CHAPTER III
第三章
THE BRAIN AND NERVOUS SYSTEM
大脑及神经系统
A fine brain, or a good mind. These terms are often used interchangeably, as if they stood for the same thing. Yet the brain is material substance—so many cells and fibers, a pulpy protoplasmic mass weighing some three pounds and shut away from the outside world in a casket of bone. The mind is a spiritual thing—the sum of the processes by which we think and feel and will, mastering our world and accomplishing our destiny.
"一个优秀的大脑，或者说一个好的心智。这些术语常常被交替使用，就好像它们代表的是同一个东西。然而，大脑是物质实体——由许多细胞和纤维组成，一团浆状的原浆质质量，重约三磅，被封闭在一个骨头的盒子里，与外部世界隔绝。心智则是一种精神事物——它是我们思考、感受和意志的过程的总和，掌控我们的世界并实现我们的命运。"
1. THE RELATIONS OF MIND AND BRAIN
1.心智和大脑的关系
Interaction of Mind and Brain.—How, then, come these two widely different facts, mind and brain, to be so related in our speech? Why are the terms so commonly interchanged?—It is because mind and brain are so vitally related in their processes and so inseparably connected in their work. No movement of our thought, no bit of sensation, no memory, no feeling, no act of decision but is accompanied by its own particular activity in the cells of the brain. It is this that the psychologist has in mind when he says, no psychosis without its corresponding neurosis.
心智与大脑的相互作用——那么，这两个截然不同的事实，即心智和大脑，为何在我们的言语中如此相关呢？为什么这些术语常常被互换使用呢？——这是因为在我们的思维过程中，心智和大脑是至关重要的相关，且在其工作中密不可分地连接着。我们的思考、感觉、记忆、情感或决定，无一不在大脑细胞中伴随着其特定的活动。正是这一点，心理学家常说“没有心理疾病就没有对应的神经疾病”。
So far as our present existence is concerned, then, no mind ever works except through some brain, and a brain without a mind becomes but a mass of dead matter,31 so much clay. Mind and brain are perfectly adapted to each other. Nor is this mere accident. For through the ages of man's past history each has grown up and developed into its present state of efficiency by working in conjunction with the other. Each has helped form the other and determine its qualities. Not only is this true for the race in its evolution, but for every individual as he passes from infancy to maturity.
就我们目前的存在而言，没有心智能够不通过大脑而工作，而一个没有心智的大脑只不过是一堆死物质，31就像那么多的黏土。心智和大脑彼此完美适应，这不是偶然的。因为在人类过去的漫长岁月中，每一个都通过与另一个的结合工作，成长并发展成了它现在的效能状态。每一个都帮助塑造了另一个，并确定了它的特质。这不仅在种族的进化中是真实的，而且对于每一个从婴儿期到成熟期的个体都是如此。
The Brain as the Mind's Machine.—In the first chapter we saw that the brain does not create the mind, but that the mind works through the brain. No one can believe that the brain secretes mind as the liver secretes bile, or that it grinds it out as a mill does flour. Indeed, just what their exact relation is has not yet been settled. Yet it is easy to see that if the mind must use the brain as a machine and work through it, then the mind must be subject to the limitations of its machine, or, in other words, the mind cannot be better than the brain through which it operates. A brain and nervous system that are poorly developed or insufficiently nourished mean low grade of efficiency in our mental processes, just as a poorly constructed or wrongly adjusted motor means loss of power in applying the electric current to its work. We will, then, look upon the mind and the brain as counterparts of each other, each performing activities which correspond to activities in the other, both inextricably bound together at least so far as this life is concerned, and each getting its significance by its union with the other. This view will lend interest to a brief study of the brain and nervous system.32
大脑作为心智的机器——在第一章中，我们看到大脑并不创造心智，而是心智通过大脑工作。没有人能相信大脑像肝脏分泌胆汁那样分泌心智，或者像磨坊磨面粉那样磨出心智。事实上，他们之间的确切关系尚未确定。然而，很容易看出，如果心智必须将大脑用作机器并通过它来工作，那么心智就必须受到其机器的限制，或者换句话说，心智不能比它所操作的大脑更好。一个发育不良或营养不足的大脑和神经系统意味着我们心理过程中的效率低下，就像一个构造不良或调整不当的电机意味着在将其应用于工作时电力的损失。因此，我们将视心智和大脑为彼此的对应物，每个都执行与另一个中的活动相对应的活动，至少在这种生活方面它们密不可分地结合在一起，并且每个都通过与另一个的结合获得了它的意义。这种观点将引发人们简要研究大脑和神经系统的兴趣。32
2. THE MIND'S DEPENDENCE ON THE EXTERNAL WORLD
2. 心智对外部世界的依赖
But can we first see how in a general way the brain and nervous system are primarily related to our thinking? Let us go back to the beginning and consider the babe when it first opens its eyes on the scenes of its new existence. What is in its mind? What does it think about? Nothing. Imagine, if you can, a person born blind and deaf, and without the sense of touch, taste, or smell. Let such a person live on for a year, for five years, for a lifetime. What would he know? What ray of intelligence would enter his mind? What would he think about? All would be dark to his eyes, all silent to his ears, all tasteless to his mouth, all odorless to his nostrils, all touchless to his skin. His mind would be a blank. He would have no mind. He could not get started to think. He could not get started to act. He would belong to a lower scale of life than the tiny animal that floats with the waves and the tide in the ocean without power to direct its own course. He would be but an inert mass of flesh without sense or intelligence.
