In this case the action of the brain was clearly automatic, i. e., reflex. The lawyer had worried his brain by his anxiety, and thus prevented his mind from doing its best. But it had received an impulse in a certain direction, and when left to itself, worked out the result. (See Appendix for other illustrations.)] Thus we wink involuntarily at a flash of light or a threatened blow. [Footnote: A very eminent chemist a few years ago was making an experiment upon some extremely explosive compound which he had discovered. He had a small quantity of this compound in a bottle, and was holding it up to the light, looking at it intently; and whether it was a shake of the bottle or the warmth of his hand, I do not know, but it exploded in his hand, and the bottle was shivered into a million of minute fragments, which were driven in every direction. His first impression was that they had penetrated his eyes, but to his intense relief he found presently that they had only struck the outside of his eyelids. You may conceive how infinitesimally short the interval was between the explosion of the bottle and the particles reaching his eyes; and yet in that interval the impression had been made upon his sight, the mandate of the reflex action, so to speak, had gone forth, the muscles of his eyelids had been called into action, and he had closed his eyelids before the particles had reached them, and in this manner his eyes were saved. You see what a wonderful proof this is of the way in which the automatic action of our nervous apparatus enters into the sustenance of our lives, and the protection of our most important organs from injury.— DR. CARPENTER.] We start at a sudden sound. We jump back from a precipice before the mind has time to reason upon the danger. The spinal cord conducts certain impressions to the brain, but responds to others without troubling that organ. [Footnote: There is a story told of a man, who, having injured his spinal cord, had lost feeling and motion in his lower extremities. Dr. John Hunter experimented upon him. Tickling his feet, he asked him if he felt it; the man, pointing to his limbs, which were kicking vigorously about, answered, "No, but you see my legs do." Illustrations of this independent action of the spinal cord are common in animals. A headless wasp will ply its sting energetically. A fowl, after its head is cut off, will flap its wings and jump about as if in pain, although, of course, all sensation has ceased. "A water beetle, having had its head removed, remained motionless as long as it rested on a dry surface, but when cast into water, it executed the usual swimming motions with great energy and rapidity, striking all its comrades to one side by its violence, and persisting in these for more than half an hour."] The medulla oblongata carries on the process of respiration. The great sympathetic system binds together all the organs of the body.
USES OF REFLEX ACTION.—We breathe eighteen times every minute; we stand erect without a consciousness of effort; [Footnote: In this way we account for the perilous feats performed by the somnambulist. He is not conscious, as his operations are not directed by the cerebrum, but by the other nervous centers. Were he to attempt their repetition when awake, the emotion of fear might render it impossible.] we walk, eat, digest, and at the same time carry on a train of thought. Our brain is thus emancipated from the petty detail of life. If we were obliged to attend to every breath, every pulsation of the heart, every wink of the eye, our time would be wasted in keeping alive. Mere standing would require our entire attention. Besides, an act which at first demands all our thought soon requires less, and at last becomes mechanical, [Footnote: "As every one knows," says Huxley, "it takes a soldier a long time to learn his drill— for instance, to put himself into the attitude of 'attention' at the instant the word of command is heard. But, after a time, the sound of the word gives rise to the act, whether the soldier be thinking of it or not. There is a story, which is credible enough, though it may not be true, of a practical joker, who, seeing a discharged veteran carrying home his dinner, suddenly called out 'Attention!' whereupon the man instantly brought his hands down and lost his mutton and potatoes in the gutter. The drill had been thorough, and its effects had become embodied in the man's nervous structure."] as we say, i. e., reflex. Thus we play a familiar tune upon an instrument and carry on a conversation at the same time. All the possibilities of an education and the power of forming habits are based upon this principle. No act we perform ends with itself. It leaves behind it in the nervous centers a tendency to do the same thing again. Our physical being thus conspires to fix upon us the habits of a good or an evil life. Our very thoughts are written in our muscles, so that the expression of our face and even our features grow into harmony with the life we live.
BRAIN EXERCISE.—The nervous system demands its life and activity. The mind grows by what it feeds on. One who reads mainly light literature, who lolls on the sofa or worries through the platitudes of an idle or fashionable life, decays mentally; his system loses tone, and physical weakness follows mental poverty. On the other hand, an excessive use of the mind withdraws force from the body, whose weakness, reacting on the brain, produces gradual decay and serious diseases. (See p. 331.)
The brain grows by the growth of the body. The body grows through good food, fresh air, and work and rest in suitable proportion. For the full development and perfect use of a strong mind, a strong body is essential. Hence, in seeking to expand and store the intellect, we should be equally thoughtful of the growth and health of the body.
SLEEP [Footnote: Sleep procured by medicine is rarely as beneficial as that secured naturally. The disturbance to the nervous system is often sufficient to counterbalance all the good results. The habit of seeking sleep in this way, without the advice of a physician, is to be most earnestly deprecated. The dose must be constantly increased to produce the effect, and thus great injury may be caused. Often, too, where laudanum or morphine is used, the person unconsciously comes into a terrible and fatal bondage. (See p. 342.) Especially should infants never be dosed with cordials, as is a common family practice. The damage done to helpless childhood by the ignorant and reckless use of soothing syrups is frightful to contemplate. All the ordinary sleeping draughts have life-destroying properties, as is proved by the fatal effects of an overdose. At the best, they paralyze the nerve centers, disorder the digestion, and poison the blood. Their promiscuous use is therefore full of danger.] is as essential as food. During the day, the process of tearing down goes on; during the night, the work of building up should make good the loss. In youth more sleep is needed than in old age, when nature makes few permanent repairs, and is content with temporary expedients. The number of hours required for sleep must be decided by each person. Napoleon took only five hours, but most people need from six to eight hours,—brain workers even more. In general, one should sleep until he naturally wakes. If one's rest be broken, it should be made up as soon as possible. (See p. 334.)
SUNLIGHT.—The influence of the sun's rays upon the nervous system is very marked. [Footnote: The necessity of light for young children is not half appreciated. Many of their diseases, and nearly all the cadaverous looks of those brought up in great cities, are ascribable to the deficiency of light and air. When we see the glass room of the photographers in every street, in the topmost story, we grudge them their application to what is often a mere personal vanity. Why should not a nursery be constructed in the same manner? If parents knew the value of light to the skin, especially to children of a scrofulous tendency, we should have plenty of these glass house nurseries, where children might run about in a proper temperature, free from much of that clothing which at present seals up the skin—that great supplementary lung—against sunlight and oxygen. They would save many a weakly child who now perishes from lack of these necessaries of infant life.—DR. WINTER.] It is said also to have the effect of developing red disks in the blood. All vigor and activity come from the sun. Vegetables grown in subdued light have a bleached and faded look. An infant kept in absolute darkness would grow into a shapeless idiot. That room is the healthiest to which the sun has the freest access. Epidemics frequently attack the inhabitants of the shady side of a street, and exempt those on the sunny side. If, on a slight indisposition, we should go out into the open air and bright sunlight, instead of shutting ourselves up in a close, dark chamber, we might often avoid a serious illness. The sun bath is doubtless a most efficient remedy for many diseases. Our window blinds and curtains should be thrown back and open, and we should let the blessed air and sun stream in to invigorate and cheer. No house buried in shade, and no room with darkened windows, is fit for human habitation. In damp and darkness, lies in wait almost every disease to which flesh is heir. The sun is their only successful foe. (See p. 336.)
