The continued congestion of the minute structure of the kidney cuts off the needed nutrition of the organ, and forms the primary step in the series of disasters. Sometimes from this continued irritation, with the resulting inflammation, and sometimes from change of structure of the kidney by fatty degeneration, comes the failure to perform its proper function. Then, with this two-edged sword of disaster, the urea, which becomes a poisonous element, and should be removed, is retained in the system, while the albumen, which is essential to healthy blood, is filtered away through the diseased kidney.

259. Alcoholic Liquors as a Cause of Bright's Disease. The unfortunate presence of albumen in the urine is often a symptom of that insidious and fatal malady known as albuminuria or Bright's disease, often accompanied with dropsy and convulsions. One of the most constant causes of this disease is the use of intoxicants. It is not at all necessary to this fatal result that a person be a heavy drinker. Steady, moderate drinking will often accomplish the work. Kidney diseases produced by alcoholic drinks, are less responsive to medical treatment and more fatal than those arising from any other known cause.[39]

Experiment 129. Obtain a sheep's kidney in good order. Observe that its shape is something like that of a bean, and note that the concave part (hilus), when in its normal position, is turned towards the backbone. Notice that all the vessels leave and enter the kidney at the hilus. Observe a small thick-walled vessel with open mouth from which may be pressed a few drops of blood. This is the renal artery. Pass a bristle down it. With the forceps, or even with a penknife, lift from the kidney the fine membrane enclosing it. This is the kidney capsule.

Divide the kidney in halves by a section from its outer to near its inner border. Do not cut directly through the hilus. Note on the cut surfaces, on the outer side, the darker cortical portion, and on the inner side, the smooth, pale, medullary portion. Note also the pyramids of Malpighi.



Chapter X.

The Nervous System.



260. General View of the Nervous System. Thus far we have learned something of the various organs and the manner in which they do their work. Regarding our bodily structure as a kind of living machine, we have studied its various parts, and found that each is designed to perform some special work essential to the well-being of the whole. As yet we have learned of no means by which these organs are enabled to adjust their activities to the needs of other tissues and other organs. We are now prepared to study a higher, a more wonderful and complex agency,—the nervous system, the master tissue, which controls, regulates, and directs every other tissue of the human body.

The nervous system, in its properties and mode of action, is distinct from all the other systems and organs, and it shares with no other organ or tissue the power to do its special work. It is the medium through which all impressions are received. It connects all the parts of the body into an organism in which each acts in harmony with every other part for the good of the whole. It animates and governs all movements, voluntary or involuntary,—secretion, excretion, nutrition; in fact all the processes of organic life are subject to its regulating power. The different organs of the body are united by a common sympathy which regulates their action: this harmonious result is secured by means of the nervous system.

This system, in certain of its parts, receives impressions, and generates a force peculiar to itself. We shall learn that there can be no physical communication between or cooerdination of the various parts of organs, or harmonious acts for a desire result, without the nerves. General impressions, as in ordinary sensation, or special impressions, as in sight, smell, taste, or hearing,—every instinct, every act of the will, and every thought are possible only through the action of the nerve centers.

261. Nerve Cells. However complicated the structure of nerve tissue in man seems to be, it is found to consist of only two different elements, nerve cells and nerve fibers. These are associated and combined in many ways. They are arranged in distinct masses called nerve centers, or in the form of cords known as nerves. The former are made up of nerve fibers; the latter of both cells and fibers.



Nerve cells, which may be regarded as the central organs of the nerve fibers, consist of masses of cell protoplasm, with a large nucleus and nucleolus. They bear a general resemblance to other cells, but vary much in size and shape. Nerve cells grow, become active, and die, as do other cells. A number of processes branch off from them, some cells giving one or two, others many. The various kinds of nerve cells differ much in the shape and number of processes. One of the processes is a strand which becomes continuous with the axis cylinder of the nerve fibers; that is, the axis cylinders of all nerve fibers are joined in one place or another with at least one cell.

Each part of this system has its own characteristic cell. Thus we have in the spinal cord the large, irregular cells with many processes, and in the brain proper the three-sided cells with a process jutting out from each corner. So characteristic are these forms of cells, that any particular part of nerve structure may be identified by the kind of cells seen under the microscope. Nerve cells and nerve fibers are often arranged in groups, the various cells of the groups communicating with one another. This clustered arrangement is called a nerve center.

262. Nerve Fibers. The nerve fibers, the essential elements of the nerves, somewhat resemble tubes filled with a clear, jelly-like substance. They consist of a rod, or central core, continuous throughout the whole length of the nerve, called the axis cylinder. This core is surrounded by the white substance of Schwann, or medullary sheath, which gives the nerve its characteristic ivory-white appearance. The whole is enclosed in a thin, delicate sheath, known as neurilemma.



The axis cylinder generally passes without any break from the nerve centers to the end of the fibers.[40] The outer sheath (neurilemma) is also continuous throughout the length of the fibers. The medullary sheath, on the other hand, is broken at intervals of about 1/25 of an inch, and at the same intervals nuclei are found along the fiber, around each of which is a minute protoplasmic mass. Between each pair of nuclei the sheath is interrupted. This point is known as the node of Ranvier.

Some nerve fibers have no inner sheath (medullary), the outer alone protecting the axis cylinder. These are known as the non-medullary fibers. They are gray, while the ordinary medullary fibers are white in appearance. The white nerve fibers form the white part of the brain and of the spinal cord, and the greater part of the cerebro-spinal nerves. The gray fibers occur chiefly in branches from the sympathetic ganglia, though found to some extent in the nerves of the cerebro-spinal system.

In a general way, the nerve fibers resemble an electric cable wire with its central rod of copper, and its outer non-conducting layer of silk or gutta percha. Like the copper rod, the axis cylinder along which the nerve impulse travels is the essential part of a nerve fiber. In a cut nerve this cylinder projects like the wick of a candle. It is really the continuation of a process of a nerve cell. Thus the nerve cells and nerve fibers are related, in that the process of one is the axis cylinder and essential part of the other.

The separate microscopic threads or fibers, bound together in cords of variable size, form the nerves. Each strand or cord is surrounded and protected by its own sheath of connective tissue, made up of nerves. According to its size a nerve may have one or many of these strands. The whole nerve, not unlike a minute tendon in appearance, is covered by a dense sheath of fibrous tissue, in which the blood-vessels and lymphatics are distributed to the nerve fibers.



263. The Functions of the Nerve Cells and Nerve Fibers. The nerve cells are a highly active mass of living material. They find their nourishment in the blood, which is supplied to them in abundance. The blood not only serves as nourishment, but also supplies new material, as it were, for the cells to work over for their own force or energy. Thus we may think of the nerve cells as a sort of a miniature manufactory, deriving their material from the blood, and developing from it nervous energy.

The nerve fibers, on the other hand, are conductors of nervous energy. They furnish a pathway along which the nerve energy generated by the cells may travel. Made up as they are of living nerve substance, the fibers can also generate energy, yet it is their special function to conduct influences to and from the cells.



264. The Nervous System Compared to a Telegraphic System. In men and other highly organized animals, nerves are found in nearly every tissue and organ of the body. They penetrate the most minute muscular fibers; they are closely connected with the cells of the glands, and are found in the coats of even the smallest blood-vessels. They are among the chief factors of the structure of the sense organs, and ramify through the skin. Thus the nervous system is the system of organs through the functions of which we are brought into relation with the world around us. When we hear, our ears are bringing us into relation with the outer world. So sight opens up to us another gateway of knowledge.

It will help us the better to understand the complicated functions of the nervous system, if we compare it to a telegraph line. The brain is the main office, and the multitudes of nerve fibers branching off to all parts of the body are the wires. By means of these, nerve messages are constantly being sent to the brain to inform it of what is going on in various parts of the body, and asking what is to be done in each case. The brain, on receiving the intelligence, at once sends back the required instructions. Countless messages are sent to and fro with unerring accuracy and marvelous rapidity.

Thus, when we accidentally pick up something hot, it is instantly dropped. A nerve impulse passes from the nerves of touch in the fingers to the brain, which at once hurries off its order along another set of nerves for the hand to drop the burning object. These examples, so common in daily life, may be multiplied to any extent. Almost every voluntary act we perform is executed under the direction of the nervous system, although the time occupied is so small that it is beyond our power to estimate it. The very frequency with which the nerves act tends to make us forget their beneficent work.

265. Divisions of the Nervous System. This system in man consists of two great divisions. The first is the great nerve center of the body, the cerebro-spinal system, which rules the organs of animal life. This includes the brain, the spinal cord, and the cerebro-spinal nerves. Nerves are given off from the brain and the cord, and form the mediums of communication between the external parts of the body, the muscles or the sense organs, and the brain.

The second part is the sympathetic system, which regulates the organic life. This consists of numerous small nerve centers arranged in oval masses varying greatly in size, called ganglia or knots. These are either scattered irregularly through the body, or arranged in a double chain of knots lying on the front of the spine, within the chest and abdomen. From this chain large numbers of nerves are given off, which end chiefly in the organs of digestion, circulation, and respiration. The sympathetic system serves to bring all portions of the animal economy into direct sympathy with one another.

266. The Brain as a Whole. The brain is the seat of the intellect, the will, the affections, the emotions, the memory, and sensation. It has also many other and complex functions. In it are established many reflex, automatic, and coordinating centers, which are as independent of consciousness as are those of the spinal cord.

The brain is the largest and most complex mass of nerve tissue in the body, made up of an enormous collection of gray cells and nerve fibers. This organ consists of a vast number of distinct ganglia, or separate masses of nerve matter, each capable of performing separate functions, but united through the cerebral action into a harmonious whole.



