A MANUAL OF HEALTH.

CHAPTER VIII.

ON THE BRAIN AND NERVES.

hair-like bodies that the plant moves. Cilia are almost universally present in the animal kingdom. They are found on the surface of the minute one-celled animals called Infusorial animalcules and some worms, and they NE of the distinguishing features are present in the interior organs of all higher between plants and animals is the animals. They are especially seen in the possession by the latter of a nervous respiratory organs, and may be conveniently system. Not that all animals pos-examined on the gills of an oyster or mussel. sess nerves, but it is through these They are found in the mucous membrane of organs that the great variety and multitude of the human nose and windpipe, in the hollow the actions of higher animals are performed. parts of the brain, and other parts of the body. The great feature of a nerve is that it acts under In those parts their function is to act upon the the influence of anything irritating it, which is mucus secreted by the membrane, and to sweep called a stimulus. Some plants possess the it, as it were, in the direction in which it ought power of moving, as is seen amongst the more to pass from the organs on which they are minute forms, only detected by the aid of the placed. In these cases four or five of these microscope; whilst the moving of the leaves of minute cilia are placed upon a single cell. In the sensitive plant, the turning of sunflowers, man they are not more than from the 1-4000th and the closing of other flowers at night are to the 1-2500th of an inch in length. Yet on familiar instances of higher plants having the these minute agents the life of the animal kingpower of motion. These movements, however, dom may be said to depend. Though influenced do not depend on the plant possessing either a by external stimuli, their movements are quite nervous or a muscular system, but on their independent of the nervous system, and they possessing a living matter which combines the will continue to move for hours after they have two properties of sensibility to a stimulus and been removed from the body. motion, properties which are found respectively in the nerves and muscles of the higher animals. Many of the lower animals possess no visible nervous system, and are influenced by external stimuli in the same way as plants.

Many of the minute plants which move in water are endowed with organs called cilia. They are always found on the surface of the motile plant, which usually consists of a single vesicle or cell. Sometimes there is only one of these little organs, or one at each end of the cell; at other times the whole cell is covered with them. They are brought into action by the agency of heat and light, and are constantly moving, and it is by the lashing of these minute

The nervous matter is composed of two things, viz., minute cells and delicate tubes, which can only be seen by the aid of the microscope. The cells are of various shapes, generally containing a minute spot or nucleus in the centre. The nerve-tubes are very fine and delicate cylinders, with a second cylinder in their interior, around which is contained a fluid peculiar to these organs. The nerve-cells or corpuscles are minute bodies with a kernel and long branching processes, which unite either. with each other, or with nerve-tubes. The nerve-cells or corpuscles are found in the ganglions, or swellings of the nerves, whilst the tubes are found in the nerves themselves. A number of these delicate

