Part 3
A vast number of plants and animals, moreover, are single cells. Such among plants are the yeasts with which most of us make our bread, and a few of us brew our beer. Such also are the hundreds of different sorts of bacteria, which tho some of them are the germs of various catching diseases, are for the most part useful enough. But of these we shall learn more by and by. The green spots and patches on the bark of old trees and fences, and sometimes even on damp earth, are due to enormous numbers of minute plants, green with the same green pigment as the leaves of the largest tree; while the green tint of the gray lichens on rocks and tree trunks is caused by similar single-celled plants which grow among the white fibers of the lichen proper. Besides these, there are many like plants which float about in fresh water, each a single cell.
The diatoms which one finds in the mud at the bottom of ditches and mud-puddles, tho they have shells and move about, are usually counted among plants; but the water of most ditches and puddles swarms with amoebas, infusoria, animalcules of various sorts, most of them large enough to be made out with the unaided eye when seen in a tumbler against the light, and each a single cell.
Many animals, then, and many plants are just one single cell and no more. Many others, like pond scums and sea-lettuces,—which are plants,—and sponges and jelly-fishes,—which are animals,—are composed of many cells, but all pretty much alike. But the animals and plants which we know best, kittens and oak trees and horses and grass, and the creatures we know best of all which are ourselves, are made up of many cells, and many different sorts—skin and bark and wood, flesh and fat and leaves and hair and all the rest, so many that it would take half an hour merely to write them all down.
These “cells” then, are the living part of every plant and animal. Each of them became by the splitting in halves of an older cell; each of these in turn by the splitting in halves of a still older cell, until we get back to the egg which is the great-great-great-grandfather of them all. But the egg itself arose by the splitting of still another cell, which, of course, was part of the parent’s body. This came from yet another, and so on back to the beginning of life on this earth, tho nobody knows how long ago that was.
So the living flesh of us has always been alive. Most of it will die; but some of it will live on in our children and our children’s children, until the and of the world.
VII
How Much of Us Is Alive
How much of a tree is alive? Certainly not the outer bark. That falls off in dry scales, or can be scraped off down to the white layers within, and the tree be none the worse. Certainly not the wood. One often comes across old trees that have lost limbs or been carelessly pruned, which are entirely decayed out on the inside, so that nothing is left but a thin shell next the bark. Yet these trees grow as vigorously as ever, and bear leaves and fruit like a solid tree. The bark is dead; and the wood is dead. Between the two is a thin layer, perhaps a quarter inch thru, which is alive. On one side, it is changing into dead wood. On the other side, it is changing into dead bark. The new wood is alive, and the new bark. Between them is something neither wood nor bark, but just living tree-stuff. The green leaves also are alive, and the green twigs, and the blossoms, and the growing buds. But at least half of every living tree is already dead; while the larger and longer lived a tree is, the smaller proportion of it is alive at one time.
How much of a hen’s egg is alive? Not the shell, for that is mostly just chalk. Not the white, for that is merely the little chicken’s pantry shelf where it keeps the food on which it is to grow. The living part of the egg is the yolk—unless somebody boils the egg and so kills it. Sometimes, too, the egg dies, as any living thing may; then we usually find it out.
Even we ourselves are not all alive. I have already pointed out that our hair and nails are not alive at all, and that our outer skin, the thin skin, that is, which we tear off when we bark our shins, is fully alive only on the inside. Our “bark” in fact, is very like a tree’s. Each has a soft, thin, living layer on the inside, which grows, hardens, dies, forms a water-tight layer over the rest of the body, cracks into scales, and drops off. Where one forms cork, the other forms horn. Indeed the cork stoppers of our bottles are made from nothing more than an especially thick corky bark of a certain kind of oak, like the especially thick and homy soles of all bare-footed savages and some bare-footed little boys.
“The blood,” we say, “is the life.” And yet the blood itself is dead. The watery part is just soup; water and salt and fat and jelly. The minute, coin-like, red blood corpuscles carry the oxygen of the air from the lungs all over the body. But there are similar oxygen-carriers, likewise dead, in bottles in the drug-stores. The corpuscles are dead cells alive once, and like the hard skin cells, a great deal more useful dead than alive.
As for our teeth, the hard white enamel on the outside is just about as much alive as a clam shell. The baby tooth, as I have already explained, is formed in a little pocket in the gum. The inner part of the tooth grows up from the cells at the bottom, very much as a hair grows out from the bottom of the still smaller pocket where it starts. In fact, the tusks of pigs and the long front gnawing teeth of squirrels and rats are still more like hairs, for they keep growing from the root, and wear off at the outer end. The tooth pushes thru the gum; and as it goes by, the cells at the sides of the pocket and on top plaster it with a coating of enamel. Therefore, as most of us find out to our cost, this enamel once destroyed, can never grow again. Once clear of the pocket where it was formed, it has to last us the rest of our lives; and little boys and girls who don’t keep their teeth clean when they are young, have to put up with something not nearly so good when they are grown up.
