86 Skin

CHAPTER 1 Skin THE ORGAN THAT'S ALWAYS ON DISPLAY. When we think of our body's organs, words like heart, brain, or stomach come to mind. However, there is one we often forget about— our skin. Skin is so important that it even forms part of our personal identity. Our skin's color, created by a chemical in the body called melanin, is one of the first things other people notice about us. The amount of melanin in our skin depends on our genes, though it can be increased through contact with sunlight. Skin is made up of three layers: the epidermis, the dermis, and the subcutis. The epidermis, the outer layer, includes dead skin cells that are constantly falling away and being replaced. It is a defensive layer that protects us from the sun, wind, and water.

第1章剥掉经常被展出的器官。 当我们想到我们身体的器官时，会想到心脏、大脑或胃等词。 然而，有一点我们经常忘记——我们的皮肤。 皮肤是如此重要，它甚至构成了我们个人身份的一部分。 我们皮肤的颜色是由体内一种叫做黑色素的化学物质产生的，是别人注意到我们的第一件事。 我们皮肤中黑色素的数量取决于我们的基因，尽管它可以通过接触阳光而增加。 皮肤由三层组成：表皮、真皮层和皮下。 表皮，即外层，包括不断脱落和被替换的死皮细胞。 它是一层防御层，保护我们免受阳光、风和水的侵害。

Below the epidermis lies the dermis. This layer has small organs called sweat glands. These help control our body's temperature by sending a water-rich liquid— sweat— up to the epidermis. When this sweat reaches the skin, it has a cooling effect on the body. In the dermis are also millions of tiny nerve endings. These let us feel and judge everything we come into contact with, from a breath of wind to the temperature of water. The nerve endings in the dermis are found at different depths and react to the movement of body hair, pressure, vibration, and temperature. These nerve endings let us react quickly to our environment and avoid objects that might hurt us. Our sense of touch is possibly the most noticeable of the skin's characteristics because the feelings of pleasure or pain it provides are so powerful. Below the dermis lies the subcutis. It is made up of many fat cells that help the body hold in heat. These cells also help soften the stresses placed on the body. This layer also contains the roots of our hair.

表皮下面是真皮层。 这一层有叫做汗腺的小器官。 它们通过向表皮输送一种富含水分的液体——汗液来帮助控制我们的体温。 当汗液到达皮肤时，它对身体有冷却作用。 真皮中也有数百万个微小的神经末梢。 这些让我们感觉和判断我们接触到的一切，从一阵风到水温。 真皮中的神经末梢分布在不同的深度，并对体毛、压力、振动和温度的运动做出反应。 这些神经末梢让我们对环境做出快速反应，避免可能伤害我们的物体。 我们的触觉可能是皮肤特征中最引人注目的，因为它提供的快乐或痛苦的感觉是如此强大。 真皮下面是皮下。 它由许多脂肪细胞组成，帮助身体保持热量。 这些细胞还有助于减轻身体承受的压力。 这一层也包含了我们头发的根部。

CHAPTER 2 The First Line of Defense THE SKIN PLAYS A KEY ROLE IN THE FIGHT TO STAY ALIVE. Human skin can vary from as thick as 1.5 millimeters on the hands and feet to as thin as 0.05 millimeters around the eyes, which is why this is often the first place to show signs of aging. However, some animals, the rhinoceros for example, have skin that can be four centimeters thick! Skin, however, is more than just physical armor. It can also camouflage an animal from hunters, predators, or prey. This effect makes it possible for an animal to almost disappear into the background. Perhaps the best example of the power of camouflage is the chameleon. This lizard is so good at changing its appearance that we use the word chameleon to describe people who change depending on the situation.

第一道防线皮肤在生存的战斗中起着关键的作用。 人体皮肤的厚度从手脚的1.5毫米到眼睛周围的0.05毫米不等，这就是为什么眼睛通常是第一个显示衰老迹象的地方。 然而，有些动物，比如犀牛，皮肤厚可达4厘米！然而，皮肤不仅仅是物理盔甲。 它还可以伪装动物，使其不受猎人、掠食者或猎物的伤害。 这种效果使动物几乎消失在背景中成为可能。 也许伪装力量的最好例子是变色龙。 这种蜥蜴非常善于改变自己的外表，所以我们用变色龙这个词来形容那些根据情况而改变的人。