但首先我们能否看到大脑和神经系统与我们的思维是如何基本相关的呢？让我们回到起点，考虑婴儿第一次睁开眼睛看到它的新生活场景时。它心里想的是什么？它在想些什么？什么都没有。想象一下，如果可以的话，一个天生失明、失聪，没有触觉、味觉或嗅觉的人。让这样的人生活一年、五年、甚至一生。他能知道什么？什么智慧的光芒会进入他的心智？他会想些什么？他的眼睛看到的一切都是黑暗的，他的耳朵听到的一切都是寂静的，他的嘴巴尝到的一切都是无味的，他的鼻孔闻到的一切都是无嗅的，他的皮肤触摸到的一切都是无触感的。他的心智将是一片空白。他将没有心智。他无法开始思考。他无法开始行动。他将属于比海洋中随波逐流的小动物更低等的生命形式，没有能力指导自己的方向。他将只是一坨没有感觉或智力的惰性肉体。
The Mind at Birth.—Yet this is the condition of the babe at birth. It is born practically blind and deaf, without definite sense of taste or smell. Born without anything to think about, and no way to get anything to think about until the senses wake up and furnish some material from the outside world. Born with all the mechanism of muscle and nerve ready to perform the countless complex movements of arms and legs and body which characterize every child, he could not successfully start these activities without a message from the senses to set them going. At birth the child probably has only33 the senses of contact and temperature present with any degree of clearness; taste soon follows; vision of an imperfect sort in a few days; hearing about the same time, and smell a little later. The senses are waking up and beginning their acquaintance with the outside world.
出生时的心智——然而，这就是婴儿出生时的条件。它出生时几乎是失明和失聪的，没有明确的味觉或嗅觉。出生时没有任何可以思考的东西，也无法获得任何东西来思考，直到感觉苏醒并从外部世界提供一些材料。出生时具备了肌肉和神经的所有机制，准备执行手臂、腿部和身体无数复杂动作，这些动作是每个孩子的特征，如果没有来自感觉的信息来启动它们，他就无法成功地开始这些活动。出生时，孩子可能只具备接触和温度的感觉，而且相当清晰；味觉很快跟随；几天后是不完美的视觉；大约在同一时间是听觉，稍晚一点是嗅觉。感觉正在苏醒，并开始与外部世界相识。
Fig. 5.—A Neurone from a Human Spinal Cord. The central portion represents the cell body. N, the nucleus; P, a pigmented or colored spot; D, a dendrite, or relatively short fiber,—which branches freely; A, an axon or long fiber, which branches but little.
图5.—来自人类脊髓的神经元。中央部分代表细胞体。N，细胞核；P，一个有色素或有色的斑点；D，树突，或相对较短的纤维——它自由分支；A，轴突或长纤维，它很少分支。
The Work of the Senses.—And what a problem the senses have to solve! On the one hand the great universe of sights and sounds, of tastes and smells, of contacts and temperatures, and whatever else may belong to the material world in which we live; and on the other hand the little shapeless mass of gray and white pulpy matter called the brain, incapable of sustaining its own shape, shut away in the darkness of a bony case with no possibility of contact with the outside world, and possessing no means of communicating with it except through the senses. And yet this universe of external things must be brought into communication with the seemingly insignificant but really wonderful34 brain, else the mind could never be. Here we discover, then, the two great factors which first require our study if we would understand the growth of the mind—the material world without, and the brain within. For it is the action and interaction of these which lie at the bottom of the mind's development. Let us first look a little more closely at the brain and the accompanying nervous system.
感官的工作——感官必须解决多么复杂的问题！一方面，是视觉和声音、味觉和嗅觉、触觉和温度的巨大宇宙，以及可能属于我们生活的物质世界的其他任何东西；另一方面，是被称为大脑的无形的小团灰色和白色浆质物质，它无法维持自己的形状，被封闭在一个骨质的黑暗箱子里，与外部世界接触的可能性为零，并且除了通过感官之外，没有与外界交流的手段。然而，这个外部事物的宇宙必须与看似微不足道但实际上非常奇妙的大脑建立联系，否则心智永远不会存在。在这里，我们发现，如果我们要理解心智的成长，首先需要研究的两个重要因素——外部的物质世界和内部的大脑。因为正是这些因素的行动和相互作用构成了心智发展的基础。让我们首先更仔细地看一下大脑和伴随的神经系统。
3. STRUCTURAL ELEMENTS OF THE NERVOUS SYSTEM
3.神经系统的结构元素
It will help in understanding both the structure and the working of the nervous system to keep in mind that it containsbut one fundamental unit of structure. This is the neurone. Just as the house is built up by adding brick upon brick, so brain, cord, nerves and organs of sense are formed by the union of numberless neurones.
在理解神经系统的结构和工作原理时，要记住它只包含一个基本的结构单元。这就是神经元。就像房子是通过一块块砖叠加建造起来的一样，大脑、脊髓、神经和感觉器官也是通过无数神经元的结合形成的。
Fig. 6.—Neurones in different stages of development, from a to e. In a, the elementary cell body alone is present; in c, a dendrite is shown projecting upward and an axon downward.—After Donaldson.