The inside of the tooth is not quite so dead as the outside—one sometimes gets the impression during a visit to the dentist that it isn’t dead at all. The tooth, inside the enamel, is mostly bone; and bone is mostly lime, like clam-shells, mortar and chalk, plaster, and the great boulders and ledges of rock in a limestone country. The rest of the bone is living substance, scattered cells far apart from one another with long roots, that look as if they had grown out into the bone like tree roots into the soil. Really, however, it is the other way. Before there were bones, there were bone cells. These build themselves round with the hard bone substance, pushing their neighbors away and leaving only the long root-like strands of living substance. It is thru these root-like living strands that we feel the dentist’s auger bore into the solid tooth. But cutting the outer enamel does not hurt at all simply because no part of that is alive.
We are, then, built of living bricks, but of living bricks set in dead mortar. We saw that the great trees, complex and long lived, have more wood and bark and other dead substances in them than the shrubs, herbs, and grass. These in turn are less alive than the lowly water plants and yeasts and molds which have no wood or bark at all. The same is true of animals. The jelly-fishes and infusoria have neither skin, hair, bones, nails, nor blood, and are pretty much all alive. So the more a creature’s life is worth, the less of it is alive.
Even the living cells themselves are not wholly alive. The thin living jelly always contains water and salt, which are—just water and salt. Fat cells contain drops of oil, which are simply stored up food material, no more alive than the oil in an oil can. Plants, on their side, store up their food largely as starch, no more alive than that in a package from the grocers. Besides oil and starch, some cells contain gum or rosin or saliva or milk or sweat, which they pour out from time to time. These substances, too, can hardly be considered more alive while they are in the body than when they are outside.
So the living substance is the cell jelly. Everything outside the cell is dead; many cells even are dead, while not a few, even while alive, contain so much dead stuff within them, that there is more oil in a young hen’s egg than there is chick, and more starch than corn-plant in a grain of corn.
VIII
How We Grow
By “we” I mean all living things, trees and grass and dogs and cats and boys and girls. For as you, my reader, have I hope already discovered, we who have the breath of life in us are a good deal alike, whether we are oaks or men. We don’t look much alike, to be sure. But when we consider the things that are not alive—the stones and stoves and bats and balls and such—and see how very different we are from these, then we get some idea of what being alive is, and understand how being alive makes us blood-brothers with everything else that is alive also.
Now things that are alive usually do more or less growing. We have already learned something of this growing of little creatures in the egg—how the eye buds out as a ball and afterwards folds into a cup, how the limbs sprout out from the body as shapeless lumps which only gradually turn into hands or feet or wings. We have learned something of the way the bones grow, and the skin, and the hair, and the nails. Now we have to learn something more about the way a little child or a little tree grows up to be a big one.
The tree, we already know, grows larger round only between bark and wood. It grows taller only at the tips of its branches. The solid wood, once formed, does not change. If then, you drive two nails into the trunk of a little tree, say a foot apart and one above the other, even if that tree should grow to be a hundred feet high, those two nails would remain just where they were, a foot apart and just the same height from the ground as before. The little tree looks so much like the big one, that one cannot help thinking that it has simply grown thruout, so that the same branch which was once at the height of one’s head has now been lifted to the height of the house eaves. But this is not the fact. The lower branches of the little tree have died and dropped off; what are now the lower branches of the large tree, were once the top twigs of the little one, which have always been at the same level where they now are. The top branches of the large tree, as the tree grows still larger, will in their turn become, first the middle branches, then the lower ones, then will drop off entirely.
Now this growing at one end which looks like growing thruout is pretty common in our own bodies. We have seen how the hair grows at the inner end only, and the nails likewise, and the skin. Ignorant people will tell you that cutting off the ends of your hair, or singeing the ends; and that smearing various messes on the outside of your skins will change the quality of either. Don’t you believe them. After wood and skin and hair and teeth are once grown, all we can do is to protect them. Really to affect their growth for good or ill, we have to do something to the growing end.
The bones also grow in spots. The child’s leg bones and arm bones and finger bones do not simply swell up to become the man’s. The head of each bone, the rounding end, that is, where it touches the next, grows on the outside. But the shaft does its growing chiefly at two spots, one at each end where the shaft joins the head.