tubes are bound together by means of a mem- in those muscles which move the body. Such a branous sheath composed of connective tissue. system is called excito-motory; and it is the The same tissue binds the muscular bundles means by which simple movements of the body together, and is found all over the body binding are effected in all animals. When the digestive and keeping the other organs together. When and respiratory functions in animals require the matter of which the nerves are composed is special superintendence, nervous ganglia are examined, it is found to contain about ten per added for this purpose; and in the higher shellcent. of an albumen, ten per cent. of fatty and fish ganglia are observed accompanying the saline matters, and eighty per cent. of water. development of the digestive and respiratory The simplest form of a nervous system con- organs. The movements accompanying the sists of a ganglion containing nerve-cells, and a performance of the functions of these organs nerve containing nerve-tubes. Such a simple are all the result of the stimulus of the food structure is, however, seldom found even amongst and of the air or oxygenated water on the nerves. the lowest animals which have nerves. What In man, and the vertebrate animals, the nerves we find, as for instance in the starfish, is a series which receive impressions from without, and of ganglia, arranged in a circle round the mouth, those which go to mucles subject to the will or and attached together by nervous cords, and consciousness, spring from a great mass of nerve giving off in various directions little nervous tubes and cells which lies in a bony case, and twigs. In worms, insects, crabs, and lobsters, forms the brain and spinal cord. we find a double row of nervous ganglia, forming When the organs of the senses begin to be two lines, which are connected together by developed in the lower animals, they are connervous cords, and give off to the legs and nected with special ganglionic masses, and the other organs nervous twigs. In whelks, snails, nerve which receives the external impression, oysters, and other shell-fish, the ganglia are runs to the ganglion. In these cases, motion is situated in various parts of the body, and are produced as the result of impressions on a all connected together to form a common nervous special organ of sense. The organ of sense system. which is first developed in the lower animals is The function of a nervous system, however the eye; and we see, amongst the insects espesimply constructed, is to receive impressions cially, a ganglion supplied to the nerves of the from without, and to convey force from within. eye. The movements of insects seen more The ganglion is always the centre of these two especially determined by the impression of actions. It may be compared to the terminus external objects on their eyes. Such movements, of a railway; and the nerves which bring im- whether they result from impressions on nerves pressions from without are like the up-lines of of sight, hearing, taste, smelling, or ordinary railway, whilst the nerves which convey impres- sensation (pinching, &c.) are called sensorisions from within are like the down-lines. The motor. In man and the higher animals such nerves which go up to the ganglia are called by ganglia of great size are seen at the base of the various names; they are called sensory or sensi- brain, and are connected with the nerves of the tive, as they receive the impressions which pro nose, eye, and tongue, and also with nerve-fibres duce what we call sensations. They are also from the furthest parts of the body through the called afferent, and, since they run to a centre, spinal cord. These great masses are called the are also called centripetal. On the other hand, "ganglia of the brain," also the corpora striata, the nerves which convey impressions from the optic-thalami, corpora quadrigemina, &c. The ganglia always have the power of causing some movements due to these ganglia in man, and to kind of motion. They are hence called motory their representatives in lower animals, are quite or motor nerves. In the higher animals they independent of will. But these sensori-motor are under the control of the will, and are also actions differ from excito-motor actions in that called volitionary. As they come from a centre we know or feel the stimulus, though we can not they are said to be centrifugal, and as they go prevent the action. Such are blinking when a outwards are called efferent. The efferent and bright object is placed before the eye, sneezing afferent nerve fibres are bound together in the when snuff is applied to the nose, starting when same nerve, and can not be distinguished by the sound is applied to the ear, jumping when eye. Nerves end differently according to the pinched, also the first act of swallowing is of different uses they have. Those going to the this nature, as also is breathing in part; for muscles (motor) spread out in very fine network these actions can not go on when the sensation all round the muscle-fibres, whilst those nerve- of the throat or lung is lost by the destruction tubes which carry sensations end in little nobs of nervous connection with the great brain in the skin, or in organs like the eye. ganglia.

The result of impressions on a chain of There is a last stage in the development of ganglia like that in a worm is to produce motion the nervous system of animals, which consists

in the production of an organ which is not con-volutions. When cut into, this great reflected nected with any special group of nerves. This mass presents externally a greyish color, and consists of two masses of nerve matter, called internally is white. The grey matter consists sometimes the "hemispheres," sometimes the principally of nerve-cells, and is supposed to be brain-proper or cerebrum, but best distinguished the source of that power which the brain and from the other parts lying in the skull or brain- ganglionic masses exert on the nerves. The case, as the fore-brain. It is peculiar to the white matter is composed of nerve-tubes or