图6.—不同发育阶段的神经元，从a到e。在a中，只存在基本的细胞体；在c中，显示了一个向上突出的树突和一个向下的轴突。—根据唐纳森（DONALDSON）的研究。
The Neurone.—What, then, is a neurone? What is its structure, its function, how does it act? A neurone35 is a protoplasmic cell, with its outgrowing fibers. The cell part of the neurone is of a variety of shapes, triangular, pyramidal, cylindrical, and irregular. The cells vary in size from 1/250 to 1/3500 of an inch in diameter. In general the function of the cell is thought to be to generate the nervous energy responsible for our consciousness—sensation, memory, reasoning, feeling and all the rest, and for our movements. The cell also provides for the nutrition of the fibers.
神经元——那么，什么是神经元？它的结构是什么，它的功能是什么，它是如何作用的？神经元是一种带有其生长纤维的原浆细胞。神经元的细胞部分有各种形状，三角形、锥体形、圆柱形和不规则形。这些细胞的大小从直径1/250到1/3500英寸不等。总的来说，细胞的功能被认为产生负责我们的意识——感觉、记忆、推理、情感以及所有其他活动，以及我们的运动的神经能量。细胞还为纤维提供营养。
Fig. 7.—Longitudinal (A) and transverse (B) section of nerve fiber. The heavy border represents the medullary, or enveloping sheath, which becomes thicker in the larger fibers.—After Donaldson.
图7.—神经纤维的纵向（A）和横向（B）截面。粗边框代表髓鞘，即包裹性的鞘，它在较大的纤维中变得更厚。—根据唐纳森（DONALDSON）的研究。
Neurone Fibers.—The neurone fibers are of two kinds, dendrites and axons. The dendrites are comparatively large in diameter, branch freely, like the branches of a tree, and extend but a relatively short distance from the parent cell. Axons are slender, and branch but little, and then approximately at right angles. They reach a much greater distance from the cell body than the dendrites. Neurones vary greatly in length. Some of those found in the spinal cord and brain are not more than 1/12 of an inch long, while others which reach from the extremities to the cord, measure several feet. Both dendrites and axons are of diameter so small as to be invisible except under the microscope.
神经元纤维——神经元纤维有两种类型，树突和轴突。树突的直径相对较大，像树的分支一样自由分枝，并且从母细胞延伸出相对较短的距离。轴突纤细，几乎不分枝，即使分枝也大约是以直角分枝。它们从细胞体到达的距离比树突要远得多。神经元的长度差异很大。在脊髓和大脑中发现的一些神经元长度不超过1/12英寸，而其他从肢体延伸到脊髓的神经元，长度可达几英尺。树突和轴突的直径都非常小，除了在显微镜下否则是看不见的。
Neuroglia.—Out of this simple structural element, the neurone, the entire nervous system is built. True, the neurones are held in place, and perhaps insulated, by a kind of soft cement called neuroglia. But this seems to possess no strictly nervous function. The number of the36 microscopic neurones required to make up the mass of the brain, cord and peripheral nervous system is far beyond our mental grasp. It is computed that the brain and cord contain some 3,000 millions of them.
神经胶质——整个神经系统就是由这种简单的结构元素，即神经元，构建而成的。的确，神经元被一种叫做神经胶质的软性水泥固定在位，也许还起到绝缘作用。但这似乎并不具备严格的神经功能。组成大脑、脊髓和外周神经系统所需的微小神经元的数量远远超出我们的心理理解能力。据计算，大脑和脊髓包含大约30亿个神经元。
Complexity of the Brain.—Something of the complexity of the brain structure can best be understood by an illustration. Professor Stratton estimates that if we were to make a model of the human brain, using for the neurone fibers wires so small as to be barely visible to the eye, in order to find room for all the wires the model would need to be the size of a city block on the base and correspondingly high. Imagine a telephone system of this complexity operating from one switch-board!
大脑的复杂性——通过一个示例可以最好地理解大脑结构的复杂性。斯特拉顿教授估计，如果我们使用几乎无法用肉眼看到的细小电线来制作人脑模型，为了找到足够的空间来容纳所有的电线，这个模型需要有一个城市街区那么大的基底，并且相应地高。想象一下，一个如此复杂的电话系统在一个交换台上运作！
"Gray" and "White" Matter.—The "gray matter" of the brain and cord is made up of nerve cells and their dendrites, and the terminations of axons, which enter from the adjoining white matter. A part of the mass of gray matter also consists of the neuroglia which surrounds the nerve cells and fibers, and a network of blood vessels. The "white matter" of the central system consists chiefly of axons with their enveloping or medullary, sheath and neuroglia. The white matter contains no nerve cells or dendrites. The difference in color of the gray and the white matter is caused chiefly by the fact that in the gray masses the medullary sheath, which is white, is lacking, thus revealing the ashen gray of the nerve threads. In the white masses the medullary sheath is present.
