英语听力文摘 English Digest 151、当头发变白

　　Your teenage son wrecks¹ the car. Your daughter shows up with her recently paroled boyfriend.
These are the sorts of things that can make your hair turn gray overnight.
Actually, it's impossible for hair to completely change color overnight. Hair color comes from a pigment² called melanin. When hair grows, the cells that form the growing hair accumulate melanin and distribute it throughout the shaft³ at the center of a strand⁴ of hair. The hair's color depends on the number, size, and color of the melanin particles.
Gray hair results when, for some reason, the production of melanin is reduced, or stops completely. When this happens, the hair becomes transparent⁵ and all we see are the colorless cells that make up the hair shaft. Although it is common for melanin production to decrease and eventually stop as a person grows older, there is no specific explanation as to why this happens. Heredity seems to play a significant role in determining when the cells that make hair stop making pigment. If you have inherited genes⁶ programmed to shut off the production of melanin at an early age, you'll go gray sooner than later.
The phenomenon of suddenly going gray due to stress has more to do with hair loss than with actually losing color. A significant amount of stress can cause hair to fall out prematurely⁷. If you already have a significant amount of gray hair, the remaining dark hairs might be in a non-growing, resting phase, and thus are more likely to fall out. The sudden loss of dark hair will make it seem as though you've gone gray overnight.

1 wrecks   

n.沉船( wreck的名词复数 )；（事故中）遭严重毁坏的汽车（或飞机等）；（身体或精神上）受到严重损伤的人；状况非常糟糕的车辆（或建筑物等）v.毁坏[毁灭]某物( wreck的第三人称单数 )；使（船舶）失事，使遇难，使下沉

参考例句：

• The shores are strewn with wrecks. 海岸上满布失事船只的残骸。 来自《现代英汉综合大词典》
• My next care was to get together the wrecks of my fortune. 第二件我所关心的事就是集聚破产后的余财。 来自辞典例句

2 pigment   

n.天然色素，干粉颜料

参考例句：

• The Romans used natural pigments on their fabrics and walls.古罗马人在织物和墙壁上使用天然颜料。
• Who thought he might know what the skin pigment phenomenon meant.他自认为可能知道皮肤色素出现这种现象到底是怎么回事。

3 shaft   

n.(工具的)柄，杆状物

参考例句：

• He was wounded by a shaft.他被箭击中受伤。
• This is the shaft of a steam engine.这是一个蒸汽机主轴。

4 strand   

vt.使（船）搁浅，使（某人）困于（某地）

参考例句：

• She tucked a loose strand of hair behind her ears.她把一缕散发夹到了耳后。
• The climbers had been stranded by a storm.登山者被暴风雨困住了。

5 transparent   

adj.明显的，无疑的；透明的

参考例句：

• The water is so transparent that we can see the fishes swimming.水清澈透明，可以看到鱼儿游来游去。
• The window glass is transparent.窗玻璃是透明的。

6 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

7 prematurely   

adv.过早地，贸然地

参考例句：

• She was born prematurely with poorly developed lungs. 她早产，肺部未发育健全。 来自《简明英汉词典》
• His hair was prematurely white, but his busy eyebrows were still jet-black. 他的头发已经白了，不过两道浓眉还是乌黑乌黑的。 来自辞典例句