Part 14
But when the enemy has broken through our first line of defense, and begun to lay siege to our bodies, we still have a second line of fortifications to protect us. One thing our skins are for is to stop germs. So long as we keep a whole skin, it is pretty hard for many sorts of germs to gain an entrance. And where the skin is thin, as it is inside the mouth and nose, there is always a somewhat thick and sticky mucous to catch the germs; while the eye has tears to wash them out. We are like fortified cities; and we must not let the enemy make a breach in the wall.
So we must be careful not to neglect even small cuts, sores, scratches, and the like, thru which the foe can enter. People sometimes get most loathsome and dreadful diseases by drinking from dirty cups when the skin of their lips is cracked in cold weather; while the little plant that causes blood poisoning, often gets in by way of a cut so small as to be hardly noticed. No child would ever die of lockjaw, if he did not first cut or blow a hole in his skin.
Strangely enough, a great many of the lesser catching diseases of children, measles and colds and the like, make their way into the blood because of holes in the teeth. A hollow in a tooth gets filled with food. A germ or two finds its way into this food, and grows there till it becomes many millions. So naturally, an assault by an army is more likely to be successful than an assault by a mere handful. Merely by keeping the teeth and mouth clean, and by having a dentist stop the holes in the teeth, one can cut down to less than half, the number of days’ sickness in a year. Some people go beyond this, and always after they have been in dust or bad air, wash out their noses with some fluid that will dispose of any of the enemy who have lodged there. In fact, people who have suffered almost continually from colds and grin are sometimes cured at once and completely, by merely a slight operation on the nose, which opens up to the fresh air some hollow in which the besieging hosts were wont to lurk.
Our second line of defense, then, is keeping skin and teeth and nose clean and whole, that the enemy may have no place wherein to hide, and no breach through which to enter. If this gives way, then we must engage the enemy hand to hand.
Then it gets to be a pretty even thing between us. The invaders try to poison us, and we try to poison them. We form an acid in our stomachs—the same acid, by the way, that tin-men use to solder with; one can buy it anywhere. Regularly, we use this to digest meat with; but if any living things get into our stomachs, we give them a dose of this acid, and usually bowl them over.
If they get by this, we poison them with bile. The bile is made in that most useful organ, the liver, and is partly waste matter, more or less hurtful to the body, which we are getting rid of. So since we don’t want it to poison us, we use it to poison other living creatures inside us.
That, then, is our third line of defense. If the enemy gets by that, then the war has to be fought out in the blood. Even if we win, we shall suffer damage, and very likely take to our beds and have to call on the doctor for reinforcements.
The blood itself, good healthy blood, that is, will poison the germs; for the blood of any sort of creature, as I have explained, will poison any other sort. Besides that, we manufacture special poisons with which to combat each special creature that makes a special poison to assault us. So each side poisons the other, and the battle becomes a question of which can kill the other first. In one case, we are sick and recover; in the other case, we are sick and die.
When the doctor takes a hand in the battle, he begins by giving us food and medicine, to make us strong for the war. Sometimes, besides these, he gives us something which, while it harms us a little, harms the enemy a great deal more. In a few cases now-a-days, he pumps into our bodies some of the blood of another animal, generally a horse, which has been fighting the same disease, and so has its hand in and can manufacture many times as much stuff to kill the germs as we can. Many, many people have been saved by this means, who otherwise would certainly have died.
In a few cases, too, small-pox especially, by means of vaccination, long before the enemy attacks us, we can be loaded up with ammunition to repel the invader when it does come. The vaccination gives a mild form of the disease (not so very mild perhaps you think, when your vaccinated arm gets nice and red); we defeat this triumphantly, but we manufacture so much “anti-toxin” to do it with, that for years afterwards we are all ready for the first germ that shows its face in our blood, and slay him before he gets a chance at us. The “anti-toxin,” as you know, is the substance which we make with which to get back at the germs that are trying to poison us with the “toxin” which they make.
But even the battle in the blood is not fought quite in the open. We have, so to say, breastworks and rifle pits, where we can still make a stand, even after the invaders have gained a footing in our bodies.
Perhaps you have sometimes felt small roundish hard bunches as big as a pea or a marble, under the skin at the side of the neck, under the arm pit, or in the groin. Sometimes these swell up and get sore. These nodules are the lymph glands. They surround the passages through the flesh along which the invading germs are likely to come, after they have burst through the skin. They are then like the fortifications along a road over which the enemy is likely to march. We can feel them only in certain places; but they are all over the body, under the skin, and beneath the membranes of the lungs and the digestive organs, wherever the body is most open to attack.