“灰质”和“白质”——大脑和脊髓的“灰质”由神经细胞及其树突，以及从相邻白质进入的轴突末梢组成。灰质的一部分还由包围神经细胞和纤维的神经胶质，以及血管网络组成。中央系统的“白质”主要由带有其包裹性或髓鞘和神经胶质的轴突组成。白质不包含任何神经细胞或树突。灰质和白质的颜色差异主要是由以下事实引起的：在灰色块中，白色的髓鞘缺失，因此揭示了神经线的灰白色。在白色块中，髓鞘存在。
4. GROSS STRUCTURE OF THE NERVOUS SYSTEM
4. 神经系统的整体结构
Divisions of the Nervous System.—The nervous system may be considered in two divisions: (1) The central system, which consists of the brain and spinal cord, and37 (2) the peripheral system, which comprises the sensory and motor neurones connecting the periphery and the internal organs with the central system and the specialized end-organs of the senses. The sympathetic system, which is found as a double chain of nerve connections joining the roots of sensory and motor nerves just outside the spinal column, does not seem to be directly related to consciousness and so will not be discussed here. A brief description of the nervous system will help us better to understand how its parts all work together in so wonderful a way to accomplish their great result.
神经系统的划分。---神经系统可以分为两个部分：（1）中枢系统，包括大脑和脊髓；（2）周围系统，包括连接外围和内脏器官与中枢系统的感官和运动神经元，以及感觉的特殊终端器官。交感神经系统，作为一条双链式的神经连接，连接着脊髓外的感官和运动神经根，似乎与意识没有直接关系，因此在这里不进行讨论。对神经系统的简要描述将帮助我们更好地理解其各部分是如何以如此奇妙的方式协同工作，以实现它们伟大的功能。
The Central System.—In the brain we easily distinguish three major divisions—the cerebrum, the cerebellum and the medulla oblongata. The medulla is but the enlarged upper part of the cord where it connects with the brain. It is about an inch and a quarter long, and is composed of both medullated and unmedullated fibers—that is of both "white" and "gray" matter. In the medulla, the unmedullated neurones which comprise the center of the cord are passing to the outside, and the medullated to the inside, thus taking the positions they occupy in the cerebrum. Here also the neurones are crossing, or changing sides, so that those which pass up the right side of the cord finally connect with the left side of the brain, and vice versa.
中枢系统。---在大脑中，我们可以轻松地区分出三个主要部分——大脑、小脑和延髓。延髓是脊髓上端扩大的部分，它与大脑相连。它长约一英寸四分之一，由有髓鞘和无髓鞘纤维组成，即包含“白质”和“灰质”。在延髓中，构成脊髓中心的无髓鞘神经元向外延伸，而有髓鞘的向内延伸，这样它们就占据了在大脑中的位置。在这里，神经元也在交叉或改变侧边，使得那些沿着脊髓右侧上升的最终连接到大脑的左侧，反之亦然。
The Cerebellum.—Lying just back of the medulla and at the rear part of the base of the cerebrum is the cerebellum, or "little brain," approximately as large as the fist, and composed of a complex arrangement of white and gray matter. Fibers from the spinal cord enter this mass, and others emerge and pass on into the cerebrum, while its two halves also are connected with each other by means of cross fibers.38
小脑。---位于延髓正后方，大脑底部后侧的是小脑，或称为“小脑”，大约有一个拳头那么大，由复杂的白质和灰质组成。来自脊髓的纤维进入这个区域，其他纤维则从中发出并传入大脑，同时它的两半也通过交叉纤维相互连接。
Fig. 8.—View of the under side of the brain. B, basis of the crura; P, pons; Mo, medulla oblongata; Ce, cerebellum; Sc, spinal cord.
图8.——大脑底部视图。B, 小脑脚的基底；P, 桥脑；Mo, 延髓；Ce, 小脑；Sc, 脊髓。
The Cerebrum.—The cerebrum occupies all the upper part of the skull from the front to the rear. It is divided symmetrically into two hemispheres, the right and the left. These hemispheres are connected with each other by a small bridge of fibers called the corpus callosum. Each hemisphere is furrowed and ridged with convolutions, an arrangement which allows greater surface for the distribution of the gray cellular matter over it. Besides these irregularities of surface, each hemisphere is marked also by two deep clefts or fissures—the fissure of Rolando, extending from the middle upper part of the hemisphere downward and forward, passing a little in front of the ear and stopping on a level with the upper part of it; and the fissure of Sylvius, beginning at the base of the brain somewhat in front of the ear39 and extending upward and backward at an acute angle with the base of the hemisphere.
大脑。---大脑占据了头骨从前到后的所有上部区域。它被对称地分为两个半球，即右半球和左半球。这些半球通过一座名为胼胝体的纤维小桥相互连接。每个半球都被沟壑和褶皱覆盖，这种结构使得灰质细胞物质在其表面有更大的分布面积。除了这些表面的不规则外，每个半球还被两个深裂缝或裂隙标记——罗兰多裂隙，从中上部向下前延伸，略过耳朵前方并停止在与耳朵上部平行的位置；以及西尔维乌斯裂隙，从大脑底部开始，稍位于耳朵前方，并以锐角向上后方向延伸至半球底部。
Fig. 9.—Diagrammatic side view of brain, showing cerebellum (CB) and medulla oblongata (MO). F' F'' F''' are placed on the first, second, and third frontal convolutions, respectively; AF, on the ascending frontal; AP, on the ascending parietal; M, on the marginal; A, on the angular. T' T'' T''' are placed on the first, second, and third temporal convolutions. R-R marks the fissure of Rolando; S-S, the fissure of Sylvius; PO, the parieto-occipital fissure.
