The shape and position of the teeth literally make the lower half of the face and give it half its expression. A properly grown and developed set of teeth not only is necessary to health and comfort, but helps greatly to make the face and expression attractive or unattractive. Few faces with bright eyes, clear skin, and white, regular, well-kept teeth are unpleasing to look at. Beauty and health are closely related, and we ought to try to have both. In fact, nine times out of ten, what we call beauty is the outward and visible sign of inward health. The healthier you are, the handsomer you'll be.

It is particularly important to understand the natural growth and proper care of the teeth because there are few organs in the body for which we are able to do so much by direct personal attention. Our stomachs, our livers, and our kidneys, for instance, are entirely out of sight, and more or less out of reach; but our teeth are both easily got at and in full view; and, to a large degree, upon the care that we give them while they are young, will depend not only their regularity and whiteness, but also the length of their life and the vigor and comfort of our digestion all our lives.

[Ill.u.s.tration: TEETH--A QUESTION OF CARE]

The first thing to be remembered about the teeth is that, hard and shiny and different from almost everything else in the body as they look, they are simply a part of the skin lining the mouth, hardened and shaped for their special work of biting and chewing. Much of the care needed to prevent decay should be given, not to the teeth themselves directly, but to the gums and the mucous membrane of the whole mouth. The gums and the mouth literally _grew_ the teeth in the first place; and when they become diseased, they secrete acids which slowly eat away the crowns and roots of the teeth. Their diseases come chiefly from irritation by decaying sc.r.a.ps of food, or from the blocking of the nose so that air is breathed in through the mouth, drying and cracking the soft mucous membrane. After the acids from the diseased gums have attacked the teeth, the poisons of the germs that breed in the warmth and moisture of the mouth cause the teeth to decay. Eight times out of ten, if you take care of the gums the teeth will take care of themselves.

Structure of the Teeth. The upper half of the tooth, which pushes through and stands up above the jaw and the gum, we call the _crown_; and this is the portion that is covered with _enamel_, or "living gla.s.s." The body of the tooth under the enamel is formed of a hard kind of bone called _dentine_. The lower half of the tooth, which still is buried in the jaw, we call the _root_. Wrenching the lower or root part of the tooth loose from its socket in the jaw is what hurts so when a tooth is pulled. The crown of the tooth is hollow, and this hollow is filled with a soft, sensitive pulp, in which we feel toothache. Tiny blood vessels and nerve-twigs run up from the jaw to supply this pulp through ca.n.a.ls in the roots of the tooth.

[Ill.u.s.tration: A TOOTH

(Lengthwise section.)

_E_, enamel; _D_, dentine; _P_, pulp cavity; _C_, cement; _B_, blood vessels; _N_, nerve.]

Kinds of Teeth. If you look at your own teeth in a mirror, the first thing that strikes you is your broad, white, shiny front teeth, four above and four below, shaped like the blade of a rather blunt chisel.

Their shape tells what they are used for. Like chisels, they cut, or bite, the food into appropriate sizes and lengths for chewing between the back teeth; and from this use they are called the _incisors_, or "cutters." From having been used for so many generations upon the kind of food we live on, they have grown broader than the _canines_, the teeth next to them, and almost as long.

The canines are of a cone-like shape, although it is a pretty blunt cone, or peg. Those in the upper jaw lie almost directly under the centre of each eye, and are called the "eye-teeth"; though their proper name, from the fact that they are the most prominent teeth in the dog, is the canine teeth. These are our oldest and least changed teeth; and as you might guess from their shape, like a heavy, blunt spear-head, were originally the fighting and tearing teeth, and still have the longest and heaviest roots of any teeth in our jaws. If you slip your finger up under your upper lip, you can feel the great ridge of this root, standing out from the surface of the gum.

Lastly, looking farther back into our mouths, we see behind our canines a long row of broad, flat-topped, square-looking teeth, which fill up the largest part of our jaws. Again their shape tells what they are used for. They are not sharp enough to cut with, or pointed enough to tear with, but are just suited for crushing and grinding into a pulp, between their broad, flat tops, any food that may be placed between them; and from this grinding they are called the _molars_, or "mill" teeth. If you will look closely at the back ones, you will see that each of them has four corners, or _cusps_, with a cross-shaped, sunken furrow in the centre, where they come together. After they have been used in grinding food for some years and rubbing against each other, these little corner projections become worn away, and their tops become almost flat. Those in the upper jaw have three roots, and those in the lower jaw have two, so that they are solidly anch.o.r.ed for their heavy, grinding work. The first two molars in each jaw, behind the canines, are smaller than the others and made up of only two pieces instead of four, and hence are called the _bicuspids_, or "two-cusped" teeth.