The average weight of the adult human brain is about 50 ounces for men and 45 ounces for women. Other things being equal, the size and weight of the brain bear a general relation to the mental power of the individual. As a rule, a large, healthy brain stands for a vigorous and superior intellect. The brains of many eminent men have been found to be 8 to 12 ounces above the average weight, but there are notable exceptions. The brains of idiots are small; indeed, any weight under a certain size, about 30 ounces, seems to be invariably associated with an imbecile mind.

The human brain is absolutely heavier than that of any other animal, except the whale and elephant. Comparing the size of these animals with that of man, it is instructive to notice how much larger in proportion to the body is man's brain. The average proportion of the weight of the brain to the weight of the body is greater in man than in most animals, being about 1 to 36. In some small birds, in the smaller monkeys, and in some rodents, the proportional weight of the brain to that of the body is even greater than in man.

267. The Cerebrum. The three principal masses which make up the brain when viewed as a whole are:

1. The cerebrum, or brain proper. 2. The cerebellum, or lesser brain. 3. The medulla oblongata.

The cerebrum comprises nearly seven-eighths of the entire mass, and fills the upper part of the skull. It consists of two halves, the right and left cerebral hemispheres. These are almost separated from each other by a deep median fissure. The hemispheres are united at the bottom of the fissure by a mass of white fibers passing from side to side. Each of these hemispheres is subdivided into three lobes, so that the entire cerebrum is made up of six distinct lobes.

The cerebrum has a peculiar convoluted appearance, its deep folds being separated by fissures, some of them nearly an inch in depth.

It is composed of both white and gray matter. The former comprises the greater part of the mass, while the latter is spread over the surface in a layer of about 1/8 of an inch thick. The gray matter is the portion having the highest functions, and its apparent quantity is largely increased by being formed in convolutions.

The convolutions of the cerebrum are without doubt associated with all those higher actions which distinguish man's life; but all the convolutions are not of equal importance. Thus it is probable that only the frontal part of the brain is the intellectual region, while certain convolutions are devoted to the service of the senses.

The cerebrum is the chief seat of the sensations, the intellect, the will, and the emotions. A study of cerebral injuries and diseases, and experiments upon the lower animals, prove that the hemispheres, and more especially the gray matter, are connected with mental states. The convolutions in the human brain are more prominent than in that of the higher animals, most nearly allied to man, although some species of animals, not especially intelligent, have marked cerebral convolutions. The higher races of men have more marked convolutions than those less civilized.

A view of the under surface of the brain, which rests on the floor of the skull, shows the origin of important nerves, called the cranial nerves, the cerebellum, the structure connecting the optic nerves (optic commissure), the bridge of nervous matter (pons Varolii) connecting the two hemispheres of the cerebellum, and lastly numerous and well-marked convolutions.

268. The Cerebellum. The cerebellum, or lesser brain, lies in the back of the cranium, and is covered over in man by the posterior lobe of the cerebrum. It is, at it were, astride of the back of the cerebro-spinal axis, and consists of two hemispheres joined by a central mass. On its under surface is a depression which receives the medulla oblongata. The cerebellum is separated from the cerebrum by a horizontal partition of membrane, a portion of the dura mater. In some animals, as in the cat, this partition is partly bone.

The cerebellum is connected with other parts of the nervous system by strands of white matter on each side, radiating from the center and divided into numerous branches. Around these branches the gray matter is arranged in a beautiful manner, suggesting the leaves of a tree: hence its name, arbor vitae, or the tree of life.

The functions of the cerebellum are not certainly known. It appears to influence the muscles of the body so as to regulate their movements; that is, it serves to bring the various muscular movements into harmonious action. The mechanism by which it does this has not yet been clearly explained. In an animal from which the cerebellum has been removed, the functions of life do not appear to be destroyed, but all power of either walking or flying straight is lost.



Disease or injury of the cerebellum usually produces blindness, giddiness, a tendency to move backwards, a staggering, irregular gait, and a feeling of insecurity in maintaining various positions. There is no loss of consciousness, or other disturbance of the mental functions.

269. The Membranes of the Brain. The brain and spinal cord are protected by three important membranes, known as the meninges,—the dura mater, the arachnoid, and the pia mater.

The outer membrane, the dura mater, is much thicker and stronger than the others, and is composed of white fibrous and elastic connective tissue. It closely lines the inner surface of the skull, and forms a protective covering for the brain. Folds of it pass between the several divisions of the brain and serve to protect them.

The arachnoid is a thin membrane which lies beneath the dura mater. It secretes a serous fluid which keeps the inner surfaces moist.

The pia mater is a very delicate, vascular membrane which covers the convolutions, dips into all the fissures, and even penetrates into the interior of the brain. It is crowded with blood-vessels, which divide and subdivide very minutely before they penetrate the brain. The membranes of the brain are sometimes the seat of inflammation, a serious and painful disease, commonly known as brain fever.

270. The Medulla Oblongata. This is the thick upper part of the spinal cord, lying within the cavity of the skull. It is immediately under the cerebellum, and forms the connecting link between the brain and the spinal cord. It is about an inch and a quarter long, and from one-half to three-fourths of an inch wide at its upper part. The medulla oblongata consists, like the spinal cord, of columns of white fibers and masses of gray matter, but differently arranged. The gray matter is broken up into masses which serve as centers of origin for various nerves. The functions of the medulla oblongata are closely connected with the vital processes. It is a great nerve tract for transmitting sensory and motor impressions, and also the seat of a number of centers for reflex actions of the highest importance to life. Through the posterior part of the medulla the sensory impressions pass, that is, impressions from below upwards to the brain resulting in sensation or feeling. In the anterior part of the medulla, pass the nerves for motor transmission, that is, nerve influences from above downwards that shall result in muscular contractions in some part of the body.

The medulla is also the seat of a number of reflex centers connected with the influence of the nervous system on the blood-vessels, the movements of the heart, of respiration, and of swallowing, and on the secretion of saliva. This spot has been called the "vital knot." In the medulla also are centers for coughing, vomiting, swallowing, and the dilatation of the pupil of the eye. It is also in part the deep origin of many of the 'important cranial nerves.



271. The Cranial Nerves. The cranial or cerebral nerves consist of twelve pairs of nerves which pass from the brain through different openings in the base of the skull, and are distributed over the head and face, also to some parts of the trunk and certain internal organs. These nerves proceed in pairs from the corresponding parts of each side of the brain, chiefly to the organs of smell, taste, hearing, and sight.

The cranial nerves are of three kinds: sensory, motor, and both combined, viz., mixed.

Distribution and Functions of the Cranial Nerves. The cranial nerves are thus arranged in pairs:

The first pair are the olfactory nerves, which pass down through the ethmoid bone into the nasal cavities, and are spread over the inner surface of the nose. They are sensory, and are the special nerves of smell.

The second pair are the optic nerves, which, under the name of the optic tracts, run down to the base of the brain, from which an optic nerve passes to each eyeball. These are sensory nerves, and are devoted to sight.

The third, fourth, and sixth pairs proceed to the muscles of the eyes and control their movements. These are motor nerves, the movers of the eye.

Each of the fifth pair of nerves is in three branches, and proceeds mainly to the face. They are called tri-facial, and are mixed nerves, partly sensory and partly motor. The first branch is purely sensory, and gives sensibility to the eyeball. The second gives sensibility to the nose, gums, and cheeks. The third (mixed) gives the special sensation of taste on the front part of the tongue, and ordinary sensation on the inner side of the cheek, on the teeth, and also on the scalp in front of the ear. The motor branches supply the chewing muscles.

The seventh pair, the facial, proceed to the face, where they spread over the facial muscles and control their movements. The eighth pair are the auditory, or nerves of hearing, and are distributed to the special organs of hearing.

The next three pairs of nerves all arise from the medulla, and escape from the cavity of the skull through the same foramen. They are sometimes described as one pair, namely, the eighth, but it is more convenient to consider them separately.

The ninth pair, the glosso-pharyngeal, are partly sensory and partly motor. Each nerve contains two roots: one a nerve of taste, which spreads over the back part of the tongue; the other a motor nerve, which controls the muscles engaged in swallowing.

The tenth pair, the pneumogastric, also known as the vagus or wandering nerves, are the longest and most complex of all the cranial nerves. They are both motor and sensory, and are some of the most important nerves in the body. Passing from the medulla they descend near the oesophagus to the stomach, sending off, on their way, branches to the throat, the larynx, the lungs, and the heart. Some of their branches restrain the movements of the heart, others convey impressions to the brain, which result in quickening or slowing the movements of breathing. Other branches pass to the stomach, and convey to the brain impressions which inform us of the condition of that organ. These are the nerves by which we experience the feelings of pain in the stomach, hunger, nausea, and many other vague impressions which we often associate with that organ.



The eleventh pair, the spinal accessory, are strictly motor, and supply the muscles of the neck and the back.

The twelfth pair, the hypoglossal, are also motor, pass to the muscles of the tongue, and help control the delicate movements in the act of speech.

272. The Spinal Cord. This is a long, rod-like mass of white nerve fibers, surrounding a central mass of gray matter. It is a continuation of the medulla oblongata, and is lodged in the canal of the spinal column. It extends from the base of the skull to the lower border of the first lumbar vertebra, where it narrows off to a slender filament of gray substance.

The spinal cord is from 16 to 18 inches long, and has about the thickness of one's little finger, weighing about 1-1/2 ounces. Like the brain, it is enclosed in three membranes, which in fact are the continuation of those within the skull. They protect the delicate cord, and convey vessels for its nourishment. The space between the two inner membranes contains a small quantity of fluid, supporting the cord, as it were in a water-bath. It is thus guarded against shocks.