However, only a few species of chameleon change color to camouflage themselves. One of them is the Smith's dwarf chameleon, which can seem almost invisible when not moving. Although many species of chameleons can change color, most do so not to hide, but because of changes in their emotional state or body temperature. The Namaqua Chameleon lives in the desert. It changes color to protect itself from the extreme temperatures. In the cool morning it turns dark to absorb, or take in, heat more efficiently. In the hot sun it turns a light gray to reflect, or keep out, the sun's heat. Some animals take advantage of color changes to protect themselves from predators over a longer period of time. Arctic foxes have two different coats, one for summer and one for winter. The winter coat is white to hide the fox in the snow. The fox loses this fur in spring and replaces it with a gray coat more suited to the gray rocks of the arctic summer. Interestingly, the arctic hare, a common prey of the fox, takes advantage of exactly the same color changes!

然而，只有少数种类的变色龙改变颜色来伪装自己。 其中之一是史密斯的侏儒变色龙，它在不移动的时候几乎是看不见的。 虽然许多种类的变色龙可以改变颜色，但大多数不是为了隐藏，而是因为它们的情绪状态或体温的变化。 纳玛卡变色龙生活在沙漠中。 它改变颜色是为了保护自己不受极端温度的影响。 在凉爽的早晨，它变暗，以便更有效地吸收热量。 在炎热的阳光下，它会变成浅灰色，以反射或遮挡太阳的热量。 一些动物利用颜色的变化来保护自己在较长一段时间内免受捕食者的伤害。 北极狐有两种不同的皮毛，一种用于夏季，一种用于冬季。 冬衣是白色的，是为了把狐狸藏在雪里。 狐狸在春天会掉掉这种皮毛，取而代之的是更适合北极夏季灰色岩石的灰色皮毛。 有趣的是，北极兔，狐狸的常见猎物，利用完全相同的颜色变化！

Other animals have permanent camouflage. A polar bear's white fur makes it almost disappear against the snow and ice, despite its huge size. Strangely enough, the skin below the polar bear's fur is black! Although the patterns on the fur of tigers and leopards are very different, both serve the same purpose to make it harder for their prey to see them. The patterns are different because they live in different places.

其他动物有永久的伪装。 北极熊的白色皮毛使它几乎消失在冰雪中，尽管它的体型巨大。 奇怪的是，北极熊皮毛下面的皮肤是黑色的！尽管老虎和豹子皮毛上的图案非常不同，但它们的目的都是为了让猎物更难发现它们。 图案不同是因为他们生活在不同的地方。

Leopards hunt in bush country. Their spots allow them to disappear into the surrounding bushes. Tigers live in the jungle. Their stripes help them hide in the light and shade from the trees and long grass. These stripes are so effective that "tiger stripe" camouflage is used by many armies as a jungle uniform. Sometimes, however, an animal's skin color seems like a strange choice, almost a mistake. Take the zebra, which seems to draw attention to itself with its striking black and white pattern. Although scientists don't yet know the exact reason for the pattern, one theory is that when many zebras run together in a group, they make a pattern which is visually confusing. This makes it difficult for predators, such as lions, to identify one zebra to attack. This idea was copied in the First World War when British boats were painted in many different patterns to confuse the enemy. However, the technique, known as dazzle camouflage, was never proven to work. Another theory suggests that zebra stripes are actually very effective in hiding the animal in long grass because lions are in fact colorblind!

豹子在丛林中猎食。 它们的斑点使它们能够消失在周围的灌木丛中。 老虎生活在丛林里。 它们的条纹帮助它们隐藏在树木和长草的明处和阴凉处。 这些条纹非常有效，许多军队都把“虎纹”迷彩作为丛林制服。 然而，有时动物的肤色似乎是一个奇怪的选择，几乎是一个错误。 以斑马为例，它引人注目的黑白图案似乎吸引了人们的注意力。 虽然科学家们还不知道这种图案的确切原因，但有一种理论认为，当许多斑马成群结队地奔跑时，它们会形成一种视觉上令人困惑的图案。 这使得像狮子这样的掠食者很难识别出一只要攻击的斑马。 这个想法在第一次世界大战中被复制，当时英国的船只被涂成许多不同的图案，以迷惑敌人。 然而，这种被称为炫目伪装的技术从未被证明是有效的。 另一种理论认为，斑马条纹实际上非常有效地将动物隐藏在长草中，因为狮子实际上是色盲！