The garrison of these little forts are a peculiar sort of naked cells, which having no walls or covering to hold them in, can change their shape, reach out, and draw back again, as if they were sea-anemones or polyps or some other sort of water creature, and not part of our bodies at all. These cells are twenty or more times larger than the bacteria. And when the bacteria or other germs come along through the passages of the body on their way to the blood vessels, these guardian cells of ours reach out and grab them, drag them in, and devour them, like ogres that devour travelers who go by their castles, over the high road. Only in this case, our sympathy must be entirely on the side of the ogres.
But these lymph cells do not always stay in the lymph glands. When they like, they let go their anchorage, and go floating off through the blood, or through the lymph; for the lymph is only the watery part of the blood without the red corpuscles, which doesn’t stay in the blood vessels but soaks everywhere through the body, feeding and moistening the cells. These lymph cells, or white blood corpuscles, can go everywhere over the body, pushing and squeezing and elbowing their way among the other cells or traveling in the open spaces between them.
When the enemy enters the body, and begins to poison the blood, the white corpuscles smell them, and at once begin to crawl toward the smell, to reinforce their brothers in the particular lymph glands which happen to be at the point of attack. You get a sliver in your finger. The sliver opens a hole in your defense, and carries in some hostile germs. If, therefore, your lymph cells did not come to the rescue, you would inevitably die of blood poisoning. But they do come to the rescue. The white “matter” or “pus,” which in a few days comes out of the wound, is in large part the dead bodies of the fallen enemy and of the defenders who have perished in the fight. So in general, the invasion is stopped at the first lymph gland. A few thousand white corpuscles fall in the war. The enemy is massacred to the last man. And the body is saved.
Or else the foe get the upper hand; increase faster than the defenders can kill them off; break through the defense; enter the blood stream; invade the whole body; overrun the country; and put the inhabitants to the sword.
All our lives long, every day of our lives, we keep up this fight against disease. When measles does not threaten us, then it is colds. The game, therefore, is to strengthen our outer defenses, by keeping our food and houses clean, and our skins and teeth, and the air we breathe. And while we are doing that, we ought also to keep our bodies strong and resistant, with proper food and exercise and sleep, ready to put up a good fight if the enemy should break in. We know so much now about the causes of disease, that being sick or keeping well is a good deal under our own control.
XLII
More About The Great War
We are not the only creatures who have to fight for our lives, every day of them, against an ever-present but unseen enemy. All other animals have to do the same, if they are big enough for any thing else to live inside them. There are parts of this earth where no cattle or horses can live, and where all the heavy work has to be by machinery or by hand, because there are flies there which bite all the larger animals, both wild and tame, and plant germs in their blood. After that the tamed creatures, at least, almost invariably die.
Animals, therefore, have their catching diseases just as we have. Sometimes they are the same as ours; more often they are different—things that dogs or cats or horses catch, and we do not. Once, I remember, it must have been more than sixty years ago, all the horses over entire states suddenly fell sick. One hardly saw a horse on the street or anywhere; and because that was long before the days of automobiles or trolley cars, people had to walk or to drive oxen, and sometimes even to harness up cows. But after a few months, the horses all either died or got well again. Those that got well had their white blood corpuscles trained to fight that particular germ; so there was no more serious trouble. But it would make you laugh to see a span of cows haul a milk wagon.
There is a distemper that kills puppies. There is a chicken cholera which wipes out whole flocks of hens. The monkeys in the menageries succumb to colds and consumption, which they catch from the people who come to look at them. When the plague enters a city, the cattle and the various small animals of the house begin to die first before the human beings, and thus often give them warning, and time to flee. In all cases, some particular living and growing thing breaks through into the blood, or gets a foothold somewhere in the body, and begins to poison it. Then the invaders and the blood cells fight it out—and the best man wins.
There is a disease called anthrax which attacks various animals, ourselves and the birds among the number. A hen, for example, fighting anthrax, will almost always win, if it is kept warm. The lymph cells fight better when the blood is hot. But if the hen’s feet are kept in cold water, then the anthrax wins. The cool blood gives it the advantage.
That is how we and all other creatures catch cold. Mere cold would never give us chills or grip or colds. But our being chilled, or getting our feet wet, or sitting in a draught, just cools down some part of the body enough so that the blood cells can’t fight quite so well. Perhaps it is only for a moment; but in that moment the enemy gets its footing. Some people say that the reason why a dog’s nose gets hot when he is sick, and why human beings and animals have fever when they have anything catching, is so that their bodies may be well warmed up, and their lymph cells may do their fighting in hot blood.