The cord is suspended and kept in position in the canal by delicate ligaments at regular intervals between the inner and outer membranes. Finally, between the canal, enclosed by its three membranes, and the bony walls of the spinal canal, there is considerable fatty tissue, a sort of packing material, imbedded in which are some large blood-vessels.

273. Structure of the Spinal Cord. The arrangement of the parts of the spinal cord is best understood by a transverse section. Two fissures, one behind, the other in front, penetrate deeply into the cord, very nearly dividing it into lateral halves. In the middle of the isthmus which joins the two halves, is a very minute opening, the central canal of the cord. This tiny channel, just visible to the naked eye, is connected with one of the openings of the medulla oblongata, and extends, as do the anterior and posterior fissures, the entire length of the cord.

The spinal cord, like the brain, consists of gray and white matter, but the arrangement differs. In the brain the white matter is within, and the gray matter is on the surface. In the cord the gray matter is arranged in two half-moon-shaped masses, the backs of which are connected at the central part. The white matter, consisting mainly of fibers, running for the most part in the direction of the length of the cord, is outside of and surrounds the gray crescents. Thus each half or side of the cord has its own gray crescent, the horns of which point one forwards and the other backwards, called respectively the anterior and posterior cornua or horns.

It will also be seen that the white substance itself, in each half of the cord, is divided by the horns of the gray matter and by fibers passing from them into three parts, which are known as the anterior, posterior, and lateral columns.

Experiment 130. Procure at the market an uninjured piece of the spinal cord from the loin of mutton or the sirloin or the rib of beef. After noting its general character while fresh, put it to soak in dilute alcohol, until it is sufficiently hard to be cut in sections.

274. The Spinal Nerves. From the gray matter on each side of the spinal cord 31 spinal nerves are given off and distributed chiefly to the muscles and the skin. They pass out at regular intervals on each side of the canal, by small openings between the vertebrae. Having escaped from the spine, they pass backwards and forwards, ramifying in the soft parts of the body. The first pair pass out between the skull and the atlas, the next between the atlas and the axis, and so on down the canal. The eighth pair, called cervical, pass out in the region of the neck; twelve, called dorsal, in the region of the ribs; five are lumbar, and five sacral, while the last pair leave the cord near the coccyx.

Each spinal nerve has two roots, one from the anterior, the other from the posterior portion of the cord. These unite and run side by side, forming as they pass between the vertebrae one silvery thread, or nerve trunk. Although bound up in one bundle, the nerve fibers of the two roots remain quite distinct, and perform two entirely different functions.

After leaving the spinal cord, each nerve divides again and again into finer and finer threads. These minute branches are distributed through the muscles, and terminate on the surface of the body. The anterior roots become motor nerves, their branches being distributed to certain muscles of the body, to control their movements. The posterior roots develop into sensory nerves, their branches being distributed through the skin and over the surface of the body to become nerves of touch. In brief, the spinal nerves divide and subdivide, to reach with their twigs all parts of the body, and provide every tissue with a nerve center, a station from which messages may be sent to the brain.



275. The Functions of the Spinal Nerves. The messages which pass along the spinal nerves to and from the brain are transmitted mostly through the gray matter of the cord, but some pass along the white matter on the outer part. As in the brain, however, all the active powers of the cord are confined to the gray matter. The spinal nerves themselves have nothing to do with sensation or will. They are merely conductors to carry messages to and fro. They neither issue commands nor feel a sensation. Hence, they consist entirely of white matter.

276. Functions of the Spinal Cord. The spinal cord is the principal channel through which all impulses from the trunk and extremities pass to the brain, and all impulses to the trunk and extremities pass from the brain. That is, the spinal cord receives from various parts of the body by means of its sensory nerves certain impressions, and conveys them to the brain, where they are interpreted.

The cord also transmits by means of its motor nerves the commands of the brain to the voluntary muscles, and so causes movement. Thus, when the cord is divided at any point, compressed, as by a tumor or broken bone, or disorganized by disease, the result is a complete loss of sensation and voluntary movement below the point of injury. If by accident a man has his spinal cord injured at some point, he finds he has lost all sensation and power of motion below that spot. The impulse to movement started in his brain by the will does not reach the muscles he wishes to move, because traveling down the spinal cord, it cannot pass the seat of injury.

So the impression produced by pricking the leg with a pin, which, before pain can be felt, must travel up the spinal cord to the brain, cannot reach the brain because the injury obstructs the path. The telegraph wire has been cut, and the current can no longer pass.

277. The Spinal Cord as a Conductor of Impulses. The identity in structure of the spinal nerves, whether motor or sensory, and the vast number of nerves in the cord make it impossible to trace for any distance with the eye, even aided by the microscope and the most skillful dissection, the course of nerve fibers. The paths by which the motor impulses travel down the cord are fairly well known. These impulses originate in the brain, and passing down keep to the same side of the cord, and go out by nerves to the same side of the body.

The sensory impulses, however, soon after they enter the cord by the nerve of one side, cross in the cord to the opposite side, up which they travel to the brain. Thus the destruction of one lateral half of the cord causes paralysis of motion on the same side as the injury, but loss of sensation on the opposite side, because the posterior portion destroyed consists of fibers which have crossed from the opposite side.

Experiment proves that if both roots of a spinal nerve be cut, all those parts of the body to which they send branches become paralyzed, and have neither sense of pain nor power of voluntary movement. The parts might even be cut or burned without pain. It is precisely like cutting a telegraph wire and stopping the current.



Experiment also proves that if only the posterior root of a spinal nerve be cut, all sensation is lost in the parts to which the nerve passes, but the power of moving these parts is retained. But if the anterior root alone be divided, all power of motion in the parts supplied by that nerve is lost, but sensation remains. From these and many other experiments, it is evident that those fibers of a nerve which are derived from the anterior root are motor, and those from the posterior root sensory, fibers. Impulses sent from the brain and spinal cord to muscles will, therefore, pass along the anterior roots through those fibers of the nerves which are derived from these (motor) roots. On the other hand, impressions or sensations passing to the brain will enter the spinal cord and reach the brain through the posterior or sensory roots.

278. The Spinal Cord as a Reflex Center. Besides this function of the spinal cord as a great nerve conductor to carry sensations to the brain, and bring back its orders, it is also an independent center for what is called reflex action. By means of its sensory nerves it receives impressions from certain parts of the body, and on its own authority sends back instructions to the muscles by its motor nerves, without consulting the brain. This constitutes reflex action, so called because the impulse sent to the spinal cord by certain sensory nerves is at once reflected or sent back as a motor impulse to the muscles.

This reflex action is a most important function of the spinal cord. This power is possessed only by the gray matter of the cord, the white substance being simply a conductor.

The cells of gray matter are found all along the cord, but are grouped together in certain parts, notably in the cervical and lumbar regions. The cells of the anterior horns are in relation with the muscles by means of nerve fibers, and are also brought into connection with the skin and other sensory surfaces, by means of nerve fibers running in the posterior part of the cord. Thus there is established in the spinal cord, without reference to the brain at all, a reflex mechanism.

279. Reflex Centers. For the purpose of illustration, we might consider the body as made up of so many segments piled one on another, each segment presided over by a similar segment of spinal cord. Each bodily segment would have sensory and motor nerves corresponding to its connection with the spinal cord. The group of cells in each spinal segment is intimately connected with the cells of the segments above and below. Thus an impression reaching the cells of one spinal segment might be so strong as to overflow into the cells of other segments, and thus cause other parts of the body to be affected.

Take as an example the case of a child who has eaten improper food, which irritates its bowels. Sensory nerves of the bowels are disturbed, and powerful impressions are carried up to a center in the spinal cord. These impressions may now overflow into other centers, from which spasmodic discharges of nerve energy may be liberated, which passing to the muscles, throw them into violent and spasmodic contraction. In other words, the child has a fit, or convulsion. All this disturbance being the result of reflex action (the spasmodic motions being quite involuntary, as the brain takes no part in them), the child meanwhile is, of course, entirely unconscious and, however it may seem to be distressed, really suffers no pain.

Scattered along the entire length of the spinal cord, especially in the upper part, are groups of nerve cells which preside over certain specific functions of animal life; that is, definite collections of cells which control definite functions. Thus there are certain centers for maintaining the action of the heart, and the movements of breathing; and low down in the cord, in the lumbar regions, are centers for the control of the various abdominal organs.

Numerous other reflex centers are described by physiologists, but enough has been said to emphasize the great importance of the spinal cord as an independent nerve center, besides its function as a conductor of nervous impulses to and from the brain.

280. The Brain as a Reflex Center. The brain, as we have just stated, is the seat of consciousness and intelligence. It is also the seat of many reflex, automatic, and coordinating centers. These give rise to certain reflex actions which are as entirely independent of consciousness as are those of the spinal cord. These acts take place independently of the will, and often without the consciousness of the individual. Thus, a sudden flash of light causes the eyes to blink, as the result of reflex action. The optic nerves serve as the sensory, and the facial nerves as the motor, conductors. The sudden start of the whole body at some loud noise, the instinctive dodging a threatened blow, and the springing back from sudden danger, are the results of reflex action. The result ensues in these and in many other instances, without the consciousness of the individual, and indeed beyond his power of control.