WONDERS OF THE BRAIN.—After having seen the beautiful contrivances and the exquisite delicacy of the lower organs, it is natural to suppose that when we come to the brain we should find the most elaborate machinery. How surprising, then, it is to have revealed to us only cells and fibers! The brain is the least solid and most unsubstantial looking organ in the body. Eighty per cent of water, seven of albumen, some fat, and a few minor substances constitute the instrument which rules the world. Strangest of all, the brain, which is the seat of sensation, is itself without sensation. Every nerve, every part of the spinal cord, is keenly alive to the slightest touch, yet "the brain may be cut, burned, or electrified without producing pain."
ALCOHOLIC DRINKS AND NARCOTICS.
ALCOHOL (Continued from p. 187).
EFFECT UPON THE NERVOUS SYSTEM.—In the progressive influence of alcohol upon the nervous system, there are, according to the researches of Dr. Richardson, four successive stages.
1. THE STAGE OF EXCITEMENT. [Footnote: The pupil should be careful to note here that alcohol does not act upon the heart directly, and cause it to contract with more force. The idea that alcohol gives energy and activity to the muscles is entirely false. It really, as we have seen (p. 183), weakens muscular contraction. The enfeeblement begins in the first stage, and continues in the other stages with increased effect. The heart beats quickly merely because the resistance of the minute controlling vessels is taken off, and it works without being under proper regulation. What is called a stimulation or excitement is, in absolute fact, a relaxation, a partial paralysis of one of the most important mechanisms in the animal body. Alcohol should be ranked among the narcotics.—RICHARDSON.]— The first effect of alcohol, as we have already described on page 144, is to paralyze the nerves that lead to the extreme and minute blood vessels, and so regulate the passage of the blood through the capillary system. The vital force, thus drawn into the nervous centers, drives the machinery of life with tremendous energy. The heart jumps like the mainspring of a watch when the resistance of the wheels is removed. The blood surges through the body with increased force. Every capillary tube in the system is swollen and flushed, like the reddened nose and cheek.
In all this there is exhilaration, but no nourishment; there is animation, but no permanent power conferred on brain or muscle. Alcohol may cheer for the moment. It may set the sluggish blood in motion, start the flow of thought, and excite a temporary gayety. "It may enable a wearied or feeble organism to do brisk work for a short time. It may make the brain briefly brilliant. It may excite muscle to quick action, but it does nothing at its own cost, fills up nothing it has destroyed, and itself leads to destruction." Even the mental activity it has excited is an unsafe state of mind, for that just poise of the faculties so essential to good judgment is disturbed by the presence of the intruder. Johnson well remarked, "Wine improves conversation by taking the edge off the understanding."
2. THE STAGE OF MUSCULAR WEAKNESS.—If the action of the alcohol be still continued, the spinal cord is next affected by this powerful narcotic. The control of some of the muscles is lost. Those of the lower lip usually fail first, then those of the lower limbs, and the staggering, uncertain steps betray the result. The muscles themselves, also, become feebler as the power of contraction diminishes. The temperature, which, for a time, was slightly increased, soon begins to fall as the heat is radiated; the body is cooled, and the well-known "alcoholic chill" is felt.
3. THE STAGE OF MENTAL WEAKNESS.—The cerebrum is now implicated. The ideal and emotional faculties are quickened, while the will is weakened. The center of thought being overpowered, the mind is a chaos. Ideas flock in thick and fast. The tongue is loosened. The judgment loses its hold on the acts. The reason giving way, the animal instincts generally assume the mastery of the man. The hidden nature comes to the surface. All the gloss of education and social restraint falls off, and the lower nature stands revealed. The coward shows himself more craven, the braggart more boastful, the bold more daring, and the cruel more brutal. The inebriate is liable to become the perpetrator of any outrage that the slightest provocation may suggest.
4. THE STAGE OF UNCONSCIOUSNESS.—At last, prostration ensues, and the wild, mad revel of the drunkard ends with utter senselessness. In common speech, the man is "dead drunk." Brain and spinal cord are both benumbed. Fortunately, the two nervous centers which supply the heart and the diaphragm are the slowest to be influenced. So, even in this final stage, the breathing and the circulation still go on, though the other organs have stopped. Were it not for this, every person thoroughly intoxicated would die. [Footnote: Cold has a wonderful influence in hastening this stage, so that a person, previously only in the first stage of excitement, on going outdoors on a winter night, may rapidly sink into a lethargy (become comatose), fall, and die. He is then commonly said to have perished with cold. The signs of this coma are of great practical importance, since so many persons die in police stations and elsewhere who are really comatose, when they are supposed to be only sound asleep. The pulse is slow, and almost imperceptible. The face is pale, and the skin cold. "If the arm be pinched, it is not moved; if the eyeballs are touched, the lids will not sink." The respiration becomes slower and slower, and, if the person dies, it is because liquid collects in the bronchial tubes, and stops the passage of the air. The man then actually drowns in his own secretions.]
EFFECT UPON THE BRAIN.—Alcohol seems to have a special affinity for the brain. This organ absorbs more than any other, and its delicate structure is correspondingly affected. The "Vascular enlargement" here reaches its height. The tiny vessels become clogged with blood that is unfitted to nourish, because loaded with carbonic acid, and deprived of the usual quantity of the life-giving oxygen.—HINTON. The brain is, in the language of the physiologist, malfunctioned. The mind but slowly rallies from the stupor of the fourth stage, and a sense of dullness and depression remains to show with what difficulty the fatigued organ recovers its normal condition. So marked is the effect of the narcotic poison, that some authorities hold that "a once thoroughly intoxicated brain never fully becomes what it was before."
In time, the free use of liquor hardens and thickens the membrane enveloping the nervous matter; the nerve corpuscles undergo a "Fatty degeneration"; the blood vessels lose their elasticity; and the vital fluid, flowing less freely through the obstructed channels, fails to afford the old-time nourishment. The consequent deterioration of the nervous substance—the organ of thought—shows itself in the weakened mind [Footnote: The habitual use of fermented liquors, even to an extent far short of what is necessary to produce intoxication, injures the body, and diminishes the mental power.—Sir Henry Thompson.] that we so often notice in a person accustomed to drink, and at last lays the foundation of various nervous disorders—epilepsy, paralysis, and insanity. [Footnote: Casper, the great statistician of Berlin, says: "So far as that city is concerned, one third of the insane coming from the poorer classes, were made so by spirit drinking."] The law of heredity here again asserts itself, and the inebriate's children often inherit the disease which he has escaped.
Chief among the consequences of this perverted and imperfect nutrition of the brain is that intermediate state between intoxication and insanity, well known as Delirium Tremens. "It is characterized by a low, restless activity of the cerebrum, manifesting itself in muttering delirium, with occasional paroxysms of greater violence. The victim almost always apprehends some direful calamity; he imagines his bed to be covered with loathsome reptiles; he sees the walls of his apartment crowded with foul specters; and he imagines his friends and attendants to be fiends come to drag him down to a fiery abyss beneath."—CARPENTER. (See p. 287.)
INFLUENCE UPON THE MENTAL AND MORAL POWERS.—So intimate is the relation between the body and the mind, that an injury to one harms the other. The effect of alcoholized blood is to weaken the will. The one habitually under its influence often shocks us by his indecision and his readiness to break a promise to reform. The truth is, he has lost, in a measure, his power of self-control. At last, he becomes physically unable to resist the craving demand of his morbid appetite.