图9.——大脑的示意图侧视图，展示了小脑(CB)和延髓(MO)。F' F'' F'''分别位于第一、第二和第三额回上；AF位于上升额回上；AP位于上升顶回上；M位于边缘回上；A位于角回上。T' T'' T'''分别位于第一、第二和第三颞回上。R-R标记了罗兰多裂隙；S-S标记了西尔维乌斯裂隙；PO标记了顶枕裂隙。
The surface of each hemisphere may be thought of as mapped out into four lobes: The frontal lobe, which includes the front part of the hemisphere and extends back to the fissure of Rolando and down to the fissure of Sylvius; the parietal lobe, which lies back of the fissure of Rolando and above that of Sylvius and extends back to the occipital lobe; the occipital lobe, which includes the extreme rear portion of the hemisphere; and the temporal lobe, which lies below the fissure of Sylvius and extends back to the occipital lobe.
每个半球的表面可以被认为是被划分成四个叶：额叶，包括半球的前部并延伸至罗兰多裂隙以及向下至西尔维乌斯裂隙；顶叶，位于罗兰多裂隙的后方和西尔维乌斯裂隙的上方，并延伸至枕叶；枕叶，包括半球的最后端部分；颞叶，位于西尔维乌斯裂隙的下方并延伸至枕叶。
The Cortex.—The gray matter of the hemispheres, unlike that of the cord, lies on the surface. This gray exterior portion of the cerebrum is called the cortex, and40 varies from one-twelfth to one-eighth of an inch in thickness. The cortex is the seat of all consciousness and of the control of voluntary movement.
大脑皮层。---半球的灰质与脊髓的不同，它位于表面。大脑的这个灰色外部区域被称为皮层，厚度从八分之一英寸到十二分之一英寸不等。皮层是所有意识和自主运动控制的所在。
Fig. 10.—Different aspects of sections of the spinal cord and of the roots of the spinal nerves from the cervical region: 1, different views of anterior median fissure; 2, posterior fissure; 3, anterior lateral depression for anterior roots; 4, posterior lateral depression for posterior roots; 5 and 6, anterior and posterior roots, respectively; 7, complete spinal nerve, formed by the union of the anterior and posterior roots.
图10.——来自颈部的脊髓和脊髓神经根的不同切面视图：1，前正中裂的不同视角；2，后裂；3，前侧凹陷，用于前根；4，后侧凹陷，用于后根；5和6，分别是前根和后根；7，由前根和后根联合形成的完整脊神经。
The Spinal Cord.—The spinal cord proceeds from the base of the brain downward about eighteen inches through a canal provided for it in the vertebræ of the spinal column. It is composed of white matter on the outside, and gray matter within. A deep fissure on the anterior side and another on the posterior cleave the cord nearly in twain, resembling the brain in this particular. The gray matter on the interior is in the form of two crescents connected by a narrow bar.
脊髓。---脊髓从大脑底部向下延伸约十八英寸，通过脊椎提供的管道。它由外部的白质和内部的灰质组成。前侧的一个深裂和后侧的另一个深裂几乎将脊髓分成两半，这一点与大脑相似。内部的灰质呈两个新月形，通过一条狭窄的条带相连。
Theperipheral nervous system consists of thirty-one pairs of nerves, with their end-organs, branching off from the cord, and twelve pairs that have their roots in the brain. Branches of these forty-three pairs of nerves reach to every part of the periphery of the body and to all the internal organs.41
周围神经系统由三十一对神经及其末端器官组成，这些神经从脊髓分支出来，还有十二对神经的根源在大脑。这四十三对神经的分支到达身体周边的每一个部分和所有内部器官。
Fig. 11.—The projection fibers of the brain. I-IX, the first nine pairs of cranial nerves.
图11.——大脑的投射纤维。I-IX，前九对颅神经。
It will help in understanding the peripheral system to remember that anerve consists of a bundle of neurone fibers each wrapped in its medullary sheath and sheath of Schwann. Around this bundle of neurones, that is around the nerve, is still another wrapping, silvery-white, called the neurilemma. The number of fibers going to make up a nerve varies from about 5,000 to 100,000. Nerves can easily be identified in a piece of lean beef, or even at the edge of a serious gash in one's own flesh!
为了帮助理解周围系统，需要记住神经由一束神经元纤维组成，每条纤维都被髓鞘和施万细胞鞘包裹。围绕这束神经元，即围绕神经的，还有另一层银白色的包裹，称为神经膜。构成一条神经的纤维数量从大约5000到100000不等。在一块瘦牛肉中，或者甚至在自己肉体上严重的伤口边缘，都能轻松识别出神经！
Bundles of sensory fibers constituting a sensory nerve root enter the spinal cord on the posterior side through holes in the vertebræ. Similar bundles of motor fibers in the form of a motor nerve root emerge from the cord at the same level. Soon after their emergence from the cord, these two nerves are wrapped together in the42 same sheath and proceed in this way to the periphery of the body, where the sensory nerve usually ends in a specialized end-organ fitted to respond to some certain stimulus from the outside world. The motor nerve ends in minute filaments in the muscular organ which it governs. Both sensory and motor nerves connect with fibers of like kind in the cord and these in turn with the cortex, thus giving every part of the periphery direct connection with the cortex.