As we are what the scientists call an omnivorous, or "all-devouring,"

animal, able to eat and live upon practically every kind of food that any animal on earth can deal with,--animal and vegetable, soft and hard, wet and dry; fruits, nuts, crabs, roots, seaweeds, insects, anything that we can get our teeth into,--we have kept in working condition some of every kind of teeth possessed by any living animal; and the most important rule for keeping our teeth in health is to give all these kinds something to do.

Just as in other animals the teeth appear when needed, and grow into the shape required, so they grow in our own mouths when they are wanted, and of the size and shape required at the time. We are born without any teeth at all; and it is only when we begin to need a little solid food added to our milk diet,--when we are about seven months old,--that our first teeth appear; and these are incisors, first of all in the lower jaw. Then, at average intervals of about three months, the other incisors and the canines appear and, last of all, the molars, so that at about two years of age we have a complete set of twenty teeth. These are called the _milk teeth_.

Most animals (_mammals_) have formed the habit of growing two sets of teeth--a smaller, slighter set for use during the first few months or years of life, and a larger, heavier set to come in and take their place after the jaws have grown to somewhat more nearly their permanent size.

In our mouths, at about seven years of age, a larger, heavier tooth pushes up behind the last milk tooth,--called the "seventh year molar,"--the milk teeth begin to loosen and fall out, and their places are taken by other new teeth budding up out of the jaw just as the first set did. These take a still longer time to grow, so that the last four of the full set of thirty-two do not come through the gums until somewhere between our eighteenth and twentieth years. These last four teeth, for the rather absurd reason that they do not appear until we are old enough to be wise, are known as the "wisdom teeth." Instead of being, as one might expect, the hardest and longest-lived of all our teeth, they are the smallest and worst built of our molars and among the first of our permanent teeth to break down and disappear. Not only so, but our jaws are so much shorter than they were in the days when man fought with his teeth and knew nothing about cooking and had no tools or utensils with which to grind and prepare his food, that there is scarcely room in them for these last teeth to come through. They often cause a great deal of pain in the process, and may even break through at the side of the jaw and cause abscesses and other troubles.

[Ill.u.s.tration: THE REPLACING OF THE MILK TEETH

The "second teeth" are shown fully formed in the gums, ready to push out the milk teeth. The wisdom teeth, which appear later, cannot be shown at this stage.--After Gray.]

Care of the Teeth. The most important thing for the health of any organ in the body is to give it plenty of exercise, and this is especially true of our teeth. This exercise can be secured by thoroughly chewing, or _masticating_, all our food, of whatever sort, especially breads, biscuits, and cereals. Thorough chewing not only gives valuable exercise to the teeth, but, by grinding up these foods thoroughly, makes them easier for the stomach to digest; and, by mixing them well with the saliva, enables it to change the starch into sugar. Meats, fish, eggs, cheese, etc., do not need to be mixed with the saliva, nor to be ground so fine for easy digestion in the stomach, and hence do not require such thorough chewing, though it is better to make a rule of chewing all food well. We can exercise our teeth also by eating plenty of foods that require a good deal of chewing, especially the crusts of bread, and vegetables such as corn, celery, lettuce, nuts, parched grains, and popcorn.

It is most important to keep the nasal pa.s.sages clear and free, and the teeth sound and regular by proper dental attention, so that the jaws will grow properly, and each tooth will strike squarely against its fellow in the opposite jaw, and both jaws fit snugly and closely to each other, making the bite firm and clean, and the grinding close and vigorous. If we are mouth-breathers, our jaws will grow out of shape, so that our teeth are crowded and irregular and do not meet each other properly in chewing. Pressure upon the roots of the teeth, from meeting their fellows of the opposite jaw in firm, vigorous mastication, is one of the most important means of keeping them sound and healthy. Whenever a tooth becomes idle and useless, from failing to meet its fellow tooth in the jaw above or below properly, or from having no fellow tooth to meet, it is very likely to begin to decay.