281. The Importance of Reflex Action. Reflex action is thus a marvelous provision of nature for our comfort, health, and safety. Its vast influence is not realized, as its numberless acts are so continually going on without our knowledge. In fact, the greater part of nerve power is expended to produce reflex action. The brain is thus relieved of a vast amount of work. It would be impossible for the brain to serve as a "thinking center" to control every act of our daily life. If we had to plan and to will every heart-beat or every respiration, the struggle for life would soon be given up.

The fact that the gray cells of the spinal cord can originate a countless number of reflex and automatic activities is not only of great importance in protecting the body from injury, but increases vastly the range of the activities of our daily life.

Even walking, riding the bicycle, playing on a piano, and numberless other such acts may be reflex movements. To learn how, requires, of course, the action of the brain, but with frequent repetition the muscles become so accustomed to certain successive movements, that they are continued by the cord without the control of the brain. Thus we may acquire a sort of artificial reflex action, which in time becomes in a way a part of our organization, and is carried on without will power or even consciousness.

So, while the hands are busily doing one thing, the brain can be intently thinking of another. In fact, any attempt to control reflex action is more apt to hinder than to help. In coming rapidly down stairs, the descent will be made with ease and safety if the spinal cord is allowed entire charge of the act, but the chances of stumbling or of tripping are very much increased if each step be taken as the result of the will power. The reflex action of the cord may be diminished, or inhibited as it is called, but this power is limited. Thus, we can by an effort of the will stop breathing for a certain time, but beyond that the reflex mechanism overcomes our will and we could not, if we would, commit suicide by holding our breath. When we are asleep, if the palm of the hand be tickled, it closes; when we are awake we can prevent it.

[Illustration: Fig. 120.—Dr. Waller's Diagrammatic Illustration of the Reflex Process.

From the sentient surface (1) an afferent impulse passes along (2) to the posterior root of the spinal cord, the nerve fibers of the posterior root ending in minute filaments among the small cells of this part of the cord (3). In some unknown way this impulse passes across the gray part of the cord to the large cells of the anterior root (5), the cells of this part being connected by their axis-cylinder with the efferent fibers (6). These convey the stimulus to the fibers of the muscle (7), which accordingly contract. Where the brain is concerned in the action the circuit is longer through S and M.]

Experiment 131. To illustrate reflex action by what is called knee-jerk. Sit on a chair, and cross the right leg over the left one. With the tips of the fingers or the back of a book, strike the right ligamentum patellae. The right leg will be raised and thrown forward with a jerk, owing to the contraction of the quadriceps muscles. An appreciable time elapses between the striking of the tendon and the jerk. The presence or absence of the knee-jerk may be a most significant symptom to the physician.

282. The Sympathetic System. Running along each side of the spine, from the base of the skull to the coccyx, is a chain of nerve knots, or ganglia. These ganglia, twenty-four on each side, and their branches form the sympathetic system, as distinguished from the cerebro-spinal system consisting of the brain and spinal cord and the nerves springing from them. The ganglia of the sympathetic system are connected with each other and with the sensory roots of the spinal nerves by a network of gray nerve fibers.

At the upper end the chain of each side passes up into the cranium and is closely connected with the cranial nerves. In the neck, branches pass to the lungs and the heart. From the ganglia in the chest three nerves form a complicated network of fibers, from which branches pass to the stomach, the liver, the intestines, the kidneys, and other abdominal organs. A similar network of fibers is situated lower down in the pelvis, from which branches are distributed to the pelvic organs. At the coccyx the two chains unite into a single ganglion.

Thus, in general, the sympathetic system, while intimately connected with the cerebro-spinal, forms a close network of nerves which specially accompany the minute blood-vessels, and are distributed to the muscles of the heart, the lungs, the stomach, the liver, the intestines, and the kidneys—that is, the hollow organs of the body.

283. The Functions of the Sympathetic System. This system exercises a superintending influence over the greater part of the internal organs of the body, controlling to a certain extent the functions of digestion, nutrition, circulation, and respiration. The influence thus especially connected with the processes of organic life is generally different from, or even opposed to, that conveyed to the same organs by fibers running in the spinal or cranial nerves. These impulses are beyond the control of the will.

[Illustration: Fig. 121.—The Cervical and Thoracic Portion of the Sympathetic Nerve and its Main Branches.

A, right pneumogastric; B, spinal accessory; C, glosso-pharyngeal; D, right bronchus; E, right branch of pulmonary artery; F, one of the intercostal nerves; H, great splanchnic nerve; K, solar plexus; L, left pneumogastric; M, stomach branches of right pneumogastric; N, right ventricle; O, right auricle; P, trunk of pulmonary artery; R, aorta; S, cardiac nerves; T, recurrent laryngeal nerve; U, superior laryngeal nerve; V, submaxillary ganglion; W, lingual branch of the 5th nerve; X, ophthalmic ganglion; Y, motor oculi externus. ]

Hence, all these actions of the internal organs just mentioned that are necessary to the maintenance of the animal life, and of the harmony which must exist between them, are controlled by the sympathetic system. But for this control, the heart would stop beating during sleep, digestion would cease, and breathing would be suspended. Gentle irritation of these nerves, induced by contact of food in the stomach, causes that organ to begin the churning motion needed for digestion. Various mental emotions also have a reflex action upon the sympathetic system. Thus, terror dilates the pupils, fear acts upon the nerves of the small blood-vessels of the face to produce pallor, and the sight of an accident, or even the emotions produced by hearing of one, may excite nausea and vomiting.

The control of the blood-vessels, as has been stated (sec. 195), is one of the special functions of the sympathetic system. Through the nerves distributed to the muscular coats of the arteries, the caliber of these vessels can be varied, so that at one moment they permit a large quantity of blood to pass, and at another will contract so as to diminish the supply. This, too, is beyond the control of the will, and is brought about by the vaso-motor nerves of the sympathetic system through a reflex arrangement, the center for which is the medulla oblongata.

284. Need of Rest. The life of the body, as has been emphasized in the preceding chapters, is subject to constant waste going on every moment, from the first breath of infancy to the last hour of old age. We should speedily exhaust our life from this continual loss, but for its constant renewal with fresh material. This exhaustion of life is increased by exertion, and the process of repair is vastly promoted by rest. Thus, while exercise is a duty, rest is equally imperative.

The eye, when exactingly used in fine work, should have frequent intervals of rest in a few moments of darkness by closing the lids. The brain, when urged by strenuous study, should have occasional seasons of rest by a dash of cold water upon the forehead, and a brief walk with slow and deep inspirations of fresh air. The muscles, long cramped in a painful attitude, should be rested as often as may be, by change of posture or by a few steps around the room.

It is not entirely the amount of work done, but the continuity of strain that wears upon the body. Even a brief rest interrupts this strain; it unclogs the wheels of action. Our bodies are not designed for continuous toil. An alternation of labor and rest diminishes the waste of life. The benign process of repair cannot go on, to any extent, during strenuous labor, but by interposing frequent though brief periods of rest, we lessen the amount of exhaustion, refresh the jaded nerves, and the remaining labor is more easily endured.

285. Benefits of Rest. There is too little repose in our American nature and in our modes of life. A sense of fatigue is the mute appeal of the body for a brief respite from labor, and the appeal should, if possible, be heeded. If this appeal be not met, the future exertion exhausts far more than if the body had been even slightly refreshed. If the appeal be met, the brief mid-labor rest eases the friction of toil, and the remaining labor is more easily borne. The feeling that a five-minute rest is so much time lost is quite an error. It is a gain of physical strength, of mental vigor, and of the total amount of work done.

The merchant burdened with the cares of business life, the soldier on the long march, the ambitious student over-anxious to win success in his studies, the housewife wearied with her many hours of exacting toil, each would make the task lighter, and would get through it with less loss of vital force, by occasionally devoting a few minutes to absolute rest in entire relaxation of the strained muscles and overtaxed nerves.

286. The Sabbath as a Day of Physiological Rest. The divine institution of a Sabbath of rest, one day in seven, is based upon the highest needs of our nature. Rest, to be most effective, should alternate in brief periods with labor.

It is sound physiology, as well as good morals and manners, to cease from the usual routine of six days of mental or physical work, and rest both the mind and the body on the seventh. Those who have succeeded best in what they have undertaken, and who have enjoyed sound health during a long and useful life, have studiously lived up to the mandates of this great physiological law. It is by no means certain that the tendency nowadays to devote the Sabbath to long trips on the bicycle, tiresome excursions by land and sea, and sight-seeing generally, affords that real rest from a physiological point of view which nature demands after six days of well-directed manual or mental labor.

287. The Significance of Sleep as a Periodical Rest. Of the chief characteristics of all living beings none is so significant as their periodicity. Plants as well as animals exhibit this periodic character. Thus plants have their annual as well as daily periods of activity and inactivity. Hibernating animals pass the winter in a condition of unconsciousness only to have their functions of activity restored in early spring. Human beings also present many instances of a periodic character, many of which have been mentioned in the preceding pages. Thus we have learned that the heart has its regular alternating periods of work and rest. After every expiration from the lungs there is a pause before the next inspiration begins.