构成感觉神经根的感觉纤维束通过脊椎的孔洞进入脊髓的后侧。类似的感觉纤维束以运动神经根的形式在同一水平从脊髓中出现。这些神经从脊髓出现后不久，这两条神经就被包裹在同一个42鞘中，并以这种方式继续向身体的周边前进，在那里感觉神经通常在一个特化的终末器官结束，该器官适合于响应来自外部世界的某种特定刺激。运动神经在其控制的肌肉器官中以微小的丝状物结束。感觉和运动神经都与脊髓中的同类纤维相连，这些纤维又与皮层相连，因此使身体的每一部分都直接与皮层连接。
Fig. 12.—Schematic diagram showing association fibers connecting cortical centers with each other.—After James and Starr.
图12.——示意图，展示了连接皮层中心彼此之间的联合纤维。——根据James和Starr的资料。
Theend-organs of the sensory nerves are nerve masses, some of them, as the taste buds of the tongue, relatively simple; and others, as the eye or ear, very complex. They are all alike in one particular; namely, that each is fitted for its own particular work and can do no other. Thus the eye is the end-organ of sight, and is a wonderfully complex arrangement of nerve structure combined with refracting media, and arranged to respond to the rapid ether waves of light. The ear has43 for its essential part the specialized endings of the auditory nerve, and is fitted to respond to the waves carried to it in the air, giving the sensation of sound. The end-organs of touch, found in greatest perfection in the finger tips, are of several kinds, all very complicated in structure. And so on with each of the senses. Each particular sense has some form of end-organ specially adapted to respond to the kind of stimulus upon which its sensation depends, and each is insensible to the stimuli of the others, much as the receiver of a telephone will respond to the tones of our voice, but not to the touch of our fingers as will the telegraph instrument, and vice versa. Thus the eye is not affected by sounds, nor touch by light. Yet by means of all the senses together we are able to come in contact with the material world in a variety of ways.
感觉神经的终末器官是神经团块，其中一些如舌头上的味蕾相对简单；而另一些如眼睛或耳朵则非常复杂。它们在一个特定方面都是相同的；即每个器官都适合其特定的工作，且无法执行其他功能。因此，眼睛是视觉的终末器官，是一种与折射介质结合、响应快速光波的极其复杂的神经结构。耳朵作为听觉的基本部分，具有专门化的听觉神经末梢，适合于响应空气中传来的声波，产生声音的感觉。触觉的终末器官在指尖最为完美，有几种类型，结构都非常复杂。每种感觉都有某种形式的终末器官，专门适应于响应其感觉所依赖的刺激类型，且对其他刺激无感，就像电话接收器会响应我们的声音音调，但不会像电报仪器那样响应我们手指的触摸，反之亦然。因此，眼睛不受声音影响，触觉也不受光线影响。然而，通过所有感官的共同作用，我们能够以多种方式与物质世界接触。
5. LOCALIZATION OF FUNCTION IN THE NERVOUS SYSTEM
5. 神经系统中功能的定位
Division of Labor.—Division of labor is the law in the organic world as in the industrial. Animals of the lowest type, such as the amœba, do not have separate organs for respiration, digestion, assimilation, elimination, etc., the one tissue performing all of these functions. But in the higher forms each organ not only has its own specific work, but even within the same organ each part has its own particular function assigned. Thus we have seen that the two parts of the neurone probably perform different functions, the cells generating energy and the fibers transmitting it.
劳动分工。——在有机世界和工业世界中，劳动分工都是规律。最低等的动物，如阿米巴，没有分离的器官来执行呼吸、消化、吸收、排泄等功能，而是由同一组织执行所有这些功能。但在高等形态中，每个器官不仅拥有自己的特定工作，甚至在同一器官内，每个部分都被分配了特定的功能。因此，我们已经看到神经元的两个部分可能执行不同的功能，细胞产生能量，纤维传递能量。
It will not seem strange, then, that there is also a division of labor in the cellular matter itself in the nervous system. For example, the little masses of ganglia44 which are distributed at intervals along the nerves are probably for the purpose of reënforcing the nerve current, much as the battery cells in the local telegraph office reënforce the current from the central office. The cellular matter in the spinal cord and lower parts of the brain has a very important work to perform in receiving messages from the senses and responding to them in directing the simpler reflex acts and movements which we learn to execute without our consciousness being called upon, thus leaving the mind free from these petty things to busy itself in higher ways. The cellular matter of the cortex performs the highest functions of all, for through its activity we have consciousness.
那么，在神经系统的细胞物质本身中也存在劳动分工就不会显得奇怪了。例如，沿着神经分布的小团神经节44很可能是为了加强神经电流的目的，就像地方电报局的电池单元加强来自中央办公室的电流一样。脊髓和大脑较低部分的细胞物质执行着接收感觉信息并响应它们的非常重要的工作，指导我们学会执行的简单反射行为和动作，而无需调用我们的意识，从而让心灵从这些琐碎的事情中解脱出来，忙于更高层次的活动。皮层的细胞物质执行所有功能中最高的，因为通过其活动我们拥有意识。
Fig. 13.—Side view of left hemisphere of human brain, showing the principal localized areas.