Other faculties share in this mental wreck. The intellectual vision becomes less penetrating, the decisions of the mind less reliable, and the grasp of thought less vigorous. The logic grows muddy. A thriftless, reckless feeling is developed. Ere long, self-respect is lost, and then ambition ceases to allure, and the high spirit sinks.
Along with this mental deterioration comes also a failure of the moral sense. The fine fiber of character undergoes a "degeneration" as certain as that of the muscles themselves. Broken promises tell of a lowered standard of veracity, and a dulled sense of honor, quite as much as of an impaired will. Under the subtle influence of the ever-present poison, signs of spiritual weakness multiply fast. Conscience is lulled to rest. Reason is enfeebled. Customary restraints are easily thrown off. The sensibilities are blunted. There is less ability to appreciate nice shades of right and wrong. Great moral principles and motives lose their power to influence. The judgment fools with duty. The future no longer reaches back its hand to guide the present. The better nature has lost its supremacy.
The wretched victim of appetite will now gratify his tyrannical passion for drink at any expense of deceit or crime. He becomes the blind instrument of his insane impulses, and commits acts from which he would once have shrunk with horror. [Footnote: Richardson sums up the various diseases caused by alcohol, as follows: "(a). Diseases of the brain and nervous system, indicated by such names as apoplexy, epilepsy, paralysis, vertigo, softening of the brain, delirium tremens, dipsomania or inordinate craving for drink, loss of memory, and that general failure of the mental power, called dementia. (b). Diseases of the lungs: one form of consumption, congestion, and subsequent bronchitis. (c). Diseases of the heart: irregular beat, feebleness of the muscular walls, dilatation, disease of the valves. (d). Diseases of the blood: scurvy, excess of water or dropsy, separation of fibrin. (e). Diseases of the stomach: feebleness of the stomach, indigestion, flatulency, irritation, and sometimes inflammation. (f). Diseases of the bowels: relaxation or purging, irritation. (g). Diseases of the liver: congestion, hardening and shrinking, cirrhosis. (h). Diseases of the kidneys: change of structure into fatty or waxy-like condition and other results leading to dropsy, or sometimes to fatal sleep. (i). Diseases of the muscles: fatty change in the muscles, by which they lose their power for proper active contraction. (j). Diseases of the membranes of the body: thickening and loss of elasticity, by which the parts wrapped up in the membrane are impaired for use, and premature decay is induced."] Sometimes he even takes a malignant pleasure in injuring those whom Nature has ordained he should protect. [Footnote: It has been argued that a man should not be punished for any crime he may commit during intoxication, but rather for knowingly giving up the reins of reason and conscience, and thus subjecting himself to the rule of his evil passions. Voluntarily to stimulate the mind and put it into a condition where it may drive one to ruin, is very like the act of an engineer who should get up steam in his engine, and then, having opened the valves, desert his post, and let the monster go thundering down the track to sure destruction. Certain persons are thrown into the stage of mental weakness by a single glass of liquor. How can they be excused when the fact of their peculiar liability lends additional force to the argument of abstemiousness, and they know that their only safety lies in total abstinence?—CARPENTER'S Physiology.]
2. TOBACCO.
The Constituents of Tobacco Smoke are numerous, but the prominent ones are carbonic-acid, carbonic-oxide, and ammonia gases; carbon, or soot; and nicotine. The proportion of these substances varies with different kinds of tobacco, the pipe used, and the rapidity of the combustion. Carbonic acid tends to produce sleepiness and headache. Carbonic oxide, in addition, causes a tremulous movement of the muscles, and so of the heart. Ammonia bites the tongue of the smoker, excites the salivary glands, and causes dryness of the mouth and throat. Nicotine is a powerful poison. The amount contained in one or two strong cigars, if thrown directly into the blood, would cause death. Nicotine itself is complex, yielding a volatile substance that gives the odor to the breath and clothing; and also a bitter extract which produces the sickening taste of an old pipe. In smoking, some of the nicotine is decomposed, forming pyridine, picoline, and other poisonous alkaloids. [Footnote: The analysis of tobacco as given by different authorities varies greatly. The one stated in the text suffices for the purposes of this chapter. Von Eulenberg names several other products of the combustion. One hundred pounds of the dry leaf may yield as high as seven pounds of nicotine. Havana tobacco contains about two per cent, and Virginia about six per cent.—See JOHNSTON & CHURCH'S Chemistry of Common Life, and MILLER'S Organic Chemistry.]
PHYSIOLOGICAL EFFECTS.—The poison of tobacco, set free by the process either of chewing or smoking, when for the first time it is swept through the system by the blood, powerfully affects the body. Nausea is felt, and the stomach seeks to throw off the offending substance. The brain is inflamed, and headache follows. The motor nerves becoming irritated, giddiness ensues. Thus Nature earnestly protests against the formation of this habit. But, after repeated trials, the system adjusts itself to the new conditions. A "tolerance" of the poison is finally established, and smoking causes none of the former symptoms. Such powerful substances can not, however, be constantly inhaled without producing marked changes. The three great eliminating organs—the lungs, the skin, and the kidneys— throw off a large part of the products, but much remains in the system. When the presence of the poison is constant, and especially when the smoking or chewing is excessive, the disturbance that at first is merely functional, must necessarily, in many cases at least, lead to a chronic derangement.
Probably in this, as in the case of other deleterious articles of diet, the strong and healthy will seem to escape entirely, while the weak and those predisposed to disease will be injured in direct proportion to the extent of the indulgence. Those whose employment leads to active, outdoor work, will show no sign of nicotine poisoning, while the man of sedentary habits will sooner or later be the victim of dyspepsia, sleeplessness, nervousness, paralysis, or other organic difficulties. Even where the user of tobacco himself escapes harm, the law of heredity asserts itself, and the innocent offspring only too often inherit an impaired constitution, and a tendency to nervous complaints.
THE VARIOUS DISTURBANCES produced in different individuals and constitutions by smoking have been summed up by Dr. Richardson as follows: "(a) In the blood, it causes undue fluidity, and change in the red corpuscles; (b) in the stomach, it gives rise to debility, nausea, and vomiting; (c) in the mucous membrane of the mouth, it produces enlargement and soreness of the tonsils—smoker's sore throat—redness, dryness, and occasional peeling of the membrane, and either unnatural firmness and contraction, or sponginess of the gums; and, where the pipe rests on the lips, oftentimes 'epithelial cancer'; (d) in the heart, it causes debility of the organ, and irregular action; (e) in the bronchial surface of the lungs, when that is already irritable, it sustains irritation, and increases the cough; (f) in the organs of sense, it produces dilation of the pupils of the eye, confusion of vision, bright lines, luminous or cobweb specks, and long retention of images on the retina, with analogous symptoms affecting the ear, viz., inability to define sounds clearly, and the occurrence of a sharp, ringing noise like a whistle; (g) in the brain, it impairs the activity of the organ, oppressing it if it be nourished, but soothing it if it be exhausted; (h) it leads to paralysis in the motor and sympathetic nerves, and to over-secretion from the glands which the sympathetic nerves control."
IS TOBACCO A FOOD?—Here, as in the case of alcohol, the reply is a negative one. Tobacco manifests no characteristic of a food. It can not impart to the blood an atom of nutritive matter for building up the body. It does not add to, but rather subtracts from, the total vital force. It confers no potential power upon muscle or brain. It stimulates by cutting off the nervous supply from the extremities and concentrating it upon the centers. But stimulation is not nourishment; it is only a rapid spending of the capital stock. There is no greater error than to mistake the exciting of an organ for its strengthening.