Now sleep is just another manifestation of this periodic and physiological rest by which Nature refreshes us. It is during the periods of sleep that the energy expended in the activities of the waking hours is mainly renewed. In our waking moments the mind is kept incessantly active by the demands made on it through the senses. There is a never-ceasing expenditure of energy and a consequent waste which must be repaired. A time soon comes when the brain cells fail to respond to the demand, and sleep must supervene. However resolutely we may resist this demand, Nature, in her relentless way, puts us to sleep, no matter what objects are brought before the mind with a view to retain its attention.[41]

288. Effect of Sleep upon the Bodily Functions. In all the higher animals, the central nervous system enters once at least in the twenty-four hours into the condition of rest which we call sleep. Inasmuch as the most important modifications of this function are observed in connection with the cerebro-spinal system, a brief consideration of the subject is properly studied in this chapter. In Chapter IV. we learned that repose was as necessary as exercise to maintain muscular vigor. So after prolonged mental exertion, or in fact any effort which involves an expenditure of what is often called nerve-force, sleep becomes a necessity. The need of such a rest is self-evident, and the loss of it is a common cause of the impairment of health. While we are awake and active, the waste of the body exceeds the repair; but when asleep, the waste is diminished, and the cells are more actively rebuilding the structure for to-morrow's labor. The organic functions, such as are under the direct control of the sympathetic nervous system,—circulation, respiration, and digestion,—are diminished in activity during sleep. The pulsations of the heart and the respiratory movements are less frequent, and the circulation is slower. The bodily temperature is reduced, and the cerebral circulation is diminished. The eyes are turned upward and inward, and the pupils are contracted.

The senses do not all fall to sleep at once, but drop off successively: first the sight, then the smell, the taste, the hearing and lastly the touch. The sleep ended, they awake in an inverse order, touch, hearing, taste, smell, and sight.

289. The Amount of Sleep Required. No precise rule can be laid down concerning the amount of sleep required. It varies with age, occupation, temperament, and climate to a certain extent. An infant whose main business it is to grow spends the greater part of its time in sound sleep. Adults of average age who work hard with their hands or brain, under perfectly normal physiological conditions, usually require at least eight hours of sleep. Some need less, but few require more. Personal peculiarities, and perhaps habit to a great extent, exert a marked influence. Some of the greatest men, as Napoleon I., have been very sparing sleepers. Throughout his long and active life, Frederick the Great never slept more than five or six hours in the twenty-four. On the other hand, some of the busiest brain-workers who lived to old age, as William Cullen Bryant and Henry Ward Beecher, required and took care to secure at least eight or nine hours of sound sleep every night.

In old age, less sleep is usually required than in adult life, while the aged may pass much of their time in sleep. In fact, each person learns by experience how much sleep is necessary. There is no one thing which more unfits one for prolonged mental or physical effort than the loss of natural rest.

290. Practical Rules about Sleep. Children should not be played with boisterously just before the bedtime hour, nor their minds excited with weird goblin stories, or a long time may pass before the wide-open eyes and agitated nerves become composed to slumber. Disturbed or insufficient sleep is a potent factor towards producing a fretful, irritable child.

At all ages the last hour before sleep should, if possible, be spent quietly, to smooth the way towards sound and refreshing rest. The sleep induced by medicine is very often troubled and unsatisfactory. Medicines of this sort should not be taken except on the advice of a physician.

While a hearty meal should not usually be taken just before bedtime, it is not well to go to bed with a sense of positive faintness and hunger. Rather, one should take a very light lunch of quite simple food as a support for the next eight hours.



It is better, as a rule, not to engage in severe study during the hours just before bedtime. Neither body nor mind being at its best after the fatigues of the day, study at that time wears upon the system more, and the progress is less than at earlier hours. One hour of morning or day study is worth a much longer time late at night. It is, therefore, an economy both of time and of nerve force to use the day hours and the early evening for study.

The so-called "cat naps" should never be made to serve as a substitute for a full night's sleep. They are largely a matter of habit, and are detrimental to some as well as beneficial to others. Late hours are usually associated with exposure, excitement, and various other drains upon the nerve force, and hence are injurious.

It is better to sleep on one or other side than on the back. The head should be somewhat raised, and a mattress is better than a feather bed. The bedclothes should be sufficient, but not too heavy. Light tends to prevent sleep, as do loud or abrupt sounds, but monotonous sounds aid it.

291. Alcohol and the Brain. The unfortunate effects which alcoholic drinks produce upon the brain and nervous system differ from the destructive results upon other parts of the body in this respect, that elsewhere the consequences are usually both less speedy and less obvious. The stomach, the liver, and even the heart may endure for a while the trespass of the narcotic poison, and not betray the invasion. But the nervous system cannot, like them, suffer in silence.

In the other parts of the body the victim may (to a certain extent) conceal from others the suffering of which he himself is painfully conscious. But the tortured brain instantly reveals the calamity and the shame, while the only one who may not fully realize it is the victim himself. Besides this, the injuries inflicted upon other organs affect only the body, but here they drag down the mind, ruin the morals, and destroy the character.

The brain is indeed the most important organ of the body, as it presides over all the others. It is the lofty seat of power and authority. Here the king is on his throne. But if, by this malignant adversary, the king himself be dethroned, his whole empire falls to ruins.

292. How Alcohol Injures the Brain. The brain, the nerve centers, and the nerves are all made up of nerve pulp, the softest and most delicate tissue in the whole bodily structure. Wherever this fragile material occurs in our bodies,—in the skull, the spine, the trunk, or the limbs,—the all-wise Architect has carefully protected it from violence, for a rough touch would injure it, or even tender pressure would disturb its function.

It is a further indication of the supreme importance of the brain, that about one-fifth of the entire blood of the body is furnished to it. Manifestly, then, this vital organ must be tenderly cared for. It must indeed be well nourished, and therefore the blood sent to it must be highly nutrient, capable of supplying oxygen freely. This condition is essential to successful brain action. But intoxicants bring to it blood surcharged with a poisonous liquid, and bearing only a limited supply of oxygen.

Another condition of a healthy brain is that the supply of blood to it shall be equable and uniform. But under the influence of strong drink, the blood pours into the paralyzed arteries a surging tide that floods the head, and hinders and may destroy the use of the brain and the senses. Still another requirement is that whatever is introduced into the cerebral tissues, having first passed through the stomach walls and thence into the blood, shall be bland, not irritating. But in the brain of the inebriate are found not only the distinct odor but the actual presence of alcohol. Thus we plainly see how all these three vital conditions of a healthy brain are grossly violated by the use of intoxicants.

"I think there is a great deal of injury being done by the use of alcohol in what is supposed by the consumer to be a most moderate quantity, to persons who are not in the least intemperate, and to people supposed to be fairly well. It leads to degeneration of the tissues; it damages the health; it injures the intellect. Short of drunkenness, that is, in those effects of it which stop short of drunkenness, I should say from my experience that alcohol is the most destructive agent we are aware of in this country."—Sir William Gull, the most eminent English physician of our time.

293. Why the Brain Suffers from the Alcoholic Habit. We do not find that the alcoholic habit has produced in the brain the same coarse injuries that we see in other organs, as in the stomach, the liver, or the heart. Nor should we expect to find them; for so delicate and so sensitive is the structure of this organ, that a very slight injury here goes a great way,—a disturbance may be overwhelming to the brain that would be only a trifle to some of the less delicate organs.

Alcohol has different degrees of affinity for different organs of the body, but much the strongest for the cerebral tissues. Therefore the brain feels more keenly the presence of alcohol than does any other organ. Almost the moment that the poison is brought into the stomach, the nerves send up the alarm that an invading foe has come. At once there follows a shock to the brain, and very soon its paralyzed blood-vessels are distended with the rush of blood. This first effect is, in a certain sense, exhilarating, and from this arousing influence alcohol has been erroneously considered a stimulant; but the falsity of this view is pointed out elsewhere in this book.

294. Alcohol, the Enemy of Brain Work. The healthy brain contains a larger proportion of water than does any other organ. Now alcohol, with its intense affinity for water, absorbs it from the brain, and thus condenses and hardens its structure. One of the important elements of the brain is its albumen; this also is contracted by alcohol. The nerve cells and fibers gradually become shriveled and their activity is lowered, the elasticity of the arteries is diminished, the membranes enveloping the brain are thickened, and thus all proper brain nutrition is impaired. The entire organ is slowly hardened, and becomes unfitted for the proper performance of its delicate duties. In brief, alcohol in any and every form is the enemy of successful and long-continued brain work.



295. Other Physical Results of Intoxicants. What are some of the physical results observed? First, we note the failure of the vaso-motor nerves to maintain the proper tone of the blood-vessels, as in the turgid face and the congested cornea of the eye. Again, we observe the loss of muscular control, as is shown by the drop of the lower lip, the thickened speech, and the wandering eye. The spinal cord, too, is often affected and becomes unable to respond to the demand for reflex action, as appears from the trembling hands, the staggering legs, the swaying body, and the general muscular uncertainty. All these are varied results of the temporary paralysis of the great nerve centers.

Besides, the sensibility of the nerves is deadened. The inebriate may seize a hot iron and hardly know it, or wound his hand painfully and never feel the injury. The numbness is not of the skin, but of the brain, for the drunken man may be frozen or burned to death without pain. The senses, too, are invaded and dulled. Double vision is produced, the eyes not being so controlled as to bring the image upon corresponding points of the retina.

296. Diseases Produced by Alcohol. The diseases that follow in the train of the alcoholic habit are numerous and fatal. It lays its paralyzing hand upon the brain itself, and soon permanently destroys the integrity of its functions. In some the paralysis is local only, perhaps in one of the limbs, or on one side of the body; in others there is a general muscular failure. The vitality of the nerve centers is so thoroughly impaired that general paralysis often ensues. A condition of insomnia, or sleeplessness, often follows, or when sleep does come, it is in fragments, and is far from refreshing to the jaded body.

In time follows another and a terrible disease known as delirium tremens; and this may occur in those who claim to be only moderate drinkers, rarely if ever intoxicated. It accompanies an utter breakdown of the nervous system. Here reason is for the time dethroned, while at some times wild and frantic, or at others a low, mumbling delirium occurs, with a marked trembling from terror and exhaustion.