back-boned animals, and is not even represented fibres. The whole brain is covered over with in insects, mollusc, &c. The fore-brain is three membranes, one a strong, fibrous memaltogether the most important mass of nervous brane, called the dura mater, which lies next matter. It receives impressions from all the the bone, another, more delicate, the pia mater, other parts of the body; and the impressions it through which pass the blood-vessels that thus receives are more or less permanent, and nourish the brain, and a spongy intermediate are called ideas. It thus becomes the seat of membrane. It is these membranes which beconsciousness, and above all of memory; and come inflamed in inflammation of the brain, by its action the animal has the power of deter- and which become congested under the influence mining which of two lines of action it shall of alcoholic drinks. By habitual drunkenness take; and this is called will. Hence the cere- these membranes become thickened and rendered brum is also the seat of volition or voluntary opaque, and thus offer an obstruction to the action. At the same time it acts on the muscles, circulation in the brain, leading to apoplexy, sometimes independently of the consciousness; which is caused by blood being effused on the and such actions are called ideo-motor. Such brain, and softening of its substance. It is the actions as these are seen when persons are action of alcohol on the circulation of the brain asleep, when they can be persuaded to act on that leads to the disease known as delirium any suggestion made to them by persons stand-tremens, which so frequently terminates the ing by. An illustration of such action is seen existence of drunkards.

in the exhibitions of the so-called "electro- Behind the fore brain, and quite covered in biologists," in which by means not fully under- by its lobes, is the mid-brain, almost entirely stood persons are deprived of the natural influ- made up of ganglionic grey matter, and intience of their consciousness, and they perform mately connected with the nerves of sight and very absurd movements under the idea that other sensation. In fishes this is much the they are drunk, or on fire, or in danger of biggest part of the brain. Behind this again, falling, or other accidents. and not closed in by the great hemispheres, Having thus described the general characters though overlapped by them, is the hind-brain. of the nervous system in the animal kingdom, This has two parts, the cerebellum (an outwe now proceed to describe that which exists in growth like the cerebrum), and a lower part the human being more fully. In man we have called medulla oblongata. The cerebellum is a brain and spinal cord, or cerebro-spinal sys-about a sixth of the size of the brain proper, tem, and a second system called sympathetic, and is seated at the back of the skull, and which is particularly connected with the soft divided from it by a thick membrane, called the organs. The brain is divided into a fore-brain, tentorium. Like the lobes of the fore-brain, it a mid-brain, and a hind-brain. The fore-brain consists of both white and grey nervous matter. or "hemispheres" is split down the middle, and The white matter is so distributed as to give it is curiously wrinkled and folded; in man it is the appearance of a shrub or little tree, which very large, and spreads backwards over both the has been fancifully named arbor vitæ, the tree mid-and-hind-brain. At its base, or rather of life. The medulla oblongata is a mass of enveloped by it, is one of the large ganglia of nervous matter connecting the spinal cord with the brain. The two sides of the fore-brain are, the great mass of nerve matter in the skull as we said, separated by a deep groove, running called "brain." From the base of the brain from front to back, but at the bottom of this is are given off various nerves, whose branches a mass of nervous matter, which unites the two pass through holes in the skull, and reach either sides together. This mass of nervous substance the organs of special sense, or the muscles and contains nerve-tubes, which run across each skin in the neighborhood of the head. The other from one side to the other, and explains medulla oblongata also gives off nerves within the curious fact, that when one side of the brain the skull. The spinal cord runs from the brain is injured the functions of the opposite side of through the great hole (foramen magnum) at the nervous system, below the spot where the the base of the skull, in a canal made by the tubes cross, is affected. The outside of the union of the vertebræ or separate bones of the lobes of the fore-brain present a series of ele- back. This is called the spinal canal. The vations and depressions, which are called con- spinal cord or marrow consists of grey and

white nervous matter, of the same kind as that take their origin in the medulla oblongata. in the brain. The grey matter is found in the Below these important nerves originate two inside of the spinal cord, and the white matter is outside.

others within the skull, called the ninth pair, the branches of which go to the muscles of the tongue, and are the source of its movements.