THE INFLUENCE UPON YOUTH.—Here, too, science utters no doubtful voice. Experience asserts only one conviction. Tobacco retards the development of mind and body. [Footnote: Cigarettes are especially injurious from the irritating smoke of the paper covering, taken into the lungs, and also because the poison fumes of the tobacco are more directly inhaled. In case of the cheap cigarettes often smoked by boys the ingredients used are harmful, while one revolts at the thought of the filthy materials, refuse cigar stumps, etc., employed in their manufacture.] The law of nature is that of steady growth. It can not admit of a daily, even though it be merely a functional, disturbance that weakens the digestion, that causes the heart to labor excessively, that prevents the perfect oxidation of the blood, that interferes with the assimilation, and that deranges the nervous system. [Footnote: There is one influence of tobacco that every young man should understand. In many cases, like alcohol, it seems to blunt the sensibilities, and to make its user careless of the rights and feelings of others. This is often noticed in common life. We meet everywhere "devotees of the weed," who, ignoring the fact that tobacco is disagreeable to many persons, think only of the gratification of their selfish appetite. They smoke or chew in any place or company. They permit the cigar fumes to blow into the faces of passers-by. They sit where the wind carries the smoke of their pipes so that others must inhale it. They expectorate upon the floor of cars, hotels, and even private homes. They take no pains to remove the odor that lingers about their person and clothing. They force all who happen to be near, their companions, their fellow-travelers, to inhale the nauseating odor of tobacco. Everything must be sacrificed to the one primal necessity of such persons—a smoke. Now, a young man just beginning life, with his fortune to make, and his success to achieve, can not afford to burden himself with a habit that is costly, that will make his presence offensive to many persons, and that may perhaps render him less sensitive to the best influences and perceptions of manhood.] No one has a right thus to check and disturb continually the regular processes of his physical and mental progress. Hence, the young man (especially if he be of a nervous, sensitive organization) who uses tobacco deliberately diminishes the possible energy with which he might commence the work of life; [Footnote: In the Polytechnic School at Paris, the pupils were divided into two classes—the smokers, and the non-smokers. The latter not only excelled on the entrance examinations, but during the entire course of study. Dr. Decaisne examined thirty-eight boys who smoked, and found twenty-seven of them diseased from nicotine poisoning. So long ago as 1868, in consequence of these results, the Minister of Public Instruction forbade the use of tobacco by the pupils.
Dr. Gihon, medical director of the Naval Academy at Annapolis, in his report for 1881, says: "The most important matter in the health history of the students is that relating to tobacco, and its interdiction is absolutely essential to their future health and usefulness. In this view I have been sustained by my colleagues, and by all sanitarians in civil and military life whose views I have been able to obtain."] while he comes under the bondage of a habit that may become stronger than his will, and under the influence of a narcotic that may beguile his faculties and palsy his strength at the very moment when every power should be awake.
Another peril still lies in the wake of this masterful poison habit. Tobacco causes thirst and depression that only too often and naturally lead to the use of liquor. (See p. 338.)
3. OPIUM.
Opium is the dried juice of the poppy. In Eastern countries, this flower is cultivated in immense fields for the sake of this product. When a cut is made in the poppy head, a tiny tear of milky juice exudes, and hardens. These little drops are gathered and prepared for the market, an acre yielding, it is said, about twenty-five pounds. Throughout the East, opium is generally smoked; but in Western countries laudanum and paregoric (tinctures of opium), and morphine—a powerful alkaloid contained in opium, are generally used. The drug itself is also eaten.
PHYSIOLOGICAL EFFECT.—Opium, in its various forms, acts directly upon the nerves, a small dose quieting pain, and a larger one soothing to sleep. It arouses the brain, and fires the imagination to a wonderful pitch. [Footnote: So far as its effects are concerned, it matters little in what form opium is taken, whether solid as in pills, liquid as in laudanum, or vaporized, as when inhaled from a pipe. The opium slave is characterized by trembling steps, a curved spine, sunken glassy eyes, sallow withered features, and often by contraction of the muscles of the neck and fingers. In the East, when the drug ceases its influence, the opium eater renews it with corrosive sublimate till, finally, this also fails of effect, and he gradually sinks into the grave.] The reaction from this unnatural excitant is correspondingly depressing; and the melancholy, the "overwhelming horror" that ensues, calls for a renewal of the stimulus. The dose must be gradually increased to produce the original exhilaration. [Footnote: The victim of opium is bound to a drug from which he derives no benefits, but which slowly deprives him of health and happiness, finally to end in idiocy or premature death. Whatever the victim's condition or surroundings may be, the opium must be taken at certain times with inexorable regularity. The liquor or tobacco user can, for a time, go without the use of these agents, and no regular hours are necessary. During sickness, and more especially during the eruptive fevers, he does not desire tobacco or liquor. The opium eater has no such reprieves; his dose must be taken, and, in painful complications affecting the stomach, a large increase is demanded to sustain the system. If, in forming the habit, two doses are taken each day, the victim is obliged to maintain that number. It is the unceasing, everlasting slavery of regularity that humiliates opium eaters by a sense of their own weakness.—HUBBARD on The Opium Habit and Alcoholism.] The seductive nature of the drug leads the unfortunate victim on step by step until he finds himself fast bound in the fetters of one of the most tyrannical habits known to man.
To go on is to wreck all one's powers—physical and mental. To throw off the habit, requires a determination that but few possess. Yet even when the custom is broken, the system is long in recovering from the shock. There seems to be a failure of every organ. The digestion is weakened, food is no longer relished, the muscles waste, the skin shrivels, the nervous centers are paralyzed, and a premature old age comes on apace. De Quincey, four months after he had cast away the opium bonds, wrote, "Think of me as one still agitated, writhing, throbbing, palpitating, shattered."
No person can be too careful in the use of laudanum, paregoric, and morphine. They may be taken on a physician's prescription as a sedative from racking pain, [Footnote: Many persons learn to inject morphine beneath the skin by means of a "hypodermic syringe." The operation is painless, and seems an innocent one. It throws the narcotic directly into the circulation, and relief from pain is often almost instantaneous. But the danger of forming the opium habit is not lessened, and the effect of using the drug in this form for a long time is just as injurious as opium smoking itself. Opium in one of its forms enters largely into the composition of many of the painkillers and patent medicines so freely advertised for domestic use in the present day, and for this reason the greatest care is needed in having recourse to any of them. Taken, perhaps, in the first instance, to alleviate the torments of neuralgia or toothache, what proves to be a remedy soon becomes a source of gratification, which the wretchedness that follows on abstinence renders increasingly difficult to lay aside. The same must be said of bromide of potassium and hydrate of chloral, frequently resorted to as a remedy for sleeplessness: the system quickly becomes habituated to their use, and they can then be relinquished only at the cost of much suffering. Indeed, the last mentioned of these two drugs obtains over the mind a power which may be compared to that of opium, and is, moreover, liable to occasion the disease known as chloralism, by which the system ultimately becomes a complete wreck. Looking at the whole question of the medicinal use of narcotics, it is perhaps not too much to say that they should never be employed except with the authority of a competent medical adviser.— Chambers's Journal.] but if followed up for any length of time, the powerful habit may be formed ere one is aware. Then comes the opium eater's grave, or the opium eater's struggle for life!