The next important thing in keeping the teeth healthy is to keep them thoroughly clean. The greatest enemies of our teeth are the acids that form in the sc.r.a.ps of food that are left between them after eating.

Meats are not so dangerous in this regard as starches and sugars, because the fluids resulting from their decay are alkaline instead of acid; but it is best to keep the teeth clear of sc.r.a.ps of all kinds.

This can best be done by the moderate and gentle use of a quill, or _rolled_ wooden tooth-pick, followed by a thorough brushing after each meal with a rather stiff, firm brush. Then use floss-silk, or linen or rubber threads to "saw" out such pieces as have lodged between the teeth.

This brushing should be given, not merely to the teeth, but to the entire surface of the gums as well; for, as we have seen, it is the gums that make or spoil the health of the teeth, and they, like all other parts of the body, require plenty of exercise and pressure in order to keep them healthy. In the early days of man, when he had no knives and gnawed his meat directly off the bones, and when he cracked nuts and ground all his grain with his teeth, the gums got an abundance of pressure and friction and were kept firm and healthy and red; but now that we take out the bones of the meat and stew or hash it, have all our grain ground, and strip off all the husks of our vegetables and skins of our fruits, though we have made our food much more digestible, we have robbed our gums of a great deal of valuable friction and exercise. The most practical way to make up for this is by vigorous ma.s.sage and scrubbing with a tooth-brush for five minutes at least three times a day. It will hurt and even make the gums bleed at first; but you will be surprised how quickly they will get used to it, so that it will become positively enjoyable.

[Ill.u.s.tration: A TOOTH-BRUSH DRILL

A school in which the children are taught the importance of using the tooth brush, are supplied with brushes at cost, and required to report both on their care of their teeth and on the condition of the brushes.]

It is good to use some cleansing alkaline powder upon the brush. The old-fashioned precipitated chalk, which makes the bulk of most tooth powders, is very good; but an equally good and much cheaper and simpler one is ordinary baking soda, or saleratus, though this will make the gums smart a little at first. Any powder that contains pumice-stone, cuttle-fish bone, charcoal, or gritty substances of any sort, as many unfortunately do, is injurious, because these scratch the enamel of the teeth and give the acids in the mouth a c.h.i.n.k through which they may begin to attack the softer dentine underneath the "glaze" of enamel.

Antiseptic powders and washes, while widely advertised, are not of much practical value, except for temporary use when you have an abscess in your gums, or your teeth are in very bad condition. It is almost impossible to get them strong enough to have any real effect in checking putrefaction of the food or diseases of the gums, without making them too irritating or poisonous. If you keep the gums and teeth well brushed and healthy, you will need no antiseptics.

Not only should the teeth be kept thoroughly clean and sweet for their own sake, but also for the sake of the stomach and the health of the blood and the whole body. The mouth, being continually moist and warm and full of c.h.i.n.ks and pockets, furnishes an ideal breeding ground for all kinds of germs; and the average, uncleansed human mouth will be found to contain regularly more than thirty different species of germs, each numbering its millions! Among them may sometimes be found the germs of serious diseases such as pneumonia, diphtheria, and blood-poisoning, just waiting, as it were, their opportunity to attack the body. In fact, a dirty, neglected mouth is one of the commonest causes of disease.

CHAPTER XXVI

INFECTIONS, AND HOW TO AVOID THEM

What Causes Disease. The commonest and most dangerous accident that is likely to happen to you is to catch some disease. Fortunately, however, this is an accident that is as preventable as it is common. Indeed, if everybody would help the Board of Health in its fight against the spread of the common "catchable" diseases, these diseases could soon be wiped out of existence. Every one of them is due to dirt of some sort; and absolute cleanness would do away with them altogether.

Diseases that are "catching," or will spread from one person to another, are called _infections_; and all of them, as might be supposed from their power of spreading, are due to tiny living particles, called _germs_--so tiny that they cannot be seen except under a powerful microscope. Nine-tenths of these disease germs are little plants of the same cla.s.s as the moulds that grow upon cheese or stale bread, and are called bacteria, or bacilli. The different kinds of bacteria, or bacilli, are usually named after the diseases they produce, or else after the scientists who discovered them. For instance, the germ that causes typhoid fever is called the _bacillus typhosus_; that which causes tuberculosis is called the bacillus tuberculosis; while the germ of diphtheria known as the _Klebs-Loeffler bacillus_, after the two men who discovered it.