The principal nerves of the body are given off from the brain and spinal cord, and belong The spinal cord, in its course down the to what is called the cerebro-spinal nervous sys- spinal canal, gives off thirty-one pairs of nerves. tem. This is to distinguish them from that These nerves are all of one kind, that is, they other set of nerves which are called the sympa- are nerves of common sensation and motion. thetic, and which are found forming a network They are distributed to the skin of the trunk of nerves on each side of the body, from the and extremities, producing the common sense neck to the lower parts of the body. This sys- of touch, and to the muscles, producing motion. tem of nerves is composed of a series of ganglia, Each of the spinal nerves has two roots in the which are connected together by nervous cords spinal cord, the one coming off from behind, and twigs, and constitute the two great sympa- containing the nerves of sensation, and others thetic nerves. The twigs of these nerves inter-passing off from before, forming the nerves of lace freely with those passing from the brain motion. These roots unite together, forming a and spinal cord. The appearance of the nervous single nerve, which possesses both the property matter of the sympathetic, under the microscope, of carrying up sensations and bringing down differs from that of the cerebro-spinal system, volitions. For the discovery of this great fact in having many more nerve-cells and soft nerve- in the action of the nerves, we are indebted to fibres, which are easily distinguished by the absence of a dark outline. Small twigs of this nerve are sent to the whole of the blood-vessels and to the minute capillaries, and by this means the whole of the organs of the body are brought within the control of the nervous system.

The nerves generally terminate by means of loops in the various parts of the body to which they are sent. From these loops again little processes are sent into the tissues around the

Sir Charles Bell. He showed that when the posterior roots of the nerves were cut, an animal lost the power of feeling, and that when the anterior root was cut it lost the power of motion. The spinal cord and the nerves which issue from it, form what is called an excito-motor The nerves that come from the brain and nervous system, and although the sensations medulla oblongata are all numbered, and as they produced on it may be, and generally are, pass out on each side of the brain they are recognized by the brain, and the motor nerves called pairs. Thus we have nine pairs. The are acted on by the will, it nevertheless can act first pair are the olfactory nerves, which divide entirely independent of the brain. The brain into a number of small twigs, and pass through of a frog or a turtle can be removed without a sieve-like bone at the top of the nose, and are pain to the animal, and if this is done, and the distributed to the mucous membrane of the animal is pinched or irritated in any way, it nostrils. The second pair are the optic nerves, exhibits movements in the corresponding nerves. which pass through holes at the bottom of the Thus, a frog will jump when its legs are pinched, sockets of the eye-balls, and are expanded into although its head is cut off. a delicate nervous membrane called the retina, which lies at the back of each eye. The third, fourth, and sixth pair of nerves are distributed to the six muscles of the eye, whilst each great fifth nerve divides into three branches, one nerves. Sometimes the nerve terminates in a giving common sensation to the upper part of minute sac or capsule. This is especially the the face, eye, and nose; the second to the upper case in the nerves sent to the fingers, and this jaw and teeth; the third to the lower jaw, and arrangement is found also in other parts of the giving off too the nerve of taste. It is this body. These minute swellings are called nerve which gives us tooth-aches and face-aches. Pacinian bodies, after Professor Pacini of Pisa The seventh pair of nerves are singular; they who first accurately described them. Their use have two branches, one of which goes to the is undoubtedly connected with the more delicate ear, and receives impressions from the waves of tactile function that is found to exist in the sound, producing hearing, whilst the other tips of the finger in man. A wonderful modibranch goes to the face, and is a motor nerve, fication of nervous structure is seen in the giving the wonderful powers of expression to electric organs of some fishes. A peculiar the human face. The eighth pair have each apparatus composed of hexagonal plates is three branches, which are distributed to various placed on each side of the fish, and on this important organs; they descend down through arrangement of plates the nerves are distributed. the neck, giving branches to the tongue and the The animal has the power through this apparatus mouth, the lungs and the stomach, and having of discharging its nervous force in the form of connections with the sympathetic nerve. They electricity. It is clearly seen from the history