4. CHLORAL HYDRATE.
CHLORAL HYDRATE is a drug frequently used to cause sleep. It leaves behind no headache or lassitude, as is often the case with morphine. It is, however, a treacherous remedy. It is cumulative in its effects, i. e., even a small and harmless dose, persisted in for a long period, may produce a gradual accumulation of evil results that in the end will prove fatal.
THE PHYSIOLOGICAL EFFECT of its prolonged use is very marked. The appetite becomes capricious. The secretions are unnatural. Nausea and flatulency often ensue. Then the nervous system is involved. The heart is affected. Sleep, instead of responding to the drug, as at first, is broken and disturbed. The eyesight fails. The circulation is enfeebled, and the pulse becomes weak, rapid, and irregular. There is a tendency to fainting and to difficult respiration. Sometimes the impoverished blood induces a disease resembling scurvy, the ends of the fingers ulcerate, and the face is disfigured by blotches. An excessive dose may result in death.
Prolonged habitual use of chloral hydrate tends to debase the mind and morals of the subject in the same manner as indulgence in alcohol, ether, or chloroform.
5. CHLOROFORM.
CHLOROFORM is an artificial product generally obtained, by distillation, from a mixture of chloride of lime, water, and alcohol. It was discovered in 1831 by Samuel Guthrie, of Sackett's Harbor, New York. It is a colorless, transparent volatile liquid, with a strong ethereal odor.
PHYSIOLOGICAL EFFECT.—Chloroform is a powerful anæsthetic, which, when inhaled, causes a temporary paralysis of the nervous system, and thus a complete insensibility to pain. There is great peril attending its use, even in the hands of the most skillful and experienced practitioners. It is sometimes prescribed by a physician, and afterward (as in the case of laudanum, morphine, and chloral) the sufferer, charmed with the release from pain and the peaceful slumber secured, buys the Lethean liquid for himself. Its use soon becomes an apparent necessity. The craving for the narcotic at a stated time is almost irresistible. The patient, compelled to give up the use of chloroform, will demand, entreat, pray for another dose, in a heartrending manner, never to be forgotten. Paleness and debility, the earliest symptoms, are followed by mental prostration. Familiarity with this dangerous drug begets carelessness, and its victims are frequently found dead in their beds, with the handkerchief from which they inhaled the volatile poison clutched in their lifeless hands.
6. COCAINE.
Cocaine is an alkaloid prepared from the erythroxylon coca, a shrub, five or six feet high, found wild in the mountainous regions of Ecuador and Peru, where it is also cultivated by the natives. The South American Indians, for centuries, have chewed coca leaves as a stimulant, but the highly poisonous principle, now called cocaine, to which the plant owes its peculiar effects, was not discovered till 1859. Within a few years this drug has come into favor as an agent to produce local anæsthesia, and has proved exceedingly valuable in surgical operations upon the eye and other sensitive organs. It has already, however, been diverted from its legitimate use as a benefaction, and to the other evils of the day is now added the "cocaine habit," which is, perhaps, even more dangerous and difficult to abandon than either the alcohol or the opium habit.
PHYSIOLOGICAL EFFECT.—Applied locally, cocaine greatly lessens and even annihilates pain. Taken internally, it acts as a powerful stimulant to the nervous system, its physiological action being similar to that of theine (p. 170), caffeine, and theobromine. Used hypodermically, its immediate effect, says one to whom it was thus administered, is to cause "great pallor of countenance, profuse frontal perspiration, sunken eyes, enlarged pupils, lessened sensitiveness of the cornea and conjunctiva, lowered arterial tension, and a feeble pulse and heart beat. Under its influence I could not reason. Everything seemed to run through my brain, and in vain I summoned all my will power to overcome an overwhelming sleepiness." A few doses of this drug will in some persons produce temporary insanity. Used to excess, it leads to permanent madness or idiocy. "Cocaine," says a writer in the Medical Review, "is a dangerous therapeutic toy not to be used as a sensational plaything. If it should come into as general use as the other intoxicants of its class, it will help to fill the asylums, inebriate and insane."
PRACTICAL QUESTIONS.
1. Why is the pain of incipient hip disease frequently felt in the knee?
2. Why does a child require more sleep than an aged person?
3. When you put your finger in the palm of a sleeping child, why will he grasp it?
4. How may we strengthen the brain?
5. What is the object of pain?
6. Why will a blow on the stomach sometimes stop the heart?
7. How long will it take for the brain of a man six feet high to receive news of an injury to his foot, and to reply?
8. How can we grow beautiful?
9. Why do intestinal worms sometimes affect a child's sight?
10. Is there any indication of character in physiognomy?
11. When one's finger is burned, where is the ache?
12. Is a generally closed parlor a healthful room?
13. Why can an idle scholar read his lesson and at the same time count the marbles in his pocket?
14. In amputating a limb, what part, when divided, will cause the keenest pain?
15. What is the effect of bad air on nervous people?
16. Is there any truth in the proverb that "he who sleeps dines"?
17. What does a high, wide forehead indicate?
18. How does indigestion frequently cause a headache?
19. What is the cause of one's foot being "asleep"? [Footnote: Here the nervous force is prevented from passing by compression. Just how this is done, or what is kept from passing, we can not tell. If a current of electricity were moving through a rubber tube full of mercury, a slight squeeze would interrupt it. These cases may depend on the same general principle, but we can not assert it.—HUXLEY. The tingling sensation caused by the compression is transferred to the foot, whence the nerve starts.]
20. When an injury to the nose has been remedied by transplanting skin from the forehead, why is a touch to the former felt in the latter?
21. Are closely curtained windows healthful?
22. Why, in falling from a height, do the limbs instinctively take a position to defend the important organs?
23. What causes the pylorus to open and close at the right time?
24. Why is pleasant exercise most beneficial?
25. Why does grief cause one to lose his appetite?
26. Why should we never study directly after dinner?
27. What produces the peristaltic movement of the stomach?
28. Why is a healthy child so restless and full of mischief?
29. Why is a slight blow on the back of a rabbit's neck fatal?
30. Why can one walk and carry on a conversation at the same time?
31. What are the dangers of overstudy?
32. What is the influence of idleness upon the brain?
33. State the close relation which exists between physical and mental health and disease.
34. In what consists the value of the power of habit?
35. How many pairs of nerves supply the eye?
36. Describe the reflex actions in reading aloud.
37. Under what circumstances does paralysis occur?
38. If the eyelids of a profound sleeper were raised, and a candle brought near, would the iris contract?
39. How does one cough in his sleep?
40. Give illustrations of the unconscious action of the brain.
41. Is chewing tobacco more injurious than smoking?
42. Ought a man to retire from business while his faculties are still unimpaired?
43. Which is the more exhaustive to the brain, worry or severe mental application?
44. Is it a blessing to be placed beyond the necessity for work?
45. Show how anger, hate, and the other degrading passions are destructive to the brain. [Footnote: "One of the surest means for keeping the body and mind in perfect health consists in learning to hold the passions in subservience to the reasoning faculties. This rule applies to every passion. Man, distinguished from all other animals by the peculiarity that his reason is placed above his passions to be the director of his will, can protect himself from every mere animal degradation resulting from passionate excitement. The education of the man should be directed not to suppress such passions as are ennobling, but to bring all under governance, and specially to subdue those most destructive passions, anger, hate, and fear."]
46. Are not amusements, to repair the waste of the nervous energy, especially needed by persons whose life is one of care and toil?
