是由若干層不同類型的皮膚構(gòu)成。

　　表層是一些壞死的硬細胞，通常有25個細胞那么厚，表層細胞不斷的脫落，取而代之的是下層硬的壞死細胞，由此而完成自我更替過程。

　　一切皆由摩擦引起

　　假如皮膚受到不尋常量的摩擦，這層壞死細胞將會增加，新的壞死細胞增長速度比舊細胞脫落的速度快，這就致使皮膚表層的厚度增加到100個細胞那么厚，由此，老繭便形成。

　　雖然一般來講，繭是有益的，但如不控制其過程，老繭厚度就會增加到被稱作雞眼的錐形結(jié)構(gòu)，那樣就會很疼，甚至需要去看醫(yī)生。