Nor is it only for human beings and animals that all these catching things lie in wait. Plants have their troubles as well. Perhaps you have noticed on wild cherry trees growing by the roadside, or on plumb trees, that sometimes almost every tree in a clump, and even every branch on a tree, will have a hard black lump, as large as your fist, growing out of the bark. The tree is sick; sick with a patching disease of trees called the black knot.
The disease itself is something like a mold. It breaks through at the growing tip of the branch where the bark is new and thin. Thence it grows down the branch sucking up the living substance of the plant and killing everything as it goes. The “black knots” are the fruiting of the invading plant, where it has broken through the bark and is growing fine dust-like “spores,” which are its seeds and will spread the trouble to neighboring trees. When a tree comes down with this trouble, the only thing to do is to cut off every diseased branch a foot or more below the lowest knot, and burn it up. Possibly then, we may get ahead of the enemy, and so save the rest of the tree.
Almost every cultivated plant has its diseases. The brown spots on leaves and fruit of a pear tree are the plant’s measles. The hard lumps in an apple are its mumps. There is a sort of black scarlet fever of wheat, rust it is called, which destroys a million dollars’ worth of grain each year. Some plants look wilted because they need water; some, because they are sick and need medicine.
And they get medicine, too. Sometimes the plant-doctor gives it by soaking the seeds in the remedy; sometimes by spraying it on the leaves with a pump and a hose. In any case, the medicine is some sort of poison that kills the living creature that makes the disease, but does no special harm to the cultivated plant.
We even speak now of diseases of soils. Because there are minute animals that get into soil and lessen its fertility so that no plant will do well in it. Green-house keepers often bake their earth before setting out plants in it, in order to cure it of any disease that it may have caught while the last crop was growing; while a healthy soil will catch a disease from a sick one, exactly as a healthy animal or plant will do.
The fact that most diseases of men, animals, plants, timber, and soils are living things is something that has not been known many years. Indeed, it is only since the twentieth century came in, that we have really made much of a start at finding out just what plant or animal is responsible for the sickness of any other. It is only a question of time, probably a few centuries at the outside, before we shall have killed off all the common diseases. Then nobody can possibly catch anything any more—measles, mumps, chicken pox, colds, grip, diphtheria, scarlet fever, or anything else. There will not be anything left to catch; and nobody will be sick any more, unless he eats more than is good for him, or does something else that he might just as well not have done.
XLIII
Living Apothecary Shops
Not only are the bodies of all except the very smallest animals and plants at the same time gas engines and battlegrounds; they are also living apothecary shops. Indeed, it is a pretty well stocked drug store that has more different chemicals in it than a man and his horse, and his dog, and the garden that he works in, all together, manufacture every day of their lives.
Think to begin with, of all the different perfumes of all the different flowers, and all the various tastes of all the different vegetables which we eat, and of all the various spices and herbs which we use for flavorings in our food. Think of all the different coloring matters in flowers and leaves. Think of the tar, rosin, pitch, maple syrup, turpentine, gum, varnish, shelac, india rubber, tan bark, and the rest, that we get from a few trees alone. The chemicals made by even the ordinary plants could fit out the shelves of a fair-sized drug store.
We animals have vastly more different things inside us than any plant. Every time we move a muscle, we manufacture soda water. Every time we think, we turn a half dozen different chemicals into the blood. We take a mouthful of cracker, which is mostly starch; and straightway a ferment, or “enzyme,” in the mouth begins to turn the starch into sugar. That is why a cracker or a potato tastes sweeter and sweeter the longer one chews it. When the sugar gets into the blood, another enzyme (the “y” is like “i,” and the word sounds like en-zime) in the liver turns it back to starch again, so that it stays there in the liver, and can’t get out. Then as you know, this liver-starch slowly turns back to sugar again, and leaks out into the blood to feed the muscles. In the muscles, still another enzyme helps it to explode into carbon dioxid and water, only sometimes it forms lactic acid instead, which is the acid of sour milk. Because of these enzymes in the muscles, the gas engines which they are, can run when only moderately warm, instead of needing to be too hot to touch, like other engines when they are at work.
But if instead of making flour into crackers, or having the baker do it, and then eating them, we had made the flour into bread with yeast: then the yeast, which is a living and growing plant, would have formed another enzyme, which in turn would have turned the sugar in the bread into carbon dioxid and alcohol, and the carbon dioxid would have puffed up the bread and made it light. That is what yeast is for. The yeast of beer also, turns the sugar of the grain into carbon dioxid and alcohol. The first of these gives us the fizz, the second we use to poison ourselves with.
Even the color of our hair and eyes depends on an enzyme which manufactures the coloring matter. People who have the enzyme, have dark hair and brown eyes. People who haven’t it, have light hair and blue eyes.