47. Is not severe mental labor incompatible with a rapidly growing body?
48. How shall we induce the system to perform all its functions regularly
49. How does alcohol interfere with the action of the nerves?
50. What is the general effect of alcohol upon the character?
51. Does alcohol tend to produce clearness and vigor of thought?
52. What is the general effect of alcohol on the muscles?
53. Does alcohol have any effect on the bones? The skin?
54. What is the cause of the "alcoholic chill"?
55. Show how alcohol tends to develop man's lower, rather than his higher, nature.
56. When we wish really to strengthen the brain, should we use alcohol?
57. Why is alcohol used to preserve anatomical specimens?
58. What is meant by an inherited taste for liquor?
59. Ought a person to be punished for a crime committed during intoxication?
60. Should a boy ever smoke?
61. To what extent are we responsible for the health of our body?
62. Why does alcohol tend to collect in the brain?
63. Does the use of alcohol tend to increase crime and poverty?
VIII.
THE SPECIAL SENSES.
"See how yon beam of seeming white
Is braided, out of seven-hued light;
Yet in those lucid globes no ray
By any chance shall break astray.
Hark, how the rolling surge of sound,
Arches and spirals circling round,
Wakes the hush'd spirit through thine ear
With music it is heaven to hear."
HOLMES.
"Let us remember that if we get a glimpse of the details of natural phenomena, and of those movements which constitute life, it is not in considering them as a whole, but in analyzing them as far as our limited means will permit. In the vibrations of the globe of air which surrounds our planet, as in the undulations of the ether which fills the immensity of space, it is always by molecules which are intangible for us, put in motion by nature, always by the infinitely little, that she acts in exciting the organs of sense, and she has modeled these organs in a proportion which enables them to partake in the movement which she impresses upon the universe. She can paint with equal facility on a fraction of a line of space on the retina, the grandest landscape or the nervelets of a rose leaf; the celestial vault on which Sirius is but a luminous point, or the sparkling dust of a butterfly's wing; the roar of the tempest, the roll of thunder, the echo of an avalanche, find equal place in the labyrinth whose almost imperceptible cavities seem destined to receive only the most delicate sounds."
| 1. THE TOUCH…| 1. Description of the Organ. | |2. Its Uses. | | 2. THE TASTE…| 1. Description of the Organ. | |2. Its Uses. | | 3. THE SMELL…| 1. Description of the Organ. | |2. Its Uses. | _ | | 1. Description of the | a. External Ear. | | Organ……………| b. Middle Ear. | 4. THE HEARING.| |_c. Internal Ear. | | 2. How we Hear | |3. Hygiene of the Ear. | | | 1. Description of the Organ. | | 2. Eyelids, and Tears. | | 3. Structure of the Retina. |_5. THE SIGHT…| 4. How we see. | 5. The Use of the Crystalline Lens. | 6. Near and Far Sight. | 7. Color Blindness. |_8. Hygiene of the Eyes.
THE SPECIAL SENSES
1. TOUCH.
DESCRIPTION.—Touch is sometimes called the "common sense," since its nerves are spread over the whole body. It is most delicate, however, in the point of the tongue and the tips of the fingers. The surface of the cutis is covered with minute, conical projections called papillæ (Fig. 24). [Footnote: In the palm of the hand, where there are at least twelve thousand in a square inch, we can see the fine ridges along which they are arranged.] Each one of these papillæ contains its tiny nerve twigs, which receive the impression and transmit it to the brain, where the perception is produced.
USES.—Touch is the first of the senses used by a child. By it we obtain our idea of solidity, and throughout life rectify all other sensations. Thus, when we see anything curious, our first desire is to handle it.
The sensation of touch is generally relied upon, yet, if we hold a marble in the manner shown in Fig. 57, it will seem like two marbles; and if we touch the fingers thus crossed to our tongue, we shall seem to feel two tongues. Again, if we close our eyes and let another person move one of our fingers over a plane surface, first lightly, then with greater pressure, and then lightly again, we shall think the surface concave.
FIG. 57.
[Illustration:]
This organ is capable of wonderful cultivation. The physician acquires by practice the tactus eruditus, or learned touch, which is often of great service, while the delicacy of touch possessed by the blind almost compensates the loss of the absent sense. [Footnote: The sympathy between the different organs shows how they all combine to make a home for the mind. When one sense fails, the others endeavor to remedy the defect. It is touching to see how the blind man gets along without eyes, and the deaf without ears. Cuthbert, though blind, was the most efficient polisher of telescopic mirrors in London. Saunderson, the successor of Newton as professor of mathematics at Cambridge, could distinguish between real and spurious medals. There is an instance recorded of a blind man who could recognize colors. The author knew one who could tell when he was approaching a tree, by what he described as the "different feeling of the air."] (See p. 346.)
2. TASTE.
DESCRIPTION.—This sense is located in the papillæ of the tongue and palate. These papillaæ start up when tasting, as you can see by placing a drop of vinegar on another person's tongue, or your own before a mirror. The velvety look of this organ is given by hair-like projections of the cuticle upon some of the papillæ. They absorb the liquid to be tasted, and convey it to the nerves. [Footnote: An insoluble substance is therefore tasteless.] The back of the tongue is most sensitive to salt and bitter substances, and, as this part is supplied by the ninth pair of nerves (Fig. 56), in sympathy with the stomach, such flavors, by sympathy, often produce vomiting. The edges of the tongue are most sensitive to sweet and sour substances, and as this part is supplied by the fifth pair of nerves, which also goes to the face, an acid, by sympathy, distorts the countenance.
FIG. 58.
[Illustration: The Tongue, showing the several kinds of Papillæ—the conical (D) the whip like (K, I), the circumvallate or entrenched (H, L); E, F, G, nerves; C, glottis.—LANKESTER.]
THE USE OF THE TASTE was originally to guide in the selection of food; but this sense has become so depraved by condiments and the force of habit that it would be a difficult task to tell what are one's natural tastes.
3. SMELL. [Footnote: The sense of smell is so intimately connected with that of taste that we often fail to distinguish between them. Garlic, vanilla, coffee and various spices, which seem to have such distinct taste, have really a powerful odor, but a feeble flavor.]
DESCRIPTION.—The nose, the seat of the sense of smell, is composed of cartilage covered with muscles and skin, and joined to the skull by small bones. The nostrils open at the back into the pharynx, and are lined by a continuation of the mucous membrane of the throat. The olfactory nerves (first pair, Fig. 55) enter through a sieve-like, bony plate at the roof of the nose, and are distributed over the inner surface of the two olfactory chambers. (See p. 346.) The object to be smelled need not touch the nose, but tiny particles borne on the air enter the nasal passages. [Footnote: Three quarters of a grain of musk placed in a room will cause a powerful smell for a considerable length of time without any sensible diminution in weight, and the box in which musk has been placed retains the perfume for almost an indefinite period. Haller relates that some papers which had been perfumed by a grain of ambergris, were still very odoriferous after a lapse of forty years. Odors are transported by the air to a considerable distance. A dog recognizes his master's approach by smell even when he is far away; and we are assured by navigators that the winds bring the delicious odors of the balmy forests of Ceylon to a distance of ten leagues from the coast. Even after making due allowance for the effects of the imagination, it is certain that odors act as an excitant on the brain, which may be dangerous when long continued. They are especially dreaded by the Roman women. It is well known that in ancient times the women of Rome indulged in a most immoderate use of baths and perfumes; but those of our times have nothing in common with them in this respect; and the words of a lady are quoted, who said on admiring an artificial rose, "It is all the more beautiful that it has no smell." We are warned by the proverb not to discuss colors or tastes, and we may add odors also. Men and nations differ singularly in this respect. The Laplander and the Esquimaux find the smell of fish oil delicious. Wrangel says his compatriots, the Russians, are very fond of the odor of pickled cabbage, which forms an important part of their food; and asaftida, it is said, is used as a condiment in Persia, and, in spite of its name, there are persons who do not find its odor disagreeable any more than that of valerian.—Wonders of the Human body.]