There is still another depth of ruin in this downward course, and that is insanity. In fact, every instance of complete intoxication is a case of temporary insanity, that is, of mental unsoundness with loss of self-control. Permanent insanity may be one of the last results of intemperance. Alcoholism sends to our insane asylums a large proportion of their inmates, as ample records testify.

297. Mental and Moral Ruin Caused by Alcoholism. Alcoholism, the evil prince of destroyers, also hastens to lay waste man's mental and moral nature. Just as the inebriate's senses, sight, hearing, and touch, fail to report correctly of the outer world, so the mind fails to preside properly over the inner realm. Mental perceptions are dulled. The stupefied faculties can hardly be aroused by any appeal. Memory fails. Thus the man is disqualified for any responsible labor. No railroad company, no mercantile house, will employ any one addicted to drinking. The mind of the drunkard is unable to retain a single chain of thought, but gropes about with idle questionings. The intellect is debased. Judgment is impossible, for the unstable mind cannot think, compare, or decide.

The once active power of the will is prostrate, and the victim can no longer resist the feeblest impulse of temptation. The grand faculty of self-control is lost; and as a result, the baser instincts of our lower nature are now uppermost; greed and appetite rule unrestrained.

But the moral power is also dragged down to the lowest depths. All the finer sensibilities of character are deadened; all pride of personal appearance, all nice self-respect and proper regard for the good opinion of others, every sense of decorum, and at last every pretence of decency. Dignity of behavior yields to clownish silliness, and the person lately respected is now an object of pity and loathing. The great central convictions of right and wrong now find no place in his nature; conscience is quenched, dishonesty prevails. This is true both as to the solemn promises, which prove mere idle tales, and also as to property, for he resorts to any form of fraud or theft to feed the consuming craving for more drink.

298. Evil Results of Alcoholism Inherited. But the calamity does not end with the offender. It may follow down the family line, and fasten itself upon the unoffending children. These often inherit the craving for drink, with the enfeebled nature that cannot resist the craving, and so are almost inevitably doomed to follow the appalling career of their parents before them.

Nor does this cruel taint stop with the children. Even their descendants are often prone to become perverse. As one example, careful statistics of a large number of families, more than two hundred descended from drunkards, show that a very large portion of them gave undoubted proof of well-marked degeneration. This was plain in the unusual prevalence of infant mortality, convulsions, epilepsy, hysteria, fatal brain diseases, and actual imbecility.[42]

It is found that the long-continued habitual user of alcoholic drinks, the man who is never intoxicated, but who will tell you that he has drunk whiskey all his life without being harmed by it, is more likely to transmit the evil effects to his children than the man who has occasional drunken outbreaks with intervals of perfect sobriety between. By his frequently repeated small drams he keeps his tissues constantly "alcoholized" to such an extent that they are seldom free from some of the more or less serious consequences. His children are born with organisms which have received a certain bias from which they cannot escape; they are freighted with some heredity, or predisposition to particular forms of degeneration, to some morbid tendency, to an enfeebled constitution, to various defective conditions of mind and body. Let the children of such a man attempt to imitate the drinking habits of the father and they quickly show the effects. Moderate drinking brings them down.

Among other consequences of an alcoholic inheritance which have been traced by careful observers are: Morbid changes in the nerve centers, consisting of inflammatory lesions, which vary according to the age in which they occur; alcoholic insanity; congenital malformations; and a much higher infant death rate, owing to lack of vitality, than among the children of normal parents.

Where the alcoholic inheritance does not manifest itself in some definite disease or disorder, it can still be traced in the limitations to be found in the drinking man's descendants. They seem to reach a level from which they cannot ascend, and where from slight causes they deteriorate. The parents, by alcoholic poisoning, have lowered the race stock of vitality beyond the power of ascent or possibility to rise above or overcome the downward tendency.

Of course these effects of alcoholics differ widely according to the degree of intoxication. Yet, we must not forget that the real nature of inebriety is always the same. The end differs from the beginning only in degree. He who would avoid a life of sorrow, disgrace, and shame must carefully shun the very first glass of intoxicants.

299. Opium. Opium is a gum-like substance, the dried juice of the unripe capsule of the poppy. The head of the plant is slit with fine incisions, and the exuding white juice is collected. When it thickens and is moulded in mass, it becomes dark with exposure. Morphine, a white powder, is a very condensed form of opiate; laudanum, an alcoholic solution of marked strength; and paregoric, a diluted and flavored form of alcoholic tincture.

300. Poisonous Effects of Opium. Some persons are drawn into the use of opium, solely for its narcotic and intoxicating influence. Every early consent to its use involves a lurking pledge to repeat the poison, till soon strong cords of the intoxicant appetite bind the now yielding victim.

Opium thus used lays its benumbing hand upon the brain, the mind is befogged, thought and reasoning are impossible. The secretions of the stomach are suspended, digestion is notably impaired, and the gastric nerves are so deadened that the body is rendered unconscious of its needs.

The moral sense is extinguished, persons once honest resort to fraud and theft, if need be, to obtain the drug, till at last health, character, and life itself all become a pitiful wreck.

301. The Use of Opium in Patent Medicines. Some forms of this drug are found in nearly all the various patent medicines so freely sold as a cure-all for every mortal disease. Opiates are an ingredient in different forms and proportions in almost all the soothing-syrups, cough medicines, cholera mixtures, pain cures, and consumption remedies, so widely and unwisely used. Many deaths occur from the use of these opiates, which at first seem indeed to bring relief, but really only smother the prominent symptoms, while the disease goes on unchecked, and at last proves fatal.

These patent medicines may appear to help one person and be fraught with danger to the next, so widely different are the effects of opiates upon different ages and temperaments. But it is upon children that these fatal results oftenest fall. Beyond doubt, thousands of children have been soothed and soothed out of existence.[43]

302. The Victim of the Opium Habit. Occasionally persons convalescing from serious sickness where anodynes were taken, unwisely cling to them long after recovery. Other persons, jaded with business or with worry, and unable to sleep, unwisely resort to some narcotic mixture to procure rest. In these and other similar cases, the use of opiates is always most pernicious. The amount must be steadily increased to obtain the elusive repose, and at best the phantom too often escapes.

Even if the desired sleep is procured, it is hardly the coveted rest, but a troubled and dreamy slumber, leaving in the morning the body quite unrefreshed, the head aching, the mouth dry, and the stomach utterly devoid of appetite. But far worse than even this condition is the slavish yielding to the habit, which soon becomes a bondage in which life is shorn of its wholesome pleasures, and existence becomes a burden.

303. Chloral. There are other preparations which have become instruments of direful and often fatal injury. Chloral is a powerful drug that has been much resorted to by unthinking persons to produce sleep. Others, yielding to a morbid reluctance to face the problems of life, have timidly sought shelter in artificial forgetfulness. To all such it is a false friend. Its promises are treason. It degrades the mind, tramples upon the morals, overpowers the will, and destroys life itself.

304. Cocaine, Ether, Chloroform, and Other Powerful Drugs. Another dangerous drug is Cocaine. Ether and chloroform, those priceless blessings to the human race if properly controlled, become instruments of death when carelessly trifled with. Persons who have been accustomed to inhale the vapor in slight whiffs for neuralgia or similar troubles do so at imminent hazard, especially if lying down. They are liable to become slowly unconscious, and so to continue the inhalation till life is ended.

There is still another class of drugs often carelessly used, whose effect, while less directly serious than those mentioned, is yet far from harmless. These drugs, which have sprung into popular use since the disease la grippe began its dreaded career, include phenacetine, antipyrine, antifebrine, and other similar preparations. These drugs have been seized by the public and taken freely and carelessly for all sorts and conditions of trouble. The random arrow may yet do serious harm. These drugs, products of coal-oil distillation, are powerful depressants. They lower the action of the heart and the tone of the nervous centers. Thus the effect of their continued use is to so diminish the vigor of the system as to aggravate the very disorder they are taken to relieve.

305. Effect of Tobacco on the Nervous System. That the use of tobacco produces a pernicious effect upon the nervous system is obvious from the indignant protest of the entire body against it when it is first used. Its poisonous character is amply shown by the distressing prostration and pallor, the dizziness and faintness, with extreme nausea and vomiting, which follow its employment by a novice.

The morbid effects of tobacco upon the nervous system of those who habitually use it are shown in the irregular and enfeebled action of the heart, with dizziness and muscular tremor. The character of the pulse shows plainly the unsteady heart action, caused by partial paralysis of the nerves controlling this organ. Old, habitual smokers often show an irritable and nervous condition, with sleeplessness, due doubtless to lack of proper brain nutrition.

All these results tend to prove that tobacco is really a nerve poison, and there is reason to suspect that the nervous breakdown of many men in mature life is often due to the continued use of this depressing agent. This is shown more especially in men of sedentary life and habits, as men of active habits and out-door life, experience less of the ill effects of tobacco.

Few, if any, habitual users of tobacco ever themselves approve of it. They all regret the habit, and many lament they are so enslaved to it that they cannot throw it off. They very rarely advise any one to follow their example.

306. Effects of Tobacco on the Mind. With this continuously depressing effect of tobacco upon the brain, it is little wonder that the mind may become enfeebled and lose its capacity for study or successful effort. This is especially true of the young. The growth and development of the brain having been once retarded, the youthful user of tobacco (especially the foolish cigarette-smoker) has established a permanent drawback which may hamper him all his life.