A few kinds of disease germs belong to the animal kingdom, though all germs are so tiny that you would have to have a very powerful microscope to tell the difference between the animal germs and the bacilli, or little plants. Most of these animal germs are called _protozoa_ and cause diseases found in, or near, the tropics, like malaria and the terrible "sleeping sickness" of Africa. Smallpox, yellow fever, and hydrophobia--the disease that results from the bite of a mad dog--are also probably due to animal germs.

So far as prevention is concerned, however, it makes practically little difference whether infectious diseases are due to an animal or a vegetable germ, or to one bacillus or another. They all have two things in common: they can be spread only by the touch of an infected person, and "touch" includes breath,--indeed "by touch" is the meaning of both infectious and contagious; and they can all be prevented by the strictest cleanness, or killed by various poisons known as germicides ("germ-killers"), or disinfectants. Most of these germicides are, unfortunately, poisonous to us as well; for, as you will remember, our bodies are made up of ma.s.ses of tiny animal cells, not unlike the animal germs. Most of the germicides, therefore, have to be used against germs while they are outside of our bodies.

Scripture says that "a man's foes shall be they of his own household,"

and this is true of disease germs. They grow and flourish--and, so far as history tells us, the diseases they cause seem to have started--only where people are crowded together in huts or houses, breathing one another's breaths and one another's perspiration, and drinking one another's waste substances in the well water. This fact has, however, its encouraging side; for, since this habit of crowding together, which we call civilization, or "citification," has caused and keeps causing these diseases, it can also cure them and prevent their spread if all the people will fight them in dead earnest. No amount of money, or of time, that a town or a county can spend in stamping out these infectious diseases would be wasted. Indeed, every penny of it would be a good investment; for, taken together, they cause at least half, and probably nearly two-thirds, of all deaths. Not only so, but most of the so-called chronic diseases of the heart, kidneys, lungs, bones, and brain are due to the after-effects of their toxins, or poisons.

How Disease Germs Grow and Spread. But perhaps you will ask, "If these bacteria and protozoa are so tiny that we have to use a microscope, and one of the most powerful made, in order even to see them, how is it that they can overrun our whole body and produce such dangerous fevers and so many deaths?" The answer is simply, "Because there are so many millions of them; and because they breed, or multiply, at such a tremendously rapid rate." When one of these little bacilli breeds, it doesn't take time to form buds and flowers and seeds, like other plants, or even the trouble to lay eggs like an insect or a bird, but simply stretches itself out a little longer, pinches itself in two, and makes of each half a new bacillus.

This is known as _fission_ or "splitting," and is of interest because this is the way in which the little cells that make up our own bodies increase in number; as, for instance, when a muscle is growing and enlarging under exercise, or when more of the white blood cells are needed to fight some disease. Remember that we and the disease germs are both cells; and that, if they are numbered by millions, we are by billions; and that we are made up of far the older and the tougher cells of the two. Except in a few of the most virulent and deadly of fevers, like the famous "Black Death," or _bubonic plague_, and lock-jaw, or _teta.n.u.s_, ninety-five times out of a hundred when disease germs get into our bodies, it is our bodies that eat up the germs instead of the germs our bodies. Keep away from disease germs all that you reasonably and possibly can; but don't forget that the best protection against infectious diseases, in the long run, is a strong, vigorous, healthy body that can literally "eat them alive."

Grow that kind of body, keep it perfectly clean inside and out, and you have little need to fear fevers, or indeed any other kind of disease; for you will live until you are old enough to die--and then you'll want to, just as you want to go to sleep when you are tired. Remember that this fight against the fevers is a winning fight, this study of disease germs a cheering and encouraging one, because it will end in our conquering them, not merely nine times out of ten, but ninety-nine times out of a hundred.

We are not making this fight just to escape death; what we are fighting for is to live out a full, useful, and happy life. And we already have five chances to one of gaining this, and the chances are improving every year; for science has already raised the average length of life from barely twenty years to over forty. Broadly speaking, if you will keep away from every one whom you know to have an infectious disease; wash your hands always before you eat, or put anything into your mouth; keep your fingers, pencils, pennies, and pins out of your mouth,--where they _don't_ belong; live and play in the open air as much as possible and keep your windows well open day and night, you will avoid nine-tenths of the risks from germs and the dangers that they bring in their wake.