In fact, almost anything that any living part of the body has to do, whether to take its food out of the blood stream and build it into its own substance, or to do its work, or merely to grow, it generally has to employ one or more of these enzymes to do it with. These are, in fact, the tools of the living jelly, or protoplasm, which makes our bodies and does our living for us. Without them we could not live a single hour.
I suppose there must be hundreds, or perhaps even thousands, of different chemicals and drugs and medicines and poisons and antitoxins and enzymes forming all the time in different parts of the body. The various organs put them to all sorts of various uses. Among others, they employ certain of them as messengers, to carry signals from one part of the body to another.
I have already explained that the head is one of the first organs in the body to be formed. It gets a start, therefore, over the rest, and a little baby’s head is something like four times as big as it need be to fit its body. But the baby’s legs and arms, which started late, are not nearly large enough to fit the rest of him. So the limbs have to grow fast, and the head to grow slowly, in order to come out right in the end. How do they know enough?
How fast little girls’ feet sometimes grow! At twelve they can wear their mamma’s shoes. Then the feet stop growing and the rest of the body catches up. Or when it is time for a boy’s voice to change, all of a sudden, his Adam’s apple, where the voice comes from, starts growing. In a few months it has increased from boy’s size to man’s, and the voice has dropped to a deep, if uncertain, growl. Everywhere throughout the body, the different parts start growing, and stop, and keep along together, or get ahead of each other in the most complicated fashion, but always right.
How they manage it, we do not altogether know. We do, however, know that the different parts of the body do signal to one another by means of these substances which they form within their cells, and turn loose in the blood stream. In this way, each organ of the body is able to send messages to the rest—“Start growing,” “Steady now,” “Slow down,” “Stop”—as the case may be. You already know how a working muscle signals to the heart and lungs, and how the blood cells get wind of an invasion, by the altered smell or taste of the blood, and rush to the point where the enemy has broken through the defense, and the fight is on.
So in general, when a message has to go quickly from one part of the body to another, it goes by way of the nerves. But when there is no special hurry, or when the signal must go to some tissue or organ which, like the blood corpuscles, has no nerve connection, then the message has to go by way of the blood.
If then, our legs want to say: “We’re sitting on something hard and sharp, please may we move,” they call us up over the nerves. If they want to say: “We have been growing too fast, and it’s high time we stopped and gave something else a chance,” they do it by turning something into the blood. But if they want to say: “We’re so dead tired that we simply can’t walk another step,” then as you know, they use both methods—fatigue toxins and very dreadful aches.
XLIV
What Becomes Of The Tadpole’s Tail
The lymph cells, blood cells, white blood corpuscles, as they are variously called, are a sort of standing army, always on duty to repel invasion by any living germs of disease. In times of peace, however, when there is no enemy to be set upon and devoured, they have to work. All soldiers have to work when there is no fighting to be done; and sailors on a battle ship have to keep it clean and in order, row the captain about in his boat, and take turns paring potatoes for the cook. So the cells in our blood are in this like other fighting men.
Their particular work is to keep the body cleaned up, especially the blood. Besides this, they take down and cart away any tissue or organ or part of the body that is no longer any use.
There, for example, is the polywog’s tail, after he becomes a frog—also his gills. The polywog, of course, is pretty nearly a fish, with gills and tail, who breathes water. But Brer Frog is pretty nearly a land animal. He breathes with lungs, tho not to be sure especially good ones, so that he has to breathe thru his skin also to help out. At any rate, he has lost his fishy gills, and no longer has any tail.
Where has the tail gone? The white blood corpuscles have eaten it up; and with it, a lot of other things, gills among the number, which the tadpole has to have, but the frog has no use for.
The tadpole, as you know, has no legs. When they start growing (you can see them under the skin, almost the first sign of the coming change) these growing legs turn something into the blood which is a signal to the blood cells to get to work eating up the tail. So the blood cells do get to work. They devour the flesh, cutting into it much as certain insects gnaw into wood, or a woodchuck digs a hole in the ground. Then as fast as the blood cells take down the flesh that is no longer useful, it is used again to build up the new legs. So really the tadpole’s tail is used over to make the frog’s legs.
Much the same thing happens when a caterpillar turns to a butterfly. The caterpillar, as you have no doubt often seen, shuts himself up in a hard shell. Inside this coffin, or chrysalis, the body of the caterpillar is taken to pieces, and changed over into a sort of thick milk. Then out of this thick milk, the butterfly is formed.
So the caterpillar does not become a butterfly simply by growing wings. It is really almost a new creature, built up out of the material of the old, as one might rip up an old coat and have it woven into a rug; and we may be very sure that no butterfly ever has the slightest recollection of the time when it crawled on a dozen legs, and chewed leaves for its food.