The young man addicted to the use of tobacco is often through its use retarded in his career by mental languor or weakening will power, and by mental incapacity. The keenness of mental perception is dulled, and the ability to seize and hold an abstract thought is impaired. True, these effects are not sharply obvious, as it would be impossible to contrast the present condition of any one person with what it might have been. But the comparison of large numbers conveys an instructive lesson. Scholars who start well and give promise of a good future fail by the way. The honors of the great schools, academies, and colleges are very largely taken by the tobacco abstainers. This is proved by the result of repeated and extensive comparisons of the advanced classes in a great number of institutions in this country and in Europe. So true is this that any young man who aspires to a noble career should bid farewell either to his honorable ambition or to his tobacco, for the two very rarely travel together. Consequently our military and naval academies and very many seminaries and colleges prohibit the use of tobacco by their students. For the same reasons the laws of many states very properly forbid the sale to boys of tobacco, and especially of cigarettes.

307. Effect of Tobacco upon Character. Nor does tobacco spare the morals. The tobacco-user is apt to manifest a selfish disregard of the courtesies due to others. He brings to the presence of others a repulsive breath, and clothing tainted with offensive odors. He poisons the atmosphere that others must inhale, and disputes their rights to breathe a pure, untainted air. The free use of tobacco by young people dulls the acuteness of the moral senses, often leads to prevarication and deceit in the indulgence, and is apt to draw one downward to bad associates. It is not the speed but the direction that tells on the future character and destiny of young men.



Additional Experiments.

Experiment 132. To illustrate the cooperation of certain parts of the body. Tickle the inside of the nose with a feather. This does not interfere with the muscles of breathing, but they come to the help of the irritated part, and provoke sneezing to clear and protect the nose.

Experiment 133. Pretend to aim a blow at a person's eye. Even if he is warned beforehand, the lids will close in spite of his effort to prevent them.

Experiment 134. To illustrate how sensations are referred to the ends of the nerves. Strike the elbow end of the ulna against anything hard (commonly called "hitting the crazy bone") where the ulna nerve is exposed, and the little finger and the ring finger will tingle and become numb.

Experiment 135. To show that every nerve is independent of any other. Press two fingers closely together. Let the point of the finest needle be carried ever so lightly across from one finger to another, and we can easily tell just when the needle leaves one finger and touches the other.

Experiment 136. To paralyze a nerve temporarily. Throw one arm over the sharp edge of a chair-back, bringing the inner edge of the biceps directly over the edge of the chair. Press deep and hard for a few minutes. The deep pressure on the nerve of the arm will put the arm "asleep," causing numbness and tingling. The leg and foot often "get asleep" by deep pressure on the nerves of the thigh.

Experiment 137. Press the ulnar nerve at the elbow, the prickling sensation is referred to the skin on the ulnar side of the hand.

Experiment 138. Dip the elbow in ice-cold water; at first one feels the sensation of cold, owing to the effect on the cutaneous nerve-endings. Afterwards, when the trunk of the ulnar nerve is affected, pain is felt in the skin of the ulnar side of the hand, where the nerve terminates.



Chapter XI.

The Special Senses.



308. The Special Senses. In man certain special organs are set apart the particular duty of which is to give information of the nature of the relations which he sustains to the great world of things, and of which he is but a mere speck. The special senses are the avenues by which we obtain this information as to our bodily condition, the world around us, and the manner in which it affects us.

Animals high in the scale are affected in so many different ways, and by so many agencies, that a subdivision of labor becomes necessary that the sense avenues may be rigidly guarded. One person alone may be a sufficient watch on the deck of a sloop, but an ocean steamer needs a score or more on guard, each with his special duty and at his own post. Or the senses are like a series of disciplined picket-guards, along the outposts of the mind, to take note of events, and to report to headquarters any information which may be within the range of their duty.

Thus it is that we are provided with a number of special senses, by means of which information is supplied regarding outward forces and objects. These are touch, taste, smell, seeing, and hearing, to which may be added the muscular sense and a sense of temperature.

309. General Sensations. The body, as we have learned, is made up of a great number of complicated organs, each doing its own part of the general work required for the life and vigor of the human organism. These organs should all work in harmony for the good of the whole. We must have some means of knowing whether this harmony is maintained, and of receiving timely warning if any organ fails to do its particular duty.

Such information is supplied by the common or general sensations. Thus we have a feeling of hunger or thirst indicating the need of food, and a feeling of discomfort when imperfectly clad, informing us of the need of more clothing.

To these may be added the sensation of pain, tickling, itching, and so on, the needs of which arise from the complicated structure of the human body. The great majority of sensations result from some stimulus or outward agency; and yet some sensations, such as those of faintness, restlessness, and fatigue seem to spring up within us in some mysterious way, without any obvious cause.

310. Essentials of a Sense Organ. Certain essentials are necessary for a sensation. First, there is a special structure adapted to a particular kind of influence. Thus the ear is formed specially for being stimulated by the waves of sound, while the eye is not influenced by sound, but responds to the action of light. These special structures are called terminal organs.

Again, a nerve proceeds from the special structure, which is in direct communication with nerve cells in the brain at the region of consciousness. This last point is important to remember, for if on some account the impression is arrested in the connecting nerve, no sensation will result. Thus a man whose spine has been injured may not feel a severe pinch on either leg. The impression may be quite sufficient to stimulate a nerve center in a healthy cord, so as to produce a marked reflex act, but he has no sensation, because the injury has prevented the impression from being carried up the cord to the higher centers in the brain.

311. The Condition of Sensation. It is thus evident that while an impression may be made upon a terminal organ, it cannot strictly be called a sensation until the person becomes conscious of it. The consciousness of an impression is, therefore, the essential element of a sensation.

It follows that sensation may be prevented in various ways. In the sense of sight, for example, one person may be blind because the terminal organ, or eye, is defective or diseased. Another may have perfect eyes and yet have no sight, because a tumor presses on the nerve between the eye and the brain. In this case, the impression fails because of the break in the communication. Once more, the eye may be perfect and the nerve connection unbroken, and yet the person cannot see, because the center in the brain itself is injured from disease or accident, and cannot receive the impression.

312. The Functions of the Brain Center in the Perception of an Impression. Sensation is really the result of a change which occurs in a nerve center in the brain, and yet we refer impressions to the various terminal organs. Thus, when the skin is pinched, the sensation is referred to the skin, although the perception is in the brain. We may think it is the eyes that see objects; in reality, it is only the brain that takes note of them.

This is largely the result of education and habit. From a blow on the head one sees flashes of light as vividly as if torches actually dance before the eyes. Impressions have reached the seeing-center in the brain from irritation of the optic nerve, producing the same effect as real lights would cause. In this case, however, knowing the cause of the colors, the person is able to correct the erroneous conclusion.

As a result of a depraved condition of blood, the seeing-center itself may be unduly stimulated, and a person may see objects which appear real. Thus in an attack of delirium tremens, the victim of alcoholic poisoning sees horrible and fantastic creatures. The diseased brain refers them as usual to the external world; hence they appear real. As the sufferer's judgment is warped by the alcoholic liquor, he cannot correct the impressions, and is therefore deceived by them.

313. Organs of Special Sense. The organs of special sense, the means by which we are brought into relation with surrounding objects, are usually classed as five in number. They are sometimes fancifully called "the five gateways of knowledge"—the skin, the organ of touch; the tongue, of taste; the nose, of smell; the eye, of sight; and the ear, of hearing.



314. The Organ of Touch. The organ of touch, or tactile sensibility, is the most widely extended of all the special senses, and perhaps the simplest. It is certainly the most precise and certain in its results. It is this sense to which we instinctively appeal to escape from the illusions into which the other senses may mislead us. It has its seat in the skin all over the body, and in the mucous membrane of the nostrils. All parts of the body, however, do not have this sense in an equal degree.

In Chapter IX. we learned that the superficial layers of the skin covers and dips in between the papillae. We also learned that these papillae are richly provided with blood-vessels and sensory nerve fibers (sec. 234). Now these nerve fibers terminate in a peculiar way in those parts of the body which are endowed with a very delicate sense of touch. In every papilla are oval-shaped bodies about 1/300 of an inch long, around which the nerve fibers wind, and which they finally enter. These are called touch-bodies, or tactile corpuscles, and are found in great numbers on the feet and toes, and more scantily in other places, as on the edges of the eyelids.

Again, many of the nerve fibers terminate in corpuscles, the largest about 1/20 of an inch long, called Pacinian corpuscles. These are most numerous in the palm of the hand and the sole of the foot. In the papillae of the red border of the lips the nerves end in capsules which enclose one or more fibers, and are called end-bulbs.

The great majority of the nerve fibers which supply the skin do not end in such well-defined organs. They oftener divide into exceedingly delicate filaments, the terminations of which are traced with the greatest difficulty.

315. The Sense of Touch. Touch is a sensation of contact referred to the surface of the body. It includes three things,—the sense of contact, the sense of pressure, and the sense of heat and cold.

The sense of contact is the most important element in touch. By it we learn of the form, size, and other properties of objects, as their smoothness and hardness. As we all know, the sense of touch varies in different parts of the skin. It is most acute where the outer skin is thinnest. The tips of the fingers, the edges of the lips, and the tip of the tongue are the most sensitive parts.

Even the nails, the teeth, and the hair have the sense of touch in a slight degree. When the scarf skin is removed, the part is not more sensitive to sense of contact. In fact, direct contact with the unprotected true skin occasions pain, which effectually masks the feeling of touch. The sense of touch is capable of education, and is generally developed to an extraordinary degree in persons who are deprived of some other special sense, as sight or hearing. We read of the famous blind sculptor who was said to model excellent likenesses, guided entirely by the sense of touch. An eminent authority on botany was a blind man, able to distinguish rare plants by the fingers, and by the tip of the tongue. The blind learn to read with facility by passing their fingers over raised letters of a coarse type. It is impossible to contemplate, even for a moment, the prominence assigned to the sense of touch in the physical organism, without being impressed with the manifestations of design—the work of an all-wise Creator.