The bony part of the tooth, on the other hand, starts as a paper-thin sheet, but full sized. The living cells which build the hard bone, lie on the inside of this shell. They keep building on more bone on the inner surface, pushing themselves toward the middle of the tooth, until the tooth wall is so thick that only a narrow space is left in the center. But their long roots which they leave behind, still reach thru to the outer surface of the bone, ready to ache when there is occasion. Meantime, the outside of the tooth pocket, as we have learned, has been plastering on enamel on the outside of the shell, and pushing itself farther and farther away.
A plant’s roots, like its branches, grow at the tips; and the nerves in our own bodies grow in somewhat the same way, beginning at the inner end, and somehow finding their way thru and around the other tissues of the body, till they find the place to which they were sent. But the muscles and the fat grow thruout their mass, like dough being raised for bread. Most of the hollow tubes of the body—the blood vessels, for example, and the red lane down which our breakfast goes—grow in this way. But the hollow bones, as they grow, are taken down on the inside to enlarge the hollow, and built up again on the outside with old material and new to enlarge the shaft.
Even the blood grows, the watery portion coming from the food we eat and the water we drink; but the red and white corpuscles which float in the watery part, are made in special factories in the body (some of them in the marrow of the bones) and turned loose in the blood stream.
Growing, you see, tho easy to do, is by no means so simple as it appears.
IX
How We Grow Up
Ten years from now, you who are reading these sentences will be grown up. Once you were little pink and white babies, all soft and sweet and clean. And because you were soft and unresisting, you grew at a tremendous rate. At first you probably doubled your weight in six months. Then it took three years; then six or eight. By the time you are twelve, you probably will be half as heavy as you ever will be. In all the rest of your lives, you will do no more growing than you did in the first 180 days of them.
You will grow, too, as you have grown, by fits and starts. Sometimes you will shoot up like sunflower stalks. Sometimes, again, you will stop growing large, and begin growing hard. You will not seem to be getting bigger; but you will be getting stronger. Then, when you start growing again, you will perhaps find that you really can’t do so much as you could when you were a year younger, nor do it so well.
So you will keep on, sometimes growing large and sometimes growing hard, but almost never both at once, until you come to the full stature of men and women, and your soft baby flesh that couldn’t lift its head from the pillow has changed to tough muscle and hard bone. That is, of course, supposing that you have taken care of yourselves. If you haven’t—why then it may be different.
This growing up is so common an affair, so many of us do it, puppies and calves and kittens and little rabbits and baby birds, that we usually forget how wonderful a matter it is. Wonderful indeed it is; yet hardly less strange is it that after we have grown a while, then we stop. Yet our hair, as we know, doesn’t stop, nor the skin, nor the nails. Sometimes parts of the body which have hardly grown at all in youth, start up and grow in middle life. But the parts of the body which count, the parts which if they did grow would make us larger, these somehow know enough to stop.
It is not so with some other living creatures. A tree does not stop growing so long as it lives; nor does a fish. The big oak or the big trout may have grown faster than the little one; most likely it has simply been growing longer. We call any creature adult when it is large enough to have children of its own. But the oak bears acorns and the trout lays eggs, and then keeps on growing till it is ten, twenty, fifty times bigger than it was when it first had little ones. It is as if the cat, when her kittens were growing up, kept on growing along with them; and next year when there were more kittens kept on growing nearly as fast as they; and kept on year after year as long as it lived until it got to be as large as an elephant. And still its kittens would be just kittens, no larger than before.
Many animals manage their growing this way. The star-fish egg, you remember, is for size like a minute grain of dust, and the baby star when he first hatches out is hardly bigger. After that, he eats all he can get and grows as fast as he can, like any other kind of baby.
But suppose the little star-fish, as large say as a pin head, doesn’t find enough to eat. Does he then starve? Not a bit. He simply doesn’t grow. The eggs hatch out in the late spring within a few weeks of one another, and the little stars which do not happen upon a good boarding place, go practically without food all summer long. They remain perfectly healthy; but they scarcely grow at all, so that at the end of the summer they are still the pin heads that they were six months before.
On the other hand, when a star-fish happens to be born where he can find plenty of barnacles or small clams or mussels, he doesn’t do much but eat, and grows to match. It may happen, then, that of two stars, hatched on the same day, the one which has been well fed will be no less than five thousand times larger than the other which has gone hungry. Now a grown man is only about fifteen times as large as a new-born babe. But this is as if two babies, each six months old, should be, one no heavier than at birth, while the other weighed twenty-five tons and was as large as a whale.