Children's Diseases. We have already studied two of the greatest and most dangerous diseases, and the way to conquer them--tuberculosis, or consumption, in the chapter on the lungs; and typhoid fever, in the chapter on our drink. One of the next most important groups of "catching" diseases--important because, though very mild, they are so exceedingly common,--is that known as the "diseases of childhood," or "diseases of infancy" because they are most likely to occur in childhood. So common are they that you know their names almost as well as you know your own--measles, mumps, whooping cough, scarlet fever, and chicken-pox. Though they are in no way related to one another, so far as we know (indeed, the precise germs that cause two of them--measles and scarlet fever--have not yet positively been determined), yet they can be practically taken together, because they are all spread in much the same way, they all begin with much the same sort of sneezing and inflammation of the nose and throat, they can all be prevented by the same means, and, if properly taken care of, they result in complete recovery ninety-five times out of a hundred.

[Ill.u.s.tration: THE WINNING FIGHT

Statistics for the population of the old City of New York. The chart shows a decrease from 95 out of every 1,000 in 1891-92 to 48 out of every 1,000 in 1909. This is due very largely to the careful methods of prevention enforced by the Board of Health, especially the inspection of milk.]

Any child who has sneezing, running at the nose or eyes, sore throat, or cough, especially with headache or backache, a flushed face and feverishness, ought to be kept at home from school and placed in a well-ventilated, well-lighted room by himself for a day or two, until it can be seen whether he has one of these children's diseases, or only a common cold. If it turns out to be measles, scarlet fever, or whooping cough, he should then be kept entirely away from other children in a separate room, or, where that is impossible, in a special hospital or ward for the purpose; he should be kept in bed and given such remedies as the doctor may advise. Then no one else will catch the disease from him; and within from two to five weeks, he will be well again. The most important thing is not to let him get up and begin to run about, or expose himself, too soon; five times as many deaths are caused by taking cold, or becoming over-tired, or by injudicious eating, during recovery after measles, scarlet fever, and whooping cough, as by the disease itself. This one caution will serve two purposes; for, as a sick child's breath, and the scales from his skin, and what he coughs out from his mouth and nose are full of germs, and will give the disease to other children from two to four weeks after the fever has left him, he ought to be kept by himself--"in quarantine," as we say--for this length of time, which is just about the period needed to protect him from the dangers of relapse or taking cold. Boards of Health fix this period of quarantine by law and put a colored placard on the house to warn others of the danger of infection.

[Ill.u.s.tration: DEATH-RATE FROM MEASLES

Note that, after the quarantining of measles in 1896, the death-rate dropped at once. Statistics for the old City of New York.]

Colds and Sore Throats. A milder and even more common kind of infection is that known as common colds. These, as shown by their name, were once supposed to be due to exposure to cold air, or drafts, or to becoming wet or chilled. But, while a few of them are so caused, at least eight, and probably nine, out of ten are due to germs caught from somebody else. They are never caught in the open air and very seldom in cold, pure fresh air of any sort, but almost always in the hot, foul, stuffy, twice-breathed air of bedrooms, schoolrooms, churches, theatres, halls, sleeping cars, etc. The colds, for instance, that you catch when traveling, are usually due not to drafts or damp sheets, but to the crop of cold germs left behind by the last victim.

You have probably known of colds that have run through a family or a school or a shop. It is well worth trying to keep away from the infection of colds, because not only is their coughing and sore throat and hoa.r.s.eness and running at the nose very disagreeable and uncomfortable, but they may cause almost as many different kinds of serious troubles in heart, kidneys, and nervous system as any of the other infections. In fact, they probably cause more than any other, because they are at least ten times as common and frequent. For instance, many cases of rheumatism, or rheumatic fever, come after attacks in the nose and throat, which cannot be distinguished from a common cold or ordinary tonsilitis. Indeed, it is more than probable that one of the ten or a dozen different germs that may get into your nose or throat and give you a cold, is the germ that causes rheumatism.

At all events, it would be fairly safe to say, "No colds, no rheumatism."