316. Muscular Sense; Sense of Temperature; Pain. When a heavy object is laid upon certain parts of the body, it produces a sensation of pressure. By it we are enabled to estimate differences of weight. If an attempt be made to raise this object, it offers resistance which the muscles must overcome. This is known as the muscular sense. It depends on sensory nerves originating in the muscles and carrying impressions from them to the nerve centers.

The skin also judges, to a certain extent, of heat and cold. These sensations can be felt only by the skin. Direct irritation of a nerve does not give rise to them. Thus, the exposed pulp of a diseased tooth, when irritated by cold fluids, gives rise to pain, and not to a sensation of temperature. Various portions of the body have different degrees of sensibility in this respect. The hand will bear a degree of heat which would cause pain to some other parts of the body. Then, again, the sensibility of the outer skin seems to affect the sensibility to heat, for parts with a thin skin can bear less heat than portions with a thick cuticle.

Experiment 139. To illustrate how the sense of touch is a matter of habit or education. Shut both eyes, and let a friend run the tips of your fingers first lightly over a hard plane surface; then press hard, then lightly again, and the surface will seem to be concave.

Experiment 140. Cross the middle over the index finger, roll a small marble between the fingers; one has a distinct impression of two marbles. Cross the fingers in the same way, and rub them against the point of the nose. A similar illusion is experienced.

Experiment 141. To test the sense of locality. Ask a person to shut his eyes, touch some part of his body lightly with the point of a pin, and ask him to indicate the part touched.

As to the general temperature, this sense is relative and is much modified by habit, for what is cold to an inhabitant of the torrid zone would be warm to one accustomed to a very cold climate.

Pain is an excessive stimulation of the sensory nerves, and in it all finer sensations are lost. Thus, when a piece of hot iron burns the hand, the sensation is the same as when the iron is very cold, and extreme cold feels like intense heat.

317. The Organ of Taste. The sense of taste is located chiefly in the tongue, but may also be referred even to the regions of the fauces. Taste, like touch, consists in a particular mode of nerve termination.

The tongue is a muscular organ covered with mucous membrane, and is richly supplied with blood-vessels and nerves. By its complicated movements it is an important factor in chewing, in swallowing, and in articulate speech. The surface of the tongue is covered with irregular projections, called papillae,—fine hair-like processes, about 1/12 of an inch high. Interspersed with these are the fungiform papillae. These are shaped something like a mushroom, and may often be detected by their bright red points when the rest of the tongue is coated.

Towards the root of the tongue is another kind of papillae, the circumvallate, eight to fifteen in number, arranged in the form of the letter V, with the apex directed backwards. These are so called because they consist of a fungiform papilla surrounded by a fold of mucous membrane, presenting the appearance of being walled around.

In many of the fungiform and most of the circumvallate papillae are peculiar structures called taste buds or taste goblets. These exist in great numbers, and are believed to be connected with nerve fibers. These taste buds are readily excited by savory substances, and transmit the impression along the connected nerve.

The tongue is supplied with sensory fibers by branches from the fifth and eighth pairs of cranial nerves. The former confers taste on the front part of the tongue, and the latter on the back part. Branches of the latter also pass to the soft palate and neighboring parts and confer taste on them. The motor nerve of the tongue is the ninth pair, the hypoglossal.



318. The Sense of Taste. The sense of taste is excited by stimulation of the mucous membrane of the tongue and of the palate, affecting the ends of the nerve fibers. Taste is most acute in or near the circumvallate papillae. The middle of the tongue is scarcely sensitive to taste, while the edges and the tip are, as a rule, highly sensitive.

Certain conditions are necessary that the sense of taste may be exercised. First, the substance to be tasted must be in solution, or be soluble in the fluids of the mouth. Insoluble substances are tasteless. If we touch our tongue to a piece of rock crystal, there is a sensation of contact or cold, but no sense of taste. On the other hand, when we bring the tongue in contact with a piece of rock salt, we experience the sensations of contact, coolness, and saline taste.

Again, the mucous membrane of the mouth must be moist. When the mouth is dry, and receives substances not already in solution, there is no saliva ready to dissolve them; hence, they are tasteless. This absence of taste is common with the parched mouth during a fever.

The tongue assists in bringing the food in contact with the nerves, by pressing it against the roof of the mouth and the soft palate, and thus is produced the fullest sense of taste.

319. Physiological Conditions of Taste. The tongue is the seat of sensations which are quite unlike each other. Thus, besides the sense of taste, there is the sensation of touch, pressure, heat and cold, burning or acrid feelings, and those produced by the application of the tongue to an interrupted electric current. These are distinct sensations, due to some chemical action excited probably in the touch cells, although the true tastes may be excited by causes not strictly chemical. Thus a smart tap on the tongue may excite the sensation of taste.

In the majority of persons the back of the tongue is most sensitive to bitters, and the tip to sweets. Saline matters are perceived most distinctly at the tip, and acid substances at the sides. The nerves of taste are sensitive in an extraordinary degree to some articles of food and certain drugs. For example, the taste of the various preparations of quinine, peppermint, and wild cherry is got rid of with difficulty.

Like the other special senses, that of taste may become fatigued. The repeated tasting of one substance rapidly deadens the sensibility, probably by over-stimulation. Some savors so impress the nerves of taste that others fail to make any impression. This principle is used to make disagreeable medicine somewhat tasteless. Thus a few cloves, or grains of coffee, or a bit of pepper, eaten before a dose of castor oil, renders it less nauseous.

Flavor is something more than taste. It is in reality a mixed sensation, in which smell and taste are both concerned, as is shown by the common observation that one suffering from a cold in the head, which blunts his sense of smell, loses the proper flavor of his food. So if a person be blindfolded, and the nose pinched, he will be unable to distinguish between an apple and an onion, if one be rubbed on the tongue after the other. As soon as the nostrils are opened the difference is at once perceived.

Experiment 142. Put a drop of vinegar on a friend's tongue, or on your own. Notice how the papillae of the tongue start up.

Experiment 143. Rub different parts of the tongue with the pointed end of a piece of salt or gum-aloes, to show that the back of the tongue is most sensitive to salt and bitter substances.

Experiment 144. Repeat the same with some sweet or sour substances, to show that the edges of the tongue are the most sensitive to these substances.

Experiment 145. We often fail to distinguish between the sense of taste and that of smell. Chew some pure, roasted coffee, and it seems to have a distinct taste. Pinch the nose hard, and there is little taste. Coffee has a powerful odor, but only a feeble taste. The same is true of garlic, onions, and various spices.

Experiment 146. Light helps the sense of taste. Shut the eyes, and palatable foods taste insipid. Pinch the nose, close the eyes, and see how palatable one half of a teaspoonful of cod-liver oil becomes.

Experiment 147. Close the nostrils, shut the eyes, and attempt to distinguish by taste alone between a slice of an apple and one of a potato.

320. Modifications of the Sense of Taste. Taste is modified to a great extent by habit, education, and other circumstances. Articles of food that are unpleasant in early life often become agreeable in later years. There is occasionally a craving, especially with people of a peculiar nervous organization, for certain unnatural articles (as chalk and laundry starch) which are eaten without the least repugnance. Again, the most savory dishes may excite disgust, while the simplest articles may have a delicious flavor to one long deprived of them. The taste for certain articles is certainly acquired. This is often true of raw tomatoes, olives, and especially of tobacco.

The organs of taste and smell may be regarded as necessary accessories of the general apparatus of nutrition, and are, therefore, more or less essential to the maintenance of animal life. While taste and smell are generally maintained until the close of life, sight and hearing are often impaired by time, and may be altogether destroyed, the other vital functions remaining unimpaired.

321. Effect of Tobacco and Alcohol upon Taste. It would be remarkable if tobacco should fail to injure the sense of taste. The effect produced upon the tender papillae of the tongue by the nicotine-loaded juices and the acrid smoke tends to impair the delicate sensibility of the entire surface. The keen appreciation of fine flavors is destroyed. The once clear and enjoyable tastes of simple objects become dull and vapid; thus highly spiced and seasoned articles of food are in demand, and then follows continued indigestion, with all its suffering.

Again, the burning, almost caustic effect of the stronger alcoholic drinks, and the acrid pungency of tobacco smoke, are disastrous to the finer perceptions of both taste and odors.

322. Smell. The sense of smell is lodged in the delicate membrane which lines the nasal cavities. The floor, sides, and roof of these cavities are formed by certain bones of the cranium and the face. Man, in common with all air-breathing animals, has two nasal cavities. They communicate with the outer air by two nostrils opening in front, while two other passages open into the pharynx behind.

To increase the area of the air passages, the two light, spongy turbinated bones, one on each side, form narrow, winding channels. The mucous membrane, with the branches of the olfactory nerve, lines the dividing wall and the inner surfaces of these winding passages. Below all these bones the lower turbinated bones may be said to divide the olfactory chamber above from the ordinary air passages.



The nerves which supply the nasal mucous membrane are derived from the branches of the fifth and the first pair of cranial nerves,—the olfactory. The latter, however, are the nerves of smell proper, and are spread out in a kind of thick brush of minute nerve filaments. It is in the mucous membrane of the uppermost part of the cavity of the nostril that the nerve endings of smell proper reside. The other nerves which supply the nostrils are those of common sensation (sec. 271).