So you can’t judge by appearances. The star-fish that you pick up at the shore may be a very young animal which has been well fed, or a very old one which has gone on short rations, while a young star, still growing, may be twenty times larger than his own great-grandfather.
X
How We Grow Old
After we grow up, we grow old. People say that we first grow up to men and women; then we continue adults; then we grow old. Really, however, we begin to grow old the day we are born; while we shall never again grow old so fast as we did when we were babes in arms.
For growing old is simply growing hard. We begin life as squashy little babies. Our bones are like green sticks. Our flesh is like dough, only the softest cloth must touch our skins, and Nurse has to hold her hand under our poor backs to keep our heads from dropping off. Children are not squashy, but they are still soft. You can pinch children. Sometimes you do. But you can’t pinch a grown man, any more than you can pinch a board. Children are of course, much harder than babies. All the same, if you put your fingers in your mouths, or stand too much on one leg or slouch over your books or shrug your shoulders up beside your ears when you play first base, or sit on one foot when you curl up in the big chair in the library, or do any other of the forty-leven things that somebody has to tell you forty-leven times a day not to do, then you will pull your bones all out of shape as if they were so much India rubber; and when you grow up and your bones and muscles set, then you can’t get back into shape again—tho you’ll wish you could.
For get hard you will. Then you will be grown up. When you are just hard enough, you will be in the prime of life, able to work as easily as you now play, and liking it, I hope, even better. But still you will keep on getting hard; and when you get too hard, then you are old.
So growing old is growing hard. And since the younger you are, the faster you grow, you never grew old so fast as when you were a tiny baby, and you never again will grow old so fast as you are growing old now.
And the moral is, as the Duchess used to tell Alice, that since we stay young and soft only a very short while, and grown-up and hard most of our days, we’d better, as much as we possibly can, make the short end of our lives help out the long one.
What I mean is this. While we are young, we are soft and plastic and teachable. As we grow older, not only do our bodies harden, but our minds also. We can do a great deal more after we are grown up than we can while we are children; and I think we are, if less light-hearted, on the whole quite as happy. But we shall be a great deal less able to take up anything new. Let us, therefore, practice while we are young those things which will bring us most happiness, after we are too old to change.
For example, suppose a boy is fond of out-door games, as every normal and healthy boy ought to be. He plays baseball all the spring, tennis all summer, football thruout the autumn, and what there is left of the year goes into ice hockey. He plays expertly, has a glorious time; and he grows up manly and strong. This is as it should be—so far.
But suppose the same boy, thru school and college and at work. There is no more football for him, and no more ice hockey. For a few years he may get an occasional game of baseball; if he is very lucky he will get a little tennis. But tell me, boy who is reading this page, how many of your father’s friends and associates ever play at all the games at which you spend your spare time?
Now while we are supposing, let us suppose that this boy of ours, instead of spending all his spare time at games, spent only half. The other half he shall devote to sports which are not games. He shall learn to ride a horse, to fish, to handle a sail boat, to swim, row, paddle, to climb mountains, to take care of himself in the woods, and above all to walk thru level country and enjoy the sight of all he sees. By and by, this boy will grow up. In the natural course of things, he will put away bat and ball and hockey stick before he is thirty, but rod and saddle and oar will bring him happiness and health almost to the end of his days.
There is a difference too in games. One plays football thru school and perhaps in college—eight years at the outside. But one world’s champion tennis player was well by forty; he must have played thirty years. A golfer gets forty or fifty years of pleasure for the trouble of learning his game. You may think you will learn the boy’s game now, and the man’s game later. But you won’t. You will learn the man’s game now along with the boy’s, or else you won’t learn it at all. You will be too old to learn, and go gameless to your grave.
Or suppose a girl is fond of music, and learns to play, very nicely, the banjo. It will be charming enough, summer evenings on the porch—so long as one is young and has only a girl’s soul to express in music. But by and by she will grow up to be a woman, and have little children of her own. Will she get out her banjo Sunday evenings and play for them hymns and solemn songs, or tinkle coon melodies for them when they are sick? Indeed she will not. She will put that banjo on the top shelf of the spare bed room closet, and wish she had spent her effort learning some other instrument more worth while.
So it is with everything else. If, while we are young, we train our ears to enjoy good music, and our eyes to love good pictures and good furniture, cloudy landscapes and great trees, and our minds to care for the important things of life, literature and religion and art and science and politics and history, we shall still possess growing sources of happiness longer after we have ceased to care to read stories or to be able to play ball. A wise child will study the happiest adults whom he knows, and learn to like and to do whatever most helps to make them blessed.
However, I meant to tell about how we grow old, rather than how we can best get ready to be so.