When we are young，our skin stretches tightly over the muscles of the face，much like a rubber mask．As we grow older，our skin loses some of its elasticity，or stretch．Our face also shrinks a little．But because of the loss of elasticity，the skin no longer stretches tightly over the face．Little creases，or wrinkles，appear according to the way in which the skin has been moved and stretched for many years．
为什么老人有皱纹
当人们年轻时，皮肤紧绷在脸部的肌肉上，很像橡皮面罩。年纪大了以后，皮肤就失去了一部分弹性或伸缩性，脸上就会产生一些皱纹。由于弹性的消失，皮肤再不能紧绷在脸上。因此，在皮肤长年来经常运动和伸展的地方就出现了小小的折缝，它就叫皱纹。
Where Do Tears Come From
Your tears come from tiny sacs located in the outer corners of each eye．Each time you blink，the eyelids squeeze drops of tears from the tear sacs．The tears help to wash away dust and keep your eyes moist and healthy．The tears collect in the corners of the eye and drain out tiny openings into your nose．when you cry，the tears flow too fast to drain away．They spill over your eyelids and run down your cheeks．
眼泪是从哪里来的
你的眼泪是从眼睛外角里的小液囊流出来的。每当你眨眼时，眼睑就从泪囊里挤出一些泪水。这些泪水帮助洗去灰尘，并保持眼睛湿润和健康。这些眼泪聚集在眼角并通过鼻泪管排入鼻腔。当你哭时，眼泪涌出太快，来不及排掉，就溢出眼睑，沿着面颊流下。
Why Doesn’t It Hurt When Your Hair Is Cut
The hair that grows outward from the skin consists of dead cells，similar to those in the fingernails．These dead cells contain no nerves．Thus you fell no pain when your hair or nails are cut．But the hair is rooted in a layer of the skin which contains many nerve cells．That is why it hurts when someone yanks your hair hard．
为什么剪发时不感到痛
从头皮里长出的头发是由死细胞组成的，这和指甲相类似。这些死细胞没有神经。因此，当你剪头发或剪指甲时，不会感到疼痛。但是，头发的根是长在一层含有很多神经细胞的皮肤上的，这就是当有人使劲拉你的头发时，你会感到疼痛的原因。
Why Does a Mosquito Bite Itch
The itchy welt you get from a mosquito bite is caused by a liquid that the mosquito puts into your skin．When one bites it pricks your skin with its sharp beak．Then it sucks up a drop of blood for food．A liquid in the insect’s mouth keeps the blood thin and easy to suck．Some of this liquid gets under your skin．Most people are allergic to the liquid．It causes the bite to swell and itch．
为什么被蚊子叮后会发痒
人们被蚊子叮后会发痒，这是由于蚊子将其唾液注入皮肤中而引起的。蚊子叮人时，它用其尖嘴刺穿人的皮肤，然后吮吸血液作为食物。蚊子嘴里的唾液能使人的血液变稀，使之易于吮吸，这种液体部分留在皮肤里。多数人对这种液体过敏，以致蚊叮处又肿又痒。
What Is Ringworm
Ringworm is the name of a common skin disease．Ringworm is not caused by a worm．It is an infection caused by tiny plants known as fungi．The infection seems to heal in the center，and the ringworm sore appears as a red，scaly ring．The disease is highly infections，and can spread to other parts of the body．It can be easily cured by a doctor．
什么是金钱癣
金钱癣是一种常见的皮肤病。它并不是由寄生虫所引起的，而是由一种叫真菌的小菌苗所引起的一种传染病。金钱癣患处呈红色鳞状环形。从表面上看，患处的中心似乎已经痊愈。这种皮肤病容易传染并能扩大到身体的其他部位。然而，医生要治好这种皮肤病并不困难。
Why Do Indians Wear Feathers
The feathers an Indian warrior wore in his hair were awards given for special deeds in war．Each feather meant something．A feather that was split or dyed red，for example，meant that the warrior had been wounded．The position of the feather meant something，too．A feather standing straight up meant“brave deed”．A feather pointing down meant“less brave deed”—but still brave．
印第安人为什么头戴羽毛
印第安人勇士头戴羽毛。这羽毛是对勇士的奖赏，它象征勇士在战斗中立下了特殊战功。每种羽毛都有一定的含义。一根被折断或被染成红色的羽毛便意味着这位勇士在战斗中负过伤。羽毛戴在头上的方位也表示一定的意义。笔直竖立的羽毛表示“勇敢行为”。指向下方的羽毛则说明比“勇敢行为”稍逊一等，但仍然是勇敢的标志。
How Does a Broken Bone Heal
If you accidentally break a bone，the broken bone begins at once to produce new bone making material to bridge the broken ends．At first the new bone material is soft and easily injured．and the broken ends must be held firmly in place with a cast or splint as the bone heals．Gradually the new bone hardens until it forms a solid connection between the broken ends．
折断的骨头是怎样愈合的
如果你偶然骨折了，新的骨质马上会在骨折处生长起来，并将断了的两端连接起来。起初，新的骨质松软易损，所以在骨头愈合期间，断骨必须牢固地固定在模子里或夹板中。新骨逐渐变硬，直到能坚固地连接断骨的两端。
What Are Blackandblue Marks
When you receive a sharp blow，tiny blood vessels break inside your skin．Blood flows into the bruised area，and the bump becomes swollen and red．The blood that gets trapped in the bump later becomes dark and discoloured．When the bluish colour shows through your skin，we say you have a blackandblue mark．
青一块、紫一块的伤痕是怎样形成的
当你受到猛烈的碰撞时，微小的血管就破裂在皮肤里。血液流到受伤的部位，伤处便红肿起来。淤积在肿块里的血液随后变成黑色，接着又渐渐褪色。当这种浅蓝色透过皮肤显露出来时，我们就说，你身上有青一块紫一块的伤痕。
What Is the Blind Spot in the Eye
Your eyes contain lightsensitive cells that allow you to see．But there’s one part of your eye that has none of these visual cells．It is called the blind spot．Anything that comes in line with this blind spot becomes invisible．Ordinarily，we do not notice this partial blindness，because the eye is always moving and only a small part of any image falls on
the blind spot．
眼睛里的盲点是什么
人的眼睛有对光很敏感的细胞，有了这种细胞，人才能看见东西。但是，眼睛里还有一部分没有这种视觉细胞，这部分叫做盲点。任何东西反射到盲点上时，就会看不见。通常，我们并没有意识到这种局部的失明情况。因为眼珠始终在不停地移动着，任何形象，只有其中一小部分落在盲点上来。