FIG. 59.
[Illustration: A, b, c, d, interior of the nose, which is lined by a mucous membrane; n, the nose; e, the wing of the nose; q, the nose bones; o, the upper lip; g, section of the upper jaw-bone; h, the upper part of the mouth, or hard palate; m, frontal bone of the skull; k, the ganglion or bulb of the olfactory nerve in the skull, from which are seen the branches of the nerve passing in all directions.]
THE USES of the sense of smell are to guide us in the choice of our food, and to warn us against bad air, and unhealthy localities. (See p. 348.)
4. HEARING.
DESCRIPTION.—The ear is divided into the external, middle, and internal ear.
1. The External Ear is a sheet of cartilage curiously folded for catching sound. The auditory canal, B, or tube of this ear trumpet, is about an inch long. Across the lower end is stretched the membrane of the tympanum or drum, which is kept soft by a fluid wax.
FIG. 60.
[Illustration: The Ear.]
2. The Middle Ear is a cavity, at the bottom of which is the Eustachian tube, G, leading to the mouth. Across this chamber hangs a chain of three singular little bones, C, named from their shape the hammer, the anvil, and the stirrup. All together these tiny bones weigh only a few grains, yet they are covered by a periosteum, are supplied with blood vessels, and they articulate with perfect joints (one a ball-and-socket, the other a hinge), having synovial membranes, cartilages, ligaments, and muscles.
3. The Internal Ear, or labyrinth, as it is sometimes called from its complex character, is hollowed out of the solid bone. In front, is the vestibule or antechamber, A, about as large as a grain of wheat; from it open three semicircular canals, D, and the winding stair of the cochlea, or snail shell, E. Here expand the delicate fibrils of the auditory nerve. Floating in the liquid which fills the labyrinth is a little bag containing hair-like bristles, fine sand, and two ear stones (otoliths). All these knocking against the ends of the nerves, serve to increase any impulse given to the liquid in which they lie. Finally, to complete this delicate apparatus, in the cochlea are minute tendrils, named the fibers of Corti, from their discoverer. These are regularly arranged,—the longest at the bottom, and the shortest at the top. Could this spiral plate, which coils two and a half times around, be unrolled and made to stand upright, it would form a beautiful microscopic harp of three thousand strings. If it were possible to strike these cords as one can the keyboard of a piano, he could produce in the mind of the person experimented upon every variety of tone which the ear can distinguish.
HOW WE HEAR.—Whenever one body strikes another in the air, waves are produced, just as when we throw a stone into the water a series of concentric circles surrounds the spot where it sinks. These waves of air strike upon the membrane. This vibrates, and sends the motion along the chain of bones in the middle ear to the fluids of the labyrinth. Here bristles, sand, and stones pound away, and the wondrous harp of the cochlea, catching up the pulsations, [Footnote: The original motion is constantly modified by the medium through which it passes. The bristles, otoliths, and Cortian fibers of the ear, and the rods and cones of the eye (p. 239) serve to convert the vibrations into pulsations which act as stimuli of the appropriate nerve. The molecular change thus produced in the nerve fibers is propagated to the brain.—See Popluar Physics, p. 182.] carries them to the fibers of the auditory nerve, which conveys them to the brain, and gives to the mind the idea of sound.
CARE OF THE EAR.—The delicacy of the ear is such that it needs the greatest care. Cold water should not be allowed to enter the auditory canal. If the wax accumulate, never remove it with a hard instrument, lest the delicate membrane be injured, but with a little warm water, after which turn the head to let the water run out, and wipe the ear dry. The hair around the ears should never be left wet, as it may chill this sensitive organ. If an insect get in the external ear, pour in a little oil to kill it, and then remove with tepid water. The object of the Eustachian tube is to admit air into the ear, and thus equalize the pressure on the membrane. If it become closed by a cold, or if, from any cause, the pressure be made unequal, so as to produce an unpleasant feeling in the ear, relief may often be obtained by grasping the nose and forcibly swallowing. (See p. 350.)
5. SIGHT.
FIG. 61.
[Illustration: The Eye.]
DESCRIPTION.—The eye is lodged in a bony cavity, protected by the overhanging brow. It is a globe, about an inch in diameter. The ball is covered by three coats—(l) the sclerotic, d, a tough, horny casing, which gives shape to the eye, the convex, transparent part in front forming a window, the cornea, d; (2) the choroid, e, a black lining, to absorb the superfluous light [Footnote: Neither white rabbits nor albinos have this black lining, and hence their sight is confused.] and (3) the retina, b, a membrane in which expand fibers of the optic nerve, o. The crystalline lens, a, brings the rays of light to a focus on the retina. The lens is kept in place by the ciliary processes, g, arranged like the rays in the disk of a passion flower. Between the cornea and the crystalline lens is a limpid fluid termed the aqueous humor; while the vitreous humor—a transparent, jelly-like liquid fills the space (h) back of the crystalline lens. The pupil, k, is a hole in the colored, muscular curtain, i, the iris (rainbow). (See p. 352.)
FIG. 62.
[Illustration: The Eyelashes and the Tear Glands.]
EYELIDS AND TEARS.—The eyelids are close-fitting shutters to screen the eye. The inner side is lined with a mucous membrane that is exceedingly sensitive, and thus aids in protecting the eye from any irritating substance. The looseness of the skin favors swelling from inflammation or the effusion of blood, as in a "black eye." The eyelashes serve as a kind of sieve to exclude the dust, and, with the lids, to shield against a blinding light. Just within the lashes are oil glands, which lubricate the edges of the lids, and prevent them from adhering to each other. The tear or lachrymal gland, G, is an oblong body lodged in the bony wall of the orbit. It empties by several ducts upon the inner surface, at the outer edge of the upper eyelid. Thence the tears, washing the eye, run into the lachrymal lake, D, a little basin with a rounded border fitted for their reception. On each side of this lake two canals, C, C, drain off the overplus through the duct, B, into the nose. In old age and in disease, these canals fail to conduct the tears away, and hence the lachrymal lake overflows upon the face.
FIG. 63.
[Illustration: Structure of the Retina.]
STRUCTURE OF THE RETINA.—In Fig. 63 is shown a section of the retina, greatly magnified, since this membrane never exceeds 1/80 an inch in thickness. On the inner surface next to the vitreous humor, is a lining membrane not shown in the cut. Next to the choroid and comprising about 1/4 the entire thickness of the retina, is a multitude of transparent, colorless, microscopic rods, a, evenly arranged and packed side by side, like the seeds on the disk of a sunflower. Among them, at regular intervals, are interspersed the cones, b. Delicate nerve fibers pass from the ends of the rods and cones, each expanding into a granular body, c, thence weaving a mesh, d, and again expanding into the granules, f. Last is a layer of fine nerve fibers, g, and gray, ganglionic cells, h, like the gray matter of the brain, whence filaments extend into i, the fibers of the optic nerve. (See p. 354.)