of these animals that the nervous force can be existence of man from this world to another. transformed into electrical force. When ideas have been received in the brain, Of all the parts of the nervous system the they do not remain passive. The brain has the brain is most important. All other parts of power of recalling the ideas it has received in the nervous system terminate more or less the past. This faculty is called memory, and directly in the brain. In proportion to the upon this faculty much of the power of man. rest of the nervous matter in the body, it is over the external world depends. It is thus larger in man than in any of the lower animals. that he becomes more learned the longer he It is the function which the brain performs that lives; and that life in old age is filled with the distinguishes man from all other animals, and it recollections of the past. When we consider is by the action of his brain that he becomes a the vast amount of knowledge exhibited by the conscious, intelligent, and responsible being. intellect of men of mature age in the vigor of The brain is the seat of that knowledge which health, we can not but feel astonished at the we express when we say I. I know it, I feel it, power possessed by this material organ of man's I saw it, are expressions of our individual con- highest life. Not only has man the power of sciousness, the seat of which is the brain. It recalling the ideas that have been once impressed is when the brain is at rest in sleep that there upon his senses in the same order in which he is least consciousness. The brain may be put has received them, but he has the power of under the influence of poisons, such as alcohol combining these ideas, and making them to and chloroform, and then the body is without consciousness. From these and other facts the brain is regarded as the seat of consciousness.

of the ideas which we receive from without, and the arrival at conclusions which are called judgment and reasoning. Whatever qualities, in fact, can be properly attributed to the human mind, must have their source in the brain.

assume new forms, such as never were actually presented to him by his senses. This faculty of combining ideas, and reproducing them in new Not only is the brain the means by which the forms, is called imagination, and lies at the impression of our own existence is made foundation of the arts of poetry, music, painting, evident, but it is the recipient of all those im- and sculpture. The result, also, of the activity pressions from without which are called ideas. of the brain is that arrangement and comparison Thus we see with our eyes a particular color, and it is as it were registered in the brain in the form of an image or idea. In the same way we feel a hot body, and we get the idea of heat, and so on with our other senses; and the act by which we apprehend the properties of bodies When ideas are received into the mind, they outside of us, is called perception. It is in this frequently produce impressions, which are way that man, by the exercise of the nerves of called feelings and desires. These feelings, smelling, seeing, hearing, tasting, and feeling, is some of which are called emotions and passions, enabled to accumulate ideas in his brain. Of all have their seat in the brain. Amongst these all these ideas which are thus taken up and feelings is that of love-the love of the sexes, registered in his brain, he is made conscious by the love of children, the love of home, benevothe same organ, and thus man becomes a con-lence, the love of man, self-love, the love of scious intelligent being. approbation, the desire of doing right, conscience, Although the brain is said to be the seat of the feeling of adoration, and the recognition of consciousness, it must not be supposed that man a good and allwise God. There has been a dishas no consciousness without the brain. Man pute amongst writers upon the nature of the is a spiritual as well as a material being; and mind of man, as to whether certain ideas, such lying beneath all natural forces is the soul of as those of the existence of God, and a sense man. This is the recipient of all that man gets of right and wrong, are innate or are acquired to know by the material instincts of his body, by the action of our senses upon the external and survives the destruction of the human world, and by instruction from others. Whatframe. It is this spiritual part of man's nature ever be the view taken of this great philosophithat carries on his identity from month to cal question, all are agreed that the brain is the month, and year to year, and makes him to seat of the thought, and connected with these know that he is the same individual from the ideas. The result of the action of ideas on the day of his birth to that of his death. The brain, in connection with the emotions, procomposition of the organs of man's body are duces those effects in the muscular system constantly changing. A quantity of matter, which are called voluntary movements. When equal to the weight of the whole body, is lost man is conscious of these motions, and deterin forty days; hence we may conclude that mines upon them as the result of the action of whilst the matter is constantly passing away his ideas, he is said to exercise his will. The from the body, the human spirit remains, brain is, therefore, the true organ of the will; retaining the consciousness and carrying on the and a man is regarded as responsible for his