图13.——人脑左半球的侧视图，展示了主要的定位区域。
The gray matter of the cerebellum, the medulla, and the cord may receive impressions from the senses and respond to them with movements, but their response is in all cases wholly automatic and unconscious. A person45 whose hemispheres had been injured in such a way as to interfere with the activity of the cortex might still continue to perform most if not all of the habitual movements of his life, but they would be mechanical and not intelligent. He would lack all higher consciousness. It is through the activity of this thin covering of cellular matter of the cerebrum, the cortex, that our minds operate; here are received stimuli from the different senses, and here sensations are experienced. Here all our movements which are consciously directed have their origin. And here all our thinking, feeling, and willing are done.
小脑、延髓和脊髓的灰质可以从感觉中接收印象并以动作作出反应，但它们在所有情况下的反应都是完全自动和无意识的。一个45大脑半球受到损伤的人，如果这种损伤干扰了皮层的活动，他可能仍然会继续执行他生活中的大多数习惯性动作，如果不是全部的话，但这些动作将是机械的而不是智能的。他将缺乏所有更高级的意识。正是通过大脑皮层这层薄薄的细胞物质的活动，我们的心灵才能运作；在这里接收来自不同感官的刺激，并在这里经历感觉。这里，我们所有有意识指导的动作都起源于此。在这里，我们所有的思考、感受和意愿都得以完成。
Division of Labor in the Cortex.—Nor does the division of labor in the nervous system end with this assignment of work. The cortex itself probably works essentially as a unit, yet it is through a shifting of tensions from one area to another that it acts, now giving us a sensation, now directing a movement, and now thinking a thought or feeling an emotion. Localization of function is the rule here also. Certain areas of the cortex are devoted chiefly to sensations, others to motor impulses, and others to higher thought activities, yet in such a way that all work together in perfect harmony, each reënforcing the other and making its work significant. Thus the front portion of the cortex seems to be devoted to the higher thought activities; the region on both sides of the fissure of Rolando, to motor activities; and the rear and lower parts to sensory activities; and all are bound together and made to work together by the association fibers of the brain.
皮层中的劳动分工。——神经系统中的劳动分工并未因这项工作的分配而结束。皮层本身可能本质上作为一个整体工作，但它是通过从一个区域到另一个区域的张力转移来发挥作用的，时而给我们一个感觉，时而指导一个动作，时而思考一个想法或感受一种情感。功能定位在这里也是规则。皮层的特定区域主要致力于感觉，其他区域则致力于运动冲动，还有的区域致力于更高级的思维活动，但所有区域以完美的和谐共同工作，每个区域都相互加强并使其工作变得有意义。因此，皮层的前部似乎专门用于更高级的思维活动；罗兰多裂隙两侧的区域，用于运动活动；后部和下部区域用于感觉活动；所有这些都通过大脑的联合纤维联系在一起，并使其协同工作。
In the case of the higher thought activities, it is not probable that one section of the frontal lobes of the cortex is set apart for thinking, one for feeling, and one for willing, etc., but rather that the whole frontal46 part of the cortex is concerned in each. In the motor and sensory areas, however, the case is different; for here a still further division of labor occurs. For example, in the motor region one small area seems connected with movements of the head, one with the arm, one with the leg, one with the face, and another with the organs of speech; likewise in the sensory region, one area is devoted to vision, one to hearing, one to taste and smell, and one to touch, etc. We must bear in mind, however, that these regions are not mapped out as accurately as are the boundaries of our states—that no part of the brain is restricted wholly to either sensory or motor nerves, and that no part works by itself independently of the rest of the brain. We name a tract from the predominance of nerves which end there, or from the chief functions which the area performs. The motor localization seems to be the most perfect. Indeed, experimentation on the brains of monkeys has been successful in mapping out motor areas so accurately that such small centers as those connected with the bending of one particular leg or the flexing of a thumb have been located. Yet each area of the cortex is so connected with every other area by the millions of association fibers that the whole brain is capable of working together as a unit, thus unifying and harmonizing our thoughts, emotions, and acts.
在更高级的思维活动中，不太可能是皮层的前额叶中一个部分专门用于思考，另一个用于感受，还有一个用于意愿等，而是整个前额部分的皮层都参与其中。然而，在运动和感觉区域，情况有所不同；因为这里发生了更进一步的劳动分工。例如，在运动区域，一个小区域似乎与头部的运动有关，一个与手臂有关，一个与腿部有关，一个与面部有关，另一个与言语器官有关；同样在感觉区域，一个区域致力于视觉，一个致力于听觉，一个致力于味觉和嗅觉，一个致力于触觉等。然而，我们必须记住，这些区域的划分并不像我们的州界那样精确——大脑的任何部分都不完全限于感觉或运动神经，也没有哪个部分能够独立于大脑的其他部分单独工作。我们根据神经的主要分布或该区域执行的主要功能来命名一个区域。运动定位似乎是最完善的。实际上，对猴子大脑的实验成功地准确绘制了运动区域，以至于像与弯曲特定一条腿或弯曲拇指相关的这样的小中心都被定位了。然而，每个皮层区域通过数以百万计的联合纤维与每个其他区域相连，使得整个大脑能够作为一个整体一起工作，从而统一和协调我们的思想、情感和行为。
6. FORMS OF SENSORY STIMULI
6. 感觉刺激的形式
Let us next inquire how this mechanism of the nervous system is acted upon in such a way as to give us sensations. In order to understand this, we must first know that all forms of matter are composed of minute atoms which are in constant motion, and by imparting this47 motion to the air or the ether which surrounds them, are constantly radiating energy in the form of minute waves throughout space. These waves, or radiations, are incredibly rapid in some instances and rather slow in others. In sending out its energy in the form of these waves, the physical world is doing its part to permit us to form its acquaintance. The end-organs of the sensory nerves must meet this advance half-way, and be so constructed as to be affected by the different forms of energy which are constantly beating upon them.