The layer of rods and cones is to the eye what the bristles, otoliths, and Cortian fibers are to the ear. Indeed, the nerve itself is insensible to light. At the point where it enters the eye, there are no rods and cones, and this is called the blind spot. A simple experiment will illustrate the fact. Hold this book directly before the face, and, closing the left eye, look steadily with the right at the left-hand circle in Fig. 64. Move the book back and forth, and a point will be found where the right-hand circle vanishes from sight. At that moment its light falls upon the spot where the rods and cones are lacking.
FIG. 64.
[Illustration:]
HOW WE SEE.—There is believed to be a kind of universal atmosphere, termed ether, filling all space. This substance is infinitely more subtle than the air, and occupies its pores, as well as those of all other substances. As sound is caused by waves in the atmosphere, so light is produced by waves in the ether. A lamplight, for example, sets in motion waves of ether, which pass in through the pupil of the eye, to the retina, where the rods and cones transmit the vibration through the optic nerve to the brain, and then the mind perceives the light. (Note, p. 236.)
THE USE OF THE CRYSTALLINE LENS. [Footnote: The uses of the eye and ear are dependent upon the principles of Optics and Acoustics. They are therefore best treated in Physics.]—A convex lens, as a common burning glass, bends the rays of light which pass through it, so that they meet at a point called the focus. The crystalline lens converges the rays of light which enter the eye, and brings them to a focus on the retina. [Footnote: The cornea and the humors of the eye act in the same manner as the crystalline lens, but not so powerfully.] The healthy lens has a power of changing its convexity so as to adapt [Footnote: The simplest way of experimenting on the "adjustment of the eye" is to stick two stout needles upright into a straight piece of wood,—not exactly, but nearly in the same straight line, so that, on applying the eye to one end of the piece of wood, one needle (A) shall be seen about six inches off, and the other (B) just on one side of it, at twelve inches distance. If the observer looks at the needle B he will find that he sees it very distinctly, and without the least sense of effort; but the image of A is blurred, and more or less double. Now, let him try to make this blurred image of the needle A distinct. He will find he can do so readily enough, but that the act is accompanied by a sense of fatigue. And in proportion as A becomes distinct, B will become blurred. Nor will any effort enable him to see A and B distinctly at the same time.—HUXLEY.] itself to near and to distant objects. (See Fig. 66.)
FIG. 65.
[Illustration: Diagram showing how an image of an object is formed upon the Retina by the Crystalline Lens.]
NEAR AND FAR SIGHT.—If the lens be too convex, it will bring the rays to a focus before they reach the retina; if too flat, they will reach the retina before coming to a focus. In either case, the sight will be indistinct. A more common defect, however, is in the shape of the globe of the eye, which is either flattened or elongated. In the former case (see G, Fig. 67), objects at a distance can be seen most distinctly— hence that is called farsightedness. [Footnote: This should not be confounded with the long sight of old people, which is caused by the stiffness of the ciliary muscles, whereby the lens can not adapt itself to the varying distances of objects.] In the latter, objects near by are clearer, and hence this is termed nearsightedness. Farsightedness is remedied by convex glasses; nearsightedness, by concave. When glasses will improve the sight they should be worn; [Footnote: Dr. Henry W. Williams, the celebrated ophthalmologist, says that, in some cases, glasses are more necessary at six or eight years of age than to the majority of healthy eyes at sixty. Sometimes children find accidentally that they can see better through grandmother's spectacles. They should then be supplied with their own.] any delay will be liable to injure the eyes, by straining their already impaired power. Cataract is a disease in which there is an opacity of the crystalline lens or its capsules, which obscures the vision. The lens may be caused to be absorbed, or may be removed by a skillful surgeon and the defect remedied by wearing convex glasses.
FIG. 66.
[Illustration: Adjustment of the Crystalline Lens.—A, for far objects, and B, for near.]
FIG. 67.
[Illustration: Diagram illustrating the position of the Retina.—B, in natural sight; G, in far sight; and C, in near sight.]
COLOR-BLIND PERSONS receive only two of the three elementary color sensations (green, red, violet). The spectrum appears to them to consist of two decidedly different colors, with a band of neutral tint between. The extreme red end is invisible, and a bright scarlet and a deep green appear alike. They are unable to distinguish between the leaves of a cherry tree and its fruit by the color of the two, and see no difference between blue and yellow cloth. Whittier, the poet, it is said, could not tell red from green unless in direct sunlight. Once he patched some damaged wall paper in his library by matching a green vine in the pattern with one of a bright autumnal crimson. This defect in the eye is often unnoticed, and many railway accidents have doubtless happened through an inability to detect the color of signal lights.
CARE OF THE EYES.—The shape of the eye can not be changed by rubbing and pressing it, as many suppose, but the sight may thus be fatally injured. Children troubled by nearsightedness should not lean forward at their work, as thereby the vessels of the eye become overcharged with blood. They should avoid fine print, and try, in every possible way, to spare their eyes. If middle age be reached without especial difficulty of sight, the person is comparatively safe. Most cases of squinting are caused by longsightedness, the muscles being strained in the effort to obtain distinct vision. In childhood, it may be cured by a competent surgeon, who will generally cut the muscle that draws the eye out of place.
After any severe illness, especially after measles, scarlatina, or typhoid fever, the eyes should be used with extreme caution, since they share in the general debility of the body, and recover their strength slowly. Healthy eyes even should never be used to read fine print or by a dim light. Serious injury may be caused by an imprudence of this kind. Reading upon the cars is also a fruitful source of harm. The lens, striving to adapt itself to the incessantly varying distance of the page, soon becomes wearied. Whenever the eyes begin to ache, it is a warning that they are being overtaxed and need rest.
Objects that get into the eye should be removed before they cause inflammation; rubbing in the meantime only irritates and increases the sensitiveness. If the eye be shut for a few moments, so as to let the tears accumulate, and the upper lid be then lifted by taking hold of it at the center, the cinder or dust is often washed away at once. Trifling objects can be removed by simply drawing the upper lid as far as possible over the lower one; when the lid flies back to its place, the friction will detach any light substance. If it becomes necessary, turn the upper lid over a pencil, and the intruder may then be wiped off with a handkerchief. "Eye-stones" are a popular delusion. When they seem to take out a cinder, it is only because they raise the eyelid, and allow the tears to wash it out. No one should ever use an eyewash, except by medical advice. The eye is too delicate an organ to be trifled with, and when any disease is suspected, a reliable physician should be consulted. This is especially necessary, since, when one eye is injured, the other, by sympathy, is liable to become inflamed, and perhaps be destroyed.
When reading or working, the light should be at the left side, or at the rear; never in front.
The constant increase of defective eyesight among the pupils in our schools is an alarming fact. Dr. Agnew considers that our schoolrooms are fast making us a spectacle-using people. Nearsightedness seems to increase from class to class, until in the upper departments, there are sometimes as high as fifty per cent of the pupils thus afflicted. The causes are (1), desks so placed as to make the light from the windows shine directly into the eyes of the scholars; (2), cross lights from opposite windows; (3), insufficient light; (4), small type that strains the eyes; and (5), the position of the pupil as he bends over his desk or slate, causing the blood to settle in his eyes. All these causes can be remedied; the position of the desks can be changed; windows can be shaded, or new ones inserted; books and newspapers that try the eyes can be rejected; and every pupil can be taught how to sit at study.