让我们接下来探究神经系统的这一机制是如何被激活的，以便给我们带来感觉。为了理解这一点，我们必须首先知道所有物质形式都是由微小的原子组成的，这些原子处于不断运动中，并通过将这种47运动传递给围绕它们的空气或以太，不断地以微小波浪的形式向空间辐射能量。这些波浪或辐射在某些情况下速度惊人地快，在其他情况下则相当慢。物理世界通过以这些波浪的形式发出其能量，是在尽自己的一份力量，使我们能够形成对它的认识。感觉神经的末梢器官必须对这些不断冲击它们的不同形式的能量做出反应，并且必须如此构造，以至于能够受到它们的影响。
Fig. 14.—The prism's analysis of a bundle of light rays. On the right are shown the relation of vibration rates to temperature stimuli, to light and to chemical stimuli. The rates are given in billions per second.—After Witmer.
图14.——棱镜对一束光线的分析。右侧展示了振动频率与温度刺激、光和化学刺激的关系。频率以每秒数十亿次给出。——根据WITMER的资料。
The End-organs and Their Response to Stimuli.—Thus the radiations of ether from the sun, our chief source of light, are so rapid that billions of them enter the eye in a second of time, and the retina is of such a nature that its nerve cells are thrown into activity by these waves; the impulse is carried over the optic nerve to the occipital lobe of the cortex, and the sensation of sight is the result. The different colors also, from the red48 of the spectrum to the violet, are the result of different vibration rates in the waves of ether which strike the retina; and in order to perceive color, the retina must be able to respond to the particular vibration rate which represents each color. Likewise in the sense of touch the end-organs are fitted to respond to very rapid vibrations, and it is possible that the different qualities of touch are produced by different vibration rates in the atoms of the object we are touching. When we reach the ear, we have the organ which responds to the lowest vibration rate of all, for we can detect a sound made by an object which is vibrating from twenty to thirty times a second. The highest vibration rate which will affect the ear is some forty thousand per second.
末梢器官及其对刺激的响应。——因此，来自太阳（我们主要光源）的以太辐射如此迅速，以至于数十亿的它们在一秒钟内进入眼睛，视网膜的性质使得其神经细胞被这些波浪激活；冲动通过视神经传递到皮层的枕叶，视觉感觉便产生了。不同的颜色，从光谱的红色48到紫色，也是由于撞击视网膜的以太波中不同振动频率的结果；为了感知颜色，视网膜必须能够响应代表每种颜色的特定振动频率。同样，在触觉中，末梢器官适应于响应非常快速的振动，可能我们触摸的物体的原子中不同振动频率产生了触觉的不同品质。当我们谈到耳朵时，我们有一个响应所有振动频率最低的器官，因为我们可以探测到一个物体每秒钟振动二十到三十次所发出的声音。影响耳朵的最高振动频率是每秒大约四万次。
Thus it is seen that there are great gaps in the different rates to which our senses are fitted to respond—a sudden drop from billions in the case of the eye to millions in touch, and to thousands or even tens in hearing. This makes one wonder whether there are not many things in nature which man has never discovered simply because he has not the sense mechanism enabling him to become conscious of their existence. There are undoubtedly "more things in heaven and earth than are dreamt of in our philosophy."
由此可见，我们的感官适应响应的不同频率之间存在巨大的差距——从眼睛的数十亿次突然下降到触觉的数百万次，再到听觉的数千甚至数十次。这让人不禁思考，是否因为在自然界中有许多东西是人类从未发现过的，仅仅是因为他没有能够使他意识到它们存在的感官机制。毫无疑问，“天堂和地球上的东西比我们的哲学所梦想的要多。”
Dependence of the Mind on the Senses.—Only as the senses bring in the material, has the mind anything with which to build. Thus have the senses to act as messengers between the great outside world and the brain; to be the servants who shall stand at the doorways of the body—the eyes, the ears, the finger tips—each ready to receive its particular kind of impulse from nature and send it along the right path to the part of the cortex where it belongs, so that the mind can say, "A sight," "A sound," or "A touch." Thus does the49 mind come to know the universe of the senses. Thus does it get the material out of which memory, imagination, and thought begin. Thus and only thus does the mind secure the crude material from which the finished superstructure is finally built.
心灵对感官的依赖。——只有当感官带来物质时，心灵才有东西可以构建。因此，感官必须充当广阔外部世界与大脑之间的信使；成为站在身体门口的仆人——眼睛、耳朵、指尖——每个都准备好从自然界接收其特定类型的冲动，并将其沿着正确的路径发送到皮层的相应部分，以便心灵能够说：“一个景象”、“一个声音”或“一个触感”。这样，心灵就得以了解感官的宇宙。这样，它就获得了记忆、想象和思考开始的素材。只有这样，心灵才能获得最终构建完成的上层建筑所需的原始材料。
